High-Frequency Electron Beam Modulation in an Electron Source with a Plasma-Filled Optical System

Abstract

Experiments are reported demonstrating the generation of a wide-aperture electron beam with high-frequency modulation in a plasma-cathode electron source with a diode-type bipolar plasma-filled optical system. The plasma optical system is formed by a plasma cathode (plasma electron emitter) with a grid-stabilized emission surface and a lengthy plasma anode with an open movable plasma boundary. The system with its low impedance and high perveance can provide the required electron beam power density at a relatively low accelerating voltage (tens of kilovolts). The plasma in its anode region is produced by a plasma dynamic device based on a closed drift accelerator. The plasma cathode presents a hollow plasma electron emitter with a vacuum arc plasma generator on the inside. The electron source operates in repetitive pulsed mode at a pulse duration of $100 \mu\mathrm{s}$ , pulse repetition frequency of 10 pps, and electron emission current of up to 140 A. The experiments show that the beam in the acceleration gap of the plasma optical system gets into high-frequency modulation mostly at an accelerating voltage of $10\div 20 \mathrm{kV}$ and arc current greater than 60 A. High-frequency modulation is also observed in the emission current with no plasma in the anode region of the plasma optical system. The basic modulation frequencies are about 18 and 54 MHz.