Physics – Plasma Physics
Scientific paper
Jun 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004jgra..10906105g&link_type=abstract
Journal of Geophysical Research, Volume 109, Issue A6, CiteID A06105
Physics
Plasma Physics
32
Space Plasma Physics: Kinetic And Mhd Theory, Space Plasma Physics: Waves And Instabilities, Space Plasma Physics: Wave/Particle Interactions, Interplanetary Physics: Plasma Waves And Turbulence
Scientific paper
Linear Vlasov dispersion theory for a homogeneous, collisionless electron-proton plasma with Maxwellian velocity distributions is used to examine the damping of Alfvén-cyclotron fluctuations. Fluctuations of sufficiently long wavelength are essentially undamped, but as k$\parallel$, the wave vector component parallel to the background magnetic field Bo, reaches a characteristic dissipation value kd, the protons become cyclotron resonant and damping begins abruptly. For proton cyclotron damping, kdc/ωp ~ 1 for 10-3 $\lesssim$ βp $\lesssim$ 10-1, where βp ≡ 8πnpkBTp/Bo2 and ωp/c is the proton inertial length. At k$\parallel$ < kd, me/mp < βe, and βp $\lesssim$ 0.10 the electron Landau resonance becomes the primary contributor to fluctuation dissipation, yielding a damping rate that scales as ωr $\sqrt \beta_{e (k$\perp$c/ωp)2, where ωr is the real frequency and k$\perp$ is the wave vector component perpendicular to Bo. As βp increases from 0.10 to 10, the proton Landau resonance makes an increasing contribution to damping of these waves at k$\parallel$ < kd and 0° < $\theta$ < 30°, where $\theta$ = arccos($\hat {\bf k . $\hat {\bf Bo). The maximum damping rate due to the proton Landau resonance scales approximately as βp(kc/ωp)2 over 0.50 <= βp <= 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 Alfvén-cyclotron fluctuations.
Borovsky Joseph E.
Gary Peter S.
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