Thèses sur le sujet « Acceleraton of particles »
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Waldman, Zachary J. « Majorana Neutrinos in the Jacob-Wick phase convention ». Diss., Online access via UMI:, 2008.
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Verhagen, Erik. « Development of the new trigger and data acquisition system for the CMS forward muon spectrometer upgrade ». Doctoral thesis, Universite Libre de Bruxelles, 2015. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209110.
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La physique des particules élémentaires, aussi appelé physique des hautes énergies, est l'étude de l'infiniment petit, popularisée récemment par la découverte de nouvelles particules fondamentales permettant de consolider notre connaissance de la matière. Pour réaliser des mesures à une échelle aussi réduite, une méthode consiste à augmenter l’énergie des constituants de la matière, à l'aide d'accélérateur de particules, puis de les briser pour révéler leur constitution. Au-delà de l'intérêt en termes de physique expérimentale, réaliser des expériences de ce type est devenu une prouesse technologique grandissante avec les niveaux d’énergie atteints. La complexité de l’expérience CMS, cadre dans laquelle ce travail a été réalisé, donne une bonne mesure des défis technologiques relevés.Afin d'affiner encore notre connaissance des processus mis en jeu lors collision de particules dans CMS, une mise à niveau du détecteur est prévue avant la fin de cette décennie. Certains sous-détecteurs actuellement installés, et notamment le spectromètre à muon dans la zone des bouchons, sont d’ores et déjà identifiés comme offrant des performances trop faibles pour l'augmentation du nombres d’événements prévu après cette mise à jour. Ce travail propose de réaliser une étude de faisabilité sur l'utilisation d'une technologie alternative pour ce sous-détecteur, notamment le Triple-GEM, pour combler ces limitations.
Une première partie de ce travail consiste en l'étude de cette nouvelle technologie de détecteur à gaz. Cependant, la mise en œuvre de cette technologie conduit à des modifications dans le système d'acquisition de données de CMS. La situation actuelle puis les implications d'un point de vue technique des modifications sont donc détaillées par la suite. Enfin, après avoir identifié les composants et les solutions permettant la collecte de résultats à l’échelle de l'ensemble du sous-détecteur, un système d'acquisition de données similaire a été réalisé et est décrit dans une dernière partie de ce travail.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Johnson, Samantha. « Optimizing the ion source for polarized protons ». Thesis, University of the Western Cape, 2005. http://etd.uwc.ac.za/index.php?module=etd&.
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Beams of polarized protons play an important part in the study of the spin dependence of the nuclear force by measuring the analyzing power in nuclear reactions. The source at iThemba LABS produces a beam of polarized protons that is pre-accelerated by an injector cyclotron (SPC2) to a energy of 8 MeV before acceleration by the main separated-sector cyclotron to 200 MeV for physics research. The polarized ion source is one of the two external ion sources of SPC2. Inside the ion source hydrogen molecules are dissociated into atoms in the dissociator and cooled to a temperature of approximately 30 K in the nozzle. The atoms are polarized by a pair of sextupole magnets and the nucleus is polarized by RF transitions between hyperfine levels in hydrogen atoms. The atoms are then ionized by electrons in the ionizer. The source has various sensitive devices, which influence beam intensity and polarization. Nitrogen gas is used to prevent recombination of atoms after dissociation. The amount of nitrogen and the temperature at which it is used plays a very important role in optimizing the beam current. The number of electrons released in the ionizer is influenced by the size and shape of the filament. Optimization of the source will ensure that beams of better quality (a better current and stability) are produced.
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Weathersby, Stephen. « Damping higher order modes in the PEP-II B-factory storage ring collider ». Diss., Connect to online resource - MSU authorized users, 2007.
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Thesis (Ph.D.)--Michigan State University. Dept. of Physics and Astronomy, 2007.Title from PDF t.p. (viewed on August 18, 2009) Includes bibliographic references (p. 175-179). Also issued in print.
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Williams, Logan Todd. « Ion acceleration mechanisms of helicon thrusters ». Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47691.
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A helicon plasma source is a device that can efficiently ionize a gas to create high density, low temperature plasma. There is growing interest in utilizing a helicon plasma source in propulsive applications, but it is not yet known if the helicon plasma source is able to function as both an ion source and ion accelerator, or whether an additional ion acceleration stage is required. In order to evaluate the capability of the helicon source to accelerate ions, the acceleration and ionization processes must be decoupled and examined individually. To accomplish this, a case study of two helicon thruster configurations is conducted. The first is an electrodeless design that consists of the helicon plasma source alone, and the second is a helicon ion engine that combines the helicon plasma source with electrostatic grids used in ion engines. The gridded configuration separates the ionization and ion acceleration mechanisms and allows for individual evaluation not only of ion acceleration, but also of the components of total power expenditure and the ion production cost.
In this study, both thruster configurations are fabricated and experimentally characterized. The metrics used to evaluate ion acceleration are ion energy, ion beam current, and the plume divergence half-angle, as these capture the magnitude of ion acceleration and the bulk trajectory of the accelerated ions. The electrode-less thruster is further studied by measuring the plasma potential, ion number density, and electron temperature inside the discharge chamber and in the plume up to 60 cm downstream and 45 cm radially outward. The two configurations are tested across several operating parameter ranges: 343-600 W RF power, 50-450 G magnetic field strength, 1.0-4.5 mg/s argon flow rate, and the gridded configuration is tested over a 100-600 V discharge voltage range.
Both configurations have thrust and efficiency below that of contemporary thrusters of similar power, but are distinct in terms of ion acceleration capability. The gridded configuration produces a 65-120 mA ion beam with energies in the hundreds of volts that is relatively collimated. The operating conditions also demonstrate clear control over the performance metrics. In contrast, the electrodeless configuration generally produces a beam current less than 20 mA at energies between 20-40 V in a very divergent plume. The ion energy is set by the change in plasma potential from inside the device to the plume. The divergence ion trajectories are caused by regions of high plasma potential that create radial electric fields.. Furthermore, the operating conditions have limited control of the resulting performance metrics. The estimated ion production cost of the helicon ranged between 132-212 eV/ion for argon, the lower bound of which is comparable to the 157 eV/ion in contemporary DC discharges. The primary power expenditures are due to ion loss to the walls and high electron temperature leading to energy loss at the plasma sheaths.
The conclusion from this work is that the helicon plasma source is unsuitable as a single-stage thruster system. However, it is an efficient ion source and, if paired with an additional ion acceleration stage, can be integrated into an effective propulsion system.
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Linz, Thomas M. « Self-Force on Accelerated Particles ». Thesis, The University of Wisconsin - Milwaukee, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3712619.
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The likelihood that gravitational waves from stellar-size black holes spiraling into a supermassive black hole would be detectable by a space based gravitational wave observatory has spurred the interest in studying the extreme mass-ratio inspiral (EMRI) problem and black hole perturbation theory (BHP). In this approach, the smaller black hole is treated as a point particle and its trajectory deviates from a geodesic due to the interaction with its own field. This interaction is known as the gravitational self-force, and it includes both a damping force, commonly known as radiation reaction, as well as a conservative force. The computation of this force is complicated by the fact that the formal expression for the force due to a point particle diverges, requiring a careful regularization to find the finite self-force.
This dissertation focuses on the computation of the scalar, electromagnetic and gravitational self-force on accelerated particles. We begin with a discussion of the "MiSaTaQuWa" prescription for self-force renormalization (Mino, Sasaki, Takasugi 1999 and Quinn and Wald, 1999) along with the refinements made by Detweiler and Whiting (2003), and demonstrate how this prescription is equivalent to performing an angle average and renormalizing the mass of the particle. With this background, we shift to a discussion of the "mode-sum renormalization" technique developed by Barack and Ori (2000), who demonstrated that for particles moving along a geodesic in Schwarzschild spacetime (and later in Kerr spacetime), the regularization parameters can be described using only the leading and subleading terms (known as the A and B terms). We extend this to demonstrate that this is true for fields of spins 0, 1, and 2, for accelerated trajectories in arbitrary spacetimes.
Using these results, we discuss the renormalization of a charged point mass moving through an electrovac spacetime; extending previous studies to situations in which the gravitational and electromagnetic contributions are comparable. We renormalize by using the angle average plus mass renormalization in order to find the contribution from the coupling of the fields and encounter a striking result: Due to a remarkable cancellation, the coupling of the fields does not contribute to the renormalization. This means that the renormalized mass is obtained by subtracting (1) the purely electromagnetic contribution from a point charge moving along an accelerated trajectory and (2) the purely gravitational contribution of an electrically neutral point mass moving along the same trajectory. In terms of the mode-sum regularization, the same cancellation implies that the regularization parameters are merely the sums of their purely electromagnetic and gravitational values.
Finally, we consider the scalar self-force on a point charge orbiting a Schwarzschild black-hole following a non-Keplerian circular orbit. We utilize the techniques of Mano, Suzuki, and Takasugi (1996) for generating analytic solutions. With this tool, it is possible to generate a solution for the field as a series in the Fourier frequency, which allows researchers to naturally express the solutions in a post Newtonian series (see Shah et. al. 2014). We make use of a powerful insight by Hikida et. al.(2005), which allows us to perform the renormalization analytically. We investigate the details of this procedure and illuminate the mechanisms through which it works. We finish by demonstrating the power of this technique, showing how it is possible to obtain the post Newtonian expressions by only explicitly computing a handful of modes.
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Alton, Andrew K. « Evidence for the existence of jets in photon-parton interaction events at center of mass energies from 18 to 28 GEV ». Virtual Press, 1995. http://liblink.bsu.edu/uhtbin/catkey/1014850.
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Experiment E683 at Fermi National Accelerator Laboratory (FNAL) in Batavia, Illinois, uses a modular, high-energy sampling calorimeter as the basis of the detector system. This detector provides information on the energy and position of particles that exit a collision of a photon or pion with a target proton. While exiting particles are thought to form what are described as "jets", and several E683 projects involve working with these jets, it has not yet been demonstrated that jets indeed have been detected.The solution proposed here involves demonstrating that E683 data has a statistically significant "jettiness" even in a data sample which has not been biased. Towards this, a data sample was selected based on criteria unrelated to the presumption of jets. Planarity and the Et Flow were chosen as measures of how oblong(jetlike) an event is. The sample was then examined for planarity and Et flow in a number of kinematic ranges and the results demonstrate that over a certain kinematic range, events in our sample are increasingly planar, as we hypothesized.Department of Physics and Astronomy
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Hosack, Michael G. « Optimization of particle tracking for experiment E683 at Fermi National Laboratory ». Virtual Press, 1995. http://liblink.bsu.edu/uhtbin/catkey/941370.
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The subject of this thesis is the improvement of particle tracking through the identification and correction of small systematic errors in particle "hit" locations due to positioning of tracking detectors. These errors call be as large or larger than the statistical spatial resolution of tracking detectors themselves, and therefore must be corrected. The focus is on identification and correction of errors due to rotations and beam axis translations.An algorithm is developed for use with proportional wire chamber and drift chamber detectors in experiment E683 at the Wideband facility of Fermi National Laboratory. In this experiment, high energy (tens of GeV) particles, primarily mesons, were produced when photons with energies of 40-400 GeV struck a metal or liquid target.At the present time, the method and code developed for this thesis has not been applied to real data, although an analysis of its effectiveness as a function of detector resolution has been investigated with Monte-Carlo simulations.Department of Physics and Astronomy
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Guo, Fan. « Effects of Turbulent Magnetic Fields on the Transport and Acceleration of Energetic Charged Particles : Numerical Simulations with Application to Heliospheric Physics ». Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/255156.
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Turbulent magnetic fields are ubiquitous in space physics and astrophysics. The influence of magnetic turbulence on the motions of charged particles contains the essential physics of the transport and acceleration of energetic charged particles in the heliosphere, which is to be explored in this thesis. After a brief introduction on the energetic charged particles and magnetic fields in the heliosphere, the rest of this dissertation focuses on three specific topics: 1. the transport of energetic charged particles in the inner heliosphere, 2. the acceleration of ions at collisionless shocks, and 3. the acceleration of electrons at collisionless shocks. We utilize various numerical techniques to study these topics. In Chapter 2 we study the propagation of charged particles in turbulent magnetic fields similar to the propagation of solar energetic particles in the inner heliosphere. The trajectories of energetic charged particles in the turbulent magnetic field are numerically integrated. The turbulence model includes a Kolmogorov-like magnetic field power spectrum containing a broad range of scales from those that lead to large-scale field-line random walk to small scales leading to resonant pitch-angle scattering of energetic particles. We show that small-scale variations in particle intensities (the so-called "dropouts") and velocity dispersions observed by spacecraft can be reproduced using this method. Our study gives a new constraint on the error of "onset analysis", which is a technique commonly used to infer information about the initial release of energetic particles. We also find that the dropouts are rarely produced in the simulations using the so-called "two-component" magnetic turbulence model (Matthaeus et al., 1990). The result questions the validity of this model in studying particle transport. In the first part of Chapter 3 we study the acceleration of ions in the existence of turbulent magnetic fields. We use 3-D self-consistent hybrid simulations (kinetic ions and fluid electrons) to investigate the acceleration of low-energy particles (often termed as "injection problem") at parallel shocks. We find that the accelerated particles always gain the first amount of energy by reflection and acceleration at the shock layer. The protons can move off their original field lines in the 3-D electric and magnetic fields. The results are consistent with the acceleration mechanism found in previous 1-D and 2-D simulations. In the second part of Chapter 3, we use a stochastic integration method to study diffusive shock acceleration in the existence of large-scale magnetic variations. We show that the 1-D steady state solution of diffusive shock acceleration can be significantly modified in this situation. The results suggest that the observations of anomalous cosmic rays by Voyager spacecraft can be explained by a 2-D shock that includes the large-scale magnetic field variations. In Chapter 4 we study electron acceleration at a shock passing into a turbulent magnetic field by using a combination of hybrid simulations and test-particle electron simulations. We find that the acceleration of electrons is greatly enhanced by including the effect of large-scale magnetic turbulence. Since the electrons mainly follow along the magnetic lines of force, the large-scale braiding of field lines in space allows the fast-moving electrons interacting with the shock front multiple times. Ripples in the shock front occurring at various scales also contribute to the acceleration by mirroring the electrons. Our calculation shows that this process favors electron acceleration at perpendicular shocks. We discuss the application of this process in interplanetary shocks and flare termination shocks. We also discuss the implication of this study to solar energetic particles (SEPs) by comparing the acceleration of electrons with that of protons. The intensity correlation of electrons and ions in SEP events indicates that perpendicular or quasi-perpendicular shocks play an important role in accelerating charged particles. In Chapter 5 we summarize the results of this thesis and discuss possible future work.
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Rosencranz, Daniela Necsoiu. « Monte Carlo simulation and experimental studies of the production of neutron-rich medical isotopes using a particle accelerator ». Thesis, University of North Texas, 2002. https://digital.library.unt.edu/ark:/67531/metadc3077/.
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The developments of nuclear medicine lead to an increasing demand for the production of radioisotopes with suitable nuclear and chemical properties. Furthermore, from the literature it is evident that the production of radioisotopes using charged-particle accelerators instead of nuclear reactors is gaining increasing popularity. The main advantages of producing medical isotopes with accelerators are carrier free radionuclides of short lived isotopes, improved handling, reduction of the radioactive waste, and lower cost of isotope fabrication. Proton-rich isotopes are the result of nuclear interactions between enriched stable isotopes and energetic protons. An interesting observation is that during the production of proton-rich isotopes, fast and intermediately fast neutrons from nuclear reactions such as (p,xn) are also produced as a by-product in the nuclear reactions. This observation suggests that it is perhaps possible to use these neutrons to activate secondary targets for the production of neutron-rich isotopes. The study of secondary radioisotope production with fast neutrons from (p,xn) reactions using a particle accelerator is the main goal of the research in this thesis.
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Edespong, Erik. « GPU Accelerated Surface Reconstruction from Particles ». Thesis, Linköpings universitet, Institutionen för teknik och naturvetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-93543.
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Realistic uid eects, such as smoke and water has been pursued by the visual eects industry for a long time. In recent years, particle simulations have gained a lot of popularity for achieving such eects. One problem noted by researchers has been the diculty of generating surfaces from the particles. This thesis investigates current techniques for particle surface reconstruction. In addition to this, a GPU-based implementation using constrained mesh smoothing is described. The result is globally smooth surfaces which closely follows the distribution of the particles, though some problems are still apparent. The performance of the algortihm is approximately an order of magnitude faster than its CPU counterpart, but is clogged by bottlenecks in sections still runnning on the CPU.
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Nodes, Christoph. « Particle Acceleration in Pulsar Wind Nebulae ». Diss., lmu, 2008. http://nbn-resolving.de/urn:nbn:de:bvb:19-80683.
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Burge, Christina Alice. « Particle acceleration in noisy magnetised plasmas ». Thesis, University of Glasgow, 2012. http://theses.gla.ac.uk/3588/.
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Particle dynamics in the solar corona are of interest since the behaviour of the coronal plasma is important for the understanding of how the solar corona is heated to such high temperatures compared to the photosphere (≈ 1 million Kelvin, compared to a photospheric temperature of ≈ 6 thousand Kelvin ). This thesis deals with particle behaviour in various forms of magnetic and electric fields. The method via which particles are accelerated at reconnection regions is of particular interest as particle acceleration at a magnetic reconnection region is the basis for many solar flare models. Solar flares are releases of energy in the solar corona. The amounts of energy released range from the very small amounts released by nanoflares, that cannot be observed individually, to large events such as X-class flares and coronal mass ejections. Chapter one provides background information about the structure of the Sun and about various forms of solar activity, including solar flares, sunspots, and the generation of the solar magnetic field. Chapter 2 explores various theories of magnetic reconnection. Magnetic reconnection re- gions are usually characterised as containing a central ’null’, a region where the magnetic field is zero, and particles can be freely accelerated in the presence of an electric field, as they decouple from the magnetic field and move non-adiabatically. Chapter 2 gives examples of how such reconnection regions could be formed. Chapter 3 deals with the construction of a ’noisy’ reconnection region. For the purposes of this work, ’noisy’ fields were created by perturbing the magnetic and electric fields with a superposition of eigenmode oscillations. The method for the calculation of such eigenmodes, and the creation of the electric and magnetic fields is detailed here. Chapter 4 details the consequences for particle behaviour in a noisy reconnection region. The behaviour of electrons and protons in such fields was studied. It was found that adding perturbations to the magnetic field caused many smaller nulls to form, which increased the size of the non-adiabatic region. This increased non-adiabatic region led to greater energisa- tion of particles. The X-ray spectra that could be produced by the accelerated electrons were 4 5 also calculated. In this chapter I also investigate the consequences of altering the distribution of the spectrum of modes, and altering the value of the inertial resistivity. In chapter 5, the effects of collisional scattering on particles was also investigated. Colli- sional scattering was introduced by integrating particle trajectories using a stochastic Runge- Kutta method (which is a form of numerical integration). It was found that adding collisional scattering at a reconnection region causes a significant change in particle dynamics in suffi- ciently small electric fields. Particles which undergo collisional scattering in the presence of a small electric field gain more energy than those which do not undergo collisional scatter- ing. This effect decreases as the size of the electric field is increased. The correct relativistic expressions for particle collisions were derived. It was found that collisions have a negligible effect on relativistic particles. Collisional scattering was also used to simulate the drift of particles across magnetic fields. It was found that adding more scattering caused the trajectories of the particles to change from normal gyromotion around the magnetic field, and that particles instead travelled across the magnetic field. I also developed a diffusion coefficient to allow the calculation of a particle’s drift across a magnetic field using only 1D equations. Chapter 6 discusses the findings made in this thesis, and explores how these findings could be built upon in the near future.
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Ptychion, Panagiota Petkaki. « Particle acceleration in dynamical collisionless reconnection ». Thesis, University of Glasgow, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296962.
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Wang, Xin, Joe Giacalone, Yihua Yan, Mingde Ding, Na Wang et Hao Shan. « Particle Acceleration in Two Converging Shocks ». IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624679.
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Observations by spacecraft such as ACE, STEREO, and others show that there are proton spectral "breaks" with energy E-br at 1-10 MeV in some large CME-driven shocks. Generally, a single shock with the diffusive acceleration mechanism would not predict the "broken" energy spectrum. The present paper focuses on two converging shocks to identify this energy spectral feature. In this case, the converging shocks comprise one forward CME-driven shock on 2006 December 13 and another backward Earth bow shock. We simulate the detailed particle acceleration processes in the region of the converging shocks using the Monte Carlo method. As a result, we not only obtain an extended energy spectrum with an energy "tail" up to a few 10 MeV higher than that in previous single shock model, but also we find an energy spectral "break" occurring on similar to 5.5 MeV. The predicted energy spectral shape is consistent with observations from multiple spacecraft. The spectral "break," then, in this case is caused by the interaction between the CME shock and Earth's bow shock, and otherwise would not be present if Earth were not in the path of the CME.
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Aryan, Homayon. « Particle acceleration in near earth geospace ». Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/7846/.
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The radiation belts occupy a vast region of near Earth geospace where many important communication, navigation, Earth observation, and defence satellites operate. In recent decades, demand for space technology has grown dramatically and this is set to grow further as humans become more and more dependent on space technology. Without the operation of currently hundreds of satellites around the Earth, the world would face a huge catastrophe to support a population of 7 billion plus. Trapped energetic radiation belt electrons represent a serious hazard to spacecraft electronic components. At the geostationary orbit, which is located at the edge of the outer radiation belt, these highly energetic electrons are accelerated to high energies, in the range of keV to MeV, through various processes. Therefore, it is considerably important to understand the basic properties of the Van Allen radiation belts and the main processes that are thought to be important in the acceleration and loss mechanisms of the radiation belt electrons that ultimately change the dynamics of the radiation belts. This thesis investigates particle acceleration in near Earth geospace. The findings of this research expanded our knowledge of the Van Allen radiation belts through studying the relationship between solar wind parameters and energetic electron fluxes at the outer radiation belt, the study of naturally occurring electromagnetic waves and their crucial role in the acceleration and loss of energetic electrons in the inner magnetosphere, and the study of particle acceleration in the vicinity of the Earth and interplanetary medium by strong interplanetary collisionless shocks associated with Coronal Mass Ejection (CME), in particular, in the case of strong collisionless shock formation associated with shock coalescence. The results can be used to help improve forecasting and nowcasting of changes in energetic electron population and ultimately help mitigate the damage caused to the satellites and other space based systems. Subsequently, this would help increase satellite lifetime and improve reliability.
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Doche, Antoine. « Particle acceleration with beam driven wakefield ». Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX023/document.
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Les accélérateurs par onde de sillage plasma produites par faisceaux de particules (PWFA) ou par faisceaux laser (LWFA) appartiennent à un nouveau type d’accélérateurs de particules particulièrement prometteur. Ils permettent d’exploiter des champs accélérateurs jusqu’à cent Gigaélectronvolt par mètre alors que les dispositifs conventionnels se limitent à cent Megaélectronvolt par mètre. Dans le schéma d’accélération par onde de sillage plasma, ou par onde de sillage laser, un faisceau de particules ou une impulsion laser se propage dans un plasma et créé une structure accélératrice dans son sillage : c’est une onde de densité électronique à laquelle sont associés des champs électromagnétiques dans le plasma. L’un des principaux résultats de cette thèse a été la démonstration de l’accélération par onde de sillage plasma d’un paquet distinct de positrons. Dans le schéma utilisé, un plasma de Lithium était créé dans un four, et une onde plasma était excitée par un premier paquet de positrons (le drive ou faisceau excitateur) et l’énergie était extraite par un second faisceau (le trailing ou faisceau témoin). Un champ accélérateur de 1,36 GeV/m a ainsi été obtenu durant l’expérience, pour une charge accélérée typique de 40 pC. Nous montrons également ici la possibilité d’utiliser différents régimes d’accélération qui semblent très prometteurs. Par ailleurs, l’accélération de particule par sillage laser permet quant à elle, en partant d’une impulsion laser femtoseconde de produire un faisceau d’électron quasi-monoénergétique d’énergie typique de l’ordre de 200 MeV. Nous présentons les résultats d’une campagne expérimentale d’association de ce schéma d’accélération par sillage laser avec un schéma d’accélération par sillage plasma. Au cours de cette expérience un faisceau d’électrons créé par laser est refocalisé lors d’une interaction dans un second plasma. Une étude des phénomènes associés à cette plateforme hybride LWFA-PWFA est également présentée. Enfin, le schéma hybride LWFA-PWFA est prometteur pour optimiser l’émission de rayonnement X par les électrons du faisceau de particule crée dans l’étage LWFA de la plateforme. Nous présentons dans un dernier temps la première réalisation expérimentale d’un tel schéma et ses résultats prometteursPlasma wakefield accelerators (PWFA) or laser wakefield accelerators (LWFA) are new technologies of particle accelerators that are particularly promising, as they can provide accelerating fields of hundreds of Gigaelectronvolts per meter while conventional facilities are limited to hundreds of Megaelectronvolts per meter. In the Plasma Wakefield Acceleration scheme (PWFA) and the Laser Wakefield Acceleration scheme (LWFA), a bunch of particles or a laser pulse propagates in a gas, creating an accelerating structure in its wake: an electron density wake associated to electromagnetic fields in the plasma. The main achievement of this thesis is the very first demonstration and experimental study in 2016 of the Plasma Wakefield Acceleration of a distinct positron bunch. In the scheme considered in the experiment, a lithium plasma was created in an oven, and a plasma density wave was excited inside it by a first bunch of positrons (the drive bunch) while the energy deposited in the plasma was extracted by a second bunch (the trailing bunch). An accelerating field of 1.36 GeV/m was reached during the experiment, for a typical accelerated charge of 40 pC. In the present manuscript is also reported the feasibility of several regimes of acceleration, which opens promising prospects for plasma wakefield accelerator staging and future colliders. Furthermore, this thesis also reports the progresses made regarding a new scheme: the use of a LWFA-produced electron beam to drive plasma waves in a gas jet. In this second experimental study, an electron beam created by laser-plasma interaction is refocused by particle bunch-plasma interaction in a second gas jet. A study of the physical phenomena associated to this hybrid LWFA-PWFA platform is reported. Last, the hybrid LWFA-PWFA scheme is also promising in order to enhance the X-ray emission by the LWFA electron beam produced in the first stage of the platform. In the last chapter of this thesis is reported the first experimental realization of this last scheme, and its promising results are discussed
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Lowe, Robert Edward. « Simulation of electron acceleration at collisionless plasma shocks ». Thesis, Queen Mary, University of London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246324.
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Ballard, Keith Richard. « Particle acceleration and synchrotron emission in blazars ». Thesis, University of Edinburgh, 1991. http://hdl.handle.net/1842/26210.
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An optical and infrared observing programme which provides the most detailed information yet available for blazars is described. From this it is possible to make progress in understanding the physical processes which are occurring on the smallest scales within the emission region. Later theoretical calculations including a treatment of synchrotron emission incorporating losses and a realistic source geometry are presented together with a model of particle acceleration at relativistic shocks in disordered magnetic fields. The work contained in this thesis can explain the radiation and make predictions regarding future observations. The conclusion is that the observations support the idea that the synchrotron emitting electrons are being accelerated at a collisionless shock front in a disordered field.
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Guyot, Julien. « Particle acceleration in colliding laser-produced plasmas ». Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS616.
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Les particules chargées énergétiques sont omniprésentes dans l'Univers et sont accélérées par des sources galactiques et extragalactiques. Comprendre l'origine de ces "rayons cosmiques" est crucial en astrophysique et dans le cadre de l'astrophysique de laboratoire à haute densité d'énergie, nous avons développé une nouvelle plate-forme sur les installations laser LULI pour étudier l'accélération de particules. Dans les expériences, la collision de deux plasmas contre-propageant produits par laser génère une distribution non thermique de particules allant jusqu'à 1 MeV d'énergie. L'objectif de ce travail est de fournir un cadre théorique pour comprendre leur origine. Des simulations magnéto-hydrodynamiques avec des particules tests montrent que la collision des plasmas conduit à la croissance de structures caractéristiques de l'instabilité de Rayleigh-Taylor magnétique et à la génération de forts champs électriques. Nous constatons que les particules sont accélérées à des énergies allant jusqu'à quelques centaines de keV en moins de 20 ns, par des interactions répétées avec les perturbations de Rayleigh-Taylor. Les simulations et un modèle d'accélération stochastique reproduisent bien le spectre expérimental. En conclusion, nous avons identifié en laboratoire un nouveau mécanisme d'accélération de particules qui repose sur la croissance de l'instabilité de Rayleigh-Taylor magnétique pour accélérer de manière stochastique les particules. Cette instabilité est fréquente dans les plasmas astrophysiques, avec par exemple les restes de supernovæ et les éjections de masse coronale, et nous suggérons qu'elle peut contribuer à l'accélération de particules dans ces systèmesEnergetic charged particles are ubiquitous in the Universe and are accelerated by galactic and extragalactic sources. Understanding the origin of these "cosmic rays" is crucial in astrophysics and within the framework of high-energy-density laboratory astrophysics we have developed a novel platform on the LULI laser facilities to study particle acceleration in the laboratory. In the experiments, the collision of two laser-produced counter-propagating plasmas generates a distribution of non-thermal particles with energies up to 1 MeV. The aim of this work is to provide a theoretical framework to understand their origin. Magneto-hydrodynamic simulations with test particles show that the plasma collision leads to the growth of bubble and spike structures driven by the magnetic Rayleigh-Taylor instability and the generation of strong electric fields. We find that particles are accelerated to energies up to a few hundred of keV in less than 20 ns, by repeated interactions with these growing magnetic Rayleigh-Taylor perturbations. The simulations and a stochastic acceleration model recover very well the experimentally measured non-thermal energy spectrum. In conclusion, we have identified in the laboratory a new particle acceleration mechanism that relies on the growth of the magnetic Rayleigh-Taylor instability to stochastically energize particles. This instability is very common in astrophysical plasmas, with examples including supernovae remnants and coronal mass ejections, and we suggest that it may contribute to the energization of particles in these systems
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Taheri, Faissal Bakkali. « Numerical and experimental studies of coherent Smith-Purcell radiation ». Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:d483c501-ba46-4e08-9d38-5af29211aedc.
Texte intégralRésumé :
This thesis investigates the properties of coherent Smith-Purcell radiation (cSPr) at femtosecond-scale in the case of electrons bunches in the ultrarelativistic regimes. Of particular interest is the use of cSPR as a diagnostic tool to determine the longitudinal time profiles of such bunches, the study of azimuthal distribution of the radiated energy, and a contribution to the understanding of polarization properties. The study consists in a first theoretical part carried mostly in the context of the surface-current theory, supported with insights from particle-in-cell simulations. Then, as a step toward a better determination of time profile, the question of phase reconstruction is addressed through the design of a new algorithm proposed in this thesis and tested in known challenging cases. Experimental results are then presented, spanning shifts having taken place at the FACET facility at SLAC, Stanford, between 2013 and 2015.
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Hauck, John C. « Electrodynamics of accelerated systems / ». free to MU campus, to others for purchase, 2003. http://wwwlib.umi.com/cr/mo/fullcit?p3101024.
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Sheehy, Suzanne Lyn. « Design of a non-scaling fixed field alternating gradient accelerator for charged particle therapy ». Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:d9cd977c-35db-45cc-ad33-67710fc3e82f.
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This thesis describes the design a novel type of particle accelerator for charged particle therapy. The accelerator is called a non-scaling, Fixed Field Alternating Gradient (ns-FFAG) accelerator, and will accelerate both protons and carbon ions to energies required for clinical use. The work is undertaken as part of the PAMELA project. An existing design for a ns-FFAG is taken as a starting point and analysed in terms of its ability to suit the charged particle therapy application. It is found that this design is particularly sensitive to alignment errors and would be unable to accelerate protons and carbon ions at the proposed acceleration rate due to betatron resonance crossing phenomena. To overcome this issue, a new type of non-linear ns-FFAG is developed which avoids resonance crossing and meets the requirements provided by clinical considerations. Two accelerating rings are required, one for protons up to 250 MeV and fully stripped carbon ions to 68 MeV/u, the other to accelerate the carbon ions up to 400-430 MeV/u. Detailed studies are undertaken to show that this new type of accelerator is suitable for the application. An alignment accuracy of 50 micrometers will not have a detrimental effect on the beam and the dynamic aperture for most lattice configurations is found to be greater than 50 pi.mm.mrad normalised in both the horizontal and vertical plane. Verification of the simulation code used in the PAMELA lattice design is carried out using experimental results from EMMA, the world's first ns-FFAG for 10-20 MeV electrons built at Daresbury Laboratory, UK. Finally, it is shown that the described lattice can translate into realistic designs for the individual components of the accelerator. The integration of these components into the PAMELA facility is discussed.
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Petit, Valentine. « Conditioning of surfaces in particle accelerators ». Thesis, Toulouse, ISAE, 2020. http://www.theses.fr/2020ESAE0002.
Texte intégralRésumé :
Le nuage d'électrons se développant dans les chambres à vide du LHC lors de l'opérationdes faisceaux de protons engendre une charge thermique sur le système cryogénique deses aimants supraconducteurs. La valeur de cette charge thermique présente une fortedispersion entre les différents arcs du LHC, pourtant identiques par design, dont certainssont actuellement proches de la limite de la capacité cryogénique. Sous l'effet du nuaged'électrons, le conditionnement de la surface de cuivre des chambres à vide du LHCa lieu, réduisant son rendement d'électrons secondaires. Un tel processus est supposédécroitre l'activité du nuage vers un niveau acceptable pour l'opération du LHC et sembledonc localement mis en défaut. Ce travail a analysé les phénomènes de conditionnementdu cuivre ayant lieu dans le LHC afin d'expliquer les différences d'activités du nuageélectronique observées dans l'accélérateur. L'étude des mécanismes de conditionnementdu cuivre en laboratoire, à température ambiante, en remplaçant le nuage par un canon àélectrons, a mis en évidence le rôle crucial du carbone dans la décroissance du rendementd'électrons secondaires. L'étude du déconditionnement, ayant lieu à la remise à l'air d'unesurface irradiée (étape nécessaire à l'extraction de tubes faisceau du LHC) a permisd'établir une procédure limitant l'effacement de l'état de conditionnement in-situ de cescomposants en vue de l'analyse de leur surface en laboratoire. Des analyses réaliséessur des tubes faisceau extraits d'un aimant à faible charge thermique montrent que cessurfaces présentent des caractéristiques similaires à celles conditionnées en laboratoire.En revanche, les tubes faisceau extraits d'un aimant à forte charge thermique présententdu CuO ainsi qu'un taux de carbone surfacique extrêmement faible. Il est prouvé que cesmodifications résultent de l'opération du LHC et conduisent à un conditionnement altéréde ces surfaces. Ces modifications sont actuellement le meilleur candidat pour expliquerl'origine des différences de charge thermique observées dans le LHCThe electron cloud developing in the vacuum chambers of the LHC during the protonbeam operation is responsible for heat load on the cryogenic system of the superconductingmagnets. The observed heat load exhibits a strong dispersion between the differentLHC arcs, although identical by design. Some of them are currently close to the limitof the cryoplant capacity. Under the effect of the cloud itself, conditioning of the coppersurface of the LHC beam pipes is expected, decreasing thus the secondary electronyield of the surface and leading to a decrease of the cloud intensity down to operationcompatiblelevels. Such a process seems therefore to be hindered in some parts of theLHC ring. This work aims to understand the copper conditioning processes occurringin the LHC, to unravel the origin of the heat load dispersion observed along the ring.Copper conditioning mechanisms were studied in the laboratory at room temperature bymimicking the electron cloud by an electron gun. The fundamental role of carbon, amongthe surface chemical components, in the reduction of the secondary electron yield duringconditioning was evidenced. Studying the deconditioning, occurring while exposing aconditioned surface to air (necessary step to extract beam pipes from the LHC) allowedestablishing a procedure to limit the erasing of the in-situ conditioning state of suchcomponents before the analysis of their surface in the laboratory. The surface of beampipes extracted from a low heat load magnet were found to have similar characteristicsas the ones conditioned in the laboratory. However, beam pipes extracted from a highheat load magnet exhibit cupric oxide CuO and a very low amount of surface carbon. Itis demonstrated that these modifications are induced by the LHC operation and lead toa slower conditioning of these surfaces. Therefore, these modifications are currently thebest candidate to explain the heat load dispersion observed in the LHC
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Debba, Djihad. « Etude locale des mécanismes de réentrainement des microparticules en conduite ventilée ». Thesis, Ecole nationale supérieure Mines-Télécom Atlantique Bretagne Pays de la Loire, 2017. http://www.theses.fr/2017IMTA0059/document.
Texte intégralRésumé :
L’objectif de cette étude est de bien décrire les mécanismes impliqués dans la remise en suspension des microparticules en conduite ventilée. Une méthodologie expérimentale est utilisée, et cela en tenant compte de la période d’accélération de l’écoulement qui précède l’atteinte du régime permanent. Une méthode optique a été choisi pour étudier le mouvement initial des particules, et leur cinétique de remise en suspension. Parallèlement, nous avons recueilli des données locales de l’écoulement en période d’accélération et au régime permanent.Le démarrage de la remise en suspension a été analysé relativement à l’évolution temporelle de trois paramètres pouvant influencer le démarrage de la remise en suspension, le premier est la vitesse instantanée en proche paroi, le second est l’intensité turbulente, et enfin le troisième est l’énergie cinétique turbulente. Le paramètre prépondérant sur le démarrage de la remise en suspension semble être l’énergie cinétique turbulenteThe objective of this study is to well describe the mechanisms involved in the resuspension of particles in ventilated duct by using an experimental methodology and taking into account the acceleration of the air flow which always precedes steady state. For that purpose, we chose an optical method in order to investigate the initial movement of particles, and to quantify the resuspension kinetics. In parallel we collected local data of the flow during acceleration and steady state.We observed that the resuspension kinetics starts during the acceleration period and extends to steady state. We highlighted the relevant velocity characteristics (critical velocity at the center duct and close to the wall, critical kinetic energy range) to explain this phenomenon. The resuspension start seems to be linked with a critical kinetic energy range
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Silvestri, Alessandra. « Modifying gravity : Cosmic acceleration and the large scale structure of the universe ». Related electronic resource : Current Research at SU : database of SU dissertations, recent titles available full text, 2008. http://wwwlib.umi.com/cr/syr/main.
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Kawate, Tomoko. « Observational Study of Particle Acceleration in Solar Flares ». 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157777.
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Walton, Barney Richard. « Optical diagnostics of laser plasma particle acceleration experiments ». Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.418083.
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Grady, Keith J. « Solar flare particle acceleration in collapsing magnetic traps ». Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/2839.
Texte intégralRésumé :
The topic of this thesis is a detailed investigation of different aspects of the particle acceleration mechanisms operating in Collapsing Magnetic Traps (CMTs), which have been suggested as one possible mechanism for particle acceleration during solar flares. The acceleration processes in CMTs are investigated using guiding centre test particle calculations. Results including terms of different orders in the guiding centre approximation are compared to help identify which of the terms are important for the acceleration of particles. For a basic 2D CMT model the effects of different initial conditions (position, kinetic energy and pitch angle) of particles are investigated in detail. The main result is that the particles that gain most energy are those with initial pitch angles close to 90° and start in weak field regions in the centre of the CMT. The dominant acceleration mechanism for these particles is betatron acceleration, but other particles also show signatures of Fermi acceleration. The basic CMT model is then extended by (a) including a magnetic field component in the invariant direction and (b) by making it asymmetric. It is found that the addition of a guide field does not change the characteristics of particle acceleration very much, but for the asymmetric models the associated energy gain is found to be much smaller than in symmetric models, because the particles can no longer remain very close to the trap centre throughout their orbit. The test particle method is then also applied to a CMT model from the literature which contains a magnetic X-line and open and closed field lines and the results are compared with the previous results and the findings in the literature. Finally, the theoretical framework of CMT models is extended to 2.5D models with shear flow and to fully 3D models, allowing the construction of more realistic CMT models in the future.
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Bjerke, Henrik Hemmestad. « Application of Novel Accelerator Research for Particle Therapy ». Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-24658.
Texte intégralRésumé :
This thesis seeks to review the latest trends in hadron therapy devices, and evaluate the potential of novel, researched accelerator concepts for future application. Although the clinical benefits of hadron therapy over photon therapy is unproven or disputed for many cancer types, there are several cases where hadron therapy presents a superior option. Many governments and medical institutions are planning or already executing development of new hadron treatment facilities. However, the higher associated costs have been a formidable obstacle for hadron therapy endeavors. This may be about to change; recent years have seen the introduction of economic single-room devices, and novel accelerator concepts hold potential to reduce cost further through improved compactness. Single-room gantry-mounted cyclotrons have already entered the market at prices competitive with X-ray facilities, and advanced, compact proton and ion accelerators offering unprecedented treatment could soon be ready for commercialization. Novel accelerator research may further contribute to improve the efficacy and economic aspects of future particle therapy devices.Keywords: Hadron therapy, hadrontherapy, particle therapy, radiation therapy, medical accelerators.
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Li, Lulu Ph D. Massachusetts Institute of Technology. « Acceleration methods for Monte Carlo particle transport simulations ». Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112521.
Texte intégralRésumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 166-175).
Performing nuclear reactor core physics analysis is a crucial step in the process of both designing and understanding nuclear power reactors. Advancements in the nuclear industry demand more accurate and detailed results from reactor analysis. Monte Carlo (MC) eigenvalue neutron transport methods are uniquely qualified to provide these results, due to their accurate treatment of space, angle, and energy dependencies of neutron distributions. Monte Carlo eigenvalue simulations are, however, challenging, because they must resolve the fission source distribution and accumulate sufficient tally statistics, resulting in prohibitive run times. This thesis proposes the Low Order Operator (LOO) acceleration method to reduce the run time challenge, and provides analyses to support its use for full-scale reactor simulations. LOO is implemented in the continuous energy Monte Carlo code, OpenMC, and tested in 2D PWR benchmarks. The Low Order Operator (LOO) acceleration method is a deterministic transport method based on the Method of Characteristics. Similar to Coarse Mesh Finite Difference (CMFD), the other acceleration method evaluated in this thesis, LOO parameters are constructed from Monte Carlo tallies. The solutions to the LOO equations are then used to update Monte Carlo fission sources. This thesis deploys independent simulations to rigorously assess LOO, CMFD, and unaccelerated Monte Carlo, simulating up to a quarter of a trillion neutron histories for each simulation. Analysis and performance models are developed to address two aspects of the Monte Carlo run time challenge. First, this thesis demonstrates that acceleration methods can reduce the vast number of neutron histories required to converge the fission source distribution before tallies can be accumulated. Second, the slow convergence of tally statistics is improved with the acceleration methods for the earlier active cycles. A theoretical model is developed to explain the observed behaviors and predict convergence rates. Finally, numerical results and theoretical models shed light on the selection of optimal simulation parameters such that a desired statistical uncertainty can be achieved with minimum neutron histories. This thesis demonstrates that the conventional wisdom (e.g., maximizing the number of cycles rather than the number of neutrons per cycle) in performing unaccelerated MC simulations can be improved simply by using more optimal parameters. LOO acceleration provides reduction of a factor of at least 2.2 in neutron histories, compared to the unaccelerated Monte Carlo scheme, and the CPU time and memory overhead associated with LOO are small.
by Lulu Li.
Ph. D.
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Voshchepynets, Andrii. « Interaction faisceau-plasma dans un plasma aleatoirement non-homogene du vent solaire ». Thesis, Orléans, 2015. http://www.theses.fr/2015ORLE2035/document.
Texte intégralRésumé :
Dans cette thèse nous avons présenté un modèle probabiliste auto cohérent décrivant la relaxation d'un faisceau d'électrons dans un vent solaire dont les fluctuations aléatoires de la densité ont les mêmes propriétés spectrales que celles mesurées à bord de satellites. On a supposé que, le système possédait différentes échelles caractéristiques en plus de l'échelle caractéristique des fluctuations de densité. Ceci nous a permis de décrire avec précision l'interaction onde-particule à des échelles inférieures à l'échelle caractéristique des fluctuations de densité en supposant que des paramètres d'onde sont connus: notamment, la phase, la fréquence et l'amplitude. Cependant, pour des échelles suffisamment plus grandes que l'échelle caractéristique des irrégularités de densité, l'interaction des ondes et des particules ne peut être caractérisée déterminé que par des quantités statistiques moyennes dans l'espace des vitesses à savoir: le taux de croissance/amortissement et le coefficient de diffusion des particules. En utilisant notre modèle, nous décrivons l'évolution de la fonction de distribution des électrons et d'énergie des ondes de Langmuir. Le schéma 1D suggérée est applicable pour des paramètres physiques de plasma du vent solaire à différentes distances du Soleil. Ainsi, nous pouvons utiliser nos calculs pour décrire des émissions solaires de Type III, ainsi que les interactions de faisceau avec le plasma, à des distances d'une Unité Astronomique du Soleil dans l'héliosphère et au voisinage des chocs planétairesThis thesis is dedicated to effects of plasma density fluctuations in the solar wind on the relaxation of the electron beams ejected from the Sun. The density fluctuations are supposed to be responsible for the changes in the local phase velocity of the Langmuir waves generated by the beam instability. Changes in the wave phase velocity during the wave propagation can be described in terms of probability distribution function determined by distribution of the density fluctuations. Using these probability distributions we describe resonant wave particle interactions by a system of equations, similar to well known quasi-linear approximation, where the conventional velocity diffusion coefficient and the wave growth rate are replaced by the averaged in the velocity space. It was shown that the process of relaxation of electron beam is accompanied by transformation of significant part of the beam kinetic energy to energy of the accelerated particles via generation and absorption of the Langmuir waves. We discovered that for the very rapid beams the relaxation process consists of two well separated steps. On first step the major relaxation process occurs and the wave growth rate almost everywhere in the velocity space becomes close to zero or negative. At the seconde stage the system remains in the state close to state of marginal stability enough long to explain how the beam may be preserved traveling distances over 1 AU while still being able to generate the Langmuir waves
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Lindau, Ludvig. « Hardware accelerated ray tracing of particle systems ». Thesis, Blekinge Tekniska Högskola, Institutionen för datavetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-20231.
Texte intégralRésumé :
Background. Particle systems are a staple feature of most modern renderers. There are several technical challenges when it comes to rendering transparent particles. Particle sorting along the view direction is required for proper blending and casting shadows from particles requires non-standard shadow algorithms. A recent technology that could be used to adress these technical challenges is hardware accelerated ray tracing. However there is a lack of performance data gathered from this type of hardware. Objectives. The objective of this thesis is to measure the performance of a prototype that uses hardware accelerated ray tracing to render particles that cast shadows. Methods. A prototype is created and measurements of the ray tracing time are made. The scene used for the benchmark test is a densely packed particle volume of highly transparent particles, resulting in a scene that looks similar to smoke. Particles are sorted along a ray by repeatedly tracing rays against the scene and incrementing the ray origin past the previous intersection point until it has passed all the objects that lie along the ray. Results. Only a small number of particles can be rendered if real time rendering speeds are desired. High quality shadows can be produced in a way that is very simple compared to texture based methods. Conclusions. Future hardware speed ups can improve the rendering speeds but more sophisticated sorting methods are needed to render larger amounts of particles.
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Begley, Alison Margaret. « Particle cascades in quasar central engines ». Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289767.
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Sironi, Lorenzo. « Particle Acceleration and Nonthermal Emission in Relativistic Astrophysical Shocks ». PRINCETON UNIVERSITY, 2012. http://pqdtopen.proquest.com/#viewpdf?dispub=3481715.
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Messmer, Peter. « Observations and simulations of particle acceleration in solar flares / ». Aachen : Shaker, 2001. http://www.gbv.de/dms/goettingen/338805397.pdf.
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Meli, Athina. « Particle acceleration at relativistic and ultra-relativistic shock waves ». Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399116.
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Eradat, Oskoui Solmaz. « New aspects of particle acceleration in collapsing magnetic traps ». Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/11954.
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Collapsing magnetic traps (CMTs) have been suggested as one of the mechanisms that could contribute to particle energisation in solar flares. The basic idea behind CMTs is that charged particles will be trapped on the magnetic field lines below the reconnection region of a flare. This thesis discusses a number of important new aspects in particle energisation processes in CMTs, based on the model by Giuliani et al. (2005). In particular, we extend previous studies of particle acceleration in this CMT model to the relativistic regime and compare our results obtained using relativistic guiding centre theory with results obtained using the non-relativistic guiding centre theory. The similarities and differences found are discussed. We then present a detailed study of the question, what leads to the trapping or escape of particle orbits from CMTs. The answer to this question is investigated by using results from the non-relativistic orbit calculations with guiding centre theory and a number of simple models for particle energy gain in CMTs. We find that there is a critical pitch angle dividing trapped particle orbits from the escaping particle orbits and that this critical pitch angle does not coincide with the initial loss cone angle. Furthermore, we also present a calculation of the time evolution of an anisotropic pressure tensor and of the plasma density under the assumptions that they evolve in line with our kinematic MHD CMT model and that the pressure tensor satisfies the double-adiabatic Chew-Goldburger-Low (CGL) theory. Finally, we make a first step to introduce Coulomb scattering by a Maxwellian background plasma into our guiding centre equations by changing them into a set of stochastic differential equations. We study the influence of a static background plasma onto selected particle orbits by pitch angle scattering and energy losses, and look at its effect on the particle energy and the trapping conditions.
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Truter, J. N. J. « Using CAMAC hardware for access to a particle accelerator ». Master's thesis, University of Cape Town, 1988. http://hdl.handle.net/11427/17049.
Texte intégralRésumé :
Includes bibliographical references and index.The design and implementation of a method to software interface high level applications programs used for the control and monitoring of a Particle Accelerator is described. Effective methods of interfacing the instrumentation bus system with a Real time multitasking computer operating system were examined and optimized for efficient utilization of the operating system software and available hardware. Various methods of accessing the instrumentation bus are implemented as well as demand response servicing of the instruments on the bus.
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Stanier, Adam. « Magnetic reconnection and particle acceleration in semi-collisional plasmas ». Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/magnetic-reconnection-and-particle-acceleration-in-semicollisional-plasmas(26c3b17d-87ca-4d98-b5b5-3a3d78e0dd03).html.
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Magnetic reconnection is an important mechanism for the restructuring of magnetic fields, and the conversion of magnetic energy into plasma heating and non-thermal particle kinetic energy in a wide range of laboratory and astrophysical plasmas. In this thesis, reconnection is studied in two semi-collisional plasma environments: flares in the solar corona, and the start-up phase of the Mega-Ampere Spherical Tokamak (MAST) magnetic confinement device. Numerical simulations are presented using two different plasma descriptions; the test-particle approach combined with analytical magnetohydrodynamic fields is used to model populations of high-energy particles, and a two-fluid approach is used to model the bulk properties of a semi-collisional plasma. With the first approach, a three-dimensional magnetic null-point is examined as a possible particle acceleration site in the solar corona. The efficiency of acceleration, both within the external drift region and in the resistive current sheet, is studied for electrons and protons using two reconnection models. Of the two models, it is found that the fan-reconnection scenario is the most efficient, and can accelerate bulk populations of protons due to fast and non-uniform electric drifts close to the fan current-sheet. Also, the increasing background field within the fan-current sheet is shown to stabilise particle orbits, so that the energy gain is not limited by ejection. With the second approach, the effects of two-fluid physics on merging flux-ropes is examined, finding fast two-fluid tearing-type instabilities when the strength of dissipation is weak. The model is then extended to the tight-aspect ratio toroidal-axisymmetric geometry of the MAST device, where the final state after merging is a MAST-like spherical tokamak with nested flux-surfaces and a monotonically increasing q-profile. It is also shown that the evolution of simulated 1D radial density profiles closely resembles the Thomson scattering electron density measurements in MAST. An intuitive explanation for the origin of the measured density structures is proposed, based upon the results of the toroidal Hall-MHD simulations.
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Zakharian, Aramais Robert. « Numerical studies of waves and particle acceleration in shocks ». Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/284189.
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Aspects of the self consistent acceleration and transport of cosmic rays in astrophysical fluid flows and associated numerical methods are studied. Problems investigated are: (i) magnetohydrodynamic (MHD) wave interactions and instabilities in two-fluid models of cosmic ray modified shocks and flows; (ii) two dimensional, self consistent models of cosmic ray acceleration by the first order Fermi mechanism in supernova remnant shocks; (iii) new Riemann solver for the two-dimensional Euler equations and adaptive mesh refinement scheme for the coupled MHD and cosmic ray transport equations. The interaction of short wavelength MHD waves and instabilities in cosmic ray modified flows are investigated using asymptotic analysis and numerical simulations, with application to cosmic ray driven squeezing instabilities in supernova remnant shocks. In the linear wave regime, the waves are coupled by wave mixing due to gradients in the background flow; cosmic-ray squeezing instability effects, and damping due to the diffusing cosmic-rays. Numerical solutions of the fully nonlinear two-fluid cosmic ray MHD equations are compared with solutions of the wave mixing equations for oblique, cosmic ray modified shocks. A two-dimensional, self-consistent, adaptive mesh refinement numerical algorithm is developed for the solution of the ideal magnetohydrodynamic equations coupled to the kinetic transport equation for energetic charged particles. The method is used to simulate the evolution of the momentum distribution function of the cosmic rays accelerated at supernova remnant shocks. The numerical methods were tested on a variety of fluid dynamics and MHD problems, and previous models of cosmic ray modified supernova remnant shocks. A Riemann solver based on two-dimensional multi-state Riemann problems was developed. The scheme generalizes the traditional one-dimensional flux calculation to include contributions to the flux through the cell edges of the waves originating at cell corners. The multidimensional flux corrections increase the accuracy and stability of the scheme. An adaptive mesh refinement technique was used to study the Von Neumann paradox associated with the formation of three shocks, when a low Mach number, supersonic flow impinges on a thin wedge. For the first time, the region near the triple point has been resolved in a numerical solution of the Euler equations.
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Wood, Paul D. « Elements of solar activity : particle acceleration and filament formation ». Thesis, University of St Andrews, 2005. http://hdl.handle.net/10023/11309.
Texte intégralRésumé :
This thesis studies the acceleration of particles to super-thermal energies in explosive solar events as well as the magnetic changes in connectivity that may be responsible for changes in the morphology of quiescent filaments. Firstly a review of some of the observations of solar flare dynamics is given, as well as an introduction to the competing theories attempting to explain both particle acceleration and filament formation. An explanation of the numerical FORTRAN code that is used to calculate the trajectories of particle distribution functions in prescribed electromagnetic fields is given. Examples of known fields are used to test the accuracy of the code and the simple example of the well-known Litvinenko current sheet field is investigated. The results of charged particle orbit calculations in prescribed electric and magnetic fields motivated by magnetic reconnection models are then presented. The electromagnetic fields are chosen to resemble a current sheet with a localised reconnection region. The dependence of the model on the important physical parameters is considered. An introduction to the mathematical formulation of a collapsing magnetic trap is given. The same numerical code is used to calculate single electron orbits in this more complicated time dependent electromagnetic field. Consideration of important previous work is given before describing the best attempts to model the movement of flare loops in a realistic fashion. Finally the process of flux cancellation and filament formation is studied using a range of data including ground-based Hα and SoHO MDI magnetograms. It is found that the cancellation occurs at the ends of Hα sections of the filament and is accompanied by a noticeable increase in the Hα intensity and linkage of the sections. Measurements of the amount of flux cancelled at each site show it is in agreement with an estimate of the axial flux contained in the filament.
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Yakovleva, Elizaveta. « Dark Photon decay generated by muons in the SHiP experiment ». Thesis, Uppsala universitet, Institutionen för materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-414520.
Texte intégralRésumé :
This project has investigated the muon background of the SHiP experiment to determine whether it can boost the experiment sensitivity to visible Dark Photon decay. Using Fermi-Weizsäcker-Williams approximation to muon scattering we found the probability of muons generating massive photons, using Bremsstrahlung and direct lepton pair production as an estimation of the frequency of muon EM-interactions. In this work we only considered muons with momenta above 10 GeV/c. The number of visible Dark Photon decays was calculated for a range of the coupling constant and photon mass. The resulting range that promised visible decay has already been excluded by previous experiments, but the method could be used to further investigate enhanced production of Dark Photons from muons and electrons, and possibly also production of Axion-like particles. The work could also be used to estimate sensitivities of other experiments using muons.
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Metral, Elias. « Coupled Landau damping of transverse coherent instabilities in particle accelerators ». Université Joseph Fourier (Grenoble), 1999. http://www.theses.fr/1999GRE10048.
Texte intégralRésumé :
L'effet du couplage lineaire entre les plans transversaux d'un accelerateur circulaire sur l'amortissement de landau des instabilites coherentes est etudie en considerant deux distributions caracteristiques de frequences (lorentzienne et elliptique). Celles-ci correspondent a des cas limites modelisant des spectres avec et sans longues queues. Un critere general de stabilite, ou interviennent la force du couplage (du aux quadrupoles tournes) et la distance des nombres d'ondes betatroniques aux resonances de couplage, est obtenu dans les deux cas. Ce dernier revele la possibilite de partager les dispersions de frequences stabilisatrices entre les deux plans, ce qui peut considerablement ameliorer la stabilite coherente du faisceau, en particulier dans les cas ou la situation est plus critique dans un plan. Une seconde observation importante est que l'effet d'une grande partie imaginaire de l'impedance de couplage, qui normalement requiert une dispersion de frequences equivalente pour l'amortissement de landau, peut etre compense (du moins dans un plan) par un choix judicieux du couplage. Les resultats d'experiences effectuees au synchrotron a protons (ps) du cern confirment le comportement general predit par la theorie. Le mecanisme de l'amortissement de landau couple pourrait donc expliquer pourquoi une machine comme le ps peut etre stabilisee en rapprochant le point de fonctionnement pres d'une resonance de couplage. Il peut par consequent etre utilise pour determiner des valeurs optimales du point de fonctionnement et de la force du couplage lineaire.
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Becker, Stefan. « Dynamics and Transport of Laser-Accelerated Particle Beams ». Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-114449.
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Blanco-Pillado, José Juan. « Topological defects and ultra-high energy cosmic rays / ». Thesis, Connect to Dissertations & ; Theses @ Tufts University, 2001.
Trouver le texte intégralRésumé :
Thesis (Ph.D.)--Tufts University, 2001.Adviser: Alexander Vilenkin. Submitted to the Dept. of Physics. Includes bibliographical references (leaves 108-114). Access restricted to members of the Tufts University community. Also available via the World Wide Web;
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Yorkston, John. « Wide angle and out-of-plane correlations in 7Li fragmentation ». Thesis, University of Edinburgh, 1988. http://hdl.handle.net/1842/11649.
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DIAKHATE, LAURENCE. « Acceleration de particules par onde de sillage dans un plasma ». Paris 6, 1990. http://www.theses.fr/1990PA066744.
Texte intégralRésumé :
Injecter un paquet d'electrons relativistes de forme donnee dans un plasma permet de generer une onde de sillage supportant des champs tres intenses, proportionnels a la racine carree de la densite plasma. En utilisant un guide d'onde plasma, on excite des ondes electromagnetiques rapides (onde plasma et onde de surface). Du fait de la predominance de ses champs, l'onde de surface permet d'accelerer un plus grand nombre d'electrons et leur confere une plus grande energie. Cela se fait au detriment de l'emittance et de l'etalement en energie du faisceau. Un traitement non lineaire monodimensionnel est donne. Remplacer le faisceau entraineur par une impulsion laser permet d'ameliorer plus encore les parametres relatifs a l'acceleration. Enfin, l'etude d'un plasma infini et thermalise montre une tres nette degradation de l'acceleration. Cette derniere configuration est a deconseiller
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Usami, Shunsuke, et Yukiharu Ohsawa. « Motions of ultrarelativistic particles accelerated in an oblique plasma wave ». American Institute of Physics, 2004. http://hdl.handle.net/2237/7033.
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Kong, Xiangliang, Fan Guo, Joe Giacalone, Hui Li et Yao Chen. « The Acceleration of High-energy Protons at Coronal Shocks : The Effect of Large-scale Streamer-like Magnetic Field Structures ». IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626416.
Texte intégralRésumé :
Recent observations have shown that coronal shocks driven by coronal mass ejections can develop and accelerate particles within several solar radii in large solar energetic particle (SEP) events. Motivated by this, we present an SEP acceleration study that including the process in which a fast shock propagates through a streamer-like magnetic field with both closed and open field lines in the low corona region. The acceleration of protons is modeled by numerically solving the Parker transport equation with spatial diffusion both along and across the magnetic field. We show that particles can be sufficiently accelerated to up to several hundred MeV within 2-3 solar radii. When the shock propagates through a streamer-like magnetic field, particles are more efficiently accelerated compared to the case with a simple radial magnetic field, mainly due to perpendicular shock geometry and the natural trapping effect of closed magnetic fields. Our results suggest that the coronal magnetic field configuration is an important factor for producing large SEP events. We further show that the coronal magnetic field configuration strongly influences the distribution of energetic particles, leading to different locations of source regions along the shock front where most high-energy particles are concentrated. This work may have strong implications for SEP observations. The upcoming Parker Solar Probe will provide in situ observations for the distribution of energetic particles in the coronal shock region, and test the results of the study.