M. Rubin-Zuzic

Dynamics of Lane Formation in Driven Binary Complex Plasmas

The dynamical onset of lane formation is studied in experiments with binary complex plasmas under microgravity conditions. Small microparticles are driven and penetrate into a cloud of big particles, revealing a strong tendency towards lane formation. The observed time-resolved lane-formation process is in good agreement with computer simulations of a binary Yukawa model with Langevin dynamics. The laning is quantified in terms of the anisotropic scaling index, leading to a universal order parameter for driven systems.

Auto-oscillations in complex plasmas

Experimental results on an auto-oscillatory pattern observed in a complex plasma are presented. The experiments are performed with an argon plasma, which is produced under microgravity conditions using a capacitively coupled rf discharge at low power and gas pressure. The observed intense wave activity in the complex plasma cloud correlates well with the low-frequency modulation of the discharge voltage and current and is initiated by periodic void contractions. Particle migrations forced by the waves are of long-range repulsive and attractive character.

Crystallization Waves in a Dusty Plasma

Crystallization waves in the dusty component of a complex plasma, which were recently observed experimentally, have been investigated numerically. The evolution of the system of charged microparticles whose interaction between each other is described by a screened Coulomb potential (Yukawa potential) has been numerically simulated using the molecular dynamics method. It has been shown that the process of the formation and propagation of a crystallization wave in such a system is fundamentally three-dimensional. Analysis of the local structure of dust particles behind the crystallization wave front indicates the coexistence of different types of the crystal lattice including the metastable phase, i.e., a nonequilibrium phase transition.

PKE-Nefedov - compley plasma research on the International Space Station

Complex plasma research is a new and rapidly developing field, with investigations under gravity and microgravity conditions. The complex plasma consists of a common plasma — with electrons, ions and neutrals — and an additional component of small solid particles typically in the range of micrometers. This heavy component in the plasma makes it necessary to perform experiments under microgravity conditions although it is possible to levitate the particles in the laboratory as well. The microparticles in the plasma are charged through the absorption of free electrons and ions to thousands of elementary charges. On Earth, the particles can be levitated in a strong electric field. But this induces stresses to the particle cloud which can only be eliminated under microgravity conditions. It also implies that under gravity conditions only a small part of the parameter phase space of complex plasmas can be investigated. Therefore, to complete the research on complex plasmas, investigations under microgravity conditions are mandatory. This paper overviews the research on complex plasmas on the International Space Station ISS achieved with the first long-term experiment, PKE-Nefedov, used for this research.

Bursting Bubbles in a Complex Plasma

Time-space plots called “periodgrams” are used to study a complex plasma under the influence of a temperature gradient. The plasma contained microparticles that were illuminated with a laser. The complex plasma spontaneously formed bubbles that induced the movement of particles upward through the discharge chamber. We visualize this particle movement with periodgrams and use these images to study a possible influence of the discharge stability on the particle dynamics.

Laser-stimulated melting of a two-dimensional complex plasma crystal

The melting of a two-dimensional plasma crystal was induced in a principally stable monolayer by laser-stimulated localized melting. Depending on the energy amount injected by the laser, the melted spot expanded outwards in a similar fashion to the mode-coupling instability (MCI) induced melting or recrystallized. As fluid MCI always exists in a melted monolayer, if the spot exceeded a critical size, the fluid MCI growth rate surpassed the damping rate and MCI-like melting was then observed. This behavior exhibits remarkable similarities with impulsive spot heating and thermal explosion in ordinary matter.

Single Particle Dynamics in a Radio-Frequency Produced Plasma Sheath

Recently different research groups have investigated the motion of a single dust particle levitated in a rf plasma. Here we describe a highly resolved experiment where a single spherical melamine formaldehyde microparticle is suspended in the plasma sheath above the lower electrode of a capacitively coupled radio-frequency discharge at controlled pressure, power and neutral gas flow rate. The particle’s horizontal oscillation is investigated, from which its neutral gas damping rate, kinetic temperature and eigenfrequency of the potential trap are measured. Compared to prior experiments we report about inhomogeneous and anisotropic velocity variations.

New Directions of Research in Complex Plasmas on the International Space Station

PK‐3 Plus is the second generation laboratory for investigations of complex plasmas under microgravity conditions on the International Space Station. Compared to its pre‐cursor PKE‐Nefedov, operational 2001–2005, it has an advanced hardware and software. Improved diagnostics and especially a much better homogeneity of the complex plasma allow more detailed investigations, helping to understand the fundamentals of complex plasmas. Typical investigations are performed to observe the structure of homogeneous and isotropic complex plasmas and instabilities occurring at high particle densities. In addition, the new setup allows the tuning of the interaction potential between the microparticles by using external ac electric fields. Thus, we are able to initiate electrorheological phenomena in complex plasma fluids in the PK‐3 Plus laboratory, and observe the phase transition from a normal fluid to a string fluid state at the individual particle level for the first time. Such new possibilities open up new direct...

Fluid complex plasmas—studies at the particle level

Complex plasmas are ideal laboratory systems to investigate kinetics of strongly coupled many‐particle ensembles. In contrast to colloidal suspensions, the particle dynamics in complex plasmas is virtually undamped. This makes complex plasmas particularly suited to study kinetics of fluids, by observing fully resolved motion of individual particles. In this paper we focus on three major experimental highlights characterizing kinetics of fluid plasmas—laminar shear flows, onset and development of hydrodynamic instabilities, and heterogeneous nucleation in supercooled fluids. Analysis of elementary processes observed in these experiments provides important insights into fundamental generic processes governing fluid behavior, demonstrating significant interdisciplinary potential of the complex plasma research.