Long-delayed reignitions of the vacuum arc

Peculiar long-delayed (up to 200 mu s) breakdowns at voltages much below the interelectrode gap static breakdown limit have been observed following the forced extinction of the cathode-governed vacuum arc. The overall probability of such breakdowns has been determined in several combinations of the test voltage (5, 10, and 15 kV) and chopped arc current amplitude (50, 100, and 150 A). A time distribution of the long-delayed breakdowns has also been determined. A model of breakdown initiation, based on the action of droplets of molten electrode material, is proposed. It is shown by time-dependent model calculation that the macroscopic gap breakdown might be initiated by localized ionization growth in the region of an incandescent microparticle contact with a negatively polarized electrode. The statistics of the long-delayed breakdowns are correlated accordingly to the emission statistics of the microparticles capable of breakdown initiation.