I have never heard such a recommendation before. I know of magnets that have been "on field" for decades. As long as there is no uncommon increase in helium boil-off (this would indicate that the quality of the vacuum and thus the thermal insulation have become worse) I would leave the magnet untouched.

I agree with Wolfgang Baumann . There are many supercons that weer energized 20 years ago that show no signs of deterioration (I am in the field since a long time and in a very "social" way, meaning that I know in excess of 200 or so labs).

Of course, some vendors may be starting to enforce new maintenance-quality rules (by itself, that would make sense). But, apart from the contradicting experience, insisting on so frequent full maintenance is strange (and suspicious). Today, few vendors guarantee service after 7-10 years. After that, if a User's magnet quenches, it is not their problem and the vendor can only rejoyce (new magnet).

And supercon magnets, once energized, were always one of the most reliable pieces of technology. Nothing breaks less frequently. Even though basic physics tells us that the probability of a spontaneous quench can never be zero, proper technology has lowered it a lot.

Moreover, full maintenance of a magnet is actually a quite risky operation - it involves de-energization, venting out the cryogens, bringing the vacuum in the dewars to normal pressure, replacing quite a few things, repumping the high vacuum, refilling the cryogens, reenergizing the magnets and its cryo-shims, and shimming them properly. All that is risky (frequent quenches), can be done more or less properly (field homogeneity) and can change the magnet boil-off rate (in both directions). Actually, it should cost a very significant portion of the magnet price!!! And all that just to avoid a very remote chance of a spontaneous quench (which, in the worst case, can be followed by the same procedure after it happens, if it happens)?

Come on; somebody is pulling your leg :-)

Thank you all of you for detailed answers. Actually it was recommended by NMR engineer only but I was a bit reluctant to go ahead for that. This helps a lot. Thank you all once again.

I have to second to Wolfgang Baumann and Stan Sykora - there is no need to uncharge and warm up a perfectly functioning NMR solenoid - normally they last untouched 25-30 years; the reason to replace them may be either disturbing stray field (newer ones are much better shielded) or too low field strength (2-3 times higher fields may be available for even cheaper price)...

Some NMR magnets contain a stability coil, a secondary circuit that couples to the main magnet to reduce the apparent field drift of the magnet. As the induced current in this secondary circuit increases it will eventually reach its limiting performance and quench. This could quench the main field coil or just cause a shift in the frequency. Typically the coils are designed to last a minimum of 10yrs but may last much longer depending on the base drift of the magnet. This is probably why it was recommended to re-ramp the magnet.