Shock drift acceleration for a near-perpendicular shock in a turbulent astrophysical plasma

Details Shock drift acceleration for a near-perpendicular shock in a turbulent astrophysical plasma Shock drift acceleration for a near-perpendicular shock in a turbulent astrophysical plasma

Feb 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992a%26a...255..443n&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 255, no. 1-2, p. 443-452.

Physics

8

Energy Transfer, Magnetohydrodynamic Turbulence, Plasma-Particle Interactions, Shock Waves, Space Plasmas, Acceleration (Physics), Electromagnetic Fields, Mathematical Models, Monte Carlo Method, Particle Trajectories

Scientific paper

Analytical theory of diffusive shock acceleration from the microscopic view-point depends upon a knowledge of the mean energy gain per cycle across the shock. A numerical study is carried out on the basic shock drift energization in a situation where two important assumptions of the analytical theory are broken. One violation is due to the introduction of a high degree of turbulence in the plasma, allowing continuous scattering right up to the shock surface. The second involves employing a near perpendicular shock and an injection energy such that transformation to the electric-field-free frame involves the introduction of a significant anisotropy. The turbulent field is modelled employing in situ measurements of an interplanetary travelling shock. This turbulence keeps some particles in the drift acceleration region longer than expected and allows enhanced acceleration for some pitch angles if the results are compared with a scatter-free model employing a single discontinuity between two homogeneous fields. Furthermore, additional upstream acceleration occurs in the preshock foot and ramp structure. However, the mean energization for the turbulent model is about the same as the computed mean energy gain for the scatter-free case. Both these computed energy gains nevertheless exceed analytical theory estimates by 18 percent or more, the discrepancy probably being due to the large anisotropy introduced in the E = 0 frame. First adiabatic conservation is found to hold to within 20 percent.

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