Elastic dust particle particle interaction in an rf plasma provides a charge measurement method independent of the knowledge of plasma parameters. Assuming a screened Coulomb potential surrounding each particle with a constant charge at fixed plasma conditions, the charge and the screening length can be calculated from the trajectories of two colliding particles. With this method, we determine the charge and screening length of dust particles in the sheath of an rf discharge. The method can also be used to determine plasma parameters taking the dust particles as local probes.

• Received 25 February 1997

DOI:https://doi.org/10.1103/PhysRevLett.79.1269