Waves in Magnetized Plasmas

Abstract

The linear response tensor contains all information on the linear response of a medium. In particular, it determines the properties of the natural wave modes of the medium. Magnetized plasmas can support a large variety of different wave modes. There is no systematic classification of wave modes, leading to a confusing variety of names. Some modes are given historical names (e.g., Alfvén, Bernstein and Langmuir waves), some are given names associated with the theory used to derive them (e.g., cold-plasma, magnetoionic and MHD waves), and many are given names descriptive of the wave itself (e.g., longitudinal, lower-hybrid and electron-cyclotron waves). Moreover, there is arbitrariness in the definition of a wave mode: a single dispersion curve can be interpreted as one mode in one limit and as another mode in another limit. Even the concept of a wave mode is ill-defined in the presence of damping (or growth); for example, there are many natural peaks in the spectrum of fluctuations in a thermal plasma and when a particular peak is to be interpreted as a natural wave mode is ill-defined. Let the properties of an arbitrary wave mode, labeled as mode M, be regarded as a function of the independent variable