Behavior of conductive microparticles under electric field in vacuum and their influence on breakdown characteristics

Impulse breakdown voltage (BDV) for the gap which was injected with copper microparticles with a diameter from 7 to 500 /spl mu/m is measured. Electrode materials are copper, stainless steel, and an alloy of copper and chromium. In the short gap (approximately <5 mm), the BDV does not depend on the particle size or electrode material. However, in the long gap (>5 mm), the BDV varies according to the particle size and electrode material. Compared with the short gap, incrementation of the BDV with an increase in gap length is gradual. For both gap ranges, the BDV under negatively charged particles is lower than the BDV under positive polarity. The effectiveness of electrode surface roughness on the BDV is small compared with the clear gap. Further, AC voltages are applied to a rod-plate gap which was injected in the particles in order to observe their dynamic behavior. The particles begin to move when the upper direction electrostatic force originated by the AC field competes to the gravity force acting on the particles, and are finally removed from the area where the electrostatic force exceeds the gravity force as a result of reflection movements between electrodes.