Cosmic Ray Tracing in Turbulent MHD with a Strong Guide Field

The transport of cosmic rays through turbulent astrophysical magnetic fields is a fundamental problem in plasma astrophysics. The mean free path (λ) of these particles is a crucial parameter governing their diffusive propagation, yet its dependence on various particle and field properties remains an active area of research. We present results from numerical simulations investigating the trajectories and transport properties of test particles in strong guide field magnetohydrodynamic (MHD) turbulence.

Our study focuses on a regime where the particle gyroradius (ρ) falls within the turbulence inertial scale (l) and the field perturbation is relatively weak (dB/B = 0.25). Test particles are initialized with a uniform energy and launched into the turbulent magnetic field in distinct groups, each characterized by a specific initial pitch angle (α). We meticulously track the three-dimensional trajectories of a large ensemble of these particles and statistically estimate their path lengths. We determine the dependence of the particle mean free path on the initial pitch angle and explore the impact of numerical domain size on transport by comparing simulations in small versus large MHD domains, aiming to elucidate the effects of resolving or truncating the turbulence inertial scales. Our findings contribute to a more comprehensive understanding of energetic particle transport in turbulent magnetized plasmas.