ELECTRON CONCENTRATION MEASUREMENTS IN COMBUSTION MHD FLOWS.

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