Particle Transport in intense small scale magnetic turbulence with a mean field

Abstract

Various astrophysical studies have motivated the investigation of the transport of high energy particles in magnetic turbulence, either in the source or en route to the observation sites. For strong turbulence and large rigidity, the pitch-angle scattering rate is governed by a simple law involving a mean free path that increases proportionally to the square of the particle energy. In this paper, we show that perpendicular diffusion deviates from this behavior in the presence of a mean field. We propose an exact theoretical derivation of the diffusion coefficients and show that a mean field significantly changes the transverse diffusion even in the presence of a stronger turbulent field. In particular, the transverse diffusion coefficient is shown to reach a finite value at large rigidity instead of increasing proportionally to the square of the particle energy. Our theoretical derivation is corroborated by a dedicated Monte Carlo simulation. We briefly discuss several possible applications in astrophysics.

(9 pages, 6 figures, revised version with minor changes)

References in corpus (3)

• On the efficiency of Fermi acceleration at relativistic shocks
• On Fermi acceleration and MHD-instabilities at ultra-relativistic magnetized shock waves
• Cosmic-Ray Acceleration at Ultrarelativistic Shock Waves: Effects of Downstream Short-Wave Turbulence

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• Anisotropic cosmic-ray diffusion in isotropic Kolmogorov turbulence
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• Pitch-angle scattering of energetic particles with adiabatic focusing
• Electron heating in high Mach number collisionless shocks
• Acceleration of cosmic rays in presence of magnetohydrodynamic fluctuations at small scales
• Revisiting Propagation Delays of Ultra-High-Energy Cosmic Rays from Long-lived Sources
• Velocity decorrelation functions of high-energy cosmic rays propagating in magnetic fields
• Transport of charged particles propagating in turbulent magnetic fields as a red-noise process
• Particle Acceleration in Colliding Flows: Binary Star Winds and Other Double-Shock Structures
• High-energy Particle Transport in Three-dimensional Anisotropic Turbulent Magnetic Fields