Gopal -
Sounds a bit mysterious to me. Best and surest thing in this case
is to get someone experienced with LHe fills in there next time you
do a fill to see what's going on and show you the alternatives. It's
a bit of an art as well as science, and there's plenty of slips
possible. Lacking that someone in your own institution, a paid visit
from the magnet vendor, or from someone like MR Resources might be
worth it. Keeping the LHe under control is important.
Good luck !!
- Alan Olson, NIH
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From Alan Olson, Instrument Engineer
National Institutes of Health, NINDS
MRI Research Facility
10 CENTER DR, Room B1D-69, MSC 1060
Bethesda, Maryland 20892-1060
Phone: 301 496 8139, FAX: 301 402 0119
e-mail: awo_at_helix.nih.gov, olsoncna_at_adelphia.net(Alan)
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At 3:16 PM -0500 3/19/04, Gopal Subramaniam wrote:
>Dear AMMRL members:
>For the past 3 Helium fills (400 MHz) we couldn't get a complete fill.
>After sighting liquid helium out of the transfer line I insert short stem
>into magnet. A steady flow of helium gas plume from magnet slowed
>considerably after some 20 minutes or so. We used to stop at the point
>when the fill slowed. Last time I determined to wait as long as it takes
>to fill the magnet. I tried to increase the flow of gas & raised and
>lowered the transfer line into the Dewar to increase the fill rate. After 2
>hours I gave up and stopped. The fill was only 73%.
>As per the height chart on the Dewar, I had about 30L Helium to begin
>with, but after I finished I had nothing.
>I wonder whether I lost some Helium liquid from magnet because I
>filled for a long time. How do we know if the Dewar is empty during a
>fill?
>We use to take only 30 minutes for a fill, but I was concerned about
>low fills for the past 3 times and that's why I tried for a long time.
>Wonder if there is a problem with the transfer line, or it is simply the
>Dewar from our suppliers. Are there any extra fittings to assure a
>smooth helium fill.
>Appreciate your suggestions.
>---------------------------------------------------------------------------------------------
>Dr. Gopal subramaniam
>Department of Chemistry & Biochemistry
>Queens College, CUNY
>Flushing, NY 11367
>Tel: (718)-997-4123 FAX: (718)-997-5531
--
Received on Fri Mar 19 2004 - 16:34:14 MST