30 Years of Complex Plasma Research - Predhiman Kaw Legacy Award in Plasma Physics and Fusion Studies 2025

Abstract

In 1994 the research field of dusty plasmas changed fundamentally due to the discovery of the crystallization of dusty plasmas in the laboratory. Before, dusty plasmas where mainly discussed theoretically concerning the interaction of dust particles with plasma in space, including interstellar clouds, circumstellar and protoplanetary accretion discs, nova ejecta, and planetary magnetospheres. In the late 80ies and early 90ies of the last century laboratory research in low-temperature plasmas started since dust particle growth became one of the leading problems in plasma processing industry. With the discovery of the so-called plasma crystals a new research field in classical condensed matter physics was born – a topic merging plasma and solid-state physics. It was named “Complex Plasma” in comparison to complex fluids – small solid particles in a fluid environment. One of the main properties of this new state of matter is the investigation of fluid and solid processes on the most fundamental – the kinetic – level due to the individual observation of the dust particles forming liquid and crystalline structures. A review is collecting major theoretical processes and experiments observed in this state of soft matter. Gravity strongly affects micron sized dust particles and leads to their sedimentation. In Earth-bound labs 2-dimensional plasma crystals can be formed and investigated by e.g. levitating the charged dust particles in the sheath electric field. For the formation of large 3- dimensional systems microgravity experiments are necessary and have been performed in parabolic flights, sounding rockets and onboard the International Space Station ISS. The latter generated a longstanding program on the ISS over more than 20 years up to now. In this presentation I will review the research over the last 30 years by showing some of the highlight topics of complex plasma research.