Russian Cosmonaut Sergey Prokopyev during the Plasma Krystall-4 (PK-4) Experiment

iss057e074488 (11/7/2018) --- Russian Cosmonaut Sergey Prokopyev, during the Plasma Krystall-4 (PK-4) Experiment. PK-4 is a scientific collaboration between the European Space Agency (ESA) and the Russian Federal Space Agency (Roscosmos), performing research in the field of "Complex Plasmas". Complex or dusty plasmas are plasmas which contain beside electrons, ions, and neutral gas in addition micro-particles, e.g., dust grains. Due to the strong influence of gravity on the micro-particles, most experiments on complex plasmas are strongly distorted or even impossible on earth, and therefore, require microgravity conditions.