CURRENT DRIVE VIA MAGNETOHYDRODYNAMIC HELICITY WAVES IN A NONUNIFORM PLASMA

Fundamentals of low-frequency current drive produced by a packet of arbitrarily polarized nonlinear Alfvén waves in an incompressible plasma with an inhomogeneous equilibrium magnetic field and aligned fluid velocity are explored. Analysis of the equations of magnetohydrodynamics with electrical conductivity and kinematic viscosity using an eikonal formulation yields coupled nonlinear equations for the Alfvén wave amplitude and an induced magnetic field and fluid velocity. Introduction of suitable variables allows simplification of the nonlinear system into a system of coupled linear integrodifferential equations. Particular solutions relate the plasma current to the helicity of the Alfvén wave. Two separate and distinct agents contribute to the current drive process: (1) wave dissipation, and (2) spatial inhomogeneity of the plasma medium. The plasma inhomogeneities cause a direct transfer of helicity from the applied Alfvén wave to the equilibrium magnetic field and are connected to the damping of a single component of the wave fluctuation due to phase mixing. © 1990 American Institute of Physics.