Dissipation of obliquely propagating Alfvénic turbulence and related ion heating and acceleration -- 2D hybrid simulations

The dissipation of fluid scale fluctuations in a collisionless plasma can occur via turbulent cascade, followed by many different wave-particle interactions. The partitioning of energy between heavy ions, protons and electrons and the efficiency of the heating depends on the character of the waves, the wave vector direction and the anisotropy of the fluctuations carrying energy at small scales. Here we perform 2.5D hybrid simulations to investigate the problem of the turbulent evolution and wave dissipation of a broad band spectrum of oblique Alfvén cyclotron waves in collisionless low plasma beta conditions. This set up is motivated by the typical conditions observed in the fast solar wind near the Sun. We vary the waves propagation angle and compare the evolution of the related anisotropic heating and differential acceleration of protons and alpha particles to simulations initialized with pure parallel propagating waves. We discuss the influence of changing the amplitude, the spectral range and the spectral index for the initial fluctuations, as well as the relative drift speed between the two ion species. We find that the differential acceleration can be strongly reduced when the effect of the solar wind expansion is taken into account. Both simulation setup and outcome are compared to magnetic field power spectra and particle behavior as observed in situ in the solar wind and provide relevant predictions for the plasma properties in the acceleration region to be tested by the upcoming Solar Orbiter and Solar Probe Plus missions.