Lichtenberg Figures Produced by High-Voltage Discharges in Vacuum

Abstract
The formation of Lichtenberg figures on aluminum and titanium electrodes covered by oxide and nitride layers while being exposed to high vacuum and 100-kV (rms) 60-Hz voltage is recorded. The observations were made in the course of research on high-voltage vacuum insulation for cryocables. The Lichtenberg figures have several technological implications. They provide evidence for the occurrence of 1) focused ion beams, and 2) tangential discharges in the adsorbed layer of gas on the vacuum side of dielectric coverings on metal conductors. As Lichtenberg figures can only be produced by fast high-voltage pulses, they prove that the discharge duration was short compared with the period of the 60-Hz voltage wave.