Attractive interactions between negatively charged dust particles in a plasma

Summary form only given. Plasma dust particle interactions, charges, and screening lengths are derived from measurements of time-dependent particle positions in a simplified geometry. The magnitude and structure of the ion wake-field potential below a negatively-charged dust particle levitated in the plasma sheath region were measured as functions of the pressure and interparticle spacing. Attractive and repulsive components of the interaction force were extracted from a trajectory analysis of low-energy dust collisions between different mass particles in a well-defined electrostatic potential that constrained the dynamics of the collisions to be one dimensional. Typical peak attractions varied between 60 and 230 fN while the peak particle-particle repulsion was on the order of 60 fN. Random thermal motion of the particles contributed to observable rates for transitions between different equilibrium configurations of vertically separated particles. We also observed a slight potential barrier that impeded the formation of vertically aligned pairs. The influence of nearest- and non-nearest-neighbor interactions on calculated particle parameters are examined using several methods. Implications for plasma/surface interactions and plasma dielectric charging will be discussed.