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 in H2 and N2 at pressures between 30 and 750 mTorr with applied voltages up to 30 kV. A capacitive probe array is used to measure the spatial and temporal evolution of plasma formation in the interelectrode spacing. The results obtained are consistent with the formation of a moving virtual anode. The growth and evolution of the virtual anode are closely linked to the formation of electron beams emitted from the hollow cathode region before and at the time of electric breakdown.