Impulse-voltage breakdown of cold pressurised helium

Experiments on impulse breakdowns between uniform-field electrodes in helium are described. The breakdown fields of gaps from 1.27 to 6.35 mm are reported for helium conditions varying from 4.5 to 10 K and 0.395 to 0.82 MPa, corresponding to a density range from 25 to 140 kg m¿3. Comparisons with published direct-voltage breakdowns are made and the mechanisms discussed.