2009/08/28 by Remi Lehe, Remi Lehé, Ian J. Parrish +1 · 1 citation
Physics and Astronomy · #Alfvén wave #Astrophysics #Charged particle #Computational physics #Coronal mass ejection #Gamma-ray bursts and supernovae #Geophysics #Gyrokinetics #Gyroradius #Ion #Ionosphere and magnetosphere dynamics #Magnetic field #Magnetic reconnection #Magnetohydrodynamic drive #Magnetohydrodynamic turbulence #Magnetohydrodynamics #Mechanics #Nuclear physics #Physics #Pitch angle #Plasma #Solar and Space Plasma Dynamics #Solar energetic particles #Solar wind #Tokamak #Turbulence #astro-ph.HE #astro-ph.SR
paper · pdf · doi:10.1088/0004-637x/707/1/404
Submitted to ApJ
arxiv created 2009/08/28 · openalex publication_date 2009/11/20 · arxiv updated 2015/05/14 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We study the heating of charged test particles in three-dimensional numerical simulations of weakly compressible magnetohydrodynamic (MHD) turbulence ("Alfvénic turbulence"); we focus on plasmas with comparable thermal and magnetic energy densities, i.e., β ∼ 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 Ω 0 is comparable to the frequency of a turbulent fluctuation ω that is resolved on the computational domain. Particles with Ω 0 ∼ ω undergo strong perpendicular heating (relative to the local magnetic field) and pitch angle scattering . By contrast, particles with Ω 0 ≫ ω 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 Alfvén and slow magnetosonic waves that make up Alfvénic 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 Alfvénic turbulence produces significant parallel heating via the interaction between particles and magnetic field compressions ("slow waves"). However, on scales above the proton Larmor radius Alfvénic 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 Alfvén wave energy cascades to perpendicular scales below the proton Larmor radius, initiating a kinetic Alfvén wave cascade.