Formation of Ring-Shaped Fine-Particle Clouds in a DC Plasma

Abstract

Fine-particles in the plasma, negatively charge up due to fast electrons, are known to form Coulomb crystal under strong repulsive force. Fine particles interact with the plasma, and various collective behaviors are observed. The collective behaviors of fine particles, especially in strongly coupled state, are very complicated, because the various forces, such as electrostatic force, electromagnetic force, ion drag force, and friction force with gas, act on these particles. This chapter discusses various structures of fine-particle clouds by controlling the potential profile in a DC ion sheath. Fine particles in a strongly-coupled state are found to form a ring-shaped and a cone-shaped cloud. Wave propagations in the cloud are also observed. By compressing the fine particle clouds in radial direction with increasing the external electric field, the Coulomb crystal changes into an unstable state, and the particles begin to oscillate in vertical direction.