The lower hybrid frequency range wave emission in the ohmic discharge of the FT-2 tokamak

Abstract

The paper presents observations of plasma intermediate frequency range wave emission ((200--1000) MHz) performed in ohmic discharge of the FT-2 tokamak. The dependencies of the RF signal amplitude and spectrum on the plasma parameters and on the location of the probes are presented. Two possible explanations for this effect is proposed. One of them is related to the distortion of the electron distribution function due to the strong ripple of the magnetic field in the FT-2 tokamak. Second one is related to the existence of a beam of run-away electrons, the buildup of a fan instability responsible for the generation of synchrotron radiation in the range (10-80) GHz, and a complex chain of nonlinear decay instabilities leading to such a strong decrease in the frequency of the observed oscillations. Keywords: tokamak, lower hybrid current drive, high frequency oscillations, parametric decay instabilities.