Damping of long-wavelength kinetic Alfven fluctuations: Linear theory

The full electromagnetic linear dispersion equation for kinetic Alfven fluctuations in a homogeneous, isotropic, collisionless, Maxwellian electron-proton plasma is solved numerically in the long-wavelength limit. At propagation sufficiently oblique to the background magnetic field B-o, the wave number dependence of the damping rate of such modes is summarized by an analytic expression which scales as k(perpendicular to)(2)k(parallel to) where the subscripts denote directions relative to B-o. This damping progressively (although not monotonically) increases with increasing electron and proton beta, corresponding to four distinct damping regimes: nonresonant, electron Landau, proton Landau, and proton transit-time damping.