  Low-energy cosmic rays (CRs) are confined by self-generated MHD waves in the
mostly neutral ISM. We show that the CR transport equation can be expressed as
a continuity equation for the CR number density involving an effective
convection velocity. Assuming balance between wave growth and ion-neutral
damping, this equation gives a steady-state condition n_cr ~ n_i^1/2 up to a
critical density for free streaming. This relation naturally accounts for the
heretofore unexplained difference in CR ionization rates derived for dense
diffuse clouds (McCall et al. 2003) and dark clouds, and predicts large spatial
variations in the CR heating rate and pressure.
