Particle Magnetic Moment Conservation and Resonance in a Pure Magnetohydrodynamic Shock and Field Inclination Influence on Diffusive Shock Acceleration
Abstract
Computational and analytical methods have been used in a study of particle acceleration by MHD shocks. Numerical simulations of singleparticle trajectories indicate that magnetic moment is conserved quite accurately for an encounter with a nearperpendicular shock, and for all pitch angles except the very small ones. Acceleration is most effective for particles which are reflected by the shock at small pitch angles. If future encounters with the shock are possible, large acceleration will be repeated only for relativistic plasma flow velocities. Results for the pure MHD shock are then considered within the context of a diffusion model (hence a diffusive MHD shock). The microscopic approach is employed whereby one follows the history of a test particle and explicitly takes into account the possibility of reflection by the shock. Exact analytical solutions are currently available to order V/c, where V is the plasma flow speed, and are found to be in complete agreement with diffusion theory. More specifically, the presence of electromagnetic effects leads to a shortening of acceleration time scale but does not change the steady state spectrum of energetic particles.
 Publication:

The Astrophysical Journal
 Pub Date:
 February 1990
 DOI:
 10.1086/168420
 Bibcode:
 1990ApJ...350..692L
 Keywords:

 Conservation Laws;
 Magnetic Moments;
 Magnetohydrodynamic Waves;
 Particle Acceleration;
 PlasmaParticle Interactions;
 Shock Waves;
 Computerized Simulation;
 Incidence;
 Magnetic Field Configurations;
 Particle Trajectories;
 Relativistic Plasmas;
 Plasma Physics;
 HYDROMAGNETICS;
 PARTICLE ACCELERATION;
 SHOCK WAVES