ABSTRACT
This chapter explains that the low-frequency long-wavelength perturbations in an inhomogeneous finite–ßplasma are subdivided into the inertialess and Alfven oscillation branches. The theory of Alfven perturbations in an inhomogeneous finite–ßplasma was further developed in connection with the study of instabilities in a two-energy component plasma. In addition, the Alfven perturbations in a straight magnetic field are of interest as a limiting case of such perturbations in curvilinear magnetic fields. In the theory of a homogeneous plasma, the compression and extension of the magnetic field lines are typical for magnetoacoustic perturbations but not for the Alfven ones. The clarification of the correspondence between Alfven perturbations and the flute instability also clarifies the problem of the finite ion Larmor radius stabilization of such an instability at finite ß. The notion of the perturbations is significant for the problem of instabilities in force-free and almost force-free high–ßand in the theory of electromagnetic drift Kelvin–Helmholtz instabilities.
