Measuring the particle charge in the bulk of a complex plasma

A complex plasma consists beside electrons, ions and neutrals also of a more massive, often purposely introduced component, the charged dust (nano-/micro-particles). Its acquired charge is a result of the dust—plasma interaction. Due to the relative high dust particle mass, the dynamics of the combined (complex) plasma system, is governed by the dust inertia. This allows to study the complex plasma at the level of the motion and positions of the individual dust particles. A major factor also plays the dust charge. It is often estimated theoretically using orbit motion limited (OML) or similar theories that rely on a background plasma model as well as several crucial assumptions. Experimental determination of the charge is difficult and thus rare, especially for particles in the bulk plasma. In this paper we will discuss an approach to determine an effective dust particle charge in the discharge bulk by analyzing the individual particle motion. We will utilize a free-fall experiment facility for complex plasma, such as the international space station experiment PK-4, to get access to particle motion in the bulk of the discharge.