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 arc (FVA) method have attracted much attention due to their superior mechanical and optical properties. However, the instability of the arc 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. Arc 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 arc spot movement. A tapered cathode exhibited a more stable arc 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 arc 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.