Langmuir probe diagnostics in the IMPF device and comparison with simulations and tracer particle experiments

The plasma parameters in the IMPF (International Microgravity Plasma Facility) device for studying complex plasmas are determined with a 2D-scanning Langmuir probe system, which is suitable for operation on the International Space Station. The probe characteristics in low density, low pressure radio frequency (rf) discharges are evaluated in the framework of the radial-motion theory with corrections for collisions. A critical comparison between experimental values for plasma potential and ion density with SIGLO simulations (Kinema Software) is made, which yields good overall agreement. In particular, the shaping of the plasma profile by different rf power in the plasma centre and in an outer ring is well described. Small amounts of dust particles are used as a novel method to mark the boundary, where ion-drag force and electric field force are balanced. Again close agreement with simulation is found and demonstrates the applicability of the tracer technique as a quantitative diagnostic means.