Renormalized Compton scattering and nonlinear damping of collisionless drift waves

A kinetic theory for the nonlinear damping of collisionless drift waves in a shear-free magnetic field is presented. The general formalism is a renormalized version of induced scattering on the ions and reduces correctly to weak turbulence theory. The approximation studied explicitly reduces to Compton scattering, systematizes and corrects the earlier calculations of Dupree and Tetreault [Phys. Fluids 21, 425 (1978)], and extends that theory to finite ion gyroradius. Certain conclusions differ significantly from those of Dupree and Tetreault. In particular, at long wavelengths the nonlinear ion growth rate is large and positive, proportional to k2⊥D both at zero and at finite gyroradius. (Here, k⊥ is the perpendicular wavenumber and D is the test particle diffusion coefficient.) Nevertheless, the rate of change of total mean kinetic energy due to the nonlinear interaction is small and proportional to q2∥, where q∥ is a typical parallel wavenumber.