A second look at void closure in complex plasmas

Abstract

Complex Plasmas are small micrometer sized particles injected into a low temperature rf-plasma. The particles are getting charged by electron and ion fluxes and form systems with gaseous, liquid and solid properties. Normally complex plasmas are compressed to 2D systems in laboratory conditions while they form a 3D cloud in micro-gravity with a particle free region in the center which is called void. The void can be suppressed by gas flow or additional electric fields, however, both ways add stress to the system. Another way is the reduction of rf-power, which was successfully used on the ISS before. The comparison of simulations and emission patterns reveal a lot of open questions, which were targeted by experiments of the 29. DLR parabolic flight campaign. The absence of a void in 1D self-consistent simulations indicates that the void is caused by 2D effects or more difficult geometries. In the experiments we could close and reopen the void by decreasing and increasing the rf-power. Other effects, such as particle mixtures in the former void region and dust density waves across the particle cloud, were observed.