Electrical breakdown characteristics of electroformed copper electrodes in vacuum

The effects of copper deposits produced by three kinds of electroforming techniques on the breakdown characteristics in vacuum were compared. The electroforming was performed in (i) an acid sulfate bath with brighteners, (ii) a pyrophosphate bath, and (iii) an acid copper sulfate bath with periodic reverse electrolysis and electropolishing. Vacuum degassed oxygen-free copper was used as the substrate material. Electrical breakdown characteristics measured by repetitive breakdowns by applying impulse voltages revealed that the breakdown fields at the first application of voltage in vacuum were 13.4, 10.0, and 40.8 MV/m for the electrodes processed in the first, second and third baths, respectively. In addition an excellent conditioning effect was achieved without in situ electrode surface cleaning.