Alfven-cyclotron fluctuations: Linear Vlasov theory

Linear Vlasov dispersion theory for a homogeneous, collisionless electron-proton plasma with Maxwellian velocity distributions is used to examine the damping of Alfven-cyclotron fluctuations. Fluctuations of sufficiently long wavelength are essentially undamped, but as k(parallel to), the wave vector component parallel to the background magnetic field B-o, reaches a characteristic dissipation value k(d), the protons become cyclotron resonant and damping begins abruptly. For proton cyclotron damping, k(d)c/omega(p) similar to 1 for 10(-3) less than or similar to beta(p) less than or similar to 10(-1), where beta(p) = 8pin(p)k(B)T(p)/B-o(2) and omega(p)/c is the proton inertial length. At k(parallel to) < k(d), m(e)/m(p) < beta(e), and beta(p) less than or similar to 0.10 the electron Landau resonance becomes the primary contributor to fluctuation dissipation, yielding a damping rate that scales as omega(r)rootbeta(e) (k(perpendicular to)c/omega(p))(2), where omega(r) is the real frequency and k(perpendicular to) is the wave vector component perpendicular to B-o. As beta(p) increases from 0.10 to 10, the proton Landau resonance makes an increasing contribution to damping of these waves at k(parallel to) < k(d) and 0 degrees < theta < 30 degrees, where theta = arccos(<(k)over cap> . (B) over cap (o)). The maximum damping rate due to the proton Landau resonance scales approximately as beta(p)(kc/omega(p))(2) over 0.50 less than or equal to beta(p) less than or equal to 10. Both magnetic transit time damping and electric Landau damping may contribute to Landau resonant dissipation; in the electron Landau resonance regime the former is important only at propagation almost parallel to Bo, whereas proton transit time damping can be relatively important at both quasi-parallel and quasi-perpendicular propagation of Alfven-cyclotron fluctuations.