Re: helium blowoff

Jincheng Xiong (jincheng@lamar.ColoState.EDU)
Wed, 16 Aug 1995 12:43:24 -0600

We have 8 superconducting magnets (ranging from 90 MHz to 600 MHz)
in our lab. In my experience, the variation of LHe and LN2 boiloff
rate is more related to the variation of room temperature. Your
observation may be explained by the cycle of room temperature.

Another thing is that the variation of boiloff rate over time may
be due to the check valve installed on the exausted He gas vent
port of the magnet. Only when the internal pressure of LHe dewar
reach to a certain pressure (set on the check valve), you can observe
the flow of the venting He gas. I don't know if you have a
check valve installed on the magnet or not. It's better to install
one to avoid ice jam formed in the LHe dewar. I also found that
a check valve with proper pressure threshold setting installed on
the He gas vent port can sometimes effectively cut down the
He boiloff rate by 1/2.

Jincheng Xiong
Chemistry Department
Colorado State University
Fort Collins, CO 80523
Tel: (970)491-5404
Fax: (970)491-1801
email: jincheng@lamar.colostate.edu