WorldWideScience

Sample records for external magnetic flux

  1. Flow boiling critical heat flux enhancement by using magnetic nanofluids and external magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Lee, T.; Jeong, Y.H. [Korea Advanced Inst. of Science and Tech., Daejeon (Korea, Republic of)

    2011-07-01

    By using the nanofluid as a working fluid, we can expect the enhancement in the flow boiling critical heat flux mainly due to the deposition of nanoparticles on the heat transfer surface. In this study, we suggest the magnetic nanofluid, or magnetite-water nanofluid, as a working fluid which is regarded as a controllable nanofluid, that is, nanoparticles or magnetite nanoparticles in a nanofluid can be controlled by an external magnetic field. Therefore, we can expect the advantages of magnetic nanofluid such as, i) control of nanofluid concentration to maintain nanoparticle suspension and to localize nanofluid concentration, and ii) removal of nanoparticle from nanofluid when we want. In this study, we focused on the investigation of flow boiling critical heat flux characteristics for the magnetic nanofluid. Series of experiments were performed under the low pressure and low flow conditions, and based on the experimental results; we can conclude that the use of magnetic nanofluid improves the flow boiling critical heat flux characteristics. This is mainly due to the deposition of magnetite nanoparticles on the heat transfer surface, which results in the improvement of wettability and re-wetting characteristics of heat transfer surface. Preliminary results of the magnetic field effects on the flow boiling critical heat flux would be presented also. (author)

  2. Design Enhancement and Performance Examination of External Rotor Switched Flux Permanent Magnet Machine for Downhole Application

    Science.gov (United States)

    Kumar, R.; Sulaiman, E.; Soomro, H. A.; Jusoh, L. I.; Bahrim, F. S.; Omar, M. F.

    2017-08-01

    The recent change in innovation and employments of high-temperature magnets, permanent magnet flux switching machine (PMFSM) has turned out to be one of the suitable contenders for seaward boring, however, less intended for downhole because of high atmospheric temperature. Subsequently, this extensive review manages the design enhancement and performance examination of external rotor PMFSM for the downhole application. Preparatory, the essential design parameters required for machine configuration are computed numerically. At that point, the design enhancement strategy is actualized through deterministic technique. At last, preliminary and refined execution of the machine is contrasted and as a consequence, the yield torque is raised from 16.39Nm to 33.57Nm while depreciating the cogging torque and PM weight up to 1.77Nm and 0.79kg, individually. In this manner, it is inferred that purposed enhanced design of 12slot-22pole with external rotor is convenient for the downhole application.

  3. Theoretical magnetic flux emergence

    OpenAIRE

    MacTaggart, David

    2011-01-01

    Magnetic flux emergence is the subject of how magnetic fields from the solar interior can rise and expand into the atmosphere to produce active regions. It is the link that joins dynamics in the convection zone with dynamics in the atmosphere. In this thesis, we study many aspects of magnetic flux emergence through mathematical modelling and computer simulations. Our primary aim is to understand the key physical processes that lie behind emergence. The first chapter intro...

  4. Solar Magnetic Flux Ropes

    Indian Academy of Sciences (India)

    Boris Filippov; Olesya Martsenyuk; Abhishek K. Srivastava; Wahab Uddin

    2015-03-01

    In the early 1990s, it was found that the strongest disturbances of the space–weather were associated with huge ejections of plasma from the solar corona, which took the form of magnetic clouds when moved from the Sun. It is the collisions of the magnetic clouds with the Earth's magnetosphere that lead to strong, sometimes catastrophic changes in space–weather. The onset of a coronal mass ejection (CME) is sudden and no reliable forerunners of CMEs have been found till date. The CME prediction methodologies are less developed compared to the methods developed for the prediction of solar flares. The most probable initial magnetic configuration of a CME is a flux rope consisting of twisted field lines which fill the whole volume of a dark coronal cavity. The flux ropes can be in stable equilibrium in the coronal magnetic field for weeks and even months, but suddenly they lose their stability and erupt with high speed. Their transition to the unstable phase depends on the parameters of the flux rope (i.e., total electric current, twist, mass loading, etc.), as well as on the properties of the ambient coronal magnetic field. One of the major governing factors is the vertical gradient of the coronal magnetic field, which is estimated as decay index (). Cold dense prominence material can be collected in the lower parts of the helical flux tubes. Filaments are, therefore, good tracers of the flux ropes in the corona, which become visible long before the beginning of the eruption. The perspectives of the filament eruptions and following CMEs can be estimated by a comparison of observed filament heights with calculated decay index distributions. The present paper reviews the formation of magnetic flux ropes, their stable and unstable phases, eruption conditions, and also discusses their physical implications in the solar corona.

  5. Disconnecting Solar Magnetic Flux

    CERN Document Server

    DeForest, C E; McComas, D J

    2011-01-01

    Disconnection of open magnetic flux by reconnection is required to balance the injection of open flux by CMEs and other eruptive events. Making use of recent advances in heliospheric background subtraction, we have imaged many abrupt disconnection events. These events produce dense plasma clouds whose distinctie shape can now be traced from the corona across the inner solar system via heliospheric imaging. The morphology of each initial event is characteristic of magnetic reconnection across a current sheet, and the newly-disconnected flux takes the form of a "U"-shaped loop that moves outward, accreting coronal and solar wind material. We analyzed one such event on 2008 December 18 as it formed and accelerated at 20 m/s^2 to 320 km/s, expanding self-similarly until it exited our field of view 1.2 AU from the Sun. From acceleration and photometric mass estimates we derive the coronal magnetic field strength to be 8uT, 6 Rs above the photosphere, and the entrained flux to be 1.6x10^11 Wb (1.6x10^19 Mx). We mod...

  6. Magnetic Flux Emergence in the Solar Photosphere

    Science.gov (United States)

    Cheung, M. C. M.; Schüssler, M.; Moreno-Insertis, F.

    2008-04-01

    The most prominent magnetic structures on the surface of the Sun are bipolar active regions. These magnetic complexes are comprised of a hierarchy of magnetic structures of different sizes, the largest of which are sunspots. Observations indicate that the appearance of active regions on the solar surface result from the emergence of bundles of magnetic flux from the underlying convection zone. We study the emergence process by means of 3D radiation MHD simulations. In the simulations, an initially buoyant magnetic flux tube is introduced into the near-surface layers of the convection zone. Subject to the buoyancy force, the flux tube rises towards the photosphere. Our simulations highlight the importance of magneto-convection on the evolution of the magnetic flux tube. The external convective flow field has an important influence on the emergence morphology of the emerging magnetic field. Depending on the initial properties of the magnetic flux tube (e.g. field strength, twist, entropy etc.), flux emergence may lead to a disturbance of the local granulation pattern. The observational signatures associated with emerging magnetic flux in our simulations are in qualitative and quantitative agreement with observational studies of emerging flux regions on the Sun.

  7. Permanent magnet flux-biased magnetic actuator with flux feedback

    Science.gov (United States)

    Groom, Nelson J. (Inventor)

    1991-01-01

    The invention is a permanent magnet flux-biased magnetic actuator with flux feedback for adjustably suspending an element on a single axis. The magnetic actuator includes a pair of opposing electromagnets and provides bi-directional forces along the single axis to the suspended element. Permanent magnets in flux feedback loops from the opposing electromagnets establish a reference permanent magnet flux-bias to linearize the force characteristics of the electromagnets to extend the linear range of the actuator without the need for continuous bias currents in the electromagnets.

  8. Magnetic Flux Controllers for Induction Heating Applications

    Institute of Scientific and Technical Information of China (English)

    Valentin Nemkov; Robert Goldstein; Robert Ruffini

    2004-01-01

    Application of magnetic flux controllers/concentrators to induction heating coils can drastically improve the process efficiency and heat pattern control. Presentation includes: benefits provided by flux controllers, materials available for controllers, application techniques, computer assisted design of induction coils with concentrators, examples of applications. Depending on induction system design, magnetic flux controllers can concentrate heating in a specified area,change heat source distribution and shield a particular part zone or external area preventing unintended eddy current heating.Besides of the coil efficiency improvement and optimal power distribution, magnetic flux controllers reduce the coil current demand from a supplying circuitry thus strongly reducing losses in busswork, cables, transformers and inverter components.Improvement that can be achieved due to magnetic flux controllers is case dependable. 2D and 3D computer simulation allows the designer to predict accurately effect of controllers on the coil parameters and temperature distribution and optimize the whole electromagnetic system. Special attention in presentation is paid to new magnetodielectric materials optimized for induction heating conditions. These materials have high magnetic permeability and saturation flux density,excellent machinability, good chemical and temperature resistance. Concentrators from these materials can work in a wide range of frequencies and specific powers. Examples of magnetic flux controller application include surface hardening of shafts and gears, induction surface hardfacing and brazing.

  9. External trabeculectomy with T-Flux implant.

    LENUS (Irish Health Repository)

    Jungkim, S

    2012-02-03

    PURPOSE: To evaluate the efficacy and safety of T-Flux implant in nonpenetrating glaucoma surgery. METHODS: This clinical interventional case series study included 35 eyes of 35 patients with medically uncontrolled primary open angle glaucoma. External trabeculectomy with T-Flux (ETTF) is a technique of nonpenetrating glaucoma surgery, in which after removing deep scleral tissue and un-roofing the canal of Schlemn (CS) the external trabecular tissue is peeled off to enhance the aqueous drainage without opening the anterior chamber. A non-absorbable T-Flux implant (IOL TECH Laboratories, France) was sutured in deep intrascleral space to keep it patent. Snellen\\'s best-corrected visual acuity, slit lamp biomicroscopy, intraocular pressure (IOP), gonioscopy, funduscopy, and optic disc assessment were performed preoperatively and postoperatively at 1 day, 1 week, and 1, 3 , 6, and 12 months. Visual field testing was performed preoperatively and at 6 and 12 months postoperatively. RESULTS: For three eyes, surgery was converted to standard trabeculectomy owing to the perforation of trabeculo-Descemet\\'s membrane and iris prolapse and excluded from the study. The results of the remaining 32 eyes were included in the study. Preoperative IOP (mean +\\/- SD) of 32.88 +\\/- 5.7 mmHg decreased to 15.44 +\\/- 1.6 mmHg after 12 months. Ten eyes (28.6%) had microhyphema that resolved spontaneously; 3 eyes (8.6%) had microperforation without iris prolapse so ETTF was proceeded routinely. The preoperative number of antiglaucoma medications per patient reduced from (mean +\\/- SD) 2.74 +\\/- 0.61 to 0.11 +\\/- 0.32 postoperatively at 12 months. Visual acuity and visual fields remained stable. CONCLUSIONS: ETTF appears to provide significant control of IOP and have low incidence of complications.

  10. Periodicities in photospheric magnetic flux

    Institute of Scientific and Technical Information of China (English)

    SONG; Wenbin; WANG; Jingxiu

    2006-01-01

    Magnetic field plays an important role in solar structure and activity. In principle, the determination of magnetic flux would provide the best general-purpose index of solar activity. Currently, the periodicity studies corresponding to photospheric magnetic flux (PMF) are very few possibly due to the absence of a uniform flux sequence. In this paper, by using 383 NSO/Kitt Peak magnetic synoptic charts we reconstruct a flux sequence from February 1975 to August 2003 and perform a relatively systemic periodicity analysis with two methods of the Scargle periodogram and the Morlet wavelet transform. As a result, four periods are found at around 1050, 500, 300 and 160 days. We analyze these periods' temporal variabilities in detail and discuss their respective origins briefly.

  11. Physics of magnetic flux tubes

    CERN Document Server

    Ryutova, Margarita

    2015-01-01

    This book is the first account of the physics of magnetic flux tubes from their fundamental properties to collective phenomena in an ensembles of flux tubes. The physics of magnetic flux tubes is absolutely vital for understanding fundamental physical processes in the solar atmosphere shaped and governed by magnetic fields. High-resolution and high cadence observations from recent space and  ground-based instruments taken simultaneously at different heights and temperatures not only show the ubiquity of filamentary structure formation but also allow to study how various events are interconnected by system of magnetic flux tubes. The book covers both theory and observations. Theoretical models presented in analytical and phenomenological forms are tailored for practical applications. These are welded with state-of-the-art observations from early decisive ones to the most recent data that open a new phase-space for exploring the Sun and sun-like stars. Concept of magnetic flux tubes is central to various magn...

  12. Magnetic flux reconstruction methods for shaped tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Tsui, Chi-Wa

    1993-12-01

    The use of a variational method permits the Grad-Shafranov (GS) equation to be solved by reducing the problem of solving the 2D non-linear partial differential equation to the problem of minimizing a function of several variables. This high speed algorithm approximately solves the GS equation given a parameterization of the plasma boundary and the current profile (p` and FF` functions). The author treats the current profile parameters as unknowns. The goal is to reconstruct the internal magnetic flux surfaces of a tokamak plasma and the toroidal current density profile from the external magnetic measurements. This is a classic problem of inverse equilibrium determination. The current profile parameters can be evaluated by several different matching procedures. Matching of magnetic flux and field at the probe locations using the Biot-Savart law and magnetic Green`s function provides a robust method of magnetic reconstruction. The matching of poloidal magnetic field on the plasma surface provides a unique method of identifying the plasma current profile. However, the power of this method is greatly compromised by the experimental errors of the magnetic signals. The Casing Principle provides a very fast way to evaluate the plasma contribution to the magnetic signals. It has the potential of being a fast matching method. The performance of this method is hindered by the accuracy of the poloidal magnetic field computed from the equilibrium solver. A flux reconstruction package has been implemented which integrates a vacuum field solver using a filament model for the plasma, a multi-layer perception neural network as an interface, and the volume integration of plasma current density using Green`s functions as a matching method for the current profile parameters. The flux reconstruction package is applied to compare with the ASEQ and EFIT data. The results are promising.

  13. Novel Switched Flux Permanent Magnet Machine Topologies

    Institute of Scientific and Technical Information of China (English)

    诸自强

    2012-01-01

    This paper overviews various switched flux permanent magnet machines and their design and performance features,with particular emphasis on machine topologies with reduced magnet usage or without using magnet,as well as with variable flux capability.

  14. Magnetic flux concentration and zonal flows in magnetorotational instability turbulence

    Energy Technology Data Exchange (ETDEWEB)

    Bai, Xue-Ning [Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-51, Cambridge, MA 02138 (United States); Stone, James M., E-mail: xbai@cfa.harvard.edu [Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544 (United States)

    2014-11-20

    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 turbulent 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, and may have important implications for magnetic flux transport in accretion disks. The physical origin of magnetic flux concentration may be related to the development of channel flows followed by magnetic reconnection, which acts to decrease the mass-to-flux ratio in localized regions. The association of enhanced zonal flows with magnetic flux concentration may lead to global pressure bumps in protoplanetary disks that helps trap dust particles and facilitates planet formation.

  15. Physics of Magnetic Flux Ropes

    CERN Document Server

    Priest, E R; Lee, L C

    1990-01-01

    The American Geophysical Union Chapman Conference on the Physics of Magnetic Flux Ropes was held at the Hamilton Princess Hotel, Hamilton, Bermuda on March 27–31, 1989. Topics discussed ranged from solar flux ropes, such as photospheric flux tubes, coronal loops and prominences, to flux ropes in the solar wind, in planetary ionospheres, at the Earth's magnetopause, in the geomagnetic tail and deep in the Earth's magnetosphere. Papers presented at that conference form the nucleus of this book, but the book is more than just a proceedings of the conference. We have solicited articles from all interested in this topic. Thus, there is some material in the book not discussed at the conference. Even in the case of papers presented at the conference, there is generally a much more detailed and rigorous presentation than was possible in the time allowed by the oral and poster presentations.

  16. Force sensor using changes in magnetic flux

    Science.gov (United States)

    Pickens, Herman L. (Inventor); Richard, James A. (Inventor)

    2012-01-01

    A force sensor includes a magnetostrictive material and a magnetic field generator positioned in proximity thereto. A magnetic field is induced in and surrounding the magnetostrictive material such that lines of magnetic flux pass through the magnetostrictive material. A sensor positioned in the vicinity of the magnetostrictive material measures changes in one of flux angle and flux density when the magnetostrictive material experiences an applied force that is aligned with the lines of magnetic flux.

  17. Initiation of CMEs by Magnetic Flux Emergence

    Indian Academy of Sciences (India)

    Govind Dubey; Bart van der Holst; Stefaan Poedts

    2006-06-01

    The initiation of solar Coronal Mass Ejections (CMEs) is studied in the framework of numerical magnetohydrodynamics (MHD). The initial CME model includes a magnetic flux rope in spherical, axisymmetric geometry. The initial configuration consists of a magnetic flux rope embedded in a gravitationally stratified solar atmosphere with a background dipole magnetic field. The flux rope is in equilibrium due to an image current below the photosphere. An emerging flux triggering mechanism is used to make this equilibrium system unstable. When the magnetic flux emerges within the filament below the flux rope, this results in a catastrophic behavior similar to previous models. As a result, the flux rope rises and a current sheet forms below it. It is shown that the magnetic reconnection in the current sheet below the flux rope in combination with the outward curvature forces results in a fast ejection of the flux rope as observed for solar CMEs.We have done a parametric study of the emerging flux rate.

  18. Lattice Planar QED in external magnetic field

    CERN Document Server

    Cea, Paolo; Giudice, Pietro; Papa, Alessandro

    2011-01-01

    We investigate planar Quantum ElectroDynamics (QED) with two degenerate staggered fermions in an external magnetic field on the lattice. Our preliminary results indicate that in external magnetic fields there is dynamical generation of mass for two-dimensional massless Dirac fermions in the weak coupling region. We comment on possible implications to the quantum Hall effect in graphene.

  19. Flux emergence in a magnetized convection zone

    CERN Document Server

    Pinto, R F

    2013-01-01

    We study the influence of a dynamo magnetic field on the buoyant rise and emergence of twisted magnetic flux-ropes, and their influence on the global external magnetic field. We ran 3D MHD numerical simulations using the ASH code and analysed the dynamical evolution of such buoyant flux-ropes from the bottom of the convection zone until the post-emergence phases. The global nature of this model represents very crudely and inaccurately the local dynamics of the buoyant rise, but allows to study the influence of global effects such as self-consistently generated differential rotation, meridional circulation and Coriolis forces. Although motivated by the solar context, this model cannot be thought of as a realistic model of the rise of magnetic structures and their emergence in the Sun where the local dynamics are completely different. The properties of initial phases of the buoyant rise in good agreement with previous studies. However, the effects of the interaction of the background dynamo field become increas...

  20. Magnetic flux emergence in fast rotating stars

    OpenAIRE

    Holzwarth, V.

    2007-01-01

    Fast rotating cool stars are characterised by high magnetic activity levels and frequently show dark spots up to polar latitudes. Their distinctive surface distributions of magnetic flux are investigated in the context of the solar-stellar connection by applying the solar flux eruption and surface flux transport models to stars with different rotation rates, mass, and evolutionary stage. The rise of magnetic flux tubes through the convection zone is primarily buoyancy-driven, though their evo...

  1. Magnetic Flux Compression in Plasmas

    Science.gov (United States)

    Velikovich, A. L.

    2012-10-01

    Magnetic flux compression (MFC) as a method for producing ultra-high pulsed magnetic fields had been originated in the 1950s by Sakharov et al. at Arzamas in the USSR (now VNIIEF, Russia) and by Fowler et al. at Los Alamos in the US. The highest magnetic field produced by explosively driven MFC generator, 28 MG, was reported by Boyko et al. of VNIIEF. The idea of using MFC to increase the magnetic field in a magnetically confined plasma to 3-10 MG, relaxing the strict requirements on the plasma density and Lawson time, gave rise to the research area known as MTF in the US and MAGO in Russia. To make a difference in ICF, a magnetic field of ˜100 MG should be generated via MFC by a plasma liner as a part of the capsule compression scenario on a laser or pulsed power facility. This approach was first suggested in mid-1980s by Liberman and Velikovich in the USSR and Felber in the US. It has not been obvious from the start that it could work at all, given that so many mechanisms exist for anomalously fast penetration of magnetic field through plasma. And yet, many experiments stimulated by this proposal since 1986, mostly using pulsed-power drivers, demonstrated reasonably good flux compression up to ˜42 MG, although diagnostics of magnetic fields of such magnitude in HED plasmas is still problematic. The new interest of MFC in plasmas emerged with the advancement of new drivers, diagnostic methods and simulation tools. Experiments on MFC in a deuterium plasma filling a cylindrical plastic liner imploded by OMEGA laser beam led by Knauer, Betti et al. at LLE produced peak fields of 36 MG. The novel MagLIF approach to low-cost, high-efficiency ICF pursued by Herrmann, Slutz, Vesey et al. at Sandia involves pulsed-power-driven MFC to a peak field of ˜130 MG in a DT plasma. A review of the progress, current status and future prospects of MFC in plasmas is presented.

  2. External-field-free magnetic biosensor

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yuanpeng; Wang, Yi; Klein, Todd; Wang, Jian-Ping, E-mail: jpwang@umn.edu [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

    2014-03-24

    In this paper, we report a magnetic nanoparticle (MNP) detection scheme without the presence of any external magnetic field. The proposed magnetic sensor uses a patterned groove structure within the sensor so that no external magnetic field is needed to magnetize the MNPs. An example is given based on a giant magnetoresistance (GMR) sensing device with a spin valve structure. For this structure, the detection of MNPs located inside the groove and near the free layer is demonstrated under no external magnetic field. Micromagnetic simulations are performed to calculate the signal to noise level of this detection scheme. A maximum signal to noise ratio (SNR) of 18.6 dB from one iron oxide magnetic nanoparticle with 8 nm radius is achieved. As proof of concept, this external-field-free GMR sensor with groove structure of 200 nm × 200 nm is fabricated using a photo and an electron beam integrated lithography process. Using this sensor, the feasibility demonstration of the detection SNR of 9.3 dB is achieved for 30 μl magnetic nanoparticles suspension (30 nm iron oxide particles, 1 mg/ml). This proposed external-field-free sensor structure is not limited to GMR devices and could be applicable to other magnetic biosensing devices.

  3. A time-varying magnetic flux concentrator

    Science.gov (United States)

    Kibret, B.; Premaratne, M.; Lewis, P. M.; Thomson, R.; Fitzgerald, P. B.

    2016-08-01

    It is known that diverse technological applications require the use of focused magnetic fields. This has driven the quest for controlling the magnetic field. Recently, the principles in transformation optics and metamaterials have allowed the realization of practical static magnetic flux concentrators. Extending such progress, here, we propose a time-varying magnetic flux concentrator cylindrical shell that uses electric conductors and ferromagnetic materials to guide magnetic flux to its center. Its performance is discussed based on finite-element simulation results. Our proposed design has potential applications in magnetic sensors, medical devices, wireless power transfer, and near-field wireless communications.

  4. On the generation of flux tube waves in stellar convection zones. I - Longitudinal tube waves driven by external turbulence

    Science.gov (United States)

    Musielak, Z. E.; Rosner, R.; Ulmschneider, P.

    1989-01-01

    The source functions and the energy fluxes for wave generation in magnetic flux tubes embedded in an otherwise magnetic field-free, turbulent, and compressible fluid are derived. The calculations presented here assume that the tube interior is not itself turbulent, e.g., that motions within the flux tube are due simply to external excitation. Specific results for the generation of longitudinal tube waves are presented.

  5. Self-organization in magnetic flux ropes

    Science.gov (United States)

    Lukin, Vyacheslav S.

    2014-06-01

    This cross-disciplinary special issue on 'Self-organization in magnetic flux ropes' follows in the footsteps of another collection of manuscripts dedicated to the subject of magnetic flux ropes, a volume on 'Physics of magnetic flux ropes' published in the American Geophysical Union's Geophysical Monograph Series in 1990 [1]. Twenty-four years later, this special issue, composed of invited original contributions highlighting ongoing research on the physics of magnetic flux ropes in astrophysical, space and laboratory plasmas, can be considered an update on our state of understanding of this fundamental constituent of any magnetized plasma. Furthermore, by inviting contributions from research groups focused on the study of the origins and properties of magnetic flux ropes in a variety of different environments, we have attempted to underline both the diversity of and the commonalities among magnetic flux ropes throughout the solar system and, indeed, the universe. So, what is a magnetic flux rope? The answer will undoubtedly depend on whom you ask. A flux rope can be as narrow as a few Larmor radii and as wide as the Sun (see, e.g., the contributions by Heli Hietala et al and by Angelous Vourlidas). As described below by Ward Manchester IV et al , they can stretch from the Sun to the Earth in the form of interplanetary coronal mass ejections. Or, as in the Swarthmore Spheromak Experiment described by David Schaffner et al , they can fit into a meter-long laboratory device tended by college students. They can be helical and line-tied (see, e.g., Walter Gekelman et al or J Sears et al ), or toroidal and periodic (see, e.g., John O'Bryan et al or Philippa Browning et al ). They can form in the low plasma beta environment of the solar corona (Tibor Török et al ), the order unity beta plasmas of the solar wind (Stefan Eriksson et al ) and the plasma pressure dominated stellar convection zones (Nicholas Nelson and Mark Miesch). In this special issue, Setthivoine You

  6. Regulation of the interplanetary magnetic flux

    Energy Technology Data Exchange (ETDEWEB)

    McComas, D.J.; Gosling, J.T.; Phillips, J.L.

    1991-01-01

    In this study we use a recently developed technique for measuring the 2-D magnetic flux in the ecliptic plane to examine (1) the long term variation of the magnetic flux in interplanetary space and (2) the apparent rate at which coronal mass ejections (CMEs) may be opening new flux from the Sun. Since there is a substantial variation ({approximately}50%) of the flux in the ecliptic plane over the solar cycle, we conclude that there must be some means whereby new flux can be opened from the Sun and previously open magnetic flux can be closed off. We briefly describe recently discovered coronal disconnections events which could serve to close off previously open magnetic flux. CMEs appear to retain at least partial magnetic connection to the Sun and hence open new flux, while disconnections appear to be likely signatures of the process that returns closed flux to the Sun; the combination of these processes could regulate the amount of open magnetic flux in interplanetary space. 6 refs., 3 figs.

  7. Magnetic flux concentration methods for magnetic energy harvesting module

    Directory of Open Access Journals (Sweden)

    Wakiwaka Hiroyuki

    2013-01-01

    Full Text Available This paper presents magnetic flux concentration methods for magnetic energy harvesting module. The purpose of this study is to harvest 1 mW energy with a Brooks coil 2 cm in diameter from environmental magnetic field at 60 Hz. Because the harvesting power is proportional to the square of the magnetic flux density, we consider the use of a magnetic flux concentration coil and a magnetic core. The magnetic flux concentration coil consists of an air­core Brooks coil and a resonant capacitor. When a uniform magnetic field crossed the coil, the magnetic flux distribution around the coil was changed. It is found that the magnetic field in an area is concentrated larger than 20 times compared with the uniform magnetic field. Compared with the air­core coil, our designed magnetic core makes the harvested energy ten­fold. According to ICNIRP2010 guideline, the acceptable level of magnetic field is 0.2 mT in the frequency range between 25 Hz and 400 Hz. Without the two magnetic flux concentration methods, the corresponding energy is limited to 1 µW. In contrast, our experimental results successfully demonstrate energy harvesting of 1 mW from a magnetic field of 0.03 mT at 60 Hz.

  8. Metamaterial anisotropic flux concentrators and magnetic arrays

    CERN Document Server

    Bjørk, R; Bahl, C R H

    2014-01-01

    A metamaterial magnetic flux concentrator is investigated in detail in combination with a Halbach cylinder of infinite length. A general analytical solution to the field is determined and the magnetic figure of merit is determined for a Halbach cylinder with a flux concentrator. It is shown that an ideal flux concentrator will not change the figure of merit of a given magnet design, while the non-ideal will always lower it. The geometric parameters producing maximum figure of merit, i.e. the most efficient devices, are determined. The force and torque between two concentric Halbach cylinders with flux concentrators is determined and the maximum torque is found. Finally, the effect of non-ideal flux concentrators and the practical use of flux concentrators, as well as demagnetization issues, is discussed.

  9. Magnetic Flux Cancellation and Formation of Prominence

    Science.gov (United States)

    Miley, George; Kim, Mun Song; Chon Nam, Sok; Kim, Kyong Chol

    2015-08-01

    Magnetic flux cancellation appears to be closely related to various kinds of solar activities such as flares, microflares/surges/jets, X-ray bright points, erupting mini-filaments, transition region explosive events, filament formation, filament activation and eruption, and coronal mass ejections. It is commonly believed that magnetic reconnections in the low atmosphere are responsible for canceling magnetic features, and magnetic fragments are observed to originate as bipoles. According to the Sweet-Parker type reconnection model, the inflow speed closely corresponds to the converging speed of each pole in a canceling magnetic feature and the rate of flux cancellation must be explained by the observed converging speed. As distinct from the corona, the efficiency of photospheric magnetic reconnection may be due to the small Cowling conductivity, instead of the Spitzer, of weakly ionized and magnetized plasma in the low atmosphere of the sun. Using the VAL-C atmospheric model and Cowling conductivity, we have computed the parameters describing Sweet-Parker type reconnecting current sheets in the plasma of the solar photosphere and chromosphere, and particularly for the phenomena of magnetic flux cancellation and dark filament formation which occurred on July 2, 1994 we have estimated the rate of flux cancellation, the inflow speed(the converging speed) and the upward mass flux to compare with the observation. The results show that when taking account of the Cowling conductivity in the low atmosphere, large flux cancellation rates(>1019Mxhr-1) in solar active regions are better explained than by the Spitzer conductivity-considered reconnection model. Particularly for the flux cancellation event on July 2, 1994, the inflow speed(0.26kms-1)is almost similar to the converging speed(0.22kms-1)and the upward mass flux(3.3X1012gs-1) in the model is sufficient for the large dark filament formation in a time of several hours through magnetic flux cancellation process.

  10. Magnetic flux biasing of magnetostrictive sensors

    Science.gov (United States)

    Deng, Zhangxian; Dapino, Marcelo J.

    2017-05-01

    The performance of magnetostrictive materials, especially those with high initial magnetic permeability and associated low magnetic reluctance, is sensitive to not just the amount of magnetic bias but also how the bias is applied. Terfenol-D and Galfenol have been characterized under constant magnetic field and constant magnetomotive force, which require active control. The application of a magnetic flux bias utilizing permanent magnets allows for robust magnetostrictive systems that require no active control. However, this biasing configuration has not been thoroughly investigated. This study presents flux density versus stress major loops of Terfenol-D and Galfenol at various magnetic flux biases. A new piezomagnetic coefficient {d}33φ is defined as the locally-averaged slope of flux density versus stress. Considering the materials alone, the maximum {d}33φ is 18.42 T GPa-1 and 19.53 T GPa-1 for Terfenol-D and Galfenol, respectively. Compared with the peak piezomagnetic coefficient {d}33* measured under controlled magnetic fields, the piezomagnetic coefficient {d}33φ is 26% and 74% smaller for Terfenol-D and Galfenol, respectively. This study shows that adding parallel magnetic flux paths to low-reluctance magnetostrictive components can partially compensate for the performance loss. With a low carbon steel flux path in parallel to the Galfenol specimen, the maximum {d}33φ increased to 28.33 T GPa-1 corresponding to a 45% improvement compared with the case without a flux path. Due to its low magnetic permeability, Terfenol-D does not benefit from the addition of a parallel flux path.

  11. Metamaterial anisotropic flux concentrators and magnetic arrays

    DEFF Research Database (Denmark)

    Bjørk, Rasmus; Smith, Anders; Bahl, Christian R.H.

    2013-01-01

    A metamaterial magnetic flux concentrator is investigated in detail in combination with a Halbach cylinder of infinite length. A general analytical solution to the field is determined and the magnetic figure of merit is determined for a Halbach cylinder with a flux concentrator. It is shown...... that an ideal flux concentrator will not change the figure of merit of a given magnet design, while the non-ideal will always lower it. The geometric parameters producing maximum figure of merit, i.e., the most efficient devices, are determined. The force and torque between two concentric Halbach cylinders...

  12. Behaviour of ferrocholesterics under external magnetic fields

    Science.gov (United States)

    Petrescu, Emil; Motoc, Cornelia

    2001-08-01

    The influence of an external magnetic field on the orientational behaviour of a ferrocholesteric with a positive magnetic anisotropy is investigated. Both the phenomena arising when the field was switched on or switched off are considered. It is found that the field needed for a ferrocholesteric-ferronematic transition BFC↑ is higher when compared to that obtained for the pure cholesteric ( BC↑). A similar result was obtained when estimating the critical field for the homeotropic ferronematic-ferrocholesteric (focal conic) transition, occurring when the magnetic field was decreased or switched off. We found that BFC↓> BC↓. These results are explained when considering that the magnetic moments of the magnetic powder are not oriented parallel to the liquid crystal molecular directors, therefore hindering their orientation under a magnetic field.

  13. The Pressure Limitations on Flux Pile-Up Magnetic Reconnection

    Science.gov (United States)

    Litvinenko, Y. E.

    1999-05-01

    Flux pile-up magnetic reconnection was thought to be able to provide fast energy dissipation a strongly magnetized plasma, for example, in solar flares. We examine the problem of the plasma pressure limitations on the rapidity of flux pile-up reconnection. It is shown that for a two-dimensional stagnation point flow with nonzero vorticity the magnetic merging rate cannot exceed the Sweet-Parker scaling in a low-beta plasma, which is too slow to explain flares. Moreover, the solution has some undesireable properties such as a diffusion layer at the external boundary and the massively increasing inflow speed. The pressure limitation appears to be somewhat less restrictive for three-dimensional flux pile-up. This work was supported by NSF grant ATM-9813933.

  14. Strongly magnetized accretion discs require poloidal flux

    Science.gov (United States)

    Salvesen, Greg; Armitage, Philip J.; Simon, Jacob B.; Begelman, Mitchell C.

    2016-08-01

    Motivated by indirect observational evidence for strongly magnetized accretion discs around black holes, and the novel theoretical properties of such solutions, we investigate how a strong magnetization state can develop and persist. To this end, we perform local simulations of accretion discs with an initially purely toroidal magnetic field of equipartition strength. We demonstrate that discs with zero net vertical magnetic flux and realistic boundary conditions cannot sustain a strong toroidal field. However, a magnetic pressure-dominated disc can form from an initial configuration with a sufficient amount of net vertical flux and realistic boundary conditions. Our results suggest that poloidal flux is a necessary prerequisite for the sustainability of strongly magnetized accretion discs.

  15. Strongly magnetized accretion discs require poloidal flux

    CERN Document Server

    Salvesen, Greg; Simon, Jacob B; Begelman, Mitchell C

    2016-01-01

    Motivated by indirect observational evidence for strongly magnetized accretion discs around black holes, and the novel theoretical properties of such solutions, we investigate how a strong magnetization state can develop and persist. To this end, we perform local simulations of accretion discs with an initially purely toroidal magnetic field of equipartition strength. We demonstrate that discs with zero net vertical magnetic flux and realistic boundary conditions cannot sustain a strong toroidal field. However, a magnetic pressure-dominated disc can form from an initial configuration with a sufficient amount of net vertical flux and realistic boundary conditions. Our results suggest that poloidal flux is a necessary prerequisite for the sustainability of strongly magnetized accretion discs.

  16. Magnetic flux generator for balanced membrane loudspeaker

    DEFF Research Database (Denmark)

    Rehder, Jörg; Rombach, Pirmin; Hansen, Ole

    2002-01-01

    This paper reports the development of a magnetic flux generator with an application in a hearing aid loudspeaker produced in microsystem technology (MST). The technology plans for two different designs for the magnetic flux generator utilizing a softmagnetic substrate or electroplated NiCoFe as c......CoFe as core material are presented and the production and characterization of four different mono- and double-layer planar coil types are reported....

  17. Magnetic Flux Emergence on Different Scales

    Science.gov (United States)

    Hagenaar, M.; Cheung, M.

    2009-12-01

    Magnetic flux emerges on the Sun on many different scales, from weak intranetwork to network concentrations and (ephemeral) active regions. Methods previously developed to recognize regions of magnetic emergence on MDI Full Disk magnetograms fail when applied to Hinode/SOT Stokes maps: the resolution is so much higher that simple bipoles on MDI are observed as collections of fragments. We present a new method for the automatic detection and characterization of flux emergence on a range of scales.

  18. Wave heating in magnetic flux tubes

    Science.gov (United States)

    Kalkofen, Wolfgang

    1990-01-01

    The bright chromosphere in the quiet sun is confined to magnetic elements (flux tubes), which are located in the interior of the supergranulation cells and within the network that surrounds the cells. The paper discusses the heating of the gas in the magnetic elements of the cell interior. These intranetwork flux tubes are closely associated with bright points, which are heated by large-amplitude compressive waves with periods near the acoustic cutoff that travel outward from the photosphere and dissipate their energy in the chromosphere. The energy flux of these long-period waves appears to be sufficient for the heating of the low and middle chromosphere in the bright points.

  19. Magnetic response to applied electrostatic field in external magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Adorno, T.C. [Universidade de Sao Paulo, Instituto de Fisica, Caixa Postal 66318, Sao Paulo, SP (Brazil); University of Florida, Department of Physics, Gainesville, FL (United States); Gitman, D.M. [Universidade de Sao Paulo, Instituto de Fisica, Caixa Postal 66318, Sao Paulo, SP (Brazil); Tomsk State University, Department of Physics, Tomsk (Russian Federation); Shabad, A.E. [P. N. Lebedev Physics Institute, Moscow (Russian Federation)

    2014-04-15

    We show, within QED and other possible nonlinear theories, that a static charge localized in a finite domain of space becomes a magnetic dipole, if it is placed in an external (constant and homogeneous) magnetic field in the vacuum. The magnetic moment is quadratic in the charge, depends on its size and is parallel to the external field, provided the charge distribution is at least cylindrically symmetric. This magneto-electric effect is a nonlinear response of the magnetized vacuum to an applied electrostatic field. Referring to the simple example of a spherically symmetric applied field, the nonlinearly induced current and its magnetic field are found explicitly throughout the space; the pattern of the lines of force is depicted, both inside and outside the charge, which resembles that of a standard solenoid of classical magnetostatics. (orig.)

  20. Magnetic response to applied electrostatic field in external magnetic field

    CERN Document Server

    Adorno, T C; Shabad, A E

    2014-01-01

    We show, within QED and other possible nonlinear theories, that a static charge localized in a finite domain of space becomes a magnetic dipole, if it is placed in an external (constant and homogeneous) magnetic field in the vacuum. The magnetic moment is quadratic in the charge, depends on its size and is parallel to the external field, provided the charge distribution is at least cylindrically symmetric. This magneto-electric effect is a nonlinear response of the magnetized vacuum to an applied electrostatic field. Referring to a simple example of a spherically-symmetric applied field, the nonlinearly induced current and its magnetic field are found explicitly throughout the space, the pattern of lines of force is depicted, both inside and outside the charge, which resembles that of a standard solenoid of classical magnetostatics.

  1. Flux-Feedback Magnetic-Suspension Actuator

    Science.gov (United States)

    Groom, Nelson J.

    1990-01-01

    Flux-feedback magnetic-suspension actuator provides magnetic suspension and control forces having linear transfer characteristics between force command and force output over large range of gaps. Hall-effect devices used as sensors for electronic feedback circuit controlling currents flowing in electromagnetic windings to maintain flux linking suspended element at substantially constant value independent of changes in length of gap. Technique provides effective method for maintenance of constant flux density in gap and simpler than previous methods. Applications include magnetic actuators for control of shapes and figures of antennas and of precise segmented reflectors, magnetic suspensions in devices for storage of angular momentum and/or kinetic energy, and systems for control, pointing, and isolation of instruments.

  2. MHD waves on solar magnetic flux tubes - Tutorial review

    Science.gov (United States)

    Hollweg, Joseph V.

    1990-01-01

    Some of the highly simplified models that have been developed for solar magnetic flux tubes, which are intense photospheric-level fields confined by external gas pressure but able to vary rapidly with height, are presently discussed with emphasis on the torsional Alfven mode's propagation, reflection, and non-WKB properties. The 'sausage' and 'kink' modes described by the thin flux-tube approximation are noted. Attention is also given to the surface waves and resonance absorption of X-ray-emitting loops, as well as to the results of recent work on the resonant instabilities that occur in the presence of bulk flows.

  3. Solar Intranetwork Magnetic Elements: bipolar flux appearance

    OpenAIRE

    Wang, Jingxiu; Zhou, Guiping; Jin, Chunlan; Li, Hui

    2012-01-01

    The current study aims to quantify characteristic features of bipolar flux appearance of solar intranetwork (IN) magnetic elements. To attack such a problem, we use the Narrow-band Filter Imager (NFI) magnetograms from the Solar Optical Telescope (SOT) on board \\emph{Hinode}; these data are from quiet and an enhanced network areas. Cluster emergence of mixed polarities and IN ephemeral regions (ERs) are the most conspicuous forms of bipolar flux appearance within the network. Each of the clus...

  4. Turbulent dynamo with advective magnetic helicity flux

    CERN Document Server

    Del Sordo, Fabio; Brandenburg, Axel

    2012-01-01

    Many astrophysical bodies harbor magnetic fields that are thought to be sustained by dynamo processes. However, it has been argued that the production of large-scale magnetic fields by a mean-field dynamo is strongly suppressed at large magnetic Reynolds numbers owing to the conservation of magnetic helicity. This phenomenon is known as catastrophic quenching. Advection of magnetic field toward the outer boundaries and away from the dynamo is expected to alleviate such quenching. Examples are stellar and galactic winds. Such advection might be able to overcome the constraint imposed by the conservation of magnetic helicity, transporting a fraction of it outside the domain in which the dynamo operates. We study how the dynamo process is affected by advection. In particular, we study the relative roles played by advective and diffusive fluxes of magnetic helicity. We do this by performing direct numerical simulations of a turbulent dynamo of alpha^2 type driven by forced turbulence in a Cartesian domain in the ...

  5. MAGNETIC FLUX SUPPLEMENT TO CORONAL BRIGHT POINTS

    Energy Technology Data Exchange (ETDEWEB)

    Mou, Chaozhou; Huang, Zhenghua; Xia, Lidong; Li, Bo; Fu, Hui; Jiao, Fangran; Hou, Zhenyong [Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, 264209 Shandong (China); Madjarska, Maria S., E-mail: z.huang@sdu.edu.cn [Armagh Observatory, College Hill, Armagh BT61 9DG (United Kingdom)

    2016-02-10

    Coronal bright points (BPs) are associated with magnetic bipolar features (MBFs) and magnetic cancellation. Here we investigate how BP-associated MBFs form and how the consequent magnetic cancellation occurs. We analyze longitudinal magnetograms from the Helioseismic and Magnetic Imager to investigate the photospheric magnetic flux evolution of 70 BPs. From images taken in the 193 Å passband of the Atmospheric Imaging Assembly (AIA) we dermine that the BPs’ lifetimes vary from 2.7 to 58.8 hr. The formation of the BP MBFs is found to involve three processes, namely, emergence, convergence, and local coalescence of the magnetic fluxes. The formation of an MBF can involve more than one of these processes. Out of the 70 cases, flux emergence is the main process of an MBF buildup of 52 BPs, mainly convergence is seen in 28, and 14 cases are associated with local coalescence. For MBFs formed by bipolar emergence, the time difference between the flux emergence and the BP appearance in the AIA 193 Å passband varies from 0.1 to 3.2 hr with an average of 1.3 hr. While magnetic cancellation is found in all 70 BPs, it can occur in three different ways: (I) between an MBF and small weak magnetic features (in 33 BPs); (II) within an MBF with the two polarities moving toward each other from a large distance (34 BPs); (III) within an MBF whose two main polarities emerge in the same place simultaneously (3 BPs). While an MBF builds up the skeleton of a BP, we find that the magnetic activities responsible for the BP heating may involve small weak fields.

  6. MAGNETIC FLUX TUBE INTERCHANGE AT THE HELIOPAUSE

    Energy Technology Data Exchange (ETDEWEB)

    Florinski, V., E-mail: vaf0001@uah.edu [Department of Space Science and Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 35899 (United States)

    2015-11-01

    The magnetic field measured by Voyager 1 prior to its heliocliff encounter on 2012.65 showed an unexpectedly complex transition from the primarily azimuthal inner-heliosheath field to the draped interstellar field tilted by some 20° to the nominal azimuthal direction. Most prominent were two regions of enhanced magnetic field strength depleted in energetic charged particles of heliospheric origin. These regions were interpreted as magnetic flux tubes connected to the outer heliosheath that provided a path for the particles to escape. Despite large increases in strength, the field’s direction did not change appreciably at the boundaries of these flux tubes. Rather, the field’s direction changed gradually over several months prior to the heliocliff crossing. It is shown theoretically that the heliopause, as a pressure equilibrium layer, can become unstable to interchange of magnetic fields between the inner and the outer heliosheaths. The curvature of magnetic field lines and the anti-sunward gradient in plasma kinetic pressure provide conditions favorable for an interchange. Magnetic shear between the heliosheath and the interstellar fields reduces the growth rates, but does not fully stabilize the heliopause against perturbations propagating in the latitudinal direction. The instability could create a transition layer permeated by magnetic flux tubes, oriented parallel to each other and alternately connected to the heliosheath or the interstellar regions.

  7. Coronal Magnetic Flux Rope Equilibria and Magnetic Helicity

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Using a 2.5-dimensional (2.5-D) ideal MHD model, this paper ana lyzes the equilibrium properties of coronal magnetic flux ropes in a bipolar ambient magnetic field. It is found that the geometrical features of the magnetic flux rope,including the height of the rope axis, the half-width of the rope, and the length of the vertical current sheet below the rope, are determined by a single magnetic parameter, the magnetic helicity, which is the sum of the self-helicity of the rope and the mutual helicity between the rope field and the ambient magnetic field. All the geometrical parameters increase monotonically with increasing magnetic helicity.The implication of this result in solar active phenomena is briefly discussed.

  8. Holographic fermions in external magnetic fields

    CERN Document Server

    Gubankova, E; Cubrovic, M; Schalm, K; Schijven, P; Zaanen, J

    2011-01-01

    We study the Fermi level structure of 2+1-dimensional strongly interacting electron systems in external magnetic field using the AdS/CFT correspondence. The gravity dual of a finite density fermion system is a Dirac field in the background of the dyonic AdS-Reissner-Nordstrom black hole. In the probe limit the magnetic system can be reduced to the non-magnetic one, with Landau-quantized momenta and rescaled thermodynamical variables. We find that at strong enough magnetic fields, the Fermi surface vanishes and the quasiparticle is lost either through a crossover to conformal regime or through a phase transition to an unstable Fermi surface. In the latter case, the vanishing Fermi velocity at the critical magnetic field triggers the non-Fermi liquid regime with unstable quasiparticles and a change in transport properties of the system. We associate it with a metal-"strange metal" phase transition. Next we compute compute the DC Hall and longitudinal conductivities using the gravity-dressed fermion propagators....

  9. Photospheric Magnetic Flux Transport - Supergranules Rule

    Science.gov (United States)

    Hathaway, David H.; Rightmire-Upton, Lisa

    2012-01-01

    Observations of the transport of magnetic flux in the Sun's photosphere show that active region magnetic flux is carried far from its origin by a combination of flows. These flows have previously been identified and modeled as separate axisymmetric processes: differential rotation, meridional flow, and supergranule diffusion. Experiments with a surface convective flow model reveal that the true nature of this transport is advection by the non-axisymmetric cellular flows themselves - supergranules. Magnetic elements are transported to the boundaries of the cells and then follow the evolving boundaries. The convective flows in supergranules have peak velocities near 500 m/s. These flows completely overpower the superimposed 20 m/s meridional flow and 100 m/s differential rotation. The magnetic elements remain pinned at the supergranule boundaries. Experiments with and without the superimposed axisymmetric photospheric flows show that the axisymmetric transport of magnetic flux is controlled by the advection of the cellular pattern by underlying flows representative of deeper layers. The magnetic elements follow the differential rotation and meridional flow associated with the convection cells themselves -- supergranules rule!

  10. EXTERNAL MAGNETIC PULSE STRAIGHTENING – NEW TECHNOLOGY CAR BODY REPAIR

    Directory of Open Access Journals (Sweden)

    А. Gnatov

    2015-07-01

    Full Text Available Innovative equipment of external contactless magnetic impulse straightening developed by the laboratory of Electromagnetic Technology of Kharkiv National Automobile and Highway University is presented in this paper. The effect of metal hyper-plasticity at magnetic impulse acting is described. Suggestions concerning practical testing of advanced technology of damaged car body panels by external contactless magnetic impulse straightening are presented. The processing route of external contactless magnetic impulse straightening process is specified.

  11. Helioseismic Detection of Emerging Magnetic Flux

    CERN Document Server

    Ilonidis, Stathis; Kosovichev, Alexander G

    2012-01-01

    Investigating the properties of magnetic flux emergence is one of the most important problems of solar physics. In this study we present a newly developed deep-focus time-distance measurement scheme which is able to detect strong emerging flux events in the deep solar interior, before the flux becomes visible on the surface. We discuss in detail the differences between our method and previous methods, and demonstrate step-by-step how the signal-to-noise (S/N) ratio is increased. The method is based on detection of perturbations in acoustic phase travel times determined from cross-covariances of solar oscillations observed on the surface. We detect strong acoustic travel-time reductions of an order of 12 - 16 seconds at a depth of 42 - 75 Mm. These acoustic anomalies are detected 1 - 2 days before high peaks in the photospheric magnetic flux rate implying that the average emerging speed is 0.3 - 0.6 km/s. The results of this work contribute to our understanding of solar magnetism and benefit space weather fore...

  12. Relativistic Two-Dimensional Harmonic Oscillator Plus Cornell Potentials in External Magnetic and AB Fields

    Directory of Open Access Journals (Sweden)

    Sameer M. Ikhdair

    2013-01-01

    Full Text Available The Klein-Gordon (KG equation for the two-dimensional scalar-vector harmonic oscillator plus Cornell potentials in the presence of external magnetic and Aharonov-Bohm (AB flux fields is solved using the wave function ansatz method. The exact energy eigenvalues and the wave functions are obtained in terms of potential parameters, magnetic field strength, AB flux field, and magnetic quantum number. The results obtained by using different Larmor frequencies are compared with the results in the absence of both magnetic field (ωL = 0 and AB flux field (ξ=0 cases. Effect of external fields on the nonrelativistic energy eigenvalues and wave function solutions is also precisely presented. Some special cases like harmonic oscillator and Coulombic fields are also studied.

  13. Coronal Magnetic Flux Ropes in Quadrupolar Magnetic Fields

    Science.gov (United States)

    Zhang, Yingzhi; Hu, Youqiu; Wang, Jingxiu

    Using a 2.5-D, time-dependent ideal MHD model in spherical coordinates, we carry out a numerical study of the equilibrium properties of coronal magnetic flux ropes in a quadrupolar background magnetic field. For such a flux rope system, a catastrophic occurs: the flux rope is detached from the photosphere and jumps to a finite altitude with a vertical current sheet below. There is a transversal current sheet formed above the rope, and the whole system stays in quasi-equilibrium. We argue that the additional Lorentz force provided by the transversal current sheet on the flux rope plays an important role in keeping the system in quasi-equilibrium in the corona.

  14. Magnetic Flux Cancellation in Ellerman Bombs

    CERN Document Server

    Reid, A; Doyle, J G; Scullion, E; Henriques, V; Nelson, C; Ray, T

    2016-01-01

    Ellerman Bombs (EBs) are often found co-spatial with bipolar photospheric magnetic fields. We use H$\\alpha$ imaging spectroscopy along with Fe I 6302.5 \\AA\\ spectro-polarimetry from the Swedish 1-m Solar Telescope (SST), combined with data from the Solar Dynamic Observatory (SDO) to study EBs and the evolution of the local magnetic fields at EB locations. The EBs are found via an EB detection and tracking algorithm. We find, using NICOLE inversions of the spectro-polarimetric data, that on average (3.43 $\\pm$ 0.49) x 10$^{24}$ ergs of stored magnetic energy disappears from the bipolar region during the EBs burning. The inversions also show flux cancellation rates of 10$^{14}$ - 10$^{15}$ Mx s$^{-1}$, and temperature enhancements of 200 K at the detection footpoints. We investigate near-simultaneous flaring of EBs due to co-temporal flux emergence from a sunspot, which shows a decrease in transverse velocity when interacting with an existing, stationary area of opposite polarity magnetic flux and the EBs are f...

  15. Galactic dynamos supported by magnetic helicity fluxes

    CERN Document Server

    Sur, S; Subramanian, K; Sur, Sharanya; Shukurov, Anvar; Subramanian, Kandaswamy

    2006-01-01

    We present a simple semi-analytical model of nonlinear, mean-field galactic dynamos and use it to study the effects of various magnetic helicity fluxes. The dynamo equations are reduced using the `no-$z$' approximation to a nonlinear system of ordinary differential equations in time; we demonstrate that the model reproduces accurately earlier results, including those where nonlinear behaviour is driven by a magnetic helicity flux. We discuss the implications and interplay of two types of magnetic helicity flux, one produced by advection (e.g., due to the galactic fountain or wind) and the other, arising from anisotropy of turbulence as suggested by Vishniac & Cho(2001). We argue that the latter is significant if the galactic differential rotation is strong enough: in our model, for $\\Rw\\la-10$ in terms of the corresponding turbulent magnetic Reynolds number. We confirm that the intensity of gas outflow from the galactic disc optimal for the dynamo action is close to that expected for normal spiral galaxie...

  16. Stochastic flux freezing and magnetic dynamo.

    Science.gov (United States)

    Eyink, Gregory L

    2011-05-01

    Magnetic flux conservation in turbulent plasmas at high magnetic Reynolds numbers is argued neither to hold in the conventional sense nor to be entirely broken, but instead to be valid in a statistical sense associated to the "spontaneous stochasticity" of Lagrangian particle trajectories. The latter phenomenon is due to the explosive separation of particles undergoing turbulent Richardson diffusion, which leads to a breakdown of Laplacian determinism for classical dynamics. Empirical evidence is presented for spontaneous stochasticity, including numerical results. A Lagrangian path-integral approach is then exploited to establish stochastic flux freezing for resistive hydromagnetic equations and to argue, based on the properties of Richardson diffusion, that flux conservation must remain stochastic at infinite magnetic Reynolds number. An important application of these results is the kinematic, fluctuation dynamo in nonhelical, incompressible turbulence at magnetic Prandtl number (Pr(m)) equal to unity. Numerical results on the Lagrangian dynamo mechanisms by a stochastic particle method demonstrate a strong similarity between the Pr(m)=1 and 0 dynamos. Stochasticity of field-line motion is an essential ingredient of both. Finally, some consequences for nonlinear magnetohydrodynamic turbulence, dynamo, and reconnection are briefly considered.

  17. Magnetic Flux Transport at the Solar Surface

    CERN Document Server

    Jiang, J; Cameron, R H; Solanki, S K; Gizon, L; Upton, L

    2014-01-01

    After emerging to the solar surface, the Sun's magnetic field displays a complex and intricate evolution. The evolution of the surface field is important for several reasons. One is that the surface field, and its dynamics, sets the boundary condition for the coronal and heliospheric magnetic fields. Another is that the surface evolution gives us insight into the dynamo process. In particular, it plays an essential role in the Babcock-Leighton model of the solar dynamo. Describing this evolution is the aim of the surface flux transport model. The model starts from the emergence of magnetic bipoles. Thereafter, the model is based on the induction equation and the fact that after emergence the magnetic field is observed to evolve as if it were purely radial. The induction equation then describes how the surface flows -- differential rotation, meridional circulation, granular, supergranular flows, and active region inflows -- determine the evolution of the field (now taken to be purely radial). In this paper, we...

  18. Magnetic Flux Compression Experiments Using Plasma Armatures

    Science.gov (United States)

    Turner, M. W.; Hawk, C. W.; Litchford, R. J.

    2003-01-01

    Magnetic flux compression reaction chambers offer considerable promise for controlling the plasma flow associated with various micronuclear/chemical pulse propulsion and power schemes, primarily because they avoid thermalization with wall structures and permit multicycle operation modes. The major physical effects of concern are the diffusion of magnetic flux into the rapidly expanding plasma cloud and the development of Rayleigh-Taylor instabilities at the plasma surface, both of which can severely degrade reactor efficiency and lead to plasma-wall impact. A physical parameter of critical importance to these underlying magnetohydrodynamic (MHD) processes is the magnetic Reynolds number (R(sub m), the value of which depends upon the product of plasma electrical conductivity and velocity. Efficient flux compression requires R(sub m) less than 1, and a thorough understanding of MHD phenomena at high magnetic Reynolds numbers is essential to the reliable design and operation of practical reactors. As a means of improving this understanding, a simplified laboratory experiment has been constructed in which the plasma jet ejected from an ablative pulse plasma gun is used to investigate plasma armature interaction with magnetic fields. As a prelude to intensive study, exploratory experiments were carried out to quantify the magnetic Reynolds number characteristics of the plasma jet source. Jet velocity was deduced from time-of-flight measurements using optical probes, and electrical conductivity was measured using an inductive probing technique. Using air at 27-inHg vacuum, measured velocities approached 4.5 km/s and measured conductivities were in the range of 30 to 40 kS/m.

  19. Axial flux permanent magnet brushless machines

    CERN Document Server

    Gieras, Jacek F; Kamper, Maarten J

    2008-01-01

    Axial Flux Permanent Magnet (AFPM) brushless machines are modern electrical machines with a lot of advantages over their conventional counterparts. They are being increasingly used in consumer electronics, public life, instrumentation and automation system, clinical engineering, industrial electromechanical drives, automobile manufacturing industry, electric and hybrid electric vehicles, marine vessels and toys. They are also used in more electric aircrafts and many other applications on larger scale. New applications have also emerged in distributed generation systems (wind turbine generators

  20. Negativity in the Extended Hubbard Model under External Magnetic Field

    Institute of Scientific and Technical Information of China (English)

    YANG Zhen; NING Wen-Qiang

    2008-01-01

    We exactly calculate the negativity,a measurement of entanglement,in the two-site extended Hubbard model with external magnetic field.Its behaviour at different temperatures is presented.The negativity reduces with the increasing temperature or with the increasing uniform external magnetic field.It is also found that a non-uniform external magnetic field can be used to modulate or to increase the negativity.

  1. Magnetic flux stabilizing thin accretion disks

    CERN Document Server

    Sadowski, Aleksander

    2016-01-01

    We calculate the minimal amount of large-scale poloidal magnetic field that has to thread the inner, radiation-over-gas pressure dominated region of a thin disk for its thermal stability. Such a net field amplifies the magnetization of the saturated turbulent state and makes it locally stable. For a $10 M_\\odot$ black hole the minimal magnetic flux is $10^{24}(\\dot M/\\dot M_{\\rm Edd})^{20/21}\\,\\rm G\\cdot cm^{2}$. This amount is compared with the amount of uniform magnetic flux that can be provided by the companion star -- estimated to be in the range $10^{22}-10^{24}\\,\\rm G\\cdot cm^2$. If accretion rate is large enough, the companion is not able to provide the required amount and such a system, if still sub-Eddington, must be thermally unstable. The peculiar variability of GRS 1915+105, an X-ray binary with the exceptionally high BH mass and near-Eddington luminosity, may result from the shortage of large scale poloidal field of uniform polarity.

  2. Magnetic flux stabilizing thin accretion discs

    Science.gov (United States)

    Sądowski, Aleksander

    2016-10-01

    We calculate the minimal amount of large-scale poloidal magnetic field that has to thread the inner, radiation-over-gas pressure dominated region of a thin disc for its thermal stability. Such a net field amplifies the magnetization of the saturated turbulent state and makes it locally stable. For a 10 M⊙ black hole the minimal magnetic flux is 10^{24}(dot{M}/dot{M}_Edd)^{20/21} G cm2. This amount is compared with the amount of uniform magnetic flux that can be provided by the companion star - estimated to be in the range 1022-1024 G cm2. If accretion rate is large enough, the companion is not able to provide the required amount and such a system, if still sub-Eddington, must be thermally unstable. The peculiar variability of GRS 1915+105, an X-ray binary with the exceptionally high BH mass and near-Eddington luminosity, may result from the shortage of large-scale poloidal field of uniform polarity.

  3. Relativistic Killingbeck energy states under external magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Eshghi, M. [Islamic Azad University, Researchers and Elite Club, Central Tehran Branch, Tehran (Iran, Islamic Republic of); Mehraban, H. [Semnan University, Faculty of Physics, Semnan (Iran, Islamic Republic of); Ikhdair, S.M. [An-Najah National University, Department of Physics, Faculty of Science, Nablus, West Bank, Palestine (Country Unknown); Near East University, Department of Electrical Engineering, Nicosia, Northern Cyprus (Turkey)

    2016-07-15

    We address the behavior of the Dirac equation with the Killingbeck radial potential including the external magnetic and Aharonov-Bohm (AB) flux fields. The spin and pseudo-spin symmetries are considered. The correct bound state spectra and their corresponding wave functions are obtained. We seek such a solution using the biconfluent Heun's differential equation method. Further, we give some of our results at the end of this study. Our final results can be reduced to their non-relativistic forms by simply using some appropriate transformations. The spectra, in the spin and pseudo-spin symmetries, are very similar with a slight difference in energy spacing between different states. (orig.)

  4. Divertor heat load in ASDEX Upgrade L-mode in presence of external magnetic perturbation

    Science.gov (United States)

    Faitsch, M.; Sieglin, B.; Eich, T.; Herrmann, A.; Suttrop, W.; the ASDEX Upgrade Team

    2017-09-01

    Power exhaust is one of the major challenges for a future fusion device. Applying a non-axisymmetric external magnetic perturbation is one technique that is studied in order to mitigate or suppress large edge localized modes which accompany the high confinement regime in tokamaks. The external magnetic perturbation induces breaking in the axisymmetry of a tokamak and leads to a 2D heat flux pattern on the divertor target. The 2D heat flux pattern at the outer divertor target is studied on ASDEX Upgrade in stationary L-mode discharges. The amplitude of the 2D characteristic of the heat flux depends on the alignment between the field lines at the edge and the vacuum response of the applied magnetic perturbation spectrum. The 2D characteristic reduces with increasing density. The increasing divertor broadening, S, with increasing density is proposed as the main actuator. This is supported by a generic model using field line tracing and the vacuum field approach that is in quantitative agreement with the measured heat flux. The perturbed heat flux, averaged over a full toroidal rotation of the magnetic perturbation, is identical to the non-perturbed heat flux without magnetic perturbation. The transport qualifiers, power fall-off length {λ }q and divertor broadening, S, are the same within the uncertainty compared to the unperturbed reference. No additional cross field transport is observed.

  5. SEED BANKS FOR MAGNETIC FLUX COMPRESSION GENERATORS

    Energy Technology Data Exchange (ETDEWEB)

    Fulkerson, E S

    2008-05-14

    In recent years the Lawrence Livermore National Laboratory (LLNL) has been conducting experiments that require pulsed high currents to be delivered into inductive loads. The loads fall into two categories (1) pulsed high field magnets and (2) the input stage of Magnetic Flux Compression Generators (MFCG). Three capacitor banks of increasing energy storage and controls sophistication have been designed and constructed to drive these loads. One bank was developed for the magnet driving application (20kV {approx} 30kJ maximum stored energy.) Two banks where constructed as MFCG seed banks (12kV {approx} 43kJ and 26kV {approx} 450kJ). This paper will describe the design of each bank including switching, controls, circuit protection and safety.

  6. Exploring ISEE-3 magnetic cloud polarities with electron heat fluxes

    Energy Technology Data Exchange (ETDEWEB)

    Kahler, S.W. [Air Force Research Laboratory, 29 Randolph Rd, Hanscom AFB, Massachusetts 01731 (United States); Crooker, N.U. [Center for Space Physics, Boston University, 725 Commonwealth Ave., Boston, Massachusetts 02215 (United States); Gosling, J.T. [Los Alamos National Laboratory, MS D 466, Los Alamos, New Mexico 87545 (United States)

    1999-06-01

    We have used solar wind electron heat fluxes to determine the magnetic polarities of the interplanetary magnetic fields (IMF) during the ISEE-3 observations in 1978{endash}1982. That period included 14 magnetic clouds (MCs) identified by Zhang and Burlaga. The MCs have been modeled as single magnetic flux ropes, and it is generally assumed that they are magnetically closed structures with each end of the flux rope connected to the Sun. The flux rope model is valid only if the magnetic polarity of each MC does not change during the passage of ISEE-3 through the MC. We test this model with the heat flux data, using the dominant heat flux in bidirectional electron heat fluxes to determine the MC polarities. The polarity changes within at least 2, and possibly 6, of the 14 MCs, meaning that those MCs can not fit the model of a single flux rope. {copyright} {ital 1999 American Institute of Physics.}

  7. Exploring ISEE-3 magnetic cloud polarities with electron heat fluxes

    Science.gov (United States)

    Kahler, S. W.; Crooker, N. U.; Gosling, J. T.

    1999-06-01

    We have used solar wind electron heat fluxes to determine the magnetic polarities of the interplanetary magnetic fields (IMF) during the ISEE-3 observations in 1978-1982. That period included 14 magnetic clouds (MCs) identified by Zhang and Burlaga. The MCs have been modeled as single magnetic flux ropes, and it is generally assumed that they are magnetically closed structures with each end of the flux rope connected to the Sun. The flux rope model is valid only if the magnetic polarity of each MC does not change during the passage of ISEE-3 through the MC. We test this model with the heat flux data, using the dominant heat flux in bidirectional electron heat fluxes to determine the MC polarities. The polarity changes within at least 2, and possibly 6, of the 14 MCs, meaning that those MCs can not fit the model of a single flux rope.

  8. Design of a Linear Variable Differential Transformer With High Rejection to External Interfering Magnetic Field

    CERN Document Server

    Martino, M; Losito, R; Masi, A; Danisi, A

    2010-01-01

    The sensitivity of linear variable differential transformer (LVDT) position sensors to external slowly varying magnetic fields represents a critical issue when these sensors are installed close to high-current cables or electrical motors with significant fringe fields. The resulting position error can reach several hundreds of micrometers against a specified uncertainty normally below a few micrometers. In this paper, the design of a LVDT position sensor with high rejection to external constant or slowly varying magnetic fields is addressed by exploiting the finite element method (FEM) simulator FLUX. A shield, isolated from the sensor's magnetic circuit, has been considered to reduce the effect of magnetic fields on the secondary voltages of the LVDT. In addition, a dc current is used in order to polarize the magnetic circuit to reduce the sensitivity of the sensor to external interferences.

  9. Linear magnetic motor/generator. [to generate electric energy using magnetic flux for spacecraft power supply

    Science.gov (United States)

    Studer, P. A. (Inventor)

    1982-01-01

    A linear magnetic motor/generator is disclosed which uses magnetic flux to provide mechanical motion or electrical energy. The linear magnetic motor/generator includes an axially movable actuator mechanism. A permament magnet mechanism defines a first magnetic flux path which passes through a first end portion of the actuator mechanism. Another permament magnet mechanism defines a second magnetic flux path which passes through a second end portion of the actuator mechanism. A drive coil defines a third magnetic flux path passing through a third central portion of the actuator mechanism. A drive coil selectively adds magnetic flux to and subtracts magnetic flux from magnetic flux flowing in the first and second magnetic flux path.

  10. Chiral Symmetry Breaking in Planar QED in External Magnetic Fields

    CERN Document Server

    Cea, Paolo; Giudice, Pietro; Papa, Alessandro

    2012-01-01

    We investigate planar quantum electrodynamics (QED) with two degenerate staggered fermions in an external magnetic field on the lattice. We argue that in external magnetic fields there is dynamical generation of mass for two-dimensional massless Dirac fermions in the weak-coupling region. We extrapolate our lattice results to the quantum Hall effect in graphene.

  11. Decoupling Suspension Controller Based on Magnetic Flux Feedback

    Directory of Open Access Journals (Sweden)

    Wenqing Zhang

    2013-01-01

    Full Text Available The suspension module control system model has been established based on MIMO (multiple input and multiple output state feedback linearization. We have completed decoupling between double suspension points, and the new decoupling method has been applied to CMS04 magnetic suspension vehicle in national mid-low-speed maglev experiment field of Tangshan city in China. Double suspension system model is very accurate for investigating stability property of maglev control system. When magnetic flux signal is taken back to the suspension control system, the suspension module’s antijamming capacity for resisting suspension load variety has been proved. Also, the external force interference has been enhanced. As a result, the robustness and stability properties of double-electromagnet suspension control system have been enhanced.

  12. Stop of magnetic flux movement in levitating superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Smolyak, B.M., E-mail: b-smolyak@yandex.ru; Zakharov, M.S., E-mail: maksim.s.zakharov@gmail.com

    2017-01-15

    Highlights: • A direct experimental study of magnetic flux creep in the levitating superconductor. • When a levitating object is in a fixed position, magnetic flux movement is observed. • Levitation stops flux creep process. - Abstract: A phenomenon of magnetic relaxation stopping in a levitating superconductor was studied. It was experimentally shown that magnetic flux creep (diffusion of flux lines to regions with lower vortex density) is absent in magnetic suspension of the superconductor. Magnetic relaxation arises, when a rigid constraint that fixes a position of the superconductor relative to a magnet is imposed on a levitating object. It is assumed that oscillations of magnetic structure, which is due to free oscillations of the levitating superconductor, stop magnetic relaxation.

  13. Magnetic flux array for spontaneous magnetic reconnection experiments.

    Science.gov (United States)

    Kesich, A; Bonde, J; Egedal, J; Fox, W; Goodwin, R; Katz, N; Le, A

    2008-06-01

    Experimental investigation of reconnection in magnetized plasmas relies on accurate characterization of the evolving magnetic fields. In experimental configurations where the plasma dynamics are reproducible, magnetic data can be collected in multiple discharges and combined to provide spatially resolved profiles of the plasma dynamics. However, in experiments on spontaneous magnetic reconnection recently undertaken at the Versatile Toroidal Facility at MIT, the reconnection process is not reproducible and all information on the plasma must be collected in a single discharge. This paper describes a newly developed magnetic flux array which directly measures the toroidal component of the magnetic vector potential, A(phi). From the measured A(phi), the magnetic field geometry, current density, and reconnection rate are readily obtained, facilitating studies of the three-dimensional dynamics of spontaneous magnetic reconnection. The novel design of the probe array allows for accurate characterization of profiles of A(phi) at multiple toroidal angles using a relatively small number of signal channels and with minimal disturbance of the plasma.

  14. N{sub f}=1 QCD in external magnetic fields: staggered fermions

    Energy Technology Data Exchange (ETDEWEB)

    Cea, Paolo [INFN, Sezione di Bari, Via Amendola 173, I-70126 Bari (Italy); Dipartimento di Fisica dell’Università di Bari, Via Amendola 173, I-70126 Bari (Italy); Cosmai, Leonardo [INFN, Sezione di Bari, Via Amendola 173, I-70126 Bari (Italy)

    2015-12-10

    We investigate N{sub f}=1 QCD in external magnetic fields on the lattice. The background field is introduced by means of the so-called Schrödinger functional. We adopt standard staggered fermions with constant bare mass am=0.025 and magnetic fields with constant magnetic flux up to a{sup 2}eH≃2.3562. We find that the the deconfinement and chiral symmetry restoration temperatures do not depend on the strength of the applied magnetic field. Our method allow us to easily study the effects of the external magnetic fields on the QCD thermodynamics. We determine the influences of applied magnetic fields to the free energy, pressure, and equation of state of strongly interacting matter.

  15. Magnetic flux noise in copper oxide superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Ferrari, M.J.

    1991-11-01

    Magnetic flux noise and flux creep in thin films and single crystals of YBa{sub 2}Cu{sub 3}O{sub 7-x}, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x}, Tl{sub 2}Ca{sub 2}Ba{sub 2}Cu{sub 3}O{sub x}, and TlCa{sub 2}Ba{sub 2}Cu{sub 3}O{sub x} are measured with a superconducting quantum interference device (SQUID). The noise power spectrum generally scales as 1/f (f is frequency) from 1 Hz to 1 kHz, increases with temperature, and decreases in higher-quality films. It is proportional to the magnetic field B in which the sample is cooled, at least in the range 0.1 mT < B < 3 mT. A model of thermally activated vortex motion is developed which explains the dependence of the noise on frequency, temperature, current, and applied magnetic field. The pinning potential is idealized as an ensemble of double wells, each with a different activation energy separating the two states. From the noise measurements, this model yields the distribution of pinning energies in the samples, the vortex hopping distance, the number density of mobile vortices, and the restoring force on a vortex at a typical pinning site. The distribution of pinning energies in YBa{sub 2}Cu{sub 3}O{sub 7-x} shows a broad peak below 0.1 eV. The small ambient magnetic field, and the detection of noise even in the absence of a driving force, insure that the measured pinning energies are characteristic of isolated vortices near thermal equilibrium. The observed vortex density in fields much less than 0.1 mT is too large to be explained by the ambient field, suggesting a mechanism intrinsic to the sample which produces trapped vortices.

  16. Measurements of Magnetic Helicity within Two Interacting Flux Ropes

    Science.gov (United States)

    Dehaas, Timothy; Gekelman, Walter

    2016-10-01

    Magnetic helicity (HM) has become a useful tool in the exploration of astrophysical plasmas. Its conservation in the MHD limit (and even some fluid approaches) constrains the global behavior of large plasma structures. One such astrophysical structure is a magnetic flux rope: a rope-like, current-carrying plasma embedded in an external magnetic field. Bundles of these ropes are commonly observed extending from the solar surface and can be found in the near-earth environment. In this well-diagnosed experiment (3D measurements of ne, Te, Vp, B, J, E, uflow) , two magnetic flux ropes were generated in the Large Plasma Device at UCLA. These ropes were driven kink-unstable, commencing complex motion. As they interact, helicity conservation is broken in regions of reconnection, turbulence, and instabilities. The changes in helicity can be visualized as 1) the transport of helicity (ϕB +E × A) and 2) the dissipation of the helicity (-2EB). Magnetic helicity is observed to have a negative sign and its counterpart, cross helicity, a positive one. These qualities oscillate 8% peak-to-peak. As the ropes move and the topology of the field lines change, a quasi-separatrix layer (QSL) is formed. The volume averaged HM and the largest value of Q both oscillate but not in phase. In addition to magnetic helicity, similar quantities such as self-helicity, mutual-helicity, vorticity, and canonical helicity are derived and will be presented. This work is supported by LANL-UC research Grant and done at the Basic Plasma Science Facility, which is funded by DOE and NSF.

  17. Automatic magnetic flux measurement of micro plastic-magnetic rotors

    Science.gov (United States)

    Wang, Qingdong; Lin, Mingxing; Song, Aiwei

    2015-07-01

    Micro plastic-magnetic rotors of various sizes and shapes are widely used in industry, their magnetic flux measurement is one of the most important links in the production process, and therefore some technologies should be adopted to improve the measurement precision and efficiency. In this paper, the automatic measurement principle of micro plastic-magnetic rotors is proposed and the integration time constant and the integrator drift’s suppression and compensation in the measurement circuit are analyzed. Two other factors influencing the measurement precision are also analyzed, including the relative angles between the rotor magnetic poles and the measurement coil, and the starting point of the rotors in the coil where the measurement begins. An instrument is designed to measure the magnetic flux of the rotors. Measurement results show that the measurement error is within  ±1%, which meets the basic requirements in industry application, and the measurement efficiency is increased by 10 times, which can cut down labor cost and management cost when compared with manual measurement.

  18. Flux ropes in the magnetic solar convection zone

    DEFF Research Database (Denmark)

    Dorch, S. B. F.

    2006-01-01

    In this contribution results are presented on how twisted magnetic flux ropes interact with a magnetized model envelope similar to the solar convection zone. Both the flux ropes and the atmosphere are modelled as idealized 2.5-dimensional concepts using high resolution numerical MHD simulations (on...... of the magnetic flux ropes interact with the magnetic field in the atmosphere in a manner that depends, among other things, on the polarity and strength of the atmospheric field. The results include limits on the necessary and possible twist and polarity of solar magnetic flux ropes....

  19. Magnetic flux concentrations from turbulent stratified convection

    CERN Document Server

    Käpylä, P J; Kleeorin, N; Käpylä, M J; Rogachevskii, I

    2015-01-01

    (abridged) Context: The mechanisms that cause the formation of sunspots are still unclear. Aims: We study the self-organisation of initially uniform sub-equipartition magnetic fields by highly stratified turbulent convection. Methods: We perform simulations of magnetoconvection in Cartesian domains that are $8.5$-$24$ Mm deep and $34$-$96$ Mm wide. We impose either a vertical or a horizontal uniform magnetic field in a convection-driven turbulent flow. Results: We find that super-equipartition magnetic flux concentrations are formed near the surface with domain depths of $12.5$ and $24$ Mm. The size of the concentrations increases as the box size increases and the largest structures ($20$ Mm horizontally) are obtained in the 24 Mm deep models. The field strength in the concentrations is in the range of $3$-$5$ kG. The concentrations grow approximately linearly in time. The effective magnetic pressure measured in the simulations is positive near the surface and negative in the bulk of the convection zone. Its ...

  20. Downward catastrophe of solar magnetic flux ropes

    CERN Document Server

    Zhang, Quanhao; Hu, Youqiu; Liu, Rui

    2016-01-01

    2.5D time-dependent ideal magnetohydrodynamic (MHD) models in Cartesian coordinates were used in previous studies to seek MHD equilibria involving a magnetic flux rope embedded in a bipolar, partially open background field. As demonstrated by these studies, the equilibrium solutions of the system are separated into two branches: the flux rope sticks to the photosphere for solutions at the lower branch but is suspended in the corona for those at the upper branch. Moreover, a solution originally at the lower branch jumps to the upper, as the related control parameter increases and reaches a critical value, and the associated jump is here referred to as upward catastrophe. The present paper advances these studies in three aspects. First, the magnetic field is changed to be force-free. The system still experiences an upward catastrophe with an increase in each control parameter. Secondly, under the force-free approximation, there also exists a downward catastrophe, characterized by a jump of a solution from the u...

  1. Surface Magnetic Flux Maintenance In Quiet Sun

    CERN Document Server

    Iida, Y

    2013-01-01

    We investigate surface processes of magnetic patches, namely merging, splitting, emergence, and cancellation, by using an auto-detection technique. We find that merging and splitting are locally predominant in the surface level, while the frequencies of the other two are less by one or two orders of magnitude. The frequency dependences on flux con- tent of surface processes are further investigated. Based on these observations, we discuss a possible whole picture of the maintenance. Our conclusion is that the photospheric magnetic field structure, especially its power-law nature, is maintained by the processes locally in the surface not by the interactions between different altitudes. We suggest a scenario of the flux maintenance as follows: The splitting and merging play a crucial role for the generation of the power-law distribution, not the emergence nor cancellation do. This power-law distribution results in another power-law one of the cancellation with an idea of the random convective transport. The can...

  2. Relationships of a growing magnetic flux region to flares

    NARCIS (Netherlands)

    Schadee, A.; Martin, S.F.; Bentley, R.D.; Antalova, A.; Kucera, A.; Dezs, L.; Gesztelyi, L.; Harvey, K.L.; Jones, H.; Livi, S.H.B.; Wang, J.

    1984-01-01

    Some sites for solar flares are known to develop where new magnetic flux emerges and becomes abutted against opposite polarity pre-existing magnetic flux (review by Galzauskas/1/). We have identified and analyzed the evolution of such flare sites at the boundaries of a major new and growing magnetic

  3. Magnetic flux emergence in granular convection: radiative MHD simulations and observational signatures

    Science.gov (United States)

    Cheung, M. C. M.; Schüssler, M.; Moreno-Insertis, F.

    2007-05-01

    Aims:We study the emergence of magnetic flux from the near-surface layers of the solar convection zone into the photosphere. Methods: To model magnetic flux emergence, we carried out a set of numerical radiative magnetohydrodynamics simulations. Our simulations take into account the effects of compressibility, energy exchange via radiative transfer, and partial ionization in the equation of state. All these physical ingredients are essential for a proper treatment of the problem. Furthermore, the inclusion of radiative transfer allows us to directly compare the simulation results with actual observations of emerging flux. Results: We find that the interaction between the magnetic flux tube and the external flow field has an important influence on the emergent morphology of the magnetic field. Depending on the initial properties of the flux tube (e.g. field strength, twist, entropy etc.), the emergence process can also modify the local granulation pattern. The emergence of magnetic flux tubes with a flux of 1019 Mx disturbs the granulation and leads to the transient appearance of a dark lane, which is coincident with upflowing material. These results are consistent with observed properties of emerging magnetic flux. Movies are only available in electronic form at http://www.aanda.org

  4. Topology of magnetic flux ropes and formation of fossil flux transfer events and boundary layer plasmas

    Science.gov (United States)

    Lee, L. C.; Ma, Z. W.; Fu, Z. F.; Otto, A.

    1993-01-01

    A mechanism for the formation of fossil flux transfer events and the low-level boundary layer within the framework of multiple X-line reconnection is proposed. Attention is given to conditions for which the bulk of magnetic flux in a flux rope of finite extent has a simple magnetic topology, where the four possible connections of magnetic field lines are: IMF to MSP, MSP to IMF, IMF to IMF, and MSP to MSP. For a sufficient relative shift of the X lines, magnetic flux may enter a flux rope from the magnetosphere and exit into the magnetosphere. This process leads to the formation of magnetic flux ropes which contain a considerable amount of magnetosheath plasma on closed magnetospheric field lines. This process is discussed as a possible explanation for the formation of fossil flux transfer events in the magnetosphere and the formation of the low-latitude boundary layer.

  5. Simulations of Emerging Magnetic Flux. II. The Formation of Unstable Coronal Flux Ropes and the Initiation of Coronal Mass Ejections

    Science.gov (United States)

    Leake, James E.; Linton, Mark G.; Antiochos, Spiro K.

    2014-01-01

    We present results from three-dimensional magnetohydrodynamic simulations of the emergence of a twisted convection zone flux tube into a pre-existing coronal dipole field. As in previous simulations, following the partial emergence of the sub-surface flux into the corona, a combination of vortical motions and internal magnetic reconnection forms a coronal flux rope. Then, in the simulations presented here, external reconnection between the emerging field and the pre-existing dipole coronal field allows further expansion of the coronal flux rope into the corona. After sufficient expansion, internal reconnection occurs beneath the coronal flux rope axis, and the flux rope erupts up to the top boundary of the simulation domain (approximately 36 Mm above the surface).We find that the presence of a pre-existing field, orientated in a direction to facilitate reconnection with the emerging field, is vital to the fast rise of the coronal flux rope. The simulations shown in this paper are able to self-consistently create many of the surface and coronal signatures used by coronal mass ejection (CME) models. These signatures include surface shearing and rotational motions, quadrupolar geometry above the surface, central sheared arcades reconnecting with oppositely orientated overlying dipole fields, the formation of coronal flux ropes underlying potential coronal field, and internal reconnection which resembles the classical flare reconnection scenario. This suggests that proposed mechanisms for the initiation of a CME, such as "magnetic breakout," are operating during the emergence of new active regions.

  6. Superconducting Sphere in an External Magnetic Field Revisited

    Science.gov (United States)

    Sazonov, Sergey N.

    2013-01-01

    The purpose of this article is to give the intelligible procedure for undergraduate students to grasp proof of the fact that the magnetic field outside the hollow superconducting sphere (superconducting shell) coincides with the field of a point magnetic dipole both when an uniform external magnetic field is applied as when a ferromagnetic sphere…

  7. Measuring the Magnetic Flux Density with Flux Loops and Hall Probes in the CMS Magnet Flux Return Yoke

    CERN Document Server

    Curé, B; Ball, A; Gaddi, A; Gerwig, H; Hervé, A; Klyukhin, V I; Loveless, R; Mulders, M

    2016-01-01

    The Compact Muon Solenoid (CMS) is a general purpose detector, designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting solenoid with 6-m-diameter by 12.5-m-length free bore, enclosed inside a 10,000-ton return yoke made of construction steel. The flux return yoke consists of five dodecagonal three-layered barrel wheels and four end-cap disks at each end comprised of steel blocks up to 620 mm thick, which serve as the absorber plates of the muon detection system. To measure the field in and around the steel, a system of 22 flux loops and 82 3-D Hall sensors is installed on the return yoke blocks. A TOSCA 3-D model of the CMS magnet is developed to describe the magnetic field everywhere outside the tracking volume that was measured with the field-mapping machine. The voltages induced in the flux loops by the magnetic flux changing during the CMS magnet standard ramps down are measured with six 16-bit DAQ modules. The off-line inte...

  8. Magnetic flux noise in copper oxide superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Ferrari, Mark Joseph [Univ. of California, Berkeley, CA (United States)

    1991-11-01

    Magnetic flux noise and flux creep in thin films and single crystals of YBa2Cu3O7-x, Bi2Sr2CaCu2O8+x, Tl2Ca2Ba2Cu3Ox, and TlCa2Ba2Cu3Ox are measured with a superconducting quantum interference device (SQUID). The noise power spectrum generally scales as 1/f (f is frequency) from 1 Hz to 1 kHz, increases with temperature, and decreases in higher-quality films. It is proportional to the magnetic field B in which the sample is cooled, at least in the range 0.1 mT < B < 3 mT. A model of thermally activated vortex motion is developed which explains the dependence of the noise on frequency, temperature, current, and applied magnetic field. The pinning potential is idealized as an ensemble of double wells, each with a different activation energy separating the two states. From the noise measurements, this model yields the distribution of pinning energies in the samples, the vortex hopping distance, the number density of mobile vortices, and the restoring force on a vortex at a typical pinning site. The distribution of pinning energies in YBa2Cu3O7-x shows a broad peak below 0.1 eV. The small ambient magnetic field, and the detection of noise even in the absence of a driving force, insure that the measured pinning energies are characteristic of isolated vortices near thermal equilibrium. The observed vortex density in fields much less than 0.1 mT is too large to be explained by the ambient field, suggesting a mechanism intrinsic to the sample which produces trapped vortices.

  9. Magnetic Properties of Heisenberg Thin Films in an External Field

    Institute of Scientific and Technical Information of China (English)

    CHEN Hong; ZHANG Jing

    2004-01-01

    The magnetic properties of Heisenberg ferromagnetic films in an external magnetic field are investigated by means of the variational cumulant expansion (VCE). The magnetization can be in principle calculated analytically as the function of the temperature and the number of atomic layers in the film to an arbitrary order of accuracy in the VCE. We calculate the spontaneous magnetization and coercivity to the third order for spin-1/2 Heisenberg films with simple cubic lattices by using a graphic technique.

  10. Flux Loop Measurements of the Magnetic Flux Density in the CMS Magnet Yoke

    CERN Document Server

    Klyukhin, V I; Ball, A.; Curé, B.; Gaddi, A.; Gerwig, H.; Mulders, M.; Hervé, A.; Loveless, R.

    2016-01-01

    The Compact Muon Solenoid (CMS) is a general purpose detector, designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting solenoid with 6-m-diameter by 12.5-m-length free bore, enclosed inside a 10,000-ton return yoke made of construction steel. The return yoke consists of five dodecagonal three-layered barrel wheels and four end-cap disks at each end comprised of steel blocks up to 620 mm thick, which serve as the absorber plates of the muon detection system. To measure the field in and around the steel, a system of 22 flux loops and 82 3-D Hall sensors is installed on the return yoke blocks. A TOSCA 3-D model of the CMS magnet is developed to describe the magnetic field everywhere outside the tracking volume measured with the field-mapping machine. The first attempt is made to measure the magnetic flux density in the steel blocks of the CMS magnet yoke using the standard magnet discharge with the current ramp down speed of 1.5 A/...

  11. Separation of the Magnetic Field into External and Internal Parts

    DEFF Research Database (Denmark)

    Olsen, Nils; Glassmeier, K.-H.; Jia, X.

    2010-01-01

    The magnetic field of a planet or a planetary moon contains contributions from a variety of sources in the environment of the body (external sources) and its interior (internal sources). This chapter describes different methods that have been developed for the separation of external and internal...

  12. Magnetized black holes in an external gravitational field

    Science.gov (United States)

    Kunz, Jutta; Nedkova, Petya; Yazadjiev, Stoytcho

    2017-07-01

    We obtain a family of exact solutions describing magnetized black holes in an external gravitational field. Locally the solutions can be interpreted as representing the near-horizon region of a black hole, which interacts with a surrounding matter distribution producing a strong magnetic field. Thus, the solutions reflect the influence of both a gravitational and an electromagnetic external potential in the strong field regime. The static members in the family are generalizations of the Schwarzschild solution in the described environment, while the rotating ones generalize the magnetized Reissner-Nordström solution when the influence of an external gravitational source is also taken into account. Technically, the solutions are obtained by means of a Harrison transformation, applied on the (electro-)vacuum distorted black holes constructed by Bretón et al. We examine the thermodynamical properties of the solutions, and compare them with the corresponding isolated black holes, and with the particular cases when the interaction with only one of the external potentials is taken into account. For the static black holes the influence of the external gravitational and magnetic fields is factorized in a sense, both affecting different properties, and leaving the rest intact. For the rotating solutions the external gravitational and magnetic fields are coupled through the conditions for avoiding conical singularities. The Meissner effect is observed for extremal rotating solutions only in the zero-charge limit, similar to the magnetized Reissner-Nordström black hole.

  13. Hall Effect–Mediated Magnetic Flux Transport in Protoplanetary Disks

    Science.gov (United States)

    Bai, Xue-Ning; Stone, James M.

    2017-02-01

    The global evolution of protoplanetary disks (PPDs) has recently been shown to be largely controlled by the amount of poloidal magnetic flux threading the disk. The amount of magnetic flux must also coevolve with the disk, as a result of magnetic flux transport, a process that is poorly understood. In weakly ionized gas as in PPDs, magnetic flux is largely frozen in the electron fluid, except when resistivity is large. When the disk is largely laminar, we show that the relative drift between the electrons and ions (the Hall drift), and the ions and neutral fluids (ambipolar drift) can play a dominant role on the transport of magnetic flux. Using two-dimensional simulations that incorporate the Hall effect and ambipolar diffusion (AD) with prescribed diffusivities, we show that when large-scale poloidal field is aligned with disk rotation, the Hall effect rapidly drags magnetic flux inward at the midplane region, while it slowly pushes flux outward above/below the midplane. This leads to a highly radially elongated field configuration as a global manifestation of the Hall-shear instability. This field configuration further promotes rapid outward flux transport by AD at the midplane, leading to instability saturation. In quasi-steady state, magnetic flux is transported outward at approximately the same rate at all heights, and the rate is comparable to the Hall-free case. For anti-aligned field polarity, the Hall effect consistently transports magnetic flux outward, leading to a largely vertical field configuration in the midplane region. The field lines in the upper layer first bend radially inward and then outward to launch a disk wind. Overall, the net rate of outward flux transport is about twice as fast as that of the aligned case. In addition, the rate of flux transport increases with increasing disk magnetization. The absolute rate of transport is sensitive to disk microphysics, which remains to be explored in future studies.

  14. Photospheric and Subphotospheric Dynamics of Emerging Magnetic Flux

    CERN Document Server

    Kosovichev, A G

    2009-01-01

    Magnetic fields emerging from the Sun's interior carry information about physical processes of magnetic field generation and transport in the convection zone. Soon after appearance on the solar surface the magnetic flux gets concentrated in sunspot regions and causes numerous active phenomena on the Sun. This paper discusses some properties of the emerging magnetic flux observed on the solar surface and in the interior. A statistical analysis of variations of the tilt angle of bipolar magnetic regions during the emergence shows that the systematic tilt with respect to the equator (the Joy's law) is most likely established below the surface. However, no evidence of the dependence of the tilt angle on the amount of emerging magnetic flux, predicted by the rising magnetic flux rope theories, is found. Analysis of surface plasma flows in a large emerging active region reveals strong localized upflows and downflows at the initial phase of emergence but finds no evidence for large-scale flows indicating future appe...

  15. Magnetic Flux Transport by turbulent reconnection in astrophysical flows

    CERN Document Server

    Pino, Elisabete M de Gouveia Dal; Santos-Lima, Reinaldo; Guerrero, Gustavo; Kowal, Grzegorz; Lazarian, Alex

    2011-01-01

    The role of MHD turbulence in astrophysical environments is still highly debated. An important question that permeates this debate is the transport of magnetic flux. This is particularly important, for instance, in the context of star formation. When clouds collapse gravitationally to form stars, there must be some magnetic flux transport. otherwise the new born stars would have magnetic fields several orders of magnitude larger than the observed ones. Also, the magnetic flux that is dragged in the late stages of the formation of a star can remove all the rotational support from the accretion disk that grows around the protostar. The efficiency of the mechanism which is often invoked to allow the transport of magnetic fields in the different stages of star formation, namely, the ambipolar diffusion, has been lately put in check. We here discuss an alternative mechanism for magnetic flux transport which is based on turbulent fast magnetic reconnection. We review recent results obtained from 3D MHD numerical si...

  16. Flux ropes in the magnetic solar convection zone

    DEFF Research Database (Denmark)

    Dorch, S. B. F.

    2006-01-01

    In this contribution results are presented on how twisted magnetic flux ropes interact with a magnetized model envelope similar to the solar convection zone. Both the flux ropes and the atmosphere are modelled as idealized 2.5-dimensional concepts using high resolution numerical MHD simulations (on...

  17. Magnetic flux distribution in the amorphous modular transformers

    Science.gov (United States)

    Tomczuk, B.; Koteras, D.

    2011-06-01

    3D magnetic fluxes in one-phase and three-phase transformers with amorphous modular cores have been studied. Scalar potentials were implemented for the 3D Finite Element field calculation. Due to the inability to simulate each thin amorphous layer, we introduced supplementary permeabilities along the main directions of magnetization. The calculated fluxes in the cores were tested on the prototypes.

  18. Design Considerations of Permanent Magnet Transverse Flux Machines

    DEFF Research Database (Denmark)

    Lu, Kaiyuan; Rasmussen, Peter Omand; Ritchie, Ewen

    2011-01-01

    Permanent magnet transverse flux machine (PMTFM) is well known for its high torque density and is interested in various direct-drive applications. Due to its complicated 3-D flux components, design and design optimization of a PMTFM is more difficult and time consuming than for radial flux...

  19. More on Electric and Magnetic Fluxes in SU(2)

    CERN Document Server

    Von Smekal, L; Jahn, O; Smekal, Lorenz von; Forcrand, with Philippe de; Jahn, Oliver

    2002-01-01

    The free energies of static charges and center monopoles are given by their fluxes. While electric fluxes show the universal behaviour of the deconfinement transition, the monopole free energies vanish in the thermodynamic limit at all temperatures and are thus irrelevant for the transition. Magnetic fluxes may, however, be used to measure the topological susceptibility without cooling.

  20. Influence of Slot Defect Length on Magnetic Flux Leakage

    Institute of Scientific and Technical Information of China (English)

    Songling HUANG; Luming LI; Haiqing YANG; Keren SHI

    2004-01-01

    A key issue, which influences the applications of magnetic flux leakage testing, is defect quantification. There have been many research on the relationship between width, depth and magnetic flux leakage of slot defect. However, the length factor is often ignored. The relationship between characteristics of defect leakage field and defect length was investigated. The magnetic flux leakages of a series of plate specimens with the same width, same depth and different length slot defects were tested under the same magnetizing conditions. Testing results show that defect length is an important parameter needed to consider in quantifying defects.

  1. Holographic superconductors with Lifshitz scaling in external magnetic field

    CERN Document Server

    Zhao, Zixu; Jing, Jiliang

    2014-01-01

    We analytically study the holographic superconductors with Lifshitz scaling in presence of an external magnetic field. We observe that Lifshitz scaling can hinder the condensation to be formed, which can be used to back up the existing numerical results. Moreover, we find that the dynamical exponent $z$ does have effects on the upper critical magnetic field. However, we note that Lifshitz scaling does not modify the well-known relation obtained from the Ginzburg-Landau theory for the upper critical magnetic field.

  2. Tuning plasmonic cloaks with an external magnetic field

    CERN Document Server

    Kort-Kamp, W J M; Pinheiro, F A; Farina, C

    2013-01-01

    We propose a mechanism to actively tune the operation of plasmonic cloaks with an external magnetic field by investigating electromagnetic scattering by a dielectric cylinder coated with a magneto-optical shell. In the long wavelength limit we show that the presence of an external magnetic field may drastically reduce the scattering cross-section at all observation angles. We demonstrate that the application of external magnetic fields can modify the operation wavelength without the need of changing material and/or geometrical parameters. We also show that applied magnetic fields can reversibly switch on and off the cloak operation. These results, which could be achieved for existing magneto-optical materials, are shown to be robust to material losses, so that they may pave the way for developing actively tunable, versatile plasmonic cloaks.

  3. Flux Transport and the Sun's Global Magnetic Field

    Science.gov (United States)

    Hathaway, David H.

    2010-01-01

    The Sun s global magnetic field is produced and evolved through the emergence of magnetic flux in active regions and its transport across the solar surface by the axisymmetric differential rotation and meridional flow and the non-axisymmetric convective flows of granulation, supergranulation, and giant cell convection. Maps of the global magnetic field serve as the inner boundary condition for space weather. The photospheric magnetic field and its evolution determine the coronal and solar wind structures through which CMEs must propagate and in which solar energetic particles are accelerated and propagate. Producing magnetic maps which best represent the actual field configuration at any instant requires knowing the magnetic field over the observed hemisphere as well as knowing the flows that transport flux. From our Earth-based vantage point we only observe the front-side hemisphere and each pole is observable for only six months of the year at best. Models for the surface magnetic flux transport can be used to provide updates to the magnetic field configuration in those unseen regions. In this presentation I will describe successes and failures of surface flux transport and present new observations on the structure, the solar cycle variability, and the evolution of the flows involved in magnetic flux transport. I find that supergranules play the dominant role due to their strong flow velocities and long lifetimes. Flux is transported by differential rotation and meridional flow only to the extent that the supergranules participate in those two flows.

  4. The initiation of coronal mass ejections by magnetic flux emergence

    Science.gov (United States)

    Dubey, G.; van der Holst, B.; Poedts, S.

    2006-12-01

    Aims.The initiation of solar Coronal Mass Ejections (CMEs) is studied in the framework of computational Magneto-Hydro-Dynamics (MHD). Methods: .The initial configuration includes a magnetic flux rope that is embedded in a gravitationally stratified solar atmosphere with a background dipole magnetic field in spherical, axi-symmetric geometry. The flux rope is in equilibrium due to an image current below the photosphere. An emerging magnetic flux triggering mechanism is used to make this equilibrium configuration unstable. Results: . When the magnetic flux emerges within the filament below the flux rope this results in a catastrophic behavior similar to earlier, more simple models. As a result, the flux rope rises and a current sheet forms below it. It is shown that the magnetic reconnection in the current sheet below the flux rope in combination with the outward curvature forces results in a fast ejection of the flux rope as observed for solar CMEs. We have done a parameter study of the effect of the flux emergence rate on the velocity and the acceleration of the resulting CMEs.

  5. Studying the Formation and Evolution of Eruptive Magnetic Flux Ropes

    Science.gov (United States)

    Linton, Mark

    2017-08-01

    Solar magnetic eruptions are dramatic sources of solar activity, and dangerous sources of space weather hazards. Many of these eruptions take the form of magnetic flux ropes, i.e., magnetic fieldlines wrapping around a core magnetic flux tube. Investigating the processes which form these flux ropes both prior to and during eruption, and investigating their evolution after eruption, can give us a critical window into understanding the sources of and processes involved in these eruptions. This presentation will discuss modeling and observational investigations into these various phases of flux rope formation, eruption, and evolution, and will discuss how these different explorations can be used to develop a more complete picture of erupting flux rope dynamics.

  6. Flux-limitation of the Nernst effect in magnetized ICF

    Science.gov (United States)

    Ridgers, Christopher; Barrois, Rion; Wengraf, Joshua; Bissell, John; Brodrick, Jonathan; Kingham, Robert; Read, Martin

    2016-10-01

    Magnetized ICF is a promising scheme which combines the advantages of magnetic and inertial confinement fusion. In the relevant high-energy density plasmas magnetic field evolution is often controlled by the Nernst effect where the magnetic field advects with the electron heat flow. It is well known that non-local thermal transport necessitates a flux-limiter on the heat flow. This suggests that a flux-limiter should also be applied to the Nernst effect. We have shown that this is the case using Vlasov-Fokker-Planck simulations and that the flux-limter is not the same as that required for the heat flow itself, for example when a NIF-relevant flux-limiter of 0.15 is required to limit the heat flow a Nernst flux limiter of 0.08 is required. We acknowledge support from EPSRC Grant No. EPM011372/1.

  7. Do the legs of magnetic clouds contain twisted flux-rope magnetic fields?

    OpenAIRE

    Owens, Mathew

    2016-01-01

    Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs) characterised primarily by a smooth rotation in the magnetic field direction indicative of the presence of a magnetic flux rope. Energetic particle signatures suggest MC flux ropes remain magnetically connected to the Sun at both ends, leading to widely used model of global MC structure as an extended flux rope, with a loop-like axis stretching out from the Sun into the heliosphere and back to the Sun. The tim...

  8. On the interaction between the external magnetic field and nanofluid inside a vertical square duct

    Directory of Open Access Journals (Sweden)

    Kashif Ali

    2015-10-01

    Full Text Available In this paper, we numerically study how the external magnetic field influences the flow and thermal characteristics of nanofluid inside a vertical square duct. The flow is considered to be laminar and hydrodynamically as well as thermally developed, whereas the thermal boundary condition of constant heat flux per unit axial length with constant peripheral temperature at any cross section, is assumed. The governing equations are solved using the spectral method and the finite difference method. Excellent comparison is noted in the numerical results given by the two methods but the spectral method is found to be superior in terms of both efficiency and accuracy. We have noted that the flow reversal due to high Raleigh number may be controlled by applying an external magnetic field of suitable strength. Moreover, the Nusselt number is found to be almost a linear function of the nanoparticle volume fraction parameter, for different values of the Raleigh number and the magnetic parameter.

  9. On the interaction between the external magnetic field and nanofluid inside a vertical square duct

    Energy Technology Data Exchange (ETDEWEB)

    Ali, Kashif; Ahmad, Shabbir; Ahmad, Shahzad, E-mail: shahzadahmadbzu@gmail.com; Ashraf, Muhammad; Asif, Muhammad [Centre for Advanced Studies in Pure and Applied Mathematics, Bahauddin Zakariya University, Multan (Postal Code: 60800) (Pakistan)

    2015-10-15

    In this paper, we numerically study how the external magnetic field influences the flow and thermal characteristics of nanofluid inside a vertical square duct. The flow is considered to be laminar and hydrodynamically as well as thermally developed, whereas the thermal boundary condition of constant heat flux per unit axial length with constant peripheral temperature at any cross section, is assumed. The governing equations are solved using the spectral method and the finite difference method. Excellent comparison is noted in the numerical results given by the two methods but the spectral method is found to be superior in terms of both efficiency and accuracy. We have noted that the flow reversal due to high Raleigh number may be controlled by applying an external magnetic field of suitable strength. Moreover, the Nusselt number is found to be almost a linear function of the nanoparticle volume fraction parameter, for different values of the Raleigh number and the magnetic parameter.

  10. Magnetic flux tubes as sources of wave generation

    Science.gov (United States)

    Musielak, Z. E.; Rosner, R.; Ulmschneider, P.

    1987-01-01

    The structure of solar, and very likely stellar, surface magnetic fields is highly inhomogeneous: at the photospheric level, the fields are locally strong, and show concentration into a flux tube structure. In this case, the wave energy generated in stellar convection zones may be largely carried away by flux tube waves, which can then become important sources for the heating of the outer atmospheric layers. Such flux tube wave generation may help to explain the UV and X-ray fluxes observed by the IUE and Einstein observatories. The generation of longitudinal tube waves in magnetic flux tubes embedded in an otherwise magnetic field-free, turbulent, and stratified medium was considered. It is shown that compressible tube waves are generated by dipole emission and that the generation efficiency is a strong function of the magnetic field strength. Energy flux calculations are presented for different magnetic flux tubes, and show how the results depend on the magnetic field strength and the characteristics of the convective turbulence.

  11. Unsteady wandering magnetic field lines, turbulence and laboratory flux ropes

    Science.gov (United States)

    Intrator, T.; Sears, J.; Weber, T.; Liu, D.; Pulliam, D.; Lazarian, A.

    2011-12-01

    We describe earth bound laboratory experiment investigations of patchy, unsteady, bursty, patchy magnetic field structures that are unifying features of magnetic reconnection and turbulence in helio, space and astro physics. Macroscopic field lines occupy cross sectional areas, fill up three dimensional (3D) volumes as flux tubes. They contain mass with Newtonian dynamics that follow magneto-hydro-dynamic (MHD) equations of motion. Flux rope geometry can be ubiquitous in laminar reconnection sheet geometries that are themselves unstable to formation of secondary "islands" that in 3D are really flux ropes. Flux ropes are ubiquitous structures on the sun and the rest of the heliosphere. Understanding the dynamics of flux ropes and their mutual interactions offers the key to many important astrophysical phenomena, including magnetic reconnection and turbulence. We describe laboratory investigations on RSX, where 3D interaction of flux ropes can be studied in great detail. We use experimental probes inside the the flux ropes to measure the magnetic and electric fields, current density, density, temperatures, pressure, and electrostatic and vector plasma potentials. Macroscopic magnetic field lines, unsteady wandering characteristics, and dynamic objects with structure down to the dissipation scale length can be traced from data sets in a 3D volume. Computational approaches are finally able to tackle simple 3D systems and we sketch some intriguing simulation results that are consistent with 3D extensions of typical 2D cartoons for magnetic reconnection and turbulence.

  12. Plasma Braking Due to External Magnetic Perturbations

    Science.gov (United States)

    Frassinetti, L.; Olofsson, Kejo; Brunsell, P. R.; Khan, M. W. M.; Drake, J. R.

    2010-11-01

    The RFP EXTRAP T2R is equipped with a comprehensive active feedback system (128 active saddle coils in the full-coverage array) and active control of both resonant and non-resonant MHD modes has been demonstrated. The feedback algorithms, based on modern control methodology such as reference mode tracking (both amplitude and phase), are a useful tool to improve the ``state of the art'' of the MHD mode control. But this tool can be used also to improve the understanding and the characterization of other phenomena such as the ELM mitigation with a resonant magnetic perturbation or the plasma viscosity. The present work studies plasma and mode braking due to static RMPs. Results show that a static RMP produces a global braking of the flow profile. The study of the effect of RMPs characterized by different helicities will also give information on the plasma viscosity profile. Experimental results are finally compared to theoretical models.

  13. Quantum transport in coupled resonators enclosed synthetic magnetic flux

    Energy Technology Data Exchange (ETDEWEB)

    Jin, L., E-mail: jinliang@nankai.edu.cn

    2016-07-15

    Quantum transport properties are instrumental to understanding quantum coherent transport processes. Potential applications of quantum transport are widespread, in areas ranging from quantum information science to quantum engineering, and not restricted to quantum state transfer, control and manipulation. Here, we study light transport in a ring array of coupled resonators enclosed synthetic magnetic flux. The ring configuration, with an arbitrary number of resonators embedded, forms a two-arm Aharonov–Bohm interferometer. The influence of magnetic flux on light transport is investigated. Tuning the magnetic flux can lead to resonant transmission, while half-integer magnetic flux quantum leads to completely destructive interference and transmission zeros in an interferometer with two equal arms. -- Highlights: •The light transport is investigated through ring array of coupled resonators enclosed synthetic magnetic field. •Aharonov–Bohm ring interferometer of arbitrary configuration is investigated. •The half-integer magnetic flux quantum leads to destructive interference and transmission zeros for two-arm at equal length. •Complete transmission is available via tuning synthetic magnetic flux.

  14. Photospheric and Subphotospheric Dynamics of Emerging Magnetic Flux

    Science.gov (United States)

    Kosovichev, A. G.

    2009-04-01

    Magnetic fields emerging from the Sun’s interior carry information about physical processes of magnetic field generation and transport in the convection zone. Soon after appearance on the solar surface the magnetic flux gets concentrated in sunspot regions and causes numerous active phenomena on the Sun. This paper discusses some properties of the emerging magnetic flux observed on the solar surface and in the interior. A statistical analysis of variations of the tilt angle of bipolar magnetic regions during the emergence shows that the systematic tilt with respect to the equator (the Joy’s law) is most likely established below the surface. However, no evidence of the dependence of the tilt angle on the amount of emerging magnetic flux, predicted by the rising magnetic flux rope theories, is found. Analysis of surface plasma flows in a large emerging active region reveals strong localized upflows and downflows at the initial phase of emergence but finds no evidence for large-scale flows indicating future appearance a large-scale magnetic structure. Local helioseismology provides important tools for mapping perturbations of the wave speed and mass flows below the surface. Initial results from SOHO/MDI and GONG reveal strong diverging flows during the flux emergence, and also localized converging flows around stable sunspots. The wave speed images obtained during the process of formation of a large active region, NOAA 10488, indicate that the magnetic flux gets concentrated in strong field structures just below the surface. Further studies of magnetic flux emergence require systematic helioseismic observations from the ground and space, and realistic MHD simulations of the subsurface dynamics.

  15. Phase diagram of strong interactions in an external magnetic field

    CERN Document Server

    Mizher, Ana Julia; Chernodub, M N

    2011-01-01

    We obtain the phase diagram of strong interactions in the presence of a magnetic field within the linear sigma model coupled to quarks and to the Polyakov loop, and show that the chiral and deconfinement lines can split. We also study the behavior of the chiral condensate in this magnetic environment and find an approximately linear dependence on the external field, in accordance with lattice data.

  16. Magnetic anisotropy in Fe-25Cr-12Co-1Si alloy induced by external magnetic field

    Institute of Scientific and Technical Information of China (English)

    ZHEN Liang; SUN Xue-yin; XU Cheng-yan; GAO Run-sheng; XU Ren-gen; QIN Lu-chang

    2007-01-01

    Structural and magnetic properties of Fe-25Cr-12Co-1Si alloy thermo-magnetically treated under different external magnetic field conditions were investigated. Orientation and morphology of the ferromagnetic α1 phase embedded in α2 phase matrix before and after step ageing are characterized by transmission electron microscope(TEM). The results show that the ellipsoidal particles of ferromagnetic α1 phase are aligned along the direction of external magnetic field during isothermal magnetic ageing. Approximately 28% of the total coercivity can be attributed to the shape anisotropy of α1 phase particles induced by external magnetic field for Fe-25Cr-12Co-1Si alloy thermo-magnetically treated with a parallel magnetic field.

  17. Quantum transport in coupled resonators enclosed synthetic magnetic flux

    Science.gov (United States)

    Jin, L.

    2016-07-01

    Quantum transport properties are instrumental to understanding quantum coherent transport processes. Potential applications of quantum transport are widespread, in areas ranging from quantum information science to quantum engineering, and not restricted to quantum state transfer, control and manipulation. Here, we study light transport in a ring array of coupled resonators enclosed synthetic magnetic flux. The ring configuration, with an arbitrary number of resonators embedded, forms a two-arm Aharonov-Bohm interferometer. The influence of magnetic flux on light transport is investigated. Tuning the magnetic flux can lead to resonant transmission, while half-integer magnetic flux quantum leads to completely destructive interference and transmission zeros in an interferometer with two equal arms.

  18. On Bosonic Magnetic Flux Operator and Bosonic Faraday Operator Formula

    Institute of Scientific and Technical Information of China (English)

    FAN Hong-Yi; WANG Tong-Tong; WANG Ji-Suo

    2007-01-01

    In the literature about mesoscopic Josephson devices the magnetic flux is considered as an operator, the fundamental commutative relation between the magnetic flux operator and the Cooper-pair charge operator is usually preengaged. In this paper we show that such a relation can be deduced from the basic Bose operators' commutative relation through the entangled state representation. The Faraday formula in bosonic form is then equivalent to the second Josephson equation. The current operator equation for LC mesoscopic circuit is also derived.

  19. Quantum Transport in a Biphenyl Molecule: Effects of Magnetic Flux

    OpenAIRE

    Maiti, Santanu K.

    2009-01-01

    Electron transport properties of a biphenyl molecule are studied based on the Green's function formalism. The molecule is sandwiched between two metallic electrodes, where each benzene ring is threaded by a magnetic flux $\\phi$. The results are focused on the effects of the molecule to electrode coupling strength and the magnetic flux $\\phi$. Our numerical study shows that, for a fixed molecular coupling, the current amplitude across the bridge can be {\\em regulated} significantly just by tun...

  20. Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

    Energy Technology Data Exchange (ETDEWEB)

    Ma, X., E-mail: xzm0005@auburn.edu; Maurer, D. A.; Knowlton, S. F.; ArchMiller, M. C.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Pandya, M. D.; Roberds, N. A.; Traverso, P. J. [Physics Department, Auburn University, Auburn, Alabama 36849 (United States); Cianciosa, M. R. [Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37830 (United States)

    2015-12-15

    Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. The inversion radius of standard sawteeth is used to infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.

  1. Spatial Transport of Magnetic Flux Surfaces in Strongly Anisotropic Turbulence

    Science.gov (United States)

    Matthaeus, W. H.; Servidio, S.; Wan, M.; Ruffolo, D. J.; Rappazzo, A. F.; Oughton, S.

    2013-12-01

    Magnetic flux surfaces afford familiar descriptions of spatial structure, dynamics, and connectivity of magnetic fields, with particular relevance in contexts such as solar coronal flux tubes, magnetic field connectivity in the interplanetary and interstellar medium, as well as in laboratory plasmas and dynamo problems [1-4]. Typical models assume that field-lines are orderly, and flux tubes remain identifiable over macroscopic distances; however, a previous study has shown that flux tubes shred in the presence of fluctuations, typically losing identity after several correlation scales [5]. Here, the structure of magnetic flux surfaces is numerically investigated in a reduced magnetohydrodynamic (RMHD) model of homogeneous turbulence. Short and long-wavelength behavior is studied statistically by propagating magnetic surfaces along the mean field. At small scales magnetic surfaces become complex, experiencing an exponential thinning. At large scales, instead, the magnetic flux undergoes a diffusive behavior. The link between the diffusion of the coarse-grained flux and field-line random walk is established by means of a multiple scale analysis. Both large and small scales limits are controlled by the Kubo number. These results have consequences for understanding and interpreting processes such as magnetic reconnection and field-line diffusion in plasmas [6]. [1] E. N. Parker, Cosmical Magnetic Fields (Oxford Univ. Press, New York, 1979). [2] J. R. Jokipii and E. N. Parker, Phys. Rev. Lett. 21, 44 (1968). [3] R. Bruno et al., Planet. Space Sci. 49, 1201 (2001). [4] M. N. Rosenbluth et al., Nuclear Fusion 6, 297 (1966). [5] W. H. Matthaeus et al., Phys. Rev. Lett. 75, 2136 (1995). [6] S. Servidio et al., submitted (2013).

  2. The Research and Development of the External Magnetic Field Acting on Electro-Deposition Process

    OpenAIRE

    Wu Menghua; Jia Weiping

    2016-01-01

    The research and development status of the electro-deposition technology under the action of external magnetic field are introduced. The basic characteristics and applied manners of external magnetic field in electro-deposition process are summarized. The acting principle of external magnetic field, the effects of magnetic hydrodynamics (MHD) caused by the Lorentz force, and the acting of magnetic force on the metal ions and particles are described. The main actions of external magnetic field...

  3. Fluxon propagation in long Josephson junctions with external magnetic field

    DEFF Research Database (Denmark)

    Olsen, O.H.; Samuelsen, Mogens Rugholm

    1981-01-01

    of breather-like waves depending on the velocity of the incident fluxon and the magnitude of the external magnetic field. Approximations based on energy analysis describing the border lines between regions of different processes are presented. Journal of Applied Physics is copyrighted by The American...... Institute of Physics....

  4. INVESTIGATION OF SOLAR ABSORPTANCE OF BUILDING EXTERNAL SURFACES FROM HEAT FLUX POINT OF VIEW

    Directory of Open Access Journals (Sweden)

    Meral ÖZEL

    2006-02-01

    Full Text Available In this study, solar absorptance of external surfaces of buildings has been numerically investigated from the heat gain and losses point of view. For this purpose, external surface solar absorptance was icreased from 0 to 1with an ratio of 0.1 and, for the summer and winter conditions, heat fluxs was calculated by considering orientations of the wall and its roof for brick and concrete structure materials. Besides, external surface absorptance was assumed as 0.2, 0.5 and 0.9, respectively. Than, heat gain and losses were calculated to insulation thickness increasing on the outdoor surface of wall. Results obtained were presented as graphics

  5. Computing the External Magnetic Scalar Potential due to an Unbalanced Six-Pole Permanent Magnet Motor

    Energy Technology Data Exchange (ETDEWEB)

    Selvaggi J, Salon S, Kwon O, Chari MVK

    2007-02-12

    The accurate computation of the external magnetic field from a permanent magnet motor is accomplished by first computing its magnetic scalar potential. In order to find a solution which is valid for any arbitrary point external to the motor, a number of proven methods have been employed. Firstly, A finite element model is developed which helps generate magnetic scalar potential values valid for points close to and outside the motor. Secondly, charge simulation is employed which generates an equivalent magnetic charge matrix. Finally, an equivalent multipole expansion is developed through the application of a toroidal harmonic expansion. This expansion yields the harmonic components of the external magnetic scalar potential which can be used to compute the magnetic field at any point outside the motor.

  6. Magnetic hysteresis and magnetic flux patterns measured by acoustically stimulated electromagnetic response in a steel plate

    Science.gov (United States)

    Yamada, Hisato; Watanabe, Kakeru; Ikushima, Kenji

    2015-08-01

    Magnetic hysteresis loops are measured by ultrasonic techniques and used in visualizing the magnetic-flux distribution in a steel plate. The piezomagnetic coefficient determines the amplitude of acoustically stimulated electromagnetic (ASEM) fields, yielding the hysteresis behavior of the intensity of the ASEM response. By utilizing the high correspondence of the ASEM response to the magnetic-flux density, we image the specific spatial patterns of the flux density formed by an artificial defect in a steel plate specimen. Magnetic-flux probing by ultrasonic waves is thus shown to be a viable method of nondestructive material inspection.

  7. Correlations Between Magnetic Flux and Levitation Force of HTS Bulk Above a Permanent Magnet Guideway

    Science.gov (United States)

    Huang, Huan; Zheng, Jun; Zheng, Botian; Qian, Nan; Li, Haitao; Li, Jipeng; Deng, Zigang

    2017-06-01

    In order to clarify the correlations between magnetic flux and levitation force of the high-temperature superconducting (HTS) bulk, we measured the magnetic flux density on bottom and top surfaces of a bulk superconductor while vertically moving above a permanent magnet guideway (PMG). The levitation force of the bulk superconductor was measured simultaneously. In this study, the HTS bulk was moved down and up for three times between field-cooling position and working position above the PMG, followed by a relaxation measurement of 300 s at the minimum height position. During the whole processes, the magnetic flux density and levitation force of the bulk superconductor were recorded and collected by a multipoint magnetic field measurement platform and a self-developed maglev measurement system, respectively. The magnetic flux density on the bottom surface reflected the induced field in the superconductor bulk, while on the top, it reveals the penetrated magnetic flux. The results show that the magnetic flux density and levitation force of the bulk superconductor are in direct correlation from the viewpoint of inner supercurrent. In general, this work is instructive for understanding the connection of the magnetic flux density, the inner current density and the levitation behavior of HTS bulk employed in a maglev system. Meanwhile, this magnetic flux density measurement method has enriched present experimental evaluation methods of maglev system.

  8. SQUIDs De-fluxing Using a Decaying AC Magnetic Field

    Energy Technology Data Exchange (ETDEWEB)

    Matlashov, Andrei Nikolaevich [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Semenov, Vasili Kirilovich [State Univ. of New York (SUNY), Plattsburgh, NY (United States); Anderson, Bill [Senior Scientific, LLC, Albuquerque, NM (United States)

    2016-06-08

    Flux trapping is the Achilles’ heel of all superconductor electronics. The most direct way to avoid flux trapping is a prevention of superconductor circuits from exposure to magnetic fields. Unfortunately this is not feasible if the circuits must be exposed to a strong DC magnetic field even for a short period of time. For example, such unavoidable exposures take place in superparamagnetic relaxation measurements (SPMR) and ultra-low field magnetic resonance imaging (ULF MRI) using unshielded thin-film SQUID-based gradiometers. Unshielded SQUIDs stop working after being exposed to DC magnetic fields of only a few Gauss in strength. In this paper we present experimental results with de-fluxing of planar thin-film LTS SQUID-based gradiometers using a strong decaying AC magnetic field. We used four commercial G136 gradiometers for SPMR measurements with up to a 10 mT magnetizing field. Strong 12.9 kHz decaying magnetic field pulses reliably return SQUIDs to normal operation 50 ms after zeroing the DC magnetizing field. This new AC de-fluxing method was also successfully tested with seven other different types of LTS SQUID sensors and has been shown to dissipate extremely low energy.

  9. Magnetic flux generation and transport in cool stars

    CERN Document Server

    Işık, Emre; Schüssler, Manfred

    2011-01-01

    The Sun and other cool stars harbouring outer convection zones manifest magnetic activity in their atmospheres. The connection between this activity and the properties of a deep-seated dynamo generating the magnetic flux is not well understood. By employing physical models, we study the spatial and temporal characteristics of the observable surface field for various stellar parameters. We combine models for magnetic flux generation, buoyancy instability, and transport, which encompass the entire convection zone. The model components are: (1) a thin-layer alpha-Omega dynamo at the base of the convection zone; (2) buoyancy instabilities and the rise of flux tubes through the convection zone in 3D, which provides a physically consistent determination of emergence latitudes and tilt angles; and (3) horizontal flux transport at the surface. For solar-type stars and rotation periods longer than about 10 days, the latitudinal dynamo waves generated by the deep-seated alpha-Omega dynamo are faithfully reflected by th...

  10. Magnetic Flux Dynamics in Horizontally Cooled Superconducting Cavities

    CERN Document Server

    Martinello, M; Grassellino, A; Crawford, A C; Melnychuk, O; Romanenko, A; Sergatkov, D A

    2015-01-01

    Previous studies on magnetic flux expulsion as a function of cooling details have been performed for superconducting niobium cavities with the cavity beam axis placed parallel respect to the helium cooling flow, and findings showed that for sufficient cooling thermogradients all magnetic flux could be expelled and very low residual resistance could be achieved. In this paper we investigate the flux trapping and its impact on radio frequency surface resistance when the resonators are positioned perpendicularly to the helium cooling flow, which is representative of how superconducting radio-frequency (SRF) cavities are cooled in an accelerator. We also extend the studies to different directions of applied magnetic field surrounding the resonator. Results show that in the cavity horizontal configuration there is a different impact of the various field components on the final surface resistance, and that several parameters have to be considered to understand flux dynamics. A newly discovered phenomenon of concent...

  11. Two-dimensional model of intrinsic magnetic flux losses in helical flux compression generators

    CERN Document Server

    Haurylavets, V V

    2012-01-01

    Helical Flux Compression Generators (HFCG) are used for generation of mega-amper current and high magnetic fields. We propose the two dimensional HFCG filament model based on the new description of the stator and armature contact point. The model developed enables one to quantitatively describe the intrinsic magnetic flux losses and predict the results of experiments with various types of HFCGs. We present the effective resistance calculations based on the non-linear magnetic diffusion effect describing HFCG performance under the strong conductor heating by currents.

  12. Forced three-dimensional magnetic reconnection due to linkage of magnetic flux tubes

    Science.gov (United States)

    Otto, A.

    1995-01-01

    During periods of southward interplanetary magnetic field (IMF) orientation the magnetic field geometry at the dayside magnetopause is susceptible to magnetic reconnection. It has been suggested that reconnection may occur in a localized manner at several patches on the magnetopause. A major problem with this picture is the interaction of magnetic flux ropes which are generated by different reconnection processes. An individual flux rope is bent elbowlike where it intersects the magnetopause and the magnetic field changes from magnetospheric to interplanetary magnetic field orientation. Multiple patches of reconnection can lead to the formation of interlinked magnetic flux tubes. Although the corresponding flux is connected to the IMF the northward and southward connected branches are hooked into each other and cannot develop independently. We have studied this problem in the framework of three-dimensional magnetohydrodynamic simulations. The results indicate that a singular current sheet forms at the interface of two interlinked flux tubes if no resistivity is present in the simulation. This current sheet is strongly tilted compared to the original current sheet. In the presence of resistivity the interaction of the two flux tubes forces a fast reconnection process which generates helically twisted closed magnetospheric flux. This linkage induced reconnection generates a boundary layer with layers of open and closed magnetospheric flux and may account for the brightening of auroral arcs poleward of the boundary between open and closed magnetic flux.

  13. Scaling laws of free magnetic energy stored in a solar emerging flux region

    CERN Document Server

    Magara, Tetsuya

    2014-01-01

    This Letter reports scaling laws of free magnetic energy stored in a solar emerging flux region which is a key to understanding the energetics of solar active phenomena such as solar flares and coronal mass ejections. By performing 3-dimensional magnetohydrodynamic simulations that reproduce several emerging flux regions of different magnetic configurations, we derive power law relationships among emerged magnetic flux, free magnetic energy and relative magnetic helicity in these emerging flux regions. Since magnetic flux is an observable quantity, the scaling law between magnetic flux and free magnetic energy may give a way to estimate invisible free magnetic energy responsible for solar active phenomena.

  14. The solar internetwork. I. Contribution to the network magnetic flux

    Energy Technology Data Exchange (ETDEWEB)

    Gošić, M.; Rubio, L. R. Bellot; Del Toro Iniesta, J. C. [Instituto de Astrofísica de Andalucía (CSIC), Apdo. 3004, E-18080 Granada (Spain); Orozco Suárez, D. [Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife (Spain); Katsukawa, Y., E-mail: mgosic@iaa.es [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

    2014-12-10

    The magnetic network (NE) observed on the solar surface harbors a sizable fraction of the total quiet Sun flux. However, its origin and maintenance are not well known. Here we investigate the contribution of internetwork (IN) magnetic fields to the NE flux. IN fields permeate the interior of supergranular cells and show large emergence rates. We use long-duration sequences of magnetograms acquired by Hinode and an automatic feature tracking algorithm to follow the evolution of NE and IN flux elements. We find that 14% of the quiet Sun (QS) flux is in the form of IN fields with little temporal variations. IN elements interact with NE patches and modify the flux budget of the NE either by adding flux (through merging processes) or by removing it (through cancellation events). Mergings appear to be dominant, so the net flux contribution of the IN is positive. The observed rate of flux transfer to the NE is 1.5 × 10{sup 24} Mx day{sup –1} over the entire solar surface. Thus, the IN supplies as much flux as is present in the NE in only 9-13 hr. Taking into account that not all the transferred flux is incorporated into the NE, we find that the IN would be able to replace the entire NE flux in approximately 18-24 hr. This renders the IN the most important contributor to the NE, challenging the view that ephemeral regions are the main source of flux in the QS. About 40% of the total IN flux eventually ends up in the NE.

  15. Torsional Alfven waves in stratified and expanding magnetic flux tubes

    OpenAIRE

    2011-01-01

    The effects of both density stratification and magnetic field expansion on torsional Alfven waves in magnetic flux tubes are studied. The frequencies, the period ratio P1/P2 of the fundamental and its first-overtone, and eigenfunctions of torsional Alfven modes are obtained. Our numerical results show that the density stratification and magnetic field expansion have opposite effects on the oscillating properties of torsional Alfven waves.

  16. Magnetic flux density in the heliosphere through several solar cycles

    Energy Technology Data Exchange (ETDEWEB)

    Erdős, G. [Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Balogh, A., E-mail: erdos.geza@wigner.mta.hu [The Blackett Laboratory, Imperial College London, London SW7 2BZ (United Kingdom)

    2014-01-20

    We studied the magnetic flux density carried by solar wind to various locations in the heliosphere, covering a heliospheric distance range of 0.3-5.4 AU and a heliolatitudinal range from 80° south to 80° north. Distributions of the radial component of the magnetic field, B{sub R} , were determined over long intervals from the Helios, ACE, STEREO, and Ulysses missions, as well as from using the 1 AU OMNI data set. We show that at larger distances from the Sun, the fluctuations of the magnetic field around the average Parker field line distort the distribution of B{sub R} to such an extent that the determination of the unsigned, open solar magnetic flux density from the average (|B{sub R} |) is no longer justified. We analyze in detail two methods for reducing the effect of fluctuations. The two methods are tested using magnetic field and plasma velocity measurements in the OMNI database and in the Ulysses observations, normalized to 1 AU. It is shown that without such corrections for the fluctuations, the magnetic flux density measured by Ulysses around the aphelion phase of the orbit is significantly overestimated. However, the matching between the in-ecliptic magnetic flux density at 1 AU (OMNI data) and the off-ecliptic, more distant, normalized flux density by Ulysses is remarkably good if corrections are made for the fluctuations using either method. The main finding of the analysis is that the magnetic flux density in the heliosphere is fairly uniform, with no significant variations having been observed either in heliocentric distance or heliographic latitude.

  17. Design of Magnetic Flux Feedback Controller in Hybrid Suspension System

    Directory of Open Access Journals (Sweden)

    Wenqing Zhang

    2013-01-01

    Full Text Available Hybrid suspension system with permanent magnet and electromagnet consumes little power consumption and can realize larger suspension gap. But realizing stable suspension of hybrid magnet is a tricky problem in the suspension control sphere. Considering from this point, we take magnetic flux signal as a state variable and put this signal back to suspension control system. So we can get the hybrid suspension mathematical model based on magnetic flux signal feedback. By application of MIMO feedback linearization theory, we can further realize linearization of the hybrid suspension system. And then proportion, integral, differentiation, magnetic flux density B (PIDB controller is designed. Some hybrid suspension experiments have been done on CMS04 magnetic suspension bogie of National University of Defense Technology (NUDT in China. The experiments denote that the new hybrid suspension control algorithm based on magnetic flux signal feedback designed in this paper has more advantages than traditional position-current double cascade control algorithm. Obviously, the robustness and stability of hybrid suspension system have been enhanced.

  18. Reconstruction of Open Solar Magnetic Flux and Interplanetary Magnetic Field in the 20Th Century

    Science.gov (United States)

    Ivanov, V. G.; Miletsky, E. V.

    2004-10-01

    We reconstruct mean magnitudes of the open solar magnetic field since 1915 using α magnetic synoptic charts of the Sun. The obtained series allows estimation of the interplanetary magnetic field. They also confirm the known conclusion about the secular increase of the solar open magnetic flux in the first half of the 20th century.

  19. Measurement of induced magnetic flux density using injection current nonlinear encoding (ICNE) in MREIT.

    Science.gov (United States)

    Park, Chunjae; Lee, Byung Il; Kwon, Ohin; Woo, Eung Je

    2007-02-01

    Magnetic resonance electrical impedance tomography (MREIT) measures induced magnetic flux densities subject to externally injected currents in order to visualize conductivity distributions inside an electrically conducting object. Injection currents induce magnetic flux densities that appear in phase parts of acquired MR image data. In the conventional current injection method, we inject currents during the time segment between the end of the first RF pulse and the beginning of the reading gradient in order to ensure the gradient linearity. Noting that longer current injections can accumulate more phase changes, we propose a new pulse sequence called injection current nonlinear encoding (ICNE) where the duration of the injection current pulse is extended until the end of the reading gradient. Since the current injection during the reading gradient disturbs the gradient linearity, we first analyze the MR signal produced by the ICNE pulse sequence and suggest a novel algorithm to extract the induced magnetic flux density from the acquired MR signal. Numerical simulations and phantom experiments show that the new method is clearly advantageous in terms of the reduced noise level in measured magnetic flux density data. The amount of noise reduction depends on the choice of the data acquisition time and it was about 24% when we used a prolonged data acquisition time of 10.8 ms. The ICNE method will enhance the clinical applicability of the MREIT technique when it is combined with an appropriate phase artefact minimization method.

  20. Turbulent Erosion of Magnetic Flux Tubes

    CERN Document Server

    Petrovay, K

    1997-01-01

    Results from a numerical and analytical investigation of the solution of a nonlinear axially symmetric diffusion equation for the magnetic field are presented for the case when the nonlinear dependence of the diffusivity $\

  1. Nonlinear subelliptic Schrodinger equations with external magnetic field

    Directory of Open Access Journals (Sweden)

    Kyril Tintarev

    2004-10-01

    Full Text Available To account for an external magnetic field in a Hamiltonian of a quantum system on a manifold (modelled here by a subelliptic Dirichlet form, one replaces the the momentum operator $frac 1i d$ in the subelliptic symbol by $frac 1i d-alpha$, where $alphain TM^*$ is called a magnetic potential for the magnetic field $eta=dalpha$. We prove existence of ground state solutions (Sobolev minimizers for nonlinear Schrodinger equation associated with such Hamiltonian on a generally, non-compact Riemannian manifold, generalizing the existence result of Esteban-Lions [5] for the nonlinear Schrödinger equation with a constant magnetic field on $mathbb{R}^N$ and the existence result of [6] for a similar problem on manifolds without a magnetic field. The counterpart of a constant magnetic field is the magnetic field, invariant with respect to a subgroup of isometries. As an example to the general statement we calculate the invariant magnetic fields in the Hamiltonians associated with the Kohn Laplacian and for the Laplace-Beltrami operator on the Heisenberg group.

  2. Dynamics of molecular superrotors in external magnetic field

    CERN Document Server

    Korobenko, Aleksey

    2015-01-01

    We excite diatomic oxygen and nitrogen to high rotational states with an optical centrifuge and study their dynamics in external magnetic field. Ion imaging is employed to directly visualize, and follow in time, the rotation plane of molecular superrotors. The two different mechanisms of interaction between the magnetic field and the molecular angular momentum in paramagnetic oxygen and non-magnetic nitrogen lead to the qualitatively different behaviour. In nitrogen, we observe the precession of the molecular angular momentum around the field vector. In oxygen, strong spin-rotation coupling results in faster and richer dynamics, encompassing the splitting of the rotation plane in three separate components. As the centrifuged molecules evolve with no significant dispersion of the molecular wave function, the observed magnetic interaction presents an efficient mechanism for controlling the plane of molecular rotation.

  3. Sensitivity of detachment extent to magnetic configuration and external parameters

    Science.gov (United States)

    Lipschultz, Bruce; Parra, Felix I.; Hutchinson, Ian H.

    2016-05-01

    Divertor detachment may be essential to reduce heat loads to magnetic fusion tokamak reactor divertor surfaces. Yet in experiments it is difficult to control the extent of the detached, low pressure, plasma region. At maximum extent the front edge of the detached region reaches the X-point and can lead to degradation of core plasma properties. We define the ‘detachment window’ in a given position control variable C (for example, the upstream plasma density) as the range in C within which the front location can be stably held at any position from the target to the X-point; increased detachment window corresponds to better control. We extend a 1D analytic model [1] to determine the detachment window for the following control variables: the upstream plasma density, the impurity concentration and the power entering the scrape-off layer (SOL). We find that variations in magnetic configuration can have strong effects; increasing the ratio of the total magnetic field at the X-point to that at the target, {{B}×}/{{B}t} , (total flux expansion, as in the super-x divertor configuration) strongly increases the detachment window for all control variables studied, thus strongly improving detachment front control and the capability of the divertor plasma to passively accommodate transients while still staying detached. Increasing flux tube length and thus volume in the divertor, through poloidal flux expansion (as in the snowflake or x-divertor configurations) or length of the divertor, also increases the detachment window, but less than the total flux expansion does. The sensitivity of the detachment front location, z h , to each control variable, C, defined as \\partial {{z}h}/\\partial C , depends on the magnetic configuration. The size of the radiating volume and the total divertor radiation increase \\propto {{≤ft({{B}×}/{{B}t}\\right)}2} and \\propto {{B}×}/{{B}t} , respectively, but not by increasing divertor poloidal flux expansion or field line length. We

  4. Fuel magnetization without external field coils (AutoMag)

    Science.gov (United States)

    Slutz, Stephen; Jennings, Christopher; Awe, Thomas; Shipley, Gabe; Lamppa, Derek; McBride, Ryan

    2016-10-01

    Magnetized Liner Inertial Fusion (MagLIF) has produced fusion-relevant plasma conditions on the Z accelerator where the fuel was magnetized using external field coils. We present a novel concept that does not need external field coils. This concept (AutoMag) magnetizes the fuel during the early part of the drive current by using a composite liner with helical conduction paths separated by insulating material. The drive is designed so the current rises slowly enough to avoid electrical breakdown of the insulators until a sufficiently strong magnetic field is established. Then the current rises more quickly, which causes the insulators to break down allowing the drive current to follow an axial path and implode the liner. Low inductance magnetically insulated power feeds can be used with AutoMag to increase the drive current without interfering with diagnostic access. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  5. Magnetic Flux Emergence Observed with the Advanced Stokes Polarimeter

    Science.gov (United States)

    Lites, B.; Martinez Pillet, V.

    1996-05-01

    We have carried out quantitative observations of the vector magnetic field during the emergence of three small bipolar active regions in June, 1992, July 1993, and September 1994 using the Advanced Stokes Polarimeter (ASP). The region of horizontal magnetic field at the actual site of emergence is always characterized by low magnetic field strength (i.e. considerably less than 1000 Gauss). We find a strong relationship between field strength and inclination in these regions. This suggests that 1) flux emerging from below the photosphere does not coalesce into strong flux tubes until it reaches the photosphere, becomes nearly vertical as a result of magnetic buoyancy, and is then acted upon by convective collapse, and 2) the field strength of flux rising through the convection zone may be in rough equipartition with the fluid motions. We find the flux emergence zone to be characterized by highly variable (both spatially and temporally) fill factors for the magnetic field, suggesting that the flux below the surface is filamentary, that it rises rapidly through the photosphere to form a magnetic canopy above the emergence region. Sequences of Hα on- and off-band images obtained with the ASP reveal the accompanying development of the arch-filament system, and suggest that the material within the Hα structures is supplied by a siphon flow as evidenced by apparent chromospheric red shifts on the sides of the loops closest to a large pore, and blue shifts where the fields anchor in plage regions. Proper motions of the magnetic flux images throughout a day's observation indicate the presence of a persistent vortex flow on a small scale (a few arcseconds). The National Center for Atmospheric Research is sponsored by the National Science Foundation.

  6. Holographic equilibration in confining gauge theories under external magnetic fields

    CERN Document Server

    Demircik, Tuna

    2016-01-01

    We investigate the effect of external magnetic fields on equilibration in the improved holographic QCD theory in the deconfined phase using the AdS/CFT correspondence. In particular we calculate the quasinormal mode spectra in the corresponding black brane solutions and study their dependence on temperature, momentum and magnetic field, both in the scalar and the shear channels. We find complex patterns in the motion of quasinormal modes on the complex plane, including certain cross overs between the lowest lying modes under varying momentum. We also find a curious dynamical instability that arise at a certain value of momentum.

  7. The Evolution of Open Magnetic Flux Driven by Photospheric Dynamics

    Science.gov (United States)

    Linker, Jon A.; Lionello, Roberto; Mikic, Zoran; Titov, Viacheslav S.; Antiochos, Spiro K.

    2010-01-01

    The coronal magnetic field is of paramount importance in solar and heliospheric physics. Two profoundly different views of the coronal magnetic field have emerged. In quasi-steady models, the predominant source of open magnetic field is in coronal holes. In contrast, in the interchange model, the open magnetic flux is conserved, and the coronal magnetic field can only respond to the photospheric evolution via interchange reconnection. In this view the open magnetic flux diffuses through the closed, streamer belt fields, and substantial open flux is present in the streamer belt during solar minimum. However, Antiochos and co-workers, in the form of a conjecture, argued that truly isolated open flux cannot exist in a configuration with one heliospheric current sheet (HCS) - it will connect via narrow corridors to the polar coronal hole of the same polarity. This contradicts the requirements of the interchange model. We have performed an MHD simulation of the solar corona up to 20R solar to test both the interchange model and the Antiochos conjecture. We use a synoptic map for Carrington Rotation 1913 as the boundary condition for the model, with two small bipoles introduced into the region where a positive polarity extended coronal hole forms. We introduce flows at the photospheric boundary surface to see if open flux associated with the bipoles can be moved into the closed-field region. Interchange reconnection does occur in response to these motions. However, we find that the open magnetic flux cannot be simply injected into closed-field regions - the flux eventually closes down and disconnected flux is created. Flux either opens or closes, as required, to maintain topologically distinct open and closed field regions, with no indiscriminate mixing of the two. The early evolution conforms to the Antiochos conjecture in that a narrow corridor of open flux connects the portion of the coronal hole that is nearly detached by one of the bipoles. In the later evolution, a

  8. Decadal period external magnetic field variations determined via eigenanalysis

    DEFF Research Database (Denmark)

    Shore, R. M.; Whaler, K. A.; Macmillan, S.

    2016-01-01

    We perform a reanalysis of hourly mean magnetic data from ground-based observatories spanning 1997-2009 inclusive, in order to isolate (after removal of core and crustal field estimates) the spatiotemporal morphology of the external fields important to mantle induction, on (long) periods of months......-the form of the decomposition is controlled by the data. We apply a spherical harmonic analysis to the EOF outputs in a joint inversion for internal and external coefficients. The results justify our assumption that the EOF procedure responds primarily to the long-period external inducing field...... contributions. Though we cannot determine uniquely the contributory source regions of these inducing fields, we find that they have distinct temporal characteristics which enable some inference of sources. An identified annual-period pattern appears to stem from a north-south seasonal motion of the background...

  9. Chromospheric and Coronal Wave Generation in a Magnetic Flux Sheath

    CERN Document Server

    Kato, Yoshiaki; Hansteen, Viggo; Gudiksen, Boris; Wedemeyer, Sven; Carlsson, Mats

    2016-01-01

    Using radiation magnetohydrodynamic simulations of the solar atmospheric layers from the upper convection zone to the lower corona, we investigate the self-consistent excitation of slow magneto-acoustic body waves (slow modes) in a magnetic flux concentration. We find that the convective downdrafts in the close surroundings of a two-dimensional flux slab "pump" the plasma inside it in the downward direction. This action produces a downflow inside the flux slab, which encompasses ever higher layers, causing an upwardly propagating rarefaction wave. The slow mode, excited by the adiabatic compression of the downflow near the optical surface, travels along the magnetic field in the upward direction at the tube speed. It develops into a shock wave at chromospheric heights, where it dissipates, lifts the transition region, and produces an offspring in the form of a compressive wave that propagates further into the corona. In the wake of downflows and propagating shock waves, the atmosphere inside the flux slab in ...

  10. Van der Waals torque induced by external magnetic fields

    CERN Document Server

    Esquivel-Sirvent, R; Palomono-Ovando, M

    2010-01-01

    We present a method for inducing and controlling van der Waals torques between two parallel slabs using a constant magnetic field. The torque is calculated using the Barash theory of dispersive torques. In III-IV semiconductors such as $InSb$, the effect of an external magnetic field is to induce an optical anisotropy, in an otherwise isotropic material, that will in turn induce a torque. The calculations of the torque are done in the Voigt configuration, with the magnetic field parallel to the surface of the slabs. As a case study we consider a slab made of calcite and a second slab made of $InSb$. In the absence of magnetic field there is no torque. As the magnetic field increases, the optical anisotropy of $InSb$ increases and the torque becomes different from zero, increasing with the magnetic field. The resulting torque is of the same order of magnitude as that calculated using permanent anisotropic materials when the magnetic fields is close to 1 T.

  11. Van der Waals torque induced by external magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Esquivel-Sirvent, R.; Cocoletzi, G. H.; Palomino-Ovando, M.

    2010-01-01

    We present a method for inducing and controlling van der Waals torques between two parallel slabs using a constant magnetic field. The torque is calculated using the Barash theory of dispersive torques. In III–IV semiconductors such as InSb, the effect of an external magnetic field is to induce an optical anisotropy, in an otherwise isotropic material, that will in turn induce a torque. The calculations of the torque are done in the Voigt configuration, with the magnetic field parallel to the surface of the slabs. As a case study we consider a slab made of calcite and a second slab made of InSb. In the absence of magnetic field there is no torque. As the magnetic field increases, the optical anisotropy of InSb increases and the torque becomes different from zero, increasing with the magnetic field. The resulting torque is of the same order of magnitude as that calculated using permanent anisotropicmaterials when the magnetic fields is close to 1 T.

  12. Magnetic Flux Expulsion Studies in Niobium SRF Cavities

    Energy Technology Data Exchange (ETDEWEB)

    Posen, Sam [Fermilab; Checchin, Mattia [Fermilab; Crawford, Anthony [Fermilab; Grassellino, Anna [Fermilab; Martinello, Martina [Fermilab; Melnychuk, Oleksandr [Fermilab; Romanenko, Alexander [Fermilab; Sergatskov, Dmitri [Fermilab; Trenikhina, Yulia [Fermilab

    2016-06-01

    With the recent discovery of nitrogen doping treatment for SRF cavities, ultra-high quality factors at medium accelerating fields are regularly achieved in vertical RF tests. To preserve these quality factors into the cryomodule, it is important to consider background magnetic fields, which can become trapped in the surface of the cavity during cooldown and cause Q₀ degradation. Building on the recent discovery that spatial thermal gradients during cooldown can significantly improve expulsion of magnetic flux, a detailed study was performed of flux expulsion on two cavities with different furnace treatments that are cooled in magnetic fields amplitudes representative of what is expected in a realistic cryomodule. In this contribution, we summarize these cavity results, in order to improve understanding of the impact of flux expulsion on cavity performance.

  13. Do the Legs of Magnetic Clouds Contain Twisted Flux-rope Magnetic Fields?

    Science.gov (United States)

    Owens, M. J.

    2016-02-01

    Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs) characterized primarily by a smooth rotation in the magnetic field direction indicative of the presence of a magnetic flux rope. Energetic particle signatures suggest MC flux ropes remain magnetically connected to the Sun at both ends, leading to widely used model of global MC structure as an extended flux rope, with a loop-like axis stretching out from the Sun into the heliosphere and back to the Sun. The time of flight of energetic particles, however, suggests shorter magnetic field line lengths than such a continuous twisted flux rope would produce. In this study, two simple models are compared with observed flux rope axis orientations of 196 MCs to show that the flux rope structure is confined to the MC leading edge. The MC “legs,” which magnetically connect the flux rope to the Sun, are not recognizable as MCs and thus are unlikely to contain twisted flux rope fields. Spacecraft encounters with these non-flux rope legs may provide an explanation for the frequent observation of non-MC ICMEs.

  14. DO THE LEGS OF MAGNETIC CLOUDS CONTAIN TWISTED FLUX-ROPE MAGNETIC FIELDS?

    Energy Technology Data Exchange (ETDEWEB)

    Owens, M. J. [Space and Atmospheric Electricity Group, Department of Meteorology, University of Reading, Earley Gate, P.O. Box 243, Reading RG6 6BB (United Kingdom)

    2016-02-20

    Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs) characterized primarily by a smooth rotation in the magnetic field direction indicative of the presence of a magnetic flux rope. Energetic particle signatures suggest MC flux ropes remain magnetically connected to the Sun at both ends, leading to widely used model of global MC structure as an extended flux rope, with a loop-like axis stretching out from the Sun into the heliosphere and back to the Sun. The time of flight of energetic particles, however, suggests shorter magnetic field line lengths than such a continuous twisted flux rope would produce. In this study, two simple models are compared with observed flux rope axis orientations of 196 MCs to show that the flux rope structure is confined to the MC leading edge. The MC “legs,” which magnetically connect the flux rope to the Sun, are not recognizable as MCs and thus are unlikely to contain twisted flux rope fields. Spacecraft encounters with these non-flux rope legs may provide an explanation for the frequent observation of non-MC ICMEs.

  15. Effects of MHD slow shocks propagating along magnetic flux tubes in a dipole magnetic field

    Directory of Open Access Journals (Sweden)

    N. V. Erkaev

    2002-01-01

    Full Text Available Variations of the plasma pressure in a magnetic flux tube can produce MHD waves evolving into shocks. In the case of a low plasma beta, plasma pressure pulses in the magnetic flux tube generate MHD slow shocks propagating along the tube. For converging magnetic field lines, such as in a dipole magnetic field, the cross section of the magnetic flux tube decreases enormously with increasing magnetic field strength. In such a case, the propagation of MHD waves along magnetic flux tubes is rather different from that in the case of uniform magnetic fields. In this paper, the propagation of MHD slow shocks is studied numerically using the ideal MHD equations in an approximation suitable for a thin magnetic flux tube with a low plasma beta. The results obtained in the numerical study show that the jumps in the plasma parameters at the MHD slow shock increase greatly while the shock is propagating in the narrowing magnetic flux tube. The results are applied to the case of the interaction between Jupiter and its satellite Io, the latter being considered as a source of plasma pressure pulses.

  16. Measurement of magnetic fluctuation-induced particle flux (invited).

    Science.gov (United States)

    Ding, W X; Brower, D L; Yates, T Y

    2008-10-01

    Magnetic field fluctuation-induced particle transport has been directly measured in the high-temperature core of the MST reversed field pinch plasma. Measurement of radial particle transport is achieved by combining various interferometry techniques, including Faraday rotation, conventional interferometry, and differential interferometry. It is observed that electron convective particle flux and its divergence exhibit a significant increase during a sawtooth crash. In this paper, we describe the basic techniques employed to determine the particle flux.

  17. Numerical simulations of sunspot rotation driven by magnetic flux emergence

    OpenAIRE

    Sturrock, Zoe

    2017-01-01

    Magnetic flux continually emerges from the Sun, rising through the solar interior, emerging at the photosphere in the form of sunspots and expanding into the atmosphere. Observations of sunspot rotations have been reported for over a century and are often accompanied by solar eruptions and flaring activity. In this thesis, we present 3D numerical simulations of the emergence of twisted flux tubes from the uppermost layers of the solar interior, examining the rotational movements of sunspots i...

  18. Magnetic Field Analysis of Interior Composite-Rotor Controllable-Flux Permanent Magnet Synchronous Machine

    Institute of Scientific and Technical Information of China (English)

    CHEN Yiguang; PAN Wei; SHEN Yonghuan; TANG Renyuan

    2006-01-01

    Conventional permanent magnet synchronous machine(PMSM)has the problem of large stator copper loss and narrow speed range. To solve this problem, an interior composite-rotor controllable-flux PMSM adaptive to multi-polar is proposed. This machine has the characteristics of low stator copper loss and wide-speed operation. The half-radial-set and half-tangential-set permanent magnets(PMs)are NdFeB that has high remanent flux density and high coercive force. The tangential-set PMs are AlNiCo that has high remanent flux density and low coercive force. By applying the pulse of d-axis stator current id, the magnetized intensity and direction of AlNiCo can be controlled. The flux created by NdFeB is repelled to stator and air-gap PM-flux is intensified, or is partially bypassed by AlNiCo in the rotor, so the air-gap PM-flux is weakened. The internal magnetic field distribution in two ultra magnetized situations is analyzed by finite element method. The dimension of PMs and magnetic structure are demonstrated. Especially when the q-axis magnetic resistance is larger and the q-axis inductance is smaller, the result of flux-weakening is better and the influence of armature reaction on air-gap PM-flux is weakened.

  19. Determining the axis orientation of cylindrical magnetic flux rope

    Science.gov (United States)

    Rong, Zhaojin; Wan, Weixing; Shen, Chao; Zhang, Tielong; Lui, Anthony; Wang, Yuming; Dunlop, malcolm; Zhang, Yongcun; Zong, Qiugang

    2013-04-01

    We develop a new simple method for inferring the orientation of a magnetic flux rope, which is assumed to be a time-independent cylindrically symmetric structure via the direct single-point analysis of magnetic field structure. The model tests demonstrate that, for the cylindrical flux rope regardless of whether it is force-free or not, the method can consistently yield the axis orientation of the flux rope with higher accuracy and stability than the minimum variance analysis of the magnetic field and the Grad-Shafranov reconstruction technique. Moreover, the radial distance to the axis center and the current density can also be estimated consistently. Application to two actual flux transfer events observed by the four satellites of the Cluster mission demonstrates that the method is more appropriate to be used for the inner part of flux rope, which might be closer to the cylindrical structure, showing good agreement with the results obtained from the optimal Grad-Shafranov reconstruction and the least squares technique of Faraday's law, but fails to produce such agreement for the outer satellite that grazes the flux rope. Therefore, the method must be used with caution.

  20. Magnetic Flux in Toroidal Type I Compactification

    CERN Document Server

    Blumenhagen, R; Körs, B; Lüst, Dieter; Blumenhagen, Ralph; Goerlich, Lars; Kors, Boris; Lust, Dieter

    2001-01-01

    We discuss the compactification of type I strings on a torus with additional background gauge flux on the D9-branes. The solutions to the cancellation of the RR tadpoles display various phenomenologically attractive features: supersymmetry breaking, chiral fermions and the opportunity to reduce the rank of the gauge group as desired. We also point out the equivalence of the concept of various different background fields and noncommutative deformations of the geometry on the individual D9-branes by constructing the relevant boundary states to describe such objects.

  1. Coronal Flux Rope Equilibria in Closed Magnetic Fields

    Institute of Scientific and Technical Information of China (English)

    Zhen Wang; You-Qiu Hu

    2003-01-01

    Using a 2.5-dimensional ideal MHD model in Cartesian coordinates, weinvestigate the equilibrium properties of coronal magnetic flux ropes in backgroundmagnetic fields that are completely closed. The background fields are produced by adipole, a quadrupole, and an octapole, respectively, located below the photosphereat the same depth. A magnetic flux rope is then launched from below the photo-sphere, and its magnetic properties, i.e., the annular magnetic flux φp and the axialmagnetic flux φz, are controlled by a single emergence parameter. The whole sys-tem eventually evolves into equilibrium, and the resultant flux rope is characterizedby three geometrical parameters: the height of the rope axis, the half-width of therope, and the length of the vertical current sheet below the rope. It is found thatthe geometrical parameters increase monotonically and continuously with increasingφ p and φz: no catastrophe occurs. Moreover, there exists a steep segment in theprofiles of the geometrical parameters versus either φp or φz, and the faster thebackground field decays with height, the larger both the gradient and the growthamplitude within the steep segment will be.

  2. Chromospheric and Coronal Wave Generation in a Magnetic Flux Sheath

    Science.gov (United States)

    Kato, Yoshiaki; Steiner, Oskar; Hansteen, Viggo; Gudiksen, Boris; Wedemeyer, Sven; Carlsson, Mats

    2016-08-01

    Using radiation magnetohydrodynamic simulations of the solar atmospheric layers from the upper convection zone to the lower corona, we investigate the self-consistent excitation of slow magneto-acoustic body waves (slow modes) in a magnetic flux concentration. We find that the convective downdrafts in the close surroundings of a two-dimensional flux slab “pump” the plasma inside it in the downward direction. This action produces a downflow inside the flux slab, which encompasses ever higher layers, causing an upwardly propagating rarefaction wave. The slow mode, excited by the adiabatic compression of the downflow near the optical surface, travels along the magnetic field in the upward direction at the tube speed. It develops into a shock wave at chromospheric heights, where it dissipates, lifts the transition region, and produces an offspring in the form of a compressive wave that propagates further into the corona. In the wake of downflows and propagating shock waves, the atmosphere inside the flux slab in the chromosphere and higher tends to oscillate with a period of ν ≈ 4 mHz. We conclude that this process of “magnetic pumping” is a most plausible mechanism for the direct generation of longitudinal chromospheric and coronal compressive waves within magnetic flux concentrations, and it may provide an important heat source in the chromosphere. It may also be responsible for certain types of dynamic fibrils.

  3. Sausage Mode Propagation in a Thick Magnetic Flux Tube

    CERN Document Server

    Pardi, Anabele-Linda; Marcu, Alexandru; Orza, Beniamin

    2013-01-01

    The aim of this paper is to model the propagation of slow magnetohydrodynamic (MHD) sausage waves in a thick expanding magnetic flux tube in the context of the quiescent (VAL C) solar atmosphere. The propagation of these waves is found to be described by the Klein-Gordon equation. Using the governing MHD equations and the VAL C atmosphere model we study the variation of the cut-off frequency along and across the magnetic tube guiding the waves. Due to the radial variation of the cut-off frequency the flux tubes act as low frequency filters for waves.

  4. Advection of magnetic flux by accretion disks around neutron stars

    Science.gov (United States)

    Flores-Tulian, S.; Reisenegger, A.

    The aim of our research is to address why millisecond pulsars have relatively weak surface magnetic fields, of about 10^8 G, with a narrow spread. We propose that the accretion of plasma from the companion star fully screens the original neutron star field, but the accretion disk carries additional magnetic flux from the companion star, or itself can generate field by means of dynamo processes. For a strongly magnetized star, the field prevents the disk from approaching the star. The accretion is along the field lines and deposits the matter on the polar cap. Then, the accreted plasma flows, dragging with itself the magnetic field lines, from the pole to the equator (Payne & Melatos 2004). In a following stage, when the star becomes non-magnetic, because the field has been buried, the disk touches the star. We suggest that some effective mechanism of magnetic flux transport such as that proposed by Spruit & Uzdensky 2005 (or Bisnovatyi-Kogan & Lovelace 2007), operates and necessarily leads to a "strongly magnetized disk''. It becomes laminar because the magneto-rotational instability saturates (it is considered to be responsible for turbulence in the disk), and the magnetic difussivity is negligible. Then, the loss of angular momentum allowing the accretion is only caused by the magneto-centrifugal disk-wind (Blandford & Payne 1982). Meanwhile, the wind-driven transport of the magnetic flux by the disk re-magnetizes the star. This process continues until the Lorentz force due to the star's magnetic field forbids any further accretion of matter and magnetic flux, in the Ideal Magneto-Hydro-Dynamics approach. Additional of material can fall onto the star (but at lower rate) if some instability process sets in, allowing the diffusion of mass through the magnetic field lines (e.g the Interchange Instability, Spruit & Taam 1990). All these processes might lead to an asymptotic magnetic field of 10^8 G,as is inferred from observations. We are developing a self

  5. Magnetic Flux Cancelation as the Trigger of Solar Quiet-region Coronal Jets

    Science.gov (United States)

    Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.; Chakrapani, Prithi

    2016-11-01

    We report observations of 10 random on-disk solar quiet-region coronal jets found in high-resolution extreme ultraviolet (EUV) images from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly and having good coverage in magnetograms from the SDO/Helioseismic and Magnetic Imager (HMI). Recent studies show that coronal jets are driven by the eruption of a small-scale filament (called a minifilament). However, the trigger of these eruptions is still unknown. In the present study, we address the question: what leads to the jet-driving minifilament eruptions? The EUV observations show that there is a cool-transition-region-plasma minifilament present prior to each jet event and the minifilament eruption drives the jet. By examining pre-jet evolutionary changes in the line of sight photospheric magnetic field, we observe that each pre-jet minifilament resides over the neutral line between majority-polarity and minority-polarity patches of magnetic flux. In each of the 10 cases, the opposite-polarity patches approach and merge with each other (flux reduction between 21% and 57%). After several hours, continuous flux cancelation at the neutral line apparently destabilizes the field holding the cool-plasma minifilament to erupt and undergo internal reconnection, and external reconnection with the surrounding coronal field. The external reconnection opens the minifilament field allowing the minifilament material to escape outward, forming part of the jet spire. Thus, we found that each of the 10 jets resulted from eruption of a minifilament following flux cancelation at the neutral line under the minifilament. These observations establish that magnetic flux cancelation is usually the trigger of quiet-region coronal jet eruptions.

  6. Magnetic field generation from shear flow in flux ropes

    Science.gov (United States)

    Intrator, T. P.; Sears, J.; Gao, K.; Klarenbeek, J.; Yoo, C.

    2012-10-01

    In the Reconnection Scaling Experiment (RSX) we have measured out of plane quadrupole magnetic field structure in situations where magnetic reconnection was minimal. This quadrupole out of plane magnetic signature has historically been presumed to be the smoking gun harbinger of reconnection. On the other hand, we showed that when flux ropes bounced instead of merging and reconnecting, this signature could evolve. This can follow from sheared fluid flows in the context of a generalized Ohms Law. We reconstruct a shear flow model from experimental data for flux ropes that have been experimentally well characterized in RSX as screw pinch equilibria, including plasma ion and electron flow, with self consistent profiles for magnetic field, pressure, and current density. The data can account for the quadrupole field structure.

  7. FLUXCAP: A flux-coupled ac/dc magnetizing device

    CERN Document Server

    Gopman, Daniel B; Kent, Andrew D

    2012-01-01

    We report on an instrument for applying ac and dc magnetic fields by capturing the flux from a rotating permanent magnet and projecting it between two adjustable pole pieces. This can be an alternative to standard electromagnets for experiments with small samples or in probe stations in which an applied magnetic field is needed locally, with advantages that include a compact form-factor, very low power requirements and dissipation as well as fast field sweep rates. This flux capture instrument (FLUXCAP) can produce fields from -400 to +400 mT, with field resolution less than 1 mT. It generates static magnetic fields as well as ramped fields, with ramping rates as high as 10 T/s. We demonstrate the use of this apparatus for studying the magnetotransport properties of spin-valve nanopillars, a nanoscale device that exhibits giant magnetoresistance.

  8. Experimental Results from Railgun Firings Involving Magnetic Flux Probes.

    Science.gov (United States)

    1986-12-01

    report is unlimited KEYWORDS Railgun Accelerators Current Distribution Electromagnetic Launchers Magnetic Fields Plasma Armature COSATI GROUPS 2009 1906...series are presented. 2 3. EXPERIMENTAL DETAILS The power source for the RAPID railgun fi] used in the MRAP series consisted of a 2.0 mF capacitor bank...MEUKOURNE, VICTORIA TECHNICAL NOTE MRL-TN-509 EXPERIMENTAL RESULTS FROM RAILGUN FIRINGS INVOLVING MAGNETIC FLUX PROBES V. Kowalenko THE UNITED STATES

  9. Catastrophe of coronal magnetic flux ropes in fully open magnetic field

    Institute of Scientific and Technical Information of China (English)

    LI; Guoqiang(李国强); HU; Youqiu(胡友秋)

    2002-01-01

    The catastrophe of coronal magnetic flux ropes is closely related to solar explosive phenomena, such as prominence eruptions, coronal mass ejections, and two-ribbon solar flares. Using a 2-dimensional, 3-component ideal MHD model in Cartesian coordinates, numerical simulations are carried out to investigate the equilibrium property of a coronal magnetic flux rope which is embedded in a fully open background magnetic field. The flux rope emerges from the photosphere and enters the corona with its axial and annular magnetic fluxes controlled by a single "emergence parameter". For a flux rope that has entered the corona, we may change its axial and annular fluxes artificially and let the whole system reach a new equilibrium through numerical simulations. The results obtained show that when the emergence parameter, the axial flux, or the annular flux is smaller than a certain critical value, the flux rope is in equilibrium and adheres to the photosphere. On the other hand, if the critical value is exceeded, the flux rope loses equilibrium and erupts freely upward, namely, a catastrophe takes place. In contrast with the partly-opened background field, the catastrophic amplitude is infinite for the case of fully-opened background field.

  10. Radiation-induced magnetization reversal causing a large flux loss in undulator permanent magnets.

    Science.gov (United States)

    Bizen, Teruhiko; Kinjo, Ryota; Hasegawa, Teruaki; Kagamihata, Akihiro; Kida, Yuichiro; Seike, Takamitsu; Watanabe, Takahiro; Hara, Toru; Itoga, Toshiro; Asano, Yoshihiro; Tanaka, Takashi

    2016-11-29

    We report an unexpectedly large flux loss observed in permanent magnets in one of the undulators operated in SACLA, the x-ray free electron laser facility in Japan. Characterizations of individual magnets extracted from the relevant undulator have revealed that the flux loss was caused by a homogeneous magnetization reversal extending over a wide area, but not by demagnetization of individual magnets damaged by radiation. We show that the estimated flux-loss rate is much higher than what is reported in previous papers, and its distribution is much more localized to the upstream side. Results of numerical and experimental studies carried out to validate the magnetization reversal and quantify the flux loss are presented, together with possible countermeasures against rapid degradation of the undulator performance.

  11. Estimating effects from trapped magnetic fluxes in superconducting magnetic levitation measurement

    Institute of Scientific and Technical Information of China (English)

    Masakazu Nakanishi

    2008-01-01

    Superconducting magnetic levitation measurement is one of the most promising approaches to define mass standard based on the fundamental physical constants. However, the present system has unknown factors causing error larger than 50 ppm. We examined the effects of magnetic fluxes trapped in the superconducting coil and the superconducting floating body. When fluxes were trapped in either coil or floating body, their effects were able to be cancelled by reversing polarities of current and magnetic field, as had been believed. However, fluxes trapped in both coil and body induced an attractive force between them and caused error. In order to reduce the fluxes, the coil and the floating body should be cooled in low magnetic field in magnetic and electromagnetic shields.

  12. Radiation-induced magnetization reversal causing a large flux loss in undulator permanent magnets

    Science.gov (United States)

    Bizen, Teruhiko; Kinjo, Ryota; Hasegawa, Teruaki; Kagamihata, Akihiro; Kida, Yuichiro; Seike, Takamitsu; Watanabe, Takahiro; Hara, Toru; Itoga, Toshiro; Asano, Yoshihiro; Tanaka, Takashi

    2016-11-01

    We report an unexpectedly large flux loss observed in permanent magnets in one of the undulators operated in SACLA, the x-ray free electron laser facility in Japan. Characterizations of individual magnets extracted from the relevant undulator have revealed that the flux loss was caused by a homogeneous magnetization reversal extending over a wide area, but not by demagnetization of individual magnets damaged by radiation. We show that the estimated flux-loss rate is much higher than what is reported in previous papers, and its distribution is much more localized to the upstream side. Results of numerical and experimental studies carried out to validate the magnetization reversal and quantify the flux loss are presented, together with possible countermeasures against rapid degradation of the undulator performance.

  13. Laser-driven magnetic-flux compression in high-energy-density plasmas.

    Science.gov (United States)

    Gotchev, O V; Chang, P Y; Knauer, J P; Meyerhofer, D D; Polomarov, O; Frenje, J; Li, C K; Manuel, M J-E; Petrasso, R D; Rygg, J R; Séguin, F H; Betti, R

    2009-11-20

    The demonstration of magnetic field compression to many tens of megagauss in cylindrical implosions of inertial confinement fusion targets is reported for the first time. The OMEGA laser [T. R. Boehly, Opt. Commun. 133, 495 (1997)10.1016/S0030-4018(96)00325-2] was used to implode cylindrical CH targets filled with deuterium gas and seeded with a strong external field (>50 kG) from a specially developed magnetic pulse generator. This seed field was trapped (frozen) in the shock-heated gas fill and compressed by the imploding shell at a high implosion velocity, minimizing the effect of resistive flux diffusion. The magnetic fields in the compressed core were probed via proton deflectrometry using the fusion products from an imploding D3He target. Line-averaged magnetic fields between 30 and 40 MG were observed.

  14. Zero modes on cosmic strings in an external magnetic field

    CERN Document Server

    Ferrer, F; Starkman, G D; Vachaspati, T; Ferrer, Francesc; Mathur, Harsh; Starkman, Glenn D.; Vachaspati, Tanmay

    2006-01-01

    A classical analysis suggests that an external magnetic field can cause trajectories of charge carriers on a superconducting domain wall or cosmic string to bend, thus expelling charge carriers with energy above the mass threshold into the bulk. We study this process by solving the Dirac equation for a fermion of mass $m_f$ and charge $e$, in the background of a domain wall and a magnetic field of strength $B$. We find that the modes of the charge carriers get shifted into the bulk, in agreement with classical expectations. However the dispersion relation for the zero modes changes dramatically -- instead of the usual linear dispersion relation, $\\omega_k =k$, the new dispersion relation is well fit by $\\omega \\approx m_f tanh(k/k_*)$ where $k_*=m_f$ for a thin wall in the weak field limit, and $k_*=eBw$ for a thick wall of width $w$. This result shows that the energy of the charge carriers on the domain wall remains below the threshold for expulsion even in the presence of an external magnetic field. If char...

  15. Behavior of Compact Toroid in the External Magnetic Fields

    Science.gov (United States)

    Fukumoto, N.; Ioroi, A.; Nagata, M.; Uyama, T.

    1999-11-01

    We have investigated the possibility of refueling and density control of tokamak plasmas by the spheromak-type Compact Toroid (CT) injection in the JFT-2M tokamak in collaboration with JAERI. We demonstrated the CT injection into OH plasmas and observed the core penetration at B_T=0.8 T. The tokamak electron density increased ~0.2× 10^19m-3 at a rate of 2× 10^21m-3/s. We also observed the decrease of the CT velocity by the external magnetic field of the tokamak, which is applied across the CT acceleration region. We have examined the behavior of the CT translated in the external fields B_ext using the magnetic probes and the fast framing camera at Himeji Inst. of tech.. CT plasma in the acceleration region is deformed by the Lorentz force of Jg × B_ext, where Jg is the gun current for CT acceleration. The magnetic field structures of a long CT in the drift region has been revealed to be the mixed relaxed state of m=0 and m=1. Results from CT acceleration and injection in a transverse field will be presented.

  16. Magnetic flux periodicities and finite momentum pairing in unconventional superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Loder, Florian

    2009-12-22

    This work contains a thorough study of the magnetic flux periodicity of loops of conventional and unconventional, especially d-wave, superconductors. Although already in 1961, several independent works showed that the flux period of a conventional superconducting loop is the superconducting flux quantum hc/2e, this question has never been investigated deeply for unconventional superconductors. And indeed, we show here that d-wave superconducting loops show a basic flux period of the normal flux quantum hc/e, a property originating from the nodal quasi-particle states. This doubling of the flux periodicity is best visible in the persistent current circulating in the loop, and it affects other properties of the superconductor such as the periodicity of d-wave Josephson junctions. In the second part of this work, the theory of electron pairing with finite center-of-mass momentum, necessary for the description of superconducting loops, is extended to systems in zero magnetic field. We show that even in the field free case, an unconventional pairing symmetry can lead to a superconducting ground state with finite-momentum electron pairs. Such a state has an inhomogeneous charge density and therefore is a basis for the description of coexistence of superconductivity and stripe order. (orig.)

  17. Basal magnetic flux and the local solar dynamo

    CERN Document Server

    Stenflo, J O

    2012-01-01

    The average unsigned magnetic flux density in magnetograms of the quiet Sun is generally dominated by instrumental noise. Due to the entirely different scaling behavior of the noise and the solar magnetic pattern it has been possible to determine the standard deviation of the Gaussian noise distribution and remove the noise contribution from the average unsigned flux density for the whole 15-yr SOHO/MDI data set and for a selection of SDO/HMI magnetograms. There is a very close correlation between the MDI disk-averaged unsigned vertical flux density and the sunspot number, and regression analysis gives a residual level of 2.7 G when the sunspot number is zero. The selected set of HMI magnetograms, which spans the most quiet phase of solar activity, has a lower limit of 3.0 G to the noise-corrected average flux density. These apparently cycle-independent levels may be identified as a basal flux density, which represents an upper limit to the possible flux contribution from a local dynamo, but not evidence for ...

  18. Holographic description of strongly correlated electrons in external magnetic fields

    CERN Document Server

    Gubankova, E; Cubrovic, M; Schalm, K; Schijven, P; Zaanen, J

    2013-01-01

    We study the Fermi level structure of (2+1)-dimensional strongly interacting electron systems in external magnetic field using the AdS/CFT correspondence. The gravity dual of a finite density fermion system is a Dirac field in the background of the dyonic AdS-Reissner-Nordstrom black hole. In the probe limit the magnetic system can be reduced to the non-magnetic one, with Landau-quantized momenta and rescaled thermodynamical variables. We find that at strong enough magnetic fields, the Fermi surface vanishes and the quasiparticle is lost either through a crossover to conformal regime or through a phase transition to an unstable Fermi surface. In the latter case, the vanishing Fermi velocity at the critical magnetic field triggers the non-Fermi liquid regime with unstable quasiparticles and a change in transport properties of the system. We associate it with a metal-"strange metal" phase transition. We compute the DC Hall and longitudinal conductivities using the gravity-dressed fermion propagators. As expecte...

  19. Scanning SQUID microscopy for magnetic flux systems

    CERN Document Server

    Suzuki, J I; Hata, Y

    2003-01-01

    Recently, vortices confined into micro-scale superconductors with shapes like a disk, triangle, square, etc., have attracted much attention because of the quantum phase transition of the self-organized vortex arrangement occurring within such geometrical constraints. Such a transition can be observed using a scanning SQUID microscope with high spatial resolution. We have successfully improved spatial resolution by incorporating a microfabrication technique that reduces both the size of the pick-up coil of the micro DC-SQUID and the standoff distance between the pick-up coil and the sample surface. Using this microscope, we have studied vortex arrangements in micro-scale superconductors made of Nb and YBa sub 2 Cu sub 3 O sub 7 sub - subdelta films with various sizes and geometrical shapes. A peculiar oscillating behavior of diamagnetic magnetization corresponding to the particular vortex state was observed.

  20. Weibel instability in a plasma with nonzero external magnetic field

    Directory of Open Access Journals (Sweden)

    O. A. Pokhotelov

    2012-07-01

    Full Text Available The theory of the Weibel instability is generalized for the case of a plasma immersed in a nonzero external magnetic field. It is shown that the presence of this external field modifies the dispersion relation for this mode which now possesses a nonzero frequency. The explicit expression for the real and imaginary parts of the frequency is then calculated. It turns out that the linear growth rate remains unchanged, whereas the frequency becomes nonzero due to the finite value of the electron cyclotron frequency. The frequency of the Weibel mode is found to be proportional to the electron temperature anisotropy. The formal similarity of the Weibel and drift-mirror instabilities is outlined.

  1. High-resolution dichroic imaging of magnetic flux distributions in superconductors with scanning x-ray microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Ruoss, Stephen; Stahl, Claudia; Weigand, Markus; Schuetz, Gisela [Max-Planck-Institut fuer Intelligente Systeme, Stuttgart (Germany); Albrecht, Joachim [Research Institute for Innovative Surfaces, FINO, Aalen University (Germany)

    2015-07-01

    The penetration of magnetic flux into the high-temperature superconductor YBCO has been observed using a new high-resolution technique based on X-ray magnetic circular dichroism (XMCD). Superconductors coated with thin soft magnetic layers of CoFeB are observed in a scanning x-ray microscope providing cooling of the sample down to 83 K under the influence of external magnetic fields. Resulting electrical currents create an inhomogeneous magnetic field distribution above the superconductor which leads to a local reorientation of the ferromagnetic layer. X-ray absorption measurements with circular polarized radiation allows the analysis of the magnetic flux distribution in the superconductor via the ferromagnetic layer. In this work we present first images taken at 83K with high spatial resolution in the nanoscale.

  2. Flux line depinning in a magnet-superconductor levitation system

    Science.gov (United States)

    Terentiev, A. N.; Hull, J. R.; De Long, L. E.

    The AC loss characteristics of a magnet-superconductor system were studied with the magnet fixed to the free end of an oscillating cantilever located near a stationary melt-textured YBCO pellet. Below a threshold AC field amplitude ≈2 Oe, the dissipation of the oscillator is amplitude-independent, characteristic of a linear, non-hysteretic regime. Above threshold, dissipation increases with amplitude, reflecting the depinning and hysteretic motion of flux lines. The threshold AC field is an order of magnitude higher than that measured for the same YBCO material via AC susceptometry in a uniform DC magnetic field. A partial lock-in of flux lines between YBCO ab planes is proposed as the mechanism for the substantial increase of the depinning threshold.

  3. A charged spinless particle in scalar–vector harmonic oscillators with uniform magnetic and Aharonov–Bohm flux fields

    Directory of Open Access Journals (Sweden)

    Sameer M. Ikhdair

    2014-10-01

    Full Text Available The two-dimensional solution of the spinless Klein–Gordon (KG equation for scalar–vector harmonic oscillator potentials with and without the presence of constant perpendicular magnetic and Aharonov–Bohm (AB flux fields is studied within the asymptotic function analysis and Nikiforov–Uvarov (NU method. The exact energy eigenvalues and normalized wave functions are analytically obtained in terms of potential parameters, magnetic field strength, AB flux field and magnetic quantum number. The results obtained by using different Larmor frequencies are compared with the results in the absence of both magnetic field (ωL = 0 and AB flux field (ξ = 0 case. Effects of external fields on the non-relativistic energy eigenvalues and wave functions solutions are also precisely presented.

  4. Adaptive control of an active magnetic bearing with external disturbance.

    Science.gov (United States)

    Dong, Lili; You, Silu

    2014-09-01

    Adaptive back stepping control (ABC) is originally applied to a linearized model of an active magnetic bearing (AMB) system. Our control goal is to regulate the deviation of the magnetic bearing from its equilibrium position in the presence of an external disturbance and system uncertainties. Two types of ABC methods are developed on the AMB system. One is based on full state feedback, for which displacement, velocity, and current states are assumed available. The other one is adaptive observer based back stepping controller (AOBC) where only displacement output is measurable. An observer is designed for AOBC to estimate velocity and current states of AMB. Lyapunov approach proves the stabilities of both regular ABC and AOBC. Simulation results demonstrate the effectiveness and robustness of two controllers. Copyright © 2013 ISA. Published by Elsevier Ltd. All rights reserved.

  5. Helicity Transformation under the Collision and Merging of Magnetic Flux Ropes

    Science.gov (United States)

    Dehaas, Timothy

    2016-10-01

    A magnetic flux rope is a tube-like, current carrying plasma embedded in an external magnetic field. The magnetic field lines resemble threads in a rope, which vary in pitch according to radius. Flux ropes are ubiquitous in astrophysical plasmas, and bundles of these structures play an important role in the dynamics of the space environment. They are observed in the solar atmosphere and near-earth environment where they are seen to twist, merge, tear, and writhe. In this MHD context, their global dynamics are bound by rules of magnetic helicity conservation, unless, under a non-ideal process, helicity is transformed through magnetic reconnection, turbulence, or localized instabilities. These processes are tested under experimental conditions in the Large Plasma Device (LAPD). The device is a twenty-meter long, one-meter diameter, cylindrical vacuum vessel designed to generate a highly reproducible, magnetized plasma. Reliable shot-to-shot repetition of plasma parameters and over four hundred diagnostic ports enable the collection of volumetric datasets (measurements of ne, Te, Vp, B, J, E, uflow) as two kink-unstable flux ropes form, move, collide, and merge. Similar experiments on the LAPD have utilized these volumetric datasets, visualizing magnetic reconnection through a topological quasi-separatrix layer, or QSL. This QSL is shown to be spatially coincident with the reconnection rate, ∫ E . dl , and oscillates (although out of phase) with global helicity. Magnetic helicity is observed to have a negative sign and its counterpart, cross helicity, a positive one. These quantities oscillate 8% peak-to-peak, and the changes in helicity are visualized as 1) the transport of helicity (ϕB + E × A) and 2) the dissipation of the helicity - 2 E . B . This work is supported by LANL-UC research Grant and done at the Basic Plasma Science Facility, which is funded by DOE and NSF.

  6. RECONCILING MODELS OF LUMINOUS BLAZARS WITH MAGNETIC FLUXES DETERMINED BY RADIO CORE-SHIFT MEASUREMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Nalewajko, Krzysztof; Begelman, Mitchell C. [JILA, University of Colorado and National Institute of Standards and Technology, 440 UCB, Boulder, CO 80309 (United States); Sikora, Marek, E-mail: knalew@stanford.edu [Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw (Poland)

    2014-11-20

    Estimates of magnetic field strength in relativistic jets of active galactic nuclei, obtained by measuring the frequency-dependent radio core location, imply that the total magnetic fluxes in those jets are consistent with the predictions of the magnetically arrested disk (MAD) scenario of jet formation. On the other hand, the magnetic field strength determines the luminosity of the synchrotron radiation, which forms the low-energy bump of the observed blazar spectral energy distribution (SED). The SEDs of the most powerful blazars are strongly dominated by the high-energy bump, which is most likely due to the external radiation Compton mechanism. This high Compton dominance may be difficult to reconcile with the MAD scenario, unless (1) the geometry of external radiation sources (broad-line region, hot-dust torus) is quasi-spherical rather than flat, or (2) most gamma-ray radiation is produced in jet regions of low magnetization, e.g., in magnetic reconnection layers or in fast jet spines.

  7. Reconciling models of luminous blazars with magnetic fluxes determined by radio core shift measurements

    CERN Document Server

    Nalewajko, Krzysztof; Begelman, Mitchell C

    2014-01-01

    Estimates of magnetic field strength in relativistic jets of active galactic nuclei (AGN), obtained by measuring the frequency-dependent radio core location, imply that the total magnetic fluxes in those jets are consistent with the predictions of the magnetically-arrested disk (MAD) scenario of jet formation. On the other hand, the magnetic field strength determines the luminosity of the synchrotron radiation, which forms the low-energy bump of the observed blazar spectral energy distribution (SED). The SEDs of the most powerful blazars are strongly dominated by the high-energy bump, which is most likely due to the external radiation Compton (ERC) mechanism. This high Compton dominance may be difficult to reconcile with the MAD scenario, unless 1) the geometry of external radiation sources (broad-line region, hot-dust torus) is quasi-spherical rather than flat, or 2) most gamma-ray radiation is produced in jet regions of low magnetization, e.g., in magnetic reconnection layers or in fast jet spines.

  8. Tuning an rf-SQUID flux qubit system's potential with magnetic flux bias

    Institute of Scientific and Technical Information of China (English)

    Hua Tao; Xu Wei-Wei; Shi Jian-Xin; An De-Yue; Sun Guo-Zhu; Yu Yang; Wu Pei-Heng

    2012-01-01

    At an extremely low temperature of 20 mK,we measured the loop current in a tunable rf superconducting quantum interference device (SQUID) with a dc-SQUID.By adjusting the magnetic flux applied to the rf-SQUID loop (φf) and the small dc-SQUID (φcjjf),respectively,the potential shape of the system can be fully controlled in situ.Variation in the transition step and overlap size in the switching current with a barrier flux bias are analyzed,from which we can obtain some relevant device parameters and build a model to explain the experimental phenomenon.

  9. Female external genitalia on fetal magnetic resonance imaging.

    Science.gov (United States)

    Nemec, S F; Nemec, U; Weber, M; Rotmensch, S; Brugger, P C; Kasprian, G; Krestan, C R; Rimoin, D L; Graham, J M; Prayer, D

    2011-12-01

    To characterize the normal development of the female external genitalia on fetal magnetic resonance imaging (MRI). This retrospective study included MRI examinations of 191 female fetuses (20-36 gestational weeks) with normal anatomy or minor abnormalities, following suspicion of anomalies on prenatal ultrasound examination. Using a 1.5-Tesla unit, the bilabial diameter was measured on T2-weighted sequences. Statistical description, as well as correlation and regression analyses, was used to evaluate bilabial diameter in relation to gestational age. MRI measurements were compared with published ultrasound data. The morphological appearance and signal intensities of the external genitalia were also assessed. Mean bilabial diameters, with 95% CIs and percentiles, were defined. The bilabial diameter as a function of gestational age was expressed by the regression equation: bilabial diameter = - 11.336 + 0.836 × (gestational age in weeks). The correlation coefficient, r = 0.782, was statistically significant (P < 0.001). Bilabial diameter on MRI was not significantly different from that on ultrasound (P < 0.001). In addition, on MRI we observed changes in morphology of the external genitalia and in signal intensities with increasing gestational age. We have provided a reference range of fetal bilabial diameter on MRI, which, in addition to ultrasound findings, may be helpful in the identification of genital anomalies. Copyright © 2011 ISUOG. Published by John Wiley & Sons, Ltd.

  10. Turbulence-induced magnetic flux asymmetry at nanoscale junctions.

    Science.gov (United States)

    Bushong, Neil; Pershin, Yuriy; Di Ventra, Massimiliano

    2007-11-30

    It was recently predicted [J. Phys. Condens. Matter 18, 11059 (2006)] that turbulence of electron flow may develop at nonadiabatic nanoscale junctions under appropriate conditions. Here we show that such an effect leads to an asymmetric current-induced magnetic field on the two sides of an otherwise symmetric junction. We propose that measuring the fluxes ensuing from these fields across two surfaces placed at the two sides of the junction would provide direct and noninvasive evidence of the transition from laminar to turbulent electron flow. The flux asymmetry is predicted to first increase, reach a maximum, and then decrease with increasing current, i.e., with increasing amount of turbulence.

  11. The Solar Internetwork. II. Magnetic Flux Appearance and Disappearance Rates

    CERN Document Server

    Gošić, Milan; Iniesta, Jose Carlos Del Toro; Suárez, David Orozco; Katsukawa, Yukio

    2016-01-01

    Small-scale internetwork magnetic fields are important ingredients of the quiet Sun. In this paper we analyze how they appear and disappear on the solar surface. Using high resolution \\textit{Hinode} magnetograms, we follow the evolution of individual magnetic elements in the interior of two supergranular cells at the disk center. From up to 38 hr of continuous measurements, we show that magnetic flux appears in internetwork regions at a rate of $120\\pm3$~Mx~cm$^{-2}$~day$^{-1}$ ($7.3 \\pm 0.2 \\times 10^{24}$~Mx~day$^{-1}$ over the entire solar surface). Flux disappears from the internetwork at a rate of $125 \\pm 6$~Mx~cm$^{-2}$~day$^{-1}$ ($7.6\\pm 0.4 \\times 10^{24}$~Mx~day$^{-1}$) through fading of magnetic elements, cancellation between opposite-polarity features, and interactions with network patches, which converts internetwork elements into network features. Most of the flux is lost through fading and interactions with the network, at nearly the same rate of about 50~Mx~cm$^{-2}$~day$^{-1}$. Our results ...

  12. MAGNETIC FLUX CONSERVATION IN THE HELIOSHEATH INCLUDING SOLAR CYCLE VARIATIONS OF MAGNETIC FIELD INTENSITY

    Energy Technology Data Exchange (ETDEWEB)

    Michael, A. T.; Opher, M. [Astronomy Department, Boston University, Boston, MA 02115 (United States); Provornikova, E. [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States); Richardson, J. D. [Kavli Center for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Tóth, G., E-mail: atmich@bu.edu, E-mail: mopher@bu.edu, E-mail: elena.a.provornikova@nasa.gov, E-mail: jdr@space.mit.edu, E-mail: gtoth@umich.edu [University of Michigan, Ann Arbor, MI 48109 (United States)

    2015-04-10

    In the heliosheath (HS), Voyager 2 has observed a flow with constant radial velocity and magnetic flux conservation. Voyager 1, however, has observed a decrease in the flow’s radial velocity and an order of magnitude decrease in magnetic flux. We investigate the role of the 11 yr solar cycle variation of the magnetic field strength on the magnetic flux within the HS using a global 3D magnetohydrodynamic model of the heliosphere. We use time and latitude-dependent solar wind velocity and density inferred from Solar and Heliospheric Observatory/SWAN and interplanetary scintillations data and implemented solar cycle variations of the magnetic field derived from 27 day averages of the field magnitude average of the magnetic field at 1 AU from the OMNI database. With the inclusion of the solar cycle time-dependent magnetic field intensity, the model matches the observed intensity of the magnetic field in the HS along both Voyager 1 and 2. This is a significant improvement from the same model without magnetic field solar cycle variations, which was over a factor of two larger. The model accurately predicts the radial velocity observed by Voyager 2; however, the model predicts a flow speed ∼100 km s{sup −1} larger than that derived from LECP measurements at Voyager 1. In the model, magnetic flux is conserved along both Voyager trajectories, contrary to observations. This implies that the solar cycle variations in solar wind magnetic field observed at 1 AU does not cause the order of magnitude decrease in magnetic flux observed in the Voyager 1 data.

  13. In-Plane Si Nanowire Growth Mechanism in Absence of External Si Flux.

    Science.gov (United States)

    Curiotto, Stefano; Leroy, Frédéric; Cheynis, Fabien; Müller, Pierre

    2015-07-01

    We report on a new mechanism of nanowire formation: during Au deposition on Si(110) substrates, Au-Si droplets grow, move spontaneously, and fabricate a Si nanowire behind them in the absence of Si external flux. Nanowires are formed by Si dissolved from the substrate at the advancing front of the droplets and transported backward to the crystallization front. The droplet shape is determined by the Si etching anisotropy. The nanowire formation can be tuned by changing experimental parameters like substrate temperature and Au deposition rate.

  14. Mathematical model for prediction of pyrolysis and ignition of wood under external heat flux

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The pyrolysis and ignition of combustible materials is an important aspect of the processes taking place in an unwanted fire. A prediction model presented in this paper is to study pyrolysis and ignition time of wood under external heat flux. The solution of the model provides the temperature at each point of the solid and the local solid conversion. And the time to ignition of the wood is predicted with the solution of surface temperature. In general, a good agreement between experimental and theoretical results is obtained.

  15. Magnetic anisotropy of single Mn acceptors in GaAs in an external magnetic field

    OpenAIRE

    Bozkurt, M Murat; Mahani, MR; Studer, P; Tang, J-M; Schofield, SR; Curson, NJ; Flatté, ME Michael; Silov, AY Andrei; Hirjibehedin, CF; Canali, CM; Koenraad, PM Paul

    2013-01-01

    We investigate the effect of an external magnetic field on the physical properties of the acceptor hole states associated with single Mn acceptors placed near the (110) surface of GaAs. Crosssectional scanning tunneling microscopy images of the acceptor local density of states (LDOS) show that the strongly anisotropic hole wavefunction is not significantly affected by a magnetic field up to 6 T. These experimental results are supported by theoretical calculations based on a tightbinding model...

  16. Spontaneous axisymmetry breaking of Saturn's external magnetic field

    CERN Document Server

    Goldreich, P; Goldreich, Peter; Farmer, Alison J.

    2006-01-01

    Saturn's magnetic field is remarkably axisymmetric. Its dipole axis is inclined by less than 0.2 deg with respect to its rotation axis. Rotationally driven convection of magnetospheric plasma breaks the axisymmetry of its external magnetic field. Field aligned currents transfer angular momentum from the planet to a tongue of outflowing plasma. This transfer slows the rate of rotation of the ionosphere relative to that of the underlying atmosphere. The currents are the source for the non-axisymmetric components of the field. The common rotation rates of these components and Saturn's kilometric radio (SKR) bursts is that of the plasma near the orbit of Enceladus, and by extension the rotation rate in the ionosphere to which this plasma is coupled. That rate tells us nothing about the rotation rate of Saturn's deep interior. Of that we remain ignorant. Magnetic perturbations with magnitudes similar to those observed by Cassini are produced for Mdot ~ 10^4 g/s, a value similar to estimates for the rate of product...

  17. Reconnection Experiments with Flux Ropes near 3D Magnetic Nulls

    Science.gov (United States)

    Vrublevskis, A.; Egedal, J.; Le, A.

    2012-12-01

    Magnetic reconnection has been predominantly investigated in two dimensions. However, depending on the topology and geometry of the magnetic field, a rich collection of magnetic reconnection scenarios is possible in 3D including reconnection at magnetic nulls. Nulls have been reported in the solar corona [1] and in Earth's magnetosphere [2], yet there are a limited number of laboratory observations. At the Versatile Toroidal Facility (VTF) we have implemented a new magnetic geometry with a pair of 3D null points in the background toroidal field. We form a flux rope along the background field and observe it to rapidly restructure and rewire as the nulls develop. We can adjust the topology of the configuration from one where a field line connects the nulls to one where the nulls are no longer linked. A suit of diagnostics will be deployed and results presented for the dynamics of the flux rope. [1] Fletcher et al., Astrophys. J. 554, 451(2001) [2] Xiao et al., Nat. Phys. 2, 478 (2006)

  18. Evidence of Magnetic Helicity in Emerging Flux and Associated Flare

    CERN Document Server

    Chandra, R; Aulanier, G; Malherbe, J M

    2009-01-01

    The aim of this paper is to look at the magnetic helicity structure of an emerging active region and show that both emergence and flaring signatures are consistent with a same sign for magnetic helicity. We present a multi-wavelength analysis of an M1.6 flare occurring in the active region NOAA 10365 on 27 May, 2003, in which a large new bipole emerges in a decaying active region. The diverging flow pattern and the "tongue" shape of the magnetic field in the photosphere with elongated polarities are highly suggestive of the emergence of a twisted flux tube. The orientation of these tongues indicates the emergence of a flux tube with a right hand twist, i.e. positive magnetic helicity. The flare signatures in the chromosphere are ribbons observed in H-alpha by the MSDP spectrograph in the Meudon solar tower and in 1600 A by TRACE. These ribbons have a `J' shape and are shifted along the inversion line. The pattern of these ribbons suggests that the flare was triggered by magnetic reconnection at coronal height...

  19. On Signatures of Twisted Magnetic Flux Tube Emergence

    CERN Document Server

    Dominguez, Santiago Vargas; Green, Lucie; van Driel-Gesztelyi, Lidia; Hood, Alan

    2011-01-01

    Recent studies of NOAA active region 10953, by Okamoto {\\it et al.} ({\\it Astrophys. J. Lett.} {\\bf 673}, 215, 2008; {\\it Astrophys. J.} {\\bf 697}, 913, 2009), have interpreted photospheric observations of changing widths of the polarities and reversal of the horizontal magnetic field component as signatures of the emergence of a twisted flux tube within the active region and along its internal polarity inversion line (PIL). A filament is observed along the PIL and the active region is assumed to have an arcade structure. To investigate this scenario, MacTaggart and Hood ({\\it Astrophys. J. Lett.} {\\bf 716}, 219, 2010) constructed a dynamic flux emergence model of a twisted cylinder emerging into an overlying arcade. The photospheric signatures observed by Okamoto {\\it et al.} (2008, 2009) are present in the model although their underlying physical mechanisms differ. The model also produces two additional signatures that can be verified by the observations. The first is an increase in the unsigned magnetic fl...

  20. Magnetic-flux dynamics of high-Tc superconductors in weak magnetic fields

    DEFF Research Database (Denmark)

    Il’ichev, E. V.; Jacobsen, Claus Schelde

    1994-01-01

    Aspects of magnetic-flux dynamics in different types of samples of the high-temperature superconductor YBa2Cu3Ox have been investigated in magnetic fields below 1 Oe and at 77 K. The experiments were carried out in an arrangement including a field coil, a flat sample perpendicular to the field...

  1. Magnetic Bipoles in Emerging Flux Regions on the Sun

    Science.gov (United States)

    Barth, C. S.; Livi, S. H. B.

    1990-11-01

    ABSTRACT. We analyse magnetograms and H-alpha filtergrams of an Emerging Flux Region. Small bipoles have been observed on the magnetograms emerging between opposite polarities. Separation velocities of the opposite poles for 45 bipoles observed on June 9, 1985 have been measured and are in the range 0.5 contribuciones de los bipolos emergentes. Key words: SUN-CHROMOSPHERE - SUN-MAGNETIC FIELDS

  2. Turbulence-induced magnetic flux asymmetry at nanoscale junctions

    OpenAIRE

    2007-01-01

    It was recently predicted [J. Phys.: Condens. Matter 18, 11059 (2006)] that turbulence of the electron flow may develop at nonadiabatic nanoscale junctions under appropriate conditions. Here we show that such an effect leads to an asymmetric current-induced magnetic field on the two sides of an otherwise symmetric junction. We propose that by measuring the fluxes ensuing from these fields across two surfaces placed at the two sides of the junction would provide direct and noninvasive evidence...

  3. Quench-induced trapping of magnetic flux in annular

    DEFF Research Database (Denmark)

    Aaroe, M.; Monaco, R.; Rivers, R.;

    2008-01-01

    over 4 orders of magnitude. After the quench the result of the spontaneous production of topological defects, trapped fluxons, is unambiguously observed as zero-field steps in the DC I-V characteristic of the junction. A power-law scaling behavior of trapping probability versus quench rate is found...... with a critical exponent of 0.5 (within experimental error). The main experimental challenges are to generate many identical quenches with accurate cooling rate, to automate data analysis and acquisition, and to suppress external magnetic fields and noise by passive magnetic shielding and compensation....

  4. Stability and Bifurcation in Magnetic Flux Feedback Maglev Control System

    Directory of Open Access Journals (Sweden)

    Wen-Qing Zhang

    2013-01-01

    Full Text Available Nonlinear properties of magnetic flux feedback control system have been investigated mainly in this paper. We analyzed the influence of magnetic flux feedback control system on control property by time delay and interfering signal of acceleration. First of all, we have established maglev nonlinear model based on magnetic flux feedback and then discussed hopf bifurcation’s condition caused by the acceleration’s time delay. The critical value of delayed time is obtained. It is proved that the period solution exists in maglev control system and the stable condition has been got. We obtained the characteristic values by employing center manifold reduction theory and normal form method, which represent separately the direction of hopf bifurcation, the stability of the period solution, and the period of the period motion. Subsequently, we discussed the influence maglev system on stability of by acceleration’s interfering signal and obtained the stable domain of interfering signal. Some experiments have been done on CMS04 maglev vehicle of National University of Defense Technology (NUDT in Tangshan city. The results of experiments demonstrate that viewpoints of this paper are correct and scientific. When time lag reaches the critical value, maglev system will produce a supercritical hopf bifurcation which may cause unstable period motion.

  5. Influence of High Harmonics of Magnetic Fields on Trapped Magnetic Fluxes in HTS Bulk

    Science.gov (United States)

    Yamagishi, K.; Miyagi, D.; Tsukamoto, O.

    Various kinds of HTS bulk motors are proposed and have been developed. Generally, those motors are driven by semiconductor inverters and currents fed to the armature windings contain high harmonics. Therefore, the bulks are exposed to high harmonics magnetic fields and AC losses are produced in the bulks. The AC losses deteriorate the efficiency of the motors and cause temperature rise of the bulks which decrease the trapped magnetic fluxes of the bulks. Usually, electro-magnetic shielding devices are inserted between the bulks and armature windings. However, the shielding devices degrade compactness of the motors. Therefore, it is important to have knowledge of the influence of the high harmonics magnetic fields on the AC losses and trapped magnetic fluxes of the bulk for optimum design of the shielding devices. In this work, the authors experimentally study the influence of high harmonics magnetic fields.

  6. Characteristics of Magnetic Tribology on High Flux Pair of Magnetic Driving Mechanism

    Institute of Scientific and Technical Information of China (English)

    ZHOUQiang; XURui-qing; XUHong-qiu

    2004-01-01

    The rectangle-like pulsed magnetic field acted on the rubbing pair was presents through analyzing the exciting property in the reciprocationg travel the test of wear in NG-x tester shows that the wear between the electromagnetic core and down magnetic board distributes in the high veloctity slip region of reciprocating travel,an the adhesive wear in the low velocity slip region nearby up and down dead points is depressed owing to the presence of high flux magnetic field.the lubrication by magnetic fluid with high permeability effectively reduces the friction and wear of high flux rubbing pair and mproves the conductiong property of magnetic circuit constructed by the rubbing pair which is beneficial to increase the operation performance of magnetic driving mechanism.

  7. Effect of Finite Larmor Radius on the Cosmic Ray Penetration into an Interplanetary Magnetic Flux Rope

    OpenAIRE

    Kubo, Yuki; Shimazu, Hironori

    2010-01-01

    We discuss a mechanism for cosmic ray penetration into an interplanetary magnetic flux rope, particularly the effect of the finite Larmor radius and magnetic field irregularities. First, we derive analytical solutions for cosmic ray behavior inside a magnetic flux rope, on the basis of the Newton-Lorentz equation of a particle, to investigate how cosmic rays penetrate magnetic flux ropes under an assumption of there being no scattering by small-scale magnetic field irregularities. Next, we pe...

  8. Ferrofluid nucleus phase transitions in an external uniform magnetic field

    Institute of Scientific and Technical Information of China (English)

    B. M. Tanygin; S. I. Shulyma; V. F. Kovalenko; M. V. Petrychuk

    2015-01-01

    The phase transition between a massive dense phase and a diluted superparamagnetic phase has been studied by means of a direct molecular dynamics simulation. The equilibrium structures of the ferrofluid aggregate nucleus are obtained for different values of a temperature and an external magnetic field magnitude. An approximate match of experiment and simulation has been shown for the ferrofluid phase diagram coordinates “field–temperature”. The provided phase coexistence curve has an opposite trend comparing to some of known theoretical results. This contradiction has been discussed. For given experimental parameters, it has been concluded that the present results describe more precisely the transition from linear chains to a dense globes phase. The theoretical concepts which provide the opposite binodal curve dependency trend match other experimental conditions:a diluted ferrofluid, a high particle coating rate, a high temperature, and/or a less particles coupling constant value.

  9. ADAPTIVE FLUX OBSERVER FOR PERMANENT MAGNET SYNCHRONOUS MOTORS

    Directory of Open Access Journals (Sweden)

    A. A. Bobtsov

    2015-01-01

    Full Text Available The paper deals with the observer design problem for a flux in permanent magnet synchronous motors. It is assumed that some electrical parameters such as resistance and inductance are known numbers. But the flux, the angle and the speed of the rotor are unmeasurable. The new robust approach to design an adaptive flux observer is proposed that guarantees globally boundedness of all signals and, moreover, exponential convergence to zero of observer error between the true flux value and an estimate obtained from the adaptive observer. The problem of an adaptive flux observer design has been solved with using the trigonometrical properties and linear filtering which ensures cancellation of unknown terms arisen after mathematical calculations. The key idea is the new parameterization of the dynamical model containing unknown parameters and depending on measurable current and voltage in the motor. By applying the Pythagorean trigonometric identity the linear equation has found that does not contain any functions depending on angle or angular velocity of the rotor. Using dynamical first-order filters the standard regression model is obtained that consists of unknown constant parameters and measurable functions of time. Then the gradient-like estimator is designed to reconstruct unknown parameters, and it guarantees boundedness of all signals in the system. The proposition is proved that if the regressor satisfies the persistent excitation condition, meaning the “frequency-rich” signal, then all errors in observer exponentially converges to zero. It is shown that observer error for the flux explicitly depends on estimator errors. Exponential convergence of parameter estimation errors to zero yields exponential convergence of the flux observer error to zero. The numerical example is considered.

  10. Improvement in magnetic field immunity of externally-coupled transcutaneous energy transmission system for a totally implantable artificial heart.

    Science.gov (United States)

    Yamamoto, Takahiko; Koshiji, Kohji; Homma, Akihiko; Tatsumi, Eisuke; Taenaka, Yoshiyuki

    2008-01-01

    Transcutaneous energy transmission (TET) that uses electromagnetic induction between the external and internal coils of a transformer is the most promising method to supply driving energy to a totally implantable artificial heart without invasion. Induction-heating (IH) cookers generate magnetic flux, and if a cooker is operated near a transcutaneous transformer, the magnetic flux generated will link with the external and internal coils of the transcutaneous transformer. This will affect the performance of the TET and the artificial heart system. Hence, it is necessary to improve the magnetic field immunity of the TET system. During operation of the system, if the transcutaneous transformer is in close proximity to an IH cooker, the electric power generated by the cooker and coupled to the transformer can drive the artificial heart system. To prevent this coupling, the external coil was shielded with a conductive shield that had a slit in it. This reduces the coupling between the transformer and the magnetic field generated by the induction cooker. However, the temperature of the shield increased due to heating by eddy currents. The temperature of the shield can be reduced by separating the IH cooker and the shield.

  11. Effect of heat capacity and conductivity of NbTi normal matrix of a composite superconductor on the stability to magnetic flux jumps

    Science.gov (United States)

    Kruglov, S. L.; Shutova, D. I.; Shcherbakov, V. I.

    2017-02-01

    The stability against magnetic flux jumps has experimentally been studied in the external magnetic field for three samples from NbTi composite superconductors, one monofilamentary and two multifilamentary. A comparison between the experiment and theory of thermomagnetic stability of composite superconductors has been carried out. We have determined threshold values of the rates of the external magnetic fields, starting from which heat capacity and conductivity of the normal composite matrix become determining stabilizing factors. For the first time, the increasing dependence of field of first magnetic flux jump on the rate of the rise in the external magnetic field has been experimentally registered in the superconducting wire for MRI. The reason for this effect is the shunting effect of a high pure copper matrix and the low volume fraction of a superconductor in the composite ( 10%).

  12. Evaluation of Surface Cracks Using Magnetic Flux Leakage Testing

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The magnetic field distribution characteristics of surface cracks with various widths are discussed based on finite element (FEM) results. The crack depth was 0.20 mm, the width range was from 0.02 to 1.00 mm. The results showed that crack width and lift-off (the distance between surface and sensor) will influence signals. Discussed in this paper is the influence of various lift-off parameters on the peak to peak values of the normal component in magnetic flux leakage testing. The effects can be applied to evaluate surface breaking cracks of different widths and depths.An idea is presented to smooth narrow, sharp crack tips using alternating current (AC) field magnetization.

  13. Thermal conditions on the International Space Station: Heat flux and temperature investigation of main radiators for the Alpha Magnetic Spectrometer

    Energy Technology Data Exchange (ETDEWEB)

    Xie, Min, E-mail: alice.m.xie@icloud.com; Gao, Jianmin; Wu, Shaohua; Qin, Yukun

    2016-09-11

    The investigation on heat flux can clarify the thermal condition and explain temperature behavior on the main radiators of the Alpha Magnetic Spectrometer (AMS). In this paper, a detailed investigation of heat flux on the AMS main radiators is proposed. The heat transfer process of the AMS main radiators is theoretically analyzed. An updated thermal model of the AMS on the International Space Station (ISS) is developed to calculate the external heat flux density on the AMS main radiators. We conclude the ISS components and operations affect on the solar flux density of the AMS main radiators by reflecting or shading solar illumination. According to the energy conservation on the AMS main radiators, the temperature variation mainly depends on the solar flux change. The investigations are conducive to reference for the long-duration thermal control of the AMS, and knowledge for the thermal conditions on the ISS.

  14. Thermal conditions on the International Space Station: Heat flux and temperature investigation of main radiators for the Alpha Magnetic Spectrometer

    Science.gov (United States)

    Xie, Min; Gao, Jianmin; Wu, Shaohua; Qin, Yukun

    2016-09-01

    The investigation on heat flux can clarify the thermal condition and explain temperature behavior on the main radiators of the Alpha Magnetic Spectrometer (AMS). In this paper, a detailed investigation of heat flux on the AMS main radiators is proposed. The heat transfer process of the AMS main radiators is theoretically analyzed. An updated thermal model of the AMS on the International Space Station (ISS) is developed to calculate the external heat flux density on the AMS main radiators. We conclude the ISS components and operations affect on the solar flux density of the AMS main radiators by reflecting or shading solar illumination. According to the energy conservation on the AMS main radiators, the temperature variation mainly depends on the solar flux change. The investigations are conducive to reference for the long-duration thermal control of the AMS, and knowledge for the thermal conditions on the ISS.

  15. Flavoured Large N Gauge Theory in an External Magnetic Field

    CERN Document Server

    Filev, V G; Rashkov, R C; Viswanathan, K S; Filev, Veselin G.; Johnson, Clifford V.

    2007-01-01

    We consider a D7-brane probe of AdS$_{5}\\times S^5$ in the presence of pure gauge $B$-field. In the dual gauge theory, the $B$-field couples to the fundamental matter introduced by the D7-brane and acts as an external magnetic field. The $B$-field supports a 6-form Ramond-Ramond potential on the D7-branes world volume that breaks the supersymmetry and enables the dual gauge theory to develop a non-zero fermionic condensate. We explore the dependence of the fermionic condensate on the bare quark mass $m_{q}$ and show that at zero bare quark mass a chiral symmetry is spontaneously broken. A study of the meson spectrum reveals a coupling between the vector and scalar modes, and in the limit of weak magnetic field we observe Zeeman splitting of the states. We also observe the characteristic $\\sqrt{m_{q}}$ dependence of the ground state corresponding to the Goldstone boson of spontaneously broken chiral symmetry.

  16. A Mechanism of ELM Mitigation by External Magnetic Field Perturbations

    Science.gov (United States)

    Singh, Raghvendra; Jhang, H.; Kim, J.-H.; Hahm, T. S.

    2016-10-01

    We study the impact of external magnetic perturbations (EMP) on the stability of ballooning mode (BM). We use: 1) the two-step process; 2) standard four wave interactions. In two-step process, we consider EMP are long wave-length perturbations interacting with short scale BM and generating side-bands of higher harmonics. This calculates contributions from all the high toroidal mode numbers. EMP can modify the dispersion characteristics of BM - the growth spectrum becomes broader in kBM space. The increase in high kBM can lead to the mitigation of an ELM crash by increasing turbulent transport. New nonlinear instability is also found even below the BM threshold at large EMP amplitude. In four wave interaction, EMP act like a short scale pump wave interacting with BM and creating two sidebands. The side-bands couple with the pump and produce the ponderomotive force, magnetic stress at BM frequency. EMP may enhance the BM instability threshold if RMP K->BM RMP and reduce the threshold if K->BM >K->RMP .

  17. Exponentially Localized Wannier Functions in Periodic Zero Flux Magnetic Fields

    CERN Document Server

    De Nittis, Giuseppe

    2011-01-01

    n this work, we investigate conditions which ensure the existence of an exponentially localized Wannier basis for a given periodic hamiltonian. We extend previous results [Pan07, Kuc09] to include periodic zero flux magnetic fields. The new notion of magnetic symmetry plays a crucial r\\^ole; to a large class of symmetries for a non-magnetic system, one can associate "magnetic" symmetries of the related magnetic system. Observing that the existence of an exponentially localized Wannier basis is equivalent to the triviality of the so-called Bloch bundle, a rank m hermitian vector bundle over the Brillouin zone, we prove that magnetic time-reversal symmetry is sufficient to ensure the triviality of the Bloch bundle in spatial dimension d = 1, 2, 3. For d = 4, an exponentially localized Wannier basis exists provided that the trace per unit volume of a suitable function of the Fermi projection vanishes. For d > 4 and d \\leq 2m (stable rank regime) only the exponential localization of a subset of Wannier functions ...

  18. Magnetization switching in ferromagnets by adsorbed chiral molecules without current or external magnetic field

    Science.gov (United States)

    Ben Dor, Oren; Yochelis, Shira; Radko, Anna; Vankayala, Kiran; Capua, Eyal; Capua, Amir; Yang, See-Hun; Baczewski, Lech Tomasz; Parkin, Stuart Stephen Papworth; Naaman, Ron; Paltiel, Yossi

    2017-01-01

    Ferromagnets are commonly magnetized by either external magnetic fields or spin polarized currents. The manipulation of magnetization by spin-current occurs through the spin-transfer-torque effect, which is applied, for example, in modern magnetoresistive random access memory. However, the current density required for the spin-transfer torque is of the order of 1 × 106 A·cm−2, or about 1 × 1025 electrons s−1 cm−2. This relatively high current density significantly affects the devices' structure and performance. Here we demonstrate magnetization switching of ferromagnetic thin layers that is induced solely by adsorption of chiral molecules. In this case, about 1013 electrons per cm2 are sufficient to induce magnetization reversal. The direction of the magnetization depends on the handedness of the adsorbed chiral molecules. Local magnetization switching is achieved by adsorbing a chiral self-assembled molecular monolayer on a gold-coated ferromagnetic layer with perpendicular magnetic anisotropy. These results present a simple low-power magnetization mechanism when operating at ambient conditions. PMID:28230054

  19. Magnetic reconnection in high-energy-density plasmas in the presence of an external magnetic field

    Science.gov (United States)

    Fox, W.; Bhattacharjee, A.; Fiksel, G.; Nilson, P.; Hu, S.; Chang, P.-Y.; Barnak, D.; Betti, R.

    2012-10-01

    Magnetic reconnection has recently been observed and studied in high-energy-density, laser-produced plasmas. These experiments are interesting both for obtaining fundamental data on reconnection, and may also be relevant for inertial fusion, as this magnetic reconnection geometry, with multiple, colliding, magnetized plasma bubbles, occurs naturally inside ICF hohlraums. We present initial results of experiments conducted on the OMEGA EP facility on magnetic reconnection between colliding, magnetized blowoff plasmas. While in previous experiments the magnetic fields were self-generated in the plasma by the Biermann battery effect, in these experiments the seed magnetic field is generated by pulsing current through a pair of external foils using the MIFEDS current generator (Magneto-Inertial Fusion Electrical Discharge System) developed at LLE. Time-resolved images of the magnetic fields and plasma dynamics are obtained from proton radiography and x-ray self-emission, respectively. We present initial results of the experiments, including comparison to ``null'' experiments with zero MIFEDS magnetic field, and associated modeling using the radiation-hydro code DRACO and the particle-in-cell code PSC.

  20. Magnetization switching in ferromagnets by adsorbed chiral molecules without current or external magnetic field.

    Science.gov (United States)

    Ben Dor, Oren; Yochelis, Shira; Radko, Anna; Vankayala, Kiran; Capua, Eyal; Capua, Amir; Yang, See-Hun; Baczewski, Lech Tomasz; Parkin, Stuart Stephen Papworth; Naaman, Ron; Paltiel, Yossi

    2017-02-23

    Ferromagnets are commonly magnetized by either external magnetic fields or spin polarized currents. The manipulation of magnetization by spin-current occurs through the spin-transfer-torque effect, which is applied, for example, in modern magnetoresistive random access memory. However, the current density required for the spin-transfer torque is of the order of 1 × 10(6) A·cm(-2), or about 1 × 10(25) electrons s(-1) cm(-2). This relatively high current density significantly affects the devices' structure and performance. Here we demonstrate magnetization switching of ferromagnetic thin layers that is induced solely by adsorption of chiral molecules. In this case, about 10(13) electrons per cm(2) are sufficient to induce magnetization reversal. The direction of the magnetization depends on the handedness of the adsorbed chiral molecules. Local magnetization switching is achieved by adsorbing a chiral self-assembled molecular monolayer on a gold-coated ferromagnetic layer with perpendicular magnetic anisotropy. These results present a simple low-power magnetization mechanism when operating at ambient conditions.

  1. Study on a magnetic spiral-type wireless capsule endoscope controlled by rotational external permanent magnet

    Energy Technology Data Exchange (ETDEWEB)

    Ye, Bo, E-mail: yebo@hubu.edu.cn [School of Mechanical Science & Engineering, Huazhong University of Science & Technology, Wuhan 430074 (China); School of Computer Science and Information Engineering, HuBei University, Wuhan 430062 (China); Zhang, Wei [Department of Mechanical Engineering, Hubei University of Automotive Technology, Shiyan 442002 (China); Sun, Zhen-jun [School of Mechanical Science & Engineering, Huazhong University of Science & Technology, Wuhan 430074 (China); Guo, Lin [School of Computer Science and Information Engineering, HuBei University, Wuhan 430062 (China); Deng, Chao [School of Mechanical Science & Engineering, Huazhong University of Science & Technology, Wuhan 430074 (China); Chen, Ya-qi [Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030 (China); Zhang, Hong-hai [School of Mechanical Science & Engineering, Huazhong University of Science & Technology, Wuhan 430074 (China); Liu, Sheng [School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072 (China)

    2015-12-01

    In this paper, the authors propose rotating an external permanent magnet (EPM) to manipulate the synchronous rotation of a magnetic spiral-type wireless capsule endoscope (WCE), and the synchronous rotation of the WCE is converted to its translational motion in intestinal tract. In order to preliminarily verify the feasibility of this method, a handheld actuator (HA) controlled by micro controller unit, a magnetic spiral-type WCE and a bracket were fabricated, theoretical analysis and simulations about the control distance of this method were performed, and in ex-vivo tests were examined in porcine small intestine to verify the control distance and control performances of this method. It was demonstrated that this method showed good performances in controlling the translational motion of the magnetic spiral-type WCE, and this method has great potential to be used in clinical application. - Highlights: • A new magnetic control method for spiral-type wireless capsule endoscope is proposed. • Wireless capsule endoscope rotates synchronously with external permanent magnet. • The method controls the wireless capsule endoscope well in porcine small intestine. • Long control distance makes the method may be used in future medical application. • Experimental setup has great advantages: high cost performance and easy operation.

  2. Foucault imaging and small-angle electron diffraction in controlled external magnetic fields.

    Science.gov (United States)

    Nakajima, Hiroshi; Kotani, Atsuhiro; Harada, Ken; Ishii, Yui; Mori, Shigeo

    2016-12-01

    We report a method for acquiring Foucault images and small-angle electron diffraction patterns in external magnetic fields using a conventional transmission electron microscope without any modification. In the electron optical system that we have constructed, external magnetic fields parallel to the optical axis can be controlled using the objective lens pole piece under weak excitation conditions in the Foucault mode and the diffraction mode. We observe two ferromagnetic perovskite-type manganese oxides, La0.7Sr0.3MnO3 (LSMO) and Nd0.5Sr0.5MnO3, in order to visualize magnetic domains and their magnetic responses to external magnetic fields. In rhombohedral-structured LSMO, pinning of magnetic domain walls at crystallographic twin boundaries was found to have a strong influence on the generation of new magnetic domains in external applied magnetic fields.

  3. The revised electromagnetic fields directive and worker exposure in environments with high magnetic flux densities.

    Science.gov (United States)

    Stam, Rianne

    2014-06-01

    Some of the strongest electromagnetic fields (EMF) are found in the workplace. A European Directive sets limits to workers' exposure to EMF. This review summarizes its origin and contents and compares magnetic field exposure levels in high-risk workplaces with the limits set in the revised Directive. Pubmed, Scopus, grey literature databases, and websites of organizations involved in occupational exposure measurements were searched. The focus was on EMF with frequencies up to 10 MHz, which can cause stimulation of the nervous system. Selected studies had to provide individual maximum exposure levels at the workplace, either in terms of the external magnetic field strength or flux density or as induced electric field strength or current density. Indicative action levels and the corresponding exposure limit values for magnetic fields in the revised European Directive will be higher than those in the previous version. Nevertheless, magnetic flux densities in excess of the action levels for peripheral nerve stimulation are reported for workers involved in welding, induction heating, transcranial magnetic stimulation, and magnetic resonance imaging (MRI). The corresponding health effects exposure limit values for the electric fields in the worker's body can be exceeded for welding and MRI, but calculations for induction heating and transcranial magnetic stimulation are lacking. Since the revised European Directive conditionally exempts MRI-related activities from the exposure limits, measures to reduce exposure may be necessary for welding, induction heating, and transcranial nerve stimulation. Since such measures can be complicated, there is a clear need for exposure databases for different workplace scenarios with significant EMF exposure and guidance on good practices.

  4. Study on a magnetic spiral-type wireless capsule endoscope controlled by rotational external permanent magnet

    Science.gov (United States)

    Ye, Bo; Zhang, Wei; Sun, Zhen-jun; Guo, Lin; Deng, Chao; Chen, Ya-qi; Zhang, Hong-hai; Liu, Sheng

    2015-12-01

    In this paper, the authors propose rotating an external permanent magnet (EPM) to manipulate the synchronous rotation of a magnetic spiral-type wireless capsule endoscope (WCE), and the synchronous rotation of the WCE is converted to its translational motion in intestinal tract. In order to preliminarily verify the feasibility of this method, a handheld actuator (HA) controlled by micro controller unit, a magnetic spiral-type WCE and a bracket were fabricated, theoretical analysis and simulations about the control distance of this method were performed, and in ex-vivo tests were examined in porcine small intestine to verify the control distance and control performances of this method. It was demonstrated that this method showed good performances in controlling the translational motion of the magnetic spiral-type WCE, and this method has great potential to be used in clinical application.

  5. Optimization of magnetic flux density measurement using multiple RF receiver coils and multi-echo in MREIT.

    Science.gov (United States)

    Jeong, Woo Chul; Chauhan, Munish; Sajib, Saurav Z K; Kim, Hyung Joong; Serša, Igor; Kwon, Oh In; Woo, Eung Je

    2014-09-01

    Magnetic Resonance Electrical Impedance Tomography (MREIT) is an MRI method that enables mapping of internal conductivity and/or current density via measurements of magnetic flux density signals. The MREIT measures only the z-component of the induced magnetic flux density B = (Bx, By, Bz) by external current injection. The measured noise of Bz complicates recovery of magnetic flux density maps, resulting in lower quality conductivity and current-density maps. We present a new method for more accurate measurement of the spatial gradient of the magnetic flux density gradient (∇ Bz). The method relies on the use of multiple radio-frequency receiver coils and an interleaved multi-echo pulse sequence that acquires multiple sampling points within each repetition time. The noise level of the measured magnetic flux density Bz depends on the decay rate of the signal magnitude, the injection current duration, and the coil sensitivity map. The proposed method uses three key steps. The first step is to determine a representative magnetic flux density gradient from multiple receiver coils by using a weighted combination and by denoising the measured noisy data. The second step is to optimize the magnetic flux density gradient by using multi-echo magnetic flux densities at each pixel in order to reduce the noise level of ∇ Bz and the third step is to remove a random noise component from the recovered ∇ Bz by solving an elliptic partial differential equation in a region of interest. Numerical simulation experiments using a cylindrical phantom model with included regions of low MRI signal to noise ('defects') verified the proposed method. Experimental results using a real phantom experiment, that included three different kinds of anomalies, demonstrated that the proposed method reduced the noise level of the measured magnetic flux density. The quality of the recovered conductivity maps using denoised ∇ Bz data showed that the proposed method reduced the conductivity

  6. Electrostatic particle-in-cell simulation of heat flux mitigation using magnetic fields

    Science.gov (United States)

    Lüskow, Karl Felix; Kemnitz, S.; Bandelow, G.; Duras, J.; Kahnfeld, D.; Matthias, P.; Schneider, R.; Konigorski, D.

    2016-10-01

    The particle-in-cell (PIC) method was used to simulate heat flux mitigation experiments with partially ionised argon. The experiments demonstrate the possibility of reducing heat flux towards a target using magnetic fields. Modelling using the PIC method is able to reproduce the heat flux mitigation qualitatively. This is driven by modified electron transport. Electrons are magnetised and react directly to the external magnetic field. In addition, an increase of radial turbulent transport is also needed to explain the experimental observations in the model. Close to the target an increase of electron density is created. Due to quasi-neutrality, ions follow the electrons. Charge exchange collisions couple the dynamics of the neutrals to the ions and reduce the flow velocity of neutrals by radial momentum transport and subsequent losses. By this, the dominant heat-transport channel by neutrals gets reduced and a reduction of the heat deposition, similar to the experiment, is observed. Using the simulation a diagnostic module for optical emission is developed and its results are compared with spectroscopic measurements and photos from the experiment. The results of this study are in good agreement with the experiment. Experimental observations such as a shrank bright emission region close to the nozzle exit, an additional emission in front of the target and an overall change in colour to red are reproduced by the simulation.

  7. Analytical Calculation of the Magnetic Field distribution in a Flux-Modulated Permanent-Magnet Brushless Motor

    DEFF Research Database (Denmark)

    Zhang, Xiaoxu; Liu, Xiao; Chen, Zhe

    2015-01-01

    This paper presents a rapid approach to compute the magnetic field distribution in a flux-modulated permanent-magnet brushless motor. Partial differential equations are used to describe the magnet field behavior in terms of magnetic vector potentials. The whole computational domain is divided int...... magnetic field with those calculated by finite element method....

  8. Novel behavior of magnetic flux lines in type II superconductors

    Science.gov (United States)

    Mohler, Gregory Allan

    In this thesis we present several studies in the properties of magnetic flux lines in type II superconductors. We have carried out a model calculation of the flux noise produced by vortex avalanches in a Type-II superconductor, using a simple kinetic model proposed by Bassler and Paczuski. Over a broad range of frequencies, we find that the flux noise SFw has a power-law dependence on frequency, SFw ˜ w-s , with s ˜ 1.4 in reasonable agreement with experiment. In addition, for small lattices, the calculated SFw has a high-frequency knee, which is seen in some experiments, and which is due to the finite lattice size. We have analyzed the Lawrence-Doniach free energy in a tilted magnetic field within the lowest Landau level (LLL) approximation for the case of a highly anisotropic high temperature superconductor. The free energy maps onto that of a strictly c-axis field, but with a reduced interlayer coupling. We use this result to calculate the tilt modulus C44 of a vortex lattice and vortex liquid. The vortex contribution to C44 can be expressed in terms of the squared c-axis Josephson plasmon frequency w2pl . We find that the transverse component of the field has very little effect on the position of the melting curve. We present a simple numerical model for the IV characteristics of a highly anisotropic high temperature superconductor in different geometries. An array of grains coupled together by Josephson junctions is used, with a triangular structure in the planes normal to an applied magnetic field and a square structure otherwise. Overdamped junctions are used to describe the CuO2 planes, while underdamped junctions are used to describe the interplanar coupling. Each grain has a capacitive shunt to ground. We measure the depinning current strength, decoupling current strength, and the critical coupling value in the "flux-transformer geometry." We also examine voltage branches in the I--V hysteresis curve for c-axis transport. Finally, we have used a simple

  9. Energy flux determines magnetic field strength of planets and stars.

    Science.gov (United States)

    Christensen, Ulrich R; Holzwarth, Volkmar; Reiners, Ansgar

    2009-01-08

    The magnetic fields of Earth and Jupiter, along with those of rapidly rotating, low-mass stars, are generated by convection-driven dynamos that may operate similarly (the slowly rotating Sun generates its field through a different dynamo mechanism). The field strengths of planets and stars vary over three orders of magnitude, but the critical factor causing that variation has hitherto been unclear. Here we report an extension of a scaling law derived from geodynamo models to rapidly rotating stars that have strong density stratification. The unifying principle in the scaling law is that the energy flux available for generating the magnetic field sets the field strength. Our scaling law fits the observed field strengths of Earth, Jupiter, young contracting stars and rapidly rotating low-mass stars, despite vast differences in the physical conditions of the objects. We predict that the field strengths of rapidly rotating brown dwarfs and massive extrasolar planets are high enough to make them observable.

  10. Energy flux determines magnetic field strength of planets and stars

    Science.gov (United States)

    Christensen, Ulrich R.; Holzwarth, Volkmar; Reiners, Ansgar

    2009-01-01

    The magnetic fields of Earth and Jupiter, along with those of rapidly rotating, low-mass stars, are generated by convection-driven dynamos that may operate similarly (the slowly rotating Sun generates its field through a different dynamo mechanism). The field strengths of planets and stars vary over three orders of magnitude, but the critical factor causing that variation has hitherto been unclear. Here we report an extension of a scaling law derived from geodynamo models to rapidly rotating stars that have strong density stratification. The unifying principle in the scaling law is that the energy flux available for generating the magnetic field sets the field strength. Our scaling law fits the observed field strengths of Earth, Jupiter, young contracting stars and rapidly rotating low-mass stars, despite vast differences in the physical conditions of the objects. We predict that the field strengths of rapidly rotating brown dwarfs and massive extrasolar planets are high enough to make them observable.

  11. Supergranular-scale magnetic flux emergence beneath an unstable filament

    CERN Document Server

    Palacios, J; Guerrero, A; Saiz, E; Cerrato, Y

    2015-01-01

    Here we report evidence of a large solar filament eruption on 2013, September 29. This smooth eruption, which passed without any previous flare, formed after a two-ribbon flare and a coronal mass ejection towards Earth. The coronal mass ejection generated a moderate geomagnetic storm on 2013, October 2 with very serious localized effects. The whole event passed unnoticed to flare-warning systems. We have conducted multi-wavelength analyses of the Solar Dynamics Observatory through Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) data. The AIA data on 304, 193, 211, and 94 \\AA sample the transition region and the corona, respectively, while HMI provides photospheric magnetograms, continuum, and linear polarization data, in addition to the fully inverted data provided by HMI. [...] We have observed a supergranular-sized emergence close to a large filament in the boundary of the active region NOAA11850. Filament dynamics and magnetogram results suggest that the magnetic flux emergenc...

  12. Tracking of magnetic flux concentrations over a five-day observation, and an insight into surface magnetic flux transport

    Directory of Open Access Journals (Sweden)

    Iida Yusuke

    2016-01-01

    Full Text Available The solar dynamo problem is the question of how the cyclic variation in the solar magnetic field is maintained. One of the important processes is the transport of magnetic flux by surface convection. To reveal this process, the dependence of the squared displacement of magnetic flux concentrations on the elapsed time is investigated in this paper via a feature-recognition technique and a continual five-day magnetogram. This represents the longest time scale over which a satellite observation has ever been performed for this problem. The dependence is found to follow a power law and differ significantly from that of diffusion transport. Furthermore, there is a change in the behavior at a spatial scale of 103.8 km. A super-diffusion behavior with an index of 1.4 is found at smaller scales, while changing to a sub-diffusion behavior with an index of 0.6 on larger ones. We interpret this difference in the transport regime as coming from the network-flow pattern.

  13. Tracking of magnetic flux concentrations over a five-day observation and an insight into surface magnetic flux transport

    CERN Document Server

    Iida, Y

    2016-01-01

    The solar dynamo problem is the question of how the cyclic variation in the solar magnetic field is maintained. One of the important processes is the transport of magnetic flux by surface convection. To reveal this process, the dependence of the squared displacement of magnetic flux concentrations upon the elapsed time is investigated in this paper via a feature-recognition technique and a continual five-day magnetogram. This represents the longest time scale over which a satellite observation has ever been performed for this problem. The dependence is found to follow a power-law and differ significantly from that of diffusion transport. Furthermore there is a change in the behavior at a spatial scale of 10^{3.8} km. A super-diffusion behavior with an index of 1.4 is found on smaller scales, while changing to a sub-diffusion behavior with an index of 0.6 on larger ones. I interpret this difference in the transport regime as coming from the network-flow pattern.

  14. 3D low-beta magnetized plasma equilibria from external shaping

    Science.gov (United States)

    Hassam, A.; Tenbarge, J.; Landreman, M.; Dorland, W.; Sengupta, W.

    2016-10-01

    A 3D nonlinear dissipative MHD code is in development to allow relaxation to low-beta MHD equilibrium inside a shaped 3D conducting boundary with prescribed conserved axial magnetic flux and no external current. Formation of magnetic islands is expected. Heat sources would be eventually introduced to allow the possibility of non-stationary convection depending on the stability properties of the accessible MHD equilibria. The initial development will be done using the code UMHD. The initial emphasis will be on recovering expected physics in simpler 3D geometries. A primary objective is to minimize numerical boundary noise. In particular, codes which specify the normal magnetic field B.n on bounding surfaces are prone to noise generation. We plan to shape the boundary to conform to the desired field shape so that B.n is zero on the boundary. Non-orthogonal coordinates will be chosen to effect this. We will test noise reduction within the tangential field approach. Results obtained to date support this conjecture. Initial results from simple 2D code equilibria have been verified against analytic solution of equilibria in weak shaping. Initial results also recover the expected features of the Hahm- Kulsrud island formation solution. Work supported by US DOE.

  15. Anomalous behavior of a confined two-dimensional electron within an external magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Rosas, R; Riera R; Marin, J. L. [Universidad de Sonora, Hermosillo, Sonora (Mexico); Leon, H. [Instituto Superior Jose Antonio Echeverria, La Habana (Cuba)

    2001-10-01

    An anomalous diamagnetic behavior of a confined two-dimensional electron within an external magnetic field (perpendicular to the confining plane) is discussed in this letter. Although this finding is consistent with the pioneering work of Robnik, it has not been previously reported. When this effect occurs, the ratio between the typical length of spatial and magnetic confinement is an integer number. This property leads also to a quantization of the magnetic flux across the confining circle. The possible consequences of the peculiar behavior of the electron within such a structure are discussed. [Spanish] Se estudia una posible anomalia en las propiedades diamagneticas de un electron bidimensional confinado en presencia de un campo magnetico externo perpendicular al plano de confinamiento. Aunque los resultados obtenidos son consistentes con el trabajo pionero de Robnik, no han sido reportados anteriormente, a pesar de sus posibles aplicaciones, ya que cuando ocurre, el cociente entre la longitud magnetica y el tamano de la region de confinamiento es un numero entero, propiedad que establece una cuantizacion del flujo magnetico que atraviesa el circulo confinante. Se discuten las posibles consecuencias del comportamiento peculiar del electron en este tipo de estructura.

  16. Knot energy in unstretching ergodic magnetic flux tubes

    CERN Document Server

    de Andrade, Garcia

    2009-01-01

    Recently Titov et al [ApJ \\textbf{693},(2009) and ApJ (2007)] have made use of a covariant model to investigate magnetic reconnection of astrophysical plasmas. Earlier R Ricca [Phys Rev A (1991)] has used another covariant formalism, to investigated vortex filaments and solitons. This formalism, called Ricci rotation coefficients (RRC), is applied here, to the Chui and Moffatt [PRSA (1995)] knotted magnetic flux tube (MFT) Riemann metric in the case of vanishing stretch. It is shown that, the vanishing of some components of the (RRC) leads to unstretching knotted tubes. Computing of magnetic knot energy in terms of the RCC, shows that, uniform, unstretching and constant cross-section tubes leads to a marginal dynamo action over magnetic surfaces. Recent investigation on the role of stretching in plasma dynamo action showed that in diffusive media [Phys Plasma \\textbf{14} (2008)], unstretching unknotted tubes would not support fast dynamo action. This result was generalized here to much more general knotted MF...

  17. Numerical Modeling of a Magnetic Flux Compression Experiment

    Science.gov (United States)

    Makhin, Volodymyr; Bauer, Bruno S.; Awe, Thomas J.; Fuelling, Stephan; Goodrich, Tasha; Lindemuth, Irvin R.; Siemon, Richard E.; Garanin, Sergei F.

    2007-06-01

    A possible plasma target for Magnetized Target Fusion (MTF) is a stable diffuse z-pinch in a toroidal cavity, like that in MAGO experiments. To examine key phenomena of such MTF systems, a magnetic flux compression experiment with this geometry is under design. The experiment is modeled with 3 codes: a slug model, the 1D Lagrangian RAVEN code, and the 1D or 2D Eulerian Magneto-Hydro-Radiative-Dynamics-Research (MHRDR) MHD simulation. Even without injection of plasma, high- Z wall plasma is generated by eddy-current Ohmic heating from MG fields. A significant fraction of the available liner kinetic energy goes into Ohmic heating and compression of liner and central-core material. Despite these losses, efficiency of liner compression, expressed as compressed magnetic energy relative to liner kinetic energy, can be close to 50%. With initial fluctuations (1%) imposed on the liner and central conductor density, 2D modeling manifests liner intrusions, caused by the m = 0 Rayleigh-Taylor instability during liner deceleration, and central conductor distortions, caused by the m = 0 curvature-driven MHD instability. At many locations, these modes reduce the gap between the liner and the central core by about a factor of two, to of order 1 mm, at the time of peak magnetic field.

  18. PROPAGATION AND DISPERSION OF SAUSAGE WAVE TRAINS IN MAGNETIC FLUX TUBES

    Energy Technology Data Exchange (ETDEWEB)

    Oliver, R.; Terradas, J. [Departament de Física, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain); Ruderman, M. S., E-mail: ramon.oliver@uib.es [School of Mathematics and Statistics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH (United Kingdom)

    2015-06-10

    A localized perturbation of a magnetic flux tube produces wave trains that disperse as they propagate along the tube, where the extent of dispersion depends on the physical properties of the magnetic structure, on the length of the initial excitation, and on its nature (e.g., transverse or axisymmetric). In Oliver et al. we considered a transverse initial perturbation, whereas the temporal evolution of an axisymmetric one is examined here. In both papers we use a method based on Fourier integrals to solve the initial value problem. We find that the propagating wave train undergoes stronger attenuation for longer axisymmetric (or shorter transverse) perturbations, while the internal to external density ratio has a smaller effect on the attenuation. Moreover, for parameter values typical of coronal loops axisymmetric (transverse) wave trains travel at a speed 0.75–1 (1.2) times the Alfvén speed of the magnetic tube. In both cases, the wave train passage at a fixed position of the magnetic tube gives rise to oscillations with periods of the order of seconds, with axisymmetric disturbances causing more oscillations than transverse ones. To test the detectability of propagating transverse or axisymmetric wave packets in magnetic tubes of the solar atmosphere (e.g., coronal loops, spicules, or prominence threads) a forward modeling of the perturbations must be carried out.

  19. Propagation and Dispersion of Sausage Wave Trains in Magnetic Flux Tubes

    Science.gov (United States)

    Oliver, R.; Ruderman, M. S.; Terradas, J.

    2015-06-01

    A localized perturbation of a magnetic flux tube produces wave trains that disperse as they propagate along the tube, where the extent of dispersion depends on the physical properties of the magnetic structure, on the length of the initial excitation, and on its nature (e.g., transverse or axisymmetric). In Oliver et al. we considered a transverse initial perturbation, whereas the temporal evolution of an axisymmetric one is examined here. In both papers we use a method based on Fourier integrals to solve the initial value problem. We find that the propagating wave train undergoes stronger attenuation for longer axisymmetric (or shorter transverse) perturbations, while the internal to external density ratio has a smaller effect on the attenuation. Moreover, for parameter values typical of coronal loops axisymmetric (transverse) wave trains travel at a speed 0.75-1 (1.2) times the Alfvén speed of the magnetic tube. In both cases, the wave train passage at a fixed position of the magnetic tube gives rise to oscillations with periods of the order of seconds, with axisymmetric disturbances causing more oscillations than transverse ones. To test the detectability of propagating transverse or axisymmetric wave packets in magnetic tubes of the solar atmosphere (e.g., coronal loops, spicules, or prominence threads) a forward modeling of the perturbations must be carried out.

  20. Measuring the Magnetic Flux Density in the CMS Steel Yoke

    CERN Document Server

    Klyukhin, V I; Ball, A; Curé, B; Gaddi, A; Gerwig, H; Hervé, A; Mulders, M; Loveless, R

    2012-01-01

    The Compact Muon Solenoid (CMS) is a general purpose detector, designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting solenoid with 6-m-diameter by 12.5-m-length free bore, enclosed inside a 10000-ton return yoke made of construction steel. The return yoke consists of five dodecagonal three-layered barrel wheels and four end-cap disks at each end comprised of steel blocks up to 620 mm thick, which serve as the absorber plates of the muon detection system. Accurate characterization of the magnetic field everywhere in the CMS detector is required. To measure the field in and around the steel, a system of 22 flux-loops and 82 3-D Hall sensors is installed on the return yoke blocks. Fast discharges of the solenoid (190 s time-constant) made during the CMS magnet surface commissioning test at the solenoid central fields of 2.64, 3.16, 3.68 and 4.01 T were used to induce voltages in the flux-loops. The voltages are measured on-line a...

  1. Counterstreaming electrons in small interplanetary magnetic flux ropes

    Science.gov (United States)

    Feng, H. Q.; Zhao, G. Q.; Wang, J. M.

    2015-12-01

    Small interplanetary magnetic flux ropes (SIMFRs) are commonly observed by spacecraft at 1 AU, and their origin still remains disputed. We investigated the counterstreaming suprathermal electron (CSE) signatures of 106 SIMFRs measured by Wind during 1995-2005. We found that 79 (75%) of the 106 flux ropes contain CSEs, and the percentages of counterstreaming vary from 8% to 98%, with a mean value of 51%. CSEs are often observed in magnetic clouds (MCs), and this indicates these MCs are still attached to the Sun at both ends. CSEs are also related to heliospheric current sheets (HCSs) and the Earth's bow shock. We divided the SIMFRs into two categories: The first category is far from HCSs, and the second category is in the vicinity of HCSs. The first category has 57 SIMFRs, and only 7 of 57 ropes have no CSEs. This ratio is similar to that of MCs. The second category has 49 SIMFRs; however, 20 of the 49 events have no CSEs. This ratio is larger than that of MCs. These two categories have different origins. One category originates from the solar corona, and most ropes are still connected to the Sun at both ends. The other category is formed near HCSs in the interplanetary space.

  2. The expected imprint of flux rope geometry on suprathermal electrons in magnetic clouds

    OpenAIRE

    Owens, Mathew James; Crooker, N. U.; Horbury, T. S.

    2009-01-01

    Magnetic clouds are a subset of interplanetary coronal mass ejections characterized by a smooth rotation in the magnetic field direction, which is interpreted as a signature of a magnetic flux rope. Suprathermal electron observations indicate that one or both ends of a magnetic cloud typically remain connected to the Sun as it moves out through the heliosphere. With distance from the axis of the flux rope, out toward its edge, the magnetic field winds more tightly about the axis and electrons...

  3. Influence of External Magnetic Fields on Tunneling of Spin-1 Bose Condensate

    Institute of Scientific and Technical Information of China (English)

    YU Zhao-Xian; JIAO Zhi-Yong; SUN Jin-Zuo

    2005-01-01

    In this letter, we have studied the influence of the external magnetic fields on tunneling of the spin-1 Bose condensate. We find that the population transfer between spin-0 and spin-±1 exhibits the step structure under the external cosinusoidal magnetic field and a combination of static and cosinusoidal one, respectively. Compared with the longitudinal component of the external magnetic field, the smaller the transverse component of the magnetic field is, the larger the time scale of exhibiting the step structure does. The tunneling current may exhibit periodically oscillation behavior when the ratio of the transverse component of the magnetic field is smaller than that of the longitudinal component, otherwise it exhibits a damply oscillating behavior. This means that the dynamical spin localization can be adjusted by the external magnetic fields.

  4. External magnetic fields affect the biological impacts of superparamagnetic iron nanoparticles.

    Science.gov (United States)

    Shanehsazzadeh, Saeed; Lahooti, Afsaneh; Hajipour, Mohammad Javad; Ghavami, Mahdi; Azhdarzadeh, Morteza

    2015-12-01

    Superparamagnetic iron oxide nanoparticles (SPIONs) are recognized as one of the promising nanomaterials for applications in various field of nanomedicine such as targeted imaging/drug delivery, tissue engineering, hyperthermia, and gene therapy. Besides their suitable biocompatibility, SPIONs' unique magnetic properties make them an outstanding candidate for theranostic nanomedicine. Very recent progress in the field revealed that the presence of external magnetic fields may cause considerable amount of SPIONs' agglomeration in their colloidal suspension. As variation of physicochemical properties of colloidal nanoparticles has strong effect on their biological outcomes, one can expect that the SPIONs' agglomeration in the presence of external magnetic fields could change their well-recognized biological impacts. In this case, here, we probed the cellular uptake and toxicity of the SPIONs before and after exposure to external magnetic fields. We found that the external magnetic fields can affect the biological outcome of magnetic nanoparticles.

  5. Magnetic Fields in Massive Stars. II. The Buoyant Rise of Magnetic Flux Tubes Through the Radiative Interior

    CERN Document Server

    MacGregor, K B

    2003-01-01

    We present results from an investigation of the dynamical behavior of buoyant magnetic flux rings in the radiative interior of a uniformly rotating early-type star. Our physical model describes a thin, axisymmetric, toroidal flux tube that is released from the outer boundary of the convective core, and is acted upon by buoyant, centrifugal, Coriolis, magnetic tension, and aerodynamic drag forces. We find that rings emitted in the equatorial plane can attain a stationary equilibrium state that is stable with respect to small displacements in radius, but is unstable when perturbed in the meridional direction. Rings emitted at other latitudes travel toward the surface along trajectories that largely parallel the rotation axis of the star. Over much of the ascent, the instantaneous rise speed is determined by the rate of heating by the absorption of radiation that diffuses into the tube from the external medium. Since the time scale for this heating varies like the square of the tube cross-sectional radius, for t...

  6. The Research and Development of the External Magnetic Field Acting on Electro-Deposition Process

    Directory of Open Access Journals (Sweden)

    Wu Menghua

    2016-01-01

    Full Text Available The research and development status of the electro-deposition technology under the action of external magnetic field are introduced. The basic characteristics and applied manners of external magnetic field in electro-deposition process are summarized. The acting principle of external magnetic field, the effects of magnetic hydrodynamics (MHD caused by the Lorentz force, and the acting of magnetic force on the metal ions and particles are described. The main actions of external magnetic field include MHD effect, magnetizing force, affecting the physical and chemical properties of the bath, affecting the disperse ability and coverage capacity of bath, affecting the mass transfer process of electro-deposition, affecting the chemical reaction process and current distribution of electrode surface. Some examples of electro-depositing single metal coatings, alloy coatings and composite coatings under action of magnetic field are explained. During the electro-depositing process, the external magnetic field has different degrees of impact on solution properties, mass transfer, charge transfer, content of composited nanoparticles, crystal growth and crystal orientation etc. The specific impact of magnetic field during the electro-depositing is also classified and summarized. The problems that existed in electro-deposition process while applying magnetic field and the next development trend were summarized.

  7. Dynamic inversion enables external magnets to concentrate ferromagnetic rods to a central target.

    Science.gov (United States)

    Nacev, A; Weinberg, I N; Stepanov, P Y; Kupfer, S; Mair, L O; Urdaneta, M G; Shimoji, M; Fricke, S T; Shapiro, B

    2015-01-14

    The ability to use magnets external to the body to focus therapy to deep tissue targets has remained an elusive goal in magnetic drug targeting. Researchers have hitherto been able to manipulate magnetic nanotherapeutics in vivo with nearby magnets but have remained unable to focus these therapies to targets deep within the body using magnets external to the body. One of the factors that has made focusing of therapy to central targets between magnets challenging is Samuel Earnshaw's theorem as applied to Maxwell's equations. These mathematical formulations imply that external static magnets cannot create a stable potential energy well between them. We posited that fast magnetic pulses could act on ferromagnetic rods before they could realign with the magnetic field. Mathematically, this is equivalent to reversing the sign of the potential energy term in Earnshaw's theorem, thus enabling a quasi-static stable trap between magnets. With in vitro experiments, we demonstrated that quick, shaped magnetic pulses can be successfully used to create inward pointing magnetic forces that, on average, enable external magnets to concentrate ferromagnetic rods to a central location.

  8. Thermal entanglement in a mixed-spin Heisenberg XXZ model under a nonuniform external magnetic field

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The thermal entanglement in (1/2,1) mixed-spin Heisenberg XXZ model is investigated under an external nonuniform magnetic field. In the uniform magnetic field system,the critical magnetic field Bc and critical temperature Tc are increased by increasing the anisotropic parameter k. The degree of magnetic field b plays an important role in improving the critical temperature and enlarging the region of entan-glement in the nonuniform magnetic field system.

  9. Electromagnetic Flux Analysis of Permanent Magnet Brushless DC Motor Using Magnet Software

    Directory of Open Access Journals (Sweden)

    G.R.Puttalakshmi

    2013-08-01

    Full Text Available Permanent Magnet Brushless DC (PMBLDC motors is emerging as a suitable motor for a number of drive applications in industrial and consumer products. Cogging torque is one of the important drawbacks of PMBLDC motor which results in shaft vibrations and noise. The focus of this work is to minimize the electromagnetic flux and cogging torque in PMBLDC by introducing structural design modifications. The performance of the machine is analyzed by varying the magnet pole shape, magnet pole width and by using magnetic material with different remenance value. For analyzing the performance of the machine, machine is modeled using Finite Element Analysis (FEA based software package Magnet. Cogging torque and average torque are taken as performance measures to determineoptimum pole shape and pole width.

  10. Solar Magnetic Flux Tube Simulations with Time-Dependent Ionization

    CERN Document Server

    Fawzy, Diaa E; Rammacher, Wolfgang

    2012-01-01

    In the present work we expand the study of time-dependent ionization previously identified to be of pivotal importance for acoustic waves in solar magnetic flux tube simulations. We focus on longitudinal tube waves (LTW) known to be an important heating agent of solar magnetic regions. Our models also consider new results of wave energy generation as well as an updated determination of the mixing length of convection now identified as 1.8 scale heights in the upper solar convective layers. We present 1-D wave simulations for the solar chromosphere by studying tubes of different spreading as function of height aimed at representing tubes in environments of different magnetic filling factors. Multi-level radiative transfer has been applied to correctly represent the total chromospheric emission function. The effects of time-dependent ionization are significant in all models studied. They are most pronounced behind strong shocks and in low density regions, i.e., the middle and high chromosphere. Concerning our m...

  11. Flexible magnetic filaments under the influence of external magnetic fields in the limit of infinite dilution.

    Science.gov (United States)

    Cerdà, Joan J; Sánchez, Pedro A; Lüsebrink, Daniel; Kantorovich, Sofia; Sintes, Tomàs

    2016-05-14

    In the present work we use Langevin dynamics computer simulations to understand how the presence of a constant external magnetic field modifies the conformational phase diagram of magnetic filaments in the limit of infinite dilution. We have considered the filaments immersed in either a good (non-sticky filaments) or a poor (Stockmayer polymers) solvent. It has been found that in the presence of an applied field, filaments turn out to be much more susceptible to parameters such as temperature and solvent conditions. Filaments owe this increased susceptibility to the fact that the external magnetic field tends to level the free energy landscape as compared to the zero-field case. The field induces equalization in the free energy of competing conformational states that were separated by large energy differences in the zero-field limit. In this new scenario multistability arises, and manifests itself in the existence of broad regions in the phase diagram where two or more equilibrium configurations coexist. The existence of multistability greatly enhances the possibility of tuning the properties of the filament.

  12. Pull-in control due to Casimir forces using external magnetic fields

    CERN Document Server

    Esquivel-Sirvent, R; Cocoletzi, G H

    2009-01-01

    We present a theoretical calculation of the pull-in control in capacitive micro switches actuated by Casimir forces, using external magnetic fields. The external magnetic fields induces an optical anisotropy due to the excitation of magneto plasmons, that reduces the Casimir force. The calculations are performed in the Voigt configuration, and the results show that as the magnetic field increases the system becomes more stable. The detachment length for a cantilever is also calculated for a cantilever, showing that it increases with increasing magnetic field. At the pull-in separation, the stiffness of the system decreases with increasing magnetic field.

  13. FeNi-based flat magnetoimpedance nanostructures with open magnetic flux: New topological approaches

    Energy Technology Data Exchange (ETDEWEB)

    Kurlyandskaya, G.V., E-mail: galina@we.lc.ehu.es [Universidad del País Vasco, UPV/EHU, Dpto. de Electricidad y Electrónica, P.O. Box 644, Bilbao 48080 (Spain); Ural Federal University, Department of Magnetism and Magnetic Nanomaterials, Mira 19, 620002 Ekaterinburg (Russian Federation); Chlenova, A.A. [Ural Federal University, Department of Magnetism and Magnetic Nanomaterials, Mira 19, 620002 Ekaterinburg (Russian Federation); Fernández, E. [Universidad del País Vasco, UPV/EHU, Dpto. de Electricidad y Electrónica, P.O. Box 644, Bilbao 48080 (Spain); Lodewijk, K.J. [Universidad del País Vasco, UPV/EHU, Dpto. de Electricidad y Electrónica, P.O. Box 644, Bilbao 48080 (Spain); Department of Material Sciences, University of Groningen, Nijenborgh 4, 9747 AG Groningen (Netherlands)

    2015-06-01

    Classic flat MI multilayers consist of top and bottom ferromagnetic parts of equal thickness separated by a conductive lead. In previous studies symmetric MI structures were considered because they provide the highest sensitivity with respect to uniform external magnetic fields. There are a number of applications where non-uniform magnetic fields of complex configurations must be detected. Non-symmetric MI structures can be advantageous in this particular case. We describe our experience in design, fabrication and characterization of symmetric and non-symmetric MI multilayers with open magnetic flux. Non-symmetry of the structures was obtained by the deposition of top and bottom ferromagnetic parts of MI element of different thickness. MI responses of the structures with even or odd configurations of the FeNi layers were also considered. - Highlights: • Classic flat MI multilayer consists of ferromagnetic parts of equal thickness separated by a conductive lead. • In previous studies symmetric MI structures were considered. • Non-symmetric MI structures can be advantageous for applications where non-uniform magnetic fields are detected. • MI responses of the structures with even or odd configuration can be very different.

  14. First-principles calculation of transport property in nano-devices under an external magnetic field

    Institute of Scientific and Technical Information of China (English)

    Chen Jing-Zhe; Zhang Jin; Han Ru-Shan

    2008-01-01

    The mesoscopic quantum interference phenomenon (QIP) can be observed and behaves as the oscillation of conductance in nano-devices when the external magnetic field changes. Excluding the factor of impurities or defects, specific QIP is determined by the sample geometry. We have improved a first-principles method based on the matrix Green's function and the density functional theory to simulate the transport behaviour of such systems under a magnetic field. We have studied two kinds of QIP: universal conductance fluctuation (UCF) and Aharonov-Bohm effect (A-B effect). We find that the amplitude of UCF is much smaller than the previous theoretical prediction. We have discussed the origin of difference and concluded that due to the failure of ergodic hypothesis, the ensemble statistics is not applicable, and the conductance fluctuation is determined by the flux-dependent density of states (DOSs). We have also studied the relation between the UCF and the structure of sample. For a specific structure, an atomic circle, the A-B effect is observed and the origin of the oscillation is also discussed.

  15. The magnetic flux leakage measurement by the hall sensor in the longitudinal magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Joo, Gwang Tae [Korea Industrial Testing Co., Ltd., Seoul (Korea, Republic of); Son, Dae Rok; Han, Jung Hee; Park, Jae Hyung [Dept. of Physics, Hannam University, Daejeon (Korea, Republic of)

    1998-05-15

    This paper is concerned with magnetic leakage flux measurement using by the hall sensor in the longitudinal magnetic field of the feromagnetic specimen. For detection sensitivity by the hall probe according to various depth of the subsurface defects, the specimen are prepared by six drilled holes of 0.5 mm φ from 1 mm depth to 4 mm depth in the carbon steel plate(10 x 35 x 265 mm). When the specimen applied by various frequency(2 - 9 Hz) of the AC through synthesizer and power amplifier in the yoke, the signals of the magnetic flux leakage using lack-in amplifier and synthesizer are decreased linearly with defect depth at 2 Hz, but these signals are decreased suddenly with defect depth from the surface and obscured with increasing frequency. And, when the specimen applied range of 1 Amp. to 5 Amp. by DC power supply in the yoke, the signals of the magnetic flux leakage through DVM decreased linearly with defect depth up to 2.5 mm depth and change slightly defect depth above 2.5 mm depth from the surface, but its signals appeared predominately.

  16. Quantum-mechanical relaxation model for characterization of fine particles magnetic dynamics in an external magnetic field

    Science.gov (United States)

    Mischenko, I.; Chuev, M.

    2016-12-01

    Principal difference of magnetic nanoparticles from the bulk matter which cannot be ignored when constructing upon them combined metamaterials and modern devices is the essential influence on their behavior thermal fluctuations of the environment. These disturbances lead to specific distributions of the particles characteristics and to stochastic reorientations of their magnetic moments. On the basis of quantum-mechanical representation of the particle possessing intrinsic magnetic anisotropy and being placed onto the external magnetic field we developed general approach to describe equilibrium magnetization curves and relaxation Mössbauer spectra of magnetic nanoparticles for diagnostics of magnetic nanomaterials in the whole temperature or external field ranges. This approach has universal character and may be applied not only to the systems under thermal equilibrium, but may in principle describe macroscopic dynamical phenomena such as magnetization reversal.

  17. Magnetic Simulation and Analysis of Radial Flux Permanent Magnet Generator using Finite Element Method

    Directory of Open Access Journals (Sweden)

    Pudji Irasari

    2012-07-01

    Full Text Available This paper discusses magnetic simulation and analysis of radial flux permanent magnet generator (PMG using finite element method (FEM by utilizing open source software FEMM 4.2. The specification of generator is 25 V, 28 A, 3 phase, 300 rpm. The analyzed magnetic flux was in the air gap, stator teeth and slots to find out the distribusian pattern and its fluctuation. The simulations were conducted in no-load and nominal load (28 A conditions. Furthermore the maximum flux density of simulation (Bg(sim was used to calculate phase voltage Eph to find out the magnitude of generated electromotive force (EMF. The calculation results were presented as voltage vs. rotation graph in no-load condition and voltage vs. current graph in nominal load condition. Both graphs were validated with Eph of experiment result (Eph(exp and Eph that the value of Bg obtained from analytical calculation (Eph(calc. The final results showed that in no-load condition, Eph graph with Bg(sim (Eph(sim was close to Eph(exp and Eph(calc. The error rate with respect to the experiment was 6,9%. In nominal load condition, Eph(sim graph almost coincides with Eph(calc. graph, with the voltage drop of both was 0,441 V. Both graphs however were far different from Eph(exp graph, which has 9 V of voltage drop. The overall results demonstrated that magnetic distribution pattern presented by FEM was very helpful to avoid magnetic flux accumulation in a particular segment. Besides Bg(sim facilitated to predict the value of Eph.

  18. Magnetohydrostatic equilibrium. II. Three-dimensional multiple open magnetic flux tubes in the stratified solar atmosphere

    CERN Document Server

    Gent, Frederick A; Erd'elyi, Rebertus

    2014-01-01

    A system of multiple open magnetic flux tubes spanning the solar photosphere and lower corona is modelled analytically, within a realistic stratified atmosphere subject to solar gravity. This extends results for a single magnetic flux tube in magnetohydrostatic equilibrium, described in Gent et al. (MNRAS, 435, 689, 2013). Self-similar magnetic flux tubes are combined to form magnetic structures, which are consistent with high-resolution observations. The observational evidence supports the existence of strands of open flux tubes and loops persisting in a relatively steady state. Self-similar magnetic flux tubes, for which an analytic solution to the plasma density and pressure distribution is possible, are combined. We calculate the appropriate balancing forces, applying to the equations of momentum and energy conservation to preserve equilibrium. Multiplex flux tube configurations are observed to remain relatively stable for up to a day or more, and it is our aim to apply our model as the background conditi...

  19. The QCD phase diagram in the presence of an external magnetic field: the role of the inverse magnetic catalysis

    CERN Document Server

    Ferreira, Márcio; Providência, Constança

    2015-01-01

    The effect of an external magnetic field in QCD phase diagram, namely, in the the location of the critical end point (CEP) is investigated. Using the 2+1 flavor Nambu--Jona-Lasinio model with Polyakov loop, it is shown that when an external magnetic field is applied its effect on the CEP depends on the strength of the coupling. If the coupling depends on the magnetic field, allowing for inverse magnetic catalysis, the CEP moves to lower chemical potentials eventually disappearing, and the chiral restoration phase transition is always of first order.

  20. Evaluation of the toroidal torque driven by external non-resonant non-axisymmetric magnetic field perturbations in a tokamak

    Energy Technology Data Exchange (ETDEWEB)

    Kasilov, Sergei V. [Fusion@ÖAW, Institut für Theoretische Physik—Computational Physics, Technische Universität Graz Petersgasse 16, A–8010 Graz (Austria); Institute of Plasma Physics National Science Center “Kharkov Institute of Physics and Technology” ul. Akademicheskaya 1, 61108 Kharkov (Ukraine); Kernbichler, Winfried; Martitsch, Andreas F.; Heyn, Martin F. [Fusion@ÖAW, Institut für Theoretische Physik—Computational Physics, Technische Universität Graz Petersgasse 16, A–8010 Graz (Austria); Maassberg, Henning [Max-Planck Institut für Plasmaphysik, D-17491 Greifswald (Germany)

    2014-09-15

    The toroidal torque driven by external non-resonant magnetic perturbations (neoclassical toroidal viscosity) is an important momentum source affecting the toroidal plasma rotation in tokamaks. The well-known force-flux relation directly links this torque to the non-ambipolar neoclassical particle fluxes arising due to the violation of the toroidal symmetry of the magnetic field. Here, a quasilinear approach for the numerical computation of these fluxes is described, which reduces the dimension of a standard neoclassical transport problem by one without model simplifications of the linearized drift kinetic equation. The only limiting condition is that the non-axisymmetric perturbation field is small enough such that the effect of the perturbation field on particle motion within the flux surface is negligible. Therefore, in addition to most of the transport regimes described by the banana (bounce averaged) kinetic equation also such regimes as, e.g., ripple-plateau and resonant diffusion regimes are naturally included in this approach. Based on this approach, a quasilinear version of the code NEO-2 [W. Kernbichler et al., Plasma Fusion Res. 3, S1061 (2008).] has been developed and benchmarked against a few analytical and numerical models. Results from NEO-2 stay in good agreement with results from these models in their pertinent range of validity.

  1. The Study of Magnetic Flux Shunts Effects on the Leakage Reactance of Transformers via FEM

    Directory of Open Access Journals (Sweden)

    Karim Abbaszadeh

    2010-09-01

    Full Text Available The influence of arrangement, dimensions, and magnetic permeability of the magnetic flux shunts on the flux distribution and leakage reactance of the power transformers is studied in this paper by using a finite elements method and a simple modeling approach. By using magneto-static analysis and finite element method, first the flux distribution in the 2D model of a core-type three phase power transformer and then using the magnetic stored energy method the leakage reactance of the transformer windings is calculated. By studying the different models including magnetic flux shunts, the effect of the arrangement, geometric dimensions as well as the magnetic permeability of the magnetic flux shunt on the leakage reactance of the transformer are studied and some interesting results are obtained. It is shown that the variation of these parameters in the transformer model has significant effects on the leakage reactance of the transformer.

  2. Analysis of an eddy-current brake considering finite radius and induced magnetic flux

    Science.gov (United States)

    Lee, Kapjin; Park, Kyihwan

    2002-11-01

    Since the eddy-current problem usually depends on the geometry of the moving conductive sheet and the pole shape, there is no general method to find an analytical solution. The analysis of the eddy currents in a rotating disk with an electromagnet is performed in the case of time-invariant field with the consideration of the boundary conditions of the rotating disk and induced magnetic flux. First, the concept of Coulomb's law and the method of images are introduced with the consideration of the boundary conditions. Second, the induced magnetic flux density is calculated by using Ampere's law. Third, the net magnetic flux density is introduced by defining the magnetic Reynolds number Rm as the ratio of the induced magnetic flux density to the applied magnetic flux density. Finally, the braking torque is calculated by applying the Lorentz force law and the computed results are compared with experimental ones.

  3. On the Role of Repetitive Magnetic Reconnections in Evolution of Magnetic Flux Ropes in Solar Corona

    Science.gov (United States)

    Kumar, Sanjay; Bhattacharyya, R.; Joshi, Bhuwan; Smolarkiewicz, P. K.

    2016-10-01

    Parker's magnetostatic theorem, extended to astrophysical magnetofluids with large magnetic Reynolds number, supports ceaseless regeneration of current sheets and, hence, spontaneous magnetic reconnections recurring in time. Consequently, a scenario is possible where the repeated reconnections provide an autonomous mechanism governing emergence of coherent structures in astrophysical magnetofluids. In this work, such a scenario is explored by performing numerical computations commensurate with the magnetostatic theorem. In particular, the computations explore the evolution of a flux rope governed by repeated reconnections in a magnetic geometry resembling bipolar loops of solar corona. The revealed morphology of the evolution process—including onset and ascent of the rope, reconnection locations, and the associated topology of the magnetic field lines—agrees with observations, and thus substantiates physical realizability of the advocated mechanism.

  4. Effects of slotting and unipolar flux on magnetic pull in a two-pole induction motor with an extra four-pole stator winding

    Energy Technology Data Exchange (ETDEWEB)

    Sinervo, A.

    2013-06-01

    This thesis is about the radial magnetic forces between the rotor and stator in twopole induction machines. The magnetic forces arise from rotor eccentricity. The asymmetric air-gap makes the flux density on one side of the rotor stronger than on the opposite side. This produces magnetic pull. The magnetic flux density distribution in the air-gap can be expressed with spatial harmonics, i.e. flux densities with different pole-pair numbers. In two-pole machines, the main part of the magnetic force is produced by the interaction of two- and fourpole flux unless the four-pole flux is damped by parallel paths in the stator winding or an extra four-pole stator winding. The rest of the force comes from the interaction of two-pole and unipolar flux and from the higher harmonics of the air-gap flux of which the slot harmonics are a major part. The force caused by the higher harmonics and the unipolar flux is studied in the case where a four-pole stator winding is used to reduce the four-pole flux. The higher harmonics are found to produce, in addition to the traditional unbalanced magnetic pull, a force similar to the effect of the unipolar flux and the two can be distinguished only by measuring the unipolar flux. In measurements at various operation points, the higher harmonics are found to produce much more force than the unipolar flux and two-pole flux but the unipolar flux is still significant. The four-pole winding also is used to actively control the four-pole flux and the magnetic forces. Designing the controller requires a low order model of the system. Such a model is derived and the effect of the slot harmonics and the unipolar flux are included in the model. Different measurements techniques and methods are presented to identify and validate the control model. The operation point dependence of the system dynamics is studied via measurements. All results are obtained from a 30 kW test motor. The rotor of the test machine has a long flexible shaft on external

  5. A new measurement method of magnetic flux density using magnetorheological fluid characteristics and a variable resistor circuit

    Science.gov (United States)

    Kim, Hwan-Choong; Han, Chulhee; Kim, Pyunghwa; Choi, Seung-Bok

    2015-08-01

    This work proposes a new approach with which to measure the magnetic flux density using the characteristics of magnetorheological fluid (MRF) that is integrated with a variable resistor. For convenience, it is called a magnetorheological fluid variable resistor (MRF-VR) system in this study. The mechanism of the MRF-VR is based on the interaction between ferromagnetic iron particles of the MRF due to an external magnetic field, which causes its electrical resistance to be field dependent. Using this salient principle, the proposed MRF-VR system is constructed with electrodes and MRF, and its performance is demonstrated by evaluating its electrical resistive characteristics such as dimensional influence, response time, hysteresis and frequency response. After evaluating the performance characteristics, a feedback control system with a proportional-integral-derivative (PID) controller is established, and resistance-trajectory control experiments are carried out. Based on this MRF-VR system, a magnetic field-sensing system is constructed using a Wheatstone bridge circuit, and a polynomial model for calculating the magnetic flux density is formulated from the measured voltage. Finally, the accuracy and effectiveness of the proposed sensing system associated with the empirical polynomial model is successfully verified by comparing the calculated values of magnetic flux density with those measured by a commercial tesla meter.

  6. Topology optimized and 3D printed polymer-bonded permanent magnets for a predefined external field

    Science.gov (United States)

    Huber, C.; Abert, C.; Bruckner, F.; Pfaff, C.; Kriwet, J.; Groenefeld, M.; Teliban, I.; Vogler, C.; Suess, D.

    2017-08-01

    Topology optimization offers great opportunities to design permanent magnetic systems that have specific external field characteristics. Additive manufacturing of polymer-bonded magnets with an end-user 3D printer can be used to manufacture permanent magnets with structures that had been difficult or impossible to manufacture previously. This work combines these two powerful methods to design and manufacture permanent magnetic systems with specific properties. The topology optimization framework is simple, fast, and accurate. It can also be used for the reverse engineering of permanent magnets in order to find the topology from field measurements. Furthermore, a magnetic system that generates a linear external field above the magnet is presented. With a volume constraint, the amount of magnetic material can be minimized without losing performance. Simulations and measurements of the printed systems show very good agreement.

  7. Slow twists of solar magnetic flux tubes and the polar magnetic field of the sun

    Science.gov (United States)

    Hollweg, Joseph V.; Lee, Martin A.

    1989-01-01

    The solar wind model of Weber and Davis (1967) is generalized to compute the heliospheric magnetic field resulting from solar rotation or a steady axisymmetric twist including a geometrical expansion which is more rapid than spherical. The calculated increase in the ratio of the toroidal to poloidal field components with heliocentric radial distance r clarifies an expression derived recently by Jokipii and Kota (1989). Magnetic-field components transverse to r do not in general grow to dominate the radial component at large r. The analysis also yields expressions for the Poynting flux associated with the steady twists.

  8. Diffusive, convective and Nernst-effect losses of magnetic flux and heat from a wall-confined magnetized plasma

    Science.gov (United States)

    Velikovich, A. L.; Giuliani, J. L.; Zalesak, S. T.

    2013-10-01

    The recently proposed MAGLIF approach to inertial fusion ignition involves compression and heating of plasma with frozen-in magnetic flux by a heavy cylindrical liner. To reach fusion conditions, the compressed plasma should retain a large fraction of the magnetic flux and thermal energy enclosed by the liner. Magnetic flux and heat losses from strongly magnetized plasma to a cold liner wall are significantly influenced by the Nernst and Ettingshausen thermomagnetic effects. We present exact analytical solutions of 1D MHD equations with Ohmic heating, heat conductivity and thermomagnetic terms included and discuss relative roles of diffusive, conductive and Nernst-effect-related losses of magnetic flux and heat from the magnetized plasma to the wall. These solutions are compared to our 1D simulation results. They can serve for verification of plasma transport modeling by MHD codes. Work supported by DOE/NNSA.

  9. Handling magnetic anisotropy and magnetoimpedance effect in flexible multilayers under external stress

    Science.gov (United States)

    Agra, K.; Bohn, F.; Mori, T. J. A.; Callegari, G. L.; Dorneles, L. S.; Correa, M. A.

    2016-12-01

    We investigate the dynamic magnetic response though magnetoimpedance effect of ferromagnetic flexible NiFe/Ta and FeCuNbSiB/Ta multilayers under external stress. We explore the possibility of handling magnetic anisotropy, and consequently the magnetoimpedance effect, of magnetostrictive multilayers deposited onto flexible substrates. We quantify the sensitivity of the multilayers under external stress by calculating the ratio between impedance variations and external stress changes, and show that considerable values can be reached by tuning the magnetic field, frequency, magnetostriction constant, and external stress. The results extend possibilities of application of magnetostrictive multilayers deposited onto flexible substrates when under external stress and place them as very attractive candidates as element sensor for the development of sensitive smart touch sensors.

  10. Mean-field approximation for the potts model of a diluted magnet in the external field

    Science.gov (United States)

    Semkin, S. V.; Smagin, V. P.

    2016-07-01

    The Potts model of a diluted magnet with an arbitrary number of states placed in the external field has been considered. Phase transitions of this model have been studied in the mean-field approximation, the dependence of the critical temperature on the external field and the density of magnetic atoms has been found, and the magnetic susceptibility has been calculated. An improved mean-field technique has been proposed, which provides more accurate account of the effects associated with nonmagnetic dilution. The influence of dilution on the first-order phase transition curve and the magnetization jump at the phase transition has been studied by this technique.

  11. EXTERNAL MAGNETIC-PULSE STRAIGHTENING OF CARS BODY PANELS

    Directory of Open Access Journals (Sweden)

    A. Hnatov

    2014-10-01

    Full Text Available The basics of magnetic-pulse attraction of both ferromagnetic and non-ferromagnetic thin-wall sheet metals are investigated. The design models of inductor systems-magnetic-pulse straightening tools are presented. The final analytical expressins for excited efforts design in the tools under consideration are introduced. The practical testing of magnetic-pulse straightening with the tools under study is given.

  12. Critical mass flux for flaming ignition of wood as a function of external radiant heat flux and moisture content

    Science.gov (United States)

    S. McAllister; M. Finney; J. Cohen

    2011-01-01

    Extreme weather often contributes to crown fires, where the fire spreads from one tree crown to the next as a series of piloted ignitions. An important aspect in predicting crown fires is understanding the ignition of fuel particles. The ignition criterion considered in this work is the critical mass flux criterion - that a sufficient amount of pyrolysis gases must be...

  13. Comparing a current-carrying circular wire with polygons of equal perimeter; Magnetic field versus magnetic flux

    OpenAIRE

    J P Silva; Silvestre, A. J.

    2006-01-01

    We compare the magnetic field at the center of and the self-magnetic flux through a current-carrying circular loop, with those obtained for current-carrying polygons with the same perimeter. As the magnetic field diverges at the position of the wires, we compare the self-fluxes utilizing several regularization procedures. The calculation is best performed utilizing the vector potential, thus highlighting its usefulness in practical applications. Our analysis answers some of the intuition chal...

  14. Characteristic Analysis and Experimental Study of a Hybrid Permanent Magnet Variable Flux Memory Motor

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    Variable flux permanent magnet (PM) memory motors (VFMM), which combine the advantages of PM machines with high power density and electrically excited machines with controllable air-gap magnetic flux, have been widely concerned and researched in recent years.

  15. Magnetohydrostatic Equilibrium. II. Three-dimensional Multiple Open Magnetic Flux Tubes in the Stratified Solar Atmosphere

    Science.gov (United States)

    Gent, F. A.; Fedun, V.; Erdélyi, R.

    2014-07-01

    A system of multiple open magnetic flux tubes spanning the solar photosphere and lower corona is modeled analytically, within a realistic stratified atmosphere subject to solar gravity. This extends results for a single magnetic flux tube in magnetohydrostatic equilibrium, described in Gent et al. Self-similar magnetic flux tubes are combined to form magnetic structures, which are consistent with high-resolution observations. The observational evidence supports the existence of strands of open flux tubes and loops persisting in a relatively steady state. Self-similar magnetic flux tubes, for which an analytic solution to the plasma density and pressure distribution is possible, are combined. We calculate the appropriate balancing forces, applying to the equations of momentum and energy conservation to preserve equilibrium. Multiplex flux tube configurations are observed to remain relatively stable for up to a day or more, and it is our aim to apply our model as the background condition for numerical studies of energy transport mechanisms from the solar surface to the corona. We apply magnetic field strength, plasma density, pressure, and temperature distributions consistent with observational and theoretical estimates for the lower solar atmosphere. Although each flux tube is identical in construction apart from the location of the radial axis, combinations can be applied to generate a non-axisymmetric magnetic field with multiple non-uniform flux tubes. This is a considerable step forward in modeling the realistic magnetized three-dimensional equilibria of the solar atmosphere.

  16. Interaction between granulation and small-scale magnetic flux observed by Hinode

    Institute of Scientific and Technical Information of China (English)

    Jun Zhang; Shu-Hong Yang; Chun-Lan Jin

    2009-01-01

    With the polarimetric observations obtained by the Spectro-Polarimeter on board Hinode, we study the relationship between granular development and magnetic field evolution in the quiet Sun. Six typical cases are displayed to exhibit interaction be-tween granules and magnetic elements, and we have obtained the following results. (1) A granule develops centrosymmetrically when no magnetic flux emerges within the gran-ular cell. (2) A granule develops and splits noncentrosymmetrically while flux emerges at an outer part of the granular cell. (3) Magnetic flux emergence in a cluster of mixed polarities is detected at the position of a granule as soon as the granule breaks up. (4) A dipole emerges accompanied by the development of a granule, and the two elements of the dipole are rooted in the adjacent intergranular lanes and face each other across the gran-ule. Advected by the horizontal granular motion, the positive element of the dipole then cancels with the 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 in a granular cell, the granule shrinks and then disappears. (7) Horizontal magnetic fields are enhanced at the places where dipoles emerge and where opposite polarities cancel each other, but only the horizontal fields between the dipolar elements point in an orderly way from the positive elements to the negative ones. Our results reveal that granules and small-scale magnetic fluxes influence each other. Granular flow advects magnetic flux, and magnetic flux evolution suppresses granular development. There exist extremely large Doppler blue-shifts at the site of one canceling magnetic element. This phenomenon may be caused by the upward flow pro-duced by magnetic reconnection below the photosphere.

  17. Magnetic flux inversion in Charged BPS vortices in a Lorentz-violating Maxwell-Higgs framework

    CERN Document Server

    Cantanhede, C M; Ferreira, M M; da Hora, E

    2012-01-01

    We demonstrate by first the existence of electrically charged BPS vortices in a Maxwell-Higgs model supplemented with a parity-odd Lorentz-violating (LV) structure belonging to the CPT-even gauge sector of the standard model extension and a fourth order potential (in the absence of the Chern-Simons term). The modified first order BPS equations provide charged vortex configurations endowed with some interesting features: localized and controllable spatial thickness, integer flux quantization, electric field inversion and magnetic flux reversion. This model could possibly be applied on condensed matter systems which support charged vortices carrying localized and integer quantized magnetic flux, endowed with flipping of the magnetic flux.

  18. Empirical Modeling of Radiative versus Magnetic Flux for the Sun-as-a-Star

    CERN Document Server

    Preminger, Dora; Chapman, Gary; Martens, Petrus C H; 10.1007/s11207-010-9560-1

    2010-01-01

    We study the relationship between full-disk solar radiative flux at different wavelengths and average solar photospheric magnetic-flux density, using daily measurements from the Kitt Peak magnetograph and other instruments extending over one or more solar cycles. We use two different statistical methods to determine the underlying nature of these flux-flux relationships. First, we use statistical correlation and regression analysis and show that the relationships are not monotonic for total solar irradiance and for continuum radiation from the photosphere, but are approximately linear for chromospheric and coronal radiation. Second, we use signal theory to examine the flux-flux relationships for a temporal component. We find that a well-defined temporal component exists and accounts for some of the variance in the data. This temporal component arises because active regions with high magnetic field strength evolve, breaking up into small-scale magnetic elements with low field strength, and radiative and magnet...

  19. Influence of the external solution in the electroosmotic flux induced by realkalisation

    Directory of Open Access Journals (Sweden)

    Castellote, M.

    2003-12-01

    Full Text Available Electrochemical repair methods are based on the application of an impressed direct current between the reinforcement and an auxiliary electrode placed at the concrete surface. In the case of realkalisation, the aim of the treatment consists in restoring the alkalinity of the concrete around the rebar to repassivate it. The realkalisation seems to be primarily provided by the generation of OH- at the rebar which is acting as cathode, through the reaction of water hydrolysis. It had been claimed that also carbonate ions penetrate towards the rebar by the electroosmosis; however it was not until very recently that the authors were able to demonstrate and quantify it through hardened carbonated concrete. In the present paper, laboratory trials are reported showing the influence of the external solution in the electroosmotic flux. The experiments have been carried out on normalised carbonated OPC mortars and 4 different solutions have been tested, ranging from 0.1 to 2M in Na2CO3. As a result, it has been proved that the electroosmotic flux is not constant during the experiment. The pH in the anolyte is the determining parameter on the zeta potential and consequently in the electroosmotic flux, reaching its maximum, for the experiments of this research, at the pH of the buffer carbonate/'bicarbonate.

    Los métodos electroquímicos de reparación de estructuras dañadas por corrosión de armaduras se basan en la aplicación de corriente continua entre la armadura y un electrodo auxiliar colocado sobre la superficie del hormigón. En el caso de la realcalinización, el objetivo del tratamiento consiste en restaurar la alcalinidad del hormigón alrededor de la armadura, con lo que se consigue la repasivación de la misma. Esta alcalinización se alcanza por la generación de OH- en la hidrólisis del agua que tiene lugar en el acero que actúa como cátodo, aunque también se postula la penetración de

  20. Influence of External Magnetic Field on Anomalous Skin Effects in Inductively Coupled Plasmas

    Institute of Scientific and Technical Information of China (English)

    MAO Ming; WANG You-Nian

    2004-01-01

    @@ Using a one-dimensional slab model, we study the influence of the external static magnetic field on the anomalous skin effects in the inductively coupled plasma. The rf electromagnetic field in the plasma is determined by solving the linearized Boltzmann equation incorporating with the Maxwell equations. The numerical results show that,due to the existence of the external magnetic field, the anomalous skin effects are greatly enhanced and the number of regions with negative absorption is decreased.

  1. Angular dependence of direct current decay in a closed YBCO double-pancake coil under external AC magnetic field and reduction by magnetic shielding

    Science.gov (United States)

    Geng, J.; Zhang, H.; Li, C.; Zhang, X.; Shen, B.; Coombs, T. A.

    2017-03-01

    High T c superconducting (HTS) coils are ideal candidates in the use of high field magnets. HTS coils carrying a direct current, however, suffer a non-negligible loss when they are exposed to an external AC magnetic field. Although this phenomenon is well known, no study concerning AC magnetic field angular dependence of direct current decay has ever been shown. In this work, we experimentally investigate the direct current decay characteristics in a closed double pancake coil made of a YBCO coated conductor under external AC field. AC field of different angles with respect to the coil plane is applied. Results show that the current decay rate presents a strong angular dependence. The fastest decay occurs when the field is parallel to the coil plane, in which case the surface of the tape in the outermost layer experiences most flux variation. To reduce the decay rate, we propose wrapping superconducting tapes around the outermost layer of the coil to shield external AC field. This method significantly reduces direct current decay rate under parallel field, without affecting the perpendicular self-field of the coil.

  2. The expected imprint of flux rope geometry on suprathermal electrons in magnetic clouds

    Directory of Open Access Journals (Sweden)

    M. J. Owens

    2009-10-01

    Full Text Available Magnetic clouds are a subset of interplanetary coronal mass ejections characterized by a smooth rotation in the magnetic field direction, which is interpreted as a signature of a magnetic flux rope. Suprathermal electron observations indicate that one or both ends of a magnetic cloud typically remain connected to the Sun as it moves out through the heliosphere. With distance from the axis of the flux rope, out toward its edge, the magnetic field winds more tightly about the axis and electrons must traverse longer magnetic field lines to reach the same heliocentric distance. This increased time of flight allows greater pitch-angle scattering to occur, meaning suprathermal electron pitch-angle distributions should be systematically broader at the edges of the flux rope than at the axis. We model this effect with an analytical magnetic flux rope model and a numerical scheme for suprathermal electron pitch-angle scattering and find that the signature of a magnetic flux rope should be observable with the typical pitch-angle resolution of suprathermal electron data provided ACE's SWEPAM instrument. Evidence of this signature in the observations, however, is weak, possibly because reconnection of magnetic fields within the flux rope acts to intermix flux tubes.

  3. Distribution of Magnetic Flux Density in Soft-Contact EMCC Rectangular Mold

    Institute of Scientific and Technical Information of China (English)

    ZHANG Lin-tao; WANG En-gang; DENG An-yuan; HE Ji-cheng

    2006-01-01

    The distribution of the magnetic flux density in a soft-contact electromagnetic continuous casting (EMCC) rectangular mold was investigated. The experimental results show that with an increase in electric power, the magnetic flux density increases. The position where the maximum magnetic flux density appears will shift up when the coil moves to the top of the mold. At the same time, the maximum magnetic flux density will increase and the effective acting range of electromagnetic pressure will widen. As a result, in practice, the coil should be placed near the top part of the mold. The meniscus should be controlled near the top part of the coil, as this not only remarkably improves the billet surface quality but also saves energy. With the same electric power input, the higher the frequency, the lower the magnetic flux density.

  4. Design of axial-flux permanent-magnet low-speed machines and performance comparison between radial-flux and axial-flux machines

    Energy Technology Data Exchange (ETDEWEB)

    Parviainen, A.

    2005-07-01

    This thesis presents an alternative approach to the analytical design of surface-mounted axial-flux permanent-magnet machines. Emphasis has been placed on the design of axial-flux machines with a one-rotor-two-stators configuration. The design model developed in this study incorporates facilities to include both the electromagnetic design and thermal design of the machine as well as to take into consideration the complexity of the permanent-magnet shapes, which is a typical requirement for the design of high-performance permanent-magnet motors. A prototype machine with rated 5 kW output power at 300 min{sup -1} rotation speed has been designed and constructed for the purposes of ascertaining the results obtained from the analytical design model. A comparative study of low-speed axial-flux and low-speed radial-flux permanent-magnet machines is presented. The comparative study concentrates on 55 kW machines with rotation speeds 150 min{sup -1}, 300 min{sup -1} and 600 min{sup -1} and is based on calculated designs. A novel comparison method is introduced. The method takes into account the mechanical constraints of the machine and enables comparison of the designed machines, with respect to the volume, efficiency and cost aspects of each machine. It is shown that an axial-flux permanent-magnet machine with one-rotor-two-stators configuration has generally a weaker efficiency than a radial-flux permanent-magnet machine if for all designs the same electric loading, air-gap flux density and current density have been applied. On the other hand, axial-flux machines are usually smaller in volume, especially when compared to radial-flux machines for which the length ratio (axial length of stator stack vs. air-gap diameter) is below 0.5. The comparison results show also that radial-flux machines with a low number of pole pairs, p < 4, outperform the corresponding axial-flux machines. (orig.)

  5. DEVELOPMENT OF THE CONTROL METHODOLOGY OF THE GIANT MAGNETOSTRICTIVE ACTUATOR BASED ON MAGNETIC FLUX DENSITY

    Institute of Scientific and Technical Information of China (English)

    Jia Zhenyuan; Yang Xing; Shi Chun; Guo Dongming

    2003-01-01

    According to the principle of the magnetostriction generating mechanism, the control model of giant magnetostriction material based on magnetic field and the control method with magnetic flux density are developed. Furthermore, this control method is used to develop a giant magnetostrictive micro-displacement actuator (GMA) and its driving system. Two control methods whose control variables are current intensity and magnetic flux density are compared with each other by experimental studies. Finally, effective methods on improving the linearity and control precision of micro-displacement actuator and reducing the hysteresis based on the controlling magnetic flux density are obtained.

  6. Magnetic flux pinning in superconductors with hyperbolic-tessellation arrays of pinning sites

    Science.gov (United States)

    Misko, V. R.; Nori, Franco

    2012-05-01

    We study magnetic flux interacting with arrays of pinning sites (APSs) placed on vertices of hyperbolic tessellations (HTs). We show that, due to the gradient in the density of pinning sites, HT APSs are capable of trapping vortices for a broad range of applied magnetic fluxes. Thus, the penetration of magnetic field in HT APSs is essentially different from the usual scenario predicted by the Bean model. We demonstrate that, due to the enhanced asymmetry of the surface barrier for vortex entry and exit, this HT APS could be used as a “capacitor” to store magnetic flux.

  7. Oscillations of critical superconducting current in thin doubly-connected Sn films in an external perpendicular magnetic field

    Science.gov (United States)

    Sivakov, A. G.; Pokhila, A. S.; Glukhov, A. M.; Kuplevakhsky, S. V.; Omelyanchouk, A. N.

    2014-05-01

    We report the results of experimental and theoretical studies of critical current oscillations in thin doubly-connected Sn films in an external perpendicular magnetic field. The experiments were performed on samples that consisted of two wide electrodes joined together by two narrow channels. The length of the channels l satisfied the condition l ≫ ξ (ξ is the Ginzburg-Landau coherence length). At temperatures close to the critical temperature Tc, the dependence of the critical current Ic on average external magnetic flux Φ¯e has the form of a piecewise linear function, periodic with respect to the flux quantum Φ0. The amplitude of the Ic oscillation at a given temperature is proportional to the factor ξ/l. Moreover, the dependence Ic=Ic(Φ ¯e) is found to be multivalued, hence indicating the presence of metastable states. Based on the Ginzburg-Landau approximation, a theory was constructed that explains the above features of the oscillation phenomenon taking a perfectly symmetric system as an example. Further, the experiments displayed the effects related to the critical currents imbalance between the superconducting channels, i.e., shift of the maxima of the dependence Ic=Ic(Φ ¯e) accompanied by an asymmetry with respect to the transport current direction.

  8. Fracture problem for an external circumferential crack in a functionally graded superconducting cylinder subjected to a parallel magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Z. [Department of Engineering Mechanics, Shijiazhuang Tiedao University, Shijiazhuang 050043 (China); Gao, S.W. [College of Civil Engineering, Hebei Institute of Architecture and Civil Engineering, Zhangjiakou 075000 (China); Feng, W.J., E-mail: wjfeng9999@126.com [Department of Engineering Mechanics, Shijiazhuang Tiedao University, Shijiazhuang 050043 (China)

    2016-02-15

    Highlights: • External circumferential crack problem of superconducting cylinder is investigated. • A functionally graded superconducting cylinder is analyzed. • The magnetically impermeable crack surface condition is applied. • The generalized Irie-Yamafuji critical state model outside the crack region is adopted. - Abstract: In this study, the multiple isoparametric finite element method (MIFEM) is used to investigate external circumferential crack problem of a functionally graded superconducting cylinder subjected to electromagnetic forces. The superconducting cylinder is composed by Bi2223/Ag composite with material parameters varying. A crack reference region is defined to reflect the effects of crack on flux and current densities, and the magnetically impermeable crack surface condition and the generalized Irie–Yamafuji critical state model outside the crack region are adopted. The distributions of magnetic flux density in the superconducting cylinder are obtained analytically for both the zero-field cooling (ZFC) and the field cooling (FC) activation processes. Based on the MIFEM, the stress intensity factors (SIFs) at crack fronts in the process of field ascent and/or descent are then numerically calculated. It is interesting to note from numerical results that for the present crack model in the ZFC activation process, the crack is easily propagate and grow with the applied field increases, and that in the field descent process of either the ZFC case or FC case, the crack generally does not propagate. In addition, in the field ascent process of the ZFC case, the SIFs depend on not only the crack depths and model parameters but also the applied field. The present study should be helpful to the design and application of high-temperature superconductors with external edge cracks.

  9. Quantitative evaluation of magnetic flux density in a magnetic recording head and pseudo soft underlayer by electron holography.

    Science.gov (United States)

    Xia, Weixing; Hirata, Kei; Yanagisawa, Keiichi; Ishida, Yoichi; Kasai, Hiroto; Yanagiuchi, Katsuaki; Shindo, Daisuke; Tonomura, Akira

    2010-01-01

    The magnetic interaction between the pole tip of a single-pole head and a pseudo soft underlayer in perpendicular magnetic recording was observed by electron holography. The magnetic flux density inside the soft underlayer was quantitatively evaluated. The distribution of magnetic flux density was calculated using the finite element method, and the influences of the modulation of the reference wave and stray fields were investigated by comparison with experimental results. The flux density observed was found to be underestimated due to the modulation of the phase shift in reference wave. The magnetic flux measured experimentally was larger than that inside the specimen because of the relatively large stray fields above and below the specimen in the direction of the electron beam.

  10. Local imaging of magnetic flux in superconducting thin films

    Energy Technology Data Exchange (ETDEWEB)

    Shapoval, Tetyana

    2010-01-26

    Local studies of magnetic flux line (vortex) distribution in superconducting thin films and their pinning by natural and artificial defects have been performed using low-temperature magnetic force microscopy (LT-MFM). Taken a 100 nm thin NbN film as an example, the depinning of vortices from natural defects under the influence of the force that the MFM tip exerts on the individual vortex was visualized and the local pinning force was estimated. The good agreement of these results with global transport measurements demonstrates that MFM is a powerful and reliable method to probe the local variation of the pinning landscape. Furthermore, it was demonstrated that the presence of an ordered array of 1-{mu}m-sized ferromagnetic permalloy dots being in a magneticvortex state underneath the Nb film significantly influences the natural pinning landscape of the superconductor leading to commensurate pinning effects. This strong pinning exceeds the repulsive interaction between the superconducting vortices and allows vortex clusters to be located at each dot. Additionally, for industrially applicable YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin films the main question discussed was the possibility of a direct correlation between vortices and artificial defects as well as vortex imaging on rough as-prepared thin films. Since the surface roughness (droplets, precipitates) causes a severe problem to the scanning MFM tip, a nanoscale wedge polishing technique that allows to overcome this problem was developed. Mounting the sample under a defined small angle results in a smooth surface and a monotonic thickness reduction of the film along the length of the sample. It provides a continuous insight from the film surface down to the substrate with surface sensitive scanning techniques. (orig.)

  11. Measurements and Phenomenological Modeling of Magnetic FluxBuildup in Spheromak Plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Romero-Talamas, C A; Hooper, E B; Jayakumar, R; McLean, H S; Wood, R D; Moller, J M

    2007-12-14

    Internal magnetic field measurements and high-speed imaging at the Sustained Spheromak Physics Experiment (SSPX) [E. B. Hooper, L. D. Pearlstein, R. H. Bulmer, Nucl. Fusion 39, 863 (1999)] are used to study spheromak formation and field buildup. The measurements are analyzed in the context of a phenomenological model of magnetic helicity based on the topological constraint of minimum helicity in the open flux before reconnecting and linking closed flux. Two stages are analyzed: (1) the initial spheromak formation, i. e. when all flux surfaces are initially open and reconnect to form open and closed flux surfaces, and (2) the stepwise increase of closed flux when operating the gun on a new mode that can apply a train of high-current pulses to the plasma. In the first stage, large kinks in the open flux surfaces are observed in the high-speed images taken shortly after plasma breakdown, and coincide with large magnetic asymmetries recorded in a fixed insertable magnetic probe that spans the flux conserver radius. Closed flux (in the toroidal average sense) appears shortly after this. This stage is also investigated using resistive magnetohydrodynamic simulations. In the second stage, a time lag in response between open and closed flux surfaces after each current pulse is interpreted as the time for the open flux to build helicity, before transferring it through reconnection to the closed flux. Large asymmetries are seen during these events, which then relax to a slowly decaying spheromak before the next pulse.

  12. Effects of an external magnetic field in pulsed laser deposition

    Energy Technology Data Exchange (ETDEWEB)

    Garcia, T. [Universidad Autonoma de la Ciudad de Mexico (UACM), Prolongacion San Isidro 151, Col. San Lorenzo Tezonco, C.P. 09790, Mexico DF (Mexico)], E-mail: tupacgarcia@yahoo.com; Posada, E. de [CINVESTAV-IPN Unidad Merida, Applied Physics Department, A.P. 73, Cordemex, C.P. 97130 Merida, Yuc. (Mexico); Villagran, M. [CCADET, Universidad Nacional Autonoma de Mexico (UNAM), A.P. 70-186, C.P. 04510, Mexico DF (Mexico); Ll, J.L. Sanchez [Laboratorio de Magnetismo, Facultad de Fisica-IMRE, Universidad de La Habana, La Habana 10400 (Cuba); Bartolo-Perez, P.; Pena, J.L. [CINVESTAV-IPN Unidad Merida, Applied Physics Department, A.P. 73, Cordemex, C.P. 97130 Merida, Yuc. (Mexico)

    2008-12-30

    Thin films were grown by pulsed laser deposition, PLD, on Si (1 0 0) substrates by the ablation of a sintered ceramic SrFe{sub 12}O{sub 19} target with and without the presence of a nonhomogeneous magnetic field of {mu}{sub 0}H = 0.4 T perpendicular to substrate plane and parallel to the plasma expansion axis. The field was produced by a rectangular-shaped Nd-Fe-B permanent magnet and the substrate was just placed on the magnet surface (Aurora method). An appreciable increment of optical emission due to the presence of the magnetic field was observed, but no film composition change or thickness increment was obtained. It suggests that the increment of the optical emission is due mainly to the electron confinement rather than confinement of ionic species.

  13. Differential rotation of stretched and twisted thick magnetic flux tube dynamos in Riemannian spaces

    OpenAIRE

    de Andrade, Garcia

    2007-01-01

    The topological mapping between a torus of big radius and a sphere is applied to the Riemannian geometry of a stretched and twisted very thick magnetic flux tube, to obtain spherical dynamos solving the magnetohydrodynamics (MHD) self-induction equation for the magnetic flux tubes undergoing differential (non-uniform) rotation along the tube magnetic axis. Constraints on the shear is also computed. It is shown that when the hypothesis of the convective cyclonic dynamo is used the rotation is ...

  14. Approximate energy states and thermal properties of a particle with position-dependent mass in external magnetic fields

    CERN Document Server

    Eshghi, Mahdi; Ikhdair, Sameer M

    2016-01-01

    We solve the Schr\\"odinger equation with a position-dependent mass (PDM) charged particle interacted via the superposition of the Morse and Coulomb potentials and exposed to external magnetic and Aharonov-Bohm (AB) flux fields. The non-relativistic bound state energies together with their wave functions are calculated for two spatially-dependent mass distribution functions. We also study the thermal quantities of such a system. Further, the canonical formalism is used to compute various thermodynamic variables for second choosing mass by using the Gibbs formalism. We give plots for energy as a function of various physical parameters. The behavior of the internal energy, specific heat and entropy as functions of temperature and mass density parameter in the inverse-square mass case for different values of magnetic field are shown.

  15. Tuning the Colloidal Crystal Structure of Magnetic Particles by External Field

    NARCIS (Netherlands)

    Pal, Antara; Malik, Vikash; He, Le; Erne, Ben H.; Yin, Yadong; Kegel, Willem K.; Petukhov, A. V.

    2015-01-01

    Manipulation of the self-assembly of magnetic colloidal particles by an externally applied magnetic field paves a way toward developing novel stimuli responsive photonic structures. Using microradian X-ray scattering technique we have investigated the different crystal structures exhibited by self-a

  16. Surface field in an ensemble of superconducting spheres under external magnetic field

    CERN Document Server

    Peñaranda, A; Ramírez-Piscina, L

    1999-01-01

    We perform calculations of the magnetic field on the surface of an ensemble of superconducting spheres when placed into an external magnetic field, which is the configuration employed in superheated superconducting granule detectors. The Laplace equation is numerically solved with appropriate boundary conditions by means of an iterative procedure and a multipole expansion.

  17. Bogomolnyi-type bounds in unconventional superconductors without external magnetic fields

    NARCIS (Netherlands)

    Achucarro, A; Manes, JL

    1996-01-01

    Following Bogomolnyi's classical. treatment of vortices, we develop a method for finding rigorous lower bounds to the Landau-Ginzburg free energy, describing unconventional superconductors in the absence of external magnetic fields. This allows a more precise description of the magnetic instabilitie

  18. Tunable defect modes in 2D photonic crystals by means of external magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Soltani Vala, A., E-mail: asoltani@tabrizu.ac.i [Physics Department, University of Tabriz, Tabriz (Iran, Islamic Republic of); Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz (Iran, Islamic Republic of); Rezaei, B. [Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz (Iran, Islamic Republic of); Kalafi, M. [Physics Department, University of Tabriz, Tabriz (Iran, Islamic Republic of); Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz (Iran, Islamic Republic of)

    2010-07-15

    We investigate the tunable defect modes in 2D photonic crystal of silicon rods in air background in which one of the rods is replaced by ferrite material and an external static magnetic field is applied in the ferrite rod direction. Using the supercell method, the dependence of E-polarized defect modes on the magnetic field has been reported.

  19. Properties of color-flavor locked strange quark matter in an external strong magnetic field

    Institute of Scientific and Technical Information of China (English)

    崔帅帅; 彭光雄; 陆振烟; 彭程; 徐建峰

    2015-01-01

    The properties of color-flavor locked strange quark matter in an external strong magnetic field are investigated in a quark model with density-dependent quark masses. Parameters are determined by stability arguments. It is found that the minimum energy per baryon of the color-flavor locked (MCFL) matter decreases with increasing magnetic-field strength in a certain range, which makes MCFL matter more stable than other phases within a proper magnitude of the external magnetic field. However, if the energy of the field itself is added, the total energy per baryon will increase.

  20. The Suppression and Promotion of Magnetic Flux Emergence in Fully Convective Stars

    Science.gov (United States)

    Weber, Maria A.; Browning, Matthew K.; Boardman, Suzannah; Clarke, Joshua; Pugsley, Samuel; Townsend, Edward

    2017-10-01

    Evidence of surface magnetism is now observed on an increasing number of cool stars. The detailed manner by which dynamo-generated magnetic fields giving rise to starspots traverse the convection zone still remains unclear. Some insight into this flux emergence mechanism has been gained by assuming bundles of magnetic field can be represented by idealized thin flux tubes (TFTs). Weber & Browning (2016) have recently investigated how individual flux tubes might evolve in a 0.3M⊙ M dwarf by effectively embedding TFTs in time-dependent flows representative of a fully convective star. We expand upon this work by initiating flux tubes at various depths in the upper ~50-75% of the star in order to sample the differing convective flow pattern and differential rotation across this region. Specifically, we comment on the role of differential rotation and time-varying flows in both the suppression and promotion of the magnetic flux emergence process.

  1. Spectropolarimetric evidence for a siphon flow along an emerging magnetic flux tube

    CERN Document Server

    Requerey, Iker S; Iniesta, J C Del Toro; Suárez, D Orozco; Rodríguez, J Blanco; Solanki, S K; Barthol, P; Gandorfer, A; Gizon, L; Hirzberger, J; Riethmüller, T L; van Noort, M; Schmidt, W; Pillet, V Martínez; Knölker, M

    2016-01-01

    We study the dynamics and topology of an emerging magnetic flux concentration using high spatial resolution spectropolarimetric data acquired with the Imaging Magnetograph eXperiment on board the Sunrise balloon-borne solar observatory. We obtain the full vector magnetic field and the line-of-sight (LOS) velocity through inversions of the Fe I line at 525.02 nm with the SPINOR code. The derived vector magnetic field is used to trace magnetic field lines. Two magnetic flux concentrations with different polarity and LOS velocities are found to be connected by a group of arch-shaped magnetic field lines. The positive polarity footpoint is weaker (1100 G) and displays an upflow, while the negative polarity footpoint is stronger (2200 G) and shows a downflow. This configuration is naturally interpreted as a siphon flow along an arched magnetic flux tube.

  2. EXTERNAL-LOOP AIRLIFT MAGNETICALLY STABILIZED BED--MINIMUM STABILIZATION AND FLUIDIZATION CONDITIONS

    Institute of Scientific and Technical Information of China (English)

    Jordan Hristov

    2005-01-01

    Experimental study of an airlift with a magnetically stabilized bed in the riser bottom has been performed.External magnetic field allows easy control of magnetized bed structure and liquid circulation rate. Minimum stabilization and fluidization conditions have been determined experimentally and by a three-line graphical method. Semi-empirical data correlations of sections of the experimental curves have been performed. Scaling relationships known from non-magnetic airlift are applicable too, but with the assumption that the magnetic field affects the loop friction coefficient only.

  3. Phase diagram of hot QCD in an external magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Fraga, Eduardo; Mizher, Ana Julia [Instituto de Fisica, Universidade Federal do Rio de Janeiro, CP 68528, Rio de Janeiro, 21945-970 RJ (Brazil); Chernodub, Maxim [Laboratoire de Mathematiques et Physique Theorique - LMPT, CNRS UMR 6083 Tours, Federation Denis Poisson, Faculte des Sciences et Techniques, Universite Francois Rabelais, Parc de Grandmont, 37200 Tours (France)

    2010-07-01

    The structure of the phase diagram for strong interactions becomes richer in the presence of a magnetic background, which enters as a new control parameter for the thermodynamics, and can exhibit new phases and interesting features. Motivated by the relevance of this physical setting for current and future high-energy heavy ion collision experiments and for the cosmological QCD transitions, we use the linear sigma model coupled to quarks and to Polyakov loops as an effective theory to investigate how the chiral and the deconfining transitions are affected, and present a general picture for the temperature-magnetic field phase diagram. We compute and discuss each contribution to the effective potential for the approximate order parameters, and uncover new phenomena such as the para-magnetically-induced breaking of Z(3). (authors)

  4. Spin polarization in high density quark matter under a strong external magnetic field

    CERN Document Server

    Tsue, Yasuhiko; Providencia, Constanca; Yamamura, Masatoshi; Bohr, Henrik

    2016-01-01

    In high density quark matter under a strong external magnetic field, possible phases are investigated by using the Nambu-Jona-Lasinio model with axial vector-type four-point interaction or tensor-type four-point interaction between quarks. In the axial vector-type interaction, it is shown that a quark spin polarized phase is realized in all region of the quark chemical potential under a strong external magnetic field within the lowest Landau level approximation. Each phase is characterized by the chiral condensate or dynamical quark mass. On the other hand, in the tensor-type interaction, it is also shown that the quark spin polarized phase does not appear even if there exists the strong external magnetic field. However, if the anomalous magnetic moment of quark is taken into account, it may be possible to realize the quark spin polarized phase.

  5. Magnetic Flux Rope Identification and Characterization from Observationally Driven Solar Coronal Models

    Science.gov (United States)

    Lowder, Chris; Yeates, Anthony

    2017-09-01

    Formed through magnetic field shearing and reconnection in the solar corona, magnetic flux ropes are structures of twisted magnetic field, threaded along an axis. Their evolution and potential eruption are of great importance for space weather. Here we describe a new methodology for the automated detection of flux ropes in simulated magnetic fields, utilizing field-line helicity. Our Flux Rope Detection and Organization (FRoDO) code, which measures the magnetic flux and helicity content of pre-erupting flux ropes over time, as well as detecting eruptions, is publicly available. As a first demonstration, the code is applied to the output from a time-dependent magnetofrictional model, spanning 1996 June 15–2014 February 10. Over this period, 1561 erupting and 2099 non-erupting magnetic flux ropes are detected, tracked, and characterized. For this particular model data, erupting flux ropes have a mean net helicity magnitude of 2.66× {10}43 Mx2, while non-erupting flux ropes have a significantly lower mean of 4.04× {10}42 Mx2, although there is overlap between the two distributions. Similarly, the mean unsigned magnetic flux for erupting flux ropes is 4.04× {10}21 Mx, significantly higher than the mean value of 7.05× {10}20 Mx for non-erupting ropes. These values for erupting flux ropes are within the broad range expected from observational and theoretical estimates, although the eruption rate in this particular model is lower than that of observed coronal mass ejections. In the future, the FRoDO code will prove to be a valuable tool for assessing the performance of different non-potential coronal simulations and comparing them with observations.

  6. Diffusion of external magnetic fields into the cone-in-shell target in the fast ignition

    Science.gov (United States)

    Sunahara, Atsushi; Johzaki, Tomoyui; Nagatomo, Hideo; Sakata, Shouhei; Matsuo, Kazuki; Lee, Seungho; Fujioka, Shinsuke; Shiraga, Hiroyuki; Azechi, Hiroshi; Firex-Project Team

    2016-10-01

    We simulated the diffusion of externally applied magnetic fields into cone-in-shell target in the fast ignition. In this ignition scheme, the externally magnetic fields up to kilo-Tesla is used to guide fast electrons to the high-dense imploded core, and understanding diffusion of the magnetic field is one of the key issues for increasing the coupling efficiency from the heating laser to the imploded core. In order to study the magnetic field, we have developed 2D cylindrical Maxwell equation solver with Ohm's law, and carried out simulations of diffusion of externally applied magnetic fields into a cone-in-shell target. Also, we estimated the conductivity of the cone and shell target based on the assumption of Saha-ionization equilibrium. We present our results of diffusion of magnetic fields. We also show that the target is heated by the eddy current. Because of the density and temperature dependence of the conductivity, the magnetic fields diffuse into the material with varying conductivity. Consequently, the magnetic fields into the cone-in-shell target depend on the temporal profile of the magnetic fields as well as the electrical and thermal properties of the material.

  7. Role of external magnetic field and current closure in the force balance mechanism of a magnetically stabilized plasma torch

    Science.gov (United States)

    G, Ravi; Goyal, Vidhi

    2012-10-01

    Experimental investigations on the role of applied external magnetic field and return current closure in the force balance mechanism of a plasma torch are reported. The plasma torch is of low power and has wall, gas and magnetic stabilization mechanisms incorporated in it. Gas flow is divided into two parts: axial-central and peripheral-shroud, applied magnetic field is axial and return current is co-axial. Results indicate that application of large external magnetic field gives rise to not only J x B force but also, coupled with gas flow, to a new drag-cum-centrifugal force that acts on the plasma arc root and column. The magnetic field also plays a role in the return current closure dynamics and thus in the overall force balance mechanism. This in turn affects the electro-thermal efficiency of the plasma torch. Detailed experimental results, analytical calculations and physical model representing the processes will be presented and discussed.

  8. Effects of Magnetic Flux Circulation on Radiation Belt and Ring Current Populations

    Science.gov (United States)

    Mitchell, E. J.; Fok, M. H.

    2011-12-01

    The orientation of the interplanetary magnetic field (IMF) determines the location of the dayside merging line and the magnetic flux circulation patterns. Magnetic flux circulation determines the amount of energy which enters the magnetosphere and ionosphere. We use the Lyon-Fedder-Mobarry (LFM) global Magneto-Hydro-Dynamic (MHD) code to simulate both idealized and real solar wind cases. We use several satellites to validate the LFM simulation results for the real solar wind case studies. With these cases, we examine the magnetic flux circulation under differing IMF orientations. We also use the Comprehensive Ring Current Model (CRCM) and Radiation Belt Environment (RBE) model to examine the inner magnetospheric response to the orientation of the IMF. We will present the different magnetic flux circulation patterns and the resulting effects on the radiation belt and ring current population.

  9. Testing a Solar Coronal Magnetic Field Extrapolation Code with the Titov-Demoulin Magnetic Flux Rope Model

    CERN Document Server

    Jiang, Chaowei

    2015-01-01

    In the solar corona, magnetic flux rope is believed to be a fundamental structure accounts for magnetic free energy storage and solar eruptions. Up to the present, the extrapolation of magnetic field from boundary data is the primary way to obtain fully three-dimensional magnetic information of the corona. As a result, the ability of reliable recovering coronal magnetic flux rope is important for coronal field extrapolation. In this paper, our coronal field extrapolation code (CESE-MHD-NLFFF, Jiang & Feng 2012) is examined with an analytical magnetic flux rope model proposed by Titov & Demoulin (1999), which consists of a bipolar magnetic configuration holding an semi-circular line-tied flux rope in force-free equilibrium. By using only the vector field in the bottom boundary as input, we test our code with the model in a representative range of parameter space and find that the model field is reconstructed with high accuracy. Especially, the magnetic topological interfaces formed between the flux rop...

  10. Instability of current sheets with a localized accumulation of magnetic flux

    Science.gov (United States)

    Pritchett, P. L.

    2015-06-01

    The longstanding problem of whether a current sheet with curved magnetic field lines associated with a small "normal" Bz component is stable is investigated using two-dimensional electromagnetic particle-in-cell simulations, employing closed boundary conditions analogous to those normally assumed in energy principle calculations. Energy principle arguments [Sitnov and Schindler, Geophys. Res. Lett. 37, L08102 (2010)] have suggested that an accumulation of magnetic flux at the tailward end of a thin current sheet could produce a tearing instability. Two classes of such current sheet configurations are probed: one with a monotonically increasing Bz profile and the other with a localized Bz "hump." The former is found to be stable (in 2D) over any reasonable time scale, while the latter is prone to an ideal-like instability that shifts the hump peak in the direction of the curvature normal and erodes the field on the opposite side. The growth rate of this instability is smaller by an order of magnitude than previous suggestions of an instability in an open system. An example is given that suggests that such an unstable hump configuration is unlikely to be produced by external driving of a current sheet with no Bz accumulation even in the presence of open boundary conditions.

  11. Sausage Instabilities on top of Kinking Lengthening Current-Carrying Magnetic Flux Tubes

    Science.gov (United States)

    von der Linden, Jens; You, Setthivoine

    2015-11-01

    Observations indicate that the dynamics of magnetic flux tubes in our cosmos and terrestrial experiments involve fast topological change beyond MHD reconnection. Recent experiments suggest that hierarchies of instabilities coupling disparate plasma scales could be responsible for this fast topological change by accessing two-fluid and kinetic scales. This study will explore the possibility of sausage instabilities developing on top of a kink instability in lengthening current-carrying magnetic flux tubes. Current driven flux tubes evolve over a wide range of aspect ratios k and current to magnetic flux ratios λ . An analytical stability criterion and numerical investigations, based on applying Newcomb's variational approach to idealized magnetic flux tubes with core and skin currents, indicate a dependence of the stability boundaries on current profiles and overlapping kink and sausage unstable regions in the k - λ trajectory of the flux tubes. A triple electrode planar plasma gun (Mochi.LabJet) is designed to generate flux tubes with discrete core and skin currents. Measurements from a fast-framing camera and a high resolution magnetic probe are being assembled into stability maps of the k - λ space of flux tubes. This work was sponsored in part by the US DOE Grant DE-SC0010340.

  12. Infrared polarimetry and the magnetic field in external galaxies

    Science.gov (United States)

    Jones, Terry Jay

    1990-01-01

    Here researchers report for the first time infrared polarimetry of the normal edge on spiral NGC 4565 and the interacting pair NGC 3690/IC 694 (Arp 299). These observations, as well as previous observations, were made with the Minnesota Infrared Polarimeter on the Space Infrared Telescope Facility during the past year. The goal is to explore the magnetic field geometry in these galaxies and to determine the extent to which the field is ordered and uniform.

  13. Optical properties and magnetic flux-induced electronic band tuning of a T-graphene sheet and nanoribbon.

    Science.gov (United States)

    Bandyopadhyay, Arka; Nandy, Atanu; Chakrabarti, Arunava; Jana, Debnarayan

    2017-08-16

    Tetragonal graphene (T-graphene) is a theoretically proposed dynamically stable, metallic allotrope of graphene. In this theoretical investigation, a tight binding (TB) model is used to unravel the metal to semiconductor transition of this 2D sheet under the influence of an external magnetic flux. In addition, the environment under which the sheet exposes an appreciable direct band gap of 1.41 ± 0.01 eV is examined. Similarly, the electronic band structure of the narrowest armchair T-graphene nanoribbon (NATGNR) also gets modified with different combinations of magnetic fluxes through the elementary rings. The band tuning parameters are critically identified for both systems. It is observed that the induced band gaps vary remarkably with the tuning parameters. We have also introduced an exact analytical approach to address the band structure of the NATGNR in the absence of any magnetic flux. Finally, the optical properties of the sheet and NATGNR are also critically analysed for both parallel and perpendicular polarizations with the help of density functional theory (DFT). Our study predicts that this material and its nanoribbons can be used in optoelectronic devices.

  14. Numerical evaluation of external magnetic effect on electromagnetic wave transmission through reentry plasma layer

    Science.gov (United States)

    Zhao, Qing; Bo, Yong; Lei, Mingda; Liu, Shuzhang; Liu, Ying; Liu, Jianwei; Zhao, Yizhe

    2016-11-01

    Numerical study of electromagnetic (EM) wave transmission through the magnetized plasma layer is presented in this paper. The plasma parameters are derived from computational fluid dynamics simulation of the flow field around a blunt body flying at supersonic speed and serve as the background plasma condition in the numerical modeling for EM wave transmission. The EM wave is generated by our newly designed coaxial feed GPS patch antenna. The external magnetic field is applied and assumed to vary linearly as a function of wall distance. The effects of the external applied magnetic field and the plasma parameters on wave transmission are studied, and the results show that EM wave propagation in the non-uniformly magnetized plasma is a matter of impedance matching, and the EM wave transmission can be adjusted only when the proper strength of the magnetic field is applied.

  15. Earth's external magnetic fields at low orbital altitudes

    Science.gov (United States)

    Klumpar, D. M.

    1990-01-01

    Under our Jun. 1987 proposal, Magnetic Signatures of Near-Earth Distributed Currents, we proposed to render operational a modeling procedure that had been previously developed to compute the magnetic effects of distributed currents flowing in the magnetosphere-ionosphere system. After adaptation of the software to our computing environment we would apply the model to low altitude satellite orbits and would utilize the MAGSAT data suite to guide the analysis. During the first year, basic computer codes to run model systems of Birkeland and ionospheric currents and several graphical output routines were made operational on a VAX 780 in our research facility. Software performance was evaluated using an input matchstick ionospheric current array, field aligned currents were calculated and magnetic perturbations along hypothetical satellite orbits were calculated. The basic operation of the model was verified. Software routines to analyze and display MAGSAT satellite data in terms of deviations with respect to the earth's internal field were also made operational during the first year effort. The complete set of MAGSAT data to be used for evaluation of the models was received at the end of the first year. A detailed annual report in May 1989 described these first year activities completely. That first annual report is included by reference in this final report. This document summarizes our additional activities during the second year of effort and describes the modeling software, its operation, and includes as an attachment the deliverable computer software specified under the contract.

  16. The Formation of Magnetic Depletions and Flux Annihilation Due to Reconnection in the Heliosheath

    Science.gov (United States)

    Drake, J. F.; Swisdak, M.; Opher, M.; Richardson, J. D.

    2017-03-01

    The misalignment of the solar rotation axis and the magnetic axis of the Sun produces a periodic reversal of the Parker spiral magnetic field and the sectored solar wind. The compression of the sectors is expected to lead to reconnection in the heliosheath (HS). We present particle-in-cell simulations of the sectored HS that reflect the plasma environment along the Voyager 1 and 2 trajectories, specifically including unequal positive and negative azimuthal magnetic flux as seen in the Voyager data. Reconnection proceeds on individual current sheets until islands on adjacent current layers merge. At late time, bands of the dominant flux survive, separated by bands of deep magnetic field depletion. The ambient plasma pressure supports the strong magnetic pressure variation so that pressure is anticorrelated with magnetic field strength. There is little variation in the magnetic field direction across the boundaries of the magnetic depressions. At irregular intervals within the magnetic depressions are long-lived pairs of magnetic islands where the magnetic field direction reverses so that spacecraft data would reveal sharp magnetic field depressions with only occasional crossings with jumps in magnetic field direction. This is typical of the magnetic field data from the Voyager spacecraft. Voyager 2 data reveal that fluctuations in the density and magnetic field strength are anticorrelated in the sector zone, as expected from reconnection, but not in unipolar regions. The consequence of the annihilation of subdominant flux is a sharp reduction in the number of sectors and a loss in magnetic flux, as documented from the Voyager 1 magnetic field and flow data.

  17. Geothermal Heat Flux Underneath Ice Sheets Estimated From Magnetic Satellite Data

    DEFF Research Database (Denmark)

    Fox Maule, Cathrine; Purucker, M.E.; Olsen, Nils

    The geothermal heat flux is an important factor in the dynamics of ice sheets, and it is one of the important parameters in the thermal budgets of subglacial lakes. We have used satellite magnetic data to estimate the geothermal heat flux underneath the ice sheets in Antarctica and Greenland....... By using satellite data, we are able to make heat flux maps covering the entire Antarctic continent and all of Greenland. We find that the heat flux varies from less than 50 to more than 150~mW/m2 underneath the ice sheets. To validate our results, we have compared our heat flux estimate with geologic...

  18. The continuum intensity as a function of magnetic field II. Local magnetic flux and convective flows

    CERN Document Server

    Kobel, P; Borrero, J M

    2014-01-01

    To deepen our understanding of the role of small-scale magnetic fields in active regions (ARs) and in the quiet Sun (QS) on the solar irradiance, it is fundamental to investigate the physical processes underlying their continuum brightness. Previous results showed that magnetic elements in the QS reach larger continuum intensities than in ARs at disk center, but left this difference unexplained. We use Hinode/SP disk center data to study the influence of the local amount of magnetic flux on the vigour of the convective flows and the continuum intensity contrasts. The apparent (i.e. averaged over a pixel) longitudinal field strength and line-of-sight (LOS) plasma velocity were retrieved by means of Milne-Eddington inversions (VFISV code). We analyzed a series of boxes taken over AR plages and the QS, to determine how the continuum intensity contrast of magnetic elements, the amplitude of the vertical flows and the box-averaged contrast were affected by the mean longitudinal field strength in the box (which sca...

  19. Peculiarities of the magnetic flux emerging in the equatorial solar zone

    Science.gov (United States)

    Merzlyakov, V. L.; Starkova, L. I.

    2016-12-01

    The magnetic flux longitudinal distribution in the equatorial solar zone has been studied. The magnetic synoptic maps of the Wilcox Solar Observatory (WSO) during Carrington rotations (CRs) 2052-2068 in 2007 and early 2008 have been analyzed. The longitudinal distributions of the area of the zones where the photospheric magnetic field locally enhanced have been constructed for each CR. The obtained distributions indicate that the zones are located discretely and that a clearly defined one narrow longitudinal interval with the maximum flux is present. The longitudinal position of this maximum shifted discretely by ≈130° at an interval of 5.5 ± 0.5 CRs. A longitudinal shift of the zones with an increased magnetic flux multiple of 60° was observed between the hemispheres. In addition, a time shift of ≈2.5 CRs existed between the instants when the position of maximum fluxes in different hemispheres shifted. The established peculiarities of the magnetic flux longitudinal distribution and time dynamics are interpreted as an action of supergiant convection cells. These actions result in that magnetic fields are removed from the generation region through the channels that are formed between such cells at a longitudinal interval of 120°. The average synodic rotation velocity of the considered equatorial channels, through which the magnetic flux emerges, is 13.43° day-1.

  20. Reduction of flux-creep in magnetized bulk HTS by use of permanent magnets

    Science.gov (United States)

    Parks, D.; Weinstein, R.; Davey, K.; Sawh, R.-P.; Carpenter, K.

    2017-01-01

    We report the effect of permanent magnet (PM) collars on the flux-creep rate of magnetized bulk HTS. The creep rates of single-grain, cylindrical samples are measured with attached collars activated to various fields, B PM, in the range 0 ≤ B PM ≤ B PM,max, where B PM,max is the fully saturated field of the PM. As B PM varies, the creep rate of the HTS is found to maintain its well-known form—a constant fractional loss λ, of original residual field, per decade of time. However, the magnitude of λ decreases as B PM increases. The decrease in λ is found to be linearly dependent on increasing B PM. The collar field for which flux-creep extrapolates to zero is found to be comparable to the maximum trappable field of the HTS bulk, B T,max. The properties of the dependence of λ on the HTS peak field, B T,max, the PM field, B PM, and the creep rate λ 0 with B PM = 0 permit the reduced creep rate in these experiments to be predicted by a universal equation.

  1. EFFECTS OF CARBOXYMETHLY DEXTRAN MAGNETIC NANOPARTICLES CARRIER SYSTEM ASSOCIATED WITH EXTERNAL MAGNETIC FIELDS ON KILLING TUMOR CELLS AND GENE TRANSFECTION

    Institute of Scientific and Technical Information of China (English)

    CAO Zheng-guo; ZHOU Si-wei; LIU Ji-hong

    2005-01-01

    Objective: To investigate the preparation of the carboxymethly dextran iron oxide magnetic nanoparticles (CDMN) and the effects of CDMN carrier system associated with external magnetic fields on killing tumor cells and gene transfection in vitro. Methods: Epirubicin-CDMN (EPI-CDMN) and green fluorescent protein (GFP) plasmid-CDMN (GFP-CDMN) were prepared by the oxidation-reduction procedure and their characters were detected, respectively. The effects of EPI-CDMN associated with external pulsed electromagnetic fields (PEMFs) (10 mT) on killing human bladder cancer BIU-87 cells were studied by MTT assay and Annexin-V/PI double-labeled flow cytometry technique, respectively. And the transfection efficiency of GFP when CDMN were used as gene carrier associated with the external magnetic fields was evaluated under fluorescence microscope in vitro. Results: The diameter of EPI-CDMN and GFP-CDMN were about 8~10 nm and 5~9 nm, respectively, and saturation magnetization were 0.22 emu/g and 0.26 emu/g, respectively. EPI-CDMN associated with PEMFs could significantly inhibit the proliferation of BIU-87 cells and induce cells apoptosis, the growth inhibitory rate and apoptosis rate were (21.82(3.18)% and (16.79(3.37)%, respectively. The transfection efficiency of GFP-CDMN combined with PEMFs was significant higher than that of GFP-CDMN without PEMFs [(45.70(4.32)% vs (35.85(2.16)%, P<0.05]. Conclusion: It seemed that EPI-CDMN associated with external magnetic fields could significantly killed human bladder cancer BIU-87 cells and CDMN could effectively transfer GFP gene into tumors cells with the help of external magnetic fields which provided experimental basis for the magnetic targeting therapy of tumor.

  2. Wavefunction Properties of a Single and a System of Magnetic Flux Tube(s) Oscillations

    CERN Document Server

    Esmaeili, Shahriar; Dadashi, Neda; Safari, Hossein

    2015-01-01

    In this study, the properties of wavefunctions of the MHD oscillations for a single and a system of straight flux tubes are investigated. Magnetic flux tubes with a straight magnetic field and longitudinally density stratification under coronal conditions were considered. With repect to the density inhomogeneity in the radial direction of the flux tube, a smoothed step function at the lateral surface is employed. A single three-dimensional wave equation for longitudinal component of the perturbed magnetic field is solved using the finite element method (FEM). Wavefunctions of the MHD oscillations are categorized into kink, sausage, and torsional modes. Concerning the amplitude location of the waves which are arisen from the flux tube, those waves identified as body, surface, and leaky waves and appeared in both a single and a system of flux tubes cases. Exact recognition of the wavefunctions can be used in coronal seismology and also helps to future the high resolution instruments that would be designed for s...

  3. Temporal and spatial patterns of internal and external stem CO2 fluxes in a sub-Mediterranean oak.

    Science.gov (United States)

    Salomón, Roberto L; Valbuena-Carabaña, María; Gil, Luis; McGuire, Mary Anne; Teskey, Robert O; Aubrey, Doug P; González-Doncel, Inés; Rodríguez-Calcerrada, Jesús

    2016-11-01

    To accurately estimate stem respiration (RS), measurements of both carbon dioxide (CO2) efflux to the atmosphere (EA) and internal CO2 flux through xylem (FT) are needed because xylem sap transports respired CO2 upward. However, reports of seasonal dynamics of FT and EA are scarce and no studies exist in Mediterranean species under drought stress conditions. Internal and external CO2 fluxes at three stem heights, together with radial stem growth, temperature, sap flow and shoot water potential, were measured in Quercus pyrenaica Willd. in four measurement campaigns during one growing season. Substantial daytime depressions in temperature-normalized EA were observed throughout the experiment, including prior to budburst, indicating that diel hysteresis between stem temperature and EA cannot be uniquely ascribed to diversion of CO2 in the transpiration stream. Low internal [CO2] (90%). Internal [CO2] was found to vary vertically along the stems. Seasonality in resistance to radial CO2 diffusion was related to shoot water potential. The low internal [CO2] and FT observed in our study may result from the downregulation of xylem respiration in response to a legacy of coppicing as well as high radial diffusion of CO2 through cambium, phloem and bark tissues, which was related to low water content of stems. Long-term studies analyzing temporal and spatial variation in internal and external CO2 fluxes and their interactions are needed to mechanistically understand and model respiration of woody tissues.

  4. Invariance properties of the Dirac equation with external electro-magnetic field

    Indian Academy of Sciences (India)

    N D Sen Gupta

    2003-01-01

    In this paper, we attempt to obtain the nature of the external field such that the Dirac equation with external electro-magnetic field is invariant. The Poincar´e group, which is the maximal symmetry group for field free case, is constrained by the presence of the external field. Introducing infinitesimal transformation of x andψ, we apply Lie’s extended group method to obtain the class of external field which admit of the invariance of the equation. It is important to note that the constraints for the existence of invariance are explicity on the electric and magnetic field, though only potentials explicity appears in the equation.

  5. Magnetic Activity in Thick Accretion Disks and Associated Observable Phenomena I. Flux Expulsion

    OpenAIRE

    Chakrabarti, Sandip K.; D'Silva, Sydney

    1993-01-01

    We study the dynamics of toroidal magnetic flux tubes, symmetric about the rotation axis, inside non-magnetic thick accretion disks around black holes. We present model equations which include effects of gravity, centrifugal force, pressure gradient force, Coriolis force, drag, magnetic tension and magnetic buoyancy. We solve them assuming the disk to be adiabatic. We show that under a wide range of parameters describing the size and the field strength, as well as angular momentum distributio...

  6. On the Characteristics of Footpoints of Solar Magnetic Flux Ropes during the Eruption

    OpenAIRE

    Cheng, X; Ding, M. D.

    2016-01-01

    We investigate the footpoints of four erupted magnetic flux ropes (MFRs) that appear as sigmoidal hot channels prior to the eruptions in the Atmospheric Imaging Assembly high temperaure passbands. The simultaneous Helioseismic and Magnetic Imager observations disclose that one footpoint of the MFRs originates in the penumbra or penumbra edge with a stronger magnetic field, while the other in the moss region with a weaker magnetic field. The significant deviation of the axis of the MFRs from t...

  7. Heat flux anomalies in Antarctica revealed from satellite magnetic data

    DEFF Research Database (Denmark)

    Maule, Cathrine Fox; Purucker, Michael E.; Olsen, Nils

    2005-01-01

    The geothermal heat flux is an important factor in the dynamics of ice sheets; it affects the occurrence of subglacial lakes, the onset of ice streams, and mass losses from the ice sheet base. Because direct heat flux measurements in ice-covered regions are difficult to obtain, we developed a met...

  8. BaBar technical design report: Chapter 9, Magnet coil and flux return

    Energy Technology Data Exchange (ETDEWEB)

    O`Connor, T.; The BaBar Collaboration

    1995-03-01

    The BaBar magnet is a thin, 1.5 T superconducting solenoid with a hexagonal flux return. This chapter discusses the physics requirements and performance goals for the magnet, describes key interfaces, and summarizes the projected magnet performance. It also presents the design of the superconducting solenoid, including magnetic design, cold mass design, quench protection and stability, cold mass cooling, cryostat design, and coil assembly and transportation. The cryogenic supply system and instrumentation are described briefly, and the flux return is described.

  9. Hadronic matter under an external magnetic field: in medium modification of the pion mass

    CERN Document Server

    Aguirre, R

    2016-01-01

    The covariant propagator of a fermion with anomalous magnetic moment interacting with an uniform external magnetic field at finite temperature and baryonic density is presented . The case of a scalar boson is also considered. The final expressions are given in terms of a 4-dimensional momentum representation. These results, which take account of the full effect of the magnetic field, are used to evaluate the modification of the pion mass at zero temperature as a function of the density and the magnetic intensity. For this purpose a self-consistent calculation, including one and two pion vertices, is employed.

  10. Cu Films Deposited by Unbalanced Magnetron Sputtering Enhanced by ICP and External Magnetic Field Confinement

    Institute of Scientific and Technical Information of China (English)

    QI Xuelian; REN Chunsheng; MA Tengcai; WANG Younian

    2008-01-01

    Metallic copper(Cu) films were deposited on a Si (100) substrate by unbalanced magnetron sputtering enhanced by radio-frequency plasma and external magnetic field confine-ment. The morphology and structure of the films were examined by scanning electron microscopy (SEM), atomic force microscope (AFM) and X-ray diffraction (XRD). The surface average rough-ness of the deposited Cu films was characterized by AFM data and resistivity was measured by a four-point probe. The results show that the Cu films deposited with radio-frequency discharge enhanced ionization and external magnetic field confinement have a smooth surface, low surface roughness and low resistivity. The reasons may be that the radio-frequency discharge and external magnetic field enhance the plasma density, which further improves the ion bombardment effect under the same bias voltage conditions. Ion bombardment can obviously influence the growth features and characteristics of the deposited Cu films.

  11. Effects of external magnetic field on biodistribution of nanoparticles: A histological study

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Tony [Department of Neurology, Chang Gung University College of Medicine and Memorial Hospital, 199 Tung-Hwa N Rd, Taipei, Taiwan (China); Hua, M.-Y. [Department of Chemical and Material Engineering, Chang Gung University, 259 Wen-Hwa 1st Road, Kwei-Shan, Tao-Yuan, Taiwan (China); Chen Jyhping [Department of Chemical and Material Engineering, Chang Gung University, 259 Wen-Hwa 1st Road, Kwei-Shan, Tao-Yuan, Taiwan (China); Wei, K.-C. [Department of Neurosurgery, Chang Gung University College of Medicine and Memorial Hospital, 199 Tung-Hwa N Rd, Taipei, Taiwan (China); Jung, S.-M. [Department of Pathology, Chang Gung University College of Medicine and Memorial Hospital, 199 Tung-Hwa N Rd, Taipei, Taiwan (China); Chang, Y.-J. [Department of Neurology, Chang Gung University College of Medicine and Memorial Hospital, 199 Tung-Hwa N Rd, Taipei, Taiwan (China); Jou, M.-J. [Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, 259 Wen-Hwa 1st Road, Kwei-Shan, Tao-Yuan 333, Taiwan (China); Ma, Y.-H. [Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, 259 Wen-Hwa 1st Road, Kwei-Shan, Tao-Yuan 333, Taiwan (China)]. E-mail: yhma@mail.cgu.edu.tw

    2007-04-15

    This study investigates the effect of external magnetic fields on the biodistribution of nanoparticles (NP). A NdFeB magnet of 2.4 kG was externally applied over the left femoral artery or right kidney. The 250 nm dextran-coated Fe{sub 3}O{sub 4} NP was injected via tail vein in healthy rats, and organs were taken 1 or 24 h later. Prussian blue stain revealed that NP were more rapidly retained in the liver and spleen than in the lungs. NP aggregation observed in the kidney and femoral artery after application of external magnets was time dependent. Hollow organs such as the intestine, colon, and urinary bladder retained little NP.

  12. Nonlinear evolution of electron shear flow instabilities in the presence of an external guide magnetic field

    CERN Document Server

    Jain, Neeraj

    2016-01-01

    The dissipation mechanism by which the magnetic field reconnects in the presence of an external (guide) magnetic field in the direction of the main current is not well understood. In thin electron current sheets (ECS) (thickness ~ an electron inertial length) formed in collisionless magnetic reconnection, electron shear flow instabilities (ESFI) are potential candidates for providing an anomalous dissipation mechanism which can break the frozen-in condition of the magnetic field affecting the structure and rate of reconnection. We investigate the evolution of ESFI in guide field magnetic reconnection. The properties of the resulting plasma turbulence and their dependence on the strength of the guide field are studied. Utilizing 3-D electron-magnetohydrodynamic simulations of ECS we show that, unlike the case of ECS self-consistently embedded in anti-parallel magnetic fields, the evolution of thin ECS in the presence of a guide field (equal to the asymptotic value of the reconnecting magnetic field or larger) ...

  13. Dynamics of magnetic flux tubes in close binary stars II. Nonlinear evolution and surface distributions

    CERN Document Server

    Holzwarth, V R

    2003-01-01

    Observations of magnetically active close binaries with orbital periods of a few days reveal the existence of starspots at preferred longitudes (with respect to the direction of the companion star). We numerically investigate the non-linear dynamics and evolution of magnetic flux tubes in the convection zoneof a fast-rotating component of a close binary system and explore whether the tidal effects are able to generate non-uniformities in the surface distribution of erupting flux tubes. Assuming a synchronised system with a rotation period of two days and consisting of two solar-type components, both the tidal force and the deviation of the stellar structure from spherical shape are considered in lowest-order perturbation theory. The magnetic field is initially stored in the form of toroidal magnetic flux rings within the stably stratified overshoot region beneath the convection zone. Once the field has grown sufficiently strong, instabilities initiate the formation of rising flux loops, which rise through the...

  14. A practical nonlinear controller for levitation system with magnetic flux feedback

    Institute of Scientific and Technical Information of China (English)

    李金辉; 李杰

    2016-01-01

    This work proposes a practical nonlinear controller for the MIMO levitation system. Firstly, the mathematical model of levitation modules is developed and the advantages of the control scheme with magnetic flux feedback are analyzed when compared with the current feedback. Then, a backstepping controller with magnetic flux feedback based on the mathematical model of levitation module is developed. To obtain magnetic flux signals for full-size maglev system, a physical method with induction coils installed to winding of the electromagnet is developed. Furthermore, to avoid its hardware addition, a novel conception of virtual magnetic flux feedback is proposed. To demonstrate the feasibility of the proposed controller, the nonlinear dynamic model of full-size maglev train with quintessential details is developed. Based on the nonlinear model, the numerical comparisons and related experimental validations are carried out. Finally, results illustrating closed-loop performance are provided.

  15. Turbulent ${\\alpha}$-effect in twisted magnetic flux tubes dynamos in Riemannian space

    CERN Document Server

    de Andrade, Garcia

    2007-01-01

    Analytical solution of first order torsion ${\\alpha}$-effect in twisted magnetic flux tubes representing a flux tube dynamo in Riemannian space is presented. Toroidal and poloidal component of the magnetic field decays as $r^{-1}$, while grow exponentially in time. The rate of speed of the helical dynamo depends upon the value of Frenet curvature of the tube. The $\\alpha$ factor possesses a fundamental contribution from constant torsion tube approximation. It is also assumed that the curvature of the magnetic axis of the tube is constant. Though ${\\alpha}$-effect dynamo equations are rather more complex in Riemann flux tube coordinates, a simple solution assuming force-free magnetic fields is shown to be possible. Dynamo solutions are possible if the dynamo action is able to change the signs of torsion and curvature of the dynamo flux tube simultaneously.

  16. Twisted versus braided magnetic flux ropes in coronal geometry. II. Comparative behaviour

    Science.gov (United States)

    Prior, C.; Yeates, A. R.

    2016-06-01

    Aims: Sigmoidal structures in the solar corona are commonly associated with magnetic flux ropes whose magnetic field lines are twisted about a mutual axis. Their dynamical evolution is well studied, with sufficient twisting leading to large-scale rotation (writhing) and vertical expansion, possibly leading to ejection. Here, we investigate the behaviour of flux ropes whose field lines have more complex entangled/braided configurations. Our hypothesis is that this internal structure will inhibit the large-scale morphological changes. Additionally, we investigate the influence of the background field within which the rope is embedded. Methods: A technique for generating tubular magnetic fields with arbitrary axial geometry and internal structure, introduced in part I of this study, provides the initial conditions for resistive-MHD simulations. The tubular fields are embedded in a linear force-free background, and we consider various internal structures for the tubular field, including both twisted and braided topologies. These embedded flux ropes are then evolved using a 3D MHD code. Results: Firstly, in a background where twisted flux ropes evolve through the expected non-linear writhing and vertical expansion, we find that flux ropes with sufficiently braided/entangled interiors show no such large-scale changes. Secondly, embedding a twisted flux rope in a background field with a sigmoidal inversion line leads to eventual reversal of the large-scale rotation. Thirdly, in some cases a braided flux rope splits due to reconnection into two twisted flux ropes of opposing chirality - a phenomenon previously observed in cylindrical configurations. Conclusions: Sufficiently complex entanglement of the magnetic field lines within a flux rope can suppress large-scale morphological changes of its axis, with magnetic energy reduced instead through reconnection and expansion. The structure of the background magnetic field can significantly affect the changing morphology of a

  17. Computer model simulation of null-flux magnetic suspension and guidance

    Energy Technology Data Exchange (ETDEWEB)

    He, Jianliang; Rote, D.M.

    1992-06-01

    This paper discusses the magnetic force computations in a null-flux suspension system using dynamic circuit theory. A computer simulation model that can be used to compute magnetic forces and predict the system performance is developed on the basis of dynamic circuit theory. Numerical examples are presented to demonstrate the application of the model. The performance of the null-flux suspension system is simulated and discussed. 8 refs.

  18. Computer model simulation of null-flux magnetic suspension and guidance

    Energy Technology Data Exchange (ETDEWEB)

    He, Jianliang; Rote, D.M.

    1992-01-01

    This paper discusses the magnetic force computations in a null-flux suspension system using dynamic circuit theory. A computer simulation model that can be used to compute magnetic forces and predict the system performance is developed on the basis of dynamic circuit theory. Numerical examples are presented to demonstrate the application of the model. The performance of the null-flux suspension system is simulated and discussed. 8 refs.

  19. MAGNETIC FIELD GRADIENT EFFECTS ON ION FLUX BEHAVIORS IN ECR PLASMA SOURCES

    Institute of Scientific and Technical Information of China (English)

    1998-01-01

    The available electron cyclotron resonance plasma source has been simulated in two-dimensional configuration space (z, r) and three-dimensional velocity space (Vz, Vr Vθ). The simulation is focused on the magnetic field gradient effects on ion flux behaviors in electron cyclotron resonance plasma sources. The simulation results show that, when the magnetic field gradients increase, electron temperature, plasma density, ionization rate, and ion flux in Zdirection would decrease, while ion energy and plasma potential would increase.

  20. Gap-related trapped magnetic flux dependence between single and combined bulk superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Z., E-mail: zgdeng@gmail.co [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, Tokyo 135-8533 (Japan); Miki, M.; Felder, B.; Tsuzuki, K.; Shinohara, N.; Uetake, T.; Izumi, M. [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, Tokyo 135-8533 (Japan)

    2011-05-15

    Highlights: {yields} Rectangular YBCO bulks to realize a compact combination. {yields} The gap effect was added to consider in the trapped flux density mapping. {yields} The trapped-flux dependence between single and combined bulks is gap related. {yields} It is possible to estimate the total magnetic flux of bulk combinations. - Abstract: Aiming at examining the trapped-flux dependence between single and combined bulk superconductors for field-pole applications, three rectangular Y{sub 1.65}Ba{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) bulks with a possibly compact combination were employed to investigate the trapped-flux characteristics of single and combined bulks with a field-cooling magnetization (FCM) method. A gap-related dependence was found between them. At lower gaps of 1 mm and 5 mm, the peak trapped fields and total magnetic flux of combined bulks are both smaller than the additive values of each single bulk, which can be ascribed to the demagnetization influences of the field around the bulk generated by the adjacent ones. While, at larger gaps like 10 mm, the situation becomes reversed. The combined bulks can attain bigger peak trapped fields as well as total magnetic flux, which indicates that the magnetic field by the bulk combination can reach higher gaps, thanks to the bigger magnetic energy compared with the single bulk. The presented results show that, on one hand, it is possible to estimate the total trapped magnetic flux of combined bulks by an approximate additive method of each single bulk while considering a demagnetization factor; on the other hand, it also means that the performance of combined bulks will be superior to the addition of each single bulk at larger gaps, thus preferable for large-scaled magnet applications.

  1. Construction and Design of a Modular Permanent Magnet Transverse Flux Generator

    Directory of Open Access Journals (Sweden)

    VIOREL, I.-A.

    2010-02-01

    Full Text Available A simple construction of a modular transverse flux generator with permanent magnets in the rotor is proposed in the paper. The specific technology is detailed and an analytical design algorithm is developed. A simplified model is proposed for calculating the machine heating and three dimensions magnetic flux calculation via finite element method (FEM is carried on in order to check the main generator characteristics.

  2. Magneto Hydrodynamic Simulations of a Magnetic Flux Compression Generator Using ALE3D

    Science.gov (United States)

    2017-07-13

    ARL-TR-8055 ● JULY 2017 US Army Research Laboratory Magneto-Hydrodynamic Simulations of a Magnetic Flux Compression Generator...Simulations of a Magnetic Flux Compression Generator Using ALE3D by George B Vunni Weapons and Materials Research Directorate, ARL... a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1

  3. Design and Finite Element Analysis of a Novel Transverse Flux Permanent Magnet Disk Generator

    DEFF Research Database (Denmark)

    Hosseini, Seyedmohsen; Moghani, Javad Shokrollahi; Ershad, Nima Farrokhzad;

    2011-01-01

    This paper presents a novel structure of a transverse flux permanent magnet disk generator. The proposed disk shape structure simplifies prototyping by using simple laminated steel sheets in comparison with previous transverse flux structures that employ bent laminations and soft magnetic composi...... and then optimized. The necessity of optimization is to find the best inner radius which maximizes output power to weight ratio, power factor and efficiency. To this end, the optimization process needs three dimensional finite element analyses....

  4. Fast modeling of flux trapping cascaded explosively driven magnetic flux compression generators.

    Science.gov (United States)

    Wang, Yuwei; Zhang, Jiande; Chen, Dongqun; Cao, Shengguang; Li, Da; Liu, Chebo

    2013-01-01

    To predict the performance of flux trapping cascaded flux compression generators, a calculation model based on an equivalent circuit is investigated. The system circuit is analyzed according to its operation characteristics in different steps. Flux conservation coefficients are added to the driving terms of circuit differential equations to account for intrinsic flux losses. To calculate the currents in the circuit by solving the circuit equations, a simple zero-dimensional model is used to calculate the time-varying inductance and dc resistance of the generator. Then a fast computer code is programmed based on this calculation model. As an example, a two-staged flux trapping generator is simulated by using this computer code. Good agreements are achieved by comparing the simulation results with the measurements. Furthermore, it is obvious that this fast calculation model can be easily applied to predict performances of other flux trapping cascaded flux compression generators with complex structures such as conical stator or conical armature sections and so on for design purpose.

  5. Flow-orthogonal bead oscillation in a microfluidic chip with a magnetic anisotropic flux-guide array.

    Science.gov (United States)

    van Pelt, Stijn; Derks, Roy; Matteucci, Marco; Hansen, Mikkel Fougt; Dietzel, Andreas

    2011-04-01

    A new concept for the manipulation of superparamagnetic beads inside a microfluidic chip is presented in this paper. The concept allows for bead actuation orthogonal to the flow direction inside a microchannel. Basic manipulation functionalities were studied by means of finite element simulations and results were oval-shaped steady state oscillations with bead velocities up to 500 μm/s. The width of the trajectory could be controlled by prescribing external field rotation. Successful verification experiments were performed on a prototype chip fabricated with excimer laser ablation in polycarbonate and electroforming of nickel flux-guides. Bead velocities up to 450 μm/s were measured in a 75 μm wide channel. By prescribing the currents in the external quadrupole magnet, the shape of the bead trajectory could be controlled.

  6. An introduction to the propellant-driven magnetic flux compression generator

    Energy Technology Data Exchange (ETDEWEB)

    Williams, P.E. [Los Alamos National Lab., NM (United States)

    1995-12-01

    An introduction to the concept of a propellant-driven magnetic flux compression generator is presented, together with the theory of its operation. The principles of operation of the propellant flux compression generator combine generator principles, derived from lumped parameter circuit theory, and interior ballistic principles.

  7. Estimation of the magnetic flux emergence rate in the quiet Sun from Sunrise data

    CERN Document Server

    Smitha, H N; Solanki, S K; Riethmueller, T

    2016-01-01

    The small-scale internetwork (IN) features are thought to be the major source of fresh magnetic flux in the quiet Sun. During its first science flight in 2009, the balloon-borne observatory Sunrise captured images of the magnetic fields in the quiet Sun at a high spatial resolution. Using these data we measure the rate at which the IN features bring magnetic flux to the solar surface. In a previous paper it was found that the lowest magnetic flux in small-scale features detected using the Sunrise observations is 9 x 10^14 Mx. This is nearly an order of magnitude smaller than the smallest fluxes of features detected in observations from Hinode satellite. In this paper, we compute the flux emergence rate (FER) by accounting for such small fluxes, which was not possible before Sunrise. By tracking the features with fluxes in the range 10^15-10^18 Mx, we measure an FER of 1100 Mx cm^-2 day^-1. The smaller features with fluxes less than or equal to 10^16 Mx are found to be the dominant contributors to the solar ma...

  8. Enhancement of critical current in mesoscopic superconducting strips by external magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Ilin, Konstantin; Henrich, Dagmar; Luck, Yannick; Fuchs, Lea; Meckbach, Johannes Maximilian; Siegel, Michael [Institut fuer Mikro- und Nanoelektronische Systeme, Karlsruher Institut fuer Technologie, Hertzstrasse 16, 76187 Karlsruhe (Germany)

    2013-07-01

    Current crowding in superconducting mesoscopic strips with bends results in decrease of critical current in these structures with respect to the strips without geometrical non-uniformities. Recently it has been shown that Meissner currents induced by externally applied magnetic field of appropriate direction allow to suppress this effect so that I{sub c}(B) can exceed I{sub c}(0). Experimental dependencies of critical current in mesoscopic bended strips made from ultra-thin superconducting films on externally applied magnetic field and their comparison to the theoretical predictions are presented and discussed.

  9. Tunneling effect of the spin-2 Bose condensate driven by external magnetic fields

    OpenAIRE

    Yu, Zhao-xian; Jiao, Zhi-yong

    2003-01-01

    In this paper, we have studied tunneling effect of the spin-2 Bose condensate driven by external magnetic field. We find that the population transfers among spin-0 and spin-$\\pm1$, spin-0 and spin-$\\pm2$ exhibit the step structure under the external cosinusoidal magnetic field respectively, but there do not exist step structure among spin-$\\pm1$ and spin-$\\pm2$. The tunneling current among spin-$\\pm1$ and spin-$\\pm2$ may exhibit periodically oscillation behavior, but among spin-0 and spin-$\\p...

  10. Modeling Coronal Response in Decaying Active Regions with Magnetic Flux Transport and Steady Heating

    Science.gov (United States)

    Ugarte-Urra, Ignacio; Warren, Harry P.; Upton, Lisa A.; Young, Peter R.

    2017-09-01

    We present new measurements of the dependence of the extreme ultraviolet (EUV) radiance on the total magnetic flux in active regions as obtained from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. Using observations of nine active regions tracked along different stages of evolution, we extend the known radiance—magnetic flux power-law relationship (I\\propto {{{Φ }}}α ) to the AIA 335 Å passband, and the Fe xviii 93.93 Å spectral line in the 94 Å passband. We find that the total unsigned magnetic flux divided by the polarity separation ({{Φ }}/D) is a better indicator of radiance for the Fe xviii line with a slope of α =3.22+/- 0.03. We then use these results to test our current understanding of magnetic flux evolution and coronal heating. We use magnetograms from the simulated decay of these active regions produced by the Advective Flux Transport model as boundary conditions for potential extrapolations of the magnetic field in the corona. We then model the hydrodynamics of each individual field line with the Enthalpy-based Thermal Evolution of Loops model with steady heating scaled as the ratio of the average field strength and the length (\\bar{B}/L) and render the Fe xviii and 335 Å emission. We find that steady heating is able to partially reproduce the magnitudes and slopes of the EUV radiance—magnetic flux relationships and discuss how impulsive heating can help reconcile the discrepancies. This study demonstrates that combined models of magnetic flux transport, magnetic topology, and heating can yield realistic estimates for the decay of active region radiances with time.

  11. Comparing a current-carrying circular wire with polygons of equal perimeter: magnetic field versus magnetic flux

    Science.gov (United States)

    Silva, J. P.; Silvestre, A. J.

    2005-09-01

    We compare the magnetic field at the centre and the self-magnetic flux through a current-carrying circular loop, with those obtained for current-carrying polygons with the same perimeter. As the magnetic field diverges at the position of the wires, we compare the self-fluxes utilizing several regularization procedures. The calculation is best performed utilizing the vector potential, thus highlighting its usefulness in practical applications. Our analysis answers some of the intuition challenges students face when they encounter a related simple textbook example. These results can be applied directly to the determination of mutual inductances in a variety of situations.

  12. Multifield measurement of magnetic fluctuation-induced particle flux in a high-temperature toroidal plasma

    Science.gov (United States)

    Lin, L.; Ding, W. X.; Brower, D. L.

    2016-12-01

    Magnetic fluctuation-induced particle transport is explored in the high-temperature, high-beta interior of the Madison symmetric torus (MST) reversed-field pinch by performing a multifield measurement of the correlated product of magnetic and density fluctuations associated with global resistive tearing modes. Local density fluctuations are obtained by inverting the line-integrated interferometry data after resolving the mode helicity through correlation techniques. The local magnetic and current density fluctuations are then reconstructed using a parameterized fit of Faraday-effect polarimetry measurements. Reconstructed 2D images of density and current density perturbations in a poloidal cross section exhibit significantly different spatial structure. Combined with their relative phase, the magnetic-fluctuation-induced particle transport flux and its spatial distribution are resolved. The convective magnetic fluctuation-induced particle flux profile is measured for both standard and high-performance plasmas in MST with tokamak-like confinement, showing large reduction in the flux during improved confinement.

  13. Effects of relative orientation of magnetocaloric inserts with the magnetic flux

    Energy Technology Data Exchange (ETDEWEB)

    Risser, M.; Vasile, C. [National Institute of Applied Sciences (INSA) Strasbourg, 24 Bd de la Victoire, 67084 Strasbourg, Cedex (France); Laboratoire de Genie de la Conception (LGeCo), 24 Bd de la Victoire, 67084 Strasbourg, Cedex (France); Engel, T. [National Institute of Applied Sciences (INSA) Strasbourg, 24 Bd de la Victoire, 67084 Strasbourg, Cedex (France); Laboratoire des Systemes Photoniques (LSP), 24 Bd de la Victoire, 67084 Strasbourg, Cedex (France)

    2009-08-15

    This paper presents the study of the magnetic change of the magnetic flux density into the magnetocaloric materials (MCMs). The MCMs are shaped in thin parallel plates separated by a fluid forming together an insert. It is shown that keeping all the parameters equal, the unique modification of the orientation of the insert induces a change of the magnetic flux density into the magnetocaloric materials. Like all paramagnetic and ferromagnetic materials, the MCMs have variable magnetic permeability according to the density of flux that crosses them. The influence of a thermal circuit on a permanent magnetic circuit assembly is also evaluated. In order to ensure the heat exchange between the magnetocaloric materials and the outside space, the use of a heat transfer fluid is needed. The heat transfer fluid goes along the mini plates and is also placed inside the magnetic field. Because a fluid is generally a diamagnetic element, this increases the total magnetic reluctance of the assembly. Two different configurations named serial and parallel have been studied and evaluated in order to find the configuration that causes minimal disturbances to the magnetic flux and thus increases the magnetocaloric effect (MCE). Both configurations were also compared in respect to the induction obtained inside the vacuum gap of the magnet assembly. (author)

  14. Self propagating high temperature synthesis of metal oxides. Reactions in external magnetic fields

    CERN Document Server

    Aguas, M D

    2001-01-01

    The preparation of metal oxides by Self-Propagating High-Temperature Synthesis is reported. The reactions are started with a point source of ignition; typically a hot wire. A synthesis wave is observed moving out from the point source and reactions terminate in seconds. Products obtained can be classified into ferrites (magnetic applications) and stannates (gas sensing applications). Ferrites were synthesised under variable external magnetic fields. The synthesis wave is hotter in the presence of an external magnetic field for hard ferrite synthesis. For spinel ferrites the opposite was observed. Materials synthesised in the field show differences in their bulk magnetic properties (coercivity and saturation magnetisation), structures and microstructures. Combustion reactions in large fields revealed changes in unit cell volume (shrinkage was observed for hard ferrites while expansion was observed for spinel ferrites). SHS synthesised hard ferrites show two distinct components; one has large grain structure co...

  15. High Mach-number collisionless shock driven by a laser with an external magnetic field

    Directory of Open Access Journals (Sweden)

    Morita T.

    2013-11-01

    Full Text Available Collisionless shocks are produced in counter-streaming plasmas with an external magnetic field. The shocks are generated due to an electrostatic field generated in counter-streaming laser-irradiated plasmas, as reported previously in a series of experiments without an external magnetic field [T. Morita et al., Phys. Plasmas, 17, 122702 (2010, Kuramitsu et al., Phys. Rev. Lett., 106, 175002 (2011] via laser-irradiation of a double-CH-foil target. A magnetic field is applied to the region between two foils by putting an electro-magnet (∼10 T perpendicular to the direction of plasma expansion. The generated shocks show different characteristics later in time (t > 20ns.

  16. Enhanced magnetic field probe array for improved excluded flux calculations on the C-2U advanced beam-driven field-reversed configuration plasma experiment

    Energy Technology Data Exchange (ETDEWEB)

    Roche, T., E-mail: troche@trialphaenergy.com; Thompson, M. C.; Mendoza, R.; Allfrey, I.; Garate, E.; Romero, J.; Douglass, J. [Tri Alpha Energy, P.O. Box 7010, Rancho Santa Margarita, California 92688 (United States)

    2016-11-15

    External flux conserving coils were installed onto the exterior of the C-2U [M. W. Binderbauer et al., Phys. Plasmas 22, 056110 (2015)] confinement vessel to increase the flux confinement time of the system. The 0.5 in. stainless steel vessel wall has a skin time of ∼5 ms. The addition of the external copper coils effectively increases this time to ∼7 ms. This led to better-confined/longer-lived field-reversed configuration (FRC) plasmas. The fringing fields generated by the external coils have the side effect of rendering external field measurements invalid. Such measurements were key to the previous method of excluded flux calculation [M. C. Thompson et al., Rev. Sci. Instrum. 83, 10D709 (2012)]. A new array of B-dot probes and Rogowski coils were installed to better determine the amount of flux leaked out of the system and ultimately provide a more robust measurement of plasma parameters related to pressure balance including the excluded flux radius. The B-dot probes are surface mountable chip inductors with inductance of 33 μH capable of measuring the DC magnetic field and transient field, due to resistive current decay in the wall/coils, when coupled with active integrators. The Rogowski coils measure the total change in current in each external coil (150 A/2 ms). Currents were also actively driven in the external coils. This renders the assumption of total flux conservation invalid which further complicates the analysis process. The ultimate solution to these issues and the record breaking resultant FRC lifetimes will be presented.

  17. Enhanced magnetic field probe array for improved excluded flux calculations on the C-2U advanced beam-driven field-reversed configuration plasma experiment

    Science.gov (United States)

    Roche, T.; Thompson, M. C.; Mendoza, R.; Allfrey, I.; Garate, E.; Romero, J.; Douglass, J.

    2016-11-01

    External flux conserving coils were installed onto the exterior of the C-2U [M. W. Binderbauer et al., Phys. Plasmas 22, 056110 (2015)] confinement vessel to increase the flux confinement time of the system. The 0.5 in. stainless steel vessel wall has a skin time of ˜5 ms. The addition of the external copper coils effectively increases this time to ˜7 ms. This led to better-confined/longer-lived field-reversed configuration (FRC) plasmas. The fringing fields generated by the external coils have the side effect of rendering external field measurements invalid. Such measurements were key to the previous method of excluded flux calculation [M. C. Thompson et al., Rev. Sci. Instrum. 83, 10D709 (2012)]. A new array of B-dot probes and Rogowski coils were installed to better determine the amount of flux leaked out of the system and ultimately provide a more robust measurement of plasma parameters related to pressure balance including the excluded flux radius. The B-dot probes are surface mountable chip inductors with inductance of 33 μH capable of measuring the DC magnetic field and transient field, due to resistive current decay in the wall/coils, when coupled with active integrators. The Rogowski coils measure the total change in current in each external coil (150 A/2 ms). Currents were also actively driven in the external coils. This renders the assumption of total flux conservation invalid which further complicates the analysis process. The ultimate solution to these issues and the record breaking resultant FRC lifetimes will be presented.

  18. Flux pileup in collisionless magnetic reconnection: bursty interaction of large flux ropes.

    Science.gov (United States)

    Karimabadi, H; Dorelli, J; Roytershteyn, V; Daughton, W; Chacón, L

    2011-07-08

    Using fully kinetic simulations of the island coalescence problem for a range of system sizes greatly exceeding kinetic scales, the phenomenon of flux pileup in the collisionless regime is demonstrated. While small islands on the scale of λ ≤ 5 ion inertial length (d(i)) coalesce rapidly and do not support significant flux pileup, coalescence of larger islands is characterized by large flux pileup and a weaker time averaged reconnection rate that scales as √(d(i)/λ) while the peak rate remains nearly independent of island size. For the largest islands (λ = 100d(i)), reconnection is bursty and nearly shuts off after the first bounce, reconnecting ~20% of the available flux.

  19. The effect of magnetic activity saturation in chromospheric flux-flux relationships

    CERN Document Server

    Martínez-Arnáiz, R M; Crespo-Chacón, I; Montes, D

    2011-01-01

    We present a homogeneous study of chromospheric and coronal flux-flux relationships using a sample of 298 late-type dwarf active stars with spectral types F to M. The chromospheric lines were observed simultaneously in each star to avoid spread due to long term variability. Unlike other works, we subtract the basal chromospheric contribution in all the spectral lines studied. For the first time, we quantify the departure of dMe stars from the general relations. We show that dK and dKe stars also deviate from the general trend. Studying the flux-colour diagrams we demonstrate that the stars deviating from the general relations are those with saturated X-ray emission and that those stars also present saturation in the H$\\alpha$ line. Using several age spectral indicators, we show that they are younger stars than those following the general relationships. The non-universality of flux-flux relationships found in this work should be taken into account when converting between fluxes in different chromospheric activ...

  20. Particle with spin 2 and anomalous magnetic moment in external electromagnetic and gravitational fields

    CERN Document Server

    Kisel, V V; Red'kov, V M

    2011-01-01

    Tensor 50-component form of the first order relativistic wave equation for a particle with spin 2 and anomalous magnetic moment is extended to the case of an arbitrary curved space-time geometry. An additional parameter considered in the presence of only electromagnetic field as related to anomalous magnetic moment, turns to determine additional interaction terms with external geometrical background through Ricci R_{kl} and Riemann R_{klmn} tensors.

  1. Deconfinement Phase Transition with External Magnetic Field in the Friedberg—Lee Model

    Science.gov (United States)

    Mao, Shi-Jun

    2016-11-01

    The deconfinement phase transition with external magnetic field is investigated in the Friedberg-Lee model. In the frame of functional renormalization group, we extend the often used potential expansion method for continuous phase transitions to the first-order phase transition in the model. By solving the flow equations we find that, the magnetic field displays a catalysis effect and it becomes more difficult to break through the confinement in hot and dense medium.

  2. Effect of an External Oriented Magnetic Field on Entropy Generation in Natural Convection

    OpenAIRE

    Atef El Jery; Nejib Hidouri; Mourad Magherbi; Ammar Ben Brahim

    2010-01-01

    The influence of an external oriented magnetic field on entropy generation in natural convection for air and liquid gallium is numerically studied in steady-unsteady states by solving the mass, the momentum and the energy conservation equations. Entropy generation depends on five parameters which are: the Prandtl number, the irreversibility coefficients, the inclination angle of the magnetic field, the thermal Grashof and the Hartmann numbers. Effects of these parameters on total and local ir...

  3. The effective potential of composite fields in weakly coupled QED in a uniform external magnetic field

    CERN Document Server

    Lee, D S; Ng, Y J; Shovkovy, I A

    1999-01-01

    The effective potential for the composite fields responsible for chiral symmetry breaking in weakly coupled QED in a magnetic field is derived. The global minimum of the effective potential is found to acquire a non-vanishing expectation value of the composite fields that leads to generating the dynamical fermion mass by an external magnetic field. The results are compared with those for the Nambu-Jona-Lasinio model.

  4. Deconfinement Phase Transition with External Magnetic Field in Friedberg-Lee Model

    CERN Document Server

    Mao, Shijun

    2015-01-01

    The deconfinement phase transition with external magnetic field is investigated in the Friedberg-Lee model. In the frame of functional renormalization group, we extend the often used potential expansion method for continuous phase transitions to the first-order phase transition in the model. By solving the flow equations we find that, the magnetic field displays a catalysis effect and it becomes more difficult to break through the confinement in hot and dense medium.

  5. A portable magnetic field of >3 T generated by the flux jump assisted, pulsed field magnetization of bulk superconductors

    Science.gov (United States)

    Zhou, Difan; Ainslie, Mark D.; Shi, Yunhua; Dennis, Anthony R.; Huang, Kaiyuan; Hull, John R.; Cardwell, David A.; Durrell, John H.

    2017-02-01

    A trapped magnetic field of greater than 3 T has been achieved in a single grain GdBa2Cu3O7-δ (GdBaCuO) bulk superconductor of diameter 30 mm by employing pulsed field magnetization. The magnet system is portable and operates at temperatures between 50 K and 60 K. Flux jump behaviour was observed consistently during magnetization when the applied pulsed field, Ba, exceeded a critical value (e.g., 3.78 T at 60 K). A sharp dBa/dt is essential to this phenomenon. This flux jump behaviour enables the magnetic flux to penetrate fully to the centre of the bulk superconductor, resulting in full magnetization of the sample without requiring an applied field as large as that predicted by the Bean model. We show that this flux jump behaviour can occur over a wide range of fields and temperatures, and that it can be exploited in a practical quasi-permanent magnet system.

  6. Magnetic flux and heat losses by diffusive, advective, and Nernst effects in magnetized liner inertial fusion-like plasma

    Energy Technology Data Exchange (ETDEWEB)

    Velikovich, A. L.; Giuliani, J. L. [Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375 (United States); Zalesak, S. T. [Berkeley Research Associates, Beltsville, Maryland 20705 (United States)

    2015-04-15

    The magnetized liner inertial fusion (MagLIF) approach to inertial confinement fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010); Cuneo et al., IEEE Trans. Plasma Sci. 40, 3222 (2012)] involves subsonic/isobaric compression and heating of a deuterium-tritium plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion, and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstrates that the heat loss from the hot compressed magnetized plasma to the cold liner is dominated by transverse heat conduction and advection, and the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter (ω{sub e}τ{sub e}≫1), the effective diffusion coefficients determining the losses of heat and magnetic flux to the liner wall are both shown to decrease with ω{sub e}τ{sub e} as does the Bohm diffusion coefficient cT/(16eB), which is commonly associated with low collisionality and two-dimensional transport. We demonstrate how this family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics.

  7. Magnetic flux and heat losses by diffusive, advective, and Nernst effects in magnetized liner inertial fusion-like plasma

    Science.gov (United States)

    Velikovich, A. L.; Giuliani, J. L.; Zalesak, S. T.

    2015-04-01

    The magnetized liner inertial fusion (MagLIF) approach to inertial confinement fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010); Cuneo et al., IEEE Trans. Plasma Sci. 40, 3222 (2012)] involves subsonic/isobaric compression and heating of a deuterium-tritium plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion, and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstrates that the heat loss from the hot compressed magnetized plasma to the cold liner is dominated by transverse heat conduction and advection, and the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter ( ωeτe≫1 ), the effective diffusion coefficients determining the losses of heat and magnetic flux to the liner wall are both shown to decrease with ωeτe as does the Bohm diffusion coefficient c T /(16 e B ) , which is commonly associated with low collisionality and two-dimensional transport. We demonstrate how this family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics.

  8. Crossing and anti-crossing effects of polaritons in a magnetic-semiconductor superlattice influenced by an external magnetic field

    Science.gov (United States)

    Tuz, Vladimir R.; Fesenko, Volodymyr I.; Fedorin, Illia V.; Sun, Hong-Bo; Shulga, Valeriy M.

    2017-03-01

    Crossing and anti-crossing effects in dispersion characteristics of both bulk and surface polaritons in a magnetic-semiconductor superlattice influenced by an external static magnetic field being in the Faraday geometry are discussed. The bulk polaritons are classified as eigenwaves with right-handed and left-handed elliptically polarized states, whereas the surface polaritons are considered as hybrid modes having a predominant effect of either magnetic or semiconductor subsystem, and distinctions in dispersion characteristics of such polaritons are revealed involving the concept of critical points.

  9. Linear and nonlinear absorption coefficients of spherical quantum dot inside external magnetic field

    Science.gov (United States)

    Çakır, Bekir; Yakar, Yusuf; Özmen, Ayhan

    2017-04-01

    We have calculated the wavefunctions and energy eigenvalues of spherical quantum dot with infinite potential barrier inside uniform magnetic field. In addition, we have investigated the magnetic field effect on optical transitions between Zeeman energy states. The results are expressed as a function of dot radius, incident photon energy and magnetic field strength. The results present that, in large dot radii, the external magnetic field affects strongly the optical transitions between Zeeman states. In the strong spatial confinement case, energy level is relatively insensitive to the magnetic field, and electron spatial confinement prevails over magnetic confinement. Also, while m varies from -1 to +1, the peak positions of the optical transitions shift toward higher energy (blueshift).

  10. Linear and nonlinear absorption coefficients of spherical quantum dot inside external magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Çakır, Bekir, E-mail: bcakir@selcuk.edu.tr [Physics Department, Faculty of Science, Selcuk University, Campus, 42075 Konya (Turkey); Yakar, Yusuf, E-mail: yuyakar@yahoo.com [Physics Department, Faculty of Arts and Science, Aksaray University, Campus, 68100 Aksaray (Turkey); Özmen, Ayhan [Physics Department, Faculty of Science, Selcuk University, Campus, 42075 Konya (Turkey)

    2017-04-01

    We have calculated the wavefunctions and energy eigenvalues of spherical quantum dot with infinite potential barrier inside uniform magnetic field. In addition, we have investigated the magnetic field effect on optical transitions between Zeeman energy states. The results are expressed as a function of dot radius, incident photon energy and magnetic field strength. The results present that, in large dot radii, the external magnetic field affects strongly the optical transitions between Zeeman states. In the strong spatial confinement case, energy level is relatively insensitive to the magnetic field, and electron spatial confinement prevails over magnetic confinement. Also, while m varies from −1 to +1, the peak positions of the optical transitions shift toward higher energy (blueshift).

  11. Effect of external and internal magnetic fields on the bias stability in a Zeeman laser gyroscope

    Energy Technology Data Exchange (ETDEWEB)

    Kolbas, Yu Yu; Saveliev, I I; Khokhlov, N I [Open Joint-Stock Company M.F. Stel' makh Polyus Research Institute, Moscow (Russian Federation)

    2015-06-30

    With the specific features of electronic systems of a Zeeman laser gyroscope taken into account, the basic physical mechanisms of the magnetic field effect on the bias stability and the factors giving rise to the internal magnetic fields are revealed. The hardware-based methods of reducing the effect of external and internal magnetic fields are considered, as well as the algorithmic methods for increasing the stability of the bias magnetic component by taking into account its reproducible temperature and time dependences. Typical experimental temperature and time dependences of the magnetic component of the Zeeman laser gyro bias are presented, and by their example the efficiency of the proposed methods for reducing the effect of magnetic fields is shown. (laser gyroscopes)

  12. Experimental investigation on heat transfer rate of Co–Mn ferrofluids in external magnetic field

    Directory of Open Access Journals (Sweden)

    Margabandhu M.

    2016-06-01

    Full Text Available Manganese substituted cobalt ferrite (Co1–xMnxFe2O4 with x = 0, 0.3, 0.5, 0.7 and 1 nanopowders were synthesized by chemical coprecipitation method. The synthesized magnetic nanoparticles were investigated by various characterization techniques, such as X-ray diffraction (XRD, vibrating sample magnetometry (VSM, scanning electron microscopy (SEM and thermogravimetric and differential thermal analysis (TG/DTA. The XRD results confirmed the presence of cubic spinel structure of the prepared powders and the average crystallite size of magnetic particles ranging from 23 to 45 nm. The VSM results showed that the magnetic properties varied with an increase in substituted manganese while SEM analysis showed the change in the morphology of obtained magnetic nanoparticles. The TG/DTA analysis indicated the formation of crystalline structure of the synthesized samples. The heat transfer rate was measured in specially prepared magnetic nanofluids (nanoparticles dispersed in carrier fluid transformer oil as a function of time and temperature in presence of external magnetic fields. The experimental analysis indicated enhanced heat transfer rate of the magnetic nanofluids which depended upon the strength of external magnetic field and chemical composition.

  13. Reversal of Flux Closure States in Cobalt Nanoparticle Rings With Coaxial Magnetic Pulses

    DEFF Research Database (Denmark)

    Kasama, T; Dunin-Borkowski, Rafal E.; Scheinfein, MR

    2008-01-01

    Bistable flux closure (FC) states in Co nanoparticle rings can be switched reversibly by applying a coaxial magnetic field (H-z). The FC switching phenomena can be reproduced by micromagnetics simulations, which also reveal novel magnetic states at intermediate applied field strengths....

  14. Self-assembly and flux closure studies of magnetic nanoparticle rings

    DEFF Research Database (Denmark)

    Wei, Alexander; Kasama, Takeshi; Dunin-Borkowski, Rafal E.

    2011-01-01

    Thermoremanent magnetic nanoparticles (MNPs) can self-assemble into rings through dipolar interactions, when dispersed under appropriate conditions. Analysis of individual MNP rings and clusters by off-axis electron holography reveals bistable flux closure (FC) states at ambient temperatures......, and their reversible switching by magnetic field gradients. We introduce a line-bond formalism to describe the coupling between MNPs....

  15. Least-Squares Fitting Methods for Estimating the Winding Rate in Twisted Magnetic-Flux Tubes

    CERN Document Server

    Crouch, Ashley D

    2012-01-01

    We investigate least-squares fitting methods for estimating the winding rate of field lines about the axis of twisted magnetic-flux tubes. These methods estimate the winding rate by finding the values for a set of parameters that correspond to the minimum of the discrepancy between magnetic-field measurements and predictions from a twisted flux-tube model. For the flux-tube model used in the fitting, we assume that the magnetic field is static, axisymmetric, and does not vary in the vertical direction. Using error-free, synthetic vector magnetic-field data constructed with models for twisted magnetic-flux tubes, we test the efficacy of fitting methods at recovering the true winding rate. Furthermore, we demonstrate how assumptions built into the flux-tube models used for the fitting influence the accuracy of the winding-rate estimates. We identify the radial variation of the winding rate within the flux tube as one assumption that can have a significant impact on the winding-rate estimates. We show that the e...

  16. A Magnetic Flux Leakage and Magnetostrictive Guided Wave Hybrid Transducer for Detecting Bridge Cables

    Directory of Open Access Journals (Sweden)

    Jiang Xu

    2012-01-01

    Full Text Available Condition assessment of cables has gained considerable attention for the bridge safety. A magnetic flux leakage and magnetostrictive guided wave hybrid transducer is provided to inspect bridge cables. The similarities and differences between the two methods are investigated. The hybrid transducer for bridge cables consists of an aluminum framework, climbing modules, embedded magnetizers and a ribbon coil. The static axial magnetic field provided by the magnetizers meets the needs of the magnetic flux leakage testing and the magnetostrictive guided wave testing. The magnetizers also provide the attraction for the climbing modules. In the magnetic flux leakage testing for the free length of cable, the coil induces the axial leakage magnetic field. In the magnetostrictive guided wave testing for the anchorage zone, the coil provides a pulse high power variational magnetic field for generating guided waves; the coil induces the magnetic field variation for receiving guided waves. The experimental results show that the transducer with the corresponding inspection system could be applied to detect the broken wires in the free length and in the anchorage zone of bridge cables.

  17. Magnetic flux inversion in charged BPS vortices in a Lorentz-violating Maxwell-Higgs framework

    Energy Technology Data Exchange (ETDEWEB)

    Casana, R., E-mail: rodolfo.casana@gmail.com [Departamento de Fisica, Universidade Federal do Maranhao, 65085-580, Sao Luis, Maranhao (Brazil); Ferreira, M.M. [Departamento de Fisica, Universidade Federal do Maranhao, 65085-580, Sao Luis, Maranhao (Brazil); Hora, E. da [Departamento de Fisica, Universidade Federal do Maranhao, 65085-580, Sao Luis, Maranhao (Brazil); Departamento de Fisica, Universidade Federal da Paraiba, 58051-900, Joao Pessoa, Paraiba (Brazil); Miller, C. [Departamento de Fisica, Universidade Federal do Maranhao, 65085-580, Sao Luis, Maranhao (Brazil); Instituto de Fisica Teorica, UNESP - Universidade Estadual Paulista, R. Dr. Bento T. Ferraz 271 - Bl. II, 01140-070, Sao Paulo, SP (Brazil)

    2012-12-05

    We demonstrate for the first time the existence of electrically charged BPS vortices in a Maxwell-Higgs model supplemented with a parity-odd Lorentz-violating (LV) structure belonging to the CPT-even gauge sector of the standard model extension and a fourth order potential (in the absence of the Chern-Simons term). The modified first order BPS equations provide charged vortex configurations endowed with some interesting features: localized and controllable spatial thickness, integer flux quantization, electric field inversion and localized magnetic flux reversion. This model could possibly be applied on condensed matter systems which support charged vortices carrying integer quantized magnetic flux, endowed with localized flipping of the magnetic flux.

  18. Magnetic flux inversion in charged BPS vortices in a Lorentz-violating Maxwell-Higgs framework

    Science.gov (United States)

    Casana, R.; Ferreira, M. M.; da Hora, E.; Miller, C.

    2012-12-01

    We demonstrate for the first time the existence of electrically charged BPS vortices in a Maxwell-Higgs model supplemented with a parity-odd Lorentz-violating (LV) structure belonging to the CPT-even gauge sector of the standard model extension and a fourth order potential (in the absence of the Chern-Simons term). The modified first order BPS equations provide charged vortex configurations endowed with some interesting features: localized and controllable spatial thickness, integer flux quantization, electric field inversion and localized magnetic flux reversion. This model could possibly be applied on condensed matter systems which support charged vortices carrying integer quantized magnetic flux, endowed with localized flipping of the magnetic flux.

  19. Photospheric Magnetic Flux Emergence: A comparative study between Hinode/SOT Observations and MHD simulations

    Science.gov (United States)

    Cheung, M. C.; Schüssler, M.; Moreno-Insertis, F.; Tarbell, T. D.

    2007-12-01

    With high angular resolution, high temporal cadence and a stable point spread function, the Solar Optical Telescope (SOT) onboard the Hinode satellite is the ideal instrument for the study of magnetic flux emergence and its manifestations on the solar surface. In this presentation, we focus on the development of ephemeral regions and small active regions. In many instances, SOT has been able to capture the entire emergence process from beginning to end: i.e. from the initial stages of flux appearance in granule interiors, through the intermediate stages of G-band bright point formation, and finally to the coalescence of small vertical flux elements to form pores. To investigate the physics of the flux emergence process, we performed 3D numerical MHD simulations with the MURaM code. The models are able to reproduce, and help us explain, various observational signatures of magnetic flux emergence.

  20. Quantum transport through two series Aharonov-Bohm interferometers with zero total magnetic flux

    Institute of Scientific and Technical Information of China (English)

    Wang Jian-Ming; Wang Rui; Zhang Yong-Ping; Liang Jiu-Qing

    2007-01-01

    With the help of nonequilibrium Green's function technique, the electronic transport through series AharonovBohm (AB) interferometers is investigated. We obtain the AB interference pattern of the transition probability characterized by the algebraic sum φ and the difference θ of two magnetic fluxes, and particularly a general rule of AB oscillation period depending on the ratio of integer quantum numbers of the fluxes. A parity effect is observed, showing the asymmetric AB oscillations with respect to the even and odd quantum numbers of the total flux in antiparallel AB interferometers. It is also shown that the AB flux can shift the Fano resonance peaks of the transmission spectrum.

  1. Global-scale external magnetic fields at Mars from Mars Global Surveyor data

    Science.gov (United States)

    Mittelholz, A.; Johnson, C. L.

    2015-12-01

    The martian magnetic field is unique among those of the terrestrial planets. It is the net result of the interaction of the solar wind and interplanetary magnetic field (IMF) with crustal remnant magnetization and a planetary ionosphere. Internal fields of crustal origin have been the subject of extensive studies; the focus of our work is identification and characterization of contributions from external magnetic fields using the Mars Global Surveyor (MGS) vector magnetic field data. We investigate the magnitude, average spatial structure and temporal variability of the external magnetic field at the MGS mapping altitude of 400 km by first subtracting expected contributions from crustal fields using existing global crustal field models. We identify contributions to the residual dayside fields from two sources: the draped IMF and a source that we interpret to be of ionospheric origin. As observed in previous work, nightside external fields are minimal at mapping orbit altitudes. The IMF contribution changes polarity every 13 days due to the geometry of the heliospheric magnetic field and Mars' orbit. This allows us to calculate the amplitude of the IMF at mapping orbit altitudes. The ionospheric contribution results in a quasi-steady dayside signal in the MGS observations because of the limited local time sampling of the MGS mapping orbit. The ionospheric contribution can be isolated by averaging the external fields over timescales longer than several Carrington rotations, to average out the IMF contribution. We present a global average of the ionopsheric field for the duration of the mapping orbit (2000-2006) and analyze daytime and nightime fields separately. We show that some structure in the time-averaged ionospheric field is organized in the Mars body-fixed frame, due for example, to the influence of crustal fields. We also show that the ionospheric fields vary in amplitude and geometry with martian season. Broader local time coverage over a restricted latitude

  2. Numerical simulation of a helical shape electric arc in the external axial magnetic field

    Science.gov (United States)

    Urusov, R. M.; Urusova, I. R.

    2016-10-01

    Within the frameworks of non-stationary three-dimensional mathematical model, in approximation of a partial local thermodynamic equilibrium, a numerical calculation was made of characteristics of DC electric arc burning in a cylindrical channel in the uniform external axial magnetic field. The method of numerical simulation of the arc of helical shape in a uniform external axial magnetic field was proposed. This method consists in that that in the computational algorithm, a "scheme" analog of fluctuations for electrons temperature is supplemented. The "scheme" analogue of fluctuations increases a weak numerical asymmetry of electrons temperature distribution, which occurs randomly in the course of computing. This asymmetry can be "picked up" by the external magnetic field that continues to increase up to a certain value, which is sufficient for the formation of helical structure of the arc column. In the absence of fluctuations in the computational algorithm, the arc column in the external axial magnetic field maintains cylindrical axial symmetry, and a helical form of the arc is not observed.

  3. Exact solutions for quantum mechanical particle with spin 1 in the external homogeneous magnetic field

    CERN Document Server

    Kisel, V V; Red'kov, V M

    2010-01-01

    With the use of the general covariant matrix 10-dimensional Petiau -- Duffin -- Kemmer formalism in cylindrical coordinates and tetrad there are constructed exact solutions of the quantum-mechanical equation for a particle with spin 1 in presence of an external homogeneous magnetic field. There are separated three linearly independent types of solutions; in each case the formula for energy levels has been found.

  4. Critical values of the external magnetic field leading biological effects in the human organism

    CERN Document Server

    Kanokov, Zakirjon

    2013-01-01

    In the framework of the simplified stochastic model the critical values of an induction of the external magnetic field leading to sharp increase of fluctuations of a casual current of biologically important ions in different blood vessels of a human body are calculated.

  5. Plasma excitations in a single-walled carbon nanotube with an external transverse magnetic field

    Indian Academy of Sciences (India)

    K A Vijayalakshmi; T P Nafeesa Baby

    2013-02-01

    The effect of different uniform transverse external magnetic fields in plasma frequency when propagated parallel to the surface of the single-walled metallic carbon nanotubes is studied. The classical electrodynamics as well as Maxwell’s equations are used in the calculations. Equations are developed for both short- and long-wavelength limits and the variations are studied graphically.

  6. Influence of externally applied magnetic perturbations on neoclassical tearing modes at ASDEX Upgrade

    NARCIS (Netherlands)

    Fietz, S.; Bergmann, A.; Classen, I.; Maraschek, M.; M. García-Muñoz,; Suttrop, W.; Zohm, H.; ASDEX Upgrade team,

    2015-01-01

    The influence of externally applied magnetic perturbations (MPs) on neoclassical tearing modes (NTM) and the plasma rotation in general is investigated at the ASDEX Upgrade tokamak (AUG). The low n resonant components of the applied field exert local torques and influence the stability of NTMs. The

  7. Further Investigation on Chiral Symmetry Breaking in a Uniform External Magnetic Field

    CERN Document Server

    Jasinski, P

    2004-01-01

    We study chiral symmetry breaking in QED when a uniform external magnetic field is present. We calculate higher order corrections to the dynamically generated fermion mass and find them to be small. In so doing we correct an error in the literature regarding the matrix structure of the fermion self-energy.

  8. Electron Weibel instability in relativistic counterstreaming plasmas with flow-aligned external magnetic fields

    Science.gov (United States)

    Grassi, A.; Grech, M.; Amiranoff, F.; Pegoraro, F.; Macchi, A.; Riconda, C.

    2017-02-01

    The Weibel instability driven by two symmetric counterstreaming relativistic electron plasmas, also referred to as current-filamentation instability, is studied in a constant and uniform external magnetic field aligned with the plasma flows. Both the linear and nonlinear stages of the instability are investigated using analytical modeling and particle-in-cell simulations. While previous studies have already described the stabilizing effect of the magnetic field, we show here that the saturation stage is only weakly affected. The different mechanisms responsible for the saturation are discussed in detail in the relativistic cold fluid framework considering a single unstable mode. The application of an external field leads to a slight increase of the saturation level for large wavelengths, while it does not affect the small wavelengths. Multimode and temperature effects are then investigated. While at high temperature the saturation level is independent of the external magnetic field, at low but finite temperature the competition between different modes in the presence of an external magnetic field leads to a saturation level lower with respect to the unmagnetized case.

  9. Generating buoyant magnetic flux ropes in solar-like convective dynamos

    CERN Document Server

    Nelson, Nicholas J

    2014-01-01

    Our Sun exhibits strong convective dynamo action which results in magnetic flux bundles emerging through the stellar surface as magnetic spots. Global-scale dynamo action is believed to generate large-scale magnetic structures in the deep solar interior through the interplay of convection, rotation, and shear. Portions of these large-scale magnetic structures are then believed to rise through the convective layer, forming magnetic loops which then pierce the photosphere as sunspot pairs. Previous global simulations of 3D MHD convection in rotating spherical shells have demonstrated mechanisms whereby large-scale magnetic wreaths can be generated in the bulk of the convection zone. Our recent simulations have achieved sufficiently high levels of turbulence to permit portions of these wreaths to become magnetically buoyant and rise through the simulated convective layer through a combination of magnetic buoyancy and advection by convective giant cells. These buoyant magnetic loops are created in the bulk of the...

  10. Superconducting flux pump for high-temperature superconductor insert coils of NMR magnets

    Science.gov (United States)

    Jeong, S.; Lee, H.; Iwasa, Y.

    2002-05-01

    This paper describes a prototype flux pump recently operated at the MIT Francis Bitter Magnet Laboratory. The results of the prototype flux pump will be used in the development of a full-scale flux pump that will be coupled to a high-temperature superconductor (HTS) insert coil of a high-field NMR magnet. Such an HTS insert is unlikely to operate in persistent mode because of the conductor's low index (n). The flux pump can compensate for field decay in the HTS insert coil and make the insert operate effectively in persistent mode. The flux pump, comprised essentially of a transformer and two switches, all made of superconductor, transfers into the insert coil a fraction of a magnetic energy that is first introduced in the secondary circuit of the transformer by a current supplied to the primary circuit. A prototype flux pump has been designed, fabricated, and operated to demonstrate that a flux pump can indeed supply a small metered current into a load superconducting magnet. A current increment in the range of microamperes has been measured in the magnet after each pumping action. The superconducting prototype flux pump is made of Nb3Sn tape. The pump is placed in a gaseous environment above the liquid helium level to keep its heat dissipation from directly discharged in the liquid; the effluent helium vapor maintains the thermal stability of the flux pump. [This paper is also published in Advances in Cryogenic Engineering Volume 47A, AIP Conference Proceedings Volume 613, pp. 441-448.

  11. Eddy current loss calculation and thermal analysis of axial-flux permanent magnet couplers

    Directory of Open Access Journals (Sweden)

    Di Zheng

    2017-02-01

    Full Text Available A three-dimensional magnetic field analytical model of axial-flux permanent magnet couplers is presented to calculate the eddy current loss, and the prediction of the copper plate temperature under various loads is analyzed. The magnetic field distribution is calculated, and then the eddy current loss is obtained, with the magnetic field analytical model established in cylindrical coordinate. The influence of various loads on eddy current loss is analyzed. Furthermore, a thermal model of axial-flux permanent magnet couplers is established by taking the eddy current loss as the heat source, using the electromagnetic-thermal coupled method. With the help of the thermal model, the influence of various loads on copper plate temperature rise is also analyzed. The calculated results are compared with the results of finite element method and measurement. The comparison results confirm the validity of the magnetic field analytical model and thermal model.

  12. Sausage instabilities on top of kinking lengthening current-carrying magnetic flux tubes

    Science.gov (United States)

    von der Linden, Jens; You, Setthivoine

    2017-05-01

    We theoretically explore the possibility of sausage instabilities developing on top of a kink instability in lengthening current-carrying magnetic flux tubes. Observations indicate that the dynamics of magnetic flux tubes in our cosmos and terrestrial experiments can involve topological changes faster than time scales predicted by resistive magnetohydrodynamics. Recent laboratory experiments suggest that hierarchies of instabilities, such as kink and Rayleigh-Taylor, could be responsible for initiating fast topological changes by locally accessing two-fluid and kinetic regimes. Sausage instabilities can also provide this coupling mechanism between disparate scales. Flux tube experiments can be classified by the flux tube's evolution in a configuration space described by a normalized inverse aspect-ratio k ¯ and current-to-magnetic flux ratio λ ¯ . A lengthening current-carrying magnetic flux tube traverses this k ¯ - λ ¯ space and crosses stability boundaries. We derive a single general criterion for the onset of the sausage and kink instabilities in idealized magnetic flux tubes with core and skin currents. The criterion indicates a dependence of the stability boundaries on current profiles and shows overlapping kink and sausage unstable regions in the k ¯ - λ ¯ space with two free parameters. Numerical investigation of the stability criterion reduces the number of free parameters to a single one that describes the current profile and confirms the overlapping sausage and kink unstable regions in k ¯ - λ ¯ space. A lengthening, ideal current-carrying magnetic flux tube can therefore become sausage unstable after it becomes kink unstable.

  13. Emergence and cancellation of small-scale magnetic flux in a quiet region

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    This paper studies the relationship between the development of granules and emergence (cancellation) of magnetic flux at small spatial scales (~1 ) in a quiet region taken with the spectro-polarimeter (SP) of the Solar Optical Telescope (SOT) aboard the Hinode satellite. By examining 6 granular cell events, we have uncovered that a granular structure develops in a regular shape with a size as large as 2-3 , while the granule is pure, i.e. no magnetic flux emerges in the granule during its development. However, a granular structure develops in an irregular shape while emerging flux accompanies the granular development. Magnetic flux cancellation takes place between new emerging flux and pre-existing one. The transverse magnetic field significantly appears at the place where a tiny bipole emerges and where two opposite polarities cancel each other, but only the transverse field of emerging bipole points from the positive element to the negative element. In some cases, violent Doppler blueshifts at the early emerging stage of the magnetic elements appear. We suggest that the excess of the blue-shifts in the inter-granular lanes are produced by the magnetic reconnection below the photosphere

  14. Emergence and cancellation of small-scale magnetic flux in a quiet region

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jun; JIN ChunLan

    2009-01-01

    This paper studies the relationship between the development of granules and emergence (cancellation) of magnetic flux at small spatial scales (~1″) in a quiet region taken with the spectro-polarimeter (SP) of the Solar Optical Telescope (SOT) aboard the Hinode satellite. By examining 6 granular cell events, we have uncovered that a granular structure develops in a regular shape with a size as large as 2-3″, while the granule is pure, i.e. no magnetic flux emerges in the granule during its development. How-ever, a granular structure develops in an irregular shape while emerging flux accompanies the granular development. Magnetic flux cancellation takes place between new emerging flux and pre-existing one. The transverse magnetic field significantly appears at the place where a tiny bipole emerges and where two opposite polarities cancel each other, but only the transverse field of emerging bipole points from the positive element to the negative element. In some cases, violent Doppler blueshifts at the early emerging stage of the magnetic elements appear. We suggest that the excess of the blue-shifts in the inter-granular lanes are produced by the magnetic reconnection below the photosphere

  15. Dynamics of local isolated magnetic flux tubes in a fast-rotating stellar atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    Chou, W.; Tajima, C.T. [Univ. of Texas, Austin, TX (United States). Dept. of Physics; Matsumoto, R. [Chiba Univ. (Japan)]|[ASRC, JAERI, Naka (Japan); Shibata, K. [National Astronomical Observatory, Mitaka (Japan)

    1998-01-01

    Dynamics of magnetic flux tubes in the fast rotating stellar atmosphere is studied. We focus on the effects and signatures of the instability of the flux tube emergence influenced by the Coriolis force. We present the result from a linear stability analysis and discuss its possible signatures in the course of the evolution of G-type and M-type stars. We present a three dimensional magnetohydrodynamical simulation of local isolated magnetic flux tubes under a magnetic buoyancy instability in co-rotating Cartesian coordinates. We find that the combination of the buoyancy instability and the Coriolis effect gives rise to a mechanism, to twist the emerging magnetic flux tube into a helical structure. The tilt angle, east-west asymmetry and magnetic helicity of the Twisted flux tubes in the simulations are studied in detail. The linear and nonlinear analyses provide hints as to what kind of pattern of large spots in young M-type main-sequence stars might be observed. We find that young and old G-type stars may have different distributions of spots while M-type stars may always have low latitudes spots. The size of stellar spots may decrease when a star becomes older, due to the decreasing of magnetic field. A qualitative comparison with solar observations is also presented.

  16. Magnetic flux transport and the sun's dipole moment - New twists to the Babcock-Leighton model

    Science.gov (United States)

    Wang, Y.-M.; Sheeley, N. R., Jr.

    1991-01-01

    The mechanisms that give rise to the sun's large-scale poloidal magnetic field are explored in the framework of the Babcock-Leighton (BL) model. It is shown that there are in general two quite distinct contributions to the generation of the 'alpha effect': the first is associated with the axial tilts of the bipolar magnetic regions as they erupt at the surface, while the second arises through the interaction between diffusion and flow as the magnetic flux is dispersed over the surface. The general relationship between flux transport and the BL dynamo is discussed.

  17. CONDITIONS FOR TRANSVERSE WAVES PROPAGATION ALONG THIN MAGNETIC FLUX TUBES ON THE SUN

    Energy Technology Data Exchange (ETDEWEB)

    Lopin, Igor [Ussuriisk Astrophysical Observatory, Russian Academy of Sciences, Ussuriisk (Russian Federation); Nagorny, Ivan, E-mail: lopin78@mail.ru [Institute of Automation and Control Processes FEB RAS, Vladivostok (Russian Federation)

    2013-09-10

    The propagation of kink waves in the thin gravity stratified flux tubes with a generalized magnetic field distribution model is considered in cylindrical geometry. The new kink wave equations for both wave variables are obtained. It is shown that the inclusion of the radial component of an unperturbed tube magnetic field sufficiently transforms the conditions for the propagation of transverse waves. It is demonstrated that, for the models of isothermal and polytropic atmosphere in the tube and its environment, the propagation of kink waves along thin magnetic flux tubes is cutoff-free.

  18. Parametric instabilities in shallow water magnetohydrodynamics of astrophysical plasma in external magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Klimachkov, D.A., E-mail: klimachkovdmitry@gmail.com [Space Research Institute of Russian Academy of Science, 84/32, Profsoyuznaya str., Moscow, 117997 (Russian Federation); Petrosyan, A.S. [Space Research Institute of Russian Academy of Science, 84/32, Profsoyuznaya str., Moscow, 117997 (Russian Federation); Moscow Institute of Physics and Technology (State University), 9 Institutskyi per., Dolgoprudny, Moscow Region, 141700 (Russian Federation)

    2017-01-15

    This article deals with magnetohydrodynamic (MHD) flows of a thin rotating layer of astrophysical plasma in external magnetic field. We use the shallow water approximation to describe thin rotating plasma layer with a free surface in a vertical external magnetic field. The MHD shallow water equations with external vertical magnetic field are revised by supplementing them with the equations that are consequences of the magnetic field divergence-free conditions and reveal the existence of third component of the magnetic field in such approximation providing its relation with the horizontal magnetic field. It is shown that the presence of a vertical magnetic field significantly changes the dynamics of the wave processes in astrophysical plasma compared to the neutral fluid and plasma layer in a toroidal magnetic field. The equations for the nonlinear wave packets interactions are derived using the asymptotic multiscale method. The equations for three magneto-Poincare waves interactions, for three magnetostrophic waves interactions, for the interactions of two magneto-Poincare waves and for one magnetostrophic wave and two magnetostrophic wave and one magneto-Poincare wave interactions are obtained. The existence of parametric decay and parametric amplifications is predicted. We found following four types of parametric decay instabilities: magneto-Poincare wave decays into two magneto-Poincare waves, magnetostrophic wave decays into two magnetostrophic waves, magneto-Poincare wave decays into one magneto-Poincare wave and one magnetostrophic wave, magnetostrophic wave decays into one magnetostrophic wave and one magneto-Poincare wave. Following mechanisms of parametric amplifications are found: parametric amplification of magneto-Poincare waves, parametric amplification of magnetostrophic waves, magneto-Poincare wave amplification in magnetostrophic wave presence and magnetostrophic wave amplification in magneto-Poincare wave presence. The instabilities growth rates

  19. Plasma expansion into a vacuum with an arbitrarily oriented external magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    García-Rubio, F., E-mail: fernando.garcia.rubio@upm.es; Sanz, J. [E.T.S.I. Aeronáutica y del Espacio, Universidad Politécnica de Madrid, Madrid 28040 (Spain); Ruocco, A. [Universitá degli studi di Napoli Federico II, 80138 Napoli (Italy)

    2016-01-15

    Plasma expansion into a vacuum with an external magnetic field is studied under the ideal magnetohydrodynamic hypothesis. The inclination of the magnetic field with respect to the expansion direction is arbitrary, and both the perpendicular and the oblique cases are separately analyzed. A self-similar solution satisfying the boundary conditions is obtained. The interface with the vacuum is treated as a fluid surface, and jump conditions concerning the momentum conservation are imposed. The effect of the intensity of the magnetic field and its inclination is thoroughly studied, and the consistency of the solution for small and large inclinations is investigated.

  20. The Mass of Kerr-Newman Black Holes in an external magnetic field

    CERN Document Server

    Astorino, M; Oliveri, R; Vandevoorde, N

    2016-01-01

    The explicit solution for a Kerr-Newman black hole immersed in an external magnetic field, sometimes called the Melvin-Kerr-Newman black hole, has been derived by Ernst and Wild in 1976. In this paper, we clarify the first law and Smarr formula for black holes in a magnetic field. We then define the unique mass which is integrable and reduces to the Kerr-Newman mass in the absence of magnetic field. This defines the thermodynamic potentials of the black hole. Quite strikingly, the mass coincides with the standard Christodoulou-Ruffini mass of a black hole as a function of the entropy, angular momentum and electric charge.

  1. Electron beam guiding by external magnetic fields in imploded fuel plasma

    Science.gov (United States)

    Johzaki, T.; Sentoku, Y.; Nagatomo, H.; Sunahara, A.; Sakagami, H.; Fujioka, S.; Shiraga, H.; Endo, T.; FIREX project Group

    2016-05-01

    For enhancing the core heating efficiency in fast ignition laser fusion, we proposed the fast electron beam by externally-applied the kilo-tesla (kT) class longitudinal magnetic field. We evaluated the imploded core and the magnetic field profiles formed through the implosion dynamics by resistive MHD radiation hydro code. Using those profiles, the guiding effect was evaluated by fast electron transport simulations, which shows that in addition to the feasible field configuration (moderate mirror ratio), the kT-class magnetic field is required at the fast electron generation point. In this case, the significant enhancement in heating efficiency is expected.

  2. Supersymmetric models on magnetized orbifolds with flux-induced Fayet-Iliopoulos terms

    CERN Document Server

    Abe, Hiroyuki; Sumita, Keigo; Tatsuta, Yoshiyuki

    2016-01-01

    We study supersymmetric (SUSY) models derived from the ten-dimensional SUSY Yang- Mills theory compactified on magnetized orbifolds, with nonvanishing Fayet-Iliopoulos (FI) terms induced by magnetic fluxes in extra dimensions. Allowing the presence of FI-terms relaxes a constraint on flux configurations in SUSY model building based on magnetized backgrounds. In this case, charged fields develop their vacuum expectation values (VEVs) to cancel the FI-terms in the D-flat directions of fluxed gauge symmetries, which break the gauge symmetries and lead to a SUSY vacuum. Based on this idea, we propose a new class of SUSY magnetized orbifold models with three generations of quarks and leptons. Especially, we construct a model where the right-handed sneutrinos develop their VEVs which restore the supersymmetry but yield lepton number violating terms below the compactification scale, and show their phenomenological consequences.

  3. Numerical simulations of three-dimensional magnetic swirls in a solar flux-tube

    Science.gov (United States)

    Chmielewski, Piotr; Murawski, Krzysztof; Solov'ev, Alexandr A.

    2014-07-01

    We aim to numerically study evolution of Alfvén waves that accompany short-lasting swirl events in a solar magnetic flux-tube that can be a simple model of a magnetic pore or a sunspot. With the use of the FLASH code we numerically solve three-dimensional ideal magnetohydrodynamic equations to simulate twists which are implemented at the top of the photosphere in magnetic field lines of the flux-tube. Our numerical results exhibit swirl events and Alfvén waves with associated clockwise and counterclockwise rotation of magnetic lines, with the largest values of vorticity at the bottom of the chromosphere, and a certain amount of energy flux.

  4. Helical ${\\alpha}$-dynamos as twisted magnetic flux tubes in Riemannian space

    CERN Document Server

    de Andrade, Garcia

    2007-01-01

    Analytical solution of ${\\alpha}$-dynamo equation representing strongly torsioned helical dynamo is obtained in the thin twisted Riemannian flux tubes approximation. The $\\alpha$ factor possesses a fundamental contribution from torsion which is however weaken in the thin tubes approximation. It is shown that assuming that the poloidal component of the magnetic field is in principle time-independent, the toroidal magnetic field component grows very fast in time, actually it possesses a linear time dependence, while the poloidal component grows under the influence of torsion or twist of the flux tube. The toroidal component decays spatially with as $r^{-2}$ while vorticity may decay as $r^{-5}$ (poloidal component) where r represents the radial distance from the magnetic axis of flux tube. Toroidal component of vorticity decays as $r^{-1}$. In turbulent dynamos unbounded magnetic fields may decay at least as $r^{-3}$.

  5. Supersymmetric models on magnetized orbifolds with flux-induced Fayet-Iliopoulos terms

    Science.gov (United States)

    Abe, Hiroyuki; Kobayashi, Tatsuo; Sumita, Keigo; Tatsuta, Yoshiyuki

    2017-01-01

    We study supersymmetric (SUSY) models derived from the ten-dimensional SUSY Yang-Mills theory compactified on magnetized orbifolds, with nonvanishing Fayet-Iliopoulos (FI) terms induced by magnetic fluxes in extra dimensions. Allowing the presence of FI-terms relaxes a constraint on flux configurations in SUSY model building based on magnetized backgrounds. In this case, charged fields develop their vacuum expectation values to cancel the FI-terms in the D-flat directions of fluxed gauge symmetries, which break the gauge symmetries and lead to a SUSY vacuum. Based on this idea, we propose a new class of SUSY magnetized orbifold models with three generations of quarks and leptons. Especially, we construct a model where the right-handed sneutrinos develop their vacuum expectation values which restore the supersymmetry but yield lepton number violating terms below the compactification scale, and show their phenomenological consequences.

  6. Magnetic damping forces in figure-eight-shaped null-flux coil suspension systems

    Energy Technology Data Exchange (ETDEWEB)

    He, Jianliang; Coffey, H.

    1997-08-01

    This paper discusses magnetic damping forces in figure-eight-shaped null-flux coil suspension systems, focusing on the Holloman maglev rocket system. The paper also discusses simulating the damping plate, which is attached to the superconducting magnet by two short-circuited loop coils in the guideway. Closed-form formulas for the magnetic damping coefficient as functions of heave-and-sway displacements are derived by using a dynamic circuit model. These formulas are useful for dynamic stability studies.

  7. The formation of magnetic depletions and flux annihilation due to reconnection in the heliosheath

    OpenAIRE

    Drake, J F; Swisdak, M.; Opher, M.; Richardson, J.D.

    2017-01-01

    The misalignment of the solar rotation axis and the magnetic axis of the Sun produces a periodic reversal of the Parker spiral magnetic field and the sectored solar wind. The compression of the sectors is expected to lead to reconnection in the heliosheath (HS). We present particle-in-cell simulations of the sectored HS that reflect the plasma environment along the Voyager 1 and 2 trajectories, specifically including unequal positive and negative azimuthal magnetic flux as seen in the Voyager...

  8. First-principles study on magnetism of Ru monolayer under an external electric field

    Science.gov (United States)

    Kitaoka, Yukie; Imamura, Hiroshi

    Electric field control of magnetic properties such as magnetic moment and magnetic anisotropy has been attracted. For the 4 d TM films, on the other hand, it was recently reported that the ferromagnetism Pd thin-film is induced by application of an external electric field otherwise Pd thin-film shows paramagnetic. However, little attention has been paid to the magnetism of other 4 d TMs. Here, we investigate the magnetism of the free-standing Ru monolayer and that on MgO(001) substrate under an external electric field by using first-principles FLAPW method. We found that the free-standing Ru monolayer is ferromagnet with magnetic moment of 1.50 ¥muB /atom. The MA energy is 3.45 meV/atom, indicating perpendicular MA, at zero electric field (E=0) and increases up to 3.84 meV/atom by application of E=1 (V/¥AA). The Ru monolayer on MgO(001) substrate is also ferromagnet with magnetic moment of 0.89 ¥muB /atom. The MA energy is 1.49 meV/atom, indicating perpendicular MA, at E=0 and decreases to 1.33 meV/atom by application of E=1 (V/¥AA).

  9. Data Mining Solar X-Ray Flares Triggered by Emerging Magnetic Flux

    Science.gov (United States)

    Loftus, Kaitlyn; Saar, Steven H.; Schanche, Nicole

    2017-01-01

    We investigate the association between emerging magnetic flux and solar X-ray flares to identify, and if possible quantify, distinguishing physical properties of flares triggered by flux emergence versus those triggered by other sources. Our study uses as its basis GOES-classified solar flares from March 2011 through June 2016 that have been identified by the Space Weather Prediction Center’s flare detection algorithm. The basic X-ray flare data is then enriched with data about related EUV-spectrum flares, emerging fluxes, active regions, eruptions, and sigmoids, which are all characterized by event-specific keywords, identified via SDO feature finding tools, and archived in the Heliophysics Events Knowledgebase (HEK). Using appropriate spatial and temporal parameters for each event type to determine association, we create a catalogue of solar events associated with each GOES-classified flare. After accounting for the primitive state of many of these event detection algorithms, we statistically analyze the compiled dataset to determine the effects of an emerging flux trigger on flare properties. A two-sample Kolmogorov-Smirnov test confirms with 99.9% confidence that flares triggered by emerging flux have a different peak flux distribution than non-emerging-flux-associated flares. We observe no linear or logarithmic correlations between flares’ and their associated emerging fluxes’ individual properties and find flares triggered by emerging flux are ~ 10% more likely to cause an eruption inside an active region while outside of an active region, the flare’s association with emerging flux has no effect on its likeliness to cause an eruption. We also compare the morphologies of the flares triggered by emerging flux and flares not via a superposed epoch analysis of lightcurves. Our results will be of interest for predicting flare behavior as a function of magnetic activity (where we can use enhanced rates of emerging flux as a proxy for heightened stellar

  10. Structure, Stability, and Evolution of Magnetic Flux Ropes from the Perspective of Magnetic Twist

    CERN Document Server

    Liu, Rui; Titov, Viacheslav S; Chen, Jun; Wang, Yuming; Wang, Haimin; Liu, Chang; Xu, Yan; Wiegelmann, Thomas

    2015-01-01

    We investigate the evolution of NOAA Active Region 11817 during 2013 August 10--12, when it developed a complex field configuration and produced four confined, followed by two eruptive, flares. These C-and-above flares are all associated with a magnetic flux rope (MFR) located along the major polarity inversion line, where shearing and converging photospheric flows are present. Aided by the nonlinear force-free field modeling, we identify the MFR through mapping magnetic connectivities and computing the twist number $\\mathcal{T}_w$ for each individual field line. The MFR is moderately twisted ($|\\mathcal{T}_w| < 2$) and has a well-defined boundary of high squashing factor $Q$. We found that the field line with the extremum $|\\mathcal{T}_w|$ is a reliable proxy of the rope axis, and that the MFR's peak $|\\mathcal{T}_w|$ temporarily increases within half an hour before each flare while it decreases after the flare peak for both confined and eruptive flares. This pre-flare increase in $|\\mathcal{T}_w|$ has li...

  11. Non-Uniqueness of the Geometry of Interplanetary Magnetic Flux Ropes Obtained from Model-Fitting

    Science.gov (United States)

    Marubashi, K.; Cho, K.-S.

    2015-12-01

    Since the early recognition of the important role of interplanetary magnetic flux ropes (IPFRs) to carry the southward magnetic fields to the Earth, many attempts have been made to determine the structure of the IPFRs by model-fitting analyses to the interplanetary magnetic field variations. This paper describes the results of fitting analyses for three selected solar wind structures in the latter half of 2014. In the fitting analysis a special attention was paid to identification of all the possible models or geometries that can reproduce the observed magnetic field variation. As a result, three or four geometries have been found for each of the three cases. The non-uniqueness of the fitted results include (1) the different geometries naturally stemming from the difference in the models used for fitting, and (2) an unexpected result that either of magnetic field chirality, left-handed and right-handed, can reproduce the observation in some cases. Thus we conclude that the model-fitting cannot always give us a unique geometry of the observed magnetic flux rope. In addition, we have found that the magnetic field chirality of a flux rope cannot be uniquely inferred from the sense of field vector rotation observed in the plane normal to the Earth-Sun line; the sense of rotation changes depending on the direction of the flux rope axis. These findings exert an important impact on the studies aimed at the geometrical relationships between the flux ropes and the magnetic field structures in the solar corona where the flux ropes were produced, such studies being an important step toward predicting geomagnetic storms based on observations of solar eruption phenomena.

  12. Manipulating Majorana zero modes on atomic rings with an external magnetic field

    Science.gov (United States)

    Li, Jian; Neupert, Titus; Bernevig, B. Andrei; Yazdani, Ali

    2016-01-01

    Non-Abelian quasiparticles have been predicted to exist in a variety of condensed matter systems. Their defining property is that an adiabatic braid between two of them results in a non-trivial change of the quantum state of the system. The simplest non-Abelian quasiparticles--the Majorana bound states--can occur in one-dimensional electronic nano-structures proximity-coupled to a bulk superconductor. Here we propose a set-up, based on chains of magnetic adatoms on the surface of a thin-film superconductor, in which the control over an externally applied magnetic field suffices to create and manipulate Majorana bound states. We consider specifically rings of adatoms and show that they allow for the creation, annihilation, adiabatic motion and braiding of pairs of Majorana bound states by varying the magnitude and orientation of the external magnetic field.

  13. Spin polarization in high density quark matter under a strong external magnetic field

    DEFF Research Database (Denmark)

    Tsue, Yasuhiko; Da Providência, João; Providência, Constança

    2016-01-01

    In high density quark matter under a strong external magnetic field, possible phases are investigated by using the two-flavor Nambu-Jona-Lasinio (NJL) model with tensor-type four-point interaction between quarks, as well as the axial-vector-type four-point interaction. In the tensor......-type interaction under the strong external magnetic field, it is shown that a quark spin polarized phase is realized in all regions of the quark chemical potential under consideration within the lowest Landau level approximation. In the axial-vector-type interaction, it is also shown that the quark spin polarized...... phase appears in the wide range of the quark chemical potential. In both the interactions, the quark mass in zero and small chemical potential regions increases which indicates that the chiral symmetry breaking is enhanced, namely the magnetic catalysis occurs....

  14. Matter-induced magnetic moment and neutrino helicity rotation in external fields

    Science.gov (United States)

    Ternov, Alexei I.

    2016-11-01

    The induced magnetic moment that arises due to the propagation of neutrinos in a dispersive medium can affect the dynamics of the neutrino spin in an external electromagnetic field. In particular, it can cause a helicity flip of a massive neutrino in a magnetic field. In some astrophysical media, this helicity transition mechanism could be more effective than a similar process caused by the anomalous magnetic moment of the neutrino. If the neutrino energy is sufficiently high, the two helicity transition mechanisms mentioned above can compensate each other. Then a helicity flip in an external field will not occur. Calculations are carried out using both the methods of relativistic quantum mechanics and the quasiclassical Bargmann-Michel-Telegdi equation.

  15. Effect of buffer layer and external stress on magnetic properties of flexible FeGa films

    Science.gov (United States)

    Zhang, Xiaoshan; Zhan, Qingfeng; Dai, Guohong; Liu, Yiwei; Zuo, Zhenghu; Yang, Huali; Chen, Bin; Li, Run-Wei

    2013-05-01

    We systematically investigated the effect of a Ta buffer layer and external stress on the magnetic properties of magnetostrictive Fe81Ga19 films deposited on flexible polyethylene terephthalate (PET) substrates. The Ta buffer layers could effectively smoothen the rough surface of PET. As a result, the FeGa films grown on Ta buffer layers exhibit a weaker uniaxial magnetic anisotropy and lower coercivity, as compared to those films directly grown on PET substrates. By inward and outward bending the FeGa/Ta/PET samples, external in-plane compressive and tensile stresses were applied to the magnetic films. Due to the inverse magnetostrictive effect of FeGa, both the coercivity and squareness of hysteresis loops for FeGa/Ta films could be well tuned under various strains.

  16. Parametric instabilities in shallow water magnetohydrodynamics of astrophysical plasma in external magnetic field

    Science.gov (United States)

    Klimachkov, D. A.; Petrosyan, A. S.

    2017-01-01

    This article deals with magnetohydrodynamic (MHD) flows of a thin rotating layer of astrophysical plasma in external magnetic field. We use the shallow water approximation to describe thin rotating plasma layer with a free surface in a vertical external magnetic field. The MHD shallow water equations with external vertical magnetic field are revised by supplementing them with the equations that are consequences of the magnetic field divergence-free conditions and reveal the existence of third component of the magnetic field in such approximation providing its relation with the horizontal magnetic field. It is shown that the presence of a vertical magnetic field significantly changes the dynamics of the wave processes in astrophysical plasma compared to the neutral fluid and plasma layer in a toroidal magnetic field. The equations for the nonlinear wave packets interactions are derived using the asymptotic multiscale method. The equations for three magneto-Poincare waves interactions, for three magnetostrophic waves interactions, for the interactions of two magneto-Poincare waves and for one magnetostrophic wave and two magnetostrophic wave and one magneto-Poincare wave interactions are obtained. The existence of parametric decay and parametric amplifications is predicted. We found following four types of parametric decay instabilities: magneto-Poincare wave decays into two magneto-Poincare waves, magnetostrophic wave decays into two magnetostrophic waves, magneto-Poincare wave decays into one magneto-Poincare wave and one magnetostrophic wave, magnetostrophic wave decays into one magnetostrophic wave and one magneto-Poincare wave. Following mechanisms of parametric amplifications are found: parametric amplification of magneto-Poincare waves, parametric amplification of magnetostrophic waves, magneto-Poincare wave amplification in magnetostrophic wave presence and magnetostrophic wave amplification in magneto-Poincare wave presence. The instabilities growth rates

  17. Convective radial energy flux due to resonant magnetic perturbations and magnetic curvature at the tokamak plasma edge

    CERN Document Server

    Marcus, F A; Fuhr, G; Monnier, A; Benkadda, S

    2014-01-01

    With the resonant magnetic perturbations (RMPs) consolidating as an important tool to control the transport barrier relaxation, the mechanism on how they work is still a subject to be clearly understood. In this work we investigate the equilibrium states in the presence of RMPs for a reduced MHD model using 3D electromagnetic fluid numerical code (EMEDGE3D) with a single harmonic RMP (single magnetic island chain) and multiple harmonics RMPs in cylindrical and toroidal geometry. Two different equilibrium states were found in the presence of the RMPs with different characteristics for each of the geometries used. For the cylindrical geometry in the presence of a single RMP, the equilibrium state is characterized by a strong convective radial thermal flux and the generation of a mean poloidal velocity shear. In contrast, for toroidal geometry the thermal flux is dominated by the magnetic flutter. For multiple RMPs, the high amplitude of the convective flux and poloidal rotation are basically the same in cylindr...

  18. Magnetic Flux Ropes from the Sun to 1 AU*

    Science.gov (United States)

    Krall, J.; Yurchyshyn, V. B.; St. Cyr, O. C.; Chen, J.

    2004-12-01

    Any practical model of the dynamics of a coronal mass ejection (CME) and its interplanetary counterpart (ICME) must conform to available observational constraints from sun and to the earth; the upcoming STEREO mission will add significantly to those constraints. We present model/data comparisons for specific CME/ICME events near the sun (using coronagraph image data) and in the heliosphere (using in situ measurements) to show that the flux rope model of Chen and Krall[1-2] provides an accurate physics-based characterization of flux-rope CMEs over this range. We further show that quantitative results, such as the field energy required for eruption, depend on specific aspects of the flux rope geometry, such as the ratio (length/width) of the elliptical shape traced out by the flux-rope axis. It is this geometry that will be determined, for the first time, by STEREO. [1] Chen, J. 1996, JGR, 101, 27499 [2] Krall, J. et al., 2000, ApJ, 539, 964 *Work supported by ONR, NASA and NSF

  19. Theory and simulation of quasilinear transport from external magnetic field perturbations in a DIII-D plasma

    Science.gov (United States)

    Waltz, R. E.; Ferraro, N. M.

    2015-04-01

    The linear response profiles for the 3D perturbed magnetic fields, currents, ion velocities, plasma density, pressures, and electric potential from low-n external resonant magnetic field perturbations (RMPs) are obtained from the collisional two-fluid M3D-C1 code [N. M. Ferraro and S. C. Jardin, J. Comput. Phys. 228, 7742 (2009)]. A newly developed post-processing RMPtran code computes the resulting quasilinear E×B and magnetic (J×B) radial transport flows with respect to the unperturbed flux surfaces in all channels. RMPtran simulations focus on ion (center of mass) particle and transient non-ambipolar current flows, as well as the toroidal angular momentum flow. The paper attempts to delineate the RMP transport mechanisms that might be responsible for the RMP density pump-out seen in DIII-D [M. A. Mahdavi and J. L. Luxon, Fusion Sci. Technol. 48, 2 (2005)]. Experimentally, the starting high toroidal rotation does not brake to a significantly lower rotation after the pump-out suggesting that convective and E×B transport mechanisms dominate. The direct J×B torque from the transient non-ambipolar radial current expected to accelerate plasma rotation is shown to cancel much of the Maxwell stress J×B torque expected to brake the plasma rotation. The dominant E×B Reynolds stress accelerates rotation at the top of the pedestal while braking rotation further down the pedestal.

  20. An Improved Stator Flux Observation Method of Permanent Magnet Synchronous Motor

    Institute of Scientific and Technical Information of China (English)

    Guangjing Su; Hongmei Li; Ying Dai; Zheng Li

    2016-01-01

    The stator flux and electromagnetic torque observation is the basis of direct torque controlled permanent magnet synchronous motor ( PMSM) drive system. However, the traditional stator flux observer based on voltage model is affected by integral initial values and integral drift, that based on current model is affected by the parameters of PMSM, so a new stator flux observation method is proposed based on an improved second⁃order generalized integrator ( SOGI) . Compared to the stator flux observation method based on the conventional SOGI, the proposed method can not only overcome the influence of integral initial values and integral drift, but also completely eliminate the DC offset’ s influence. Therefore, the observation accuracy of stator flux is further improved. The simulation and experimental results both show that the proposed method has a higher stator flux and electromagnetic torque observation precision.

  1. Passive Superconducting Flux Conservers for Rotating-Magnetic-Field-Driven Field-Reversed Configurations

    Energy Technology Data Exchange (ETDEWEB)

    Oz, E.; Myers, C. E.; Edwards, M. R.; Berlinger, B.; Brooks, A.; Cohen, S. A.

    2011-01-05

    The Princeton Field-Reversed Configuration (PFRC) experiment employs an odd-parity rotating magnetic field (RMFo) current drive and plasma heating system to form and sustain high-Β plasmas. For radial confinement, an array of coaxial, internal, passive, flux-conserving (FC) rings applies magnetic pressure to the plasma while still allowing radio-frequency RMFo from external coils to reach the plasma. The 3 ms pulse duration of the present experiment is limited by the skin time (τfc) of its room-temperature copper FC rings. To explore plasma phenomena with longer characteristic times, the pulse duration of the next-generation PFRC-2 device will exceed 100 ms, necessitating FC rings with (τfc > 300 ms. In this paper we review the physics of internal, discrete, passive FCs and describe the evolution of the PFRC's FC array. We then detail new experiments that have produced higher performance FC rings that contain embedded high-temperature superconducting (HTS) tapes. Several HTS tape winding configurations have been studied and a wide range of extended skin times, from 0.4 s to over 103 s, has been achieved. The new FC rings must carry up to 3 kA of current to balance the expected PFRC-2 plasma pressure, so the dependence of the HTS-FC critical current on the winding configuration and temperature was also studied. From these experiments, the key HTS-FC design considerations have been identified and HTS-FC rings with the desired performance characteristics have been produced.

  2. Analytical magnetic torque calculations and experimental testing of radial flux permanent magnet-type eddy current brakes

    Science.gov (United States)

    Choi, Jang-Young; Jang, Seok-Myeong

    2012-04-01

    This paper reports on analytical magnetic torque calculations and experimental tests of a radial flux permanent magnet (RFPM)-type eddy current brake (ECB). Analytical solutions for permanent magnet-generated magnetic fields that consider the eddy current reaction are obtained by using a magnetic vector potential and a two dimensional (2D) polar coordinate system. On the basis of these solutions, the analytical expressions for a magnetic torque are also derived. All analytical results are validated extensively by non-linear finite element calculations. In particular, magnetic torque measurements are obtained in tests to confirm the analyses. Finally, practical issues related to the analytical study of RFPM-type ECBs are fully discussed.

  3. Magnetic Flux Cancellation as the Origin of Solar Quiet-region Pre-jet Minifilaments

    Science.gov (United States)

    Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.

    2017-08-01

    We investigate the origin of 10 solar quiet-region pre-jet minifilaments, using EUV images from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and magnetograms from the SDO Helioseismic and Magnetic Imager (HMI). We recently found that quiet-region coronal jets are driven by minifilament eruptions, where those eruptions result from flux cancellation at the magnetic neutral line under the minifilament. Here, we study the longer-term origin of the pre-jet minifilaments themselves. We find that they result from flux cancellation between minority-polarity and majority-polarity flux patches. In each of 10 pre-jet regions, we find that opposite-polarity patches of magnetic flux converge and cancel, with a flux reduction of 10%-40% from before to after the minifilament appears. For our 10 events, the minifilaments exist for periods ranging from 1.5 hr to 2 days before erupting to make a jet. Apparently, the flux cancellation builds a highly sheared field that runs above and traces the neutral line, and the cool transition region plasma minifilament forms in this field and is suspended in it. We infer that the convergence of the opposite-polarity patches results in reconnection in the low corona that builds a magnetic arcade enveloping the minifilament in its core, and that the continuing flux cancellation at the neutral line finally destabilizes the minifilament field so that it erupts and drives the production of a coronal jet. Thus, our observations strongly support that quiet-region magnetic flux cancellation results in both the formation of the pre-jet minifilament and its jet-driving eruption.

  4. Mechanisms of the outer radiation belt electron flux variation during magnetic storms

    Science.gov (United States)

    Nakamura, M.; Obara, T.; Koshiishi, H.; Koga, K.; Matsumoto, H.; Goka, T.

    2003-12-01

    We have investigated variations of the energetic electron flux (> 0.4 MeV) and the magnetic field in the outer radiation belt obtained from the Standard DOse Monitor (SDOM) and the MAgnetoMeter (MAM) of the Space Environment Data Acquisition equipment (SEDA) onboard Tsubasa (Mission Demonstration Test Satellite (MDS)-1). Since Tsubasa operates in geostationary transfer orbit (GTO) with an orbital period of 10 hours and an inclination of 28.5 degrees, it has provided a rare opportunity for directly observing near-equatorial radiation belt plasma particles and the magnetic field during magnetic storms. The decreases of the energetic electron flux during the main phase of the magnetic storms, and the subsequent recoveries and enhancements during the recovery phase in the outer radiation belt are linked respectively to typical variations of the magnetic field. At the moment that the outer radiation belt flux sharply drops during the main phase of the 17 April 2002 magnetic storm, the butterfly distribution is observed at L=5 and the magnetic equator where the magnitude of magnetic field is much smaller than the IGRF model. Calculating the drift motions of the energetic electrons in the Tyganenko 2001 magnetospheric magnetic field model, shows that the drift-shell splitting mechanism could generate the butterfly distribution due to loss of the near-equatorially mirroring electrons through dayside magnetopause boundary. We evaluate roles and contributions of the other possible mechanisms to explain the flux decreases. We discuss the three-dimensional field configuration in the magnetopause to compare with the low earth orbital observation of the outer radiation belt flux.

  5. Pose control of the chain composed of magnetic particles using external uniform and gradient magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, J. F., E-mail: zhoujianfeng@njtech.edu.cn; Shao, C. L.; Gu, B. Q. [Nanjing Tech University, School of Mechanical and Power Engineering (China)

    2016-01-15

    Magnetic particles (MPs) are known to respond to a magnetic field and can be moved by magnetic force, which make them good carriers in bioengineering and pharmaceutical engineering. In this paper, a pose control method for the straight chain composed of MPs is proposed, and the chain with one pose can be moved to another position with another pose using alternately employed uniform and gradient magnetic fields. Based on computer simulations, it is revealed that in the uniform magnetic field, the MPs form a straight chain with the same separation space along the field lines, and once the uniform magnetic field rotates, the chain also rotates with the field. In the gradient magnetic field, the MPs move toward the higher field so that the translation of the chain can be realized. The simulation results indicate that while the uniform magnetic field is rotating, there exists certain hysteresis between the chain and the field, and the chain is not straight anymore. So the uniform magnetic field should rest at the target angle for a period to make the chain fully relax to be straight. For nanoMP, its magnetic moment directly determines the gradient magnetic force which is much smaller than the dipole–dipole force among MPs. Therefore, the translation of the chain is much more time-consuming than rotation. To enlarge the translational velocity, it is suggested to increase the size of MPs or the magnetic field gradient.

  6. Potential Magnetic Field around a Helical Flux-rope Current Structure in the Solar Corona

    CERN Document Server

    Petrie, G J D

    2007-01-01

    We consider the potential magnetic field associated with a helical electric line current flow, idealizing the near-potential coronal field within which a highly localized twisted current structure is embedded. It is found that this field has a significant axial component off the helical magnetic axis where there is no current flow, such that the flux winds around the axis. The helical line current field, in including the effects of flux rope writhe, is therefore more topologically complex than straight line and ring current fields sometimes used in solar flux rope models. The axial flux in magnetic fields around confined current structures may be affected by the writhe of these current structures such that the field twists preferentially with the same handedness as the writhe. This property of fields around confined current structures with writhe may be relevant to classes of coronal magnetic flux rope, including structures observed to have sigmoidal forms in soft X-rays and prominence magnetic fields. For ex...

  7. Fourier transform magnetic resonance current density imaging (FT-MRCDI) from one component of magnetic flux density.

    Science.gov (United States)

    Ider, Yusuf Ziya; Birgul, Ozlem; Oran, Omer Faruk; Arikan, Orhan; Hamamura, Mark J; Muftuler, L Tugan

    2010-06-01

    Fourier transform (FT)-based algorithms for magnetic resonance current density imaging (MRCDI) from one component of magnetic flux density have been developed for 2D and 3D problems. For 2D problems, where current is confined to the xy-plane and z-component of the magnetic flux density is measured also on the xy-plane inside the object, an iterative FT-MRCDI algorithm is developed by which both the current distribution inside the object and the z-component of the magnetic flux density on the xy-plane outside the object are reconstructed. The method is applied to simulated as well as actual data from phantoms. The effect of measurement error on the spatial resolution of the current density reconstruction is also investigated. For 3D objects an iterative FT-based algorithm is developed whereby the projected current is reconstructed on any slice using as data the Laplacian of the z-component of magnetic flux density measured for that slice. In an injected current MRCDI scenario, the current is not divergence free on the boundary of the object. The method developed in this study also handles this situation.

  8. Graphene nanoflakes in external electric and magnetic in-plane fields

    Energy Technology Data Exchange (ETDEWEB)

    Szałowski, Karol, E-mail: kszalowski@uni.lodz.pl

    2015-05-15

    The paper discusses the influence of the external in-plane electric and magnetic fields on the ground state spin phase diagram of selected monolayer graphene nanostructures. The calculations are performed for triangular graphene nanoflakes with armchair edges as well as for short pieces of armchair graphene nanoribbons with zigzag terminations. The mean field approximation (MFA) is employed to solve the Hubbard model. The total spin for both classes of nanostructures is discussed as a function of external fields for various structure sizes, for charge neutrality conditions as well as for weak charge doping. The variety of nonzero spin states is found and their stability ranges are determined. For some structures, the presence of antiferromagnetic orderings is predicted within the zero-spin phase. The process of magnetization of nanoflakes with magnetic field at constant electric field is also investigated, showing opposite effect of electric field at low and at high magnetic fields. - Highlights: • Magnetic ground-state phase diagram of graphene nanoflakes was constructed. • The combined effect of in-plane electric and magnetic fields on total spin was studied. • A rich phase diagram with both disordered and ordered (nonzero spin) phases was found. • The importance of size and edge geometry of the nanostructure was emphasized.

  9. Positioning and aligning CNTs by external magnetic field to assist localised epoxy cure

    Directory of Open Access Journals (Sweden)

    Ariu G.

    2016-01-01

    Full Text Available This work focuses on the generation of conductive networks through the localised alignment of nano fillers, such as multi-walled carbon nanotubes (MWCNTs. The feasibility of alignment and positioning of functionalised MWCNTs by external DC magnetic fields was investigated. The aim of this manipulation is to enhance resin curing through AC induction heating due to hysteresis losses from the nanotubes. Experimental analyses focused on in-depth assessment of the nanotube functionalisation, processing and characterisation of magnetic, rheological and cure kinetics properties of the MWCNT solution. The study has shown that an external magnetic field has great potential for positioning and alignment of CNTs. The study demonstrated potential for creating well-ordered architectures with an unprecedented level of control of network geometry. Magnetic characterisation indicated cobalt-plated nanotubes to be the most suitable candidate for magnetic alignment due to their high magnetic sensitivity. Epoxy/metal-plated CNT nanocomposite systems were validated by thermal analysis as induction heating mediums. The curing process could therefore be optimised by the use of dielectric resins. This study offers a first step towards the proof of concept of this technique as a novel repair technology.

  10. Tailoring of in-plane magnetic anisotropy in polycrystalline cobalt thin films by external stress

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Dileep, E-mail: dkumar@csr.res.in [UGC-DAE Consortium for Scientic Research, Khandwa Road, Indore 452001 (India); Singh, Sadhana [UGC-DAE Consortium for Scientic Research, Khandwa Road, Indore 452001 (India); Vishawakarma, Pramod [School of Nanotechnology, RGPV, Bhopal 462036 (India); Dev, Arun Singh; Reddy, V.R. [UGC-DAE Consortium for Scientic Research, Khandwa Road, Indore 452001 (India); Gupta, Ajay [Amity Center for Spintronic Materials, Amity University, Sector 125, Noida 201303 (India)

    2016-11-15

    Polycrystalline Co films of nominal thickness ~180 Å were deposited on intentionally curved Si substrates. Tensile and compressive stresses of 100 MPa and 150 MPa were induced in the films by relieving the curvature. It has been found that, within the elastic limit, presence of stress leads to an in-plane magnetic anisotropy in the film and its strength increases with increasing stress. Easy axis of magnetization in the films is found to be parallel/ transverse to the compressive /tensile stresses respectively. The origin of magnetic anisotropy in the stressed films is understood in terms of magneto- elastic coupling, where the stress try to align the magnetic moments in order to minimize the magneto-elastic as well as anisotropy energy. Tensile stress is also found to be responsible for the surface smoothening of the films, which is attributed to the movement of the atoms associated with the applied stress. The present work provides a possible way to tailor the magnetic anisotropy and its direction in polycrystalline and amorphous films using external stress. - Highlights: • Tensile and compressive stresses were induced in Co films by removing the bending force from the substrates after film deposition. • Controlled external mechanical stress is found to be responsible for magnetic anisotropies in amorphous and polycrystalline thin films, where crystalline anisotropy is absent. • Tensile stress leads to surface smoothening of the polycrystalline Co films.

  11. Tunable magnetic flux sensor using a metallic Rashba ring with half-metal electrodes

    Science.gov (United States)

    Chen, J.; Jalil, M. B. A.; Tan, S. G.

    2011-04-01

    We propose a magnetic field sensor consisting of a square ring made of metal with a strong Rashba spin-orbital coupling (RSOC) and contacted to half-metal electrodes. Due to the Aharonov-Casher effect, the presence of the RSOC imparts a spin-dependent geometric phase to conduction electrons in the ring. The combination of the magnetic flux emanating from the magnetic sample placed below the ring, and the Aharonov-Casher effect due to RSOC results in spin interference, which modulates the spin transport in the ring nanostructure. By using the tight-binding nonequilibrium Green's function formalism to model the transport across the nanoring detector, we theoretically show that with proper optimization, the Rashba ring can function as a sensitive and tunable magnetic probe to detect magnetic flux.

  12. Effect of uncertainties in solar synoptic magnetic flux maps in modeling of solar wind

    Science.gov (United States)

    Pevtsov, Alexei A.; Bertello, Luca; MacNeice, Peter

    2015-12-01

    Recently, the NSO/SOLIS team developed variance (error) maps that represent uncertainties in magnetic flux synoptic charts. These uncertainties are determined by the spatial variances of the magnetic flux distribution from full disk magnetograms that contribute to each bin in the synoptic chart. Here we present a study of the effects of variances on solar wind parameters (wind speed, density, magnetic field, and temperature) derived using the WSA-ENLIL model and ensemble modeling approach. We compare the results of the modeling with near-Earth solar wind magnetic field and plasma data as extracted from NASA/GSFC's OMNI data set. We show that analysis of uncertainties may be useful for understanding the sensitivity of the model predictions to short-term evolution of magnetic field and noise in the synoptic magnetograms.

  13. Reduction in Flux Loss of an Nd-Fe-B Bonded Ring Magnet for an SPM Motor

    OpenAIRE

    Yanai, Takeshi; Horita, Satoshi; Nakano, Masaki; Tsutsumi, Shinichi; Fukunaga, Hirotoshi

    2014-01-01

    We have previously proposed a simulation method of an initial flux loss in permanent magnets using finite element method, and confirmed that predicted flux loss of an Nd-Fe-B boned ring magnet showed good agreement with measured flux loss. In this paper, we applied our proposed method to an Nd-Fe-B boned ring magnet in an SPM motor. We modeled a rotor composed of an Nd-Fe-B bonded ring magnet and a soft magnetic core made from silicon steels, and carried out the simulations for magnetizing pr...

  14. Simulation of magnetic drug targeting through tracheobronchial airways in the presence of an external non-uniform magnetic field using Lagrangian magnetic particle tracking

    Energy Technology Data Exchange (ETDEWEB)

    Pourmehran, O., E-mail: oveis87@yahoo.com; Rahimi-Gorji, M.; Gorji-Bandpy, M., E-mail: gorji@nit.ac.ir; Gorji, T.B.

    2015-11-01

    Drug delivery technologies are an important area within biomedicine. Targeted drug delivery aims to reduce the undesired side effects of drug usage by directing or capturing the active agents near a desired site within the body. Herein, a numerical investigation of magnetic drug targeting (MDT) using aerosol drugs named polystyrene particle (PMS40) in human lung is presented considering one-way coupling on the transport and capture of the magnetic particle. A realistic 3D geometry based on CT scan images is provided for CFD simulation. An external non-uniform magnetic field is applied. Parametric investigation is conducted and the influence of particle diameter, magnetic source position, and magnetic number (Mn) on the deposition efficiency and particle behavior is reported. According to the results, the magnetic field increased deposition efficiency of particles in a target region, the efficiency of deposition and MDT technique has a direct relation with increasing the particle diameter for magnetic number of 1 Tesla (T) and lower (Mn≤1(T)). Also it can be seen that there is an inverse relation between the particle diameter and deposition efficiency when Mn is more than 1 (T). - Highlights: • A realistic 3D geometry of human tracheobronchial airway based on CT scan image. • External non-uniform magnetic field applied to target the magnetic drug career. • Lagrangian particle tracking using discrete phase model applied. • The efficiency of deposition is dependent of magnetic number and particle diameter.

  15. High sensitivity microwave detection using a magnetic tunnel junction in the absence of an external applied magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Gui, Y. S.; Bai, L. H.; Hu, C.-M. [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada); Xiao, Y.; Guo, H. [Department of Physics, Center for the Physics of Materials, McGill University, Montreal, Quebec H3A 2T8 (Canada); Hemour, S.; Zhao, Y. P.; Wu, K. [Ecole Polytechnique de Montreal, Montreal, Quebec H3T 1J4 (Canada); Houssameddine, D. [Everspin Technologies, 1347 N. Alma School Road, Chandler, Arizona 85224 (United States)

    2015-04-13

    In the absence of any external applied magnetic field, we have found that a magnetic tunnel junction (MTJ) can produce a significant output direct voltage under microwave radiation at frequencies, which are far from the ferromagnetic resonance condition, and this voltage signal can be increase by at least an order of magnitude by applying a direct current bias. The enhancement of the microwave detection can be explained by the nonlinear resistance/conductance of the MTJs. Our estimation suggests that optimized MTJs should achieve sensitivities for non-resonant broadband microwave detection of about 5000 mV/mW.

  16. Laser-field-induced magnon amplification in a magnetic semiconductor quantum well under an external magnetic field

    Institute of Scientific and Technical Information of China (English)

    Peng Feng

    2003-01-01

    The laser-field induced magnon amplification in a magnetic semiconductor quantum well under an external magnetic field was discussed, it is shown that when the laser frequency is near to the electron cyclotron frequency, no matter how weaker the laser field is, the magnon amplification always occurs. In case of fixed laser frequency, the optical absorption of magnons obeys the definite selection rule to the laser field strength. The rate of change of magnon occupation is calculated, and the amplification condition is given.

  17. Accurate periodicity measurement of superconducting quantum interference device magnetic flux response.

    Science.gov (United States)

    Nakanishi, Masakazu

    2010-09-01

    It is theoretically explained that a response of a superconducting quantum interference device (SQUID) is periodically dependent on total magnetic flux coupling to the SQUID ring (Φ) and its period is a flux quantum (Φ(o)=h/2e, where h and e, respectively, express Planck's constant and elementary charge). For example, the voltage of an electromagnetically oscillated rf-SQUID or a current biased dc-SQUID is thought to be periodically dependent on Φ with a period of Φ(o). In this paper, we propose an accurate method to check the periodicity of a SQUID response by using a set of sensing coils covered with a superconducting sheath. As a demonstration, we measured periodicity of a commercially available thin-film type rf-SQUID response in magnetic flux ranging up to approximately 4300Φ(o). Its flux dependence was periodic below about 3400Φ(o).

  18. Performance comparison of three-phase flux reversal permanent magnet motors in BLDC and BLAC operation mode

    Science.gov (United States)

    Štumberger, B.; Štumberger, G.; Hadžiselimović, M.; Hamler, A.; Goričan, V.; Jesenik, M.; Trlep, M.

    The paper presents a comparison of torque capability and flux-weakening performance of three-phase flux reversal permanent magnet motors with surface and inset permanent magnets. Finite element analysis is employed to determine the performance of each motor in BLDC and BLAC operation mode. It is shown that the torque capability and flux-weakening performance of surface or inset permanent magnet configuration is strongly dependent on the stator teeth number/rotor pole number combination.

  19. Performance comparison of three-phase flux reversal permanent magnet motors in BLDC and BLAC operation mode

    Energy Technology Data Exchange (ETDEWEB)

    Stumberger, B. [Faculty of Electrical Engineering and Computer Science, University of Maribor, Smetanova ulica 17, Maribor SI-2000 (Slovenia)], E-mail: bojan.stumberger@uni-mb.si; Stumberger, G.; Hadziselimovic, M.; Hamler, A.; Gorican, V.; Jesenik, M.; Trlep, M. [Faculty of Electrical Engineering and Computer Science, University of Maribor, Smetanova ulica 17, Maribor SI-2000 (Slovenia)

    2008-10-15

    The paper presents a comparison of torque capability and flux-weakening performance of three-phase flux reversal permanent magnet motors with surface and inset permanent magnets. Finite element analysis is employed to determine the performance of each motor in BLDC and BLAC operation mode. It is shown that the torque capability and flux-weakening performance of surface or inset permanent magnet configuration is strongly dependent on the stator teeth number/rotor pole number combination.

  20. Magnetar Giant Flares in Multipolar Magnetic Fields --- I. Fully and Partially Open Eruptions of Flux Ropes

    CERN Document Server

    Huang, Lei

    2014-01-01

    We propose a catastrophic eruption model for magnetar's enormous energy release during giant flares, in which a toroidal and helically twisted flux rope is embedded within a force-free magnetosphere. The flux rope stays in stable equilibrium states initially and evolves quasi-statically. Upon the loss of equilibrium point is reached, the flux rope cannot sustain the stable equilibrium states and erupts catastrophically. During the process, the magnetic energy stored in the magnetosphere is rapidly released as the result of destabilization of global magnetic topology. The magnetospheric energy that could be accumulated is of vital importance for the outbursts of magnetars. We carefully establish the fully open fields and partially open fields for various boundary conditions at the magnetar surface and study the relevant energy thresholds. By investigating the magnetic energy accumulated at the critical catastrophic point, we find that it is possible to drive fully open eruptions for dipole dominated background...

  1. Numerical simulations of magnetic Kelvin-Helmholtz instability at a twisted solar flux tube

    Science.gov (United States)

    Murawski, K.; Chmielewski, P.; Zaqarashvili, T. V.; Khomenko, E.

    2016-07-01

    The paper aims to study the response of a solar small-scale and weak magnetic flux tube to photospheric twisting motions. We numerically solve three-dimensional ideal magnetohydrodynamic equations to describe the evolution of the perturbation within the initially static flux tube, excited by twists in the azimuthal component of the velocity. These twists produce rotation of the magnetic field lines. Perturbation of magnetic field lines propagates upwardly, driving vertical and azimuthal flow as well as plasma compressions and rarefactions in the form of eddies. We conclude that these eddies result from the sheared azimuthal flow which seeds Kelvin-Helmholtz instability (KHI) between the flux tube and the ambient medium. Numerically obtained properties of the KHI confirm the analytical predictions for the occurrence of the instability.

  2. Evolution of a typical ion-scale magnetic flux rope caused by thermal pressure enhancement

    Science.gov (United States)

    Teh, W.-L.; Nakamura, T. K. M.; Nakamura, R.; Baumjohann, W.; Russell, C. T.; Pollock, C.; Lindqvist, P.-A.; Ergun, R. E.; Burch, J. L.; Torbert, R. B.; Giles, B. L.

    2017-02-01

    With high time-resolution field and plasma measurements by the Magnetospheric Multiscale spacecraft, interior fine structures of two ion-scale magnetic flux ropes ( 5 and 11 ion inertial length radius) separated by 14 s are resolved. These two ion-scale flux ropes (FR1 and FR2) show non-frozen-in ion behavior and consist of a strong axial magnetic field at the reversal of the negative-then-positive bipolar field component. The negative bipolar field component of the FR2 is found to be depressed, where magnetic pressure and total pressure decrease, but ion and electron thermal pressures increase, a feature akin to a crater-like flux rope. The pressure enhancement is due to the magnetosheath plasma feeding into the flux rope along the field lines. Magnetic field draping and energetic electrons are also observed in the trailing part of the FR2. The ratio of perpendicular and parallel currents indicates that the FR1 appears force-free but the FR2 seems not. Moreover, the FR2 is time-dependent as a result of a low correlation coefficient (CC = 0.75) for the derivation of the deHoffmann-Teller frame using the direct measured electric fields, while the FR1 is in quasi-steady conditions (CC = 0.94). It is concluded that the crater formation within the FR2 can be interpreted by the analytical flux rope simulation as the evolution of typical flux rope to crater-like one due to the thermal pressure enhancement, which could be induced by the depression of transverse magnetic fields of the flux rope.

  3. Torque Ripple Suppression in an External-Meshed Magnetic Gear Train

    Directory of Open Access Journals (Sweden)

    Yi-Chang Wu

    2013-01-01

    Full Text Available Magnetic gear trains transmit torque through noncontact magnetic couplings rather than conjugate gear teeth; they have the unique advantages of reduced maintenance and improved reliability, inherent overload protection, high efficiency, precise peak torque transmission, and tolerance for misalignment. Smooth and steadily transmitted torque is an important characteristic for a magnetic gear train. It is necessary for the reduction of possible mechanical vibration, position inaccuracy, and acoustic noise. This paper investigates the transmitted torque characteristics, especially torque ripple reduction, of an external-meshed magnetic gear train using finite-element analysis (FEA. The topological structure and working principles of a simple magnetic gear train with parallel axes are introduced. With the aid of a commercial FEA package, the transmitted torque waveform of a magnetic gear train is numerically calculated. The effects of geometrical parameters on the maximum transmitted torque and torque ripple are further discussed in terms of obtaining a magnetic gear train with high transmitted torque or low torque ripple. This examination offers insights beneficial to future magnetic gear mechanism design.

  4. Magnetic-field decay of three interlocked flux rings with zero linking number.

    Science.gov (United States)

    Del Sordo, Fabio; Candelaresi, Simon; Brandenburg, Axel

    2010-03-01

    The resistive decay of chains of three interlocked magnetic flux rings is considered. Depending on the relative orientation of the magnetic field in the three rings, the late-time decay can be either fast or slow. Thus, the qualitative degree of tangledness is less important than the actual value of the linking number or, equivalently, the net magnetic helicity. Our results do not suggest that invariants of higher order than that of the magnetic helicity need to be considered to characterize the decay of the field.

  5. Magnetic field decay of three interlocked flux rings with zero linking number

    CERN Document Server

    del Sordo, Fabio; Brandenburg, Axel

    2009-01-01

    The resistive decay of chains of three interlocked magnetic flux rings is considered. Depending on the relative orientation of the magnetic field in the three rings, the late-time decay can be either fast or slow. Thus, the qualitative degree of tangledness is less important than the actual value of the linking number or, equivalently, the net magnetic helicity. Our results do not suggest that invariants of higher order than that of the magnetic helicity need to be considered to characterize the decay of the field.

  6. Influence of an external magnetic field on forced turbulence in a swirling flow of liquid metal

    CERN Document Server

    Gallet, Basile; Mordant, Nicolas

    2009-01-01

    We report an experimental investigation on the influence of an external magnetic field on forced 3D turbulence of liquid gallium in a closed vessel. We observe an exponential damping of the turbulent velocity fluctuations as a function of the interaction parameter N (ratio of Lorentz force over inertial terms of the Navier-Stokes equation). The flow structures develop some anisotropy but do not become bidimensional. From a dynamical viewpoint, the damping first occurs homogeneously over the whole spectrum of frequencies. For larger values of N, a very strong additional damping occurs at the highest frequencies. However, the injected mechanical power remains independent of the applied magnetic field. The simultaneous measurement of induced magnetic field and electrical potential differences shows a very weak correlation between magnetic field and velocity fluctuations. The observed reduction of the fluctuations is in agreement with a previously proposed mechanism for the saturation of turbulent dynamos and wit...

  7. Effect of an External Oriented Magnetic Field on Entropy Generation in Natural Convection

    Directory of Open Access Journals (Sweden)

    Atef El Jery

    2010-05-01

    Full Text Available The influence of an external oriented magnetic field on entropy generation in natural convection for air and liquid gallium is numerically studied in steady-unsteady states by solving the mass, the momentum and the energy conservation equations. Entropy generation depends on five parameters which are: the Prandtl number, the irreversibility coefficients, the inclination angle of the magnetic field, the thermal Grashof and the Hartmann numbers. Effects of these parameters on total and local irreversibilities as well as on heat transfer and fluid flow are studied. It was found that the magnetic field tends to decrease the convection currents, the heat transfer and entropy generation inside the enclosure. Influence of inclination angle of the magnetic field on local irreversibility is then studied.

  8. Holographic Superconductors with Logarithmic Nonlinear Electrodynamics in an External Magnetic Field

    Science.gov (United States)

    Sheykhi, A.; Shamsi, F.

    2017-03-01

    Based on the matching method, we explore the effects of adding an external magnetic field on the s-wave holographic superconductors when the gauge field is in the form of the logarithmic nonlinear source. First, we obtain the critical temperature as well as the condensation operator in the presence of logarithmic nonlinear electrodynamics and understand that they depend on the nonlinear parameter b. We show that the critical temperature decreases with increasing b, which implies that the nonlinear gauge field makes the condensation harder. Then, we turn on the magnetic field in the bulk and find the critical magnetic field, B c , in terms of the temperature, which also depends on the nonlinear parameter b. We observe that for temperature smaller than the critical temperature, T superconductor with magnetic field in Maxwell theory.

  9. Influence of external resonant magnetic perturbation field on edge plasma of small tokamak HYBTOK-II

    Energy Technology Data Exchange (ETDEWEB)

    Hayashi, Y., E-mail: hayashi-yuki13@ees.nagoya-u.ac.jp [Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan); Suzuki, Y.; Ohno, N. [Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan); Okamoto, M. [Ishikawa National College of Technology, Kitachujo, Tsubata-cho, Kahoku-gun, Ishikawa 929-0392 (Japan); Kikuchi, Y. [University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280 (Japan); Sakakibara, S.; Watanabe, K.; Takemura, Y. [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki, Gifu 509-5292 (Japan)

    2015-08-15

    Radial profile of externally applied resonant magnetic perturbation (RMP) field with mode numbers of m = 6 and n = 2 in a small tokamak device HYBTOK-II have been investigated using a magnetic probe array, which is able to measure the radial profile of magnetic field perturbation induced by applying RMP. Results of RMP penetration into the plasma show that the RMP decreased toward the plasma center, while they were amplified around the resonant surface with a safety factor q = 3 due to the formation of magnetic islands. This suggests that RMP fields for controlling edge plasmas may trigger some kind of MHD instabilities. In addition, simulation results, based on a linearized four-field model, which agrees with the experimental ones, indicates that the penetration and amplification process of RMP strongly depend on a Doppler-shifted frequency between the RMP and plasma rotation.

  10. Magnetic flux annihilation waves in inhomogeneous high-temperature superconductors

    NARCIS (Netherlands)

    Rudnev, IA; Khodot, AE; Eremin, AV; Mikhailov, BP

    2004-01-01

    The process of magnetic field penetration into polycrystalline high-T-c superconductors of the YBa2Cu3O7 - x and Bi2Sr2Ca2Cu3O10 - x systems has been studied using traditional magnetooptical methods and scanning Hall probe microscopy. It is established that remagnetization of a sample is accompanied

  11. Measurements of flux pumping activation of trapped field magnets

    Energy Technology Data Exchange (ETDEWEB)

    Weinstein, Roy; Parks, Drew; Sawh, Ravi-Persad [Texas Center for Superconductivity, 202 Houston Science Center, University of Houston, Houston, TX 77204-5002 (United States); Davey, Kent [Physics Department, 617 Science and Research Building I, University of Houston, Houston, TX 77204-5005 (United States)

    2010-11-15

    Large grains of high temperature superconducting (HTS) material can be utilized as trapped field magnets (TFMs). Persistent currents are set up in the HTS when it is cooled in a magnetic field, or exposed to a magnetic field after cooling. TFMs have been improved over the past two decades by the efforts of a large number of worldwide research groups. However, applications using TFMs have lagged, in part due to the problem of high fields needed for activation. We describe herein experiments designed to observe the behaviour of TFM activation using repeated applications of low fields (called 'pumping'). Significant partial activation is obtained using a non-uniform pumping field (e.g., a small permanent magnet) which is higher in the centre of the HTS than at the periphery. Cooling in zero field followed by pumping with such a field results in trapping the full applied field, in comparison to half of the applied field being trapped by cooling in zero field followed by application of a uniform field. We find that for partial activation by cooling in a field and subsequent activation by pumping, the resulting fields are additive. We also conclude that for activation by fluxoid pumping, creep assists the process.

  12. Moving magnetic tubes: fragmentation, vortex streets and the limit of the approximation of thin flux tubes

    Science.gov (United States)

    Cheung, M. C. M.; Moreno-Insertis, F.; Schüssler, M.

    2006-05-01

    Aims.We study the buoyant rise of magnetic flux tubes in a stratified layer over a range of Reynolds numbers (25 ⪉ Re ⪉ 2600) by means of numerical simulations. Special emphasis is placed on studying the fragmentation of the rising tube, its trailing wake and the formation of a vortex street in the high-Reynolds number regime. Furthermore, we evaluate the relevance of the thin flux tube approximation with regard to describing the evolution of magnetic flux tubes in the simulations. Methods: .We used the FLASH code, which has an adaptive mesh refinement (AMR) algorithm, thus allowing the simulations to be carried out at high Reynolds numbers. Results: .The evolution of the magnetic flux tube and its wake depends on the Reynolds number. At Re up to a few hundred, the wake consists of two counter-rotating vortex rolls. At higher Re, the vortex rolls break up and the shedding of flux into the wake occurs in a more intermittent fashion. The amount of flux retained by the central portion of the tube increases with the field line twist (in agreement with previous literature) and with Re. The time evolution of the twist is compatible with a homologous expansion of the tube. The motion of the central portion of the tube in the simulations is very well described by the thin flux tube model whenever the effects of flux loss or vortex forces can be neglected. If the flux tube has an initial net vorticity, it undergoes asymmetric vortex shedding. In this case, the lift force accelerates the tube in such a way that an oscillatory horizontal motion is super-imposed on the vertical rise of the tube, which leaves behind a vortex street. This last result is in accordance with previous simulations reported in the literature, which were carried out at lower Reynolds number.

  13. Externally Phase-Locked Flux Flow Oscillator for Submm Integrated Receivers; Achievements and Limitations

    DEFF Research Database (Denmark)

    Koshelets, V. P.; Shitov, S. V.; Dmitriev, P. N.;

    2003-01-01

    to 712 GHz, limited only by the gap frequency of Nb. This enabled us to phase lock the FFO in the frequency range 500-712 GHz where continuous frequency tuning is possible; resulting in an absolute FFO phase noise as low as -80 dBc at 707 GHz. Comprehensive measurements of the FFO radiation linewidth...... have been performed using an integrated SIS harmonic mixer. The influence of FFO parameters on radiation linewidth, particularly the effect of the differential resistances associated both with the bias current and the applied magnetic field has been studied in order to further optimize the FFO design....... A new approach with a self-shielded FFO has been developed and experimentally tested....

  14. SU(3) Polyakov linear-σ model in an external magnetic field

    Science.gov (United States)

    Tawfik, Abdel Nasser; Magdy, Niseem

    2014-07-01

    In the present work, we analyze the effects of an external magnetic field on the chiral critical temperature Tc of strongly interacting matter. In doing this, we can characterize the magnetic properties of the quantum chromodynamics (QCD) strongly interacting matter, the quark-gluon plasma (QGP). We investigate this in the framework of the SU(3) Polyakov linear sigma model (PLSM). To this end, we implement two approaches representing two systems, in which the Polyakov-loop potential added to PLSM is either renormalized or non-normalized. The effects of Landau quantization on the strongly interacting matter are conjectured to reduce the electromagnetic interactions between quarks. In this case, the color interactions will be dominant and increasing, which in turn can be achieved by increasing the Polyakov-loop fields. Obviously, each of them equips us with a different understanding about the critical temperature under the effect of an external magnetic field. In both systems, we obtain a paramagnetic response. In one system, we find that Tc increases with increasing magnetic field. In the other one, Tc significantly decreases with increasing magnetic field.

  15. The stretching of magnetic flux tubes in the convective overshoot region

    Science.gov (United States)

    Fisher, George H.; Mcclymont, Alexander N.; Chou, Dean-Yi

    1991-01-01

    The present study examines the fate of a magnetic flux tube initially lying at the bottom of the solar convective overshoot region. Stretching of the flux tube, e.g., by differential rotation, reduces its density, causing it to rise quasi-statically (a process referred to as vertical flux drift) until it reaches the top of the overshoot region and enters the buoyantly unstable convection region, from which a portion of it may ultimately protrude to form an active region on the surface. It is suggested that vertical flux drift and flux destabilization are inevitable consequences of field amplification, and it is surmised that these phenomena should be considered in self-consistent models of solar and stellar dynamos operating in the overshoot region.

  16. Multiple Triangulation Analysis: another approach to determine the orientation of magnetic flux ropes

    Directory of Open Access Journals (Sweden)

    X.-Z. Zhou

    2006-07-01

    Full Text Available Another approach (Multiple Triangulation Analysis, MTA is presented to determine the orientation of magnetic flux rope, based on 4-point measurements. A 2-D flux rope model is used to examine the accuracy of the MTA technique in a theoretical way. It is found that the precision of the estimated orientation is dependent on both the spacecraft separation and the constellation path relative to the flux rope structure. However, the MTA error range can be shown to be smaller than that of the traditional MVA technique. As an application to real Cluster data, several flux rope events on 26 January 2001 are analyzed using MTA, to obtain their orientations. The results are compared with the ones obtained by several other methods which also yield flux rope orientation. The estimated axis orientations are shown to be fairly close, suggesting the reliability of the MTA method.

  17. Influence of Josephson current second harmonic on stability of magnetic flux in long junctions

    Science.gov (United States)

    Atanasova, P. K. H.; Boyadjiev, T. L.; Shukrinov, Y. U. M.; Zemlyanaya, E. V.; Seidel, P.

    2010-11-01

    We study the long Josephson junction (LJJ) model which takes into account the second harmonic of the Fourier expansion of Josephson current. The dependence of the static magnetic flux distributions on parameters of the model are investigated numerically. Stability of the static solutions is checked by the sign of the smallest eigenvalue of the associated Sturm-Liouville problem. New solutions which do not exist in the traditional model, have been found. Investigation of the influence of second harmonic on the stability of magnetic flux distributions for main solutions is performed.

  18. 2D and 3D fault basis for fuel cell diagnosis by external magnetic field measurements

    Science.gov (United States)

    Ifrek, Lyes; Cauffet, Gilles; Chadebec, Olivier; Bultel, Yann; Rosini, Sébastien; Rouveyre, Luc

    2017-07-01

    An original approach used for the identification of faults in fuel cell stacks is presented. It is based on the 3D reconstruction of the current density from external magnetic field measurements which is an ill-posed magnetostatic linear inverse problem. A suitable and original current density and magnetic field basis are proposed in order to define both local and global faults on a fuel cell stack. The inverse problem is regularized by truncated singular value decomposition (SVD) to ensure the uniqueness of the solution. Contribution to the topical issue "Electrical Engineering Symposium (SGE 2016)", edited by Adel Razek

  19. Structurization of ferrofluids in the absence of an external magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Zubarev, A. Yu., E-mail: Andrey.Zubarev@usu.ru; Iskakova, L. Yu. [Ural Federal University (Russian Federation)

    2013-02-15

    Structural transformations in a model ferrofluid in the absence of an external magnetic field have been theoretically studied. The results agree with well-known laboratory experiments and computer simulations in showing that, if the concentration of particles and their magnetic interaction energy are below certain critical values, most particles form separate linear chains. If these parameters exceed the critical values, most particles concentrate so as to form branched network structures. The passage from chains to network has a continuous character rather than represents a discontinuous first-order phase transition.

  20. Geometric Phase of Polarized Hydrogenlike Atoms in an External Magnetic Field

    Science.gov (United States)

    Tang, Zhong; Finkelstein, David

    1995-04-01

    We show that the motion of polarized hydrogenlike atoms in an external magnetic field B is a cyclic evolution. The geometric phase they exhibit is dependent on both the initial state and the Hamiltonian. Properties of the geometric phase in the cases of weak (called Zeeman limit) and strong (called Paschen-Back limit) magnetic fields are presented. We point out that the results of the two limits are interpolated in the intermediate B region. Some observable effects in a specially devised interferometer are predicted.

  1. Surface and body waves in magnetic flux tubes. [in solar convection zone, photosphere, and corona

    Science.gov (United States)

    Abdelatif, T. E.

    1988-01-01

    The dispersion relation of surface and body waves in a magnetic flux tube is studied in detail. The properties of the fast and slow bodywaves are described in terms of the filtering characteristics of the flux tube. In addition to the axisymmetric and nonaxisymmetric distinction between the modes, an additional distinction is made between the fundamental mode and the rest of the modes. New results concerning the thin and large flux tube approximation are derived. The behavior of surface and body waves in the solar convection zone, photosphere, and corona is discussed.

  2. Analytical model of particle and heat flux collection by dust immersed in dense magnetized plasmas

    Science.gov (United States)

    Vignitchouk, L.; Ratynskaia, S.; Tolias, P.

    2017-10-01

    A comprehensive analytical description is presented for the particle and heat fluxes collected by dust in dense magnetized plasmas. Compared to the widely used orbital motion limited theory, the suppression of cross-field transport leads to a strong reduction of the electron fluxes, while ion collection is inhibited by thin-sheath effects and the formation of a potential overshoot along the field lines. As a result, the incoming heat flux loses its sensitivity to the floating potential, thereby diminishing the importance of electron emission processes in dust survivability. Numerical simulations implementing the new model for ITER-like detached divertor plasmas predict a drastic enhancement of the dust lifetime.

  3. Tests of the frozen-flux and tangentially geostrophic assumptions using magnetic satellite data

    DEFF Research Database (Denmark)

    Chulliat, A.; Olsen, Nils; Sabaka, T.

    the very large number of flows explaining the observed secular variation under the frozen-flux assumption alone. More recently, it has been shown that the combined frozen-flux and tangentially geostrophic assumptions translate into constraints on the secular variation whose mathematics are now well...... understood. Using these constraints, we test the combined frozen-flux and tangentially geostrophic assumptions against recent, high-precision magnetic data provided by the and CHAMP satellites. The methodology involves building constrained field models using least-squares methods. Two types of models...

  4. Electromagnetically induced transparency in a spherical quantum dot with hydrogenic impurity in the external magnetic field

    Science.gov (United States)

    Pavlović, Vladan; Stevanović, Ljiljana

    2016-04-01

    In this paper we analyzed the realization of the electromagnetically induced transparency (EIT) effect in the spherical quantum dot with on-center hydrogenic impurity under the influence of the external magnetic field. Three energy levels of hydrogen impurity 1s0, 2p-1, and 3d-2, together with the probe and control laser fields, which induce σ- transitions between the given states, form a ladder configuration. Optical Bloch equations for such a system are solved in a stationary regime. Dependence of the susceptibility for such a system on the Rabi frequency of the control field, intensity of the external magnetic field, detuning of the control field, and decay rates coefficients are then discussed in detail. Finally, the explanation in dressed state picture is given.

  5. Effects of external magnetic field on oblique propagation of ion acoustic cnoidal wave in nonextensive plasma

    Science.gov (United States)

    Farhad Kiyaei, Forough; Dorranian, Davoud

    2017-01-01

    Effects of the obliqueness and the strength of external magnetic field on the ion acoustic (IA) cnoidal wave in a nonextensive plasma are investigated. The reductive perturbation method is employed to derive the corresponding KdV equation for the IA wave. Sagdeev potential is extracted, and the condition of generation of IA waves in the form of cnoidal waves or solitons is discussed in detail. In this work, the domain of allowable values of nonextensivity parameter q for generation of the IA cnoidal wave in the plasma medium is considered. The results show that only the compressive IA wave may generate and propagate in the plasma medium. Increasing the strength of external magnetic field will increase the frequency of the wave and decrease its amplitude, while increasing the angle of propagation will decrease the frequency of the wave and increase its amplitude.

  6. On Cluster Properties of Classical Ferromagnets in an External Magnetic Field

    Science.gov (United States)

    Fröhlich, Jürg; Rodríguez, Pierre-François

    2017-02-01

    Correlation functions of ferromagnetic spin systems satisfying a Lee-Yang property are studied. It is shown that, for classical systems in a non-vanishing uniform external magnetic field h, the connected correlation functions decay exponentially in the distances between the spins, i.e., the inverse correlation length ("mass gap"), m( h), is strictly positive. Our proof is very short and transparent and is valid for complex values of the external magnetic field h, provided that Re h not = 0. It implies a mean-field lower bound on m( h), as h searrow 0, first established by Lebowitz and Penrose for the Ising model. Our arguments also apply to some quantum spin systems.

  7. Complete Form of Fermion Self-energy in NJL Model with External Magnetic Field

    CERN Document Server

    Shi, Song; Cui, Zhu-Fang; Xia, Yong-Hui; Zong, Hong-Shi

    2016-01-01

    In this paper, we aim to study the complete form of self-energy in fermion propagator within two-flavor NJL model in the case of finite temperature, chemical potential and external magnetic field. Through self-consistency analysis we prove that the self-energy is not simply proportional to dynamical mass in the presence of chemical potential, moreover, it could be more complicated after introducing external magnetic field. We find out the appropriate and complete form of self-energy and establish new gap equations. The numerical results show that the dynamical mass only has small quantitative modification rather than qualitative change by using these new gap equations, but the new self-energy does generate split in the dispersion relation with fixed momentum and Landau level.

  8. Estimation of electrical conductivity distribution within the human head from magnetic flux density measurement.

    Science.gov (United States)

    Gao, Nuo; Zhu, S A; He, Bin

    2005-06-01

    We have developed a new algorithm for magnetic resonance electrical impedance tomography (MREIT), which uses only one component of the magnetic flux density to reconstruct the electrical conductivity distribution within the body. The radial basis function (RBF) network and simplex method are used in the present approach to estimate the conductivity distribution by minimizing the errors between the 'measured' and model-predicted magnetic flux densities. Computer simulations were conducted in a realistic-geometry head model to test the feasibility of the proposed approach. Single-variable and three-variable simulations were performed to estimate the brain-skull conductivity ratio and the conductivity values of the brain, skull and scalp layers. When SNR = 15 for magnetic flux density measurements with the target skull-to-brain conductivity ratio being 1/15, the relative error (RE) between the target and estimated conductivity was 0.0737 +/- 0.0746 in the single-variable simulations. In the three-variable simulations, the RE was 0.1676 +/- 0.0317. Effects of electrode position uncertainty were also assessed by computer simulations. The present promising results suggest the feasibility of estimating important conductivity values within the head from noninvasive magnetic flux density measurements.

  9. Magnetic flux density reconstruction using interleaved partial Fourier acquisitions in MREIT.

    Science.gov (United States)

    Park, Hee Myung; Nam, Hyun Soo; Kwon, Oh In

    2011-04-01

    Magnetic resonance electrical impedance tomography (MREIT) has been introduced as a non-invasive modality to visualize the internal conductivity and/or current density of an electrically conductive object by the injection of current. In order to measure a magnetic flux density signal in MREIT, the phase difference approach in an interleaved encoding scheme cancels the systematic artifacts accumulated in phase signals and also reduces the random noise effect. However, it is important to reduce scan duration maintaining spatial resolution and sufficient contrast, in order to allow for practical in vivo implementation of MREIT. The purpose of this paper is to develop a coupled partial Fourier strategy in the interleaved sampling in order to reduce the total imaging time for an MREIT acquisition, whilst maintaining an SNR of the measured magnetic flux density comparable to what is achieved with complete k-space data. The proposed method uses two key steps: one is to update the magnetic flux density by updating the complex densities using the partially interleaved k-space data and the other is to fill in the missing k-space data iteratively using the updated background field inhomogeneity and magnetic flux density data. Results from numerical simulations and animal experiments demonstrate that the proposed method reduces considerably the scanning time and provides resolution of the recovered B(z) comparable to what is obtained from complete k-space data.

  10. Torsional Alfven Waves in Solar Magnetic Flux Tubes of Axial Symmetry

    CERN Document Server

    Murawski, K; Musielak, Z E; Srivastava, A K; Kraskiewicz, J

    2015-01-01

    Aims: Propagation and energy transfer of torsional Alfv\\'en waves in solar magnetic flux tubes of axial symmetry is studied. Methods: An analytical model of a solar magnetic flux tube of axial symmetry is developed by specifying a magnetic flux and deriving general analytical formulae for the equilibrium mass density and a gas pressure. The main advantage of this model is that it can be easily adopted to any axisymmetric magnetic structure. The model is used to simulate numerically the propagation of nonlinear Alfv\\'en waves in such 2D flux tubes of axial symmetry embedded in the solar atmosphere. The waves are excited by a localized pulse in the azimuthal component of velocity and launched at the top of the solar photosphere, and they propagate through the solar chromosphere, transition region, and into the solar corona. Results: The results of our numerical simulations reveal a complex scenario of twisted magnetic field lines and flows associated with torsional Alfv\\'en waves as well as energy transfer to t...

  11. A miniaturized human-motion energy harvester using flux-guided magnet stacks

    Science.gov (United States)

    Halim, M. A.; Park, J. Y.

    2016-11-01

    We present a miniaturized electromagnetic energy harvester (EMEH) using two flux-guided magnet stacks to harvest energy from human-generated vibration such as handshaking. Each flux-guided magnet stack increases (40%) the magnetic flux density by guiding the flux lines through a soft magnetic material. The EMEH has been designed to up-convert the applied human-motion vibration to a high-frequency oscillation by mechanical impact of a spring-less structure. The high-frequency oscillator consists of the analyzed 2-magnet stack and a customized helical compression spring. A standard AAA battery sized prototype (3.9 cm3) can generate maximum 203 μW average power from human hand-shaking vibration. It has a maximum average power density of 52 μWcm-3 which is significantly higher than the current state-of-the-art devices. A 6-stage multiplier and rectifier circuit interfaces the harvester with a wearable electronic load (wrist watch) to demonstrate its capability of powering small- scale electronic systems from human-generated vibration.

  12. The Total Solar Irradiance, UV Emission and Magnetic Flux during the Last Solar Cycle Minimum

    Directory of Open Access Journals (Sweden)

    E. E. Benevolenskaya

    2013-01-01

    Full Text Available We have analyzed the total solar irradiance (TSI and the spectral solar irradiance as ultraviolet emission (UV in the wavelength range 115–180 nm, observed with the instruments TIM and SOLSTICE within the framework of SORCE (the solar radiation and climate experiment during the long solar minimum between the 23rd and 24th cycles. The wavelet analysis reveals an increase in the magnetic flux in the latitudinal zone of the sunspot activity, accompanied with an increase in the TSI and UV on the surface rotation timescales of solar activity complexes. In-phase coherent structures between the midlatitude magnetic flux and TSI/UV appear when the long-lived complexes of the solar activity are present. These complexes, which are related to long-lived sources of magnetic fields under the photosphere, are maintained by magnetic fluxes reappearing in the same longitudinal regions. During the deep solar minimum (the period of the absence of sunspots, a coherent structure has been found, in which the phase between the integrated midlatitude magnetic flux is ahead of the total solar irradiance on the timescales of the surface rotation.

  13. Reduction of Thermal Loss in HTS Windings by Using Magnetic Flux Deflection

    Science.gov (United States)

    Tsuzuki, K.; Miki, M.; Felder, B.; Koshiba, Y.; Izumi, M.; Umemoto, K.; Aizawa, K.; Yanamoto, T.

    Efforts on the generation of intensified magnetic flux have been made for the optimized shape of HTS winding applications. This contributes to the high efficiency of the rotating machines using HTS windings. Heat generation from the HTS windings requires to be suppressed as much as possible, when those coils are under operation with either direct or alternative currents. Presently, the reduction of such thermal loss generated by the applied currents on the HTS coils is reported with a magnetic flux deflection system. The HTS coils are fixed together with flattened magnetic materials to realize a kind of redirection of the flux pathway. Eventually, the magnetic flux density perpendicular to the tape surface (equivalent to the a-b plane) of the HTS tape materials is reduced to the proximity of the HTS coil. To verify the new geometry of the surroundings of the HTS coils with magnetic materials, a comparative study of the DC coil voltage was done for different applied currents in prototype field-pole coils of a ship propulsion motor.

  14. EXPERIMENTAL DETERMINATION OF LONGITUDINAL COMPONENT OF MAGNETIC FLUX IN FERROMAGNETIC WIRE OF SINGLE-CORE POWER CABLE ARMOUR

    Directory of Open Access Journals (Sweden)

    I.A. Kostiukov

    2014-12-01

    Full Text Available A problem of determination of effective longitudinal magnetic permeability of single core power cable armour is defined. A technique for experimental determination of longitudinal component of magnetic flux in armour spiral ferromagnetic wire is proposed.

  15. Schwinger pair creation in Dirac semimetals in the presence of external magnetic and electric fields

    Science.gov (United States)

    Abramchuk, R. A.; Zubkov, M. A.

    2016-12-01

    We discuss the Schwinger pair creation process for the system of massless Dirac fermions in the presence of constant external magnetic and electric fields. The pair production rate remains finite unlike the vacuum decay rate. In the recently discovered Dirac semimetals, where the massless Dirac fermions emerge, this pair production may be observed experimentally through the transport properties. We estimate its contribution to the ordinary conductivity of the semimetals.

  16. Effect of external magnetic field on the coexistence of SC and AFM in iron based superconductors

    Science.gov (United States)

    Goi, S. K.; Pradhan, B.; Behera, Srikanta; Parida, P. K.; Mishra, R. N.

    2017-03-01

    We have studied the interplay of antiferromagnetism and superconductivity in presence of an applied external magnetic field for the iron based superconductors. For the purpose we have proposed a model Hamiltonian and solved it self-consistently by using the Zubarev's technique of double time Green's function technique. The self-consistent gap equations are solved numerically and interpreted the gap values from the of density of states plots.

  17. $Er^{3+}$ luminescence as a sensor of high pressure and strong external magnetic fields

    NARCIS (Netherlands)

    Valiente, R.; Millot, M.; Rodriguez, F.; Gonzalez, J.; Broto, J-M.; George, S.; Garcia-Revilla, S.; Romanyuk, Y.; Pollnau, M.

    2009-01-01

    In this paper, we present the preliminary results of the combined effect of high pressure (up to 7.5 GPa) and strong external magnetic fields (up to 28.5 T) on the photoluminescence (PL) properties of $Er^{3+}–Yb^{3+}$ co-doped single-crystal thin films of well-oriented $KY(WO_4)_2$ at low temperat

  18. Small-scale ion flux and magnetic field fluctuations in solar wind, foreshock and magnetosheath

    Institute of Scientific and Technical Information of China (English)

    N. N. Shevyrev; Du Jian; G. N. Zastenker; Wang Chi; P. E. Eigesa

    2007-01-01

    We have continued investigation of waves in the regions of undisturbed solar wind, foreshock and magnetosheath. The analysis of ion flux and magnetic field variations with the time interval l-240s was performed in the regions above. Very large variation in such a time interval can be considered the common feature of the foreshock and magnetosheath. The results of case and statistical studies showed that the level of relative variations of ion flux and magnetic field magnitude in foreshock is about 3 times larger than in undisturbed solar wind. Variations of these parameters in the magnetosheath topologically connected with the quasi-parallel bow shock are about two times larger than those behind the quasi-perpendicular. We also compared the results from Interball-1 data analysis with those from statistical analysis of cluster magnetic field measurements. The magnetic field variations obtained from the different satellite data coincide with each other very well not only in quality but also in quantity.

  19. QCD spectroscopy and quark mass renormalisation in external magnetic fields with Wilson fermions

    CERN Document Server

    Bali, Gunnar; Endrodi, Gergely; Glaessle, Benjamin

    2015-01-01

    We study the change of the QCD spectrum of low-lying mesons in the presence of an external magnetic field using Wilson fermions in the quenched approximation. Motivated by qualitative differences observed in the spectra of overlap and Wilson fermions for large magnetic fields, we investigate the dependence of the additive quark mass renormalisation on the magnetic field. We provide evidence that the magnetic field changes the critical quark mass both in the free case and on our quenched ensemble. The associated change of the bare quark mass with the magnetic field affects the spectrum and is relevant for the magnetic field dependence of a number of related quantities. We derive Ward identities for lattice and continuum QCD+QED from which we can extract the current quark masses. We also report on a first test of the tuning of the quark masses with the magnetic field using the current quark masses, and show that this tuning resolves the qualitative discrepancy between the Wilson and overlap spectra.

  20. Transport of magnetic flux and the vertical structure of accretion discs - I. Uniform diffusion coefficients

    Science.gov (United States)

    Guilet, Jérôme; Ogilvie, Gordon I.

    2012-08-01

    Standard models of accretion discs study the transport of mass on a viscous time-scale but do not consider the transport of magnetic flux. The evolution of a large-scale poloidal magnetic field is, however, an important problem because of its role in the launching of jets and winds and in determining the intensity of turbulence. As a consequence, the transport of poloidal magnetic flux should be considered on an equal basis to the transport of mass. In this paper, we develop a formalism to study such a transport of mass and magnetic flux in a thin accretion disc. The governing equations are derived by performing an asymptotic expansion in the limit of a thin disc, in the regime where the magnetic field is dominated by its vertical component. Turbulent viscosity and resistivity are included, with an arbitrary vertical profile that can be adjusted to mimic the vertical structure of the turbulence. At a given radius and time, the rates of transport of mass and magnetic flux are determined by a one-dimensional problem in the vertical direction, in which the radial gradients of various quantities appear as source terms. We solve this problem to obtain the transport rates and the vertical structure of the disc. This paper is then restricted to the idealized case of uniform diffusion coefficients, while a companion paper will study more realistic vertical profiles of these coefficients. We show the advection of weak magnetic fields to be significantly faster than the advection of mass, contrary to what a crude vertical averaging might suggest. This results from the larger radial velocities away from the mid-plane, which barely affect the mass accretion owing to the low density in these regions but do affect the advection of magnetic flux. Possible consequences of this larger accretion velocity include a potentially interesting time dependence with the magnetic flux distribution evolving faster than the mass distribution. If the disc is not too thin, this fast advection

  1. Recent advances in understanding the origin of magnetic flux concentrations in strongly stratified turbulence

    CERN Document Server

    Brandenburg, Axel; Kleeorin, Nathan

    2016-01-01

    In the presence of strong density stratification, hydromagnetic turbulence attains qualitatively new properties: the formation of magnetic flux concentrations. We review here the theoretical foundations of this mechanism in terms of what is now called the negative effective magnetic pressure instability. We also present direct numerical simulations of forced turbulence in strongly stratified layers and discuss the qualitative and quantitative similarities with corresponding mean-field simulations. Finally, the relevance to sunspot formation is discussed.

  2. Propagation of Long-Wavelength Nonlinear Slow Sausage Waves in Stratified Magnetic Flux Tubes

    Science.gov (United States)

    Barbulescu, M.; Erdélyi, R.

    2016-05-01

    The propagation of nonlinear, long-wavelength, slow sausage waves in an expanding magnetic flux tube, embedded in a non-magnetic stratified environment, is discussed. The governing equation for surface waves, which is akin to the Leibovich-Roberts equation, is derived using the method of multiple scales. The solitary wave solution of the equation is obtained numerically. The results obtained are illustrative of a solitary wave whose properties are highly dependent on the degree of stratification.

  3. The stabilize of current of load by redistribution of magnetic fluxes

    Directory of Open Access Journals (Sweden)

    Р. I. Tinsky

    1966-12-01

    Full Text Available The supply transformer must have step up characteristic to stabilize the current of the electrical arc, when voltage and distance between coals of electrical arc are changed. The curves of the transformer voltage are parallel when the supply voltage is varied, therefore the load current is not constant. To stabilize the load current it is necessary to redistribute magnetic flux between the first pivot and magnetic pivot. The vector diagram of the reactive transformer for nominal regime is obtained

  4. Sensing magnetic flux density of artificial neurons with a MEMS device.

    Science.gov (United States)

    Tapia, Jesus A; Herrera-May, Agustin L; García-Ramírez, Pedro J; Martinez-Castillo, Jaime; Figueras, Eduard; Flores, Amira; Manjarrez, Elías

    2011-04-01

    We describe a simple procedure to characterize a magnetic field sensor based on microelectromechanical systems (MEMS) technology, which exploits the Lorentz force principle. This sensor is designed to detect, in future applications, the spiking activity of neurons or muscle cells. This procedure is based on the well-known capability that a magnetic MEMS device can be used to sense a small magnetic flux density. In this work, an electronic neuron (FitzHugh-Nagumo) is used to generate controlled spike-like magnetic fields. We show that the magnetic flux density generated by the hardware of this neuron can be detected with a new MEMS magnetic field sensor. This microdevice has a compact resonant structure (700 × 600 × 5 μm) integrated by an array of silicon beams and p-type piezoresistive sensing elements, which need an easy fabrication process. The proposed microsensor has a resolution of 80 nT, a sensitivity of 1.2 V.T(-1), a resonant frequency of 13.87 kHz, low power consumption (2.05 mW), quality factor of 93 at atmospheric pressure, and requires a simple signal processing circuit. The importance of our study is twofold. First, because the artificial neuron can generate well-controlled magnetic flux density, we suggest it could be used to analyze the resolution and performance of different magnetic field sensors intended for neurobiological applications. Second, the introduced MEMS magnetic field sensor may be used as a prototype to develop new high-resolution biomedical microdevices to sense magnetic fields from cardiac tissue, nerves, spinal cord, or the brain.

  5. Influence of AC external magnetic field on guidance force relaxation between HTS bulk and NdFeB guideway

    Science.gov (United States)

    Zhang, Longcai; Wang, Suyu; Wang, Jiasu; Zheng, Jun

    2007-12-01

    Superconducting maglev vehicle is one of the most promising applications of HTS bulks. In such a system, the HTS bulks are always exposed to time-varying external magnetic field, which is generated by the inhomogeneous surface magnetic field of the NdFeB guideway. So it is required to study whether the guidance force of the bulks is influenced by the inhomogeneity. In this paper, we studied the characteristics of the guidance force relaxation between the HTS bulk and the NdFeB guideway by an experiment in which AC external magnetic field generated by an electromagnet was used to simulate the time-varying external magnetic field caused by the inhomogeneity of the guideway. From the experiment results, it was found that the guidance force was decreased with the application of the AC external magnetic field, and the decay increased with the amplitude and was almost independent of the frequency.

  6. Effect of External Magnetic Field on Critical Current for the Onset of Virtual Cathode Oscillations in Relativistic Electron Beams

    CERN Document Server

    Hramov, Alexander E; Morozov, Mikhail; Mushtakov, Alexander

    2008-01-01

    In this Letter we research the space charge limiting current value at which the oscillating virtual cathode is formed in the relativistic electron beam as a function of the external magnetic field guiding the beam electrons. It is shown that the space charge limiting (critical) current decreases with growth of the external magnetic field, and that there is an optimal induction value of the magnetic field at which the critical current for the onset of virtual cathode oscillations in the electron beam is minimum. For the strong external magnetic field the space charge limiting current corresponds to the analytical relation derived under the assumption that the motion of the electron beam is one-dimensional [High Power Microwave Sources. Artech House Microwave Library, 1987. Chapter~13]. Such behavior is explained by the characteristic features of the dynamics of electron space charge in the longitudinal and radial directions in the drift space at the different external magnetic fields.

  7. Effects of External Magnetic Fields on the Excited States of (ND)8 Metal Complexes.

    Science.gov (United States)

    Helms, Charles Alan

    Large changes in the steady state emissions and lifetimes as a function of external magnetic field strength have been observed for (nd)^8 mononuclear and binuclear complexes. These unusually pronounced effects are attributed to a field-induced symmetry reduction leading to a relaxation of transition dipole selection rules. Both spin-orbit coupling and magnetic field strength appear to play a role in determining the magnitude of the observed effect. A theoretical model has been developed to rationalize the results obtained for the Pt_2(H _2P_2O _5)_sp{4}{4-} ion. An analogous model should pertain to the mononuclear systems. Closed-shell (La(III), Lu(III)) rare earth salts of the Pt_2(H_2P _2O_5)_sp{4 }{4-} ion show the same dependence on an externally applied magnetic field as the previously examined K and Ba analogs, in all respects. However, the luminescence properties of the openshell salts are markedly different, even in the absence of a magnetic field. The zero-field phosphorescence lifetime of GdKPt_2 (H_2P_2O _5)_4 is one-tenth that of the closed-shell lifetime, but the position of the phosphorescence is unchanged from the closed-shell case. The application of an external magnetic field produces no further changes in the electronic properties of the open-shell salts. Salts containing rare earth ions with low-lying atomic states (Eu(III)) exhibit complete quenching of the Pt _2(H_2P_2 O_5)_sp{4}{4 -} phosphorescence, indicating efficient energy transfer. Results from complexes containing rare earth ions are analyzed in terms of an angular momentum coupling scheme. A recently published derivation of basis functions for the Pt_2(H_2 P_2O_5)_sp {4}{4-} ion including spin-orbit interactions was repeated and confirmed.

  8. Analysis of recoverable current from one component of magnetic flux density in MREIT and MRCDI.

    Science.gov (United States)

    Park, Chunjae; Lee, Byung Il; Kwon, Oh In

    2007-06-01

    Magnetic resonance current density imaging (MRCDI) provides a current density image by measuring the induced magnetic flux density within the subject with a magnetic resonance imaging (MRI) scanner. Magnetic resonance electrical impedance tomography (MREIT) has been focused on extracting some useful information of the current density and conductivity distribution in the subject Omega using measured B(z), one component of the magnetic flux density B. In this paper, we analyze the map Tau from current density vector field J to one component of magnetic flux density B(z) without any assumption on the conductivity. The map Tau provides an orthogonal decomposition J = J(P) + J(N) of the current J where J(N) belongs to the null space of the map Tau. We explicitly describe the projected current density J(P) from measured B(z). Based on the decomposition, we prove that B(z) data due to one injection current guarantee a unique determination of the isotropic conductivity under assumptions that the current is two-dimensional and the conductivity value on the surface is known. For a two-dimensional dominating current case, the projected current density J(P) provides a good approximation of the true current J without accumulating noise effects. Numerical simulations show that J(P) from measured B(z) is quite similar to the target J. Biological tissue phantom experiments compare J(P) with the reconstructed J via the reconstructed isotropic conductivity using the harmonic B(z) algorithm.

  9. Momentum transport and non-local transport in heat-flux-driven magnetic reconnection in HEDP

    Science.gov (United States)

    Liu, Chang; Fox, Will; Bhattacharjee, Amitava

    2016-10-01

    Strong magnetic fields are readily generated in high-energy-density plasmas and can affect the heat confinement properties of the plasma. Magnetic reconnection can in turn be important as an inverse process, which destroys or reconfigures the magnetic field. Recent theory has demonstrated a novel physics regime for reconnection in high-energy-density plasmas where the magnetic field is advected into the reconnection layer by plasma heat flux via the Nernst effect. In this work we elucidate the physics of the electron dissipation layer in this heat-flux-driven regime. Through fully kinetic simulation and a new generalized Ohm's law, we show that momentum transport due to the heat-flux-viscosity effect provides the dissipation mechanism to allow magnetic field line reconnection. Scaling analysis and simulations show that the characteristic width of the current sheet in this regime is several electron mean-free-paths. These results additionally show a coupling between non-local transport and momentum transport, which in turn affects the dynamics of the magnetic field. This work was supported by the U.S. Department of Energy under Contract No. DE-SC0008655.

  10. A flux extraction device to measure the magnetic moment of large samples; application to bulk superconductors.

    Science.gov (United States)

    Egan, R; Philippe, M; Wera, L; Fagnard, J F; Vanderheyden, B; Dennis, A; Shi, Y; Cardwell, D A; Vanderbemden, P

    2015-02-01

    We report the design and construction of a flux extraction device to measure the DC magnetic moment of large samples (i.e., several cm(3)) at cryogenic temperature. The signal is constructed by integrating the electromotive force generated by two coils wound in series-opposition that move around the sample. We show that an octupole expansion of the magnetic vector potential can be used conveniently to treat near-field effects for this geometrical configuration. The resulting expansion is tested for the case of a large, permanently magnetized, type-II superconducting sample. The dimensions of the sensing coils are determined in such a way that the measurement is influenced by the dipole magnetic moment of the sample and not by moments of higher order, within user-determined upper bounds. The device, which is able to measure magnetic moments in excess of 1 A m(2) (1000 emu), is validated by (i) a direct calibration experiment using a small coil driven by a known current and (ii) by comparison with the results of numerical calculations obtained previously using a flux measurement technique. The sensitivity of the device is demonstrated by the measurement of flux-creep relaxation of the magnetization in a large bulk superconductor sample at liquid nitrogen temperature (77 K).

  11. Design improvement of permanent magnet flux switching motor with dual rotor structure

    Science.gov (United States)

    Soomro, H. A.; Sulaiman, E.; Kumar, R.; Rahim, N. S.

    2017-08-01

    This paper presents design enhancement to reduce permanent magnet (PM) volume for 7S-6P-7S dual rotor permanent magnet flux-switching machines (DRPMFSM) for electric vehicle application. In recent years, Permanent magnet flux switching (PMFS) motor and a new member of brushless permanent magnet machine are prominently used for the electric vehicle. Though, more volume of Rare-Earth Permanent Magnet (REPM) is used to increase the cost and weight of these motors. Thus, to overcome the issue, new configuration of 7S-6P- 7S dual rotor permanent magnet flux-switching machine (DRPMFSM) has been proposed and investigated in this paper. Initially proposed 7S-6P-7S DRPMFSM has been optimized using “deterministic optimization” to reduce the volume of PM and to attain optimum performances. In addition, the performances of initial and optimized DRPMFSM have been compared such that back-emf, cogging torque, average torque, torque and power vs speed performances, losses and efficiency have been analysed by 2D-finite element analysis (FEA) using the JMAG- Designer software ver. 14.1. Consequently, the final design 7S-6P-7S DRPMFSM has achieved the efficiency of 83.91% at reduced PM volume than initial design to confirm the better efficient motor for HEVs applications.

  12. Precise Measurement of a Magnetic Field Generated by the Electromagnetic Flux Compression Technique

    CERN Document Server

    Nakamura, D; Matsuda, Y H; Takeyama, S

    2013-01-01

    The precision of the values of a magnetic field generated by electromagnetic flux compression was investigated in ultra-high magnetic fields of up to 700 T. In an attempt to calibrate the magnetic field measured by pickup coils, precise Faraday rotation (FR) measurements were conducted on optical (quartz and crown) glasses. A discernible "turn-around" phenomenon was observed in the FR signal as well as the pickup coils before the end of a liner implosion. We found that the magnetic field measured by pickup coils should be corrected by taking into account the high-frequency response of the signal transmission line. Near the peak magnetic field, however, the pickup coils failed to provide reliable values, leaving the FR measurement as the only method to precisely measure an extremely high magnetic fields.

  13. On the Characteristics of Footpoints of Solar Magnetic Flux Ropes during the Eruption

    CERN Document Server

    Cheng, X

    2016-01-01

    We investigate the footpoints of four erupted magnetic flux ropes (MFRs) that appear as sigmoidal hot channels prior to the eruptions in the Atmospheric Imaging Assembly high temperaure passbands. The simultaneous Helioseismic and Magnetic Imager observations disclose that one footpoint of the MFRs originates in the penumbra or penumbra edge with a stronger magnetic field, while the other in the moss region with a weaker magnetic field. The significant deviation of the axis of the MFRs from the main polarity inversion lines and associated filaments suggests that the MFRs have ascended to a high altitude, thus being distinguishable from the source sigmoidal ARs. The more interesting thing is that, with the eruption of the MFRs, the average inclination angle and direct current at the footpoints with stronger magnetic field tend to decrease, which is suggestive of a straightening and untwisting of the magnetic field in the MFR legs. Moreover, the associated flare ribbons also display an interesting evolution. Th...

  14. Precise measurement of a magnetic field generated by the electromagnetic flux compression technique.

    Science.gov (United States)

    Nakamura, D; Sawabe, H; Matsuda, Y H; Takeyama, S

    2013-04-01

    The precision of the values of a magnetic field generated by electromagnetic flux compression was investigated in ultra-high magnetic fields of up to 700 T. In an attempt to calibrate the magnetic field measured by pickup coils, precise Faraday rotation (FR) measurements were conducted on optical (quartz and crown) glasses. A discernible "turn-around" phenomenon was observed in the FR signal as well as the pickup coils before the end of a liner implosion. We found that the magnetic field measured by pickup coils should be corrected by taking into account the high-frequency response of the signal transmission line. Near the peak magnetic field, however, the pickup coils failed to provide reliable values, leaving the FR measurement as the only method to precisely measure extremely high magnetic fields.

  15. Nonlinear fast sausage waves in homogeneous magnetic flux tubes

    Science.gov (United States)

    Mikhalyaev, Badma B.; Ruderman, Michael S.

    2015-12-01

    > We consider fast sausage waves in straight homogeneous magnetic tubes. The plasma motion is described by the ideal magnetohydrodynamic equations in the cold plasma approximation. We derive the nonlinear Schrödinger equation describing the nonlinear evolution of an envelope of a carrier wave. The coefficients of this equation are expressed in terms Bessel and modified Bessel functions. They are calculated numerically for various values of parameters. In particular, we show that the criterion for the onset of the modulational or Benjamin-Fair instability is satisfied. The implication of the obtained results for solar physics is discussed.

  16. Synthesis of cobalt nanowires in aqueous solution under an external magnetic field

    Directory of Open Access Journals (Sweden)

    Xiaoyu Li

    2016-07-01

    Full Text Available In contrast to the majority of related experiments, which are carried out in organic solvents at high temperatures and pressures, cobalt nanowires were synthesized by chemical reduction in aqueous solution with the assistance of polyvinylpyrrolidone (PVP as surfactant under moderate conditions for the first time, while an external magnetic field of 40 mT was applied. Uniform linear cobalt nanowires with relatively smooth surfaces and firm structure were obtained and possessed an average diameter of about 100 nm with a coating layer of PVP. By comparison, the external magnetic field and PVP were proven to have a crucial influence on the morphology and the size of the synthesized cobalt nanowires. The prepared cobalt nanowires are crystalline and mainly consist of cobalt as well as a small amount of platinum. Magnetic measurements showed that the resultant cobalt nanowires were ferromagnetic at room temperature. The saturation magnetization (Ms and the coercivity (Hc were 112.00 emu/g and 352.87 Oe, respectively.

  17. Filament Activation in Response to Magnetic Flux Emergence and Cancellation in Filament Channels

    CERN Document Server

    Li, Ting; Ji, Haisheng

    2015-01-01

    We make a comparative analysis for two filaments that showed quite different activation in response to the flux emergence within the filament channels. The observations from the Solar Dynamics Observatory (SDO) and Global Oscillation Network Group (GONG) are carried out to analyze the two filaments on 2013 August 17-20 and September 29. The first event showed that the main body of the filament was separated into two parts when an active region (AR) emerged with a maximum magnetic flux of about 6.4*10^21 Mx underlying the filament. The close neighborhood and common direction of the bright threads in the filament and the open AR fan loops suggest similar magnetic connectivity of these two flux systems. The equilibrium of the filament was not destroyed within 3 days after the start of the emergence of the AR. To our knowledge, similar observations have never been reported before. In the second event, the emerging flux occurred nearby a barb of the filament with a maximum magnetic flux of 4.2*10^20 Mx, about one ...

  18. Aharonov-Casher-effect suppression of macroscopic tunneling of magnetic flux.

    Science.gov (United States)

    Friedman, Jonathan R; Averin, D V

    2002-02-04

    We suggest a system in which the amplitude of macroscopic flux tunneling can be modulated via the Aharonov-Casher effect. The system is an rf SQUID with the Josephson junction replaced by a Bloch transistor--two junctions separated by a small superconducting island on which the charge can be induced by an external gate voltage. When the Josephson coupling energies of the junctions are equal and the induced charge is q = e, destructive interference between tunneling paths brings the flux tunneling rate to zero. The device may also be useful as a qubit for quantum computation.

  19. Hot spot model of MagLIF implosions: Nernst term effect on magnetic flux losses

    Science.gov (United States)

    Garcia Rubio, Fernando; Sanz Recio, Javier; Betti, Riccardo

    2016-10-01

    An analytical model of a collisional plasma being compressed by a cylindrical liner is proposed and solved in a magnetized liner inertial fusion-like context. The implosion is assumed to be isobaric, and the magnetic diffusion is confined to a thin layer near the liner. Both unmagnetized and magnetized plasma cases are considered. The model reduces to a system of two partial differential equations for temperature and magnetic field. Special attention is given to the effect of the Nernst term on the evolution of the magnetic field. Scaling laws for temperature, magnetic field, hot spot mass increase and magnetic field losses are obtained. The temperature and magnetic field spatial profiles tend to a self-similar state. It is found that when the Nernst term is taken into account, the magnetic field is advected towards the liner, and the magnetic flux losses are independent of the magnetic Lewis number. Research supported by the Spanish Ministerio de Economía y Competitividad, Project No. ENE2014-54960R. Acknowledgements to the Laboratory of Laser Energetics (Rochester) for its hospitality.

  20. Magnetic Flux Fluctuations Due to Eddy Currents and Thermal Noise in Metallic Disks

    NARCIS (Netherlands)

    Uzunbajakau, S.; Rijpma, A.P.; Dolfsma, J.; Krooshoop, H.J.G.; Brake, ter H.J.M.; Peters, M.J.; Rogalla, H.

    2003-01-01

    We derive expressions for the magnetic flux in a circular loop due to eddy currents and thermal noise in coaxial metallic disks. The eddy currents are induced by an applied field that changes sinusoidally in time. We give expressions for the eddy current noise when the frequency of the applied field