High-frequency electron beam generation by ferroelectric cathode with anomalous plasma resistance caused by ion-acoustic instability

Abstract

Summary form only given. We report results of spectroscopic research of high-frequency oscillations in the plasma produced on the surface of a ferroelectric ceramic sample which serves as a cathode. These oscillations appear when the accelerating pulse is applied to the sample and they are accompanied by emission of a high-frequency modulated electron beam. The plasma electron density and temperature were determined by comparison of the experimental results with the results of collision-radiative modeling. During the high-frequency oscillations a stationary pattern of spatial variation of the plasma density was obtained. An anisotropic electric field of amplitude /spl sim/1 kV/cm was found in the plasma by polarization spectroscopy of hydrogen lines. The obtained data are explained by excitation of nonlinear ion-acoustic waves in the plasma. These waves are excited at the vicinity of the cathode output grid and propagate towards the cathode. These waves turn into standing waves at the location where the wave velocity becomes equal to the velocity of the plasma propagating outward the ceramic surface. The measured electric field is explained by anomalous plasma resistance which is developed by interaction between the current carrying electrons and the ion sound waves. The high-frequency modulated electron emission is explained by the fast plasma potential variations at the vicinity of the output cathode grid. These fast potential variations are in resonance with the self-frequency of the external circuit.