Ion distributions in coronal holes and fast solar wind

We perform 1D hybrid simulations to investigate the nonlinear kinetic behavior of the tenuous collisionless magnetized plasma in coronal holes and fast solar wind. Initially isotropic ion distributions are reshaped via wave-particle interactions with resonant daughter waves that are born by parametrically unstable large-amplitude Alfven-cyclotron waves. Decay processes lead to the formation of both acoustic and electromagnetic micro-turbulence, which further influence the motion of the ions via Landau damping and pitch-angle scattering. This leads to a depletion of the pump and destroys the fluid coherence of the medium. Parametric instabilities act to randomize the ion distributions, causing anisotropic heating and resulting in differential streaming and formation of ion beams. Due to their low mass densities and charge-to-mass ratios heavy ions are preferentially heated and obtain higher anisotropies than protons.