High‐frequency Alfvén waves in multi‐ion coronal plasma: Observational implications

We investigate the effects of high‐frequency (of order ion gyrofrequency) Alfvén and ion‐cyclotron waves on ion emission lines by studying the dispersion of these waves in a multi‐ion coronal plasma. For this purpose we solve the dispersion relation of the linearized multifluid and Vlasov equations in a magnetized multi‐ion plasma with coronal abundances of heavy ions. We also calculate the dispersion relation using nonlinear one‐dimensional hybrid kinetic simulations of the multi‐ion plasma. When heavy ions are present the dispersion relation of parallel propagating Alfvén cyclotron waves exhibits the following branches (in the positive Ω − k quadrant): right‐hand polarized nonresonant and left‐hand polarized resonant branch for protons and each ion. We calculate the ratio of ion to proton velocities perpendicular to the direction of the magnetic field for each wave modes for typical coronal parameters and find strong enhancement of the heavy ion perpendicular fluid velocity compared with proton perpendicular fluid velocity. The linear multifluid cold plasma results agree with linear warm plasma Vlasov results and with the nonlinear hybrid simulation model results. In view of our findings we discuss how the observed nonthermal line broadening of minor ions in coronal holes may relate to the high‐frequency wave motions.