Proton Perpendicular Heating by Kinetic Alfvén Waves

The preferential heating of protons in the perpendicular direction with respect to the ambient magnetic field is a well-known phenomenon in the solar corona. One of the physical mechanisms proposed to explain such a feature is the nonresonant wave–particle interaction between protons and kinetic Alfvén waves. The present paper examines this mechanism by employing a novel analytical method based upon the Hamiltonian dynamical test particle approach. The analytical nature of the present method reveals an interesting fact that the pure inductive component of parallel electric field associated with the kinetic Alfvén wave in the limit Ti/Te ≪ 1 has little contribution. The parallel and perpendicular diffusion of protons by kinetic Alfvén waves is investigated through computing the autocorrelation function. The calculations unambiguously demonstrate that the proton heating is achieved mainly by nonresonant wave–particle interaction involving the wave magnetic field, and that the effects of the parallel electric field are minimal. It is also found that the perpendicular diffusion is orders of magnitude stronger than parallel diffusion, implying effective perpendicular heating.