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The nature of cosmic ray (CR) transport in the Milky Way remains elusive. Thepredictions of current micro-physical CR transport models inmagneto-hydrodynamic (MHD) turbulence are drastically different from what isobserved. These models usually focus on MHD turbulence with a strong guidefield and ignore the impact of turbulent intermittency on particle propagation.This motivates our studying the alternative regime of large-amplitudeturbulence with $\delta B/B_0 \gg 1$, in which intermittent small-scalemagnetic field reversals are ubiquitous. We study particle transport in suchturbulence by integrating trajectories in stationary snapshots. To quantifyspatial diffusion, we use a setup with continuous particle injection andescape, which we term the turbulent leaky box. We find that particle transportis very different from the strong-guide-field case. Low-energy particles arebetter confined than high-energy particles, despite less efficient pitch-angleisotropization at small energies. In the limit of weak guide field,energy-dependent confinement is driven by the energy-dependent (in)ability tofollow reversing magnetic field lines exactly and by the scattering in regionsof ``resonant curvature", where the field line bends on a scale that is oforder the local particle gyro-radius. We derive a heuristic model of particletransport in magnetic folds that approximately reproduces the energy dependenceof transport found numerically. We speculate that CR propagation in the Galaxyis regulated by the intermittent field reversals highlighted here and discussthe implications of our findings for CR transport in the Milky Way.

Cosmic ray transport in large-amplitude turbulence with small-scale field reversals