Jorna and Wood recently developed a program that numerically solved the Fokker-Planck equation in spherical geometry. In this thesis, we describe how the original program has been redeveloped to produce a program that is an order of magnitude quicker and that has superior energy and density conservation. The revised version of the program has been used to extend the work of Jorna and Wood on thermal conduction in laser produced plasmas. It has been shown that the effect of curvature on heat flow can be described from a purely geometrical argument and that for aspect ratios similar to those found in targets, the heat flow is reduced by approximately 10%. Also, it has been shown, in contradiction with Jorna and Wood, that the inclusion of the anisotropic portion of the Rosenbluth potentials does not have a significant effect on the heat flow. Even for highly anisotropic plasmas, the inclusion of the anisotropic portion only increases the heat flow by 10%. In addition, the revised version of the program has been used to study the energy relaxation of model distributions It has been shown that the relaxation time of most non - thermal distributions depends on the detailed structure of the distribution and that the normal Spitzer collision time can under-estimate or over-estimate the time required for energy relaxation.

Laser-Induced Breakdown Spectroscopy (LIBS) is a method of analytical chemistry that provides a qualitative and quantitative analysis of a sample. The ablation process of a sample is fast and dynamic and the change of plasma in time and space is a question of a few microseconds. An examination that provides a good time and space resolution is necessary to understand better the physical processes. For this reason, the goal of this thesis is to design a basic optomechanic construction for this type of experiment. Furthermore, it is important to check the functionality of this design and to use it for a basic comparison between the spectroscopic and imaging data. Also, the time development of plasma will be observed under different experimental conditions. The goal of this thesis, in general, is to prove that the morphology of plasma is as it is described in available related literature.

Spectroscopic investigations have been carried out on an argon inductively coupled plasma operating at non-atmospheric pressure. The relationship between torch pressure and a number of plasma operating characteristics was explored for torch pressures between 100 and 3000 torr. The plasma operating characteristics examined include observed analyte emission intensities, electron densities, ion to atom ratios, and the deviation of plasma conditions from local thermodynamic equilibrium. The effect of pressure on the observed analyte emission intensities was found to include factors in addition to the change in density of species within the torch. Emission lines originating from ions and atoms with high ionization potentials (greater than 7 eV) increased in intensity with increasing torch pressure, in excess of that predicted by the increase in density of species present. Conversely, emission lines originating from atoms of low ionization potential decreased in intensity with increasing torch pressure despite the increase in density. The results of the spatial determination of electron densities and ion to atom ratios indicate that excitation conditions within the central channel of the plasma are shifted towards conditions of local thermodynamic equilibrium as the pressure within the torch is increased. In addition, it is possible to obtain improved limits of detection by optimizing the torch pressure for the analyte element of interest.

A thesis submitted to the faculty of science, university of the Witwatersrand, Johannesburg,in fulfilment of the requirements for the degree of Doctor of Philosophy, 1994 / Alternative sample manipulation and sample introduction methods for inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS) have been investigated. The broad objectives of the study were to broaden the scope and improve the analytical performance of the techniques. The methods which were investigated were: 1) Laser ablation. This technique was used only in combination with ICP-MS. The technique was not applied to ICP-MS because the laser ablation system is dedicated to the ICP-MS instrument. The laser ablation system was applied to the direct analysis of solid refractory materials, without dissolution of the sample. The main advantages of avoiding the dissolution step are that the sample preparation is rapid, there is no dilution or contamination of the sample, and no loss of volatile analyte elements. The problems which were encountered with the use of laser ablation were firstly, poor precision of measurement relative to solution analysis due to sample particles of widely varying size entering the plasma, and secondly, memory effects when changing from one sample type to another. 2) Flow injection. This sample manipulation method was used in combination with pneumatic nebulization for ICP-AES and ICP-MS. The technique was applied to a number of different analytical problems, with the objectives of speeding up analysis times, increasing the matrix tolerance of the instruments, and automating a variety of sample preparation processes. 3) Hydride generation. This technique was applied to the determination of arsenic and selenium by ICP-AES and ICP-MS, using a novel type of gas, liquid separator. The advantages of the technique were the separation of the analyte elements from interfering matrix species, and increased analyte sensitivity due to the excellent transport efficiency of hydride generation relative to solution nebulization. Numerous advantages have been obtained from the application of these sample manipulation and sample introduction techniques. Methods have been developed for the analysis of materials which are not suited to conventional solution nebulization, and the techniques have been used to improve the efficiency of analysis, to achieve lower detection eliminate, and to eliminate interferences. / GR2017

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Thesis (Ph.D.)--University of California, Berkeley, 1963. / "UC-20, Controlled Themonuclear Processes" -t.p. "TID-4500 (19th Ed.)" -t.p. Includes bibliographical references (p. 107-112).

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The Babington principle nebulizer, useful for the introduction of samples containing suspended solids, or having high viscosities, into flames or plasmas, has been developed and characterized. Smaller versions of the nebulizer have been shown to provide higher sensitivity and reduced memory relative to the larger devices used previously. Data showing the sensitivities observed with a Babington type nebulizer and a flame emission spectrophotometer at varying flow rates of both the nebulizing gas and the sample solution are presented, along with an evaluation of several nebulizer configurations and tip sytles. The effect of nebulizing gas orifice size upon sensitivity is discussed. Although the Babington principle nebulizer will tolerate samples of varying viscosity, the nebulization efficiency is affected by the sample solution viscosity. A Babington type nebulizer employing a sample heater has been constructed and evaluated using motor oils of differing grades, and has been shown to reduce the effect of viscosity for this class of samples. This heated Babington type nebulizer has been used to develop a method for the analysis of wear metals in oil which does not require sample pretreatment. The effect of polymeric viscosity index improving additives commonly added to motor oils on the sensitivity of the method has been explored, as well as the effect of different complexing agents which may be used in the preparation of standards. A new method is described for numerically evaluating the inverted Abel integral equation, used to extract information about interior regions of flames and plasmas from spatially resolved data obtained from side-on measurements. This method, based upon cubic spline approximations, is compared to modifications of two methods drawn from the literature over a range of data set sizes and with varying amounts of noise superimposed upon the signal. The results of this study give a basis for selecting the best method for transforming experimental data of varying quality, and also for estimating the reliability of the results of the computation. An appendix describes the design and development of an instrument, computer interface, and software package which allow spatial mapping of spectroscopic sources at high speed. Suggestions are given for future work in these areas.