Saturation of a single mode driven by an energetic injected beam. II. Electrostatic ‘‘universal’’ destabilization mechanism

The formalism to describe the saturation of a discrete mode that is destabilized by hot particles fed by neutral beam injection is extended. The destabilization mechanism described in this work arises from the density gradient in the distribution function formed from a spatially inhomogeneous source. Energetic particles are injected at a fixed speed and collisionally relax through drag and pitch-angle scattering with the background plasma. The distribution formed is solved self-consistently in the presence of a finite amplitude wave in a sheared magnetic field. Three regimes of collisionality are found and the expressions for the nonlinear wave–particle power transfer is determined in each regime. With the dissipation processes of the background plasma given, the wave saturation level is then determined. When pitch-angle scattering is sufficiently weak, particles trapped in a wave convect across the magnetic field as they slow down, a phenomenon similar to the Ware pinch.