Cryogenic: How to check the impedance of the dilution refrigerator
Here we write how to remove the impedance of the dilution refrigerator and check the value.
1. Remove the impedance.
Remove the solder which fixes the impedance.
Apply pressure to 3, 4He line and cool the pipe with wet wipes to prevent the solder going into the pipe. A solder remover with a pump (for example, HAKKO 484) works well.
2. Check the value of the impedance.
Set the impedance to a pipe with solder. Connect the pipe to a gas bottle and apply pressure.
Set the other side into a syringe. If the impedance is not blocked, we will see bubbles. If the impedance is blocked, remove the block by washing with organic solvent.
When we applied 0.1 MPa to the main impedance of out dilution refrigerator, the amount of the gas was 2.8 ml in 5 minutes.
3. Set the impedance as the way it was.
Solder the impedance.
Check there is no leak or block in the 3, 4He line by using a He detector.
When we apply 10 mbar with He gas at the injection side of our dilution refrigerator, the He flow at pump side was 3e-8 mbar l/s at 3 minutes later.
Opening the 3, 4He line has some risks.
Work with experts.
Reference
「低温技術」, 小林俊一, 大塚洋一, 東京大学出版会 東京, pp 117 (1987) (In Japanese).