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Electrostatic turbulence driven by high magnetohydrodynamic activity in Tokamak Chauffage Alfven Bresilien

Guimarães Filho, Zwinglio de Oliveira; Caldas, Ibere Luiz; Viana, Ricardo Luiz; Heller, Maria Vittoria Adelina Prario; Nascimento, Ivan Cunha; Kuznetsov, Yurii; Bengtson, Roger D
Fonte: AMER INST PHYSICS Publicador: AMER INST PHYSICS
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.66%
In Tokamak Chauffage Alfven Bresilien [R. M. O. Galvao , Plasma Phys. Controlled Fusion 43, 1181 (2001)], high magnetohydrodynamic (MHD) activity may appear spontaneously or during discharges with a voltage biased electrode inserted at the plasma edge. The turbulent electrostatic fluctuations, measured by Langmuir probes, are modulated by Mirnov oscillations presenting a dominant peak with a common frequency around 10 kHz. We report the occurrence of phase locking of the turbulent potential fluctuations driven by MHD activity at this frequency. Using wavelet cross-spectral analysis, we characterized the phase and frequency synchronization in the plasma edge region. We introduced an order parameter to characterize the radial dependence of the phase-locking intensity. (c) 2008 American Institute of Physics.

Alfven eigenmode properties and dynamics in the TJ-II stellarator

Melnikov, A. V.; Eliseev, L. G.; Ascasibar, E.; Chmyga, A. A.; Hidalgo, C.; Ido, T.; Jimenez-Gomez, R.; Komarov, A. D.; Kozachek, A. S.; Krupnik, L. I.; Khrebtov, S. M.; Koenies, A.; Kuznetsov, Yu K.; Lopez-Fraguas, A.; Lysenko, S. E.; Mavrin, V. A.; Naga
Fonte: INT ATOMIC ENERGY AGENCY; VIENNA Publicador: INT ATOMIC ENERGY AGENCY; VIENNA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.56%
Alfven eigenmodes (AEs) were studied in neutral beam injection (NBI) heated plasmas in the TJ-II stellarator using a heavy ion beam probe (HIBP) in the core, and by Langmuir (LP) and Mirnov probes (MP) at the edge. AEs were detected over the whole plasma radius by the HIBP with a spatial resolution of about 1 cm. AE-induced oscillations were detected in the plasma density n(e), electric potential phi and poloidal magnetic field B-pol with frequencies 50 kHz < f(AE) < 300 kHz. The LP, MP and HIBP data showed a high level of coherency for specific branches of AEs. Poloidal mode wave-vectors k(theta), mode numbers m (m < 8) and propagation velocities V-theta similar to 30 km s(-1) were detected for various branches of AEs, having different radial locations. When the density rose due to NBI fuelling, the AE frequency decreased as predicted by the Alfven law f(AE) similar to n(e)(-1/2). During the AE frequency decay the following new AE features were observed: (i) the poloidal wave-vector k(theta) and mode number m remained constant, (ii) the cross-phases between the oscillations in B-pol, n(e) and electric potential remained constant, having an individual value for each AE branch, (iii) V-theta decreased proportional to the AE frequency. The interaction of the AEs with the bulk (thermal) plasma resulted in clearly pronounced quasi-coherent peaks in the electrostatic turbulent particle flux spectra. Various AE branches exhibited different contributions to the particle flux: outward...

Turbulência Eletrostática e Magnética em Tokamaks; Electrostatic and magnetic turbulence in Tokamaks

Castro, Raul Murete de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 22/10/1996 PT
Relevância na Pesquisa
105.98%
Neste trabalho foi realizado um estudo experimental da turbulência e do transporte de partículas e energia induzido por flutuações na borda do plasma do tokamak TBR-1. Para isto, foi utilizado um conjunto de sondas eletrostáticas (incluindo uma sonda tripla de resposta rápida) e magnéticas, especialmente construído para este fim. Técnicas de análise espectral foram aplicadas aos dados e permitiram verificar a influência das flutuações da temperatura nos parâmetros de transporte. Os resultados mostram que o nível relativo das flutuações da temperatura é da ordem de 10% e os da densidade e do potencial variam de ~10 a ~ 30 %. As flutuações eletrostáticas possuem faixas largas de freqüência e números de onda, o que caracteriza a borda do plasma como um meio turbulento. Estas flutuações se propagam no sentido da deriva diamagnética dos íons. A correção das flutuações das grandezas do plasma utilizando as flutuações da temperatura causou mudanças significativas nos transportes de partículas e energia induzidos por flutuações, nas posições mais internas da borda do plasma. O tempo de confinamento de partículas, calculado a partir deste transporte, está na faixa de ~1 a ~ 1,5 ms, que é da mesma ordem do tempo de confinamento obtido por outros métodos...

Estudo do Funcionamento do Tokamak TBR-1 sob a Influência de Perturbações Elétricas e Magnéticas; Study Operation TBR Tokamak-1 Influence Electrical Magnetic Disturbances

Chamaa Neto, Ibrahim El
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 14/08/1998 PT
Relevância na Pesquisa
25.67%
Neste trabalho foram realizados estudos experimentais de operação do tokamak TBR-I sob condições extremas de densidade e de campo magnético toroidal e, também, sob a influência de perturbações elétricas radiais e magnéticas helicoidais aplicadas na região periférica da coluna de plasma. Realizou-se, também, uma análise preliminar das características das descargas na região da corrente de plasma com predominância de elétrons fugitivos. Para isso foi utilizada a maioria dos diagnósticos já construídos no Laboratório de Física de Plasmas da USP, que são: diagnóstico por sondas eletrostáticas, bobinas de Mirnov, espectroscopia óptica, interferômetro de micro ondas, detector de raios-X duros, detector de H, bobinas de Rogowski, bobinas de posição, espiras das tensões de enlace e medição da pressão com "ion-gauges" e analisador de gás residual. Os resultados permitiram obter uma lei de escala para as descargas do TBR-1 associando a densidade média de partículas com a densidade média de corrente de plasma. Foram observados efeitos muito interessantes nas oscilações magnéticas do plasma sob ação dos campos perturbativos. Em particular, para os campos elétricos radiais com polarização negativa...

Geometry of Hydrogen Bonds Formed by Lipid Bilayer Nitroxide Probes: A High Frequency Pulsed ENDOR/EPR Study

Smirnova, Tatyana I.; Smirnov, Alex I.; Pachtchenko, Serguei; Poluektov, Oleg G.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
25.56%
Solvent effects on magnetic parameters of nitroxide spin labels in combination with side-directed spin labeling EPR methods provide very useful means for elucidating polarity profiles in lipid bilayers and mapping local electrostatic effects in complex biomolecular systems. One major contributor to these solvent effects is the hydrogen bonds that could be formed between the nitroxide moiety and water and/or the available hydroxyl groups. Here, formation of hydrogen bonds between a lipid bilayer spin probe -5-doxyl stearic acid, 5DSA – and hydrogen bond donors has been studied using high-frequency (HF) pulsed ENDOR and EPR. A hydrogen-bonded deuteron was directly detected in HF ENDOR (130 GHz) spectra of 5DSA dissolved in several deuterated alcohols while the characteristic signal was absent in non-polar toluene-d8. The length of the hydrogen bond, 1.74±0.06 Å, and its geometry were found to be essentially the same for all four alcohols studied, indicating that nearly identical hydrogen bonds have been formed regardless of the solvent dielectric constant. This strengthens a hypothesis that HF EPR spectra are exclusively sensitive to formation of hydrogen bonds and could be used for probing the hydrogen bond network in complex biomolecular assemblies and lipid bilayers with site-directed spin-labeling methods.

Variation and Analysis of Second-sphere Interactions and Axial Histidinate Character in c-type Cytochromes

Bowman, Sarah E. J.; Bren, Kara L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 06/09/2010 EN
Relevância na Pesquisa
25.56%
The electron-donating properties of the axial His ligand to heme iron in cytochromes c (cyts c) are found to be correlated with midpoint reduction potential (Em) in variants of Hydrogenobacter thermophilus cytochrome c552 (Ht cyt c552) in which mutations have been made in and near the Cys-X-X-Cys-His (CXXCH) heme-binding motif. To probe the strength of the His-Fe(III) interaction, we have measured 13C nuclear magnetic resonance (NMR) chemical shifts for 13CN− bound to heme iron trans to the axial His in Ht Fe(III) cyt c552 variants. We observe a linear relationship between these 13C chemical shifts and Em, indicating that the His-Fe(III) bond strength correlates with Em. To probe a conserved hydrogen bonding interaction between the axial His Hδ1 and the backbone carbonyl of a Pro residue, we measured the pKa of the axial His Hδ1 proton (pKa(2)), which we propose to relate to the His-Fe(III) interaction, reduction potential and local electrostatic effects. The observed linear relationship between the axial His 13Cβ chemical shift and Em is proposed to reflect histidinate (anionic) character of the ligand. A linear relationship also is seen between the average heme methyl 1H chemical shift and Em which may reflect variation in axial His electron-donating properties or in the ruffling distortion of the heme plane. In summary...

Electron densities inferred from plasma wave spectra obtained by the Waves instrument on Van Allen Probes

Kurth, W S; De Pascuale, S; Faden, J B; Kletzing, C A; Hospodarsky, G B; Thaller, S; Wygant, J R
Fonte: BlackWell Publishing Ltd Publicador: BlackWell Publishing Ltd
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
35.61%
The twin Van Allen Probe spacecraft, launched in August 2012, carry identical scientific payloads. The Electric and Magnetic Field Instrument Suite and Integrated Science suite includes a plasma wave instrument (Waves) that measures three magnetic and three electric components of plasma waves in the frequency range of 10 Hz to 12 kHz using triaxial search coils and the Electric Fields and Waves triaxial electric field sensors. The Waves instrument also measures a single electric field component of waves in the frequency range of 10 to 500 kHz. A primary objective of the higher-frequency measurements is the determination of the electron density ne at the spacecraft, primarily inferred from the upper hybrid resonance frequency fuh. Considerable work has gone into developing a process and tools for identifying and digitizing the upper hybrid resonance frequency in order to infer the electron density as an essential parameter for interpreting not only the plasma wave data from the mission but also as input to various magnetospheric models. Good progress has been made in developing algorithms to identify fuh and create a data set of electron densities. However, it is often difficult to interpret the plasma wave spectra during active times to identify fuh and accurately determine ne. In some cases...

Scanning Probe Microscopies for the Study at Nanoscale of Nanomaterials and Nanosystems:

DONG, CHUNHUA
Fonte: La Sapienza Universidade de Roma Publicador: La Sapienza Universidade de Roma
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
35.8%
Magnetic nanomaterials due to their various features different from the ordinary bulk matter in their mechanical, thermal, magnetic, optical properties, are attracting more and more attention in both theoretical research and practical applications in various fields. Magnetic nanoparticles (MNPs) are a very important branch of magnetic nanomaterials due to their nanoscale sizes, being relatively long in vivo half-life and limited agglomeration. These make them ideal for biomedical applications such as magnetic labeling, hyperthermia cancer treatment, targeted drug delivery, and contrast enhancement agents in magnetic resonance imaging (MRI). In drug delivery applications, MNPs can be determined with high accuracy [1]. It would be of interest to localize and characterize MNPs at the nanoscale for biological applications. However, very limited studies exist on detecting and characterizing the magnetic signals of nanoparticles in biological science. Many methods in surface structure analysis are used as nano-characterization techniques, such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), field electron microscopy (FEM), field ion microscope (FIM), low energy electron diffraction (LEED), Auger electron spectroscopy (AES)...

Advances in magnetic force microscopy

Iglesias Freire, Óscar
Fonte: Universidade Autônoma de Madrid Publicador: Universidade Autônoma de Madrid
Tipo: Tese de Doutorado
SPA; ENG
Relevância na Pesquisa
35.76%
Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica de la Materia Condensada. Fecha de lectura: 02-06-2014; La piedra angular sobre la que se basa esta tesis es la microscopía de fuerza magnética y su uso para extraer información añadida del estudio de muestras ferromagnéticas. A lo largo del manuscrito, se ha estudiado una extensa variedad de materiales. Éste está dividido en cinco capítulos, cada uno de los cuales se centra en una temática diferente. Si bien aconsejamos seguir el orden establecido, el manuscrito está escrito de tal forma que el lector pueda leer cada capítulo de manera independiente. En algunas partes específicas se hace referencia a otros capítulos, en los que se comenta en más detalle algún asunto en particular. El primer capítulo, a modo de introducción, repasa conceptos básicos que serán utilizados con frecuencia durante la descripción de los resultados experimentales. En primer lugar, se da una visión general sobre la situación actual en la que se encuentra el campo del nanomagnetismo, así como las principales razones que han motivado la realización de esta tesis. En segundo lugar, se recuerdan fundamentos básicos de magnetismo clásico y se introducen algunas de sus ecuaciones básicas. Después...

SIMULTANEOUS GROUND AND ROCKET BASED MEASUREMENTS OF ELECTRIC FIELDS AND CURRENTS IN AN AURORAL ARC

ROBINSON, ROBERT MELVIN
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Thesis; Text Formato: application/pdf
ENG
Relevância na Pesquisa
25.56%
A Terrier-Malemute sounding rocket was launched into a stable, premidnight auroral arc. Among the instruments carried by the payload were a cesium vapor magnetometer, electrostatic curved-plate electron energy analyzers, and two sets of Langmuir double-probes. Simultaneous line-of-sight velocity and electron density measurements were made during the flight by Chatanika radar operating in an elevation scan mode in the magnetic meridian. Data from the magnetometer indicated that a broad region of eastward current flowed within the diffuse aurora equatorward of the arc, while westward current flowed within the arc itself. The field aligned current was downward in the diffuse aurora and uniformly upward in a 100 km wide region which contained the arc. This current pattern suggests that the payload traversed the entire Region 1 field aligned current system. The narrowness of the current was probably due to the expansion of the auroral oval associated with the growth phase of a substorm which occurred one hour after the flight. The double probe measured a 40 mV/m northward electric field just equatorward of the arc. Within the arc the northward electric field was zero. The tangential component of the electric field was 7 mV/m and was constant across the arc boundaries. Since the electric field in the arc was not strong enough to account for the westward current measured by the magnetometer...

Experiments and theory of an upstream ionization instability excited by an accelerated electron beam through a current-free double layer

Aanesland, A.; Lieberman, M. A.; Charles, C.; Boswell, R. W.
Fonte: American Institute of Physics (AIP) Publicador: American Institute of Physics (AIP)
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.68%
A low-frequency instability varying from 10 to 20kHz has been discovered in the presence of a current-free double layer (DL) in a low-pressure expanding helicon plasma. The instability is observed using various electrostatic probes, such as Langmuir probes floating or biased to ion saturation and emissive probes measuring the plasma potential. A retarding field energy analyzer measuring the ion energy distribution function downstream of the double layer is used together with the LP to simultaneously observe the DL and the instability, confirming their coexistence. The frequency of the instability decreases with increasing neutral pressure, increases with increasing magnetic field in the source and increases with increasing rf power. A theory for an upstream ionizationinstability has been developed, in which electrons accelerated through the DL increase the ionization upstream and are responsible for the observed instability. The theory is in good agreement with the experimental results and shows that the frequency increases with the potential drop of the double layer and with decreasing chamber radius.

Diagnóstico de um plasma criado por RF e imerso em campo magnético

Geraldo Pereira Galvão
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 23/07/1981 PT
Relevância na Pesquisa
25.69%
Este trabalho se constitui de duas partes principais: projeto de um analisador de energia de íons para medida de temperatura e outras propriedades de um plasma e estudo de um gás ionizado por radiofrequência e confinado em geometria de espelho magnético. Como diagnóstico desse sistema é usado, além do analisador de energia, sondas de Langmuir. O analisador é do tipo eletrostático. com placas metálicas cilíndricas paralelas e ângulo entre fendas de entrada e saída de 127° 17' .O detector de íons positivos é montado numa configuração denominada "Daly", e se constitui de um alvo metálico, fonte negativa de alta tensão, cintilador e fotomultiplicadora. Esse sistema é adequado para se trabalhar com correntes muito baixas de íons em plasmas estacionários ou pulsados. O emprego de sondas permite o estudo do comportamento da temperatura eletrônica paralela, da densidade e do potencial de plasma, sobretudo na ressonância de ciclotron dos elétrons. É desenvolvido um método para se calcular a temperatura perpendicular ao campo magnético. Com o analisador é feito um exame do comportamento do potencial de plasma com pressão e campo magnético. Observa-se uma variação na energia dos íons com estas grandezas. A interpretação desta variação em termos dá temperatura dos íons e/ou potencial de plasma é discutida no texto. Quando é possível comparam-se os dois métodos de medida; The work presented here has two major parts. Firstly...

DNA hybridization : fundamental studies and applications in directed assembly; Deoxyribonucleic acid hybridization : fundamental studies and applications in directed assembly

Bajaj, Manish G. (Manish Gopal)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 193 p.; 9291803 bytes; 9303791 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
45.63%
Programmed self-assembly using non-covalent DNA-DNA interactions is a promising technique for the creation of next-generation functional devices for electronic, optical, and magnetic applications. This thesis develops the ability to tailor surfaces for the DNA-driven assembly of molecular, nano-, and micron-sized objects. Specifically, DNA hybridization was employed to direct the regiospecific assembly of DNA molecules onto substrates and in the targeted assembly of supraparticulate structures from nanoparticles and microparticles that express DNA molecules on their surfaces. These studies provide fundamental information needed for deploying a programmable process for the 'bottom-up' assembly of smaller species into large aggregates. DNA-based assembly spans areas of molecular biology and nanotechnology. In the former area, DNA microarrays have become a standard tool for gene expression analysis. In spite of the large number of studies that employ DNA microarrays, fundamental aspects of DNA hybridization on these platforms have been largely unexplored. In this thesis, the effects of immobilized probe density on DNA hybridization were examined by employing a mixed silane chemistry to systematically control the density of immobilized probe DNA strands (0.2 x 10¹³ probes/cm² to 5.2 x 10¹³ probes/cm²) on glass surfaces. The surface density of the immobilized species was found to significantly affect the hybridization yields; the equilibrium dsDNA amounts being highest on surfaces with ss-DNA probe densities corresponding to average inter- strand distances of 18 [Angstroms]. The strong effects of surface probe density on hybridization performance indicate that it can be a useful parameter for improving the signal-to-noise ratios for assays performed on microarrays.; (cont.) A target in nanotechnology is the generation of larger functional units from smaller nanoscale objects. Using a mixed silane chemistry...

Model of the boundary layer of a vacuum-arc magnetic filter

Minotti, Fernando Oscar; Giuliani, Leandro Estanislao; Grondona, Diana Elena; Della Torre, H.; Kelly, Hector Juan
Fonte: Amer Inst Physics Publicador: Amer Inst Physics
Tipo: info:eu-repo/semantics/article; info:ar-repo/semantics/artículo; info:eu-repo/semantics/publishedVersion Formato: application/pdf
ENG
Relevância na Pesquisa
45.66%
A model is developed to describe the electrostatic boundary layer in a positively biased magnetic filter in filtered arcs with low collisionality. The set of equations used includes the electron momentum equation, with an anomalous collision term due to micro-instabilities leading to Bohm diffusion, electron mass conservation, and Poisson equation. Analytical solutions are obtained, valid for the regimes of interest, leading to an explicit expression to determine the electron density current to the filter wall as a function of the potential of the filter and the ratio of electron density at the plasma to that at the filter wall. Using a set of planar and cylindrical probes it is verified experimentally that the mentioned ratio of electron densities remains reasonably constant for different magnetic field values and probe bias, which allows to obtain a closed expression for the current. Comparisons are made with the experimentally determined current collected at different sections of a positively biased straight filter.; Fil: Minotti, Fernando Oscar. Consejo Nacional de Invest.cientif.y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Fisica del Plasma; Argentina;; Fil: Giuliani, Leandro Estanislao. Consejo Nacional de Invest.cientif.y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Fisica del Plasma; Argentina;; Fil: Grondona...

Estudio y aplicaciones de un filtro magnético recto en una descarga arco de baja presión; Straight magnetized filter of a pulsed vacuum arc: study and applications

Giuliani, Leandro Estanislao
Fonte: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires Publicador: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires
Tipo: info:eu-repo/semantics/doctoralThesis; tesis doctoral; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Publicado em //2009 SPA
Relevância na Pesquisa
35.69%
Los equipos de descargas arco en vacío son una fuente de plasma atractiva para la producción de películas delgadas. En estos equipos se produce un intenso jet de plasma metálico formado por iones de relativamente alta energía que son producidos con mucha eficiencia en la superficie del cátodo. Sin embargo, estos arcos también producen macropartículas de material catódico derretido que son depositadas en los sustratos. La presencia de estas macropartículas aumenta la porosidad y rugosidad de los recubrimientos afectando las propiedades de los films. Se han desarrollado varios sistemas de filtrado para separar las macropartículas del plasma, pero el filtrado magnético es el más empleado en la actualidad. Este tipo de filtro consiste en un tubo con un campo magnético axial que transporta el plasma a lo largo del mismo. En este trabajo se presenta un estudio del plasma generado mediante una descarga arco pulsada en vacío en un filtro magnético recto y de los recubrimientos obtenidos con este equipo. El estudio del plasma involucró mediciones con sondas electrostáticas y analizadores por campo retardador. Los resultados obtenidos para la energía cinética de los iones son similares a los hallados por otros autores, pero también se encontró que la energía era independiente de la intensidad del campo magnético dentro del rango estudiado en este trabajo. La temperatura electrónica también resultó independiente del campo magnético y de la posición a lo largo del filtro...

Characterization of a helicon plasma source in low diverging magnetic fields

Lafleur, Trevor; Charles, Christine; Boswell, Roderick
Fonte: Institute of Physics Publishing Publicador: Institute of Physics Publishing
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
25.63%
A detailed experimental characterization has been performed of a helicon mode in low nonuniform magnetic fields (B0 < 5 mT) for pressures between 0.04 Pa < p0 < 0.4 Pa and rf powers between 50W < P0 < 400W, using a number of electrostatic probes as well a

Electron temperature characterization and power balance in a low magnetic field helicon mode

Lafleur, Trevor; Charles, Christine; Boswell, Roderick
Fonte: Institute of Physics Publishing Publicador: Institute of Physics Publishing
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
25.63%
The electron temperature in a low-field helicon mode has been characterized in the presence of a diverging magnetic field (B0 < 5 mT), using a number of electrostatic probes. At the low pressures investigated (<0.3 Pa) the electron energy probability func

Cooper-pair qubit and Cooper-pair electrometer in one device

Zorin, A. B.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/12/2001
Relevância na Pesquisa
35.56%
An all-superconductor charge qubit enabling a radio-frequency readout of its quantum state is described. The core element of the setup is a superconducting loop which includes the single-Cooper-pair (Bloch) transistor. This circuit has two functions: First, it operates as a charge qubit with magnetic control of Josephson coupling and electrostatic control of the charge on the transistor island. Secondly, it acts as the transducer of the rf electrometer, which probes the qubit state by measuring the Josephson inductance of the transistor. The evaluation of the basic parameters of this device shows its superiority over the rf-SET-based qubit setup.; Comment: 4 pages incl. 3 figues; the SQUID'2001 paper, to be published in Physica C

Signatures of Rashba Spin-Orbit Interaction in Charge and Spin Properties of Quantum Hall Systems

Hernangomez-Perez, Daniel; Florens, Serge; Champel, Thierry
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.66%
We study the local equilibrium properties of two-dimensional electron gases at high magnetic fields in the presence of random smooth electrostatic disorder, Rashba spin-orbit coupling, and the Zeeman interaction. Using a systematic magnetic length ($l_B$) expansion within a Green's function framework we derive quantum functionals for the local spin-resolved particle and current densities which can be useful for future studies combining disorder and mean-field electron-electron interaction in the quantum Hall regime. We point out that the spin polarization presents a peculiar spatial dependence which can be used to determine the strength of the Rashba coupling by local probes. The spatial structure of the current density, consisting of both compressible and incompressible contributions, also essentially reflects the effects of Rashba spin-orbit interaction on the energy spectrum. We show that in the semiclassical limit $l_B \rightarrow 0$ the local Hall conductivity remains, however, still quantized in units of $e^2/h$ for any finite strength of the spin-orbit interaction. In contrast, it becomes half-integer quantized when the latter is infinite, a situation which corresponds to a disordered topological insulator surface consisting of a single Dirac cone. Finally...

Electrostatic potential variations along flux surfaces in stellarators

Pedrosa, M. A.; Alonso, J. A.; García-Regaña, J. M.; Hidalgo, C.; Velasco, J. L.; Calvo, I.; Silva, C.; Helander, P.; Kleiber, R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
25.65%
First observations of electrostatic potential variations within the flux surfaces of a toroidal magnetic confinement device are presented. Measurements are taken in the TJ-II stellarator with two distant Langmuir probe arrays. The edge floating potentials display differences of several tens of Volts in electron-root wave-heated plasmas. The differences are reduced for higher densities and lower electron temperatures after the ion-root electric field forms at the plasma edge. Neoclassical Monte Carlo simulations estimate the correct order of magnitude for the overall variation in potential and predict the trend observed with the radial electric field. However, for the specific location of the probes, the simulations give differences smaller than those observed experimentally.