Electrical Breakdown Mechanism of Cryogenic Liquid Coolants in the Presence of Thermal Bubbles

Abstract

Electrical breakdown mechanism of liquid nitrogen or liquid helium is investigated in the presence of thermally induced bubbles to simulate the quemching state in superconducting magnets. The results show that the mechanisms are classified into three categories which are related to the slope of the applied voltage: breakdown without deformation of suspended bubble at fast rising voltage, breakdown with elongation of suspended bubble at medium rising voltage and breakdown through locked vapor at slow rising voltage. The investigated subjects may relate closely to the phenomena in superconducting pulsed magnets or AC superconducting apparatus in which AC loss is produced together with a high voltage.