Hi Hia,
We had a leak in a similar spot, but the magnet was even older. The O-ring
had crumbled. Note that in our case the apparent boil off on the flow gauges
had gone down, not up, and the helium decrease in the can was normal. We
Replaced the O-ring.
I’m concerned like others that consumption has gone up. Pumping on
the dewar is short term fix to buy you time if the dewar has gone soft. If
there is a touch (and I have seen that also), pumping on it won’t
help, but would be diagnostic.
I can recommend a Helium sniffer
https://www.lesman.com/gg1saxxs-x that will
detect Helium leaks to atmosphere. And if you have recovery system, you should
probably have one - especially when setting up the system. It is a bit expensive,
but that is how we nailed down the leaking O-ring.
Good Luck!
Jeff
On Oct 1, 2024, at 8:22 AM, Bob Berno via groups.io wrote:
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. I hope to resolve the issue soon.
Thanks.
Hla
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