Cosmic-Ray Diffusion and Galactic Magnetic Field Models
2019 July 22
We calculate numerically the parallel and perpendicular diffusion coefficients of cosmic-rays (CR) propagating in regular and turbulent magnetic fields. For isotropic turbulence, and in the absence of any strong regular field, CRs would reside too long in the Galactic disc and overproduce secondary nuclei like boron for any reasonable value of the coherence length and strength of the turbulent field. We conclude that the propagation of Galactic CRs has to be strongly anisotropic because of a sufficiently strong regular field and, or because of an anisotropy in the turbulent field. As a consequence, the number of sources contributing to the local CR flux is found to be reduced by about two orders of magnitude compared to the case of isotropic CR diffusion.