The Low Frequency Instability in a Plasma Produced by a Local Electron Cyclotron Resonance

Abstract

A low frequency oscillation, having a backward wave-type dispersion relation, is spontaneously excited in a plasma produced by local electron cyclotron resonance. The fundamental frequency of the oscillation is smaller than ion cyclotron frequency and is nearly proportional to the magnetic field intensity, Radially, the wave amplitude has maxima near the regions of maximum density gradient. The wave is observed to propagate in the direction of the ion diamagnetic velocity. The phase angle between density and potential wave is about 90° and density wave is leading. These characteristics of the oscillation are compared with those of the collisional drift wave. Further, a nonlinear effect characterized by the self-excitation of the subharmonic oscillations of 1/2, 1/3 and 1/4, and their higher harmonics are also observed.