On the Theory of Wave Energy in a Plasma

Abstract

A general theory of wave energy in a plasma is developed in terms of a linear response of the field intensity to an externally applied infinitesimal disturbance. The theory is applicable to any situations, including the case when the conventional definition becomes invalid. An external disturbance can cause both frequency shift and amplitude change of the wave, and the sign of the wave energy in general depends on their relative importance and hence on the external disturbance. This feature is illustrated for the case of a cold-electron and cold-beam system. For the case when the dielectric function has a small anti-hermitian part, the conventional definition of the wave energy is recovered except for a special case where the frequency shift predominates over the amplitude change.