The influence of surface contaminations on the ignition and maintenance of vacuum discharges is discussed qualitatively. Surface analysis of the electrodes and gas analysis during the discharges demonstrate that fresh electrodes contain always impurities within the upper surface layers, which affect the behaviour of vacuum arcs and vacuum breakdowns. The most effective way for cleaning the surfaces are the dischnrges themselves, if they burn in UHV. During that cleaning the following variations have been found: Arc cnthodes spots change from rapid moving ones with small erosion (type 1) to slow ones with strong erosion (type 2). The ignition of nanosecond discharges needs higher field strength and field emission current density. Polishing effects by short discharges (< 5 n s ) become more pronounced. Erosion craters in nanosecond discharges increase.
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