Parametric Excitation of Drift Waves in a Resistive Plasma

The parametric excitation of drift waves in an inhomogeneous resistive plasma is derived from the fluid equations. In the particular case studied, the plasma is pumped by a drift wave at ω0 and responds at a frequency ω1 = 12ω0. Plane geometry is assumed throughout this paper but periodic boundary conditions in z (direction of the uniform magnetic field) and in y (azimuthal direction) are assumed, to simulate experimental conditions with cylindrical or toroidal geometry. The resulting discrete spectrum of drift waves is assumed stabilized by end plate effects (for lower-frequency modes) or by ion-ion collisions (at higher frequencies). The threshold amplitude for parametric excitation is calculated and the enhancement of fluctuations below threshold leading to enhanced particle diffusion toward regions of decreasing density is calculated. The possibility of measuring the enhanced fluctuation spectrum by microwave scattering experiments is also studied.