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A superheterodyne Dicke type radiometer suitable for the measurement of radiation from a high temperature plasma in the 35 GHz range has been developed. The radiometer employs a balanced mixer at the radiometer frequency, a 3.5 GHz parametric amplifier using a varactor diode as the first IF amplifier, a broad-band transistor amplifier at the second IF of 7Q MHz and a commutator detector. The performance of the radiometer has been measured by conducting hot load tests and by using an S-band argon noise source. The minimum detectable temperature change was found from the hot load tests to be 11 deg K for an output bandwidth of 0.32 Hz. However, from argon noise source measurements, a minimum detectable temperature change of 1.4 x 10³ deg K was determined for an output bandwidth of 6.4 KHz and 9.5 x 10³ deg K for an output bandwidth of 160 KHz. The equation for the minimum detectable temperature change for the Dicke radiometer has been deduced following conventional analysis. It has been found that there are two errors in Goldstein's derivation the effects of which cancel out and his final formula is correct. Thus, the change suggested by Ring does not appear to be valid. For the two channel subtraction radiometer it has been found that the expression given by Graham should be multiplied by √2. The d.c. radiometer has also been analysed and it has been found that its minimum detectable signal power is independent of both the radiometer bandwidth and the output bandwidth. The effect of noise at the radiometer input before the modulating switch has been investigated and it is shown that this noise could produce a cutoff condition in the Dicke radiometer and the two channel subtraction radiometer. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The theory of Prigogine and Balescu has been applied to a homogeneous single-species plasma in a static uniform magnetic field. A kinetic equation has been obtained for the one particle velocity distribution, which is assumed initially isotropic in directions perpendicular to the field. The only stationary solutions of the kinetic equation are the Maxwellian equilibrium distributions, and an H- theorem has been established. The neglect of "collisions" of the order of duration of one cyclotron period or less (a strong magnetic field approximation) modifies the kinetic equation so that it no longer predicts any relaxation of the velocity components parallel to the magnetic field. An equation for the binary correlation function has been obtained in terms of the one particle velocity distribution, which is in turn determined toy the kinetic equation. Equations for the binary spatial correlation function and the binary correlation function for the guiding centers have also been obtained. It is demonstrated that the binary spatial correlation function represents the well-known Debye-screened equilibrium correlations when the one particle velocity distribution is the equilibrium distribution. The assumptions and approximations of the theory are clearly stated, and are discussed in some detail. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The phenomenon of anodization in the plasma of a dc low pressure oxygen glow discharge is investigated, both from the viewpoint of the mechanisms involved and for potential applications. Aspects studied include the effect of discharge conditions on anodization rate, the significance of negative oxygen ions in the plasma, the ionic current field strength relation in the oxide, and the anodization of metal films on silicon for MIS devices. It was found that the process does not utilize gaseous negative ions from the neutral plasma, and that species transport through the oxide is by high field ionic conduction. The variation of anodization rate with discharge conditions was attributed principally to a dependence of the oxide field strength on the electron energy distribution and density in the plasma. Double oxide layer MIS structures were fabricated, and charge storage effects were investigated. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The profiles of the He I lines with forbidden components in plasmas with electron densities below 10¹⁵ electrons per cc. are of astro-physical interest. A pulsed-arc plasma device has been constructed and operated at such initial conditions that in the afterglow (i.e. up to 200 μsec after breakdown), the steadily decreasing electron density passes through the range of interest. The plasma was observed end-on with a monochromator at a wavelength near 4471 angstroms for each discharge, and the intensity recorded as a functions of time. Good shot-to-shot reproducibility of the plasma permitted the line profile to be reconstructed for different times by repeating the measurements at different wavelengths spanning the line. The profile of He I 4471 has been measured for 10¹⁵ cm ̄³ and agreement has been found with the results of Burgess and Cairns (1971) and recent calculations of Barnard and Cooper (to be published). / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis is concerned mainly with developing accurate microwave methods for determining electron-density distributions in transient plasma columns. Two new methods have been developed and these have been evaluated by comparing with other methods. The first is a microwave refraction technique which depends on multiple reflections of an obliquely-incident microwave beam between the plasma critical layer and the walls of the discharge tube. It offers several advantages over previous techniques using microwave refraction; it is simpler and faster to implement, and yields accurate and more reliable results. Several methods for reconstructing profiles from refraction data are described. The second method depends on reflection measurements at normal incidence, and is suitable for plasmas in which the maximum plasma frequency is greater than the applied frequency. This method is based on measuring the rate of change in phase of the reflected signal due to Doppler shift in frequency produced by motion of the plasma critical layer. It has the advantage that the required data can be obtained from relative phase measurements which are less subject to experimental error than absolute phase measurements. Several methods of reconstructing profiles are developed. Approximate profiles can be determined from data at two frequencies only, while more detailed profiles involve applying a step-by-step procedure to data obtained at several frequencies. The sensitivity of the method to certain experimental errors is investigated and the validity of ray theory in the normal-incidence application is examined. A few related measurements were carried out in order to examine the validity of some assumptions made in connection with the microwave methods for determining profiles. The effect of polarization, the effect of altering the discharge-current waveform, and the possibility of a density gradient in the axial direction were investigated. Iangmuir double probes were used in a few cases to obtain an independent measurement of the electron-density distribution. Using the microwave refraction technique, extensive measurements were carried out in an afterglow plasma for various discharge conditions. A few interesting characteristics were observed, and a possible reason for the observed shape of electron-density profiles is suggested. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

A discussion of probe measurement of the magnetic field in a plasma is presented with particular reference to the perturbation of the magnetic field caused by the probe. A correction procedure is developed to compensate for this perturbation. Using magnetic probes, radial variation of the current density distributions are obtained for an argon plasma in a z-pinch discharge. Initial argon pressures of 100, 250, and 500 μHg are investigated. The current density distributions are determined for 1 μsec intervals between the initiation of the discharge and the occurrence of the first pinch. These current density distributions are compared with photographic observations. The experimental results are discussed in terms of the snowplow model and the shock wave model. Mathematically, the non-linear snowplow equation is solved using an approximation technique which results in analytic solutions. The shock wave equation is solved by a graphical technique. An extension of the shock wave model is proposed for a better understanding of the experimental results. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The suppression of radial hydromagnetic oscillations of a theta pinch plasmoid produced in air has been investigated with magnetic probes and a framing camera. In the presence of essentially static and uniform magnetic bias fields (produced by Helmholtz coils) it was found that the oscillations are suppressed by a flip instability of the plasmoid and the direction of flip is controlled by the transverse magnetic field. Using the suppression of radial hydromagnetic oscillation as the criterion for flip, it is found experimentally that if [formula omitted] is greater than a critical value, then the plasma ring flips. [formula omitted] is the strength of the bias field perpendicular to the axis of the theta coil, 'a' the radius of the discharge vessel and 'p' is the gas pressure. The experimental results are interpreted in terms of a snowplough model for the discharge, in which the plasma current forms two concentric cylinders. The predictions of the theory agree with the experimental observations. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The temperature of a Helium plasma produced in a shock tube has been determined from absolute intensity measurements. The plasma was considered to be homogeneous, transparent and in local thermodynamic equilibrium. The emissivity of the plasma has been measured by comparing the plasma radiation to the radiation from a carbon arc through a simple optical system. The influence of errors in measured parameters and the presence of impurities is discussed. Temperatures which depend on large exponential terms are relatively insensitive to both errors in measurement and the impurity content of the plasma. The accuracy of absolute intensity measurements is at best comparable to relative intensity measurements. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Improvements to the laser excited interferometer previously constructed in this laboratory are described. The use of a rotating retro-reflector in the interferometer cavity, and electronic circuitry, permit direct recording of electron densities. The sensitivity of the interferometer is 5 x 1015 cm-2, and the temporal resolution is 0.1 usee. Pyrex tubes, terminated by windows, enclosing the laser beam, have been used to improve spatial resolution. The effects of the tubes, and of all other sources of error associated with interferometric measurements of electron densities, have been carefully assessed. A Z-pinch discharge in 4 torr helium has been studied with this instrument, and with spectroscopic determinations of electron temperature. Under the conditions chosen, the pinching plasma does not reach the axis of the discharge tube, but stops at a radius of 2.7 cm. The shock front caused by the pinching action has been shown to be weak. Longitudinal structure, due to heat flux, characteristic cathode behaviour, and variations in timing of the pinching action, has been found. The discharge has been assessed as a spectroscopic source and as a medium for laser scattering experiments. The characteristics of two suitable regions are presented. These are the axial region and the hollow cylinder of plasma formed by the arrest of the pinching plasma. Both are free of instabilities. At the appropriate time the latter is also current free, and shows longitudinal electron density variations of less than 2%. The length of time that the current spends near the wall of the vessel is determined by the balance between kinetic and magnetic pressures. / Science, Faculty of / Physics and Astronomy, Department of / Graduate