Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aipc.1085..349n&link_type=abstract
HIGH ENERGY GAMMA-RAY ASTRONOMY: Proceedings of the 4th International Meeting on High Energy Gamma-Ray Astronomy. AIP Conferenc
Astronomy and Astrophysics
Astronomy
Turbulence, Cosmic Rays, Supernova Remnants, Particle Acceleration
Scientific paper
We present results of two- and three-dimensional Particle-In-Cell simulations of magnetic turbulence production by isotropic cosmic-ray ions drifting upstream of supernova remnant shocks. The studies aim at testing predictions of a strong amplification of short-wavelength nonresonant wave modes and at studying the subsequent evolution of the magnetic turbulence and its backreaction on cosmic ray trajectories. The detailed knowledge of the upstream turbulence properties is crucial to ascertain all aspects of the shock acceleration process-the transport properties of cosmic rays, the shock structure, thermal particle injection and heating processes. An amplification of magnetic field would also facilitate the acceleration of particles beyond the ``knee'' in the cosmic-ray spectrum. We confirm the generation of the turbulent magnetic field due to the drift of cosmic-ray ions in the upstream plasma but find that the amplitude of the turbulence saturates at about δB/B~1. The backreaction of the magnetic turbulence on the particles leads to an alignment of the bulk-flow velocities of the cosmic rays and the background medium. This is an essential characteristic of cosmic-ray modified shocks: the upstream flow speed is continuously changed by the cosmic rays. The deceleration of the cosmic-ray drift and the simultaneous bulk acceleration of the background plasma account for the saturation of the instability at moderate amplitudes of the magnetic field. A strong magnetic field amplification to amplitudes δB>>B0 has not been demonstrated yet.
Niemiec Jacek
Nishikawa Ken-Ichi
Pohl Martin
Stromal Thomas
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