Vacuum Arc Plasma Beam Produced From an Erbium Cathode

Er plasma was produced by a vacuum arc source with a truncated cone-shaped Er cathode and an annular copper anode. The plasma beam propagated into a cylindrical duct through the annular anode aperture and flowed in vacuum or in a low-pressure oxygen background along an axial magnetic field toward a substrate or an electrostatic ion current probe positioned on the duct axis. The cathode spot location and motion, the cathode erosion, the transport of the plasma beam in the duct, and the coating deposition rate were studied as a function of arc current, axial magnetic field, and oxygen pressure. Favorable conditions for stable arcs were obtained with relatively low arc current (I _arc = 30 - 50 A) and an axial magnetic field of 12 mT, which confined the spot motion on the cathode apex. Under such conditions, the rates of the cathode erosion and coating deposition were ~235 mug/C and 2-5 mum/min, respectively. With higher I _arc (150-175 A), the cathode spots tended to move on the circumference of the large cone base, eroding a deep groove, which significantly decreased the cathode life.