Vertical dust particle chains - mass and charge measurements

Dusty plasmas have generated a large amount of interest since the discovery of ordered structure (crystal) formation in experimentally generated complex plasmas in 1994. Dust particles within the plasma sheath generated in these complex plasmas can form vertical chains due to the streaming ion wakefield. For the simplest of these configurations (a two particle chain), the particle closest to the lower electrode will generally remain in the shadow of the particle farthest from the lower electrode. These results in the two particles feeling differing ion drag forces: the top particle is acted on by the ion drag force directed from the plasma to the lower electrode, while the bottom particle is acted upon by the resulting ‘wakefield’ produced by the interaction of the upper particle with the ion drag force. This dynamic situation currently provides the best known experimental environment for examining the physics behind the ion drag force and its interaction with the plasma sheath. An experimental method for investigating the interaction between pair-particle chains based on modulating the bias on the lower electrode employing a DC bias modulation technique will be presented.