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