Interesting that they're still providing 1-5 MW during the multi-year shutdown. The LHC won't even be running but the cooling infrastructure keeps going. Makes me wonder what the steady-state thermal output is across all of CERN. 200 MW peak during operations, but clearly something substantial even when the collider is off.
Yeah, it's probably not good to let your miles and miles of superconducting magnets get warm and expand, even slightly. At the scale of the LHC you're probably looking at meters of displacement across the whole structure.
A superconducting magnet that gets above superconducting temperature is probably a pain to reset.
First, all the stored circulating current instantly turns into heat, spiking the temperature and boiling the remaining liquid helium coolant, which expands and explodes its container if you didn't give it a way out. If you did, it asphyxiates everyone in the tunnel. If you have really good ventilation in the tunnel, you still lost a bunch of expensive helium.
Second, you have to refill the cooling system and cool the magnets down again.
Third, you have to reinject the circulating current that makes the magnetic field.
There's probably more fractal–complexity practical concerns as well.
I wonder if it’s to avoid thermal expansion, and maybe fatigue related to cycling of expansion and contraction.