Resonant Plasma Heating Below the Cyclotron Frequency
Authors: Roscoe White, Liu Chen, and Zhihong Lin
Date of PPPL Report: November 2001
Published in: Physics of Plasmas 9 (May 2002) 1890-1897. (Presented at the American Physical Society Division of Plasma Physics in Long Beach, CA, October 29 through November 2, 2001.)
Resonant heating of a magnetized plasma by low-frequency waves of large amplitude is considered. It is shown that the magnetic moment can be changed nonadiabatically by a single large amplitude wave, even at frequencies normally considered nonresonant. Two examples clearly demonstrate the existence of the resonances leading to chaos and the generic nature of heating below the cyclotron frequency. First, the classical case of an electrostatic wave of large amplitude propagating across a confining uniform magnetic field, and second, a large amplitude Alfvén wave, propagating obliquely across the magnetic field. Waves with frequencies a small fraction of the cyclotron frequency are shown to produce significant heating; bringing, in the case of Alfvén waves, particles to speeds comparable to the Alfvén velocity in a few hundred cyclotron periods. Stochastic threshold for heating occurs at significantly lower amplitude with a perturbation spectrum consisting of a number of modes. This phenomenon may have relevance for the heating of ions in the solar corona as well as for ion heating in some toroidal confinement fusion devices.