  Remote observations of coronal holes have strongly implicated the resonant
interactions of ion-cyclotron waves with ions as a principal mechanism for
plasma heating and acceleration of the fast solar wind. In order to study these
waves, a WKB (Wentzel-Kramers-Brillouin) linear perturbation analysis is used
in the work frame of the collisionless multi-fluid model where we consider in
addition to the protons a second ion component made of alpha particles. We
consider a non-uniform background plasma describing a funnel region in the open
coronal holes and we use the ray tracing Hamiltonian type equations to compute
the ray path of the waves and the spatial variation of their properties.
