Structure of Wind-Driven Plasma Turbulence as Resolved by Continuum Ion Probes

Argon gas is forced through a discharge tube to set up subsonic turbulent pipe flow. The resulting fluctuations in plasma density (excited by the ``mixing-in-gradient'') are investigated with continuum ion probes; the limits within which such probes can be used for fluctuation measurements are delineated. The flow is frozen and the small scale structure of the plasma turbulence is homogeneous. For Reynolds number greater than 6000, the rms value of plasma density fluctuation approaches 100% of the mean plasma density, the fluctuation intensity is essentially constant along the tube axis, and a nascent inertial subrange (K−5/3) appears in the plasma spectrum. The electrons are not in thermal equilibrium with the gas, and differences between the plasma and neutral spectra result.