Suppression of High-Frequency Electron Beam Modulation in a Plasma-Filled Diode

The article presents the results of recent experimental studies of spontaneous electron beam modulation with a frequency of several tens of megahertz in a plasma-filled diode. The diode comprises a plasma cathode with a grid-stabilized emission boundary and a plasma anode with an open (conditionally electrodeless) movable boundary. The cathode plasma is formed by a cathodic arc and the anode plasma by toroidal plasma generators based on an anode-layer closed drift thruster. According to our previous studies, the beam current starts to modulate as the arc current goes above 50–55 A at an accelerating voltage of 12–22 kV. Here, we analyze how such electron beam modulation and its frequency are influenced by the grid geometry at a current of about 100–110 A and what methods can be used for its removal. The idea of removal consists in decreasing the effect of the accelerating voltage on the cathode plasma, for example, via a negative current feedback. It is shown that the most efficient modulation suppression is attained when the negative feedback is frequency-dependent and that the modulation frequency decreases to its complete disappearance as the grid mesh size is decreased.