Energetic Particle Acceleration in Compressible Magnetohydrodynamic Turbulence
2021
Magnetohydrodynamic (MHD) turbulence is an important agent of energetic
particle acceleration. Focusing on the compressible properties of magnetic
turbulence, we adopt test particle method to study the particle acceleration
from Alfv\'en, slow and fast modes in four turbulence regimes that may appear
in a realistic astrophysical environment. Our studies show that (1) the
second-order Fermi mechanism drives the acceleration of particles in the
cascade processes of three modes by particle-turbulence interactions,
regardless of whether the shock wave appears; (2) not only can the power
spectra of maximum acceleration rates reveal the inertial range of compressible
turbulence, but also recover the scaling and energy ratio relationship between
the modes; (3) fast mode dominates the acceleration of particles, especially in
the case of super-Alfv\'enic and supersonic turbulence, slow mode dominates the
acceleration for sub-Alfv\'enic turbulence in the very high energy range, and
the acceleration of Alfv\'en mode is significant at the early stage of the
acceleration; (4) particle acceleration from three modes results in a power-law
distribution in the certain range of evolution time. From the perspective of
particle-wave mode interaction, this paper promotes the understanding for both
the properties of turbulence and the behavior of particle acceleration, which
will help insight into astrophysical processes involved in MHD turbulence.
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