Dear Piotr,
yes, have experience with exactly those observations. A very bad experience.
The magnet in question had a broken sealing anywhere. If everything is fine
there is an slight overpressure and if you open the magnet to insert the
transfer line, some cold helium gas comes out of the magnet. Nothing in my
case. Zero overpressure.
Helium level meter stopped to work about one year ago. Permanently showed a
helium level of about 46%.
Trying to fill helium either gave your observation or if your moved the
transfer line a little bit upwards, You immediately could see the "helium flame".
And the very bad part: the magnet quenched about 3 months ago.
What happened?
Due to the missing overpressure and the broken sealing anywhere air came
into the magnet and froze.
The ice first deactivated the helium level sensor, later it closed step by
step the tube to insert the transfer line
And the parts below within the magnet.
Tried to deice the magnet. Take the transfer line and blow gaseous helium
into the tube for the transfer line.
Requires some time, because the heat capacity of helium gas is low. After this
deicing procedure it was possible
To insert the transfer line without any problem, but the helium meter still
showed the unchanged value.
We tried to fill helium, but apparently there was much more ice not accessible
to the procedure mentioned above.
About one week later the magnet started to drift and quenched two days later.
Greetings
Rainer
> Von: main_at_ammrl.groups.io Im Auftrag von Piotr Dobrowolski
> Gesendet: Freitag, 12. Juli 2024 18:11
> An: main_at_ammrl.groups.io
> Betreff: [AMMRL] Helium fill problem
Dear NMR Managers,
Recently, we started having problem with helium fill on our old (about 25
years) 500 MHz Inova. Transfer line precooling takes a little longer than
before (I think) but there is no water condensation on the line. However,
from the beginning of the transfer the pressure in the transport dewar (60 L)
is high. We try to keep it below 2 psi by setting low gas flow (about 2 L/min).
I guess because of that the fill takes very long time - about 1 hour to
transfer 50-55 L. Unfortunately, our Oxford helium level monitor does not
work. We just fill-up every 3 months.
I've been taking care of this magnet for more than 6 years and the fill was
always efficient (20-25 minutes) with gas flow set to 5 L/min (pressure 1.5-2 psi).
Transfer line vacuum was pumped last year.
Has anyone experienced such issue? Does this indicate transfer line or magnet
problem?
Thank you,
Piotr
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Received on Fri Jul 12 2024 - 09:54:52 MST