OBSERVATION OF ENHANCED PREBREAKDOWN ELECTRON-BEAMS IN A VACUUM SPARK WITH A HOLLOW-CATHODE CONFIGURATION

The generation of prebreakdown electron beams in a low-energy vacuum spark with a hollow-cathode configuration is observed under a range of experimental conditions. The vacuum spark studied is powered by either a 25 kV, 3.3 nF single capacitor discharge or a two-stage, 50 kV, 1.65 nF Marx. The electron beams are detected by observing the X-ray emission from the anode tip produced by electron impact. Results show that an electron beam is formed well before the onset of the electrical breakdown. This prebreakdown electron beam bas an initial slow buildup phase followed by an exponential rise, leading to the breakdown of the discharge. The electron beam intensity drops sharply at breakdown. This behavior of the electron beam evolution is in good qualitative agreement with the model simulation of the pseudospark phenomenon obtained for a transient hollow-cathode discharge.