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 directions of research under microgravity conditions.