Fine-Particle Clouds Controlled in a DC Discharge Plasma

The spatial shape of fine-particle clouds in a strongly coupled state is controlled by varying a radial potential profile provided by radially segmented electrode for particle levitation and confinement under a completely dc configuration. Fine-particle clouds change their shapes from a usual two-dimensional disk to a three-dimensional cone, and finally concave cone with an increase in the radial potential slope. These profiles are closely related to an axial variation of the radial potential profile in the ion sheath above the segmented electrode. When we apply to the segmented electrode a potential profile with peaks between the radial center and edge, fine particles are rearranged to form azimuthal rings on the horizontal plane. The radial width of the rings is controlled by changing the peak width of the radial potential profile. Index Terms--Coulomb crystal, dc discharge plasma, dusty plasma, fine-particle cloud, potential control, segmented electrode, strongly coupled plasma.