RESONANCE BROADENING AND HEATING OF CHARGED PARTICLES IN MAGNETOHYDRODYNAMIC TURBULENCE

Journal Article · Sat Oct 20 04:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/758/2/78· OSTI ID:22086554

Lynn, Jacob W ^[1]; Parrish, Ian J; Quataert, Eliot ^[2]; Chandran, Benjamin D. G., ^[3]

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1. Physics Department, University of California, Berkeley, CA 94720 (United States)
2. Astronomy Department and Theoretical Astrophysics Center, University of California, Berkeley, CA 94720 (United States)
3. Space Science Center and Department of Physics, University of New Hampshire, Durham, NH 03824 (United States)

The heating, acceleration, and pitch-angle scattering of charged particles by magnetohydrodynamic (MHD) turbulence are important in a wide range of astrophysical environments, including the solar wind, accreting black holes, and galaxy clusters. We simulate the interaction of high-gyrofrequency test particles with fully dynamical simulations of subsonic MHD turbulence, focusing on the parameter regime with {beta} {approx} 1, where {beta} is the ratio of gas to magnetic pressure. We use the simulation results to calibrate analytical expressions for test particle velocity-space diffusion coefficients and provide simple fits that can be used in other work. The test particle velocity diffusion in our simulations is due to a combination of two processes: interactions between particles and magnetic compressions in the turbulence (as in linear transit-time damping; TTD) and what we refer to as Fermi Type-B (FTB) interactions, in which charged particles moving on field lines may be thought of as beads sliding along moving wires. We show that test particle heating rates are consistent with a TTD resonance that is broadened according to a decorrelation prescription that is Gaussian in time (but inconsistent with Lorentzian broadening due to an exponential decorrelation function, a prescription widely used in the literature). TTD dominates the heating for v{sub s} >> v{sub A} (e.g., electrons), where v{sub s} is the thermal speed of species s and v{sub A} is the Alfven speed, while FTB dominates for v{sub s} << v{sub A} (e.g., minor ions). Proton heating rates for {beta} {approx} 1 are comparable to the turbulent cascade rate. Finally, we show that velocity diffusion of collisionless, large gyrofrequency particles due to large-scale MHD turbulence does not produce a power-law distribution function.

• OSTI ID: 22086554
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 758; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCELERATION
ASTROPHYSICS
BLACK HOLES
COMPUTERIZED SIMULATION
DIFFUSION
DISTRIBUTION FUNCTIONS
GALAXY CLUSTERS
GYROFREQUENCY
HEATING
IONS
MAGNETIC COMPRESSION
MAGNETOHYDRODYNAMICS
PLASMA
SOLAR ELECTRONS
SOLAR PROTONS
SOLAR WIND
STAR ACCRETION
TURBULENCE
VELOCITY