Laser Scattering Measurements of Thermal Ion-Acoustic Fluctuations in Collisional Plasmas

The thermal ion-acoustic fluctuation spectrum of a high-density, low-temperature (2 eV, ${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$), collisional plasma was measured in a C${\mathrm{O}}_2$-laser scattering experiment. The measured spectra differed substantially from spectra observed in collisionless plasmas. Fluctuations at the ion-acoustic frequency were strongly enhanced and the width of the resonance was significantly narrowed in comparison to the collisionless case. The Bhatnagar-Gross-Krook theory proved most successful in describing the data.