Plasma Electron Velocity Distributions Determined from the Polarization of Free-Free Bremsstrahlung

The degree of polarization of the free-free bremsstrahlung from a plasma, as measured by Compton scattering, may be used to determine the electron velocity distribution. In this experiment, a hot electron plasma was made by means of electron cyclotron resonance heating in a magnetic mirror. The measured degree of polarization varied as mirror ratio and amount of lower off-resonance heating were changed. A theoretical computation of polarization, utilizing a nonrelativistic quantum mechanical theory, which matched the experimental conditions, showed that either a loss-cone or a Harris distribution could fit the observed data, except when lower off-resonance heating filled the loss cone. Under these conditions, only the Harris distribution was correct.