Dissertations / Theses: 'Gas discharge physics'

1

Ingram, S. G. "Investigations of low pressure RF discharges in argon." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.480534.

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Goruppa, Alexander. "Modifications of radiofrequency capacitive discharge for deposition of carbon coatings." Thesis, Open University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251396.

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Vigstrand, Oscar. "Development of an absorption model for gas discharge lamp simulation." Thesis, Malmö universitet, Malmö högskola, Institutionen för materialvetenskap och tillämpad matematik (MTM), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-42518.

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Ultraviolet (UV) light has been used for disinfection purposes for over 100 years. Irradiation by UV light is a method to disinfect surfaces in order to prevent microbiological growth. At Tetra Pak this is of great importance as they are manufacturer of filling machines. Those filling machines must ensure a certain level of sterility on all packages produced. The irradiation process can be simulated using Geant4 which is a software package that tracks particles through matter. The simulation model used today does not consider the absorption of photons inside of medium-pressure UV lamps. By understanding the absorption that takes place in the lamp, one can quantify how changes in the design would impact the emitter output. In this master's thesis, the aim is to develop a model that can describe the interaction of photons with a medium-pressure UV lamp. An absorption model was suggested and developed with the assumption of local thermodynamical equilibrium and existing Hg radiative data. A simulation including the collision process in Geant4 was used. In this collision process the non-radiative transition probabilities were assumed to be the same as that of the radiative, this was done in order to demonstrate how it can be done. It resulted in collisions populating other states allowing more transitions to be present in the final output spectrum. The collision process and a method for computing the Einstein's emission coefficient with the software package General Relativistic Atomic Structure Package is proposed as future work.
I över 100 år har ultraviolet (UV) ljus använts till desinficering. UV bestrålning är en metod för att desinficera ytor med målet att förhindra mikrobiologisk tillväxt. För Tetra Pak som är ledande inom tillverkning av fyllmaskiner är det extra viktigt. Förpackningarna inuti fyllningsmaskinerna måste garantera en viss nivå av sterilitet för alla förpackningar. Dagens simuleringar av medeltrycks UV lampa utförs i Geant4 som är ett mjukvarupaket som möjliggör följandet av partiklar genom olika medium. Detta görs utan att ta hänsyn till absorptionen av fotoner. Genom att förstå absorptionen som sker i lampans gas kan man kvantifiera hur förändringar i design skulle påverka emittorns utgående effekt. I detta examensarbete är målet att utveckla en modell som kan beskriva hur fotoner växelverkar med gasen i en medeltrycks UV lampa. En modell utvecklas och föreslås med antagandet att lokalt termodynamisk jämvikt råder och att enbart Hg strålnings data används. En simulering med en kollisionsprocess i Geant4 inkluderades. I denna kollisionsprocess antas den icke-optiska övergångssannolikheten vara densamma som för de optiska övergångarna. Detta inkluderades för att demonstrera hur en sådan process kan gå till. Detta resulterade i att kollisionerna populerade andra tillstånd vilket gjorde att dessa övergångar visade sig i utgående spektrum. Kollisionsprocessen och en metod för att beräkna Einsteins emissions koefficient med mjukvarupaketet General Relativistic Atomic Structure Package föreslås även som framtida arbete.

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Barrios, Andrés J. "Yield of metastable atoms from a rare gas discharge in a longitudinal magnetic field." FIU Digital Commons, 1993. http://digitalcommons.fiu.edu/etd/1415.

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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.

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Kemaneci, Efe H. "Numerical Investigation Of A Dc Glow Discharge In An Argon Gas: Two-component Plasma Model." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12610917/index.pdf.

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This thesis deals with a one and two dimensional numerical modeling of a low-pressure DC glow discharge in argon gas. We develop two-component fluid model which uses the diffusion-drift theory for the gas discharge plasma and consists of continuity equations for electrons and ions, as well as Poisson equation for electric field. Numerical method is based on the control volume technique. Calculations are carried out in MATLAB environment. Computed results are compared with the classic theory of glow discharges and available experimental data.

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Eylenceoglu, Ender. "Numerical Investigation Of Self-organization And Stable Burning Conditions Of Moderate Pressure Glow Discharges In Argon Gas." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613634/index.pdf.

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In this study numerical modelling of a moderate pressure DC glow discharge plasma is car- ried out in 1D and 2D geometry. The governing equations include continuity equations for the plasma species (electrons, positive ions and metastable atoms), the electron energy equation (EEE), Poisson equation for the electric

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Sanabria, Edgar Rodolfo Rondán. ""Teoria e modelamento computacional de aquecimento de plasma por ondas de alfvén no tokamak TCABR"." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-20102006-111511/.

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Neste trabalho apresentamos o estudo da possivilidade de melhores regimes para o uso dos experimentos de aquecimento e geracao de corrente e fluxo de plasma no tokamak TCABR. Apresentamos um estudo dos efeitos de rotacao de plasma em baixa frequencia (low-frequency (LF)), penetração de campo eletromagnético, absorção e forças ponderomotoras no Tokamak Chauffage Alfvén Brésilien (TCABR) com ênfase na faixa de frequências de 0, 510, 0kHz. Os campos de LF são dirigidos pelo limitador magnético ergódico (ergodic magnetic limiter (EML)) no TCABR. Foi feito um estudo analítico das ondas de Alfvén e ressonância usando modelos simples. Um estudo num´erico tembém foi realizado utilizando três códigos, quais sejam, o código cinético toroidal, o código cilíndrico e o código ALTOK.
In this work we present the study of the determination the best regimes and parameters¶for the heating experiments and current generation and plasma flow in the tokamak TCABR. Study of effects of plasma rotation in low frequency (LF), field penetration, absorption and ponderomotive forces in Tokamak Chauffage Alfvén Brésilien (TCABR)is investigated with emphasis in the frequency range of 0, 510, 0kHz. The fields of LF are driven by the ergodic magnetic limiter (EML) in TCABR. A qualitative analytical study of the Alfvén waves and their resonances is performed using simple models. A numeric study was carried out using through three codes, called the kinetic totoidal code, the cylindrical code and the ALTOK code.

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Malik, N. K. "Studies in vacuum discharges." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370286.

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Chen, Bing-Hung. "Inductively coupled radio-frequency discharges." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244566.

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Woodcock, Benjamin Kane. "Spectroscopic studies of RF glow discharges." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318464.

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11

Maciel, H. S. "Double layers in mercury arc discharges." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355761.

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12

Moss, Graham James. "A time-dependent collisional-radiative model of low pressure gas discharges." Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269399.

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Al-Jibouri, Abdul-Rahman Mohammed Abdul-Muhsen. "Photodetachment studies of negative hydrogen ion in discharges." Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264011.

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Ford, Michael John. "Fundamental studies of mixed gas plasmas in ICP-MS." Thesis, University of Plymouth, 1993. http://hdl.handle.net/10026.1/1941.

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Inductively coupled plasma - mass spectrometry is widely accepted as the leading technique for trace element analysis. It suffers however, from a range of interferences both spectral and non - spectral which limit the range of analytes and substrates which may be successfully analyzed. This study has investigated the use of mixed gas plasmas as a means of reducing or removing these interference effects. In addition the use of mixed gas plasmas for sensitivity enhancement has been assessed using both wet and dry sample introduction systems. Simplex optimization procedures have been used throughout. The addition of nitrogen to all three argon gas flows of the ICP was evaluated, and the instrumental operating conditions were optimized to allow for the maximum removal of the ArCl+ interference on As and Se. The addition of nitrogen to the nebulizer gas was particularly effective in the removal of the ArCl+. The use of nitrogen addition also facilitated the determination of arsenic in samples where it was previously found to be impossible. The addition of methane was also applied to all three gas flows of the ICP, however, in this case only the addition to the nebulizer gas was successful in removing interferences. These included ArO+, ClO+ and CeO+ in addition to ArCl+ . Detection limits, recoveries and CRM analysis were all improved by the use of methane addition when compared to nitrogen addition or standard argon plasmas. Hydrogen addition was applied solely to the nebulizer gas and found to significantly increase the magnitude of the interferences from argon based polyatomic ions, whilst reducing those from metal oxides. The addition of hydrogen was useful in reducing MO+ interferences, but the removal of other interferences proved unsuccessful. The addition of ethene to the nebulizer gas has been used to remove many of the polyatomic interferences encountered in ICP-MS, including those based on Na, S and P. Ethene addition was as effective as, and usually better than, the addition of both methane and nitrogen. Detection limits, recoveries, calibrations and CRM analysis were all improved by its use. The use of ethene addition has lead to improvement in the determination of As, Cu, Fe, Gd, Ni, Se, and V in the presence of the relevant interference precursors. Most importantly it has been shown that a whole range of interferences can be reduced simultaneously with the addition of ethene. The plasma operating parameters and ion optics settings of a commercial ICP-MS instrument were optimized to yield maximum SBRs for elements across the mass range. It was shown that simple manual tuning of the instrument did not effect the SBRs, when compared to the simplex optimized conditions. Finally it was shown that the addition of molecular gases to the ICP, did not result in any significant improvements in sensitivity, when compared to the all argon system. Finally it has been shown that the addition of a relatively small amount of hydrogen to the nebulizer gas can lead to an enhancement in the signal obtained using laser ablation sampling. This enhancement was greatest for low mass elements and had no effect on the heavy mass element signal.

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15

Yuan, Qiulin. "Studies of electric discharges and their interactions with gases." Thesis, Loughborough University, 1997. https://dspace.lboro.ac.uk/2134/22086.

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Measurements of the effect of increasing the discharge column voltage gradient were investigated using argon based mixtures with nitrogen, oxygen and sulphur hexafluoride in a plasma torch. The theoretical calculation of the voltage gradient and the electron number density was based on the Saha equation which was modified for application to the gas mixtures. The investigations showed that a mixture of Ar and SF6 was most effective and increased the voltage gradient to 0.5 V/mm from 0.3 V/mm. The best mixture was 89% Ar, 10% N2 , 1% SF6 based on the highest increase of the voltage gradient and the least added gas. A model has been developed to illustrate the effects of dissociation, excitation, ionisation of gases and their effects on the discharge column voltage gradient: The mode of an electric discharge in Ar was investigated using spectroscopy. The study showed that for a glow discharge the 520.0 nm line and for an arc discharge the 427.1 nm line were unique. These lines were used to investigate a Glydarc electric discharge which was shown to be a mixture of the glow and the arc discharges. Measurements of the transition of the glow to arc in Ar with discharge current ranging from 0.1 A to 1.0 A at atmospheric pressure showed that at the lower value of discharge current (O. 25 A) the spectral lines were dominated by the near infra-red lines whereas at the higher value of discharge current (1.0 A) the spectral lines were included from the near infra-red to the near UV. The Glydarc electric discharge has been studied in still and fast air flows at atmospheric pressure over a range of discharge currents from 100 mA to 3 A. The results showed that the increase of the discharge voltage with increasing discharge current was due to increase of the discharge column length which varied with time and the air flow rate and was not due to a positive dynamic characteristic.

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16

Coumar, Sandra. "Etude des mécanismes physiques induits pas un actionneur plasma appliqué au contrôle d’écoulements raréfiés super/hypersoniques dans le cadre de rentrées atmosphériques." Thesis, Orléans, 2017. http://www.theses.fr/2017ORLE2025/document.

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Ces dernières années, les missions spatiales bénéficient d'un regain d'intérêt. Cependant, lorsqu’arrive laphase d’entrée dans l’atmosphère, nous faisons encore face à d’importantes difficultés. Afin de répondre àce problème, une nouvelle technique est proposée : le contrôle par plasma pour augmenter la force detraînée sur le véhicule et ainsi, décroître sa vitesse. Dans cette thèse, un actionneur plasma est testé danstrois écoulements supersoniques (N1(M2-8Pa), N2(M4-8Pa) and N3(M4-71Pa)) et un hypersonique (M20-0.062Pa), ces écoulements étant simulés par la soufflerie MARHy.L’actionneur plasma induit des modifications de l’écoulement autour du modèle étudié, comme unemodification de la géométrie de l’onde de choc et une augmentation de l’angle de choc. Afin de mieuxcomprendre les phénomènes gouvernant ces modifications, la pression Pitot, la température surfacique etvolumique, les données électroniques et des mesures spectroscopiques ont été analysées. Les résultatsmontrèrent que deux types d’effets interviennent : thermiques (surface et volume) et l’ionisation. De plus, il aété démontré que ces effets n’ont pas la même importance suivant les conditions d’écoulements.L’actionneur plasma lui-même a été modifié dans un but d’amélioration. En particulier, deux types degénérateurs ont été étudiés pour alimenter la cathode : DC et pulsé. Finalement, il est montré que pour unepuissance de décharge de 80 W, une augmentation de 13% de la traînée et donc, une diminution de plus de25% des flux de chaleur peuvent être attendus. Par conséquent, les actionneurs plasma semblent être descandidats idéaux pour les missions spatiales et les (r)entrées atmosphérique
Space missions are arousing renewed interest in these recent years. However, when coming to the entryinto the atmosphere, major issues are still to be considered. To answer this problem, a new Entry DescentLanding technique is proposed: plasma actuation to increase the drag force over the vehicle body and thus,decrease its speed. In this thesis, a plasma actuator is tested in three supersonic rarefied flows (N1(M2-8Pa), N2(M4-8Pa) and N3(M4-71Pa)) and a hypersonic one (M20-0.062Pa), all generated by the wind tunnelMARHy.The plasma actuator induces flow modifications over the studied model, such as a change in the shock waveshape and an increase in the shock wave angle. In order to better understand the phenomena governingthese modifications, Pitot pressure, surface and gas temperature, electron data and spectroscopicmeasurements were analyzed. The results shown that two types of effects are involved: thermal (bulk andsurface) and ionization. Moreover, it was demonstrated that these effects had not the same importancedepending on the flow conditions.The plasma actuator was also modified in order to improve it. In particular, two types of generators wereused to biase the cathode: DC and pulsed. Finally, it was shown that, for a discharge power of 80 W, a 13%increase in the drag force could be expected and thus, a decrease in the heat load over the model body ofmore than 25%. Therefore, plasma actuators seem to be promising applications for space missions andatmospheric entries

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Preston, Stephen Gareth. "Investigations of short-pulse ultraviolet laser interactions with gas targets." Thesis, University of Oxford, 1995. https://ora.ox.ac.uk/objects/uuid:10c12437-3d88-4166-aa34-540b938f61bd.

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This thesis presents investigations of interactions of a 380 fs, 248.6 nm KrF laser beam focused to intensities up to 10¹⁸ W/cm² with gas targets of Helium and Neon. At these intensities, the targets are rapidly ionised by the process of optical field ionisation. The purpose of these investigations is two-fold. Firstly, we determine the relative importance of plasma heating mechanisms and investigate the scaling of electron temperature with density to ascertain whether an optically-ionised XUV recombination laser, utilising the 3s-2p transition in a Lithium-like ion, is viable. Such a laser requires, for the case of Neon, the production of very cold (<50 eV) electron temperatures at electron densities of the order of 5 x 10²⁰ cm^-3 , and optical-ionisation to the Helium-like stage of Neon (Ne⁸⁺). The results are compared and contrasted to computer simulations of the electron temperature. Secondly, we investigate the process of harmonic generation. We show that, contrary to commonly held beliefs, it is possible to generate shorter harmonic wavelengths from ions using a short wavelength laser than from atoms using longer wavelengths. We also show high harmonic generation efficiencies from neutral Helium at lower intensities (~10¹⁵ W/cm²) away from the laser focus. The results are compared to, and found to be matched well by, simulations which predict the single atom/ion harmonic response.

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18

Richardson, I. M. "Properties of the constricted gas tungsten (plasma) welding arc at elevated pressures." Thesis, Cranfield University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280909.

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Stenton, J. A. C. "A study for a high power millimetric-wave gyrotron." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355863.

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Najmundin, Zulfikar. "Parametric instabilities in the interaction of high intensity short pulse lasers with underdense plasmas." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339173.

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21

Dunne, Anthony Michael. "Measurements of thermal and radiation energy transport in laser and soft X-ray heated targets." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336433.

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Sharma, Atul Stefan. "Tokamak modelling & control." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270120.

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Tabasso, Alberto. "Spatially resolved measurement of photon fluxes from the JET divertor on the visible range." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286688.

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Zradokovic, David. "Theoretical studies of the effect of radial dynamics on Z pinch stability." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251578.

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Kingham, Robert Joseph. "High intensity short-pulse laser-plasma interactions." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267882.

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Tatarakis, Michael. "Optical probing of dense z-pinch and laser produced plasmas." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267298.

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Botha, Gert Johannes Jacobus. "A two-dimensional simulation of electrostatic drift wave turbulance in plasmas." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265065.

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Counsell, G. F. "Ionisation mechanisms in an optically pumped mercury vapour plasma." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253318.

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Howling, A. A. "Fluctuations in the edge plasma of the TOSCA tokamak." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370261.

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Bennett, Guy Richard. "Inertially-confined laser-produced partially-degenerate strongly-coupled plasmas." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282411.

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Sucksmith, John Peter. "Studies of plasmas used for semiconductor etching." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335818.

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32

Vayakis, George. "Anomalous transport in the tokamak edge." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291539.

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Mynors, Diane Julie. "Modelling of volume ion sources." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333192.

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Rossi, Adriana M. T. "Plasma particle balance and analysis of the gas released from the JET tokamak vessel." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284465.

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Graneau, P. Neal. "Ion dynamics of diffuse vacuum arcs." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306534.

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Darke, Susan A. "A study of solid sample introduction methods for inductively coupled plasma spectrometry." Thesis, Loughborough University, 1989. https://dspace.lboro.ac.uk/2134/10367.

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The development of sample introduction techniques for solid materials is a desirable goal in analytical atomic spectrometry. Traditional techniques have involved the introduction of samples as liquids by processes such as nebulisation. However some solid materials are not readily amenable to dissolution procedures and for the determination of elements at the ultra-trace level the reagents used for dissolution may produce undesired contamination. An additional problem for such determinations is that the dissolution process- may dilute the sample below the level which can be measured by the selected technique. The relative merits of three techniques for the introduction of solids for inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) have been evaluated in this thesis. The techniques studied were a laser ablation system based on a Nd:YAG laser, slurry nebulisation and an electrothermal vaporisation (ETV) system. The parameters which affect the performance of these techniques have been discussed. The application of each technique to the analysis of some geochemical samples has been described. Results are presented for the determination of various elements in fly ash and standard rock samples. The results obtained for each technique are compared. A value of merit has been defined to allow comparison of the results in this thesis with results published in the literature. A comparison of the plasma source in the presence and in the absence of water has been included in this thesis. Ionisation temperature and electron number density measurements were made usinq traditional nebulisation and compared to those obtained using laser ablation.

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Davies, Peter George. "Charge exchange in ion-atom collisions relevant to fusion plasma diagnostics." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4740/.

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Total charge exchange and excitation cross-sections are presented for collisions between He(^2+) ions and helium atoms, the laboratory frame collision energy being in the range 16-800keV. Cross-sections from the helium ground state and the He(ls2s(^1)S) and He(ls2s(^3)S) metastable states are calculated. The calculations were performed using the semiclassical impact parameter model where wave-functions are expressed as an expansion of two-electron atomic basis states. Transfer channels included plane-wave translation factors. The transition He(^+)(n = 4) → He(^+)(n = 3) results in the emission of visible light (468.5nm) which is observed in the JET fusion device. Helium beam injection into the JET device introduces some of the atoms in initially excited states. Even a small fraction of metastable helium effects the observed 468.5nm spectrum significantly because of the very large charge exchange cross-sections. Accurate charge exchange cross-sections to the He(^+)(n = 4) states are required to analyse the spectroscopic data used in the diagnosis of the plasma. The cross-sections produced are therefore also presented in a form suitable for direct inclusion into the plasma analysis database. Where possible the current results are compared to previous calculations. Total charge exchange cross-sections from the He(ls2s(^1)S) state are in good agreement with the previous one-electron calculation. Charge exchange cross-sections from the triplet state are found to differ with those from the singlet. The results are discussed in the context of their usefulness in the diagnosis of fusion plasmas. Suggestions for further work are made.

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Monk, Raymond David. "Langmuir probe measurements in the divertor plasma of the JET tokamak." Thesis, Royal Holloway, University of London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336515.

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This thesis describes the design and application of a new array of Langmuir probes to measure the plasma parameters in the divertor region of the Joint European Torus (JET) tokamak. A novel probe tip design was developed to withstand the high heat fluxes in the divertor region following thermal analysis and beam tests to identify the most suitable material. The probes operate in the "very strong magnetic field" regime with a large projected area (4mm2) and incidence angle to the magnetic field (> 10°) to avoid the sheath expansion effects associated with flush mounted divertor probes. The probes may be remotely configured as single, triple or floating probes. The combination of triple probe measurements and strike point sweeping has provided unique high resolution profiles of plasma parameters across the divertor target. Emphasis is placed upon the evaluation of probe interpretation assumptions and comparison with non-disturbing diagnostics to assess the reliability of the measurements. The distortion of the probe current-voltage characteristics is strongest for high recycling and detached divertor conditions. Single probe analysis methods overestimate the electron temperature while the virtual asymmetric double probe assumption matches well the functional form of the current-voltage characteristics and is more consistent with independent measurements and numerical modelling than single probe interpretation. However, the effects of plasma resistivity remain difficult to evaluate quantitatively. Analysis of the divertor plasma parameters over a wide range of conditions is presented. The behavior of the ion fluxes and parallel gradients during high recycling and detached discharges is studied and compared with predictions from simple analytical models of detachment. Numerical models are used to study the impurity production from the divertor target plate. A new technique of evaluating the plasma parameters both between and during Edge Localized Modes (ELMs) using the triple probes is applied to study the influence of active pumping on the divertor parameters.

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O'Connor, Gavin Thomas. "Development of a low pressure-inductively coupled plasma-ion source for mass spectrometry." Thesis, University of Plymouth, 1998. http://hdl.handle.net/10026.1/1764.

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A low pressure-inductively coupled plasma (LP-ICP) ion source has been investigated for the production of atomic and molecular ions for mass spectrometry (MS). A dedicated LPICP- MS was constructed, by modifying a Hewlett Packard mass selective detector, to detect ions from the LP-ICP. The ion sampling interface and ion optics were designed using established theory and the use of a computer simulation program. Perfluorotributylamine was continuously introduced into the LP-ICP, via a molecular leak, and the ion sampling interface, plasma forward power, and plasma gas flow rates, were optimised. When the LP-ICP ion source was sustained at 6W with a gas flow of 6 ml min'* helium, and iodobenzene and dibromobenzene, introduced via GC, only atomic signals for iodine and bromine were observed. Detection limits were 4 and 76 pg for iodobenzene and dibromobenzene respectively. The addition of nitrogen to a LP helium ICP increased the molecular signal for chlorobenzene, resulting in a detection limit of 2 pg. However, the addition of nitrogen did not aid the production of molecular ions of iodobenzene and dibromobenzene. When 0.07 ml min' of isobuiane was added to the LP-ICP mass spectra similar to those obtained by an electron impact source were observed. However, on the addition of more isobutane only the molecular ions (M*) for chlorobenzene, iodobenzene and dibromobenzene were observed. The detection limits for the instrument operating in the molecular mode were 100, 140 and 229 pg for chlorobenzene, iodobenzene and dibromobenzene respectively. Langmuir probe measurements were used to asses the effect of plasma forward power and gas flow rate on the local plasma potential, ion number density, electron temperature and electron number density within the LP-ICP. The local plasma potential varied from +50 V to -20 V depending on the plasma conditions used. The ion and electron number densities increased with increasing plasma power, with ion number densities of approximately 10^ cm' ^ and electron number densities of approximately at 10* cm ^ The effect of extra plasma gas had a less distinct affect on the plasma excited species. A plasma sustained at 6 W, 7 ml min'' helium and 1.8 ml min'* isobutane was used to provide both quantitative and qualitative information of tetraethyllead in the standard reference friel (NBS SRM 1637 II), with .the determined value of 13.06 ± 0.91 being in good agreement with the certified value of 12.9 ± 0.07 expressed as total lead.

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40

Qayyum, Asif. "Preparation and characterisation of plasma CVD a-Si:C:H alloys for solar cells." Thesis, Heriot-Watt University, 1989. http://hdl.handle.net/10399/951.

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41

Burke, P. E. "A study of microwave induced plasmas." Thesis, London Metropolitan University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376442.

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42

Hocking, Matthew James. "An advanced wide bandwidth ultrasound absorption and velocity spectrometer for industrial applications." Thesis, Keele University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319023.

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43

Shard, Alexander Gordon. "Plasma assisted thin film formation." Thesis, Durham University, 1992. http://etheses.dur.ac.uk/5736/.

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Thin films of fluorocarbon-based polymers can be deposited by plasma assisted polymerisation of various perfluorocarbons. The chemical natures of plasma polymers of hexafluoropropene and perfluorohexane were examined as a function of power, flow rate and position in reactor. Polymerised hexafluoropropene displayed increased fluorine contents at high powers; this is at odds with perfluorohexane which demonstrated lower fluorine contents. Differing reaction mechanisms between saturated and unsaturated perfluorocarbons were proposed to explain this. Both perfluorocarbons were found to give increased CF(_2) contents out of the plasma glow region. This was demonstrated to be a function of distance from the monomer inlet, and was ascribed to the production of long lived polymer forming species in the gas phase. Plasma oxidation of low density polyethylene, polystyrene and poly (ether ether ketone) with oxygen and carbon dioxide was modelled by corresponding photooxidation reactions. Correlations between the structure of the polymer, the treatment used, and the final products were drawn. Aliphatic components tended to give carbon-oxygen single bonds, phenyl rings were oxidised to carbonyl and acid groups, and carbonyl groups to acids. Metal-containing polymeric thin films were produced from plasmas of zinc acetylacetonate and aluminium tri-sec -butoxide. The products from each monomer were different, with the zinc compound resulting in a high proportion of zinc carboxylate and the aluminium compound giving the oxide or hydroxide. Incorporation of these compounds into a perfluorohexane plasma resulted in the formation of metal fluoride containing thin films.

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44

Till, Clare. "An investigation of plasma polymerization and copolymerization using fluoroaromatic compounds." Thesis, Durham University, 1986. http://etheses.dur.ac.uk/6834/.

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The work detailed in this thesis concerns polymers synthesised by R.F. inductively coupled plasmas excited in fluorine containing monomer vapours. The structure and bonding in a series of polymers prepared from per-fluoroaromatic monomers by plasma polymerization was investigated by ESCA. The composition and structural features of these films were compared and contrasted with each other and with plasma polymers derived from the same parent compounds with lower degrees of fluorination. Critical emission spectra, ~260-600nm, from these plasmas were recorded and a correlation made between certain species fluorescing in the gas phase and functional groups within the polymer. An association hcis also been made between the peaks at ~280 and ~510nm in the optical emission spectrum. Difluorocarbene is responsible for the peak at ~280nm but the peak at 510nm has an unknown origin. The effect of copolymerizing a fluoroaronatic compound with a second component on polymer composition has been examined, where the comonomer has ranged from an inert gas to an organic hydrocarbon analogue. Copolymerizaticn resulted in a stabilisation of the rearrangement mechanisms normally associated with the plasma polymerization of a perfluoroaromatic compound; CF=CF(_n) and CF(_2) groups were greatly reduced in intensity in the ccpolymer. The binding energy of the CF-CF(_n) peak indicated that the component peak was, in fact, due to CF-CF(_aromatic) i.e. copolymerization had also resulted in a greater retention of the aromatic nature of the parent fluorocotpound. Polymers were also prepared by irradiating the monomer vapour with wavelengths >130nm. Perfluorobenzene could not be polymerized with UV irradiation of wavelengths greater than 200nm, but could however be polymerized with wavelengths below 200nm. This produced a polymer whose composition, as determined by ESCA, was very similar to the composition of plasma polymers derived from the same monomer indicating that the mechanisms involved in both polymerizations are similar. Vibrationally excited ground state perfluorobenzene is thought to be involved in the reaction pathway.

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Mollart, T. P. "Electron emission processes in cold cathode thermal arcs." Thesis, Durham University, 1993. http://etheses.dur.ac.uk/5546/.

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In this Thesis the processes of electron emission from cathode electrodes are studied theoretically, and the applicability of these mechanisms to the non refractory cathodes that can be used to sustain thermal arcs was examined. Apparatus that was used to generate and manipulate thermal arcs along rail electrodes is described in this thesis. Techniques for driving arcs over polished sample electrodes with magnetic or aerodynamic forces are outlined. Scanning electron microscopy was used to study emission site formation on highly polished electrodes with a natural 2.5 nm oxide layer. Theoretical maximum electron current densities that can be extracted by the arc were calculated and these were used, in conjunction with information from the experimental work, to make estimates of the lifetime of emission spots that are seen on the cathode electrodes of thermal arc devices. The lifetime was found to be dependent on the arc velocity over a range of velocity values from 3 to 80 ms(^-1). The lifetime measured ranged from 2.4 µs to 0.024 µs. Experiments on arcs driven at a constant velocity using a combination of aerodynamic and magnetic forces showed that the formation of emission spots was independent of die applied external magnetic field. The presence of artificially grown copper (11) oxide layers, 50 nm and 100 nm thick, were found to influence the lifetime. The effect of the oxide layer was predicted using a simple model accounting for the change of resistance that such an oxide layer would be expected to cause. Additional experiments showed that the resistance of the arc was independent of the oxide layer thickness, as predicted by the model.

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Phillips, M. E. "Studies of high temperature laboratory and astrophysical plasmas." Thesis, Queen's University Belfast, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252580.

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Hughes, Ian G. "Electron ion and ion-ion collisions." Thesis, Queen's University Belfast, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335410.

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Cheshire, Roisin Christine. "Atomic hydrogen density measurements in diamond film producing plasmas." Thesis, Queen's University Belfast, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282126.

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McCann, S. M. "Spectroscopic diagnostics for high temperature astrophysical and laboratory plasmas." Thesis, Queen's University Belfast, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335434.

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Coffey, Ivor H. "Studies of K and L shell spectra of impurity ions in tokamak plasmas." Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333781.

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Dissertations / Theses on the topic 'Gas discharge physics'

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