Effect of Charge Carriers on the Prebreakdown Current Flowing Through a Parallel-Plate Vacuum Gap

Electrical charges carried by ions and microparticles passing through probe holes of a cathode were measured by means of a collector electrode, positioned behind the cathode. The contribution of these carriers to the prebreakdown current was discussed. The characteristics of the observed charge increase on the collector electrode composed of two parts; one was the abruptly increasing part caused by the sporadic arrival of microparticles, while the other part linearly increased with time due to the continuous arrival of ions. The ion current estimated from the latter and the prebreakdown current were dependent on the roughness of the anode surface rather than that of the cathode. Consequently, it was assumed that, besides cathode protrusion, a space charge effect caused by ions from the anode region plays an important role in forming the potential distribution near the cathode region.