Hello Hla,
I am concerned that the "leak" you have observed may not be the root problem you are facing.
Your image shows the rate of helium boil-off as it escapes through the one-way valve, correct?
So in other words, it doesn't matter how much helium might be escaping through the leak, you
also see increased helium flow through the one-way valve.
Therefore, that leads to the question: why are you seeing an increase rate of helium boiloff?
There are two answers that immediately come to mind.
The first one has been mentioned previously: perhaps the vacuum has gone
a little soft in the Dewar. The usual indications that the vacuum has
gone soft is that you will see cold spots on the magnet Dewar. Maybe a
little condensation, or in the extreme case frost. If you have access to
a thermal camera, it might show you different temperatures along the
surface of the Dewar even if the temperature gradient isn't leading to
the formation of condensation.
If it is a problem that your magnet vacuum has gone a little soft, then
I think the only solution is to rebuild the magnet.
The second possible cause happened to me about 5-6 years ago.  We had
an issue with the pneumatic anti-vibration lift system of one of our
magnets leading to one of the three legs becoming over-inflated. The
effect was subtle, but instead of being perfectly vertical, the magnet
tilted forward ever so slightly. The tilt was enough to cause the
liquid nitrogen Dewar to make thermal contact with the outer wall of the
magnet, and we saw increased boiloff of the liquid nitrogen.
I adjusted the height of the third leg so that the magnet was perfectly
vertical, and the magnet has been behaving well ever since.
You mentioned connecting your magnet to a helium recovery system.
Perhaps somehow the magnet was inadvertently disturbed from the usual
vertical orientation. Using a simple bubble level (non-magnetic, of
course), can you check to see if your magnet is perfectly vertical?
Or, perhaps a simpler experiment, what happens when you turn off the
pneumatic legs? Does the helium boil-off rate change?
Good luck,
Bob.
On 2024-09-30 7:10 p.m., Hla Win via groups.io wrote:
>
>
>
> I have attached a few pictures in this mail. The area where the leak
> is, tape it off with electrical tape. I have contacted several people
> to access the magnet. I thought it's an o-rings, but then it's not.C2
> I hope to resolve the issue soon.
> Thanks.
> Hla
>
--
Dr. Bob Berno
Manager, NMR Facility
McMaster University, ABB-156
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Received on Tue Oct 01 2024 - 08:30:53 MST