Energetic Particle Diffusion In Critically Balanced Turbulence

Abstract

Observations and modelling suggest that the fluctuations in magnetised plasmas exhibit scale-dependent anisotropy, with more energy in the fluctuations perpendicular to the mean magnetic field than in the parallel fluctuations and the anisotropy increasing at smaller scales. The scale-dependence of the anisotropy has not been studied in full-orbit simulations of particle transport in turbulent plasmas so far. In this paper, we construct a model of critically balanced turbulence, as suggested by \cite{GoSr1995}, and calculate energetic particle spatial diffusion coefficients using full-orbit simulations. The model uses an enveloped turbulence approach, where each 2-dimensional wave mode with wavenumber $k_{\perp }$ is packed into envelopes of length $L$ following the critical balance condition, $L\propto k_{\perp }^{-2/3}$, with the wave mode parameters changing between envelopes. Using full-orbit particle simulations, we find that both the parallel and perpendicular diffusion coefficients increase by a factor 2, compared to previous models with scale-independent anisotropy.

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• Numerical study of Cosmic Ray Diffusion in MHD turbulence
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• Stellar energetic particles in the magnetically turbulent habitable zones of TRAPPIST-1-like planetary systems
• Pitch-angle scattering in magnetostatic turbulence. I. Test-particle simulations and the validity of analytical results
• Cross-field transport in Goldreich-Sridhar MHD turbulence