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1
Cullen, Jason. "Inverse compton scattering in high energy astrophysics." Connect to full text, 2001. http://hdl.handle.net/2123/849.
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Thesis (Ph. D.)--University of Sydney, 2002.Title from title screen (viewed Apr. 23, 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Research Centre for Theoretical Astrophysics & Theoretical Physics Group, School of Physics. Degree awarded 2002; thesis submitted 2001. Includes bibliography. Also available in print form.
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Cullen, Jason Graham. "Inverse compton scattering in high energy astrophysics." Thesis, The University of Sydney, 2001. http://hdl.handle.net/2123/849.
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This thesis investigates some aspects of the inverse Compton scattering process within various physical contexts in high energy astrophysics. Initially an introduction to the key results of Comptonization theory for the case of scattering in optically thick plasmas is given, using a diffusion approach, since these results are required for the interpreta- tion of Comptonized spectra. Since Comptonization in astrophysical systems is frequently treated using numerical techniques, an introduction to these is then presented. Such linear Monte Carlo photon transport codes are typically applied to scattering in plasmas without temperature and density gradients. Additionally, treating bulk motion can be difficult even for simple cases. It is demonstrated that these problems can be made tractable numerically with the use of algorithms associated with non-linear Monte Carlo codes. Such codes can already treat scattering within arbitrary velocity structures in a plasma, and an extension of the algo- rithm is proposed that enables the easy calculation of photon transport in plasmas with non-constant density as well as non-constant temperature and/or bulk motion. This algorithm and code has been developed to treat scattering in astrophysical situations where bulk motion, temperature gradients and density gradients are simultaneously present in a plasma. Both a semi-analytic approach and the numerical approach are then used to treat Comp- tonization problems of current interest. Firstly, the standard two-phase disk-corona model for the high-energy spectra of Active Galactic Nuclei is modified to include an an outflow or wind which may provide an additional source of disk cooling. Earlier slab disk-corona models predict a spectral index which is consistent with observations only if all the accretion power is dissipated in the corona. For the models investigated here, energy spectral indices that are consistent with observations can be obtained with less accretion power being dissipated in the corona, as a result of an outflow/wind. However, it is required that the wind extract large amounts of power from the disk, and it it yet to be seen if this is a plausible scenario.
3
Cullen, Jason Graham. "Inverse compton scattering in high energy astrophysics." University of Sydney. Physics, 2001. http://hdl.handle.net/2123/849.
Full textAbstract:
This thesis investigates some aspects of the inverse Compton scattering process within various physical contexts in high energy astrophysics. Initially an introduction to the key results of Comptonization theory for the case of scattering in optically thick plasmas is given, using a diffusion approach, since these results are required for the interpreta- tion of Comptonized spectra. Since Comptonization in astrophysical systems is frequently treated using numerical techniques, an introduction to these is then presented. Such linear Monte Carlo photon transport codes are typically applied to scattering in plasmas without temperature and density gradients. Additionally, treating bulk motion can be difficult even for simple cases. It is demonstrated that these problems can be made tractable numerically with the use of algorithms associated with non-linear Monte Carlo codes. Such codes can already treat scattering within arbitrary velocity structures in a plasma, and an extension of the algo- rithm is proposed that enables the easy calculation of photon transport in plasmas with non-constant density as well as non-constant temperature and/or bulk motion. This algorithm and code has been developed to treat scattering in astrophysical situations where bulk motion, temperature gradients and density gradients are simultaneously present in a plasma. Both a semi-analytic approach and the numerical approach are then used to treat Comp- tonization problems of current interest. Firstly, the standard two-phase disk-corona model for the high-energy spectra of Active Galactic Nuclei is modified to include an an outflow or wind which may provide an additional source of disk cooling. Earlier slab disk-corona models predict a spectral index which is consistent with observations only if all the accretion power is dissipated in the corona. For the models investigated here, energy spectral indices that are consistent with observations can be obtained with less accretion power being dissipated in the corona, as a result of an outflow/wind. However, it is required that the wind extract large amounts of power from the disk, and it it yet to be seen if this is a plausible scenario.
4
Resta, Giacomo Rosario. "Three-dimensional simulation of coherent inverse Compton scattering." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92692.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (page 49).
Novel compact X-ray sources using coherent ICS have the potential to positively impact a wide range of sectors by making hard x-ray techniques more accessible. However, the analysis of such novel sources requires improvements to existing simulation routines to incorporate Coulomb forces among particles and effects related to the phase of emitted radiation. This thesis develops a numerical routine for calculating the radiation scattered by electrons counter-propagating with a linearly-polarized, Gaussian laser pulse. The routine takes into account electron-electron repulsion and the constructive and destructive interference between the radiation emitted by each electron, making it suitable for characterizing the properties of inverse Compton scattering (ICS) sources where the electron density varies on the order of the laser wavelength. Finally, an analysis of the emission characteristics for an example ICS source with coherent emission at 10 nm wavelength is included. The source uses a 2 MeV electron bunch and a 1 /pm wavelength laser. The coherent emission demonstrates a significantly narrowed linewidth and greatly increased output power when compared to traditional ICS.
by Giacomo Rosario Resta.
S.B.
5
CARDARELLI, Paolo. "Devices and techniques for the characterization of inverse Compton sources." Doctoral thesis, Università degli studi di Ferrara, 2013. http://hdl.handle.net/11392/2388872.
Full textAbstract:
Innovative intense monochromatic x/
-ray sources are of great interest in the scientific
community. A large number of applications in basic and applied physics
research, as well as in different science fields, require an intense, monochromatic
or quasi-monochromatic, tunable radiation source. Synchrotron radiation is
optimal for low energy applications (< 100 keV) but the size and cost of synchrotron
facilities prevent a large-scale spread of this kind of source, that is
fundamental for applications such as routine clinical diagnostic. Moreover, synchrotron
light is not suitable in the case of high energy applications (> 1 MeV),
needed primarily for nuclear physics experiments, due to limitations on the
maximum energy obtainable for monochromatic beams with synchrotron light.
Alternative sources that can overcome such limitations are those based on inverse
Compton interaction, which permit to obtain compact and cost-effective
sources for low energy applications and can provide monochromatic collimated
beam in the high energy range. Inverse Compton is the process in which a photon
interacts with a relativistic electron, in this case the electron can transfer a
fraction of its energy in the collision, resulting in a backscattered photon with
an increased energy. This process can be used to produce hard x/
-rays by the
backscattering of low-energy laser photons by a relativistic electron beam. A
radiation source based on this interaction is usually called an inverse Compton
source, alternatively, it can be called Thomson source when the energies
involved allow a classical description of the process, as in the case of Thomson
scattering.
The work described in this dissertation concerns the devices and techniques
developed to perform a characterization of inverse Compton sources. In particular,
the work is focused on two major projects: BEATS2 experiment and
ELI-NP-GBS proposal of E-Gammas collaboration.
BEATS2 is an experiment funded by Istituto Nazionale di Fisica Nucleare
(INFN) aimed to study medical applications, specially to mammographic imaging,
of the SL-Thomson source of SPARC-LAB at the INFN-LNF that will be
commissioned in the first half of 2013.
E-Gammas is an international collaboration composed by several Universities
and Institutions including: INFN and Universit`a di Roma La Sapienza,
in Italy, Universitè de Paris Sud and IN2P3/CNRS, in France, and ASTeC
of STFC, in UK. The collaboration is aimed to the preparation of a Technical
Design Report for the ELI-NP Gamma Beam System (ELI-NP-GBS) to be
commissioned by the end of 2016. This Gamma Beam System will be a high
energy inverse Compton source, included in the Extreme Light Infrastructure -
Nuclear physics (ELI-NP), an European project dedicated to the development
of laser beams and the generation of high intensity gamma beams for frontier research in nuclear physics.
6
Ciccarelli, Cristiano. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/19940/.
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Con il termine scattering si indica una vasta gamma di processi dovuti all’interazione onda-particella, dove la prima viene deflessa (ossia cambia
traiettoria) a causa di un urto con la seconda. Qui saranno analizzati due
fenomeni basati su quest’interazione; a seconda dell’energia dell’onda incidente infatti abbiamo: lo scattering Thomson a basse energie, processo in cui
l’onda viene esclusivamente deviata, e lo scattering Compton ad alte energie,
in cui il fotone, tramite l’urto, trasferisce parte della propria energia alla particella ferma (tipicamente un elettrone). Verr`a studiato anche il caso in cui
sia l’elettrone ad essere pi`u energetico del fotone, questo processo `e chiamato
Inverse Compton (IC) e tramite questo fenomeno l’onda, urtando, acquisisce
energia dalla particella. Nel Capitolo 1 saranno analizzati questi tre scenari e, successivamente, i fenomeni di Synchrothron Self-Compton, Catastrofe
Compton e Comptonizzazione, dovuti alla combinazione del processo di IC
rispettivamente con l’emissione per Sincrotrone e con lo scattering Compton.
Nel secondo capitolo verranno invece illustrate tre applicazioni astrofisiche
di questi fenomeni: prima con lo scattering Thomson e il suo ruolo nello studio degli AGN, qualora questi siano nascosti dai loro tori oscuranti, poi con
l’Inverse Compton e il suo contributo alla Radiazione Extragalattica di Fondo
e infine con una conseguenza fondamentale del fenomeno della Comptonizzazione, l’ effetto Sunyaev Zel’dovich, che permette di identificare ammassi di
galassie studiando la Radiazione Cosmica di Fondo.
7
Fornasiero, Ilaria. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24834/.
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I processi di scattering, anche chiamati processi di diffusione, riguardano le interazioni tra onde elettromagnetiche e particelle libere. Nel primo capitolo saranno analizzati i due processi fondamentali, quali la diffusione Thomson e la diffusione Compton. Nel primo caso si affrontano interazioni tra onde elettromagnetiche ed elettroni a riposo determinate dalle basse energie dell'onda incidente rispetto all'elettrone e in cui non avvengono trasferimenti energetici, mentre nel secondo caso si considera l'interazione, tra un fotone e un elettrone, come un urto elastico, dove quindi saranno conservate l'energia totale e la quantità di moto. Successivamente verranno descritti i processi di Inverse Compton, cioè l'interazione energetica tra un elettrone con energia cinetica sufficientemente alta e un fotone, e la Comptonizzazione, dove gli effetti della diffusione Compton e Inverse Compton si trovano in competizione.
Nel secondo capitolo verranno descritte due importanti applicazioni astrofisiche dei processi di diffusione, cioè l'effetto Sunyaev-Zeldovich, in cui i fotoni di bassa energia della radiazione cosmica di fondo interagiscono con il gas caldo degli ammassi di galassie, e la radiazione emessa a causa dei fenomeni di accrescimento negli AGN.
8
Jochmann, Axel. "Development and Characterization of a tunable ultrafast X-ray source via Inverse Compton Scattering." Forschungszentrum Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-154801.
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Ultrashort, nearly monochromatic hard X-ray pulses enrich the understanding of the dynamics and function of matter, e.g., the motion of atomic structures associated with ultrafast phase transitions, structural dynamics and (bio)chemical reactions. Inverse Compton backscattering of intense laser pulses from relativistic electrons not only allows for the generation of bright X-ray pulses which can be used in a pumpprobe experiment, but also for the investigation of the electron beam dynamics at the interaction point.
The focus of this PhD work lies on the detailed understanding of the kinematics during the interaction of the relativistic electron bunch and the laser pulse in order to quantify the influence of various experiment parameters on the emitted X-ray radiation.
The experiment was conducted at the ELBE center for high power radiation sources using the ELBE superconducting linear accelerator and the DRACO Ti:sapphire laser system. The combination of both these state-of-the-art apparatuses guaranteed the control and stability of the interacting beam parameters throughout the measurement.
The emitted X-ray spectra were detected with a pixelated detector of 1024 by 256 elements (each 26μm by 26μm) to achieve an unprecedented spatial and energy resolution for a full characterization of the emitted spectrum to reveal parameter influences and correlations of both interacting beams. In this work the influence of the electron beam energy, electron beam emittance, the laser bandwidth and the energy-anglecorrelation on the spectra of the backscattered X-rays is quantified.
A rigorous statistical analysis comparing experimental data to ab-initio 3D simulations enabled, e.g., the extraction of the angular distribution of electrons with 1.5% accuracy and, in total, provides predictive capability for the future high brightness hard X-ray source PHOENIX (Photon electron collider for Narrow bandwidth Intense X-rays) and potential all optical gamma-ray sources.
The results will serve as a milestone and starting point for the scaling of the Xray flux based on available interaction parameters of an ultrashort bright X-ray source at the ELBE center for high power radiation sources. The knowledge of the spatial and spectral distribution of photons from an inverse Compton scattering source is essential in designing future experiments as well as for tailoring the X-ray spectral properties to an experimental need.
9
Jochmann, Axel. "Development and Characterization of a tunable ultrafast X-ray source via Inverse Compton Scattering." Forschungszentrum Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-162231.
Full textAbstract:
Ultrashort, nearly monochromatic hard X-ray pulses enrich the understanding of the dynamics and function of matter, e.g., the motion of atomic structures associated with ultrafast phase transitions, structural dynamics and (bio)chemical reactions. Inverse Compton backscattering of intense laser pulses from relativistic electrons not only allows for the generation of bright X-ray pulses which can be used in a pumpprobe experiment, but also for the investigation of the electron beam dynamics at the interaction point. The focus of this PhD work lies on the detailed understanding of the kinematics during the interaction of the relativistic electron bunch and the laser pulse in order to quantify the influence of various experiment parameters on the emitted X-ray radiation. The experiment was conducted at the ELBE center for high power radiation sources using the ELBE superconducting linear accelerator and the DRACO Ti:sapphire laser system. The combination of both these state-of-the-art apparatuses guaranteed the control and stability of the interacting beam parameters throughout the measurement. The emitted X-ray spectra were detected with a pixelated detector of 1024 by 256 elements (each 26μm by 26μm) to achieve an unprecedented spatial and energy resolution for a full characterization of the emitted spectrum to reveal parameter influences and correlations of both interacting beams. In this work the influence of the electron beam energy, electron beam emittance, the laser bandwidth and the energy-anglecorrelation on the spectra of the backscattered X-rays is quantified. A rigorous statistical analysis comparing experimental data to ab-initio 3D simulations enabled, e.g., the extraction of the angular distribution of electrons with 1.5% accuracy and, in total, provides predictive capability for the future high brightness hard X-ray source PHOENIX (Photon electron collider for Narrow bandwidth Intense X-rays) and potential all optical gamma-ray sources. The results will serve as a milestone and starting point for the scaling of the Xray flux based on available interaction parameters of an ultrashort bright X-ray source at the ELBE center for high power radiation sources. The knowledge of the spatial and spectral distribution of photons from an inverse Compton scattering source is essential in designing future experiments as well as for tailoring the X-ray spectral properties to an experimental needUltrakurze, quasi-monochromatische harte Röntgenpulse erweitern das Verständnis für die dynamischen Prozesse und funktionalen Zusammenhänge in Materie, beispielsweise die Dynamik in atomaren Strukturen bei ultraschnellen Phasenübergängen, Gitterbewegungen und (bio)chemischen Reaktionen. Compton-Rückstreuung erlaubt die Erzeugung der für ein pump-probe-Experiment benötigten intensiven Röntgenpulse und ermöglicht gleichzeitig einen Einblick in die komplexen kinematischen Prozesse während der Wechselwirkung von Elektronen und Photonen. Ziel dieser Arbeit ist, ein quantitatives Verständnis der verschiedenen experimentellen Einflüsse auf die emittierte Röntgenstrahlung bei der Streuung von Laserphotonen an relativistischen Elektronen zu entwickeln. Die Experimente wurden am ELBE - Zentrum für Hochleistungs-Strahlenquellen des Helmholtz-Zentrums Dresden - Rossendorf durchgeführt. Der verwendete supraleitende Linearbschleuniger ELBE und der auf Titan-Saphir basierende Hochleistungslaser DRACO garantieren ein Höchstmaß an Kontrolle und Stabilität der experimentellen Bedingungen. Zur Messung der emittierten Röntgenstrahlung wurde ein Siliziumdetektor mit 1024x256 Pixeln (Pixelgröße 26μm × 26μm) verwendet, welcher für eine bisher nicht erreichte spektrale und räumliche Auflösung sorgt. Die so erfolgte vollständige Charakterisierung der Energie-Winkel-Beziehung erlaubt Rückschlüsse auf Parametereinflüsse und Korrelationen von Elektronen- und Laserstrahl. Eine umfassende statistische Analyse, bei der ab-initio 3D Simulationen mit den experimentellen Daten verglichen und ausgewertet wurden, ermöglichte u.a. die Bestimmung der Elektronenstrahldivergenz mit einer Genauigkeit von 1.5% und erlaubt Vorhersagen zur zu erwartenden Strahlung der zukünftigen brillianten Röntgenquelle PHOENIX (Photon electron collider for Narrow bandwidth Intense X-rays) und potentiellen lasergetriebenen Gammastrahlungsquellen. Die Ergebnisse dienen als Fixpunkt für die Skalierung des erwarteten Photonenflusses der Röntgenquelle für die verfügbaren Ausgangsgrößen am Helmholtz-Zentrum Dresden - Rossendorf. Das Wissen um die räumliche und spektrale Verteilung der Röntgenstrahlung ist entscheidend für die Planung zukünftiger Experimente sowie zur Anpassung der Quelle an experimentelle Bedürfnisse
10
Pires, Abel. "Optimisation de la source X impulsionnelle par diffusion Compton inverse d'un accélérateur linéaire d'électrons." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASP156.
Full textAbstract:
Ma thèse porte sur l’optimisation d’une source de rayons X par effet Compton inverse, ce qui consiste à faire interagir un paquet d’électrons provenant d’un accélérateur avec un faisceau laser. J’ai travaillé sur l’optimisation du passage du compresseur magnétique (permettant de réduire la durée des paquets d’électrons). J’ai étudié cet élément avec 3 codes de simulation, et expérimentalement, pour déterminer les effets physiques responsables de l’évolution de la qualité du paquet (émittance), en fonction du nombre d’électrons.Pour le laser, mes travaux permettent d’atteindre des énergies laser plus élevées au niveau du point d’interaction. J’ai mis en place un système CPA (Chirped Pulse Amplification), ce qui consiste à étirer la durée des impulsions laser avant de les amplifier pour éviter le risque de casse. J’ai aussi travaillé sur un dispositif, le SMILE 2, permettant de superposer 8 impulsions laser au point d’interaction. La nouvelle version permet d’automatiser l’alignementMy thesis focuses on optimizing an X-ray source through inverse Compton scattering, which consists in the interaction between an electron bunch from an accelerator and a laser beam.I worked on optimizing the transport through the magnetic compressor, which reduces the duration of electron bunches. I analyzed this component using three simulation codes, as well as experimentally, to identify the physical effects that influence the bunch quality (emittance) as a function of the number of electrons in the bunch.For the laser, my work enables us to achieve higher laser energies at the interaction point. I implemented a Chirped Pulse Amplification (CPA) system, which stretches the laser pulse duration before amplification to prevent damage. I also worked on a device, SMILE 2 that enables the superposition of 8 laser pulses at the interaction point. The new version allows for automated alignment
11
Guerrero, prado Patricio. "Reconstruction tridimensionnelle des objets plats du patrimoine à partir du signal de diffusion inélastique." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLV035/document.
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La caractérisation tridimensionnelle de matériaux anciens plats est restée une activité non évidente à accomplir par des méthodes classiques de tomographie à rayons X en raison de leur morphologie anisotrope et de leur géométrie aplatie.Pour surmonter les limites de ces méthodologies, une modalité d'imagerie basée sur le rayonnement diffusé Compton est étudiée dans ce travail. La tomographie classique aux rayons X traite les données de diffusion Compton comme du bruit ajouté au processus de formation d'image, tandis que dans la tomographie du rayonnement diffusé, les conditions sont définies de sorte que la diffusion inélastique devienne le phénomène dominant dans la formation d'image. Dans ces conditions, les rotations relatives entre l'échantillon et la configuration d'imagerie ne sont plus nécessaires. Mathématiquement, ce problème est résolu par la transformée de Radon conique. Le problème direct où la sortie du système est l'image spectrale obtenue à partir d'un objet d'entrée est modélisé. Dans le problème inverse une estimation de la distribution tridimensionnelle de la densité électronique de l'objet d'entrée à partir de l'image spectrale est proposée. La faisabilité de cette méthodologie est supportée par des simulations numériquesThree-dimensional characterization of flat ancient material objects has remained a challenging activity to accomplish by conventional X-ray tomography methods due to their anisotropic morphology and flattened geometry.To overcome the limitations of such methodologies, an imaging modality based on Compton scattering is studied in this work. Classical X-ray tomography treats Compton scattering data as noise in the image formation process, while in Compton scattering tomography the conditions are set such that Compton data become the principal image contrasting agent. Under these conditions, we are able to avoid relative rotations between the sample and the imaging setup. Mathematically this problem is addressed by means of the conical Radon transform. A model of the direct problem is presented where the output of the system is the spectral image obtained from an input object. The inverse problem is addressed to estimate the 3D distribution of the electronic density of the input object from the spectral image. The feasibility of this methodology is supported by numerical simulations
12
Rigaud, Gaël. "Study of generalized Radon transforms and applications in Compton scattering tomography." Phd thesis, Université de Cergy Pontoise, 2013. http://tel.archives-ouvertes.fr/tel-00945739.
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Since the advent of the first ionizing radiation imaging devices initiated by Godfrey Newbold Hounsfield and Allan MacLeod Cormack, Nobel Prizes in 1979, the requirement for new non-invasive imaging techniques has grown. These techniques rely upon the properties of penetration in the matter of X and gamma radiation for detecting a hidden structure without destroying the illuminated environment. They are used in many fields ranging from medical imaging to non-destructive testing through. However, the techniques used so far suffer severe degradation in the quality of measurement and reconstructed images. Usually approximated by a noise, these degradations require to be compensated or corrected by collimating devices and often expensive filtering. These degradation is mainly due to scattering phenomena which may constitute up to 80% of the emitted radiation in biological tissue. In the 80's a new concept has emerged to circumvent this difficulty : the Compton scattering tomography (CST).This new approach proposes to measure the scattered radiation considering energy ranges ( 140-511 keV) where the Compton effect is the phenomenon of leading broadcast. The use of such imaging devices requires a deep understanding of the interactions between radiation and matter to propose a modeling, consistent with the measured data, which is essential to image reconstruction. In conventional imaging systems (which measure the primary radiation) the Radon transformdefined on the straight lines emerged as the natural modeling. But in Compton scattering tomography, the measured information is related to the scattering energy and thus the scattering angle. Thus the circular geometry induced by scattering phenomenon makes the classical Radon transform inadequate.In this context, it becomes necessary to provide such Radon transforms on broader geometric manifolds.The study of the Radon transform on new manifolds of curves becomes necessary to provide theoretical needs for new imaging techniques. Cormack, himself, was the first to extend the properties of the conventional Radon transform of a family of curves of the plane. Thereafter several studies have been done in order to study the Radon transform defined on different varieties of circles, spheres, broken lines ... . In 1994 S.J. Norton proposed the first modality in Compton scattering tomography modeled by a Radon transform on circular arcs, the CART1 here. In 2010, Nguyen and Truong established the inversion formula of a Radon transform on circular arcs, CART2, to model the image formation in a new modality in Compton scattering tomography. The geometry involved in the integration support of new modalities in Compton scattering tomography lead them to demonstrate the invertibility of the Radon transform defined on a family of Cormack-type curves, called C_alpha. They illustrated the inversion procedure in the case of a new transform, the CART3, modeling a new modeling of Compton scattering tomography. Based on the work of Cormack and Truong and Nguyen, we propose to establish several properties of the Radon transform on the family C_alpha especially on C1. We have thus demonstrated two inversion formulae that reconstruct the original image via its circular harmonic decomposition and itscorresponding transform. These formulae are similar to those established by Truong and Nguyen. We finally established the well-known filtered back projection and singular value decomposition in the case alpha = 1. All results established in this study provide practical problems of image reconstruction associated with these new transforms. In particular we were able to establish new inversion methods for transforms CART1,2,3 as well as numerical approaches necessary for the implementation of these transforms. All these results enable to solve problems of image formation and reconstruction related to three Compton scattering tomography modalities.In addition we propose to improve models and algorithms es
13
SUERRA, EDOARDO. "DEVELOPMENT OF A HIGH GAIN LASER SYSTEM FOR THE INVERSE COMPTON SCATTERING SOURCE BRIXSINO." Doctoral thesis, Università degli Studi di Milano, 2021. http://hdl.handle.net/2434/885509.
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BriXS is a project of the University of Milan and the Italian Institute of Nuclear Physics (INFN) aiming at the realization of an Inverse Compton Scattering (ICS) source. This source is based on electrons superconducting cavities with energy recirculation and on a high-power laser system at a repetition rate of 100 MHz and producing monochromatic X-Rays in the energy range of 20 keV to 180 keV, mainly devoted to medical applications. A demonstrator is currently under development at the Accelerators and Applied Superconductivity Laboratories of (INFN) and University of Milan, in Segrate, Milan, consisting in a smaller version of BriXS, called BriXSino, also finding the collaboration of Ospedale San Raffaele of Milan, which is interested in the medical applications of X-rays produced with BriXSino.
The high optical power (>100 kW) necessary for the Compton interaction of both BriXS and BriXSino is supposed to be reached with a combined use of active and passive amplification, where, in particular, implementing both a fiber amplifier and an optical cavity. In this thesis work, we developed and realized the whole optical stages for BriXS/BriXSino up to an average power of 11 kW, consisting of a mode locking laser source, a first stage of fiber amplification up to 4 kW and, the most important part of my work, an optical cavity for passive pulses stacking up to 11 kW.
Besides the realization of this complex system, during this thesis we have developed several new techniques with a general interest in optics. In particular, a new and very general technique for the measurement of the Finesse of an optical cavity is presented, also focusing on the effect of the Carrier Envelope Offset of the laser on this parameter, which determines the passive gain. As far as the Carrier Envelope Offset is concerned, we found that it can be exploited to dramatically reduce the power noise of the laser beam coupled in the optical cavity, allowing to reach the same passive gain but with a much lower noise.
During this thesis work, we developed a new technique to shift the focus of our optical cavity while maintaining the high-power level stored in it. Since this approach allows a large movement >100 μm in a time of 50 ms, faster than biological dynamics of some hundreds of milliseconds, it enables for the first time the implementation of the dual color X-rays technique with an ICS source, by switching the interaction of the electron beam between two optical cavities with two different interaction angles, thus activating two different ICS spectral lines in sequence.
Thanks to the similarities between the optical cavity used for BriXS/BriXSino and the Optical Parametric Oscillator (OPO) implemented in our laboratory for the generation of quantum optical squeezed states, in this work we present a study of a new technique to stabilize the relative phase between the seed and the pump involved in the squeezing process, greatly improving the stability of the system. This setup up also allowed to study a new method to counteract phase noise on quantum optical states, squeezing their phase diffusion.
14
Ceccotti, Emilio. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/14066/.
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Lo scattering è il processo in cui un’onda elettromagnetica interagisce con la materia, tipicamente un elettrone libero. In tale interazione l’onda cambia direzione e può modificare la propria energia. Se lo scattering produce solo un cambio di direzione, si parla di scattering Thomson, che risulta particolarmente importante per la definizione di sezione d’urto classica. Quando invece la radiazione perde energia e la trasferisce all’elettrone, si ha lo scattering Compton, viceversa, quando la radiazione guadagna energia sottraendola all’elettrone, si ha l’inverse Compton. Questi ultimi due processi producono una modifica nello spettro energetico (SED) di alcune regioni, fenomeno noto come Comptonizzazione. Nel caso in cui la Comptonizzazione agisca sullo spettro della radiazione cosmica di fondo (CMB), si ha l’effetto Sunyaev-Zel’dovich. In particolare, questo si suddivide in un effetto termico, dovuto agli elettroni liberi molto energetici di una regione che fanno inverse Compton sui fotoni della CMB, e in un effetto cinetico, dovuto al moto relativo della regione rispetto alla CMB. Nel presente scritto si focalizzerà l’attenzione su come si può misurare l’evoluzione della temperatura della CMB fino a redshift z = 1, che è un’applicazione del Sunyaev-Zel’dovich termico, e sul calcolo dell’effetto cinetico nell’alone di gas del Gruppo Locale.
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Webber, James. "Radon transforms and microlocal analysis in Compton scattering tomography." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/radon-transforms-and-microlocal-analysis-in-compton-scattering-tomography(c1ad3583-01ce-4147-8576-2e635090cb15).html.
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In this thesis we present new ideas and mathematical insights in the field of Compton Scattering Tomography (CST), an X-ray and gamma ray imaging technique which uses Compton scattered data to reconstruct an electron density of the target. This is an area not considered extensively in the literature, with only two dimensional gamma ray (monochromatic source) CST problems being analysed thus far. The analytic treatment of the polychromatic source case is left untouched and while there are three dimensional acquisition geometries in CST which consider the reconstruction of gamma ray source intensities, an explicit three dimensional electron density reconstruction from Compton scatter data is yet to be obtained. Noting this gap in the literature, we aim to make new and significant advancements in CST, in particular in answering the questions of the three dimensional density reconstruction and polychromatic source problem. Specifically we provide novel and conclusive results on the stability and uniqueness properties of two and three dimensional inverse problems in CST through an analysis of a disc transform and a generalized spindle torus transform. In the final chapter of the thesis we give a novel analysis of the stability of a spindle torus transform from a microlocal perspective. The practical application of our inversion methods to fields in X-ray and gamma ray imaging are also assessed through simulation work.
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Zangarelli, Riccardo. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21201/.
Full textAbstract:
L'elaborato contiene una descrizione generale dei principali processi di scattering di importanza astrofisica, a partire dal più semplice fenomeno di scattering Thomson; si prosegue con lo scattering Compton e inverse Compton, del quale si evidenzia la relazione con il sincrotrone (synchrotron self-Compton). Viene analizzata l'evoluzione di uno spettro dominato dai processi Compton e inverse Compton (Comptonizzazione), e si conclude la trattazione dei processi in sè con una breve descrizione dello scattering ad opera della polvere. Infine, vengono esposti degli esempi di applicazioni dei processi in modo da giustificare l'importanza astrofisica di questi ultimi.
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Macconi, Duccio. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/11466/.
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L'attenzione è stata posta su tre fenomeni fondamentali di scattering: Thomson, Compton e Compton inverso. Sono state sottolineate alcune ed eventuali applicazioni astrofisiche di questi e valutate le implicazioni o generalizzazioni che da tali fenomeni possono derivare: Synchrotron Self-Compton, Comptonizzazione ed effetto Sunyaev-Zeldovich termico.
Infine è stato preso un caso astrofisico come applicazione di questi fenomeni: Sagittarius A*, una fonte radio proveniente dal centro della nostra galassia, molto studiata negli anni, citando un articolo pubblicato su una rivista scientifica nel 2012.
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Cerqui, Valeria. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15545/.
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Lo scattering, o diffusione, è un processo di interazione tra radiazione e materia. In particolare a livello astrofisico i processi rilevanti sono interazioni con particelle libere, solitamente elettroni. Essi vengono suddivisi in: scattering Thomson, in
cui lo scattering produce solamente un cambio di direzione, lasciando invariata l'energia del fotone incidente; scattering Compton, dove il fotone incidente perde energia, trasferendola all'elettrone; Compton inverso, dove viceversa allo scattering
Compton, è l'elettrone a trasferire energia al fotone incidente. Lo studio della variazione dello spettro energetico (SED) dei fotoni in caso di scattering multiplo (Compton e Inverse Compton) viene chiamato Comptonizzazione. Nel caso in cui la Comptonizzazione agisca sullo spettro della radiazione cosmica di fondo
(CMB), si presenta l'effetto Sunyaev-Zel'dovich dove si ha uno shift dello spettro di corpo nero della CMB ad energie lievemente maggiori. Nel presente scritto si focalizzerà l'attenzione sulla profondità ottica Thomson, che si presta a varie applicazioni
astrofisiche. Nello specifico verrà trattato il caso di scattering Thomson nell'ambiente delle symbiotic stars (SS) e come la profondità ottica vari a seconda delle fasi del sistema binario.
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Lojacono, Xavier. "Image reconstruction for Compton camera with application to hadrontherapy." Thesis, Lyon, INSA, 2013. http://www.theses.fr/2013ISAL0126/document.
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La caméra Compton est un dispositif permettant d’imager les sources de rayonnement gamma. Ses avantages sont sa sensibilité (absence de collimateur mécanique) et la possibilité de reconstruire des images 3D avec un dispositif immobile. Elle également adaptée pour des sources à large spectre énergétique. Ce dispositif est un candidat prometteur en médecine nucléaire et en hadronthérapie. Ces travaux, financés par le projet européen ENVISION (European NoVel Imaging Systems for ION therapy) Coopération-FP7, portent sur le développement de méthodes de reconstruction d’images pour la caméra Compton pour la surveillance de la thérapie par ions. Celle-ci nécessite idéalement une reconstruction temps réel avec une précision millimétrique, même si le nombre de données acquises est relativement faible. Nous avons développé des méthodes analytiques et itératives. Leurs performances sont analysées dans le contexte d’acquisitions réalistes (géométrie de la caméra, nombre d’événements). Nous avons développé une méthode analytique de rétroprojection filtrée. Cette méthode est rapide mais nécessite beaucoup de données. Nous avons également développé des méthodes itératives utilisant un algorithme de maximisation de la fonction de vraisemblance. Nous avons proposé un modèle probabiliste pour l’estimation des éléments de la matrice système nécessaire à la reconstruction et nous avons développé différentes approches pour le calcul de ses éléments : l’une néglige les incertitudes de mesure sur l’énergie, l’autre les prend en compte en utilisant une distribution gaussienne. Nous avons étudié une méthode simplifiée utilisant notre modèle probabiliste. Plusieurs reconstructions sont menées à partir de données simulées, obtenues avec Geant4, mais provenant aussi de plusieurs prototypes simulés de caméra Compton proposés par l’Institut de Physique Nucléaire de Lyon (IPNL) et par le Centre de recherche de Dresde-Rossendorf en Allemagne. Les résultats sont prometteurs et des études plus poussées, à partir de données encore plus réalistes, viseront à les confirmerThe Compton camera is a device for imaging gamma radiation sources. The advantages of the system lie in its sensitivity, due to the absence of mechanical collimator, and the possibility of imaging wide energy spectrum sources. These advantages make it a promising candidate for application in hadrontherapy. Funded by the european project ENVISION, FP7-Cooperation Work Program, this work deals with the development of image reconstruction methods for the Compton camera. We developed both analytical and iterative methods in order to reconstruct the source from cone-surface projections. Their performances are analyzed with regards to the context (geometry of the camera, number of events). We developped an analytical method using a Filtered BackProjection (FBP) formulation. This method is fast but really sensitive to the noise. We have also developped iterative methods using a List Mode-Maximum Likelihood Expectation Maximization (LM-MLEM) algorithm. We proposed a new probabilistic model for the computation of the elements of the system matrix and different approaches for the calculation of these elements neglecting or not the measurement uncertainties. We also implemented a simplified method using the probabilistic model we proposed. The novelty of the method also lies on the specific discretization of the cone-surface projections. Several studies are carried out upon the reconstructions of simulated data worked out with Geant4, but also simulated data obtained from several prototypes of Compton cameras under study at the Institut de Physique Nucléaire de Lyon (IPNL) and at the Research Center of Dresden-Rossendorf. Results are promising, and further investigations on more realistic data are to be done
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De, Nichilo Elisa. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/23916/.
Full textAbstract:
Con il termine scattering si definisce un processo fisico che descrive l’interazione di una particella con la radiazione elettromagnetica; in base all’energia coinvolta nel processo, si possono identificare diverse tipologie di scattering che vengono descritte nel primo capitolo di questo elaborato.
Un caso estremamente rilevante è lo scattering Thomson, dove un elettrone in quiete subisce un urto elastico con un fotone di bassa energia che viene diffuso con una frequenza pari a quella iniziale.
Per energie elevate l'effetto dominante è lo scattering Compton. In questo meccanismo un fotone, effettuando un urto elastico con un elettrone, trasferisce ad esso parte della sua energia e diminuisce la sua frequenza. Al contrario, se è l'elettrone a trasferire parte della sua energia al fotone, si parla di Inverse Compton.
Quando i fotoni appartenenti alla radiazione di sincrotrone effettuano scattering con elettroni relativistici, si ha Synchrotron Self-Compton.
I processi di scattering Compton e Compton Inverso si possono riassumere in un fenomeno più generale chiamato Comptonizzazione, che concerne le modifiche sullo spettro di radiazione avvenute in seguito all'interazione Compton tra fotoni ed elettroni. Un caso specifico di Comptonizzazione è l’effetto Sunyaev-Zeldovich che riguarda i fotoni della Radiazione Cosmica di Fondo.
Nel secondo capitolo si esaminano alcuni esempi in cui lo scattering riveste un ruolo importante nella Fisica dell’accrescimento: la Luminosità di Eddington, per cui è importante introdurre il concetto di sezione d’urto di Thomson, e l'emissione in banda X della radiazione elettromagnetica in seguito a Comptonizzazione, che ha sede nelle regioni coronali dei buchi neri.
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Chaleil, Annaïg. "Développement d’une source de rayonnement X par diffusion Compton inverse sur l'accélérateur ELSA et optimisation à l'aide d'un système d'empilement de Photons." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS398/document.
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La diffusion Compton inverse est l’interaction entre un photon et un électron de haute énergie. Il en résulte l’émission d’un nouveau photon d’énergie supérieure à celle du photon incident suivant la trajectoire de l’électron. Ces propriétés rendent possible la création d’une source de rayonnement X hautement directive, monochromatique accordable dans une large gamme spectrale. Il suffit d’accélérer les électrons sur quelques mètres pour leur faire gagner l’énergie minimale requise. Les photons proviennent d’une chaîne laser fortement amplifiée. Une telle source est donc relativement compacte, peu couteuse à mettre en oeuvre et facilement accessible aux utilisateurs. Elle est particulièrement adaptée aux besoins des musées ou des hôpitaux pour des applications comme l’analyse d’oeuvres historiques ou la radiothérapie. L’objectif de cette thèse est de mettre en oeuvre une source de rayonnement X par diffusion Compton inverse en bout de ligne de l’accélérateur ELSA (Electrons et Laser, Sources X et applications). L’installation ELSA comprend un accélérateur linéaire d’électrons appartenant à la Direction des Applications Militaires du Commissariat à l’Energie Atomique à Bruyères-le-Châtel (CEA DAM). Le but est de produire des impulsions de rayonnement X ultra-courtes dans une gamme énergétique allant de 10 à 100 keV. Elle servira notamment à la caractérisation de détecteurs à réponse ultra-rapide développés à la DAM. Un système optique destiné à augmenter le flux de rayonnement X produit a été développé. Il consiste à replier la trajectoire du laser pour empiler les impulsions au point d’interaction. Dans le même but, une mise à niveau de l’installation à été réalisée afin d’augmenter l’énergie des électrons de 18 à 30 MeV. Les résultats expérimentaux ont enfin été comparés aux résultats obtenus à l’aide de simulations PIC 3DX-ray sources based on inverse Compton scattering process produce tunable near-monochromatic and highly directive X-rays. Recent advances in laser and accelerator technologies make the development of such very compact hard X-ray sources possible. These sources are particularly attractive in several applications such as medical imaging, cancer therapy or culture-heritage study, currently performed in size-limited infrastructures. The main objective of this thesis is the development of an inverse Compton scattering source on the ELSA linac of CEA at Bruyères-le-Châtel as a calibration tool for ultra-fast detectors.A non-resonant cavity was designed to multiply the number of emitted X-ray photons. The laser optical path is folded to pile-up laser pulses at the interaction point, thus increasing the interaction probability. Another way of optimizing the X-ray yield consists in increasing the electron bunch density at the interaction point, which is strongly dependent on the electron energy. A facility up-grade was performed to increase the electron energy up to 30 MeV. The X-ray output gain obtained thanks to this system was measured and compared with calculated expectations and 3D PIC simulations
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Mariaud, Christian. "Etude des systèmes binaires galactiques à très haute energie avec HESS et HESS-II." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX030/document.
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En astronomie gamma, les systèmes binaires sont des objets stellaires impliquant une étoile massive et un objet compact, le plus léger des deux en orbite autour de l’autre. Ils émettent de façon régulière à haute et très haute énergie (E > 100 GeV) et peuvent être détectés par le réseau de télescopes H.E.S.S.. Malgré leur faible nombre, ils présentent une grande diversité de comportement et sont caractérisés par une modulation de flux dépendant de la position de l’objet compact. 2 systèmes binaires sont étudiés : LS 5039 et PSR B1259–63, en effet un jeu de données conséquent est disponible puisque ces sources sont observées maintenant depuis plus de 10 ans. En 2012, le cinquième télescope de plus grande taille a commencé ses observations et permet ainsi de faire la connexion avec le domaine du GeV.Une modélisation de ces deux systèmes binaires dans le cas d’une diffusion anisotrope inverse Compton dans le régime de Klein–Nishina sera aussi proposée avec une prise en compte du disque circumstellaire pour PSR B1259¡63. Les données recueillies lors d’une observation peuvent être détériorées par une atmosphère dégradée, affectant ainsi le flux de photons ° collectés. Un coefficient traduisant la qualité de l’atmosphère est donc nécessaire. De plus les gerbes peuvent être déformées à cause de laprésence du champ magnétique terrestre, les études de ces phénomènes sont donc nécessaires pour essayer de corriger ces effetsBinary systems in gamma astronomy are stellar objects involving a massive star with a compact object, the lightest in orbit around the other. They emit regularly at high energy and very high energy (E > 100 GeV) for detection by H.E.S.S. telescopes. Despite their low relative number, they are all characterized by a modulation of gamma photon flux which depends on the position of the lightest object. We will focus more on 2 binary systems : LS 5039 and PSR B1259–63, we have a susbstantial data, H.E.S.S. telescopes have regularly observed these objects for more than 10 years. In 2012, a fifth telescope much larger size, began observations and enables to get events at lower energy and then make the connection with other experiments such as Fermi-LAT. A modelling of these two binary systems in anisotropic inverse Compton in Klein–Nishina regime are also presented and the circumstellar disk is taken into account for PSR B1259–63. Data taken by theH.E.S.S. telescopes can be improved. During observations, atmosphere can be degraded and thus affecting the flux of gamma photons collected. It’s therefore important to know the transparency coefficient of the atmosphere during an analysis. Furthermore, the electromagnetic air showers are more distorted because of the Earth’s magnetic field, a study of these phenomenas is necessary to correct these effects
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Laborie, Jean-Marc. "Expérience de diffusion neutrino-électron auprès d'un réacteur nucléaire : étude et développement du détecteur anti-Compton." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10036.
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L'experience munu consiste a mesurer la diffusion neutrino-electron aupres d'un reacteur nucleaire du centre de production electrique du bugey. Le detecteur central est une chambre a projection temporelle contenant 1 m#3 de cf#4 gazeux sous 5 bars et le seuil de detection des electrons de recul est place a 500 kev. La chambre est entouree d'un detecteur anti-compton et de blindages passifs. Le detecteur anti-compton est fait de 8 m#3 de scintillateur liquide et de 48 photomultiplicateurs de 20 cm de diametre, avec un seuil en energie de 100 kev. Il permet de detecter la plupart des photons ayant interagi dans le gaz et de porter le taux de bruit de fond a un niveau comparable a celui du signal. D'une part les photomultiplicateurs et l'electronique logique et analogique associee ont ete mis en oeuvre, l'anti-compton a ete assemble et teste. D'autre part, un code de simulation a ete developpe : la collection de lumiere dans l'anti-compton a ete etudiee, l'influence des conditions electroniques de prise de decision sur son efficacite a ete estimee, une methode d'etalonnage a ete proposee.
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You, Yan. "Pulsed Laser Injected Enhancement Cavity for Laser-electron Interaction." Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01011958.
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X-ray diffraction and scattering, X-ray spectroscopy, and X-ray crystallography are widely used in the life sciences, material science, and medical diagnosis. High-quality and high-brightness X-rays are a strong requirement to improve applications. Inverse Compton scattering (ICS) X-ray source has attracted great interests worldwide lately. To significantly enhance the average X-ray photon flux, a compact electron storage-ring combined with a high finesse optical enhancement cavity (OEC) can be utilized. In such a system, the collision rate between the electron beam and the laser pulse is greatly increased to the MHz range, enabling a photon flux up to 10¹³ph/s.In the first chapter, I describe the motivation behind the development of OEC based on ICS X-ray source. The characteristics of this kind of X-ray source are summarized, compared to those of the conventional low-repetition-rate Terawatt laser system based on ICS X-ray source. The latest progress and research status of OEC based on ICS X-ray source are presented. Pulsed-laser injected high-finesse OEC stacking theory and properties are discussed in Chapter 2. Not only does the OEC based on ICS X-ray source require the laser pulse repetition rate to be matched to the free spectral range (FSR) of the cavity, where both also have to match the electron storage-ring circulation frequency. In addition, we have to match the phase shift of the laser repetition rate to the phase offset introduced by the dispersion of the cavity mirrors, since our cavity finesse design value is quite high. The stacking theory is analyzed in the frequency domain. Cavity properties, including cavity mirror dispersion, finesse, and FSR, are discussed in detail. A laser frequency comb and OEC coupling is analyzed also. The laser source development is presented in Chapter 3. We constructed a mode-locked fiber laser based on nonlinear polarization rotation. The locking model, locking techniques, and the theory, simulations and experimental tests of tilt locking (TL) in the pulsed laser injected high-finesse OEC are discussed in Chapter 4. We succeeded in locking a pulsed laser to a high-finesse cavity with the TL technique. The experimental results show that the TL and the Pound-Drever-Hall techniques have the same performance: stable locking, high sensitivity, and the same power coupling rate for picosecond laser pulse case, while the test results for full spectrum TL locking show that it is uneasy to align the split-photodiode to the beam waist.Based on the above experimental study and tests, we design the OEC system for Tsinghua University X-ray project in Chapter 5. The expected X-ray flux is 10¹º to 10¹³ ph/s. We detail every subsystem requirement.
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Gradl, Regine [Verfasser], Franz [Akademischer Betreuer] Pfeiffer, Jan J. [Gutachter] Wilkens, and Franz [Gutachter] Pfeiffer. "Dynamic Phase-Contrast X-ray Imaging at an Inverse Compton Source / Regine Gradl ; Gutachter: Jan J. Wilkens, Franz Pfeiffer ; Betreuer: Franz Pfeiffer." München : Universitätsbibliothek der TU München, 2019. http://d-nb.info/1200547918/34.
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Labaye, François. "Amplification passive d'un laser à fibre optique dans une cavité Fabry-Perot : application à la production de rayonnement gamma par diffusion Compton inverse." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00837822.
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La nécessité de prouver l'existence de nouvelles particules comme les quarks et le boson de Higgs a entrainé le développement de deux nouveaux pans de la recherche : la physique des hautes énergies ou physique des particules, dédiée à prouver expérimentalement l'existence de ces particules puis à étudier leurs propriétés et la physique des accélérateurs, dédiée au développement de nouveaux instruments pour la physique des hautes énergies.Dans ce contexte, des collisionneurs linéaires électrons/positrons polarisés de forte luminosité dont l'énergie serait connue et accordable pourrait permettre d'étudier plus finement des particules se situant dans des énergies autour du TeV telles que le Boson de Higgs. C'est dans ce sens que le projet International Linear Collider (ILC) est conçu et c'est dans le cadre du développement de ce collisionneur linéaire de particules que cette thèse de doctorat se situe. Un des points critiques de l'ILC est la source de positrons polarisés. Sans entrer dans des explications sur la physique du processus de création de positrons polarisés, nous précisons simplement que ceux-ci sont créés lorsque des rayons gamma polarisés circulairement interagissent avec la matière. Le point critique est donc la source de rayons gamma polarisés circulairement. Une alternative pour cette source est la diffusion Compton inverse et c'est finalement dans le cadre de la recherche et du développement de systèmes lasers de fortes puissances moyennes asservis à des cavités Fabry-Perot pour la production de rayons gamma polarisés par diffusion Compton inverse que se situe cette thèse.Dans un premier temps, nous posons plus précisément le contexte de cette thèse, le principe de la diffusion Compton inverse ainsi que le choix d'une architecture optique basée sur un laser fibré et une cavité Fabry-Perot. Nous finissons sur une énumération des différentes applications possibles de la diffusion Compton inverse montrant que les travaux présentés pourraient bénéficier de transfert technologique vers d'autres domaines. Dans un second temps, nous présentons les différentes architectures d'amplification laser fibrée étudiées ainsi que les résultats obtenus. Dans un troisième temps, nous faisons un rappel du principe de fonctionnement d'une cavité Fabry-Perot et présentons celle utilisée pour notre expérience ainsi que ses spécificités. Dans un quatrième temps, nous abordons l'expérience de diffusion Compton inverse qui nous a permis de présenter pour la première fois à notre connaissance l'utilisation conjointe d'un laser à fibre optique et d'une cavité Fabry-Perot dans le cadre d'un accélérateur de particules pour générer des rayons gamma. Le dispositif expérimental ainsi que les résultats obtenus sont alors présentés. Finalement, nous résumons les résultats présentés dans ce manuscrit et proposons différentes possibilités d'évolution pour le système dans une conclusion générale.
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Andersson, Tom. "Inverse Compton gamma-rays from Markarian 421 : A study of GeV and TeV emission from Mrk 421 based on Fermi-LAT and H.E.S.S. data." Thesis, Linnéuniversitetet, Institutionen för fysik och elektroteknik (IFE), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-57861.
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This thesis summarizes a senior project on the Active Galactic Nucleus (AGN) Markarian 421 (Mrk 421). Observations of Gev and TeV flux with Fermi Large Area Telescope (LAT) and High Energy Stereoscopic System (H.E.S.S.) were compared with previous reports and publications of flux analyses of the gamma-ray emission from Mrk 421. Power laws with exponential cutoffs made consistent fits to most SEDs in the GeV and TeV bands.
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Jochmann, Axel [Verfasser], Roland [Akademischer Betreuer] Sauerbrey, and Todd [Akademischer Betreuer] Ditmire. "Development and characterization of a tunable ultrafast X-ray source via Inverse-Compton-Scattering / Axel Jochmann. Gutachter: Roland Sauerbrey ; Todd Ditmire. Betreuer: Roland Sauerbrey." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://d-nb.info/106904055X/34.
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Caloni, Luca. "Fisica dell'accrescimento." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9594/.
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L'accrescimento è un processo fondamentale in astrofisica data la sua grandissima
efficienza. Nel 1959 venne individuato il primo Quasar (pur non sapendo realmente
di cosa si trattasse) e nel 1963 l'astronomo tedesco Maarten Schmidt scoprì che tale
oggetto, di magnitudine apparente 13 (si credeva fosse una stella), aveva un redshift
z = 0:37. Stelle di magnitudine 13 non dovrebbero avere un redshift così grande.
Tale oggetto doveva trovarsi a grande distanza ed emettere una luminosità molto alta, superiore anche a quella di un'intera galassia.
Processi termonucleari non erano sufficientemente efficienti per spiegare un'emissione di questo tipo: si capì presto che tale emissione dovesse avere origine gravitazionale, fosse cioè dovuta all'accrescimento di materia su un buco nero.
In questa tesi, dopo aver spiegato come l'accrescimento rappresenti un'importante fonte di energia in astrofisica, presenterò, nel Capitolo 1, il modello di Bondi,
presentato nel 1952 da Hermann Bondi. Tale modello è il più semplice modello di
accrescimento e, pur essendo basato su ipotesi (che vedremo) che trascurano diversi
aspetti importanti, risulta comunque un modello fondamentale, perché permette di
ricavare quantità rilevanti in astrofisica.
Successivamente, nel Capitolo 2, ricaverò il valore della Luminosità di Eddington, che esprime la massima luminosità che può emettere un corpo in simmetria sferica. Anche questo risultato verrà ricavato imponendo ipotesi abbastanza restrittive,
quindi non andrà interpretato come un limite invalicabile.
Nel Capitolo 3 parlerò (più qualitativamente, e senza la pretesa di entrare nei
dettagli) di come si formano i dischi di accrescimento, che si originano quando la
materia che va ad accrescere ha un momento angolare non nullo: quindi non siamo
più nel caso di accrescimento a simmetria sferica.
Infine, parlerò dei processi che originano gli spettri osservati degli AGN, riferendomi
prevalentemente a quei processi che originano il continuo dello spettro.
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Siena, Matteo. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/19469/.
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Con il termine Scattering si indica un insieme di meccanismi di diffusione della radiazione da parte della materia. Quando interagiscono con una particella carica, i fotoni possono essere assorbiti e quindi riemessi subito dopo in un'altra direzione cambiando la loro energia iniziale oppure no: nel primo caso si parla di Scattering Compton (SC) mentre nel secondo di Scattering Thomson. Inoltre vi è un processo nel quale è la particella carica (l'elettrone nei processi astrofisici) ad avere un'energia maggiore, che la trasferisce così al fotone incidente; si tratta del caso dell'Inverse Compton (IC) ed è un meccanismo molto rilevante in Astrofisica. Tutti questi processi vengono analizzati nel Capitolo 1, mentre nel Capitolo 2 vengono discusse alcune principali applicazioni dell' IC e dello Scattering Thomson, in particolare nel paragrafo 2.1.1 si approfondisce il fenomeno della Catastrofe Compton, che consiste in uno spropositato aumento della luminosità della sorgente che arriverebbe a produrre fotoni via via sempre più energetici diventando una potente sorgente di raggi X e gamma. Queste emissioni, però, non sono state osservate finora e nonostante questo possa essere spiegato per alcune sorgenti tramite una semplice applicazione dell'effetto Doppler, per altre, come le Intra-Day Variable Sources (IDVS), ciò non è possibile, come mostrato nel lavoro pubblicato (e riassunto nella seguente trattazione sempre nel paragrafo 2.1.1) da O. Tsang e J.G. Kirk nel 2007, i quali riesaminano il problema della catastrofe per tali sorgenti mostrando che l'assenza del fenomeno appena descritto può essere spiegato apportando delle modifiche ai processi in gioco. Infine, nell'ultimo paragrafo si analizza il concetto di Luminosità di Eddington, una delle principali applicazioni in ambito astrofisico dello Scattering Thomson.
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Yassine, Manal. "The prompt emission of Gamma-Ray Bursts : analysis and interpretation of Fermi observations." Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTS006/document.
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Les sursauts gamma (GRBs pour "Gamma-Ray Bursts" en anglais) sont de brèves bouffées très énergétiques de rayonnement de haute énergie qui sont émises sur de courtes échelles de temps (fraction de seconde à plusieurs minutes). L'émission intense des sursauts gamma à haute énergie est supposée provenir d'un trou noir de masse stellaire nouvellement formé, accompagné d'un vent collimaté (i.e. un jet) se propageant à vitesse relativiste. L'émission est observée suivant deux phases successives, la phase prompte très erratique, et la phase de rémanence, moins lumineuse. Les deux instruments embarqués sur le satellite Fermi, le "Gamma-ray Burst Monitor" (GBM) et le "Large Area Telescope" (LAT), permettent d'étudier l'émission prompte des sursauts gamma sur une grande plage d'énergie (de ~10 keV à ~100 GeV). L'objectif principal de ma thèse est l'analyse et l'interprétation des propriétés spectrales et temporelles de l'émission prompte des GRBs observés par Fermi, en particulier avec les nouvelles données du LAT (Pass 8) qui ont été rendues publiques en juin 2015.La première partie de mon travail est une analyse spectrale résolue en temps de la phase prompte du sursaut GRB 090926A avec les données du GBM et du LAT. Mes résultats confirment avec un meilleur niveau de confiance la présence d'une cassure spectrale à ~400 MeV, qui est observée en coincidence avec un pic d'émission très court. Ils révèlent que cette atténuation spectrale est présente durant toute l'émission prompte du sursaut, et que l'énergie de cassure augmente jusqu'au GeV. L'interprétation de la cassure spectrale en termes d'absorption gamma ou de courbure naturelle du spectre d'émission Compton inverse (CI) dans le régime Klein-Nishina fournit des contraintes fortes sur le facteur de Lorentz du jet. Mes résultats conduisent en outre à des rayons d'émission R ∼10^14 cm qui sont compatibles avec une origine interne de l'émission du keV au GeV au-dessus de la photosphère du jet.La seconde partie de mon travail est une exploration du modèle de chocs internes développé par des collaborateurs à l'Institut d'Astrophysique de Paris (IAP). Ce modèle simule la dynamique du jet et les processus d'émission (synchrotron et CI) d'une population d'électrons accélérés aux chocs. J'ai simulé la réponse instrumentale de Fermi à un sursaut synthétique fourni par ce code numérique, et j'ai construit une fonction paramétrique qui peut être utilisée pour ajuster le modèle aux spectres de sursauts du keV au MeV. J'ai appliqué cette fonction avec succès à un échantillon de 64 sursauts brillants détectés par le GBM. J'ai aussi confronté le modèle de l'IAP au spectre d'émission prompte de GRB 090926A. Mes résultats montrent un bon accord, et j'ai identifié quelques pistes pour les améliorer. Les spectres synthétiques sont plus larges que tous les spectres dans l'échantillon du GBM. En conséquence, je discute brièvement quelques pistes de développements théoriques qui pourraient améliorer l'accord du modèle avec les observations, ainsi que des avancées observationnelles attendues dans le futurGamma-Ray Bursts (GRBs) are very energetic and brief flashes of high-energy radiations which are emitted in a short time scale (fraction of a second to several minutes). The GRB bright emission is thought to be powered by a newly formed stellar-mass black hole that is accompanied by a collimated outflow (i.e. a jet) moving at a relativistic speed. The emission is observed as two successive phases: the highly variable “prompt” phase and the late and less luminous “afterglow” phase. The two instruments on board the Fermi space telescope, the Gamma-ray Burst Monitor (GBM) and the Large Area Telescope (LAT), allow the study of GRB prompt emission over a broad energy range (from ~10 keV to ~100 GeV). In June 2015, a new set of LAT data (Pass 8) was publicly released, which were generated using improved algorithms of reconstruction and classification of gamma-ray events. The main goal of my thesis is the analysis and interpretation of the spectral and temporal properties of the prompt emission phase of the GRBs observed by Fermi, especially using LAT Pass8 data.In the first part of my work, I performed a detailed time-resolved spectral analysis of the prompt phase of GRB 090926A with GBM and LAT data. My results confirm with a greater significance the spectral break at ∼400 MeV that is observed during a fast variability pulse, and they also reveal the presence of a spectral attenuation throughout the GRB prompt emission, as well as an increase of the break energy up to the GeV domain. I interpreted the spectral break in terms of gamma-ray absorption or as a natural curvature of the inverse Compton (IC) emission in the Klein-Nishina regime. Strong constraints on the jet Lorentz factor were obtained in both scenarios. My results lead also to emission radii R ∼10^14 cm, which are consistent with an internal origin of both the keV-MeV and GeV prompt emissions above the jet photosphere.The second part of my work is an exploration of the internal shock model that has been developed by collaborators at the "Institut d'Astrophysique de Paris" (IAP). This model simulates the GRB jet dynamics and the radiations (synchrotron and IC processes) from a population of shock-accelerated electrons. I simulated the response of the Fermi instruments to the synthetic GRB spectra provided by this numerical code. From these simulations, I built a new parametric function that can be used to fit the keV-MeV spectra of GRBs with the model. I applied successfully this function to a sample of 64 GBM bright GRBs. I confronted also the IAP model to the prompt emission spectrum of GRB 090926A. I obtained a relatively good agreement and I identified a couple of solutions that may improve it. The synthetic spectra are wider than any GRB spectra in the GBM sample. I present some theoretical developments that could improve the data-model agreement in the future, and I discuss possible advances from future GRB missions as well
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Bini, Lorenzo. "Caratteristiche principali dell'emissione di galassie a spirale." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21203/.
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Le galassie sono i mattoni fondamentali dell’Universo. Esse sono composte da stelle, gas e polvere; questi ultimi costituiscono il Mezzo Interstellare, noto anche come ISM, il quale viene suddiviso in quattro fasi caratterizzate da diverse temperature e densità. In questo elaborato si andranno ad analizzare innanzitutto le proprietà delle suddette fasi dell’ISM; successivamente ci si concentrerà sui vari processi di emissione delle galassie a spirale, i quali vengono divisi in due tipologie: processi nel continuo (Corpo nero, Bremsstrahlung, Sincrotrone, Inverse Compton, emissione da parte di polveri e di raggi cosmici), dove la radiazione viene emessa in un intervallo di frequenze, e processi in riga (righe di ricombinazione, riga a 21cm dell'HI, righe molecolari), dove la radiazione viene emessa ad una frequenza caratteristica.
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Curatolo, C. "High brilliance photon pulses interacting with relativistic electron and proton beams." Doctoral thesis, Università degli Studi di Milano, 2016. http://hdl.handle.net/2434/358227.
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We present a detailed study of the interaction between relativistic electron beams and high intensity laser pulses aimed at the production, through Inverse Compton scattering, of high brilliance gamma rays. In particular, we focus on the simulations of the emitted photon beams for the Extreme Light Infrastructure Nuclear Physics Gamma Beam System. The machine, presently under construction, is designed to deliver gamma ray photon beams in the 0.2-19.5 MeV energy range characterized by unprecedented performances in terms of monochromaticity, brilliance, spectral density, tunability and polarization.
The possibility to generate low emittance TeV-class energy pion and muon beams via photo-production in a highly relativistic Lorentz boosted frame is discussed in the second part of the dissertation. The kinematics of all the events given by the proton-photon beams interaction has been considered: pion photo-production and further decay into muon and neutrino, lepton pair photo-production (electron/positron and muon pairs) and Inverse Compton scattering. We analyze the brightness of the secondary beams achievable by the coupling of advanced high efficiency high repetition rate Free Electron Laser pulses and Large Hadron Collider or Future Circular Collider proton beams.
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Lobet, Mathieu. "Effets radiatifs et d'électrodynamique quantique dans l'interaction laser-matière ultra-relativiste." Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0361/document.
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Cette thèse a pour objet l'étude de l'interaction laser-matière dans un régime d'éclairement extrême que visent à atteindre plusieurs installations multi-pétawatt en cours de développement (CILEX-Apollon, ELI, IZEST, etc.). Pour un éclairement supérieur à 1022 Wcm-2, la dynamique relativiste des électrons accélérés dans l'onde laser est modiée par un important rayonnement Compton inverse non-linéaire. Au-delà de 1023 Wcm2, les photons ainsi produits peuvent, en interagissant à leur tour avec le champ laser, se désintégrer en paires électron-positron via le mécanisme de Breit-Wheeler non-linéaire. Ces mécanismes d'électrodynamique quantique, dont l'étude expérimentale était jusqu'ici l'apanage des grands accélérateurs de particles, peuvent grandement affecter les mécanismes usuels d'interaction laser-plasma, notamment ceux régissant l'accélération de particules chargées et, par conséquent, le bilan global de l'interaction. Afin de modéliser ce régime inédit d'interaction, qui combine processus collectifs, relativistes et d'électrodynamique quantique, nous avons enrichi des mécanismes précédents le code de simulation particle-in-cell calder développé de longue date au CEA/DIF. L'influence de ces mécanismes est d'abord explorée dans le cas d'une impulsion laser interagissant avec une cible dense de taille micrométrique. Un rendement de conversion de l'énergie laser en photons supérieur à 10% est observée au-dessus de 1023 Wcm-2, tandis que la production d'anti-matière s'emballe, via un mécanisme de cascade, à partir de 1024 Wcm2. Dans un second temps, nous étudions la génération de positrons lors de la collision frontale entre un faisceau d'électrons ultra-relativistes issu d'un accélérateur plasma et une impulsion laser ultra-intense. Dans une dernière partie, nous considérons un scénario prospectif d'intérêt astrophysique, à savoir la collision de plasmas de paires issus de cibles solides irradiées à 1024 Wcm-2 montrant la croissance rapide d'une instabilité de lamentation magnétique combinée à d'intenses effets radiatifsThis PhD thesis is concerned with the regime of extreme-intensity laser-matter interaction that should be accessed on upcoming multi-petawatt facilities (e.g. CILEX-Apollon, ELI, IZEST). At intensities IL > 1022 Wcm-2, the relativistic dynamics of the laser-driven electrons becomes significantly modified by high-energy radiation emission through nonlinear inverse Compton scattering. For IL > 1023 Wcm-2, the emitted-ray photons can, in turn, interact with the laser field and decay into electron-positron pairs via the nonlinear Breit-Wheeler process. These quantum electrodynamic processes, which until recently could only be explored on large-scale particle accelerators, can greatly alter the "standard" mechanisms of laser-plasma interaction, and therefore its overall energy budget. In order to model their intricate interplay with the laser-induced plasma processes, they have been implemented within the particle-in-cell code calder developed at CEA. In a first part, we study these QED processes in the interaction of an ultra-intense laser with a micrometric overdense target. It is found that the laser-to--ray energy conversion efficiency can by far exceed 10% for intensities IL > 1023 Wcm-2, while copious pair production (through pair cascading) kicks in for IL > 1024 Wcm-2. In a second part, we consider positron generation in the collision between a GeV electron bunch issued from a laser-wake eld accelerator and a counterpropagating laser pulse. In a third part, we analyze a prospective scheme of astrophysical interest, consisting in the collision between two dense pair plasmas produced from solid targets irradiated at 1024 Wcm-2 showing a fast-growing magnetic lamentation instability amplified by intense synchrotron emission
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Lucertini, Francesca. "Emissione di Compton inverso e applicazioni astrofisiche." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8869/.
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Con questa Tesi si vuole illustrare L'effetto Compton inverso e alcune delle sue applicazioni astrofisiche. Poichè l'effetto Compton inverso è un processo di scattering si è ritenuto importante spiegare, brevemente, la diffusione Thomson e la diffusione Compton per mostrare le differenze tra i tre processi. Successivamente si è studiata l'emissione per Compton inverso dovuta a una singola interazione, la potenza e lo spettro del caso generale. Tra le applicazioni astrofisiche si sono riportate la Comptonizzazione e il Synchrotron self-Compton, per poi approfondire ognuna con una esempio specifico. Nel caso della Comptonizzazione si è discusso l'effetto Sunyaev-zeldovich mentre i BL Lacertae rappresentano l'approfondimento relatico al Synchrotron self-Compton.
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Trupia, Denise. "Caratteristiche principali dell'emissione di galassie a spirale." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/17072/.
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Le galassie a spirale sono galassie come la nostra caratterizzate da un bulge, un disco (che mostra una configurazione a bracci) e un alone. In questo elaborato sono trattati i processi di emissione in galassie a spirali. Essi distinguono in processi nel continuo (Corpo nero, Bremsstrahlung, Sincrotrone, Inverse Compton, emissione da parte di polveri e di raggi cosmici) e processi in riga (righe di ricombinazione, riga a 21cm dell'HI, righe molecolari).
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Miola, Andrea. "Emissione di Compton inverso e applicazioni astrofisiche." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/12354/.
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Lo scopo di questo elaborato è quello di descrivere il fenomeno del Compton
inverso, uno dei meccanismi di emissione più importanti in ambito astrofisico,
attraverso una trattazione matematico-fisica per comprenderne le varie caratteristiche fondamentali e quindi, una volta compreso il suo funzionamento, fornire degli esempi pratici della sua applicabilità e rilevabilità in ambito astrofisico.
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Bottazzi, Giulio. "Emissione di Compton inverso e applicazioni astrofisiche." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9592/.
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Descrizione dell'effetto Compton inverso (IC) e sue implicazioni nell'ambito astrofisico. Vengono anche trattati altri effetti, tutti correlati con lo scattering IC, quali Comptonizzazione, Synchrotron-self-Compton e effetto Sunyaev-Zeldovich.
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Iemmi, Erik. "Emissione di Compton inverso e applicazioni astrofisiche." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/11432/.
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Nell'elaborato viene affrontato il processo di diffusione di fotoni denominato Compton Inverso.
Per prima cosa c'è una breve introduzione dove vengono elencati i vari processi di diffusione di radiazione e alcune applicazioni astrofisiche del Compton inverso che saranno poi affrontate nella seconda parte.
Nel capitolo 1 viene fatta una trattazione fisica del processo e vengono analizzati potenza emessa e spettro risultante.
Infine nel capitolo finale vengono approfondite le applicazioni astrofisiche più importanti del Compton inverso: Comptonizzazione, effetto Sunyaev-Zeldovich e Synchrotron Self Compton.
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Cotellucci, Alessandro. "Emissione di Compton inverso e applicazioni astrofisiche." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16339/.
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L'emissione di Compton inverso è uno dei principali processi di radiazione in astrofisica. Non è un'emissione intrinseca in quanto è legata all'interazione di elettroni relativistici con un campo di radiazione già esistente, che per alcune sorgenti può essere prodotto dai medesimi elettroni. Ripetute interazioni Compton possono portare alla modifica dello spettro di radiazione esterna, questo fenomeno è detto comptonizzazione. La comptonizzazione è alla base dell'effetto Sunyaev-Zeldovich che avviene negli ammassi di galassie con la radiazione cosmica di fondo (CMB) e che ha importanza sia per lo studio degli ammassi e della CMB sia per fini cosmologici, quale la stima della costante di Hubble citata in questo elaborato. L'elaborato si conclude con la spiegazione dell'emissione del vento della Crab pulsar attraverso l'emissione di Compton inverso.
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Zanetti, Andrea. "Emissione di Compton inverso e applicazioni astrofisiche." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Find full textAbstract:
Questo elaborato è una presentazione delle caratteristiche del processo fisico di Compton inverso. E' diviso in due capitoli: nel primo si discutono le basi teoriche (soluzioni delle equazioni di Maxwell esplicite, tramite i potenziali scalare e vettore, ed ondulatorie; loro connessione nell'ambito di densità di carica/corrente oscillanti nel tempo; emissione da singole particelle accelerate) che portano alle relazioni/quantità fondamentali per il processo di Compton inverso: formula di Larmor e sezione d'urto di Thomson. Nel secondo si tratta il Compton inverso con la discussione di alcune applicazioni astrofisiche.
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Belardi, Luca Enrico. "Emissione di Compton inverso e applicazioni astrofisiche." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/23910/.
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La seguente tesi si occupa di illustrare il fenomeno generale di emissione per Compton inverso (CI) e alcune delle sue utili applicazioni in Astrofisica. Il Compton inverso è un fenomeno ideale di scattering in cui elettroni molto energetici, urtando con fotoni a frequenze più basse, cedono energia a quest'ultimi permettendogli di raggiungere frequenze elevate. Utilizzo il termine ideale per sottolineare il fatto che il CI è una estremizzazione di un processo che si verifica in natura, ovvero la Comptonizzazione. Questa, infatti, risuta essere un'unione del processo protagonista di questa tesi, e dello scattering Compton, il quale identifica uno scambio di energia tra fotoni molto energetici con elettroni a basse energie, di conseguenza in completa antitesi al Compton inverso. Un interessante caso di Comptonizzazione è l'effetto Sunyaev-Zeldovich, che si verifica in presenza di ammassi di galassie. In Astrofisica, altri fenomeni osservabili sono costituiti dall'unione del CI e dell'emissione di Sincrotrone. Tale processo viene identificato con il termine Synchrotron-self Compton, che si verifica durante l'interazione di fotoni generati da elettroni in presenza di campi magnetici (Sincrotrone) e gli elettroni stessi.
Lo studio del Compton inverso non può quindi trascendere questi vincoli con altri effetti radiativi, se non creando un modello ideale che ci permetta di capire come questa emissione possa agire in solitaria.
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Circosta, Chiara. "Emissione di Compton inverso e applicazioni astrofisiche." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/5651/.
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Matassoni, Filippo. "Emissione di compton inverso e applicazioni astrofisiche." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7395/.
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Nella tesi vengono trattati i fenomeni di urto tra fotoni e elettroni, nella fattispecie si riconoscono tre urti differenti: lo scattering Thomson, Compton e Compton Inverso (IC). L'attenzione viene focalizzata sull'effetto IC. Una volta riportati i risultati sui tre processi sopracitati, il testo prosegue con la trattazione del problema di interesse astrofisico, ovvero la Comptonizzazione. La Comptonizzazione è il caso più generale in cui IC e effetto Compton competono, e stabilisce come lo spettro fotonico viene modificato a causa delle interazioni col plasma.
Vengono in seguito trattati due interessanti applicazioni astrofisiche della Comptonizzazione: l' effetto Sunyaev-Zel'Dovich e il Synchrotron-self-Compton.
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Vorobiov, Serguei͏̈. "Observations de la méthode du Crabe de 1996 à 2002 avec le télescope à effet Tcherenkov atmosphérique CAT et mise en oeuvre d'une nouvelle méthode d'analyse des gerbes atmosphériques." Palaiseau, Ecole polytechnique, 2004. http://www.theses.fr/2004EPXX0001.
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Mari, Alessandro. "Effetti relativistici in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/17099/.
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L'obiettivo di questa tesi è presentare alcuni effetti relativistici che si possono osservare in astrofisica. Al fine di ottenere una trattazione sufficientemente rigorosa verrà introdotta inizialmente la teoria della relatività ristretta, esaminata attraverso i postulati di Einstein e necessaria per chiarire alcune nozioni e fattori che compariranno nei capitoli successivi. Quindi verranno illustrate le caratteristiche principali del processo di radiazione di sincrotrone e dello scattering Compton inverso associati in particolare al fenomeno di Synchrotron Self-Compton derivante dalla combinazione dei due meccanismi. Infine, per avvalorare quanto descritto, negli ultimi capitoli sarà dato spazio ad alcune applicazioni astrofisiche quali i moti superluminali e i blazars, una categoria di oggetti extragalattici noti per la loro forte e persistente luminosità.
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Marques, Antonio Luiz Fernandes. "Geração de fótons muito duros por espalhamento Compton inverso da radiação síncrotron." [s.n.], 1993. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277524.
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Orientador: Carola Dobrigkeit ChinellatoDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-07-18T07:15:02Z (GMT). No. of bitstreams: 1 Marques_AntonioLuizFernandes_M.pdf: 2362696 bytes, checksum: 7c202163d926993db9c6b3135f451246 (MD5) Previous issue date: 1993
Resumo: O mecanismo mais eficiente para se gerar fótons com energia da ordem de 100 MeV ou acima é o espalhamento Compton inverso de luz de laser por elétrons relativisticos. Pode-se elevar a energia dos fótons emitidos aumentando-se a energia dos elétrons (o que encarece muito os experimentos) ou a energia do fóton. S. Caticha-Ellis sugeriu (1983) que um feixe intenso de raios X pode ser obtido pela retrodifração da radiação sincrotron em um cristal, abrindo assim a possibilidade de se gerar fótons duros pelo espalhamento Compton inverso da própria radiação sincrotron. Dessa forma os fótons emitidos podem ter energias maiores do que a energia do feixe de elétrons (vários GeV), sendo altamente colimados e não polarizados. Esses fótons podem ser usados em experiências de física nuclear e para se testar a eletrodinâmica quântica
Abstract: The most efficient mechanism to generate photons in the 100 MeV energy range is by Inverse Compton scattering (ICS) of laser from relativistic electron. The energy of the emitted photons can be increased by raising either the energy of the electron, which is very expensive, or that of the photon. with the suggestion (S. Caticha-Ellis, 1983) that intense X-ray beams could be obtained by back-reflecting synchrotron radiation using a crystal diffracting at normal incidence, the possibility is now open of generating very hard photons by ICS of the synchrotron radiation itself. The photons emitted in this way will have energies ranging all the way up to the electron beam energy (up to the several GeV), will be non-polarized and highly collimated. The photons may be used to study phenomena of quantum electrodynamics and nuclear physics
Mestrado
Física
Mestre em Física
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Piron, Frédéric. "Etude des propriétés spectrales et de la variabilité de l'emission gamma supérieure à 250 GeV des noyaux actifs de galaxies de type blazar observés dans le cadre de l'expérience C.A.T." Phd thesis, Université Paris Sud - Paris XI, 2000. http://tel.archives-ouvertes.fr/tel-00002448.
Full textAbstract:
Après un rappel des principaux enjeux de l'astronomie y des hautes énergies, l'imageur C.A.T. ("Cerenkov Array at Thémis") est présenté, l'accent étant mis sur les résultats récents de calibration, qui est un aspect particulièrement délicat des détecteurs à effet Tcherenkov atmosphérique: aucune calibration directe n'étant possible, la maîtrise du télescope doit passer par une confrontation constante des résultats obtenus sur la base de modélisations numériques et de données réelles, dont celles prises sur la source de référence qu'est la nébuleuse du Crabe. Au fil de leur présentation, les procédures d'extraction du signal gamma et de reconstruction de spectres sont ainsi testées et validées. Les résultats d'observation des blazars Markarian 501 et Markarian 421 sont ensuite exposés: une corrélation entre l'émission de rayons X (> keV) et de gamma au TeV est établie pour ces deux sources; au TeV, une rapide variabilité est observée, parfois à l'échelle de l'heure pour Markarian 421; Markarian 501 apparaît cependant plus extrême: son maximum de puissance est atteint vers 500 GeV, et un durcissement spectral est mis en évidence lors des sursauts les plus intenses. Tous ces résultats consolident la séquence spectrale récemment proposée pour unifier la classe des blazars; ils suggèrent une zone d'émission très compacte (N10-3 parsec), se propageant à vitesse relativiste à la base des jets radio de ces objets, et contenant une unique population d'électrons responsables de l'émission non thermique observée sur un large domaine de longueur d'onde. Un modèle de type Synchrotron Self-Compton est appliqué avec succès aux données prises sur Markarian 501 en Avril 1997. Enfin, la recherche de signal en provenance de 20 autres blazars candidats au TeV est entreprise, et aboutit à une limite supérieure à l'émission gamma de chacun d'eux.
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Penz, Sébastien. "Modélisation et inversion de données électriques en courant continu : vers une prise en compte efficace de la topographie." Electronic Thesis or Diss., Paris, ENMP, 2012. http://www.theses.fr/2012ENMP0016.
Full textAbstract:
L'imagerie électrique est un outil de plus en plus important pour un large domaine d'applications relatives à la caractérisation de la subsurface proche. D'importants développements ont été réalisés au cours des vingt dernières années pour l'amélioration des systèmes d'acquisitions et des algorithmes d'inversions. L'acquisition et le traitement de gros jeux de données reste toutefois une tâche délicate, en particulier en présence de topographie. Afin d'améliorer la gestion de la topographie, nous avons développé un nouvel algorithme d'inversion électrique 2.5D et 3D. Nous avons proposé deux nouvelles formulations pour supprimer la singularité à la source. Le problème direct est résolu en utilisant la méthode des Différences Finies Généralisées et des maillages non structurés, permettant une représentation précise de la topographie. Le code d'inversion utilise la méthode de l'état adjoint pour calculer le gradient de la fonction objective de manière économique. Cette approche a donné de bons résultats avec des données synthétiques. Les premiers résultats sur des données réelles ont permis de retrouver les principales structures de la subsurface, ainsi que plusieurs zones de faibles résistivités pouvant correspondre à des zones fracturéesDC resistivity imaging plays an important role for a wide range of applications related to the characterization of the shallow subsurface. Major developments have been made over the last two decades to improve acquisition systems as well as resistivity inversion. Nevertheless, large-scale data sets still represent a challenging task, in particular with arbitrary topography. In order to better take into account topography, we have developed a new 2.5D/3D tomographic inversion code. Two new formulations for the singularity removal have been proposed. The direct problem is solved in the framework of the Generalized Finite Differences Method, that allows the use of unstructured meshes yielding a fine represention of topography. The inversion code uses the adjoint state method to compute the gradient of the misfit function in a numerically efficient way, giving goodresults on synthetic data. First results on real data have shown the main subsurface structures, as well as several low resistivity zones possibly corresponding to fractured areas
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Penz, Sébastien. "Modélisation et inversion de données électriques en courant continu : vers une prise en compte efficace de la topographie." Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2012. http://pastel.archives-ouvertes.fr/pastel-00796438.
Full textAbstract:
L'imagerie électrique est un outil de plus en plus important pour un large domaine d'applications relatives à la caractérisation de la subsurface proche. D'importants développements ont été réalisés au cours des vingt dernières années pour l'amélioration des systèmes d'acquisitions et des algorithmes d'inversions. L'acquisition et le traitement de gros jeux de données reste toutefois une tâche délicate, en particulier en présence de topographie. Afin d'améliorer la gestion de la topographie, nous avons développé un nouvel algorithme d'inversion électrique 2.5D et 3D. Nous avons proposé deux nouvelles formulations pour supprimer la singularité à la source. Le problème direct est résolu en utilisant la méthode des Différences Finies Généralisées et des maillages non structurés, permettant une représentation précise de la topographie. Le code d'inversion utilise la méthode de l'état adjoint pour calculer le gradient de la fonction objective de manière économique. Cette approche a donné de bons résultats avec des données synthétiques. Les premiers résultats sur des données réelles ont permis de retrouver les principales structures de la subsurface, ainsi que plusieurs zones de faibles résistivités pouvant correspondre à des zones fracturées.