String fluids, turbulence, and waves studied on the level of the constituent particles using complex plasmas

Abstract

Complex plasmas are low-temperature plasmas with embedded microparticles. The microparticles in the plasma acquire high charges and strongly interact with each other. They form a classical condensed matter system, which can be used to investigate many generic phenomena on the level of individual particles. The microparticles are significantly affected by gravity, and unstressed three-dimensional microparticle clouds can only be studied under microgravity conditions. Here, we present studies of fluid complex plasmas performed in the RussianGerman complex plasma laboratory PK-3 Plus and the Russian-European PK-4 on board the International Space Station (ISS). The heart of PK-3 Plus was a capacitively coupled plasma chamber, and that of the successor PK-4 a DC plasma tube. Micropaticles can be injected in the plasma, which are illuminated from the side with light from a laser that is spread into a plane. The light scattered by the microparticles is recorded with digital cameras, with enables studying their movement in detail. Under certain conditions, instabilities turbulize the microparticle movement, or induce waves, which can then be studied in detail on the level of individual particles. When the applied electric field is quickly switched in polarity, ions flowing around the microparticles cause positive space charges (wakes), which attract other microparticles. This leads to the formation of microparticle strings - an electrorhelogical fluid. Fig. 1 shows an example of waves propagating in such a string fluid.