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Production of Magnetic Turbulence by Cosmic Rays Drifting Upstream of Supernova Remnant ShocksI will present results of our recent two- and three-dimensional Particle-In-Cell simulations of magnetic-turbulence production by cosmic-ray ions drifting upstream of supernova remnant shocks. These studies' aim is twofold: test recent predictions of strong amplification in short wavelength, non-resonant wave modes, and study the subsequent evolution of the magnetic turbulence, including its backreaction on cosmic-ray trajectories. We confirm that the drifting cosmic rays give rise to a turbulent magnetic field, but show that an oblique filamentary mode grows more rapidly than the non-resonant parallel modes found in analytical theory. The field perturbations grow more slowly than estimated using a quasi-linear analytical approach for the parallel plane-wave mode, and saturate in amplitude at deltaB/B approximately equal to 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 reduction of relative drift between cosmic rays and background medium accounts for the saturation of the instability at only moderate magnetic-field amplitudes. It is possible that the prolonged magnetic field growth observed in recent MHD simulations results from a cosmic-ray current assumed to be constant and thus immune to the backreaction from the turbulent field. We speculate that the parallel plane-wave mode found in analytical treatments very quickly leads co filamentation, which we observe in our PIC modeling and is also apparent in the MHD simulations.
Document ID
20080036823
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Stroman, Thomas
(Iowa State Univ. Ames, IA, United States)
Niemiec, Jacek
(Institute of Nuclear Physics Kracow, Poland)
Pohl, Martin
(Iowa State Univ. Ames, IA, United States)
Nishikawa, Ken-ichi
(Alabama Univ. Huntsville, AL, United States)
Date Acquired
August 24, 2013
Publication Date
July 13, 2008
Subject Category
Astrophysics
Meeting Information
Meeting: 37th COSPAR Scientific Assembly
Location: Montreal
Country: Canada
Start Date: July 13, 2008
End Date: July 20, 2008
Sponsors: Committee on Space Research
Distribution Limits
Public
Copyright
Other

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