GAP SIZE EFFECT ON LIQUID-HELIUM BREAKDOWN

Liquid helium breakdown depends strongly on gap size among other param eters such as liquid state, electrode surface quality and the kind of stressing voltage. A comparative study based on various references has been carried out to identify the type of size effect. A volume effect power law, indicating a d.c. breakdown strength decrease with an incr ease in the stressed liquid volume, has been evaluated as the most pro bable simple size effect formula. This simple formula can be used with great benefit for the design of superconducting apparatus. Specific w ithstand voltages across large liquid helium filled channels or gaps c an be reliably predicted.