Excitation of ion-cyclotron harmonic waves in lower-hybrid heating

Abstract

The parametric excitation of ion-cyclotron waves by lower-hybrid pump field is studied assuming that the magnitude of the pump is constant. The spatial amplification factor is calculated including the wavenumber mismatch as produced by the plasma density gradient, and the linear damping rates of the excited ion-cyclotron and sideband waves. The analysis is applied to plasma edge parameters relevant to the JFT2 heating experiment. It is found that ion-cyclotron harmonic modes are excited depending on pump frequency and plasma density. These modes are shown to have finite damping rates. The parallel refractive indices nIr of the excited sideband fields are found to be always larger than that of the driven pump field. Transition to quasi-mode decay is observed for the largest possible excited nl,, either by decreasing the pump frequency or by increasing the applied Rf-power.