アフタグロー法を用いた両極性拡散から自由拡散への移行の研究

抄録

The electron density-dependence of effective diffusion coefficient D_s for electrons in argon Maxwellianized plasmas has been verified experimentally by means of afterglow technique. A calibrated microwave resonant cavity was used for measuring the electron density. By appending a synchronous detector to a conventional circuit, the sensitivity for the electron density <n_e> averaged over the volume of the cavity increased by about three orders of magnitude. Temporal behavior of the electron density between 1016 and 2.5×10¹¹ m^-3 at pressures of 46.6 and 66.5Pa was measured. In order to compare the experimental with theoretical results, <n_e> was transformed into the axial dcnsity, by the decay rate of which D_s was determined. The values of D_s were compared with those obtained theoretically by several authors in the range of ratios between 4 and 500 of the characteristic diffusion length Λ of the discharge tube to the Debye length λ_D0 for electrons. It was found experimentally that diffusion mode changed from ambipolar diffusion to transition modes when Λ/λ_D0 became smaller than about 100.