HIGH-CURRENT ELECTRON-BEAM GENERATION IN A VACUUM TRANSIENT HOLLOW-CATHODE DISCHARGE

Experimental observations are presented of prebreakdown electron beam generation in a Transient Hollow Cathode Discharge (THCD) in a vacuum. The discharge driver consists of a 400 kV maximum voltage, 25 nF Marx operated at 450 J stored energy coupled to a 120 ns, 1.5 Omega coaxia l line. Electron beams with peak currents up to tens of kA are observe d when a pulsed Nd-YAG laser is used to produce a plasma at the back O f the cathode surface, inside the Hollow Cathode Region (HCR). It is f ound that a plasma density of a few 10(18) cm(-3) in a volume of a few mm(3) is required to generate intense electron beams. Optimal conditi ons are determined by varying the position of the laser focal spot ins ide the HCR and the time delay between the laser and the applied volta ge. The main features of the electron beams are similar to those obser ved in conventional THCD at pressures in the 10-200 mtorr range.