Coulomb Dust Spheres in a Glow Discharge in Neon at Cryogenic Temperatures

Abstract

The discharge parameters for the formation of charged spherical dust structures (Coulomb dust spheres) in neon plasma at a discharge tube wall temperature of 77 K are determined. The dust spheres were experimentally observed at fixed neon pressures of 0.15, 0.9, and 1.2 Torr. They were also obtained by extrapolation at pressures of 0.42 and 0.65 Torr. The dust spheres form at the discharge current corresponding to the intersection points of the dependences of the radial and axial dimensions of the dust structures on the discharge current. The correlation between the plasma parameters at which the dust spheres are formed and their composition, phase and dynamic states of their components, and dimensions of the dust spheres is analyzed. The variations in the parameters of the discharge plasma and dust spheres caused by a change in the gas pressure are numerically simulated. A continuous second-order phase transition is discovered in dust spheres at pressures of 0.15–0.65 Torr. An increase in the “chemical potential” of dust spheres is found near the liquidus line and the line separating the dust mixture components on the P–I phase diagram.