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Electron densities and collision frequencies were obtained on a number of gases in a dc discharge at low pressures (0.70-2mm of Hg). These measurements were performed by microwave probing of a filament of the dc discharge placed coaxially in a resonant cavity operating in a TM010 mode. the equipment and techniques for making the microwave measurements employing the resonant cavity are described.

Atomic beam experiments are limited by intensity. Intensity limitations are specially critical in the measurements of metastable atoms, since their relative population is several order of magnitude smaller than the beam population. This thesis provides a method for increasing the intensity of metastable argon and neon beams effusing from a hot cathode, glow discharge by use of a longitudinal magnetic field. The argon and neon metastable atom intensities have been measured for a range of discharge pressure, voltage, and current for a magnetic field strengths from 0 to 31 mT. For both argon and neon, the metastable atom beam intensity rises to a maximum value about one order of magnitude above the zero field case. A qualitative discussion of the theory of this phenomenon is also presented.

Single Point Diamond Turning (SPDT) is a technology widely applied for the fabrication of contact lenses. One of the limiting factors in polymer machining is wear of the diamond tool due to electrostatic discharge resulting in poor surface quality of the machined products. The research work presented in this dissertation highlights the electrostatic properties of contact lenses during machining operations and the effects these properties have on the surface quality of the work piece materials. Two contact lens samples were experimented on, Definitive 74 (Silicone Hydrogel) and Tyro 97 (Rigid Gas Permeable). The electrostatic surface potentials (ESPs) were measured during turning operations using an electrostatic voltmeter and the surface roughness measurements were taken using a surface profilometer. Response Surface Methodology (RSM) techniques were employed to create predictive models for both surface roughness and ESPs with respect to the cutting speed, feed rate and depth of cut. Predictive surface roughness models were successfully generated for both materials and the cutting speed and feed rate were identified as the parameters with most effect on surface roughness. In addition, an electrostatic model was successfully generated for the Definitive 74 contact lens material which cited the cutting speed and feed rate as the most effective parameters on the material’s electrostatic behaviour. However, no relationship was evident between the machining parameters and electrostatic behaviour of Tyro 97.

The cylindrical column of plasma produced in the first stage of a z-pinch discharge is theoretically unstable. For one particular type of instability, the amplitude of a surface perturbation increases at a rate dependent on the acceleration of the surface (Rayleigh-Taylor instabilities). An experimental study of these instabilities has been carried out by photographing the discharge column with a high-speed framing-camera. Simple rotationally symmetric instabilities have been excited in the normally stable initial stage of an argon z-pinch discharge by means of a set of equally spaced glass rings. The framing camera photographs show that the instabilities develope approximately in accordance with the Rayleigh-Taylor theory. No axial drift of the instabilities is observed, but the new technique of studying instabilities reveals that the acceleration of the discharge boundary changes appreciably three or four times during the initial stage of the discharge. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Electromagnetic shock tubes were used to generate plasmas having a number density of the order of 10¹⁷ per cm³ and an energy per particle of 1-3 ev. In the shock tubes employed, the driving current was passed via electrodes through a discharge at one end of the tube. The discharge gases that were driven down the shock tube plus the ambient gas that was picked up and heated constituted the plasma that was studied. Many workers have assumed that shock equations can describe the discontinuity at the front of the plasma. An investigation into the effects of changes in the geometry of the driver mechanism has disclosed that the luminosity structure that can be attributed to the discharge gases stays very close to the luminosity front. The amount of ambient gas that is entrained in front of the discharge gases is thus small. Therefore, some doubt exists about the applicability of the shock equations both in the present shock tube and in the electromagnetic shock tubes of other workers. The shape of the luminosity front of the plasma was found to be affected by the properties of the driving discharge, even at a time long after the driving current had ceased to flow. Instabilities of the discharge and contamination by electrode material were found to drastically affect the homogeneity of the plasma. The homogeneity and reproducibility of the plasma produced by a small-cathode driver were found to be fairly good. However, there was a large amount of contamination in the plasma. The plasma was used to investigate the electro-dynamic response of an inductive magnetohydrodynamic power generator. Expressions for the output power were derived and compared with the experimental results. The electrodynamical response of a novel electrode-type Bɵ magnetohydrodynamic power generator was calculated. In an experiment performed with this generator a magnetohydrodynamic Interaction was observed indicating that the plasma was transporting an azimuthal magnetic field. No output power was obtained. The probable cause for this was that the applied magnetic field was insufficient to break down the sheath on the electrodes. A low pressure spark gap switch suitable for use as a main switch and as a "crowbar" switch on a capacitor bank was developed. The switch was operated over a voltage range of 0.5 to 25 kV, at energies up to 4 kJ and currents up to 500 kA. Under normal operating conditions the triggering time was 40 nsec and the jitter approximately 10 nsec. The inductance of the main switch was 4 nH and the inductance of the crowbar switch was about 1 nH. Other contributions are presented on a wide-voltage-range open-air spark gap switch, high voltage trigger circuits and on the dynamics of the plasma in an electromagnetic shock tube. The latter consists of an elementary treatment of the electromagnetic acceleration processes and a proposal of a model for the decelerating plasma. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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