Troubleshooting Quenched NMR: Stuck on Superconducting Shim Z2

[zen loki]

I have a real stumper for you guys. We have an 7T (300 MHz) NMR in our lab that recently quenched – the superconductors went normal and we lost all our helium. That is can be pretty bad for a magnet, but we think ours got through it without significant harm. We have been getting it back up and running but there is one point we are stuck on. We need to get the superconducting shims operating, but there is a single shim (Z2) that we don't know the proper pinning for. The rest of them we know exactly but that last one has us stuck. The only pinning information we have has nothing about Z2 superconducting shim, though we know we have one. Our best guess is that the z2 shim is activated at the same time as the main coil, though that seems really odd.

What makes this all the more frustrating is the fact that there is no model number or make, printed on the exterior and the only the only documentation is for related machines - again without names. It was put together by Varian, though they don't have documentation for it any more. It is 13 or more years older. The magnet itself was made by Oxford and the internal dewars by Kadel Engineering.



Does this look familiar to anyone ?

 

[Mike H]

The possibility that there may be some sort of interplay between the main coil and the Z2 superconducting coil makes a vague sort of sense based on the fact I've heard of Z2 coils being wrecked during a quench. (You're lucky I've been going through my magnetic resonance literature and had my memory jogged at the moment, the citation for this wrecked Z2 coil is "Design and Assembly of an 8 Tesla Whole-Body MR Scanner". Nov./Dec. 1999. Journal of Computer Aided Tomography. Vol. 23(6): 808-820.) However, your magnet doesn't ring any specific bells in my memory, it looks like all of the other 7 T magnets I've seen.

I would suggest doing one or all of the following:

- contact Oxford Instruments;

- contact your nearest university NMR facility (there's usually at least one or two engineers in every NMR facility I've seen), unless this magnet belongs to such a facility. Am guessing that this is a specific lab magnet, based on the clutter on the bench, as most facility managers try to keep things slightly more orderly. ;)

- if you have an electronics shop, you may want to check over there for a useful word or two.

I hope you and your colleagues get your magnet back up and running. Good luck!