Conventional Fusion FAQ Glossary Part 0/26 (intro)

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Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/intro
Last-modified: 25-Feb-1995
Posting-frequency: More-or-less-monthly
Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary of Frequently Used Terms in Plasma Physics
and Fusion Energy Research

Edited by Robert F. Heeter,

### This file introduces the Conventional Fusion Glossary ###

# Editorial Note:

Like any discipline, fusion research has evolved terminology used
to facilitate discussion. This includes the scientific vocabulary
of the discipline, the names of various research machines and
devices used, the names of various researchers in the field, the
names of the various research labs and funding authorities, the
mathematical symbols used, and the acronyms frequently used as
shorthand for some of the above.

In the case of conventional (magnetic confinement, inertial
confinement, thermonuclear, muon-catalyzed, etc - but not Cold)
fusion, this terminology has grown to the point where newcomers
(including the author of the glossary!) may be intimidated by the
apparent obscurity of the discussions. This file is an attempt
to provide a comprehensive and detailed listing and explanation
of terms frequently used, so that those new to the group/field
will be able to understand what is being said, and to contribute
with a minimum of confusion and frustration. Many terms are still
missing, and some terms may have less-than-fully-correct entries,
so if you would like to see something added or changed, let me

# Yes, it's a big glossary!

The last time I counted, there were roughly 1000 entries, occupying
something like 300 kilobytes. But everything is organized
alphabetically, and to make things even better, each entry is
coded by type (names, acronyms, types of machines, basic physics
terms, advanced plasma terms, etc). Hopefully this will make
the glossary easier to use.

# What's in the FUT:

We started with an initial list supplied by Jim Day
( To this were added some comments from various
responses I received to the first draft. I then incorporated terms
from PPPL and other glossaries. Then acronyms, machine names,
and names of important scientists were added as they came.
I added categories for research and funding/political agencies,
tried to broaden the base of basic science terms, and wrote up
a few more preliminary definitions based upon explanations that
have appeared in the newsgroup and in my studies. Many of the
terms listed still do not have explanations given.

Recent drafts have been mostly incremental improvements to
the previous versions. New categories of terms have been made,
the organization has been improved, and of course definitions
have been added and improved.

The most recent project has been to incorporate terms from the
"Glossary of Fusion Energy" published in 1985 by the Office of
Scientific and Technical Information (OSTI) of the U.S. Department
of Energy. This has been a fairly major effort, which has
roughly doubled the size of the glossary.

My current plan for the Glossary is to write entries for terms
used in my classes. This will be useful to me, as part of
studying for my upcoming PhD qualifying exam, and hopefully will
also help incoming graduate students, both here and around the

# What's Needed to Improve the FUT:

I am looking for additional contributions (and improvements) to
the list. It would be nice if people posting to the group could
occasionally take a few moments to include definitions of a few
terms used when you use them; in browsing through the group I
can then snip out the terms and definitions and simply paste
them into the evolving Glossary files. It also would be nice if
references to the FAQ and the Reading List / Bibliography
could be given to supplement the Glossary descriptions, at least
for some of the more complicated terms.

# Comment on Sources:

The terms and definitions occurring here represent a collection
of contributions from numerous sources. Rather than include
acknowledgements for each individual definition, I have made
blanket acknowledgements below. I have tried to include
citations in most cases where only a single textual source
was used.

# Acknowledgements for the Glossary:
! = someone I believe is a scientist
* = people who are not scientists so far as I know, organizations, etc.

! Jake Blanchard, - suggested we have a
list of acronyms too.
! Arthur Carlson, - supplied additional
definitions, made corrections / amplifications / revisions to
earlier definitions.
! Edward Chao, - info on LANL fusion research,
additions and corrections to various definitions.
! Albert Chou, - supplied additional
definitions, made corrections / amplifications / revisions to
earlier definitions.
! John Cobb, - lots o' definitions.
! James Crotinger, - additional definitions,
quality control, and comments on the usefulness of the FUT.
* Jim Day, - initial list of terms, additional
definitions, modifications to earlier definitions.
! Steve Fairfax, - additional definitions
from the Alcator weekly reports.
* Robin Herman, _Fusion: Search for Endless Energy_; I borrowed a
few terms from her glossary. Cited as (from Herman). (Many
of these terms derived from the PPPL glossary I also used.)
! Paul M. Koloc, p...@prometheus.UUCP - quality control, some entries
! Emilio Martines, - quality control,
reversed-field entries & information.
! Robert Nachtrieb, - numerous acronyms
* Princeton Plasma Physics Lab, Glossary of Fusion Terms - list of
terms prepared by PPPL staff at some point. Consulted in many
cases, blatantly paraphrased in some, quoted and cited in
* Vicki Rosenzweig, - Proofreading entries
* Mike Ross, - additional Livermore info
and corrections to some entries.
* Richard Schroeppel, - suggestions/corrections to
many definitions.
! Philip Snyder, - corrections to
! Paul Stek, - additional definitions
!? Mitchell Swarz, - supplied additional
definitions / corrections and revisions to existing definitions.
* United States Department of Energy, Office of Fusion Energy -
for funding fusion research and making everything possible
* United States Department of Energy, Office of Scientific and
Technical Information - for the 1985 Glossary of Fusion Energy,
which I have utilized extensively and incorporated into this Glossary.

# This file may be freely distributed; I recommend you retain the
revision date, and in any case I'd like to be cited as the editor. #

# Any and all errors are solely my responsibility. #

Robert F. Heeter
Graduate Student, Princeton Plasma Physics Lab
(Usual disclaimers apply.)

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/d
Last-modified: 4-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 4: Terms beginning with "D"


Edited by Robert F. Heeter,

Guide to Categories:

* = vocabulary specific to plasma/fusion/energy research
& = basic/general physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


@ D: nuclear/chemical symbol for deuterium/deuteron

@ DC, dc: Direct Current; see entry

@ DCLC: Drift Cyclotron Loss Cone instabilities; see entry.

@ DT: Deuterium-Tritium; see entry labeled DT Fuel

@ DIII-D: not an acronym (anymore); see entry

@ DOE: Department of Energy (United States); see entry

@ dpa: Displacements per atom; see entry

@ DPP: Division of Plasma Physics; see APS-DPP

* D-shaped plasma: A toroidal plasma whose cross section
(poloidal plane) is a D (instead of a circle). A D-shape
has a higher beta limit (see entry) than a circular shape.

* Debye Length: The characteristic distance over which charges are
shielded in a plasma. See also: Debye shielding.
lambda_D = ( epsilon_0 k_B T_e / (n_e e^2) )^(1/2)
lambda_D[m] = (7.434*10^3)*(_e[eV])^(1/2)*n[m^(-3)]^(-1/2)
(Arthur Carlson,

! Debye, Peter Joseph: Physical chemist, studied behavior of
conductive solutions (plasmas have some similar behaviors).

* Debye Radius: See Debye Length.

* Debye Sheath: The region of strong electric field in front of
a material surface in contact with a plasma. Its characteristic
thickness is the Debye length, and it is caused by Debye shielding
of the negative surface charge resulting from electrons flowing to
the surface much faster (initially) than the ions. The lost
electrons leave behind a region of net positive charge which
gradually diminishes the strength of the electric field
over the debye length. See also: Debye Length, Debye Shielding.
(Arthur Carlson,, with modifications by
John Cobb,

* Debye Shielding: If a positive (or negative) charge is inserted
into a plasma, it will change the local charge distribution by
attracting (repelling) electrons. The net result is an additional
negative (positive) charge density which cancels the effect of the
initial charge at distances large compared to the Debye length.
(There is a corresponding effect of shielding by the ions, which,
for various and subtle reasons, usually is less important.)
See also: Debye Length.
(Arthur Carlson,

* Debye Sphere: Sphere around a charged test particle whose
radius is equal to the Debye length.

& Decay, Radioactive: See radioactive decay.

* Decay Modes: Different pathways for decay of radioactive nuclei.
The decay modes for a given unstable state can include beta
emission (negative = electron, positive = positron), electron
capture, alpha emission, fission, and gamma emission.
(Did I miss any?) See entries for each mode for more information.

* Dee-Shaped: see D-shaped plasma above.

* Degenerate Configuration: Magnetic field configuration in
which the magnetic lines of force close exactly on themselves
after passing around the configuration a finite number of times.

* Dense Plasma Focus: See Plasma Focus. (Densities of up
to 10^26 particles/m^3 have been reported.)

& Density: amount per unit of volume, or per unit surface area, or
per unit length. (Usually specified or clear from context which
of these is meant). Several types:
Charge density - amount of charge per unit (volume, area, length)
Current density - current flow per unit transverse surface area.
Energy density - amount of energy per unit volume.
Flux density - flux per unit of transverse surface area.
Mass density - mass per unit volume.
Number density - number of particles per unit volume.
Particle density - same as number density.

% Department of Energy: (DOE) Department within the
executive branch of the U.S. government (at the cabinet
level) which has managed and overseen federally-sponsored
energy research. The DOE was formed in 1977 from ERDA,
the Energy Research and Development Administration,
and (I think) the Atomic Enegy Commission (AEC).

& Deuterium: A heavy isotope of hydrogen whose nucleus
contains both a neutron and a proton.

* Deuteron: A deuterium ion; nucleus consisting of a proton
and a neutron.

* Diagnostics: (from Herman) Procedures for determining
(diagnosing) the state of a plasma during an experiment;
also refers to the instruments used for diagnosing.

* Diamagnetic Effects: Application of a magnetic field to a plasma
will tend to create circulating current within the plasma that will
reduce the strength of the magnetic field.

* Diffusion: The interpenetration of one substance into another
as a result of thermal / random motion of the individual particles.
(e.g., the diffusion of a plasma across a magnetic field as a
result of collisions which cause particles to move along new
field lines.) See also classical diffusion, neoclassical diffusion,
anomalous diffusion, transport.

* Direct Conversion: The generation of electricity by direct
recovery of the kinetic energy of the charged fusion reaction

& Direct Current: Electric current which is unchanging in
time, or at least not oscillating. Opposite of Alternating Current.

* Direct Drive: An approach to inertial-confinement fusion
in which the energy of the driver (laser or particle beam)
is directly incident on the (usually spherical) target,
causing compression heating via ablation of the target surface.

* Dispersion Relation: For a given wave, the dispersion relation
relates the temporal frequency of a wave (w, or omega) to its
wavenumber k and other physical quantities characteristic of
the system. Dispersion relations can be quite simple
(e.g., w = k * c for light; c being the speed of light),
and they can also be quite complex, with interesting
mathematical structure. The dispersion relation and its
mathematical structure provide important information
about the wave, including the phase and group velocities.
(See relevant entries.) Note that the meaning of "dispersion
relation" is different in plasma physics than in other fields.

* Displacements Per Atom: (dpa) This is a measure of the
amount of radiation damage in neutron-irradiated materials;
e.g., 10 dpa means each atom in the material has been
displaced from its structural lattice site and average of
10 times (due to interactions between the atoms and the
energetic neutrons irradiating the material.)

* Disruption: Plasma instabilities (usually oscillatory modes)
sometimes grow and cause disruptions of the carefully-engineered
plasma conditions in the reactor. Major disruptions can cause
an abrupt temperature drop and the termination of the plasma.
Stored energy in the plasma is rapidly dumped into the rest
of the plasma system (vacuum vessel walls, magnet coils, etc.)
and can cause significant damage if precautions are not taken.

* Disruptive Instability: Instability which causes a disruption;
see entry for disruption.

* Dissociative Recombination: The combination of an electron
with a positive molecular ion, followed by dissociation of
the molecule in which the resulting atoms/molecules carry
off the excess energy released in the recombination.

& Distribution Function: Function characterizing the density of
particles located at a given point in phase space (a combination
of either velocity or position coordinates) at a given time.
The velocity-space distribution function gives the number of
particles with a particular velocity; the position-space
distribution function is synonymous with the particle density
in position-space. Different combinations of position and
spatial coordinates are useful in different problems.

* Divertor: Component of a toroidal fusion device that diverts
charged particles on the outer edge of the plasma into
a separate chamber where they strike a barrier and become
neutralized. In a reactor, the divertor would incorporate a
system for pumping out the neutralized particles as exhaust
from the machine. A divertor, like a limiter, prevents the
particles from striking and degrading the chamber walls
and dislodging secondary particles that would cool and
contaminate the plasma. Whereas a limiter is a material
object used to limit the shape of the plasma, a divertor is a
magnetic-field construction. The advantage of the divertor
is that it allows the neutralization region to be
removed from the main plasma. See also: limiter.

* Doppler Broadening: Frequency spreading which causes
broadening of single-frequency radiation (e.g., spectral
lines) when the radiating bodies (atoms, molecules, etc.)
have different velocities. Radiation from each individual
radiating body has a different Doppler shift, and
the collection of radiations at different frequencies
broadens the peak of the line in an intensity-vs-frequency

& Doppler Effect: Variation in the frequency of a
wave (as measured by an observer) due to relative motion
between the observer and the source of the wave.
(The observed frequency increases if the source is moving
towards the observer.)

& Doppler Shift: The amount of change in the observed
frequency of a wave due to the Doppler effect; sometimes
called the Doppler frequency.

> DIII-D: Latest in a series of tokamaks designed
by General Atomics (formerly GA Technologies) in San Diego
making plasmas with noncircular cross sections, including
kidney shapes and D-shapes.

* Doublet Device / Doublet Plasma: Tokamak-type devices
where the plasma cross-section is kidney-shaped, with
a deep indentation in the middle so that the plasma has
two major rings of current (on top and bottom).

* Drift Cyclotron Loss Cone Instabilities: (DCLC)
This is an electrostatic microinstability (frequencies
at harmonics of the ion cyclotron frequency) which is of
major concern in small mirror devices. Mode is driven
by radial gradients in the electron density, and causes
loss of ions due to non-conservation of magnetic moment
(see adiabatic invariant) as they interact with the mode,
and are dispersed in velocity space into the loss cone.
Stabilization is accomplished by increasing the plasma
size and by partially filling the loss cone with a
continuous extermal warm plasma stream.

* Drift Motion: Ordinarily particles placed in a magnetic
field will simply orbit in circles, but if the magnetic field
is not uniform, or curves, or there is an electrical field
perpendicular to the magnetic field, or another force is applied
perpendicular to the magnetic field, then the "guiding centers"
of the particle orbits will drift (generally perpendicular to
the magnetic field and to the applied force). There are several
sorts of drifts; refer to a plasma physics text for more
information (see Section 11: Bibliography). For a good
introduction at the undergraduate physics level, see Chen.

* Drift Pumping: A process that removes ions trapped in
a thermal barrier using radial transport induced by an
exterally-applied radiofrequency field tuned to resonate
with the azimuthal drift frequency.

* Drift Surface: Surface on which the guiding center of
a particle is constrained to move, due to the effects of
the laws of adiabatic invariance on its drift motion.

* Drift Velocity: Characteristic velocity at which the center
of a particle's orbit ("guiding center") drifts when drift motion
(see above) occurs.

* Drift Waves: Oscillations in a magnetically-confined plasma
arising in the presence of density gradients (such as at the
plasma's surface). These resemble the waves that propagate
at the interface of two fluids with different density in
a gravitational field.

* DT Fuel: (Deuterium-Tritium) Easiest fuel mixture to use
in achieving fusion; unless otherwise specified, probably refers
to a 50-50 (by numbers or by moles) mix of deuterium and tritium.

* Duty Factor: Ratio of the duration of time when a system is
actually operating to the total time for a complete cycle
of the system. e.g., if a tokamak experiment runs for 5 seconds
and then sits for 500 seconds while the power supplies are
recharged, then the duty factor is 1%. Similar to capacity
factor for powerplants.

* Dye laser: A type laser in which the active material
(the material which emits the laser light) is a dye.
These lasers are tunable when the dye has very large
molecules (such as acridine red or esculin) and the laser
action takes place between the first excited and ground
electronic states, because each of these states contains
a broad continuum band of vibrational-rotational levels.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/c
Last-modified: 4-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 3: Terms beginning with "C"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary

> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# c: Speed of light; 3.0x10E+8 meters/second or 3.0x10E+10 cm/sec

@ CAMAC: Computer Automated Measurement and Control

@ CANDU: CAnadian Deuterium-Uranium class of fission reactor;
see entry

> CASCADE: See entry (not an acronym as far as I know).

@ CCD: Charge Coupled Device

@ CGS: Centimeters, Grams, Seconds; see CGS Units

@ CGS Units: see entry below; see also CGS above.

@ CFFTP: Canadian Fusion Fuels Technology Project; see entry.

@ CIT: Compact Ignition Tokamak; see entry

@ COE: Cost of Electricity

@ CT: Compact Torus; see entry

@ CTX Facility: Compact Toroid Experimental facility; see entry.

@ cw: Continuous Wave (distinct from pulsed).

@ CY: Calendar Year (as opposed to Fiscal Year, FY)

$ cm: centimeters; unit of distance. See also centi-

* C-Coil: C-shaped magnet coil

* Calorimeter: In conventional fusion research, this name
refers to any device used to measure power or energy in
a laser or particle beam. (e.g., for ICF or neutral beam
heating or a magnetically-confined plasma.)

* Canadian Deuterium-Uranium Fission Reactor: Nuclear fission
reactor type developed in, and prominent in, Canada; characterized
by use of heavy water (deuterium instead of hydrogen, D2O) as
moderator and coolant. Neutrons absorbed by the deuterium create
a source of marketable tritium.

* Canadian Fusion Fuels Technology Project: Fusion power
development project, jointly funded by the National Research
Council of Canada, the Province of Ontario, and Ontario
Hydro (energy company and project manager), to develop
and internationally apply technologies related to management
of fusion fuels. (Any current info, anyone?)

& Carbon: (C) Sixth element (Z=5) in the periodic table; has
6 protons; often described as the basis of life on earth because
of its chemical properties; has potential for use with silicon
as a low-activation structural material for fusion reactors,
in the form silicon carbide. (See relevant parts of FAQ
section 2.) Also useful as a neutron moderator. See also
low-activation materials.

& Carnot Efficiency: maximum possible efficiency for conversion
of thermal energy to useful work (such as electrical energy),
as determined by the laws of thermodynamics. The Carnot efficiency
(eta) for conversion of thermal to electric energy (e.g., the upper
limit on efficiency of a steam turbine) is given by
(eta) = [ (T-hot) - (T-cold) ] / (T-hot). That is, one gets the
efficiency from the values of the input and output temperatures
(measured in Kelvin).

& Capacitor: device used to store electrical energy by accumulating
charges on nearby conductors. Energy may be stored and withdrawn
at varying rates. Used in short-pulse plasma devices where only
a moderate amount of energy is needed.

* Capacity Factor: Index (typically in percent) indicating the
average power supplied by an energy plant, relative to its
maximum rated capacity.

* Capital: Economic term for wealth of a permanent nature, rather
than that which is consumed; includes money and other financial
goods, plant & equipment, etc. (I'm not an economist - anyone
know any better?)

> CASCADE: An inertial-fusion energy conversion concept where
a flowing, replenished layer of ceramic granules (in a rotating
chamber) protects the chamber wall from the fusion environment
while absorbing neutrons, breeding tritium fuel, and serving as
the high-temperature heat exchange fluid.

& Celsius: Temperature scale where zero degrees corresponds to the
freezing point of water (32 Fahrenheit) and 100 degrees corresponds
to the boiling point (212 Fahrenheit). Zero celsius = 273.16 Kelvin.

* Centering Force: Term for the mutual attraction
between the parallel currents in the inboard leg of the toroidal
field coils in a toroidal magnetic fusion system (e.g., a tokamak).
The portion of the coil running "through the doughnut hole" is
attracted towards the center of the hole.

& Centi-: metric prefix indicating 1/100th of a given unit.
e.g., one centimeter is 1/100th of a meter.

& Centigrade: see Celsius

& CGS Units: System of measurement where the fundamental units
are centimeters, grams, and seconds.

& Chain Reaction: (from Herman) A self-sustaining series of
chemical or nuclear reactions in which the products of the
reaction contribute directly to the propagation of the process.

* Channel Transport: In inertial fusion research using light
ion drivers, describes the use of current-carrying plasma
channels (which are magnetically confined to the channel) to
transport electron or ion beams between the ion diode and the
fusion target. This allows the ion source to stand back from
the target.

& Charge Density: See density, and apply to electrical charge.

& Charge, Electrical:
As a noun: A fundamental physical attribute of a
particle, which characterizes the particle's electromagnetic
interaction with other particles and with electric and magnetic
fields. (See also particle, field)

As a verb: Storing energy in a battery or electric capacitor by
running a current through it; opposite of discharge. (It is possible
to charge most capacitors in either direction, but batteries charge
one way, and discharge the other.)

* Charge Exchange: Phenomenon in which an ion colliding with
a molecule (or an atom) neutralizes itself by capturing an electron
from the molecule/atom, and transforming the molecule/atom into a
positive radical/ion.

* Charge Transfer: see charge exchange

* Charged Particle: a particle which carries a positive or
negative electrical charge. In plasma physics, this typically
means an ionized atom or molecule, or an electron.

* China Syndrome: American jargon/slang for a nuclear fission
meltdown accident (see meltdown) in which the molten nuclear core
heats and melts the ground beneath it, thus sinking into the
earth, and heading towards China (which is roughly on the opposite
side of the globe).

* Classical Confinement: Plasma confinement in which energy transfer is
via classical diffusion; best possible case for magnetically
confined plasmas. See entry for classical diffusion below.

* Classical Diffusion: In plasma physics, diffusion due solely
to scattering (collisions) of charged particles (with unlike
charges) via electrical ("Coulomb") interactions. (See also diffusion.)

* Coherent Radiation: Any form of radiation in which the phase
relationship between sections of the wave at different locations is
not random (or incoherent!). Typical example is a laser beam, in
which the phase is more or less uniform across the beam, and changes
along the beam in accordance with the wavelength. Radiation in
which the photons tend to "agree" with one another, rather than
being randomly distributed.

* Cold Plasma Model: Model of a plasma in which the temperature is
neglected with respect to the effects of interest.

* Collision: Refers to the close approach of two or more
particles, photons, atoms, nuclei, etc, during which such quantities
as energy, momentum, and charge may be altered. More-or-less
synonymous with "scattering," except in scattering one generally
thinks of one of the particles as being at rest, and the other
colliding particles "scatter" from their initial direction of
motion due to the collision.

& Collision Cross-Section: Effective surface area of a particle
when it collides with another; describes probability of collisions
between the two particles.

* Collisionless Plasma Model: Model of a plasma in which the density
is so low, or the temperature so high, that close binary (two-body)
collisions have practically no significance (on certain timescales)
because the time scales of interest are smaller than the
collision time. Yields valid physical results for timescales
much shorter than the average collision time in a real plasma.

& Collision Time: Typical time which passes between the time
a particle collides, and when it collides again. Inverse of the
collision frequency; equal to the mean free path divided by the
particle's velocity. The collision time decreases with increasing
density, and increases with increasing temperature.

> Compact Ignition Tokamak (CIT): Proposed U.S. successor to TFTR;
never funded. See also, BPX, TPX.

> Compact Torus: Any of a series of axially symmetric fusion
configurations having closed flux surfaces (like a tokamak, not
like a mirror machine), but having no material objects piercing
the core (as do the toroidal field coils of a tokamak). These
devices have an inherently low aspect ratio, approximately unity.
The most successful variants are the spheromak and the Field
Reversed Configuration. See also: low aspect ratio, spheromak,
field-reversed configuration. (Arthur Carlson,

> CTX Facility (Compact Toroid Experimental facility):
Los Alamos facility to investigate plasma physics of compact
toroids. (No longer in operation?)

* Compression Waves: Also known as density waves (I think!);
waves where the quantity which oscillates is the density of the
medium, that is the medium at a given point alternately
compresses and expands. Low-amplitude compression waves in
air or water are commonly known as sound waves; shock waves
are a high-amplitude form. See also waves.

& Conductivity: Degree to which a substance transmits (conducts)
a given physical property, such as heat or electricity.
See electrical conductivity, thermal conductivity.

* Confinement, Classical: See classical confinement.

* Confinement, Electrostatic: See electrostatic confinement.

* Confinement, Inertial: See inertial confinement.

* Confinement, Magnetic: See magnetic confinement.

* Confinement Time: There are several types. The general
definition is that tau = [total]/[loss per unit time];
hence Tau_E = [total energy]/[energy loss per unit time].

Tau_[E, N, ...] is the amount of time the plasma is contained
by magnetic fields before its [energy (E), particles (N or P)]
leak / dissipate away. The different types are, in general,
similar but not equal.
(Note note note: Tau_E is NOT electron confinement time!)

> Constance: Small mirror devices; formerly operated at MIT.

* Containment Vessel: Gas-tight shell or other enclosure
around a fusion (or fission) reactor, to prevent accidental
leakage of radioactive contents.

* Controlled Thermonuclear Fusion: The process in which
light nuclei, heated to a high temperature in a confined
region, undergo fusion reactions under controlled conditions,
with associated release of energy which may be harnessed
for useful purposes.

* Coolant: Substance circulated through a device (including
fusion reactors, fusion reactor magnets, etc.) to remove or
transfer heat. Common types include water, helium, and
liquid-metals such as sodium (Na).

* Cooperative Phenomena: The motion of interacting particles
acting collectively, rather than individually. Includes
plasma oscillations, turbulence, and instabilities. (Plasmas
are distinguished from collections of individual particles
in that they exhibit cooperative phenomena, whereby the plasma
particles "cooperate" with one another. Early fusion researchers
who devised fusion schemes based upon theories where plasmas
acted as merely a collection of individual particles (and
therefore sought to confine only individual particles) often
found themselves frustrated at the ability of plasma
cooperative phenomena (such as MHD instabilities) to thwart
their efforts.

* Core plasma: Hot plasma at the center of a fusion reactor;
distinguished from edge plasma. The core plasma does not
directly feel the effects of the divertor or limiter in the
way the edge plasma does. (More info anyone?)

* Corona: The outermost (?) part of a star's atmosphere;
characterized by high temperatures and low densities; home to
many plasma phenomena.

* Corrosion: Chemical interactions between a fluid, (such
as lithium or water coolant) and the containing material
(such as stainless steel), which results in wall material
dissolving into the fluid, and possibly degradation of
the mechanical properties of the containing structure

$ Coulomb: standard unit of electric charge. A single electron or
proton has a charge of (+/-) 1.6022E-19 coulombs. Hence there are
6.2414E+18 electrons in a coulomb of electrons.

* Coulomb Collision: An interparticle collision where Coulomb's Law
(electrical attraction and repulsion) is the governing force.
(See Coulomb's Law) Coulomb collisions have a number of interesting
properties, but these are better described in textbooks. The
interaction of the charged particles with each other's electric
fields results in deflections of the particles away from their
initial paths.

& Coulomb Force: See Coulomb's Law. Also called
"electrostatic force."

* Coulomb Ionization: Ionization produced by Coulomb forces
between a moving particle ("projectile") and another particle
it interacts/collides with ("target").

& Coulomb's Law: Force law governing the electrical interaction
between charged particles. Force is proportional to (charge of
first particle) * (charge of second particle) / (square of separation
between particles). Constant of proportionality depends on system
of units used. (In SI units, it is 1/(4*pi*epsilon-0), where
epsilon-0 is the permittivity of free space = 8.854 x 10^-12 )

& Cross Section: (usually symbolized with a lower-case Greek sigma)
In physics this usually refers to the (apparent) area presented
by a target particle to an oncoming particle (or electromagnetic
wave). This measures the probability of an interaction occuring.
For typical interactions between ions and electrons, or between
two nuclei, these cross sections are generally measured in barns.
(See relevant entries.)

& Cryogenic: Loosely, "very cold". Used to describe systems which
operate at very low temperatures. Superconducting magnetic field
coils currently need to operate at cryogenic temperatures (e.g.,
liquid helium at 4 Kelvin).

* Curie: Unit of radioactivity roughly equal to the rate of
radioactive decay of a gram of radium; named after Marie
Curie (see below). Corresponds to 3.7 x 10^10
disintegrations/second (37 billion). (See Becquerel)

! Curie: Marie and Pierre; husband-wife pair of French scientists.
Pierre's name is attatched to the "Curie point" in magnetism, which
is not discussed here. He and his wife shared with Antoine-Henri
Becquerel the Nobel Prize for physics in 1903. Marie Curie,
a.k.a. Madame Curie, received the Nobel Prize for chemistry
in 1911, becoming the first person to receive more than
one Nobel Prize. She remains the only person to receive Nobel
Prizes in different fields. (I believe - RFH)

& Current Density: Amount of current flowing through a substance,
per unit area perpendicular to the direction of current flow. (See
also density)

* Current Drive: Any of a variety of techniques used to cause
current flow in a plasma. See inductive current drive, RF current
drive, non-inductive current drive. Usually applied to schemes
used to generate current in tokamaks and other toroidal devices
which require internal plasma currents. See also: bootstrap current.

* Cusped Geometry: I can't figure out how to explain this one in
words; suffice it to say that this is a description of a magnetic
field configuration where the magnetic field lines, rather than
closing in on themselves, tend to squirt out and form cusps at
certain points; I recommend you look this up in a plasma physics
text (e.g., Chen - see bibliography entry) to really understand it.
The magnetic field lines are everywhere convex towards the center.
Such a geometry is interesting because it is theoretically stable
against a variety of MHD instabilities.

> Cyclops: Single-chain, 0.6 terawatt Nd-glass laser system at
Lawrence Livermore National Laboratory that was used for laser
studies and inertial-confinement fusion experiments in 1975-1976.

* Cyclotron: Particle accelerator in which a magnetic field causes
particles to orbit in circles, and an oscillating electric field
accelerates the particles.

* Cyclotron Frequency: Number of times per second that a particle
orbits in a magnetic field. (Often, and incorrectly, called the
Larmor frequency. The cyclotron or gyrofrequency is twice the
Larmor frequency of precession.)

* Cyclotron Radius: Radius of orbit of charged particle about
a magnetic field line. Also called gyroradius, Larmor radius.

* Cyclotron Radiation: See synchrotron radiation

* Cyclotron Resonance: Charged particles in a magnetic field
resonate with (and absorb energy from) an electric field
(perpendicular to the magnetic field) which oscillates at
the particles' cyclotron frequency, or at a harmonic
(multiple) of that frequency.

* Cyclotron Resonance Heating: see Electron Cyclotron Resonance
Heating, Ion Cyclotron Resonance Heating.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/g
Last-modified: 4-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 7: Terms beginning with "G"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


$ G: abbreviation for Gauss; see entry

@ GA: General Atomic; see entry.

@ GDC: Glow Discharge Cleaning; see entry.

@ GN2: Gaseous diatomic Nitrogen (N2)

@ GNP: Gross National Product; see entry.

@ GW: Gigawatt; see entry

@ GWe: Gigawatt - electrical energy; see gigawatt

@ GWt: Gigawatt - thermal energy; see gigawatt

& Gain: (Amplification) Increase in a signal transmitted
from one point to another through an amplifier.

# gamma: Third letter in the Greek alphabet; variable used for
a number of things in phyics; in plasma physics gamma is often
used as the variable for growth rates of instabilities.

* Gamma Emission: Nuclear decay process whereby the nucleus goes
from an excited state to a more stable state by emitting a gamma
ray. (See entry for gamma ray.)

* Gamma Rays: Electromagnetic radiation (photons) with energies
greater than (roughly) 100 keV (that is, 100,000 electron volts).
Gamma radiation frequently accompanies alpha and beta decays,
and always accompanies fission. Gamma rays are highly penetrating
and are best shielded against using dense materials, such as
lead or depleted uranium. (Gamma rays are similar to X-rays, but
are generally higher in energy and nuclear in origin.) See
relevant entries for more info.

% Garching: A town in Germany just north of Munich, where the Max
Planck Institute for Plasma Physics (see entry) is located. "Garching"
in plasma physics frequently refers to the Max Planck Institute.

* Gas Blanket: A cold, dense volume of gas surrounding a hot
plasma and used to protect a material wall from bombardment
by hot ions (with subsequent sputtering and impurity production).

! Gauss, Carl Friedrich: (1777-1855) German mathmetician, astronomer
and physicist.

$ Gauss - unit of magnetic field strength (CGS units)
10,000 gauss = 1 tesla (see also Tesla)

& Gaussian Units - See CGS Units

% General Atomic: U.S. corporation involved in fusion research;
operates the DIII-D device in San Diego; see also Doublet III-D.
(Officially known as GA Technologies, I believe; or is that the
name of the parent company???)

& Getters: Materials which absorb ("get") atoms and can be
used in purifying near-vacuum atmospheres.

$ Gigawatt: Unit of power equal to 10^9 watts, 1000 megawatts,
or 1 million kilowatts. See entry for watt. 1 gigawatt is a typical
size for a nuclear fission reactor, and is expected to be the typical
size of a fusion reactor.

* Glow Discharge: Low-density, low-temperature plasma discharge
(such as in a fluorescent light) which, well, glows. Sputtering
in glow discharges is useful in plasma processing of materials.
The voltage applied to the plasma must be greater than the
ionization potential of the gas used; most of the plasma voltage
drop is near the cathode, where the majority of ionization occurs.
Discharge is sustained by secondary electrons emitted when ions
or recombination radiation impact on the cathode; electrons are
accelerated away from the cathode and ionize neutral gas in the

* Glow Discharge Cleaning: Cleaning in which impurities are
removed by sputtering in a glow discharge. (?)

* Grad-Shafranov Equation: Reduced MHD-equilibrium equation for
an axisymmetric, toroidal plasma. (Similar reduced equations
can be derived for the cases of helical symmetry and for
the straight cylinder.) Analytic and numerical studies of these
equations are important in exploring potential plasma

-> Additional info Contributed by James Crotinger, with minor

The lowest order force balance in the plasma is simply that
the Lorentz force must be balanced by the pressure force.
This balance, combined with Maxwell's equations, determines
the equilibrium configuration of the magnetic field. When
the toroidal configuration is axisymmetric, and the equilibrium
plasma flow is zero, the magnetic field may be written in
terms of a stream function \psi that satisfies the
Grad-Shafranov equation

\Delta*\psi = - \mu_0 R^2 p'(\psi) - FF'(\psi).
Here p is the plasma pressure and F = R B_\phi.
(R is the radial distance from the axis of the machine)

(Alternatively, leaving out the equation):
In an axisymmetric torus, in the absence of equilibrium plasma
fluid flows, the magnetic field may be written in
terms of a scalar potential. When the plasma is in equilibrium
(forces balance and the plasma is stationary), this scalar
potential obeys a non-linear elliptic equation known as the
Grad-Shafranov equation.

& Gradient: Mathematical term for the operator which determines
the magnitude and direction of the greatest rate-of-change of a
given function with position. Similarly used to describe such
a rate-of-change. For instance, at a given point on a hill, the
slope of the hill in the steepest uphill direction is the gradient
of the altitude funtion for the hill.

& Gravitational Force: Force which attracts two bodies together
based on the product of their masses and the reciprocal of
the square of their distances. "Gravity" is the force field
created by one massive body (like the earth) which another body
(like you) will experience.

* Gross National Product: Total value of goods and services
produced in a country; measure of economic strength of a nation.

$ Gray: A unit of absorbed dose of radiation, equal to one
joule of energy per kilogram of mass. 1 Gray = 100 rads.
Defined relative to the material into which such radiation passed,
which should therefore be specified.

& Group Velocity: This is derived from the dispersion relation
(see entry) as Vgroup = dw/dk; the group velocity is the rate
at which modulations or information within a wave travel through
a given medium.

* Guiding Center: Particles placed in a magnetic field will
gyrate in circles around the magnetic field lines, and drift in
various directions. The guiding center represents the
instantaneous center of the circular motion. The idea is that
you can think of the guiding center as drifting, and the particle
as orbiting the guiding center.

* Gyrofrequency: See cyclotron frequency.

* Gyromagnetic Ratio: Ratio of the magnetic moment to the
angular momentum of a particle. (see magnetic moment, angular

* Gyroradius: radius of charged particle in magnetic field.
Same thing as cyclotron radius, Larmor radius.

* Gyrotron: A device for producing microwave energy that
utilizes a strong axial magnetic field in a cavity resonator
to produce azimuthal bunching of an electron beam.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/f
Last-modified: 4-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 6: Terms beginning with "F"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# F: Variable typically used for force; sometimes flux.

& F: Chemical symbol for the element fluorine.

* FLiBe or flibe or FLIBE: Fluorine-LIthium-BEryllium; see
entry "Flibe" below.

@ FEDC: Fusion Engineering Design Center; see entry

@ FLR: Finite Larmor Radius; see entry

@ FPD: Fusion Power Demonstration facility; see DEMO.

@ FRC: Field-Reversed Configuration; see entry

@ FY: Fiscal Year; see entry

& Fabry-Perot Interferometer: A type of interferometer with
two parallel mirrors (with a variable separation of a
few centimeters) arranged so that incoming light is reflected
between them multiple times before ultimately being transmitted.
Useful in spectroscopy because it gives very good frequency
resolution without losing too much of the incident signal.

* Faraday Rotator: A device which rotates the plane of
polarization of an optical-light pulse, typically by
using a glass disc suitably doped with a magnetic ion
and placed in a magnetic field. These devices are used
to isolate (protect) a laser amplifier chain against
back-reflection from the laser target; the Faraday rotator
in this case gives a 90-degree phase change on the round
trip, so that the returning light is rejected by a
polarizer which transmits the outgoing light.

* Fast neutron: Neutron with energy greater than roughly
100,000 electron volts (100 keV). Distinguished from slow or
thermal neutrons. (See appropriation entries.)

* Fertile Material: In nuclear physics, this refers to a nuclide
which converts to fissile material (see entry) upon neutron
capture and subsequent radioactive decay. Examples include
Uranium-238 and Thorium-232.

& Field: In physics, any macroscopic quantity which exists
(and typically varies) througout a region of space. Standard
examples include Electric and Magnetic fields, velocity flow fields,
gravitational fields, etc.

& Field Lines: Lines in space along which a field is either
changing or not changing (depends on the field) but which help
to create diagrams which characterize the behavior and effects
of the field. For instance, electric field lines run in the
direction that the electric field will push charged particles;
the strength of the field is proportional to the density of
the field lines. On the other hand, the magnetic force pushes
particles in a direction perpendicular to both the particle's
velocity and the direction of the magnetic field line.

> Field-Reversed Configuration: A compact torus produced in a
theta pinch and having (in principle) no toroidal field. The
potential advantages for a fusion reactor include a simple (linear)
machine geometry, an average plasma pressure close to the confining
field pressure, and physical separation of formation and burn
chambers. The are predicted to be violently unstable to tilting, but
this is rarely observed. See also: compact torus, theta pinch.
(Arthur Carlson,

* Field Shaping Coils: Type of poloidal field coils (in a tokamak)
which create magnetic fields which shape and control the plasma.
Used to constrain horizontal and vertical displacements of the plasma,
as well as (in some configurations) produce non-circular plasma
cross sections (poloidal cross-section) and/or create one or more
divertor separatrices. (See relevant entries.)

* Finite Larmor Radius: In many plasma theories the size of the
Larmor radius (or gyroradius - see entries) is assumed to be
negligibly small, or infinitesimal. Different effects occur when
the size of the Larmor radius is finite and needs to be considered.
(Anyone out there with a succint, but more detailed explanation?)

* First Wall: The first physical boundary that surrounds a plasma.

* Fiscal Year (FY): Year used to open and close accounting records;
not necessarily the same as the calendar year. (For instance, the
U.S. government's Fiscal Year begins Oct 1 and ends Sept 30.)

* Fishbones: Oscillations in soft x-ray emissions which occur
during intense neutral-beam heating; associated with a recurring
m=1 internal kink mode. Mode was given its name from its
characteristic signal (looked like the bones of a fish, of course).
Fishbones are associated with loss of fast ions from the plasma
and are triggered by exceeding the upper limit on plasma beta.
(see relevant entries)

* Fissile Material: Material containing a large number of
easily fissionable nuclei which give off multiple neutrons in
the fission process. Usual meaning is that if a sufficiently
large amount of fissile material is put together, a fission
chain reaction can occur. Sometimes used synonymously with
"fissionable material," i.e., material that *can* be fissioned
(though often under restricted circumstances, such as only with
thermal (slow) neutrons). A more restricted meaning use of
fissile material limits the concept to those materials which can
be fissioned by neutrons of all energies (fast & slow).
Examples include Uranium-235 and Plutonium-239.

& Fission (Nuclear): Nuclear decay process whereby a large
nucleus splits into two smaller (typically comparably-sized)
nuclei (which are thus nuclei of lighter elements), with or
without emission of other particles such as neutrons.
When it occurs, fission typically results in a large energy
release. Fission can occur spontaneously in some nuclei, but
is usually caused by nuclear absorption of gamma rays,
neutrons, or other particles. See also spallation, radioactivity.

* Fission Bomb: see atomic bomb, A-bomb.

* Fission Reactor: (from Herman) A device that can initiate
and control a self-sustaining series of nuclear fissions.

* Flat-top: Stable period in the middle of a tokamak
discharge, characterized by a flat, stable peak in a plot
of plasma (current, temperature) vs. time.

* Flibe: Molten salt of Fluorine, Lithium, and Beryllium;
candidate blanket/coolant/breeder material for fusion reactors.

* Flute Instability: Term used to describe an interchange
instability in which the perturbation is uniform parallel
to the magnetic field. In cyclindrical geometry, the structure
resembles a fluted column (as in classical architecture).
Occurs in some mirror machines.

& Flux: The total amount of a quantity passing through a given
surface per unit time. Typical "quantities" include field lines,
particles, heat, energy, mass of fluid, etc. Common usage in
plasma physics is for "flux" by itself to mean "magnetic field

& Flux Density: Total amount of a quantity passing through a
unit surface area in unit time. See also flux, above.

* Flux freezing: See frozen-in law.

* Flux surfaces: See magnetic flux surfaces.

* Flux trapping: See frozen-in law.

& F-number: In optics, denotes the ratio of the equivalent focal
length of an objective lens to the diameter of its entrance pupil.

* Fokker-Planck Equation: An equation that describes the time rate
of change of a particle's velocity as a result of small-angle
collisional deflections. Applicable when the cumulative effect of
many small-angle collisions is greater than the effect of rarer
large-angle deflections.

& Force: Rate of change of momentum with time. Forces are said
to cause accelerations via F = ma (Newton's law). There are four
primary forces known presently: the gravitational, electromagnetic,
weak nuclear, and strong nuclear forces. The gravitational and
electromagnetic forces are long-range (dropping as 1/distance^2),
while the nuclear forces are short range (effective only within
nuclei; distances on the order of 10^-15 meters). The
electromagnetic force is much stronger than the gravitational force,
but is generally cancelled over large distances because of the
balance of positive and negative charges. Refer to entries for each
force for more information. See also momentum.

* Free Electron: An electron not bound to an atom, molecule, or
other particle via electric forces.

* Free Wave: A wave (e.g., electromagnetic) travelling in a
homogeneous infinite medium (no boundary conditions).

* Frozen-in Flow Law: In a perfect conductor, the total magnetic
flux through any surface is a constant. In a plasma which is nearly
perfectly conducting, the relevant surfaces move with the plasma;
the result is that the plasma is tied to the magnetic field, and
the field is tied to the plasma. Motion of the plasma thus
deforms the magnetic field, and vice versa.

* Fusion (Nuclear): a nuclear reaction in which light atomic
nuclei combine to form heavier nuclei, typically accompanied
by the release of energy. (See also Controlled
Thermonuclear Fusion)

% Fusion Engineering Design Center: Facility managed by
ORNL and staffed mainly by industrial personnel; undertakes
detailed engineering design of planned fusion facilities.
(Is it still in operation? The reference I have is out of date.)

* Fusion Reactor: Device which creates energy in a controlled
manner through fusion reactions.

> Fusion-Fission Hybrid: Proposed nuclear reactor relying
on both fusion and fission reactions. A central fusion
chamber would produce neutrons to provoke fission in a
surrounding blanket of fissionable material.
The neutron source could also be used to convert other
materials into additional fissile fuels (breeder hybrid).
Safer than a plain fission reactor because the fission fuel
relies on the fusion neutrons, and therefore won't spontaneously
melt down. On the other hand, hybrids are more complex because
of the fusion power core, and still generate fission's radioactive
byproducts. But could be more economical and have easier technical
requirements than a straight fusion reactor.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/j
Last-modified: 4-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 10: Terms beginning with "J"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# J: variable used to indicate current density

$ J: abbreviation for Joule; see entry

@ JET: Joint European Torus; see entry

@ JT-60, JT-60U: Japan Torus - 60 (Upgrade); see entry

> Janus: Early Inertial Confinement laser system at
Livermore; used for one- and two-beam laser-target
irradiation experiments in 1974 and 1975.

> Joint European Torus: Large tokamak next to the Culham
Laboratory in Oxfordshire, England, commonly owned by the
European Community. First reactor to achieve > 1 MW of fusion
power, in 1991. Largest tokamak currently in operation (to the
best of the editor's knowledge).

> JT-60: A large Japanese tokamak, located north of Tokyo.
JT-60U is an "upgrade" to JT-60 now in operation.
See also entry in Section 5.

$ Joule: SI unit of energy. 1 Joule = 1E7 ergs = 1 Watt of
power occurring for one second. 1 Joule is roughly 0.001 BTU
and 1 calorie is roughly 4 joules. There are 3.6 million joules
in a kilowatt hour.

& Joule Heating: See ohmic heating

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/k
Last-modified: 4-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 11: Terms beginning with "K"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# k: Mathematical symbol usually used for Boltzmann's Constant.
Value is 1.4 x 10^-23 Joules/Kelvin (in SI units),
or 1.4 x 10^-16 ergs/Kelvin (in cgs units).

$ kA: KiloAmpere; see kilo, Ampere

@ KDP: Potassium Dihydrogen Phosphate; crystal used in frequency
conversion of Nd:glass laser light.

$ kW: KiloWatt (1000 watts); see also kilo, Watt

$ kWh: kilowatt-hour; see entry

& Kelvin: (K) temperature scale where zero degrees corresponds
to absolute zero (no thermal energy); degrees have same
size as in Celsius/centigrade scale. 273.16 K = zero C;
373.16 = 100 C.

! (Lord) Kelvin: honorary name given to William Thompson; 19th
century British physicist (many contributions in many subfields).

* Kerma: Kinetic Energy (of charged particles) produced by
ionizing Radiation per unit MAss of irradiated material. (ergs/gm)

& kilo: metric prefix used to indicate 1000 times the following
unit. e.g., a kiloampere is 1000 amperes.

$ kilowatt-hour: standard unit of electrical energy; equals one
kilowatt of power delivered for one hour. Equivalent to 3.6
million joules.

* Kinetic Pressure: Density of kinetic energy (energy in the
thermal motions of the plasma particles). For an ideal plasma,
pressure is given by p = nkT, that is:

pressure = (density) * (Boltzmann's constant)* (temperature),

* Kinetic Temperature: A measure of the energy of random motion
(kinetic energy) of an assembly of particles in thermodynamic

* Kinetic Theory: A theory which attempts to explain the behavior
of physical systems using the assumptions that the systems are
composed of large numbers of atoms/molecules/particles in
vigorous motion, that energy and momentum are conserved in
collisions of these particles, and that statistical methods can
be applied to deduce the behavior of such systems.

* Kink Instability: Instability resulting from excessive growth
of a kink mode; see kink mode.

* Kink Mode: Class of MHD instabilities which sometimes develop
in a thin plasma column carrying a strong axial current. If a
kink begins to develop in such a column the magnetic forces on
the inside of the kink become larger than those on the outside,
so that in general it tends to grow in magnitude. The column
then becomes unstable and can be displaced into the walls of
the discharge chamber, causing a disruption.

& Klystron: An evacuated electron-beam tube in which electrons
are given initial velocities such that the beam's charge density
is modulated; the passage of a modulated current generates
microwave radiation, some of which is then fed back to modulate the
electrons' velocities. The result is a microwave amplifier.

* Kruskal Limit: In tokamaks, a theoretical limiting value for
plasma current beyond which MHD instabilities are predicted.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/m
Last-modified: 18-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 13: Terms beginning with "M"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# m, M: variable typically used for mass.

$ MA: MegaAmpere or MegAmpere; see Mega, Ampere

$ m: meters; SI unit of distance

$ M: metric prefix "mega", meaning million

@ MARS: Mirror Advanced Reactor Study; see entry

$ MeV: Millions of electron volts; see mega, electron-volt.

@ MFE: Magnetic Fusion Energy

@ MFTF-B: Mirror Fusion Test Facility; see entry

@ MHD: Magnetohydrodynamics; see entry

@ MHD Instability: see Magnetohydrodynamic instability.

@ MHTGR: Modular High-Temperature Gas-Cooled Reactor; see entry.

@ MIT: Massachusetts Institute of Technology; see entry

@ MITL: Magnetically Insulated Transmission Line; see entry

@ MIX 1: see entry under "MIX 1"

@ MKS: Meters, Kilometers, Seconds - see SI Units

@ MKSA: Meters, Kilometers, Seconds, Amperes - See SI Units.

@ MMX: Multiple Mirror eXperiment; see entry

@ MS: Maryland Spheromak; see entry

@ MTX: Microwave Tokamak eXperiment; see entry

$ MW: Megawatt; one million watts; see entry for watts.

* Mach-Zender Interferometer: This is a variation of the Michelson
interferometer which is used mainly in measuring the spatial variation
in the refractive index of a gas (or plasma). A Mach-Zender
interferometer uses two semi-transparent mirrors and two fully
reflective mirrors located at the corners of a rectangle. The
incoming beam is split in two at the first semi-transparent mirror,
and the two halves of the beam travel along separate paths around
the edge of the rectangle, meeting at the opposite corner. Typically
one beam is a control, and the other travels through the system
under study. The two beams meet at the second semi-transparent
mirror, after which they are mixed together and interfere.

% Madison: See University of Wisconsin-Madison

* Magnetic Axis: This typically refers to the location of the
innermost flux "surface" in a toroidal device, the one which
encloses no volume and has therefore degenerated from a flux
surface into a single field line. Roughly, the circle through
the middle of the dough of the donut. Additionally, in systems
with magnetic islands (see entry below), each island has a
local magnetic axis, distinct from the overall magnetic axis
of the torus.

* Magnetic Bottle: Colorful term used to describe a magnetic
field structure which confines a plasma "like in a bottle".

* Magnetic Confinement: Use of magnetic fields to confine a
plasma. (Confinement involves restricting the volume of
the plasma and/or restricting particle or energy transport
from the center of the plasma to the edge.)

* Magnetic Confinement Fusion: Method of fusion which uses
magnetic fields / magnetic bottles to confine a hot plasma
until fusion occurs.

* Magnetic Diffusion:

* Magnetic Field:

* Magnetic Field Coil: Coiled current-carrying wires used to
generate magnetic fields.

* Magnetic Flux Surfaces:

* Magnetic Force Parameter: A dimensionless number equal to
[(magnetic permeability squared) * (magnetic field strength squared) *
electrical conductivity * characteristic length of system in question] /
[(mass density) * (fluid velocity)]. This measures the strength
of magnetic forces relative to the plasma's inertia.

* Magnetic Island: A magnetic topology near a "rational surface"
(see entry) where the flux surface is broken up into tubes which
are not connected with each other poloidally. Islands may develop
in non-ideal magnetohydrodynamic fluids, where electrical
resistance becomes important and magnetic field lines are no
longer "frozen-in" to the fluid. Then magnetic tearing and
reconnection may allow field lines to link up and form "islands"
with a local magnetic axis (see entry) in a narrow region near
a rational surface (see entry). (See also MHD, frozen-in law).

The development of islands may be caused by a small perturbation,
whether internal or external, whether deliberate or accidental,
and is usually associated with enhanced transport (i.e., reduced
confinement). The centers of the islands are magnetic O-points,
while the boundaries between islands are marked by X-points (see entries).

* Magnetic Limiter: See divertor.

* Magnetic Mach Number: A dimensionless number equal to the
ratio of the velocity of a fluid to the velocity of Alfven
waves in that fluid. (See also entry for Alfen waves.)

> Magnetic Mirror: See mirror effect, mirror device

* Magnetic Moment: (a) A vector associated with a magnet, current
loop, or particle; the cross product of this vector with the
magnetic field is equal to the torque which the field exerts on
the system. (b) The adiabatic invariant associated with the
rapid gyromotion of a charged particle in a slowly varying
magnetic field. (The value of the magnetic moment in sense (b)
is the magnitude of the vector in sense (a).)

* Magnetic Number: A dimensionless number equal to the square
root of the magnetic force parameter.

* Magnetic Pressure: Pressure which a magnetic field is capable
of exerting on a plasma; equal to the magnetic energy density;
proportional to B^2. (The proportionality constant
is 1/(2*mu-o) in SI units, 1/8pi in CGS units).

* Magnetic Probe: A conducting coil (sometimes insulated and
inserted into the plasma) will have an induced voltage due
to changes in the magnetic flux through the coil, and can therefore
be used to measure changes in magnetic field strength. Small
coils used to measure the local field strength are known as
probes. (Other plasma diagnostics using this effect are the
Rogowski coil, the voltage loop, and the diamagnetic loop.)
Magnetic probes placed outside a toroidal plasma which are used
to measure the poloidal magnetic field are also called Mirnov coils.

* Magnetic Pumping: Form of plasma heating where the plasma is
successively compressed and expanded by means of a fluctuating
external magnetic field. (See also adiabatic compression, frozen-in

* Magnetic Reconnection: (entry by John Cobb, with some
modifications) When a plasma has some resistivity, then the
frozen-in flow requirement is relaxed (see frozen-in flow). In that
case, the magnetic field can move through the plasma fluid on the
resistive (magnetic diffusion) time scale. (Typically slow compared
to MHD timescales.) This allows field lines to reconnect with each
other to change their topology in response to magnetic and other
forces in the plasma. (see also Helicity, which is not conserved when
reconnection is significant.) The predominant theory for solar
flares is based on the transfer of energy from magnetic fields to
plasma particles which can occur in reconnection. Reconnection can
also be studied in the laboratory.

* Magnetic Stress Tensor: A second-rank tensor, proportional
to the dyadic product of the magnetic field (B) with itself.
The divergence of the magnetic stress tensor gives that part
of the force which a magnetic field exerts on a unit volume of
conducting fluid due to the curvature of the magnetic field lines.

* Magnetic Switching: The use as switches of saturable inductors for
producing high power pulses without electrical arcs. This is a
principal technology for extending single-shot accelerators in
light-ion-beam-driven inertial confinement fusion to repetitively
pulsed devices for possible reactors. Three terawatt, 200 KJ
magnetic switches have been developed for fusion drivers at
Sandia National Laboratories. (Info from the 1985 OSTI Glossary
of Fusion Energy; may be out of date.)

* Magnetic Viscosity: A magnetic field in a conducting fluid will
damp fluid motions perpendicular to the field lines, similar to
ordinary viscosity, even in the absence of sizeable mechanical
forces or electric fields.

* Magnetic Well: see Minimum-B Configuration.

* Magnetically Insulated Transmission Line (MITL): Used to
transport power efficiently in vacuum lines at very high
power densities. Although the cathode is a space-charge
limited electron emitter, the electron flow is confined
by self-generated or applied magnetic fields. MITL's are
used extensively in light-ion-driven inertial confinement fusion.

* Magnetohydrodynamics (MHD): Physical model describing the
properties of electrically conducting fluids interacting with
magnetic and electric fields. MHD theory is relevant at
relatively low frequencies and for distance scales larger than
the Larmor radius. Also known as hydromagnetics.

* Magnetohydrodynamic Generator: A device that extracts
kinetic energy from a jet of plasma and generates electricity.

* Magnetohydrodynamic Instability (MHD instability):
Class of unstable (growing, not damped) waves and other
modes of oscillation which are described by MHD theory.

* Magnetohydrodynamic Turbulence: Motion of a plasma in which
velocities and pressures fluctuate irregularly.

* Magnetohydrodynamic Waves: Material waves in an electrically
conducting fluid in the presence of a magnetic field, which
are described by magnetohydrodynamics.

* Marx Generator: A pulsed-power device invented by Erwin Marx.
Capacitors are charged in parallel and then quickly discharged
in series to produce high voltage, high current (and thus
high power) pulses. Used in light-ion-driven and some
laser-driven inertial confinement fusion systems.

> Maryland Spheromak: A University of Maryland spheromak
facility, used to investigate the production, equilibrium,
stability, and confinement properties of spheromaks.
(What happened to it?)

* Mass Defect: The energy from fusion reactions comes from the
difference in mass between the reactants and the products. In an
energy-releasing reaction, some mass is converted to energy via
Einsteins famous equation E (energy) = m (mass) * c^2 (speed of
light squared). The energy released is the difference between
the binding energies of the reactants and the products (see
entry on binding energy).

% Massachusetts Institute of Technology (MIT): Located in Cambridge,
MA (just outside Boston). Home of the Plasma Fusion Center and the
Alcator series of compact tokmaks.

% Max Planck Institute for Plasma Physics (IPP): In Garching (near
Munich). The largest plasma physics institute in Germany. Presently
home of ASDEX-Upgrade and Wendelstein-7AS. (See entries)

! Maxwell, James Clerk: 19th-century British physicist, responsible
for the synthesis of the equations of electromagnetism and the
prediction of electromagnetic waves, among other things.

& Maxwell-Boltzmann Distribution: Distribution function of particle
velocities (or energies) corresponding to a system in thermal
equilibrium with a temperature value of T. See also: distribution
functions, temperature.

& Maxwellian Distribution: see Maxwell-Boltzmann Distribution

& Maxwell ('s) Equations: The key equations governing
electrical and magnetic phenomena. These are a set of four
vector partial differential equations relating electric and
magnetic fields to each other and to electric charges and

& Mean Free Path (for a given event, e.g., collisons): Average
distance a particle travels between occurrences of the given
event; e.g., between collisions. For collisions, the mean free
path is roughly equal to unity divided by the product of the
collision cross section times the particle density.

& Mega-: Metric prefix indicating 1,000,000 times a given quantity.
e.g., a megawatt is 1,000,000 watts.

* Meltdown: In a fission reactor, if there is insufficient coolant
or the fission chain reaction proceeds too rapidly, heat can
build up in the reactor fuel, causing it to melt. In extreme
cases the whole fission core can melt down to (or even through) the
reactor floor. Fusion reactors are not vulnerable to this.

& Metastable state: several types

& Micro-: Metric prefix indicating 1/1,000,000th of a given
quantity. e.g., a microampere is 1/1,000,000th of an ampere.

* Microinstability: Instabilities due to particle / kinetic-
theoretical effects, typically occuring on small scales, as opposed
to those derivable from fluid models valid on larger scales.
As with other instabilities, these are driven by various types
of available free energy. (See also kinetic theory.)

* Microwave Interferometer: See interferometer, interferometry.
A microwave interferometer uses radio waves in the microwave
frequency (or wavelength) range as the electromagnetic signal.
Microwave interferometers are used to measure the line-averaged
density of a plasma along the path through which the microwave
beam is passed, through phase shifts in the propagated beam.

* Microwave Tokamak eXperiment (MTX): a reincarnation of Alcator C
at LLNL, now shut down.

> Migma devices: Non-thermal, non-pulsed devices in which fusion
occurs among the ions of a self-colliding particle beam.

$ mill: financial unit equal to 0.1 cents or 0.001 dollars;
standard unit which electrical utilities use in charging for
electricity (e.g., 50 mills/kwh = $0.05/kwh).

> Minimum-B Configuration: Confinement configuration where the
magnetic field strength is a minimum where the plasma is to be
confined, and increases in all directions away from the confinement
region. Stability is favorable in such a configuration because the
magnetic pressure increases in all directions away from the plasma.

* Mirnov Oscillations: Fluctuations in the poloidal magnetic
field (of a toroidal magnetic confinement system) which rotate
in the electron diamagnetic drift direction at a speed comparable
to the electron diagmagnetic drift velocity and with frequencies
due to 5-20 kHz. Mirnov oscillations arise from tearing modes.
Poloidal magnetic probes used to measure the poloidal field in order
to diagnose Mirnov oscillations (and other MHD phenomena) are
often called Mirnov coils or Mirnov loops. See relevant entries...

> Mirror Advanced Reactor Study (MARS): This was a collaborative
effort between government, academia, and industry to design a
commercial-scale tandem mirror fusion power plant. Participants
included the Department of Energy (LLNL); University of Wisconsin;
TRW, Inc.; General Dynamics; EBASCO Services; Science Applications,
Inc.; and Grumman Aerospace Corp. System was never actually built.

> Mirror device, mirror machine: Generally, linear fusion machines
which confine the plasma using the mirror effect. Basically there
is a weak field in the center, and strong fields at the ends.
Particles are then reflected at the ends by the strong fields,
and are confined in the center of the device. (Some particles
will have enough velocity along the axis of the device to escape
from the mirror, however.)

* Mirror effect: A charged particle travelling into an increasing
magnetic field will (if the field becomes strong enough) reverse
direction and be reflected back. This is a direct result of
the adiabatic invariance (see entry) of the magnetic moment
(see entry). Plasmas can be confined by devices which utilize
this effect; see entry above for mirror device. The effect
also occurs in some toroidal plasmas, since the toroidal magnetic
field is stronger on the inboard side than on the outboard side;
in this case it gives rise to so-called "neoclassical" effects.
The strength of the mirror is determined by the mirror ratio.
(See relevant entries. Consult an introductory plasma physics
text for a more technical explanation.)

> Mirror Fusion Test Facility (MFTF): A large mirror device built
at LLNL from the late 1970s to the mid-1980s, but mothballed
for political reasons (decrease in magnetic fusion funding)
just before it was to begin operation.

* Mirror Ratio: In a magnetic mirror, the mirror ratio is the ratio
between the strongest value of the magnetic field on the mirror's
axis, and the value at some other point on the axis. In
a mirror confinement device, the "other point" is taken to be
the location of weakest field strength between two confining
mirrors. The mirror ratio is a key factor in determining
confinement properties of the system.

> MIX-1: A small, gun-injected mirror machine at the University
of Maryland; was used to study the drift-cyclotron loss cone
instability (see entries for DCLC, DCLC instability).

* Mobility: The ease with which a charge in a medium (e.g. a plasma)
moves in response to an electric field. Related to diffusivity and to
resistivity. Measured by the average equilibrium drift velocity
attained by the charged particle when subjected to acceleration
by a unit electric field and the opposing frictional force of
collisions with other particles.

* Mode Rational Surface: A magnetic surface on which field
lines resonate with the helicity of a particular perturbation
or instability; see also rational surface.

* Moderator: Substance used in a fission reactor to slow down
("moderate") energetic fission neutrons so that they are more
easily captured within the reactor and therefore maintain the
fission chain-reaction.

> Modular High-Temperature Gas-Cooled Reactor: Class of fission
reactors under study in the U.S.; designed to run at higher
temperatures and use gas cooling to achieve greater efficiency
of conversion from thermal to electric energy.

& Mole: The amount of given substance such that the mass in grams
is equal to its [atomic weight, molecular weight, mass number].
The number of particles in a mole of a substance is Avogadro's
Number N = 6.02497 x 10^23 (see entry). For instance, one mole
of water weighs 18 grams, since water is H2O, the H's weigh
one apiece, and the O weighs 16. Heavy water, or D2O, weighs
20 grams/mole, because each D weighs 2 instead of 1.

* Molecular ion injection: Heating concept for magnetic
confinement fusion in which energetic (accelerated) molecular
ions are injected into the plasma, dissociate, and heat the
plasma while building up the population of trapped high-energy
ions. Not widely used (see neutral beam injection).

& Momentum: Basic physical quantity measuring motion; generally
defined as momentum = mass * velocity. The total momentum of
all bodies in a system is conserved in all physical processes
known so far, I believe. Momentum is related to force in that
force = rate of change of momentum with time. See also force.

* Motor-Generator: Device used to store energy by accelerating
a rotating flywheel to high speeds; energy may be rapidly discharged
and converted to shorter-pulse energy. (Used to power TFTR; the
electric utility would be a little unhappy if TFTR were to suddenly
draw its 30 MW+ of power at random intervals. :)

> Multiple Mirror eXperiment (MMX): A 10-meter long simple
mirror facility which was located at the University of California,

> Muon-Catalyzed Fusion: Alternative approach to fusion where
muons are introduced to D-T fluid. The muon is heavy enough that
it binds more strongly to the D or T than an electron would, and
the result is that the D and T nuclei in the molecule are drawn
more tightly together, and fusion results. More detailed discussion
is given in section 4B.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/l
Last-modified: 20-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 12: Terms beginning with "L"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# L: variable typically used to indicate self-inductance;
see inductance.

# Li: chemical symbol for the element lithium; see entry.

@ L-mode: see low mode.

@ LAMPF: Los Alamos Meson Physics Facility; see entry

@ LANL: Los Alamos National Laboratory; see entry

@ Laser: Light Amplification by Stimulated Emission of Radiation.
see entry.

@ LBL: Lawrence Berkeley Laboratory; see entry

@ LCFS: Last Closed Flux Surface; see entry

@ LLE: Laboratory for Laser Energetics; see entry

@ LLNL: Lawrence Livermore National Laboratory; see entry

@ LMFBR: Liquid-Metal Fast-Breeder Reactor; see entry

@ LMR: Liquid-Metal Reactor; see entry

@ LN2: Liquid (diatomic) Nitrogen (N2)

@ LOCA: Loss-of-Coolant Accident; see entry

@ LWR: Light-Water Reactor; see entry

% Laboratory for Laser Energetics: Second-largest (?) inertial
confinement research facility in the United States; located at
the University of Rochester in New York state. Home of Omega;
future home of Improved-Omega.

& Lagrangian: The difference between the kinetic energy and the
potential energy of a system of particles, expressed as a
function of generalized coordinates and velocities. Equations
of motion can be derived from the Lagrangian. (see an intermediate
or advanced mechanics text for more information.)

* Lagrangian coordinates: coordinates which follow fluid motion.
(As distinct from Eulerian coordinates; see entry).

* Landau Damping: Damping of a wave propagating in a hot plasma,
due to the interaction of the wave with particles whose velocity
is close to the phase velocity of the wave. Depends on the shape
of the velocity-space distribution function at the phase velocity
of the wave. More info from John Cobb, with modifications:

The phenomenon is very similar to surfing on water waves at the
beach. If a particle's speed is just slightly lower than the wave,
then the particle can "catch the wave" and surf along at the wave
speed. In so doing, the particle will gain some energy, which will
be at the expense of the wave. This is called Landau Damping, since
the loss of energy tends to damp the wave. At the same time, if a
particle moves just slightly faster than the wave, then it will also
be caught on the wave. However, in this case, it will slow down,
giving the wave some extra energy. In this case particles transfer
energy to the wave; this is called inverse Landau damping. Which
effect dominates depends on whether there are more particles moving
faster than the wave or more particles moving slower. Thus it
depends on the derivative of the distribution function with respect
to velocity, evaluated at the wave's phase velocity. Landau dmaping
can lead to the decay of waves. Inverse Landau damping can be a
mechanism for some kinetic instabilities.

! Langmuir, Irving (1881-1957): American chemist, won Nobel Prize in
chemistry in 1932, developed the theory of Langmuir probes (see
entry). Numerous inventions for General Electric (lighting).

* Langmuir frequency: See plasma frequency.

* Langmuir oscillation: See electrostatic waves.

* Langmuir probe: a small conductive electrode used to measure the
density, temperature, and electric potential (voltage) of a plasma.
Plasma parameters are deduced from the probe's "Characteristic"
current-drawn vs. voltage-applied curve.

& Larmor radius: the radius of the path of a charged particle
moving in a magnetic field (and transverse to the field lines).
Also known as gyroradius and cyclotron radius.

& Laser: An optical device that amplifies and concentrates light
waves, emitting them in a narrow, intense beam. Laser light
radiation is notable for its brightness and to some extent
for its monochromaticity and spatial and temporal coherence.

> Laser Fusion: Form of inertial confinement fusion where
laser beams are used to compress and heat the fuel pellet.

* Laser interferometer: an interferometer which uses a laser
as a light source (see entries). Because of the monochromatic
nature and high brightness of laser light, laser interferometers
can operate with much longer beam paths and path differences
than conventional interferometers.

* Laser scattering device: See Thomson scattering device.

* Last Closed Flux Surface (LCFS): [from Art Carlson] The boundary
between the interior region of a tokamak (or other device), where the
field lines close back on themselves, and the scrape-off layer (see
entry), where the run into a material wall. (See also separatrix.)

% Lawrence Berkeley Laboratory: Located in Berkeley, CA; Another
large U.S. science laboratory; minor (?) U.S. fusion research center.

% Lawrence Livermore National Laboratory: Located in Livermore, CA,
about an hour east of SF in the Bay Area. Home of the Nova laser
inertial confinement fusion program; Nova is the largest
laser in the world. Home of the former mirror projects MFTF
(Mirror Fusion Test Facility, shut down on the day it became
operational, or thereabouts, due to budget cutting),
TMX-U (Tandem Mirror eXperiment Upgrade), and the recently
shut down Microwave Tokamak eXperiment (MTX). Some notable
older fusion experiments at Livermore included Table Top, Toy Top,
Baseball (and Baseball-II) and TMX (predecessor to TMX-U).
Livermore is also the site of the Rotating Target Neutron Sources
(I and II) for testing materials samples in high-intensity 14 MeV
neutron fluxes and the High Field Test Stand for testing neutral
beams. Workplace of Albert Chou and several other
sci.physics.fusion participants. :)

* Lawson Criterion: Scientific breakeven criterion based on the
product of energy confinement time and particle density. Together
with plasma temperature, the Lawson value of a plasma indicates
how close it is to self-sustained (ignited) fusion; see also

& Lenz's Law: Electromagnetism law which states that whenever
there is an induced electromotive force (emf) in a conductor,
it is always in such a direction that the current it would induce
would act in opposition to the change which caused the
induced emf.

> Levitron: Single-ring multipole device with an additional
current-carrying rod perpendicular to the ring axis.

* Light-ion fusion: Light-Ion-Beam-Driven Inertial Confinement
fusion, using beams of light ions driven at implosion targets.
Pulsed-power driven accelerators are relatively efficient and
cost-effective, but beam-focusing is a technical hurdle for
this approach.

> Light-Water Reactor: Class of fission reactors using ordinary
"light" water as a coolant, rather than liquid metal or heavy
water (water with deuterium instead of hydrogen).

* Limiters: Structures placed in contact with the edge of
a confined plasma which are used to define the shape of
the outermost magnetic surface. See also: divertor.

* Line-tying: Connection of field lines from the end of
an open-ended device (such as a mirror system) to a conducting
plate. The rigidity of field lines trapped in the plate can
be transferred to the high-field region of the mirror by using
a cold, moderately-dense plasma in between. Line-tying helps
to stabilize against interchange instabilities (see entry).

* Liquid Metal: Metal which has been heated past its melting point
and can be used as a working fluid for pumping heat out from a
powerplant. Liquid metal used as coolant in a system where
significant magnetic fields exist, it behaves differently due
to MHD effects; these cause pressure which resists fluid
circulation, suppression of turbulence, and altered flow
patterns compared to non-magnetic liquid metal systems.

> Liquid-Metal Reactor: (Fission) reactor which uses liquid metal
as the reactor coolant.

> Liquid-Metal Fast-Breeder Reactor: (LMFBR) Fission breeder
reactor concept (see entry for breeder reactor) using
liquid-metal coolant and breeding additional fuel off fast

& Lithium: (Li) Third element in the periodic table, so all isotopes
contain 3 protons. Pure lithium at room temperature is a soft
silver-white material, the lightest of all metals. It is
chemically very reactive, making it hazardous. Lithium liquefies at
355 degrees Fahrenheit, making it viable as a liquid-metal
coolant. Lithium nuclei have two stable isotopes:
Li-6 (7.5% abundance) and Li-7 (92.5%). Lithium is a candidate
for breeding tritium (for D-T fusion) from neutrons, via the

n + 6Li -> 4He + T + 4.8 MeV
n + 7Li -> 4He + T + n - 2.5 MeV.

* Longitudinal Waves: (by John Cobb, with editing) Waves where the
variation of the field is partially or totally in the direction of
propagation (parallel to wavennumber, k [a vector]). Examples
include sound waves and Langmuir waves. Contrasted with transverse
waves, where the variation is perpendicular to the direction of
propagation, such as light waves.

* Lorentz dissociation: dissociation of molecular ions by Lorentz
ionization (see entry).

& Lorentz Force: Total electromagnetic force on a charged particle
moving in electric & magnetic fields. F = q(E + (v/c)xB). See
also force, cross product, charge, velocity, and relevant
variable symbols.

* Lorentz Gas: Plasma model in which the electrons are assumed
not to interact with each other, but only with ions (Z -> infinity)
and where the ions are assumed to remain at rest/fixed (M-i ->
infinity). Also known as "electron gas."

* Lorentz ionization: Ionization of neutral atoms (taken generally
at a highly-excited state) obtained by launching them at high
velocity across a strong magnetic field. The neutral atoms feel
an electric field proportional to their perpendicular velocity
times the magnetic field strength, and if this electric field
is strong enough ionization can occur.

* Lorentz Model - see Lorentz Gas

% Los Alamos Meson Physics Facility (LAMPF): Physics research
facility at Los Alamos National Lab; major site for U.S.
muon-catalyzed fusion research in the 1980s. May be shut down soon.

% Los Alamos National Laboratory (LANL): Major DOE research
facility, located in Los Alamos, New Mexico, about an hour west of
Santa Fe. Former home of a frozen-deuterium-fiber Z-pinch device,
which was dismantled. Home to an active theory division, including
the Numerical Tokamak Grand Challenge (being performed on the CM-5
massively-parallel supercomputer).

Also home to former alternative-concepts experimental devices like
Scyllac, FRX-A, FRX-B, FRX-C/LSM, ZT40, and the aborted CPRF which
was killed in 1991 when it was almost complete (budget cuts).

Currently there are some small in-house experiments, including one on
electrostatic confinement as a possible fusion device, and/or a
compact neutron source. They also do theory and experimental
collaboration with other labs worldwide.

(Information provided by John Cobb and Ed Chao)

* Loss Cone: (from John Cobb, with modifications and additions)
In a magnetic mirror machine, particles with a large velocity
parallel to the magneitc field and a small velocity perpendicular
to the field will be able to escape past the magnetic mirror
(see magnetic mirror). In that case the velocity distribution
function (see distribution function) will be almost zero in the
region of velocity space that allows particles to escape. The
shape of that region (in a velocity space diagram with parallel
velocity and perpendicular velocity as the axes) is a cone. When a
particle undergoes a collision, its velocity gets somewhat
randomized. Particles that are scattered into that cone are lost very
quickly (in one mirror bounce time). Thus it is called a loss cone.
Because of the loss cone, the theoretical maximum particle
confinement time of a magnetic mirror machine can be only a few times
the particle collision time; this is generally seen as a showstopper
for mirror-based fusion research.

* Loss of Coolant Accident (LOCA): Powerplant accident where
the supply of coolant to the hot power-producing core is
interrupted, or where the coolant drains out for some reason.
Can lead to meldown of a fission reactor core in extreme cases,
or to small nuclear explosions (e.g., Chernobyl). Fusion
reactors are expected to be less vulnerable to LOCAs, but these
must still be designed for.

* Low-activation materials: In fission reactors, one is forced
to deal with the radioactive byproducts of the fission process,
but in fusion reactors one generally has a choice of what materials
to expose to neutrons produced by the fusion process. A major
problem for fusion reactors is developing materials (such as for
the reactor vacuum vessel structure) which can be exposed to
high levels of neutron bombardment without becoming permanently
radioactive. Candidate structural materials which have
relatively low induced radiactivation (generally relative to
stainless steel) are known as low-activation materials; these
include titanium, vanadium, and silicon-carbide.

* Low Aspect Ratio: (entry from John Cobb, slightly edited)
An aspect ratio for a torus that is small (minor radius is almost as
big as major radius). There are many fusion devices which are
designed to have a low aspect ratio. Such devices look more like
tractor tires than bicycle tires, as toruses go. There are reasons
to believe that low aspect ratio devices will offer some advantages
for a fusion reactor. Usually, ease of theoretical and/or numerical
analysis is not one of these advantages :>.

* Low-beta plasma: a plasma in which the beta value (see entry)
is typically 0 to 0.01.

* Low mode or L-Mode: (from Herman) The "normal" behavior of
a tokamak plasma, characterized by poor confinement and a particular
scaling of decreasing confinement with increasing temperature.

* Lower hybrid frequency:

* Lower Hybrid Heating: form of RF heating using Lower Hybrid Waves.

* Lower Hybrid Waves: "Electrostatic ion oscillations at a frequency
intermediate to the electron extraordinary wave (high frequency) and
the magnetosonic wave (low frequency). Not waves, strictly speaking,
because they do not propagate (I think)."
- Albert Chou,

* Luminescence: Light emission that cannot be attributed merely
to the temperature of the emitting body, but results from such
causes as chemical reactions at ordinary temperatures, electron
bombardment, electromagnetic radiation, and electric fields.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/e
Last-modified: 4-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 5: Terms beginning with "E"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# e: symbol for the electron, for the unit electric
charge (e = 1.6x10^-19 coulombs), and for a Euler's fundamental
mathematical constant e = 2.71828...

# E: Variable typically used for Energy or Electric Field
(usually in vector notation in the latter case; which is meant
is usually clear from context; when both are used in the same place
the energy is usually represented as U instead of E.)

@ EBT: Elmo Bumpy Torus; see entry

@ EC: European Community; see entry

@ ECDC: Electron Cyclotron Discharge Cleaning; see entry

@ ECE: Electron Cyclotron Emission; see entry

@ ECH: Electron Cyclotron Heating; see entry

@ ECRH: Electron Cyclotron Resonance Heating - same as ECH.

@ EF: Equilibrium (vertical) Field Electromagnet Coil; see vertical field

$ ECU: European Currency Unit

@ ELM: Edge-Localized Mode; see entry

@ EM: Electromagnetic

@ EM Wave: Electromagnetic Wave; see entry

@ EPA: Environmental Protection Agency (U.S.); see entry

@ ERDA: Energy Research and Development Agency; see entry

@ ESECOM: Reactor design study done in the mid 1980s to
evaluate the Environmental, Safety, and ECOnoMic potential
of different types of fusion and advanced fission reactors.

@ ESNET: Energy Sciences NETwork; no entry yet

@ ETF: Engineering Test Facility

@ EU: European Union; see entry

@ eV: Electron-volt; see entry

$ Exa: metric prefix for 10^18 or 1,000,000,000,000,000,000

$ Exajoule: unit of energy, 10^18 joules; often used as unit
of measure for world annual energy use. Comparable in size to
a Quad (1 EJ = 0.948 Quads); see entry for Quad.

* E-Coil: The plasma current driving (Ohmic Heating) coil
in a Doublet device (see entry for doublet). Ideally the
E-coil makes no magnetic field in the confinement system. (?)

* E-Layer: Cylinder of relativistic electrons gyrating in
a magnetic field, which produce a self-field strong enough
to dominate the externally applied field and produce a
field-reversal (where the B field changes sign) in the
system. See Field-Reversed Configuration, Field-Reversed Pinch.

* Echoes: Wave packets (pulses) which have been reflected
or otherwise returned to the detector, which are sufficiently
delayed and retain sufficient magnitude so that they are
perceived as a signal distinct from the one transmitted
directly. (In other words, just like sound echoes, only
for analogous phenomena with other waves.)

* Eddy Current: Electric current induced inside a conductor
when the conductor (a) moves through a nonuniform magnetic
field, or (b) experiences a change in the magnetic flux
through its surface.

* Eddy-Current Loss: Energy loss due to eddy currents
circulating in a resistive material.

* Edge Localized Mode: (ELM) Mode found often in H-mode plasmas.
This is a temporary relaxation of the very high edge gradients
found in H-modes. It may be a relaxation back to the L-mode.
(Borrowed from a posting by Paul Stek)

* Edge Plasma: Cooler, less dense plasma away from the center
of a reactor; affected by limiter or divertor, includes
scrape-off layer. Distinguished from core plasma. See entries
for relevant terms used.

* Edge-Localized Mode: (info from Paul Stek) Found often in
H-mode plasmas, this is a temporary relaxation of the very high
edge gradients found in H-modes. It may be a relaxation back
to the L-mode.

* Effective Collision Cross-section: (See collision cross section)

* Effective Collision Radius: Effective size of a particle
equal to the square root of (cross section/pi). Determines the
effective range of interaction of the particle.

* Effective Half-Life: Time required for a radioactive substance
contained in a biological system (such as a person or an animal)
to reduce its radioactivity by half, as a combination result
of radioactive decay and biological elimination from the system.

& Eigenfrequency: One of the characteristic frequencies at
which an oscillatory system can vibrate.

& Eigenfunction: Function describing an eigenstate of a

& Eigenstate: One of the characteristic states of an
oscillatory system, such that the system does not leave the
state unless disturbed. (?)

& Eigenvector: Same thing as an eigenfunction, only from the
perspective that the eigenfunction is a "vector" in an
appropriate mathematical vectorspace.

* Eikonal Equation: An equation for propagation of electromagnetic
or acoustic waves in an inhomogenous medium; valid only when the
scale length for variation in the properties of the medium is
small compared to a wavelength. (Similar in character to WKB?)

& Elastic: Term used to describe a process in which kinetic energy
is conserved; usually refers to (elastic) collisions or (elastic)

& Electric Charge: See charge, electrical.

& Electric Field: A property of a patch of space which causes
the acceleration of electric charges located at that patch of
space. The acceleration is given by a = qE/m, where q is the
charge, E the electric field vector, and m the mass of the

% Electric Power Research Institute: (EPRI) Research organization
funded by the electric power utilities to study, well, electric

* Electric Probe: See Langmuir Probe.

& Electrical Conductivity: Degree to which a substance conducts
electric current. Can be defined by:
(current density) = (conductivity) * (applied electric field)
Electrons and ions both contribute to current in proportion to
their mobility in the system. In a plasma with a magnetic field,
there is no longer a one-to-one correspondence between current
and electric field. Instead, the current in each direction can
be due to combinations of the electric fields in all the other
directions. In this case, the current density and the
electric field are vectors, and the conductivity becomes a
tensor (matrix) which relates them.

* Electromagnetic Coupling: A means of extracting energy from a
magnetically confined plasma, where the plasma expands and pushes
on the confining magnetic field, causing electrical energy to
be generated in the external field-generating circuits.

& Electromagnetic Force:

* Electromagnetic Radiation: Radiation (such as radio waves,
microwaves, infrared, visible light, ultraviolet, x-rays, and
gamma rays) which consists of associated, interacting electric
and magnetic field waves which travel at the speed of light
(because electromagnetic radiation *is* light, except for the
variation in frequencies!). All forms of electromagnetic
radiation can be transmitted through vacuum. Electromagnetic
waves in plasmas are generally more complex in their behavior,
depending on their frequency.

& Electromagnetic Wave: Wave characterized by combined oscillations
of both electric and magnetic fields. The particle equivalent
is the photon. There is a whole spectrum of electromagnetic
waves where the classes are distinguished by energy (or,
equivalently, wavelength or frequency); the spectrum of
electromagnetic waves includes radio waves, microwaves,
infrared light, visible light, ultraviolet light, x-rays, and
gamma rays.

& Electron: Elementary particle with a negative electric
charge. Electrons orbit around the positively charged nucleus
in an atom. The charge on an electron is -1.6x10^-19 coulombs;
the electron has a mass of 9.11 x 10^-31 kg (about 1/1837
times that of a proton.) The configuration of electrons around
an atom determines its chemical properties. The positron
is the antiparticle to the electron, and is identical except
for having a positive charge.

> Electron Beam Fusion Accelerator: See PBFA (Particle Beam
Fusion Accelerator)

* Electron Capture: Nuclear decay process whereby a proton in
the nucleus absorbs an orbiting electron and converts to a

* Electron Cyclotron Discharge Cleaning: (ECDC) Using relatively
low power microwaves (at the electron cyclotron frequency) to
create a weakly ionized, essentially unconfined hydrogen plasma
in the vacuum chamber. The ions react with impurities on the
walls of the tokamak and help remove them from the chamber. For
instance, Alcator C-mod typically applies ECDC for a few days
prior to beginning a campaign, and a few hours before each day's run.

* Electron Cyclotron Emission: (ECE) As electrons gyrate around in
a magnetic field (see also larmor radius or cyclotron radius),
they radiate radio-frequency electromagnetic waves. This is
known as electron cyclotron emission, and can be measured to
help diagnose a plasma.

* Electron Cyclotron Heating: (ECH or ECRH) Radiofrequency
(RF) heating scheme that works by injecting electromagnetic (EM)
wave energy at the electron cyclotron gyration frequency.
The electric field of the EM wave at this frequency looks to
a gyrating electron like a static electric field, and it
causes acceleration of the electron. The accelerated
electron gains energy, which is then shared with other particles
through collisions, resulting in heating.

* Electron Cyclotron Wave: Radiofrequency waves at the
electron cyclotron frequency. See also Whistler.

* Electron Density: Number of electrons in a unit volume.
See density for more info.

* Electron Temperature: The temperature corresponding to
the mean kinetic energy of the free electrons in a

$ Electron-volt: 1 eV = 1.6 x 10^-12 erg, or 1.6 x 10^-19 Joules.
This is a unit of kinetic energy equal to that of an electron
having a velocity of 5.93 x 10^5 m/sec. This is the energy
an electron (or other particle of charge=1 such as a proton),
gains as it is accelerated through a potential difference
of 1 volt. In plasma physics the eV is used as a unit of
temperature; when the mean particle energy is 1eV, the
temperature of the plasma is roughly 11,700 Kelvin.

* Electrostatic Analyzer: A device which filters an
electrn beam (band-pass), permitting only electrons within
a narrow energy (velocity) range to pass.

> Electrostatic Confinement: An approach to fusion based on
confining charged particles by means of electric fields, rather
than the magnetic fields used in magnetic confinement. See
discussion in Section 4 for more information.

* Electrostatic Waves: Longitudinal oscillations appearing in a
plasma due to a perturbation of electric neutrality. For a cold
unmagnetized plasma, or at large wavelengths, the frequency of
these waves is by definition the plasma frequency.

& Element: One of the fundamental chemical substances which
cannot be divided into simpler substances by chemical means.
Atoms with the same atomic number (# of protons) all belong
to the same element. (e.g., hydrogen, helium, oxygen, lead)
(list and perhaps periodic table in
appendix? isotope table with half-lives and decay modes
might also be useful.)

& Elementary Particles worth knowing about:
(at the nuclear-energy level)
electron & positron - seem to be stable
proton - thought to be stable, life > 10^30 sec
neutron - decays in ?10 min unless it's in a nucleus, which often
extends its life.
other particles important for nuclear energy:
muon, neutrino (m,e,tau),
muonic atoms
this part is new - maybe separate entries with listing

> Elmo Bumpy Torus: Bumpy Torus at ORNL; no longer operating.
See Bumpy Torus, ORNL.

* Elongation: parameter indicating the degree to which the cross
section of a toroidal plasma is non-circular. kappa=b/a, where "b"
and "a" are the vertical and horizontal minor radii. As kappa is
increased, the confinement in relation to the total current improves,
but the plasma also becomes more and more unstable to vertical
displacements. A circular plasma has kappa of 1, a common value for
elongated plasmas is 1.7, and the absolute limit is probably
around 2.

& Energy: Typically defined as "the ability to do work". Power
is the rate at which work is done, or the rate at which energy
is changed. "Work" characterizes the degree to which the properties
of a substance are transformed. Energy exists in many forms,
which can be converted from one to another in various ways.
Examples include: gravitational energy, electrical energy,
magnetic and electric field energy, atomic binding energy (a form
of electrical energy really), nuclear binding energy, chemical
energy (another form of electrical energy), kinetic energy (energy
due to motion), thermal energy ("heat"; a form of kinetic energy
where the motion is due to thermal vibrations/motions), and so on.

* Energy Balance: Comparison of energy put into a plasma with the
energy dissipated by the system; related to energy confinement.

* Energy Confinement Time: See energy loss time.

* Energy Loss Time: Characteristic time in which 1/e (or sometimes
1/2) of a system's energy is lost to its surroundings. In a plasma
device, the energy loss time (or the energy confinement time) is
one of three critical parameters determining whether enough
fusion will occur. (See Lawson criterion)

* Energy Replacement Time: Time required for a plasma to lose
(via radiation or other loss mechanisms) an amount of energy
equal to its average kinetic energy.

% Energy Research and Development Agency (ERDA): US Agency created
by splitting of the AEC into ERDA and NRC in about 1975, charged
with managing US energy R&D (???). Merged with ??? to become the
Department of Energy in about 1977. (???? correct? help??)

* Entropy Trapping: The process of trapping an ordered beam of
particles in a magnetic field configuration (e.g., cusp geometry)
by randomizing the ordered motion of the particles, with
corresponding increase in the entropy of the system.

% Environmental Protection Agency: Agency within the executive
branch of the U.S. government (under the Department of the Interior?
Independent?) charged with, well, protection of the environment.
Activities include research, regulatory, and cleanup functions.
(Any government people reading this who could help me out?)

* Equations of Motion: Set of equations describing the time
evolution of the variables which describe the state of a
physical system.

* Equilibrium: [ acknowledgements to John Cobb ] An equilibrium is
a state of a system where the critical parameters do not change
significantly, within a given time frame. In the case when this time
frame is infinite, It is called a Thermodynamic equilibrium. There
are many cases where a plasma equilibrium is constant on some fast
time scale, but changes over some slower time scale. For example, an
IDEAL MHD equilibrium is constant over fluid time scales
(microseconds to milliseconds), but it will evolve on the slower
resistive or viscous time scales (milliseconds to seconds). All
terrestial plasmas are NOT in thermodynamic equilibrium, but they may
be constant over very long time periods.

An equilibrium is unstable when a small change in a critical
parameter leads the state of the system to diverge from the
equilibrium. An equilibrium is stable when a small change in a
critical parameter leads to a "restoring force" which tends to
return the system to equilibrium.

* Equilibrium Field: See Vertical Field

$ Erg / ergs: CGS unit for energy. 1E7 ergs = 1 joule.

* Ergodic: A mathematical term meaning "space-filling". If a
magnetic field is ergodic, any field line will eventually pass
arbitrarily close to any point in space. Closely related to

* Ergodic Regime: In this regime, a given magnetic field
line will cover every single point on a magnetic surface
(see magnetic surface or flux surface) if the rotational
transform (or q) is not rational.

* ESECOM: Reactor design study done in the mid 1980s to
evaluate the Environmental, Safety, and ECOnoMic potential
of different types of fusion and advanced fission reactors.

* Eulerian Coordinates: Coordinates which are fixed in
an inertial reference frame.

% European Community: see European Union

% European Union: (from Herman) Organization of European
countries (formerly European Community, EC, formerly European
Economic Community, EEC) established in 1967 to coordinate policies
on the economy, energy, agriculture, and other matters. The original
member countries were France, Belgium, West Germany, Italy,
Luxembourg, and the Netherlands. Joining later were Denmark,
Ireland, the United Kingdom, Greece, Spain, and Portugal. Other
countries are in the process of joining now.

% Euratom: European Atomic Energy Community. International
organization established in 1958 by members of the European
Economic Community for the purpose of providing joint
funding and management of the scientific research of the
member countries - initially Belgium, France, Italy,
Holland, and West Germany.

* Excitation Radiation: Line radiation (at characteristic
frequencies / wavelengths) as a result of the excitation
of excited states, and the subsequent de-excitation of
these states by radiative transitions.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/a
Last-modified: 4-Feb-1995

Posting-frequency: More-or-less-monthly
Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 1: Terms beginning with "A"


Edited by Robert F. Heeter,

Guide to Categories:

* = vocabulary specific to plasma/fusion/energy research
& = basic/general physics vocabulary

> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# A: symbol used to indicate either area or magnetic
vector potential.

$ A: abbreviation for Amperes; see entry.

@ AAPT: American Assocation of Physics Teachers; see entry

@ AC: Alternating Current; see entry.

@ ACT-I: Advanced Concepts Torus I; see entry.

@ AEC: (US) Atomic Energy Commission; see entry

@ AIC: Alfven Ion Cyclotron Instability; see entry

@ AIP: American Institute of Physics; see entry

@ AJP: American Journal of Physics; see entry

@ ALEX: (see entry "ALEX" below)

@ AMBAL: (see entry "AMBAL" below)

@ ANL: Argonne National Laboratory; see entry

@ ANS: American Nuclear Society; see entry

@ APS: American Physical Society; see entry

@ APS-DPP: American Physical Society - Division of Plasma
Physics; see entry.

# Ar: Chemical symbol for the element Argon

@ ARIES: Advanced Reactor Innovative Engineering Study (?)
See Entry under ARIES

@ ASDEX: Axially Symmetric Divertor EXperiment; see entry

@ ASDEX-U: ASDEX-Upgrade; see entry for ASDEX.

@ ASME: American Society of Mechanical Engineers

@ ATF: Advanced Toroidal Facility; see entry.

* Absolute Instabilities: A class of plasma instabilities
growing exponentially with time at a point in space, in
contrast to convective instabilities (see entry).

* Absorption: In plasma physics, the loss of (electromagnetic)
energy to a medium. For instance, an electromagnetic wave
which propagates through a plasma will set the electrons
into motion. If the electrons make collisions with other
particles, they will absorb net energy from the wave.

* Absorption Coefficient: Measures the degree of wave
absorption (see Absorption above); defined as the fraction
of wave energy lost as the wave travels a unit distance.

& Activation: Activation occurs when a particle interacts
with an atomic nucleus, shifting the nucleus into an
unstable state, and causing it to become radioactive.
In fusion research, where deuterium-tritium is a common
fuel mixture, the neutron released when (D + T) combine
to form (4He + n) can activate the reactor structure.
Sometimes called "radioactivation." See also activation
product, activation analysis.

& Activation Analysis: Method for identifying and measuring
chemical elements in a sample of material. Sample is first
made radioactive by bombardment with neutrons, charged
particles, or gamma rays. Newly formed radioactive atoms
in the sample then give off characteristic radiations
(such as gamma rays) that tell what kinds of atoms are
present, and how many.

* Activation Product: The unstable nucleus formed when
activation occurs. (See activation above.)

& Adiabatic: Not involving an exchange of heat between the
system said to be adiabatic and the rest of the universe.

& Adiabatic Compression: Compression (of a gas, plasma, etc.)
not accompanied by gain or loss of heat from outside the system.
For a plasma in a magnetic field, a compression slow enough that
the magnetic moment (and other adiabatic invariants - see entry)
of the plasma particles may be taken as constant.

* Adiabatic Invariant: Characteristic parameters which do not
change as a physical system slowly evolves; the most commonly
used one in plasma physics is the magnetic moment of a charged
particle spiraling around a magnetic field line.

* Aftercooling: Cooling of a reactor after it has been
shut down.

* Afterglow: Recombination radiation emitted from a cooling
plasma when the source of ionization (heating, etc) is removed.
(See entry for recombination radiation.)

* Advanced Fuels: There are several elements/isotopes which
could be fused together, besides the DT fuel mixture. Many such
fuel combinations would have various advantages over DT, but
it is generally more difficult to achieve fusion with these
advanced fuels than with the DT mix. See fuels section of FAQ
for discussion.

> Advanced Concepts Torus I: (ACT-I) A steady-state toroidal
device built primarily for studies of RF heating (see entry)
and RF current drive (see entry). Operated at PPPL but shut
down several years ago.

> Advanced Toroidal Facility: (ATF) A large stellarator device
developed at Oak Ridge National Lab (ORNL), but recently mothballed.
See Section 5 for more information.

> Alcator: Name given to a set of tokamaks designed and built at MIT;
these machines are distinguished by high magnetic fields with
relatively small diameters. The high magnetic field helps create
plasmas with relatively high current and particle densities.
The current incarnation is Alcator C-mod, and is described further
in Section 5. Alcator C was donated to LLNL for use as the
Microwave Tokamak eXperiment (MTX), now shut down.

> Alcator A: First of the Alcator series of tokamaks at MIT;
was operational from 1969 to 1982.

> Alcator C: Commissioned in 1978; used extensively to study
plasma confinement under strong ohmic heating (see entries).
Also studied high-density plasmas and used frozen fuel pellet
injection. Set record values of Lawson product (density
times confinement time; see entries) of 8 x 10^19 m^3-seconds.
Was donated to Livermore (LLNL; see entry) for use as the
Microwave Tokamak eXperiment (MTX: see entry), now shut down.

> Alcator C-mod: Successor to Alcator C; actually a completely
new device. Currently operational; described in more detail in
Section 5.

> Alcator DCT: Proposed fully-superconducting extension of
the Alcator series; never built.

* Alcator Scaling: A proposed empirical law in which the
energy confinement time is proportional to the product
of the average density and the square of the plasma radius
(see relevant entries).

> ALEX: A single-cell, minimum-B magnetic mirror system
(see entries) in which the magnetic field was generated by a
baseball coil (see entry) wound on a 60 cm sphere. Formerly
operated at the Rensselaer Polytechnic Institute, Troy, New York.

* Alfven Ion Cyclotron instability: (AIC) An electromagnetic
microinstability near the ion cyclotron frequency; driven by
the ion loss cone in a mirror device. (See relevant entries.)

* Alfven velocity: Phase velocity of the Alfven wave;
equal to the speed of light divided by the square root
of (1 plus the ratio of the plasma frequency to the cyclotron
frequency for a given species). i.e.,

Va = c / SQRT(1 + plasma freq. / cyclotron freq.)

(As defined in Stix, _Waves in Plasmas_, 2nd ed. 1992, p. 31)

* Alfven waves: Transverse electromagnetic waves that are
propagated along lines of magnetic force in a plasma. The waves
have frequency significantly less than the ion cyclotron frequency,
and are characterized by the fact that the field lines oscillate
(wiggle) with the plasma. The propagation velocity depends on the
particle density and the strength of the magnetic field. "[Relatively]
Low frequency ion oscillation in the presence of an equilibrium
magnetic field. Also called the transverse hydromagnetic wave along Bo.
The torsional Alfven wave in cylindrical geometry was first measured
in liquid mercury by B. Lehnert. Alfven waves were first generated
and detected in plasma by Allen, Baker, Pyle, and Wilcox in Berkeley
and by Jephcott in England in 1959." (quoting from Chen's book;
see bibliography) - Albert Chou

! Alfven, Hannes Olof: Nobel Prize-Winning Plasma Physicist
and Astronomer who first suggested the possibility of MHD waves
in 1942.

* Alpha Channeling: Term for an idea (so far theoretical)
in magnetic confinement fusion; the idea is that plasma
waves can be used to control the alpha particles produced
in a fusion reactor, to transfer their energy directly to fuel
ions, and to help push them out of the plasma. This could
potentially help to substantially improve the power output
capabilities of fusion plasmas.

* Alpha emission: Form of nuclear decay where the nucleus
emits an alpha particle (see entry below).

* Alpha particle: The nucleus of a Helium-4 atom; is a
typical product of fusion reactions; also released
in various nuclear decay processes. Alpha particles readily
grab electrons from other sources, becoming neutral helium;
even energetic alpha particles are easily stopped by thin
barriers (sheets of paper, dead layers of skin, etc.), so that
as a radiological hazard alpha particles are only dangerous if
they are generated inside one's body (where the skin cannot
protect tissue from damage). Alpha particles are common
products in fusion reactions between light elements.

& Alternating Current: (AC) Electrical Current (see entry) which
alternates in direction with time. (For instance, household
electric current is AC alternating at 60 oscillations/sec
(60 Hertz) in the United States, and 50 Hertz in many other

> AMBAL: An ambipolar trap (tandem mirror) located at
Novosibirsk in Russia. (Any additional information would
be welcome.)

* Ambipolar Diffusion: Diffusion process in which buildup
of spatial charge creates electric fields which cause
electrons and ions to leave the plasma at the same rate.
(Such electric fields are self-generated by the plasma
and act to preserve charge neutrality.)

% American Association for the Advancement of Science: (AAAS)
Organization dedicated to promoting science research and
education in the United States. Publishers of _Science_.

% American Association of Physics Teachers: (AAPT) Professional
society of physics teachers in the United States. Organizes
conferences on physics education. Publishers of _American
Journal of Physics_ (AJP)

% American Institute of Physics: (AIP) Organization dedicated
to promoting physics research and the dissemination of physics
knowledge; publishers of many physics books.

% American Nuclear Society: (ANS) Professional society of nuclear
scientists in the United States.

% American Physical Society: (APS) Professional society of physicists
in the United States. Organizes major conferences and publishes
many peer-reviewed journals.

% American Physical Society - Division of Plasma Physics: (APS-DPP)
Branch of the APS for plasma physicists, including fusion scientists.
The Annual Meeting of the APS-DPP is the largest plasma physics
conference in the United States.

$ Ampere, kiloampere, megampere: (from Herman) The standard
unit for measuring the strength of an electric current
representing a flow of one coulomb of electricity per second.
1 kiloampere = 1000 amperes; 1 megampere = 1,000,000 amperes.
Common abbreviations: A, amps, kiloamps, megamps, kA, MA

! Ampere, Andre-Marie (1775-1836): French physicist responsible
for much of what is known about the fundamentals of electromagnetism.

& Ampere's Law: General equation in electromagnetism relating
the magnetic field and the currents generating it.

* Aneutronic Fuels: Advanced fusion fuels which would not
produce fusion neutrons. See fuels section of FAQ for discussion.

$ Angstrom: A unit of distance equal to 10^-10 meters or 10^-8 cm.

& Angular Momentum: Momentum involved in the rotation of a body
about an axis; conserved like ordinary momentum (see momentum).
Angular momentum is defined as the cross product of ordinary momentum
with the position vector running from the axis of rotation to the
body whose angular momentum is being determined. Torque is the
rate of change of angular momentum with time. (see also torque)

& Anisotropy: Term used to describe a medium whose characteristic
properties vary in with direction of travel through the medium.
(e.g., velocity of light transmission, conductivity of heat or
electric current, compressibility, etc.)

* Anomalous Diffusion: Diffusion in most plasma devices,
particularly tokamaks, is higher than what one would predict from
understood causes. The observed, "typical" diffusion is referred to
as "anomalous" because it has not yet been explained. Anomalous
diffusion includes all diffusion which is not due to collisions
and geometric effects. While such effects were not understood
when the term was coined, and most still aren't, diffusion due
to well-understood wave phenomena is still 'anomalous'. "Classical"
diffusion and "Neo-classical" diffusion are the two well-understood
diffusion theories, neither is adequate to fully explain the observed
"anomalous" diffusion. See also: entries for classical and
neoclassical diffusion. (Acknowledgements to Philip Snyder)

* Antares: Laser-target irradiation system (i.e., laser fusion
research device) at Los Alamos National Lab; was operational in
1982. (The author would welcome current information.)

& Aperture: The opening in an optical system which restricts the
size of the bundle of rays incident on a given surface. (Usually
circular and specified by diameter.)

* Applied-B Diode: An ion diode with an applied magnetic field
to prevent electrons flowing from cathode to anode. The applied
magnetic field also regularizes the electron swarm to reduce
beam divergence.

* Arc: A type of electrical discharge between two electrodes;
characterized by high current density. Similar in meaning
to "spark" in common language.

% Argonne National Laboratory: One of the U.S. Department of Energy
basic-research Laboratories, located in Illinois... (need more info!)

> Argus: Two-beam, 5-terawatt Nd-glass laser system used at Livermore
(LLNL) for inertial-confinement fusion research from 1976 to 1981.

* ARIES: Set of four fusion reactor design studies which investigated
the safety, economic, and environmental implications of various
advances in fusion reactor science and technology.

* Ash: Fusion reaction products trapped in a plasma. Ash is
bad because (a) it generally radiates more strongly than the fuel
ions, and thus reduces energy confinement, and (b) it creates
additional plasma pressure and/or reduces pressure available for fuel
ions. (due to beta limits, see beta) Controlling ash is a major
area of fusion research. Ideally one would be able to extract
the ash ions after diverting an appropriate fraction of their
energy to heating the fuel ions, and then convert the remaining ash
energy to electricity. Current research involves using RF waves to
transfer energy from ash ions to fuel ions, and to push the ash into
the scrape-off layer, where it can be collected via divertors.
(See also scrape-off layer, divertors)

* Ash control - see ash, divertors.

* Ash removal - see ash, divertors.

* Aspect Ratio: In toroidal geometry, the ratio of
the major diameter (total width of the torus) to the
minor diameter (width of a slice taken through one side
of the ring). (This would be much better with a picture!)

In inertial-confinement fusion, aspect ratio refers to
the ratio of a fuel pellet's radius to its wall thickness.

& Atom: (from Herman) The smallest unit of an element that
retains the characteristics of that element. At the center
of the atom is the nucleus, made up of neutrons and protons,
around which the electrons orbit. Atoms of ordinary hydrogen,
the lightest element, consists of a nucleus of one proton
orbited by one electron. (Note: distinct from a molecule,
which is the smallest unit of a substance which retains the
characteristics of that substance. It takes far less
energy to break apart a stable molecule into its constituent
atoms than to divide a stable atom into two smaller atoms.)
Note that in solids, atoms are typically two angstroms
(2 x 10^-10 meters) apart; in air the gas molecules are about
30 angstroms apart. A drop of water has on the order
of 10^21 atoms in it. Atoms are generally electrical neutral;
when an atom acquires an electrical charge (by gaining or
losing electrons) it is usually called an ion.

& Atomic Bomb, A-Bomb: (from Herman) A weapon with a large
explosive power due to the sudden release of energy when the
nuclei of heavy atoms such as plutonium-239 or uranium-235
are split. This fission is brought about by the bombardment
of the fuel with neutrons, setting off a chain reaction.
The bomb releases shock, blast, heat, light, and lethal
radiation. The world's first atomic bomb was successfully
tested by the United States on July 16, 1945.

% Atomic Energy Commission: United States governmental
authority for atomic energy; split into ERDA and NRC in 1975.
(may not be 100% correct)

& Atomic Mass: Mass of an atom relative to 1/12th the mass
of a carbon atom. Approximately equal to the sum of the
number of protons and neutrons in the nucleus of the atom.

& Atomic Number (Z): The number of protons in a nucleus; same
as the number of electrons in a neutral atom; determines the
position of an element in the periodic table, and hence its
chemical properties (see also isotope).

* Atomic Temperature: The temperature corresponding to the mean
kinetic energy of the neutral atoms in a plasma. (If there were
no ions or electrons, the atomic temperature would be what we
normally think of as the temperature of a gas, such as the air.)

* Auger effect: Transition of an electron in an atom from a
discrete electronic level to an ionized continuous
level with the same energy; also known as autoionization.

& Avogadro's number: N = 6.02497 x 10^23. Number of particles
in a mole of a substance. Coefficient relating Boltzmann's
constant to the ideal gas constant. This is the number of
atoms per gram-atom. See also: mole

> Axially Symmetric Divertor EXperiment (from Herman)
(ASDEX, Asdex: Garching, Germany) A large tokamak designed
for the study of impurities and their control by a magnetic
divertor. The H mode or high mode of operation with neutral
beam injection was first observed on ASDEX.

> Axially Symmetric Divertor EXperiment (ASDEX, Asdex): "The original
ASDEX, located in Garching, Germany and decommisioned in 1990(?),
would qualify today as a medium-sized tokamak. It was designed for
the study of impurities and their control by a magnetic divertor.
The H mode or high mode of operation with neutral beam injection was
first observed on ASDEX. Its successor ASDEX-Upgrade (a completely
new machine, not really an "upgrade") is larger and more flexible.
It is the first tokamak whose toroidal and poloidal field coils are
not linked, which will be a necessary design factor in a reactor.
It will achieve parameters at the edge which are very similar to
those needed for a power reactor." - Arthur Carlson

* Azimuth: An angle measured clockwise relative to some
reference point on a circle (e.g., "south" or "north").

* Azimuthal: Generally an angle, measured "around" an object.
In spherical geometries, the angle which is *not* the "polar angle".
On the earth, one incarnation of the azimuthal angle is the longitude
of a location relative to the prime meridian through Greenwich,
England. In toroidal geometries, the longitude idea still applies,
but the other angle is the "poloidal" angle, not the "polar" angle.
The azimuthal direction is the "long way" around a torus.
See also: poloidal.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99

Archive-name: fusion-faq/glossary/b
Last-modified: 4-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 2: Terms beginning with "B"


Edited by Robert F. Heeter,

Guide to Categories:

* = vocabulary specific to plasma/fusion/energy research
& = basic/general physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

Citations and Acknowledgements appear in Section 11 of the FAQ.



# B: variable used for Magnetic Field

# B: chemical symbol for the element boron; see entry

# Be: chemical symbol for the element beryllium; see entry

@ BCSS: Blanket Comparison and Selection Study (no entry)

@ BHP: Biological Hazard Potential; see entry

@ BPX: Burning Plasma eXperiment; see entry

@ BTU: British Thermal Unit; see entry

@ BWR: Boiling Water Reactor (fission); see entry

* Background Radiation: Level of environmental radation due to
"background" sources. Background sources can be natural, such
as cosmic rays and natural radioactive elements (principally
radon, but including other elements such as isotopes of potassium
(which people get substantial amounts of in foods like bananas)).
They can also be man-made, such as from fossil-fuel combustion,
everyday leakage from nuclear activities, and leftover from
atmospheric nuclear weapons tests. Background radiation is
usually distinguished from acute radiation, such as from medical
x-rays, nuclear accidents, radioisotope therapy, or other short-term
doses. The man-made contribution to background radiation is
quite small compared to the natural contribution; medical uses
dominate human exposure to acute radiation.

& Backscattering: Deflection of incident particle / radiation
through an angle greater than 90 degrees relative to the original
direction of motion/propagation.

* Ballooning Instability: See Ballooning Mode

* Ballooning Mode: A mode which is localized in regions of
unfavorable magnetic field curvature ("bad curvature") and
which becomes unstable when the force due to pressure
gradients (grad p) is greater than the mean magnetic
pressure force (grad B^2)/(8*pi).

* Banana Orbit: The fast spiraling of an charged particle around a
magnetic field line is accompanied by a slow movement ("drift") of
the center of the sprial. Projected onto a poloidal plane, the drift
orbit has the shape of a banana. These orbits are responsible for
neo-classical diffusion (see entry).

$ Barn: Unit of area equal to 1x10^-24 square centimeters
(or 1x10^-28 square meters). Commonly used in describing
cross sections of atomic, nuclear, and particle interactions.
(see cross section).

* Baseball Coils: Used in magnetic-mirror geometries to
produce a minimum-B configuration; so-called because of their
resemblance to the characteristic shape of lacing on a baseball.

* Beam: stream of particles or electromagnetic radiation
travelling in a single direction.

* Beam-Beam Reaction: Fusion reaction which occurs from the
collision of two fast ions originating in injected neutral beams.

* Beam Dump: A mass of shielding material which absorbs
the energy of a beam of particles or electromagnetic radiation.

* Beam-Plasma Reaction: Fusion reaction which occurs from the
collision of a fast beam ion with a thermal plasma ion.

* Beam Splitter: Optical device for dividing a beam of
electromagnetic radiation into two or more separate beams.

* Beam-Wall Reaction: Fusion reaction which occurs from the
collision of a fast beam ion with an ion embedded in or adsorbed
onto the reactor wall.

* Bean-Shaped Plasma: A toroidal plasma indented on the inboard
side (that is, on the side with the "donut hole"); results in
additional stability to ballooning modes (see entry). Moderate
indentation (does, can, may?) provide access to the
second-stability region (high beta). (see relevant entries)

! Becquerel, Antoine-Henri: French scientist and discoverer of
radioactivity; co-winner of Nobel Prize. (See Curie)

$ Becquerel: Unit of radioactivity equal to 1 disintegration per
second. (see Curie)

* Bellows: Flexible mechanical structure with walls like those
of an accordion.

* Bernstein Mode: Type of mode which propagates perpendicular
to the equilibrium magnetic field in a hot plasma. The waves
have their electric field nearly parallel to the wave propagation
vector (nearly longitudinal). The modes propagate in
frequency ranges lying between integer harmonics of the
electron cyclotron frequency. Named after Ira Bernstein.

& Beryllium: (Be) Element with atomic number 4 (four protons).
May be useful in multiplying fusion neutrons to enhance tritium
production in a lithium blanket; rather hazardous to handle.
(See relevant terms mentioned.)

* Beta, or beta-value: Ratio between plasma kinetic pressure and
magnetic-field pressure; proportional to the ratio between plasma
kinetic energy density and magnetic field energy density. Beta
is usually measured relative to the total, local field
(loosely called beta toroidal), but sometimes the plasma pressure
relative to only the poloidal component of the field (beta poloidal)
or relative to some external field (like the maximum field at the
magnetic coils) is more useful. There is also a normalized beta
(beta_N) of interest when discussing the beta limit (see entry).
(lots of help from Art Carlson with the above.)

"Because the cost of a reactor is strongly influenced by the
strength of the magnetic field that must be provided, beta values
are directly related to the economics of fusion power production.
Beta is usually expressed as a percentage, with 5% generally
believed to be the minimum value required for an economical
fusion reactor." - from the PPPL WWW page on PBX-M.
See also: pressure, kinetic pressure, magnetic pressure,
second stability.

* Beta-Normal: Beta-N, the normalized beta, is beta relative to
the beta limit (see below).

* Beta-Poloidal: Beta-P is the same as the ordinary beta, except
only the poloidal field is used in calculating the magnetic field
pressure. Beta-P is > 1 in many modern tokamaks.

* Beta Emission: Form of nuclear decay where a neutron splits
into a proton plus electron plus neutrino set. The proton
stays in the nucleus but the electron ("beta ray") is ejected.

* Beta Limit, also called Troyon Limit: If the plasma pressure in
a tokamak becomes too high, the so-called ballooning modes become
unstable and lead to a loss of confinement (sometimes catastophic,
sometimes not). The exact value at which this occurs depends
strongly on the magnetic field B, the plasma minor radius a, and
the toroidal plasma current I, such that maximum value of the
normalized beta, beta_N=beta*B*a/I, is around 4% (with B in Teslas,
a in meters, and I in Mega-amperes). The exact value depends on
details of the plasma shape, the plasma profiles, and the safety
factor. (Beta entries provided by Art Carlson.)

* Beta Particle / Beta Ray: Original term used for electrons
(and positrons) ejected from decaying nuclei via beta emission.
(Label derives from the old days when we had various kinds of
radiation emission, and they were labeled alpha, beta, and
gamma (the first letters of the Greek Alphabet) because no one
really knew what any of them were.)

* Beta value: See "beta" just above.

* Biasing: [from Art Carlson] The vacuum vessel of a tokamak
(or other device) has a variety of structures--limiters, divertor
plates, the wall itself. These are usually mechanically and
electrically connected, but it is possible to bias (charge) them to
different voltages relative to each other. This allows some control
over the electric fields and currents around the plasma, which can
influence, for example, the thickness of the scrape-off-layer, the
transition between L- and H-mode, and the equilibrium configuration.
Biasing experiments are being done on DIII-D, TEXTOR, and TdeV.

* Binary Collisions: Collisions involving only two particles;
multiparticle collisions (eg, three-body collisions) are usually

* Binding Energy: Energy required to separate two objects;
conversely, energy released when two objects are allow to bind
together. Equivalent to the mass defect (see entry) via E=mc^2.

* Biological Hazard Potential (BHP): Measure of the hazard posed by
a given quantity of radioactive material in which the variation in
biological effects of the various elements are accounted for.
(See also integrated biological hazard potential, IBHP)

& Biot-Savart Law: General formula for determining the magnetic
field due to a steady line (not space) current. Related to Ampere's

* Blanket: a region surrounding a fusion reactor core within
which the fusion neutrons (if any) are slowed down, heat
is transferred to a primary coolant, and tritium is bred
from lithium (if tritium is used as fuel). In hybrid
applications, fertile materials (U-238 or Th-232) are located
in the blanket for conversion into fissile fuels.

* Bohm diffusion: A rapid loss of plasma across magnetic field
lines caused by microinstabilities. Theory formulated by the
physicist David Bohm. From Chen's book
(see bibliography): "Semiempirical formula for the diffusion
coefficient given by Bohm in 1946 (noted by Bohm, Burhop, and
Massey, who were developing a magnetic arc for use in uranium
isotope separation)." Bohm diffusion was proposed (not derived
from first principles) to scale as 1/B rather than the 1/B^2
scaling predicted by classical diffusion. A 1/B scaling results
from assuming that particles diffuse across field lines at an
optimum rate (effective collision frequency=cyclotron frequency).
The 1/B scaling is observed (approximately) in most reactors.
(Acknowledgements to Philip Snyder) See also: diffusion,
microinstabilities, field lines...

* Boiling Water Reactor (BWR): Class of fission reactor where
water is used as a coolant and allowed to boil into steam.
(I don't remember much more about it - any help out there?)

& Boltzmann constant: k = 1.38 x 10^-16 erg/degree. This
is the ratio of the universal gas constant to Avogadro's number.
It is also used to relate temperatures (Kelvin) to energies (ergs
or Joules) via E = (constant of order unity) * kT.

& Boltzmann Distribution: See Maxwell-Boltzmann distribution;
distribution function.

* Boltzmann Equation: Fundamental equation in kinetic theory
which describes the evolution of the distribution function.
(See also Vlasov equation.)

* Bootstrap Current: Currents driven in toroidal devices by
neo-classical diffusion (see entry). They may amount to a
substantial fraction of the net current in a tokamak reactor,
thus lengthening the pulse time or decreasing the power needed
for current drive.

& Boron: (B) Fifth element (Z=5) in the periodic table; has
5 protons; potential use as an aneutronic fuel. (See FAQ section
1, part on reactions.) Also useful as a neutron-absorber.

* Boronization: Energy confinement in a fusion plasma depends
strongly on the average atomic number (Z) of the elements in the
plasma. Boronization refers to a process whereby boron (atomic
number 5) is injected into a plasma and used to coat the walls
of the reactor; the effect is that impurities from the reactor
walls which enter the fusion plasma are primarily boron (which
has a fairly low Z) rather than the higher-atomic-number metals
typically used in reactor structures. Boronization has been
associated with improved fusion plasma performance. Boronization
is an example of Wall Conditioning. See also Boron, atomic number,
wall conditioning, impurities.

* Bounce Frequency: The average frequency of oscillation of
a particle trapped in a magnetic mirror as it bounces back
and forth between its "turning points" in regions of high
magnetic field. (See also trapped particle, turning points,
banana orbit).

* Boundary Layer: In fluid flow, a narrow region next to a
fixed boundary or surface where the fluid velocity rapidly
changes from zero to some finite value. The term has been
generalized to situations with similar mathematics.

* Branching Ratio: In a fusion reaction involving two nuclei,
there are typically a variety of possible sets of products which
can form. The branching ratio for a particular set of products
is the probability that that set of products will be produced.

* Breakeven: there are several types:
Commercial: When fusion power can be converted into enough
electric power to power the reactor and generate enough
electricity to cover the costs of the plant at economically
competitive rates. (?)
Engineering: When enough energy can be generated from the
fusion power output to supply power for the reactor and
generate a surplus; sort of commercial breakeven without
the economic considerations. (?)
Scientific: When fusion power = input power; Q=1.
(See also Lawson Criterion)
Extrapolated - projected for actual reactor fuel using
an alternative fuel.
Actual - determined using the actual fusion fuel to be
used in the reactor (typically DT).

* Breeder Material: In D-T fusion, refers to lithium or
lithium-containing substances which are placed in the
blanket to convert the fusion neutrons back into tritium,
using nuclear transmutation of lithium isotopes.

* Breeder Reactor: Class of nuclear reactor (could be fission
or fusion) which uses some of the nuclear byproducts (generally
neutrons) to transmute non-fuel materials to new materials which
can be used for fuel in other reactors, in such a way that
the reactor creates more fuel than it consumes (breeding).
Term usually refers to reactors which breed fission fuel.
Use of breeder reactors would greatly extend the fuel supply for
nuclear fission energy, but also creates additional opportunities
for diversion of fissile materials to weapons production and
could exacerbate proliferation of nuclear weapons.

& Bremsstrahlung: (German for "Braking Radiation") Electromagnetic
radiation from a charged particle as it slows down (decelerates),
or as it changes direction due to near collisions with other particles.
Similar to synchrotron radiation (see also). In a plasma
bremsstrahlung occurs when electrons (which are lighter and generally
move faster) collide with ions (which are heavier and generally move
slower); the acceleration/deceleration of the electrons causes them
to radiate bremsstrahlung.

& Brewster's Angle: The angle of incidence at which
electromagnetic waves reflected from a dielectric medium are
completely polarized perpendicular to the plane of incidence;
the component polarized parallel to the plane of incidence is
completely transmitted.

* British Thermal Unit: Unit of energy needed to raise a pound of
water by one degree fahrenheit; equal to 252 calories or 1055 Joules.
(See also calorie, joule). Not part of the metric system.

> Bumpy Torus: I believe this concept tries to combine mirror
concepts with toroidal ones. My understanding is that it is
essentially a series of mirrors stuck end to end and bent into
a ring. - Albert Chou (corrections / enhancements welcome!)

* Bunching: A technique for spatial compression of a pulse
in a beam of charged particles.

* Bundle Divertor: Divertor concept where a toroidal field
coil extracts a "bundle" of toroidal field lines (flux) and
forms a separatrix in the toroidal field. (Hard to do
and tends to mess up axisymmetry of the torus; not used much.)

> Burning Plasma eXperiment (BPX): Proposed U.S. successor to TFTR;
never funded. See also: CIT, TPX.

* Burnout: Rapid reduction in the neutral particle density
in a plasma discharge; occurs when the ionization rate (which
converts neutrals to ions and electrons) exceeds the rate
of recombination (which converts ions to neutrals) and the
rate of influx of neutral particles.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/h
Last-modified: 4-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 8: Terms beginning with "H"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary

> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# H: chemical symbol for the element hydrogen; see entry

# He: chemical symbol for the element helium; see entry.

@ HIREX: High-REsolution X-ray spectroscopy

@ H-mode: see high-mode

@ HTO: (Hydrogen-Tritium-Oxygen) Water with a tritium atom
replacing a hydrogen. See entry for tritium.

* Half-life: For a given quantity of a radioactive isotope,
there is a time period in which half the nuclei will decay to
a different state; this period is called the half-life. Measured
half-lives range from less than millionths of a second (for very
short-lived isotopes) to billions of years (for isotopes which
are almost stable, but not quite). The time in which half the
atoms of a particular radioactive isotope disintegrate
to another nuclear form. By analogy, "half-life" can also be
used to describe similar time-periods for other sorts of
exponential decay phenomena.

* Hall Effect: Transverse electric field which develops in a
conductor (as a result of the Lorentz Force acting on the charge
carriers) when current is driven across a magnetic field.

* Halo: The cold, dense plasma formed outside the last closed flux
surface during a vertical displacement event. The large currents
which flow through this plasma stop the displacement and transfer the
force to the vacuum vessel. If care is not taken in design, the halo
currents can be large enough to threaten the structural integrity of
the vacuum vessel or in-vessel components. Whereas the center of a
tokamak plasma is too hot for material probes to survive, probes
(such as magnetic-field coils) can sometimes be placed in the
halo, and can measure things such as the halo current (see below).
See also entry for vertical instability.

* Halo Current: Currents in the halo region of a plasma discharge.
See entry for halo above.

* Hamada coordinates: A particular magnetic-flux coordinate
system useful for MHD calculations. In this system the current
density and magnetic field lines are straight and the Jacobian
of the coordinate transformation equals one.

& Hamiltonian Function: Function arising from the Hamiltonian
approach to mechanics which characterizes the total energy of
a system as a function of generalized coordinates and momenta
and can be used to obtain the dynamical equations of motion
of the system. (Consult an intermediate or advanced mechanics
text for more info.)

> Hard-core pinch device: plasma pinch-discharge device using a
solid central conductor ("hard-core"). The discharge then occurs
in an annular region about the central conductor.

& Hartree-Fock approximation: a refinement of the Hartree method
(see entry) in which one uses determinants of single-particle
wave functions rather than products, thereby introducing exchange
terms into the Hamiltonian.

& Hartree method: An iterative, variational method of finding an
approximate quantum-mechanical wavefunction for a system of many
electrons, in which one attempts to find a product of
single-particle wave functions, each of which is a solution of
the Schrodinger equation with the field deduced from the charge
density distribution due to all the other electrons; also known
as the self-consistent field method.

& Heat exchanger: device that transfers heat from one fluid
(liquid or gas) to another (or to an external environment).

* Heavy Hydrogen: somewhat informal alternative name for deuterium.
(see entry for deuterium).

* Heavy Water: (D2O) Water with enriched content of deuterium
relative to hydrogen (greater than the natural abundance of 1 D
per 6500 H). Heavy water is used as a moderator in some fission
reactors (see CANDU entry) because it slows down neutrons effectively
but also has a low collision cross-section for absorption of neutrons.

> Heliac: A confinement configuration which superimposes an l=1
stellarator-type field upon a tokamak-like poloidal field. The
resulting plasma configuration is a helix bent around into a loop.

* Helicity: (from John Cobb) A measurement of the topological
"tangledness" of magnetic field lines. It is formally defined as the
scalar product of the magnetic vector potential with the magnetic
field, K = A dot B. If the plasma is perfectly conducting, then
helicity is a conserved quantity. (Without resistance, field lines
cannot reconnect, and magnetic topology is conserved, so helicity is
conserved). (See frozen-in flow). If the plasma has a small amount
of resistivity, then Helicity is not exactly conserved. However, the
total helicity inside of a given flux surface is often conserved to a
good approximation. In that case, the dynamics of a plasma can be
analyzed as an evolution toward a minimum energy state subject to the
constraint of a conserved total helicity (See Taylor State, J.B.
Taylor). This is often used in analyzing the equilibrium and
relaxation of RFP's and other toroidal devices.

> Helios Facility: Los Alamos laser inertial fusion facility.

& Helium: Element whose nuclei all contain two protons.
Stable isotopes are 3He and 4He. 3He is rare on earth (only 1.3
ppm of naturally-occuring He), can be generated from decaying
tritium (half life of about 12 years), and is relatively abundant
in the crust of the moon. Helium is the second most abundant element
in the universe and in the sun, and occurs at about (I believe)
1 part per million in earth's atmosphere. Helium is also found
in significant quantities in natural gas deposits. The nucleus
of the He atom is also known as an alpha particle. Helium is
chemically inert, behaves nearly as an ideal gas under a wide
range of pressures and temperatures, and can only be liquefied
at 4 Kelvin (at atmospheric pressures). One mole of He weighs
4 grams.

! Hertz, Heinrich: 19th-century German physicist; first (?)
observed low-frequency electromagnetic waves.

$ Hertz: Unit of frequency equal to one complete oscillation (cycle)
per second. Common abbreviation is Hz.

* High-beta plasma: A plasma in which the beta value (see entry)
is typically 0.1 to 1.

* High-mode or H-mode: A regime of operation most easily
attained during auxiliary heating of diverted tokamak
plasmas when the injected power is sufficiently high.
A sudden improvement in particle confinement time leads to
increased density and temperature, distinguishing this mode
from the normal "low mode." However, H-mode has been achieved
without divertors, auxiliary heating, or a tokamak. (H-modes
have been observed in stellarators.)

& Holography: A technique for recording and later reconstructing
the amplitude and phase distribution of a wave disturbance.

& Homopolar generator: A direct-current generator in which the
poles presented to the armature are all of the same polarity,
so that the voltage generated in the active conductors has the
same polarity at all times. A pure direct current is thus
produced without commutation.

* Hot cells: Heavily radiation-shielded enclosure in which
radioactive materials can be handled by persons using remote
manipulators and viewing the materials through shielded windows
or periscopes.

* Hybrid diode: An ion diode that uses a field coil in series
with the ion diode's accelerating gap to generate sufficient
magnetic flux in the diode for electron control. The diode is
a combination of the Applied-B diode's ion source and the
Ampfion diode's field coil.

* Hybrid reactor: see fusion-fission hybrid.

* Hybrid resonance: A resonance in a magnetized plasma which
involves aspects of both bunching of lighter species parallel
to the magnetic field, characterized by the plasma frequency;
and perpendicular particle motions (heavier species) characterized
by the cyclotron frequency.

& Hydrogen: (H) Element whose nuclei all contain only one proton.
Isotopes are protium (p, no neutrons) deuterium (D or d,
one neutron), and tritium (T or t, two neutrons). Hydrogen is
the lightest and the single most abundant element in the
universe, and in the sun. Hydrogen is a major element in
organic compounds, water (H2O), and many other substances.
Hydrogen is ordinarily a gas, but can be liquefied at low
temperatures, and even solidified at low temperature and
high pressure. Hydrogen gas can burn explosively
in the presence of oxygen.

* Hydrogen bomb or H-bomb: (from Herman) An extremely
powerful type of atomic bomb based on nuclear fusion.
The atoms of heavy isotopes of hydrogen (deuterium and
tritium) undergo fusion when subjected to the immense
heat and pressure generated by the explosion of a nuclear
fission unit in the bomb.

* Hydrogen embrittlement: A decrease in the fracture
strength of metals (embrittlement) due to the incorporation
of hydrogen within the metal lattice.

* Hydromagnetic Instability: See MHD Instability

* Hydromagnetics: see magnetohydrodynamics (MHD)

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/i
Last-modified: 4-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 9: Terms beginning with "I"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# I: variable used to indicate total current through a conductor.

@ IAEA: International Atomic Energy Agency; see entry

@ IBHP: Integrated Biological Hazard Potential; see entry

@ ICE: Ion Cyclotron Emission; see entry

@ ICF: Inertial Confinement Fusion; see entry

@ ICH: Ion Cyclotron Heating - see ICRH

@ ICRF: Ion Cyclotron Range of Frequencies

@ ICRH: Ion Cyclotron Resonance Heating; see entry

@ IEEE: Institute of Electrical and Electronic Engineers; see entry

@ INEL: Idaho National Engineering Laboratory; see entry

@ IPP: Max Planck Institute for Plasma Physics; see entry

@ IR: Infrared (region of the electromagnetic spectrum)

@ ITER: International Thermonuclear Experimental Reactor; see entry

% Idaho National Engineering Laboratory: U.S. Department of energy
laboratory involved in engineering studies for fusion and fission
reactors, among other things. Not surprisingly, located in Idaho.

* Ignition: In fusion, as in an ordinary (chemical) fire,
ignition is the point where the temperature and confinement
of heat in the fuel (plasma in the case of fusion) are
such that energy released from ongoing reactions is sufficient
to maintain the temperature of the system, and no external
heating is needed. An ignited fusion plasma produces so
much energy from fusion reactions that the plasma is fully
heated by fusion reaction products (alpha particles in the
case of D-T fusion), and the plasma no longer needs any
external source of power to maintain its temperature.
(The plasma may, however, still need something to maintain
its confinement; this gives us control over the fusion
reaction and helps prevent fusion reactors from having
"meltdown" problems like fission reactors.)

* Ignition Temperature: For given values of density and
energy confinement, the temperature at which ignition occurs.
(see ignition above)

> Impact Fusion: Fusion approach where a "fuel" projectile
is acclerated and impacted into either a stationary target or
another projectile. (Valuable for scientific purposes but
not a candidate for a fusion energy source because the
likelihood of fusion occurring in a single collision is
too low. Multiple accelerated pellets colliding with spherical
symmetry might be a viable inertial confinement approach, though.)

* Impact fusion drivers: macroparticle/projectile accelerator
which could be used in inertial confinement fusion.

* Impurities: atoms of unwanted elements in the plasma,
which tend to degrade plasma performance, and in the case of
fusion plasmas tends to inhibit fusion ("poisoning the reactor").
See also poisoning.

* Impurity Control: Processes which reduce or control the level
of impurities in a plasma, and thereby improve its quality;
see also wall conditioning.

* Inboard side: portion of a tokamak (or other toroidal device)
closest to the central axis. (As distinguished from "outboard side.")

* Incoherent scattering: Type of scattering in which the scattering
elements act independently, so that no definite phase relationships
exist among the different parts of the scattered
beam (particles or photons).

& Index of Refraction: For a given wavelength, this is the ratio
of the velocity of light in vacuum (c) to the velocity of light
in a refractive material (e.g., glass, plasma, etc.).

& Inductance: Characteristic relating the magnetic flux generated
through a loop of wires to the current in the wires; Phi=LI.

& Induction: A changing magnetic flux through a current loop will
induce an electric field which will drive a current through the loop.
This is the principle behind an AC transformer, where an oscillating
electric voltage in one loop of the transformer creates a current
which generates an oscillating magnetic field, which then induces
a different voltage and current in a second loop.

* Inductive Current Drive: Method to drive current in a toroidal
plasma by using the torus of conducting plasma as the second coil
in a transformer. The primary coil usually runs down the center
of the torus; changes in the current driven through the primary
coil create changing magnetic fields which drive current in
the plasma. The current thus driven can be used to heat the plasma
as well (see also ohmic heating; induction).

* Inertial Confinement Fusion: Approach to fusion where the plasma
is imploded so quickly that the inertia of the converging particles
is so high that many fuse before they disperse. This is the method
used in a hydrogen bomb; ICF schemes for power production usually
use small pellets of fuel in an attempt to make "miniature"
h-bomb type explosions. Methods for imploding the pellet include
bombardment from all sides with high-powered laser and particle
beams, and of course implosion in a fission bomb. Parts of ICF
fusion research remain classified due to their military
implications and applications, though much ICF research was recently

* Instability: A state of a plasma (or any other physical system)
in which a small perturbation amplifies itself to a considerable
alteration of the state of the system. In plasmas instabilities
sometimes leads to disruptions (see entry). Most instabilities are
associated with waves and other natural modes of oscillation in the plasma,
which can sometimes grow. There are (unfortunately!)
many kinds. See also: Flute instability, MHD instability,
Interchange instability, microinstability, kink instability,
resistive instability, trapped particle instability,
two-stream instability, universal instability, and
velocity-space instability.

% Institute of Electrical and Electronic Engineers: Professional
society for this branch of engineering.

* Integrated Biological Hazard Potential (IBHP): Total
biological hazard potential of a collection of radioactive
materials summed over their decay lifetimes. See also BHP.
One measure of the IBHP is the amount of water one would need
to use to dilute the materials to the point where the water
would be safe to drink.

* Integrated neutron flux: Sum (integral) of the neutron
flux (neutrons per unit time per unit area, see flux)
over all time; total number of neutrons which passed through
a unit area. Important figure-of-merit in testing effects of
neutron radiation on materials, and in assessing how long
such materials can survive exposure to neutron sources
(such as fission reactor cores and D-T fusion plasmas).

* Intensity: This term has different meanings in different
contexts. Can refer to the amount of power (energy per unit
time) incident on a unit surface area, or flowing through a
unit volume. Can refer to the number of particles or photons
incident, per unit time, on a unit area, or flowing through
a unit volume. Also, for an amount of a radioactive material,
intensity can refer to the number of radioactive disintegrations
per unit time.

* Interchange Instability: In the simplest form, if you
place a high-density fluid on top of a low density fluid,
gravity will pull the high density fluid downwards so that
the low-density fluid ends up on top. The two fluids
therefore interchange places. More generally, an interchange
instability occurs when two types of fluid are situated with
an external force such that the potential energy is not
a minimum; the two fluids will then interchange locations to
bring the potential energy to a minimum. In plasmas with
magnetic fields, the plasma may interchange position with
the magnetic field. A prime example is the flute instability
in mirror machines. (See MHD, instability, flute, mirror.)

* Interference: When two waves propagate through the same
region of space, they interfere with each other. Neither
wave is altered, but the amplitudes of the waves add (or
cancel, if they're of opposite sign) to give the total
effect to the medium at that point.

* Interferometer: Device which measures changes in a medium
by looking at effects on the interference of two waves which
are passed through that medium. See interferometry,
laser interferometer, optical inteferometer, Fabry-Perot
interferometer, microwave interferometer.

* Interferometry: Method of gathering information about a
medium by using an interferometer or similar technique.
Optical - Uses light as the wave to be interfered.
Microwave - Uses microwaves instead. Microwave interferometry
is especially useful in plasma physics for measuring plasma

> Internal ring devices: Toroidal configurations in which
current-carrying rings are suspended (either mechanically
or magnetically) inside the plasma chamber.

% International Atomic Energy Agency: (from Herman) An
autonomous intergovernmental organization established in 1956
with the purpose of advancing peaceful uses of atomic energy,
with headquarters in Vienna.

> International Thermonuclear Experimental Reactor (ITER):
Huge fusion reactor being planned by the EC, US, Japan,
and Russia (former USSR?). Should generate far more
energy than it consumes. Research goals include engineering
studies of reactor materials, component designs for steady-state
devices, and testing/proving commercial feasibility. Discussed
in sections 5 and 9.

* Ioffe Bars: Special configuration of conductors which, when
added to a conventional magnetic mirror, generate a "magnetic
well" which stabilizes the mirror against MHD instabilities.

& Ion: An atom (or molecule) which has become charged as a
result of gaining or losing one or more orbiting electrons.
A completely ionized atom is one stripped of all its electrons.

* Ion acoustic wave: a longitudinal compression wave in the
ion density of a plasma, which can occur at high electron
temperatures and low frequencies, caused by a

* Ion Cyclotron Emission (ICE): As ions gyrate around in a magnetic

field (see also larmor radius or cyclotron radius), they radiate

radio-frequency electromagnetic waves. This is known as ion

cyclotron emission, and can be measured to help diagnose a plasma.

* Ion Cyclotron Resonance Heating: Like Electron Cyclotron
Heating, but heats ions using waves near the ion cyclotron
frequency. See Electron Cyclotron Heating.

* Ion diode: Device for producing and accelerating ion beams
for light ion drivers for inertial confinement fusion. Ions
are produced in an anode plasma, extracted as space-charge-limited
ion flow, and accelerated to the cathode, composed of a confined
electron swarm, by an applied electric field. Millions of
amperes of current at millions of volts have been produced this way.

* Ion Temperature: the temperature corresponding to the
mean kinetic energy of the ions in a plasma.

& Ionization: Process by which a neutral atom is converted to an ion
(or one ion is converted to another of a different type), by
removal or addition of electrons.

& Ionization Energy: Generally refers to the amount of energy
required to strip a particular electron from an atom. The
first-ionization-energy is a commonly used quantity in many fields
of physics and chemistry. Typically measured in electron-volts.
Equivalent to the atomic binding energy of the electron.

& Ionization Potential: See ionization energy.

* Ionizing radiation: Any high-energy radiation which can
displace electrons from atoms or molecules, thereby producing ions.
Examples: alpha-particle radiation; beta radiation; x-rays,
gamma, and hard ultraviolet light; and accelerated ions.
Ionizing radiation in large quantities may cause severe skin
and tissue damage and adverse effects. (On the other hand,
but not to belittle the hazards of radiation, we are
continuously exposed to a "natural background" of ionizing
radiation too.)

* Ionosphere: Ionized region of the upper earth atmosphere, which
behaves like a plasma, including reflection of AM radio waves and
generation of auroral glows.

* Irradiation: Process of exposure to radiation.

* Isomer, Nuclear: two nuclei with the same nuclear mass (total
number of protons and neutrons) but different nuclear compostions.
(e.g.: T & 3He are isomers: T has 1p, 2n; 3He has 2p, 1n)

& Isotope: One of several species of the same element,
possessing different numbers of neutrons but the same number
of protons in their nuclei. Most elements have several
stable isotopes, and also several possible unstable and
semi-stable isotopes. The chemical and physical properties
of the different isotopes are generally the same (except for the
slight mass difference and the possibility of radioactivity).
Examples include the hydrogen isotopes protium (ordinary
hydrogen), deuterium, and tritium (two neutrons, one proton);
also uranium 238, 233, and 235. The chemistry of an element
depends only on the number of protons (nuclear charge) and
is therefore the same for all isotopes of an element, but
the nuclear properties of different isotopes will be
different. There are roughly 300 known stable isotopes,
and over 1000 unstable ones.

& Isotropic: adjective which describes a medium whose
physical properties are independent of the direction in
which they are measured.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/n
Last-modified: 20-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 14: Terms beginning with "N"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# n: variable used for number density of particles.
# n: also used as the symbol for a neutron.
# n: also sometimes used for the index of refraction

@ NAS: National Academy of Sciences; see entry

@ NASA: National Aeronautics and Space Administration

$ nano: metric prefix indicating 10^-9 * the base unit

@ NBETF: Neutral Beam Engineering Test Facility

@ NBI: Neutral Beam Injection; see entry

@ NBS: National Bureau of Standards

@ ND-YAG: Neodymium yttrium Aluminum Garnet

# ne: (n subscript e) - usually electron density

# Ne: chemical symbol for Neon.

@ NERSC: National Energy Research Supercomputer Center; see entry

@ NIF: National Ignition Facility; see entry

@ NIKE: Naval? Inertial Confinement Experiment????; see entry

@ NINJA: Neutral gas INJection Array (on Alcator C-Mod)

@ NIST: National Institute for Science & Technology?

@ NRC: National Research Council *OR* Nuclear Regulatory
Commission; see entries.

@ NRL: Naval Research Laboratory; see entry

@ NSTX: National Spherical Tokamak eXperiment; see entry

% National Academy of Sciences: Elite, honorary, independent,
self-perpetuating organization of highly-successful scientists;
chartered by the U.S. Congress to provide technical advice
to the federal government upon request.

% National Energy Research Supercomputer Center (NERSC):
Formerly the National Magnetic Fusion Energy Computer Center,
or NMFECC, NERSC is a supercomputer facility located at
Livermore, CA. Originally developed to provide high-performance
computing facilities for the needs of the magnetic fusion
energy program, the facility now benefits all energy research
programs. NERSC is a part of the Energy Sciences Network, ESNET,
run by the Department of Energy, which links several of the
national laboratories.

> National Ignition Facility (NIF): Inertial-Confinement
Fusion Facility proposed to be built at Livermore and
operational around the year 2000. See Section 9 on Future
Plans for more information.

% National Research Council: Research arm of the National
Academy of Sciences.

> National Spherical Tokamak eXperiment (NSTX): Mid-sized
low aspect-ratio tokamak / spheromak experiment proposal;
still in design phase / not funded. See Section 9 on Future
Plans for more information.

% Naval Research Laboratory: Basic-science research laboratory
operated by the U.S. Navy.

* Neoclassical Diffusion: In a magnetized plasma, _classical_
diffusion refers to transport of particles due to Coulomb collisions,
taking the spiral orbits in the magnetic field into account. In a
toroidal magnetic field, the actual rate of diffusive transport is
much higher due to slow changes in the positions of the centers of the
spirals, known as banana orbits (see entry). This faster transport
is called _neo-classical_. With very few exceptions the transport
in toroidal devices is observed to be 10-100 times larger still,
presumably due to small-scale turbulence. The observed transport is
called _anomalous_ (although it actually is the "normal" state).

* Neoclassical transport: See neo-classical diffusion.

> Neutral Beam Engineering Test Facility: Facility located at
LBL which tested neutral beam injection systems that were
designed for use in magnetic fusion reactors.

* Neutral Beam Injection: This is one of the fundamental plasma
heating methods. A particle accelerator is used to create
fast ion beams (the particle energies are on the order of 100 keV);
the ion beam is then passed through a neutral gas region, where
the ions neutralize via charge-exchange reactions with the neutral
gas. The neutralized beam is then injected into a magnetically
confined plasma. The neutral atoms are unaffected (not confined)
by the magnetic field, but ionize as they penetrate into the
plasma. The high-energy ions then transfer some of their energy
to the plasma particles in repeated collisions, and heat the

* Neutral Injection Concept: See Neutral Beam Injection, above.

* Neutralized Plasma: Plasma with no net electrical charge.

& Neutron: [Symbol: n] Fundamental atomic particle with
zero electrical charge (therefore not confined by a magnetic
field) and a mass roughly equal to a proton's mass. Neutrons
are found in all nuclei except for ordinary hydrogen; they are
also products of many nuclear reactions. Neutrons will react
with nuclei, and can induce radioactivity or fission. Free
neutrons which do not collide and react with a nucleus decay into
an electron, a proton, and an neutrino, with a half life of
about 13 minutes.

* Neutron Wall Loading: Energy flux carried by fusion neutrons into
the first physical boundary that surrounds the plasma (the first
wall). (see also First Wall, Flux, Neutrons)

> NIKE: Medium-scale(?) inertial-confinement fusion facility at
the Naval Research Lab; see discussion in Section 5.

* Non-Inductive Current Drive: Current drives schemes that do not
rely upon the "transformer" effect in tokamaks. The attainment of
non-inductive current drive is crucial to the success of tokamaks
as truly steady-state devices. See also inductive current drive.

> Nova: The United States' largest laser (ICF) fusion
facility, and the world's most powerful laser; located at LLNL.
This is a 10-beam, 100 terawatt, Nd-glass laser system, which can
operate at the infrared/visible wavelengths of 1.05, 0.53, or
0.35 microns. It was completed in 1984 and is the successor to
the Shiva system. (The next flagship laser-fusion facility
currently planned in the U.S. is the National Ignition Facility.)

* Nuclear Binding Energy: The difference between the total
energy ( = mc^2) of the bound nucleus, and the energies of
the individual constituent particles ( = sum of masses * c^2).
The nuclear binding energy *per nucleon* is a maximum for iron.
Fusion releases energy because light nuclei are less tightly
bound than medium-weight nuclei, and thus energy is liberated
when they become more tightly bound after fusing. Fission
releases energy for the same reason - heavy nuclei are also
less tightly bound than medium-weight nuclei, and energy is
liberated when heavy nuclei split into lighter nuclei.

& Nuclear Force: See Weak (Nuclear) Force, Strong (Nuclear) Force.

% Nuclear Regulatory Commission: U.S. organization in charge
of overseeing safety of nuclear facilities, including fission
(and presumably fusion) reactors.

* Nucleon: Generic term for a component particle of a nucleus,
i.e., either a proton or a neutron.

& Nucleus: The tiny core of an atom, positively charged,
containing protons and neutrons (except for simple hydrogen,
which has only a single proton). In an atom, electrons "orbit"
the nucleus, forming a cloud around it.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/o
Last-modified: 20-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 15: Terms beginning with "O"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


@ OFE: Office of Fusion Energy; see entry

@ OH: Ohmic Heating; see entry

@ OH1, OH2L, OH2U: Ohmic Heating Coils (1,2, upper, lower)
on Alcator C-Mod

@ OPEC: Organization of Petroleum Exporting Countries; see entry

@ ORNL: Oak Ridge National Laboratory; see entry

% Oak Ridge National Laboratory: Located in Oak Ridge, TN.
Home of a series of various fusion devices. Recent machines
have included the Elmo Bumpy Torus and the Advanced Toroidal
Facility (stellarator). (Could use more info!)

% Office of Fusion Energy: This is the office (within the
Office of Energy Research in the U.S. Department of Energy)
which administers the fusion energy research program.
Web users can visit for more info.

! Ohm, Georg Simon (1789-1854): Physicist who discovered the
relationship between electric current, potential and resistance.
(Yes, it is Georg. Swedish, I believe.)

$ Ohm: Unit of electrical resistance.

& Ohmic heating: Heating that results from the flow of current
through a medium with electrical resistance. In plasmas
subjected to ohmic heating, ions are heated almost entirely by
transfer of energy from the hotter, more mobile electrons.

* Ohmic heating coil: On a tokamak, this is the coil (generally
a set of coils; part of the poloidal field system) used to
induce an electric field in the plasma via a transformer
effect. The electric field generates of a toroidal plasma
current, with resultant ohmic heating.

* Ohmic heating solenoid: See ohmic heating coil, solenoid.

& Ohm's Law: The relationship between the net current and
the electric field in a conducting medium. For simple
resistors, the voltage equals current times resistance,
V = I*R. In plasmas the "generalized Ohm's Law" is a
more complex tensor relationship involving the vector
current density, the vector for the electric field, and
a generalized resistance tensor that relates the two.

> OMEGA: Inertial confinement fusion facility at the Laboratory
for Laser Energetics, University of Rochester (NY). OMEGA
uses a 24-beam Nd:glass laser at wavelengths of
1.054 or .351 microns.

# Omega: Variable frequently used to denote frequencies.

* O-Point: Place where the poloidal magnetic field vanishes in such
a way that the nearby flux surfaces are elliptical, e.g. on the
magnetic axis (see entry) or at the center of a magnetic island (see
entry). (See also X-Point.)

& Optical Axis: The line passing through both the centers of
curvature of the optical surfaces of a lens; the optical
centerline for all the centers of a lens system.

& Optical Interferometer: This is an interferometer (see entry)
which uses the interference of optical-frequency light waves.
These are useful in measuring distances precisely, and can
be used to test optical system elements (lenses, mirrors, etc.)
during manufacture.

* Optical Pumping: In laser physics, this denotes the process
in which absorbed light is stored in the laser medium. If the
absorption & storage process creates a population inversion,
laser action can occur (and extract the energy stored by optical
pumping in the form of laser emission).

* Oscillator: In laser physics, this refers to a device to
generate coherent optical energy. (i.e., it's another term
for the laser-light creating device itself, minus the source
of power which pumps the oscillator.) The oscillator generally
consists of a laser medium placed within an optical resonant
cavity (pair of mirrors). Optical energy will be trapped between
the mirrors and the optical (laser) oscillations will grow
so long as the gain of the laser medium exceeds the losses at
the mirrors.

* Outboard Side: portion of a tokamak / toroidal device on
the outer side, opposite the central axis.

* Overturning Moment: Torque ("moment") on a toroidal field
coil in a tokamak, about the device's radial direction,
that results from out-of-plane forces on the coil due to
the interactions between the coil current and the poloidal
(vertical) magnetic field. This torque tends to "overturn"
the vertical toroidal field coil, and must be engineered

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/p
Last-modified: 25-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 16: Terms beginning with "P"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# p, P: Variables used for plasma (kinetic) pressure.
# p: also used as symbol for the proton
$ p: also the metric prefix for pico (10^-12 * base unit)

@ PBFA-II: Particle Beam Fusion Accelerator-II; see entry

@ PBX-M: Princeton Beta eXperiment-Modified; see entry

@ PCS: Plasma Control System (Alcator C-Mod)

@ PCX: Neutral Particle Analyzer

@ PDX: Poloidal Divertor eXperiment; see entry

@ PEOS: Plasma Erosion Opening Switch; see entry for
Plasma Opening Switch (POS)

@ PEP: Pellet Enhanced Performance; see entry on pellet injection

@ PEST: Plasma Equilibrium and STability code; see entry

@ PF: Poloidal Field; Poloidal Field Magnet Coil

@ PLT: Princeton Large Torus; see entry

@ PNL: Pacific National (Northwest?) Laboratory; no entry yet.

@ POS: Plasma Opening Switch; see entry

@ PPPL: Princeton Plasma Physics Lab; see entry

@ PV: Photo-Voltaic; see entry

@ PWR: Pressurized Water Reactor (fission); see entry

* Parametric Instability: Instability which occurs in a
system whose equilibrium is weakly modulated in time or
space. The modulation produces a coupling of the linear
eigenmodes of the system and can lead to destabilization.

& Particle:

> Particle Beam Fusion Accelerator II: Light ion accelerator
inertial confinement fusion research system at Sandia National

& Particle Density: number of particles present per unit volume
(typically a cubic centimeter). See also density; typically
represented by the variable "n".

* Pellet Injection / Pellet Injector: This is a device
which accelerates (shoots) small (less than 4 mm diameter)
frozen pellets of hydrogen (or other) isotopes; these are then
launched at high speed (ca. 1000 m/sec) into the inner
regions of hot plasmas. Use of lithium and boron pellets
allows coating of the vacuum vessel walls, and is useful for
impurity control. Pellet injection can also be used to fuel
the plasma, and the light emitted by the pellet's ablation
cloud is useful for diagnostic purposes.

* Pfirsch-Schluter Regime, P-S Transport: One of the
neoclassical transport parameter regimes in a tokamak plasma;
characterized by the collisional mean free path being shorter
than the connection length. (This is the high-collisionality
end of the spectrum; plateau transport is in the middle, and
the banana regime is on the low-collisionality end.)
In this regime the diffusion coefficient is q^2 times greater
than the classical value (q being the safety factor, q > 1).
See also classical transport, neoclassical transport,
plateau transport, banana transport, safety factor.

& Phase Velocity: Defined as w/k, this describes the rate
of propagation of a wave through space.

& Photoionization: The ionization of an atom or molecule
by the collision of a high-energy photon (i.e., electromagnetic
radiation) with the particle.

& Photo-voltaic: Adjective used to describe devices which
convert light, particularly solar energy, into electricity.

$ pico-: Metric prefix indicating 10^-12 times the base unit.

* Pinch effect: General term for a class of phenomena
whereby the plasma is compressed or restricted ("pinched").
There are a variety of types of pinches. The Z-pinch
is a constriction of a plasma carrying a large current,
caused by the interaction of that current with its own
encircling magnetic field. The Theta pinch is a constriction
of a plasma by an increase in the axial magnetic field
generated by an external solenoidal current. The Ware pinch
arises in tokamaks due to neoclassical effects. And there
are others.

> Pinch Device or Pinch Machine: Device which confines
plasma using a pinch effect. (Typically the Z or Theta pinch.)

* Pinch Reflex Diode: A self-insulated ion diode in which
the magnetic field from the ion and electron flow alone
provide electron control, and the ion source is an anode
plasma formed by relexing the electrons through a thin
plastic foil.

* Pitch Angle: For a charged particle moving in a magnetic field,
this is the angle arctan (v-perp/v-parallel), where v-parallel
is the component of the particle's velocity parallel to the
magnetic field, and v-perp is the perpendicular component.
The pitch angle is zero when the particle moves purely parallel
to the field, and 90-degrees when the particle has no parallel
velocity at all.

* Pitch Angle Scattering: Scattering (collisional, or due
to wave-particle effects) of particles in velocity space,
in which the pitch angle (see entry above) is changed.

* Plant Factor: Another term for Capacity Factor; see entry.

* Plasma: A "Fourth State of Matter" in which many of the
atoms or molecules are ionized. Plasmas have unique physics
compared to solids, liquids, and gases. (Most plasmas can be
thought of at first as extremely hot gases, but their properties
are generally quite different.) Some (but not all!) Examples:
the sun, fluorescent light bulbs and other gas-discharge tubes,
very hot flames, much of interplanetary, interstellar, and
intergalactice space, the earth's ionosphere, parts of the
atmosphere around lightning discharges, and of course fusion plasmas.

* Plasma Beta: see Beta

* Plasma, Cold: See Cold Plasma Model

* Plasma Containment: (quoting from the PPPL Glossary of Fusion
Terms) "In plasma physics experiments or nuclear fusion experiments,
operation is intended to prevent, in an effective and sufficiently
prolonged manner, the particles of a plasma from striking the walls
of the container in which this plasma is produced. Plasma
confinement is a fundamental requirement for obtaining net energy
from a fusion plasma. The reason is that scattering (hence
diffusion) is at least an order of magnitude more probable than
fusion reactions. Hence, without confinement, the plasma fuel would
disperse before enough fusion reactions could take place."

* Plasma Equilibrium and STability Code: (PEST) This is a
widely-used, well-developed computer simulation ("code") used
to calculate MHD equilibrium and stability in various fusion

> Plasma Focus: The Plasma Focus is another device which depends
on the pinch effect. Possible applications include both fusion
and plasma propulsion, as well as other plasma research. In essence
the plasma focus is generated by discharge of a current across
the ends of two coaxial insulated conducting pipes.
The Plasma Focus caused a huge stir when they generated copious
neutrons, until it was discovered that the source of the neutrons
was knockoffs from deuterium due to pinch accelerated electrons or
ions. Plasma focus is sort of a point version of the "Z"pinch.
For more information on the plasma focus, see the entry in the
section on confinement approaches (4B).

* Plasma Frequency: The natural collective oscillation frequency
of a charge species (electrons, ions, etc.) in a plasma, in the
absence of (or at least parallel to) a magnetic field. Also
known as Langmuir or Langmuir-Tonks frequency; see also
electrostatic waves, plasma oscillations.

* Plasma Oscillations: Class of electrostatic oscillations
which occur at/near the plasma frequency (see entry) and involve
oscillations in the plasma charge density. Also known as
Langmuir Oscillations; In Stix's _Waves in Plasmas_ these
are called Langmuir-Tonks Plasma Oscillations.

* Plasma-Plasma Reaction: Fusion reaction which occurs from the
collision of two thermal plasma ions. (See also beam-wall,
beam-beam, and beam-plasma reaction entries.)

* Plasma Wave: A disturbance of a plasma away from equilibrium,
involving oscillations of the plasma's constituent particles
and of an electromagnetic field. Plasma waves can propagate
from one point in the plasma to another without net motion
of the plasma.

> Plasmak: Controversial advanced spheromak-type concept using
a fluid rather than solid conducting shell and a plasma with purely
internal magnetic fields, whose pressure is supported by a
surrounding gas; for more information see entry in section 4.

* Plasmoid: An isolated plasma which holds together for a
duration much longer than the collison times for the consituent

* Plateau Region, Plateau Transport: The collision frequency
(and transport) regime characterized by an effective coulomb
scattering rate equal to or greater than the poloidal transit
("bounce") frequency, but where collisional mean free path
is less than the connection length (2qR*PI). In this regime,
the transport coefficients are independent of the collision
frequency. (Thus a plot of transport coefficients vs.
frequency becomes horizontal line in this regime, forming
a "plateau" in the graph; hence the name.)

& Plutonium: Radioactive metallic element (Pu). The primary
isotope, plutonium-239, is a product of neutron absorption
by U-238, esp. in fission reactors. Pu is used in nuclear
weapons and as a fission reactor fuel.

* Poisoning: Buildup of ash and impurities in a fusion plasma
tends to reduce the quality of the plasma and reduce the fusion
output; this sort of process is sometimes called "poisioning"
the reactor or the plasma. See also ash, impurities.

& Polarization:

* Polarization of Reacting Particles: See Spin-Polarized Fusion.

* Poloidal: In toroidal geometries, the direction along the
circumference of a slice through one side of the torus.
"The short way around a torus".
- Albert Chou,

* Poloidal Divertor: A divertor (see entry) which takes a
bundle of poloidal field lines, forming a separatrix in the
poloidal magnetic field which creates separate plasma regions
(which can then have different physical parameters, since
transport is reduced across the separatrix where q => infinity).

> Poloidal Divertor Experiment: (PDX) A medium-size, high-current
divertor tokamak which was operated at Princeton, whose primary
research objective was to determine the effectiveness of
poloidal magnetic divertors in controlling impurities in reactorlike
fusion plasmas. PDX was modified and became PBX, which was
modified again and is now PBX-M (see entry for Princeton Beta

* Poloidal Field: In toroidal devices, the magnetic field that
encircles the plasma axis. (i.e., loops around the torus
"the short way".)

* Poloidal Field Coils: In toroidal devices (eg, tokamaks), the
sets of windings which are (typically) aligned along the plasma
axis and produce poloidal fields. These include ohmic heating,
shaping, vertical, equilibrium, and divertor windings.

* Poloidal Field Windings: See Poloidal Field Coils above.

* Positive Column: The luminous glow, often striated, which
occurs between the Faraday dark space and the anode in a
glow discharge plasma tube.

& Positron: Antiparticle to the electron; this particle has the
mass of the electron but the opposite charge.

* Positron Emission: Form of nuclear decay where a proton
disintegrates into a neutron, positron, and some sort of
neutrino. (?)

& Power: Defined as amount of work per unit time, or change in
energy per unit time.

* Power Density: In fusion, the rate at which energy is
generated per unit volume in the reactor core. (See also entries
for power, density.)

& Pressure: Defined as force per unit area.

* Pressure Tensor: A generalized pressure (can be anisotropic)
which plays a role in MHD (see entry) analogous to that of
pressure in ordinary fluid mechanics.

> Pressurized-Water Reactor (fission): Type of nuclear reactor
where the coolant is water kept under pressure to prevent it
from turning to steam inside the plant. (I think!)

* Price-Anderson Act: U.S. Federal law passed in the 1950s (?)
which limits utility liability for nuclear fission plant
accident damages. U.S. Government effectively insures the
utilities against external costs associated with nuclear

* Primary Energy: Energy before conversion. For instance,
the United States uses about 30,000 megajoules of electricity
per capita per year, but electricity is generally obtained
by converting other forms of energy (primarily chemical/heat)
at an efficiency of around 30%, so the U.S. consumes 90,000
megajoules of primary energy per capita for electrical use.
(Total U.S. primary energy consumption is 300,000 megajoules
per capita.)

% Princeton - See Princeton University and/or Princeton Plasma
Physics Lab

> Princeton Beta Experiment-Modified (PBX-M): mid-sized tokamak
research device at Princeton, which evolved from the Poloidal
Divertor Experiment (PDX) machine. Research on PBX is aimed
at investigating advanced tokamak regimes, such as indented
plasmas (kidney-bean cross sections) with high-beta, providing
access to the second-stability regirme.

> Princeton Large Torus (PLT): Large tokamak formerly operated
at the Princeton Plasma Physics Laboratory (PPPL). Was operated
in the 1970s and 80s and studied RF heating and current drive,
as well as neutral beam injection heating and other aspects of
tokamak physics. Roughly a predecessor to TFTR.

% Princeton Plasma Physics Lab (PPPL): Located in Princeton,
New Jersey. Single largest fusion research facility in the
United States; sole U.S. single-purpose plasma physics
laboratory; operated by Princeton University for the Department
of Energy. Site of PLT, PBX-M, TFTR, several other past and
present experiments, and future site of TPX.
(Refer to entries for relevant machines, both here and in FAQ.)

% Princeton University: Among other research activities, the
University operates the Princeton Plasma Physics Laboratory for the
Department of Energy (see above entry for PPPL).

* Process Heat: Heat produced by a powerplant (could be a
nuclear reactor, or a fusion reactor someday) and used directly
for industrial processes, such as metals manufacturing or
chemical production.

* Project Matterhorn: Code name of the United States' first
secret controlled fusion project, started by Lyman Spitzer
at Princeton University in 1951. Became a subprogram within
Project Sherwood (see entry below.)

* Project Sherwood: Name often used to describe the U.S. controlled
fusion program in the 1950s and '60s.

* Proliferation (nuclear): Proliferation generally describes
the way something spreads (rapidly) from one area to another;
in the case of nuclear weapons, nuclear proliferation refers
to the spread of nuclear bomb-building technology from one
state to another.

> Proto II: A high-power (10 TW) pulsed (24 ns) electron
accelerator which was (is?) used for inertial-confinement

& Proton: (from Herman) An elementary particle found in the
nucleus of all atoms. It carries a single positive electrical

& Pulse Height Analyzer: Instrument which records and stores
pulses and indicates ("Analyzes") the number of pulse occurrences
falling within each of a set of amplitude ("height") ranges.

* Pulsed Power: The technology of using electrical energy
stores for producing multi-terawatt (10^12 Watts or higher)
pulses of electrical power for inertial confinement fusion,
nuclear weapon effects simulation, and directed energy weapons.
High efficiency and cost effectiveness make it desirable
technology for large energy experiments.

* Pumpout: Name given to the anomalously high loss of particles
to the walls in (some) stellarator discharges; the loss rate
when pumpout occurs is substantially greater than that expected
from normal classical diffusion processes.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/q
Last-modified: 21-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 17: Terms beginning with "Q"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# q - Variable used to indicate electric charge; also used for
the "safety factor" (see charge, safety factor). Usually clear
from context which is meant.

# Q: See Q-factor

* Q-enhancement: Refers to methods for improving the power
balance in mirror-based magnetic confinement fusion reactors.

* Q-factor: Ratio of power produced by fusion to power
put into the reactor to heat the plasma and drive the
magnetic fields. Q = 1 is the definition of scientific
breakeven, where power out = power in. Economical fusion
will require Q significantly greater than 1. Fortunately
Q increases dramatically as the plasma parameters
approach the Lawson criterion for ignition. Power to drive
the magnetic fields is frequently ignored in discussions of
Q, with the justification that a steady-state, continuous-output
fusion reactor will have superconducting magnet coils.

* Q-machine: Plasma device studied in the 1960s; noted for
its natural quiescence, which made it attractive for plasma
wave phyics experimentation.

* Q-switch: Optical switch used to rapidly change the Q of
an optical resonator (see entry for oscillator); utilized
in the optical resonator of a laser to prevent lasing action
until a high level of gain and energy storage are achieved
in the laser medium. When the switch is triggered and
rapidly increases the Q of the cavity, a stronger laser
pulse is generated.

$ Quad: Unit of energy equal to a Quadrillion BTUs (10^15)
or roughly one exajoule (see entry for joule, exajoule, BTU).

* Quasi-linear Theory: A weakly nonlinear theory of plasma
oscillations which uses perturbation theory and the random
phase approximation to find the time-evolution of the
plasma state.

* Quasi-neutral plasma: an ionized gas in which positive
and negative charges are present in approximately
equal numbers.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/r
Last-modified: 25-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 18: Terms beginning with "R"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


@ Rad: Radiation Absorbed Dose; see entry "rad"

@ Rem: Raditation (or Roentgen) Equivalent for Man; see entry "rem"

@ R&D: Research and Development.

@ RD&D: Research, Development, and Demonstration.

@ RF: Radio Frequency; see entry

@ RF Current Drive: Radio Frequency Current Drive; see entry

@ RF Heating: Radio Frequency Heating; see entry

! R.F. Heeter: Plasma physics graduate student at PPPL; the editor
of the sci.physics.fusion FAQ, bibliography, and glossary. :)
(note similarity to RF Heating.)

@ RF Plugging: See entry for radiofrequency plugging

@ RF Trapping: See entry for radiofrequency trapping

@ RFC: Reversed-Field Configuration: see Field-Reversed Configuration.

@ RFP: Reversed-Field Pinch; see entry

@ RFX: Reversed-Field eXperiment; see entry

@ RGA: Residual Gas Analyzer

$ Rad: radiation absorbed dose. A unit used to measure the
amount of radiation energy absorbed per gram of a given
substance, that is the dose. One rad means absorption of
100 ergs of energy per gram. See also gray, rem, sievert.

* Radial Ponderomotive Force Stabilization: In magnetic
mirror devices, use of rf waves in the neighborhood of
the ion cyclotron frequency to stabilize interchange
modes. The radial ponderomotive force produced by
a radial gradient in the applied rf electric field
opposes the destabilizing centrifugal force resulting
from bad magnetic field curvature. The net particle
current is in the direction that would result from
field lines with good curvature, eliminating the drive
for the interchange instability.

& Radiation: (Sense 1) Process of emission of energy from a body
in the form of light or heat waves, or energetic particles
such as alpha particles, electrons, or neutrons. (Sense 2)
Radiation also refers to *what is emitted* when an object
radiates (but not *what does the emitting*). A nucleus
which does the emitting is said to be radioactive. Electrons
in atoms can also emit radiation in the form of ordinary
visible light; such atoms are not said to be radioactive.

* Radiation Damage, Bulk: General term describing
changes in chemical and/or metallurgical properties of
structure components of fusion reactor caused by atomic
displacement and nuclear transmutation events occuring
as a result of exposure to a radiation environment
(such as the neutrons emitted from a fission or D-T fusion

* Radiation Damage, Surface: General term describing
damage to the surface of the containment structure which
directly interfaces with the thermonuclear plasma;
includes such phenomena as radiation blistering,
charged-particle (or neutron) sputtering, and spallation
or exfoliation of layers of the surface.

& Radioactive Decay: Spontaneous transformation of one
nuclide into a different nuclide or into a different energy
state of the same nuclide. This process results in a decrease,
with time, in the number of originally radioactive atoms
in a sample. See Decay Modes for a listing of the different
mechanisms by which radioactive decay can occur.

& Radioactive waste: Equipment and materials from nuclear
operations which are radioactive and for which there is
no further anticipated use. Wastes are generally classified
as high-level (having radioactivity concentrations of
hundreds to thousands of curies per gallon or cubic foot),
low-level (in the range of 1 microcurie per gallon or
cubic foot), or intermediate (between high and low).
See also curie.

& Radioactivity: Characteristic property of unstable nuclei
which decay to other nuclei by emission of radiation. A list
of common decay / transmutation modes is given under "decay

* Radio Frequency or radiofrequency: Term used to
describe electromagnetic radiation with frequencies
less than infrared, but greater than "audio frequencies,"
i.e., greater than about 15,000 Hz. Wavelengths are
therefore less than about 20,000 km and greater
than about 0.01 mm. (These numbers are not precise.)

* Radio Frequency Current Drive: Plasma waves in the
radio-frequency range can be used to push plasma particles
in such a way that current forms in the plasma; this is a
method of non-inductive current drive (see entry) which
would allow for steady-state fusion reactors to operate.

* Radio Frequency Heating: Process for heating the plasma by
transferring energy to ions or electrons using waves generated
by an external oscillator at an appropriate frequency. (This is
similar to how a microwave oven heats food.) There are various
types: see also ECRH, ICRH, and Lower Hybrid...

* Radiofrequency Plugging: Use of axial ponderomotive force
to plug an open-ended device. First demonstrated on RFC-XX,
Institute of Plasma Physics, Nagoya University, Nagoya, Japan,
and later demonstrated in the Phaedrus device at the
University of Wisconsin.

* Radiofrequency Trapping: Use of RF waves to pitch angle
scatter particles flowing axially into a magnetic mirror cell.
The particles are scattered out of the loss cone and are
trapped. (See entries for pitch angle scattering, magnetic
mirror, loss cone.)

* Railgun Accelerator: Projectile accelerator which
accelerates the particle using electromagnetic forces which
arise when the particle completes an electrical circuit between
two conducting rails connected to a source of high current.

* Raman Effect: A phenomenon observed in the scattering of
light as it passes through a transparent medium; the light
undergoes a change in frequency and a random alteration
in phase due to a change in rotational or vibrational
energy of the scattering molecules.

* Ramsauer Effect: Term for a quantum-mechanical effect
allowing free electrons within a narrow range of energies
to pass through a noble gas with very little elastic scattering.

* Rational Surface: (related to q-factor, see entry)
Magnetic flux surface (see entry for this too) where the ratio
of toroidal to poloidal field strengths is a rational number;
this means that a particle travelling along this surface makes
an integer number of turns in each direction and then its orbit
closes in on itself. The result is that the particle doesn't
sample the entire flux surface in its motion, which is important
for various technical reasons (which mostly result in reduced
confinement); see also magnetic island.

* Reactor: See fission reactor, fusion reactor.

& Recombination Coefficient: The rate of recombination of
positive ions with electrons (or negative ions) in a gas,
per unit volume, divided by the product of the particle
densities of the two species (positive ions and
electrons/negative ions) involved.

* Recombination Radiation: radiation produced when a
free electron in a plasma is captured by an ion.

& Reflectivity: Fraction of incident radiant energy which
is reflected by a given surface. (The power which is not
reflected is either absorbed or transmitted.)

& Refraction: Bending of waves as they pass from a medium
having one refractive index to a medium (or region within
a medium) having a different refractive index.

$ Rem: Radiation (or Roentgen) Equivalent for Man. Unit of
absorbed radiation dose based on the definition rem = rad * quality.
The quality factor depends on the type of radiation involved and
is used to scale the radiation dose based on the relative
harmfulness of different sorts of radiation, compared to
ordinary X-rays. Annual US average dose is about 300 millirem
(0.3 rem), of which more than 2/3 is natural (primarily radon
and cosmic rays), and the majority of the human-generated dose
is due to medical uses (primarily X-rays). See also radiation
dose, roentgen, sievert, rad, gray.

* Reserves: Amount of a substance which can be extracted from
the earth with current technology at current prices. Typically
much smaller than resources (see entry for resources).

& Resistance (electrical): Ability of a given object to
resist the flow of electrical current. To drive a given
current a voltage must be applied to overcome the resistance
according to V = I * R (V = voltage, I = current, R = resistance).
Resistance is determined by resistivity and geometrical factors.

* Resistive Instability: Instability resulting from macroscopic
equations used to model a plasma of finite conductivity / nonzero

& Resistivity: Tendency for a material/substance
to resist the flow of electrical current and to dissipate its
energy. Resistivity, when combined with certain geometry
factors (generally length and cross-sectional area for wires)
determines resistance.

* Resource: Total amount of a substance which exists in the
earth and could conceivably be extracted someday at some price
with some technology. Typically much larger than reserves.
(See also reserve.)

> Reversed-Field Pinch (RFP): A toroidal magnetic confinement scheme
which could constitute an alternative to the Tokamak for building a
fusion reactor. It is characterized by a magnetic field mostly
generated by the plasma itself, with toroidal and poloidal components
of comparable intensities, in contrast with the Tokamak where most of
the field is toroidal and externally applied. The name of the
configuration is given by the fact that the toroidal component of the
magnetic field changes sign in the outer region of the plasma. The
main attractivness of the Reversed Field Pinch is that, according to
presently established scalings, it could reach ignition without the
need of auxiliary heating.
(Emilio Martines,

> Reversed-Field eXperiment (RFX): It is the largest Reversed Field
Pinch device presently in operation. Located in Padova (Italy) it
is planned to reach a plasma current of 2 MA.
(Emilio Martines,

* Roentgen: Unit of exposure to ionizing radiation. The Roentgen
is that amount of gamma or X-rays (electromagnetic radiation)
required to produce ions carrying one electrostatic unit of
electrical charge (either positive or negative) in 1 cubic
centimeter of dry air under standard conditions. Named after
Wilhelm Roentgen. (Compare with curie, rad, gray, sievert.)

! Roentgen, Wilhelm: German scientist who discovered X rays in 1895.

* Rogowski Loop or Coil: A coiled wire loop which encircles a
current-carrying plasma. Changes in total plasma current induce a
voltage in the loop; integrating (adding up) the voltage over time
gives the plasma current.

* Rotational Transform: (labels: \iota = 2*PI/q)
Due to the combination of applied toroidal field and induced
poloidal field, the magnetic field lines wind helically around
the torus (and on most flux surfaces they fill the surface
ergodically). The rotational transform is a measure of this
helicity, and is defined as the average angle the field line
shifts in the poloidal direction per complete circuit in the
toroidal direction. The quantity q = 2*\pi / \iota is known
as the ``safety factor'' because of its role in stability theory.
(Contributed by James Crotinger)

Entry from 1985 OSTI Glossary: A magnetic field configuration
is said to posses rotational transform if the lines of force,
after one complete circuit around the configuration (e.g., a torus)
do not simply close exactly on themselves, but are instead
rotated through some angle about the magnetic axies.
(See entries for flux surface, magnetic axis, toroidal and poloidal
field, helicity, safety factor.)

* Runaway Electrons: Those electrons in a plasma that gain energy
from an applied electrical field at a faster rate than they lose
it through collisions with other particles. These electrons tend
to "run away" in *energy* (not position) from the cooler remainder
of the background plasma, because the collision cross-section
decreases as the particle's velocity increases, so that the faster
the particle goes, the less likely it is to be stopped.
See also: collision cross-section.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/s
Last-modified: 25-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 19: Terms beginning with "S"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


@ (?) SHIVA: see entry under Shiva, below.

@ SI: Systeme Internationale; see SI Units

@ SM: Symmetric Mirror

@ SN: Single Null; see entry for Divertor

@ SNL: Sandia National Laboratories; see entry

@ SOL: Scrape-Off Layer; see entry

@ STM: Symmetric Tandem Mirror experiment.

$ Sv: Sievert; see entry

* Safety Factor: (q) The number of times a field line goes around a
torus "the long way" for each time around "the short way". In a
tokamak, this number is typically near unity in the center of the
plasma and between two and 6 or 8 at the edge. So-called because it
helps to determine the degree of stability the plasma has against
certain instabilities. The safety factor is the inverse of the
rotational transform, and can be expressed mathematically
as q = (r * Bt )/(R * Bp), where r and R are the minor and major
radii of the torus, and Bt and Bp are the toroidal and poloidal
magnetic fields.

! Sakharov, Andrei: Russian physicist; among other achievements, he
is credited with the initial design of the tokamak.

% Sandia National Laboratories: Located in Albuquerque, New Mexico.
Another large DOE laboratory; has PBFA-II (Particle Beam Fusion
Accelerator, an ICF device) and some pinch devices. Some divisions
located in Livermore (Sandia-Livermore).

* Sawtooth: When a tokamak runs with enough current to achieve
q < 1 on the magnetic axis, the plasma parameters (n, T, B)
oscillate with a "sawtooth" waveform. The oscillation is
localized to a region roughly within the q=1 surface, and
arises from internal MHD effects. Confinement is degraded
within the sawtooth region.

* Scaling Laws: These are mathematical rules explaining how
variation in one quantity affects variations in other quantities.
For instance, in a tokamak reactor it's generally believed that
energy confinement depends on the size of the device and the strength
of the magnetic field, but the precise nature of the dependence is
not fully understood, so empirical "scaling laws" are tested to
see what the dependence is. Scaling laws are useful for extrapolating
from parameter regimes where the mathematical relationships
between the various quantities are known, into unexplored regimes.

& Scattering: The deflection of one particle as a result of
collisions with other particles or with waves. See also Elastic.

* Schlieren Method: An optical technique that detects density
gradients occuring in a fluid flow. In its simplest form, light
from a slit is collimated by a lens and focused onto a knife
edge by a second lens; the flow pattern is placed between the
two lenses, and the resulting diffraction pattern is observed on
a screen or photographic film placed behind the knife edge.

* Scientific Feasibility: Fusion will be considered scientifically
feasible when (a) experiments are done which reach scientific
breakeven-type plasma conditions (see entry on breakeven), and
(b) the experimental results suggest that the approach can be
"scaled up" into a power-producing system. Tokamak fusion
reactors are closing in on (a), and tokamak researchers think
(b) holds as well, so they are designing a power-producing
machine (ITER) to demonstrate net energy production from tokamak
fusion. Inertial confinement is also approaching this point.

* Scrape-Off Layer (SOL): [from Art Carlson] Outer layer of a
plasma which is affected ("scraped off") by a divertor or limiter.
That is, the outer layer of a magnetically confined plasma (ca. 2 cm
thick) where the field lines penetrate a material surface (limiter or
divertor plate) rather than close upon themselves. This region
defines the outer limit of the plasma because any plasma crossing
into the SOL is rapidly lost since transport along the field is much
faster than that across the field. That is, particles follow these
field lines into the material surface and are lost from the plasma.

* Screw Pinch: A variant on the theta pinch, in which axial
currents (as in a z pinch, but less intense) produce a poloidal
magnetic field (in addition to the usual longitudinal field),
thus making a corkscrew field configuration. See also theta pinch,
z pinch, pinch device.

* Second-stability Region: A high pressure region where the plasma
becomes stable to the pressure-gradient-driven ballooning
ballooning instability. The plasma is stable in the limit of
small pressure gradients, becomes unstable at some intermediate
pressure, and then becomes stable again at still higher pressures.
Tokamaks operating in the second-stability region would be more
attractive because the higher pressures (beta) would provide more
fusion reactivity per unit volume of plasma, allowing smaller
reactors to be built.

* Separatrix: [from Art Carlson] In a divertor tokamak (and some
other configurations), the last closed flux surface (see entry) is
formed not by inserting an object (limiter) but by manipulating the
magnetic field, so that some field lines take a topologically
different route (through the divertor, rather than simply around the
central plasma). The boundary between the two types of field lines is
called the separatrix.

* Sheared Flow: Fluid flow where the magnitude of the fluid velocity
changes along a direction perpedicular to the direction of the fluid
flow. (Freeway traffic often exhibits sheared flow in that traffic
in the "fast lane" moves more rapidly than traffic in the slow lane
with the exits...) Sheared flow typically correlates with reduced
transport and enhanced confinement. (This definition is rather
informal and may not be fully technically correct - R.F. Heeter)

* Shear Fields: As used in plasma physics, this refers to magnetic
fields having a rotational transform (or, alternatively, safety
factor) that changes with radius (e.g., in the stellarator concept,
magnetic fields that increase in pitch with distance from the
magnetic axis.)

* Sheath: See Debye Sheath

> Shiva: 20-beam Nd-glass fusion laser facility at LLNL. Was
completed in 1977 and used for target irradiation experiments
until mid-1981. Succeeded by Nova.

* Shock Heating: Heating produced by the impact of a shock wave.

* Shock Tube: A gas-filled tube used in plasma physics to
quickly ionize a gas. A capacitor bank charged to a high voltage
is discharged into the gas at one tube end to ionize and heat
the gas, producing a shock wave that may be studied as it
travels down the tube.

* Shock Wave: Wave produced (e.g., in a gas or plasma) as a
result of a sudden violent disturbance. To produce a shock
wave in a given region, the disturbance must take place
in a shorter time than the time required for sound waves to
traverse the region.

$ Sievert: International unit for radiation dose. One Sievert
equals 100 rem (see entry for rem); average per-capita exposure
is about 0.3 Sv, primarily from natural background (see entry)
and medical x-rays.

* Shock Heating: The heating produced by the impact of a shock wave.

* Shock Wave: Wave produced as a result of a sudden, violent
disturbance which occurs in a particular region faster than sound
waves can traverse the region.

* Shot: Fusion jargon for the production of a (short-lived) plasma.
In the early days, plasmas were produced by the "discharge" of
capacitor banks, which (frequently) made a BANG. A modern tokamak
produces a few dozen "shots" per day, each lasting a few seconds and,
if nothing goes wrong, inaudible. See also: capacitor, tokamak
(Arthur Carlson,

$ SI Units: (also known as MKS, MKSA Units) System of measurement
in which the fundamental units are meters, kilometers, seconds, and
the ampere.

$ Sievert: Unit of absorbed radiation dose equivalent to 100 rem.
(see also rem, rad, Gray) The sievert is based on the Gray in the
same way that the rem is based on the rad, I believe.

& Solenoid: Cylindrical coil of wire which, when current
flows through it, acts as an electromagnet. For long solenoids
with many turns, the magnetic field inside the center is
nearly uniform.

* Solid Breeder: Solid lithium-bearing compounds, usually
ceramics such as Li2O and LiAlO2, which might be used in the
blanket of a D-T fusion reactor to produce ("breed") additional
tritium fuel from the n + Li => He + T (+n) reactions.

* Solid State Laser: A laser using a transparent substance
(crystalline or glass) as the active medium, doped to provide
the energy states necessary for lasing. The pumping mechanism
is the radiation from a powerful light source, such as a
flashlamp. The ruby, Nd-YAG, and Nd:glass lasers are
solid-state lasers.

* Solitons: Stable, shape-preserving and localized solutions
of nonlinear classical field equations. Of recent interest
as possible models of extended elementary particles.

* Sound Waves: See entries on compression waves, waves.

* Space Frame or Spaceframe: Three-dimensional "optical bench"
that holds laser components stable from vibrational and
thermal excursions.

* Spallation: See radiation damage, surface.

* Spatial Filter: Device consisting of a lens pair and a pinhole
aperture stop. Intensity fluctuations over the spatial extent
of a laser beam are removed by passing the focused beam through
the aperture stop. The pinhole must be placed in a vacuum to
prevent air breakdown by the focused beam. These filters are
used to counter the effects caused by self-focusing.

> Spherator: Single-ring multipole device with an additional

current-carrying rod perpendicular to the ring axis.

> Spheromak: [from Art Carlson] A compact torus with comparable
toroidal and poloidal magnetic fields. The plasma is roughly
spherical and is usually surrounded by a close-fitting conducting
shell or cage. Both the poloidal and toroidal magnetic fields
are generated by plasma currents. There are no toroidal field
coils "linking" the plasma through the central plasma axis.
External force is supplied by poloidal field coils outside
the plasma separatrix. The resulting configuration is approximately
a force-free magnetic field. The spheromak machine geometry can
be simpler than a tokamak, but the close-fitting wall is a source
of impurities and the current cannot be inductively driven. After
early experiments failed to achieve a reasonable beta, interest
has ebbed. The spheromak can also be considered as the
low-aspect-ratio limit of the tokamak. See also: compact torus.

* Spin-Polarized Fusion: A method to enhance nuclear fusion
reaction rates in some fusion fuels by polarizing the nuclear

! Spitzer, Lyman: Early Princeton Fusion Scientist;
astrophysicist who first proposed orbiting space telescope;
inventor of the stellarator.

& Spontaneous Emission: Radiation randomly emitted by excited
atoms or ions. Contrast with stimulated emission.

* Sputtering: Process by which atoms are ejected from a solid
surface by bombardment with plasma particles. See entry
for "Radiation Damage, Surface."

* Stability: characteristic of some types of equilibrium states;
see equilibrium.

> Starfire Tokamak: A conceptual design study of a modular
tokamak reactor that operates in a steady-state condition
while using conventional power-generating systems.

& Stark Effect: The effect an electric field has on the
spectral lines emitted from excited atoms. The effect may
arise from externally-applied electric fields, from internal
fields due to the presence of neighboring ions or atoms (pressure),
or from the electric field associated with the Lorentz
(v cross B) force (motional stark effect). Spectroscopic
measurements of plasmas using the pressure-based and motional
Stark effects are useful for diagnostic purposes.

> Stellarator: (adapted from Herman) Device invented by Lyman Spitzer
for the containment of a plasma inside a racetrack-shaped
(sometimes a figure-8) tube. The plasma is contained by a magnetic
field created by helical windings around the tube. More generally,
a toroidal sort of device that attempts to average out particle
drifts that would otherwise take plasma to the walls of the vacuum
vessel by imposing a given amount of helicity to the toroidal field
lines. "A toroidal plasma configuration, which, unlike a tokamak,
is not axially symmetric. The poloidal fields necessary for
confinement are produced by external coils (rather than a current
in the plasma), either helical coils in addition to plane toroidal
field coils, or out-of-plane toroidal field coils (pioneered in
Germany on Wendelstein 7-AS). The stellarator is generally
considered to be the most serious alternative to the tokamak. Since
the concept is inherently steady state, it would not have the
tokamak's problems with thermal and mechanical cycling, current
drive, and disruptions."
-- Arthur Carlson,

& Stimulated Emission: Radiation coherently emitted by excited
ions when driven by a passing light wave and the appropriate
transition wavelength. "Laser" means Light Amplification by
Stimulated Emission of Radiation; it occurs when there is a
population inversion between the upper and lower energy states
of the transition, such that stimulated emission can dominate
excitation. Stimulated emission is coherent and codirectional
with the stimulating wave, and the rate of stimulated emission
is proportional to the intensity of the stimulating wave.

* Strong (Nuclear) Force:

* Sturm-Liouville Problem: The general problem of solving a
linear differential equation of order 2n, together with
2n boundary conditions; also known as the eigenvalue problem.

* Superconductor: A type of electrical conductor that permits
a current to flow with zero resistance. Without superconducting
coils, a toroidal magnetic-confinement fusion reactor would not
be possible, because too much energy would be required to
maintain the magnetic fields against resistive energy losses
in the coil conductors.

* Suydam Stability Criterion: A criterion for the stability
of modes localized arbitrarily close to a mode-rational surface
(see rational surface) in a circular cylindrical geometry.

& Synchrotron Radiation: (Also known as cyclotron radiation.)
Electromagnetic energy radiated from a charged particle moving
in a curved orbit (typically in a magnetic field), due to the
acceleration required to change the direction of the particle's
velocity. See also bremsstrahlung.

* Symmetry axis: [from Art Carlson] The straight line (usually
vertical) through the center of a configuration, when the
configuration is symmetric to all (axisymmetric, like the tokamak)
or some (periodic, like the stellarator) rotations about this
line. Usually the z-axis.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/t
Last-modified: 25-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 20: Terms beginning with "T"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# t: variable generally used to represent time

# tau: label generally used to represent confinement time

# T: variable generally used to represent temperature

# T: nuclear/chemical symbol for tritium/triton; see entry

$ T: abbreviation for Tesla, SI unit of magnetic field; see entry

> TARA: See entry under TARA below.

@ TCI: Two-Color Interferometry

@ TCV: Variable Configuration Tokamak - from French; see Section 5.

@ TCX: Tangential Charge Exchange

# Te: (subscript e) Electron Temperature

$ Tera: Metric prefix indicating one trillion (10^12) times base unit.

$ Terawatt: One trillion (10^12) watts.

@ TEXT-U: TEXas Tokamak-Upgrade; see entry under TEXT below.

@ TEXTOR: Tokamak EXperiment for Technology Oriented Research; see
entry for TEXTOR below.

@ TF: Toroidal Field (or Toroidal Field Coil)

@ TFR: FRench Tokamak, see entry under TFR below

@ TFTR: Tokamak Fusion Test Reactor; see entry

# Ti: Chemical Symbol for Titanium; if subscript i, Ion Temperature

@ TMX: Tandem Mirror eXperiment; see entry.

@ TMX-U: Tandem Mirror eXperiment-Upgrade; see entry.

@ TORMAC: TORoidal MAgnetic Cusps; see entry

@ TPX: Tokamak Physics Experiment; see entry

@ TRANSP: Princeton's TRANSPort Simulation Code (Tokamak)

@ TW: terawatt; 10^12 watts; see watt.

@ TWyr: terawatt-year; Unit of energy equal to
3.15 x10^19 joules or 30 Quads (see entries)

> T-3: A Soviet tokamak located at the Kurchatov Institute
in Moscow which first proved concept viability, by producing
a plasma temperature of 10 million degrees centigrage/Kelvin.
(Result was disbelieved in the West until a British team
confirmed the results using Thomson scattering.)

> T-10: A later, larger Soviet tokamak, located at the
Kurchatov Institute (Moscow). (PLT was largely a copy of
T-10, only PLT had neutral beams, whereas T-10 was (I believe)
purely ohmic-heated.

> T-11: Another Soviet tokamak (rather small) located at
the Kurchatov Institute (Moscow); studied neutral-beam heating.

> T-15: (formerly T-10M) Another, much larger Soviet tokamak
(somewhat smaller than TFTR, but similar size) with superconducting
magnets, currently (?) under construction. (Was it completed?
Is it operational?)

> T-20: A huge Soviet tokamak that was designed to operate under
reactor conditions (net energy production) but which was abandoned
for budgetary reasons.

> Tandem Mirror Experiment: (TMX) Located at LLNL, this was one of
the first devices to experiment with placing magnetic mirror
devices at either end of a (relatively) long cylindrical
central region. In TMX the plasma was supplied by neutral beams.

> Tandem Mirror Experiment-Upgrade: (TMX-U) Upgrade of TMX
which was brought on line in 1983. Incorporated rf heating
systems and improved neutral beam systems. Predecessor to
MFTF-B (see entry) as a flagship magnetic mirror in the U.S.

> TARA: Medium scale tandem mirror device commissioned at MIT
in 1984 to develop greater understanding of basic tandem mirror
physics, with emphasis on microstability properties, thermal
barrier formation, and RF heating.

* Target Plasma: Plasma used to trap a neutral atom beam. A
background plasma of sufficiently high density and temperature
can ionize neutral atoms more effectively than the Lorentz
process (where v cross B creates effective electric field?).

* Tau: See # tau above.

! Taylor, J.B.: Renowned plasma physicist; noted for helicity work??

* Taylor State: (John Cobb?)

* Tearing Mode, Tearing Instability: A resistive MHD instability
which is spatially localized near a rational surface and which
grows at a rate slower than the MHD Alfven rate, but faster than
the resistive skin diffusion rate. The instability "tears"
magnetic field lines and reconnects them into a new state of
lower magnetic energy. (see other entries for more information
about the terms used above.)

& Temperature, Kinetic: See Temperature, Plasma, and Kinetic

* Temperature, Plasma: A measure of the random (thermal) kinetic
energy of the ions or electrons in the plasma. The temperature
of each component of a plasma depends on the mean kinetic energy
of that component. An example of this is the fluorescent light bulb,
which is an example of a weakly-ionized plasma where the electrons
are at temperatures of tens of thousands of degrees, whereas the
ions and neutrals are much cooler (so that you can touch the bulb
without being burned). See atomic temperature, electron
temperature, and ion temperature.

$ Tesla - SI unit of magnetic field strength; 1 tesla = 10,000 gauss.

> TEXT-U Device: A medium-size research tokamak at the University
of Texas, Austin; upgraded version of the TEXT device, with divertor.

> TEXTOR: (Tokamak EXperiment for Technology Oriented Research.
Medium-sized European tokamak located in Julich, Germany. Research
objectives involve things like developing plasma-facing components
and studying effects of plasma-wall interactions.

> TFR: An iron-cored French Tokamak, now retired (I believe).
Pioneered a number of important tokamak ideas and innovations.

* Thermal Barrier: In magnetic mirror devices, this is a
depression of electrostatic potential formed by enhancing ion
loss in the region between the central cell and the positive
potential plug. The thermal barrier significantly reduces the
density requirements in the plug and lowers the overall power
required to sustain the solenoidal plugging by thermally decoupling
central cell electrons from the end plugs.

& Thermal Conductivity: degree to which a substance transmits heat.
(basic definition, I believe, is:
(heat flow) = (thermal conductivity) * (temperature gradient) )

& Thermal Conversion Cycle: Process of generating electrical power
with a fusion reactor by means of a steam / other gas turbine. This
is distinct from "direct conversion" cycles.

& Thermal Efficiency: Ratio of the electric power produced by
a power plant to the original amount of heat produced. This measures
the efficiency with which the thermal energy is converted to

* Thermal (Slow) Neutron: A neutron in thermal equilibrium with
its surrounding environment. Thermal neutrons are those that
have been slowed down by a moderator to speeds characteristic
of the local temperature. (Compare with fast neutron.)

& Thermodynamic Equilibrium: There is a very general result from
statistical mechanics which states that, if a system is in
thermodynamic equilibrium with another (or several other) system(s),
all processes by which the systems can exchange energy must be
exactly balanced by their reverse processes, so that there is no
net exchange of energy. For plasma systems in thermodynamic
equilibrium, ionization must be balanced by recombination,
Bremsstrahlung by absorption, and so on. When thermodynamic
equilibrium exists, the distribution function of particle energies
and excited energy levels of the atoms can be obtained from the
Maxwell-Boltzmann distribution (which is a function only of
the temperature). The Saha equation is a special application of this.

* Thermonuclear Conditions: Achievement of an adequately confined
plasma, having temperature and density sufficiently high to
yield significant release of energy from fusion reactions.

* Thermonuclear Fusion: fusion achieved by heating
up the fuel into the plasma state to the point where
ions have sufficient energy to fuse.

> Theta Pinch: A fast-pulsed pinch device in which the external
current imposed goes in the azimuthal/circumferential direction
(generally in a solenoid) around a cylindrical plasma. Use
of a fast-rising solenoidal current causes a rapidly increasing
axial magnetic field, which compresses and heats the plasma.

* Thomson Scattering: Scattering of photons by electrons, in
the classical (low photon energy) limit. Laser light passed
through a plasma will experience Thomson scattering; the
spread of the scattered light in energy provides a very good
measurement of the electron temperature of the plasma.

> Tokamak: (Acronym created from the Russian words,
"TOroidalnaya KAmera MAgnitnaya," or "Toroidal Chamber-Magnetic".)

Because the tokamak is the primary research machine for
magnetic confinement fusion today, we provide several
descriptions from various sources:

-> One of several types of toroidal discharge chamber
in which a longitudinal magnetic field is used to confine a
plasma. The tokamak is distinguished by a plasma current
running around the torus, which generates a stabilizing
poloidal magnetic field. An externally-applied vertical
magnetic field is also used to achieve plasma equilibrium.

-> (Contributed by James Crotinger,
An axisymmetric toroidal confinement device characterized by a
strong toroidal magnetic field (1-10 Tesla) and a toroidal
plasma current (several mega-Amps) that leads to a modest
poloidal magnetic field. The plasma current is usually induced
by ramping a current in a large solonoid along the symmetry axis
of the tokamak. This is an inherently pulsed mode of operation,
and other mechanisms of current drive are under investigation.

-> TOKAMAK (tokomak) (contributed by Paul M. Koloc)
"A three component magnetoplasma toroidal construct in which
the poloidal magnetic component is provided by a toroidal plasma
current. The other two components are coil driven, namely, the
vertical field (which opposes the major radial expansion) and
the toroidal field (which acts to provide a "stiff guide" field
for the plasma to gain more MHD stability.
It is better to think that the toroidal or longitudinal field
"stiffens" the plasma as against flopping or kinking, while the
plasma current driven poloidal (locally azimuthal) field provides
"confinement" pressure. Actually, the toroidal field interacting
with plasma diamagnetism may also contribute to a "magnetic
bouyancy", which is a sort of UN-confinement -- (it actually gives
the plasma a tendency to expand radially outward in the equatorial

-> (from Herman:) "Based on an original Soviet design, a device
for containing plasma inside a torus chamber by using the
combination of two magnetic fields - one created by electric
coils around the torus, the other created by intense electric
current in the plasma itself, which also servers to
heat the plasma [partially]. TFTR and JET are tokamaks."

> Tokamak Fusion Test Reactor: Large tokamak at Princeton,
first machine to use 50-50 mix of D-T fuel, current world's
record holder in fusion energy production. Largest tokamak
in the United States.

> Tokamak Physics Experiment: Smaller successor to TFTR at
Princeton. Engineering design underway; construction
scheduled to begin in FY 1995.

> Tore Supra: Large tokamak in Cadarache (southern France).
The second largest tokamak in Europe; largest tokamak using
superconducting toroidal field magnets. Tore Supra has a
circular cross-section (like TFTR), which limits the achievable
confinement time and experimental flexibility. In addition to
developing superconducting technology, it concentrates on the
physics of long pulses and ergodic magnetic limiters.
See also: ergodic; magnetic limiter; superconductor; tokamak.

* Toroidal: in the shape of a torus, or doughnut.
Or: Coordinate indicating which part of the torus a particle is in.
(Azimuthal coordinate)
Or: General term referring to toruses as opposed to other geometries.
(e.g., tokamaks and stellarators are examples of toroidal devices.)

* Toroidal Field Coils: Coils in a toroidal system, typically
wound around the torus in a solenoid-like arrangement, used to
generate the toroidal magnetic field. Each turn completely
surrounds the plasma.

> TORMAC: (TORoidal MAgnetic Cusps) Hybrid confinement scheme
operating at high beta. A region of closed toroidal magnetic
flux with high-beta plasma is separated by a narrow sheath from
the surrounding field, which contains externally produced
poloidal components arranged in a toroidal line-cusp configuration.
Plasma migrating to the outer sheath is temporarily
mirror-confined before being removed in a divertor system.

> Toroidal Pinch:

& Torque:

> Torsatron: A modification of the stellarator concept, the
torsatron has a toroidal non-axisymmetric configuration, and
rotational transform is provided by external coils. Unlike
a stellarator, however, both toroidal and poloidal fields are
generated by helical fields alone, with half the number of
helical conductors required for a stellarator.

& Transformer, Transformer Effect: See entry for Induction.

& Transmittance: Ratio of the radiant power transmitted
by an object to the incident radiant power. See also reflectivity.

& Transmutation: Transformation of atoms of one element into
atoms of another element via nuclear reactions. (e.g., the
transmutation of uranium-238 into plutonium-239 via the absorption
of a neutron and subsequent beta emission.)

* Transport: Refers to processes which cause heat energy, or
particles, or something else, to flow out of the plasma and cease
being confined. Diffusion partly determines the rate of transport.
See also: diffusion, classical diffusion, neoclassical diffusion,
anomalous diffusion.

* Transverse Waves: Waves in which the direction of the
oscillation is perpendicular ("transverse") to the direction
of the wave propagation. Examples include plucked strings and
electromagnetic waves in free space/air.

* Trapped-Particle Instability: Slowly-growing class of
instabilities driven by particles which cannot circulate
freely in a toroidal system. See also banana orbit.

* Trapped-Particle Modes: See trapped-particle instability

* Triangularity: Geometric factor measuring an aspect of
the shape (how "triangular" it is) of the cross-section of
a non-circular plasma in a toroidal device. See also elongation.

& Tritium: A radioactive isotope of hydrogen with one proton and
two neutrons in its nucleus and one orbiting electron. A more
efficient fuel than ordinary hydrogen (protium) because of the
extra neutrons. Tritium decays to helium-3 by emission of an
electron ("beta emission") with a half-life of 12.3
years. Tritium can be synthesized from deuterium via neutron
bombardment, or by fissioning lithium (see lithium).

* Tritium-Breeding Ratio: The amount of tritium generated by
the breeding blanket of a D-T fusion reactor, divided by the
amount of tritium burned in the reactor. A tritium breeding
ration greater than unity is necessary for self-sufficient fueling.

* Triton: nucleus of a tritium atom; tritium ion.

* Troyon Limit: see beta limit

* Turbulence: "Violent macroscopic fluctuations which can develop
under certain conditions in fluids and plasmas and which usually
result in the rapid transfer of energy through the medium."
(PPPL & OSTI Glossaries have same entry)

* Turbulent Heating: Technique of using turbulence induced by
large electric fields to rapidly heat a plasma.

* Two-Stream Instability: Instability which can develop when a
stream of particles of one type has a velocity distribution with
its peak well separated from that of another type of particle
through which it is flowing. A stream of energetic electrons
passing through a cold plasma can, for example, excite ion waves
which will grow rapidly in magnitude at the expense of the kinetic
energy of the electrons.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/u
Last-modified: 25-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 21: Terms beginning with "U"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# u: variable commonly used for energy density of electric or
magnetic fields; also sometimes used for velocity.

@ UT, UTA: University of Texas at Austin; see entry

@ UV: Ultraviolet (range of the electromagnetic spectrum)

@ UW, UWM: University of Wisconsin at Madsion; see entry

& Ultraviolet: Region of the electromagnetic spectrum
intermediate between the visible and the x-ray portions.
UV photons have energies greater than a few eV, but less
than (roughly) 100 ev to 1 keV.

* Unipolar Arc: Arc between a metal surface and a plasma in
contact with it. Such an arc requires only one electrode
and is maintained by the thermal energy of the electrons.

& Universal gas constant: R = 8.314 x 10^7 ergs per
degree C per mole.

* Universal Instability: Low-frequency instability resulting
from the presence of density gradients perpendicular to the
magnetic field lines. An instability of this type is generally
localized and usually has a small rate of growth.

% University of Texas at Austin (UT): Among other things, UT has
a large theoretical plasma physcs research center. (info, anyone?)
The TEXT experimental tokamak is also located here.

% University of Wisconsin at Madison: Among other facilities,
"Wisconsin" has a large research program in both plasma physics
and fusion engineering.

* Upper Hybrid Waves: Similar to lower hybrid waves, but at a
higher frequency. (more description?) Not truly propagating
waves, but plasma oscillations. (?)

& Uranium: (from Herman) A radioactive metallic element whose
isotope, uranium-235, is a nuclear fission fuel. Plutonium,
another fission fuel, can be produced from the more
plentiful isotope uranium-238.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/v
Last-modified: 25-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 22: Terms beginning with "V"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# v: variable typically used for velocity

# V: variable typically used for electrical potential (Voltage)

$ V: abbreviation for Volts; see entry

@ VDE: Vertical Displacement Event

& Vector:

& Vector Notation:

& Velocity: The rate of change of position with time for a given

& Velocity Space: Mathematical space where each point corresponds
not to a certain location in reality, but to a certain velocity.
Distribution functions typically involve mixes of both position and
velocity spaces. (See distribution function.) Contrast with
"position space" where each point corresponds to a given location.

& Velocity Space Instability: A class of instabilities driven
by particle distributions (in velocity space) which are not
in thermal equilibrium.

* Vertical Field, Vertical Field Coils: See Poloidal Field / Coils.

* Vertical Instability: [mostly by James Crotinger] A type of
MHD (n=0) instability where the plasma drifts vertically upward.
Nearly all tokamaks are vertically unstable (all highly shaped
ones are). Controlling this instability is possible in many
cases, and is an important facet of machine design. Vertical
instabilities give rise to halo effects (see entry for halo).

& Viscosity:

* Vlasov Equation:

* Voltage Loop: A wire which encircles the main axis of a tokamak
in the vicinity of the vacuum vessel. The voltage induced in this
loop during the shot is a measure of the ohmic heating voltage
induced by transformer action and applied to the plasma.

$ Volt: Unit of electrical potential.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/w
Last-modified: 25-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 23: Terms beginning with "W"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# W: Chemical symbol for Tungsten

@ W-7AS, W-7X: See Wendelstein entry

* Wall Conditioning: Describes a class of procedures used to
control the composition of materials adsorbed onto the walls of
a plasma device. Conditioning is important because material from
the walls can create impurities in the plasma, and these
impurities typically degrade plasma performance. See also
boronization, impurity control, electron cyclotron discharge

* Wall Loading: Fusion reactor thermal output power divided
by the area of the wall facing the plasma. (Neutron wall
loading is 4/5 of the total for D-T fusion.)

& Waste, Radioactive: See Radioactive Waste.

& Wavelength: The length of a single cycle of a wave; usually
measured from crest-to-crest. For electromagnetic waves, the
wavelength determines the type (radio, infrared, visible,
ultraviolet, X-Ray, gamma-ray) of radiation; in the case of
visible light, wavelength determines the color of the light.

& Waves:

& Weak (Nuclear) Force:

> Wendelstein: A family of stellarators built in Garching, Germany.
The machine currently in operation is Wendelstein-7AS (aka W-7AS).
Wendelstein ("spiral rock") is a craggy Bavarian mountain; some of
W-1 through W-6 were built, some were just paper studies; AS stands
for "advanced stellarator" and refers on the physical side to an
attempt to minimize neoclassical effects (see entry for Neo-classical
Diffusion) such as the bootstrap current (see entry), and on the
technical side to the use of out-of-plane coils as an alternative to
linked coils. W-7X, a much larger, superconducting stellarator based
on the same concepts has been proposed to be built by the European
Union in Greifswald, on the north coast of Germany.

* Whistler: A wave in a plasma which propagates parallel to the
magnetic field produced by currents outside the plasma at a frequency
less than that of the electron cyclotron frequency, and which is
circularly polarized, rotating in the same sense as the electrons
in the plasma (about the magnetic field); also known as the
electron cyclotron wave. Whistlers are so-named because of their
characteristic descending audio-frequency tone, which is a result
of the dispersion relation for the wave (higher frequencies
travel somewhat faster). This tone was frequently picked
up during World War I by large ground-loop antennas (which were
actually being used to spy on enemy field telephone signals).

% Wisconsin - See University of Wisconsin-Madison

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/x
Last-modified: 25-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 24: Terms beginning with "X"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# Xe: Chemical symbol for the element Xenon.

* X-Point: Place where the poloidal magnetic field vanishes in such
a way that two flux surfaces appear to cross, e.g. where the main
plasma joins the divertor (see entry) or between magnetic islands.
Location where magnetic reconnection takes place. (See magnetic
reconnection; see also divertors and O-point.)

& X Ray: A penetrating form of electromagnetic radiation emitted
either when the inner orbital electrons of an excited atom
return to their normal state (characteristic x-rays), or when a
high speed electron collides sharply with an ion or atomic target
(bremsstrahlung). X-rays have energies from roughly 100 eV to
roughly 100 keV. (Below X-rays are ultraviolet rays, and above
X-rays in energy are gamma rays.) X-rays are (basically by
definition) non-nuclear in origin. (Nuclear electromagnetic
radiation termed gamma radiation.) See also ultraviolet, gamma
rays, bremsstrahlung.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/y
Last-modified: 25-Feb-1995
Posting-frequency: More-or-less-quarterly

Disclaimer: While this section is still evolving, it should
be useful to many people, and I encourage you to distribute
it to anyone who might be interested (and willing to help!!!).

Glossary Part 25: Terms beginning with "Y"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


* Yin-Yang Coil: See baseball coil.

* Yucca Mountain: Proposed U.S. site for permanent storage of
high-level nuclear waste; feasibility currently being explored by
U.S. Dept. of Energy.

Robert F. Heeter

Aug 13, 1999, 3:00:00 AM8/13/99
Archive-name: fusion-faq/glossary/z

Last-modified: 25-Feb-1995
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Glossary Part 26: Terms beginning with "Z"


Edited by Robert F. Heeter,

Guide to Categories:

* = plasma/fusion/energy vocabulary
& = basic physics vocabulary
> = device type or machine name
# = name of a constant or variable
! = scientists
@ = acronym
% = labs & political organizations
$ = unit of measurement

The list of Acknowledgements is in Part 0 (intro).


# Z: see atomic number

@ ZETA: Zero Energy Thermonuclear Assembly; see entry

> Zero Energy Thermonuclear Assembly: A British fusion device in
which scientists observed fusion neutrons in 1958. They were
erroneously considered to be thermonuclear (coming from particles
with a Maxwellian velocity distribution) and were a cause for the
initial optimism that fusion energy would be easy. They were
actually due to electromagnetic acceleration during a plasma
instability, an effect which cannot be scaled up to produce useful

> Z-Pinch: Pinch device in which the externally-driven pinching
current goes in the z direction (parallel to / through the
cylindrical plasma). See discussion in Section 4B.

Chollian Newsgroup User

Aug 20, 1999, 3:00:00 AM8/20/99


Lucius Chiaraviglio

Sep 1, 1999, 3:00:00 AM9/1/99
Robert F. Heeter <> wrote:
>* Decay Modes: Different pathways for decay of radioactive nuclei.
>The decay modes for a given unstable state can include beta
>emission (negative = electron, positive = positron), electron
>capture, alpha emission, fission, and gamma emission.
>(Did I miss any?) See entries for each mode for more information.

Some heavy element isotopes occasionally decay by emission
of a nucleus heavier than helium but much lighter than common fission
fragments. I don't remember which ones do this, but some are known
to emit C-14 or Ne-24 nuclei. You can find at least one example if
you cruise around and follow the links to the
table of isotopes. As far as I know, all known decays of this type
have low branching ratios.

Some isotopes are stable against single beta decay or
electron capture but unstable to double beta decay or electron
capture. Calcium-48 has been measured to have a double beta decay
half-life of over 1E18 years (see above URL); calcium-40 should be
able to undergo double electron capture with release of energy, but
as far as I know this has yet to be observed.

Very proton-rich and neutron-rich nuclei decay by
emission of the nucleon that is in excess; in some cases (for example
beryllium-6) they can only do this by emitting two of the nucleon that
is in excess. This usually occurs immediately upon formation of the
unstable nucleus (no half-life); however, I could have sworn to
reading somewhere that some proton-rich isotope of iron had a proton
emission half-life of around 19 minutes, but now I can't seem to find
this anywhere (it may be a non-ground-state nuclear isomer -- the
thing I read said that the long half-life was due to the absurdly high
spin on the nucleus that had to be gotten rid of in order to form a
nucleus and a separate proton with less mass than the original). Very
proton-rich and neutron-rich nuclei that are not quite able to eject
one or more of the nucleon that is in excess may beta decay into
nuclei that are unstable to immediate further particle emission --
usually due to excitation of the resulting nucleus, but in some cases
even if the resulting nucleus manages to drop to ground state; the
beta-coupled alpha decay of nitrogen-12, boron-12, nitrogen-16, and
sodium-20, and the beta-coupled neutron emission of helium-8 and
lithium-11 (also has beta-coupled 2 neutron emission) are examples of
the former (the branching ratio can be low); the beta-coupled alpha
decay of boron-8 and the beta-coupled alpha+proton decay of carbon-9
are examples of the latter (because the products beryllium-8 and
boron-9 blow apart immediately upon formation -- the branching ratio
is 100% for boron-8 and essentially 100% for carbon-9, because double
beta decay/electron capture is energetically unfavorable for the
former and of extremely low probability for the latter).

Some excited nuclei can lose energy without emitting a
nucleon or a gamma ray. In some cases energy loss has a high
probability of occurring by ejection of an orbital electron (see the
_Merck Index_ Table of Isotopes for several examples); in at least one
case the amount of energy released is too small to form a gamma ray
(a recently discovered nuclear isomer of thorium(?) decays to the next
lower energy state by emission of an ultraviolet photon -- same
mechanism as gamma decay, but it won't show up on the same detector).

Lucius Chiaraviglio |
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Lucius Chiaraviglio

Sep 1, 1999, 3:00:00 AM9/1/99
Robert F. Heeter <> wrote:
>* Isomer, Nuclear: two nuclei with the same nuclear mass (total
>number of protons and neutrons) but different nuclear compostions.
>(e.g.: T & 3He are isomers: T has 1p, 2n; 3He has 2p, 1n)

Ummm -- if this is an example of nuclear isomer, what do you
call nuclei of the same isotope that differ only by the amount of
stored energy and/or magnetic moment?

Jim Carr

Sep 7, 1999, 3:00:00 AM9/7/99

"C. Cagle" wrote:
} In article <fusion-faq/glossary/>,
} Robert F. Heeter <> wrote:
} > & Gradient: Mathematical term for the operator which determines
} > the magnitude and direction of the greatest rate-of-change of a
} > given function with position. Similarly used to describe such
} > a rate-of-change. For instance, at a given point on a hill, the
} > slope of the hill in the steepest uphill direction is the gradient
} > of the altitude funtion for the hill.

In article <>
Mitchell Swartz <> writes:
> This one is slightly wrong, too.
> As relates to electrical engineering and physics:
> The gradient of a scalar field is a vector whose magnitude
>and direction come from that scalar field, such that the gradient's
>magnitude is the greatest spatial rate-of-change and, being a vector
>and not an operator, is in the direction of that rate-of-change.

Your nit about his failure to state that the function is a scalar
function rather than a vector function is a resonable one and that
should be fixed to make the contrast with curl clear.

Your nit that the term "gradient" is not used to refer to a certain
differential operator is incorrect.

James A. Carr <> | Commercial e-mail is _NOT_ | desired to this or any address
Supercomputer Computations Res. Inst. | that resolves to my account
Florida State, Tallahassee FL 32306 | for any reason at any time.

Jim Carr

Sep 7, 1999, 3:00:00 AM9/7/99
Robert F. Heeter <> wrote:
} * Isomer, Nuclear: two nuclei with the same nuclear mass (total
} number of protons and neutrons) but different nuclear compostions.
} (e.g.: T & 3He are isomers: T has 1p, 2n; 3He has 2p, 1n)

In article <> writes:
> Ummm -- if this is an example of nuclear isomer, what do you
>call nuclei of the same isotope that differ only by the amount of
>stored energy and/or magnetic moment?

Good point. I would say that his definition is not correct,
so if this is indeed a usage in the fusion community, it should
be made clear that the nuclear physics community uses "Nuclear
Isotope" to refer to that distinction and uses "Nuclear Isomer"
to refer to something else.

Jim Carr

Sep 7, 1999, 3:00:00 AM9/7/99
Robert F. Heeter <> wrote:
} * Decay Modes: Different pathways for decay of radioactive nuclei.
} The decay modes for a given unstable state can include beta
} emission (negative = electron, positive = positron), electron
} capture, alpha emission, fission, and gamma emission.
} (Did I miss any?) See entries for each mode for more information.

In article <> writes:
> Some heavy element isotopes occasionally decay by emission
>of a nucleus heavier than helium but much lighter than common fission
>fragments. I don't remember which ones do this, but some are known
>to emit C-14 or Ne-24 nuclei. You can find at least one example if
>you cruise around and follow the links to the
>table of isotopes. As far as I know, all known decays of this type
>have low branching ratios.

Very low. I am pretty sure that the 14C decay of 226Ra was the
first one seen [branch of 3 x 10^{-9} % in the Wallet Cards] but
it could have been one of the other Ra isotopes.

234U can decay by Mg or Ne emission in addition to alpha decay
and SF (spontaneous fission). 228Th has a 20O decay.

>proton-rich and neutron-rich nuclei that are not quite able to eject
>one or more of the nucleon that is in excess may beta decay into
>nuclei that are unstable to immediate further particle emission --

For Heeter: Shorthand for this is "beta-delayed proton emission".

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