Features of microseconds arc discharge with gap spacing of micrometers, between a cathode of thin tungsten wire with sharpened tip and an anode of stainless steel plate, have been experimentally investigated. The experimental setup, which consists of a micro-arc torch, precise positioning mechanisms actuated by piezoelectric devices and pulse motors, and a power supply for discharge, was constructed. Time-resolution of micro-discharge appearance was observed through microscope with high-speed shutter CCD camera. It is shown that gap length is dominant factor of not only electrical breakdown voltage but also size and/or form of melting spot at anode surface by micro-arc.
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