Stochastic Ion Heating by a Lower Hybrid Wave: II
Abstract
The motion of an ion in a coherent lower hybrid wave (characterized by |kparallel| << |kperp| and omega >> Omegai) in a tokamak plasma is studied. For ions satisfying vperp > omega/kperp, the Lorentz force law for the ions is reduced to a set of difference equations which give the Larmor radius and phase of an ion on one cyclotron orbit in terms of these quantities a cyclotron period earlier. From these difference equations an earlier result [Phys. Fluids 21, 1584 (1978)] that above a certain wave amplitude the ion motion is stochastic, is readily obtained. The stochasticity threshold is given a simple physical interpretation. In addition, the difference equations are used to derive a diffusion equation governing the heating of the ions above the stochasticity threshold. By including the effects of collisions, the heating rate for the bulk ions is obtained.
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