Electromagnetic effects in fluctuations of nonequilibrium plasmas and applications to alpha diagnostics

Abstract

A generalized fluctuation–dissipation theorem is obtained for current and density correlation spectrum of a nonequilibrium plasma. Although normally significant density fluctuations occur in only electrostatic modes, the fast mode in the lower‐hybrid range of frequencies gives an exceptional example in which the mode is nontrivially electromagnetic, and yet the density fluctuations are comparable to the slow mode, which is well approximated by electrostatic approximation. This fact has quite important implications on the scattering of electromagnetic waves by nonequilibrium plasmas such as fusion plasmas with energetic α particles. It makes microwave scattering a more plausible scheme for α diagnostics.