Single-pass ion cyclotron resonance absorption

The ion response to the rf-field during single-pass ion-cyclotron resonance heating (ICRH) can be essentially nonlinear. This paper presents a self-consistent theory of the rf-wave propagation and ion motion through the resonance. An important ingredient of the problem is the ion flow along the magnetic field. The flow velocity limits the time the ions spend at the resonance, which in turn limits the ion energy gain. A feature that makes the problem nonlinear is that the flow accelerates under the effect of the ∇B force and rf-pressure. This acceleration can produce a steep decrease in the plasma density at the resonance, resulting in partial reflection of the incident wave.