Orientador: Konstantin Georgiev Kostov / Banca: Joaquim José Barroso de Castro / Banca: Mario Ueda / Resumo: O estudo do efeito do campo magnético sobre o processo de implantação iônica por imersão em plasma (3IP) é de grande interesse para o tratamento de materiais. Sendo 3IP uma técnica relativamente nova e de grande relevância para diversas aplicações tecnológicas é importante que ela seja pesquisada e analisada detalhadamente. A aplicação de um campo magnético estático, transversal em relação ao campo elétrico formado durante este processo produz um sistema de campos cruzados ExB. Este sistema de campos cruzados gera um aumento significativo da densidade de plasma na vizinhança do alvo, resultando num maior corrente de implantação, e conseqüentemente um tratamento mais rápido e uma dose retida mais alta em relação ao processo 3IP convencional. Neste trabalho, analisamos mediante simulação numérica, o efeito da distribuição do campo magnético axial no processo 3IP. O campo magnético é produzido por um par de bobinas instaladas fora da câmara de vácuo cujos raios e distância de separação são variadas. Encontramos que a densidade de corrente de implantação depende essencialmente da configuração do campo magnético. Assim, com uma adequada configuração das bobinas (10,0 cm de raio e 42,0 cm de separação) obtivemos uma densidade de corrente quase uniforme de aproximadamente 1,5 mA/cm2 que é 1.5 vezes maior em relação ao caso do sistema 3IP sem campo magnético. O efeito da tensão aplicada assim como da pressão do gás sobre o plasma no processo 3IP é também investigado. O sistema 3IP com campos ExB cruzados é estudado utilizando a técnica de simulação numérica em duas dimensões. Esta simulação é realizada com o código computacional KARAT que emprega o algoritmo "particle-in-cell" (PIC) para simular o movimento de partículas carregadas no campo eletromagnético. / Abstract: Detailed investigation of the effect of magnetic field on the process of plasma immersion ion implantation (PIII) is of great interest for the material treatment. Being a relatively novel and of great relevance for technological applications technique, the PIII demands further research and careful analysis. The application of static magnetic field, transversal in respect to the electric field established during this process, produces a system of crossed fields ExB. This system of crossed fields promotes an increase of the plasma density, resulting in higher implantation current, and consequently in a shorter treatment time and a higher retained dose in comparison to the conventional PIII process. In this work we have analyzed by means of numerical simulation the effect of magnetic field distribution on the PIII processing. The magnetic field is produced by a pair of external coils, whose radii and separation distance were varied. We found that the density of the implantation current essentially depends on the magnetic field configuration. Thus, with an appropriate configuration of the coils (10,0 cm radius and separation of 42,0 cm) we have obtained an almost uniform current density of approximately 1,5 mA/cm2 that is 1,5 times bigger in relation to the case PIII without magnetic field. The effect of the target bias as well as the gas pressure on the ion current incident on the target is also investigated. The PIII system with crossed ExB fields has been studied using two-dimensional numerical simulation. The simulation is accomplished by the computer code KARAT which employs the particle-in-cell (PIC) algorithm for simulating the movement of charged particles in the electromagnetic field. / Mestre

abstract: Quark matter at sufficiently high density and low temperature is expected to be a color superconductor, and may exist in the interior of neutron stars. The properties of two simplest possible color-superconducting phases, i.e., the color-flavor-locked (CFL) and two-flavor superconducting (2SC) phases, are reviewed. The effect of a magnetic field on the pairing dynamics in two-flavor color-superconducting dense quark matter is investigated. A universal form of the gap equation for an arbitrary magnetic field is derived in the weakly coupled regime of QCD at asymptotically high density, using the framework of Schwinger-Dyson equation in the improved rainbow approximation. The results for the gap in two limiting cases, weak and strong magnetic fields, are obtained and discussed. It is shown that the superconducting gap function in the weak magnetic field limit develops a directional dependence in momentum space. This property of the gap parameter is argued to be a consequence of a long-range interaction in QCD. / Dissertation/Thesis / Ph.D. Physics 2012

Made available in DSpace on 2014-06-11T19:25:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-05Bitstream added on 2014-06-13T19:53:18Z : No. of bitstreams: 1 mitmapillaca_ejd_me_guara.pdf: 802438 bytes, checksum: be2c83ec017ba3f36efb9e9da538c9e6 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Universidade Estadual Paulista (UNESP) / O estudo do efeito do campo magnético sobre o processo de implantação iônica por imersão em plasma (3IP) é de grande interesse para o tratamento de materiais. Sendo 3IP uma técnica relativamente nova e de grande relevância para diversas aplicações tecnológicas é importante que ela seja pesquisada e analisada detalhadamente. A aplicação de um campo magnético estático, transversal em relação ao campo elétrico formado durante este processo produz um sistema de campos cruzados ExB. Este sistema de campos cruzados gera um aumento significativo da densidade de plasma na vizinhança do alvo, resultando num maior corrente de implantação, e conseqüentemente um tratamento mais rápido e uma dose retida mais alta em relação ao processo 3IP convencional. Neste trabalho, analisamos mediante simulação numérica, o efeito da distribuição do campo magnético axial no processo 3IP. O campo magnético é produzido por um par de bobinas instaladas fora da câmara de vácuo cujos raios e distância de separação são variadas. Encontramos que a densidade de corrente de implantação depende essencialmente da configuração do campo magnético. Assim, com uma adequada configuração das bobinas (10,0 cm de raio e 42,0 cm de separação) obtivemos uma densidade de corrente quase uniforme de aproximadamente 1,5 mA/cm2 que é 1.5 vezes maior em relação ao caso do sistema 3IP sem campo magnético. O efeito da tensão aplicada assim como da pressão do gás sobre o plasma no processo 3IP é também investigado. O sistema 3IP com campos ExB cruzados é estudado utilizando a técnica de simulação numérica em duas dimensões. Esta simulação é realizada com o código computacional KARAT que emprega o algoritmo “particle-in-cell” (PIC) para simular o movimento de partículas carregadas no campo eletromagnético. / Detailed investigation of the effect of magnetic field on the process of plasma immersion ion implantation (PIII) is of great interest for the material treatment. Being a relatively novel and of great relevance for technological applications technique, the PIII demands further research and careful analysis. The application of static magnetic field, transversal in respect to the electric field established during this process, produces a system of crossed fields ExB. This system of crossed fields promotes an increase of the plasma density, resulting in higher implantation current, and consequently in a shorter treatment time and a higher retained dose in comparison to the conventional PIII process. In this work we have analyzed by means of numerical simulation the effect of magnetic field distribution on the PIII processing. The magnetic field is produced by a pair of external coils, whose radii and separation distance were varied. We found that the density of the implantation current essentially depends on the magnetic field configuration. Thus, with an appropriate configuration of the coils (10,0 cm radius and separation of 42,0 cm) we have obtained an almost uniform current density of approximately 1,5 mA/cm2 that is 1,5 times bigger in relation to the case PIII without magnetic field. The effect of the target bias as well as the gas pressure on the ion current incident on the target is also investigated. The PIII system with crossed ExB fields has been studied using two-dimensional numerical simulation. The simulation is accomplished by the computer code KARAT which employs the particle-in-cell (PIC) algorithm for simulating the movement of charged particles in the electromagnetic field.

This diploma thesis deals with selection, construction and realization of measuring device of magnetostatic field and description of the basic laws used in magnetism. It also describes principles and functions of particular sensors and probes curently used for measuring of magnetic fields, especially fluxgate magnetometer, which has been constructed. The result of this work is a particular realisation of measuring device with functional testing measurements.

Este trabalho consistiu na implementação de um método de homogeneização de campo, denominado shimming passivo. Esse método é caracterizado pela inserção de pequenas peças ferromagnéticas no interior do magneto; a interação destas peças com o campo magnético principal produz campos locais capazes de corrigir inomogeneidades indesejadas, quando várias peças são estrategicamente combinadas. Embora esse método já tenha sido bem discutido, implementado e publicado por D.I.Hoult na década de 80, ele ainda não havia sido desenvolvido para um magneto resistivo com núcleo de ferro e peças polares, como é o caso do Artro-ToRM. Nosso objetivo era, através do Artro-ToRM, encontrar uma metodologia de modelagem e correção de campo que fosse útil para magnetos com a mesma geometria. Foram utilizados métodos computacionais de ajuste numérico que, a partir de mapas originais de campo, foram capazes de encontrar configurações de peças magnéticas que pudessem reduzir as inomogeneidades presentes. Um dos maiores desafios do trabalho, foi encontrarmos elementos passivos com comportamento previsível quando submetidos ao campo magnético principal, já que os programas de otimização presupunham que trabalhávamos com dipolos magnéticos, para efeitos de simplificação. Finalmente, considerando uma região cilíndrica com raio de 5 cm e comprimento de 10 cm, mostramos uma melhora de 390 ppm para 250 ppm na homogeneidade, após a correção passiva. / This work presents the implementation of a method for field correction, called passive shimming. The method is characterized by the insertion of small iron pieces in magnet bore; the interaction of these pieces with the main magnetic field produces local fields capable of correcting undesired inhomogenity, when some parts are strategically combined. Although this method has been already proposed by D.I.Hoult in the eighties, it still has not been developed for resistive magnets with polar pieces, such as the Artro-ToRM. Our objective were to find a method for field modeling and correction that could be useful for magnets with similar geometry. Computational methods of numerical adjustment were used from the original field maps, it was possible to find the optimal the configurations of magnetic parts for reducing the field inhomogenity. One of the biggest challenges of the work, was to find passive elements with previsible behavior when submitted to magnetic field main, since the optimization programs preassumed that we worked with magnetic dipoles, for the purpose of simplification. Finally, considering a cilindrical region, we show an improvement of 390 ppm to 250 ppm in the homogenity, after the passive correction.

[pt] Foi construído um magnetocardiógrafo supercondutor utilizando-se um SQUID (Superconductor Quantum Interference Device), capaz de medir campos magnéticos da ordem de 10 -8 gauss. Este aparelho foi utilizado para se testar a validade de um modelo cardíaco de múltiplos dipolos para magnetocardiografia. O modelo foi implementado através de um simulador elétrico e os resultados são comparados com sinais magnetocardiográficos de indivíduos normais. / [en] A superconducting magnetocardiographer using a SQUID (Superconductor Quantum Interference Device) which is capable of measuring magnetic fields down to 10 -8 gauss was built. This instrument was used in the test of a multiple dipole cardiac model in magnetocardiography. The model was accomplished through an electric simulator and the results are compared with magnetocardiographic signals of normal subjects.

La spectroscopie optique des atomes simples permet une mesure très précise des propriétés atomiques et des perturbations extérieures, comme par exemple des champs électriques ou magnétiques appliqués. Le spectre Zeeman correspond à une signature du champ magnétique. Dans cette thèse nous présentons l'étude de la réponse du rubidium aux champs magnétiques intenses, dans le but d'utiliser celle-ci comme une sonde de champ magnétique dans l'intervalle de 0.1 T à 60 T. Ce travail a été réalisé dans le cadre du projet RUHMA (RUbidium Atoms in High MAgnetic fields). Notre étude ouvre la voie à la métrologie optique des champs intenses, en déterminant un champ magnétique grâce à la mesure d'une fréquence optique. Le principe de l'expérience consiste à comparer les spectres atomiques expérimentaux et les spectres théoriques calculés, afin d'obtenir la valeur de l'intensité du champ. Nous avons réalisé des premiers tests en champ magnétiques statiques, compris entre 0.06 T et 0.2 T. Dans ce régime, nous avons étudié en détails les effets dus à la structure particulière des niveaux d'énergie du système atomique: des configurations à trois ou quatre niveaux produisent des nouvelles résonances et influencent l'amplitude des signaux observés . Après cette phase préliminaire, le régime de champs intenses (entre 1 T et 60 T) a été exploré, en utilisant les bobines pulsées du Laboratoire National des Champs Magnétiques Intenses de Toulouse. L'une des tâches critiques de ce travail a été la miniaturisation du système expérimental, dans le but de satisfaire les contraintes imposées par une expérience en champ intense. Avec ce système nous avons pu étudier la métrologie des champs pulsés jusqu'à environ 58 T , ce qui est, à ce jour, le champ le plus intense auquel un gaz atomique n'a jamais été soumis. L'incertitude relative de notre méthode est de l'ordre de 10-4. / Optical spectroscopy of simple atoms allows a very precise measurement of the atomic properties and of the external perturbations, as applied magnetic or electric fields. The Zeeman spectrum represents a magnetic field fingerprint. In this work we present our investigations about rubidium response to high magnetic fields in order to use it as magnetic field probe in the range 0.1 T - 60 T. This work was carried out in the framework of the RUHMA (RUbidium Atoms in High MAgnetic fields) project. Our investigation opens the path to magnetic field optical metrology, converting a magnetic field measurement into an optical frequency determination. The principle of the experiment is to compare experimental atomic spectra with computed theoretical spectra, in order to extract the value of the magnetic field strength. We performed our preliminary tests in static magnetic fields, ranging from 0.06 T to 0.2 T. In this framework we investigated in details some complex spectroscopic structures due to the multi-level nature of the atomic system. After this preliminary phase, the 1T-60T range have been investigated using the pulsed magnets of the Laboratoire National des Champs Magnétiques Intenses in Toulouse. We carried out an effort of miniaturization of the experimental setup in order to satisfy the constraints imposed by high magnetic field experiments. We performed metrology of pulsed magnetic field up to 58 T, which is the highest field an atomic gas has never been exposed. The accuracy of our method attained the level of 10-4.

Abstract This thesis studies the structure and evolution of the large scale heliospheric magnetic field. The work covers the space age, the period when satellite measurements revolutionized our knowledge about space. Now, this period is known to be the declining phase of the grand modern maximum of solar activity. The thesis addresses how the hemispherical asymmetry of solar activity is seen in the photospheric magnetic field and how it appears in the corona and in the heliosphere until the termination shock. According to geomagnetic and heliospheric observations, the heliospheric current sheet has been southward shifted around the solar minima since 1930s. Using Ulysses probe observations, we derive an accurate estimate of 2° for the southward shift of the heliospheric current sheet during two very different solar minimum in the mid 1990s and 2000s. The overall structure of the heliospheric magnetic field has changed significantly now when the grand modern maximum has come to an end. During the present low solar activity the polar fields are weaker and the heliospheric current sheet covered a wide latitudinal range during the previous minimum. When the heliospheric current sheet is wide the asymmetry is less visible at the Earth’s orbit. We extend our study to the outer heliosphere using measurements made by Voyager and Pioneer probes and show that the hemispherical asymmetry in the coronal hole evolution, and the related southward shift of the heliospheric current sheet, are seen until the termination shock. In order to understand the origin of the hemispherical asymmetry, we complete a multipole analysis of the solar magnetic field since 1976. We find that the minimum time southward shift of the heliospheric current sheet is due to the quadrupole component of the coronal magnetic field. The quadrupole term exists because the generation and transport of the magnetic flux in the Sun tends to proceed differently in the northern and southern hemispheres. During this and the following decade the Sun is most likely going to be less active than it has been since 1920s. Therefore it is probable that the hemispherical asymmetry of the heliospheric magnetic field will be less visible in the ecliptic plane in the near future. Now, when the Sun seems to be at the maximum of cycle 24, we are looking forward to see how the polar fields and the heliospheric magnetic field are formed when approaching the following solar minimum. It is possible that, as the activity rises again after the present and future low cycles, the hemispherical asymmetry will be opposite to that of the 20th century and the minimum time heliospheric current sheet would be northward shifted.

It is a well known fact that the visible universe is made almost entirely of baryonic matter. Yet, this is also one of the greatest puzzles that physicists are trying to solve: Where did all of this matter come from in the first place? The Standard Model (SM) of particle physics predicts a baryon asymmetry that is much smaller than what is observed in nature. In order to try and explain this discrepancy, Sakharov (1967) postulated three necessary conditions for baryogenesis in the early universe. One of these is the requirement that charge conjugation (C) and the product of C and parity (P) symmetries are violated. Because the SM fails to generate the observed baryon asymmetry, additional sources of CP violation are needed in order to help reconcile theory and observation. Thus, physicists have been looking for extensions to the SM in search of an answer. The presence of a neutron Electric Dipole Moment (nEDM) would signal a new source of CP violation. A non-vanishing nEDM would provide evidence for the breaking of both parity (P) and time-reversal symmetry (T). Because CPT symmetry is assumed to be conserved and has not been found to be broken, this would signal CP violation. To look for an nEDM, stored ultracold neutrons are placed in parallel and anti-parallel magnetic and electric fields and the Larmor precession frequency is carefully measured. A difference in the precession frequency of the neutrons in the two states of the fields would signal the existence of an nEDM. The current upper limit of the nEDM was set by the RAL-Sussex-ILL collaboration and stands at dn < 3.0x10-26 e cm (90% CL). Currently a new cryogenic apparatus is under construction at the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory (ORNL) which aims to reduce the current upper limit by two orders of magnitude. A central problem to all neutron EDM experiments is the generation of a highly uniform and stable magnetic field. Because the suppression of systematic effects that arise from magnetic field nonuniformities and temporal drifts is vital to the success of these experiments, it is important to have the ability to precisely control and monitor the magnetic field gradients inside of the experimental volume. However, it is not always possible to measure the field gradients within the region of interest directly. To remedy this issue in the SNS nEDM experiment, a field monitoring system has been designed and tested that will allow for the reconstruction of the field gradients inside of the fiducial volume using noninvasive measurements of the field components at discrete locations external to this volume. This document will outline the theoretical framework of our method and present the results of experimental and simulated studies performed and the engineering design for such a field monitoring system.

This thesis concerns itself with the scientific study of the recently discovered organic magnetoresistance (OMAR) whose underlying mechanism is currently not known with certainty. As an introduction, we briefly review the major findings from prior work done by my colleagues. They found that OMAR can be as large as ~10% magnetoresistance at 10 mT magnetic fields at room temperature. Both OMAR and other kinds of magnetic field effect data in organics can be fitted using the empirical laws B^2/(B^2+B_0^2) or B^2/(|B|+B_0)^2, dependent on material. The fitting parameter B_0 is a measure of the characteristic magnetic field strength of OMAR. We explore the dependence of B_0 on material parameters to clarify the origin of OMAR. Various pi-conjugated semiconductor OMAR devices were studied to explore the possibility that hyperfine interaction causes OMAR. For a quantitative analysis of the experiments, we developed a theoretical fitting formula to relate B_0 to the hyperfine coupling strength. In addition, organic materials with different spin-orbit coupling strengths were also measured. Fluorescence and phosphorescence spectroscopies were used to estimate the spin-orbit coupling strength from the measured spectra. For analyzing our measurements, we developed a fitting formula from the time-dependent Schrodinger equation that takes into account the combined effect of hyperfine and spin-orbit coupling on spin-dynamics. We found that in the case of strong spin-orbit coupling, it dominates the behavior, resulting in magnetic field effect traces that are much wider than those in ordinary organics. However, a small cone remains at zero field with a width equal to the hyperfine coupling strength. We find qualitative agreement between the experimental results and the model. We also investigated the question whether OMAR is related to an excitonic effect, or is primarily a transport effect. We measured the magnetic field effects on current, photocurrent and electroluminescence to address this question. By varying the injection efficiency of the minority carriers, we show that OMAR most likely is not an excitonic effect. Our results provide strong evidence in support of the claim that OMAR is caused by spin-dynamics. However, further study is required to study the mechanism connecting spin-dynamics and conductivity.