Ion cyclotron waves, instabilities and solar wind heating

The effect of alpha particles on the dispersion relation of ion cyclotron waves and its influence on the heating of the solar wind plasma are investigated. The presence of alpha particles can dramatically change the dispersion relation of ion cyclotron waves, and significantly influence the way that ion cyclotron waves heat the solar wind plasma. We find that a spectrum of ion cyclotron waves affects the thermal anisotropy of the solar wind protons and other ions differently in interplanetary space: When alpha particles have a speed u(alpha) > 0.5v(A), and both protons and alpha particles have a thermal anisotropy T-perpendicular to/T-parallel to > 1, ion cyclotron waves heat protons in the direction perpendicular to the magnetic field, cool them in the parallel direction, and exert the opposite effect on alpha particles.