In our Gemini 2000 NMR spectrometer (Varian R2D2 magnet), we have a safety tube (quench tube) that is firmly stuck with ice in the magnet's power port, so much that it can't even turn (rotate). Nor does any gas come out when we release the top of the port cap. We anticipate that it will take quite a bit of force to even pull up the port cap enough to get any helium gas down into the neck to melt the ice. Once we remove the cap and tube, we have a pretty good handle on safely removing the ice; the question is how to best remove the tube with minimal risk of damage to the magnet; we don't want to use so much force that we damage the internal layers in the magnet neck tube. I have a colleague who can use quite a bit of force on this thing, but in the past we'd damaged a port cap that way. We thought about heating up the port cap with a heat gun, but that might not be very effective. So getting the tube out is the more immediate issue. A more long-term issue is keeping ice from building up in the power port neck in the first place. This has happened to us periodically over the years, this time worse than others, and I have no idea where the ice is coming from. We tie off the Tygon tubing leading into the power port during helium fills to keep air from entering the power port; helium boiloff rates look normal, so there's not a huge leak coming out; other than that, I'm not sure where to begin looking for air leaks into the magnet.
Thanks -
Ruth
Ruth E. Nalliah, Ph.D.
Professor of Chemistry
Huntington University
Huntington, Indiana
rnalliah_at_huntington.edu<mailto:rnalliah_at_huntington.edu>
(260)359-4203 office/voicemail
Received on Thu Dec 15 2016 - 08:06:55 MST