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Position of erosion marks on the surface of single-crystal and coarse-grained cathodes after a short-pulse vacuum spark

The objects of experimental research were vacuum gaps (VGs) with electrochemically polished copper cathodes. Microscopic pre-breakdown changes on the surface of copper cathodes after exposure to the vacuum gap of short (20 ns) "high-voltage" (200 kV) triangular pulses, short (20–100 ns) "low-voltage" (25 kV) rectangular pulses in the current limiting mode with an external resistor are investigated, as well as constant voltage (8 kV) in the current limiting mode with a high-resistance electrode. The obtained results make it possible to record the pattern of microplastic changes on the cathode surface before the appearance of the first vacuum spark, as well as the pattern of the spark phase onset of the VG’s breakdown.