Plasma Diagnostics using Lasers: Relations between Scattered Spectrum and Electron-Velocity Distribution

Abstract

Laser light scattered from plasma electrons can be used to determine the electron density and velocity distribution. The process is classical Thomson scattering, and the scattered spectrum is constructed of the Doppler shifts of the electrons. The spectrum I(k), which appears at all angles and over a range of wave‐numbers, is uniquely related to the electron velocity distribution f(v). Either can be obtained from the other, and we derive the expressions I(k) = Lf(v) and f(v) = L⁻¹I(k) relativistically correctly. We also discuss the amount of information about f(v) obtainable from a simple measurement of the scattered spectrum. The electron density and mean speed can be measured easily; more subtle features depend upon accurate observation of the low‐intensity wings of the spectrum.