"Hot Point:" Question on Fusion

[giveitawhirl2008]

You know they advertise these little solar collectors that can, say,
light a cigarette. They say the temp is 2500 degrees (F, I assume).
What if you make ten similar collectors and concentrate them all on
the same point? Wouldn't you get 25,000 degrees? OK, so let's say you
want to create a point in midair (outside your laboratory, maybe)
where the temp will be 100 million degrees. The equivalent of 40,000
of those "cigarette lighters" would do that, then?

What if you have a point hanging in midair at which the temp is
constantly 100 million degrees? What kind of effects would you get off
that? First, by just letting air pass into it as it normally would.
Then by placing objects at it?

[Sam Wormley]

The upper limit of temperature that can be achieve by concentrating
sunlight (heat) is less than the surface temperature of the sun --
less than 6000 K .

http://www.google.com/search?hl=en&safe=off&q=6000+K+in+F&btnG=Search

[John Bailey]

On Sun, 5 Oct 2008 19:45:51 -0700 (PDT), giveitawhirl2008
<giveitaw...@gmail.com> wrote:

>You know they advertise these little solar collectors that can, say,
>light a cigarette. They say the temp is 2500 degrees (F, I assume).
>What if you make ten similar collectors and concentrate them all on
>the same point? Wouldn't you get 25,000 degrees? OK, so let's say you
>want to create a point in midair (outside your laboratory, maybe)
>where the temp will be 100 million degrees. The equivalent of 40,000
>of those "cigarette lighters" would do that, then?

For straightforward optics, Sam is right, the Second Law of
thermodynamics prohibits reaching temperatures hotter than the surface
of the source--HOWEVER:

http://www.nrel.gov/csp/lab_capabilities.html
"The 10-kilowatt HFSF consists of a tracking heliostat and 25
hexagonal mirrors to concentrate solar radiation. The solar furnace
can nominally provide flux at 2,500 suns, but, when required, can use
specialized secondary optics to generate significantly higher
concentrations (greater than 20,000 suns). Flux levels and
distributions can also be tailored to the needs of a particular
research activity."

Also:
"In a series of experiments conducted in January 1990, a University of
Chicago researcher under the direction of physics professor Roland
Winston achieved a record concentration of 84,000 suns, far in excess
of the most intense artificial broadband continuous light sources that
have yet been devised. Further refinements of the techniques designed
by Winston's group are expected to yield a solar furnace design that
can produce concentrations of more than 100,000 suns."
http://www.allbusiness.com/professional-scientific/scientific-research-development/155648-1.html

and http://findarticles.com/p/articles/mi_m1200/is_n13_v133/ai_6542783
"Winston and Gleckman use a 16-inch astronomical mirror borrowed from
the university's Yerkes Observatory, but to it they add a device that
squeezes the image the mirror makes. A large mirror will gather more
sunlight than a small one, but it also makes a larger image than the
small one, so it may not represent much gain in energy concentration.
The "Winston concentrator" is a precisely machined cone of silver
placed at the focus of the 16-inch mirror. It squeezes down the image
of the sun made by the mirror, which is 1 centimeter across, to a spot
less than 1 millimeter across.

"One importance of this achievement is that it is above the energy
concentration -- about 5 kilowatts per square centimeter -- needed to
energize varieties of lasers that have many scientific technical uses.
Among the possible applications, according to Winston, are laser
communication in space, development of materials, disposal of
hazardous wastes and isotope separation for nuclear fuels"

5 kw/sq cm corresponds to a black body temperature of 17,000 degrees
Kelvin.
http://www.iddl.vt.edu/TEST/testhome/javaapplets/planckRadiation/blackbody.html

Apparently, fusion at readily achieved fuel densities requires energy
concentrations considerably higher than this.
ref. http://www.lle.rochester.edu/pub/documents/ext/ICF.pdf
John

[Cwatters]

"giveitawhirl2008" <giveitaw...@gmail.com> wrote in message
news:ecca49e3-5a3c-4ec5...@c60g2000hsf.googlegroups.com...

They are going to try something like that here...

http://en.wikipedia.org/wiki/National_Ignition_Facility

..using lasers, amplified to produce a 500 terawatt flash of light focused
on a 2mm sphere of deuterium.

[tj Frazir]

The moon is hotter then the sun.
Gamma Moon google.