Time-dependent perpendicular transport of fast charged particles in a turbulent magnetic field

TL;DR

This paper analytically derives the early-time perpendicular transport behavior of charged particles in turbulent magnetic fields, revealing new insights into the influence of turbulence geometry on particle diffusion.

Contribution

It introduces a novel analytical model for particle perpendicular transport at short times, considering different turbulence geometries and scales, which was previously unexplored.

Findings

Particles in 3D isotropic turbulence diffuse from local magnetic field lines.

Magnetization depends on turbulence geometry, challenging previous assumptions.

The model provides a basis for studying solar wind anisotropies.

Abstract

We present an analytic derivation of the temporal dependence of the perpendicular transport coefficient of charged particles in magnetostatic turbulence, for times smaller than the time needed to charged particles to travel the turbulence correlation length. This time window is left unexplored in most transport models. In our analysis all magnetic scales are taken to be much larger than the particle gyroradius, so that perpendicular transport is assumed to be dominated by the guiding center motion. Particle drift from the local magnetic field lines and magnetic field lines random walk are evaluated separately for slab and 3D isotropic turbulence. Contributions of wavelength scales shorter and longer than the turbulence coherence length are compared. In contrast to slab case, particles in 3D isotropic turbulence unexpectedly diffuse from local magnetic field lines; this result questions the common assumption that particle magnetization is independent on turbulence geometry. Extensions of this model will allow for a study of solar wind anisotropies.