Analyses of attractive forces between particles in laboratory dusty plasmas

Some attractive forces act on negatively charged particles forming simple h exagonal structures of Coulomb crystals in dusty plasmas. In order to eluci date the origin of the forces, optical manipulations have been applied to a nalyze the behavior of particles in the crystal. It turned out in the analy sis that a primacy particle in the ion flow caused an attractive force acti ng on an another particle located in the lower reaches of the flow This fac t implied that the force was due to the wake potential in the flow. Further more, a molecular dynamics simulation was employed to examine structures co nstructed by particles interacting with Coulomb and wake potentials. It was clear in the numerical analysis that the wake potential could form simple hexagonal structures similar to the structure obtained in the experiment.