Hi Rong,
As far as I know, quenching usually happens when superconducting wires go "normal". I do not think that pulling out a handle or scratching the surface of the bore can cause quenching (see also more info below) although I do not have first-hand experience in dealing with such situations. I would try to avoid shaking the magnet too much.
Regarding the scratching of the surface, it could potentially be a problem for either getting the sample in and out or for homogeneity of magnetic field if scratches are too deep. I think only spectrometer manufacturer can tell you how much you should be concerned about it.
If you feel that you can not pull the handle out of the magnet without applying extreme force, you may want to accept that you have a major situation. If the handle is stuck too tight, you will not be able to get it out until you remove the magnetic field.
I think it would be a good idea to get an advice from spectrometer manufacturer and if, things do not look good, inform your NMR manager (if you are not the one).
I wish I could be more helpful...
Check also AMMRL archives
here and
here.. May be you can find similar stories there.
Good luck again and, after you fix the problem, please let us know what you have ended up doing.
Mark
From:
http://www.mrr.com/service/quench.shtml
Quote:
A cryomagnet is basically just a closed loop of superconducting wire that allows an electric current to flow perpetually through it without any resistive losses, thus generating a stable, "permanent" magnetic field. The wires that are used to wind high field cryomagnets are only superconducting when cooled to very low temperatures. For this reason, cryomagnet coils are submerged in liquid helium at 4.2 degrees Kelvin.
Although there is no resistance in a cryomagnet coil when properly cooled and energized, there is a great deal of energy stored in the electric current. If, for any reason, a very small portion of the superconducting wire stops being a superconductor (goes "normal"), then the resistive heat generated in that section of wire will cause neighboring sections of wire to also go normal, resulting in a chain reaction that swiftly warms the entire coil and causes all of the stored energy to be dissipated as heat. This process takes only a few minutes, and can result in an impressive display of rapidly boiling liquid helium, similar to a geyser.
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Quote:
Originally posted by rong@Jan 1 2006, 06:06 PM
Hi,Mark:
* Thanks a lot!
* Here is more information about the situation.
* The LN2 outlet has a loose handle and when I was unscrewing the hose, the handle dropped and sucked into the bore immdiately.
* The spectrometer is 360MHz one and has a wide bore of 89mm.The handle is about 4-5 inch and was ten inches away from the bottom of the bore.I tried to pull this out first, but I can feel that it was held very tightly.I really don't know if pushing can work.I'm also concerned with if the stick will hit the bore or scratch the surface and cause the magnet to quench.
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