Propagation of sound and spectrally resolved rayleigh scattering in weakly ionized plasmas

Abstract

The scattering mechanisms possible in weakly ionized plasmas are reviewed. The different cases can be discerned by means of the magnitude of three characteristic parameters: 2π/ωτ c being the ratio of scattering time and mean free collision time, y=1/kλ c being the scattering parameter defined as the ratio of scattering length and mean free collision path, and χω/c s, T 2 being the ratio between the product of thermometric conductivity and scattering frequency to the square of the adiabatic or isothermal sound velocity. For\({{2\pi } \mathord{\left/ {\vphantom {{2\pi } {\omega \tau _c > 1\), the scattering behavior is different from ordinary hydrodynamics. Here also do exist two types of waves, isochoric and isothermal, but none of them can propagate. Since the intensity of the scattered isochoric wave can be neglected, there is only one scattered line. Local temperatures and particle densities can be determined from the scattered spectrum. On the other hand, transport coefficients like shear and bulk viscosity as well as thermometric conductivity can be derived from sound absorption or Rayleigh scattering experiments if an independent temperature measurement is performed at the same time. The general formalism is applied to a weakly ionized hydrogen arc plasma.