Experimental verification of theoretical calculations of the static electrical conductivity in moderately non-ideal helium plasmas produced in flashlamps

Abstract
We present an experimental verification of the semiclassical theory [l] for static conductivity calculations in the case of moderately non-ideal plasmas which has been developed as a more simple approximation than the quantuum-mechanical theory based on the RPA method [2,3]. Such plasmas are produced in linear flashlamps (inner diameter 5mm, inter-electrode length 100mm) filled with pure helium and are characterized by on axis electron densities in the range 2. 10¹⁷ - 1.7 . 10¹⁸ cm^-3 and temperatures around (2-3) x 10⁴K, giving a plasma parameter Γ close to 0.1. Different methods of diagnostics based on measurements of continuum intensities, neutral line intensities and opacities (taking into account the effect of the statistical ionic microfields on the atomic levels), and infrared laser interferometry (3.39 µm), are applied to determine the radial profiles of particles and temperature. Profiles so deducted are relatively flat and show a good filling of the plasma inside the flashlamp. Such experimental conditions coupled with precise measurements of the discharge electrical parameters (current intensity and electrical field) allow for a reliable evaluation of the validity of this semiclassical theory. Finally, for each case, the impedance of the plasma so calculated is in good agreement with the experimental value, proving the validity of the semiclassical theory, and thereby of the RPA theory in our plasmas.