We used microparticles under hypergravity conditions, induced by a centrifuge, in order to measure nonintrusively and spatially resolved the electric field strength as well as the particle charge in the collisional rf plasma sheath. The measured electric field strengths demonstrate good agreement with the literature, while the particle charge shows decreasing values towards the electrode. We demonstrate that it is indeed possible to measure these important quantities without changing or disturbing the plasma.

In basic plasma physics and plasma technology, micro‐particles (dust grains) play an important role for the investigation and understanding of the behavior of different plasma species. It is well known that micrometer‐sized particles can find an equilibrium position if all acting forces to the particles are balanced. This stable point is a few millimeters above the powered electrode in the plasma sheath. In our experimental set‐up, we observed the position and the motion of microscopic test particles with a typical radius between 4.78 and 13.3 µm. In addition to the experiments, we also investigate the particle behavior by a numerical model. By comparison between the numerical model and the experimental observation, internal plasma parameters can be obtained.

measurements in the sheath of an argon RF discharge by probing with microparticles under varying gravity conditions. In

An interesting aspect in the research of complex (dusty) plasmas is the experimental study of the interaction of micro-particles of different sizes with the surrounding plasma for diagnostic purpose. In the plasma micro-disperse particles are negatively charged and confined in the sheath. They are trapped by an equilibrium of gravity, electric field force and ion drag force. From the equilibrium position and motion of the particles, local electric fields can be determined, e.g. particles are used as electrostatic probes. In combination with additional measurements of the plasma parameters with Langmuir probes and thermal probes as well as by comparison with an analytical sheath model, the structure of the sheath can be described.

Microparticles in a RF plasma under hyper gravity conditionsBeckers, J.; Stoffels, W.W.; Ockenga, T.; Wolter, M.; Kersten, H.