https://en.wikipedia.org/wiki/Superconducting_magnet#Persistent_mode https://en.wikipedia.org/wiki/Superconducting_magnet#Persist... > An alternate operating m

https://en.wikipedia.org/wiki/Superconducting_magnet#Persistent_mode https://en.wikipedia.org/wiki/Superconducting_magnet#Persist... > An alternate operating mode, once the magnet has been energized, is to short-circuit the windings with a piece of superconductor. The windings become a closed superconducting loop, the power supply can be turned off, and persistent currents will flow for months, preserving the magnetic field.