Cathode spot motion in a vacuum arc with a long roof-shaped cathode

Vacuum arc cathode spot motion was investigated on a “roof-shaped” aluminum cathode. This roof geometry included flat roof-top and four sloped sides, inclined by an angle α. A high speed camera was used to observe cathode spot motion in an external axial magnetic field. The spot velocity on the slopes and the distribution of cathode spots between the roof and slopes was determined. It was obtained that under a magnetic field the spot motion on the roof was slow (<;1m/s) and mainly random, while on the slopes fast retrograde motion was observed. This velocity increased linearly with the magnetic field, and decreased slightly with α. The general behaviour of the spot motion agreed with previously published data.