Using dust grains to measure plasma conditions: changing plasma density*

Complex plasmas are of interest as they allow the self-assembly of micron sized dust particles to form both stable and unstable structures. The dynamics of these structures can be used to probe plasma parameters which are difficult to measure experimentally. The dust particle interaction with ions flowing towards a negative electrode creates an ion wake field, affecting both the charge on the dust grains as well as the electrostatic interaction between the grains.

A molecular dynamics simulation of ions flowing past dust grains in an experimentally stable configuration can be used to determine unknowns such as the local electric field driving the ion flow and the individual grain charges. Past experiments assumed the ion and electron number density to be constant over the extent of the dust structure. However, the electron and ion density in the sheath decrease towards the negative lower electrode. Given a vertically oriented dust chain structure, the individual particles act as probes to examine the changing condition in the vertical direction. Results from iterative applications of the numerical simulation will be discussed and compared to previous results with an assumed constant number density.