Electron concentration measurements in combustion MHD flows by submillimeter laser interferometry

Methods for the determination of electron concentration are discussed as an alternative to, or a check on, measure of electrical conductivity and temperature for characterizing plasma properties in combustion MHD flows. In particular, the interferometric method of determining the free electron concentration is analyzed, and its potential assessed. A submillimeter laser Michelson interferometer is described and preliminary measures of electron concentration in the free jet of the Stanford M-8 combustor are reported. It appears that accurate measurements of the path integral of electron concentration can be made which give good agreement with values calculated from Saha equilibrium at temperatures measured by the line reversal technique. A measure of the electron mobility also may be obtained, and hence the electrical conductivity may be derived by a single nonintrusive measurement technique which is applicable to ash-laden flows.