Dissertations / Theses: 'Radial Electric Field'

1

Temple, Darren. "Experimental investigations into the radial electric field of MAST." Thesis, Imperial College London, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540683.

Full text

APA, Harvard, Vancouver, ISO, and other styles

2

Viezzer, Eleonora. "Radial electric field studies in the plasma edge of ASDEX." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-161574.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Honda, Mitsuru. "Transport simulation of tokamak plasmas including plasma rotation and radial electric field." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136227.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Wilks, Theresa M. "Calculation of the radial electric field in the DIII-D tokamak edge plasma." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/54988.

Full text

Abstract:

The application of a theoretical framework for calculating the radial electric field in the DIII-D tokamak edge plasma is discussed. Changes in the radial electric field are correlated with changes in many important edge plasma phenomena, including rotation, the L-H transition, and ELM suppression. A self-consistent model for the radial electric field may therefore suggest a means of controlling other important parameters in the edge plasma. Implementing a methodology for calculating the radial electric field can be difficult due to its complex interrelationships with ion losses, rotation, radial ion fluxes, and momentum transport. The radial electric field enters the calculations for ion orbit loss. This ion orbit loss, in turn, affects the radial ion flux both directly and indirectly through return currents, which have been shown theoretically to torque the edge plasma causing rotation. The edge rotation generates a motional radial electric field, which can influence both the edge pedestal structure and additional ion orbit losses. In conjunction with validating the analytical modified Ohm’s Law model for calculating the radial electric field, modeling efforts presented in this dissertation focus on improving calculations of ion orbit losses and x-loss into the divertor region, as well as the formulation of models for fast beam ion orbit losses and the fraction of lost particles that return to the confined plasma. After rigorous implementation of the ion orbit loss model and related mechanisms into fluid equations, efforts are shifted to calculate effects from rotation on the radial electric field calculation and compared to DIII-D experimental measurements and computationally simulated plasmas. This calculation of the radial electric field will provide a basis for future modeling of a fast, predictive calculation to characterize future tokamaks like ITER.

APA, Harvard, Vancouver, ISO, and other styles

5

Ernst, Darin R. (Darin Richard) 1965. "Momentum transport, radial electric field, and ion thermal energy confinement in very high temperature plasmas." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50337.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Viezzer, Eleonora [Verfasser], and Hartmut [Akademischer Betreuer] Zohm. "Radial electric field studies in the plasma edge of ASDEX upgrade / Eleonora Viezzer. Betreuer: Hartmut Zohm." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2013. http://d-nb.info/1042899843/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

McDermott, Rachael Marie. "Edge radial electric field studies via charge exchange recombination spectroscopy on the Alcator C-Mod Tokamak." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/54462.

Full text

Abstract:

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 189-197).
It is commonly accepted that ExB velocity shear is responsible for the suppression of edge turbulence, which reduces the losses of both energy and particles across magnetic field lines and results in the formation of edge transport barriers and high-confinement mode (H-mode) in tokamak plasmas. However, the self consistent evolution of the radial electric field profile (Er), pedestal shape and improvement in plasma confinement is not well understood. A better understanding of pedestal physics and the interplay between Er, turbulence suppression and pedestal formation should enable better control of edge transport and improve core confinement. A new, high-resolution, charge exchange recombination spectroscopy (CXRS) diagnostic has been installed on Alcator C-Mod to provide measurements of the B5+ population in the pedestal region. This diagnostic is capable of measuring the boron temperature, density, and poloidal and toroidal velocity with 3mm radial resolution and 5ms temporal resolution. These profiles, coupled with knowledge of the toroidal and poloidal magnetic fields, enable the determination of the edge radial electric field through the radial force balance equation. The new CXRS diagnostic has provided the first spatially resolved calculations of the radial electric field in the C-Mod edge and has made possible significant contributions to the study of pedestal physics. Detailed measurements of the boron population have been made in a variety of plasma regimes. The measured rotation profiles connect the SOL and core measurements and are consistent with both. The CXRS boron temperature profiles are observed to agree well with the Thomson Scattering electron temperature profiles in bothl shape and magnitude over a wide range of collisionalities. In H-mode plasmas both the boron temperature and density profiles form clear pedestals, similar to what is observed in the electron channel. The edge toroidal rotation increases in the concurrent direction at the onset of H-mode confinement and the poloidal rotation in the pedestal region increases in the electron diamagnetic direction forming a narrow
(cont.) peak (3-4mm) just inside of the LCFS. In Ohmic L-mode plasmas Er is positive near the last closed flux surface (LCFS) and becomes more negative with distance into the plasma. In H-mode plasmas E, is positive in the core, but forms a deep negative well, relative to its L-mode values, just inside of the LCFS. These results are qualitatively consistent with the observations made on other machines. However, the C-Mod H-mode Er wells are unprecedeited in depth (up to 300kV/m) and the narrow E, well widths (5mm), as compareJ to results from other tokamaks, suggest a scaling with machine size. The measured Er well widths have been compared to theoretical scalings for the edge pedestal and no significant correlation was observed with any of the predictions. In fact, very little variation of the E, well width is observed in general. Howc:ver, the depth of the E, well, or alternatively the magnitude of the E, shear (constant width), shows a strong correlation with improved plasma energy confinement. It also correlates well with the edge electron temperature and pressure pedestal heights (and gradients). It is not, however, very sensitive to variation in the edge electron density pedestal height. These results are an indication that the energy and particle transport have different relationships to Er, with energy transport more directly linked. The radial electric field results from ELM-free H-mode and I-mode plasmas support this interpretation.
by Rachael Marie McDermott.
Ph.D.

APA, Harvard, Vancouver, ISO, and other styles

8

Kumar, Santhosh Tekke Athayil, and santhosh kumar@anu edu au. "Experimental Studies of Magnetic Islands, Configurations and Plasma Confinement in the H-1NF Heliac." The Australian National University. Research School of Physical Sciences and Engineering, 2008. http://thesis.anu.edu.au./public/adt-ANU20080611.171513.

Full text

Abstract:

Rational magnetic flux surfaces in fusion (toroidal plasma confinement) devices can break the magnetic field lines and reconnect them in the form of magnetic islands. Formation of these magnetic islands can have a serious impact on the plasma confinement properties of the device. Islands can in general degrade the confinement by mixing up different regions of the plasma. However there has been experimental evidence of confinement improvement by island induced transport barriers, under certain conditions. Even though there are a large number of theoretical and experimental works on magnetic islands to date, there is clearly a paucity of convincing experimental understanding on the nature of behaviour of islands in plasma. This thesis reports detailed experimental studies conducted on the H-1NF heliac stellarator, to gain an in-depth understanding of magnetic islands and their influence in plasma confinement.¶ Work reported in this thesis can be mainly divided into three parts: (a) high resolution imaging of vacuum magnetic islands and flux surfaces of H-1NF, (b) accurate computer modeling of H-1NF magnetic geometry and (c) detailed experiments on magnetic islands in plasma configurations.¶ Electron-beam wire-tomography in the H-1NF has been used for the high resolution mapping of vacuum magnetic flux surfaces and islands. Point-to-point comparison of the mapping results with computer tracing, in conjunction with an image warping technique, has enabled systematic exploration of magnetic islands and surfaces of interest. A fast mapping technique has been developed, which significantly reduced the mapping time and made this technique suitable for mapping at higher magnetic fields.¶ Flux surface mapping has been carried out at various magnetic configurations and field strengths. The extreme accuracy of this technique has been exploited to understand the nature of error fields, by point-by-point matching with computer tracing results. This has helped in developing a best-fit computer model for H-1NF magnetic configurations, which can predict rotational transform correct to three decimal places. Results from plasma experiments on magnetic configuration studies are best explained by the new model.¶ Experiments with low order magnetic islands in plasma configurations yielded some new results. It has been observed that the low order magnetic islands (m = 2) near the core of the plasma serve as pockets of improved confinement region under favourable conditions. This results in significant profile modifications including enhancement of the radial electric field near the core to a large positive value. The characteristics of islands are found to be dependent on the plasma collisionality and the island width.¶ Experiments with a magnetic configuration which exhibits no vacuum islands, but the core rotational transform very close to low order rational value, show a spontaneous transition of the radial electric field near the core to a large positive value (nearly 5 kV/m), with a strong electric field shear (nearly 700 kV/m2) and localised improvement in confinement, during the discharge. Evidence indicates that the transition is driven by the excitation of low order magnetic islands near the axis during the plasma discharge, due to the modification of rotational transform profile by toroidal plasma currents. The situation is similar to the Core Electron-Root Confinement (CERC) observed during high temperature ECH plasma discharges on other helical devices. This result provides an experimental evidence for the hypothesis that the threshold conditions for observing CERC can be reduced by exciting magnetic islands near the core of the plasma.

APA, Harvard, Vancouver, ISO, and other styles

9

Wrench, Christopher G. "Collisional transport of trace impurity ions and the role of the radial electric field in spherical tokamak plasmas." Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/55347/.

Full text

Abstract:

The mitigation and control of impurities, or non-fuel ions, in tokamak plasmas is vital for reducing energy losses and an understanding of impurity transport is required in order to predict the performance of present and future tokamak devices. The development and application of a full orbit, test particle code to the study of the collisional transport of test impurity ions in spherical tokamak plasmas is presented. This code is tested against the standard analytic description of collisional transport in magnetised plasmas and is demonstrated to be particularly suited to the study of the tight aspect ratio of the spherical tokamak design. The principle results of the present work concern the investigation of the role of the radial electric field, a feature of high performance tokamak plasmas, on collisional ion transport. It is found that a static radial electric field leads to a significant reduction in the radial transport of test impurity ions. This effect may be explained in terms of a novel radial drift of the test ions arising due to the introduction of collisional Langevin terms to the full orbit, test particle equations of motion. This has significant implications for the confinement of impurity ions in high performance, steady state tokamak discharges. A scaling of this modification with impurity particle mass and charge numbers is derived analytically and verified numerically and a scaling with electric field parameters is derived numerically. A time dependent radial electric field, which models a number of transient events in tokamak plasmas such as the low- to high-mode transition and edge localised modes, is also investigated and attempts at a preliminary comparison between experimental and numerical observations of impurity transport in spherical tokamak devices is presented.

APA, Harvard, Vancouver, ISO, and other styles

10

Cavedon, Marco [Verfasser], Ulrich [Akademischer Betreuer] [Gutachter] Stroth, and Aliaksandr [Gutachter] Bandarenka. "The role of the radial electric field in the development of the edge transport barrier in the ASDEX Upgrade tokamak / Marco Cavedon. Betreuer: Ulrich Stroth. Gutachter: Aliaksandr Bandarenka ; Ulrich Stroth." München : Universitätsbibliothek der TU München, 2016. http://d-nb.info/1103135260/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

11

Vidal, Denis Tadeu Rajh. "Elaboração de um sistema de controle externo do fluxo eletrosmótico para eletroforese capilar com detecção condutométrica sem contato." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/46/46133/tde-21072008-151809/.

Full text

Abstract:

A presente dissertação trata da implementação, em um equipamento de eletroforese capilar (CE) com detecção condutométrica sem contato (C4D), de um sistema de controle externo do fluxo eletrosmótico (EOF) via tensão radial externa (Vrad). Através do potencial externo, aplicado diretamente ao capilar, é possível ter o controle do fluxo eletrosmótico de CE, pois, de forma simplificada, esta prática acopla vetorialmente um potencial externo aplicado com o potencial através da solução tampão dentro do capilar. O emprego da técnica possibilitou o aumento de resolução de 2 aminoácidos - Leucina e Isoleucina, cujas mobilidades diferem apenas de 0,12 cm2.V-1.s-1 entre si, em ácido acético 500 mmol.L-1 com pH = 2,55. A estratégia empregada aqui foi a que denominamos de \"coluna capilar infinita\", na qual, com as sucessivas inversões na direção do EOF, conseguimos aprisionar, dentro da coluna capilar, espécies com mobilidade eletroforética menor que a mobilidade do EOF. A literatura descreve que a inversão do EOF se torna mais difícil com o aumento do pH. Foram realizados testes em eletrólitos contendo agentes inversores de fluxo como o CTAB, o CaCl2 e o BaCl2. Ambos os aditivos foram usados em concentrações muito baixas, nas quais foi mantida a direção normal do EOF, sendo que a utilizaçãode tais agentes teve a finalidade apenas de reduzir os grupos silanolatos em soluções de pH acima de 6,0. Tal estratégia proporcionou a reversão do EOF no sistema tampão MES/HIS, cujo pH estava em torno de 6,1. Por fim, a pesquisa gerou uma perspectiva interessante que é a possibilidade de se encontrar combinações de eletrólitos de corrida e surfactantes com o intuito de se estender a faixa de alcance do Vrad para valores altos de pH.
This work presents the implementation, in an equipment for capillary electrophoresis (CE) with contactless conductivity detection (C4D), of a system for external control of the electroosmotic flow (EOF) via external radial voltage (Vrad). Through external potential, directly applied to the capillary, the electroosmotic flow can be controlled, because this practice couples the applied external potential to the zeta potential through the buffer solution within the capillary. The use of the technique allowed the baseline resolution of two amino acids (Leucine and Isoleucine), whose mobilities differ only by 0,12 cm2.V-1.s-1, using acetic acid 500 mmol.L-1 at pH = 2,55 as the running electrolyte. The approach, called \"infinite capillary column\", consists in successive reversals in the direction of the EOF, trapping species within the capillary column with electrophoretic mobility smaller than the EOF mobility. Thus, the two amino acids were retained by a period of approximately 120 minutes in the capillary that was enough to promote the baseline resolution. Previous works describe that the reversion of the EOF becoming more difficult as pH increases. In order to achieve a more effective control of EOF at high pH values (limiting the technique to a narrow performance band), tests were carried out in electrolytes containing flow reversing agents such as CTAB, CaCI2 and BaCI2. These additives were used at very low concentrations, which kept the normal direction of EOF, and the use of such agents had only the purpuse of reducing the density of silanolate groups in solutions of pH above 6,0. This approach allowed the reversion of the EOF using MES/HIS buffer, which pH was 6,1. Finally, this research has generated an interesting perspective about the possibility of finding combinations of electrolytes and surfactants aiming the Vrad range´s extension at high pH values.

APA, Harvard, Vancouver, ISO, and other styles

12

Carpenter, Joanna Katharine Hicks. "Magnetic field effects on electron transfer reactions in photosynthetic bacteria." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390466.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

Scharfe, Michelle Kristin. "Electron cross field transport modeling in radial-axial hybrid hall thruster simulations /." May be available electronically:, 2009. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Eveson, Robert W. "Geminate free radical processes and magnetic field effects." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325978.

Full text

APA, Harvard, Vancouver, ISO, and other styles

15

Wagner-Rundell, Nicola. "Electron spin relaxation effects on radical recombination reactions in weak magnetic fields." Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.497470.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

Gravestijn, Bob. "Importance of radial profiles in spectroscopic diagnostics applied to the EXTRAP-T2R reversed-field pinch." Doctoral thesis, KTH, Physics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3656.

Full text

Abstract:

The determination of the plasma confinement propertiesdemand data as the electron temperature, the ionic and electrondensity profiles and the radiative emissivity profiles. Thefocus of this thesis is the importance of radial profiles inspectroscopic diagnostics applied to the EXTRAP-T2Rreversed-field pinch.

EXTRAP-T2R is a resistive shell reversed-field pinch with amagnetic field shell penetration time much longer than therelaxation cycle time scale. Significant improvements inconfinement properties derived by quantitative plasmaspectroscopy in the vacuum ultraviolet are observed compared tothe previous device EXTRAP-T2. The low level of magneticturbulence and the good magnetic surfaces in the edge regionexplain this observed improvement. A current profile controlexperiment reduces the stochastic transport, which is connectedto the dynamo, and improves the confinement in EXTRAP-T2R evenmore.

A comparison of the electron temperature estimated by usinga ratio of line intensities from the same ionization stage ofoxygen and the Thomson scattering system shows that thedifference is explained by the different spatial dependence ofthe excited state populations and the corresponding emissivityof these spectral lines. A collisional radiative model givesestimates for radial profiles of impurities which are notmeasured in EXTRAP-T2R. The estimated profiles can in turn beused to determine the radial profile of the effective ioncharge, the emissivity and finally the radiative power. Asinput, the model uses radial profiles.

Neutral hydrogen is predominantly present in the boundaryregion of the plasma. Spectroscopic investigations in this areashow very asymmetric spectral lines of hydrogen due to themovement of atoms. The velocity of the hydrogen atoms dependson the type of plasma-wall interaction and their measurementhelps to identify the different interaction processes. Theexistence of hydrogen molecules in the edge complicates theinterpretation of the line shapes and on the determination ofthe particle confinement time.

Keywords:Reversed-field pinch, EXTRAP-T2R, quantitativeplasma spectroscopy, VUV spectroscopy, line-integrated electrontemperature, oxygen, profiles, confinement properties, powerbalance, hydrogen, particle confinement time.

APA, Harvard, Vancouver, ISO, and other styles

17

Yeung, David. "Dual-tuned radiofrequency coils for field-cycled proton-electron double resonance imaging of free radicals." Thesis, University of Aberdeen, 1995. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU078721.

Full text

Abstract:

Field-cycled proton-electron double-resonance imaging (FC-PEDRI) is a technique developed to image the distribution of free radicals in biological samples. This technique is based on the Overhauser Effect that causes an enhancement in the NMR signal by saturating the ESR resonance of unpaired electrons in the sample. FC-PEDRI requires two sources of RF irradiations. To improve the sensitivity and to reduce power deposition in samples, new dual-tuned single coil designs were needed since existing dual-tuned single-coil designs known in the literature cannot operate at two widely separated frequencies. The theory of double-tuned circuits was examined and new circuit models were developed to identify the design requirements. Four new dual-tuned RF coils were developed, namely a dual-tuned split solenoidal coil (2.5 and 78 MHz), a combined saddle-birdcage (CS-B) coil (2.5 and 110 MHz), a 3-endring (3-ER) birdcage (2.5 and 56 MHz) and a 4-endring (4-ER) birdcage (2.5 and 74 MHz). A prototype coil for each design was built for performance evaluation studies and the parameters evaluated were: the Q factors, the signal-to-noise ratio, the transmit sensitivity and the field uniformity. The performance of the NMR-mode of the 3-ER and 4-ER designs was poor because the inherently low-inductance of the birdcage meant that high-value capacitors with high dissipation factors had to be used in the fabrication. A new construction method named as the multilayer self capacitance (MLSC) technique was developed to improve the efficiency of the 4-ER design by creating efficient capacitors within the conductors of the coil itself. The unloaded Q factor of the optimised 4-ER birdcage using the MLSC technique was 267 compared to 100 when commercial capacitors were used.

APA, Harvard, Vancouver, ISO, and other styles

18

Shtogun, Yaroslav. "Properties of Carbon Nanotubes Under External Factors: Adsorption, Mechanical Deformations, Defects, and External Electric Fields." Scholar Commons, 2010. https://scholarcommons.usf.edu/etd/1771.

Full text

Abstract:

Carbon nanotubes have unique electronic, optical, mechanical, and transport properties which make them an important element of nanoscience and nanotechnology. However, successful application and integration of carbon nanotubes into new nanodevices requires fundamental understanding of their property changes under the influence of many external factors. This dissertation presents qualitative and quantitative theoretical understanding of property changes, while carbon nanotubes are exposed to the deformations, defects, external electric fields, and adsorption. Adsorption mechanisms due to Van der Waals dispersion forces are analyzed first for the interactions of graphitic materials and biological molecules with carbon nanotubes. In particular, the calculations are performed for the carbon nanotubes and graphene nanoribbons, DNA bases, and their radicals on the surface of carbon nanotubes in terms of binding energies, structural changes, and electronic properties alterations. The results have shown the importance of many-body effects and discrete nature of system, which are commonly neglected in many calculations for Van der Waals forces in the nanotube interactions with other materials at nanoscale. Then, the effect of the simultaneous application of two external factors, such as radial deformation and different defects (a Stone Wales, nitrogen impurity, and mono-vacancy) on properties of carbon nanotubes is studied. The results reveal significant changes in mechanical, electrical, and magnetic characteristics of nanotubes. The complicated interplay between radial deformation and different kinds of defects leads to the appearance of magnetism in carbon nanotubes which does not exist in perfect ones. Moreover, the combined effect of radial deformation and external electric fields on their electronic properties is shown for the first time. As a result, metal-semiconductor or semiconductor-metal transitions occur and are strongly correlated with the strength and direction of external electric field and the degree of radial deformations.

APA, Harvard, Vancouver, ISO, and other styles

19

Shet, Keerthi Vishnudas. "Development Of Instrumentation And Techniques To Adapt Proton Electron Double Resonance Imaging For Biomedical Imaging." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1227731151.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Lejosne, Solène. "Modélisation du phénomène de diffusion radiale au sein des ceintures de radiation terrestres par technique de changement d’échelle." Thesis, Toulouse, ISAE, 2013. http://www.theses.fr/2013ESAE0027/document.

Full text

Abstract:

Cette étude s’inscrit dans le domaine de la description de la dynamique des ceintures deradiation terrestres. Elle consiste à modéliser le phénomène de diffusion radiale en travaillantavec une résolution spatio-temporelle plus fine que celle utilisée pour décrire la dynamiquedes ceintures par le biais d’une équation de diffusion. La démarche s’est organisée en troistemps. Tout d’abord, l’objectif a été d’étudier le phénomène de diffusion radiale d’un point devue théorique afin de mettre en lumière les principaux pilotes du processus et d’expliciter uneformulation des coefficients de diffusion radiale. Une fois l’expression de ces coefficientsétablie, l’objectif a ensuite été de les quantifier. Pour cela, nous avons développé desprotocoles analytiques et numériques puis des protocoles expérimentaux. Nous avons discutéles résultats obtenus ainsi que les atouts et les limites de ces protocoles. Cette étude met enévidence le rôle central de l’asymétrie des variations du champ électromagnétique et deschamps électriques induits dans le processus de diffusion radiale. Elle propose des pistes pourla quantification numérique et expérimentale de ces deux pilotes. Elle apporte également unregard critique sur les travaux de la littérature. Elle ouvre la voie pour une nouvellequantification des coefficients de diffusion basée sur une modélisation adéquate de ladynamique de l’environnement électromagnétique
This study falls within the field of the Earth’s radiation belt dynamics. It consists of modelingthe radial diffusion process based on a spatiotemporal resolution higher than the resolution atwhich radiation belt dynamics are described in terms of a diffusion equation. The approachhas been organized in three parts. First, we described radial diffusion theoretically,highlighting the main drivers of the phenomenon and giving a ready-made formula of theradial diffusion coefficients. Then, based on this formula, we aimed to quantify the radialdiffusion coefficients. In order to reach this goal, we developed analytical and numericalprocedures, and then, observational procedures. Finally, we discussed the results and the prosand cons of each method. This study highlights the central role of asymmetric variations ofthe electromagnetic fields and induced electric fields in the driving of the intensity of theradial diffusion process. It provides tracks for numerical and experimental quantification ofthese two drivers. It also provides tools for a critical review of the literature. It paves the wayfor a more accurate determination of radial diffusion coefficients based on a more precisedescription of the electromagnetic environment and its variations

APA, Harvard, Vancouver, ISO, and other styles

21

Wieland, Bernd [Verfasser], Sibylle [Akademischer Betreuer] Günter, and Peter A. [Akademischer Betreuer] Feulner. "Investigations on radial electric fields in the edge transport barrier of H-mode discharges / Bernd Wieland. Gutachter: Sibylle Günter ; Peter A. Feulner. Betreuer: Sibylle Günter." München : Universitätsbibliothek der TU München, 2011. http://d-nb.info/1015627889/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Nick, Thomas Udo. "Hydrogen Bonds and Electrostatic Environment of Radical Intermediates in Ribonucleotide Reductase Ia." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2015. http://hdl.handle.net/11858/00-1735-0000-0028-877F-7.

Full text

APA, Harvard, Vancouver, ISO, and other styles

23

Loridan, Vivien. "Physical and numerical modeling of the dynamics of high-energy electrons trapped in the outer radiation belt of the Earth’s magnetosphere." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLN043/document.

Full text

Abstract:

Les satellites sont vulnérables aux particules de forte énergie piégées dans les ceintures de Van Allen. Afin d’en assurer la protection, il est nécessaire de prédire avec précision la dynamique des électrons au sein de la magnétosphère. Dans un premier temps nous proposons une méthode originale de résolution analytique de l’équation de Fokker-Planck réduite qui modélise le transport et les pertes des électrons de la magnétosphère interne. La résolution repose sur une technique de décomposition spectrale. Si la solution analytique s’avère utile pour mettre en exergue certaines propriétés physiques des ceintures de radiation, elle est également pertinente pour valider le code numérique de résolution de l’équation de Fokker-Planck réduite, développé durant la thèse. Ce dernier nous amène à généraliser l’étude précédente en illustrant l’évolution des flux d’électrons pour diverses énergies et positions. Nous prouvons notamment que la structure des ceintures de radiation ainsi que leur temps d’évolution ne dépendent que de quelques facteurs bien choisis. Dans la perspective de reproduire un événement particulier de retour au calme après un orage magnétique, mesuré par les satellites de la NASA dédiés aux ceintures de radiation, nous sommes en mesure de simuler la précipitation des électrons dans l’atmosphère terrestre causée par les interactions avec les ondes électromagnétiques de la magnétosphère. L’utilisation de conditions bâties sur des données empiriques et spécifiques à la période en question nous permet de corroborer les flux observés. Enfin, l’influence du champ magnétique terrestre sur la dynamique des ceintures de radiation est étudiée sous divers aspects. Nous nous concentrons sur la ceinture externe pour comprendre comment les asymétries du champ magnétique, considérablement façonnées par l’activité solaire, affectent notre manière de concilier théorie et observations. Nous explorons également l’importance de certains processus diffusifs nouveaux et cachés, qui émergent à cause de l’irrégularité naturelle du champ magnétique au plus proche voisinage de la Terre
Satellites are vulnerable to high-energy particles trapped in the Van Allen belts. To ensure their protection, it is necessary to predict properly the electron dynamics in the magnetosphere. We first propose an original method to find the analytical solution of the reduced Fokker-Planck equation that models the transport and loss of electrons in the inner magnetosphere. The resolution relies on an eigenfunction expansion approach. If the analytical solution is proven to be useful at uncovering some of the physical properties of the radiation belts, it is also relevant to validate the numerical code that solves the reduced Fokker-Planck equation, which has been developed during the PhD. The latter code is used to generalize the previous study in illustrating the evolution of the electron fluxes for various energies and locations. We demonstrate that the structure of the radiation belts as well as their dynamical timescales only depend on a few well-chosen parameters. In the perspective of reproducing a specific storm-recovery event reported by the NASA Van Allen Probes, we are able to simulate the electron scattering in the Earth’s atmosphere due to the interaction with magnetospheric electromagnetic waves. The consideration of data-driven and event-specific conditions enables us to corroborate the observed fluxes. Finally, various influences of the Earth’s magnetic field on the dynamics of the radiation belts are investigated. We focus on the outer belt to see how the magnetic field asymmetries, which are strongly shaped by solar activity, affect the way of conciliating theory and observations. We also explore the importance of new hidden diffusive processes that emerge due to the natural irregularity of the magnetic field in the closest vicinity of the Earth

APA, Harvard, Vancouver, ISO, and other styles

24

Richard, Cyril. "Spectroscopie électronique et effet zeeman dans le radical NiH." Phd thesis, Université Claude Bernard - Lyon I, 2010. http://tel.archives-ouvertes.fr/tel-00595685.

Full text

Abstract:

Cette thèse s'appuie sur la spectroscopie de NiH établie à la fin des années 1980 et au début des années 1990, principalement par le groupe du Pr. R. W. Field au MIT. Les mesures expérimentales ont amélioré de manière significative les travaux antérieurs, tant en spectroscopie en champ nul qu'en spectroscopie Zeeman. Le radical NiH est obtenu avec une source à décharge à température ambiante (310 K). Les radicaux formés dans la décharge sont excités par un laser continu à colorant et étudiés soit en spectroscopie d'excitation laser soit en fluorescence dispersée. Un circuit magnétique à aimants permanents (NdFeB) fournit un champ magnétique statique (0.4 - 0.9 T). En champ nul, les spectres de fluorescence par transformée de Fourier ont élargi les observations de l'état électronique fondamental jusqu'à 6000 cm-1, pour 58NiH et 60NiH. Les énergies sont modélisées avec un Hamiltonien effectif obtenu à partir du formalisme du modèle du 3d9 supermultiplet développé par le groupe de Field. Les mesures Zeeman se sont principalement concentrées sur l'étude des états Ω=3/2. Les facteurs de Landé effectifs ont été déterminés pour chaque niveau ro-vibrationnel pour les états de basse énergie et les états excités de 58NiH. L'inhabituelle dépendance en J des facteurs de Landé obtenus pour les états de basse énergie est expliquée par le modèle du supermultiplet, quantifiant alors l'ampleur des mélanges spin-orbite présents dans les états inférieurs. Les transitions étudiées ont un intérêt astrophysique depuis que plusieurs transitions d'hydrure métallique ont été observées dans les spectres d'étoiles froides et les taches solaires.

APA, Harvard, Vancouver, ISO, and other styles

25

Pooam, Marootpong. "The biological effects of applied magnetic fields on cryptochrome and response." Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS062.

Full text

Abstract:

Cryptochromes (cry) sont des flavoprotéines absorbant la lumière bleue conservées qui ont été liées à perception de stimuli électromagnétiques dans de nombreux organismes. Nous avons principalement étudié le mécanisme d'interaction entre les champs magnétiques (MF) et cry dans le cadre de la théorie des paires de radicaux. Nous avons étudié la réponse d'Arabidopsis cry-1 in vivo à MF. Les activités biologiques du cry ont été renforcées par MF. Les effets des MF ont pu être observés même si MF était donné exclusivement pendant les intervalles d'obscurité entre expositions à la lumière. Cette découverte a indiqué que l'étape de réaction magnétiquement sensible dans photocycle du cry doit se produire pendant la réoxydation des flavines. De plus, nous avons également utilisé la fréquence (RF) stimulée par cry-Arabidopsis comme outils de diagnostic pour confirmer l'hypothèse de la paire de radicaux. Dans l'étude, nous avons trouvé un effet perturbateur des RF sur l'activité du cryptochrome. Notre découverte pourrait confirmer l'apparition du mécanisme de la paire de radicaux et l'implication du cry pour la magnétoréception. De plus, nous avons également montré un effet perturbateur de la condition MF statique de bas niveau (LLF) où les champs magnétiques externes étaient presque éliminés. Le résultat de cette condition était cohérent avec l'effet de l'exposition aux RF. En outre, nous avons également signalé que LLF pourrait augmenter l'expression de certains gènes induits par le PEMF dans dans les les cellules humaines. Cette découverte pourrait fournir des preuves à l'appui de l'effet des champs électriques magnétiques et non induits sur la physiologie humaine
Cryptochromes are highly conserved blue-light-absorbing flavoproteins that have been linked to the perception of electromagnetic stimuli in numerous organisms. We mainly studied the mechanism for the interaction between magnetic fields and cryptochromes in the context of the radical-pair theory. We investigated the response of Arabidopsis cryptochrome-1 in vivo to a static magnetic field. The biological activities of cryptochrome were enhanced by the magnetic field. Interestingly, the effects of the magnetic fields could be observed even the magnetic field was given exclusively during dark intervals between light exposures. This finding indicated that the magnetically sensitive reaction step in the cryptochrome photocycle must occur during flavin reoxidation. Moreover, we also used frequency (RF) stimulated to Arabidopsis cryptochrome as the diagnostic tools to confirm the radical-pair hypothesis. In the study, we found a disruptive effect of RF on the activity of cryptochrome. Our findings could confirm the occurrence of the radical-pair mechanism and the involvement of cryptochrome for magnetoreception. Additionally, we also showed a disruptive effect of the low-level static magnetic field (LLF) condition where the external magnetic fields were almost eliminated. The result of this condition was consistent with the effect of RF exposure. Furthermore, we also reported that LLF could increase the expression of some PEMF-induced genes in human cells. This finding could provide the evidence to support the effect of magnetic, not induced electric fields in human physiology

APA, Harvard, Vancouver, ISO, and other styles

26

Kumar, Santhosh Tekke Athayil. "Experimental Studies of Magnetic Islands, Configurations and Plasma Confinement in the H-1NF Heliac." Phd thesis, 2007. http://hdl.handle.net/1885/49287.

Full text

Abstract:

Rational magnetic flux surfaces in fusion (toroidal plasma confinement) devices can break the magnetic field lines and reconnect them in the form of magnetic islands. Formation of these magnetic islands can have a serious impact on the plasma confinement properties of the device. Islands can in general degrade the confinement by mixing up different regions of the plasma. However there has been experimental evidence of confinement improvement by island induced transport barriers, under certain conditions. Even though there are a large number of theoretical and experimental works on magnetic islands to date, there is clearly a paucity of convincing experimental understanding on the nature of behaviour of islands in plasma. This thesis reports detailed experimental studies conducted on the H-1NF heliac stellarator, to gain an in-depth understanding of magnetic islands and their influence in plasma confinement. ¶ ...

APA, Harvard, Vancouver, ISO, and other styles

27

Argirevic, Tomislav. "High-field EPR and ENDOR spectroscopy for proton-coupled electron transfer investigations in E.coli ribonucleotide reductase." Doctoral thesis, 2011. http://hdl.handle.net/11858/00-1735-0000-0006-B09C-C.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Radial Electric Field'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles