Quench Protection for Superconducting Insertion Magnets

Abstract

Quench protection for Nb-Ni insertion magnets (wigglers and undulators) has not been a problem. The reasons are; the quench is relatively easy to detect, the stored energy is low, the quench propagates rapidly, quench heaters work because the coil thermal diffusivity at 4.5 K is high, and quench protection resistors will work. Superconducting insertion magnets require very high current densities in the magnet coil in order to be competitive with permanent magnet insertion magnets. The need for high coil current densities makes superconductors like Nb3Sn and ReBCO HTS tapes attractive. The higher temperature superconductors have much lower quench propagation velocities, and the high-current-density versions of these materials often have much less copper in them than Nb-Ti. Since the quench temperature for these superconductors is two to ten times higher than Nb-Ti, the coil thermal diffusivity is much lower. This paper presents a number of quench protection options for insertion magnets made from materials other than Nb-Ti.