Liquid helium breakdown in the /spl mu/s range

Breakdown time-lag characteristics in the /spl mu/s range were investigated with pool boiling liquid helium. An abrupt decrease in the statistical time lag was observed in a low electric field near 0.5 MV/cm and attributed to a change in the breakdown mechanism. Experiments were carried out using a pulse generator with 200 ns rise time and a long decay time constant of more than 1 ms. This generator provides a step voltage to the gap in the /spl mu/s range.