Author: Abhay Ram

Publisher:

Published: 2003

Total Pages: 48

ISBN-13:

The conventional ordinary and extraordinary modes in the electron cyclotron range of frequencies are not suitable for heating of and/or driving currents in spherical tori (ST) plasmas. However, electron Bernstein waves offer an attractive possibility for heating and current drive in this range of frequencies. In this paper, we summarize our theoretical and numerical results which describe the excitation of electron Bernstein waves in ST plasmas when the extraordinary mode or the ordinary mode are coupled into the plasma from an external source. In our discussion on the conversion of the ordinary mode to electron Bernstein waves (via the slow extraordinary mode) we illustrate very important physics, relevant to this conversion process, that has been ignored in previous studies. The particular physics has to do with the conversion of the slow extraordinary mode to the fast extraordinary mode that can then propagate out of the plasma and thus reduce the mode conversion to electron Bernstein waves. This reduction in the mode conversion can occur even when the wave numbers are such that the ordinary mode cutoff and the slow extraordinary mode cutoff are coincident in space. Furthermore, we also consider the emission of electron Bernstein waves from a thermal plasma. This emission mode converts to extraordinary and ordinary modes in the vicinity of the upper hybrid resonance. We describe the general relationship between the conversion coefficients when exciting electron Bernstein waves using either the extraordinary mode or the ordinary mode, and the emission coefficients when thermally emitted electron Bernstein waves convert to the extraordinary and ordinary modes.