Determination of the ion-drag force in a complex plasma

The ion-drag force acting on dust particles in the positive column of a dc discharge is measured in the pressure range of 20–120 Pa. The force is obtained by a method which does not require a priori knowledge of the particle charge, but uses the charge gradient determined from the same experiment. The method depends only on two experimentally determined quantities: the particle drift velocity and the electric field. The comparison of experimental results with theoretical models is presented and discussed.