To see the other types of publications on this topic, follow the link: Plasma interactions.
Dissertations / Theses on the topic 'Plasma interactions'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Plasma interactions.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Thomas, Christopher B. "Plasma interactions in a plasma erosion opening switch." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/27210.
Full textAbstract:
Approved for public release; distribution is unlimitedPlasma Erosion Opening Switches (PEOS) are important elements in pulsed power equipment. The conduction and opening properties of these switches are highly dependent on the near cathode electric and magnetic fields, and plasma surface interactions. The cathode interaction is highly nonuniform, and micron sized cathode spots form within nanoseconds. The mechanism for the formation of these spots and their contribution to the conduction and opening phases of the switch is not yet well understood. The existing model of explosive electron emission does not adequately explain the performance of the switch during operation. The proposed new model for the near cathode effects accounts for time delays in the onset of conduction in the switch which have been seen experimentally. This is the first experiment in a series to verify this model, and to model a possible mechanism for cessation of conduction.
2
Cameron, Richard. "Dust-plasma interactions in the plasma edge region." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/46194.
Full textAbstract:
This thesis concerns the interaction of small, particulate, solid matter - 'dust' - with plasmas, in the plasma edge region where such dust is commonly found. Dust in this region can have a significant impact on a variety of industrial plasma applications, and it is low-temperature industrial plasmas that form the focus of this work. A novel model for the sheath region at the edge of a plasma is proposed, to account for the loss of electrons at the plasma boundary. This is then compared to an existing Boltzmann electron model; significant differences are noted in the sheath structure, and consequently the charging and dynamics of dust in the plasma sheath. The effect of sparse ion collisions in the vicinity of a dust grain near the plasma edge is also investigated. The strong plasma flow in the edge region is found to significantly increase collisional charging of dust grains. Somewhat counter-intuitively, it is found that even sparse collisions can play a significant (and in fact dominant) role in the charging and shielding of dust grains at the edge of a plasma. The length-scale over which the charge on such grains is shielded by the plasma is found to be significantly less than the Debye length. Together, the altered grain charging and shielding behaviour have the potential to fundamentally alter how dust grains interact with edge-plasmas.
3
Lowry, Christopher Graham. "Plasma-limiter interactions on JET." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392350.
Full text
4
Rae, Stuart Campbell. "Short-pulse laser-plasma interactions." Thesis, University of Oxford, 1991. http://ora.ox.ac.uk/objects/uuid:c429d2ee-64d4-415a-b799-f5436d19ccc9.
Full textAbstract:
This thesis deals with several theoretical aspects of the interaction of an intense femtosecond laser pulse with a plasma. A mechanism for the enhancement of the collisional absorption of light at high intensities is described, involving the direct excitation of collective modes of the plasma, and the importance of this mechanism for a solid-density laser-produced plasma is studied under a range of conditions. An intensity-dependent collision rate is used in a numerical calculation of the reflectivity of a steep-gradient plasma, such as might be produced by an intense femtosecond laser pulse, and the conditions required to maximize absorption at high intensities are determined. The relative contributions of field-induced ionization and collisional ionization in laser-produced plasmas are studied, and it is shown that the behaviour of a gaseous plasma is almost solely governed by the field-induced process. A model is developed to simulate the propagation of an intense femtosecond laser pulse through an initially neutral gas, and this model is used to make predictions about spectral modifications to the laser pulse. Under certain conditions the spectrum is significantly broadened and suffers an overall blue shift. Quantitative fitting of theoretical spectra to experimental results in the literature is attempted, but is complicated by associated defocusing effects in the plasma. Field-induced ionization can produce a gaseous plasma which is significantly colder, for the same degree of ionization, than a plasma produced by collisional ionization. One possible application for a cold highly-ionized plasma is in a recombination x-ray laser, and the propagation model allows the calculation of the plasma temperature, which is a crucial parameter in assessing the feasibility of such schemes.
5
Blackburn, Thomas George. "QED effects in laser-plasma interactions." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:d026b091-f278-4fbe-b27e-bd6af4a91b7a.
Full textAbstract:
It is possible to reach the radiation-reaction–dominated regime in today’s high-intensity laser facilities, using the collision of a wakefield-accelerated GeV electron beam with a 30 fs laser pulse of intensity 1022 Wcm-2. This would demonstrate that the yield of high energy gamma rays is increased by the stochastic nature of photon emission: a beam of 109 electrons will emit 6300 photons with energy > 700 MeV, 60 times the number predicted classically. Detecting those photons, or a prominent low energy peak in the electron beam's post-collision energy spectrum, will provide strong evidence of quantum radiation reaction; we place constraints on the accuracy of timing necessary to achieve this. This experiment would provide benchmarking for the simulations that will be used to study the plasmas produced in the next generation of laser facilities. With focused intensities > 1023 Wcm-2, these will be powerful enough to generate high fluxes of gamma rays and electron-positron pairs from laser–laser and laser–solid interactions. It will become possible to test the physics of exotic astrophysical phenomena, such as pair cascades in pulsar magnetospheres, and explore fundamental aspects of quantum electrodynamics (QED). To that end we will discuss: classical theories of radiation reaction; QED processes in intense fields; and a Monte Carlo algorithm by which the latter may be included in particle-in-cell codes. The feedback between QED processes and classical plasma dynamics characterises a new regime we call QED-plasma physics.
6
Surdu-Bob, Carmen Cristina. "Surface : plasma interactions in GaAs subjected to capacitively coupled RF plasmas." Thesis, Aston University, 2002. http://publications.aston.ac.uk/8000/.
Full textAbstract:
Surface compositional changes in GaAs due to RF plasmas of different gases have been investigated by XPS and etch rates were measured using AFM. Angular Resolved XPS (ARXPS) was also employed for depth analysis of the composition of the surface layers. An important role in this study was determination of oxide thickness using XPS data. The study of surface - plasma interaction was undertaken by correlating results of surface analysis with plasma diagnosis. Different experiments were designed to accurately measure the BEs associated with the Ga 3d, Ga 2P3/2 and LMM peaks using XPS analysis and propose identification in terms of the oxides of GaAs. Along with GaAs wafers, some reference compounds such as metallic Ga and Ga2O3 powder were used. A separate study aiming the identification of the GaAs surface oxides formed on the GaAs surface during and after plasma processing was undertaken. Surface compositional changes after plasma treatment, prior to surface analysis are considered, with particular reference to the oxides formed in the air on the activated surface. Samples exposed to ambient air for different periods of time and also to pure oxygen were analysed. Models of surface processes were proposed for explanation of the stoichiometry changes observed with the inert and reactive plasmas used. In order to help with the understanding of the mechanisms responsible for surface effects during plasma treatment, computer simulation using SRIM code was also undertaken. Based on simulation and experimental results, models of surface phenomena are proposed. Discussion of the experimental and simulated results is made in accordance with current theories and published results of different authors. The experimental errors introduced by impurities and also by data acquisition and processing are also evaluated.
7
Neil, Alastair John. "Quasilinear theory of laser-plasma interactions." W&M ScholarWorks, 1992. https://scholarworks.wm.edu/etd/1539623827.
Full textAbstract:
The interaction of a high intensity laser beam with a plasma is generally susceptible to the filamentation instability due to nonuniformities in the laser profile. In ponderomotive filamentation high intensity spots in the beam expell plasma by ponderomotive force, lowering the local density, causing even more light to be focused into the already high intensity region. The result--the beam is broken up into a filamentary structure.;Several optical smoothing techniques have been proposed to eliminate this problem. In the Random Phase Plates (RPS) approach, the beam is split into a very fine scale, time-stationary interference pattern. The irregularities in this pattern are small enough that thermal diffusion is then responsible for smoothing the illumination. In the Induced Spatial Incoherence (ISI) approach the beam is broken up into a larger scale but non-time-stationary interference pattern. In this dissertation we propose that the photons in an ISI beam resonantly interact with the sound waves in the wake of the beam. Such a resonant interaction induces diffusion in the velocity space of the photons. The diffusion will tend to spread the distribution of photons, thus if the diffusion time is much shorter than the e-folding time of the filamentation instability, the instability will be suppressed.;Using a wave-kinetic description of laser-plasma interactions we have applied quasilinear theory to model the resonant interaction of the photons in an ISI beam with the beam's wake field. We have derived an analytic expression for the transverse diffusion coefficient. The quasilinear hypothesis was tested numerically and shown to yield an underestimate of the diffusion rate. By comparing the quasilinear diffusion rate, {dollar}\gamma\sb{lcub}D{rcub}{dollar}, with the maximum growth rate for the ponderomotive filamentation of a uniform beam, {dollar}\gamma\sb{lcub}f\sb{lcub}max{rcub}{rcub}{dollar}, we have derived a worst case criterion for stability against ponderomotive filamentation: {dollar}{dollar}{lcub}\gamma\sb{lcub}f\sb{lcub}max{rcub}{rcub}\over \gamma\sb D{rcub} \sim .5 {lcub}\tilde f\sp5/\tilde D\sp5\over \vert \tilde E\vert\sp2 \tilde\omega\sbsp{lcub}0{rcub}{lcub}2{rcub}\tilde N\sp6{rcub}\ll 1.{dollar}{dollar}The tildaed quantities are scaled to the following fusion relevant reference values; laser intensity: {dollar}\vert E\vert\sp2{dollar} = 10{dollar}\sp{lcub}15{rcub}\vert\tilde E\vert{dollar} Watts cm,{dollar}\sp{lcub}-2{rcub}{dollar} focal length: {dollar}f = 30\tilde f{dollar}m, width of each ISI echelon: {dollar}D = .75\tilde D{dollar} cm, laser carrier frequency: {dollar}\omega\sb{lcub}0{rcub} = 7.5 \times 10\sp{lcub}15{rcub}\tilde\omega\sb0{dollar} s{dollar}\sp{lcub}-1{rcub}{dollar}, and the number of ISI echelons: {dollar}N = 20\tilde N{dollar}.
8
McKenna, RossAllan D. "A study of laser plasma interactions in a cylindrical cavity." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29588.
Full textAbstract:
A CO₂ laser system delivering a 12 J pulse with a FWHM of 2 ns on target was developed to serve as a driver for studies of laser plasma interactions within a cylindrical cavity. The system consisted of a hybrid oscillator, followed by an amplifier chain, and it achieved its design goals of delivering an intense CO₂ pulse, Gaussian in time and space, with a high contrast ratio on a reliable basis.
The targets in which the plasma was produced consisted of small rectangular plates of lucite, with holes drilled through one of the long axes. The holes were 350 μm to 600 μm in diameter, and 10 mm in length. These dimensions allowed the laser beam, focused at the entrance of the hole, to produce sufficient intensity on the inner walls of the cylindrical cavity for plasma formation, while allowing the beam, with a waist diameter of 100 μm at the focus to deliver most of its energy within the cavity. The beam propagated via multiple reflections from the plasma through the cavity.
Diagnostics were performed on the beam transmitted through the target. Streak camera
images were collected of the intensity of visible emission from the plasma along the axis of the target. Anomalous results were obtained with respect to the reproducible observation
of maximum visible light emission from regions at the far end cavity from where the laser beam is injected. Another unforseen but interesting result was the small divergence
of the beam transmitted through the cavity. Preliminary models were developed to attempt to explain the observations.Science, Faculty of
Physics and Astronomy, Department of
Graduate
9
Fukumoto, Hiroshi. "Model Analysis of Plasma-Surface Interactions during Silicon Oxide Etching in Fluorocarbon Plasmas." 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/158076.
Full text
10
Slikboer, Elmar. "Investigation of Plasma Surface Interactions using Mueller Polarimetry." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX093/document.
Full textAbstract:
Cette thèse examine une nouvelle méthode de diagnostic, appelée Polarimètrie de Mueller, pour l’étude des interactions plasma-surface. Cette technique d’imagerie permet la caractérisation optique résolue en temps des cibles exposées au plasma. Les matrices de Mueller mesurées sont analysées en utilisant la décomposition logarithmique donnant des informations polarimétriques sur la diattenuation, la dépolarisation et la biréfringence. Cette dernière est exploitée en examinant des matériaux optiquement actifs afin d’identifier des aspects spécifiques de l’interaction avec le plasma, tels que les champs électriques ou la température de surface.Ce travail se concentre sur les cibles électro-optiques, qui permettent principalement la détection de champs électriques induits par la charge de surface déposée lors de l’interaction. La biréfringence est couplée analytiquement au champ électrique, en rapportant le retard de phase du faisceau sonde de lumière polarisée, à l’ellipsoïde d’index perturbé suivant l’effet Pockels. Grâce à cette approche analytique, les matériaux ayant des propriétés électrooptiques spécifiques peuvent être choisis de telle manière que toutes les composantes individuelles de champ électrique (axiales et radiales) induites à l’intérieur de l’échantillon soient imagées séparément. Pour la première fois les composantes du champ électriques peuvent être découplées permettant de mieux comprendre la dynamique du plasma proche d’une surface diélectrique.Cette technique est utilisée pour étudier l’impact d’ondes d’ionisation sur des surfaces. Ces décharges, générées par un jet de plasma à pression atmosphérique dans la gamme kHz, sont des plasmas froids filamentaires généralement utilisés pour des applications diverses telles que la fonctionnalisation de surface de polymères ou des traitements biomédicaux, mais les méthodes de diagnostic disponibles pour étudier les effets induits sur les surfaces sont limités. L’imagerie de polarimètrie Mueller appliquée aux cibles électro-optiques permet d’examiner les champs axiaux et radiaux en termes d’amplitude (3-6 kV/cm), d’échelles spatiales (<1mm axiales and <1cm radiales) et d’échelles temporelles (< 1μs pulsée and < 10μs CA) pour divers paramètres de fonctionnement du jet, e.g. amplitude de tension et gaz environnant.Simultanément à la biréfringence transitoire induite par le champ électrique, un signal de fond constant est également observé. Il est induit par la contrainte résultante du gradient de température induit à l’intérieur du matériau ciblé. Une relation analytique est obtenue en utilisant l’effet photo-élastique, permettant de développer une procédure de fitting pour retrouver la distribution de température. Cette procédure est utilisée, après calibration, pour montrer que la température de l’échantillon peut varier jusqu’`a 25 degrés par rapport aux conditions ambiantes – tandis que les changements dans le champ électrique sont également mesurés – et dépend de la fréquence de la tension d’alimentation AC du jet de plasma. La détermination précise de la température induite dans les cibles est importante car la plupart des applications visent des échantillons thermosensibles.Enfin, ce travail montre comment des échantillons complexes (aussi bien en terme d’état de surface que de composition chimique) peuvent être examinés lors d’une interaction plasma-surface, en les combinant avec une cible électrooptique. En raison de l’ajout d’un échantillon complexe, une composante de dépolarisation est ajoutée due à la diffusion du faisceau lumineux polarisé. Les changements de dépolarisation sont liés à l’évolution de l’échantillon complexe au cours du traitement par plasma. Ceux-ci, couplés aux champs électriques mesurés simultanément, fournissent un outil de diagnostic unique pour examiner les interactions plasma-surface. Cela a été appliqué à un cas test où une seule couche de cellules d’oignon est exposée aux ondes d’ionisation générées par le jet de plasma froidIn this thesis, a new diagnostic method called Mueller Polarimetry is examined for the investigation of plasma-surface interactions. This imaging technique allows the time-resolved optical characterization of targets under plasma exposure. The measured Mueller matrices are analyzed by using the logarithmic decomposition providing polarimetric data on diattenuation, depolarization, and birefringence. The latter is used by examining materials that possess optically active behavior to identify specific aspects of the plasma interaction, e.g. electric fields or temperature.This work focusses on electro-optic targets, which primarily enables the detection of electric fields induced by surface charge deposited during the interaction. The birefringence is coupled to the externally induced electric field by analytically relating the phase retardance for the probing polarized light beam to the perturbed index ellipsoid, according to the Pockels effect. Through this analytical approach, materials with specific electro-optic properties can be chosen in such a way – together with the orientation of the Mueller polarimeter itself – that all the individual electric field components (axial and radial) induced inside the sample are imaged separately. This has never been done before and allows to better understand the plasma dynamics in the vicinity of a dielectric surface.It is used to investigate the surface impact by guided ionization waves generated by a kHz-driven atmospheric pressure plasma jet. These non-thermal filamentary discharges are generally applied to various samples for e.g. surface functionalization of polymers or biomedical treatment of organic tissues. However, available diagnostic tools are limited to study these interactions. Imaging Mueller polarimetry applied to electro-optic targets examines the axial and radial field patterns in terms of amplitude (3-6 kV/cm), spatial scales (< 1mm axial and <1cm radial), and timescales (<1μs pulsed and <10μs AC) for various operating parameters of the jet, for example voltage amplitude and surrounding gas.Simultaneous with the transient birefringence induced by the electric field, a constant background pattern is also observed. This results from strain induced by temperature gradients inside the targeted material. An analytical relation is obtained following the photo-elastic effect, which allowed a fitting procedure to be designed to retrieve the temperature pattern. This procedure is used after calibration to show that the temperature of the sample can vary up to 25 degrees relative to room conditions – while changes in the electric field are seen as well – depending on the operating frequency of the AC driven plasma jet. The accurate determination of the temperature is important since most applications involve temperature sensitive samples.Lastly, this work shows how complex samples (in terms of surface geometry and/or chemical composition) can be examined during a plasma-surface interaction. This is done by combining them with the electro-optic targets. Due to the addition of a (thin) complex sample, depolarization is added to the system through scattering of the polarized light beam. In-situ observed changes of depolarization relate to the evolution of the complex sample during the plasma treatment. This, coupled with the simultaneously monitored electric field patterns, provides a unique diagnostic tool to examine the plasma-surface interactions. This has been applied for a test case where a single layer of onion cells is exposed to the ionization waves generated by the non-thermal plasma jet
11
Colina, Delacqua Ligia Maria. "Modélisation/diagnostic de production de poussières dans un plasma H₂au contact d’une cible C/W : Contribution à l’étude des interactions plasma/surface dans les machines de fusion thermonucléaire." Paris 13, 2012. http://scbd-sto.univ-paris13.fr/intranet/edgalilee_th_2012_colina_delacqua.pdf.
Full textAbstract:
Ce travail de thèse a porté sur la caractérisation expérimentale d’un plasma d’hydrogène au contact de cibles de carbone ou tungstène généré dans le réacteur microonde multi dipolaire CASIMIR II. Ce dernier, développé pendant ce projet de thèse, a pour objectif de simuler quelques des processus plasma/surface ayant lieu sous le dome du divertor et dans les régions à l’ombre du plasma (SOL) dans les tokamaks. CASIMIR II se compose de 16 sources dipolaires microondes disposées de manière circulaire le long du périmètre de l’enceinte à vide de manière à obtenir un plasma basse pression (10⁻³ à 10⁻² mbar), haute densité (10⁹ - 10¹¹ cm⁻³) homogène dans tout le volume du réacteur. Des cibles C/W ont été exposées à de tels plasmas. La mise en oeuvre de plusieurs diagnostics in situ spectroscopie optique d’émission, spectrométrie de masse et sonde de langmuir) ont permis d’identifier la nature de quelques produits d’érosion et de constater leur incidence sur les paramètres plasma (Vp' Tₑ‚ nₑ et nᵢ). Un premier modèle 1D collisionnel radial du plasma d’hydrogène généré par une source dipolaire microonde a été développé dans le but de valider et d’aider à l’interprétation des résultats expérimentauxThe work presented in the frame of this thesis dealt with the experimental characterization of a hydrogen plasma in contact with carbon or tungsten target generated in the microwave multidipolar plasma reactor CASIMIR II. This reactor, developed during this thesis project, is envisioned to simulate some plasma / surface processes occuring under the divertor dome and in the far Scrape-off Layer (SOL) regions of tokamaks. The CASIMIR II device is composed of 16 dipolar plasma sources close enough together to ensure large enough homogenous plasma density (10⁹ - 10¹¹ cm⁻³) at low presure (10⁻³ à 10⁻² mbar). Carbon/tungsten targets have been exposed to such plasma. The implementation of several in situ diagnostics (optical emission spectroscopy, mass spectrometry and Langmuir probe) provided us the possibility to identify the nature of some erosion products and observe their effect on plasma parameters (Vp' Tₑ‚ nₑ et nᵢ). A ID collisional radial model of the hydrogen plasma generated by a single microwave dipolar source was developed to validate and help understanding of the experimental results
12
Löfgren, Torbjörn. "Numerical modeling of electron beam-plasma interactions." Doctoral thesis, KTH, Alfvén Laboratory, 1999. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-2878.
Full text
13
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.
Full text
14
Streeter, Matthew. "Ultrafast dynamics of relativistic laser plasma interactions." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24854.
Full textAbstract:
This thesis documents the experimental and theoretical investigation of laser pulse evolution in relativistic laser-plasma interactions for plasma-wakefield acceleration and ion acceleration experiments. Power amplification of the Astra Gemini laser in a plasma was observed, with the compression of an initially 55 fs, 180 TW pulse down to 14 fs, with a peak power of 320 TW. This was achieved in a laser-driven plasma wakefield operating just below the self-injection threshold density for a propagation distance of 15 mm. Self-guiding of the laser pulse was observed, while pulse depletion was characterised as a function of density and propagation distance, showing that the pulse evolution scales equally with both. These measurements displayed good agreement with a depletion model based on pulse front etching. Particle-in-cell simulations were seen to closely reproduce the experimental results, which were concluded to be predominantly dependent on the longitudinal properties of the laser and wakefield. The simulations also revealed a new wakefield instability that is driven by the far red-shifted component of the laser pulse. In the case of high-contrast solid-density interactions, oscillations of the front surface of the plasma were seen to result in the generation of the second harmonic of the driving laser for a p-polarised interaction. Conversion efficiencies of 22% into the second harmonic were measured, while the total plasma reflectivity into the first and second harmonics remained relatively constant at 65% over the intensity range of 1E17 - 1E21 W/cm2. For normal incidence interactions with sub-micron thickness foils, the cycle-averaged surface motion was measured using a FROG diagnostic. Targets of a few nanometers in thickness underwent an acceleration away from the laser, but the measured surface velocities did not match the expected hole-boring velocities or the measured ion energies, due to the thermal expansion of the plasma. 2D simulations revealed that studying target motion in this way is affected by the scale length of the plasma and photon acceleration that can occur in the tenuous plasma in front of the laser-reflecting surface.
15
Quinn, Kevin Edward. "Plasma dynamics following ultraintense laser-solid interactions." Thesis, Queen's University Belfast, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.527919.
Full text
16
Tubman, Eleanor. "Magnetic field generation in laser-plasma interactions." Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/16757/.
Full textAbstract:
The primary focus of this thesis is understanding the production of magnetic fields during laser-plasma experiments. Each chapter investigates a different mechanism of producing magnetic fields. The first is from the by-product of launching asymmetric shocks which drive Biermann battery generated magnetic fields. The second looks at the reconnection of magnetic fields between two laser focal spots and the third is from fields produced around a current carrying loop target. Blast waves are investigated in the laboratory using a fast framing camera to capture multiple images on a single shot. In analysing the images, the blast wave's trajectory is compared to a Sedov-Taylor solution and the coupling of the laser energy into the shock wave is calculated to be 0.5-2%. The evolution of the blast wave's shape is characterised by fitting an ellipse to the outer edge and is observed to progress into a more symmetrical shape. Calculations show that two shocks produced in the interaction cause the change in ellipticity. We experimentally demonstrate that when two laser spots are placed in close proximity reconnection occurs. Diagnostics, including proton radiography, X-ray detectors and an optical probe, record and diagnose the existence of a semi-collisional reconnection event. The experimental data and simulations show that both Nernst and anisotropic pressure effects need to be taken into account for understanding and predicting the correct plasma dynamics observed. Magnetic fields are produced by driving a current through a loop attached to two plates and new measurements recording the voltages induced are presented in this thesis. It is found that the predicted values for the resistance, capacitance and inductance do not match those extracted from the experimental data and reasons for these are presented. Ideas for furthering this research to enhance our understanding in this area are given.
17
Kolasinski, Robert David Goodwin David G. "Fundamental ion-surface interactions in plasma thrusters /." Diss., Pasadena, Calif. : California Institute of Technology, 2007. http://resolver.caltech.edu/CaltechETD:etd-11222006-105854.
Full text
18
Johnson, David A. "Some aspects of nonlinear laser plasma interactions." Thesis, University of St Andrews, 1995. http://hdl.handle.net/10023/14318.
Full textAbstract:
Recent advances in the development of high power short pulse laser systems has opened a new regime of laser plasma interactions for study. The thesis is presented in two parts. In Part I, we consider the implications of these high power laser pulses for the interaction with a uniform underdense plasma, with particular regard to plasma-based accelerators. We present a scheme for the resonant excitation of large electrostatic Wakefields in these plasmas using a train of ultra-intense laser pulses. We also present an analysis of the resonant mechanism of this excitation based on consideration of phase space trajectories. In Part II, we consider the transition from linear Resonance Absorption to nonlinear absorption processes in a linear electron density profile as the intensity of the incident radiation increases and the scale length of the density profile decreases. We find that the electron motion excited by an electrostatic field exhibits some extremely complicated dynamics with bifurcations to period doubling and chaotic motion as the strength of the driving field is increased or the density scale length is decreased. We also present some results obtained from particle simulations of these interactions.
19
Rodrigues, Anthony. "Caractérisation des interactions entre un plasma non-thermique et des matériaux." Thesis, Poitiers, 2013. http://www.theses.fr/2013POIT2288.
Full textAbstract:
L'étude des interactions entre les espèces actives générées par un plasma non thermique et diverses surfaces de matériaux font l'objet de ce travail.Dans un premier temps, des polymères provenant de la biomasse ont été le sujet de nos recherches. Ils représentent une source importante de molécules plateforme telle que le glucose à partir desquelles peuvent être générés des produits de haute valeur ajoutée. Plus précisément, les effets d'un plasma à décharge à barrière diélectrique sur la structure et la dépolymérisation de l'inuline, de la cellulose et de l'amidon ont été étudiés. Une variation des paramètres électriques et chimiques de la décharge plasma a été effectuée et leurs effets sur les biopolymères évalués afin de comprendre les mécanismes de réaction. Nos résultats ont montré qu'un traitement initial par le plasma permettait d'augmenter considérablement le rendement final en sucre monomère (fructose ou glucose) par rapport au même produit de départ non traité par le plasma (84 et 54% de glucose à partir réciproquement de l'amidon et de la cellulose traités par plasma, au lieu de 65 et 1 % pour les mêmes produits non traités). Cet effet pourrait être du en partie à une dépolymérisation par attaque acide induite au sein du plasma sur les zones amorphes des biopolymères.Dans un second temps, l'étude a porté sur l'élimination des COV par couplage plasma non-thermique et catalyseur. Pour cette étude, nous avons conçu et mis en oeuvre un appareillage original formé par un réacteur plasma-catalyseur permettant une analyse sous atmosphère contrôlée de la surface du catalyseur par spectroscopie IR (DRIFT). Cet appareillage a permis d'étudier la décomposition de quatre COV (isopropanol, acétone, éthanol et toluène) adsorbé sur différents oxydes métalliques (g-Al2O3, CeO2 et TiO2) placés dans la zone de décharge en temps réel (in-situ). Les premiers résultats ont permis d'élucider certaines voies de décomposition de ces différents COVThe interactions between the active species generated by a non thermal plasma and various material surfaces have been studied in this work. In a first part, biopolymers coming from biomass have been the subject of our investigations as they offer a great reservoir for a platform molecule, glucose, from which valuable chemicals can be generated. More specifically, the effects of a dielectric barrier discharge plasma on the structure and depolymerization of inulin, cellulose and starch were evaluated. For that purpose, the electrical and chemical characteristics of the plasma discharge were varied and their effects on the biopolymers evaluated in order to understand the reaction mechanisms. Our results showed that a plasma pre-treatment increased considerably the final monomer yield (in glucose and fructose) compared to the untreated starting material (84 and 54 % yield in glucose from plasma treated starch and cellulose, instead of 65 and 1 % for the same untreated samples). This effect could be partly explained by the depolymerization of the amorphous areas of the polymers by and acid attack within the plasma discharge.In a second part, the study focused on the removal of VOCs by coupling non-thermal plasma and inorganic materials. For this purpose, we designed and implemented an innovative apparatus. It consists of a plasma-catalyst reactor with controlled atmosphere that allows the analysis of the catalyst surface by IR spectroscopy (DRIFT). The decomposition of four VOCs (isopropanol, acetone, ethanol and toluene) adsorbed on different metallic oxides (y-Al2O3, CeO2 and TiO2) placed within the discharge area have been studied in situ using this method. The first results have enlightened the decomposition pathways of the different VOCs
20
Gangolf, Thomas. "Intense laser-plasma interactions with gaseous targets for energy transfer and particle acceleration." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX110.
Full textAbstract:
Le plus fréquemment, l’interaction laser-matière est étudiée avec des lasers ayant des longueurs d’onde dans l’infrarouge proche (PIR), car ce sont les lasers qui peuvent générer les impulsions les plus intenses. Pour ces lasers, des cibles de densité allant de 0,05 à 2,5 fois la densité critique sont difficiles à créer mais elles offrent des perspectives intéressantes. Dans cette thèse, des jets d’hydrogène ayant de densité dans ce domaine sont utilisées dans le contexte de deux applications :Premièrement, des ions sont accélérées par choc non-collisionnel (collisionless shock acceleration, CSA). Lors de l’interaction d’une impulsion laser PIR avec une cible légè- rement sur-critique, un faisceau de protons est généré. Il est collimé, dirigé vers l’avant et quasiment monoénergetique. Des simulations indiquent que cela est lié à la formation d’un choc non-collisionnel et à l’accélération des protons par ce choc, en sus de leur accélération par le processus standard dit ”target normal sheath acceleration (TNSA)” qui est effectif en face arrière de la cible. Pour beaucoup d’applications, ces faisceaux de particules quasi-monoénergetiques sont plus appropriés que ceux à spectre large qui sont générés de façon routinière par TNSA.Deuxièmement, de l’énergie est transférée d’une impulsion laser (pump) vers une autre en contrepropagation (seed), par rétrodiffusion Brillouin stimulée, dans le régime de couplage fort (strong coupling-SBS), à des densités entre 0,05 et 0,2 fois la densité critique. Pour des impulsions à large bande (60 nanomètres), le rôle de la pré-ionisation sur la propagation et la rétrodiffusion Brillouin spontanée et stimulée est étudié, en incluant l’influence du chirp. Pour des lasers à bande plus étroite, il est démontré que l’impulsion seed peut être amplifiée par des dizaines de milliJoules, et des signatures d’amplification efficace et d’affaiblissement de l’impulsion laser pompe sont trouvées. Ce concept vise à l’amplification des impulsions laser à des puissances au-delà du seuil de dommage des amplificateurs laser basés sur des matériaux solidesLaser-matter interaction is studied mostly with near-infrared (NIR) lasers as they can generate the most intense pulses. For these lasers, targets between 0.05 to 2.5 times the critical density are challenging to create but offer interesting prospects. In this thesis, novel high-density Hydrogen gas jet targets with densities in this range are used in view of two applications:First, ions are accelerated by collisionless shock acceleration (CSA). Upon interaction of a NIR laser with a slightly overcritical gas jet target, a collimated, quasi-monoenergetic proton beam is generated in forward direction. Simulations indicate the formation of a collisionless shock and acceleration of protons both by the shock and target normal sheath acceleration (TNSA) on the target rear surface under these conditions. These directed, monoenergetic particle bunches are more suitable for many applications than the broadband particle beams already generated routinely.Second, at densities between 0.05 and 0.2 times the critical density, energy is transferred from one laser pulse (pump) to a counterpropagating pulse (seed), via Stimulated Brillouin Backscattering in the strongly-coupled regime (sc-SBS). For the case of broad- band (60 nanometers) pulses, the role of the preionization for pulse propagation and both spontaneous and stimulated Brillouin backscattering are studied, including the influence of the chirp. It is shown that for narrower bandwidths, the seed pulse is ampli- fied by tens of millijoules, and signatures of efficient amplification and pump depletion are found. This concept aims at amplifying laser pulses to powers above the damage thresholds of solid state amplifiers
21
Courrege, Maeva. "Caractérisation des interactions plasma/parois dans un disjoncteur haute tension." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30162/document.
Full textAbstract:
Les disjoncteurs à haute tension, présents dans le réseau électrique, permettent d'assurer en toute sécurité la distribution de l'électricité. Lorsqu'un défaut est détecté, ou lors d'une intervention de maintenance, l'ouverture des contacts électriques au sein du disjoncteur entraine l'apparition d'un arc électrique à ses bornes. La protection et la coupure ne seront effectives que lorsque l'arc électrique aura été coupé. De nombreux paramètres, géométriques et physiques entrent en jeu dans la capacité de coupure d'un disjoncteur. L'objectif de ces travaux de thèse consistait à analyser l'impact du plasma sur les différents matériaux constituant le disjoncteur. Une démarche purement théorique est abordée à travers l'utilisation du logiciel commercial ANSYS Fluent. Ces travaux sont menés en collaboration avec la société Siemens qui fournit les données expérimentales indispensables à la discussion et à la validation du modèle. Dans ce travail nous considérons dans un premier temps l'ablation des tuyères en téflon. Ce phénomène est pris en compte dans notre étude, au travers d'un modèle d'ablation basé sur la théorie de T. Christen. L'ablation des parois joue un rôle fondamental sur la montée en pression dans les volumes de chauffage, et a une incidence directe sur la réalisation de la coupure. Ainsi le rôle et la quantification des vapeurs de C2F4 sont discutés et détaillés. La deuxième interaction plasma/matériau qu'il convenait d'étudier est celle avec l'électrode mobile constituée d'un mélange tungstène cuivre. Cette interaction est rarement étudiée au niveau des travaux de la littérature. La mise en place nécessite le développement de modèles de sous couches, en proche voisinage de l'électrode, basés sur des balances d'énergie et de flux qui permettent de déterminer par des approches hors équilibre la température des électrodes et le taux de production de vapeurs. Sur une configuration réelle de disjoncteur les caractéristiques temporelles des grandeurs physiques (température, vitesses, pression) et électriques (courant, tension) sont présentées et discutées dans la phase fort courant. Nous concluons sur la nécessité de considérer l'ablation du C2F4 pour une bonne description de la montée en pression dans les volumes de chauffage car ils conditionnent le soufflage au moment du passage par le zéro du courant, et sur la nécessité de prendre en compte les vapeurs de cuivre car celles-ci sont présentes au passage par zéro du courant et conditionnent alors le pouvoir de coupure du disjoncteurHigh-voltage circuit breakers, present in the power grid, ensure in safety the electricity distribution. When an error is detected, or for a maintenance operation, the opening of the electrical contacts within the circuit breaker causes the appearance of an electric arc at its terminals. Protection and cut-off will only be effective if the electrical arc cut off. Many parameters, geometric and physical, are involved in the breaking capacity of a circuit breaker. The aim of this work is to analyze the impact of plasma on the various materials making up the circuit breaker. A purely theoretical approach is tackled through the use of the commercial software ANSYS Fluent. This work is carried out in collaboration with Siemens, which provides the experimental data necessary for the discussion and validation of the model. In this work, we first consider the ablation of teflon nozzles. This phenomenon is taken into account in our study, using an ablation model based on the theory of T. Christen. The ablation of the walls plays a fundamental role on the rise in pressure in the heating volumes, and has a direct effect on the cut-off realization. Thus, the role and quantification of C2F4 vapors are discussed and detailed. The second plasma / material interaction that should be studied is that with the mobile electrode made of a tungsten copper mixture. This interaction is rarely studied in the literature. The implementation requires the development of sub-layers models in the vicinity of the electrode, based on energy and flux balances, which make it possible to determine by non-equilibrium approaches the temperature of the electrodes and the rate of vapor production. On a real circuit breaker configuration, the temporal characteristics of the physical (temperature, velocities, pressure) and electrical (current, voltage) quantities are presented and discussed in the high current phase. We conclude on the need to consider the ablation of C2F4 for a good description of the rise in pressure in the heating volumes because they condition the blowing at the moment of current-zero and on the need to take into account the copper vapors because these are present at the zero crossing of the current and then condition the breaking capacity of the circuit breaker
22
Taylor, Michael J. "Plasma propellant interactions in an electrothermal-chemical gun." Thesis, Cranfield University, 2002. http://dspace.lib.cranfield.ac.uk/handle/1826/4010.
Full textAbstract:
This Thesis covers work conducted to understand the mechanisms underpinning the operation of the electrothermal-chemical gun. The initial formation of plasma from electrically exploding wires, through to the development of plasma venting from the capillary and interacting with a densely packed energetic propellant bed is included. The prime purpose of the work has been the development and validation of computer codes designed for the predictive modelling of the elect rothe rmal-ch em ical (ETC) gun. Two main discussions in this Thesis are: a proposed electrically insulating vapour barrier located around condensed exploding conductors and the deposition of metallic vapour resulting in a high energy flux to the surface of propellant, leading to propellant ignition. The vapour barrier hypothesis is important in a number of fields where the passage of current through condensed material or through plasma is significant. The importance may arise from the need to disrupt the fragments by applying strong magnetic fields (as in the disruption of metallic shaped charge jets); in the requirement to generate a metallic vapour efficiently from electrically exploding wires (as per ETC ignition systems); or in the necessity to re-use the condensed material after a discharge (as with lightning divertor strips). The ignition by metallic vapour deposition hypothesis relies on the transfer of latent heat during condensation. It is important for the efficient transfer of energy from an exploded wire (or other such metallic vapour generating device) to the surface of energetic material. This flux is obtained far more efficiently through condensation than from radiative energy transfer, because the energy required to evaporate copper is far less than that required to heat it to temperatures at which significant radiative flux would be emitted
23
Watts, Ian Frank. "Intense laser-plasma interactions : harmonics and other phenomena." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271186.
Full text
24
Gillen, David R. "A study of plasma-related ion-surface interactions." Thesis, Queen's University Belfast, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287621.
Full text
25
Ramsay, Martin. "Short-pulse laser interactions with high density plasma." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/77583/.
Full textAbstract:
The constraints on particle-in-cell (PIC) simulations of short-pulse laser interactions with solid density targets severely limit the spatial and temporal scales which can be modelled routinely. Although recent advances in high performance computing (HPC) capabilities have rendered collisionless simulations at a scale and density directly applicable to experiments tractable, detailed modelling of the fast electron transport resulting from the laser interaction is often only possible by sampling the fast electron populations and passing this information to a separate, dedicated transport code. However, this approach potentially neglects phenomena which take place or are seeded near the transition between the two codes. Consequently there is a need to develop techniques capable of efficiently modelling fast electron transport in high density plasma without being subject to the usual grid-scale and time-step constraints. The approach employed must also be compatible with retaining the standard PIC model in the laser interaction regions in order to model laser absorption and charged particle acceleration processes. Such an approach, proposed by Cohen, Kemp and Divol [J. Comput. Phys., 229:4591, 2010], has been identified, adapted and implemented in EPOCH. The final algorithm, as implemented, is presented here. To demonstrate the ability of the adapted code to model high intensity laser-plasma interactions with peak densities at, and above, solid density, the results of simulations investigating filamentation of the fast electron population and heating of the bulk target, at high densities, are presented and compared with the results of recent experiments as well as other, similar codes.
26
Taylor, M. J. "Plasma propellant interactions in an electrothermal-chemical gun." Thesis, Department of Environmental and Ordnance Systems, 2009. http://hdl.handle.net/1826/4010.
Full textAbstract:
This Thesis covers work conducted to understand the mechanisms
underpinning the operation of the electrothermal-chemical gun. The
initial formation of plasma from electrically exploding wires, through to
the development of plasma venting from the capillary and interacting
with a densely packed energetic propellant bed is included. The prime
purpose of the work has been the development and validation of
computer codes designed for the predictive modelling of the
elect rothe rmal-ch em ical (ETC) gun.
Two main discussions in this Thesis are:
a proposed electrically insulating vapour barrier located around
condensed exploding conductors and
the deposition of metallic vapour resulting in a high energy flux to
the surface of propellant, leading to propellant ignition.
The vapour barrier hypothesis is important in a number of fields where
the passage of current through condensed material or through plasma
is significant. The importance may arise from the need to disrupt the
fragments by applying strong magnetic fields (as in the disruption of
metallic shaped charge jets); in the requirement to generate a metallic
vapour efficiently from electrically exploding wires (as per ETC ignition systems); or in the necessity to re-use the condensed material after a
discharge (as with lightning divertor strips).
The ignition by metallic vapour deposition hypothesis relies on the
transfer of latent heat during condensation. It is important for the
efficient transfer of energy from an exploded wire (or other such
metallic vapour generating device) to the surface of energetic material.
This flux is obtained far more efficiently through condensation than
from radiative energy transfer, because the energy required to
evaporate copper is far less than that required to heat it to
temperatures at which significant radiative flux would be emitted
27
Brichon, Paulin. "Vers une gravure plasma de précision nanométrique : simulations de dynamique moléculaire en chimie Si-Cl." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GRENT010/document.
Full textAbstract:
Ce travail de thèse aborde le problème de la gravure de matériaux ultraminces pour la réalisation de nouvelles générations de transistors (FDSOI, FinFET) dans les dispositifs nanoélectroniques avancés. Ces transistors doivent être gravés avec une précision nanométrique pour ne pas endommager les propriétés électroniques des couches actives. Afin d'atteindre une telle précision, les dommages surfaciques et l'épaisseur des couches réactives formées lors de l'exposition plasma doivent être maintenus en-deçà du nanomètre, véritable défi auquel les plasmas ICP continus ne sont plus à même de répondre. Pour assister le développement de nouveaux procédés de gravure, des simulations de dynamique moléculaire ont été développées afin étudier l'influence de nouvelles technologies plasma (plasmas pulsés, plasma basse Te, gaz pulsés) sur les interactions entre silicium et plasmas chlorés. Les simulations montrent que l'énergie ionique (Eion) est le paramètre numéro un pour contrôler la gravure de couches de Si ultraminces, une diminution de l'énergie réduisant à la fois l'épaisseur de couche endommagée SiClx et le taux de gravure. Le rapport du flux de neutres sur flux d'ions (Γ) est le 2nd paramètre clé : son augmentation entraîne une diminution sensible l'épaisseur de couche perturbée tout en augmentant le taux de gravure. Quantitativement, cette étude montre que des plasmas caractérisés par de faibles énergies ioniques (< 15 eV) ou des rapports Γ importants (⩾ 1000) permettre d'obtenir des couches réactives d'épaisseur sub-nanométrique (cf. plasmas basse Te ou synchronisés pulsés). En mode "bias pulsé", les simulations montrent que pour une valeur Vbias donnée, pulser le bias permet de diminuer à la fois l'épaisseur de couche réactive et le taux de gravure. Cet effet est d'autant plus marqué que le rapport de cycle DC est faible, ce qui élargit la fenêtre des paramètres opératoires. Pour contrôler la gravure, une autre solution pourrait consister à contrôler l'épaisseur des couches réactives de manière dynamique. Inspiré de l'ALE (Atomic Layer Etching), ce nouveau concept consiste à pulser rapidement et alternativement différents gaz pour décomposer le procédé de gravure en cycles répétitifs de deux étapes plasma distinctes. La 1ère étape vise à limiter la formation de la couche mixte à 1nm d'épaisseur dans un plasma réactif (Cl2) en optimisant le temps d'injection du gaz; la 2nde étape vise à graver la couche ainsi formée dans un plasma de gaz rare (Ar, Xe) sans endommager le matériau sous-jacent. Nos simulations confirment la faisabilité et la répétabilité d'un tel conceptThis thesis focuses on technological challenges associated with the etching of ultrathin materials used for new generations of transistors (FDSOI, FinFET) in advanced nanoelectronics devices. These transistors must be etched with a nanometric precision in order to preserve the electronic properties of active layers. To reach such a precision, plasma-induced damage and reactive layers thicknesses formed during the etch must remain below 1nm, a challenge which cannot be addressed by continuous-waves ICP plasmas. To assist the development of new etching processes, molecular dynamics simulations have been developed to study the influence of new plasma technologies (pulsed plasmas, low-Te plasmas, gaz pulsing) on interactions between silicon and chlorine plasmas. Simulations show that the key parameter to control the etching of ultrathin Si layers is the ion energy (Eion), which lowers both the SiClx damaged layer thickness and the etch rate when it is decreased. The neutral-to-ion flux ratio (Γ) is the second key parameter: its increase strongly reduces the reactive layer thickness while the etch rate grows. Quantitatively, this study shows that plasmas with low ion energies (< 15 eV) and high Γ ratios (⩾ 1000) allow to obtain sub-nanometer thick reactive layers (cf. low-Te or synchronized pulsed plasmas). In « pulsed bias » mode, simulations show that for a given Vbias value, pulsing the bias decreases both the reactive layer thickness and the etch rate. This effect is stronger at low duty cycle DC, which can improve the control of the etching process. To control the etching of ultrathin films, another solution may be to control dynamically the reactive layers formation. Inspired from ALE (Atomic Layer Etching) principle, this new concept consists in pulsing quickly and alternatively several gases to divide the etching process into repetitive cycles of two distinct plasma steps. The first step aims to limit the mixed layer formation at 1nm in a reactive (Cl2) plasma by optimizing the gas injection time; the 2nd step aims to remove the so-formed layer in a noble gas plasma (Ar, Xe) without damaging the material below. Our simulations confirm the feasibility and the repeatability of such a concept
28
Mollica, Florian. "Interaction laser-plasma ultra-intense à densité proche-critique pour l'accélération d'ions." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX058/document.
Full textAbstract:
L'interaction d'un laser ultra-intense et ultra-court avec la matière donne naissance à une grande variété de processus issus du couplage des ondes électromagnétiques associées au laser avec les modes du plasma. Ce couplage hautement non-linéaire excite des phénomènes plasmas collectifs capables de produire des champs intenses pouvant atteindre le TV/m. Ces champs ouvrent la possibilité de réaliser des accélérateurs de particules compacts, aussi bien d'électrons que d'ions. Des sources laser-plasma d'ions de plusieurs dizaines de MeV ont été démontré au début des années 2000 et de nombreux mécanismes ont été suggérés depuis afin d'en améliorer les propriétés. Historiquement, les sources d'ions par laser ont été obtenues à partir de cibles solides dîtes sur-denses. L’innovation sur les cibles a été un moteur majeur de l’amélioration de ces sources. Dans la continuité de cette dynamique, l’utilisation de cibles gazeuses a été proposé afin d’alléger les contraintes de contraste laser et de taux de répétition. De récentes démonstrations expérimentales sont venus renforcer l’intérêt pour ces cibles, dîtes sous-denses ou proche critiques, dont la valeur est propice à la propagation, à l’absorption du laser et à la création de structures accélératrices que sont les chocs plasmas et les vortex magnétiques. Les travaux présentés dans cette thèse constituent une exploration expérimentale des paramètres plasmas nécessaires à l’accélération d’ions dans des cibles gazeuses de densité proche-critique. Pour la première fois ces régimes sont explorés avec un laser ultra-intense femtoseconde de 150TW. Une partie des travaux a été consacrée à la réalisation d’une cible innovante, adaptée aux contraintes de densité et de gradients plasma requises par ces régimes. Suivent, les travaux expérimentaux décrivant la propagation du laser et l’accélération d’électrons dans des cibles proche-critiques. Enfin une dernière partie décrit la production d’un faisceau d’atome issue d’une source d’ion laserInteraction of ultra-intense, ultra-short laser with matter gives rise to a wealth of phenomena, due to the coupling between the electromagnetic field and the plasma. The non-linear coupling excites collective plasma processes able to sustain intense electric fields up to 1TV/m. This property spurred early interest in laser accelerator as compact, next-generation source of accelerated electrons and ions. Laser-driven ion source of several MeV was demonstrated in early 2000 an various mechanisms had been suggest to improve the their properties. These first ion sources have been obtained on solid targets, called “overdense”. Target innovation has driven the improvement of these sources. In the continuity of this dynamic, new gaseous targets had been proposed in order to relax the constraints that solid targets impose on laser contrast and repetition rate. Recent experimental demonstrations of monoenergetic ion acceleration in gas renew the interest in such targets, called under-dense or near-critical because of their intermediate densities. At near-critical density the laser can propagate, but undergoes significant absorbtion, giving rise to the accelerating structures of plasma shocks and magnetic vortex.The work presented in this thesis is an experimental exploration of the plasma conditions required to drive ion acceleration in gaseous near-critical target. For the first time, these regimes are explored with an ultra-intense, femtosecond laser of 150TW. A part of this work has been dedicated to the design of an innovative gas target, suited for plasma density and gradient constraints set by these regimes. Then the experimental works describe laser propagation and electron acceleration in near-critical targets. Finally the last part report the efficient production of an atomic beam from a laser-driven ion source
29
Pan, Changkang. "Characterization of solvent-plasma interactions for inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/30536.
Full text
30
Kaufman, David A. Goodwin David G. Goodwin David G. "Investigation of an ECR plasma thruster and plasma beam interactions with a magnetic nozzle /." Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-07102007-131210.
Full text
31
Fischer, Guillaume. "Plasma Nanotexturing of Silicon for Photovoltaic Applications : Tailoring Plasma-Surface Interactions for Improved Light Management." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX087/document.
Full textAbstract:
Cette thèse est dédiée à l’étude de la texturation de surface du silicium cristallin (c-Si) à l’échelle nanométrique (nanotexturation) par un procédé de gravure ionique réactive en chimie SF6/O2 et en réacteur plasma à couplage capacitif à excitation radiofréquence. Ce travail a pour objectif générique l’optimisation du procédé de nanotexturation de surface en vue d’une intégration pour le traitement de la face avant de l’absorbeur de cellules photovoltaïques c-Si. A cette fin, une étude des interactions plasma-surface est menée dans le cas d’une excitation plasma par tension simple fréquence, ou par tension multifréquence générant des asymétries électriques dans le plasma (méthode des « forme d’ondes sur mesure », abrégé TVW, de l’anglais "Tailored Voltage Waveforms").L’étude se porte premièrement sur les différents mécanismes de chauffage électronique dans le plasma. Les modes de chauffage électronique dominants sont déterminés pour un plasma SF6/O2 à faible pression grâce à l’utilisation de l’excitation TVW. En contrepartie, ce mode d’excitation permet de générer des asymétries électriques variables dans le plasma, affectant ainsi le flux et l’énergie de bombardement ioniques sur l’électrode porte-substrats. Dans les conditions étudiées, l’excitation TVW permet d’élargir la gamme de conditions disponible pour la gravure (en termes de flux et d’énergie de bombardement ioniques) par rapport à une excitation simple fréquence.Deuxièmement, les interactions plasma-surface lors de la gravure du c-Si en chimie SF6/O2 sont étudiées. Une fenêtre process permettant d’obtenir une nanotexturation efficace de la surface de c-Si – à température ambiante – est identifiée. Il est ainsi possible de diminuer drastiquement la réflexion de la lumière en surface du c-Si (dans la gamme de longueurs d’ondes [250,1000nm]) : du « silicium noir » est obtenu. Les conditions de nanotexturation (flux et énergie des d’ions) sont variées expérimentalement grâce à l’excitation TVW. Un modèle phénoménologique de gravure est proposé : le rendement de gravure augmente en fonction avec l’énergie des ions, au-dessus d’un seuil de gravure d’environ 13eV. Grâce à ce modèle, il est démontré que la hauteur moyenne des nanostructures formées est directement (positivement) liée à la fluence ionique, pondérée par l’énergie de bombardement.Les propriétés optiques des surfaces nanotexturées sont ensuite étudiées. Lorsque la largeur des nanostructures est petite devant la longueur d’onde de la lumière (dans le c-Si), la surface nanotexturée agit comme une couche antireflet à gradient d’indice de réfraction : un lien direct entre la hauteur des nanostructures et la réflectance totale de la surface est déterminé. Une très faible réflectance (de l’ordre de 2% en incidence normale) dans une large gamme spectrale (approximativement [250,1000nm]) est atteinte. De plus, une forte diffusion de la lumière est engendrée lorsque la largeur des nanostructures dépasse un seuil déterminé expérimentalement. En conséquence, la lumière est plus efficacement piégée dans le c-Si, améliorant l’absorption dans la gamme [1000,1200nm].Les propriétés optiques des surfaces nanotexturées sont intéressantes pour améliorer la photogénération de charges électriques dans les cellules photovoltaïques c-Si. Cependant, les dommages induits en surface du c-Si par bombardement ionique (lors de la nanotexturation plasma) sont responsables d’une augmentation de la recombinaison des charges électriques en surface. Cet effet est atténué par l’application d’une faible énergie de bombardement ionique. Des conditions optimales de nanotexturation du c-Si par plasma SF6/O2 peuvent être obtenues par la maximisation du flux d’ions, en maintenant l’énergie de bombardement faible. Ces spécifications se révèlent antagonistes dans le cas d’une décharge plasma à couplage capacitif à excitation simple fréquence, mais le conflit peut être (en partie) levé par l’utilisation de l'excitation TVWThis thesis is dedicated to the study of crystalline silicon (c-Si) surface texturing at the nanoscale (nanotexturing) using capacitively coupled plasma reactive ion etching (CCP-RIE). The general objective consists in tuning the nanotextured surface properties to improve light-management in c-Si solar cells through front surface texturing. To this aim, plasma-surface interactions during etching in a SF6/O2 discharge are investigated using both single-frequency excitation and Tailored Voltage Waveforms (TVWs), i.e. a multifrequency approach triggering electrical asymmetries in the plasma.To gain a full picture of the achievable processing range, the electron heating mechanisms and ion bombardment energy on the surface are first studied. An identification of the dominant electron heating mechanisms in low pressure SF6/O2 plasma is demonstrated using TVWs as an innovative probing tool. Different electrical asymmetry effects are shown to arise depending on the dominant heating mode, which therefore affects both the ion flux and bombardment energy on the etched surface. Although a complete decoupling between ion energy and flux cannot be achieved in the investigated discharge conditions, TVWs do lead to an extended playground for SF6/O2 plasma etching of c-Si surfaces in CCP-RIE.The plasma-surface interaction mechanisms during SF6/O2 plasma etching and texturing of c-Si surfaces are then investigated. A processing window to achieve nanotextured anti-reflective c-Si surfaces (“black silicon”) at room temperature is delimited. Building on the work from the first section, the ion flux and bombardment energy on the c-Si surface are varied independently in this process window. A phenomenological model (etching yield varying with the square root of the ion energy above a threshold around 13 eV) is proposed. From this model, a direct (positive) link between the energy weighted ion fluence and the nanostructure height is identified. Importantly, the final nanostructure average width is shown to also weakly depend on the instantaneous ion flux during the process.Subsequently, anti-reflection and light scattering properties of plasma nanotextured c-Si surfaces are studied. Regarding anti-reflection, when the nanostructure average width is small compared to the wavelength (in c-Si), the nanotextured surface acts as an anti-reflective graded refractive index layer and a direct link between the nanostructure average height and the reflectance can be derived. Very low reflectance (in the order of 2% at normal incidence) on a broad wavelength range (approximately [250, 1000nm]) can be achieved, and the improved anti-reflective properties extend to high angles of incidence. Additionally, strong light scattering is shown to arise when the nanostructure average width overcomes a given threshold determined experimentally. Consequently, light is more efficiently trapped in the c-Si substrate, leading to superior absorption in the range [1000, 1200nm].The aforementioned optical properties of nanotextured c-Si surfaces are of practical interest for improved light management in c-Si photovoltaic devices. However, plasma induced damages (during plasma nanotexturing), as well as enlarged surface area, are responsible for increased carrier recombination. The contribution to recombination from plasma induced defects is shown to be mitigated when ion bombardment energy is kept low. Design rules are consequently proposed: optimized conditions for c-Si nanotexturing in SF6/O2 plasma can be achieved by maximizing the ion flux while keeping ion energy low (but above the etching threshold). These requirements are conflicting in the case of a single frequency CCP discharge, but the trade-off may be (at least partly) resolved using TVWs
32
Boucher, Isabelle. "Étude expérimentale du potentiel rayonne par une antenne dans une colonne de plasma cylindrique en champ magnétique." Nancy 1, 1992. http://www.theses.fr/1992NAN10019.
Full textAbstract:
La structure globale du potentiel rayonné par une antenne (source ponctuelle ou anneaux) dans une colonne de plasma soumis a un champ axial, limitée par un cylindre métallique, est étudiée expérimentalement. Un rappel théorique est d'abord présente à partir de deux descriptions complémentaires: la première consiste en une décomposition du potentiel suivant une base de modes propres de cavité et la seconde utilise la notion de cône de résonance avec multiples réflexions. Compte tenu des conditions expérimentales, la structure de cône de résonance est privilégiée. Celle-ci est étudiée spatialement dans toute la colonne de plasma. La mise au point d'un système de détection performant permet pour la première fois, les mesures simultanées de variations spatiales d'amplitude et de phase du potentiel. Celles-ci permettent entre autre de vérifier les propriétés du cône rayonné par une antenne ponctuelle, de définir le concept de cône isolé dans un plasma limité et d'étudier avec précision la réflexion du cône sur la couche de coupure à la fréquence plasma. Les phénomènes de convergence au point focal et d'interférences entre cônes ont été étudiés. Enfin la mesure globale du potentiel loin de la source montre la persistance de la structure de cône de résonance, ainsi que la dispersion du signal provoquée par les effets thermiques, les réflexions multiples et les interférences aux points focaux. Ces résultats sont comparés qualitativement avec des calculs approches utilisant la superposition de modes propres de cavité en plasma chaud. Les applications de ces résultats à la conception d'une expérience sur le chaos déterministe sont abordées en conclusion
33
Rojo, Mathias. "Formation et transport de poussières dans un plasma basse pression magnétisé." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30296/document.
Full textAbstract:
Depuis la fin des années 80, les plasmas poussiéreux sont l’objet d’un grand nombre d’études. Plusieurs domaines de la physique des plasmas sont confrontés à la présence de ces particules: en astrophysique, dans les procédés de dépôt ou de gravure, dans les plasmas de fusion thermonucléaire contrôlée. Les plasmas poussiéreux ont très peu été étudiés dans des décharges micro-onde basse pression. Il y a une quinzaine d’années encore, il était admis que les probabilités de recombinaisons d’espèces réactives en volume étaient négligeables à cause de la faible densité du gaz. Au LAPLACE, des poussières incandescentes sont observées en plasma RCER d’acétylène. La présente étude a pour objectif d’apporter des éléments de réponses sur les mécanismes liés à la formation, au transport et au chauffage de ces poussières. Ce document présente les résultats obtenus durant ces 4 années de thèse. Le chapitre 1 introduit brièvement l’émergence de la thématique des plasmas poussiéreux, ainsi que certains aspects théoriques importants des décharges multipolaires. Le chapitre 2 détaille le dispositif expérimental ainsi que les différents diagnostiques utilisés durant cette étude: sonde de Langmuir, sonde de Mach, sonde de flux aux parois et imagerie rapide. Le chapitre 3 présente en détail les mécanismes de chargement et de chauffage des poussières. Dans cette partie, des mesures expérimentales ainsi qu’un modèle sont couplés afin d’expliquer l’incandescence et d’estimer la charge des particules. Le chapitre 4 décrit la caractérisation du transport des poussières dans une plasma d’acétylène par imagerie rapide. Dans ce chapitre, nous discutons des forces pouvant être responsables de ce transport. Enfin, le chapitre 5 passe en revue les résultats obtenus sur l’interaction plasma surface, à l’aide d’analyses ex-situ ainsi que des mesures de sondes de flux aux paroisSince the late 1980s, dusty plasmas have been the subject of a large number of studies. Several fields of plasma physics are confronted with the presence of these particles: astrophysics, deposition or etching processes, or controlled thermonuclear fusion plasmas. However, few dusty plasma studies have been reported in low pressure microwave discharges. Fifteen years ago, it was accepted that dust particles cannot be formed in the plasma volume, due to the low probability of recombining reactive species, because of the low density of the gas. At LAPLACE, incandescent dusts are observed in RECR acetylene plasma. The present study aims to provide some answers on the mechanisms related to the formation, transportation and heating of dust particles. This document presents the results obtained during these four years of theses. Chapter 1 briefly introduces the emergence of the topic of dusty plasmas, as well as some important theoretical aspects of multipolar discharges. Chapter 2 details the experimental setup and the different diagnostics used during this study: Langmuir probe, Mach probe, wall probe current and rapid imaging. Chapter 3 details the mechanisms for charging and heating dust. In this part, experimental measurements and a model are coupled to explain the incandescence and to estimate the particles charges. Chapter 4 describes the characterisation of dust transport in acetylene plasma by rapid imaging. In this chapter, we discuss the forces that can be responsible for this transport. Finally, Chapter 5 reviews the results obtained on the plasma-surface interaction, using ex-situ analyzes as well as measurements of wall probe currents
34
Clark, Eugene Laurence. "Measurements of energetic particles from ultraintense laser plasma interactions." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271738.
Full text
35
Mangles, Stuart Peter David. "Measurements of relativistic electrons from intense laser-plasma interactions." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417730.
Full text
36
Stanyer, Lee. "Beta-amyloid/plasma lipoprotein interactions : implications for vascular damage." Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270774.
Full text
37
Mason, Philip. "Ultraintense laser-plasma interactions in one and two dimensions." Thesis, University of Essex, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324248.
Full text
38
Cannon, Patrick. "Numerical simulation of wave-plasma interactions in the ionosphere." Thesis, Lancaster University, 2016. http://eprints.lancs.ac.uk/80076/.
Full textAbstract:
Ionospheric modification by means of high-power electromagnetic (EM) waves can result in the excitation of a diverse range of plasma waves and instabilities. This thesis presents the development and application of a GPU-accelerated finite-difference time-domain (FDTD) code designed to simulate the time-explicit response of an ionospheric plasma to incident EM waves. Validation tests are presented in which the code achieved good agreement with the predictions of plasma theory and the computations of benchmark software. The code was used to investigate the mechanisms behind several recent experimental observations which have not been fully understood, including the effect of 2D density inhomogeneity on the O-mode to Z-mode conversion process and thus the shape of the conversion window, and the influence of EM wave polarisation and frequency on the growth of density irregularities. The O-to-Z-mode conversion process was shown to be responsible for a strong dependence of artificially-induced plasma perturbation on both the EM wave inclination angle and the 2D characteristics of the background plasma. Allowing excited Z-mode waves to reflect back towards the interaction region was found to cause enhancement of the electric field and a substantial increase in electron temperature. Simulations of O-mode and X-mode polarised waves demonstrated that both are capable of exciting geomagnetic field-aligned density irregularities, particularly at altitudes where the background plasma frequency corresponds to an electron gyroharmonic. Inclusion of estimated electrostatic fields associated with irregularities in the simulation algorithm resulted in an enhanced electron temperature. Excitation of these density features could address an observed asymmetry in anomalous absorption and recent unexplained X-mode heating results reported at EISCAT. Comparing simulations with ion motion allowed or suppressed indicated that a parametric instability was responsible for irregularity production. Simulation of EM wave fields confirmed that X-mode waves are capable of exceeding the threshold for parametric instability excitation under certain conditions.
39
Nazemidashtarjandi, Saeed. "Interactions of Engineered Nanomaterials with the Cell Plasma Membrane." Ohio University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1617363923755762.
Full text
40
Hua, Xuefeng. "Mechanistic studies of plasma-surface interactions during nanoscale patterning of advanced electronic materials using plasma." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/3307.
Full textAbstract:
Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
41
Harada, Yuki. "Interactions of Earth's Magnetotail Plasma with the Surface, Plasma, and Magnetic Anomalies of the Moon." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188495.
Full text
42
Tsuda, Mutsumi. "A Study of Plasma-Surface Interactions in Plasma Etching with Chlorine-and Bromine-based Chemistries." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147670.
Full text
43
Sayed, Fatema. "Modulation interactions in Quantum Plasmas." Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/10093.
Full textAbstract:
In this thesis we generalize the formalism of modulational interactions to nonrelativistic quantum plasmas, based on the Wigner kinetic description of collisionless quantum plasmas. In particular, we derive kinetically the effective cubic response of a quantum plasma (which in general is a complex-valued function), which can be used for various modulational processes. As an illustration of its use, we derive the quantum-corrected Zakharov equations for collisionless quantum plasmas by neglecting the imaginary part of the effective cubic response. We investigate the modulational and filamentational instabilities of a monochromatic Langmuir pump wave in quantum plasmas, using renormalized quantum linear and nonlinear plasma polarization responses. We analyze the effects of quantum correction terms on the growth rate of these instabilities. Using the quantum-corrected Zakharov equations we investigate the existence of envelope soliton solutions in collisionless quantum plasmas, in the kinetic case, which describes the interaction between high frequency Langmuir waves and low frequency plasma density variations. We also show the role played by quantum effects in the nonlinearity/dispersion balance leading to the formation of soliton solutions of the quantum nonlinear Schrodinger (QNLS) equation.
44
Kogelschatz, Martin. "Etude des interactions plasma–surface pendant la gravure du silicium dans des plasmas HBr/Cl2/O2." Phd thesis, Université Joseph Fourier (Grenoble), 2004. http://tel.archives-ouvertes.fr/tel-00009005.
Full textAbstract:
L'objectif de ce travail est de comprendre les interactions plasma-surface pendant la gravure du silicium dans des chimies HBr/Cl2/O2. Dans ces procédés, une couche se dépose sur les parois du réacteur et mène à la dérive du procédé. La nature chimique et les mécanismes de formation de cette couche ont été étudiés par sa gravure ultérieure avec un plasma Ar/SF6 et l'analyse résolue en temps des produits de gravure par les diagnostics d'émission optique et de spectrométrie de masse. Il a été montré que cette couche est du type SiOxCly très riche en chlore. Aussi, la cinétique des radicaux SiClx produits lors de la gravure du silicium par le plasma HBr/Cl2/O2, qui sont les précurseurs de ce dépôt, a été étudiée par la spectroscopie d'absorption large bande dans l'UV. Il a été conclu que les précurseurs du dépôt sont le Si, Si+, SiCl et SiCl+, mais la réaction de ces espèces avec les parois peut aussi mener à la formation de SiCl2 volatil.
45
Bardin, Sébastien. "Etude des interactions plasma-paroi par imagerie rapide : application aux plasmas de laboratoire et de tokamak." Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0012/document.
Full textAbstract:
La nécessité de trouver une nouvelle source d'énergie a mené les scientifiques à explorer la voie de la fusion thermonucléaire par confinement magnétique. Cependant la réalisation de tels plasmas de fusion dans les tokamaks actuels pose de nombreux défis tels que les interactions entre le plasma et les parois à l'origine de la création de poussières pouvant être néfastes au bon fonctionnement des futurs réacteurs à fusion. Une bonne connaissance de la quantité de poussières produites, de leur localisation et de leur transport durant la phase plasma est donc d'une importance fondamentale pour l'exploitation d'ITER. Un algorithme, développé et validé par l'expérience, est utilisé pour détecter et suivre les poussières dans ASDEX Upgrade (AUG) durant la phase plasma. Il permet d'analyser automatiquement des vidéos enregistrées par caméras rapides. Une large statistique sur la quantité de poussières micrométriques détectées en fonction du temps cumulé de décharge plasma est réalisée. Les premières analyses effectuées sur les cinq dernières campagnes montrent que la quantité de poussières est significativement faible voire nulle dans la plupart des décharges effectuées dans AUG, excepté pour des conditions spécifiques de décharges correspondant à des phases anormales de fonctionnement (disruptions, ELMs, déplacements du plasma vers les CFPs et absorption inefficace de la puissance de chauffage). Ces observations par caméra rapide et l'analyse via l'algorithme peuvent ainsi permettre, avec l'utilisation d'autres diagnostics plasmas, d'identifier les décharges plasmas à risque, pouvant aider à sélectionner les scénarios de fonctionnement les plus efficaces pour ITERThe necessity to find a new energy source has lead scientists to explore the way of thermonuclear fusion by magnetic confinement considered as one of the most promising possibility. However the production of such plasmas in the current tokamaks lies to several challenges like the interactions between the plasma and the first wall which spark off the creation of a lot of dust in the plasma which could be problematic for the operation of the next fusion reactors. The knowledge of dust production rates, localisation and transport through the vacuum vessel during plasma phases is of primary importance and must be investigated in preparation of ITER. A time and resource efficient algorithm named TRACE, validated thanks to a dedicated laboratory experiment, is used to detect and track dust particles in ASDEX Upgrade during plasma phase. It allows for automatically analyzing videos originating from fast framing cameras. A statistic about micron sized dust detection rate as a function of cumulated discharge duration is made on a large number of discharges (1470). First analyses covering five last campaigns clearly confirm that the amount of dust is significantly low in most of discharges realized in ASDEX Upgrade, excepted for specific conditions corresponding to off-normal plasma phases (disruptions, strong plasma fluctuations including ELMs, plasma displacement toward PFCs and inefficient absorption of heating power). These observations allow to identify the risky plasma discharges and choose the most efficient plasmas scenarios for ITER. It seems to also confirm the applicability of an all tungsten first wall for future fusion reactors as ITER
46
Parfeniuk, Dean Allister. "Studies of dense plasmas in laser generated shock wave experiments." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/27504.
Full textAbstract:
Shock waves generated by laser-driven ablation in solids have provided a great opportunity for the study of dense plasmas. The work presented in this thesis include measurements of Hugoniot curves and the reflectivity of shocked aluminum. In these experiments, planar aluminum targets were irradiated with a 0.53µm, 2ns (FWHM) laser pulse at irradiances up to ~ 10¹⁴/cm². Temporally and spectrally resolved measurements of the target rear surface luminous emission have yielded the shock speed and temperature Hugoniot curve which showed good agreement with equation of state predictions. In addition, temporally resolved reflectivity measurements of the shocked target rear surface compared well with a theoretical model for the electrical conductivity of a dense plasma. For copper and molybdenum targets, both the luminescence and the reflectivity measurements indicated that the heating of the dense target material was dominated by radiation transport from the coronal plasma rather than shock heating. An analysis of the molybdenum results indicate that x-ray shine-through may be the dominant energy transport mechanism to the target rear surface, whereas for the copper targets the transport process appears to be much more complex.Science, Faculty of
Physics and Astronomy, Department of
Graduate
47
Gremillet, Laurent Yvan André. "Etude théorique et expérimentale du transport des électrons rapides dans l'interaction laser-solide à très haut flux." Palaiseau, École polytechnique, 2001. http://www.theses.fr/2001EPXX0022.
Full text
48
Madanian, Hadi. "External Plasma Interactions with Nonmagnetized Objects in the Solar System." Thesis, University of Kansas, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10282984.
Full textAbstract:
The absence of a protecting magnetic field, such as the dipole magnetic field around Earth, makes the interaction of solar wind with unmagnetized objects particularly interesting. Long-term evolution of the object’s surface and atmosphere is closely tied to its interaction with the outer space environment. The ionospheric plasma layer around unmagnetized objects acts as an electrically conducting transition layer between lower atmospheric layers and outer space. This study considers two distinct types of unmagnetized objects: Titan and comet 67P/Churyumov-Gerasimenko (67P/CG). For many years, Titan has been a key target of the National Aeronautics and Space Administration (NASA) Cassini mission investigations; and the European Space Agency (ESA) Rosetta spacecraft explored comet 67P/CG for more than two years.
Ionospheric composition and primary ion production rate profiles for Titan are modeled for various solar activity conditions. Photoionization is the main source of ion production on the dayside; on the nightside, electron-impact ionization is the main ionization source. This dissertation uses model results and in-situ measurements by the Ion and Neutral Mass Spectrometer (INMS) and the Langmuir Probe (LP) onboard the Cassini spacecraft to show that while the solar activity cycle impacts the primary ion species significantly, there is little effect on heavy ion species. Solar cycle modulates the Titan’s ionospheric chemistry. The solar cycle effects of on each ion species are quantified n this work. In some cases the solar zenith angle significantly overshadows the solar cycle effects. How each individual ion reacts to changes in solar activity and solar zenith angle is discussed in details. A method to disentangle these effects in ion densities is introduced.
At comet 67P/CG, the fast-moving solar wind impacts the neutral coma. Two populations of electrons are recognizable in the cometary plasma. These are the hot suprathermal electrons, created by photoionization or electron-impact ionization, and the cold/thermal electrons. Even though photoionization is the dominant source of ion production, electron-impact ionization can be as high as the photoionization for certain solar events. At 3 AU, electron energy spectra from in-situ measurements of the Ion and Electron Sensor (IES) instrument exhibit enhancement of electron fluxes at particular energies. Model-data comparisons show that the flux of electrons is higher than the typical solar wind and pure photoionization fluxes. The probable cause of this enhancement is the ambipolar electric field and/or plasma compression.
This research also discusses formation of a new boundary layer around the comet near perihelion, similar to the diamagnetic cavity at comet 1P/Halley. At each crossing event to the diamagnetic cavity region, flux of suprathermal electrons with energies between 40 to 250 eV drops. The lower flux of solar wind suprathermal electrons in that energy range can cause this flux drop.
49
Zhu, Wenxi. "Studies of spectral modification in intense laser pulse-plasma interactions." Thesis, University of Maryland, College Park, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3611799.
Full textAbstract:
Laser pulses propagating through plasma undergo spectral broadening through local energy exchange with driven plasma waves. During propagation, a high power laser pulse drives large amplitude plasma waves, depleting the pulse energy. At the same time, the large amplitude plasma wave provides a dynamic dielectric response that leads to spectral shifting. The loss of laser pulse energy and the approximate conservation of laser pulse action imply that spectral red-shifts accompany the depletion. Here we examine the spectral shift and broadening, energy depletion, and action conservation of nonlinear laser pulses using the modified paraxial solver in WAKE. For pulses causing complete cavitation, large wavenumber shifts and action decay are observed at the distance where 40–50% of the pulse energy is depleted, consistent with theoretical prediction.
A tenuous plasma, enveloped, full wave solver was further implemented and compared to the modified paraxial solver through studying the University of Maryland laser-plasma system. The full wave solver has the advantage of better predicting the dispersion relation and eliminating the problematic divergence in the dispersion of the modified paraxial solver as wavenumber approaches zero, which is important especially when considering long wavelength generation.
Numerical analysis of the two propagation algorithms has been conducted via monitoring conservation laws. For large spectral shifts, numerical damping and convection of radiation out of the simulation domain result in action decay. Implementing a higher order evaluation of numerical derivatives and smaller spatial step have reduced numerical damping.
Spectral red-shifting of high power laser pulses propagating through underdensed plasma channel can be a source of ultrashort mid-infrared (MIR) radiation. Parametric dependence of MIR generation on laser pulse power, initial pulse duration, and plasma density is investigated through characteristic wavenubmer estimates and simulations.
50
Caillard, Jean. "Interactions et transferts énergétiques entre un plasma thermique et un matériau." Orléans, 2001. http://www.theses.fr/2001ORLE2015.
Full textAbstract:
Le sujet de cette étude correspond aux besoins en caractérisations du fonctionnement d'un composant électropyrotechnique à plasma utilisé dans le cadre d'un lanceur électrothermique chimique (ETC). L'objectif de la thèse est d'optimiser ces composants plasma. Le travail a consisté dans une première partie à développer un banc capacitif adapté au composant électropyrotechnique (microtorche) et à caractériser la réponse impulsionnelle de l'ensemble banc/torche. L'approche spectroscopique fait l'objet de la deuxième partie de l'étude. Après avoir défini les différentes hypothèses de travail, modèles et dispositifs expérimentaux nécessaires au diagnostic du plasma, nous donnons les températures mesurées expérimentalement pour quatre types de polymères plasmagènes (PE, PA6. 6, PET, POM). Le diagnostic du jet de plasma par spectroscopie a permis de mettre en évidence la forte dépendance des caractéristiques du jet de plasma vis à vis de la nature du matériau ablaté. La spectroscopie a par ailleurs permis de justifier l'hypothèse d'équilibre thermodynamique prise comme hypothèse de base des codes de calculs. La troisième partie traite de l'interaction du plasma avec son voisinage. Dans un premier temps, c'est la notion d'ablation du polymère qui est discutée. Dans un deuxième temps, nous nous intéressons à l'interaction mécanique du jet de plasma en expansion dans l'air. Les vitesses d'éjection sont mesurées et la présence de disques de Mach révélateurs d'un écoulement supersonique mise en évidence. L'exploitation de la perturbation de pression produite par à la décharge électrique très violente a conduit à utiliser le modèle de dépôt ponctuel et instantané d'énergie de Sedov-Taylor préalablement modifié pour tenir compte de la pression initiale du milieu de propagation. Enfin, dans un troisième et dernier temps, une étude par plans d'expériences de l'interaction plasma/poudres est réalisée