Impulse and AC breakdowns of Ln/sub 2/ in the presence of thermally induced bubbles

In any practical superconducting system, thermally induced bubbles appear during the process of quenching or cryogenic stabilization. Under these conditions, a high voltage is produced. It is therefore necessary to evaluate the dielectric strength of a coolant in the presence of thermally induced -bubbles. Hara et al./sup (1)-(3)/ investigated the dc breakdown performance of liquid helium and nitrogen under such conditions from the viewpoint of insulation designs of superconducting magnet coils. Here, this paper reports the results of an experimental study on the impulse and ac breakdown characteristics of liquid nitrogen under the condition of thermal bubbling.