Thomson scattering in inhomogeneous plasmas: The Role of the Fluctuation-Dissipation Theorem

TL;DR

This paper develops a self-consistent kinetic theory for Thomson scattering in inhomogeneous plasmas, emphasizing the importance of the Fluctuation-Dissipation Theorem and revealing how plasma inhomogeneity affects spectral line properties.

Contribution

It introduces a new theoretical framework that accounts for plasma inhomogeneity and corrects previous inconsistencies related to the Fluctuation-Dissipation Theorem in Thomson scattering.

Findings

Both the real and imaginary parts of dielectric susceptibility influence spectral lines.

Inhomogeneity causes asymmetry in spectral line properties.

A method is proposed to measure local electron density gradients using Thomson scattering.

Abstract

A self-consistent kinetic theory of Thomson scattering of an electromagnetic field by a non-uniform plasma is derived. We draw the readers' attention to the inconsistency in recent results on the Thomson scattering in inhomogeneous plasma, which leads to violation of the Fluctuation-Dissipation Theorem. We show that not only the imaginary part, but also the derivatives of the real part of the dielectric susceptibility determine the amplitude and the width of the Thomson scattering spectral lines. As a result of inhomogeneity, these properties become asymmetric with respect to inversion of the sign of the frequency. A method is proposed for measuring local gradients of the electron density with the aid of Thomson scattering.