Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988apj...324..557k&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 324, Jan. 1, 1988, p. 557-565.
Astronomy and Astrophysics
Astrophysics
12
Anisotropy, Interplanetary Medium, Ion Temperature, Particle Acceleration, Shock Waves, Diffusion Theory, Ion Motion, Solar Wind
Scientific paper
Low-energy ions at interplanetary shocks have speeds similar to that of the background plasma. Under these conditions, the pitch-angle scattering which they are thought to undergo, and which is required if they are to be accelerated by the first-order Fermi mechanism, does not imply that the upstream distribution is nearly isotropic. The diffusion approximation must, therefore, be abandoned. A theory of anisotropic transport, previously used to treat acceleration at parallel relativistic shocks, is applied to this situation, leading to predictions of the pitch-angle distribution in the precursor to the shock. In situ measurements of the pitch-angle distribution of 30 keV ions, which have a speed of about six times that of the shock, show moderate anisotropies which agree well with the predictions of the diffusion approximation. In this case, the new theory demonstrates that the exact anisotropy is indeed well represented by the diffusion approximation.
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