Plasma Diagnosis by Means of Photon-Electron Scattering

Citation

Schwarz, Steven Emanuel (1964) Plasma Diagnosis by Means of Photon-Electron Scattering. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/7Y36-RP09. https://resolver.caltech.edu/CaltechETD:etd-10042002-124348

Abstract

When a pulse of intense light from a giant-pulse laser passes through a plasma, a very small fraction of the light is scattered out of the beam as a result of ("Thomson") scattering by free electrons. Under suitable conditions the intensity of the scattered light is proportional to the density of free electrons, while its spectral distribution is related to the velocity distribution of the free electrons through the Doppler formula. Theoretical considerations, relating to the conditions of validity of the method, are discussed. Various mechanisms which could interfere with the diagnostic technique are mentioned and their importance considered. Design considerations for diagnostic experiments are then taken up, and signal-to-noise ratios calculated. An apparatus for conducting scattering experiments has been constructed. Phenomenological checks indicate that the observed scattering is by free electrons. Measurements conducted at various times in the development of an afterglow plasma indicate Doppler broadening of the scattered light; the broadening disappears as the electrons cool during the first three microseconds of the afterglow. Measurements of electron density as a function of time are made in the afterglow, and are calibrated by means of Rayleigh scattering from gas at a known pressure. Two unexpected laser-plasma interactions have been observed. The first is designated as "induced plasma luminosity" and the second as "giant scattering." Both effects appear to be related to the presence of hydrocarbon impurities in the gas.

Thesis Files