Vertical oscillations of magnetized particles in complex plasmas

Abstract

Summary form only given. In this article, we treat grain levitation in an external magnetic field and consider vertical vibrations of the magnetized particles around an equilibrium state taking into account magnetic field gradients. For a single magnetized particle a novel type of vertical vibrations in discharge plasmas is found. These vibrations can be stable or unstable depending on the distribution of the magnetic field inside the particle cloud. The vertical resonance frequency is independent of particle mass, but is completely specified by the magnetic field profile inside the complex plasma and magnetic properties of the grain material. A numerical estimate of the resonance frequency for typical complex plasma parameters in the magnetic experiments, gives magnitudes /spl sim/50-100 s/sup -1/. Such values are easily measured in experiments and the latter can provide a tool for determining the complex plasma parameters. In a one-dimensional particle string the magnetic force causes a new low-frequency oscillatory mode, which is characterized by inverse optic-mode-like dispersion when the wavelength far exceeds the inter-grain distance. The characteristics of the mode are specified by the gradients of the external magnetic field and thus can be effectively controlled in experimental conditions. This opens new opportunities for the investigation of particle behavior at the kinetic level as well as for stimulating phase transitions in the system, and for the study of self-organized structures in the experiments.