Low-pressure hollow-anode plasma sources for high-current electron beam generation

The operation features and the main physical parameters of different modifications of hollow anode (HA) plasma sources based either on multi-arc, or on magnetron-like, or on ferroelectric plasma source (FPS) ignition are described. It was found that these HA sources produce in the vicinity of the HA output grid a satisfactory unifonn plasma with a density n≈ 5×1012 cm-3. It was found that during the HA discharge the plasma acquires a positive potential of several te ns Volts. The HA with incorporated FPS demonstrated the best operation characteristics. It was found that the FPS allows reliable ignition and sustaining of the HA discharge with current amplitude Id≤1.2 kA and pulse duration ≤2×10-3 s at N2 gas pressure of ~ 10-5 Torr. During the HA discharge the density of the FPS surface plasma was found to be 8×1014 cm-3 that allows one to consider FPS as a practically unlimited electron source. In addition, the FPS allows one to decrease signiticantly the overall HA dimensions, thus providing a very compact design. All three HA modifications were used as a cathode in a diode powered by a 200 kV, 400 ns pulse. The parameters of the generated electron beam with an amplitude ≤1.5 kA and the diode characteristics are presented. It was found that the applied accelerating pulse causes a significant up to 6 kV increase of the plasma potential (φpl) inside the HA. A model that explains the electron emission from the positively charged plasma is proposed.