Ion acoustic turbulence in a large-volume plasma

Ion acoustic turbulence excited by the current-driven ion acoustic instability in a large-volume plasma is studied experimentally. As the electron drift velocity increases, the fluctuation level of the waves increases and at the same time the peak of the turbulence spectrum shifts to a lower frequency. The resulting power spectrum agrees with that predicted by Horton. The effective collision frequency ν of the plasma is measured as a function of the electron drift velocity vd in the presence of the ion acoustic turbulence. For an electron drift velocity below 0.05 ve the effective collision frequency ν/ωpe varies such that vd/ve remains approximately constant and for the drift velocity above 0.09 ve the effective collision frequency is observed to be proportional to vd/ve. It is found that these results can be explained by using the theoretical model of Horton, in which the induced ion-wave scattering dominates the turbulence spectrum and the turbulent collision frequency limits the spectrum at small kλD.