Properties of Ion-Cyclotron Waves in the Open Solar Corona

Remote observations of coronal holes have strongly suggested 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?CKramers?CBrillouin) linear perturbation analysis is used in the frame work of a collisionless multi-fluid model where we consider in addition to 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. At low frequency (smaller than the proton cyclotron frequency), the results showed a distinct behavior of the two ion-cyclotron modes found in our calculations, namely the first one propagates anisotropically guided along the magnetic field lines while the second one propagates isotropically with no preferred direction.