Past, Present and Future of Complex/Dusty Plasma research under microgravity conditions

Complex/dusty plasma is an ideal model system to study strong coupling phenomena in classical condensed matter. It offers the unique opportunity to go beyond the limits of continuous media down to the fundamental length scale of classical systems - the interparticle distance - and thus to investigate all relevant dynamic and structural processes using the fully resolved motion of individual particles, from the onset of cooperative phenomena to large strongly coupled systems. Unlike "regular" plasma species - electrons and ions - microparticles are strongly affected by gravity. A dc electric field in the rf sheath or a temperature gradient is usually employed to compensate for gravity, which provides favorable conditions to study 2D or stressed 3D systems on ground. However, in order to perform precision measurements with large isotropic 3D systems, microgravity conditions are absolutely necessary. This fact led to a complementary research on complex plasma under microgravity conditions starting in 1996 with parabolic flights and a first sounding rocket experiment, continued by experiments PK-1 and PK-2 (PK stands for “Plasma Kristall” \eq plasma crystal) on the MIR Space Station (1998-2000) and followed by research performed with the long term laboratories PKE-Nefedov (2001-2005) and PK-3 Plus (2006-2013) on the International Space Station ISS. Currently, this research on the ISS is continued with the PK-4 laboratory since 2014. In this presentation I will review important results from microgravity experiments from the last 20 years and will discuss the perspectives for future research. Acknowledgements: The research presented here has been performed in close cooperation with our partners from the Joint Institute for High Temperatures of the Russian Academy of Sciences and a large German and international team. Many thanks to everyone! The projects on the ISS were funded by DLR, BMWi, ESA, State of Bavaria, MPG, JIHT-RAS, ROSCOSMOS and the Russian Science Foundation.