Force measurements in dusty plasmas under microgravity by means of laser manipulation

Experiments in a dusty plasma under the microgravity conditions of parabolic flights are presented. Under microgravity, extended dust structures and a central dust-free region ("void") are formed. Here, the forces and the force balance at the void boundary are studied by means of laser manipulation of the dust particles: A focused laser beam is moved in a controlled way to drive particles in the extended dust cloud and at the void boundary. From the observed particle motion, the forces on the particles in the dust cloud and at the void boundary are derived. Together with Langmuir probe measurements, a quantitative description of the force balance has been achieved. Special attention has been paid to the ion drag force, which is crucial in understanding the void formation. The results are compared to prevalent ion drag models. (c) 2007 American Institute of Physics.