Experiment on the interaction between a plasma and a neutral gas. II

An interaction between a plasma and a neutral gas in relative motion is demonstrated. If the relative velocity is high enough, the interaction leads to heating of the electrons, partial ionization of the gas, and braking of the motion. The limiting velocity is found to be very close to Alfven's critical velocity. Two new means of plasma diagnostics are tried for the first time in this experiment. Measurements of the polarization of emitted spectral lines have yielded information on the velocity distribution of the electrons. An ion beam interaction technique has been employed to determine the density of energetic electrons. New evidence is also presented of electron heating and of the necessity of a magnetic field for the interaction to take place. The previously observed minimum gas density is also discussed