Abstract
This paper describes the results of an experimental study on d.c. breakdown voltage characteristics on supercritical helium under the non-uniform electric field to assist the development of superconducting magnets cooled by supercritical helium.
At a certain value of the density, ρc, a maximum breakdown voltage is observed in the breakdown voltage versus density characteristics. In the case of negative needle, the breakdown voltage is proportional to the density ρ below ρc.
When ρ>ρc, the breakdown voltage becomes almost independent of the density. The ρc v.s. temperature curve, obtained from the measurements at different temperatures, agrees well with a pseudo-critical line, which is the phase transition line between pseudo-gas and pseudo-liquid phase of supercritical helium. It is pointed out that the breakdown mechanism supercritical helium in pseudo-liquid phase is defferent from the mechanism in pseudo-gas phase.
