Obliquely propagating dust-density waves

Abstract

Self-excited dust-density waves are experimentally studied in a dusty plasma under microgravity. Two types of waves are observed: a mode inside the dust volume propagating in the direction of the ion flow and another mode propagating obliquely at the boundary between the dusty plasma and the space charge sheath. The dominance of oblique modes can be described in the frame of a fluid model. It is shown that the results fom the fluid model agree remarkably well with a kinetic electrostatic model of Rosenberg [J. Vac. Sci. Technol. A 14, 631 (1996)]. In the experiment, the instability is quenched by increasing the gas pressure or decreasing the dust density. The critical pressure and dust density are well described by the models.

Nonlinear structures of strongly coupled complex plasmas in the proximity of a presheath/sheath edge

“…In this paper, however, we address the situation when the gravitational force acting on the particles is negligible, the particles are strongly coupled and the dust cloud extends over the discharge plasma occupying the volume up to a boundary presheath/sheath. These conditions could be relevant for studies of complex plasmas under microgravity conditions (see, e.g., [15]- [18]), for thermophoretically levitated systems [19], for experiments on nanoparticle coagulation [20] and for processing plasmas dealing also with very small (submicron/nanometer-sized) particles [21,22].…”

Experimental Investigation of Dust Density Waves and Plasma Glow

“…All experiments presented here were performed on parabolic flights under microgravity conditions in the IMPF-K2 chamber, which is a modification of the device described in [4]. A schematic vertical section of the reactor is shown in Fig.…”

“…Finally, the fluctuation time series at each pixel coordinate is Fourier transformed. As described in [4], we calculate the phase from the argument of the complex Fourier coefficient corresponding to the dominant fluctuation frequency. Performing this procedure for each pixel coordinate yields a phase map.…”

“…This instability has been observed in many different types of discharge, e.g., [1]- [4], and usually spontaneously emerges at low gas pressures and high dust densities. The fundamental mechanism that drives the DDWs is a Buneman-type instability of charged massive dust grains, which interact with streaming ions and are shielded by thermal electrons [5].…”

“…However, recent experiments have shown that much more complicated situations can occur, where the propagation direction of the waves is not strictly parallel to the local ion flow [7], [8]. The authors also presented a model [4], which explains the direction of these obliquely propagating DDWs and its dependence on the ion local flow velocity. In addition to all experimental and theoretical work, many questions with regard to the nature of DDWs are still unanswered, including the processes that lead to saturation of the wave amplitude and the strongly nonsinusoidal character of the wave.…”