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   gigabecquerel (gigabecquerel@chaos.social)'s status on Wednesday, 22-Nov-2023 05:34:45 JST gigabecquerel

   • std_logic_vector

   Science is cool!
   And this thing here even more so.
   I got to take apart an Adiabatic Demagnetisation Refrigerator Cryostat with the wonderful @stdlogicvector , a small cryostat that was used to cool a transition edge sensor to ~40 mK.
   It works by applying a magnetic field to some funny materials, and when removing that field the material cools down below its original temperature, which is 4.2 kelvin in this case.
   The main cooling is done by a huge amount of LN2 and LHe.

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     gigabecquerel (gigabecquerel@chaos.social)'s status on Wednesday, 22-Nov-2023 05:34:31 JST gigabecquerel

     in reply to

     This is the magnet itself. As stated earlier it's entirely submerged in LHe to cool it down, afaik it's NbTi used at up to 7 T. It has to be in LHe because its critical temperature is around 10 k.
     Interestingly enough it consists of two separate windings with entirely different construction! Maybe one was added later for higher fields, but I don't know

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     gigabecquerel (gigabecquerel@chaos.social)'s status on Wednesday, 22-Nov-2023 05:34:34 JST gigabecquerel

     in reply to

     The cryostat coinsists of many layers, it's built like an onion.
     This serves to reduce thermal load vial radiation, with the 77k stage sinking the biggest load, after all, LN2 is a lot cheaper than LHe.

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     gigabecquerel (gigabecquerel@chaos.social)'s status on Wednesday, 22-Nov-2023 05:34:37 JST gigabecquerel

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     This is the thermal switch. It links the ADR thermally to the 4k stage when everything is being cooled down and while the magnet is being ramped up. Then the switch opens, separating the ADR themally and letting it cool down below 4k when the magnet is ramped down again.

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     gigabecquerel (gigabecquerel@chaos.social)'s status on Wednesday, 22-Nov-2023 05:34:40 JST gigabecquerel

     in reply to

     The entire cryostat consists of an LN2 tank which provides heat shielding and a LHe tank as a "warm" stage. The bottom of the LHe tank forms the base plate and thermal anchor where everything is bolted onto. Inside the tank is the ADR Magnet which we'll get to in a minute. Inside the magnet bore, held by kevlar strings, is the ADR itself. Everything is wrapped in foil for thermal insulation.

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     gigabecquerel (gigabecquerel@chaos.social)'s status on Wednesday, 22-Nov-2023 05:34:42 JST gigabecquerel

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     There was some kind of experiment left over in there, I'm guessing it's a remnant of the CRESST experiment, a crystal, a collimator and a photodiode, so maybe scintillation yield measurements?

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     James Morris (jmorris@social.kernel.org)'s status on Wednesday, 22-Nov-2023 05:38:23 JST James Morris

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     • std_logic_vector
     @gigabecquerel @stdlogicvector until seeing this, I'd assumed that going below 4K was infeasible for a hobbyist (assuming you can even get LHe now). Any idea if these turn up as 'for repair / parts' on the surplus market?
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     James Morris (jmorris@social.kernel.org)'s status on Wednesday, 22-Nov-2023 05:50:52 JST James Morris

     in reply to

     • std_logic_vector
     @gigabecquerel @stdlogicvector until seeing this, I'd assumed that going below 4K was infeasible for a hobbyist (assuming you can even get LHe now). Any idea if these turn up as 'for repair / parts' on the surplus market?
     
     ETA: or does it need He3 ?
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     gigabecquerel (gigabecquerel@chaos.social)'s status on Wednesday, 22-Nov-2023 19:12:23 JST gigabecquerel

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     • James Morris
     • std_logic_vector

     @jmorris @stdlogicvector Never seen one before, and no, it does not need ³He, just regular LHe

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     gigabecquerel (gigabecquerel@chaos.social)'s status on Saturday, 25-Nov-2023 03:48:56 JST gigabecquerel

     in reply to

     Better sample preparation should do the trick.
     Casting two pucks of epoxy with the SC wire in all directions, one to be etched, one to be left as is after polishing.
     Now comes the hardest part, waaaaaaiting

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     gigabecquerel (gigabecquerel@chaos.social)'s status on Saturday, 25-Nov-2023 03:48:58 JST gigabecquerel

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     • Breaking Taps

     the magnet is doing its best not to come apart in one piece.
     They used the *good* resin, as well as way too much glass fiber reinforcement.
     At least too much to be any fun when taking it apart again.

     I took some SEM shots of the wire, and you can kinda see how it's NbTi embedded in a copper matrix, but to be honest, I was hoping for way more contrast with the SE detector.
     BSE is broken, and EDX is in the works...
     Maybe @breakingtaps has any tipps?

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     gigabecquerel (gigabecquerel@chaos.social)'s status on Saturday, 25-Nov-2023 03:48:59 JST gigabecquerel

     in reply to

     I think that's all for now, but I'm sure I forgot something. If you have any questions feel free to ask!
     I'm sure there will be more images of everything, especially the magnet, as we want to take it apart to get to the NbTi wire.

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     gigabecquerel (gigabecquerel@chaos.social)'s status on Saturday, 25-Nov-2023 03:49:00 JST gigabecquerel

     in reply to

     And here, finally, is the ADR itself.
     At this point I was pretty tired and forgot to take pics of the good stuff :<
     You can see the two stages hanging on kevlar threads, the entire assembly would be sitting inside the magnet bore in its original position.
     The stainless tube is the second ADR stage, consisting of ferric ammonium sulfate. This salt is slightly hygroscopic, and through years of storage it accumulated water which caused it to swell.