Damping rates and (ion-neutral and turbulent) of Alfvén waves in the WNM (left-hand panel) and WIM (right-hand panel) vs. CR energy E. Different colors are used for different values of the hydrogen ionization fraction f. Unless stated otherwise, a standard χ = 0.1 He abundance is assumed. The considered parameters for the WNM and WIM are given in Table 1. Left-hand panel: the dotted lines refers to ion-neutral damping, and the dashed lines show the FG damping. The FG damping is truncated to the minimum energy, E_min, below which the background turbulence is damped by ion-neutral friction before the scale relevant for the damping of self-generated waves is reached that are resonant with a particle of energy < E_min (see Sect. 2.2). The shaded regions represent the range in which Alfvén waves do not propagate (see Sect. 2.1). Right-hand panel: the solid lines refer to ion-neutral damping, and the thin dotted lines show the case without a contribution to damping from He (χ = 0). The dashed lines show FG damping, which in the case of WIM is found to depend little on the ionization fraction f.