Role of the magnetic field in the cathode region during vacuum arc operation

Arc operation was studied in a vacuum arc deposition apparatus consisting of a Ti cathode, spacer, annular anode, straight duct, quarter torus macroparticle magnetic filter, and a deposition chamber. Superposition of fields from different magnetic coils allowed the formation of different field configurations in the vicinity of the cathode and in the cathode-anode gap. The analytical study of these fields together with the observation of cathode spot motion, made it possible to demonstrate the action of two mechanisms causing unstable arcing: (1) cathode spot movement off of the cathode surface to the side in the direction of the opening of the acute angle formed by the intersection of the field lines with the cathode surface, and (2) cutoff from the anode of the magnetized electron flow by the field lines. With an optimal field configuration both of the above mechanisms were avoided. The field configuration included (1) an arched field on the cathode surface, which rotated the cathode spots on the cathode surface, and (2) connection of a sufficient portion of the cathode surface to the anode with magnetic field lines, so that the random electron current in the vicinity of the anode can supply the required arc current.