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 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 :-)

I want to add to the previous answers, really NMR magnets are very reliable devices. They need only a field and cryo-shims correction.

If you have a field-sweep NMR magnet, then it only requires periodic pumping of vacuum insulation after a long idle. Сryo-free systems, the quality requirement for a vacuum is much higher and they require more frequent pumping of the vacuum volume. Replace O-rings is required only in case of not reaching the desired vacuum.

We have had the experience of completely discharging and transporting old SC-magnet from NMR-spectrometer Bruker MSL-300 (1986 created). Until 2010, it was always charged. In 2010, it was necessary to pump out the vacuum wall and recharge - the fireman, while checking the fire extinguisher, broke the rules, bringing the fire extinguisher close to the magnet and striking the flange.

In 2014, it was necessary to transfer it to another place. For this needed a complete disassembly and replacement the O-rings. It took a total of more than 3 months. The fact is that transportation requires complete disassembly of the magnet and mounting of the shipping inserts. Only pumping the vacuum volume to 10 ^-6 mbar took about a month. Plus, starting a magnet requires a lot of liquid nitrogen and liquid helium. Also, the charging field requires adjustment of the vertical position of the probe and a setting of cryo-shims.

The engineer said that the maximum chance of spontaneous discharge of the magnet when it is being charged, and if not to lower the level of liquid helium below the critical, then the chance of this is minimal. If a quinch magnet has occurred, then you can immediately add liquid helium and charge it, then the lost of liquid helium will not be so large.

Replacing the O-rings is only required when completely disassembling, for example, for transportation.

I opened the instructions for Sc-Magnet Bruker MSL-300 and did not find any requirements for periodic disassembly of the magnet.

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.