ELECTRON THERMAL DIFFUSIVITY IN RARE-GAS AFTERGLOW PLASMAS

This paper describes an experimental investigation of the electron thermal diffusivity D sub T in roomtemperature afterglow plasmas in neon and helium. The measurements were made in the absence of a magnetic field and covered an electron density range from 10 to the 9th power - 10 to the 12th power/cc. The principle of the experiment was to heat the electrons selectively by a short microwave pulse, and then observe electron temperature transients at different locations within the plasma. The electron temperatures were determined by taking advantage of the temperature sensitivity of the electroacoustic Tonks-Dattner resonances. For electron-ion collision frequencies much larger than the electron-neutral collision frequency, the experimental data for D sub T are inversely proportional to the electron density, and agree closely with the transport theory of Spitzer and Harm. In the limit of the weakly ionized plasma, the electron thermal diffusivity is independent of electron density, which is also in agreement with theory. (Author)