EXPERIMENTAL STUDIES OF IONIZATION PROCESSES IN THE BREAKDOWN PHASE OF A TRANSIENT HOLLOW-CATHODE DISCHARGE

The ionization process in the prebreakdown phase of a transient hollow cathode discharge (THCD) is investigated. The discharge is operated i n H-2 and N-2 at pressures between 30 and 750 mTorr with applied volta ges up to 30 kV. A capacitive probe array is used to measure the spati al and temporal evolution of plasma formation in the interelectrode sp acing. The results obtained are consistent with the formation of a mov ing virtual anode. The growth and evolution of the virtual anode are c losely linked to the formation of electron beams emitted from the holl ow cathode region before and at the time of electric breakdown.