Página 1 dos resultados de 9265 itens digitais encontrados em 0.020 segundos

DIFFUSION OF MAGNETIC FIELD AND REMOVAL OF MAGNETIC FLUX FROM CLOUDS VIA TURBULENT RECONNECTION

SANTOS-LIMA, R.; LAZARIAN, A.; PINO, E. M. de Gouveia Dal; CHO, J.
Fonte: IOP PUBLISHING LTD Publicador: IOP PUBLISHING LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
56.16%
The diffusion of astrophysical magnetic fields in conducting fluids in the presence of turbulence depends on whether magnetic fields can change their topology via reconnection in highly conducting media. Recent progress in understanding fast magnetic reconnection in the presence of turbulence reassures that the magnetic field behavior in computer simulations and turbulent astrophysical environments is similar, as far as magnetic reconnection is concerned. This makes it meaningful to perform MHD simulations of turbulent flows in order to understand the diffusion of magnetic field in astrophysical environments. Our studies of magnetic field diffusion in turbulent medium reveal interesting new phenomena. First of all, our three-dimensional MHD simulations initiated with anti-correlating magnetic field and gaseous density exhibit at later times a de-correlation of the magnetic field and density, which corresponds well to the observations of the interstellar media. While earlier studies stressed the role of either ambipolar diffusion or time-dependent turbulent fluctuations for de-correlating magnetic field and density, we get the effect of permanent de-correlation with one fluid code, i.e., without invoking ambipolar diffusion. In addition...

Conductance through two quantum dots in a ring: magnetic flux dependence

Apel,V. M.; Davidovich,Maria A.; Chiappe,G.; Anda,E. V.
Fonte: Sociedade Brasileira de Física Publicador: Sociedade Brasileira de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2006 EN
Relevância na Pesquisa
66.22%
The conductance of a double-dot system in a ring threaded by a magnetic flux is studied. The ring is connected to two leads in such a way that each dot is embedded in one arm of the structure. The currents going through each arm of the ring are determined by the Aharonov-Bohm effect and the dot charging effects. The conductance for different values of the magnetic flux is obtained as a function of the gate potentials applied to the dots, for two situations: when the dot level energies are equal, deltaE = 0, and when they are different but with deltaE smaller than the Coulomb interaction U. The conductance shows quite distinct behavior according to having a finite or zero magnetic flux threading the ring. The system presents S = 1/2 and S = 1 Kondo phenomena for no magnetic flux and is in the S = 1/2 Kondo regime in the case of half a quantum of magnetic flux.

Detection and analysis of rotor faults in induction motors by the measurement of the stray magnetic flux

Rigoni,M.; Sadowski,N.; Batistela,N. J.; Bastos,J.P. A.; Nau,S. L.; Kost,A.
Fonte: Sociedade Brasileira de Microondas e Optoeletrônica e Sociedade Brasileira de Eletromagnetismo Publicador: Sociedade Brasileira de Microondas e Optoeletrônica e Sociedade Brasileira de Eletromagnetismo
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2012 EN
Relevância na Pesquisa
55.98%
This paper presents measured data and electromagnetic FEM field calculations as techniques for detecting and analyzing eccentricity in three-phase induction motors. Also it presents experimental results for detecting broken bars in induction motor rotors. A search-coil is used as magnetic field sensor to measure the stray magnetic flux outside the motor. It is a totally non-invasive method.

An analysis on electric and magnetic behaviour on an induction planar actuator

Baggio Filho,Nolvi Francisco; Flores Filho,Aly Ferreira
Fonte: Sociedade Brasileira de Microondas e Optoeletrônica e Sociedade Brasileira de Eletromagnetismo Publicador: Sociedade Brasileira de Microondas e Optoeletrônica e Sociedade Brasileira de Eletromagnetismo
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2013 EN
Relevância na Pesquisa
56.13%
The induction planar actuator, i.e. IPA, proposed in this study presents an electromagnetic structure formed by a static ferromagnetic core with an aluminium plate that corresponds to the secondary, and a mover, also called primary. The latter comprehends two three-phase windings, mounted in an armature core, which are orthogonal to each other. When they are fed by three-phase AC excitations, a moving magnetic field takes place, and can travel along the x-axis and the y-axis direction simultaneously. The travelling magnetic field induces electrical currents in the secondary. The interaction between the moving magnetic field from the primary and the magnetic field originated by the induced current in the secondary produces a planar force. That explains the primary movement over the working area defined by the secondary. The 3D flux density distribution of the actuator suggests the employment of a grain-insulated soft magnetic composite to reduce eddy currents and losses on the core of the primary armature core. Magnetic flux density, induced current and planar traction forces are studied.

Invesigation of the Magnetic Flux Leakage Signatures of Dents and Gouges

Marble, KRISTOPHER
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 12964838 bytes; application/pdf
EN; EN
Relevância na Pesquisa
66.1%
A study of gouges and dents in the context of pipelines has been completed, using the non-destructive evaluation (NDE) techniques of magnetic flux leakage (MFL) and magnetic Barkhausen noise (MBN). The research is part of an ongoing effort by the Applied Magnetics Group (AMG) at Queen's University to improve the interpretation of the MFL signal, which is used extensively by industry for defect detection and evaluation. The gouges were found to have distinctive MFL signatures depending on their orientation relative to the magnetization axis. Features in the MFL signal were identified as superpositions of geometry-related effects and strain or work hardening of the surface material. A qualitative magnetic permeability distribution in the material near a gouge has been proposed. The distribution is expected to vary in magnitude and extent according to the defect severity. The MFL results of the dent studies, on samples made available by Gaz de France (GdF), largely agreed qualitatively with previous research of dents. However, the differences pointed to the need for study of more varied dent shapes; new signal features were observed that suggested tensile residual strain in the dent rim is more prominent than earlier studies and modeling have predicted. Additionally...

A Magnetic Flux Leakage NDE System for CANDU Feeder Pipes

Mak, Thomas
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
56.1%
This work examines the application of different magnetic flux leakage (MFL) inspection concepts to the non destructive evaluation (NDE) of residual (elastic) stresses in CANDU reactor feeder pipes. The stress sensitivity of three MFL inspection techniques was examined with flat plate samples, with stress-induced magnetic anisotropy (SMA) demonstrating the greatest stress sensitivity. A prototype SMA testing system was developed to apply magnetic NDE to feeders. The system consists of a flux controller that incorporates feedback from a wire coil and a Hall sensor (FCV2), and a magnetic anisotropy prototype (MAP) probe. The combination of FCV2 and the MAP probe was shown to provide SMA measurements on feeder pipe samples and predict stresses from SMA measurements with a mean accuracy of ±38MPa.; Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2010-03-11 15:59:23.978

Acompanhamento preditivo de motores de indução trifasicos atraves da analise de fluxo magnetico; Predictive accompaniment of three-phase induction motors by magnetic flux analysis

Paulo Cezar Monteiro Lamim Filho
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 28/02/2003 PT
Relevância na Pesquisa
66.06%
Um programa de manutenção preditiva deve englobar várias técnicas de monitoramento da condição do motor elétrico. Dentre elas, pode-se citar como clássicas, a análise de corrente elétrica e análise de vibrações. Entretanto, existe um grande número de dificuldades associadas com estas técnicas e, conseqüentemente, com suas aplicações práticas. Isto devido à abrangência de detecção de defeitos tais como: falhas de barras rotativas do rotor; falhas no estator; desbalanceamento de tensão e curto circuito (entre fase e entre espiras). O diagnóstico de defeitos a partir da análise de fluxo magnético tem sido proposto por fabricantes de equipamentos da área de monitoramento de máquinas. Entretanto, esta técnica não tem sido explorada com profundidade para aplicação num programa de manutenção. Este trabalho propõe a implementação de um transdutor (bobina de fluxo) sensível às ondas eletromagnéticas dentro dos motores de indução trifásicos, identificando as freqüências determinísticas relacionadas aos defeitos comuns a estes tipos de máquinas. Os espectros coletados com este novo sensor são comparados com um sensor comercial, mostrando sua eficiência. Este estudo é uma contribuição importante...

Simulation and parameterization by the finite element method of a C Shape Delectromagnet for application in the characterization of magnetic properties of materials

Vel??squez Torres, ??lvaro Andr??s; Baena Rodr??guez, Juliana
Fonte: World Academy of Science, Engineering and Technology; Grupo de Investigaci??n de Electromagnetismo Aplicado (Gema); Escuela de Ciencias y Humanidades Publicador: World Academy of Science, Engineering and Technology; Grupo de Investigaci??n de Electromagnetismo Aplicado (Gema); Escuela de Ciencias y Humanidades
Tipo: article; Art??culo; publishedVersion
ENG
Relevância na Pesquisa
56.24%
This article presents the simulation, parameterization and optimization of an electromagnet with the C???shaped configuration, intended for the study of magnetic properties of materials -- The electromagnet studied consists of a C-shaped yoke, which provides self???shielding for minimizing losses of magnetic flux density, two poles of high magnetic permeability and power coils wound on the poles -- The main physical variable studied was the static magnetic flux density in a column within the gap between the poles, with 4cm2 of square cross section and a length of 5cm, seeking a suitable set of parameters that allow us to achieve a uniform magnetic flux density of 1x104 Gaussor values above this in the column, when the system operates at room temperature and with a current consumption not exceeding 5A -- By means of a magnetostatic analysis by the finite element method, the magnetic flux density and the distribution of the magnetic field lines were visualized and quantified -- From the results obtained by simulating an initial configuration of electromagnet, a structural optimization of the geometry of the adjustable caps for the ends of the poles was performed -- The magnetic permeability effect of the soft magnetic materials used in the poles system...

Estudio combinado de erupciones de tubos de flujo magnético solares y su manifestación interplanetaria; Combined study of solar magnetic flux tubes eruption and their interplanetary manifestation

Nakwacki, María Soledad
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
56.12%
El medio interplanetario se conforma de un plasma tenue que fluye desde el Sol llamado viento solar (VS). El VS transporta estructuras magnéticas expulsadas desde la corona solar (por ej. eyecciones coronales de masa, ECMs). En este trabajo, se estudian teórica y observacionalmente algunos aspectos de la evolución de las ECMs en el medio interplanetario (MI); en particular, del subconjunto llamado nubes magnéticas (NMs). Se modela la evolución dinámica de varios eventos ocurridos entre 1997-2004, se cuantifica su expansión y se calculan, con los modelos desarrollados, cantidades globales invariantes (flujo y helicidad magnética), relevantes en un análisis combinado de eventos solares y sus contrapartes interplanetarias. Los modelos desarrollados se basan en la descripción magnetohidrodinámica del plasma. Se propone una evolución autosimilar de la estructura de las NMs con tasas de expansión diferentes en cada una de sus direcciones principales (radial y axial). Se comienza sólo con expansión radial y se avanza hasta incluir la expansión axial. Finalmente, se amplía la descripción con un formalismo general, basado en las observaciones, derivado en un orden jerárquico y aplicable, incluso, a estructuras más generales que las NMs. Se muestra la robustez de los invariantes globales cuando se los calcula con diferentes modelos de expansión. Se cuantifica por primera vez la cantidad típica de energía magnética perdida por unidad de tiempo en la evolución de una NM. Para algunas de las NMs estudiadas se analizan también observaciones del evento solar asociado y de su región activa (RA) fuente. Se identifican características de la zona de erupción que permiten cuantificar los invariantes globales en el Sol. Se dan cuantificaciones del flujo magnético involucrado en la eyección y estimaciones de la variación de helicidad magnética de la RA fuente. A partir de la comparación de las cantidades globales en el Sol y en el MI se proponen modelos para las erupciones y se restringen los modelos existentes. Por último se estudia la evolución de una NM particular desde que es observada cerca de la Tierra hasta más de 5 unidades astronómicas con datos de dos sondas alineadas con el Sol. Se cuantifican los invariantes globales en ambos puntos de observación. Se comparan dichas cantidades y se da una interpretación de la estructura magnética distorsionada por interacción con el VS ambiente lejos del Sol. Se extiende la comparación hasta el Sol identificando la fuente solar con lo que se tiene una descripción completa de su evolución a través de la heliósfera.; The interplanetary medium is filled with a low density plasma that flows from the Sun and is called the solar wind. This wind transports the magnetic structures that are ejected from the solar corona (e.g. coronal mass ejections...

A Coupled 2 × 2D Babcock–Leighton Solar Dynamo Model. I. Surface Magnetic Flux Evolution

Lemerle, Alexandre; Charbonneau, Paul; Carignan-Dugas, Arnaud
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
55.98%
The need for reliable predictions of the solar activity cycle motivates the development of dynamo models incorporating a representation of surface processes sufficiently detailed to allow assimilation of magnetographic data. In this series of papers we present one such dynamo model, and document its behavior and properties. This first paper focuses on one of the model's key components, namely surface magnetic flux evolution. Using a genetic algorithm, we obtain best-fit parameters of the transport model by least-squares minimization of the differences between the associated synthetic synoptic magnetogram and real magnetographic data for activity cycle 21. Our fitting procedure also returns Monte Carlo-like error estimates. We show that the range of acceptable surface meridional flow profiles is in good agreement with Doppler measurements, even though the latter are not used in the fitting process. Using a synthetic database of bipolar magnetic region (BMR) emergences reproducing the statistical properties of observed emergences, we also ascertain the sensitivity of global cycle properties, such as the strength of the dipole moment and timing of polarity reversal, to distinct realizations of BMR emergence, and on this basis argue that this stochasticity represents a primary source of uncertainty for predicting solar cycle characteristics.

Modelling magnetic flux emergence in the solar convection zone

Bushby, Paul J; Archontis, Vasilis
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/08/2012
Relevância na Pesquisa
46.3%
[Abridged] Bipolar magnetic regions are formed when loops of magnetic flux emerge at the solar photosphere. Our aim is to investigate the flux emergence process in a simulation of granular convection. In particular we aim to determine the circumstances under which magnetic buoyancy enhances the flux emergence rate (which is otherwise driven solely by the convective upflows). We use three-dimensional numerical simulations, solving the equations of compressible magnetohydrodynamics in a horizontally-periodic Cartesian domain. A horizontal magnetic flux tube is inserted into fully developed hydrodynamic convection. We systematically vary the initial field strength, the tube thickness, the initial entropy distribution along the tube axis and the magnetic Reynolds number. Focusing upon the low magnetic Prandtl number regime (Pm<1) at moderate magnetic Reynolds number, we find that the flux tube is always susceptible to convective disruption to some extent. However, stronger flux tubes tend to maintain their structure more effectively than weaker ones. Magnetic buoyancy does enhance the flux emergence rates in the strongest initial field cases, and this enhancement becomes more pronounced when we increase the width of the flux tube. This is also the case at higher magnetic Reynolds numbers...

Magnetic Flux Concentration and Zonal Flows in Magnetorotational Instability Turbulence

Bai, Xue-Ning; Stone, James M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/09/2014
Relevância na Pesquisa
46.31%
Accretion disks are likely threaded by external vertical magnetic flux, which enhances the level of turbulence via the magnetorotational instability (MRI). Using shearing-box simulations, we find that such external magnetic flux also strongly enhances the amplitude of banded radial density variations known as zonal flows. Moreover, we report that vertical magnetic flux is strongly concentrated toward low-density regions of the zonal flow. Mean vertical magnetic field can be more than doubled in low-density regions, and reduced to nearly zero in high density regions in some cases. In ideal MHD, the scale on which magnetic flux concentrates can reach a few disk scale heights. In the non-ideal MHD regime with strong ambipolar diffusion, magnetic flux is concentrated into thin axisymmetric shells at some enhanced level, whose size is typically less than half a scale height. We show that magnetic flux concentration is closely related to the fact that the magnetic diffusivity of the MRI turbulence is anisotropic. In addition to a conventional Ohmic-like turbulent resistivity, we find that there is a correlation between the vertical velocity and horizontal magnetic field fluctuations that produces a mean electric field that acts to anti-diffuse the vertical magnetic flux. The anisotropic turbulent diffusivity has analogies to the Hall effect...

Signatures of magnetic reconnection at boundaries of interplanetary small-scale magnetic flux ropes

Tian, Hui; Yao, Shuo; Zong, Qiugang; He, Jiansen; Qi, Yu
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/07/2010
Relevância na Pesquisa
46.31%
The interaction between interplanetary small-scale magnetic flux ropes and the magnetic field in the ambient solar wind is an important topic to understand- ing the evolution of magnetic structures in the heliosphere. Through a survey of 125 previously reported small flux ropes from 1995 to 2005, we find that 44 of them reveal clear signatures of Alfvenic fluctuations, and thus classify them into Alfven wave trains rather than flux ropes. Signatures of magnetic reconnection, generally including a plasma jet of ~30 km/s within a magnetic field rotational region, are clearly present at boundaries of about 42% of the flux ropes and 14% of the wave trains. The reconnection exhausts are often observed to show a local increase in the proton temperature, density and plasma beta. About 66% of the reconnection events at flux rope boundaries are associated with a magnetic field shear angle larger than 90 deg and 73% of them reveal a decrease by 20% or more in the magnetic field magnitude, suggesting a dominance of anti-parallel reconnec- tion at flux rope boundaries. The occurrence rate of magnetic reconnection at flux rope boundaries through the year of 1995 to 2005 is also investigated and we find that it is relatively low around solar maximum and much higher when ap- proaching solar minima. The average magnetic field depression and shear angle for reconnection events at flux rope boundaries also reveal a similar trend from 1995 to 2005. Our results demonstrate for the first time that boundaries of a substantial fraction of small-scale flux ropes have properties similar to those of magnetic clouds...

Evolution of the solar magnetic flux on time scales of years to millenia

Vieira, L. E. A.; Solanki, S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/11/2009
Relevância na Pesquisa
46.3%
We improve the description of the evolution of the Sun's open and total magnetic flux on time scales of years to millenia. In the model employed here the evolution of the solar total and open magnetic flux is computed from the flux emerging at the solar surface in the form of bipolar magnetic features, which is related to the sunspot number cycle parameters and can be estimated from historical records. Compared to earlier versions of the model in addition to the long-lived open flux, now also a more rapidly decaying component of the open flux is considered. The model parameters are constrained by comparing its output with observations of the total surface magnetic flux and with a reconstruction of the open magnetic flux based on the geomagnetic indexes. A method to compute the Sun's total magnetic flux and the sunspot number during the Holocene, starting from the open flux obtained from cosmogenic isotopes records, is also presented. By considering separately a rapdly evolving and a slowly evolving component of the open flux the model reproduces the Sun's open flux, as reconstructed based on the aa-index, much better and a reasonable description of the radial component of interplanetary magnetic field data are obtained. The greatest improvement is in the reproduction of the cyclic variation of the open flux...

Interaction between Granulation and Small-Scale Magnetic Flux Observed by Hinode

Zhang, Jun; Yang, Shuhong; Jin, Chunlan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/05/2009
Relevância na Pesquisa
46.29%
We study the relationship between granular development and magnetic field evolution in the quiet Sun. 6 typical cases are displayed to exhibit interaction between granules and magnetic elements, and we have obtained the following results. (1) A granule develops centrosymmetrically when no magnetic flux emerges within the granular cell. (2) A granule develops and splits noncentrosymmetrically while flux emerges at an outer part of the granular cell. (3) Magnetic flux emergence as a cluster of mixed polarities is detected at the position of a granule as soon as the granule breaks up. (4) A dipole emerges accompanying with the development of a granule, and the two elements of the dipole root in the adjacent intergranular lanes and face each other across the granule. Advected by the horizontal granular motion, the positive element of the dipole then cancels with pre-existing negative flux. (5) Flux cancellation also takes place between a positive element, which is advected by granular flow, and its surrounding negative flux. (6) While magnetic flux cancellation takes place at a granular cell, the granule shrinks and then disappears. (7) Horizontal magnetic fields enhance at the places where dipoles emerge and where opposite polarities cancel with each other...

Influence of soft ferromagnetic sections on the magnetic flux density profile of a large grain, bulk Y-Ba-Cu-O superconductor

Philippe, M. P.; Ainslie, Mark D.; W?ra, L.; Fagnard, J.-F.; Dennis, A. R.; Shi, Y.-H.; Cardwell, D. A.; Vanderheyden, B.; Vanderbemden, P.
Fonte: IOP Publicador: IOP
Tipo: Article; accepted version
EN
Relevância na Pesquisa
56.19%
This is the author accepted manuscript. The final version is available from IOP via http://dx.doi.org/10.1088/0953-2048/28/9/095008; Bulk, high temperature superconductors have significant potential for use as powerful permanent magnets in a variety of practical applications due to their ability to trap record magnetic fields. In this paper, soft ferromagnetic sections are combined with a bulk, large grain Y-Ba-Cu-O (YBCO) high temperature superconductor to form superconductor/ferromagnet (SC/FM) hybrid structures. We study how the ferromagnetic sections influence the shape of the profile of the trapped magnetic induction at the surface of each structure and report the surface magnetic flux density measured by Hall probe mapping. These configurations have been modelled using a 2D axisymmetric finite element method based on the H-formulation and the results show excellent qualitative and quantitative agreement with the experimental measurements. The model has also been used to study the magnetic flux distribution and predict the behaviour for other constitutive laws and geometries. The results show that the ferromagnetic material acts as a magnetic shield, but the flux density and its gradient are enhanced on the face opposite to the ferromagnet. The thickness and saturation magnetization of the ferromagnetic material are important and a characteristic ferromagnet thickness d* is derived: below d*...

An investigation into high temperature superconducting flux pump technology with the circular type magnetic flux pump devices and YBaCuO films

Wang, Wei
Fonte: University of Cambridge; Department of Engineering Publicador: University of Cambridge; Department of Engineering
Tipo: Thesis; doctoral; PhD
EN
Relevância na Pesquisa
56.31%
The rapid development of second generation (2G) high temperature superconducting (HTS) wires in the last decade has made it possible to wind high quality 2G HTS coils. These 2G HTS coils show promise for future applications such as magnetic resonance imaging (MRI) magnets, electrical machines, magnetic levitation trains, energy storage, etc. 2G HTS coils can be operated using either dc current or ac current. Several important issues have yet to be resolved, such as how to properly magnetise an HTS coil under dc conditions, or how to minimise losses under ac conditions. These problems should be carefully studied before the 2G HTS coils can be widely applied in scientific and industrial applications. This thesis focuses on emerging HTS flux pump technology for HTS coils operating in a dc environment. HTS flux pump technology applies a travelling magnetic wave to fully magnetise an HTS coil, which is both efficient and economical, and has in recent years been proven feasible. However, the underlying physics of this technology are so far poorly understood. In order to study the influence of a travelling magnetic wave on HTS films such as YBa2Cu3O7-?, two types of circular-type magnetic flux pump (CTMFP) devices were proposed and built. These novel devices generate an annular-shape travelling magnetic wave. The first type was the original CTMFP magnet...

Suppression of large edge-localized modes in high-confinement DIII-D plasmas with a stochastic magnetic boundary

Evans, T; Moyer, R; Thomas, P.R.; Watkins, J G; Osborne, T.H.; Boedo, J; Doyle, Edward Dermot; Fenstermacher, M E; Flux, I A; Groebner, R.J.; Groth, M; Harris, Jeffrey; La Haye, R.J.; Lasnier, C.J.; Masuzaki, S; Ohyabu, N; Pretty, David; Rhodes, T L; Reim
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.04%
The large edge-localized modes (ELM) in high confinement (H-mode) plasmas were suppressed using a magnetic boundary, produced by an applied edge resonant magnetic perturbation. The magnetic perturbations were produced by a set of control coils, referred to as I coil, located inside the vacuum vessel. The plasmas used in the experiment were double null diverted discharges with a 2 cm downward shift. The results demonstrate that stochastic boundary layers are compatible with H-mode plasmas and that a stochastic layer can suppress ELMs without degrading the global particle and energy confinement.

The Snake: A Reconnecting Coil in a Twisted Magnetic Flux Tube

Bicknell, Geoffrey; Li, J
Fonte: IOP Publishing Publicador: IOP Publishing
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.12%
We propose that the curious Galactic center filament known as the Snake is a twisted giant magnetic flux tube, anchored in rotating molecular clouds. The MHD kink instability generates coils in the tube and subsequent magnetic reconnection injects relativistic electrons. Energy-dependent diffusion of electrons away from the coil produces a flat spectral index at large distances from it. Our fit to the existing data shows that the magnetic field of ∼0.4 mG is large compared to the ambient ∼7 μG field, indicating that the flux tube is force-free. If the relative level of turbulence in the Snake and the general interstellar medium are similar, then electrons have been diffusing in the Snake for about 3 × 105 yr, comparable to the timescale at which magnetic energy is annihilated in the major kink. Estimates of the magnetic field in the G359.19-0.05 molecular complex are similar to our estimate of the magnetic field in the Snake, suggesting a strong connection between the physics of the anchoring molecular regions and the Snake. We suggest that the physical processes considered here may be relevant to other radio filaments near the Galactic center. We also suggest further observations of the Snake and other filaments that would be useful for obtaining further insights into the physics of these objects.

Dynamical evolution of magnetic flux ropes in the solar wind

Nakwacki,M. S.; Dasso,S; Démoulin,P; Mandrini,C. H.
Fonte: Instituto de Geofísica, UNAM Publicador: Instituto de Geofísica, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2008 EN
Relevância na Pesquisa
56.12%
The conservation of magnetic flux in systems of very low dissipation, as the interplanetary medium, is used to analyze magnetic clouds in significant expansion. In particular, we analyze the fast and huge event observed at one astronomical unit in the solar wind on Nov. 9-10, 2004. We compare magnetic and velocity observations to two self-similar and free expansion models that allow us to correct the mixing spatial-variation/time-evolution observed in situ by the spacecrafts. As magnetic clouds are astrophysical objects that transport a very important amount of magnetic flux and helicity from the Sun to the interplanetary medium, we compare the values of these global quantities obtained using the present models with those values coming from the commonly used static Lundquist's model.