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Simulating field-aligned diffusion of a cosmic ray gas

Lookup NU author(s): Dr Andrew Snodin, Professor Axel Brandenburg, Mr AJW William Mee, Professor Anvar Shukurov

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Abstract

The macroscopic behaviour of cosmic rays in turbulent magnetic fields is discussed. An implementation of anisotropic diffusion of cosmic rays with respect to the magnetic field in a non-conservative, high-order, finite-difference magnetohydrodynamic code is discussed. It is shown that the standard implementation fails near singular X-points of the magnetic field, which are common if the field is random. A modification to the diffusion model for cosmic rays is described and the resulting telegraph equation (implemented by solving a dynamic equation for the diffusive flux of cosmic rays) is used; it is argued that this modification may better describe the physics of cosmic ray diffusion. The present model reproduces several processes important for the propagation and local confinement of cosmic rays, including spreading perpendicular to the local large-scale magnetic field, controlled by the random-to-total magnetic field ratio, and the balance between cosmic ray pressure and magnetic tension. Cosmic ray diffusion is discussed in the context of a random magnetic field produced by turbulent dynamo action. It is argued that energy equipartition between cosmic rays and other constituents of the interstellar medium does not necessarily imply that cosmic rays play a significant role in the balance of forces.


Publication metadata

Author(s): Snodin AP, Brandenburg A, Mee AJ, Shukurov A

Publication type: Article

Publication status: Published

Journal: Monthly Notices of the Royal Astronomical Society

Year: 2006

Volume: 373

Issue: 2

Pages: 643-652

ISSN (print): 0035-8711

ISSN (electronic): 1365-2966

Publisher: Wiley-Blackwell Publishing Ltd.

URL: http://dx.doi.org/10.1111/j.1365-2966.2006.11034.x

DOI: 10.1111/j.1365-2966.2006.11034.x


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