[volt-nuts] Low-cost Josephson Junction Array
vince at mulhollon.com
Thu Oct 20 08:27:48 EDT 2016
I'd agree with, and extend, acbern's remarks
As a pure science experiment and completely inadequate certification
standard you can still have fun with one junction not an array which makes
things enormously cheaper. Of course this turns it from a calibration lab
experiment to primarily a physics experiment that can also kinda do
comparisons, sort of, poorly. But running one junction homemade niobium
junction could be an intermediate step on running an array later. After
the bugs are worked out, swap the single junction for an array and you're
The state of the art in amateur radio microwave work has been rapidly
moving even over just the last decade. Running a JJ is not really an issue
anymore for advanced ham operators between microwave radio contests.
Serious stuff, but its quite doable now.
I'm not sure what cryonic prices are like in .de but locally liq N2 dewars
are like the cost of a months groceries or a modest fraction of a mortgage
check, liq He dewars are like the cost of a really nice used car, liq N2 is
maybe a tenth the cost of gasoline per volume. So the cost of filling a
liq N2 dewar is like a night at the bar. Per liter liq He is maybe the
cost of good wine so filling a 100L dewar is a significant fraction of a
mortgage payment or the cost of a junker used car. The staggering
difference in price is why you prechill the apparatus with liq N2 and of
course liq N2 freezes well above the temp of liq He so its just SO much fun
to work with (sarcasm).
Cryocoolers are a whole nother problem. So a contemporary dual pulse tube
crycooler in a research lab on bragging day when cost is no object is like
ten KW of power in, 10001 watts of heat rejected, yeah like one watt of
cooling on the second cryo. Well, my basement does get cold in the
winter... So I need insulation that passes less than a watt thermal at a
"basement to liq He" differential in temp... Ouch. Of course you can do
things like make a bath of cheap liq N2 and pull a vacuum on it so the
differential is only maybe 60K but even so, just getting a watt is an
achievement... And of course even with a decent machine shop the best the
professionals can do in a research lab a couple years ago is not terribly
realistic. Maybe in 50 years everyone will have a cryocooler in their
basement instead of a deep freeze, but just not today.
Oh and the thermal capacity of liq He is like nothing, so that $1000 of liq
He evaporates when you stare at it harshly. All cryonic apparatus is
unfortunately ultra high pressure gas apparatus unintentionally because the
vents can freeze over or "stuff" can condense into the insulation, and of
course high pressure gas explosions are highly effective at killing people
so its just an endless pile of headaches, although maybe it can be done?
On Thu, Oct 20, 2016 at 4:53 AM, <acbern at gmx.de> wrote:
> About two years ago I started an exercise to determine what it would take
> to build a kind of DIY JJ standard and also looked at certain detail
> technical aspects of designing/building what is reasonable doable. Baseline
> was 10V DC. It was clear that it would not be cheap, and I also looked at
> this as a personal challenge. So here in a nutshell:
> I did talk to a vendor of the JJA, and we finally agreed he would be
> supporting me with supplying a JJA and related waveguide with flange
> attached. Nothing else, to save costs. What would have remained is the
> 75Ghz RF source (including further waveguides with dewar interface and
> helium block, RF source, directional coupler and RF generator. Key is a
> source with low harmonics, so using a trippler and a 26.5GHz generator
> (locked to a gps-calibrated rubidium source) was a potential solution, but
> it was not clear if that would have been sufficienly clean overall, so
> quite some risk here having to go with another solution finally (Gunn...).
> Also the amplifier portion and transmission of the RF signal to the JJA
> without too much loss is not that simple, as the power needed is not that
> low. Lots of discussions with the vendor. Helium would have been obtained
> in a loaner dewar from a gas manufacturer, I did have a quotation at pretty
> reasonable cost, no need to go with a cryocooler (which ca
> n cause a lot of voltage noise potentialy, killing the DC signal). And
> some driving electronics of course, doable with reasonable effort. While I
> had some equipment such as e.g. the RF generator and reference clock, the
> shopping list was not that short. Also some test gear such as a 75GHz power
> head and so on was also on the shopping list.
> To make a long story short, I ended up with an estimate of 30 to 40 kUSD,
> with about 10k of additional risk, with the majority being the cost of the
> JJA. Quite some expense for an in the end academic exercise, so I finally
> decided to not further pursue this. I need to add that, being an EE, with
> no experience in cryo stuff, I would have got support by a fried who is
> physicist, otherwise I would not even have considered it (you cannot just
> put the JJA into the dewar...). There are some potential ways to cut the
> costs mentioned, e.g. by going with 1V instead, or having access to
> suitable 75GHz gear, but it is still a several 10k exercise.
> Overall, at least from my perspective, it was just not worth it. Quite
> some risk and lots of time until it works. So I continue to send my
> references to a good lab with well below 1ppm of uncertainty, and I have an
> independent cal document, even though of course, it would certainly have
> been a lot of (quite expensive) fun.
> > Gesendet: Donnerstag, 20. Oktober 2016 um 00:35 Uhr
> > Von: "Ken Peek" <ken.peek at diligentminds.com>
> > An: volt-nuts <volt-nuts at febo.com>
> > Betreff: Re: [volt-nuts] Low-cost Josephson Junction Array
> > @Vince:
> > Thank you for the link! Very informative! There is also a nice video
> > showing some of the lab techniques, and some cautions working with
> > cryogenic liquids.
> > I would also like to explore miniature cryocoolers-- as these might be
> > to support a small lower power array (1V) if it doesn't dissipate too
> > power...
> > There is already some progress in this area with a QHR made from graphene
> > (at the NPL in the UK). So, maybe the same cryocooler could be used also
> > for the low-cost JJA ?
> > Having a 10V (fixed output) JJA and a 12K9 QHR would be the basis to
> > calibrate all other electrical standards in a lab. It would be nice to
> > have these sitting in their cryocoolers cranking out volts and ohms
> > practically indefinitely (or as long as you want)-- and if one has even a
> > rubidium atomic clock, then no external signals or standards of any kind
> > would be needed. Well, that and a triple-point of water cell (which I
> > have) for temperature calibrations.
> > -Ken
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