Добірка наукової літератури з теми "Transport du faisceau"
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Дисертації з теми "Transport du faisceau":
Rochdi, Nabil. "Propriétés de transport de microstructures et nanostructures de silicium." Aix-Marseille 2, 2007. http://theses.univ-amu.fr.lama.univ-amu.fr/2007AIX22068.pdf.
This thesis work deals with the study of transport properties, of both charge and spin, in silicon-based microstructures and nanostructures. We have studied the fabrication process of connected low section (100 x 8 nm2) silicon nanowires (SiNWs) using atomic force microscope (AFM) lithography on thinned silicon on insulator (SOI) samples. Electrical measurements highlighted typical Field Effect Transistor (FET) behaviour of these SiNWs. Electron trapping in oxide or at interfaces is responsible of the cumulative depletion of the wires during the successive I(V) measurements. Electron release is obtained by application of a voltage on the wire gate. So the wires exhibited a memory effect in which the writing / reading process occurs by electron trapping / de-trapping controlled by application of a positive / negative voltage on the device gate. Furthermore, we studied the spin transport in a silicon substrate. Numerical evaluation of spin transport in drift-diffusive regime reveals spin diffusion and spin precession lengths of several microns, under a weak external magnetic field. Such dimensions are compatible with present technology of ICs. Electrical measurements carried out on a magnetic memory integrated on silicon (MEMIS), specially designed for this study, showed electron injection and collection efficiency. However, no magnetoresistance was detected probably due to the low quality of interfaces in the hybrid heterojunctions ferromagnetic metal/insulator/silicon (FMIS). Thus, we proposed to test extra FMIS structures such as Co/AlO(~1 nm)/Si and Co/MgO(~1 nm) /Si, fabricated with less thermal treatments. The direct tunnelling transport in oxide was obtained in these junctions, which would allow spin injection coherence in prospective spin devices. Finally, we have characterized rectifying junctions Ferromagnetic semiconductor/semiconductor (MSS) such as Ge3Mn5/Ge which seem to be particularly suitable for spin injection
MICHAUT-BEHAR, CLAIRE. "Etude experimentale et simulation de l'acceleration et du transport d'un faisceau d'ions negatifs." Paris 6, 1993. http://www.theses.fr/1993PA066181.
Banda, Gnama Mbimbiangoye Mallys Elliazar. "Mesure et modélisation du comportement de matériaux diélectriques irradiés par faisceau d'électrons." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30208/document.
In their common uses as electrical insulators, organic solid materials are constitutive of electric power transmission cables, power control and conversion circuits as well as (micro) electronic components or embedded systems (thermal coating of satellites, batteries of accumulators, etc.). Under various constraints of use (electric field, radiation, temperature, humidity ...) they can accumulate charges in their bulk which could affect the reliability of the systems in which they are employed. One of the commonly used means to study the electrical behavior of these charges is to measure the spatiotemporal distribution of charges by subjecting the dielectrics to a continuous potential difference between two electrodes. However, this method does not always allow clearly distinguishing the contribution of charges due to generation on the one hand and the one due to transport phenomena on the other hand. This study proposes an alternative approach, consisting in generating charges (electrons) within the electrical insulation using an electron-beam under vacuum. The charges are hence deposited at a known position and in a controlled quantity. Other physical processes related to the implantation of electrons must then be taken into account in order to predict and model the behavior of these irradiated materials. Low-density polyethylene (LDPE) films, prepared by thermal molding, were irradiated by a 80 keV electron-beam with a current flux of 1 nA/cm2. Space charge measurements using the Pulsed Electro-Acoustic (PEA) method, performed first in-situ and then ex-situ under DC electrical polarization, confirm an effective localization of charges within the material. The results under electrical polarization after irradiation show an important amount of positive charges in the irradiated zone of the dielectric. The electrical characterizations of irradiated LDPE films show a completely different behavior compared to the same non-irradiated material, suggesting a modification of the chemical structure of the material. Physico-chemical measurements (infrared spectroscopy, Photoluminescence and Differential Scanning Calorimetry-DSC) on these irradiated PEbd films do not show a significant degradation of the chemical structure of the dielectric which would explain the observed electrical behavior under post-irradiation polarization. Additional measurements show the reversible behavior of the irradiated then polarized PEbd, which would be only related to the presence of the charges generated by the beam. The experimental data of this study have simultaneously fed a numerical model of charge transport, developed to take into account the irradiation constraints. This model allows reproducing the in-situ results of charge implantation by the electron beam as well as the majority of the electrical processes observed on irradiated and polarized LDPE. It confirms the impact of the electron-beam deposited charge on the behavior under polarization and allows concluding on the origin of the positive charges observed after irradiation, which would be due to injection at the electrodes as well as to the creation of electron-hole pairs by the electron-beam during irradiation
Maclossi, Mauro. "Transport dans la matière sous dense et sur dense d'un faisceau d'électrons relativistes, produit par l'interaction d'une impulsion laser à ultra haute intensité." Palaiseau, Ecole polytechnique, 2006. http://www.theses.fr/2006EPXX0063.
Alvinerie, Clara-Marie. "Etude numérique et expérimentale de la dynamique des faisceaux d'electrons dans les accélérateurs linéaires à induction." Electronic Thesis or Diss., Normandie, 2023. http://www.theses.fr/2023NORMC291.
Flash radiography allows characterizing the state of a dense object subjected to extreme physical conditions, with displacement velocities of several kilometres per second. These conditions require a specific X-ray source: small size (a few millimetres), brief duration (less than 100 ns), high energy (around 20 MeV) and high current (a few kA). This source is produced using Bremsstrahlung radiation generated by the interaction of an intense and pulsed electron beam with a high atomic number metal target. A velvet cathode emits the beam and an linear induction accelerator (LIA) transports it. The quality of radiography is mainly conditioned by the physical characteristics of the X-ray source, which are closely linked to the properties of the electron beam. The work carried out in this PhD thesis aims to model the beam dynamics in LIAs by integrating its physical characteristics, including some instabilities which degrade the beam. The developed models were validated during the commissioning of the MCH3 accelerator at CEA Valduc in Epure facility.The modelling of beam dynamics is based on the Particle-In-Cell (PIC) code LSP-Slice and the transport code EVOLI (EVOLution of Instabilities). The latter was developed during this thesis and models the size of the beam envelope and its charge centroid, as well as the "temporal" propagation of the beam by its segmentation into discs.In the first place, studies were conducted on the motion of the beam centroid during its transport. In EVOLI, the equations describe the centroid with the influence of space charge. A numerical optimization procedure allowed the simulation to reproduce the results obtained in MCH3 by incorporating the influence of the Earth's magnetic field and the misalignment of various magnetic elements (solenoids and steerers). The application of this new method to other beam transports makes possible to calculate steerer settings for numerical pre-centering of the beam. This method offers the prospect of significant time savings during the experimental beam centering process, which typically requires numerous shots.Afterward the beam modelling contributed to the commissioning of MCH3 accelerator at the end of 2022. With an initial transport attempt, the entire beam charge did not reach the conversion target, despite numerical simulations predicting nominal transport based on the envelope formalism. Experimental measurements revealed significant centroid oscillations due to the Beam Break-Up (BBU) instability. Then, a simplified BBU model was incorporated into EVOLI. By using this numerical model, a new high magnetic field transport was designed, theoretically limiting BBU intensity at the accelerator end by a factor 2.5. This result was experimentally verified by a BBU reduction by a factor 3, enabling a stable and reproducible transport of the entire beam charge to the target. However, this strong magnetic field transport strategy leads to an increase of the Corkscrew motion, which increases with magnetic field strength as shown in the work initiated in this thesis. Therefore, optimizing beam transport is a compromise between the various instabilities within the accelerator. The work of this thesis opens up prospects for considering instabilities to design innovative transports, particularly in the context of multi-pulse machines, which are currently a major development in flash radiography machines
Vay, Jean-Luc. "Transport de faisceau intense d'ions lourds dans un gaz moleculaire. Application a la fusion inertielle par particules chargees." Paris 7, 1996. http://www.theses.fr/1996PA077334.
Beaucourt-Jacquet, Céline. "Étude expérimentale du guidage du faisceau d’électrons dans le cadre de l’allumage rapide de cibles de fusion." Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14741/document.
The work presented in this thesis is realised in the framework of the fast ignition of inertial confinement fusion for energy production. In this scheme the compression and the ignition phases are decoupled. During the second phase, the electron beam must cross over 300 µm in the dense fuel to deposit its energy in the dense core and ignite the fusion reactions.The major problem of the scheme is related to the divergence of the electron beam while it crosses the dense matter. Among the different propositions to inhibit the electron divergence we consider here the schemes without cone that are based on the effect of magnetic collimation. In particular, A.P.L. Robinson and his co-authors [Phys. Rev. Lett. 100, 025002, 2008] suggested a simple way to control the electron beam divergence by using a sequence of two laser pulses. The first one creates a magnetic background favourable for the confinement of the second electron beam resulting from the second interaction. The validation of this scheme is the major goal of this thesis.We present the results of experimental sudies and numerical modeling of the electron beam guiding with help of two consequent laser pulses. The experiment was performed on the Vulcan facility at the Rutherford Appleton Laboratory at Didcot in UK, based on the proposal submitted by an international group of scientists in the framework of the European project for inertial fusion energy HiPER. This experiment allowed us to define a combination of laser and target parameters where the electron beam guiding takes place. The analysis of experimental data and numerical modelling is realised with the hydrodynamic code CHIC coupled to the charged particules transport module M1. The interpretation of the experimental results allowed us to explain the experimental data and the physical basis of guiding and to define the magnetic conditionflavourable to the electron beam guidance
Gaucher, Fabien. "Nano-structures en La2/3Sr1/3MnO3 : de la nano-structuration aux propriétés de transport." Paris 11, 2008. http://www.theses.fr/2008PA112271.
The works reported in this manuscript present the fabrication and the investigation of the transport properties of half-metallic La2/3Sr1/3MnO3 (LSMO) nano-structures. The optimization of the nano-sructuration process, particularly the electron-beam lithography and the etching steps, allowed the realization of nanowires with width down to 65 nm wide and length of several microns. The fine analysis of the transport properties shows their preservation until a thickness reduced to about 7 nm. The current conduction is then limited by different diffusion modes, depending on the temperature range. First noise measurements exhibit a very low normalized Hooge parameter ( ≈ 1. 10-32 m3). The observation of random telegraphic noise for the narrowest and thinnest nanowire in a narrow temperature range (220 K < T < 245 K) is the signature of a consequent reduction of the charge carriers at this scale. We can then imagine to use the LSMO as a full spin-polarized electrode for molecular magnets addressing. In this way, direct grafting of Mn12 magnetic molecules was prooved and opens interesting perspectives for the realization of a molecular spin valve
Debayle, Arnaud. "Theoretical study of Ultra High Intensity laser-produced high-current relativistic electron beam transport through solid targets." Thesis, Bordeaux 1, 2008. http://www.theses.fr/2008BOR13708/document.
This PhD thesis is a theoretical study of high-current relativistic electron beam transport through solid targets. In the ?rst part, we present an interpretation of a part of experimental results of laser– produced electron beam transport in aluminium foil targets. We have estimated the fast electron beam characteristics and we demonstrated that the collective e?ects dominate the transport in the ?rst tens of µm of propagation. These quantitative estimates were done with the transport models already existing at the beginning of this thesis. These models are no longer su?cient in the case a fast electron beam propagation in insulator targets. Thus, in the second part, we have developed a propagation model of the beam that includes the e?ects of electric ?eld ionization and the collisional ionization by the plasma electrons. We present estimates of the electron energy loss induced by the target ionization, and we discuss its dependence on the beam and target parameters. In the case of a relatively low fast electron density, we demonstrated that the beam creates a plasma where the electons are not in a local thermodynamic equilibrium with ions. We have examined the beam stability and we demonstrated that transverse instabilities can be excited by the relativistic electron beam over the propagation distances of 30 - 300 µm depending on the perturbation wavelength
Abrasonis, Gintautas. "Nitruration par faisceau d'ions des aciers austénitiques inoxydables : étude du transport atomique d'azote, des effets de flux et des effets structuraux." Poitiers, 2003. http://www.theses.fr/2003POIT2291.
Тези доповідей конференцій з теми "Transport du faisceau":
Culoma, A. "Propagation des faisceaux gaussiens. Transport des faisceaux de puissance." In Systèmes optiques. Les Ulis, France: EDP Sciences, 1992. http://dx.doi.org/10.1051/sfo/1992004.