Oscillations Of Dust Grain, Lattice Waves, And Stable Dust Void In Electronegative Dust Plasmas

"Dusty Plasmas" is also called "complex plasmas", which contains not only electrons, ions, neutral particles in common plasmas, but also small solid particles. Dusty Plasmas exist widely in interstellar space, interplanetary space, planetary rings, comet's tails, earth's atmosphere, and all kinds of gas discharges in experiments. Dust plasmas have many unusual characters, such as open system, variation of charge, self-organized structure, etc. Now dusty plasmas have become a very interesting research field.In the study of dusty plasmas in laboratory, when many dust grains are immersed in gasous plasmas, because the electrons speed is much larger then the ions speed, the dust grains become negatively charged, the role of negative ions comes out as the content of electrons decreases quickly. Negative ions content will change the charge procession and the surface potential of dust grains, the latter distinguishes dusty plasmas from multi-component plasmas. The dusty plasmas contain negative ions are also called electronegative dusty plasmas. The influences of negative ions content on the oscillation of dust grain, lattice wave and dust void are mainly studied in this thesis. The influences of nonuniform magnetic field on the oscillation of dust grain and lattice wave are also studied. This may provide a new method for diagnostics.Firstly, the existence (also character, method, development) of dusty plasmas are introduced, particularly, the development of dust lattice wave and dust void which is related to my research work are introduced in detail.Secondly, one dimensional electronegative radio-frequency collisional sheath is built, and the characters of sheath are investigated. The sheath voltage and thickness vary with time, the space distribution of electric field, potential, the number density and velocity of all kinds of particles are solved self-consistently. The influence of collisional intensity and negative ions content on the sheath structure is studied. The result shows with the increasment of collisional intensity or negative ions content the sheath voltage increases and the sheath thickness decreases, the number density of ions increased and the velocity of ions decreased. Then the explanation of the results is given.Thirdly, on the basis of the sheath model above, the motion of an isolated dust grain is investigated, which includes the charge, forces and oscillation, especially the influence of the forces, the negative ion content and magnetic field on the oscillation. The result shows neutral particles contribute to damping. The influence of magnetic field on oscillation is decided by magnetic field structure and the equilibrium position. The negative ions will drop the oscillation frequency, which can be explained by the influence of negative ions on the ion drag force and electric field force.Forthly, using the method of studying lattice wave in solid physics, we investigate the dust lattice wave, including one dimentional longitudinal wave and two dimentional hexagonal transverse wave. Numerical result validates the neighbourhood approximation. Using three different electric interactional potential model (Coulomb Screen, Tsytovich, Wang), we compare the dispersion property of lattice wave. The influences of the inter-grain spaces, the magnetic field intensity and the negative ions content on the dispersion property are also investigated. For transverse wave, the attractive potential will increase the stability. Enlarging inter-grain spaces and increasing the negative ions content will also increase the stability. But it is contrary for longitudinal waves.Fifthly, the stable structure of dust void is investigated. A one dimentional electronegative hydro-dynamics model for stable void is studied. The existence of negative ions will change the form of Poisson equation inside and outside of the void and also change the charging equation at the void boundary. Numerical results show the influence of ionization rate and negative ions content on the stable void. The void boundary will decrease, the electric field intensity will increase and Mach number will decrease when raise the ionization rate or the negative ions content.