Segui questo link per vedere altri tipi di pubblicazioni sul tema: Electronic secondary emission.
Tesi sul tema "Electronic secondary emission"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Electronic secondary emission".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
1
Ludwick, Jonathan. "Physics of High-Power Vacuum Electronic Systems Based on Carbon Nanotube Fiber Field Emitters". University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613745398331048.
Testo completo
2
Ransley, Chau Diem Nguyen. "Secondary electron emission from organic monolayers". Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612907.
Testo completo
3
Farhang, Mohammad Hossein. "Secondary electron emission yield from carbon samples". Thesis, University of Southampton, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318220.
Testo completo
4
Vempati, Pratyusha. "Analytical fits to Secondary Emission Yield Data". University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1523635397854801.
Testo completo
5
Cormier, Pierre Richard Sébastien. "Secondary electron emission properties of molybdenum disulfide thin films". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq31189.pdf.
Testo completo
6
Muellejans, Harald. "Secondary electron emission in coincidence with primary energy losses". Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240071.
Testo completo
7
Vaz, Raquel Maria Amaro. "Studies of the secondary electron emission from diamond films". Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616564.
Testo completoAbstract (sommario):
The aim of the present research was the development of an optimised secondary electron emission (SEE) diamond film to use as a dynode material. The project was a partnership between the School of Chemistry in the University of Bristol, the Space Research Centre (SRC) at the University of Leicester and Photek, a company specialized in the manufacture of systems for photon detection. The role of Bristol in this project consisted in the preparation of CVD diamond films and their characterization, before supply to the other collaborators. SEE characterisation of the samples was performed at SRC and Photek would proceed to further testing in actual tubes. Besides its participation in the project, Bristol went further and developed the means to do its own SEE measurements. This thesis describes the work undertaken at Bristol using the facilities at the Diamond CVD group. Diamond films were prepared by hot-filament (HF) CVD covering a range of crystallinities, thicknesses and levels of boron (B) doping, on different substrate materials. A new home-built apparatus has been developed for the acquisition of SEE data from diamond films, both in reflection and transmission configurations. The setup consists of a system of phosphor screens acting as detectors and associated to PMTs for the acquisition of signal measured from the diamond samples. A comprehensive study evaluating the effects of B-doping, crystallinity, surface termination, thickness and substrate material of diamond films on yield and yield degradation in the SEE reflection yields has been performed. In addition, SEE yields from commercial CVD diamond samples were analysed, after surface functionalization by hydrogenation, caesiation and lithiation. Moreover, the present study allowed for an improvement in the growth of thin NCD films, essentially through the optimization of the seeding processes. Finally, the development of techniques to manufacture free standing diamond films on silicon substrates were investigated, and preliminary SEE measurements in transmission were undertaken.
8
Thomson, Clint D. "Measurements of the Secondary Electron Emission Properties of Insulators". DigitalCommons@USU, 2005. https://digitalcommons.usu.edu/etd/2093.
Testo completoAbstract (sommario):
Measurements of the electron-induced electron emission properties of insulators are important to many applications including spacecraft charging, scanning electron microscopy, electron sources, and particle detection technology. However, these measurements are difficult to make since insulators can charge either negatively or positively under charge particle bombardment that in turn alters insulator emissions. In addition, incident electron bombardment can modify the conductivity, internal charge distribution, surface potential, and material structure in ways that are not well understood. A primary goal of this dissertation work has been to make consistent and accurate measurements of the uncharged electron yields for insulator materials using innovative instrumentation and techniques. Furthermore, this dissertation reports on the experimental work undertaken by our group to explore insulator charging rates as a function of incident electron energy and fluence. Specifically, these charging studies include: (i) the study of the effectiveness of charge-neutralization techniques such as low-energy electron flooding and UV light irradiation to dissipate both positive and negative surface potentials induced by incident electron irradiation, (ii) the exploration of several noncontacting methods used to determine insulator surface potentials and the insulator first and second crossover energies that are important in determining both the polarity and magnitude of spacecraft material potentials, (iii) the dynamical evolution of electron emissions and sample displacement current as a function of incident charge fluence and energy with ties to evolving surface potentials as an insulator reaches its current steady state condition, and (iv) the slow evolution of electron yields with continuous incident electron bombardment.
These charging data are explained in the context of available insulator charging models. Specific insulator materials tested included chromic acid anodized aluminum, RTVsilicone solar array adhesives, and KaptonTM on aluminum.
9
Haidara, Modibo. "Impulsions de Trichel dans le cyclohexane liquide et les gaz comprimés". Grenoble 1, 1988. http://www.theses.fr/1988GRE10160.
Testo completoAbstract (sommario):
Resultats d'etude de la conduction electrique de liquides non polaires tres purs (cyclohexane, n-propane) en geometrie pointe-plan, en fonction du rayon de courbure de la pointe et de la pression hydrostatique (p<->10**(7)pa)
10
Davies, Robert. "Measurement of Angle-Resolved Secondary Electron Spectra". DigitalCommons@USU, 1999. https://digitalcommons.usu.edu/etd/1698.
Testo completoAbstract (sommario):
Theoretical formulations of secondary electron emission over the past 20 years have exceeded the confirming ability of available measurements. An instrument has been developed and tested for the purpose of obtaining simultaneous angle- and energy-resolved (AER) secondary and backscattered electron measurements for energetic electrons incident on conducting surfaces. The instrument is found to be in good working order and the data quality found to be excellent for nearly all angles and energies investigated. A representative set of AER measurements has been acquired for 1500 e V electrons normally incident on polycrystalline gold. The data have been used to construct angle-resolved (AR) spectra and energy-resolved (ER) angular distributions, which have been examined both as surface plots and cross sections. Analysis of the measurements strongly suggests that secondary electrons comprise the bulk of emitted electrons at energies much greater than the traditionally accepted maximum secondary electron energy of 50 eV. Additional evidence suggests the ability to investigate dominant secondary and backscattered electron production mechanisms in several energy domains.
11
Tucek, John Christopher. "Collision-induced secondary electron and negative ion emission from metallic surfaces". W&M ScholarWorks, 1997. https://scholarworks.wm.edu/etd/1539623909.
Testo completoAbstract (sommario):
Absolute yields of negative ions and secondary electrons resulting from collisions of positive sodium ions (Na{dollar}\sp{lcub}+{rcub}){dollar} with polycrystalline aluminum (Al) and molybdenum (Mo) surfaces and the Mo (100) surface have been measured as a function of the oxygen (O) coverage, from none up to several monolayers, for impact energies, E {dollar}<{dollar} 500 eV. Negative oxygen ions (O{dollar}\sp{lcub}-{rcub}){dollar} are found to be the dominant sputtered negative ions and for the three surfaces at all O coverages and Na{dollar}\sp{lcub}+{rcub}{dollar} impact energies. The O{dollar}\sp{lcub}-{rcub}{dollar} and secondary electron yields share a common impact energy threshold at {dollar}\rm E\sb{lcub}th{rcub}\approx 50{dollar} eV, and both have a strong dependence on the oxygen coverage of the surface.;The kinetic energy distributions of the secondary electrons and sputtered O{dollar}\sp{lcub}-{rcub}{dollar} were determined as functions of O coverages and impact energies. The O{dollar}\sp{lcub}-{rcub}{dollar} distributions are characterized by a narrow, low energy peak (at {dollar}\sim{dollar}1-2 eV) followed by a low level, high energy tail. The secondary electrons have a narrow (FWHM {dollar}\sim{dollar} 1-2 eV) kinetic energy distribution, centered essentially at the same most probable kinetic energy as the ions. The shapes of the respective distributions and the most probable kinetic energies are essentially invariant with the impact energy, O coverage and the metal surface.;The results were analyzed in terms of conventional collision cascade model, but the calculation could not be fitted to the experimental results. An electronic excitation mechanism is proposed to augment the collision cascade and to provide a mechanism for secondary electron emission. In the model, adsorbed O, which resides on the surface essentially as O{dollar}\sp{lcub}-{rcub},{dollar} is collisionally excited into an (MO{dollar}\sp{lcub}-{rcub})\sp*{dollar} repulsive state, and as the O{dollar}\sp{lcub}-{rcub}{dollar} exits the surface along the surface potential energy curve, it can decay by emission of an electron to the metal or to the vacuum, or it can survive as an ion. The parameters of this model can be adjusted such that the calculated kinetic energy distribution, together with that of the collision cascade, can reasonably reproduce the experimental observations for the ions and provide a reasonable fit to the corresponding electron kinetic energy distributions as well.
12
Chung, To Sang Marc. "Transport électronique et émission secondaire électronique dans un propulseur de Hall". Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSES077.
Testo completoAbstract (sommario):
L'essor des activités spatiales pour satellite a permis le développement de nombreuses technologies de propulseurs électriques. Parmi elles, le propulseur à courant de Hall connaît un intérêt grandissant de par son coût, ses caractéristiques de poussée et d'impulsion spécifique. Si cette technologie existe depuis au moins cinquante ans, il n'en demeure pas moins que simuler et comprendre son fonctionnement reste hors de portée. La dynamique des particules chargées en configuration de champs croisés ExB est riche d'instabilités dont le rôle dans le fonctionnement du propulseur n'a pas atteint un consensus scientifique. Cette thèse propose de reprendre l'approche appelée "Particle-in-cell"(PIC) qui consiste à suivre les trajectoires individuelles de particules chargées dans l'espace des phases soumises à un champ électrique solution de l'équation de Poisson et calculé sur une grille de calcul. Cette méthode numérique dans sa version explicite doit répondre à des contraintes de pas d'espace et de temps qui se durcissent avec l'augmentation de la densité électronique. En trois dimensions de l'espace, l'algorithme classique PIC ne peut être appliqué aux conditions réelles d'un propulseur. Une approche récente permet de contourner ce problème au moyen de méthodes numériques de grilles parcimonieuses, appelée "Sparse-PIC". Elle repose sur le principe d'annulation des erreurs de grille lorsque l'on combine des sous-grilles de maillage grossier afin de représenter la solution sur la grille de maillage fin. Les performances de calcul obtenues avec le code implémenté pendant la thèse ont permis d'appliquer cette nouvelle approche à une configuration de champs croisés ExB dans un modèle réduit de propulseur de HallThe boom in satellite space activities has led to the development of numerous electric thruster technologies. Among these, the Hall current thruster is attracting growing interest due to its cost, thrust and specific impulse characteristics. Although this technology has been around for at least fifty years, simulating and understanding its operation remains out of reach. The dynamics of charged particles in the ExB cross-field configuration are rich in instabilities whose role in thruster operation has not yet reached scientific consensus. In this thesis, we propose to take up the "Particle-in-cell" (PIC) approach, which consists in tracking the individual trajectories of charged particles in phase space subjected to an electric field that is a solution of Poisson's equation and calculated on a computational grid. In its explicit version, this numerical method has to meet space and time step constraints that harden with increasing electron density. In three spatial dimensions, the classical PIC algorithm cannot be applied to real thruster conditions. A recent approach, called "Sparse-PIC", circumvents this problem by means of sparse grid methods. It is based on the principle of cancelling grid errors when combining coarse-mesh sub-grids to represent the solution on the fine-mesh grid. The computational performance obtained with the code implemented during the thesis has enabled us to apply this new approach to an ExB cross-field configuration in a reduced Hall thruster model
13
Pitts, R. A. "Ion energy, sheath potential and secondary electron emission in the tokamak edge". Thesis, Royal Holloway, University of London, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508346.
Testo completo
14
Wu, Qiong. "Measurements and studies of secondary electron emission of diamond amplified photo cathode". [Bloomington, Ind.] : Indiana University, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3337275.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--Indiana University, Dept. of Physics, 2008.Title from PDF t.p. (viewed on Jul 29, 2009). Source: Dissertation Abstracts International, Volume: 69-12, Section: B, page: 7588. Adviser: Shyh-Yuan Lee.
15
Pintao, Carlos Alberto Fonzar. "Novo arranjo para determinar os coeficientes de emissão e a distribuição de energia dos elétrons secundários emitidos por sólidos". Universidade de São Paulo, 1996. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-14112007-091415/.
Testo completoAbstract (sommario):
Neste trabalho estudou-se um novo arranjo de medida para se obter a distribuição de energia dos elétrons secundários emitidos e os coeficientes de emissão por um sólido. Pelo fato deste arranjo permitir a medida direta do potencial de superfície no caso dos polímeros e da ddp de contato no caso dos metais, foi possível aplicar e descrever teoricamente o método de medida empregado para determinar o espectro energético dos secundários para a platina, Teflon-FEP, Mylar, PVDF- α, PVDF- β e polimero condutor. As cargas acumuladas durante a irradiação dos polímeros foram compensadas através do próprio feixe eletrônico. Este procedimento não é muito usual em relação aqueles aplicados na literatura e mostrou-se bastante eficaz. Pela primeira vez empregou-se o método dinâmico para determinar o coeficiente de emissão total em função da energia dos elétrons incidentes nos metais e verificou-se que estes resultados são idênticos aqueles obtidos pelo método do pulso. Um desdobramento natural ao aplicar o método dinâmico aos metais foram as medidas realizadas para camadas de ouro com espessura de 50 nm, 10 nm e 2,5 nm depositada sobre o Teflon-FEP, que deram origem ao modelo das duas camadas na interpretação dos resultados experimentais.A new arrangement of measure was developed in this study, in order to obtain the energy distribution from the emitted secondaries and the emission yields by a solid. Because this arrangement allowed the direct measurement of the surface potential, in the case of metals, it was possible to apply and describe theoretically the mensuration method employed, to determine the energy distribution of the secondaries to platinum, Teflon-FEP. Mylar, PVDF α, PVDF- β and thie conducting polymer. The charges accumulated during the polymers irradiation were compensated through the electronic beam itself. This proceeding is not very usual, as referring to the ones applied in literature, and it proved to be very efficacious. The dynamic method was employed for the first time to metals in order to determine the total emission yield in function of the energy of the inciding electrons and it was found out that these results were identical to the ones obtained through the pulse method. As a natural development, by applying the dynamic method to metals, the measurements achieved were also applied to golden layers 50 nm, 10 nm and 2,5 nm wide deposited on Teflon-FEP, and they gave birth to the two layers, in the interpretation of the experimental results.
16
Kite, Jason T. "Secondary Electron Production and Transport Mechanisms By Measurement of Angle-Energy Resolved Cross Sections of Secondary and Backscattered Electron Emission from Gold". DigitalCommons@USU, 2006. https://digitalcommons.usu.edu/etd/2089.
Testo completoAbstract (sommario):
This work provides information about interactions that produce emitted electrons from polycrystalline Au. Emission energy- angle- dependent electron spectra from a polycrystalline Au surface have been measured at several incident electron beam energies. The range of incident energies (~100 eV to 2500 eV) extends from below the first crossover energy, through Emaxo, to above the second crossover energy. The conventional distinction between secondary electrons (SE) (50 eV) is found to be crude for the investigation of electron yields using these energy- angle- resolved measurements. A more realistic boundary occurs at the local minima of the emission spectra; this feature is studied as a function of incident energy and emission angle. In addition, deviations observed in the angular resolved emission spectra from isotropic behavior suggests that residual signatures exist in the emission spectra resulting from the anisotropic SE production mechanisms. Based on the disparity between our observations and recent modeling of the emission spectra, the most recent theory and simulation studies may overestimate the occurrence of randomizing collisions of scattered secondary electrons in the model of the transport mechanism. Finally, description of extensive modification to instrumental and analysis methods are described, and their effectiveness is evaluated.
17
Pigeon, Valentin. "Laser induced fluorescence study of plasma-insulator wall interaction involving secondary electron emission". Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0307.
Testo completoAbstract (sommario):
Dans les propulseurs à effet Hall, l’interaction entre le plasma et les parois en céramique a un impact sur la durée de vie et les performances de ces machines. Ceci est dû en partie à l’émission d’électrons secondaires (EES), capable de refroidir le plasma et peut déclencher de la turbulence et des instabilités. Pour ces raisons, il est nécessaire de comprendre l’interaction plasma-céramique et d’évaluer l’impact de l’EES. Cette étude est destinée principalement à caractériser les gaines plasma faisant face aux céramiques des propulseurs à effet Hall. Celles-ci sont comparées aux gaines d’autres matériaux utilisés en physique des plasmas en précisant l’influence de l’EES. La partie expérimentale de cette étude repose principalement sur le diagnostic de fluorescence induite par laser permettant de sonder les gaines plasmas de manière non-intrusive. La structure des gaines, les variations de la densité ionique et la forme des fonctions de distribution ionique sont présentées et discutées. Il apparaît que la gaine varie d’un matériau à l’autre et que l’EES des céramiques de propulseurs est plus faible que celle des autres céramiques étudiées. Ce dernier résultat est cohérent avec de précédentes études. D’autre part, la densité ionique atteint un maximum près de l’entrée de la gaine, un résultat non prédit par les théories de gaine. Les résultats expérimentaux sont comparés à un modèle de gaine 1D cinétique et à des simulations cinétiques, qui tous deux utilisent des taux d’émission secondaire disponibles dans la littérature. Enfin, la première étape pour la mesure de gaines plasma hautement émissive par fluorescence induite par laser est présentéeIn Hall-effect ion thrusters, the interaction between the plasma and the ceramic walls has an impact on the devices’ lifetime and performances. This is partially due to the secondary electron emission (SEE), a phenomenon that may cool down the plasma, resulting in a lower ionization rate, and may trigger turbulence and instabilities. For these reasons, it is necessary to understand the plasma-ceramic wall interaction and evaluate the impact of the SEE. This study mainly focuses on plasma sheaths – the fundamental mechanism involved in plasma-wall interaction – standing in front of Hall thrusters’ ceramics. Those sheaths are compared to other materials’ ones used in plasma devices, and the influence of the SEE on them is studied. The experimental part of the study mainly relies on the laser induced fluorescence diagnostic that allows to probe plasma sheaths in a non-intrusive way. The sheaths’ structure, the ion density variations and the ion distribution functions’ shape are presented and discussed. It is shown that the sheath is material dependent and that the thrusters’ ceramics’ SEE is lower than for the other studied ceramics, which is coherent with previous measurements. Also, a peak in the ion density is observed near the sheath entrance, a result not captured by the classical sheath theory. These experimental results are compared with a 1D kinetic sheath model and kinetic simulations that use the SEE yields found in the literature. Finally, the first step of highly emissive plasma sheath measured with laser induced fluorescence is presented
18
Cai, Linghui, e 蔡凌辉. "Monte Carlo simulation of positron induced secondary electrons in thincarbon foils". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B45460863.
Testo completo
19
Travia, Anderson Dingfelder Michael. "Interaction cross sections needed for simulation of secondary electron emission spectra from thin metal foils after fast proton impact". [Greenville, N.C.] : East Carolina University, 2009. http://hdl.handle.net/10342/1906.
Testo completoAbstract (sommario):
Thesis (M.S.)--East Carolina University, 2009.Presented to the faculty of the Department of Physics. Advisor: Michael Dingfelder. Title from PDF t.p. (viewed Apr. 23, 2010). Includes bibliographical references.
20
Yang, Bin, e 杨彬. "Positron beam study of carbon foil and titanium dioxide nanotubes, andproposing a design of a lifetime positron beam based on secondaryelectrons emission from carbon foil". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B47160287.
Testo completoAbstract (sommario):
Secondary electron (SE) emission from thin carbon foils induced by 1-20 keV
positrons has been investigated over a range of nominal foil thicknesses from 1.0 to 5.0 μg/cm2. The measurement of SEs was carried out in forward geometry using a microchannel plate as a detector. The SE yield γ has been measured as a function of beam energy and compared with some Monte Carlo simulation results. We also present in this thesis the material parameter Λ=? / (dE / dx) and the emitted SE energy spectra. Forincident positron energy of 5 keV or higher, the distribution is found to be characterizedby the Sickafus form, AEm and m is close to 1. For low energy incident positrons however, another form, Bexp(E / t) , is proposed for describing the SE distribution. The maximum scattering angle for SEs emitted from 5.0 μg/cm2 is found to be around 60°.
Measurements of energy loss and energy loss straggling for 1-10 keV positrons
passing through thin carbon foils of different thicknesses ranging from 1.0 to 5.0 μg/cm2 are present in this thesis. The stopping power dE / dx and positron transmission coefficient have also been investigated as a function of incident positron energy and foil thickness. Particularly, our experimental results are compared with those from Monte Carlo simulation and theory with a view to providing a way to determine the real thickness of carbon foil. The ratio of the energy loss straggling to the foil thickness seems to have a linear relation with the beam energy. The transmitted positrons after passing through 5.0 μg/cm2 C-foil have a small scattering angle which is less than 10°.
Titanium dioxide nanotube arrays fabricated by anodization of titanium foil and
annealed at different temperatures were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and positron annihilation spectroscopy (PAS). The crystallization process and morphological change of the nanotubes have been discussed. It is found that anatase (101) only appeared on the walls of the nanotube. The atomic concentration of fluoride and the ratio of Ti/O decreased when the annealing temperature increased. Vacancy type defects were found to diffuse toward the surface when the samples were annealed at 200°C and 400°C and healing of vacancies occurred at 600°C. In addition, the fluoride may form some complexes with vacancies on the surface hence lowering the value of the S parameter.
A new design of the lifetime positron beam based on the SE emission is proposed.
The observed experimental results and simulation results make it possible to construct a new type of high resolution (<250ps) lifetime positron beam. In addition, how rastering of the positron beam can be used to accurately locate the position of the C-foil is also shown; a feature that will be of value in setting up a positron lifetime system. Such a lifetime system is expected to be much simpler in construction than existing beam based lifetime spectroscopy systems.published_or_final_version
Physics
Doctoral
Doctor of Philosophy
21
Ross, William Charles. "Monte Carlo calculations of inner shell ionization profiles and the secondary electron background in electron spectroscopy". Thesis, University of York, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298446.
Testo completo
22
Davies, Robert. "An Instrument for Experimental Secondary Electron Emission Investigations, with Application to the Spacecraft Charging Problem". DigitalCommons@USU, 1996. https://digitalcommons.usu.edu/etd/1697.
Testo completoAbstract (sommario):
Secondary electron emission (SEE) and incident-particle backscattering are important processes accompanying the impact of energetic electrons and ions on surfaces. The phenomena play a key role in the buildup of electrical charge on spacecraft surfaces, and are therefore of particular interest to scientists attempting to model spacecraft charging. In response to a demonstrated need for data, techniques for determining total secondary electron (SE) and backscatter (BS) yields (del) and (neu), and associated scattering-angle-resolved,scattering-energy-resolved, and simultaneous angle-energy-resolved yields have been developed. Further, an apparatus capable of making the necessary measurements for experimental determination of these quantities---for conducting materials in an ultra-high vacuum environment-has been designed, constructed, and partially tested. The apparatus is found to be in working order, though in need of fine-tuning, and the measurement technique successful.
Investigations using a 1-3 Kev beam of monoenergetic electrons normally incident on bulk AI have been undertaken with the new apparatus. Electron-stimulated desorption of surface contaminants has been observed, as has been beam-induced carbon deposition, and an empirical model describing the resulting dynamic evolution of (del)is presented. Totalb and 11 values obtained in the present investigation are found to be in qualitative agreement with the results of previously reported investigations, though quantitative disagreement of b-values is substantial. Specifically, evidence is presented suggesting that previously reported SE yields for clean AI under electron bombardment (in the 1-3 Kev energy range) are in error by as much as 30 %.
23
Seymour, D. L. "A secondary electron emission investigation of the initial stages of oxidation of some metal surfaces". Thesis, Keele University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328716.
Testo completo
24
Ayzatskiy, N., A. Dovbnya, V. Zakutin, N. Reshetnyak, V. Romas'ko, I. Chertishchev, V. N. Boriskin, V. Mitrochenko, A. B. Galat e I. Khodak. "Experimental investigation on the time characteristics of an electron beam formed in the magnetron gun with a secondari-emission cathode". Thesis, Национальный научный центр "Харьковский физико-технический институт" (ННЦ ХФТИ), 2007. http://openarchive.nure.ua/handle/document/9244.
Testo completo
25
Nickles, Neal E. "The Role of Bandgap in the Secondary Electron Emission of Small Bandgap Semiconductors: Studies of Graphitic Carbon". DigitalCommons@USU, 2002. https://digitalcommons.usu.edu/etd/1696.
Testo completoAbstract (sommario):
The question of whether the small bandgaps of semiconductors play a significant role in their secondary electron emission properties is investigated by studying evaporated graphitic amorphous carbon, which has a roughly 0.5 eV bandgap, in comparison with microcrystalline graphite, which has zero bandgap. The graphitic amorphous carbon is found to have a 30% increase in its maximum secondary electron yield over that of two microcrystalline graphite samples with comparable secondary electron yields: highly oriented pyrolytic graphite and colloidal graphite. The potentially confounding influence of the vacuum level has been isolated through the measurement of the photoelectron onset energy of the materials. Other less significant materials parameters are also isolated and discussed. Based on these measurements, it is concluded the magnitude of bandgap may have an appreciable effect on the magnitude of the secondary electron yield and further studies of this effect with annealed graphitic amorphous carbon are warranted. In support of this work, a hemispherical two-grid, retarding field electron energy analyzer has been designed, constructed, and characterized for the present work. The advantages and disadvantages of the analyzer are discussed in comparison to other methods of measuring secondary electron emission. The analyzer has a resolution of ±(1.5 eV + 4% of the incident electron energy). A novel effort to derive theoretical, absolute correction factors that compensate for electron losses within the analyzer, mainly due to the grid transmission, is presented. The corrected secondary electron yield of polycrystalline gold is found to be 30% above comparable experimental studies. The corrected backscattered electron yield of polycrystalline gold is found to be 14% above comparable experimental studies. Corrected secondary yields for the microcrystalline graphite samples are found to range from 35-70% above those found in five experimental studies in the literature. The theoretical correction factors are estimated to have a 4-6% uncertainty. Reasons for the large discrepancy in yield measurements with the analyzer are discussed and thought to be due mainly to the lack of similar corrective factors in the previous studies. The supporting instrumentation is fully characterized, including a detailed error analysis.
26
Takamura, S., S. Mizoshita e N. Ohno. "Suppression of secondary electron emission from the material surfaces with grazing incident magnetic field in the plasma". American Institute of Physics, 1996. http://hdl.handle.net/2237/6993.
Testo completo
27
Leiber, Benjamin [Verfasser], e G. [Akademischer Betreuer] Drexlin. "Investigations of background due to secondary electron emission in the KATRIN-experiment / Benjamin Leiber. Betreuer: G. Drexlin". Karlsruhe : KIT-Bibliothek, 2014. http://d-nb.info/1056955848/34.
Testo completo
28
Costa, i. Bricha Elm. "Computer simulation of a capacitively coupled GEC cell". Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368881.
Testo completo
29
Villemant, Marc. "Modélisation et caractérisation expérimentale de l’influence de l’émission électronique sur le fonctionnement des propulseurs à courant de Hall". Thesis, Toulouse, ISAE, 2018. http://www.theses.fr/2018ESAE0038.
Testo completoAbstract (sommario):
Les propulseurs plasma à courant de Hall sont aujourd’hui une technologie mature et couramment utilisée dans l’industrie spatiale pour la mise à poste et le contrôle d’orbite de satellites. Malgré cela, la compréhension de la physique régissant le fonctionnement de ces propulseurs et encore lacunaire. Des phénomènes tels que le transport anormal des électrons dans le canal du propulseur ou la dépendance des performances du propulseur au matériau de paroi ne sont pas compris. Par conséquent le développement et la qualification de nouveaux propulseurs passent par de longues études empiriques sans garantie de succès. La compréhension de la physique des plasmas de propulseurs est donc une problématique clé pour permettre le développement et l’amélioration de cette technologie.Cette thèse consiste en la caractérisation par la modélisation et par des mesures expérimentales de l’interaction entre le plasma d’un propulseur à courant de Hall et les parois dudit propulseur. Cette thèse s’est concentrée sur le phénomène d’émission électronique induite par impact d’électrons (i.e. l’émission d’électrons par les parois du propulseur lorsque celle-ci est soumise à un flux incident d’électrons).La thèse s’est déroulée en trois étapes. Dans un premier temps un modèle d’émission électronique adapté au besoin des modélisations particulaires de plasma de propulseur a été développé et validé par comparaison à des données expérimentales réalisées à l’ONERA. Dans un second temps, ce modèle d’émission électronique a été introduit dans une simulation particulaire de plasma de propulseur développé au Laplace et modifié pour les besoins de cette thèse. Enfin une étude paramétrique a été réalisées afin d’évaluer l’influence de l’émission électronique sur le comportement global du plasma de propulseur.La première partie de cette thèse a permis de réaliser la caractérisation de l’émission électronique pour des matériaux représentatifs du canal des propulseurs à courant de Hall (silice et nitrure de bore). Par ailleurs, un travail de mesure et de calibration a été réalisé afin de caractériser le rendement énergétique de l’interaction entre une population d’électrons et une paroi. Ces nouvelles mesures et ce nouveau protocole de mesure ont donné lieu à la publication de deux articles. La seconde partie de cette thèse a permis de réaliser un modèle détaillé d’émission électronique adapté aux contraintes des modélisations particulaire (temps de calcul réduit, dépendance à différents paramètres physiques, etc.). Cette thèse a permis de montrer un impact non-négligeable de l’émission électronique sur le bilan énergétique du propulseur et sur les fonctions de distributions des ions et des électrons dans le plasma ¬du propulseurNowadays, plasma Hall thrusters are used in space industry for satellites orbit rising and satellites attitude control. Nonetheless, the comprehension their physical functioning remains patchy. Several phenomena such as abnormal electron mobility or the thrusters performance dependency to wall material are still not understood. Consequently the current process to improve and qualify Hall thrusters are involving expansive and time-consuming experimental validation which, in the end, does not ensure the release of an operational thruster. Consequently, plasma behaviour in Hall thruster is a key topic of research, which could lead to non-negligible improvement in Hall thruster technology development.This Ph.D. consists in the modelling and characterization of plasma/wall interaction in Hall thrusters and its impact on Hall thruster’s performance. This Ph.D. has focused on the influence of the electron emission under electron impact on Hall thruster’s performances. It has been divided into three parts. Firstly, an experimental investigation has been carried out in order to obtain reference data on materials commonly used as plasma thruster wall (bore nitride and silicon dioxide). A literature review has been made in order to find a theoretical basis fitted to the elaboration of an electron emission model fitting the requirement of a particle in cell simulation of a Hall thruster. In second part, a detailed electron emission model based on this literature review and validated by comparison to experimental data and to a Monte-Carlo model developed in ONERA (called OSMOSEE) has been developed. This model offers the possibility to describe electron emission yield, angular and energy distribution of emitted electrons depending on various physical parameters (e.g. incident electron energy, incident electron angle, impinged material, etc.). Besides, as it is an analytical model, it computes in a reduced time (a few minutes to one hour). In a third and last part, this electron emission model has been implemented in a Particle-In-Cell (PIC) simulation of Hall thruster’s plasma and a parametric study has been carried out in order to characterize the influence of electron emission phenomenon on global plasma behaviour. This parametric study has shown that electron emission has a non-negligible impact on energy balance at plasma/wall interface and on electron distribution function in the plasma, which can’t be considered as Maxwellian
30
Bieber, Jay A. "Design and Simulation of a Miniature Cylindrical Mirror Auger Electron Energy Analyzer with Secondary Electron Noise Suppression". Scholar Commons, 2017. https://scholarcommons.usf.edu/etd/7393.
Testo completoAbstract (sommario):
In the nanoscale metrology industry, there is a need for low-cost instruments, which have the ability to probe the structrure and elemental composition of thin films. This dissertation, describes the research performed to design and simulate a miniature Cylindrical Mirror Analyzer, (CMA), and Auger Electron Spectrometer, (AES). The CMA includes an integrated coaxial thermionic electron source. Electron optics simulations were performed using the Finite Element Method, (FEM), software COMSOL. To address the large Secondary Electron, (SE), noise, inherent in AES spectra, this research also included experiments to create structures in materials, which were intended to suppress SE backgound noise in the CMA. Laser Beam Machining, (LBM), of copper substrates was used to create copper pillars with very high surface areas, which were designed to supress SE’s. The LBM was performed with a Lumera SUPER RAPID‐HE model Neodymium Vanadate laser. The laser has a peak output power of 30 megawatts, has a 5x lens and a spot size of 16 μm. The laser wavelength is in the infrared at 1064 nm, a pulse width of 15 picoseconds, and pulse repetition rate up to 100 kHz. The spectrometer used in this research is intended for use when performing chemical analysis of the surface of bulk materials and thin films. It is applicable for metrology of thin films, as low as 0.4 nm in thickness, without the need to perform destructive sample thinning, which is required in Scanning Tranmission Electron Microscopy, (STEM).
The spectrometer design is based on the well known and widely used coaxial cylinder capacitor design known as the Cylindrical Mirror Analyzer, (CMA). The coaxial tube arrangement of the CMA allows for placing an electron source,which is mounted in the center of the inner cylinder of the spectrometer. Simulation of the electron source with an Einzel Lens was also performed. In addtion, experiments with thin film coatings and Laser Beam Machining to supress Secondary Electron emission noise within the Auger electron spectrum were completed.
Design geometry for the miniature CMA were modeled using Computer Aided Design, (CAD). Fixed Boundary Conditions, (BC), were applied and the geometry was then meshed for FEM. The electrostatic potential was then solved using the Poisson equation at each point. Having found the solution to the electrostatic potentials, electron flight simulations were performed and compared with the analytical solution. From several commercially available FEM modeling packages, COMSOL Multiphysics was chosen as the research platform for modeling of the spectrometer design. The CMA in this design was reduced in size by a factor of 4 to 5. This enabled mounting the CMA on a 2 ¾ in flange compared to the commercial PHI model 660 CMA which mounts onto a 10 in flange. Results from the Scanning Electron Microscopy measurements of the Secondary Electron emission characteristics of the LBM electron suppressor will also be presented.
31
Saion, Elias bin. "On microdosimetry of neutrons of selectable energy in mixed (n,y) fields". Thesis, University of St Andrews, 1989. http://hdl.handle.net/10023/2640.
Testo completoAbstract (sommario):
Biological damage of tissue due to intermediate energy neutrons is generally known to be very important in radiobiology and radiation protection. However, there is no suitable method to determine the quality of these neutrons in particular in the working environment of mixed (n,y) radiation fields. In this thesis, an attempt is made to develop a dosimeter based on microdosimetric principles which has the capability for such a purpose. With this object the basic concepts of microdosimetry are reviewed and discussed with emphasis on their application for radiation protection and in designing of the dosimeter. Microdosimetry based on low pressure tissue-equivalent proportional counters (TEPCs) is a powerful technique for determining microscopic distributions of energy deposition and quality of ionizing radiations. However the energy deposition spectra of intermediate energy neutrons in mixed fields of fast neutrons can only be measured using TEPC in co-axial double cylindrical form by an appropriate choice for the thickness of the common tissue-equivalent (TE) dividing wall separating the inner and outer counters and by appropriate use of coincidence/anti-coincidence pulse arrangements. An analytical calculation for the response of the inner counter operating in coincidence/anti-coincidence modes with the outer counter was developed. However there will be some events, due to fast neutrons, which will contribute to the signals from intermediate energy neutrons and which cannot be removed by anti-coincidence. For these analytical corrections must be made. Also, the events associated with the dividing wall inherent in the system can contribute to the response of the inner counter and must be corrected by calculation. The calculation was possible due to the fact that recoil particles from intermediate energy neutron interactions have effective stopping powers and projected ranges which differ significantly from the continuous slowing down approximation (CSDA) values. By incorporating these the basic CSDA formulae for energy deposition spectra of neutrons could be extended down to intermediate energy neutrons of about 1 keV. A prototype co-axial double cylindrical TEPC capable of separating the component of neutrons (≤ 850 keV) in mixed (n,y) radiation fields was manufactured and tested. The thin wall dividing the inner and outer counters was fabricated from the standard A-150 TE plastic with the thickness equivalent to the range of 850 keV protons. The operational characteristics of the dosimeter were studied to determine its applicability for use in microdosimetry. The gas gain of the inner and outer TEPCs was measured at various simulated mean chord lengths and applied voltages. The results can be expressed according to Campion's equation within a given range of the electric field strength. The resolution of the inner TEPC measured at the operating voltages is in agreement with the theoretical prediction. A series of microdosimetric experiments were performed with mixed fields of 60Co gamma-rays and neutrons from the UTR-300 nuclear reactor and from 252Cf and 241Am-Be radioactive sources. Discrimination against fast neutrons of energy > 850 keV was achieved using an anti-coincidence unit specially designed for better efficiency of data acquisition. Discrimination against fast electrons due to photon interactions was also achieved. Spectra with anti-coincidence are dominated by slow protons and electrons. Their mean lineal energies are higher than those of spectra without anti-coincidence. The quality factor and dose equivalent for spectra with anti-coincidence are higher than the spectra without anticoincidence indicating the importance of intermediate energy neutrons in mixed fields. The quality factor and the corresponding dose equivalent corrected for saturation of lineal energy corresponding to 2 nm of ionization spacing is consistently higher than those derived from the absorbed dose based formulae, the biophysical implications of which are discussed. Suggestion for future developments for microdosimetry of intermediate energy neutrons in mixed fields are made and discussed.
32
Tsuchiya, Kenji, Hitoshi Okubo, Tsugunari Ishida, Naoki Hayakawa e Hiroki Kojima. "Development Process of Impulse Surface Flashover on Alumina Dielectrics in Vacuum". IEEE, 2011. http://hdl.handle.net/2237/20729.
Testo completo
33
Pierron, Juliette. "Modèle de transport d'électrons à basse énergie (~10 eV- 2 keV) pour applications spatiales (OSMOSEE, GEANT4)". Thesis, Toulouse, ISAE, 2017. http://www.theses.fr/2017ESAE0024/document.
Testo completoAbstract (sommario):
L’espace est un milieu hostile pour les équipements embarqués à bord des satellites. Les importants flux d’électrons qui les bombardent continuellement peuvent pénétrer à l’intérieur de leurs composants électroniques et engendrer des dysfonctionnements. Leur prise en compte nécessite des outils numériques 3D très performants, tels que des codes de transport d’électrons utilisant la méthode statistique de Monte-Carlo, valides jusqu’à quelques eV. Dans ce contexte, l’ONERA a développé, en partenariat avec le CNES, le code OSMOSEE pour l’aluminium. De son côté, le CEA a développé, pour le silicium, le module basse énergie MicroElec dans le code GEANT4. L’objectif de cette thèse, dans un effort commun entre l’ONERA, le CNES et le CEA, est d’étendre ces codes à différents matériaux. Pour ce faire, nous avons choisi d’utiliser le modèle des fonctions diélectriques, qui permet de modéliser le transport des électrons à basse énergie dans les métaux, les semi-conducteurs et les isolants. La validation des codes par des mesures du dispositif DEESSE de l’ONERA, pour l’aluminium, l’argent et le silicium, nous a permis d’obtenir une meilleure compréhension du transport des électrons à basse énergie, et par la suite, d’étudier l’effet de la rugosité de la surface. La rugosité, qui peut avoir un impact important sur le nombre d’électrons émis par les matériaux, n’est habituellement pas prise en compte dans les codes de transport, qui ne simulent que des matériaux idéalement plats. En ce sens, les résultats de ces travaux de thèse offrent des perspectives intéressantes pour les applications spatialesSpace is a hostile environment for embedded electronic devices on board satellites. The high fluxes of energetic electrons that impact these satellites may continuously penetrate inside their electronic components and cause malfunctions. Taking into account the effects of these particles requires high-performant 3D numerical tools, such as codes dedicated to electrons transport using the Monte Carlo statistical method, valid down to a few eV. In this context, ONERA has developed, in collaboration with CNES, the code OSMOSEE for aluminum. For its part, CEA has developed for silicon the low-energy electron module MicroElec for the code GEANT4. The aim of this thesis, in a collaborative effort between ONERA, CNES and CEA, is to extend those two codes to different materials. To describe the interactions between electrons, we chose to use the dielectric function formalism that enables to overcome of the disparity of electronic band structures in solids, which play a preponderant role at low energy. From the validation of the codes, for aluminum, silver and silicon, by comparison with measurements from the experimental set-up DEESSE at ONERA, we obtained a better understanding of the transport of low energy electrons in solids. This result enables us to study the effect of the surface roughness. This parameter, which may have a significant impact on the electron emission yield, is not usually taken into account in Monte Carlo transport codes, which only simulate ideally flat materials. In this sense, the results of this thesis offer interesting perspectives for space applications
34
Tsuchiya, Kenji, Hitoshi Okubo, Tsugunari Ishida, Hidenori Kato e Katsumi Kato. "Influence of Surface Charges on Impulse Flashover Characteristics of Alumina Dielectrics in Vacuum". IEEE, 2009. http://hdl.handle.net/2237/14600.
Testo completo
35
Monart, Brigitte. "Etude experimentale del'emission secondaire (ions atomiques et moleculaires, agregats, electrons) induite par bombardement de surface par des ions lourds energetiques ( equiv. A mev/u) : effets de l'etat de charge des projectiles". Paris 7, 1988. http://www.theses.fr/1988PA077121.
Testo completoAbstract (sommario):
Etude de l'emission secondaire en fonction de la vitesse en projectile, de l'angle d'incidence du faisceau par rapport a la cible (minerale ou organique) et surtout de l'etat de charge au projectile, par spectrometrie de masse a temps de vol principalement: cette emission depend fortement de la charge du projectile et aussi du changement d'etat de charge a l'interieur du materiau. Interpretation des resultats a l'aide du modele de maynard et al. , en supposant l'existence d'une profondeur d'interaction ion primaire-materiau qui depend du type d'ions secondaires et de la charge de l'ion incident
36
Oving, Peter Johan. "Etude et réalisation d'un canon à électrons de grande surface à utilisation industrielle". Grenoble 1, 1989. http://www.theses.fr/1989GRE10102.
Testo completoAbstract (sommario):
Les canons etudies produisent un faisceau d'electrons de 100 a 200 voire 250 kev d'energie. Le faisceau est genere par l'emission d'electrons secondaires lors d'un impact d'ions energetiques sur une cible. L'etude d'un petit canon (section de faisceau: 815 cm) a permis d'ameliorer la conception des canons a electrons a emission secondaire. En parallele, une etude a ete faite sur un banc d'essais de grandes dimensions (section de faisceau: 18155 cm). Les resultats ont montre la possibilite d'un changement d'echelle d'un facteur dix. L'ensemble des resultats a ete utilise pour la fabrication d'un canon a electrons a emission secondaire de taille industrielle (section de faisceau: 35150 cm). Les resultats de fonctionnement du grand canon ont cependant montre que ce type de canon n'est pas encore adapte a une utilisation en milieu industriel, puisqu'il y a des problemes de tenue de la tension et que le rendement global du canon est faible. Les experiences ont confirme la valeur annoncee du rendement d'emission d'electrons secondaires qui est de 3,0 a 3,5 electrons par ion incident, pour la tranche d'energie etudiee
37
BANOUNI, MOSTAFA. "Effets de la topographie de surface induite par impact d'ions lourds sur la spectrometrie d'electrons secondaires resolue angulairement". Toulouse 3, 1986. http://www.theses.fr/1986TOU30135.
Testo completoAbstract (sommario):
Influence de la topographie de surface induite par bombardement ionique sur l'emission electronique secondaire. Presentation des resultats et description de modeles rendant compte des principeles topographiques observees sur differentes cibles d'aluminium bombardees par des ions argon et xenon de 25 kev
38
Zhang, Yu, e 張毓. "Investigation of the lifetime spectrum of monoenergetic positrons in silicon involving secondary electrons emission from a carbon foil as start signal, and positron annihilation spectroscopy studies of strontium titante". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/197507.
Testo completoAbstract (sommario):
A proposed design of the variable energy positron annihilation spectroscopy (VEPALS) system based on secondary electron (SE) emission from a thin carbon foil has been investigated practically. The SE yield and the positron transmission coefficient were investigated as a function of the positron beam energy, the annular electrode potentials, and the column lengths of the annular electrode. The positron lifetime spectra of single crystal p-type silicon(Si) sample under different annular electrode potentials were analyzed. The result gives a supposed annular electrode potential of 1.5 kV. In view of this, the positron lifetime spectra were measured under different positron beam energy by fixing the annular electrode potential. It can be seen that all the spectra have the main p-type Si bulk lifetime component of 234 ps occupying more than 60% intensities. The intensity of the 234 ps component reaches up to 84.5 ±1.3 % when the positron beam energy is 15 keV. Further, the origin of the satellite peaks in the positron lifetime spectra are also investigated. It has been shown that the satellite peaks is attributed to the overflowing positrons on the MCP detector.
The single crystal strontium titanate (STO) substrates after vacuum annealing treatment have been investigated in detail by several experimental techniques. The crystallization changes induced by the vacuum annealing were investigated by X-ray diffraction(XRD). Secondary phases were occurred after annealing treatment. The measured X-ray photoelectron spectroscopy (XPS) at O1s and C1s core levels were analyzed. The additional peaks after annealing are attributed to hydroxyl species, C-OH compounds, and carbonates. The variable energy Doppler broadening spectroscopy (VEDBS) and the traditional coincidence positron annihilation lifetime spectroscopy (PALS) were used to probe defects in STO samples. For long annealing time samples, the S parameters decrease below the reference level. The S-Wplot suggests that almost the same type of vacancy defects were induced during the annealing treatment. The positron lifetime results suggest that the main defects in annealed samples are oxygen monovacancies or divacancies and Sr-O vacancy complexes. The sample with annealing time of 110h has minimum positron effective diffusion length and maximum average lifetime, which is attributed to the increase of the vacancy-type defects during the long annealing treatment.published_or_final_version
Physics
Master
Master of Philosophy
39
Vidovic, Zvonimir. "Etude la multiplicité de l'émission éléctronique secondaire de cibles minces de carbone sous l'impact d'ions H0, H2+, H3+ et d'ions moléculaires d'énergie de l'ordre du MeV". Phd thesis, Université Claude Bernard - Lyon I, 1997. http://tel.archives-ouvertes.fr/tel-00108534.
Testo completoAbstract (sommario):
Ce travail experimental est consacre a l'etude de la multiplicite des electrons secondaires emis par des cibles minces de carbone bombardees par des protons, des atomes H0 et des ions moleculaires H2+ et H3+ d'energie variant de 0.25 a 2.2 MeV.Le phenomene d'emission electronique secondaire par les surfaces des solides a l'impact de projectiles rapides resulte des interactions inelastiques des projectiles avec les electrons du solide. Une description phenomenologique te un rappel des differents modeles theoriques sont rassembles dans un premier chapitre.
Le second chapitre est consacre a la description du dispositif experimental utilise pour la mesure evenement par evenement du nombre d'electrons emis par les deux faces d'une cible mince de carbone lors du passage des projectiles incidents. Le traitement informatique des donnees experimentales, necessaire a la determination des distributions statistiques des electrons emis est egalement presente.
L'emission electronique induite par des atomes H0 a ete mesuree en correlation avec l'etat de charge des projectiles emergeant des cibles minces. Ces experiences, dont les resultats sont presentes dans le chapitre trois, nous ont permis de montrer le role particulier de l'electron d'un projectile selon qu'il reste ou non lie au projectile.
Le chapitre quatre est consacre a l'emission electronique induite par des ions polyatomiques H2+ et H3+. Les resultats sont intepretes en termes d'effets collectifs dans les interactions de tels ions avec les solides. le role de la proximite des protons, fragments des ions moleculaires, sur l'amplitude de ces effets collectifs est montre a partir des distributions statistiques des electrons secondaires emis par la face d'emergence des cibles.
Ces experiences ont permis de mettre en evidence des aspects particuliers des interactions d'atomes et d'ions polyatomiques avec les solides.
40
Fearn, Sarah. "A SIMS based bevel-image technique for the analysis of semiconductor materials". Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312125.
Testo completo
41
Lewis, Christopher James. "Development of a Methodology for Numerical Simulation of a D C ARC Discharge in a Liquid Dielectric". BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/2394.
Testo completoAbstract (sommario):
The majority of literature regarding the numerical simulation of arc discharges in gaseous environments has used a plasma physics approach. Virtually all simulations treat the discharge as an idealized gaseous plasma, which can be described by temperature, pressure, and electric field. This approach can work well if the media is a shielding gas such as Argon; however, the approach does not work well for processes such as underwater welding, EDM, and underwater discharges used to generate high purity particles. The reason these discharges do not have many extensive simulation efforts as described in the literature is because they occur in liquid dielectric media (Oil and water) which complicates the simulation efforts. Most research efforts in these areas describe experimental methods to evaluate discharge properties In this research a new method to investigate discharges in a dielectric media using an electrostatic and particle physics approach is proposed and validated. A commercial code that has been developed to simulate charged particle beams, dielectric materials, and perform multi-physics analyses, is the Vector Fields suite of solvers from Cobham Technical Services. This research demonstrates a simulation methodology that can be used to simulate a DC electric arc discharge in a lossy dielectric media using the Vector Fields environment. This simulation is the first of its kind to simulate this type of a discharge with a commercial FEA code. As such there are some limitations to the simulation. However, the simulation can be used to investigate the following:
1.Any metal, electrode geometry, discharge gap, or dielectric media can be studied
2.Primary Beam Physics
– Electron velocity/acceleration (direct calculation of electron temperature)
– Energy deposition on the anode from all emission sources
– Effect of dielectric media on beam physics (trajectories, velocity, constriction, beam induced magnetic fields, space chare, and secondary emission)
– Beam current
– Particle trajectories (including relativistic effects)
3. Secondary Particle Generation and physics
– Atomic species (neutral particles or ions) and secondary electron emission
– Particle trajectories
– Back ion bombardment on the cathode
42
SANTOS, ROBINSON A. dos. "Estudo da influência de impurezas e da qualidade das superfícies em cristais de brometo de tálio para aplicação como um detector de radiação". reponame:Repositório Institucional do IPEN, 2016. http://repositorio.ipen.br:8080/xmlui/handle/123456789/26818.
Testo completoAbstract (sommario):
Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-11-11T13:09:25Z
No. of bitstreams: 0Made available in DSpace on 2016-11-11T13:09:25Z (GMT). No. of bitstreams: 0
Neste trabalho, cristais de TlBr foram crescidos e purificados pelo método de Bridgman Repetido, a partir de sais comerciais de TlBr, e caracterizados para serem usados como detectores de radiação à temperatura ambiente. Para avaliar a eficiência de purificação, estudos da diminuição da concentração de impurezas foram feitos após cada crescimento, analisando as impurezas traço por Espectrometria de Massas com Plasma (ICP-MS). Um decréscimo significativo da concentração de impurezas em função do número de purificações foi observado. Os cristais crescidos apresentaram boa qualidade cristalina de acordo com os resultados de análise por Difração de Raios X (DRX), boa qualidade morfológica e estequiometria adequada de acordo com os resultados de análise por MEV(SE) e MEV(EDS). Um modelo matemático definido por equações diferenciais foi desenvolvido para avaliar as concentrações de impurezas no cristal de TlBr e suas segregações em função do número de crescimentos pelo método de Bridgman. Este modelo pode ser usado para calcular o coeficiente de migração das impurezas e mostrou ser útil para prever o número necessário de repetições de crescimento Bridgman para atingir nível de pureza adequado para assegurar a qualidade do cristal como detector de radiação. Os coeficientes se segregação obtidos são parâmetros importantes para análise microestrutural e análise de transporte de cargas nos cristais detectores. Para avaliar os cristais a serem usados como detectores de radiação, medidas de suas resistividades e resposta à incidência de radiação gama das fontes de 241Am (59,5keV) e 133Ba (81 keV) foram realizadas. Essa resposta foi dependente da pureza do cristal. Os detectores apresentaram um avanço significativo na eficiência de coleta de cargas em função da pureza.
Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
43
Hueso, González Jaime. "Analysis of wedge-shaped waveguides and design of multipactor-resistant microwave bandpass filters. Análisis de guías de onda en forma de cuña y diseño de filtros de microondas paso-banda resistentes al efecto multipactor". Doctoral thesis, Editorial Universitat Politècnica de València, 2013. http://hdl.handle.net/10251/33750.
Testo completoAbstract (sommario):
El efecto multipactor de ruptura en RF ha sido objeto de numerosos estudios desde
hace más de 80 años, a partir del desarrollo de los primeros aceleradores de partículas en
la primera mitad del siglo XX. A mediados de ese siglo, con el desarrollo de fuentes de alta
potencia para aplicaciones radar y la llegada de los satélites artificiales, la investigación del
multipactor cobró una considerable relevancia, al convertirse este fenómeno en un riesgo
determinante para costosos proyectos comerciales. Las guías de onda con secciones rectas
canónicas, como las rectangulares o las coaxiales, han sido tradicionalmente las más utilizadas
en dispositivos de microondas. Sus principales ventajas son que sus campos electromagnéticos pueden resolverse analíticamente, lo que permite su aplicación directa en diseños
complejos, y la simplicidad de su fabricación. Pero las capacidades de computación y las
prestaciones de los algoritmos se han multiplicado con los años, lo que ha permitido ampliar
el espectro de posibles topologías a geometrías casi arbitrarias, ofreciendo al diseñador una
mayor libertad creativa. En todo caso, gran parte de los dispositivos de microondas actuales
siguen confiando en la madurez y fiabilidad de las tecnologías de guía de onda tradicionales,
que no requieren una inversión adicional en equipos de fabricación. La supresión del efecto
multipactor es la motivación para arriesgarse a probar topologías de guía de onda innovadoras,
como la guía en forma de cuña.
Es en este contexto donde este trabajo de doctorado pretende ofrecer una contribuci'on.
En primer lugar, se ha desarrollado un modelo numérico para predecir el efecto multipactor
de ruptura en guías de onda huecas en forma de cuña. Esta herramienta ha permitido la
identificación de criterios óptimos de diseño. Así mismo, se ha adaptado un método de
síntesis de filtros paso-banda en guía rectangular para poder realizar un diseño similar pero
basado en la nueva topología. Como culminación, las estructuras diseñadas se han fabricado
y medido, con el fin de comprobar sus prestaciones electromagnéticas y su sensibilidad al
efecto multipactor. Se ha registrado además una patente para proteger estos nuevos filtros.
En resumen, el trabajo ha abarcado el ciclo de actividades relacionadas con el desarrollo
industrial completo de un dispositivo pasivo de microondas: investigación básica, análisis,
diseño, fabricación y calificación con medidas en el laboratorio.
Estas medidas han comprobado la mejora prevista en los umbrales de multipactor de los
filtros de microondas con topología en forma de cu¿na, y han confirmado que pueden ofrecer
respuestas en frecuencia similares a aquellas de filtros basados en una guía de onda rectangular
equivalente. Las implicaciones de los resultados han sido evaluadas a fondo y resumidas en este documento. Como observación final, se ha intentado redactar esta investigación de
manera que refleje el proceso natural de aprendizaje, mostrando los aciertos y errores experimentados
en el camino, todos los cuales han conducido al resultado final. Este reto no
hubiera sido posible sin el apoyo y compromiso de varios profesionales de diferentes centros
de investigación e industrias europeas (Universidad Politécnica de Valencia, Universidad de
Valencia, Agencia Espacial Europea, Thales Alenia Espacio Espa¿na, Technische Universit¿at
Darmstadt, 'Ecole Polythecnique F'ed'erale de Lausanne, Tesat, Aurora Software and Testing
y Val Space Consortium), a los cuales estoy agradecido.The multipactor RF breakdown effect has been object of numerous studies for over 80 years, since the development of the first particle accelerators in the beginning of the 20th century. Around the middle of that century, with the development of high power sources for radar applications and with the emergence of the artificial satellites, a new impulse was given to the multipactor research, since it became a risk for expensive commercial projects. Traditionally, waveguides with canonical cross sections, like rectangular or coaxial ones, have been the building blocks of most microwave devices. Their main advantages are that their electromagnetic fields can be solved analytically, enabling their direct application in complex designs, as well as their manufacturing simplicity. But over the years the computation capabilities and algorithms have continuously evolved, which has broadened the spectrum of possible topologies to almost arbitrary geometries, offering the designer more room for creativity. However, most of the current microwave devices still trust on the mature canonical waveguide technologies, which do not require an additional investment in manufacturing equipment. The suppression of the multipactor effect is the motivation for considering an innovative waveguide topology, like the wedge-shaped waveguide. It is within this context where this PhD work aims to offer a contribution. On the one hand, a numerical model for predicting the multipactor breakdown effect in wedge-shaped hollow waveguides has been developed. This tool has aided in the derivation of optimised design criteria. On the other hand, a bandpass filter synthesis method for rectangular waveguide has been adapted in order to calculate a similar design based on the new topology. As a culmination, the designed structures have been manufactured and tested, in order to verify their electromagnetic performance and their multipactor sensibility. A patent was also filed to protect these new filters. In short, this work has comprised the cycle of activities related to the whole industrial development of a passive microwave device: basic research, analysis, design, manufacturing and qualification through testing. These measurements have verified the predicted improvement in the multipactor thresholds of microwave filters with wedge-shaped topology, and have confirmed that they can offer similar frequency responses to the equivalent rectangular waveguide ones. The implications of the results have been thoroughly evaluated and summarised in this document. As a final remark, this research document has been drafted to reflect the natural learning process, and to show the rights and wrongs experienced in the way, which all have led to the final result. Such an endeavour would not have been possible without the support and commitment of several professionals from different European research centres and industries (Universidad Polit'ecnica de Valencia, Universidad de Valencia, European Space Agency, Thales Alenia Espacio Spain, Technische Universit¿at Darmstadt, 'Ecole Polythecnique F'ed'erale de Lausanne, Tesat, Aurora Software and Testing and Val Space Consortium), for which I am grateful.
Hueso González, J. (2013). Analysis of wedge-shaped waveguides and design of multipactor-resistant microwave bandpass filters. Análisis de guías de onda en forma de cuña y diseño de filtros de microondas paso-banda resistentes al efecto multipactor [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/33750
Alfresco
44
Fil, Nicolas. "Caractérisation et modélisation des propriétés d’émission électronique sous champ magnétique pour des systèmes RF hautes puissances sujets à l’effet multipactor". Thesis, Toulouse, ISAE, 2017. http://www.theses.fr/2017ESAE0025/document.
Testo completoAbstract (sommario):
La fusion nucléaire contrôlée par confinement magnétique avec les réacteurs de type Tokamaks et les applications spatiales ont en commun d’utiliser des composants Haute-Fréquence (HF) sous vide à forte puissance. Ces composants peuvent être sujets à l’effet multipactor qui augmente la densité électronique dans le vide au sein des systèmes, ce qui est susceptible d’induire une dégradation des performances des équipements et de détériorer les composants du système. Ces recherches consistent à améliorer la compréhension et la prédiction de ces phénomènes. Dans un premier temps nous avons réalisé une étude de sensibilité de l’effet multipactor au rendement d’émission électronique totale (noté TEEY). Cette étude a permis de montrer que l’effet multipactor est sensible à des variations d’énergies autour de la première énergie critique et dans la gamme d’énergies entre la première énergie critique et l’énergie du maximum. De plus, les composants HF utilisés dans les réacteurs Tokamak et dans le domaine du spatial peuvent être soumis à un champ magnétique continu. Nous avons donc développé un nouveau dispositif expérimental afin d’étudier ce phénomène. Le fonctionnement du dispositif et la méthode de mesure ont été analysées et optimisées à l’aide de modélisations numériques avec le logiciel PIC SPIS. Une fois que l’utilisation du dispositif a été optimisée et que le protocole de mesures a été validé, nous avons étudié l’influence d’un champ magnétique uniforme et continu sur le TEEY du cuivre. Nous avons démontré que le rendement d’émission électronique totale du cuivre est influencé par la présence d’un champ magnétique et par conséquent également l’effet multipactorSpace communication payload as well as magnetic confinement fusion devices, among other applications, are affected by multipactor effect. This undesirable phenomenon can appear inside high frequency (HF) components under vacuum and lead to increase the electron density in the vacuum within the system. Multipactor effect can thus disturb the wave signal and trigger local temperature increases or breakdowns. This PhD research aims to improve our understanding and the prediction of the multipactor effect. The multipactor phenomenon is a resonant process which can appear above a certain RF power threshold. To determine this power threshold, experimental tests or/and simulations are commonly used. We have made a study to evaluate the multipactor power threshold sensitivity to the TEEY. Two particular critical parameters have been found: first cross-over energy and the energies between the first cross-over and the maximum energies. In some situations, the HF components are submitted to DC magnetic fields which might affect the electron emission properties and hence the multipactor power threshold. Current multipactor simulation codes don’t take into account the effect of the magnetic field on the TEEY. A new experimental setup specially designed to investigate this effect was developed during this work. Our new experimental setup and the associated TEEY measurement technique were analysed and optimized thanks to measurements and SPIS simulations. We used the setup to study the influence of magnetic field perpendicular to the sample surface on the TEEY of copper. We have demonstrated that the magnetic field affects the copper TEEY, and hence multipactor power threshold
45
Kersell, Heath R. "Alternative Excitation Methods in Scanning Tunneling Microscopy". Ohio University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1449074449.
Testo completo
46
Illemann, Jens. "Präzisionsmassebestimmung einzelner Partikel im Femtogrammbereich und Anwendungen in der Oberflächenphysik". Doctoral thesis, Universitätsbibliothek Chemnitz, 2000. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200000677.
Testo completoAbstract (sommario):
In this work, a new method for mass determination of single low-charged particles in the sub-picogram regime is developed. It opens applications to chemical physics and surface science via determination of growth rates. The method combines the well-known electrodynamic quadrupole ion trap in a UHV-chamber and fourier transformation of scattered light. The achieved mass resolution of down to $10^{-4}$ at 100 fg mass on a time scale of ten seconds allows a resolution of a few percent of the mass of an adsorbed monolayer and to determine growth rates down to one molecule per second on a time scale of one day. The observation of temperature dependent sticking coefficients results in the measures of the energy of an adsorption barrier. Observation of discrete steps in the rate gives information about the density of molecules in an ordered layer. Temperature dependent desorption data gives the binding energy. The dependence of these observables on the controllable curvature and charge of the substrate's surface is measurable.
The first part of this dissertation consists of a description of the common theory of the quadrupole ion trap with the completion of not widely known, newly introduced, contributions to the trapping potential. These contributions lead to systematic shifts in the mass determination. In particular the influence of the inhomogenity of the electrical field, that is used for compensating the gravitational force, is investigated analytically and corroborated experimentally. It is assumed, that the particle's finite size effects in a further shift.
In the experimental part initial demonstrative measurements are presented: the time-resolved adsorption of fullerene, anthracene and NO on silica spheres with 500nm diameter has been measured at room temperature. In addition the secondary electron yield of in-situ prepared particles during irradiation with monoenergetic electrons has been determined by analyzing the distribution of change of the number of elementary charges by single events of charging.
47
Alzaher, Ibrahim. "Les ions émis de la surface : messagers du processus initial de la nano-structuration". Phd thesis, Université de Caen, 2011. http://tel.archives-ouvertes.fr/tel-00637223.
Testo completoAbstract (sommario):
Lorsqu'un ion projectile inertagit avec une surface, il dépose son énergie tout au long de son trajet. L'énergie déposée conduit à la création d'endommagements et à l'émission de particules secondaires, neutres et chargées. Dans cette thèse, nous avons étudié l'endommagement de surfaces cristallines induit par irradiation aux ions lents et rapides. Nous avons également étudié la pulvérisation d'ions secondaires durant l'irradiation aux ions rapides. Dans le cas d'irradiation aux ions lents multichargés, nous avons déterminé les sections efficaces d'endommagement par ion incident sur les surfaces cristallines de TiO2 et de graphite. Nous avons mis en évidence que l'énergie potentielle du projectile joue un rôle improtant dans l'endommagement de la surface. Par contre, l'étude d'endommagement surfacique du silicium cristallin s'est révelé insensible à l'irradiation aux ions (Xe, Ec = 0,92 MeV), où la perte d'énergie électronique est 12 keV/nm. L'efficacité maximale pour qu'un ion produise une modification à la surface est 0,3 %. Par irradiation aux ions rapides, l'émission d'ions de CaF+ par rapport à l'émission de Ca+ est plus grande dans le cas d'irradiation d'un cristal massif que dans le cas de couches minces de CaF2.
48
Rigoudy, Charles. "Couches minces diélectriques avec des inclusions de nanoparticules d'argent réalisées par voie plasma conçues pour le contrôle du gradient de charges électriques sous irradiation électronique pour des applications spatiales". Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30268.
Testo completoAbstract (sommario):
Le phénomène d'émission électronique est étudié dans de nombreux domaines fondamentaux de la physique et pose le principe de fonctionnement d'un grand nombre de dispositifs tels que les écrans à émission de champ, les propulseurs Hall, etc. Il est mieux compris pour les métaux. Cependant pour les matériaux isolants, il constitue un phénomène critique limitant la fiabilité des composants dans les applications spatiales où les phénomènes de décharge et de claquage sont entièrement contrôlés par l'émission électronique. Selon l'énergie des électrons incidents et les propriétés des diélectriques, les électrons peuvent être piégés au sein du matériau, et/ou être à l'origine de phénomènes d'émission électronique. Ce travail de thèse se situe à l'interface de trois domaines de recherche : le dépôt par plasma de couches minces nanocomposites, le piégeage et le transport de charges électriques dans les diélectriques, et la caractérisation des matériaux sous irradiation en milieu spatial. Il explore l'effet des nanoparticules d'argent (AgNPs) enterrées dans des couches minces de silice, sur les mécanismes physiques (injection, piégeage, transport de charges et émission électronique secondaire) responsables du chargement diélectrique et des émissions d'électrons, afin de moduler ces phénomènes. Les couches minces nanostructurées de silice contenant un plan d'AgNPs ont été élaborées par procédé plasma combinant dans un même réacteur la pulvérisation d'une cible métallique et le dépôt chimique en phase vapeur activé par plasma (PECVD). La caractérisation structurale des échantillons a permis de déterminer la composition chimique de la matrice de silice plasma, la taille, la forme, la densité et la distribution des AgNPs ainsi que l'épaisseur totale de la structure. Ces analyses ont permis de corréler les paramètres structurels avec la réponse des couches diélectriques nanostructurées réalisées sous contrainte électrique et irradiation électronique. Il a été constaté que pour des électrons primaires de faible énergie (< 2keV), le rendement total d'émission d'électrons (TEEY) des couches minces de silice sans AgNPs présente une forme atypique avec un minimum local situé à environ 1 keV. Afin de mieux comprendre ce comportement, un modèle de TEEY a été développé. Il est basé sur le modèle de Dionne, et adapté aux diélectriques. Il considère le champ électrique interne résultant de l'accumulation de charges électriques dans la couche diélectrique. [...]Electron emission phenomenon is intensively studied in many fundamental areas in physics and lays down the principle of operation of a large number of devices such as field emission display devices, Hall thrusters, etc. It is better described for metals. However, when originating from insulating materials it becomes a critical phenomenon involved in reliability issues of components in space applications where surface flashover phenomena and vacuum breakdown are entirely controlled by the electron emission from solids. Depending on the energy of impinging electrons and the dielectric properties, the electrons can be trapped within the dielectric bulk, and/or be responsible of electron emission phenomena. This PhD work, carried out at the interface of three research domains: plasma deposition of thin nanocomposite layers, dielectric charging and charge transport in thin dielectrics, and characterization of materials under irradiation in space environment, aims to explore the effect of metal inclusions (silver nanoparticles, AgNPs), embedded in thin dielectric silica layers, on the physical mechanisms (charge injection, trapping, transport and secondary electron emission from the surface) responsible of the dielectric charging and electron emission from dielectrics, in order to modulate them. Nanostructured thin dielectric silica layers containing a single plan of AgNPs have been elaborated by plasma process successfully combining in the same reactor sputtering of a metallic target and plasma enhanced chemical vapor deposition (PECVD). Structural characterization of the resulting samples has been performed to determine the chemical composition of the plasma silica matrix as well as to obtain the AgNPs size, shape, density and distribution and the total thickness of the structure. These analyses allowed correlation of the structural parameters with the response of the obtained nanostructured dielectric layers under electrical stress and electronic irradiation. It was found that for low energy of the incident electrons (< 2keV) the total electron emission yield (TEEY) from thin silica layers without AgNPs presents an atypical shape with local minimum situated at around 1keV. To get closer to the description of this behavior a model for the TEEY was developed. It is based on Dionne's model, but adapted to dielectrics. It considers the internal electric field resulting from dielectric charging phenomenon.[...]
49
Giesen, Gaelle. "Dark Matter Indirect Detection with charged cosmic rays". Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112160/document.
Testo completoAbstract (sommario):
Les preuves pour l'existence de la matière noire (MN), sous forme d'une particule inconnue qui rempli les halos galactiques, sont issues d'observations astrophysiques et cosmologiques: son effet gravitationnel est visible dans les rotations des galaxies, des amas de galaxies et dans la formation des grandes structures de l'univers. Une manifestation non-gravitationnelle de sa présence n'a pas encore été découverte. L'une des techniques les plus prometteuse est la détection indirecte de la MN, consistant à identifier des excès dans les flux de rayons cosmiques pouvant provenir de l'annihilation ou la désintégration de la MN dans le halo de la Voie Lactée. Les efforts expérimentaux actuels se focalisent principalement sur une gamme d'énergie de l'ordre du GeV au TeV, où un signal de WIMP (Weakly Interacting Massive Particles) est attendu. L'analyse des mesures récentes et inédites des rayons cosmiques chargés (antiprotons, électrons et positrons) et leurs émissions secondaires et les améliorations des modèles astrophysiques sont présentées.Les données de PAMELA sur les antiprotons contraignent l'annihilation et la désintégration de la MN de manière similaire (et même légèrement meilleurs) que les contraintes les plus fortes venant des rayons gamma, même dans le cas où les énergies cinétiques inférieures à 10 GeV sont écartées. En choisissant des paramètres astrophysiques différents (modèles de propagation et profils de MN), les contraintes peuvent changer d'un à deux ordres de grandeur. Pour exploiter la totalité de la capacité des antiprotons à contraindre la MN, des effets précédemment négligés sont incorporés et se révèlent être importants dans l'analyse des données inédites de AMS-02 : ajouter les pertes d'énergie, la diffusion dans l'espace des moments et la modulation solaire peut modifier les contraintes, même à de hautes masses. Une mauvaise interprétation des données peut survenir si ces effets ne sont pas pris en compte. Avec les flux de protons et d'hélium exposé par AMS-02, le fond astrophysique et ces incertitudes du ratio antiprotons sur protons sont réévalués et comparés aux données inédites de AMS-02. Aucune indication pour un excès n'est trouvé. Une préférence pour un halo confinant plus large et une dépendance en énergie du coefficient de diffusion plus plate apparaissent. De nouvelles contraintes sur l'annihilation et la désintégration de la MN sont ainsi dérivés.Les émissions secondaires des électrons et des positrons peuvent aussi contraindre l'annihilation et la désintégration de la MN dans le halo galactique : le signal radio dû à la radiation synchrotron des électrons et positrons dans le champs magnétique galactique, les rayons gamma des processus de bremsstrahlung avec le gas galactique et de Compton Inverse avec le champs radiatif interstellaire sont considérés. Différentes configurations de champs magnétique galactique et de modèles de propagation et des cartes de gas et de champs radiatif interstellaire améliorés sont utilisées pour obtenir des outils permettant le calculs des émissions synchrotrons et bremsstrahlung venant de MN de type WIMP. Tous les résultats numériques sont incorporés dans la dernière version du Poor Particle Physicist Coookbook for DM Indirect Detection (PPPC4DMID).Une interprétation d'un possible excès dans les données de rayons gamma de Fermi-LAT au centre galactique comme étant dû à l'annihilation de MN en canaux hadronique et leptonique est analysée. Dans une approche de messagers multiples, le calcul des émissions secondaires est amélioré et se révèle être important pour la détermination du spectre pour le canal leptonique. Ensuite, les limites provenant des antiprotons sur l'annihilation en canal hadronique contraignent sévèrement l'interprétation de cet excès comme étant dû à la MN, dans le cas de paramètres de propagation et de modulation solaire standards. Avec un choix plus conservatif de ces paramètres elles s'assouplissent considérablementOverwhelming evidence for the existence of Dark Matter (DM), in the form of an unknownparticle filling the galactic halos, originates from many observations in astrophysics and cosmology: its gravitational effects are apparent on galactic rotations, in galaxy clusters and in shaping the large scale structure of the Universe. On the other hand, a non-gravitational manifestation of its presence is yet to be unveiled. One of the most promising techniques is the one of indirect detection, aimed at identifying excesses in cosmic ray fluxes which could possibly be produced by DM annihilations or decays in the Milky Way halo. The current experimental efforts mainly focus in the GeV to TeV energy range, which is also where signals from WIMPs (Weakly Interacting Massive Particles) are expected. Focussing on charged cosmic rays, in particular antiprotons, electrons and positrons, as well as their secondary emissions, an analysis of current and forseen cosmic ray measurements and improvements on astrophysical models are presented. Antiproton data from PAMELA imposes contraints on annihilating and decaying DM which are similar to (or even slightly stronger than) the most stringent bounds from gamma ray experiments, even when kinetic energies below 10 GeV are discarded. However, choosing different sets of astrophysical parameters, in the form of propagation models and halo profiles, allows the contraints to span over one or two orders of magnitude. In order to exploit fully the power of antiprotons to constrain or discover DM, effects which were previously perceived as subleading turn out to be relevant especially for the analysis of the newly released AMS-02 data. In fact, including energy losses, diffusive reaccelleration and solar modulation can somewhat modify the current bounds, even at large DM masses. A wrong interpretation of the data may arise if they are not taken into account. Finally, using the updated proton and helium fluxes just released by the AMS-02 experiment, the astrophysical antiproton to proton ratio and its uncertainties are reevaluated and compared to the preliminarly reported AMS-02 measurements. No unambiguous evidence for a significant excess with respect to expectations is found. Yet, some preference for thicker halos and a flatter energy dependence of the diffusion coefficient starts to emerge. New stringed constraints on DM annihilation and decay are derived. Secondary emissions from electrons and positrons can also be used to constrain DM annihilation or decay in the galactic halo. The radio signal due to synchrotron radiation of electrons and positrons on the galactic magnetic field, gamma rays from bremsstrahlung processes on the galactic gas densities and from Inverse Compton scattering processes on the interstellar radiation field are considered. With several magnetic field configurations, propagation scenarios and improved gas density maps and interstellar radiation field, state-of-art tools allowing the computaion of synchrotron and bremssttrahlung radiation for any WIMP DM model are provided. All numerical results for DM are incorporated in the release of the Poor Particle Physicist Coookbook for DM Indirect Detection (PPPC4DMID). Finally, the possible GeV gamma-ray excess identified in the Fermi-LAT data from the Galactic Center in terms of DM annihilation, either in hadronic or leptonic channels is studied. In order to test this tantalizing interprestation, a multi-messenger approach is used: first, the computation of secondary emisison from DM with respect to previous works confirms it to be relevant for determining the DM spectrum in leptonic channels. Second, limits from antiprotons severely constrain the DM interpretation of the excess in the hadronic channel, for standard assumptions on the Galactic propagation parameters and solar modulation. However, they considerably relax if more conservative choices are adopted
50
Chiang, Chang-Lin, e 江昌霖. "Electro-optical conversion and secondary electron emission in flat electron emission lamp by optical emission spectra". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/12845752039510786501.
Testo completoAbstract (sommario):
博士國立交通大學
電子物理系所
104
Flat Electron Emission Lamp (FEEL) is a newly developed type of uniform planar light source, featuring unique advantages of double-side lighting, transparency, and heat insulation over the conventional lighting sources. The working principle of FEEL utilizes electrons accelerated by external electric field to excite the phosphor powders coated on the anode to obtain desired luminescence. The abovementioned electrons can be generated from two different sources: the free electrons originated from gas ionization and the secondary electrons generated from the bombardment of ionized gases to the cathode material. However, since FEELs are devices with very short electrode-distance and low working pressure, (i.e. low pd values), they are inevitably operating on the left-hand side of the Paschen curve, and the detailed physical mechanisms are relatively unexplored. In this thesis, we shall focus our discussions on the discharge and lighting characteristics exhibited in typical FEEL devices based on the knowledge obtained from the conventional long discharge tubes by using optical emission spectroscopy. It is evident that, similar to that conventional long discharge tube, emissions from both of the first negative system (391.5 nm and 427.5 nm) of N2+ and the second positive system (337 nm and 357.5 nm) of N2 are present for pressures above 0.4 torr. As the pressure is further reduced to below 0.3 torr, the 391.5 nm emission from the first negative system becomes the dominant excitation, which diminishes gradually and disappears completely at 0.14 torr. Moreover, the relative emission intensity obtained at the position of 1 mm from the cathode, the emissions from the first negative system of N2+ are, in fact, already dominant over the entire pressure range (0.14-1.0 torr). The FEEL devices exhibit essentially the same pressure-dependent emission features as seen in the conventional long glow discharge tubes. In particular, similar to the long glow discharge tubes without positive columns, the FEEL devices are essentially working on the left hand side of the Paschen curve, as well. Under these circumstances, in addition to the collisional ionization processes necessary for maintaining a steady-state discharge, the primary energy transferring mechanism is utilizing electrons accelerated by external electric field to excite the phosphor powders coated on the anode to obtain desired luminescence. The results indicated that the lighting properties were dominated by first negative band B2∑u+→X2∑g+ of nitrogen ion and the secondary electrons were generated primarily from the bombardment of ionized gases to the cathode material, which, in turn, were accelerated by the applied voltage to excite the phosphor coating on the anode. Based on the proposed electro-optical transfer model, nitrogen ions emission, secondary electron coefficient of material, electron energy, and phosphor lighting efficiency were identified as the four most prominent parameters in determining the lighting of FEEL. We successfully prove the viability of using the proposed model to describe the luminance of FEEL by linking the four parameters obtained from independent experiments. The highest efficiency of FEEL is achieved presumably due to the reducing glow excitation of the nitrogen molecules as well as collisions encountered by the energetic electrons along the path across the space between cathode and anode. As a result, higher electron energy is preserved before landing on the phosphor coated on the anode to result in higher lighting efficacy. Previously, fluorine-doped tin oxide (FTO) had been used as the cathode electrode of the FEEL devices due to its transparent and conductive characteristics. Nevertheless, the requirement of relatively higher discharge voltage, presumably resulting from lower secondary electron emission coefficient ion-bombardment damage, have hindered the realization of the FEEL devices for practical use. Hence, developing protective layers capable of lowering the required discharge voltage and providing more robust endurance to ion-bombardment is necessary. Three different cathode materials, namely fluorine-doped tin oxide (FTO), aluminum oxide coated FTO (Al2O3/FTO) and magnesium oxide coated FTO (MgO/FTO) were prepared to investigate how the variations of γ and working gases influence the performance of FEEL devices, especially in lowering the breakdown voltage and pressure of the working gases. Our results show that, under the typical operation conditions of FEEL devices, the γ values for FTO, Al2O3/FTO, and MgO/FTO are 0.193, 0.263, and 0.396, respectively. The larger γ value obtained for MgO consistently accounts for both the significant reduction in breakdown voltage and marked enhancement in lighting efficacy and device lifetime.