Effect of magnetic field structure near cathode on the arc spot stability of filtered vacuum arc source of graphite

Amorphic diamond films deposited by the filtered vacuum are (FVA) method have attracted much attention due to their superior mechanical and optical properties. However, the instability of the are limits the continuous operation of the FVA source, resulting in a poor productivity. In the present work, we investigated the effects of the cathode shape and the structure of the magnetic field near the cathode on the erosion behavior by both computer simulations and experimental studies. Are instability in the configuration of parallel magnetic polarities of the source magnet and the extraction could be suppressed by placing a permanent magnet of opposite polarity behind the cathode. We show further that oscillation of the current of the source magnet was effective in extending the area of the are spot movement. A tapered cathode exhibited a more stable are than a cylindrical cathode, as confirmed by the time variation of the beam current. By using the oscillating current of the source magnet and a tapered cathode of diameter 80 mm, a continuous operation for 2000 min with an are current of 60 A was obtained, at which more than 90% of the cathode volume could be used. A stable beam current of about 350 mA was obtained under the present operating conditions. (C) 2000 Elsevier Science S.A. All rights reserved.