Studies of turbulence in complex plasmas under microgravity conditions

Kurzfassung

Complex plasmas consist of micrometer-sized particles embedded in a low-temperature plasma and are ideal model systems for nanofluids, phase transitions and transport processes. The microparticles can be visualized individually in real time, thus providing a kinetic level of observations of vortices, self-propelling, particle pairing, tunneling and channeling. For instance, vortices in complex plasmas are an ideal test bed for studying the onset of turbulence and collective effects on the microcanonical level. Specifically, driven turbulence in complex plas- mas is of low Reynolds numbers. The opportunity to study turbulence in fluids with low Reynolds numbers at the kinetic level is especially interesting in many other physical, biophysical, and industrial applications as diverse as water flow through porous media, viscoelastic liquid polymer flows, chaotic mixers, self-propelled stochastic microdevices, and bacterial quasiturbulence. Simulations of vortices in a typical laboratory setup allowed us to investigate the onset of turbulence and collective effects in complex plasmas. Velocity structure functions and the energy and enstrophy spectra show that vortex flow turbulence is present that is in essence of the "classical" Kolmogorov type. We report also on a complex plasma under microgravity conditions that is auto-oscillating due to a heartbeat instability and contains quasi-solitary wave ridges: oscillons. We demonstrate that this system can serve as a nearly ideal model system to mimic weak Kolmogorov-Zakharov type wave turbulence. The slopes of the structure functions agree rea- sonably well with power laws assuming extended self-similarity. The energy spectrum displays multiple cascades, which we attribute to the influence of friction, the heartbeat instability and a modulational instability.