The onset of vacuum trigger discharges and microparticlehyphen;induced damage has been investigated by bombarding gold and tungsten wires with various diameter iron particles using the impact velocity range 2ndash;600 m/s. It was observed that when particles exceeded the elastic limit for gold extensive craters were produced which had sharp lips. This condition could not be achieved for the harder tungsten targets. The onset of trigger discharges was observed by measuring the light output, electrode damage, and voltage waveforms. It was noted that when bombardment was carried out with cathode wire fields in excess of 4times;107V/m trigger discharges and gap breakdowns occurred for particles having radii greater than 5ndash;10 mgr;m. Scanning electron micrographs of the resulting electrode damage show the localized nature of the trigger discharge. The trigger discharge results are shown to be in agreement with a computation of the onset of extensive field emission heating in the gap between the impacting particle and electrode.
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