HOLLOW-CATHODE EFFECTS IN CHARGE DEVELOPMENT PROCESSES IN TRANSIENT HOLLOW-CATHODE DISCHARGES

A detailed experimental study of space charge formation and ionization growth in Transient Hollow Cathode Discharges (THCD) is presented, Th e experiment was performed with an applied step voltage up to 30 kV, w ith rise time less than 50 ns, The discharge was operated in different gases, at pressures in the range 50-750 mTorr, with cathode apertures ranging from 1 to 5 mm diameter and 5 to 20 mm long, with 10 cm elect rode separation, Spatial charge formation, both in the Hollow Cathode Region (HCR) and inter electrode space, has been studied with a capaci tive probe array. Properties of high energy electron beams have been m easured with a beam-target scintillator-photomultiplier arrangement, D etailed correlations of the electron beam evolution with the charge pr obe signals inside and outside the HCR clearly demonstrate the role of the electron beam in the initial formation and late evolution of a vi rtual anode and, in turn, the field enhanced ionization when the anode potential is brought close to the HCR, These results clearly identify the different regimes in which the Hollow Cathode plays a significant role in ionization growth in the inter electrode space and in the pro cesses which eventually lead to electric breakdown.