Density fluctuation spectra of a collision-dominated plasma measured by light scattering

The low-frequency electron density spectral function S(k,{ω}), having an ion acoustic peak (at {ω}{~}kcₛ) and an entropy peak ({ω}=0), has been measured by light scattering in a thermal collisional argon arc plasma. The entropy peak is for the first time observed in a plasma. A prediction of the spectrum derived from Braginskii's equations is adopted to estimate the transport coefficients. Ion viscosity, ion thermal conductivity, and electron-ion energy-transfer frequency determined from fitting to the data differ from predictions by -39%, +16%, and -22%, respectively.