Monte Carlo simulation of particle acceleration at astrophysical shocks

Details Monte Carlo simulation of particle acceleration at astrophysical shocks Monte Carlo simulation of particle acceleration at astrophysical shocks

Sep 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989asee.nasa...13c&link_type=abstract

In Maryland Univ., The 1989 NASA-ASEE Summer Faculty Fellowship Program in Aeronautics and Research p 13 (SEE N91-25914 17-82)

Astronomy and Astrophysics

Astrophysics

Astrophysics, Computerized Simulation, Monte Carlo Method, Particle Acceleration, Pascal (Programming Language), Shock Fronts, Angular Distribution, Diffusion, Energy Spectra, Galactic Cosmic Rays, Iteration, Magnetohydrodynamic Turbulence, Scattering, Self Excitation, Shock Waves, Turbulence

Scientific paper

A Monte Carlo code was developed for the simulation of particle acceleration at astrophysical shocks. The code is implemented in Turbo Pascal on a PC. It is modularized and structured in such a way that modification and maintenance are relatively painless. Monte Carlo simulations of particle acceleration at shocks follow the trajectories of individual particles as they scatter repeatedly across the shock front, gaining energy with each crossing. The particles are assumed to scatter from magnetohydrodynamic (MHD) turbulence on both sides of the shock. A scattering law is used which is related to the assumed form of the turbulence, and the particle and shock parameters. High energy cosmic ray spectra derived from Monte Carlo simulations have observed power law behavior just as the spectra derived from analytic calculations based on a diffusion equation. This high energy behavior is not sensitive to the scattering law used. In contrast with Monte Carlo calculations diffusive calculations rely on the initial injection of supra-thermal particles into the shock environment. Monte Carlo simulations are the only known way to describe the extraction of particles directly from the thermal pool. This was the triumph of the Monte Carlo approach. The question of acceleration efficiency is an important one in the shock acceleration game. The efficiency of shock waves efficient to account for the observed flux of high energy galactic cosmic rays was examined. The efficiency of the acceleration process depends on the thermal particle pick-up and hence the low energy scattering in detail. One of the goals is the self-consistent derivation of the accelerated particle spectra and the MHD turbulence spectra. Presumably the upstream turbulence, which scatters the particles so they can be accelerated, is excited by the streaming accelerated particles and the needed downstream turbulence is convected from the upstream region. The present code is to be modified to include a better description of particle scattering (pitch-angle instead of hard-sphere) and as iterative procedure for treating the self-excitation of the MHD turbulence.

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