Conductivity of a photoplasma of sodium vapor-inert gas mixtures

Parametric computations of electron energy distribution function (EEDF) and of electron mobility in photoplasma of sodium mixture with different inert gases are presented. The conditions of a weak external electric field are considered when electron heating is provided by super-elastic impacts (second kind collisions) with excited sodium atoms. It is demonstrated that nonequilibrium EEDF arising in heavy inert gases due to Ramsauer minimum on the cross section of elastic electron-atom collisions can considerably affect electron mobility. It results in complex nonmonotonous dependence of electron mobility from partial pressure of mixture components, plasma ionization degree, and from resonant-excited sodium atoms density. In Na+Kr, Na+Xe mixtures by low plasma ionization degree, the electron mobility can differ by more than two times from the one calculated with Maxwellian EEDF. In Na+Ar mixture, in certain conditions, the mobility may take on negative values. The critical plasma parameters (sodium excited atoms density, plasma ionization degree, electric field strength) determining this effect are revealed. The influence of nonequilibrium EEDF on electron mobility helps to explain abnormally low conductivity of photoplasma in Na+Ar mixture observed earlier in the experiment.