Consider a liquid helium dewar. I have a hand-made cryostat and it fits exactly to the dewar. Cryostat is glass and it consists a vacuum jacket. When I put sample holder inside cryostat, sometimes it freezes. Why does it happen? Does the oxygen freeze inside?
It is probably air humidity freezing. So this depends of the weather if it is cloudy or dry. Did you notice the weather when it appends?
Thanks Dr. Leturcq.
I am preparing myself for a probable frozen helium dewar, I did not experience. I want to learn what to do in such situation.
I had a similar experience in my measurement set up before: My sample holder for four probe resistivity measurement was frozen. I used a glass cryostat but sample holder was sticked to cryostat.
I though that O2 was frozen inside (~54K ? wikipedia). Can this be possible? How can the surface of liquid helium freeze? Because of what mistake?
1 Do you wash you sample holder by alcohol? sometimes oil or fat adsorbed at the sample holder may freeze at the end of the cryostat.
2 You must check the seal leakage at the position which is connected the sample holder and the cryostat.
You can check the leakage by a helium mass spectrometer leak detector.