Correlation of ion acoustic turbulence with self-organization in a low-temperature plasma

Abstract

The correlation between ion acoustic turbulence (IAT) and self-organization is investigated in a low-temperature, current-carrying xenon plasma. Translating probes are used to measure the dispersion and power spectra of relative fluctuations in the ion saturation current in the plume of a hollow cathode discharge. Both ion acoustic waves and a low-frequency, propagating coherent oscillation are detected. Time-resolved measurements reveal that the amplitude of the IAT modes is modulated in time and is highly correlated in space and time with the coherent fluctuations in the ion saturation current and light emission. The phase relationship between the IAT amplitude and these oscillations further suggests that fluctuations in turbulence are causally connected to the periodic, self-organized structure. These results are interpreted in the context of a zero-dimensional model for the electron energy that balances Ohmic heating from the IAT against inelastic losses from ionization. A comparison of the model with the experimental measurements supports the conclusion that this form of self-organization is hydrodynamic in nature but is possibly driven unstable by the presence of kinetic electrostatic turbulence.