Electrical breakdown triggered by free conducting spherical particle in saturated liquid HeI and HeII under uniform DC field

Pre-breakdown phenomena and breakdown characteristics in the presence of a free conducting spherical particle in saturated normal liquid helium (HeI) and saturated superfluid liquid helium (HeII) under uniform dc field are studied experimentally. The results show that microdischarge occurs between the electrode and approaching oppositely charged particle and a bubble generates at the moment of particle collision with the electrode both in HeI and in HeII. The clear discontinuity in the characteristics of breakdown voltage vs. pressure at the /spl lambda/-point is found.