Hydromagnetic Coupling Oscillations and Drift Instabilities in Nonuniform, Collisionless Plasmas

The thermal effects of resonant coupling hydromagnetic oscillations in inhomogeneous, finite-β plasmas, are studied. There are two thermal effects for such oscillations, the thermal phase mixing due to wave-particle resonance interactions and the drift effect arising from plasma inhomogeneities. Applying the drift kinetic approximation, the basic equations for the coupling modes between the Alfvén and magnetosonic waves in a nonuniform, collisionless plasma are obtained. For the plasma with β ≃ me/mi, ratio of electron to ion mass, it is shown that the electron thermal dissipation of hydromagnetic oscillations with ω/k‖ ≃ VA is most effective within the resonance coupling regions which appear in the cold plasma limit. This dissipation is very large as compared with the same dissipation process in the homogeneous plasma. On the other hand, if the hot plasma with β ∼ 1 is considered, attenuation of hydromagnetic waves due to ion-wave interaction becomes important. It will be an important process for ion heating, and the relevant equations are also derived. Next, drift instabilities in the long-wavelength limit are discussed for the most general case, including the density, temperature, and magnetic field gradients, as well as the ion Larmor radius effect. In particular, the slow mode of drift waves is unstable when Te′B0′ > 0 or Te′N0′ < 0, where prime means the spatial derivative in the radial direction. Finally, discussions of application to the magnetospheric plasma phenomena, which will be associated with inhomogeneities of the thermal constituents, are qualitatively given.