Quench protection of persistent current switches using diodes in cryogenic temperature

Transient characteristics of power diodes at cryogenic temperatures and their application to the protection of persistent current switches (PCS) in superconducting magnet systems are presented. The observed forward voltage drop was 9 V at 4.2 K and was six times larger than that at room temperature. The voltage was quickly reduced to 1 V after the diode was turned on. The transition time was less than 1 ms. A PCS with a normal state resistance of 1.5 Omega was adequately protected from quenching by the diodes.<>