Dielectric breakdown of supercritical helium

The paper reports the results of an experimental investigation into the dielectric-breakdown behaviour of super-critical helium, in the range from 4.2 to 30 K and 0.4 to 1.5 MPa under d.c., a.c. and standard impulse voltages, to assist the development of superconducting power cables. At helium densities above 80 kg m−3, the uniform-field breakdown voltage for d.c. or a.c. is about 55 MV m−1 at 0.8 MPa and has a slight pressure dependence. In nonuniform fields, the breakdown voltage with a negative electrode is considerably increased by corona stabilisation in the density range from 30 to 83 kg m−3.