Hello All,
We have an AS500 magnet that is from 2003 but was rebuilt during a move in
2019. We recently noticed during a helium fill that the flow rate coming
out of the exhaust is significantly lower than usual and we have to put
more pressure to get the liquid transfer going, indicating a
likely blockage. This was rather surprising because the exhaust port is
behind a check valve all the time and we regularly check the o-rings on the
commonly disconnected ports, like fill, exhaust, etc.. After some detective
work, we figured out that the small o-ring on the cap, where the helium
level sensor is plugged into the tower, crumbled and was barely holding on.
I tried checking for ice down the fill port with a thumper but we had just
filled the magnet and the tip of the thumper quickly reached the surface of
the liquid bath without hitting any ice. I didn't feel comfortable fishing
around blindly down there. I believe that the sensor goes down the tower
into the can parallel to the fill port so it is not clear to me where and
how the potential ice blockage is impeding the liquid flow. Unfortunately
the magnet book doesn't show the inner architecture of the magnet.
We think that the exhaust for the magnet is fine as the flow rate for boil
off has not changed from historical values. We should be fine in the short
term but this is a problem I would like to resolve before it becomes a
larger issue. I am wondering if anyone successfully dealt with a similar
issue on one of these AS500s?
I think my only remaining option, short of warming up the magnet, is to
blow warm helium gas into the fill port when the helium level is lower. The
top of the coil is at 5% sensor level according to the magnet book, and we
generally fill the magnet when it hits ~45-50% (it is a nice full 60 L fill
with a single dewar). I think the ice level is likely down there at the
physical location of the corresponding sensor level. So a gentle consistent
flow of RT helium gas at around 50% level may potentially solve the issue.
Does anyone have tips for this as this will be our first attempt for a
procedure as intrusive with a magnet?
As usual, many thanks in advance to the community.
Best,
Hasan
--
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College of Chemistry
University of California, Berkeley
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Received on Fri Aug 22 2025 - 05:53:48 MST