Apparatus is described for generating an electron beam in the presence of a gas at a pressure higher than 100 Pa. The apparatus comprises an acceleration gap defined between a metallic cathode 18 having a flat surface spaced by a uniform predetermined distance from a metallic anode (20). A cable pulse generator applies a steep edged high voltage pulse by way of a transmission line (10) to the acceleration gap. The length of the acceleration gap is determined in dependence upon the peak voltage of the applied pulse, the rise time of the leading edge of the applied pulse and the capacitance of the acceleration gap in such manner as to generate a run-away current between the cathode and the anode.

Apparatus for generating an electron beam

The high-voltage pulses excitation of a glow-discharge electron beam source has been experimentally investigated. A solid aluminum cathode 2.5 cm in diameter with a concave front face was employed. The beam source was driven at voltages ranging from tens of kilovolts to values in excess of 100 kV by means of either a capacitor discharge circuit or a Marx generator. It has been possible to extract beams whose currents vary from the tens to the hundreds of amperes in helium at pressures of 50 mtorr to 15 torr. The pulsewidths ranged from 30 ns to 300 ns, and beam generation efficiencies between 14% and 57% were obtained. It has been found that the maximum peak beam current and the corresponding beam generation efficiency occur at an optimal gas pressure which is a function of the discharge voltage. The beam generation efficiency itself is seen to be primarily a function of the discharge current. >

R.E. Daniels

Papers

Electron beam production by a high voltage pulsed glow discharge