Ion-neutral collision effect on an Alfvén wave

Abstract

This paper reports that ion-neutral collisions in a magnetized plasma cause a drastic change in the dispersion relation of the shear Alfv\'en wave with poloidal mode number m=0, connecting to the branch of the m=+1 compressional Alfv\'en wave at frequencies below the ion-cyclotron frequency. An anomaly of the dispersion then appears on the refractive index curve and a wave packet in this frequency range undergoes strong amplitude damping and profile deformation. It is confirmed that the Kramers-Kronig relation holds for the dielectric function, estimated from both the measured refractive index and damping rate.