CORRELATION OF CURRENT QUENCHING AND OCCURRENCE OF METAL VAPOR IN A PSEUDOSPARK DISCHARGE

The quenching phenomenon, i.e., a sudden interrupt of the discharge cu rrent, was investigated in a pseudospark discharge with charging volta ge of 2.5 kV, maximum current of 2 kA and discharge duration of 3 mu s . The working gas was hydrogen at a pressure of 40 Pa. Concerning elec trode material and geometric parameters, molybdenum electrodes were ch osen with hole diameters of 5 mm; the electrode distance was 3 mm. In this parameter range, a temporal correlation of current quenching and the occurrence of metal vapor could be detected by means of time-resol ved optical spectroscopy. With each current interruption a sudden incr ease of emission from neutral molybdenum atoms as well as an increase of cathode spot emission, which is spatially localized on the cathode, occurs. Also oxygen ions were observed which show a similar time-depe ndence, however with a significant delay of the order of 200 ns. The r esults are discussed in the scope of the mechanism proposed for quench ing, i,e., ion depletion in the plasma boundary layer, and the mechani sms occurring in the high current phase of a pseudospark discharge.