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Time-dependent simulation of oblique MHD cosmic-ray shocks using the two-fluid modelUsing a new, second-order accurate numerical method we present dynamical simulations of oblique MHD cosmic-ray (CR)-modified plane shock evolution. Most of the calculations are done with a two-fluid model for diffusive shock acceleration, but we provide also comparisons between a typical shock computed that way against calculations carried out using the more complete, momentum-dependent, diffusion-advection equation. We also illustrate a test showing that these simulations evolve to dynamical equilibria consistent with previously published steady state analytic calculations for such shocks. In order to improve understanding of the dynamical role of magnetic fields in shocks modified by CR pressure we have explored for time asymptotic states the parameter space of upstream fast mode Mach number, M(sub f), and plasma beta. We compile the results into maps of dynamical steady state CR acceleration efficiency, epsilon(sub c). We have run simulations using constant, and nonisotropic, obliquity (and hence spatially) dependent forms of the diffusion coefficient kappa. Comparison of the results shows that while the final steady states achieved are the same in each case, the history of CR-MHD shocks can be strongly modified by variations in kappa and, therefore, in the acceleration timescale. Also, the coupling of CR and MHD in low beta, oblique shocks substantially influences the transient density spike that forms in strongly CR-modified shocks. We find that inside the density spike a MHD slow mode wave can be generated that eventually steepens into a shock. A strong layer develops within the density spike, driven by MHD stresses. We conjecture that currents in the shear layer could, in nonplanar flows, results in enhanced particle accretion through drift acceleration.
Document ID
19950049062
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Frank, Adam
(Univ. of Minnesota, Minneapolis, MN United States)
Jones, T. W.
(Univ. of Minnesota, Minneapolis, MN United States)
Ryu, Dongsu
(Chungham National Univ. Daejeon, Korea, United States)
Date Acquired
August 16, 2013
Publication Date
March 10, 1995
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 441
Issue: 2
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
95A80661
Funding Number(s)
CONTRACT_GRANT: NAGW-2548
CONTRACT_GRANT: NSF AST-93-18959
CONTRACT_GRANT: NSF AST-91-00486
Distribution Limits
Public
Copyright
Other

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