PCB's in liquid nitrogen
gghe...@gmail.com
nitrogen temperatures? The best I could find on the web was liquid
nitrogen used for stress testing PCB's.
The boards will be single sided and have either wires or through hole
components attached, resistors and diodes (nothing active). At the
moment I'm most concerned with having the copper traces peel up from
the substrate. Would heavier copper help? (2 oz. or 4 oz.) I would
hope to use a standard substrate material FR-4, G10....
Thanks,
George Herold
Spehro Pefhany
You're cooling them by 220K ~= 400�F. What temperature difference do
they see when they go from 100�C preheat to floating on a molten
solder bath?
Okkim Atnarivik
> Does anyone have experience using printed circuit boards at liquid
> nitrogen temperatures? The best I could find on the web was liquid
> nitrogen used for stress testing PCB's.
FR4 based PCBs work just fine both in liquid nitrogen and liquid helium.
Regards,
Mikko
John Larkin
I don't think you'll have any problems with the board. Wide range temp
cycling can stress surfmount solder joints, so thru-hole parts are
probably safer.
John
gghe...@gmail.com
<Okkim.Atnari...@twentyfour.fi.invalid> wrote:
> ggher...@gmail.com kirjoitti:
Excellent! Thanks Mikko, I'll be torturing things next week,
(dunking in LN2) but thought I'd get some sage advice before
starting.
George H.
Okkim Atnarivik
> On Fri, 29 May 2009 08:42:16 -0700 (PDT), gghe...@gmail.com wrote:
>> Does anyone have experience using printed circuit boards at liquid
>> nitrogen temperatures?
>
> cycling can stress surfmount solder joints, so thru-hole parts are
> probably safer.
Large sized SMD components crack sometimes if the card gets thermally
recycled several times. But typically SMDs are no problem at all in
non-commercial experimental-type work. I'd say they are even OK in
commercial work if your circuit is typically just cooled once and
then stays at 77K or 4K for long periods of time. But for commercial
work must experiment with your particular devices because you
are likely to operate them outside the specs anyway. My colleagues
once hung a small circuit from the seconds arm of a wall clock so
that it got dipped into LN dewar and retracted from it a one-minute
cycle time.
More often there are problems because the frost and condensed
moisture may spoil some components if you just lift the circuit from
LN and let it warm up in open air.
Regards,
Mikko
gghe...@gmail.com
<Okkim.Atnari...@twentyfour.fi.invalid> wrote:
> John Larkin kirjoitti:
>
The circuit board will be go through lots of thermal cycling. It will
be used by students to measure the Johnson noise from resistors as a
function of temperature. So I expect maximum thermal stress from the
students.
I thought I might try some small surface mount diodes as temperature
sensors, but I can use the glass encapsulated variety if these won’t
work.
Since I have your attention I also need a robust heater that will
survive repeated trips to 77K. I’m going to try some of the 5 or 10
Watt aluminum housed power resistors made by Dale, Ohmite. Do you
have any advice? I’d rather not have to wrap my own out of resistance
wire, much cheaper to buy something commercial.
George Herold
John Larkin
Regular diodes should work fine.
>
>Since I have your attention I also need a robust heater that will
>survive repeated trips to 77K. I�m going to try some of the 5 or 10
>Watt aluminum housed power resistors made by Dale, Ohmite. Do you
>have any advice? I�d rather not have to wrap my own out of resistance
>wire, much cheaper to buy something commercial.
>
>George Herold
Minco makes slick stick-on flexible heaters. You can slap one on the
back of a circuit board.
This is cute, too:
ftp://jjlarkin.lmi.net/Welwyn.JPG
John
Spehro Pefhany
Kinda high tempco. Have you used it in cryogenic applications?
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
gghe...@gmail.com
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>
> - Show quoted text -
Excellent the heaters on Kapton from minco look nice. -200C to
+200C. I'm at home using dial up and couldn't see your ftp link. No
worries I'll check it out on Monday.
George Herold
gghe...@gmail.com
wrote:
> On Fri, 29 May 2009 14:15:06 -0700, the renowned John Larkin
>
>
>
>
>
>
> - Show quoted text -
Hmm, I didn't see any tempco listed. But how bad is it? If the
resistance changes by less than 50% between 300 to 77K that's fine.
It's only a heater after all.
George Herold
Spehro Pefhany
gghe...@gmail.com wrote:
>On May 29, 8:59�pm, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat>
>wrote:
>> On Fri, 29 May 2009 14:15:06 -0700, the renowned John Larkin
>>
>>
>> >Minco makes slick stick-on flexible heaters. You can slap one on the
>> >back of a circuit board.
>>
>> >This is cute, too:
>>
>> >ftp://jjlarkin.lmi.net/Welwyn.JPG
>>
>> >John
>>
>> Kinda high tempco. Have you used it in cryogenic applications?
>>
>
>Hmm, I didn't see any tempco listed. But how bad is it? If the
>resistance changes by less than 50% between 300 to 77K that's fine.
>It's only a heater after all.
Data sheet says +500~+600 ppm/K, so I only get a -11.5% change over
that range, if I did the math right, hardly out of tolerance
considering they are +/-10% parts to begin with.
I've used the Minco polyimide film heaters as well as some TO-220
parts. The parts John is suggesting look rather rugged.
TheQuickBrownFox
>Does anyone have experience using printed circuit boards at liquid
>nitrogen temperatures? The best I could find on the web was liquid
>nitrogen used for stress testing PCB's.
Certain components fail to operate well above that temp. That is likely
why you will NOT find ANY info on any such test routines.
I would suggest a perfluorocarbon fluid like "fluorinert" from Dupont.
Also, there are likely many commercial refrigerants that would be more
suitable.
What the industry typically does is use an environmental chamber at
zero humidity which will go down to a couple hundred degrees F below
zero. If you really need immersion, the fluorinert or a refrigerant that
will not evaporate too quickly would work. The fluorinert is a
dielectric fluid, meant for such purposes.
>
>The boards will be single sided and have either wires or through hole
>components attached, resistors and diodes (nothing active). At the
>moment I'm most concerned with having the copper traces peel up from
>the substrate.
Then hard wire everything, and encapsulate
> Would heavier copper help? (2 oz. or 4 oz.) I would
>hope to use a standard substrate material FR-4, G10....
If the component count is low, as a single sided solution suggests, you
could simply skip the PCB and point to point wire it, and pot the
finished assembly into a monolithic block or ball.
Anyway... what you seek is environmental chambers. Not likely wise to
play with a PCB and raw LN.
TheQuickBrownFox
<Okkim.A...@twentyfour.fi.invalid> wrote:
> More often there are problems because the frost and condensed
>moisture may spoil some components if you just lift the circuit from
>LN and let it warm up in open air.
That's why the right way is with an environmental chamber.
Robert Baer
*NON* compliant as lead solder holds up at LN temps).
No problems noted at LN temps, but..the PCB was 30 mil and a vairant
of Geteck (ie: NOT FR-4).
I would suggest thinner copper and if cannot get Geteck use a Rogers
variant (yeah,i know, more expensive).
Okkim Atnarivik
: That's why the right way is with an environmental chamber.
I mostly do LHe work and there I just leave the circuit to the
top of the dewar neck and let it warm up before opening the neck flange.
The circuit gets flushed by evaporated, warmed-up dry helium.
With LN (there is typically no flanged neck in LN dewars) you can
just quickly slip the circuit into a plastic bag and let it warm up
there. Some people like to evacuate the bag or fill it with dry
nitrogen, but IMO it is enough to just squeeze out most of the air.
The circuit catches a small amount of moisture anyway when moved from
dewar to the bag, but most of the frost (when kept in open air) comes
from the unrestricted airflow that goes by the circuit and deposits
its moisture on the cold surface.
Regards,
Mikko
Okkim Atnarivik
: On Fri, 29 May 2009 13:01:35 -0700 (PDT), gghe...@gmail.com wrote:
: >> > I don't think you'll have any problems with the board. Wide range temp
: >> > cycling can stress surfmount solder joints, so thru-hole parts are
: >> > probably safer.
My statistics is not sufficient to really draw conlusions, but my gut
feeling is that I've seen thru-hole parts break approximately as often
(i.e. not often) as SMD parts. I vaguely feel that the breaking likelihood
may be more closely tied with the physical size of the component. Large
ones break more easily - or perhaps they are just easier to observe :)
: >The circuit board will be go through lots of thermal cycling. It will
: >be used by students to measure the Johnson noise from resistors as a
OK, you cannot be completely careless then when choosing a readout
amplifier with sufficiently low noise temperature, and cannot afford
screwing up much with noise matching.
: >function of temperature. So I expect maximum thermal stress from the
: >students.
But no fatal consequences if something breaks. I think you're safe
with a quick-and-dirty PCB without taking much precautions.
: >I thought I might try some small surface mount diodes as temperature
: >sensors, but I can use the glass encapsulated variety if these won?t
: >work.
: Regular diodes should work fine.
I agree that they should work, but I think I encountered some funny
unexpected behaviour when experimenting with both Si and Ge diodes
several years ago. I forget exactly what it was (may have been below
77K anyway) and feel too lazy to find the lab notebook now. I didn't
spend much time to figure it out, because I had the official Lake Shore
sensors available anyway. I think there is a paper about using
off-the-shelf diodes as thermometers in some back issue of the Cryogenics
magazine. I'd be interested to hear about your experiences if you
end up using a diode as the thermometer.
Many off-the-shelf components work at 4K and even more work at 77K.
Resistor values change, so you need to measure and compensate. NP0 caps
hardly change at all. X7R caps fall to 1/10 and Z5U caps freeze out
completely. Inductor cores are more varied, mu collapses in most of the
high-mu cores but occasionally you find a surprise core where it does not.
GaAs devices typically keep functioning, but Si devices tend to freeze out
below 77K, except for those enhancement-type MOSFETs whose ohmic contacts
happen to be doped strongly enough (eg. 2N7000 from some manufacturers).
Some Si JFETs can work at 4K when made to dissipate enough so that they
internally heat up to 50-80K. A worn-out notebook where one lists which
parts work and which won't work in LHe or LN belongs to every cryogenic
engineers assets. I think such a notebook is what allows 'cryogenic
suppliers' to ask for hefty premiums when selling parts. Unfortunately the
contents of the notebook may vary when the manufacturer changes some tiny
bit in their fabrication process which does not affect the room-temperature
specs.
: >Since I have your attention I also need a robust heater that will
: >survive repeated trips to 77K. I?m going to try some of the 5 or 10
: >Watt aluminum housed power resistors made by Dale, Ohmite. Do you
: >have any advice? I?d rather not have to wrap my own out of resistance
: >wire, much cheaper to buy something commercial.
Our heaters are typically deposited on-chip, so I cannot comment on
durability of ordinary resistors.
Regards,
Mikko
John Larkin
Down to nitrogen temps, diodes behave pretty well as temp sensors.
PN junctions have "carrier freeze-out" starting at about 20K. Below
that, junction drop increases radically and diodes start to look like
resistors, and part-to-part variations get radical. Lake Shore
http://www.lakeshore.com/temp/sen/sd.html
sells diodes that are calibrated down to 1.4K, and somehow manage to
keep them consistant. Some other people sell cryo diodes that vary
wildly from batch to batch, and I have the scars to prove it.
John
gghe...@gmail.com
<thequickbrown...@overthelazydog.org> wrote:
Opps my mistake quickbrownfox, I don't want to stress my boards I
want to cool resistors to 77K.
George Herold
JosephKK
Based on youtube videos of PCs being sunk in liquid nitrogen and "hot
rodded" to about 5X rated clocks, i would say just go for it. Watch
the thermal gradients, both spatially and temporally though, that is
the major cause of problems.
JosephKK
Try RNR series wirewounds. They may be pricey but may be space
qualified.
gghe...@gmail.com
Robert, Thanks for the tip on staying with lead based solder. I was
also wondering if thinner traces would work better? Letting the
copper 'move' with the pcb.
I like the bigger traces, because people may be changing components
and the heavier copper will hold up better to resoldering.
George Herold
John Larkin
What are you going to use as an amplifier? It will have to be pretty
good to measure Johnson noise with any accuracy.
Some tuned phemt amps can hit noise temps around 40K. Wideband untuned
amps usually run around room temp.
It's easier to go hot than cold!
John
gghe...@gmail.com
wrote:
Thanks Mikko, I'm definitely concerned about moisture, mostly leaking
into the probe when it’s inside the nitrogen dewar. The probe will
have at least one hole in the bottom. (I don’t want to make a
nitrogen bomb!) And will spend part of the time in the vapor above
the liquid. The current idea is to try to make a ‘soft’ seal around
the top of the nitrogen dewar and control the nitrogen boil off such
that no water can leak in. The fall back idea is to use a Plexiglas
tube, sealed at the top to the probe and open at the bottom, which
extends down into the liquid. (again sealing the probes environment)
Either way you’ll be able to lift the probe up apply heat and let it
warm up dry. (and maybe 1/2 of the people will follow our
instructions.) I like the plastic bag idea! In the past I’ve always
used probes that were vacuum tight with helium exchange gas.
George Herold
gghe...@gmail.com
wrote:
> John Larkin <jjlar...@highnotlandthistechnologypart.com> wrote:
Wow, thanks again Mikko,
At $200 each I can't afford Lake Shore sensors. I'll let you know
what I find. I have it on good authority that the regular Si diodes
will work fine. I’ve got a few ideas on how they might be calibrated,
and hopefully a two point calibration will be enough for 1% accuracy,
which is about all I’m expecting from the electronics.
We use to use Dale carbon composite resistors as temperature sensors.
(But not for sensitive areas, they tended to change a bit with each
trip down to 4K)
George Herold
gghe...@gmail.com
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>
> - Show quoted text -
The amplifiers and filters will all live at room temperature.
(Nothing fancy here.)
The filter maximum bandwidth maximum is 100kHz. (A state variable
filter with 1% C’s and 0.1% R’s) The amplifiers bandwidth is up near
1MHz. Except for the first stage where the bandwidth changes with the
source impedance. The electronics seems to be working amazingly
well. (I always worry that two compensating errors are fooling me.)
If you’re interested I could post my latest shot noise data on
Monday.
George Herold
gghe...@gmail.com
>
> - Show quoted text -
Price is important, We can always make our own from resistance
wire.
George H.
Robert Baer
Maybe larger pads will help, but a heavy hand at soldering /
desoldering is going to (eventually) lift a pad.
A larger trace to a larger pad might allow a "floating" pad to be
re-used due to the greater possibility of that trace remaining adhered
to the PCB.
As far as re-flow goes, have the initial PCB be "HASL" or hot-air
solder levelled (tin-lead for low temp work).
If you can score any Multi-core Savbit, that would be the ideal alloy
to use, as the 2% copper in the solder will not change the MP enough to
talk about, but will prevent "eating" (dissolving) away of the copper pads.
Robert Baer
...is that what she said??
Carl Ijames
> and the heavier copper will hold up better to resoldering.
>
> George Herold
If there are a few components that will be changed regularly, put several
pads in parallel next to each other so if one gets messed up the board isn't
a loss. Start at the far end, and if a trace or pad lifts just cut it off
and move over to the next set.
-----
Regards,
Carl Ijames
MooseFET
>
> > - Show quoted text -
>
> Hmm, I didn't see any tempco listed. But how bad is it? If the
> resistance changes by less than 50% between 300 to 77K that's fine.
> It's only a heater after all.
I think you will find that it changes by about 77/300 between the
extremes.
>
> George Herold
MooseFET
How about:
Solder bus wire to the PCB and then solder the resistor to the bus
wire. The soldering cycle will happen to a bus wire and not the PCB.
> George Herold
JosephKK
I haven't bought any resistance wire recently. It got to be more
expensive than completed resistors for me some time ago, and that was
materials cost only.
John Larkin
What "cold" resistor value will you use? And what's the amplifier's
noise density?
A good jfet (BF862 maybe) has huge input Z and under a nv/rthz noise.
A 1M resistor has Johnson noise of around 130 nv/rthz at room temp. If
cable capacitance is kept reasonable, there will be a nice frequency
band in which the resistor absolutely dominates.
You can get jfet opamps in the 4 nv noise range, even easier.
John
Spehro Pefhany
The data sheet range of tempco indicates that those resistors are not
behaving like a pure elemental metal, or their tempco would be about
5x worse around room temperature. So, I don't think so.
gghe...@gmail.com
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
The current plan is to put three different resistors in the probe and
switch them at the top. 100k ohm is a nice value and maybe 10k and
1Meg Two feet of cable and the probe have a capacitance of 50 pF or
so. The first stage is a single opamp, there's a DIP socket so that
different flavors can be tried. Lately I've been using the OPA134
which has a FET input and 8nV/rtHz of noise, (smaller would always be
nicer). I do like the 8MHz bandwidth and only 1 or 2 pF of input
capacitance.
Which Jfet has 4nV? And what’s the current noise?
George Herold
Okkim Atnarivik
> The current plan is to put three different resistors in the probe and
> switch them at the top. 100k ohm is a nice value and maybe 10k and
> 1Meg Two feet of cable and the probe have a capacitance of 50 pF or
> so. The first stage is a single opamp, there's a DIP socket so that
> different flavors can be tried. Lately I've been using the OPA134
> which has a FET input and 8nV/rtHz of noise, (smaller would always be
> nicer). I do like the 8MHz bandwidth and only 1 or 2 pF of input
> capacitance.
BF862 is pretty good, http://www.24.fi/kiviranta/bf862.gif .
For a low source resistance http://www.24.fi/kiviranta/bfp650.gif .
Regards,
Mikko
Okkim Atnarivik
> Which Jfet has 4nV? And what�s the current noise?
I forgot to mention the venerable AD743 opamp, with <3nV/rtHz
and <7fA/rtHz spec. That has the lowest Tn spec I for a reasonable
(less than 1Mohm) source which I encountered when I made a
survey of available amps a long time ago. Does anyone know
a more modern opamp with a better Tn?
Regards,
Mikko
gghe...@gmail.com
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -
Hey Thanks for all the ideas, I also thought I might use a 'turret'
post that is 'staked' to the pcb. Keystone makes a bunch of these.
George H.
gghe...@gmail.com
<Okkim.Atnari...@twentyfour.fi.invalid> wrote:
> ggher...@gmail.com kirjoitti:
>
> > The current plan is to put three different resistors in the probe and
> > switch them at the top. 100k ohm is a nice value and maybe 10k and
> > 1Meg Two feet of cable and the probe have a capacitance of 50 pF or
> > so. The first stage is a single opamp, there's a DIP socket so that
> > different flavors can be tried. Lately I've been using the OPA134
> > which has a FET input and 8nV/rtHz of noise, (smaller would always be
> > nicer). I do like the 8MHz bandwidth and only 1 or 2 pF of input
> > capacitance.
>
> BF862 is pretty good,http://www.24.fi/kiviranta/bf862.gif.
> For a low source resistancehttp://www.24.fi/kiviranta/bfp650.gif.
>
> Regards,
> Mikko
I'm not quite up to 'rolling my own' front end. I'm sticking with
opamp solutions. And then if the students blow it out some how it's
easy to put in a new device... The opamp is the fuse ion this case.
George H.
gghe...@gmail.com
<Okkim.Atnari...@twentyfour.fi.invalid> wrote:
> > Which Jfet has 4nV? And what’s the current noise?
Ahh I have some of those in my parts box. The slew rate is a bit low,
but not that much of an issue in this case. What I really don't like
is the 20pF of input capacitance. I spent a few days 'dremeling' off
sections of the ground plane on the prototype in order to get the
capacitance below 10pF. (I'm still learning from all the mistakes I
make.)
George Herold
John Larkin
Take a look at ADA4817. It's 4 nv and 2.5 fA. Not to mention 1 GHz.
You could maybe mount it on one of those commercial adapter boards,
and then plug it into a dip socket.
John
gghe...@gmail.com
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>
> - Show quoted text -
Thanks John, Gee, I think I have a few of those that I sampled from
analog. I haven't opened the sample box yet. I want to try and use
them for a fast photodiode preamp one day (month, year.... It will
probably be obsolete by the time I get around to it.) For the current
project the supply voltages are an issue. I've got all the
electronics running from +/- 15V.
We plan on using the SMD to DIP adapters for trying opamps that don't
come in the old DIP package.
Actually the amplifer noise is not all that bad. You can certainly
see effects when the additional noise is only 10% of the amplifier
noise. Here's a link to the latest shot noise data.
http://s633.photobucket.com/albums/uu56/gherold/?action=view¤t=SN5-09100K.jpg
(I hope that works)
The measurment bandwidth was 300 Hz to 100kHz. There is a bit of
deviation at high currents. I haven't explored it very much and I
hope it that it might be due to 1/f noise in the light bulb.
George Herold
John Larkin
It is curving up. A filament can be surprising... you can send quite
decent audio by modulating the current into an ordinary light bulb. So
tiny power supply ripples could be doing what we see here. Still, the
match is very good.
>
>George Herold
>
It's great that you're teaching the brats about Johnson and shot
noise. We never studied those in school. I'm just now working on a
system where both matter a great deal, and it adds a bunch of
constraints. Problems are fun when you have a lot of constraints.
John
Okkim Atnarivik
: Take a look at ADA4817. It's 4 nv and 2.5 fA. Not to mention 1 GHz.
Ah, one of those new FastFET devices. A bit high 1/f corner although.
Thanks for the hint.
Regards,
Mikko
gghe...@gmail.com
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> > (I hope that works)
>
> >The measurment bandwidth was 300 Hz to 100kHz. There is a bit of
> >deviation at high currents. I haven't explored it very much and I
> >hope it that it might be due to 1/f noise in the light bulb.
>
> It is curving up. A filament can be surprising... you can send quite
> decent audio by modulating the current into an ordinary light bulb. So
> tiny power supply ripples could be doing what we see here. Still, the
> match is very good.
>
>
>
> >George Herold
The power supply running the light bulb is filtered for low noise.
(about 4nV/rtHz.) When I was taking the data at the highest currents
I noticed that I would get intermittent 'large' spikes in the
rectified noise voltage. (The final stage is an analog multiplier,
followed by low pass filter) I would wait for the system to recover
from these before recording the number...but I thought (later that
evening) there may be other smaller 1/f type noise spikes coming from
the light bulb. I want to use other light sources also.. But for the
moment I claimed success and moved on. I've got to make sure I can
measure the noise from a resistor on the end of a cable cooled to
77K. And that's a lot harder than measureing shot noise, which is
hugh in comparison.
>
> It's great that you're teaching the brats about Johnson and shot
> noise. We never studied those in school. I'm just now working on a
> system where both matter a great deal, and it adds a bunch of
> constraints. Problems are fun when you have a lot of constraints.
>
Yeah, I don't think I understood any of this when I was taking 'real'
data as a grad student. I remeber these noise contours in a PAR or
SRS preamp manual, showing the noise as a function of source
impedance. I was all greek to me.
George
John Larkin
You need a Phil Hobbs "Light-Bulb Noise Canceller"
John
gghe...@gmail.com
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
Well if it is 1/f noise all I have to do is increase the high pass
filter set point up to some higher frequency, (3kHz is the current
max.) But regardless of which it's always good to have a bit of hair
on the data. It gives me something to figure out...and/or maybe some
student can figure it out.
George H.
gghe...@gmail.com
wrote:
I didn't notice that Mikko, thanks. I worry about the gain peaks out
at high frequency. I assume I can tame them with a bit of C.
BTW I was reading about fluxon's today, thanks for the post to some
other ( ...) I would have replied there, but didn't want to
encourage him.
I was reading a wiki article
http://en.wikipedia.org/wiki/Magnetic_flux_tube
that mentioned electric fluxons. I've made niobium/ oxide/niobium
Josephson junctions and measured all sorts of weird stuff. But I
always thought of it as a magnetic effect. What’s with electric
fluxons?
George H.
I
Okkim Atnarivik
: I was reading a wiki article
: http://en.wikipedia.org/wiki/Magnetic_flux_tube
: that mentioned electric fluxons. I've made niobium/ oxide/niobium
: Josephson junctions and measured all sorts of weird stuff.
A colleague! Pleased to meet you.
: But I
: always thought of it as a magnetic effect. What?s with electric
: fluxons?
To me it sounds that either the creator of that wiki page has some
confused ideas about dualisms involving flux quanta, or maybe
'electric fluxons' are really constructs of some obsucre branch
of theoretical physics. You get fluxons in the traditional sense
when electrons get a chance to chase their own tails in an
environment where they don't scatter and therefore remain phase
coherent (e.g. Ahranov-Bohm effect).
I have liked to think electrons and fluxons as two complementary
aspects of the same entity. Electrons are localized in (insulating)
free space, and dissolve into a 'fluid' in conductors. Fluxons are
localized within perfect-conducting material, but become 'fluid' in
free space. But this is just nonrigorous idle thinking...
Regards,
Mikko
gghe...@gmail.com
wrote:
> ggher...@gmail.com wrote:
>
> : I was reading a wiki article
>
> :http://en.wikipedia.org/wiki/Magnetic_flux_tube
>
> : that mentioned electric fluxons. I've made niobium/ oxide/niobium
> : Josephson junctions and measured all sorts of weird stuff.
>
> A colleague! Pleased to meet you.
Oh I hope I didn't mislead you. I made these junctions long ago as a
grad student in physics. We etched or sanded niobium wire, twisted
two pieces together, then slapped them in epoxy (stycast 1266) and
dunked them into liquid helium. I made perhaps 10 or 20 of these of
which maybe 2 or 3 actually worked nicely.
>
> : But I
> : always thought of it as a magnetic effect. What?s with electric
> : fluxons?
>
> To me it sounds that either the creator of that wiki page has some
> confused ideas about dualisms involving flux quanta, or maybe
> 'electric fluxons' are really constructs of some obsucre branch
> of theoretical physics. You get fluxons in the traditional sense
> when electrons get a chance to chase their own tails in an
> environment where they don't scatter and therefore remain phase
> coherent (e.g. Ahranov-Bohm effect).
Ahh, good the article seemed a bit weird.
>
> I have liked to think electrons and fluxons as two complementary
> aspects of the same entity. Electrons are localized in (insulating)
> free space, and dissolve into a 'fluid' in conductors. Fluxons are
> localized within perfect-conducting material, but become 'fluid' in
> free space. But this is just nonrigorous idle thinking...
>
> Regards,
> Mikko
Hmm, I haven't thought about super conductivity for a long time. I've
read that charge and the quantum mechanical phase are 'complementary'
variables in QM. (I'm not sure complementary is the right word.)
I've never understood that at all! But perhaps fluxons are a way to
get at that relationship.
All I can remember is that I didn't really 'get' the physics of
Josephson J's until I read the discussion by Feynman in volume (3?) of
the "Feynman Lectures". (He makes everything 'seem' so simple.)
So are you making squids or something related?
Say have people made Josephson junctions in HTC super conductors?
Just thinking it would be nice to show the effect without having to
use liquid helium.
George Herold
(I work here, www.teachspin.com, if you're interested)
Spehro Pefhany
>
>Say have people made Josephson junctions in HTC super conductors?
>Just thinking it would be nice to show the effect without having to
>use liquid helium.
Sure, there are HTc SQUIDs, but they are significantly more noisy than
the Low Tc ones. Great for educational purposes.
John Larkin
>Say have people made Josephson junctions in HTC super conductors?
>Just thinking it would be nice to show the effect without having to
>use liquid helium.
>
>George Herold
>
>(I work here, www.teachspin.com, if you're interested)
>
Ask Mr Squid!
http://www.starcryo.com/mrsquid.htm
John
gghe...@gmail.com
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Tue, 2 Jun 2009 10:24:56 -0700 (PDT), ggher...@gmail.com wrote:
> >Say have people made Josephson junctions in HTC super conductors?
> >Just thinking it would be nice to show the effect without having to
> >use liquid helium.
>
> >George Herold
>
Opps my mistake, I've seen that already at the trade shows...
(I must be getting old... How old do I have to be before I can use
that excuse?)
George
whit3rd
That's unlikely; that formula (Drude theory for a classical
metal) only applies to pure metals (and that is the
reason that 3000 ppm/C is a common PTC 'thermistor' value).
The tempco misbehavior that WILL be important, is
of carbon resistors (film or composition). Avoid them.
Carbon is a 'semimetal' and becomes insulating at
low temperatures.
John Larkin
wrote:
Carbon comp resistors are the poor man's cryo temp sensors. They need
to be individually calibrated for decent accuracy. They work in high
magnetic fields, where some other sensors (like silicon diodes) don't.
John
Okkim Atnarivik
: > � A colleague! Pleased to meet you.
: Oh I hope I didn't mislead you. I made these junctions long ago as a
: grad student in physics. We etched or sanded niobium wire, twisted
: two pieces together, then slapped them in epoxy (stycast 1266) and
: dunked them into liquid helium. I made perhaps 10 or 20 of these of
: which maybe 2 or 3 actually worked nicely.
Great, the pioneer's way of making them. Some of the very first
SQUIDs, made by Clarke's group in Berkeley, were just solder blobs over
oxidized Nb wire.
: So are you making squids or something related?
Yes, we have a full foundry ( www.micronova.fi/facilities/index.html )
where we make those, among other things.
Regards,
Mikko
gghe...@gmail.com
wrote:
Hi Mikko, I remember first trying the Clarke slugs. (solder +
Niobium) but IIRC they didn't work very well. Whereas the niobium on
niobium had 'text book' I-V curves with nice sharp self induced
steps.
Wow, lots of cool stuff where you work (micronova) is this a
government run facility? Who pays the bills?
George Herold