An investigation of dusty plasmas

This thesis constitutes a study of micron-sized particle behaviour in low-pressure radio frequency (RF) laboratory plasmas and of the plasma sheath in which these particles were suspended. A summary of the theoretical aspects of dust in a plasma includes reviews of the mechanisms behind the formation of the plasma sheath, development of a novel approach to the determination of the limiting RF amplitude at which the sheath will collapse, and a discussion of charging theories for isolated probes in the plasma and plasma sheath. Forces that act on dust suspended in the plasma sheath, including forces on isolated dust grains and the interparticulate forces within plasma crystals are then addressed. A novel theory of damped dust oscillations in the plasma sheath is developed. The existence of a harmonic potential well is postulated to explain the suspension of the dust. It is shown that the analysis of dust trajectories can lead to the determination of a number of dust parameters, including the drag force and charge on the dust. However the theory requires knowledge of the potential function in the sheath to obtain quantitative results. A numerical model is then developed to obtain the potential functions required by the oscillation theory. It describes a collisionless to moderately collisional plasma sheath driven by low to moderate RF amplitudes at frequencies between the electron and ion plasma frequencies. Output from the model includes the potential, field, charge density, carrier densities, and ion speed as functions of height above the electrode. Parameter variation is shown to affect the model output in the expected manner. The numerical model shows that the potential function was very nearly parabolic over the entire sheath. Analysis of eight independent models demonstrates that this parabolic result was general. Finally, the experimental apparatus and procedure used to determine the dust charge and drag on suspended dust of a variety of sizes are fully described. Two methods for charge determination are discussed, one involving analysis of damped dust oscillations and the other involving the balance of forces on the dust. Results are shown to agree well with each other, with those of other researchers, and with theory. (author)Available from British Library Document Supply Centre-DSC:D209911 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo