THE HEATING OF TEST PARTICLES IN NUMERICAL SIMULATIONS OF ALFVENIC TURBULENCE

Journal Article · Thu Dec 10 04:00:00 EST 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/707/1/404· OSTI ID:21389262

Lehe, Remi ^[1]; Parrish, Ian J; Quataert, Eliot ^[2]

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1. Departement de Physique, Ecole Normale Superieure, 24 rue Lhomond, 75005 Paris (France)
2. Astronomy Department and Theoretical Astrophysics Center, 601 Campbell Hall, University of California, Berkeley, CA 94720 (United States)

We study the heating of charged test particles in three-dimensional numerical simulations of weakly compressible magnetohydrodynamic (MHD) turbulence ('Alfvenic turbulence'); we focus on plasmas with comparable thermal and magnetic energy densities, i.e., beta approx 0.1-10. Our results are relevant to particle heating and acceleration in the solar wind, accretion disks onto black holes, and other astrophysics and heliospheric environments. The physics of particle heating depends on whether the gyrofrequency of a particle OMEGA{sub 0} is comparable to the frequency of a turbulent fluctuation omega that is resolved on the computational domain. Particles with OMEGA{sub 0} approx omega undergo strong perpendicular heating (relative to the local magnetic field) and pitch angle scattering. By contrast, particles with OMEGA{sub 0} >> omega undergo strong parallel heating. Simulations with a finite resistivity produce additional parallel heating due to parallel electric fields in small-scale current sheets. Many of our results are consistent with linear theory predictions for the particle heating produced by the Alfven and slow magnetosonic waves that make up Alfvenic turbulence. However, in contrast to linear theory predictions, energy exchange is not dominated by discrete resonances between particles and waves; instead, the resonances are substantially 'broadened'. We discuss the implications of our results for solar and astrophysics problems, in particular, the thermodynamics of the near-Earth solar wind. This requires an extrapolation of our results to higher numerical resolution, because the dynamic range that can be simulated is far less than the true dynamic range between the proton cyclotron frequency and the outer-scale frequency of MHD turbulence. We conclude that Alfvenic turbulence produces significant parallel heating via the interaction between particles and magnetic field compressions ('slow waves'). However, on scales above the proton Larmor radius Alfvenic turbulence does not produce significant perpendicular heating of protons or minor ions (this is consistent with linear theory, but inconsistent with previous claims from test particle simulations). Instead, the Alfven wave energy cascades to perpendicular scales below the proton Larmor radius, initiating a kinetic Alfven wave cascade.

• OSTI ID: 21389262
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 707; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCELERATION
ACCRETION DISKS
ALFVEN WAVES
ASTROPHYSICS
BARYONS
BLACK HOLES
COMPUTERIZED SIMULATION
ELECTRIC FIELDS
ELEMENTARY PARTICLES
ENERGY DENSITY
ENERGY TRANSFER
EXTRAPOLATION
FERMIONS
FLUID MECHANICS
GYROFREQUENCY
HADRONS
HYDRODYNAMICS
HYDROMAGNETIC WAVES
INCLINATION
LARMOR RADIUS
MAGNETIC FIELDS
MAGNETOACOUSTIC WAVES
MAGNETOHYDRODYNAMICS
MATHEMATICAL SOLUTIONS
MECHANICS
NUCLEONS
NUMERICAL SOLUTION
PHYSICS
PROTONS
SIMULATION
SOLAR ACTIVITY
SOLAR WIND
STELLAR ACTIVITY
STELLAR WINDS
TEST PARTICLES
THERMODYNAMICS
THREE-DIMENSIONAL CALCULATIONS
TURBULENCE