Global diffusion of cosmic rays in random magnetic fields
| Autor: | Anvar Shukurov, A. P. Snodin, Luiz Felippe S. Rodrigues, Paul J. Bushby, Graeme R. Sarson |
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| Rok vydání: | 2016 |
| Předmět: |
Physics
010308 nuclear & particles physics Gyroradius Astrophysics::High Energy Astrophysical Phenomena Astronomy and Astrophysics Cosmic ray Random walk 01 natural sciences Charged particle Computational physics Magnetic field Space and Planetary Science Quantum mechanics 0103 physical sciences Test particle Diffusion (business) Magnetohydrodynamics 010303 astronomy & astrophysics |
| Zdroj: | Monthly Notices of the Royal Astronomical Society. 457:3975-3987 |
| ISSN: | 1365-2966 0035-8711 |
| DOI: | 10.1093/mnras/stw217 |
| Popis: | The propagation of charged particles, including cosmic rays, in a partially ordered magnetic field is characterized by a diffusion tensor whose componentsdepend on the particle’s Larmor radius RL and the degree of order in the magnetic field. Most studies of the particle diffusion presuppose a scale separation between the mean and random magnetic fields (e.g., there being a pronounced minimum in the magnetic power spectrum at intermediate scales). Scale separation is often a good approximation in laboratory plasmas, but not in most astrophysical environments such as the interstellar medium (ISM). Modern simulations of the ISM have numerical resolution of order 1pc, so the Larmor radius of the cosmic rays that dominate in energy density is at least 10 6 times smaller than the resolved scales. Large-scale simulations of cosmic ray propagationin the ISM thus rely on oversimplifiedformsof the diffusiontensor. We take the first steps towards a more realistic description of cosmic ray diffusion for such simulations, obtaining direct estimates of the diffusion tensor from test particle simulations in random magnetic fields (with the Larmor radius scale being fully resolved), for a range of particle energies corresponding to 10 2 . RL/lc . 10 3 , where lc is the magnetic correlation length. We obtain explicit expressions for the cosmic ray diffusion tensor for RL/lc ≪ 1, that might be used in a sub-grid model of cosmic ray diffusion. The diffusion coefficients obtained are closely connected with existing transport theories that include the random walk of magnetic lines. |
| Databáze: | OpenAIRE |
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