Lifetime of passive quench protection diodes in the SSC

A passive quench protection system using cold bypass diodes is being considered for the Superconducting Super Collider (SSC). The diodes would be located inside the magnet cryostat, which would subject them to liquid helium temperatures and a relatively high radiation flux. Results of experimental measurements of radiation damage to a candidate diode at 5 K and an estimate of the lifetime of this diode in the SSC are presented. An unexpected relationship was discovered between the diode turn-on voltage at 5 K and the most recent reverse voltage or temperature excursion. This turn-on voltage as a function of radiation exposure appears to be erratic and indicates a need for further investigation. High-current I-V measurements indicate that the usable lifetime of this diode, based on an estimate of the peak junction temperature during a quench pulse, is an order of magnitude greater than the expected lifetime of the SSC itself. >