## Plasmas as Dielectric Media

The plasma has been defined as a statistical ensemble of mobile charged particles; these charged particles move randomly in the system, interact with each other through their own electromagnetic forces, and respond to the electromagnetic disturbances which may be applied from external sources. The chapter lays a theoretical foundation for the electrodynamic description of plasmas as continuous dielectric media. It gives a mathematical definition of the dielectric tensor; it applies this dielectric tensor to a set of macroscopic electrodynamic equations and finds a formal solution in the form of a frequency-wave number dispersion relation. Such a dispersion relation characterizes the basic properties of both the longitudinal and the transverse excitations in the dielectric medium. The dielectric tensor contains essentially all the information about the electromagnetic properties of the plasma; it is determined from a calculation of the plasma response to an electric field disturbance. The dielectric response function is calculated simply from the dielectric tensor.