Forces acting on a coulomb crystal of microparticles in plasma

An equilibrium two-layer structure of charged microparticles in the near-electrode layer of a radio-frequency discharge was simulated numerically using the Monte Carlo method. Depending on gas pressure, the microparticles either move chaotically or form a multilayer structure with a hexagonal lattice in a horizontal plane. Based on the experiment, a mechanism is proposed that describes the unusual structure of a plasma crystal in which particles of the lower layer are located in the vertical direction strictly under the particles of the upper layer and form vertical columns.