Excitation of lower-hybrid waves by the rf heating of Elmo Bumpy Torus Scale

Abstract

The substantial ion heating of toroidal plasmas at rf frequencies between the ioncyclotron and lower-hybrid frequencies suggests that some additional process or processes must supplement conventional harmonic ion-cyclotron coupling of wave energy to particles. It is proposed in this paper that superthermal lower-hybrid turbulence excited because of the harmonic oscillating two-stream instability could contribute in a significant way to this observed heating. The threshold field strength for such a process to occur in the Elmo Bumpy Torus Scale is calculated. Specific tests of the theory, measurement of an enhanced lower-hybrid and quasimode spectrum, particularly at harmonics of the pump frequency, are indicated. The impact of the harmonic oscillating two-stream instability as allowing rf heating at frequencies a factor of 2 or 3 below the lower-hybrid frequency is described.