Cosmic-ray current-driven instabilities – revisiting environmental conditions

ABSTRACT The growth of magnetohydrodynamic fluctuations relevant to cosmic-ray (CR) confinement in and near their sources, the effects local plasma conditions is revisited. We consider cases where CRs penetrate a medium which may contain fraction neutral particles, explore possible high-order CR anisotropies. An algorithm for calculating dispersion relation arbitrary distributions, anisotropies presented, general solution power-law distributions provided. Implications resulting instabilities strong Galactic sources are discussed. argue that streaming weakly ionized plasmas eliminates need existence an evanescent band relation, conclusion be confirmed by gamma-ray observations. necessity additional multiscale numerical simulations highlighted, as understanding non-linear behaviour crucial.