STUDIES ON THERMIONIC CATHODE ANODIC VACUUM ARCS

Vacuum arc discharges with evaporating anodes employing directly as well as indirectly heated thermionic cathodes are investigated. The observed volt-ampere characteristics of these discharges depend strongly on the temperature of the thermionic cathode, the evaporated anode material, and the relative position of the electrodes. A simple model describing the observed discharge characteristics is proposed. With respect to a possible coating application, the plasma of this arc discharge is investigated at a distance of 250 mm from the evaporating anode. For arc currents between 2 and 4 A and Cu as evaporating anode material, the deposition rate is between 3.5 and 5.1 nm/s, the degree of ionization ranges from 0.6% to 6.2%, and electron temperatures are between 5.8 and 15 eV. The observed directed energy of the ions exceeds 100 eV. An examination of the deposited Cu films reveals as main results: Purity>99.5%, compact structure, and smoothening of the film surfaces with increasing degree of ionization.