INSTABILITY NEAR ELECTRON CYCLOTRON HARMONIC FREQUENCIES IN BEAM-PLASMA SYSTEM

When a weak electron beam is injected into a plasma in a thermal equilibrium, there appear the instabilities, which result in the excitation of the following waves; (i) the electrostatic cyclotron harmonic waves (CHW), (ii) the upper hybrid resonance wave, (iii) the fine structure near the cyclotron harmonic frequencies, (iv) the harmonic waves of half the cyclotron frequency and (v) the quasi-longitudinal (QL) waves in a low frequency range. The intensity of the microwave emission resulting from these instabilities is very strong and is larger by several tens d B than that emitted from the plasma in the absence of the electron beam. The excitation of CHW is ascribed to the interaction of CHW in plasma with those in the electron beam. The fine structure is due to the standing waves of CHW confined in the plasma column. The instability in the lf range is ascribed to a coupling of the QL waves in the plasma with the space charge waves in the beam. © 1969, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.