Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsh72b..01f&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SH72B-01
Physics
7859 Transport Processes
Scientific paper
Quasi-linear theory of particle scattering parallel and perpendicular to the mean magnetic field B, is applied to static fully three-dimensional MHD turbulence described by its three-dimensional wave vector spectrum Pij(k). The method follows that of Forman et al. (Ap.J.,1974), but uses a more complete evaluation of the scattering tensor and does not assume that the particle pitch angle distribution is linear in the pitch angle. The form of Pij(k) derived by Oughton, et al. (1996) is essential to this new evaluation of the scattering tensor. The particle gyrophase distribution is assumed to be a simple cosine whose amplitude and phase are parameters to be determined, giving the perpendicular elements of the scattering tensor. In this picture, scattering parallel and perpendicular to the mean field is due to power, polarization, anisotropy and helicity in the power spectral tensor at (different sets of) resonant wavevectors perpendicular to the local mean field as well as in parallel and in intermediate directions. To make the theory tractable, the Pij(k) are assumed to be cylindrically symmetric about the local mean magnetic field. Results are presented for the slab + 2D model; that is, Pij(k) is non-zero only at wavevectors parallel or perpendicular to the mean magnetic field. I find that the 2D component wavevectors perpendicular to the mean field have no effect at all on pitch angle scattering. There could be parallel scattering by wavevectors at oblique angles, not included in the present theory. For perpendicular scattering, the slab component contributes a "power at zero frequency" term as known before, but the 2D component contributes a similar term for particles with gyroradius large compared with the correlation length of the field. If the slab power is a fraction F of fluctuations, this theory predicts a parallel diffusion coefficient 1/F times larger than if all the power in fluctuations were slab modes. The perpendicular diffusion coefficient is not changed at large rigidities, but is reduced by a factor F at rigidities where the gyroradius is small compared to the correlation length. This work was supported by NASA grant NAG510995.
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