Improving far-infrared laser measurements of mhd plasma electron density and conductivity

Electron density and electrical conductivity are among the most important parameters governing performance of an MHD power generator. The far-infrared laser has offered a powerful diagnostic tool for measuring these quantities. However, clarifying the effects of the neutral gases and the laser beam refraction will improve accuracy. In the present paper, the variable-wavelength far-infrared laser was used to address these effects. In electron density measurement with a Michelson interferometer, the definite fringe shift due to neutral gases in the flame was detected, and the effects of neutral gases, especially the rotational absorption of water vapor, were quantitatively clarified. A method involving integrating beam intensity profiles is also suggested to account for the beam refraction effect of the conductivity measurements. The electron density and conductivity measured with corrections for these effects agree very well with theoretical calculations.