Shock drift acceleration for a nearperpendicular shock in a turbulent astrophysical plasma
Abstract
Analytical theory of diffusive shock acceleration from the microscopic viewpoint 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 electricfieldfree 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 scatterfree 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 scatterfree 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.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 February 1992
 Bibcode:
 1992A&A...255..443N
 Keywords:

 Energy Transfer;
 Magnetohydrodynamic Turbulence;
 PlasmaParticle Interactions;
 Shock Waves;
 Space Plasmas;
 Acceleration (Physics);
 Electromagnetic Fields;
 Mathematical Models;
 Monte Carlo Method;
 Particle Trajectories;
 Astrophysics