| Dusty plasma experiments were performed using two different experimental setups: one where particles were grown in a sputtering radio-frequency discharge forming a three-dimensional cloud, and the other where externally introduced microspheres formed a two-dimensional strongly coupled Yukawa solid.; In the experiment with growing particles two instability modes were observed: the “filamentary” and “great void” modes. The instability appeared after the particles grew to a sufficient size. It was characterized by laser light scattering, video imaging, optical emission spectroscopy, a newly developed electron temperature imaging method, Langmuir probe measurements, and Fourier analysis of the fluctuation spectrum. The electron density was found to be enhanced inside the great void, due to an absence of dust and electron depletion. The void formation is explained by the ion drag force, which becomes stronger than the opposing Coulomb force once the particle size reaches a critical diameter. When a dust-free region develops, its electron density is enhanced, the ionization rate increases, and the ion flow that pushes particles outward is further augmented.; Particle production in a sputtering discharge was demonstrated for a variety of target materials. Particles grown to a size of 300 nm to 5 μm, had either compact or fractal shape. Growth rate varied widely depending on the target material.; Mach cones in a two dimensional Yukawa solid were studied in a separate experiment. They were produced spontaneously by a fast particle moving below the main layer. The cones were found to obey the Mach cone rule. They had a double structure, first a compression wave where particles moved forward, then a rarefaction wave where particles moved backward. The cones caused only elastic deformations in the crystal lattice except on a narrow stripe behind the cone vertex. Treating the cone structure as a shock and applying the Hugoniot relations we found that the pressure increase caused by the compression wave was a factor of 1.3–1.6. The shock was classified as weak and elastic. Treating the cone structure as a dust lattice wave we calculated the electric charge of the particles forming the crystal lattice, which is a useful diagnostic tool for dusty plasmas. |
