Metalwork parts for cryostat

As already hinted in previous post I’m slowly building a full-featured cryostat for experiments with cold electronics. We got chamber, but to make it functional it has to be vacuum tight and allow mounting of cryogenic refrigerators that I got in the lab. For this to happen custom xDevs adapters were ordered at CNC fabricator, thanks to my friend David. Cryostat designed for RDK-408 head which has 8 mounting points and adapters would fit into position that mimics such head.

There are some surface marks on aluminum parts which look like tiny lightning discharge trees. Perhaps it was a result of dirty handling during electropolishing process. I can buff these marks off with ScotchBrite without much problem, so I don’t expect big problems to clean and prepare surfaces for sealing.

Just few minutes already cleaned up half of the marks on the round adapter for STI cooler:

Rectangular shape lid was manufactured to seal the interface box with huge oval opening. There is a step on the inner face to allow O-ring compression.

It looks nice and shiny, even mount holes align well!

Test fit to cryostat lid also matches well with supporting dimension for O-ring seal.

Center port is designed to fit KF40 sealing O-ring and should work with KF40 port that STI Saphirre has integrated. Just need to add standard bulkhead clamp to mount cryocooler and establish a seal.

Cryocooler is mounted in original STI chassis with two socket head bolts. Removal from the chassis was straightforward with careful removal of the wiring to the controller electronics board.

I already have a specimen for tortures to act as a heat load to the cold finger. You guessed it, it is bad LTZ1000CH chip :)

And finally cold head in a proper position, looking good together:

Now if I think about future and get serious with really cold temperatures, such as 4K I’ll need very different cold head unit. Lucky for me, Cryomech (now Bluefors) PT407 is just available on the shelf in my lab. It is much larger to baby STI Saphirre cooler and has large stainless steel flange with 6 mount points. Also because this head is much heavier and will be eventually permanently mounted to the cryostat for long-term experiments I’ve opted to fabricate adapter with proper stainless steel material.

Essentially ring converts Cryomech/Bluefors PT407 flange to SHI RDK-408 port.

Blue foam insulation helps to reduce parasitic heat radiation towards the first stage regenerator and both stages pulse tubes.

There will be minor adjustment required on the larger foam blocks to clear the cryostat lid surfaces, but should be no problem once I get to installation.

Second stage will have massive copper donut for thermal anchoring the thermal shielding for the sensitive second stage. Few more holes will be drilled in the walls for mounting future hardware on it.

And PT407 test fit with adapter ring attached confirms good dimensions, yay!

It looks pretty nice all together.

And finally all toys together. There is one more 10K 2-stage GM cryocooler hiding behind the thermal chamber.

To be continued…

Stay tuned and let us know your feedback on this post! Discussion about this and related stuff is also welcome in comment section or at our own IRC chat server: (port six-zero-ten-zero, channel: or via e-mail.

Author: Ilya Tsemenko
Created: Nov. 15, 2023, 5:34 a.m.
Modified: Nov. 24, 2023, 12:31 a.m.