Electron number density and collision frequency measurements in a microwave surface wave discharge

The results of the electron number density and the electron-neutral collision frequency measurements in an argon plasma column produced by a microwave surface wave are reported in this paper. Two different measurement methods were used in order to determine the electron number density as a function of the plasma column axial position: the first uses a moving axial microwave probe mounted over the glass tube. The second uses a double Langmuir probe system. Two dispersion equations for the wave propagation were also obtained: one where the electron-neutral atoms collision frequency is much lower than the microwave frequency (v<<ω) being expressed as a ratio of modified Bessel functions. The other when the electron-neutral atoms collision frequency can be of the same magnitude of the microwave frequency being expressed as a ratio of Hankel functions. Using these dispersion equations and the experimental results an electron number density of n/sub e/=7×10/sup 10/ cm/sup -3/ and an electron-neutral collision frequency of v≈10/sup 8/ rad s/sup -1/ were obtained for an argon pressure of 100 mTorr and a microwave power of 750 W at frequency of 2.45 GHz.