A kineticmagnetohydrodynamic model for lowfrequency phenomena
Abstract
A hybrid kineticmagnetohydrodynamic (MHD) model is presented for describing lowfrequency phenomena in highbeta (β~O(1)) anisotropic plasmas that consist of two components: a lowenergy core component and an energetic component with low density. The kineticMHD model treats the lowenergy core component by magnetohydrodynamic description, the energetic component by a kinetic approach such as the gyrokinetic equation, and the coupling between the dynamics of these two components through plasma pressure in the momentum equation. The kineticMHD model optimizes both the physics contents and the theoretical efforts in studying lowfrequency MHD waves and transport phenomena in general magnetic field geometries and can be easily modified to include the core plasma kinetic effects if necessary. It is applicable to any magnetized collisionless plasma system where the parallel electric field effects are negligibly small. In the linearized limit, two coupled eigenmode equations for describing the coupling between the transverse Alfvén type and the compressional Alfvén type waves are derived. The eigenmode equations are identical to those derived from the full gyrokinetic equation in the lowfrequency limit and were previously analyzed both analytically and numerically to obtain the eigenmode structure of the drift mirror instability (Cheng and Lin, 1987) which explains successfully the multisatellite observation of the antisymmetric fieldaligned structure of the compressional magnetic field of Pc 5 waves (Takahashi et al., 1987) in the magnetospheric ring current plasma. Finally, a quadratic form is derived to demonstrate the stability of the lowfrequency transverse and compressional Alfvén type instabilities in terms of the pressure anisotropy parameter τ and the magnetic field curvaturepressure gradient parameter α_{p} as defined in equations (31) and (69), respectively. A procedure for determining the stability of a marginally stable MHD wave due to waveparticle resonances is also presented.
 Publication:

Journal of Geophysical Research
 Pub Date:
 December 1991
 DOI:
 10.1029/91JA01981
 Bibcode:
 1991JGR....9621159C
 Keywords:

 Collisionless Plasmas;
 Kinetic Theory;
 Low Frequencies;
 Magnetohydrodynamic Waves;
 Anisotropic Media;
 Eigenvalues;
 Kinetic Equations;
 Geophysics;
 Space Plasma Physics: Kinetic and MHD theory;
 Space Plasma Physics: Waves and instabilities;
 Magnetospheric Physics: Energetic particles;
 trapped;
 Space Plasma Physics: Nonlinear phenomena