Sample records for magnetic flux noise

  1. Magnetic flux noise in strongly anisotropic superconductors

    NASA Astrophysics Data System (ADS)

    Ashkenazy, V. D.; Jung, G.; Shapiro, B. Ya.

    1995-04-01

    Magnetic noise due to thermally activated movements of flux vortices has been calculated taking into account fluctuations modes of nonrigid vortices. It has been shown that at low frequencies, below the crossover frequency, the noise spectrum of a layered superconductor is identical to that of a continuous material. Three regimes of spectral behavior, ln?, ?-1/2, and ?-3/2, have been predicted to be present in this frequency range. Characteristic frequencies separating different regimes depend on the geometry of the flux pickup loop. At high frequencies, above the crossover frequency, bending of vortices leads to a Lorentzian shape of noise spectra. The value of the crossover frquency is not influenced by the particularities of the flux-measuring arrangement and depends only on the material properties and applied magnetic field.

  2. Low frequency magnetic flux noise: role of surface adsorbates

    NASA Astrophysics Data System (ADS)

    Kumar, Pradeep; Beck, Matthew; Freeland, John; Yu, Clare; Wu, Ruqian; Wang, Zhe; Pappas, David; McDermott, Robert

    2015-03-01

    Excess low frequency 1/f flux noise is a major source of decoherence in superconducting quantum devices. It is generally accepted that the noise is due to surface magnetic defects, but the microscopic physics behind the noise mechanism is still unclear. Recent experiments suggest that adsorbates play a dominant role in the surface magnetism. Here, we describe X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) studies of magnetic adsorbates on the surfaces of superconducting thin films. We present the results of SQUID-based susceptibility and noise measurements that are part of an ongoing effort to reduce surface spin density and flux noise by improving the vacuum environment of the superconducting device.

  3. Can magnetic noise from Kondo traps explain high frequency flux noise in superconducting qubits?

    NASA Astrophysics Data System (ADS)

    Dias da Silva, Luis; de Sousa, Rogerio

    2015-03-01

    In solid state devices, charge and magnetic noise have common microscopic origin. Both occur due to the presence of Kondo traps nearby metallic wires. We use numerical renormalization group calculations to show that, despite their common origin, charge and magnetic noise have opposing behavior controlled by completely different energy scales. While magnetic noise follows an universal scaling with the Kondo temperature, charge noise remains well described by non-interacting theory even when the trap is deep into the Kondo regime. We show how these results may explain the high frequency (f= 1-10 GHz) Ohmic flux noise observed in SQUIDs and superconducting qubits. LGDS acknowledges support from Brazilian agencies FAPESP (2013/50220-7), CNPq (307107/2013-2) and PRP-USP NAP-QNano. RdS acknowledges support from the Canadian program NSERC-Discovery and a FAPESP-UVic exchange award.

  4. Noise-Produced Patterns in Images Constructed from Magnetic Flux Leakage Data

    E-print Network

    Pimenova, Anastasiya V; Levesley, Jeremy; Elkington, Peter; Bacciarelli, Mark

    2015-01-01

    Magnetic flux leakage measurements help identify the position, size and shape of corrosion-related defects in steel casings used to protect boreholes drilled into oil and gas reservoirs. Images constructed from magnetic flux leakage data contain patterns related to noise inherent in the method. We investigate the patterns and their scaling properties for the case of delta-correlated input noise, and consider the implications for the method's ability to resolve defects. The analytical evaluation of the noise-produced patterns is made possible by model reduction facilitated by large-scale approximation. With appropriate modification, the approach can be employed to analyze noise-produced patterns in other situations where the data of interest are not measured directly, but are related to the measured data by a complex linear transform involving integrations with respect to spatial coordinates.

  5. Magnetic flux density measurement in magnetic resonance electrical impedance tomography using a low-noise current source

    NASA Astrophysics Data System (ADS)

    Kim, Young Tae; Yoo, Pil Joong; In Oh, Tong; Woo, Eung Je

    2011-10-01

    Current injected into an electrically conducting object induces distributions of magnetic flux density as well as voltage and current density. In magnetic resonance electrical impedance tomography (MREIT), we measure the induced magnetic flux density using an MRI scanner to reconstruct cross-sectional conductivity images of the object. The current injection must be synchronized with a chosen MRI pulse sequence and the current source needs to be programmable to accommodate various pulse sequences. For an injected current of 1 mA, for example, we may expect an induced magnetic flux density of a few nanoteslas, and noise reduction in measured magnetic flux density data is important for better conductivity image quality. In this paper, we describe how to reduce noise in measured magnetic flux density data based on analyses of noise sources in MREIT. Given an MRI scanner and an imaging object, we found that the current source including lead wires becomes a major noise source. We designed a low-noise programmable current source with optical links, batteries and electromagnetic shields. Equipped with lead switching capability, it automates MREIT imaging experiments using multiple pairs of electrodes. We found that the new current source improves the output current SNR by about 10 dB and the MR magnitude image SNR by about 30%. Placing it near an imaging object inside the shielded room, we could reduce the noise standard deviation in measured magnetic flux density data by 40%. We propose use of this low-noise current source for in vivo animal and human MREIT imaging studies.

  6. The study of a racetrack-shaped defect in ferromagnetic steel by magnetic Barkhausen noise and flux leakage measurements

    NASA Astrophysics Data System (ADS)

    Mandal, K.; Cramer, Th; Atherton, D. L.

    2000-03-01

    Magnetic Barkhausen noise (MBN) and magnetic flux leakage (MFL) measurements are useful magnetic nondestructive techniques used for various applications. MBN measurements have been used here to study stress distributions around a racetrack-shaped defect made in the wall of a steel pipe. The study shows a stress concentration factor of ˜3 for a racetrack-shaped defect with 50% wall penetration. MFL signals from the same defect have also been studied under various circumferential hoop stresses. It is observed that the external stress can change the MFL signal by more than 40% and the effect of stress is maximum when the pipe wall flux density is ˜1.2 T.

  7. Magnetic flux compression

    SciTech Connect

    Fowler, C.M.

    1989-01-01

    Magnetic Flux Compression, as treated in this paper, is accomplished by high explosives. Flux is first captured in a closed conducting circuit, of which some or all of the conducting elements are overlaid with high explosives. Upon detonation of the explosives, these elements are driven in such a fashion as to compress the flux into regions of smaller areas or, in engineering terminology, into regions of lower inductance. The magnetic energy associated with the flux is increased by the flux compression. The additional energy is ultimately supplied by the explosive as it drives the conductors against the magnetic field pressure, which in some cases may be in the megabar range. Various names in common use for flux compression devices are flux compression generators (FCG), magneto-cumulative generators (MCG), particularly in the USSR, or simply, flux compressors. FCGs are generally used in two broadly defined categories: as compact, high-power sources to drive various loads: and as generators of very large magnetic fields. In this talk, general principles of flux compression are first discussed. This is followed by a description of several applications in which different types of FCGs are used to supply pulsed power to various devices. The talk closes with a discussion of results obtained from a number of experiments done to explore the properties of materials in very large magnetic fields or under nearly isentropic compression. As requested, the work reported here surveys the Los Alamos program. However, sources cited in the bibliography contain much of the extensive literature in the field. Individual papers cited have been selected partly to highlight other groups that have been active in the field. 25 refs., 15 figs.

  8. Solar Magnetic Flux Ropes

    E-print Network

    Filippov, Boris; Srivastava, Abhishek K; Uddin, Wahab

    2015-01-01

    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 loose 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 (n). 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 the comparison of observed filament heights with...

  9. 1/f flux noise and field-dependent spin susceptibility

    NASA Astrophysics Data System (ADS)

    Kumar, Pradeep; Klaus, Taylor; Puglielli, Antonio; Sendelbach, Steven; McDermott, Robert

    2014-03-01

    Low-frequency 1/f magnetic flux noise is a dominant source of dephasing in superconducting Qubits. It is believed that the noise originates in a high density of surface magnetic defects, but the microscopic noise mechanism is not understood. Here, we describe investigations of the field-dependent complex susceptibility of the surface magnetic system. We have fabricated and characterized asymmetric dc SQUIDs that allow injection of a low-frequency excitation current directly into the SQUID loop to allow measurement of the SQUID inductance, which contains a contribution from the surface spin system. We observe a strong dependence of the SQUID inductance on applied dc field, which we attribute to field-dependent surface spin susceptibility. The data constrains possible models for 1/f flux noise from surface spin states.

  10. Open magnetic flux and magnetic flux closure during sawtooth events

    Microsoft Academic Search

    B. Hubert; S. E. Milan; A. Grocott; S. W. H. Cowley; J. C. Gérard

    2008-01-01

    We use IMAGE-FUV observations of the polar aurora and measurements of the ionospheric convection from the SuperDARN radar network to study several sawtooth events previously reported in the literature. We estimate the amount of open magnetic flux in the Earth magnetosphere during a significant part of these sawtooth intervals as well as the magnetic flux opening and closure rates, that

  11. Flux noise in SQUIDs: Electron versus nuclear spins

    NASA Astrophysics Data System (ADS)

    de Sousa, Rogerio; Laforest, Stephanie

    2015-03-01

    Superconducting Quantum Interference Devices (SQUIDs) are limited by intrinsic flux noise whose origin is unknown. We develop a method to accurately calculate the flux produced by spin impurities in realistic superconducting thin film wires, and show that the flux produced by each spin is much larger than anticipated by former calculations. Remarkably, the total flux noise power due to electron spins at the thin side surface of the wires is found to be of similar magnitude as the one due to electrons at the wide top surface of the wires. In addition, flux noise due to lattice nuclear spins in the bulk of the wires is found to be a sizable fraction of the total noise for some SQUID geometries. We discuss the relative importance of electron and nuclear spin species in determining the total noise power, and propose strategies to design SQUIDs with lower flux noise. We acknowledge support from the Canadian agency NSERC through its Discovery and Engage programs.

  12. Simulations of Magnetic Flux Emergence

    NASA Astrophysics Data System (ADS)

    Stein, Robert; Nordlund, Aake

    Magnetic flux emerges from the solar surface on a wide range of scales. We review recent simulations of both large and small scale flux emergence. In our own simulations, we represent the magnetic flux produced by the global dynamo as uniform, untwisted, horizontal field advected into the simulation domain by supergranule scale inflows at the bottom. Our computational domain extends from the temperature minimum (half a megameter above the visible surface) to 20 Mm below the surface, which is 10% of the depth of the convection zone, but contains 2/3 of its scale heights. We investigate how magnetic flux rises through the upper solar convection zone and emerges through the surface. Convective up-flows and magnetic buoyancy bring field toward the surface. Convective down-flows pin down field and prevent its rise. Most of the field gets pumped downward by the convection, but some field rises to the surface. The convective motions both confine the flux concentrations (without the need for twist) and shred them. This process creates a hierarchy of magnetic loops with smaller loops riding "piggy-back", in a serpentine pattern, on larger loops. As a result, magnetic flux emerges in a mixed polarity, "pepper and salt" pattern. The small loops appear as horizontal field over granules with their vertical legs in the bounding intergranular lanes. The fields are quickly swept into the intergranular lanes. As the larger, parent, flux concentrations reach the surface with their legs rooted in the the downflow boundaries of the underlying, supergranule-scale, convective cells near the bottom of the simulation domain, the surface field counter-streams into separate, opposite polarity concentrations, creating pores and spots. The subsurface magnetic field lines of the pores and spots formed by the magneto-convection (without being imposed as an initial condition) are braided, some tightly, some loosely and they connect in complicated ways to the surrounding field at large depths. The pores evolve on the timescale of the underlying supergranules. Thus, long lives of solar active regions imply that they are rooted in larger, more slowly evolving, deeper convective structures. Based on these simulations we summarize the robust properties of emerging magnetic flux.

  13. Analysis of Vibration and Acoustic Noise in Permanent Magnet Motors

    Microsoft Academic Search

    Sangmoon Hwang

    1994-01-01

    The drive motor is a frequent source of vibration and acoustic noise in many precision spindle motors. One of the electromagnetic sources of vibration in permanent magnet motors is the torque ripple, consisting of the reluctance torque and electromagnetic torque fluctuation. This type of vibration is becoming more serious with the advent of new high-grade magnets with increased flux density.

  14. DISCONNECTING OPEN SOLAR MAGNETIC FLUX

    SciTech Connect

    DeForest, C. E.; Howard, T. A.; McComas, D. J. [Southwest Research Institute, 1050 Walnut Street Suite 300, Boulder, CO 80302 (United States)

    2012-01-20

    Disconnection of open magnetic flux by reconnection is required to balance the injection of open flux by coronal mass ejections 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 distinctive 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{sup -2} to 320 km s{sup -1}, thereafter 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 8 {mu}T, 6 R{sub Sun} above the photosphere, and the entrained flux to be 1.6 Multiplication-Sign 10{sup 11} Wb (1.6 Multiplication-Sign 10{sup 19} Mx). We model the feature's propagation by balancing inferred magnetic tension force against accretion drag. This model is consistent with the feature's behavior and accepted solar wind parameters. By counting events over a 36 day window, we estimate a global event rate of 1 day{sup -1} and a global solar minimum unsigned flux disconnection rate of 6 Multiplication-Sign 10{sup 13} Wb yr{sup -1} (6 Multiplication-Sign 10{sup 21} Mx yr{sup -1}) by this mechanism. That rate corresponds to {approx} - 0.2 nT yr{sup -1} change in the radial heliospheric field at 1 AU, indicating that the mechanism is important to the heliospheric flux balance.

  15. Model for l/f Flux Noise in SQUIDs and Qubits

    SciTech Connect

    Koch, Roger H.; DiVincenzo, David P.; Clarke, John

    2007-01-19

    We propose a model for 1/f flux noise in superconducting devices (f is frequency). The noise is generated by the magnetic moments of electrons in defect states which they occupy for a wide distribution of times before escaping. A trapped electron occupies one of the two Kramers-degenerate ground states, between which the transition rate is negligible at low temperature. As a result, the magnetic moment orientation is locked. Simulations of the noise produced by a plausible density of randomly oriented defects yield 1/f noise magnitudes in good agreement with experiments.

  16. Adsorbed Oxygen Molecules as a Possible Source of Flux Noise in SQUIDs

    NASA Astrophysics Data System (ADS)

    Shi, Chuntai; Wang, Hui; Hu, Jun; Yu, Clare; Wu, Ruqian

    2015-03-01

    One of the dominant source of flux noise in SQUIDs is flux noise which has been attributed to mysterious fluctuating magnetic spins on the surface. We propose that the spins producing flux noise could be adsorbed O2 molecules that have a magnetic moment of about 2 ?B. Using density functional calculations, we studied O2 molecules adsorbed on a sapphire surface. We find that the barrier for spin rotation is small enough to allow almost free spin reorientation due to thermal excitations at low temperatures. Monte Carlo simulations of a 2D XY spin model yields 1 / f noise where f is frequency. This work was supported by 1000 Talent Program of China through Fudan University. Work at UCI was supported by DOE-BES (Grant No. DE-FG02-05ER46237) and the Army Research Office (Grant No. W911NF-10-1-0494).

  17. Magnetic Flux Budget of a Decaying Sunspot

    NASA Astrophysics Data System (ADS)

    Kubo, Masahito; Lites, B. W.; Shimizu, T.; Ichimoto, K.

    2009-05-01

    We estimate how much magnetic flux is lost in a decaying sunspot and how much magnetic flux is carried away from the sunspot through its surrounding moat region. A time series of spectropolarimetric measurements with the Solar Optical Telescope aboard Hinode allows us, for the first time, to investigate an accurate flux change without any effects of atmospheric seeing. The amount of magnetic flux that decreases in the sunspot and moat region is almost equal to that of magnetic flux transported to the outer boundary of the moat region. The flux loss rates of magnetic elements with positive and negative polarities are balanced each other around the outer boundary of the moat region. These results suggest that most of the magnetic flux in the sunspot is transported to the outer boundary of the moat region as moving magnetic features, and then removed from the photosphere by flux cancellation around the moat boundary.

  18. Chaos in Magnetic Flux Ropes

    NASA Astrophysics Data System (ADS)

    Gekelman, Walter; Dehaas, Tim; van Compernolle, Bart

    2013-10-01

    Magnetic Flux Ropes Immersed in a uniform magnetoplasma are observed to twist about themselves, writhe about each other and rotate about a central axis. They are kink unstable and smash into one another as they move. Full three dimensional magnetic field and flows are measured at thousands of time steps. Each collision results in magnetic field line generation and the generation of a quasi-seperatrix layer and induced electric fields. Three dimensional magnetic field lines are computed by conditionally averaging the data. The permutation entropy can be calculated from the time series of the magnetic field data or flows is used to calculate the positions of the data on a Jensen Shannon complexity map. The location of data on this map indicates if the magnetic fields are stochastic, or fall into regions of minimal or maximal complexity. Other types of chaotic dynamical models (Gissinger , Lorentz and Henon) also fall on the map and can give a clue to the nature of the turbulence. The ropes fall in the region of the C-H plane where chaotic systems lie. The entropy and complexity change in space and time, which reflects the change and possibly type of chaos associated with the ropes. Magnetic Flux Ropes Immersed in a uniform magnetoplasma are observed to twist about themselves, writhe about each other and rotate about a central axis. They are kink unstable and smash into one another as they move. Full three dimensional magnetic field and flows are measured at thousands of time steps. Each collision results in magnetic field line generation and the generation of a quasi-seperatrix layer and induced electric fields. Three dimensional magnetic field lines are computed by conditionally averaging the data. The permutation entropy can be calculated from the time series of the magnetic field data or flows is used to calculate the positions of the data on a Jensen Shannon complexity map. The location of data on this map indicates if the magnetic fields are stochastic, or fall into regions of minimal or maximal complexity. Other types of chaotic dynamical models (Gissinger , Lorentz and Henon) also fall on the map and can give a clue to the nature of the turbulence. The ropes fall in the region of the C-H plane where chaotic systems lie. The entropy and complexity change in space and time, which reflects the change and possibly type of chaos associated with the ropes. Work sponsoerd by a LANL-UC grant and done at the Basic Plasma Science Facility (supported by DOE and NSF).

  19. Noise enhanced stability in magnetic systems

    Microsoft Academic Search

    Marco Trapanese

    2009-01-01

    In this paper noise enhanced stability in magnetic systems is studied by both an Ising-type model and a Preisach-Arrhenius model as well as a dynamic Preisach model. It is shown that in one nonequilibrium Ising system noise enhanced stability occurs and that dynamic Preisach model has the capability to predict the occurrence of noise enhanced stability in magnetic systems. On

  20. Chaos in Magnetic Flux Ropes

    NASA Astrophysics Data System (ADS)

    Gekelman, Walter; DeHaas, T.; Van Compernolle, B.; Vincena, S.

    2013-07-01

    Magnetic Flux Ropes Immersed in a uniform magnetoplasma are observed to twist about themselves, writhe about each other and rotate about a central axis. They are kink unstable and smash into one another as they move. Each collision results in magnetic field line generation and the generation of a quasi-seperatrix layer. Three dimensional magnetic field lines are computed by conditionally averaging the data using correlation techniques. When the currents associated with the ropes are large,this is possible for only a number of rotation cycles as the field line motion becomes chaotic. The permutation entropy1 can be calculated from the the time series of the magnetic field data (this is also done with flows) and used to calculate the positions of the data on a Jensen Shannon complexity map2. The power spectra of much of the magnetic and flow data is exponential and Lorentzian structures in the time domain are embedded in them. The location of data on this map indicates if the magnetic fields are stochastic, or fall into regions of minimal or maximal complexity. The complexity is a function of space and time. The complexity map, and analysis will be explained in the course of the talk. Other types of chaotic dynamical models such as the Lorentz or Gissinger process also fall on the map and can give a clue to the nature of the flux rope turbulence. The ropes fall in the region of the C-H plane where chaotic systems lie. 1 C. Bandt, B. Pompe, Phys. Rev. Lett., 88,174102 (2007) 2 O. Russo et al., Phys. Rev. Lett., 99, 154102 (2007), J. Maggs, G.Morales, “Permutation Entropy analysis of temperature fluctuations from a basic electron heat transport experiment”,submitted PPCF (2013)

  1. Chaos in magnetic flux ropes

    NASA Astrophysics Data System (ADS)

    Gekelman, Walter; Van Compernolle, Bart; DeHaas, Tim; Vincena, Stephen

    2014-06-01

    Magnetic flux ropes immersed in a uniform magnetoplasma are observed to twist about themselves, writhe about each other and rotate about a central axis. They are kink unstable and smash into one another as they move. Each collision results in magnetic field line reconnection and the generation of a quasi-separatrix layer. Three-dimensional magnetic field lines are computed by conditionally averaging the data using correlation techniques. Conditional averaging is possible for only a number of rotation cycles as the field line motion becomes chaotic. The permutation entropy can be calculated from the time series of the magnetic field data (this is also done with flows) and is used to calculate the positions of the data on a Jensen-Shannon complexity map. The location of data on this map indicates if the magnetic fields are stochastic, or fall into regions of minimal or maximal complexity. The complexity is a function of space and time. The Lyapunov and Hurst exponents are calculated and the complexity and permutation entropy of the flows and field components are shown throughout the volume.

  2. One-sided fluxes -- A magnetic curiosity?

    Microsoft Academic Search

    John C. Mallinson

    1973-01-01

    It is shown that a previously unknown class of magnetization patterns exists in planar structures which have the unique property that all the flux escapes from one surface with none leaving the other side. A simple case is a constant amplitude rotating vector magnetization where the sense of rotation dictates which surface has no flux. More complicated magnetization patterns are

  3. Evolution of magnetic flux ropes associated with flux transfer events and interplanetary magnetic clouds

    NASA Technical Reports Server (NTRS)

    Wei, C. Q.; Lee, L. C.; Wang, S.; Akasofu, S.-I.

    1991-01-01

    Spacecraft observations suggest that flux transfer events and interplanetary magnetic clouds may be associated with magnetic flux ropes which are magnetic flux tubes containing helical magnetic field lines. In the magnetic flux ropes, the azimuthal magnetic field is superposed on the axial field. The time evolution of a localized magnetic flux rope is studied. A two-dimensional compressible MHD simulation code with a cylindrical symmetry is developed to study the wave modes associated with the evolution of flux ropes. It is found that in the initial phase both the fast magnetosonic wave and the Alfven wave are developed in the flux rope. After this initial phase, the Alfven wave becomes the dominant wave mode for the evolution of the magnetic flux rope and the radial expansion velocity of the flux rope is found to be negligible. Numerical results further show that even for a large initial azimuthal component of the magnetic field, the propagation velocity along the axial direction of the flux rope remains the Alfven velocity. It is also found that the localized magnetic flux rope tends to evolve into two separate magnetic ropes propagating in opposite directions. The simulation results are used to study the evolution of magnetic flux ropes associated with flux transfer events observed at the earth's dayside magnetopause and magnetic clouds in the interplanetary space.

  4. Self-organization in magnetic flux ropes

    NASA Astrophysics Data System (ADS)

    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 describes how canonical helicity can determine the result of reconnection and merging of multiple magnetic flux ropes, John Finn et al focus on diagnosing flux rope reconnection using quasi-separatrix layers, and Stefano Markidis et al investigate how a single flux rope can become unstable and begin to fall apart. With these many examples of different magnetized plasma structures, which can all be called magnetic flux ropes, the question still stands: just what is it that makes a volume of magnetized plasma a magnetic flux rope? There may not be a strict definition of a magnetic flux rope that everyone can agree on. Nonetheless, the ingredient common to all magnetic flux ropes is that the magnetic field lines that thread nearby plasma elements at one location along the flux rope must wind around and not diverge away from each other over a sufficiently long distance to look like a piece of an ordinary rope. In a way, it is similar to turbulence—you know it when you see it. The figures and illustrations included in this special issue provide plenty of examples of observed, measured, modeled and imagined magnetic flux ropes for you, the reader, to develop an appreciation of what different members of our research community mean by a magnetic flux rope. If you have never studied magnetic flux ropes, we hope that this special issue inspires you to look into their many mysteries. If magnetic flux ropes are already an integral part of your research, we hope the diversity of perspectives presented herein refresh your interest in the underlying plasma physics of whichever kind of magnetic flux rope you happen to be working with. References [1] Russell C T, Priest E R and Lee L-C 1990 Physics of Magnetic Flux Ropes AGU Geophysical Monograph Series vol 58 (Washington, DC: American Geophysical Union)

  5. Improving Fidelity in Superconducting Xmon Qubits: Decreasing 1/f Flux Noise

    NASA Astrophysics Data System (ADS)

    O'Malley, Peter; Barends, Rami; Chiaro, Ben; Chen, Yu; Jeffrey, Evan; Kelley, Julian; Megrant, Anthony; Mutus, Josh; Neill, Charles; Roushan, Pedram; Sank, Daniel; Wenner, James; White, Theodore; Cleland, Andrew; Martinis, John

    2014-03-01

    Two qubit CZ gate fidelity in our superconducting Xmon qubits is currently 99.4 %. To achieve 99.9 % fidelity, experiments indicate that we need to reduce 1/f flux noise. We present measurements of 1/f flux noise on the Xmon from sub-Hz to MHz frequencies. At low frequencies we measure an f- 1 . 0 frequency dependence, which is in agreement with previous phase qubit measurements but significantly different from the f- 0 . 7 dependence seen in SQUIDs. We also see a dependence on geometry that agrees with a theory of magnetic defects; this points toward a qubit design that will minimize dephasing.

  6. Regulation of the interplanetary magnetic flux

    SciTech Connect

    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. Design and Testing of a Permanent Magnet Axial Flux Wind Power Generator

    Microsoft Academic Search

    Garrison F. Price; Todd D. Batzel; Mihai Comanescu; Bruce A. Muller

    The axial flux (disc shape) permanent magnet machine is an attractive alternative to radial flux (cylindrical shape) machines in wind turbine applications. The axial flux configuration is amenable to the low-speed, high-torque operation of a direct drive wind energy system. Direct drive wind energy conversion tends to decrease the system size, weight, and noise, while increasing overall efficiency and reliability.

  8. Probing noise in flux qubits via macroscopic resonant tunneling.

    PubMed

    Harris, R; Johnson, M W; Han, S; Berkley, A J; Johansson, J; Bunyk, P; Ladizinsky, E; Govorkov, S; Thom, M C; Uchaikin, S; Bumble, B; Fung, A; Kaul, A; Kleinsasser, A; Amin, M H S; Averin, D V

    2008-09-12

    Macroscopic resonant tunneling between the two lowest lying states of a bistable rf SQUID is used to characterize noise in a flux qubit. Measurements of the incoherent decay rate as a function of flux bias revealed a Gaussian-shaped profile that is not peaked at the resonance point but is shifted to a bias at which the initial well is higher than the target well. The rms amplitude of the noise, which is proportional to the dephasing rate 1/tauphi, was observed to be weakly dependent on temperature below 70 mK. Analysis of these results indicates that the dominant source of low energy flux noise in this device is a quantum mechanical environment in thermal equilibrium. PMID:18851318

  9. HELICAL LENGTHS OF MAGNETIC CLOUDS FROM THE MAGNETIC FLUX CONSERVATION

    SciTech Connect

    Yamamoto, Tetsuya T. [Solar-Terrestrial Environment Laboratory, Nagoya University, Chikusa, Nagoya, 464-8601 (Japan); Kataoka, R. [Interactive Research Center of Science, Tokyo Institute of Technology, Meguro, 152-8550 (Japan); Inoue, S., E-mail: tyamamot@stelab.nagoya-u.ac.j [National Institute of Information and Communications Technology, Koganei, 184-8795 (Japan)

    2010-02-10

    We estimate axial lengths of helical parts in magnetic clouds (MCs) at 1 AU from the magnetic flux (magnetic helicity) conservation between solar active regions (ARs) and MCs with the event list of Leamon et al. Namely, considering poloidal magnetic flux (PHI{sub P}) conservation between MCs and ARs, we estimated L{sub h} in MCs, where L{sub h} is the axial length of an MC where poloidal magnetic flux and magnetic twist exist. It is found that L{sub h} is 0.01-1.25 AU in the MCs. If the cylinder flux rope picture is assumed, this result leads to a possible new picture of the cylinder model whose helical structure (namely, poloidal magnetic flux) localizes in a part of a MC.

  10. Adsorbed Oxygen Molecules as a Source of Flux Noise in SQUIDs

    NASA Astrophysics Data System (ADS)

    Wang, Hui; Wang, Zhe; Hu, Jun; Shi, Chuntai; Yu, Clare C.; Wu, Ruqian; Department of Physics, Fudan University, Shanghai 200433, China Collaboration; Department of Physics; Astronomy, University of California, Irvine, CA 92697-4575, USA Collaboration

    2015-03-01

    A major obstacle for using superconducting quantum interference devices (SQUIDs) as qubits is the flux noise generated by fluctuating magnetic spins on the surface of SQUIDs. Using density functional theory (DFT) calculations, we investigated O2 adsorbates and various vacancies on an ?-alumina surface as spin candidates. Their spectroscopic features are directly compared to experimental data using the x-ray magnetic circular dichroism. The calculated magnetic anisotropy energy for the spin of O2 to rotate within a plane perpendicular to the axis of the O-O bond is only about 12 mK (or ~ 1 ?eV) so we believe that O2 molecules are the main source of flux noise in Al SQUIDs. Work at Fudan was supported by the 1000-Telent funds. Work at UCI was supported by DOE-BES (Grant No. DE- FG02-05ER46237) and by NERSC for computing time.

  11. Magnetic flux tubes as coherent structures

    Microsoft Academic Search

    A. Brandenburg; R. L. Jennings; Å. Nordlund; R. F. Stein

    \\u000a We perform direct simulations of turbulent MHD in which the initial magnetic field is weak. Just as vortex tubes appear spontaneously\\u000a in hydrodynamic turbulence, we find that the magnetic field occurs primarily in the form of flux tubes. The dynamical interplay\\u000a between the magnetic tubes and the flow is explored during a time interval in which the total magnetic energy

  12. Magnetic helicity fluxes in interface and flux transport dynamos

    NASA Astrophysics Data System (ADS)

    Chatterjee, P.; Guerrero, G.; Brandenburg, A.

    2011-01-01

    Context. Dynamos in the Sun and other bodies tend to produce magnetic fields that possess magnetic helicity of opposite sign at large and small scales, respectively. The build-up of magnetic helicity at small scales provides an important saturation mechanism. Aims: In order to understand the nature of the solar dynamo we need to understand the details of the saturation mechanism in spherical geometry. In particular, we aim to understand the effects of magnetic helicity fluxes from turbulence and meridional circulation. Methods: We consider a model with only radial shear confined to a thin layer (tachocline) at the bottom of the convection zone. The kinetic ? owing to helical turbulence is assumed to be localized in a region above the convection zone. The dynamical quenching formalism is used to describe the build-up of mean magnetic helicity in the model, which results in a magnetic ? effect that feeds back on the kinetic ? effect. In some cases we compare these results with those obtained from a model with a simple algebraic ? quenching formula. Results: In agreement with earlier findings, the magnetic ? effect has the opposite sign compared with the kinetic ? effect and leads to a catastrophic decrease of the saturation field strength proportional to the inverse magnetic Reynolds number. At high latitudes this quenching effect can lead to secondary dynamo waves that propagate poleward because of the opposite sign of ?. These secondary dynamo waves are driven by small-scale magnetic helicity instead of the small-scale kinetic helicity. Magnetic helicity fluxes both from turbulent mixing and from meridional circulation alleviate catastrophic quenching. Interestingly, supercritical diffusive helicity fluxes also give rise to secondary dynamo waves and grand minima-like episodes.

  13. Flux Emergence in a Magnetized Convection Zone

    NASA Astrophysics Data System (ADS)

    Pinto, R. F.; Brun, A. S.

    2013-07-01

    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 three-dimensional MHD numerical simulations using the ASH code (anelastic spherical harmonics) and analyzed 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 can only very crudely and inaccurately represent the local dynamics of the buoyant rise of the implanted magnetic structure, but nonetheless allows us to study the influence of global effects, such as self-consistently generated differential rotation and meridional circulation, and of 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 are determined essentially by the flux-rope's properties and the convective flows and consequently are in good agreement with previous studies. However, the effects of the interaction of the background dynamo field become increasingly strong as the flux ropes evolve. During the buoyant rise across the convection zone, the flux-rope's magnetic field strength scales as Bvprop??, with ? <~ 1. An increase of radial velocity, density, and current density is observed to precede flux emergence at all longitudes. The geometry, latitude, and relative orientation of the flux ropes with respect to the background magnetic field influences the resulting rise speeds, zonal flow amplitudes (which develop within the flux ropes), and the corresponding surface signatures. This influences the morphology, duration and amplitude of the surface shearing, and the Poynting flux associated with magnetic flux-rope emergence. The emerged magnetic flux influences the system's global polarity, leading in some cases to a polarity reversal while inhibiting the background dynamo from doing so in others. The emerged magnetic flux is slowly advected poleward while being diffused and assimilated by the background dynamo field.

  14. Analysis of Vibration and Acoustic Noise in Permanent Magnet Motors.

    NASA Astrophysics Data System (ADS)

    Hwang, Sangmoon

    The drive motor is a frequent source of vibration and acoustic noise in many precision spindle motors. One of the electromagnetic sources of vibration in permanent magnet motors is the torque ripple, consisting of the reluctance torque and electromagnetic torque fluctuation. This type of vibration is becoming more serious with the advent of new high-grade magnets with increased flux density. Acoustic noise of electromagnetic origin is difficult to predict and its exact mechanism is unclear. The mechanism of noise generation should be revealed to design a quieter motor which is the modern customer's demand. For motor operation at low speeds and loads, torque ripple due to the reluctance torque is often a source of vibration and control difficulty. The reluctance torque in a motor was calculated from the flux density by a finite element method and the Maxwell stress method. Effects of design parameters, such as stator slot width, permanent slot width, airgap length and magnetization direction, were investigated. Magnet pole shaping, by gradually decreasing the magnet thickness toward edges, yields a sinusoidal shape of the reluctance torque with reduced harmonics, thus reducing the vibration. This dissertation also presents two motor design techniques: stator tooth notching and rotor pole skewing with magnet pole shaping, and the effect of each method on the output torque. The analysis shows that the reluctance torque can be nearly eliminated by the suggested designs, with minimal sacrifice of the output torque. In permanent magnet DC motors, the most popular design type is the trapezoidal back electro-motive force (BEMF), for switched DC controllers. It is demonstrated that the output torque profile of one phase energized is qualitatively equivalent to the BEMF profile for motors with reduced reluctance torque. It implies that design of BEMF profile is possible by magnetic modeling of a motor, without expensive and time-consuming experiments for different designs. The effect of various design parameters on the output torque and torque ripple are discussed. Design parameters include winding patterns, magnetization direction, magnet arc length, number of segments in poles and magnet pole shaping. New designs of trapezoidal BEMF motors are proposed to reduce the electromagnetic torque ripple. Magnet stepping and magnet edge shaping with reduced arc length, significantly reduce torque ripple, with minimal sacrifice of the maximum output torque. Acoustic noise of electromagnetic origin is investigated using a magnetic frame which emulates a DC motor. The driving electromagnetic force is calculated using finite element analysis and the resulting vibration and acoustic noise is measured. Acoustic noise of purely electromagnetic origin was also tested with a DC brushless motor to confirm the results of the magnetic frame. The mechanism of noise generation in a DC motor is a quasi-static response of a stator not only at the fundamental frequency but also at higher harmonic frequencies of alternating switched DC, which is a current characteristic of a DC motor. Noise generation is significantly aggravated when some of those harmonics are close to the resonant frequencies of the stator. Therefore, acoustic noise is highly dependent upon the excitation current shape, as higher harmonics may match with resonant frequencies of the stator.

  15. Photospheric processes and magnetic flux tubes

    E-print Network

    O. Steiner

    2007-09-01

    In the first part of these lecture notes, new high-resolution observations of small-scale magnetic flux concentrations are presented and compared to results from new three-dimensional magnetohydrodynamic simulations. Special attention is paid to the physics of faculae and to new three-dimensional radiation magnetohydrodynamic simulations of the integral layers from the top of the convection zone to the mid-chromosphere. The second part is devoted to a few basic properties of magnetic flux tubes, which can be considered to be an abstraction of the more complicated flux concentrations known from observations and numerical simulations. We treat electrical current sheets, the mechanical equilibrium condition at magnetic interfaces, the equations for constructing a magnetohydrostatic flux tube embedded in a gravitationally stratified atmosphere, the condition of radiative equilibrium, and the condition for interchange stability.

  16. Heat flux viscosity in collisional magnetized plasmas

    NASA Astrophysics Data System (ADS)

    Liu, C.; Fox, W.; Bhattacharjee, A.

    2015-05-01

    Momentum transport in collisional magnetized plasmas due to gradients in the heat flux, a "heat flux viscosity," is demonstrated. Even though no net particle flux is associated with a heat flux, in a plasma there can still be momentum transport owing to the velocity dependence of the Coulomb collision frequency, analogous to the thermal force. This heat-flux viscosity may play an important role in numerous plasma environments, in particular, in strongly driven high-energy-density plasma, where strong heat flux can dominate over ordinary plasma flows. The heat flux viscosity can influence the dynamics of the magnetic field in plasmas through the generalized Ohm's law and may therefore play an important role as a dissipation mechanism allowing magnetic field line reconnection. The heat flux viscosity is calculated directly using the finite-difference method of Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], which is shown to be more accurate than Braginskii's method [S. I. Braginskii, Rev. Plasma Phys. 1, 205 (1965)], and confirmed with one-dimensional collisional particle-in-cell simulations. The resulting transport coefficients are tabulated for ease of application.

  17. What is a flux tube? On the magnetic field topology of buoyant flux structures

    E-print Network

    What is a flux tube? On the magnetic field topology of buoyant flux structures Fausto Cattaneo, visually resembling idealised magnetic flux tubes, are generated self-consistently by numerical simulation of the magnetically-active region. We discuss how these results impact our simple ideas of a magnetic flux tube

  18. Magnetic Flux Tube Reconnection: Tunneling Versus Slingshot

    E-print Network

    M. G. Linton; S. K. Antiochos

    2005-01-21

    The discrete nature of the solar magnetic field as it emerges into the corona through the photosphere indicates that it exists as isolated flux tubes in the convection zone, and will remain as discrete flux tubes in the corona until it collides and reconnects with other coronal fields. Collisions of these flux tubes will in general be three dimensional, and will often lead to reconnection, both rearranging the magnetic field topology in fundamental ways, and releasing magnetic energy. With the goal of better understanding these dynamics, we carry out a set of numerical experiments exploring fundamental characteristics of three dimensional magnetic flux tube reconnection. We first show that reconnecting flux tubes at opposite extremes of twist behave very differently: in some configurations, low twist tubes slingshot while high twist tubes tunnel. We then discuss a theory explaining these differences: by assuming helicity conservation during the reconnection one can show that at high twist, tunneled tubes reach a lower magnetic energy state than slingshot tubes, whereas at low twist the opposite holds. We test three predictions made by this theory. 1) We find that the level of twist at which the transition from slingshot to tunnel occurs is about two to three times higher than predicted on the basis of energetics and helicity conservation alone, probably because the dynamics of the reconnection play a large role as well. 2) We find that the tunnel occurs at all flux tube collision angles predicted by the theory. 3) We find that the amount of magnetic energy a slingshot or a tunnel reconnection releases agrees reasonably well with the theory, though at the high resistivities we have to use for numerical stability, a significant amount of magnetic energy is lost to diffusion, independent of reconnection.

  19. Turbulent dynamo with advective magnetic helicity flux

    E-print Network

    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 ...

  20. The dynamics of magnetic flux rings

    NASA Technical Reports Server (NTRS)

    Deluca, E. E.; Fisher, G. H.; Patten, B. M.

    1993-01-01

    The evolution of magnetic fields in the presence of turbulent convection is examined using results of numerical simulations of closed magnetic flux tubes embedded in a steady 'ABC' flow field, which approximate some of the important characteristics of a turbulent convecting flow field. Three different evolutionary scenarios were found: expansion to a steady deformed ring; collapse to a compact fat flux ring, separated from the expansion type of behavior by a critical length scale; and, occasionally, evolution toward an advecting, oscillatory state. The work suggests that small-scale flows will not have a strong effect on large-scale, strong fields.

  1. Magnetic flux penetration into superconducting thin films.

    NASA Technical Reports Server (NTRS)

    Peabody, G. E.; Meservey, R.

    1972-01-01

    The quantum-interference technique developed by Meservey (1965) is used to measure directly the absolute value of the penetration depth in lead in tin superconducting thin films. The technique assumes that the change in phase of the superconducting wave function around any contour within the superconductor must be 2 pi n, where n is a nonnegative integer. Results show that the critical current of a superconducting interferometer with two parallel junctions is not strictly periodic in the applied magnetic flux with a period equal to the flux quantum because of the magnetic field dependence of the critical currents of the junctions.

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

    NASA Astrophysics Data System (ADS)

    Jeong, Woo Chul; Chauhan, Munish; Sajib, Saurav Z. K.; Kim, Hyung Joong; Serša, Igor; In Kwon, Oh; 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 noise level up to 3-4 times at each anomaly region in comparison to the conventional method.

  3. Electric Flux Tube in Magnetic Plasma

    E-print Network

    Jinfeng Liao; Edward Shuryak

    2007-12-06

    In this paper we study a methodical problem related to the magnetic scenario recently suggested and initiated by the authors \\cite{Liao_ES_mono} to understand the strongly coupled quark-gluon plasma (sQGP): the electric flux tube in monopole plasma. A macroscopic approach, interpolating between Bose condensed (dual superconductor) and classical gas medium is developed first. Then we work out a microscopic approach based on detailed quantum mechanical calculation of the monopole scattering on electric flux tube, evaluating induced currents for all partial waves. As expected, the flux tube looses its stability when particles can penetrate it: we make this condition precise by calculating the critical value for the product of the flux tube size times the particle momentum, above which the flux tube dissolves. Lattice static potentials indicate that flux tubes seem to dissolve at $T>T_{dissolution} \\approx 1.3 T_c$. Using our criterion one gets an estimate of the magnetic density $n\\approx 4.4 \\sim 6.6 fm^{-3}$ at this temperature.

  4. Synthetic magnetic fluxes on the honeycomb lattice

    SciTech Connect

    Gorecka, Agnieszka [Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543 (Singapore); Gremaud, Benoit [Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543 (Singapore); Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore); Laboratoire Kastler Brossel, Ecole Normale Superieure, CNRS, UPMC, 4 Place Jussieu, FR-75005 Paris (France); Miniatura, Christian [Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543 (Singapore); Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore); Institut Non Lineaire de Nice, UMR 6618, UNS, CNRS, 1361 Route des Lucioles, FR-06560 Valbonne (France); Institute of Advanced Studies, Nanyang Technological university, 60 Nanyang View, Singapore 639673 (Singapore)

    2011-08-15

    We devise experimental schemes that are able to mimic uniform and staggered magnetic fluxes acting on ultracold two-electron atoms, such as ytterbium atoms, propagating in a honeycomb lattice. The atoms are first trapped into two independent state-selective triangular lattices and then further exposed to a suitable configuration of resonant Raman laser beams. These beams induce hops between the two triangular lattices and make atoms move in a honeycomb lattice. Atoms traveling around each unit cell of this honeycomb lattice pick up a nonzero phase. In the uniform case, the artificial magnetic flux sustained by each cell can reach about two flux quanta, thereby realizing a cold-atom analog of the Harper model with its notorious Hofstadter's butterfly structure. Different condensed-matter phenomena such as the relativistic integer and fractional quantum Hall effects, as observed in graphene samples, could be targeted with this scheme.

  5. Magnetic noises generated by plants in microgravity: effect of external magnetic fields.

    NASA Astrophysics Data System (ADS)

    Bogatina, N.; Sheykina, N.; Kordyum, E.

    Magnetic Noises Generated by Plants in Microgravity, Effect of External Magnetic Field. N. Bogatina(1), N. Sheykina(1), E. Kordyum(2). (1) B.Verkin Institute for Low Temperature Physics&Engineering of National Academy of Sciences of Ukraine, Kharkov, Ukraine (2) N.Cholodny Institute of Botany of National Academy of Sciences of Ukraine, Kiev, Ukraine. e-mail:bogatina@ilt.kharkov.ua/Fax: 38-0572-322370. The object of the work is to determine the correlation between the magnetic noises generated by plants and accelaration value during their development in microgravity. The amplitude of magnetic noise spectral density will be mesured. Its dependence on the magnitude of gravity accelaration and magnitudes of static and alternating magnetic fields is supposed to reflect the mechanisms of gravi- and magnitopercrption. We shall try to answer the guestion whether the same mechanism or different mechanisms are responsible for gravi- and magnitopercrption. The gravitropic reaction of plants is needed to be studied simultaneously with observation of magnetic noises. The measurements in microgravity have to be fulfilled by a flux-gate magnetometer connected with Philips spectroanalyser There are two directions of experiments. The first one is experiments that will be carried out on Earth under the conditions of weakening of gravitational force. The preliminary parameters of the required magnetic fields have to be determined in these experiments. The second one is the same experiment in the space. These experiments are supposed to allow us to define the mechanisms of a gravitropic reaction of plants because any motion of ions ( indolil-acetic ions, for instance) is accompanied by an increase of magnetic noise. The experimental results obtained under onGround conditions by using the superconducting technique wwithout weakening the weight force are disscussed. .

  6. Magnetic Flux Transport at the Solar Surface

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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 review the modeling of the various processes that determine the evolution of the surface field. We restrict our attention to their role in the surface flux transport model. We also discuss the success of the model and some of the results that have been obtained using this model.

  7. Slip Running Reconnection in Magnetic Flux Ropes

    NASA Astrophysics Data System (ADS)

    Gekelman, W. N.; Van Compernolle, B.; Vincena, S. T.; De Hass, T.

    2012-12-01

    Magnetic flux ropes are due to helical currents and form a dense carpet of arches on the surface of the sun. Occasionally one tears loose as a coronal mass ejection and its rope structure can be detected by satellites close to the earth. Current sheets can tear into filaments and these are nothing other than flux ropes. Ropes are not static, they exert mutual ?c{J}×?c{B} forces causing them to twist about each other and eventually merge. Kink instabilities cause them to violently smash into each other and reconnect at the point of contact. We report on experiments on two adjacent ropes done in the large plasma device (LAPD) at UCLA ( ne ˜ 1012, Te ˜ 6 eV, B0z=330G, Brope}\\cong{10G,trep=1 Hz). The currents and magnetic fields form exotic shapes with no ignorable direction and no magnetic nulls. Volumetric space-time data (70,600 spatial locations) show multiple reconnection sites with time-dependent locations. The concept of a quasi-separatrix layer (QSL), a tool to understand and visualize 3D magnetic field lines reconnection without null points is introduced. Three-dimensional measurements of the QSL derived from magnetic field data are presented. Within the QSL field lines that start close to one another rapidly diverge as they pass through one or more reconnection regions. The motion of magnetic field lines are traced as reconnection proceeds and they are observed to slip through the regions of space where the QSL is largest. As the interaction proceeds we double the current in the ropes. This accompanied by intense heating as observed in uv light and plasma flows measured by Mach probes. The interaction of the ropes is clearly seen by vislaulizng magnetic field data , as well as in images from a fast framing camera. Work supported by the Dept. of Energy and The National Science Foundation, done at the Basic Plasma Science Facility at UCLA.Magnetic Field lines (measured) of three flux ropes and the plasma currents associated with them

  8. SEED BANKS FOR MAGNETIC FLUX COMPRESSION GENERATORS

    SciTech Connect

    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.

  9. Turbulent Erosion of Magnetic Flux Tubes

    E-print Network

    K. Petrovay; F. Moreno-Insertis

    1998-12-29

    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 nu(B) on the magnetic field satisfies basic physical requirements. We find that for sufficiently strong nonlinearity (i.e. for sufficiently strong reduction of nu inside the tube) a current sheet is spontaneously formed around the tube within one diffusion timescale. This sheet propagates inwards with a velocity inversely proportional to the ratio of the field strength just inside the current sheet to the equipartition field strength B0/Be, so the lifetime of a tube with constant internal flux density is increased approximately by a factor not exceeding B0/Be, even for infinitely effective inhibition of turbulence inside the tube. Among the applications of these results we point out that toroidal flux tubes in the solar convective zone are subject to significant flux loss owing to turbulent erosion on a timescale of about 1 month, and that turbulent erosion may be responsible for the formation of a current sheet around a sunspot. It is further proposed that, despite the simplifying assumptions involved, our solutions correctly reflect the essential features of the sunspot decay process.

  10. Quantitative observation of magnetic flux distribution in new magnetic films for future high

    E-print Network

    Recanati, Catherine

    configuration of magnetic nanoparticles, 15 magnetic films, 16 magnetic tunnel junctions, 17 or even magnetiteQuantitative observation of magnetic flux distribution in new magnetic films for future high

  11. Rough Design of a Double-Stator Axial Flux Permanent Magnet Generator

    E-print Network

    Paris-Sud XI, Université de

    (DSAFPM) for a rim-driven Marine Current Turbine (MCT). The DSAFPM machine will be compared to a previously developed and realized Radial Flux Permanent Magnet Machine (RFPM); given the same rim-driven MCT advantages such as low visual exposure, no noise for the public and reduced environment considerations

  12. Efficiency optimization of transverse flux permanent magnet machine using genetic algorithm

    Microsoft Academic Search

    G. Q. Bao; J. H. Shil; J. Z. Jiang

    2005-01-01

    Particular interest is presently focused on electric propulsion system for the reduction of air pollution and noise. Transverse flux permanent magnet machine (TFPM) is one of the most suitable designs in such application so far as its high power production potential. In this paper a modified genetic algorithm (GA) is developed to find the independent geometrical parameters of rotor and

  13. Coronal mass ejections and magnetic flux buildup in the heliosphere

    E-print Network

    California at Berkeley, University of

    to determine the CME occurrence rates, while in situ observations are used to estimate the magnetic flux the observed doubling in the magnetic field intensity at 1 AU over the solar cycle. Such timescales signatures; no flux buildup results. The dynamic simulation yields a solar cycle flux variation with high

  14. Improvement of the superconducting magnetic levitation system for the determination of the magnetic flux quantum

    Microsoft Academic Search

    T. Endo; Y. Sakamoto; F. Shiota; K. Nakayama; Y. Nezu; M. Kikuzawa; K. Hara

    1989-01-01

    The authors describe an improvement of the preliminary superconducting magnetic levitation system in progress for the absolute determination of the magnetic flux quantum. This improvement includes the development of the flux-up method to determine the flux in terms of the Josephson voltage. The improvement is essential for the determination of the magnetic flux quantum as well as of the coil

  15. Permanent-magnet switched-flux machine

    DOEpatents

    Trzynadlowski, Andrzej M.; Qin, Ling

    2011-06-14

    A permanent-magnet switched-flux (PMSF) device has an outer rotor mounted to a shaft about a central axis extending axially through the PMSF device. First and second pluralities of permanent-magnets (PMs) are respectively mounted in first and second circles, radially outwardly in first and second transverse planes extending from first and second sections of the central axis adjacent to an inner surface of the outer rotor. An inner stator is coupled to the shaft and has i) a stator core having a core axis co-axial with the central axis; and ii) first and second pluralities of stator poles mounted in first and second circles, radially outwardly from the stator core axis in the first and second transverse planes. The first and second pluralities of PMs each include PMs of alternating polarity.

  16. Permanent-magnet switched-flux machine

    DOEpatents

    Trzynadlowski, Andrzej M.; Qin, Ling

    2010-01-12

    A permanent-magnet switched-flux (PMSF) device has a ferromagnetic outer stator mounted to a shaft about a central axis extending axially through the PMSF device. Pluralities of top and bottom stator poles are respectively mounted in first and second circles, radially outwardly in first and second transverse planes extending from first and second sections of the central axis adjacent to an inner surface of the ferromagnetic outer stator. A ferromagnetic inner rotor is coupled to the shaft and has i) a rotor core having a core axis co-axial with the central axis; and ii) first and second discs having respective outer edges with first and second pluralities of permanent magnets (PMs) mounted in first and second circles, radially outwardly from the rotor core axis in the first and second transverse planes. The first and second pluralities of PMs each include PMs of alternating polarity.

  17. Erupting Solar Magnetic Flux Ropes - Theory and Observation

    Microsoft Academic Search

    J. Krall; J. Chen; R. A. Santoro; R. T. Duffin; R. A. Howard; B. J. Thompson

    1998-01-01

    The dynamics of magnetic flux ropes near the sun and in interplanetary space are studied using a modified version of the flux rope model of Chen and Garren. (Chen and Garren, GRL, 20, 2319, 1993) In this model, a coronal mass ejection (CME) corresponds to a flux rope with foot points that remain anchored in the photosphere. The model flux

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

    NASA Astrophysics Data System (ADS)

    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.

  19. Flux Noise from a Metal Surrounding a Superconducting Wire Applied to a Gradiometer

    NASA Astrophysics Data System (ADS)

    Takada, Youichi; Ueda, Masayuki; Kado, Hisashi

    1995-06-01

    We measure the flux noise generated from a metal covering a superconducting wire. The flux noise from a twisted pair of wires wound with niobium-titanium alloy wire wrapped with copper (Nb-Ti/Cu) is both measured and calculated for various wire lengths. Flux noise is confirmed to be related to the wire length. The flux noise from a first-order gradiometer wound with Nb-Ti/Cu wire is also measured and calculated. The flux noise from this gradiometer, formed with a radius of 7 mm, a base line of 50 mm, and length of 60 mm for a twisted pair of wires, is calculated to be 4.33 µ?0/ Hz1/2 which is in good agreement with the measured result.

  20. Small scale magnetic flux-averaged magnetohydrodynamics

    SciTech Connect

    Pfirsch, D. (Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, D-8046 Garching (Germany)); Sudan, R.N. (Laboratory of Plasma Studies, Cornell University, Ithaca, New York 14853 (United States))

    1994-08-01

    By relaxing exact magnetic flux conservation below a scale [lambda] a system of flux-averaged magnetohydrodynamic equations are derived from Hamilton's principle with modified constraints. An energy principle can be derived from the linearized averaged system because the total system energy is conserved. This energy principle is employed to treat the resistive tearing instability and the exact growth rate is recovered when [lambda] is identified with the resistive skin depth. A necessary and sufficient stability criteria of the tearing instability with line tying at the ends for solar coronal loops is also obtained. The method is extended to both spatial and temporal averaging in Hamilton's principle. The resulting system of equations not only allows flux reconnection but introduces irreversibility for appropriate choice of the averaging function. Except for boundary contributions which are modified by the time averaging process total energy and momentum are conserved over times much longer than the averaging time [tau] but not for less than [tau]. These modified boundary contributions correspond to the existence, also, of damped waves and shock waves in this theory. Time and space averaging is applied to electron magnetohydrodynamics and in one-dimensional geometry predicts solitons and shocks in different limits.

  1. A review on equivalent magnetic noise of magnetoelectric laminate sensors

    PubMed Central

    Wang, Y. J.; Gao, J. Q.; Li, M. H.; Shen, Y.; Hasanyan, D.; Li, J. F.; Viehland, D.

    2014-01-01

    Since the turn of the millennium, multi-phase magnetoelectric (ME) composites have been subject to attention and development, and giant ME effects have been found in laminate composites of piezoelectric and magnetostrictive layers. From an application perspective, the practical usefulness of a magnetic sensor is determined not only by the output signal of the sensor in response to an incident magnetic field, but also by the equivalent magnetic noise generated in the absence of such an incident field. Here, a short review of developments in equivalent magnetic noise reduction for ME sensors is presented. This review focuses on internal noise, the analysis of the noise contributions and a summary of noise reduction strategies. Furthermore, external vibration noise is also discussed. The review concludes with an outlook on future possibilities and scientific challenges in the field of ME magnetic sensors. PMID:24421380

  2. Magnetization dynamics driven by a jump-noise process

    NASA Astrophysics Data System (ADS)

    Mayergoyz, I.; Bertotti, G.; Serpico, C.

    2011-01-01

    It is proposed to use a jump-noise process in magnetization dynamics equations to account for thermal bath effects. It is shown that in the case of a small jump-noise process, the Landau-Lifshitz and Gilbert damping terms can be analytically derived as deterministic (average) effects caused by the jump-noise process. Simple formulas for the damping constant are derived that relate it to the scattering rate of the jump-noise process and elucidate its dependence on magnetization. Generalized H-theorems for jump-noise-driven magnetization dynamics are presented. Random switching of magnetization caused by the jump-noise process is studied and it is demonstrated that the switching rate has different temperature dependence at relatively high and very low temperatures, which is traditionally attributed to the existence of phenomena of macroscopic magnetization tunneling.

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

    NASA Astrophysics Data System (ADS)

    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 cubic 3D XY model to simulate magnetic fields applied to a type II superconductor, tilted with respect to a cubic axis. Our model produces a "crossing lattices" state, wherein two distinct flux line lattices cross each other at right angles. We observe that the flux lines effectively form a "staircase" pattern in order to accommodate the crossing lattices structure. We also measure the helicity modulus as a function of temperature along the direction of each flux line lattice. We find that both lattices melt simultaneously, and that a small transverse field only slightly reduces the melting temperature. Similar behavior is found when this same model is treated within a simple mean field model.

  4. Magnetic Flux Concentration and Zonal Flows in Magnetorotational Instability Turbulence

    NASA Astrophysics Data System (ADS)

    Bai, Xue-Ning; Stone, James M.

    2014-11-01

    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.

  5. Spin torque dynamics with noise in magnetic nanosystems

    Microsoft Academic Search

    J. Swiebodzinski; A. Chudnovskiy; T. Dunn; A. Kamenev

    2010-01-01

    We investigate the role of equilibrium and nonequilibrium noise in the magnetization dynamics on monodomain ferromagnets. Starting from a microscopic model, we present a detailed derivation of the spin shot-noise correlator. We investigate the ramifications of the nonequilibrium noise on the spin torque dynamics, both in the steady-state precessional regime and the spin switching regime. In the latter case, we

  6. Magnetic flux array for spontaneous magnetic reconnection experiments A. Kesich, J. Bonde, J. Egedal,a

    E-print Network

    Egedal, Jan

    Magnetic flux array for spontaneous magnetic reconnection experiments A. Kesich, J. Bonde, J; published online 24 June 2008 Experimental investigation of reconnection in magnetized plasmas relies on accurate characterization of the evolving magnetic fields. In experimental configurations where the plasma

  7. Relationships of a growing magnetic flux region to flares

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

    The evolution of flare sites at the boundaries of major new and growing magnetic flux regions within complexes of active regions has been analyzed using H-alpha images. A spectrum of possible relationships of growing flux regions to flares is described. An 'intimate' interaction between old and new flux and flare sites occurs at the boundaries of their regions. Forced or 'intimidated' interaction involves new flux pushing older, lower flux density fields toward a neighboring old polarity inversion line, followed by the occurrence of a flare. In 'influential' interaction, magnetic lines of force over an old polarity inversion line reconnect to new emerging flux, and a flare occurs when the magnetic field overlying the filament becomes too weak to prevent its eruption. 'Inconsequential' interaction occurs when a new flux region is too small or has the wrong orientation for creating flare conditions. 'Incidental' interaction involves a flare occurring without any significant relationship to new flux regions.

  8. Magnetic Flux Loss and Flux Transport in a Decaying Active Region

    NASA Astrophysics Data System (ADS)

    Kubo, M.; Lites, B. W.; Shimizu, T.; Ichimoto, K.

    2008-10-01

    We estimate the temporal change of magnetic flux normal to the solar surface in a decaying active region by using a time series of the spatial distribution of vector magnetic fields in the photosphere. The vector magnetic fields are derived from full spectropolarimetric measurements with the Solar Optical Telescope aboard Hinode. We compare a magnetic flux loss rate to a flux transport rate in a decaying sunspot and its surrounding moat region. The amount of magnetic flux that decreases in the sunspot and moat region is very similar to magnetic flux transported to the outer boundary of the moat region. The flux loss rates [(dF/dt)loss] of magnetic elements with positive and negative polarities balance each other around the outer boundary of the moat region. These results suggest that most of the magnetic flux in the sunspot is transported to the outer boundary of the moat region as moving magnetic features, and then removed from the photosphere by flux cancellation around the outer boundary of the moat region.

  9. Magnetic Flux Loss and Flux Transport in a Decaying Active Region

    E-print Network

    M. Kubo; B. W. Lites; T. Shimizu; K. Ichimoto

    2008-07-28

    We estimate the temporal change of magnetic flux perpendicular to the solar surface in a decaying active region by using a time series of the spatial distribution of vector magnetic fields in the photosphere. The vector magnetic fields are derived from full spectropolarimetric measurements with the Solar Optical Telescope aboard Hinode. We compare a magnetic flux loss rate to a flux transport rate in a decaying sunspot and its surrounding moat region. The amount of magnetic flux that decreases in the sunspot and moat region is very similar to magnetic flux transported to the outer boundary of the moat region. The flux loss rates [$(dF/dt)_{loss}$] of magnetic elements with positive and negative polarities are balanced each other around the outer boundary of the moat region. These results suggest that most of the magnetic flux in the sunspot is transported to the outer boundary of the moat region as moving magnetic features, and then removed from the photosphere by flux cancellation around the outer boundary of the moat region.

  10. Noise-cancelling quadrature magnetic position, speed and direction sensor

    DOEpatents

    Preston, Mark A. (Niskayuna, NY); King, Robert D. (Schenectady, NY)

    1996-01-01

    An array of three magnetic sensors in a single package is employed with a single bias magnet for sensing shaft position, speed and direction of a motor in a high magnetic noise environment. Two of the three magnetic sensors are situated in an anti-phase relationship (i.e., 180.degree. out-of-phase) with respect to the relationship between the other of the two sensors and magnetically salient target, and the third magnetic sensor is situated between the anti-phase sensors. The result is quadrature sensing with noise immunity for accurate relative position, speed and direction measurements.

  11. Complexity and diffusion of magnetic flux surfaces in anisotropic turbulence

    SciTech Connect

    Servidio, S. [Dipartimento di Fisica, Università della Calabria, I-87036 Cosenza (Italy); Matthaeus, W. H.; Wan, M.; Rappazzo, A. F. [Department of Physics and Astronomy, University of Delaware, Newark, DE (United States); Ruffolo, D. [Department of Physics, Faculty of Science, Mahidol University, Bangkok (Thailand); Oughton, S., E-mail: sergio.servidio@fis.unical.it [Department of Mathematics, University of Waikato, Hamilton (New Zealand)

    2014-04-10

    The complexity of magnetic flux surfaces is investigated analytically and numerically in static homogeneous magnetic turbulence. Magnetic surfaces are computed to large distances in magnetic fields derived from a reduced magnetohydrodynamic model. The question addressed is whether one can define magnetic surfaces over large distances when turbulence is present. Using a flux surface spectral analysis, we show that magnetic surfaces become complex at small scales, experiencing an exponential thinning that is quantified here. The computation of a flux surface is of either exponential or nondeterministic polynomial complexity, which has the conceptual implication that global identification of magnetic flux surfaces and flux exchange, e.g., in magnetic reconnection, can be intractable in three dimensions. The coarse-grained large-scale magnetic flux experiences diffusive behavior. The link between the diffusion of the coarse-grained flux and field-line random walk is established explicitly through multiple scale analysis. The Kubo number controls both large and small scale limits. These results have consequences for interpreting processes such as magnetic reconnection and field-line diffusion in astrophysical plasmas.

  12. Influence of Photospheric Magnetic Flux Distribution on Coronal Flux Rope Catastrophe

    Microsoft Academic Search

    S. J. Sun; Y. Q. Hu; Y. Chen

    2007-01-01

    Previous studies of coronal magnetic flux rope systems indicated that these systems exhibit a catastrophic behavior for background fields with a specific photospheric flux distribution, and that the catastrophic energy threshold exceeds the associated open field energy. In this Letter, we take axisymmetrical bipolar fields in spherical geometry with different flux distributions on the photosphere as the background, and then

  13. Thermal properties of magnetic flux tubes. II. Storage of flux in the solar overshoot region

    Microsoft Academic Search

    M. Rempel

    2003-01-01

    We consider the consequences of radiative heating for the storage of magnetic flux in the overshoot region at the bottom of the solar convection zone. In the first part of the paper, we study the evolution of axisymmetric flux tubes (flux rings), which are initially in neutrally buoyant mechanical equilibrium. Radiative heating leads to a slow upward drift of the

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

    PubMed

    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 noise level up to 3-4 times at each anomaly region in comparison to the conventional method. PMID:25097180

  15. Role of small-scale magnetic elements in magnetic flux transportation on the solar surface

    NASA Astrophysics Data System (ADS)

    Kubo, Masahito

    2012-07-01

    The magnetic fields emerge into the solar surface from the convection zone. Recent observations at high spatial resolution reveal ubiquitous flux emergence at granular scale on the solar surface in the quiet Sun. The emerged small-scale magnetic elements dynamically evolve with granular convective flows, and form a network magnetic field along the boundaries of supergranular cells. Such a magneto-convection in the photosphere is an energy source for heating and dynamics in the upper atmospheres. The small-scale magnetic elements are also important for the flux transportation in active regions. We quantify the evolution of sunspot magnetic flux by using continuous vector magnetic field measurements under seeing free condition. The magnetic flux budget of the decaying sunspot reveals that small-scale magnetic elements called moving magnetic features carry away enough magnetic flux from the sunspot through the moat region. The transported magnetic flux is mostly removed from the photosphere by ``magnetic flux cancellation'' that is the mutual loss of magnetic flux due to the apparent collision of opposite-polarity magnetic elements. The granular-scale flux cancellation can be seen everywhere on the solar surface, and the flux cancellation is essential to understand the dissipation of magnetic flux from the solar surface. We find unresolved, small-scale flux cancellations along the polarity inversion line that is formed between granular-scale opposite polarity magnetic elements. Highly asymmetric Stokes-V profiles are observed along the polarity inversion line. Such asymmetric profiles can be made by the sum of the Stokes-V profiles at the opposite-polarity magnetic elements next to the polarity inversion line. This means that the approaching bipolar magnetic elements still keep their nature within the pixel where they come in contact with each other. It is suggested that the unresolved flux removal process in the photosphere or in the lower chromosphere.

  16. Magnetic flux emergence and associated dynamic phenomena in the Sun.

    PubMed

    Archontis, Vasilis

    2012-07-13

    We present a review of the process of magnetic flux emergence in the Sun. We focus on observations and numerical experiments that explore the dynamical rise of magnetic fields from the solar interior to the corona. We describe the response of the highly stratified solar atmosphere on flux emergence and, consequently, we present a comprehensive picture of the coupling between solar dynamic events and flux emergence. We discuss potential applications of this process in other astrophysical environments. PMID:22665894

  17. High-Frequency Response and Voltage Noise in Magnetic Nanocomposites

    NASA Astrophysics Data System (ADS)

    Buznikov, N. A.; Iakubov, I. T.; Rakhmanov, A. L.; Kugel, K. I.; Sboychakov, A. O.

    2010-12-01

    We study the noise spectra and high-frequency permeability of inhomogeneous magnetic materials consisting of single-domain magnetic nanoparticles embedded into an insulating matrix. Possible mechanisms of 1/f voltage noise in phase-separated manganites is analyzed. The material is modelled by a system of small ferromagnetic metallic droplets (magnetic polarons or ferrons) in insulating antiferromagnetic or paramagnetic matrix. The electron transport is related to tunnelling of charge carriers between droplets. One of the sources of the 1/f noise in such a system stems from fluctuations of the number of droplets with extra electron. In the case of strong magnetic anisotropy, the 1/f noise can arise also due to the fluctuations of the magnetic moments of ferrons. The high frequency magnetic permeability of nanocomposite film with magnetic particles in insulating non-magnetic matrix is studied in detail. The case of strong magnetic dipole interaction and strong magnetic anisotropy of ferromagnetic granules is considered. The composite is modelled by a cubic regular array of ferromagnetic particles. The high-frequency permeability tensor components are found as a functions of frequency, temperature, ferromagnetic phase content, and magnetic anisotropy. The results demonstrate that magnetic dipole interaction leads to a shift of the resonance frequencies towards higher values, and nanocomposite film could have rather high value of magnetic permeability in the microwave range.

  18. High-Frequency Response and Voltage Noise in Magnetic Nanocomposites

    NASA Astrophysics Data System (ADS)

    Buznikov, N. A.; Iakubov, I. T.; Rakhmanov, A. L.; Kugel, K. I.; Sboychakov, A. O.

    We study the noise spectra and high-frequency permeability of inhomogeneous magnetic materials consisting of single-domain magnetic nanoparticles embedded into an insulating matrix. Possible mechanisms of 1/f voltage noise in phase-separated manganites is analyzed. The material is modelled by a system of small ferromagnetic metallic droplets (magnetic polarons or ferrons) in insulating antiferromagnetic or paramagnetic matrix. The electron transport is related to tunnelling of charge carriers between droplets. One of the sources of the 1/f noise in such a system stems from fluctuations of the number of droplets with extra electron. In the case of strong magnetic anisotropy, the 1/f noise can arise also due to the fluctuations of the magnetic moments of ferrons. The high frequency magnetic permeability of nanocomposite film with magnetic particles in insulating non-magnetic matrix is studied in detail. The case of strong magnetic dipole interaction and strong magnetic anisotropy of ferromagnetic granules is considered. The composite is modelled by a cubic regular array of ferromagnetic particles. The high-frequency permeability tensor components are found as a functions of frequency, temperature, ferromagnetic phase content, and magnetic anisotropy. The results demonstrate that magnetic dipole interaction leads to a shift of the resonance frequencies towards higher values, and nanocomposite film could have rather high value of magnetic permeability in the microwave range.

  19. Spin ensembles as sensitive probes of environmental magnetic field noise

    NASA Astrophysics Data System (ADS)

    Asfaw, Abraham; Wolfowicz, Gary; Morton, John J. L.; Tyryshkin, Alexei; Lyon, Stephen

    2015-03-01

    Environmental magnetic field noise makes quantum control of electron and nuclear spins difficult. Conversely, the sensitivity of spins to small magnetic fields implies that they can be used as sensitive probes of magnetic field fluctuations. We report spin resonance measurements of donors in silicon showing that the phase information in single-shot measurements of spin ensembles combined with quadrature detection can yield useful information about environmental noise. By measuring the accumulated phase statistics with time, we extract the power spectrum of the environmental magnetic field noise. The range of noise frequencies probed in this way is set by the magnetic moment of the spins. We measure the noise power spectrum at high frequencies (100 Hz - 10 kHz) using electron spins and at low frequencies (1 - 100 Hz) using nuclear spins. We also show that a broadband measurement of the noise power spectrum can be obtained by tuning the magnetic moment of electron spins in bismuth donors over a wide range from 0.01 to 1 electron magnetic moment. Our method, which uses the full statistics of the accumulated phase, can be viewed as complementary to existing dynamical decoupling schemes which use filter functions to probe the noise power spectrum.

  20. Saturn's Magnetospheric Engine: The Magnetic Flux Return Cycle

    NASA Astrophysics Data System (ADS)

    Russell, C. T.; Leisner, J. S.; Khurana, K. K.; Kurth, W. S.; Arridge, C. S.; Dougherty, M. K.

    2005-08-01

    The ubiquitous ion cyclotron waves in the quiescent E-ring torus from about 4 to 6 Rs signals the strong mass loading of the plasma torus via the pickup of water-group ions. To achieve a steady state the ions must be transported to a region in which they can be removed from the system. Since Saturn is a rapidly rotating gas giant, with a sizeable magnetic moment, the centrifugal force of the added plasma can reach values sufficient to cause radial, outward transport of the mass-laden flux tubes. These tubes must eventually reach the tail and, through reconnection, dump their load of ions down the tail. While this process removes ions, it alone does not maintain steady state because magnetic flux has been removed from the inner magnetosphere. To return magnetic flux to the inner magnetosphere requires moving emptied flux tubes inward against the centrifugally driven outward flux. We have identified such empty flux tubes on several occasions. They are warmer than the surrounding plasma and more dipolar, consistent with their lower mass content. We believe these emptied flux tubes complete the magnetic flux return cycle, replacing the magnetic flux carried away by the mass-loaded flux tubes.

  1. Magnetic Flux Erosion and Redistribution during CME Propagation

    NASA Astrophysics Data System (ADS)

    Lavraud, B.; Ruffenach, A.; Manchester, W.; Farrugia, C. J.; Demoulin, P.; Dasso, S.; Sauvaud, J. A.; Rouillard, A. P.; Foullon, C.; Owens, M. J.; Savani, N.; Kajdic, P.; Luhmann, J. G.; Galvin, A. B.

    2014-12-01

    We will review recent works which highlight the occurrence of magnetic flux erosion and redistribution at the front of coronal mass ejections (when they have the structure of a well-defined magnetic cloud). Two main processes have been found and will be presented. The first comes from the occurrence of magnetic reconnection between the magnetic cloud and its sheath ahead, leading to magnetic flux erosion and redistribution, with associated large scale topological changes. The second may occur when dense filament material in the coronal mass ejection pushes its way through the structure and comes in direct contact with the shocked plasma in the sheath ahead. This leads to diverging non-radial flows in front of the CME which transport poloidal flux of the flux rope to the sides of the magnetic cloud.

  2. Improvement of the superconducting magnetic levitation system for the determination of the magnetic flux quantum

    SciTech Connect

    Endo, T.; Sakamoto, Y. (Electrotechnical Lab., 1-1-4 Umezono, Tsukuba-shi, Ibaraki 305 (JP)); Shiota, F.; Nakayama, K.; Nezu, Y. (National Research Lab. of Metrology, Tsukuba-shi, Ibaraki (JP)); Kikuzawa, M.; Hara, K. (Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino-shi, Chiba 275 (JP))

    1989-04-01

    The authors describe an improvement of the preliminary superconducting magnetic levitation system in progress for the absolute determination of the magnetic flux quantum. This improvement includes the development of the flux-up method to determine the flux in terms of the Josephson voltage. The improvement is essential for the determination of the magnetic flux quantum as well as of the coil current in terms of the Josephson voltage and quantized Hall resistance.

  3. Flux Leakage Measurements for Defect Characterization Using a High Precision 3-AXIAL Gmr Magnetic Sensor

    NASA Astrophysics Data System (ADS)

    Pelkner, M.; Blome, M.; Reimund, V.; Thomas, H.-M.; Kreutzbruck, M.

    2011-06-01

    High-precision magnetic field sensors are of increasing interest in non destructive testing (NDT). In particular GMR-sensors (giant magneto resistance) are qualified because of their high sensitivity, high signal-to-noise ratio and high spatial resolution. With a GMR-gradiometer and a 3D-GMR-magnetometer we performed magnetic flux leakage measurements of artificial cracks and cracks of a depth of ?50 ?m still could be dissolved with a sufficient high signal-to-noise ratio. A semi-analytic magnetic dipole model that allows realistic GMR sensor characteristics to be incorporated is used for swiftly predicting magnetic stray fields. The reliable reconstruction based on measurements of artificial rectangular-shaped defects is demonstrated.

  4. Forecasting the solar photospheric magnetic field using solar flux transport model and local ensemble Kalman filtering

    NASA Astrophysics Data System (ADS)

    Zhang, Ying; Du, Aimin; Feng, Xueshang

    2015-04-01

    Accurate forecasting the solar photospheric magnetic field distribution play an important role in the estimates of the inner boundary conditions of the coronal and solar wind model. Forecasting solar photospheric magnetic field using the solar flux transport (SFT) model can achieve an acceptable match to the actual field. The observations from ground-based or spacecraft instruments can be assimilated to update the modeled flux. The local ensemble Kalman filtering (LEnKF) method is utilized to improve forecasts and characterize their uncertainty by propagating the SFT model with different model parameters forward in time to control the evolution of the solar photospheric magnetic field. Optimal assimilation of measured data into the ensemble produces an improvement in the fit of the forecast to the actual field. Our approach offers a method to improve operational forecasting of the solar photospheric magnetic field. The LEnKF method also allows sensitivity analysis of the SFT model to noise and uncertainty within the physical representation.

  5. Vortex Avalanches and Magnetic Flux Fragmentation in Superconductors

    SciTech Connect

    Aranson, Igor; Gurevich, Alex; Vinokur, Valerii

    2001-08-06

    We report the results of numerical simulations of nonisothermal dendritic flux penetration in type-II superconductors. We propose a generic mechanism of dynamic branching of a propagating hot spot of a flux flow/normal state triggered by a local heat pulse. The branching occurs when the flux hot spot reflects from inhomogeneities or the boundary on which magnetization currents either vanish, or change direction. The hot spot then undergoes a cascade of successive splittings, giving rise to a dissipative dendritic-type flux structure. This dynamic state eventually cools down, turning into a frozen multifilamentary pattern of magnetization currents.

  6. Low noise design of perpendicular magnetic recording media

    NASA Astrophysics Data System (ADS)

    Honda, Naoki; Ouchi, Kazuhiro

    2001-10-01

    The basic comprehensive design for low noise perpendicular magnetic recording media is studied. High squareness in perpendicular M-H loop and reduced magnetic domain size are the key properties for media with a low noise property. High squareness also favors thermal stability of recorded magnetization. Co-Cr based alloys are expected to be the candidate material for high recording density media far beyond 100 Gbit/in 2 recording in terms of thermal issue while alternative materials with higher anisotropy should be introduced for the media aimed at 1 Tbit/in 2. Reducing the domain size is the present issue for decreasing medium noise in double layered media. Although it is superficially contradictory to the low noise condition, the slope of the M-H loop should be kept steep to obtain a high recording performance. Paradigm shift from simple magnetic decoupling in the design of such media might be required.

  7. Magnetic Flux Paradigm for Radio Loudness of Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Sikora, Marek; Begelman, Mitchell C.

    2013-02-01

    We argue that the magnetic flux threading the black hole (BH), rather than BH spin or Eddington ratio, is the dominant factor in launching powerful jets and thus determining the radio loudness of active galactic nuclei (AGNs). Most AGNs are radio quiet because the thin accretion disks that feed them are inefficient in depositing magnetic flux close to the BH. Flux accumulation is more likely to occur during a hot accretion (or thick disk) phase, and we argue that radio-loud quasars and strong emission-line radio galaxies occur only when a massive, cold accretion event follows an episode of hot accretion. Such an event might be triggered by the merger of a giant elliptical galaxy with a disk galaxy. This picture supports the idea that flux accumulation can lead to the formation of a so-called magnetically choked accretion flow. The large observed range in radio loudness reflects not only the magnitude of the flux pressed against the BH, but also the decrease in UV flux from the disk, due to its disruption by the "magnetosphere" associated with the accumulated flux. While the strongest jets result from the secular accumulation of flux, moderate jet activity can also be triggered by fluctuations in the magnetic flux deposited by turbulent, hot inner regions of otherwise thin accretion disks, or by the dissipation of turbulent fields in accretion disk coronae. These processes could be responsible for jet production in Seyferts and low-luminosity AGNs, as well as jets associated with X-ray binaries.

  8. Magnetic flux pumping and the structure of a sunspot penumbra

    NASA Astrophysics Data System (ADS)

    Thomas, J. H.; Weiss, N. O.; Tobias, S. M.; Brummell, N. H.

    2002-07-01

    We propose an overall scenario for the development and maintenance of a sunspot penumbra, in which turbulent magnetic flux pumping plays a key role. Recent high-resolution observations have revealed arched, "returning" magnetic flux tubes that emerge in the inner or middle penumbra, dive back down below the solar surface near the outer edge of the penumbra, and carry much of the Evershed flow. Some mechanism is required to keep the outer parts of the returning flux tubes submerged in spite of their magnetic buoyancy. We have proposed that the relevant mechanism is downward turbulent pumping of magnetic flux by granular convection in the moat outside the sunspot. This mechanism is demonstrated by means of an appropriate three-dimensional numerical simulation of turbulent compressible convection in the strongly superadiabatic granulation layer. We suggest that a penumbra first forms through a convectively driven instability at the outer edge of a growing pore. The nonlinear development of this instability pUSA)roduces the filamentary penumbra with its interlocking-comb magnetic field geometry. Downward flux pumping of some of the nearly horizontal magnetic flux in the dark filaments produces the returning flux tubes, with their associated Evershed flow, and also establishes the subcritical nature of the bifurcation that produces the filamentary penumbra, which explains why there are pores larger than the smallest sunspots.

  9. Magnetic flux tubes as sources of wave generation

    NASA Technical Reports Server (NTRS)

    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.

  10. Characteristics of Ionospheric Magnetic Flux Ropes on Venus

    NASA Astrophysics Data System (ADS)

    Steichen, Elise; McEnulty, T. R.; Molaverdikhani, K.; Brain, D.; Zhang, T.

    2013-10-01

    Because Venus has no intrinsic magnetic field, its atmosphere is more directly exposed to the solar wind than an atmosphere of a magnetized planet such as Earth. One observed consequence of this solar wind-atmosphere interaction is the presence of magnetic flux ropes, approximately cylindrical structures consisting of twisted magnetic field lines. The central region of a flux rope contains current that can transport charged particles and may therefore aid in atmospheric escape from Venus. Flux ropes in the ionosphere are observed more often during solar maximum periods, when increased photoionization creates an ionospheric thermal pressure sufficient to exclude the solar wind magnetic field. Despite the discovery of flux ropes more than 30 years ago and the availability of new observations since the arrival of Venus Express (VEX) in 2006, the formation mechanism for ionospheric flux ropes is still unresolved. We present the results of a manual survey of magnetic field data from the VEX magnetometer (MAG) for magnetic flux ropes, which present as localized peaks in magnetic field strength with field rotations consistent with flux rope geometry. We survey data from evenly spaced month-long time intervals from 2006 - 2012 to examine the effects of different stages of the solar cycle on flux rope properties such as location, half-length, and orientation relative to the planet. We present trends in the properties of observed flux ropes, how they are affected by the solar wind, and how they compare to previous results. This research is supported by a NASA Venus Express Supporting Investigator grant.

  11. How to characterize soft magnetic materials by measuring magnetic flux density in a rotating field apparatus

    Microsoft Academic Search

    Y. Azzouz; A. Mouillet

    2002-01-01

    This paper deals with the characterization of the magnetic permeability of soft magnetic materials under a rotating magnetic field. The paper reviews the principle of the rotating-flux-density device used for measurement of flux density, then describes the mathematical method used to calculate permeability from the measurements. The method combines direct and inverse solutions and is based on a functional minimization

  12. Magnetohydrodynamic simulations of the ejection of a magnetic flux rope

    NASA Astrophysics Data System (ADS)

    Pagano, P.; Mackay, D. H.; Poedts, S.

    2013-06-01

    Context. Coronal mass ejections (CME's) are one of the most violent phenomena found on the Sun. One model to explain their occurrence is the flux rope ejection model. In this model, magnetic flux ropes form slowly over time periods of days to weeks. They then lose equilibrium and are ejected from the solar corona over a few hours. The contrasting time scales of formation and ejection pose a serious problem for numerical simulations. Aims: We simulate the whole life span of a flux rope from slow formation to rapid ejection and investigate whether magnetic flux ropes formed from a continuous magnetic field distribution, during a quasi-static evolution, can erupt to produce a CME. Methods: To model the full life span of magnetic flux ropes we couple two models. The global non-linear force-free field (GNLFFF) evolution model is used to follow the quasi-static formation of a flux rope. The MHD code ARMVAC is used to simulate the production of a CME through the loss of equilibrium and ejection of this flux rope. Results: We show that the two distinct models may be successfully coupled and that the flux rope is ejected out of our simulation box, where the outer boundary is placed at 2.5 R?. The plasma expelled during the flux rope ejection travels outward at a speed of 100 km s-1, which is consistent with the observed speed of CMEs in the low corona. Conclusions: Our work shows that flux ropes formed in the GNLFFF can lead to the ejection of a mass loaded magnetic flux rope in full MHD simulations. Coupling the two distinct models opens up a new avenue of research to investigate phenomena where different phases of their evolution occur on drastically different time scales. Movies are available in electronic form at http://www.aanda.org

  13. Signal Photon Flux and Background Noise in a Coupling Electromagnetic Detecting System for High Frequency Gravitational Waves

    E-print Network

    F. Y. Li; N. Yang; Z. Y. Fang; R. M. L. Baker Jr.; G. V. Stephenson; H. Wen

    2010-06-17

    A coupling system between Gaussian type-microwave photon flux, static magnetic field and fractal membranes (or other equivalent microwave lenses) can be used to detect high-frequency gravitational waves (HFGWs) in the microwave band. We study the signal photon flux, background photon flux and the requisite minimal accumulation time of the signal in the coupling system. Unlike pure inverse Gertsenshtein effect (G-effect) caused by the HFGWs in the GHz band, the the electromagnetic (EM) detecting scheme (EDS) proposed by China and the US HFGW groups is based on the composite effect of the synchro-resonance effect and the inverse G-effect. Key parameters in the scheme include first-order perturbative photon flux (PPF) and not the second-order PPF; the distinguishable signal is the transverse first-order PPF and not the longitudinal PPF; the photon flux focused by the fractal membranes or other equivalent microwave lenses is not only the transverse first-order PPF but the total transverse photon flux, and these photon fluxes have different signal-to-noise ratios at the different receiving surfaces. Theoretical analysis and numerical estimation show that the requisite minimal accumulation time of the signal at the special receiving surfaces and in the background noise fluctuation would be $\\sim10^3-10^5$ seconds for the typical laboratory condition and parameters of $h_{r.m.s.}\\sim10^{-26}-10^{-30}$ at 5GHz with bandwidth $\\sim$1Hz. In addition, we review the inverse G-effect in the EM detection of the HFGWs, and it is shown that the EM detecting scheme based only on the pure inverse G-effect in the laboratory condition would not be useful to detect HFGWs in the microwave band.

  14. Longitudinal variations of the magnetic flux in the heliosphere

    NASA Astrophysics Data System (ADS)

    Dósa, Melinda; Erd?s, Géza

    2015-04-01

    The heliospheric magnetic flux is determined from the radial component of the magnetic field vector measured onboard interplanetary space probes. Earlier Ulysses research has shown remarkable independence of the flux from heliographic latitude. Here we investigate whether any longitudinal variation exist in the 50 year long OMNI magnetic data set. When determining the heliographic longitude of the plasma source, correction was applied for the solar wind travel time. Significant recurrent enhancements of the magnetic flux was observed during the declining phase of the solar cycles. These flux enhancements are associated with co-rotating interaction regions (CIRs), lasting several years. The recurrence period equals the equatorial rotation period of the Sun. The same, long lasting recurring features can be observed in the deviation angle of the solar wind velocity vector from the radial direction. However, the deviation angle is small, in the order of few degrees, which cannot account for the observed flux increases. An increase of the magnetic field is clearly caused by the plasma compression associated to CIRs, however the increase of the radial component is not obvious. It is suggested that the origin of that increase is caused by the compression of the plasma in the direction perpendicular to the Parker field line rather than the radial direction. The longitudinal variation of the magnetic flux during the declining phase of the solar cycle has impact on the modulation of cosmic rays as well as on the frequency and intensity of space weather events.

  15. Magnetic flux ropes in the Venus ionosphere - Observations and models

    NASA Astrophysics Data System (ADS)

    Elphic, R. C.; Russell, C. T.

    1983-01-01

    Pioneer Venus Orbiter data are used as evidence of naturally occurring magnetic field filamentary structures which can be described by a flux rope model. The solar wind is interpreted as piling up a magnetic field on the Venus ionosphere, with the incident ram pressure being expressed as magnetic field pressure. Currents flowing at the ionopause shield out the field, allowing magnetic excursions to be observed with magnitudes of tens of nT over an interval of a few seconds. A quantitative assessment is made of the signature expected from a flux rope. It is noted that each excursion of the magnetic field detected by the Orbiter magnetometer was correlated with variations in the three components of the field. A coordinate system is devised which shows that the Venus data is indicative of the presence of flux ropes whose parameters are the coordinates of the system and would yield the excursions observed in the spacecraft crossings of the fields.

  16. Triggering of Remote Flares by Magnetic Flux Emergence

    E-print Network

    Fu, Yixing

    2015-01-01

    We study the effect of new emerging solar active regions on the large-scale magnetic environment of existing regions. We first present a theoretical approach to quantify the "interaction energy" between new and pre-existing regions as the difference between (i) the summed magnetic energies of their individual potential fields and (ii) the energy of their superposed potential fields. We expect that this interaction energy can, depending upon the relative arrangements of newly emerged and pre-existing magnetic flux, indicate the existence of "topological" free magnetic energy in the global coronal field that is independent of any "internal" free magnetic energy due to coronal electric currents flowing within the newly emerged and pre-existing flux systems. We then examine the interaction energy in two well-studied cases of flux emergence, but find that the predicted energetic perturbation is relatively small compared to energies released in large solar flares. Next, we present an observational study on the infl...

  17. Localization of metal-induced gap states at the metal-insulator interface: Origin of flux noise in SQUIDs and superconducting qubits

    SciTech Connect

    Choi, SangKook; Lee, Dung-Hai; Louie, Steven G.; Clarke, John

    2009-10-10

    The origin of magnetic flux noise in Superconducting Quantum Interference Devices with a power spectrum scaling as 1/f (f is frequency) has been a puzzle for over 20 years. This noise limits the decoherence time of superconducting qubits. A consensus has emerged that the noise arises from fluctuating spins of localized electrons with an areal density of 5 x 10(17)m(-2). We show that, in the presence of potential disorder at the metal-insulator interface, some of the metal-induced gap states become localized and produce local moments. A modest level of disorder yields the observed areal density.

  18. Magnetic flux generation and transport in cool stars

    NASA Astrophysics Data System (ADS)

    I??k, E.; Schmitt, D.; Schüssler, M.

    2011-04-01

    Context. 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. Aims: By employing physical models, we study the spatial and temporal characteristics of the observable surface field for various stellar parameters. Methods: We combine models for magnetic flux generation, buoyancy instability, and transport, which encompass the entire convection zone. The model components are: (i) a thin-layer ?? dynamo at the base of the convection zone; (ii) 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 (iii) horizontal flux transport at the surface. Results: For solar-type stars and rotation periods longer than about 10 days, the latitudinal dynamo waves generated by the deep-seated ?? dynamo are faithfully reflected by the surface distribution of magnetic flux. For rotation periods of the order of two days, however, Coriolis acceleration of rising flux loops leads to surface flux emergence at much higher latitudes than the dynamo waves at the bottom of the convection zone reach. A similar result is found for a K0V star with a rotation period of two days. In the case of a rapidly rotating K1 subgiant, overlapping dynamo waves lead to noisy activity cycles and mixed-polarity fields at high latitudes. Conclusions: The combined model reproduces the basic observed features of the solar cycle. The differences between the latitude distributions of the magnetic field at the bottom of the convection zone and the emerging surface flux grow with increasing rotation rate and convection zone depth, becoming quite substantial for rapidly rotating dwarfs and subgiants. The dynamical evolution of buoyantly rising magnetic flux should be considered as an essential ingredient in stellar dynamo models. 3 movies are only available in electronic form at http://www.aanda.org

  19. How to Measure Magnetic Flux with a Single Position Measurement?

    E-print Network

    Yakir Aharonov; Eliahu Cohen

    2014-08-29

    Current methods for measuring magnetic flux are based on performing many measurements over a large ensemble of electrons. We propose a novel method for measuring the flux modulo hc/e using only a single electron. Furthermore, we show, for the first time, how to understand this result on geometric grounds when utilizing only the quantization of angular momentum. A transformation to a rotating frame of reference reveals the nonlocal effect of magnetic flux on the electron, without the need of solving the Schrodinger equation. This provides a new intuition for understanding the Aharonov-Bohm (AB) effect.

  20. Is magnetic flux quantized inside a solenoid?

    E-print Network

    F. Darabi

    2009-01-13

    In some textbooks on quantum mechanics, the description of flux quantization in a superconductor ring based on the Aharonov-Bohm effect may lead some readers to a (wrong) conclusion that flux quantization occurs as well for a long solenoid with the same quantization condition in which the charge of cooper pair $2e$ is replaced by the charge of one electron $e$. It is shown how this confusion arises and how can one avoid it.

  1. A nonpotential model for the Sun's open magnetic flux

    Microsoft Academic Search

    A. R. Yeates; D. H. Mackay; A. A. van Ballegooijen; J. A. Constable

    2010-01-01

    Measurements of the interplanetary magnetic field (IMF) over several solar cycles do not agree with computed values of open magnetic flux from potential field extrapolations. The discrepancy becomes greater around solar maximum in each cycle when the IMF can be twice as strong as predicted by the potential field model. Here we demonstrate that this discrepancy may be resolved by

  2. Magnetic Flux Dynamics in Horizontally Cooled Superconducting Cavities

    E-print Network

    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...

  3. Sigmoidal equilibria and eruptive instabilities in laboratory magnetic flux ropes

    NASA Astrophysics Data System (ADS)

    Myers, C. E.; Yamada, M.; Belova, E.; Ji, H.; Yoo, J.

    2013-12-01

    The Magnetic Reconnection Experiment (MRX) has recently been modified to study quasi-statically driven line-tied magnetic flux ropes in the context of storage-and-release eruptions in the corona. Detailed in situ magnetic measurements and supporting MHD simulations permit quantitative analysis of the plasma behavior. We find that the behavior of these flux ropes depends strongly on the properties of the applied potential magnetic field arcade. For example, when the arcade is aligned parallel to the flux rope footpoints, force free currents induced in the expanding rope modify the pressure and tension in the arcade, resulting in a confined, quiescent discharge with a saturated kink instability. When the arcade is obliquely aligned to the footpoints, on the other hand, a highly sigmoidal equilibrium forms that can dynamically erupt (see Fig. 1 and Fig. 2). To our knowledge, these storage-and-release eruptions are the first of their kind to be produced in the laboratory. A new 2D magnetic probe array is used to map out the internal structure of the flux ropes during both the storage and the release phases of the discharge. The kink instability and the torus instability are studied as candidate eruptive mechanisms--the latter by varying the vertical gradient of the potential field arcade. We also investigate magnetic reconnection events that accompany the eruptions. The long-term objective of this work is to use internal magnetic measurements of the flux rope structure to better understand the evolution and eruption of comparable structures in the corona. This research is supported by DoE Contract Number DE-AC02-09CH11466 and by the Center for Magnetic Self-Organization (CMSO). Qualitative sketches of flux ropes formed in (1) a parallel potential field arcade; and (2) an oblique potential field arcade. One-dimensional magnetic measurements from (1) a parallel arcade discharge that is confined; and (2) an oblique arcade discharge that erupts.

  4. Fluctuation-dissipation theorem and flux noise in overdamped Josephson-junction arrays

    Microsoft Academic Search

    S. E. Korshunov; L. D. Landau

    2002-01-01

    The form of the fluctuation-dissipation theorem for a resistively shunted\\u000aJosephson juction array is derived with the help of the method which\\u000aexplicitely takes into acoount screening effects. This result is used to\\u000aexpress the flux noise power spectrum in terms of frequency dependent sheet\\u000aimpedance of the array. The relation between noise amplitude and parameters of\\u000athe detection coil

  5. RATES OF PHOTOSPHERIC MAGNETIC FLUX CANCELLATION MEASURED WITH HINODE

    SciTech Connect

    Park, Soyoung; Chae, Jongchul [Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Republic of Korea (Korea, Republic of); Litvinenko, Yuri E. [Department of Mathematics, University of Waikato, P.O. Box 3105, Hamilton (New Zealand)

    2009-10-10

    Photospheric magnetic flux cancellation on the Sun is generally believed to be caused by magnetic reconnection occurring in the low solar atmosphere. Individual canceling magnetic features are observationally characterized by the rate of flux cancellation. The specific cancellation rate, defined as the rate of flux cancellation divided by the interface length, gives an accurate estimate of the electric field in the reconnecting current sheet. We have determined the specific cancellation rate using the magnetograms taken by the Solar Optical Telescope (SOT) aboard the Hinode satellite. The specific rates determined with SOT turned out to be systematically higher than those based on the data taken by the Michelson Doppler Imager (MDI) aboard the Solar and Heliospheric Observatory. The median value of the specific cancellation rate was found to be 8 x 10{sup 6} G cm s{sup -1}-a value four times that obtained from the MDI data. This big difference is mainly due to a higher angular resolution and better sensitivity of the SOT, resulting in magnetic fluxes up to five times larger than those obtained from the MDI. The higher rates of flux cancellation correspond to either faster inflows or stronger magnetic fields of the reconnection inflow region, which may have important consequences for the physics of photospheric magnetic reconnection.

  6. Magnetic helicity fluxes and their effect on stellar dynamos

    NASA Astrophysics Data System (ADS)

    Candelaresi, Simon; Brandenburg, Axel

    2012-07-01

    Magnetic helicity fluxes in turbulently driven ?2 dynamos are studied to demonstrate their ability to alleviate catastrophic quenching. A one-dimensional mean-field formalism is used to achieve magnetic Reynolds numbers of the order of 105. We study both diffusive magnetic helicity fluxes through the mid-plane as well as those resulting from the recently proposed alternate dynamic quenching formalism. By adding shear we make a parameter scan for the critical values of the shear and forcing parameters for which dynamo action occurs. For this ?? dynamo we find that the preferred mode is antisymmetric about the mid-plane. This is also verified in 3-D direct numerical simulations.

  7. Structure of sunspot penumbrae - Fallen magnetic flux tubes

    NASA Technical Reports Server (NTRS)

    Wentzel, Donat G.

    1992-01-01

    A model is presented of a sunspot penumbra involving magnetic flux tubes that have fallen into the photosphere and float there. An upwelling at the inner end of a fallen tube continuously provides additional gas. This gas flows along and lengthens the tube and is observable as the Evershed flow. Fallen flux tubes may appear as bright streaks near the upwelling, but they become dark filaments further out. The model is corroborated by recent optical high-resolution magnetic data regarding the penumbral filaments, by the 12-micron magnetic measurements relevant to the height of the temperature minimum, and by photographs of the umbra/penumbra boundary.

  8. Flow instabilities of magnetic flux tubes. IV. Flux storage in the solar overshoot region

    NASA Astrophysics Data System (ADS)

    I??k, E.; Holzwarth, V.

    2009-12-01

    Context: Flow-induced instabilities of magnetic flux tubes are relevant to the storage of magnetic flux in the interiors of stars with outer convection zones. The stability of magnetic fields in stellar interiors is of importance to the generation and transport of solar and stellar magnetic fields. Aims: We consider the effects of material flows on the dynamics of toroidal magnetic flux tubes located close to the base of the solar convection zone, initially within the overshoot region. The problem is to find the physical conditions in which magnetic flux can be stored for periods comparable to the dynamo amplification time, which is of the order of a few years. Methods: We carry out nonlinear numerical simulations to investigate the stability and dynamics of thin flux tubes subject to perpendicular and longitudinal flows. We compare the simulations with the results of simplified analytical approximations. Results: The longitudinal flow instability induced by the aerodynamic drag force is nonlinear in the sense that the growth rate depends on the perturbation amplitude. This result is consistent with the predictions of linear theory. Numerical simulations without friction show that nonlinear Parker instability can be triggered below the linear threshold of the field strength, when the difference in superadiabaticity along the tube is sufficiently large. A localised downflow acting on a toroidal tube in the overshoot region leads to instability depending on the parameters describing the flow, as well as the magnetic field strength. We determined ranges of the flow parameters for which a linearly Parker-stable magnetic flux tube is stored in the middle of the overshoot region for a period comparable to the dynamo amplification time. Conclusions: The longitudinal flow instability driven by frictional interaction of a flux tube with its surroundings is relevant to determining the storage time of magnetic flux in the solar overshoot region. The residence time for magnetic flux tubes with 2 × 1021 Mx in the convective overshoot layer can be comparable to the dynamo amplification time, provided that the average speed and the duration of an external downflow do not exceed about 50 m s -1 and 100 days, respectively, and that the lateral extension of the flow is smaller than about 10°. Appendix C and movies are only available in electronic form at http://www.aanda.org

  9. The Solar Internetwork. I. Contribution to the Network Magnetic Flux

    NASA Astrophysics Data System (ADS)

    Goši?, M.; Bellot Rubio, L. R.; Orozco Suárez, D.; Katsukawa, Y.; del Toro Iniesta, J. C.

    2014-12-01

    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 × 1024 Mx day-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.

  10. Rapid magnetic flux variability on the flare star CN Leonis

    E-print Network

    Reiners, A; Liefke, C

    2007-01-01

    We present UVES/VLT observations of the nearby flare star CN Leo covering the Wing-Ford FeH band near 1mu with high spectral resolution. Some of the FeH absorption lines in this band are magnetically sensitive and allow a measurement of the mean magnetic flux on CN Leo. Our observations, covering three nights separated by 48 hours each, allow a clear detection of a mean magnetic field of Bf~2.2kG. The differential flux measurements show a night-to-night variability with extremely high significance. Finally, our data strongly suggest magnetic flux variability on time scales as low as 6 hours in line with chromospheric variability.

  11. Rapid magnetic flux variability on the flare star CN Leonis

    E-print Network

    A. Reiners; J. H. M. M. Schmitt; C. Liefke

    2007-03-08

    We present UVES/VLT observations of the nearby flare star CN Leo covering the Wing-Ford FeH band near 1mu with high spectral resolution. Some of the FeH absorption lines in this band are magnetically sensitive and allow a measurement of the mean magnetic flux on CN Leo. Our observations, covering three nights separated by 48 hours each, allow a clear detection of a mean magnetic field of Bf~2.2kG. The differential flux measurements show a night-to-night variability with extremely high significance. Finally, our data strongly suggest magnetic flux variability on time scales as low as 6 hours in line with chromospheric variability.

  12. Solar magnetic flux tube emergence diagram

    Microsoft Academic Search

    P. AmbroŽ; E. V. Kononovich

    1994-01-01

    It is emphasized that photospheric downdrafts represent the main feature common to both quit and active regions of the solar atmosphere. The results of the magnetic field transport velocity calculations are used to specify the convection zone magnetic structure. The concept of combined interface and convection dynamo is suggested. A time-spatial diagram is proposed to represent an active region evolution.

  13. Observations of magnetic flux ropes during magnetic reconnection in the Earth's magnetotail

    NASA Astrophysics Data System (ADS)

    Borg, A. L.; Taylor, M. G. G. T.; Eastwood, J. P.

    2012-05-01

    We present an investigation of magnetic flux ropes observed by the four Cluster spacecraft during periods of magnetic reconnection in the Earth's magnetotail. Using a list of 21 Cluster encounters with the reconnection process in the period 2001-2006 identified in Borg et al. (2012), we present the distribution and characteristics of the flux ropes. We find 27 flux ropes embedded in the reconnection outflows of only 11 of the 21 reconnection encounters. Reconnection processes associated with no flux rope observations were not distinguishable from those where flux ropes were observed. Only 7 of the 27 flux ropes show evidence of enhanced energetic electron flux above 50 keV, and there was no clear signature of the flux rope in the thermal particle measurements. We found no clear correlation between the flux rope core field and the prevailing IMF By direction.

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

    SciTech Connect

    Erd?s, 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.

  15. Magnetic Flux Density in the Heliosphere through Several Solar Cycles

    NASA Astrophysics Data System (ADS)

    Erd?s, G.; Balogh, A.

    2014-01-01

    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, BR , 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 BR to such an extent that the determination of the unsigned, open solar magnetic flux density from the average lang|BR |rang 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.

  16. Low-noise nano superconducting quantum interference device operating in Tesla magnetic fields.

    PubMed

    Schwarz, Tobias; Nagel, Joachim; Wölbing, Roman; Kemmler, Matthias; Kleiner, Reinhold; Koelle, Dieter

    2013-01-22

    Superconductivity in the cuprate YBa(2)Cu(3)O(7) (YBCO) persists up to huge magnetic fields (B) up to several tens of Teslas, and sensitive direct current (dc) superconducting quantum interference devices (SQUIDs) can be realized in epitaxially grown YBCO films by using grain boundary Josephson junctions (GBJs). Here we present the realization of high-quality YBCO nanoSQUIDs, patterned by focused ion beam milling. We demonstrate low-noise performance of such a SQUID up to B = 1 T applied parallel to the plane of the SQUID loop at the temperature T = 4.2 K. The GBJs are shunted by a thin Au layer to provide nonhysteretic current voltage characteristics, and the SQUID incorporates a 90 nm wide constriction which is used for on-chip modulation of the magnetic flux through the SQUID loop. The white flux noise of the device increases only slightly from 1.3 ??(0)/(Hz)(1/2) at B = 0 to 2.3 ??(0)/(Hz))(1/2) at 1 T. Assuming that a point-like magnetic particle with magnetization in the plane of the SQUID loop is placed directly on top of the constriction and taking into account the geometry of the SQUID, we calculate a spin sensitivity S(?)(1/2) = 62 ?(B)/(Hz))(1/2) at B = 0 and 110 ?(B)/(Hz))(1/2) at 1 T. The demonstration of low noise of such a SQUID in Tesla fields is a decisive step toward utilizing the full potential of ultrasensitive nanoSQUIDs for direct measurements of magnetic hysteresis curves of magnetic nanoparticles and molecular magnets. PMID:23252846

  17. Solar noise storms and magnetic sector structures

    Microsoft Academic Search

    R. T. Stewart

    1985-01-01

    A synoptic study of the occurrence and polarization of 160 MHz noise storms recorded at Culgoora during the current solar cycle shows that the storm sources occur in large unipolar cells extending more than 90 deg in solar longitude and less than about 60 deg in latitude, with lifetimes of about 1 yr. From solar maximum onwards these large cells

  18. Solar noise storms and magnetic sector structures

    Microsoft Academic Search

    R. T. Stewart

    1985-01-01

    A synoptic study of the occurrence and polarization of 160 MHz noise storms recorded at Culgoora during the current solar cycle shows that the storm sources occur in large unipolar cells extending >90° in solar longitude and ?60° in latitude, with lifetimes of ~ 1 yr. From solar maximum onwards these large cells stretch across the solar equator to form

  19. Geometric considerations of the evolution of magnetic flux ropes.

    PubMed

    Berdichevsky, D B; Lepping, R P; Farrugia, C J

    2003-03-01

    We use flux conservation and magnetohydrodynamics (MHD) theory to discuss essential differences in the nature of the evolution of two analytical solutions describing magnetic flux tubes evolving in time. The first of these maintains the elongation of the tube, while the second maintains a constant angular extension with respect to a possible pointlike source. In the first case, free expansion of the plasma (density N) occurs only in a direction perpendicular to the flux-tube x axis. In the second case, isotropic evolution is considered. In both cases it is assumed that at initial time t(0) the flux-tube B field is the force-free magnetostatic Lundquist solution, which energetically corresponds to the most stable state for any flux-tube structure. We show that for each case conservation of magnetic flux is enough to establish the scaling with time of the B field. While both expansions may correspond to the evolution of observed flux tubes in the heliosphere, the isotropic expansion appears to capture consistently essential features associated with the actual observations of expanding coronal mass ejections within 30 solar radii. For isotropic expansion of the plasma the force-free nature of the B field is preserved for all time. As an example the MHD solutions are applied to an interplanetary magnetic cloud observed with the spacecraft Wind, which passed Earth's vicinity on June 2, 1998. PMID:12689169

  20. Regression Models for Identifying Noise Sources in Magnetic Resonance Images.

    PubMed

    Zhu, Hongtu; Li, Yimei; Ibrahim, Joseph G; Shi, Xiaoyan; An, Hongyu; Chen, Yashen; Gao, Wei; Lin, Weili; Rowe, Daniel B; Peterson, Bradley S

    2009-06-01

    Stochastic noise, susceptibility artifacts, magnetic field and radiofrequency inhomogeneities, and other noise components in magnetic resonance images (MRIs) can introduce serious bias into any measurements made with those images. We formally introduce three regression models including a Rician regression model and two associated normal models to characterize stochastic noise in various magnetic resonance imaging modalities, including diffusion-weighted imaging (DWI) and functional MRI (fMRI). Estimation algorithms are introduced to maximize the likelihood function of the three regression models. We also develop a diagnostic procedure for systematically exploring MR images to identify noise components other than simple stochastic noise, and to detect discrepancies between the fitted regression models and MRI data. The diagnostic procedure includes goodness-of-fit statistics, measures of influence, and tools for graphical display. The goodness-of-fit statistics can assess the key assumptions of the three regression models, whereas measures of influence can isolate outliers caused by certain noise components, including motion artifacts. The tools for graphical display permit graphical visualization of the values for the goodness-of-fit statistic and influence measures. Finally, we conduct simulation studies to evaluate performance of these methods, and we analyze a real dataset to illustrate how our diagnostic procedure localizes subtle image artifacts by detecting intravoxel variability that is not captured by the regression models. PMID:19890478

  1. Evidence for Magnetic Flux Saturation in Rapidly Rotating M Stars

    E-print Network

    A. Reiners; G. Basri; M. Browning

    2008-10-28

    We present magnetic flux measurements in seven rapidly rotating M dwarfs. Our sample stars have X-ray and H-alpha emission indicative of saturated emission, i.e., emission at a high level independent of rotation rate. Our measurements are made using near-infrared FeH molecular spectra observed with HIRES at Keck. Because of their large convective overturn times, the rotation velocity of M stars with small Rossby numbers is relatively slow and does not hamper the measurement of Zeeman splitting. The Rossby numbers of our sample stars are as small as 0.01. All our sample stars exhibit magnetic flux of kilo-Gauss strength. We find that the magnetic flux saturates in the same regime as saturation of coronal and chromospheric emission, at a critical Rossby number of around 0.1. The filling factors of both field and emission are near unity by then. We conclude that the strength of surface magnetic fields remains independent of rotation rate below that; making the Rossby number yet smaller by a factor of ten has little effect. These saturated M-star dynamos generate an integrated magnetic flux of roughly 3 kG, with a scatter of about 1 kG. The relation between emission and flux also has substantial scatter.

  2. Absolute determination of the magnetic flux quantum using superconducting magnetic levitation

    Microsoft Academic Search

    F. Shiota; Y. Miki; A. Namba; Y. Nezu; Y. Sakamoto; T. Morokuma; K. Hara

    1995-01-01

    The current status of our superconducting magnetic levitation experiment for determining the magnetic flux quantum is described. The flux-up system has been improved significantly by using a Josephson voltage standard. Studies are also in progress to improve the mechanical measurement relevant to the floating body with the goal of reducing the uncertainty to less than 1 ppm

  3. Casimir interactions between magnetic flux tubes in a dense lattice

    NASA Astrophysics Data System (ADS)

    Mazur, Dan; Heyl, Jeremy S.

    2015-03-01

    We use the worldline numerics technique to study a cylindrically symmetric model of magnetic flux tubes in a dense lattice and the nonlocal Casimir forces acting between regions of magnetic flux. Within a superconductor the magnetic field is constrained within magnetic flux tubes and if the background magnetic field is on the order the quantum critical field strength, Bk=m/2 e =4.4 ×1013 Gauss, the magnetic field is likely to vary rapidly on the scales where QED effects are important. In this paper, we construct a cylindrically symmetric toy model of a flux tube lattice in which the nonlocal influence of QED on neighboring flux tubes is taken into account. We compute the effective action densities using the worldline numerics technique. The numerics predict a greater effective energy density in the region of the flux tube, but a smaller energy density in the regions between the flux tubes compared to a locally constant-field approximation. We also compute the interaction energy between a flux tube and its neighbors as the lattice spacing is reduced from infinity. Because our flux tubes exhibit compact support, this energy is entirely nonlocal and predicted to be zero in local approximations such as the derivative expansion. This Casimir-Polder energy can take positive or negative values depending on the distance between the flux tubes, and it may cause the flux tubes in neutron stars to form bunches. In addition to the above results we also discuss two important subtleties of determining the statistical uncertainties within the worldline numerics technique. Firstly, the distributions generated by the worldline ensembles are highly non-Gaussian, and so the standard error in the mean is not a good measure of the statistical uncertainty. Secondly, because the same ensemble of worldlines is used to compute the Wilson loops at different values of T and xcm, the uncertainties associated with each computed value of the integrand are strongly correlated. We recommend a form of jackknife analysis which deals with both of these problems.

  4. THE EVOLUTION OF OPEN MAGNETIC FLUX DRIVEN BY PHOTOSPHERIC DYNAMICS

    SciTech Connect

    Linker, Jon A.; Lionello, Roberto; Mikic, Zoran; Titov, Viacheslav S. [Predictive Science, Inc., 9990 Mesa Rim Road, Suite 170, San Diego, CA 92121-2910 (United States); Antiochos, Spiro K., E-mail: linkerj@predsci.com, E-mail: lionel@predsci.com, E-mail: mikicz@predsci.com, E-mail: titovv@predsci.com, E-mail: spiro.antiochos@nasa.gov [NASA Goddard Space Flight Center, NASA/GSFC Code 674, Greenbelt, MD 20771 (United States)

    2011-04-20

    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 coworkers, in the form of a conjecture, argued that truly isolated open flux cannot exist in a configuration with one heliospheric current sheet-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 20 R{sub sun} 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 detached coronal hole forms, in apparent violation of the Antiochos conjecture. Further investigation reveals that this detached coronal hole is actually linked to the extended coronal hole by a separatrix footprint on the photosphere of zero width. Therefore, the essential idea of the conjecture is preserved, if we modify it to state that coronal holes in the same polarity region are always linked, either by finite width corridors or separatrix footprints. The implications of these results for interchange reconnection and the sources of the slow solar wind are briefly discussed.

  5. The classical and quantum theory of thermal magnetic noise, with applications in spintronics and quantum microscopy

    Microsoft Academic Search

    JOHN A. SIDLES; JOSEPH L. GARBINI; WILLIAM M. DOUGHERTY; Shih-Hui Chao

    2003-01-01

    Thermal fluctuations generate magnetic noise in the vicinity of any conductive and\\/or magnetically permeable solid. This magnetic noise plays a fundamental role in the design of spintronic devices: namely, it sets the time scale during which electron spins retain their coherence. This paper presents a rigorous classical and quantum analysis of thermal magnetic noise, together with practical engineering examples. Starting

  6. Probing magnetization dynamics of strongly interacting magnetic nanoparticles through magnetoresistive current noise measurements

    NASA Astrophysics Data System (ADS)

    Taub, Nurit; Markovich, Gil

    2010-12-01

    The dependence of tunnelling current fluctuations on temperature and magnetic field was studied in an organically capped magnetite (Fe3O4) nanocrystal (NC) array deposited between 30 nm spaced gold electrodes. Low-frequency Lorentzian (random telegraph) noise was observed around the magnetization freezing temperature due to magnetic moment switching of the NCs under zero magnetic fields, diminishing with a saturating magnetic field. The temperature dependence of current fluctuations followed the temperature dependence of magnetic susceptibility. This work offers a new tool for locally studying collective magnetization dynamics in strongly interacting magnetic NC arrays.

  7. Three-dimensional prominence-hosting magnetic configurations: Creating a helical magnetic flux rope

    SciTech Connect

    Xia, C.; Keppens, R. [Centre for Mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven (Belgium); Guo, Y. [School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China)

    2014-01-10

    The magnetic configuration hosting prominences and their surrounding coronal structure is a key research topic in solar physics. Recent theoretical and observational studies strongly suggest that a helical magnetic flux rope is an essential ingredient to fulfill most of the theoretical and observational requirements for hosting prominences. To understand flux rope formation details and obtain magnetic configurations suitable for future prominence formation studies, we here report on three-dimensional isothermal magnetohydrodynamic simulations including finite gas pressure and gravity. Starting from a magnetohydrostatic corona with a linear force-free bipolar magnetic field, we follow its evolution when introducing vortex flows around the main polarities and converging flows toward the polarity inversion line near the bottom of the corona. The converging flows bring the feet of different loops together at the polarity inversion line, where magnetic reconnection and flux cancellation happen. Inflow and outflow signatures of the magnetic reconnection process are identified, and thereby the newly formed helical loops wind around preexisting ones so that a complete flux rope grows and ascends. When a macroscopic flux rope is formed, we switch off the driving flows and find that the system relaxes to a stable state containing a helical magnetic flux rope embedded in an overlying arcade structure. A major part of the formed flux rope is threaded by dipped field lines that can stably support prominence matter, while the total mass of the flux rope is in the order of 4-5× 10{sup 14} g.

  8. Disentangling the magnetic force noise contribution in LISA Pathfinder

    NASA Astrophysics Data System (ADS)

    Armano, M.; Audley, H.; Auger, G.; Baird, J.; Binetruy, P.; Born, M.; Bortoluzzi, D.; Brandt, N.; Bursi, A.; Caleno, M.; Cavalleri, A.; Cesarini, A.; Cruise, M.; Danzmann, K.; Diepholz, I.; Dolesi, R.; Dunbar, N.; Ferraioli, L.; Ferroni, V.; Fitzsimons, E.; Freschi, M.; Gallegos, J.; García Marirrodriga, C.; Gerndt, R.; Gesa, L. I.; Gibert, F.; Giardini, D.; Giusteri, R.; Grimani, C.; Harrison, I.; Heinzel, G.; Hewitson, M.; Hollington, D.; Hueller, M.; Huesler, J.; Inchauspé, H.; Jennrich, O.; Jetzer, P.; Johlander, B.; Karnesis, N.; Kaune, B.; Korsakova, N.; Killow, C.; Lloro, I.; Maarschalkerweerd, R.; Madden, S.; Mance, D.; Martín, V.; Martin-Porqueras, F.; Mateos, I.; McNamara, P.; Mendes, J.; Mendes, L.; Moroni, A.; Nofrarias, M.; Paczkowski, S.; Perreur-Lloyd, M.; Petiteau, A.; Pivato, P.; Plagnol, E.; Prat, P.; Ragnit, U.; Ramos-Castro, J.; Reiche, J.; Romera Perez, J. A.; Robertson, D.; Rozemeijer, H.; Russano, G.; Sarra, P.; Schleicher, A.; Slutsky, J.; Sopuerta, C. F.; Sumner, T.; Texier, D.; Thorpe, J.; Trenkel, C.; Tu, H. B.; Vitale, S.; Wanner, G.; Ward, H.; Waschke, S.; Wass, P.; Wealthy, D.; Wen, S.; Weber, W.; Wittchen, A.; Zanoni, C.; Ziegler, T.; Zweifel, P.

    2015-05-01

    Magnetically-induced forces on the inertial masses on-board LISA Pathfinder are expected to be one of the dominant contributions to the mission noise budget, accounting for up to 40%. The origin of this disturbance is the coupling of the residual magnetization and susceptibility of the test masses with the environmental magnetic field. In order to fully understand this important part of the noise model, a set of coils and magnetometers are integrated as a part of the diagnostics subsystem. During operations a sequence of magnetic excitations will be applied to precisely determine the coupling of the magnetic environment to the test mass displacement using the on-board magnetometers. Since no direct measurement of the magnetic field in the test mass position will be available, an extrapolation of the magnetic measurements to the test mass position will be carried out as a part of the data analysis activities. In this paper we show the first results on the magnetic experiments during an end- to-end LISA Pathfinder simulation, and we describe the methods under development to map the magnetic field on-board.

  9. Magnetic flux paradigm for radio-loudness of AGN

    E-print Network

    Sikora, Marek

    2013-01-01

    We argue that the magnetic flux threading the black hole, rather than black hole spin or Eddington ratio, is the dominant factor in launching powerful jets and thus determining the radio loudness of active galactic nuclei (AGN). Most AGN are radio quiet because the thin accretion disks that feed them are inefficient in depositing magnetic flux close to the black hole. Flux accumulation is more likely to occur during a hot accretion (or thick disk) phase, and we argue that radio-loud quasars and strong emission-line radio galaxies occur only when a massive, cold accretion event follows an episode of hot accretion. Such an event might be triggered by the merger of a giant elliptical galaxy with a disk galaxy. This picture supports the idea that flux accumulation can lead to the formation of a so-called magnetically choked accretion flow (MCAF). The large observed range in radio loudness reflects not only the magnitude of the flux pressed against the black hole, but also the decrease in UV flux from the disk, du...

  10. Properties of magnetic helicity flux in turbulent dynamos

    SciTech Connect

    Vishniac, Ethan T. [Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon SK S7N 5E2 (Canada); Shapovalov, Dmitry, E-mail: ethan.vishniac@usask.ca, E-mail: dmsh@jhu.edu [Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218 (United States)

    2014-01-10

    We study the flux of small-scale magnetic helicity in simulations of driven statistically homogeneous magnetohydrodynamic turbulence in a periodic box with an imposed large-scale shear. The simulations show that in the regime of strong dynamo action the eddy-scale magnetic helicity flux has only two significant terms: advective motion driven by the large-scale velocity field and the Vishniac-Cho (VC) flux which moves helicity across the magnetic field lines. The contribution of all the other terms is negligible. The VC flux is highly correlated with the large-scale electromotive force and is responsible for large-scale dynamo action, while the advective term is not. The VC flux is driven by the anisotropy of the turbulence. We derive analytical expressions for it in terms of the small-scale velocity or magnetic field. These expressions are used to predict the existence and strength of dynamo action for different turbulent anisotropies and tested against the results of the simulations.

  11. Simulations of emerging magnetic flux. I. The formation of stable coronal flux ropes

    SciTech Connect

    Leake, James E. [College of Science, George Mason University, 4400 University Drive, Fairfax, VA 22030 (United States); Linton, Mark G. [US Naval Research Laboratory 4555 Overlook Ave., SW Washington, DC 20375 (United States); Török, Tibor, E-mail: jleake@gmu.edu [Predictive Science Inc., 9990 Mesa Rim Rd., Ste. 170, San Diego, CA 92121 (United States)

    2013-12-01

    We present results from three-dimensional visco-resistive magnetohydrodynamic simulations of the emergence of a convection zone magnetic flux tube into a solar atmosphere containing a pre-existing dipole coronal field, which is orientated to minimize reconnection with the emerging field. We observe that the emergence process is capable of producing a coronal flux rope by the transfer of twist from the convection zone, as found in previous simulations. We find that this flux rope is stable, with no evidence of a fast rise, and that its ultimate height in the corona is determined by the strength of the pre-existing dipole field. We also find that although the electric currents in the initial convection zone flux tube are almost perfectly neutralized, the resultant coronal flux rope carries a significant net current. These results suggest that flux tube emergence is capable of creating non-current-neutralized stable flux ropes in the corona, tethered by overlying potential fields, a magnetic configuration that is believed to be the source of coronal mass ejections.

  12. Jump-noise process-driven magnetization dynamics and random switching of magnetization

    NASA Astrophysics Data System (ADS)

    Liu, Z.; Lee, A.; Bertotti, G.; Serpico, C.; Mayergoyz, I.

    2012-04-01

    The Landau-Lifshitz equation driven by a jump-noise process is applied to the study of thermal magnetization switching for a very wide range of temperatures. It is demonstrated that at very low temperatures, magnetization switching deviates from the prediction of thermal activation theory and exhibits some features that have been traditionally attributed to the phenomena of "macroscopic tunneling" of magnetization.

  13. Magnetic-flux induced persistent currents in quasiperiodic mesoscopic rings

    NASA Astrophysics Data System (ADS)

    Hu, X. F.; Peng, R. W.; Cao, L. S.; Huang, X. Q.; Wang, Mu; Hu, A.; Jiang, S. S.

    2005-05-01

    Under the tight-binding approximation, we study the persistent current (PC) in the magnetic-flux-threaded mesoscopic ring which is constructed according to the Fibonacci-class model. It is shown that the energy spectra form band structures and the subbands present a self-similarity. The PC is determined by the magnetic flux, the site energy, and the Fermi level. It is found that the large PC can be observed if the Fermi level reaches a specific value. Our investigation provides detailed information on the structural influence on the PC and contributes a mechanism to understand the large PC observed in the experiments.

  14. Correlation of magnetostriction variation on magnetic loss and noise for power transformer

    NASA Astrophysics Data System (ADS)

    Cheng, Shan-Jen; Liu, Jui-Jung; Chang, Yeong-Hwa; Fu, Chao-Ming; Hsu, Chang-Hung; Lee, Chun-Yao; Chang, Chia-Wen

    2015-05-01

    Magnetostriction (MS)-caused strain in single-phase three-legged cores with different core cutting forms, which suffer from induced magnetic loss and noise, was studied. It is found that adopting each different core form types induces magnetostriction ? variation in a transformer core operating with a high-frequency AC signal. The results are compared with finite element analysis simulations. It is also indicated that magnetostriction ? variations are significant in the rolling direction and along limbs and yokes. In this paper, it is proposed that core corner sides and T-joint parts without cutting structure, the core exhibits lower core loss and lower heat dissipation due to the fact that the magnetic flux that passes through corner sides shows lower magnetostriction variation. The magnetic properties resulting from magnetostriction variation in core loss and heat dissipation phenomena are significantly different from other core forms because of stronger contributions from magnetostatic forces. The main contribution for reducing core loss and noise, making them much less in corner numbers and cutting-fabricated forms, can be expected to come from lower magnetic flux and magnetostriction variation.

  15. PARTICLE MOTION ON MAGNETIC FLUX SURFACES IN \\

    Microsoft Academic Search

    S. A. Colgate; H. P. Furth; C. W. Hartman; R. L. Spoerlein

    1961-01-01

    The stability and particle confinement properties of axial-field-; centered and hard-core linear pinches are studied. A weak, externally produced ; electron beam is passed along the pinch discharge, in order to determine the ; timevarying properties of the magnetic surfaces of various pinch configurations. ; Analysis of the emerging electron beam demonstrates the effects of turbulence on ; diffusion and

  16. Magnetic and Electric Dipole Constraints on Extra Dimensions and Magnetic Fluxes

    E-print Network

    Aaron J. Roy; Myron Bander

    2008-05-10

    The propagation of charged particles and gauge fields in a compact extra dimension contributes to $g-2$ of the charged particles. In addition, a magnetic flux threading this extra dimension generates an electric dipole moment for these particles. We present constraints on the compactification size and on the possible magnetic flux imposed by the comparison of data and theory of the magnetic moment of the muon and from limits on the electric dipole moments of the muon, neutron and electron.

  17. A magnetic flux leakage NDE system for CANDU feeder pipes

    NASA Astrophysics Data System (ADS)

    Mak, Thomas Don

    This work examines the application of different magnetic flux leakage (MFL) inspection concepts to the non destructive evaluation (NDE) of residual (elastic) stresses in CANDURTM reactor feeder pipes. The stress sensitivity of three MFL inspection techniques was examined with flat plate samples, with stress-induced magnetic anisotropy (SMA) demonstrating the greatest stress sensitivity. A prototype SMA testing system was developed to apply magnetic NDE to feeders. The system consists of a flux controller that incorporates feedback from a wire coil and a Hall sensor (FCV2), and a magnetic anisotropy prototype (MAP) probe. The combination of FCV2 and the MAP probe was shown to provide SMA measurements on feeder pipe samples and predict stresses from SMA measurements with a mean accuracy of +/-38MPa.

  18. Magnetic field generation from shear flow in flux ropes

    NASA Astrophysics Data System (ADS)

    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.

  19. Microstructured magnetic materials for RF flux guides in magnetic resonance imaging.

    PubMed

    Wiltshire, M C; Pendry, J B; Young, I R; Larkman, D J; Gilderdale, D J; Hajnal, J V

    2001-02-01

    Magnetic resonance imaging and spectroscopy systems use coils, either singly or as arrays, to intercept radio-frequency (RF) magnetic flux from regions of interest, often deep within the body. Here, we show that a new magnetic material offers novel possibilities for guiding RF flux to the receiver coil, permitting a clear image to be obtained where none might otherwise be detectable. The new material contains microstructure designed according to concepts taken from the field of photonic band gap materials. In the RF range, it has a magnetic permeability that can be produced to specification while exhibiting negligible direct-current magnetism. The latter property is vital to avoid perturbing the static and audio-frequency magnetic fields needed to obtain image and spectral data. The concept offers a new paradigm for the manipulation of RF flux in all nuclear magnetic resonance systems. PMID:11157159

  20. Predicting ICME Magnetic Fields with a Numerical Flux Rope Model

    NASA Astrophysics Data System (ADS)

    Manchester, W.; van der Holst, B.; Sokolov, I.

    2014-12-01

    Coronal mass ejections (CMEs) are a dramatic manifestation of solar activity that release vast amounts of plasma into the heliosphere, and have many effects on the interplanetary medium and on planetary atmospheres, and are the major driver of space weather. CMEs occur with the formation and expulsion of large-scale flux ropes from the solar corona, which are routinely observed in interplanetary space. Simulating and predicting the structure and dynamics of these ICME magnetic fields is essential to the progress of heliospheric science and space weather prediction. We combine observations made by different observing techniques of CME events to develop a numerical model capable of predicting the magnetic field of interplanetary coronal mass ejections (ICMES). Photospheric magnetic field measurements from SOHO/MDI and SDO/HMI are used to specify a coronal magnetic flux rope that drives the CMEs. We examine halo CMEs events that produced clearly observed magnetic clouds at Earth and present our model predictions of these events with an emphasis placed on the z component of the magnetic field. Comparison of the MHD model predictions with coronagraph observations and in-situ data allow us to robustly determine the parameters that define the initial state of the driving flux rope, thus providing a predictive model.

  1. DISTRIBUTION OF MAGNETIC HELICITY FLUX WITH SOLAR CYCLES

    SciTech Connect

    Zhang, Hongqi; Yang, Shangbin, E-mail: hzhang@bao.ac.cn [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)] [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

    2013-02-15

    It is normally believed that a magnetic field transfers helicity from the solar subatmosphere into interplanetary space. This is based on the calculation of the injected magnetic helicity near the center of the solar disk between latitude {+-}30 Degree-Sign of both solar hemispheres in the period 1996-2009. As one follows the long-term injection of magnetic helicity, one finds that the transfer of magnetic helicity does not have a monotonic sign in the northern and southern hemispheres, and that the bulk of the helicity contributed goes to the active region, while the contribution to the quiet Sun is insignificant. The consistency between the total injected magnetic helicity and the sunspot numbers has also been found statistically in the solar cycle. The estimated total injected magnetic helicity flux in our calculation is of the order of or larger than 5.0 Multiplication-Sign 10{sup 46} Mx{sup 2} in the 23rd solar cycle.

  2. Relativistic Magnetic Monopole Flux Constraints from RICE

    E-print Network

    D. P. Hogan; D. Z. Besson; J. P. Ralston; I. Kravchenko; D. Seckel

    2008-11-01

    We report an upper limit on the flux of relativistic monopoles based on the non-observation of in-ice showers by the Radio Ice Cherenkov Experiment (RICE) at the South Pole. We obtain a 95% C.L. limit of order 10^{-18}/(cm^2-s-sr) for intermediate mass monopoles of 10^7

  3. The effect of flux creep on the magnetization field in the SSC diopole magnets

    Microsoft Academic Search

    W. S. Gilber; R. F. Althaus; P. J. Barale; R. W. Benjegerdes; M. A. Green; M. I. Green; R. M. Scanlan

    1989-01-01

    The sextuple fields of model SSC dipole magnets were observed to change with time when the magnets are held at constant current under conditions similar to injection into the SSC accelerator. The changes in the sextupole component have close to a linear log time dependence, and is felt to be caused by flux creep decay of the magnetization currents in

  4. New quantum effect of confined magnetic flux on electrons

    NASA Astrophysics Data System (ADS)

    Silverman, M. P.

    1986-10-01

    A charged particle analogue of the Hanbury Brown-Twiss experiments with photons is described wherein the correlation of electron intensity at two detectors is modulated by magnetic flux confined to a region from which the electrons are excluded. The experimental conditions differ substantially from those of the Aharonov-Bohm effect.

  5. New quantum effect of confined magnetic flux on electrons

    Microsoft Academic Search

    M. P. Silverman

    1986-01-01

    A charged particle analogue of the Hanbury Brown-Twiss experiments with photons is described wherein the correlation of electron intensity at two detectors is modulated by magnetic flux confined to a region from which the electrons are excluded. The experimental conditions differ substantially from those of the Aharonov-Bohm effect. Permanent address: Department of Physics, Trinity College, Hartford, CT 06106, USA.

  6. Expansion of solar magnetic flux tubes large and small

    NASA Astrophysics Data System (ADS)

    Solanki, S. K.; Finsterle, W.; Rüedi, I.; Livingston, W.

    1999-07-01

    In the solar photosphere the magnetic field of magnetic elements and sunspots is known to expand with height. In the case of sunspots this expansion is known to be very rapid, with the field forming an almost horizontal canopy. In this contribution we present new results on the superpenumbral canopy of sunspots based on fits to Stokes I and V profiles of infrared spectral lines. The new models take pressure balance across the boundary of the canopy field into account, which leads to significantly lower canopy base heights than previously determined from similar data. Due to the lower canopy base height, the density above the canopy base is larger, so that estimates of the mass transported by the Evershed effect in the canopy need to be revised upwards: approximately 15-50% of the mass flowing through the penumbra travels beyond the sunspot boundary above the canopy base. A comparison with small flux tubes leads to the surprising result that although the two types of features have magnetic fluxes that differ by 5-6 orders of magnitude, their relative rate of expansion with height is very similar, suggesting that at least in this respect sunspots can be described by the thin-tube approximation. The remaining small differences between the relative expansion of the two types of flux tubes is qualitatively compatible with the presence of magnetic flux that returns into the solar interior at the spot boundary, as has been proposed by Westendorp Plaza et al. (1997).

  7. Non-geometric magnetic flux and crossed modules

    NASA Astrophysics Data System (ADS)

    Kalkkinen, Jussi

    2006-04-01

    It is shown that the BRST operator of twisted N=4 Yang-Mills theory in four dimensions is locally the same as the BRST operator of a fully decomposed non-Abelian gerbe. Using locally defined Yang-Mills theories we describe non-perturbative backgrounds that carry a novel magnetic flux. Given by elements of the crossed module G?AutG, these non-geometric fluxes can be classified in terms of the cohomology class of the underlying non-Abelian gerbe, and generalise the centre Z G valued magnetic flux found by 't Hooft. These results shed light also on the description of non-local dynamics of the chiral five-brane in terms of non-Abelian gerbes.

  8. Measuring of rotating magnetic flux in an integrated environment

    NASA Astrophysics Data System (ADS)

    Sari, Z.; Ivanyi, A.

    2011-01-01

    The paper describes a measuring method and the establishment of a measuring environment for two-dimensional rotating magnetic fluxes and fields. The measuring method relies on measuring currents and voltages in coils attached to the magnetic specimen. For the processing and generating of measuring signals, a PC-based system running Lab View is applied extended with a NI ELVIS II board, and two high performance KIKUSUI bipolar power supplies. The measurement results are satisfactory and show that the measuring environment established is capable of non-destructively capture the two-dimensional magnetic characteristics of the specimen investigated.

  9. Convective intensification of magnetic flux tubes in stellar photospheres

    E-print Network

    S. P. Rajaguru; R. L. Kurucz; S. S. Hasan

    2002-01-03

    The convective collapse of thin magnetic flux tubes in the photospheres of sun-like stars is investigated using realistic models of the superadiabatic upper convection zone layers of these stars. The strengths of convectively stable flux tubes are computed as a function of surface gravity and effective temperature. We find that while stars with T$_{eff}\\ge$ 5500 K and log $g$$\\ge$ 4.0 show flux tubes highly evacuated of gas, and hence strong field strengths, due to convective collapse, cooler stars exhibit flux tubes with lower field strengths. Observations reveal the existence of field strengths close to thermal equipartition limits even in cooler stars, implying highly evacuated tubes, for which we suggest possible reasons.

  10. Vortex telegraph noise in high magnetic fields

    SciTech Connect

    Shung, E.; Rosenbaum, T.F.; Coppersmith, S.N. [The James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637 (United States)] [The James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637 (United States); Crabtree, G.W.; Kwok, W. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)] [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

    1997-11-01

    We cool untwinned single crystals of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} with columnar defects down to liquid-He temperatures and study the development of pinning in the strongly interacting Bose glass with local Hall-probe magnetometry. We are able to resolve discrete fluctuations in the local vortex density resulting from reconfigurations of the vortex assembly between metastable states nearby in energy. By varying the applied magnetic field, and therefore the mean vortex density, we gain microscopic information about vortex-vortex interactions. {copyright} {ital 1997} {ital The American Physical Society}

  11. Low-Noise YBa2Cu3O7 Nano-SQUIDs for Performing Magnetization-Reversal Measurements on Magnetic Nanoparticles

    NASA Astrophysics Data System (ADS)

    Schwarz, T.; Wölbing, R.; Reiche, C. F.; Müller, B.; Martínez-Pérez, M. J.; Mühl, T.; Büchner, B.; Kleiner, R.; Koelle, D.

    2015-04-01

    We fabricate YBa2Cu3O7 (YBCO) direct-current nano- superconducting quantum-interference devices (nano-SQUIDs) based on grain-boundary Josephson junctions by focused-ion-beam patterning. Characterization of electric transport and noise properties at 4.2 K in a magnetically shielded environment yields a very small inductance L of a few pH for an optimized device geometry. This, in turn, results in very low values of flux noise <50 n ?0/Hz1 /2 in the thermal white-noise limit, which yields spin sensitivities of a few ?B/Hz1 /2 (?0 is the magnetic flux quantum, and ?B is the Bohr magneton). We observe frequency-dependent excess noise up to 7 MHz, which can be eliminated only partially by bias reversal readout. This behavior indicates the presence of fluctuators of unknown origin, possibly related to defect-induced spins in the SrTiO3 substrate. We demonstrate the potential of using YBCO nano-SQUIDs for the investigation of small spin systems, by placing a 39-nm-diameter Fe nanowire encapsulated in a carbon nanotube on top of a nonoptimized YBCO nano-SQUID and by measuring the magnetization reversal of the Fe nanowire via the change of magnetic flux coupled to the nano-SQUID. The measured flux signals upon magnetization reversal of the Fe nanowire are in very good agreement with estimated values, and the determined switching fields indicate magnetization reversal of the nanowire via curling mode.

  12. Analysis of the influence of some magnetizing parameters on magnetic Barkhausen noise using a microscopic model

    NASA Astrophysics Data System (ADS)

    Pérez-Benítez, J. A.; Espina-Hernández, J. H.; Martínez-Ortiz, P.; Chávez-González, A. F.; de la Rosa, J. M.

    2013-12-01

    A microscopic model of magnetic Barkhausen noise (MBN) in carbon steel is proposed. The model uses the quasi-static magnetic formulation of Maxwell equations for electromagnetic fields combined with a microscopic model of the magnetic Barkhausen noise, and its equations are solved by means of finite difference formulation. The simulated MBN signal obtained presents high similarities to the measured MBN signal. Using this model, the influences of the uniformity and waveform profile of the excitation magnetic field on the envelope of the MBN signal were studied. The results show that the lack of uniformity of the excitation magnetic field increases the amplitude of the MBN envelope at the right of its main peak, and the waveform profile influences the shape of the MBN envelope. The proposed model can be used as a tool for studying the influence of several excitation parameters on the Barkhausen Noise in order to improve this technique.

  13. Identification of different processes in magnetization dynamics of API steels using magnetic Barkhausen noise

    NASA Astrophysics Data System (ADS)

    Pérez-Benítez, J. A.; Espina-Hernández, J. H.; Le Man, Tu; Caleyo, F.; Hallen, J. M.

    2015-07-01

    This work presents a method to identify processes in magnetization dynamics using the angular dependence of the magnetic Barkhausen noise. The analysis reveals that three different processes of the magnetization dynamics could be identified using the angular dependence of the magnetic Barkhausen noise energy. The first process is the reversed domain nucleation which is related to the magneto-crystalline energy of the material, and the second and third ones are associated with 180° and 90° domain walls motions, respectively. Additionally, two transition regions were identified and they are located between the regions associated with the aforementioned processes. The causes involving these processes are analyzed and a method for establishing their location in the Barkhausen noise signal with respect to the applied magnetic field intensity is proposed.

  14. GRANULAR-SCALE MAGNETIC FLUX CANCELLATIONS IN THE PHOTOSPHERE

    SciTech Connect

    Kubo, M.; Low, B. C.; Lites, B. W. [High Altitude Observatory, National Center for Atmospheric Research P.O. Box 3000, Boulder, CO 80307 (United States)

    2010-04-01

    We investigate the evolution of five granular-scale magnetic flux cancellations just outside the moat region of a sunspot by using accurate spectropolarimetric measurements and G-band images with the Solar Optical Telescope (SOT) aboard Hinode. The opposite-polarity magnetic elements approach a junction of the intergranular lanes and then collide with each other there. The intergranular junction has strong redshifts, darker intensities than the regular intergranular lanes, and surface converging flows. This clearly confirms that the converging and downward convective motions are essential for the approaching process of the opposite-polarity magnetic elements. However, the motion of the approaching magnetic elements does not always match with their surrounding surface flow patterns in our observations. This suggests that, in addition to the surface flows, subsurface downward convective motions and subsurface magnetic connectivities are important for understanding the approach and collision of the opposite-polarity elements observed in the photosphere. We find that the horizontal magnetic field appears between the canceling opposite-polarity elements in only one event. The horizontal fields are observed along the intergranular lanes with Doppler redshifts. This cancellation is most probably a result of the submergence (retraction) of low-lying photospheric magnetic flux. In the other four events, the horizontal field is not observed between the opposite-polarity elements at any time when they approach and cancel each other. These approaching magnetic elements are more concentrated rather than gradually diffused, and they have nearly vertical fields even while they are in contact each other. We thus infer that the actual flux cancellations are highly time-dependent events at scales less than a pixel of Hinode SOT (about 200 km) near the solar surface.

  15. Granular-scale Magnetic Flux Cancellations in the Photosphere

    NASA Astrophysics Data System (ADS)

    Kubo, M.; Low, B. C.; Lites, B. W.

    2010-04-01

    We investigate the evolution of five granular-scale magnetic flux cancellations just outside the moat region of a sunspot by using accurate spectropolarimetric measurements and G-band images with the Solar Optical Telescope (SOT) aboard Hinode. The opposite-polarity magnetic elements approach a junction of the intergranular lanes and then collide with each other there. The intergranular junction has strong redshifts, darker intensities than the regular intergranular lanes, and surface converging flows. This clearly confirms that the converging and downward convective motions are essential for the approaching process of the opposite-polarity magnetic elements. However, the motion of the approaching magnetic elements does not always match with their surrounding surface flow patterns in our observations. This suggests that, in addition to the surface flows, subsurface downward convective motions and subsurface magnetic connectivities are important for understanding the approach and collision of the opposite-polarity elements observed in the photosphere. We find that the horizontal magnetic field appears between the canceling opposite-polarity elements in only one event. The horizontal fields are observed along the intergranular lanes with Doppler redshifts. This cancellation is most probably a result of the submergence (retraction) of low-lying photospheric magnetic flux. In the other four events, the horizontal field is not observed between the opposite-polarity elements at any time when they approach and cancel each other. These approaching magnetic elements are more concentrated rather than gradually diffused, and they have nearly vertical fields even while they are in contact each other. We thus infer that the actual flux cancellations are highly time-dependent events at scales less than a pixel of Hinode SOT (about 200 km) near the solar surface.

  16. Crossed flux tubes 3D magnetic reconnection experiment

    NASA Astrophysics Data System (ADS)

    Bellan, Paul

    2011-10-01

    The formation and dynamics of writhing, plasma-filled, twisted open magnetic flux tubes is being investigated using laboratory experiments. The behavior of these flux tubes is relevant to solar corona loops, astrophysical jets, spheromak formation, and open field lines in tokamaks and RFP's. MHD forces have been determined to drive fast axial plasma flows into the flux tube from the boundary it intercepts. These flows fill the flux tubes with plasma while simultaneously injecting linked frozen-in azimuthal flux; helicity injection is thus associated with mass injection. An upgraded experiment under construction will have two adjacent arched plasma-filled flux tubes cross over each other. It is anticipated that a localized 3D reconnection will occur at the cross-over. This reconnection should result in half-twists in the post re-connection topology and subsequent Alfven wave propagation to equilibrate the half-twists along the post-reconnection flux tubes. The electrical circuitry requires two initially independent floating capacitor bank power supplies that become series-connected as a result of reconnection. Supported by DOE, NSF and AFOSR.

  17. Origin of 1/f noise peaks of YBa{sub 2}Cu{sub 3}O{sub x} films in a magnetic field

    SciTech Connect

    Kang, W.N.; Kim, D.H.; Park, J.H. [Korea Institute of Science and Technology, Seoul (Korea, Democratic People`s Republic of). Applied Physics Group] [and others

    1994-02-01

    The temperature and magnetic field dependence of 1/f noise has been measured in epitaxial YBa{sub 2}Cu{sub 3}O{sub x} films. In a magnetic field, two noise peaks were observed as temperature decreases; one at higher temperature was found to match the thermal fluctuation of the sample resistance and the other near the foot of the transition was found to be magnetic-field dependent. The location of the latter was shifted toward low temperature and the peak height was decreased as a magnetic field increased. In a zero field only one peak from the resistance fluctuation was observed. We show that the field-dependent noises are due to flux motion interacting with the pinning potential. A classical model is used to explain the field-induced noise peaks. We interpret that the temperature dependences of the flux bundle size and the sample resistance are the reasons for the noise peaks, and a rough estimation of the temperature and field dependence of the flux bundle size is presented. Any possible relationship between the noise peaks and the flux-line-lattice phase transition is also discussed.

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

    E-print Network

    Michael, A. T.

    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 ...

  19. Flux noise resulting from vortex avalanches using a simple kinetic model

    SciTech Connect

    Mohler, G.; Stroud, D. [Department of Physics, The Ohio State University, Columbus, Ohio 43210 (United States)] [Department of Physics, The Ohio State University, Columbus, Ohio 43210 (United States)

    1999-10-01

    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 S{sub {Phi}}({omega}) has a power-law dependence on frequency, S{sub {Phi}}({omega}){approximately}{omega}{sup {minus}s}, with s{approximately}1.4 in reasonable agreement with experiment. In addition, for small lattices, the calculated S{sub {Phi}}({omega}) has a high-frequency knee, which is seen in some experiments, and which is due to the finite lattice size. Deviations between calculation and experiment are attributed mostly to uncertainties in the measured critical current densities and pinning strengths of the experimental samples. {copyright} {ital 1999} {ital The American Physical Society}

  20. Flux noise resulting from vortex avalanches using a simple kinetic model

    NASA Astrophysics Data System (ADS)

    Mohler, G.; Stroud, D.

    1999-10-01

    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 S?(?) has a power-law dependence on frequency, S?(?)~?-s, with s~1.4 in reasonable agreement with experiment. In addition, for small lattices, the calculated S?(?) has a high-frequency knee, which is seen in some experiments, and which is due to the finite lattice size. Deviations between calculation and experiment are attributed mostly to uncertainties in the measured critical current densities and pinning strengths of the experimental samples.

  1. ThreeThree--dimensional magnetic fielddimensional magnetic field line reconnection involving fluxline reconnection involving flux

    E-print Network

    Shyy, Wei

    #12;QSLs in solar flare observations QSLs at boundaries (thick lines) coincident with H brightening fluxline reconnection involving flux ropes andropes and AlfvAlfvéénn waveswaves WalterWalter Gekelman, 3D?) · role of guide field in reconnection · Generation and interaction of magnetic flux ropes

  2. Topological Transformations in Isolated Straight Magnetic Flux Tubes

    NASA Astrophysics Data System (ADS)

    Bazdenkov, Sergey; Sato, Tetsuya

    1998-06-01

    Reconnection in an isolated straight magnetic flux tube with all the field lines continuously twisted is investigated by a three-dimensional magnetohydrodynamic simulation. It is found that in the case of straight geometry, drastic topological changes and prominent burstlike thermal energy release occur, even though no ambient untwisted magnetic field exists. Three distinct phases of magnetic reconnection are observed. The first one corresponds to rapid (in the Alfvén transit timescale) kinking and splitting of the one initial flux tube into two topologically distinct well-bundled helical tubes. At the second phase these tubes rapidly reconnect each other in such a way that the configuration suffers the Möbius transformation (inversion) when each of the tubes, being compactly bundled at one end, scatters to a thin shell surrounding another tube at the opposite end. During the third phase, the magnetic configuration becomes essentially knotted and topologically uncertain, but the knots are then rapidly kicked off by reconnection with further recurrence of two well-bundled tubes observed just after the split phase. An interesting feature of magnetic reconnection associated with multilayer fine structure of electric current with near-parallel reconnecting magnetic field lines is also observed in the simulation.

  3. Experimental Design of a Magnetic Flux Compression Experiment

    NASA Astrophysics Data System (ADS)

    Fuelling, Stephan; Awe, Thomas J.; Bauer, Bruno S.; Goodrich, Tasha; Lindemuth, Irvin R.; Makhin, Volodymyr; Siemon, Richard E.; Atchison, Walter L.; Reinovsky, Robert E.; Salazar, Mike A.; Scudder, David W.; Turchi, Peter J.; Degnan, James H.; Ruden, Edward L.

    2007-06-01

    Generation of ultrahigh magnetic fields is an interesting topic of high-energy-density physics, and an essential aspect of Magnetized Target Fusion (MTF). To examine plasma formation from conductors impinged upon by ultrahigh magnetic fields, in a geometry similar to that of the MAGO experiments, an experiment is under design to compress magnetic flux in a toroidal cavity, using the Shiva Star or Atlas generator. An initial toroidal bias magnetic field is provided by a current on a central conductor. The central current is generated by diverting a fraction of the liner current using an innovative inductive current divider, thus avoiding the need for an auxiliary power supply. A 50-mm-radius cylindrical aluminum liner implodes along glide planes with velocity of about 5 km/s. Inward liner motion causes electrical closure of the toroidal chamber, after which flux in the chamber is conserved and compressed, yielding magnetic fields of 2-3 MG. Plasma is generated on the liner and central rod surfaces by Ohmic heating. Diagnostics include B-dot probes, Faraday rotation, radiography, filtered photodiodes, and VUV spectroscopy. Optical access to the chamber is provided through small holes in the walls.

  4. A system for measuring magnetic core noise as a function of the magnetization level

    Microsoft Academic Search

    Akira Yoshihiro; Kazunori Kajiwara; Kousei Mori; Toshikatsu Sonoda; Ryuzo Ueda; Yoshiteru Miki

    1995-01-01

    The problem of magnetic core noise is considered in terms of non-repeatability of the hysteresis loop trace for any repetition of the magnetization process. The examination condition is that the effect of eddy currents is reduced to as low a level as possible. Based on such premises, this paper presents a system which periodically extracts the fluctuation voltage, induced at

  5. Evidence for Magnetic Flux Saturation in Rapidly Rotating M Stars

    E-print Network

    Reiners, A; Browning, M

    2008-01-01

    We present magnetic flux measurements in seven rapidly rotating M dwarfs. Our sample stars have X-ray and H-alpha emission indicative of saturated emission, i.e., emission at a high level independent of rotation rate. Our measurements are made using near-infrared FeH molecular spectra observed with HIRES at Keck. Because of their large convective overturn times, the rotation velocity of M stars with small Rossby numbers is relatively slow and does not hamper the measurement of Zeeman splitting. The Rossby numbers of our sample stars are as small as 0.01. All our sample stars exhibit magnetic flux of kilo-Gauss strength. We find that the magnetic flux saturates in the same regime as saturation of coronal and chromospheric emission, at a critical Rossby number of around 0.1. The filling factors of both field and emission are near unity by then. We conclude that the strength of surface magnetic fields remains independent of rotation rate below that; making the Rossby number yet smaller by a factor of ten has lit...

  6. Media noise in periodic multilayered magnetic films with perpendicular anisotropy

    Microsoft Academic Search

    I. L. Sanders; D. R. Wilhoit; S. E. Lambert; G. L. Gorman; T. Yogi; V. S. Speriosu

    1990-01-01

    Periodic, finely multilayered thin-film magnetic structures (?200 A?) with high in-plane coercivity suitable for longitudinal recording investigations have been fabricated. CoPt20\\/Pd and CoPt12Cr17\\/Pd periodic multilayers can exhibit a perpendicular orientation, originating from surface anisotropy effects, with a magnitude depending on the thickness of the component layers. The perpendicular orientation influences the transition noise, but for the particular systems studied, the

  7. Statistical data analysis of magnetic recording noise mechanisms

    Microsoft Academic Search

    Samuel W. Yuan; H. Neal Bertram

    1992-01-01

    Statistical data analysis using empirical eigenfunctions, known as the Karhunen-Loeve (K-L) expansion, is applied to characterize noise mechanisms in magnetic recording. Given any original data set and hence its correlation (covariance) matrix, an empirical orthogonal set of eigenfunctions can be obtained. The original data set can be expressed as an orthonormal expansion of these eigenfunctions. This feature of the K-L

  8. Residual Magnetic Flux Leakage: A Possible Tool for Studying Pipeline Defects

    E-print Network

    Clapham, Lynann

    Residual Magnetic Flux Leakage: A Possible Tool for Studying Pipeline Defects Vijay Babbar1 weaker flux signals. KEY WORDS: Magnetic flux leakage; residual magnetization; pipeline defects; pipeline pipelines, which may develop defects such as corrosion pits as they age in service.(1) Under the ef- fect

  9. Magnetic signatures of plasma-depleted flux tubes in the Saturnian inner magnetosphere

    Microsoft Academic Search

    N. André; A. M. Persoon; J. Goldstein; J. L. Burch; P. Louarn; G. R. Lewis; A. M. Rymer; A. J. Coates; W. S. Kurth; E. C. Sittler; M. F. Thomsen; F. J. Crary; M. K. Dougherty; D. A. Gurnett; D. T. Young

    2007-01-01

    Initial Cassini observations have revealed evidence for interchanging magnetic flux tubes in the inner Saturnian magnetosphere. Some of the reported flux tubes differ remarkably by their magnetic signatures, having a depressed or enhanced magnetic pressure relative to their surroundings. The ones with stronger fields have been interpreted previously as either outward moving mass-loaded or inward moving plasma-depleted flux tubes based

  10. Particle signature of magnetic flux transfer events at the magnetopause

    NASA Technical Reports Server (NTRS)

    Daly, P. W.; Keppler, E.; Williams, D. J.; Russell, C. T.

    1981-01-01

    Energetic electron (E greater than 20 keV) and ion (E greater than 25 keV) enhancements have been observed using the Isee 1 and 2 spacecraft during magnetic flux transfer events in the dayside magnetosheath just outside the magnetopause. The ions are seen to be streaming along the magnetic field, filling the 90-180 deg pitch angle region. The electrons are more isotropic and yet exhibit slight anisotropy in the direction opposite to that of the ions. From their intensities and spectra the ions appear to be of magnetospheric origin. With the interpretation of the flux transfer events as 'patchy' interconnection of magnetosheath and magnetospheric field lines, the ions are then seen to be previously trapped magnetospheric particles escaping along freshly opened field lines.

  11. Depinning of Trapped Magnetic Flux in Bulk Niobium SRF Cavities

    E-print Network

    Aull, S

    2015-01-01

    Trapped magnetic flux is known to be a significant contribution to the residual resistance of superconducting radio frequency (SRF) cavities. The additional losses depend strongly if the vortices are depinned by the RF. The depinning is affected by the purity of the material, and the size of the pinning centers, as well as the cavity operation frequency. One may define a depinning frequency, above which significant depinning occurs. This publication presents a derivation of the depinning frequency from experimental data. We find a depinning frequency of 673 MHz for RRR 110 niobium. On this basis the currently used model is extended to describe the trapped flux sensitivity as function of residual resistance ratio (RRR) and operation frequency while also accounting for the pinning center size and the treatment history of the cavity. Moreover, the model offers an explanation for the significantly higher trapped flux sensitivity reported for nitrogen doped and 120 C baked cavities.

  12. Laser-Driven Magnetic-Flux Compression: Theory and Experiments

    NASA Astrophysics Data System (ADS)

    Chang, Po-Yu

    Laser-Driven Flux Compression (LDFC) is a technique used to compress the magnetic field in Inertial Confinement Fusion (ICF) targets driven by a laser. The compressed field in the ICF target is beneficial to the target performance. Embedding a magnetic field in a conventional ICF target reduces the heat loss if the central hot spot becomes magnetized. Higher hot spot temperatures lower the requirements on the implosion velocities, leading to larger shell masses and therefore higher energy gains. For a typical hot spot density of ˜ 10 g/cc, and temperature of ˜ 5 keV, a magnetic field B > 10 MG is required to magnetize the hot spot. Such a strong magnetic field is difficult to be externally generated. Instead of providing the strong magnetic field directly, a seed magnetic field much lower than the required field was provided and compressed by the imploding shell. The field needs to be compressed faster than its diffusion due to the finite resistivity of the fill gas and the shell. This requires the gas in the target being ionized by the shock so that the flux is frozen in the gas region and compressed by the imploding shell. In this thesis, theoretical models, numerical calculations, and basic experiments of flux compression in ICF targets are investigated. A measurable Lawson criterion, developed as a metric to assess the performance of an ICF target, is used to evaluate the benefits of suppressing the heat conductivity. A simple model is used to describe the process of field compression by shock waves during the shell implosion. The magnetohydrodynamics codes, LILAC-MHD and LILAC-MHD-SP, are used to simulate the field compression and the target performance. The Magneto-Inertial-Fusion-Electrical-Discharge-System (MIFEDS), the device providing the seed magnetic field, is described in detail. LDFC experiments using the OMEGA laser at the Laboratory for Laser Energetics are presented. The results include the first demonstration of ˜ 550-fold amplification of a 50 ˜ 60 kG seed field to a ˜ 30 MG compressed field using LDFC, and the first demonstration of 15% and 30 % ion temperature and neutron yield enhancement by compressed magnetic fields.

  13. Improvement of the Superconducting Magnetic Levitation System for an Absolute Determination of the Magnetic Flux Quantum

    Microsoft Academic Search

    Fuyuhiko Shiota; Ko Hara; Takaaki Hirata

    1984-01-01

    The superconducting magnetic levitation system for the absolute determination of the magnetic flux quantum phi0 is improved. Resolution of the vertical position of the floating body with laser interferometer becomes 1\\/100 mum order, which corresponds to 1 ppm of the gravitational potential energy of the floating body. An outline of this system and some temporary results are described.

  14. A determination of the magnetic flux quantum using superconducting magnetic levitation system

    Microsoft Academic Search

    F. Shiota; H. Hirai; Y. Nezu; K. Nakayama; T. Endo; Y. Sakamoto; K. Hara

    1990-01-01

    A refinement of a preliminary superconducting magnetic levitation system is in progress for the determination of the magnetic flux quantum ?0. A novel superconducting coil with a conic section has been fabricated, so that the Meissner effect of the system seems to remain intact and the basic characteristic of the levitation system is much improved

  15. Are heliospheric flows magnetic line- or flux-conserving?

    NASA Astrophysics Data System (ADS)

    Nickeler, D. H.; Karlický, M.

    2006-11-01

    This article discusses and tests the validity of the frozen in magnetic field paradigm (or 'ideal magnetohydrodynamics (MHD) constraint') which is usually adopted by many authors dealing with heliospheric physics. To show the problem of using ideal MHD in such a counterflow configuration like the heliosphere, we first recapitulate the basic concepts of freezing-in of magnetic fields, respectively magnetic topology conservation and its violation (= magnetic reconnection) in 3-D, already done by other authors with different methods with respect to derivations and interpretations. Then we analyse different heliospheric plasma environments. As a model of the stagnation region/stagnation point in front of the heliospheric nose, we present and discuss the general solution of the ideal MHD Ohm's law in the vicinity of a 2-D stagnation point, which was found by us. We show that ideal MHD either leads necessarily to a diverging magnetic field strength in the vicinity of such a stagnation point, or to a vanishing mass density on the heliopause boundaries. In the case that components of the electric field parallel to the magnetic field do not exist due to the chosen form of the non-ideal Ohm's law, it is always possible to formulate the transport equation of the magnetic field as a modified ideal Ohm's law. We find that the form of the Ohm's law which is often used in heliospheric physics (see e.g. Baranov and Fahr, 2003), is not able to change magnetic topology and thus cannot lead to magnetic reconnection, which necessarily has to occur at the stagnation point. The diverging magnetic field, for instance, implies the breakdown of the flux freezing paradigm for the heliosphere. Its application, especially at the heliospheric nose, is therefore rather doubtful. We conclude that it is necessary to search for an Ohm's law which is able to violate magnetic topology conservation.

  16. Magnetic and Electric Flux Quanta: the Pion Mass

    SciTech Connect

    P Cameron

    2011-12-31

    The angular momentum of the magnetic flux quantum is balanced by that of the associated supercurrent, such that in condensed matter the resultant angular momentum is zero. The notion of a flux quantum in free space is not so simple, needing both magnetic and electric flux quanta to propagate the stable dynamic structure of the photon. Considering these flux quanta at the scale where quantum field theory becomes essential, at the scale defined by the reduced Compton wavelength of the electron, exposes variants of a paradox that apparently has not been addressed in the literature. Leaving the paradox unresolved in this note, reasonable electromagnetic rationales are presented that permit to calculate the masses of the electron, muon, pion, and nucleon with remarkable accuracy. The calculated mass of the electron is correct at the nine significant digit limit of experimental accuracy, the muon at a part in one thousand, the pion at two parts in ten thousand, and the nucleon at seven parts in one hundred thousand. The accuracy of the pion and nucleon mass calculations reinforces the unconventional common notion that the strong force is electromagnetic in origin.

  17. Flux Rope Acceleration and Enhanced Magnetic Reconnection Rate

    SciTech Connect

    C.Z. Cheng; Y. Ren; G.S. Choe; Y.-J. Moon

    2003-03-25

    A physical mechanism of flares, in particular for the flare rise phase, has emerged from our 2-1/2-dimensional resistive MHD simulations. The dynamical evolution of current-sheet formation and magnetic reconnection and flux-rope acceleration subject to continuous, slow increase of magnetic shear in the arcade are studied by employing a non-uniform anomalous resistivity in the reconnecting current sheet under gravity. The simulation results directly relate the flux rope's accelerated rising motion with an enhanced magnetic reconnection rate and thus an enhanced reconnection electric field in the current sheet during the flare rise phase. The simulation results provide good quantitative agreements with observations of the acceleration of flux rope, which manifests in the form of SXR ejecta or erupting filament or CMEs, in the low corona. Moreover, for the X-class flare events studied in this paper the peak reconnection electric field is about O(10{sup 2} V/m) or larger, enough to accelerate p articles to over 100 keV in a field-aligned distance of 10 km. Nonthermal electrons thus generated can produce hard X-rays, consistent with impulsive HXR emission observed during the flare rise phase.

  18. The effect of flux creep on the magnetization field in the SSC diopole magnets

    SciTech Connect

    Gilber, W.S.; Althaus, R.F.; Barale, P.J.; Benjegerdes, R.W.; Green, M.A.; Green, M.I.; Scanlan, R.M. (Lawrence Berkeley Lab., CA (USA))

    1989-06-01

    The sextuple fields of model SSC dipole magnets have been observed to change with time when the magnets are held at constant current under conditions similar to injection into the SSC accelerator. The changes in the sextupole component have close to a linear log time dependence, and is felt to be caused by flux creep decay of the magnetization currents in the superconductor filaments. Measurements of this decay have been made under various conditions. The conditions include various central field inductions and changes of field prior to when the decay was measured. The measured field decay in the dipole's sextupole is proportional to the magnitude and sign of the sextupole due to magnetization which was measured at the start of the decay. This suggests that the decay is a bulk superconductivity flux creep. Proximity coupling appears to play only a minor role in the flux creep according to recent LBL measurements with a stable power supply. 4 refs., 6 figs., 3 tabs.

  19. Note: Magnetic noise from the inner wall of a magnetically shielded room

    NASA Astrophysics Data System (ADS)

    Khan, Sheraz; Cohen, David

    2013-05-01

    We measured the thermal magnetic noise generated by the inner high-permeability wall of a magnetically shielded room. This room houses a magnetoencephalogram (MEG), which contains 102 "small" identical magnetometers. For the measurement, we created two large magnetometers by summing the outputs of 46 magnetometers equally on the helmet's left and right side, to look at the summed noise of the right and left vertical walls. From these summed outputs, we calculated the rms noise amplitude due to all six walls at the MEG location to be ˜0.5 f T/sqrt {Hz} at 100 Hz, only slowly rising with lower frequency. This is well below the system noise of each small MEG magnetometer, hence is negligible for the MEG.

  20. Performance Comparison of Longitudinal Flux and Transverse Flux Permanent Magnet Machines for Turret Applications With Large Diameter

    Microsoft Academic Search

    Ji-Young Lee; Do-Kwan Hong; Byung-Chul Woo; Doo-Hwan Park; Byoung-Uk Nam

    2012-01-01

    The aim of this paper is to provide performance comparisons between conventional longitudinal flux and transverse flux permanent-magnet machines using three-dimensional finite element analysis considering both electro-magnetic and mechanical fields. For a turret application with 2 meters in diameter size, not only electro-magnetic performance but also mechanical structural strength is important. Therefore, the comparison is focused on the torque density,

  1. Vector Magnetic Fields of Moving Magnetic Features and Flux Removal from a Sunspot

    NASA Astrophysics Data System (ADS)

    Kubo, M.; Shimizu, T.; Tsuneta, S.

    2007-04-01

    Moving magnetic features (MMFs) are small photospheric magnetic elements moving outward in the zone (moat region) surrounding mature sunspots. Vector magnetic fields and horizontal motion of the classical MMFs (called isolated MMFs hereafter) are investigated using coordinated ASP and MDI observations. Their magnetic and velocity properties are compared to nearby magnetic features, including moat fields surrounding the isolated MMFs and penumbral uncombed structure. The moat fields are defined as nonisolated MMFs because they also move outward from sunspots. The nonisolated MMFs have nearly horizontal magnetic fields of both polarities. We find that the isolated MMFs located on the lines extrapolated from the horizontal component of the uncombed structure have magnetic fields similar to the nonisolated MMFs. This suggests that the MMFs with nearly horizontal fields are intersections of horizontal fields extended from the penumbra with the photospheric surface. We find clear evidence that the isolated MMFs located on the lines extrapolated from the vertical component of the uncombed structure have vertical field lines with polarity same as the sunspot. This correspondence shows that such MMFs are detached from the spine (vertical) component of the penumbra. We estimate that the magnetic flux carried by the vertical MMFs is about 1-3 times larger than the flux loss of the sunspot. We suggest that the isolated vertical MMFs alone can transport sufficient magnetic flux and are responsible for the disappearance and disintegration of the sunspot.

  2. The Helical Kink Instability of Isolated, Twisted Magnetic Flux Tubes

    NASA Astrophysics Data System (ADS)

    Linton, M. G.; Longcope, D. W.; Fisher, G. H.

    1996-10-01

    To understand the dynamics of twisted active region flux tubes below the solar photosphere, we investigate the linear kink stability of isolated, twisted tubes of magnetic flux. We apply linearized equations of MHD to a cylindrical magnetic equilibrium (screw pinch), but with significant differences from earlier work. The magnetic field vanishes outside a radius r = R where it is confined by the higher pressure of the unmagnetized plasma. The outside boundary of the tube is free to move, displacing the unmagnetized plasma as it does so. We concentrate on equilibria where all field lines have the same helical pitch: B?/rBζ = q = const. The main results are as follows. 1. These equilibria are stable, provided that the field line pitch does not exceed a threshold; q ?qcr for stability. The threshold is qcr=(?)½, where ? is the r2 coefficient in the series expansion of the equilibrium axial magnetic field (B?) about the tube axis (r = 0): B?(r) = BO(1 - ?r2 + ?). When this criterion is violated, there are unstable eigenmodes, ? ? e1(?+kz). The most unstable of these have a helical pitch k which is near (but not equal to) the field line pitch q. 2. For weakly twisted tubes (qR ? 1) we derive growth rates and unstable eigenfunctions analytically. For strongly twisted tubes (qR ?1), we find growth rates and unstable eigenfunctions numerically. 3. The maximum growth rate and range of unstable wavenumbers for a strongly twisted tube can be predicted qualitatively by using the analytical results from the weakly twisted case. The maximum growth rate in that case is given by ?max = ?AR(q2 - q2cr)/3.83, where ?A is the axial Alfvén speed. The range of unstable wavenumbers is (- q - ?k/2) < k <(- q + ?k/2), where ?k = 4qR(q2 -q2cr)½/3.83. 4. The kink instability we find consists mainly of internal motions. Helical translations of the entire tube are stable. 5. We argue that an emerging, twisted magnetic flux loop will tend to have a uniform q along its length. The increase in the tube radius R as it rises results in a decreasing value of qcr. This means that the apex of the flux loop will become kink unstable before the rest of the tube. 6. Our results suggest that most twisted flux tubes rising through the convection zone will be stable to kinking. Those few tubes which are kink unstable, and which presumably become knotted or kinked active regions upon emergence, only become kink unstable some time after they have begun rising through the convection zone.

  3. Magnetic perturbation effects on noise and startup in DC-operating oven magnetrons

    Microsoft Academic Search

    V. Bogdan Neculaes; Michael C. Jones; Ronald M. Gilgenbach; Y. Y. Lau; J. W. Luginsland; B. W. Hoff; W. M. White; N. M. Jordan; P. Pengvanich; Y. Hidaka; H. L. Bosman

    2005-01-01

    Previous experiments demonstrated that imposing an azimuthally varying axial magnetic field, axially asymmetric, in dc-operating oven magnetrons causes rapid mode growth (by magnetic priming) and significant noise reduction. This configuration was previously implemented by adding five perturbing magnets on the upper existing magnet of the magnetron. Experiments reported here add five perturbing magnets on each of the two existing magnets

  4. Flux Trapping Properties of Bulk HIGH-TC Superconductors in Static Field-Cooling Magnetization

    NASA Astrophysics Data System (ADS)

    Deng, Z.; Tsuzuki, K.; Miki, M.; Felder, B.; Hara, S.; Izumi, M.

    2013-06-01

    The trapping process and saturation effect of trapped magnetic flux of bulk high-temperature superconductors by static field-cooling magnetization (FCM) are reported in the paper. With a cryogenic Bell Hall sensor attached on the center of the bulk surface, the synchronous magnetic signals were recorded during the whole magnetization process. It enables us to know the flux trapping behavior since the removal of the excitation field, as well as the subsequent flux relaxation phenomenon and the flux dissipation in the quench process of the bulk sample. With the help of flux mapping techniques, the relationship between the trapped flux and the applied field was further investigated; the saturation effect of trapped flux was discussed by comparing the peak trapped field and total magnetic flux of the bulk sample. These studies are useful to understand the basic flux trapping properties of bulk superconductors.

  5. Acoustic waves in random ensembles of magnetic fluxes

    SciTech Connect

    Ryutova, M.P.

    1995-10-10

    To analyze the observational data and provide the appropriate diagnostic procedure for photospheric manifestation of solar oscillations it is necessary to take into account strong inhomogeneity of solar atmosphere with respect to distribution of magnetic fields. We study the collective phenomena in the propagation of acoustic waves and unsteady wave-packets through quite regions, sunspots and plages, including time-dependent response of these regions to solar oscillations, the energy transfer mechanisms, frequency shift effects and reradiation of the acoustic waves in higher layers of atmosphere. We show that the dynamics of differently magnetized regions, their dispersion properties, and their response to the propagation of acoustic waves are completely different. We describe the effects caused by the specific distribution and randomness of magnetic flux tubes, which can be observed and which can provide the tools for diagnostic goals.

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

    E-print Network

    Giuseppe De Nittis; Max Lein

    2011-09-09

    In this work, we investigate conditions which ensure the existence of an exponentially localized Wannier basis for a given periodic hamiltonian. We extend previous results in [Pan07] to include periodic zero flux magnetic fields which is the setting also investigated in [Kuc09]. The new notion of magnetic symmetry plays a crucial role; 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 is shown; this improves part of the analysis of [Kuc09]. Finally, for d>4 and d>2m (unstable rank regime) we show that the mere analysis of Chern classes does not suffice in order to prove trivility and thus exponential localization.

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

    E-print Network

    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 ...

  8. Measurements of EUV Coronal Holes and Open Magnetic Flux

    E-print Network

    Lowder, Chris; Leamon, Robert; Liu, Yang

    2015-01-01

    Coronal holes are regions on the Sun's surface that map the foot-prints of open magnetic field lines. We have developed an automated routine to detect and track boundaries of long-lived coronal holes using full-disk EUV images obtained by SoHO:EIT, SDO:AIA, and STEREO:EUVI. We measure coronal hole areas and magnetic flux in these holes, and compare the measurements with calculations by the PFSS model. It is shown that, from 1996 through 2010, the total area of coronal holes measured with EIT images varies between 5$\\%$ and 17$\\%$ of the total solar surface area, and the total unsigned open flux varies between $2-5 \\times 10^{22}$ Mx. The solar cycle dependence of these measurements are similar to the PFSS results, but the model yields larger hole areas and greater open flux than observed by EIT. The AIA/EUVI measurements from 2010-2013 show coronal hole area coverage of 5-10$\\%$ of the total surface area, with significant contribution from low latitudes, which is under-represented by EIT. AIA/EUVI have measur...

  9. Single-sided mobile NMR apparatus using the transverse flux of a single permanent magnet

    Microsoft Academic Search

    Wei-Hao Chang; Jyh-Horng Chen; Lian-Pin Hwang

    2010-01-01

    This study presents a simple design for a mobile, single-sided nuclear magnetic resonance (NMR) apparatus which uses the magnetic flux parallel to the magnetization direction of a single, disc-shaped permanent magnet polarized in radial direction. The stray magnetic field above the magnet is approximately parallel to the magnetization direction of the magnet and is utilized as the B0 magnetic field

  10. Magnetic flux diffusion inside a superconducting long rod with square cross section in the flux-flow regime

    NASA Astrophysics Data System (ADS)

    Nader, A.

    2002-08-01

    The nonlinear diffusion equation of the flux density in the flux-flow regime was solved numerically for a superconducting long rod with square cross section. The applied magnetic field was supposed parallel to the rod length. It was shown that when the flux diffuses inward, the flux front becomes circular, and does not keep its initial square form. On the other hand, the magnetization relaxation of the rod was found to vary with time as ( t+ t0) -1, after a time negligible compared to the constant t0.

  11. A low-noise ferrite magnetic shield T. W. Kornack,a

    E-print Network

    Romalis, Mike

    with fluctuation-dissipation theorem. In particular, magnetic viscosity effects result in an imaginary component with shield design, we also derive simple analytic relationships for Johnson current noise and magnetizationA low-noise ferrite magnetic shield T. W. Kornack,a S. J. Smullin, S.-K. Lee, and M. V. Romalis

  12. How is open solar magnetic flux lost over the solar cycle?

    Microsoft Academic Search

    M. J. Owens; N. U. Crooker; M. Lockwood

    2011-01-01

    The Sun's open magnetic field, magnetic flux dragged out into the heliosphere by the solar wind, varies by approximately a factor of 2 over the solar cycle. We consider the evolution of open solar flux in terms of a source and loss term. Open solar flux creation is likely to proceed at a rate dependent on the rate of photospheric

  13. Decoupling Suspension Controller Based on Magnetic Flux Feedback

    PubMed Central

    Zhang, Wenqing; Li, Jie; Zhang, Kun; Cui, Peng

    2013-01-01

    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. PMID:23844415

  14. Decoupling suspension controller based on magnetic flux feedback.

    PubMed

    Zhang, Wenqing; Li, Jie; Zhang, Kun; Cui, Peng

    2013-01-01

    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. PMID:23844415

  15. Three-dimensional Magnetostriction and Vector Magnetic Properties under Alternating Magnetic Flux Conditions in Arbitrary Direction

    NASA Astrophysics Data System (ADS)

    Wakabayashi, Daisuke; Todaka, Takashi; Enokizono, Masato

    This paper presents measured magnetostriction of electrical steel sheets under alternating magnetic flux conditions. In the measurements, we used a two-dimensional vector magnetic property measurement system, and a three-axial strain gauge. In order to know magnetostrictions in arbitrary direction, the strain tensor was evaluated. In addition, we try to evaluate the magnetostrictions in thickness direction. In this paper, the three-dimensional magnetostriction in non-oriented and grain-oriented silicon steel sheets are compared.

  16. Three-dimensional Magnetostriction and Vector Magnetic Properties under Alternating Magnetic Flux Conditions in Arbitrary Direction

    Microsoft Academic Search

    Daisuke Wakabayashi; Takashi Todaka; Masato Enokizono

    2010-01-01

    This paper presents measured magnetostriction of electrical steel sheets under alternating magnetic flux conditions. In the measurements, we used a two-dimensional vector magnetic property measurement system, and a three-axial strain gauge. In order to know magnetostrictions in arbitrary direction, the strain tensor was evaluated. In addition, we try to evaluate the magnetostrictions in thickness direction. In this paper, the three-dimensional

  17. Numerical Simulations of 3D Coronal Magnetic Fields Resulting from the Emergence of Twisted Magnetic Flux Tubes

    Microsoft Academic Search

    Y. Fan; S. E. Gibson

    2004-01-01

    We present MHD simulations in the low-beta regime of the evolution of the 3D coronal magnetic field as an arched, twisted magnetic flux tube is transported into a pre-existing coronal potential magnetic arcade. It is found that the line-tied emerging flux tube becomes kink unstable when a sufficient amount of twist is transported into the corona. For an emerging flux

  18. C IV fluxes from the Sun as a star, and the correlation with magnetic flux

    NASA Technical Reports Server (NTRS)

    Schrijver, C. J.; Linsky, J. L.; Bennett, J.; Brown, A.; Saar, S. H.

    1988-01-01

    A total of 144 C IV wavelength 1548 Solar Maximum Mission (SMM)-UVSP spectroheliograms of solar plages were analyzed, some of which are series of exposures of the same region on the same day. Also analyzed were the C IV wavelength 1551 rasters of plages and C IV wavelength 1548 rasters of the quiet sun. The sample contained data on 17 different plages, observed on 50 different days. The center-to-limb variations of the active regions show that the optical thickness effects in the C IV wavelength 1548 line can be neglected in the conversion from intensity to flux density. As expected for the nearly optically thin situation, the C IV wavelength 1548 line is twice as bright as the C IV 1551 line. The average C IV wavelength 1548 flux density for a quiet region is 2700 ergs/cm/s and, with surprisingly little scatter, 18,000 erg/cm/s for plages. The intensity histograms of rasters obtained at disk center can be separated into characteristic plage and quiet sun contributions with variable relative filling factors. The relationship between the C IV and magnetic flux densities for spatially resolved data is inferred to be almost the same, with only an additional factor of order unity in the constant of proportionality.

  19. Magnetic flux emergence, flares, and coronal mass ejections

    NASA Astrophysics Data System (ADS)

    Mandrini, Cristina H.; Schmieder, Brigitte; Cristiani, Germán; Demoulin, Pascal; Guo, Yang

    We study the violent events occurring in the cluster of two active regions (ARs), NOAA numbers 11121 and 11123, observed in November 2010 with instruments onboard the Solar Dynamics Observatory and from Earth. Within one day the total magnetic flux increased by 70 per cent with the emergence of new groups of bipoles in AR 11123. These emergences led to a very complex magnetic configuration in which around ten solar flares, some of them accompanied by coronal mass ejections (CMEs), occurred. A magnetic-field topology somputation indicates the presence of null points, associated separatrices and quasi-separatrix layers (QSLs) where magnetic reconnection is prone to occur. Based on this analysis, we propose a scenario to explain the origin of a low-energy event preceding a filament eruption, which is accompanied by a two-ribbon flare and CME, and a consecutive confined flare in AR 11123. The results of our topology computation can also explain the locations of flare ribbons in two other events, one preceding and one following the ones just mentioned.

  20. Mode-hopping mechanism generating colored noise in a magnetic tunnel junction based spin torque oscillator

    SciTech Connect

    Sharma, Raghav [Department of Physics, Indian Institute of Technology, Delhi, New Delhi 110016 (India); Dürrenfeld, P.; Iacocca, E. [Department of Physics, University of Gothenburg, Gothenburg 412 96 (Sweden); Heinonen, O. G. [Argonne National Laboratory, Materials Science Division, Lemont, Illinois 60439 (United States); Åkerman, J. [Department of Physics, University of Gothenburg, Gothenburg 412 96 (Sweden); Materials Physics, School of ICT, KTH-Royal Institute of Technology, Electrum 229, Kista 164 40 (Sweden); Muduli, P. K. [Department of Physics, Indian Institute of Technology, Delhi, New Delhi 110016 (India); Department of Physics, University of Gothenburg, Gothenburg 412 96 (Sweden)

    2014-09-29

    The frequency noise spectrum of a magnetic tunnel junction based spin torque oscillator is examined where multiple modes and mode-hopping events are observed. The frequency noise spectrum is found to consist of both white noise and 1/f frequency noise. We find a systematic and similar dependence of both white noise and 1/f frequency noise on bias current and the relative angle between the reference and free layers, which changes the effective damping and hence the mode-hopping behavior in this system. The frequency at which the 1/f frequency noise changes to white noise increases as the free layer is aligned away from the anti-parallel orientation w.r.t the reference layer. These results indicate that the origin of 1/f frequency noise is related to mode-hopping, which produces both white noise as well as 1/f frequency noise similar to the case of ring lasers.

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

    NASA Astrophysics Data System (ADS)

    Kobel, P.; Solanki, S. K.; Borrero, J. M.

    2012-06-01

    Context. 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. Aims: 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. Methods: 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 scales with the total unsigned flux in the box). Results: Both the continuum brightness of the magnetic elements and the dispersion of the LOS velocities anti-correlate with the mean longitudinal field strength. This can be attributed to the "magnetic patches" (here defined as areas where the longitudinal field strength is above 100 G) carrying most of the flux in the boxes. There the velocity amplitude and the spatial scale of convection are reduced. Due to this hampered convective transport, these patches appear darker than their surroundings. Consequently, the average brightness of a box decreases as the the patches occupy a larger fraction of it and the amount of embedded flux thereby increases. Conclusions: Our results suggest that as the magnetic flux increases locally (e.g. from weak network to strong plage), the heating of the magnetic elements is reduced by the intermediate of a more suppressed convective energy transport within the larger and stronger magnetic patches. This, together with the known presence of larger magnetic features, could explain the previously found lower contrasts of the brightest magnetic elements in ARs compared to the QS. The inhibition of convection also affects the average continuum brightness of a photospheric region, so that at disk center, an area of photosphere in strong network or plage appears darker than a purely quiet one. This is qualitatively consistent with the predictions of 3D MHD simulations.

  2. INTERPLANETARY MAGNETIC FLUX DEPLETION DURING PROTRACTED SOLAR MINIMA

    SciTech Connect

    Connick, David E.; Smith, Charles W.; Schwadron, Nathan A., E-mail: davideconnick@gmail.com, E-mail: Charles.Smith@unh.edu, E-mail: N.Schwadron@unh.edu [Physics Department, Space Science Center, University of New Hampshire, Durham, NH (United States)

    2011-01-20

    We examine near-Earth solar wind observations as assembled within the Omni data set over the past 15 years that constitute the latest solar cycle. We show that the interplanetary magnetic field continues to be depleted at low latitudes throughout the protracted solar minimum reaching levels below previously predicted minima. We obtain a rate of flux removal resulting in magnetic field reduction by 0.5 nT yr{sup -1} at 1 AU when averaged over the years 2005-2009 that reduces to 0.3 nT yr{sup -1} for 2007-2009. We show that the flux removal operates on field lines that follow the nominal Parker spiral orientation predicted for open field lines and are largely unassociated with recent ejecta. We argue that the field line reduction can only be accomplished by ongoing reconnection of nominally open field lines or very old closed field lines and we contend that these two interpretations are observationally equivalent and indistinguishable.

  3. Calculation of equipotentials and flux lines in axially symmetrical permanent magnet assemblies by computer

    Microsoft Academic Search

    W. Harrold

    1972-01-01

    Two equivalent theoretical models of permanent magnets are used to develop algorithms for numerically computing the magnetic scalar potential and the magnetic vector potential in the vicinity of an axially symmetric array of pole pieces and permanent magnets. A computer program based on these algorithms calculates equipotential surfaces and flux lines in and around the magnets and pole pieces. In

  4. Design and Analysis of a Permanent Magnet Claw Pole\\/Transverse Flux Motor with SMC Core

    Microsoft Academic Search

    YouGuang Guo; Jian Guo Zhu; Haiwei Lu

    2005-01-01

    This paper presents the design and analysis of a claw pole\\/transverse flux motor (CPTFM) with soft magnetic composite (SMC) core and permanent magnet flux-concentrating rotor. Three-dimensional magnetic field finite element analysis is conducted to accurately calculate key motor parameters such as winding flux, back electromotive force, winding inductance, and core loss. Equivalent electric circuit is derived under optimum brushless DC

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

    SciTech Connect

    Santos-Lima, R.; De Gouveia Dal Pino, E. M. [Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, R. do Matao, 1226, Sao Paulo, SP 05508-090 (Brazil); Lazarian, A.; Cho, J. [Department of Astronomy, University of Wisconsin, Madison, WI 53706 (United States)

    2010-05-01

    The diffusion of astrophysical magnetic fields in conducting fluids in the presence of turbulence depends on whether magnetic fields can change their topology via reconnection in highly conducting media. Recent progress in understanding fast magnetic reconnection in the presence of turbulence reassures that the magnetic field behavior in computer simulations and turbulent astrophysical environments is similar, as far as magnetic reconnection is concerned. This makes it meaningful to perform MHD simulations of turbulent flows in order to understand the diffusion of magnetic field in astrophysical environments. Our studies of magnetic field diffusion in turbulent medium reveal interesting new phenomena. First of all, our three-dimensional MHD simulations initiated with anti-correlating magnetic field and gaseous density exhibit at later times a de-correlation of the magnetic field and density, which corresponds well to the observations of the interstellar media. While earlier studies stressed the role of either ambipolar diffusion or time-dependent turbulent fluctuations for de-correlating magnetic field and density, we get the effect of permanent de-correlation with one fluid code, i.e., without invoking ambipolar diffusion. In addition, in the presence of gravity and turbulence, our three-dimensional simulations show the decrease of the magnetic flux-to-mass ratio as the gaseous density at the center of the gravitational potential increases. We observe this effect both in the situations when we start with equilibrium distributions of gas and magnetic field and when we follow the evolution of collapsing dynamically unstable configurations. Thus, the process of turbulent magnetic field removal should be applicable both to quasi-static subcritical molecular clouds and cores and violently collapsing supercritical entities. The increase of the gravitational potential as well as the magnetization of the gas increases the segregation of the mass and magnetic flux in the saturated final state of the simulations, supporting the notion that the reconnection-enabled diffusivity relaxes the magnetic field + gas system in the gravitational field to its minimal energy state. This effect is expected to play an important role in star formation, from its initial stages of concentrating interstellar gas to the final stages of the accretion to the forming protostar. In addition, we benchmark our codes by studying the heat transfer in magnetized compressible fluids and confirm the high rates of turbulent advection of heat obtained in an earlier study.

  6. The frequency and temperature dependence of noise in YBa2Cu3O7 multijunction flux-flow amplifiers

    Microsoft Academic Search

    J. C. Macfarlane; L. Hao; J. Kuznik; C. M. Pegrum

    1995-01-01

    Measurements of the absolute noise power of high Tc multijunction flux-flow amplifiers in the frequency range 0.1 Hz–60 kHz are reported. The noise is found to have maxima at the operating points corresponding to optimum transresistance and gain, and is consistent with existing models of critical current fluctuations as found in single grain boundary junctions. The frequency dependence of the

  7. Investigation of the magnetic Barkhausen noise using elementary signals parameters in 1000 commercial steel

    NASA Astrophysics Data System (ADS)

    Pérez-Benitez, J. A.; Padovese, L. R.; Capó-Sánchez, J.; Anglada-Rivera, J.

    2003-07-01

    This paper presents results on the magnetic Barkhausen noise of 1000 commercial steel using elementary signals parameters. The applied stress and grain sizes were correlated with the RMS voltage of the Magnetic Barkhausen Noise. As alternative, a new method was developed to correlate elementary signal shapes with the grain size and tensile stress, giving a physical explanation in both cases.

  8. Investigation of Flux Linkage Profile Measurement Methods for Switched Reluctance Motors and Permanent Magnet

    E-print Network

    Lu, Kaiyuan

    - 1 - Investigation of Flux Linkage Profile Measurement Methods for Switched Reluctance Motors for switched reluctance motors (SRM's) and permanent magnet motors (PMM's). Various measurement methods have reluctance motors, permanent magnet motors. I. INTRODUCTION Switched Reluctance Motors (SRM's) have very

  9. Magnetic effects on 1f noise in n-InSb

    Microsoft Academic Search

    P. Vande Voorde; W. F. Love

    1981-01-01

    1f noise has been observed in resistors fabricated from high-purity single-crystal n-InSb at 75 K. Noise levels which are much smaller than predicted by the Hooge relation are routinely observed. The 1f noise is extremely sensitive to an applied magnetic field which is perpendicular to the current. A field of 24 kG increases the fractional noise, SVV2, by a factor

  10. On-line estimation of permanent magnet flux linkage ripple for PMSM based on a Kalman filter

    Microsoft Academic Search

    Xiao Xi; Zhang Meng; Li Yongdong; Li Min

    2006-01-01

    In order to get good control performance in permanent magnet synchronous motor (PMSM) control fields, the accurate permanent magnet flux linkage (rotor flux linkage) value is needed. For stator flux estimation and full order or reduced order observer, the rotor flux linkage is treated as a known and constant parameter. But in applications, the rotor flux linkage can vary in

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

    NASA Technical Reports Server (NTRS)

    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.

  12. Simulations of emerging magnetic flux. II. The formation of unstable coronal flux ropes and the initiation of coronal mass ejections

    SciTech Connect

    Leake, James E. [College of Science, George Mason University, 4400 University Drive, Fairfax, VA 22030 (United States); Linton, Mark G. [U.S. Naval Research Lab 4555 Overlook Ave., SW Washington, DC 20375 (United States); Antiochos, Spiro K., E-mail: jleake@gmu.edu [Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20711 (United States)

    2014-05-20

    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 (?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.

  13. Testing of the Mark 101 magnetic flux compression generator

    SciTech Connect

    Freeman, B.L.; Fowler, C.M.; King, J.C.; Martinez, A.R.

    1986-01-01

    The Mark 101 explosive flux compression generator is a line-initiated, vacuum/magnetically insulated, helical generator. This device offered some unique challenges in transforming the theoretical design into a testable experiment. The two main reasons for this are that in theory an eight-turn, four-wire Mark 101 possesses a terminal dL/dt of approx.0.5 ..cap omega.. and operates with electric fields which are greater than the threshold for electron field emission. With this in mind, we designed an integral vacuum-jacket-generator configuration with a passive load inductance of less than or equal to0.5 ..mu..H. The generator contained approx.8 ..mu..H of initial inductance. The field emission required the stator to be entirely sealed within the vacuum jacket. The open, helical stator resulted in the presence of non-trivial leakage fields and voltages. To accommodate these fields, the vacuum chamber for the generator was segmented and axially insulated with rings of acrylic, similar to stacked-ring diodes. We made no attempt to break the azimuthal metal surfaces due to the physical difficulty this would incur. Diagnostics included an input current Rogowski loop, a load Rogowski loop, two dB/dt probes in the load, a Faraday fiber-optic current sensor, and two dB/dt probes in the region between the stator winding and the vacuum jacket to measure the leakage azimuthal and axial magnetic fields. The results of explosive tests are presented.

  14. Magnetic reconnection in 3D magnetosphere models: magnetic separators and open flux production

    NASA Astrophysics Data System (ADS)

    Glocer, A.; Dorelli, J.; Toth, G.; Komar, C. M.; Cassak, P.

    2014-12-01

    There are multiple competing definitions of magnetic reconnection in 3D (e.g., Hesse and Schindler [1988], Lau and Finn [1990], and Boozer [2002]). In this work we focus on separator reconnection. A magnetic separator can be understood as the 3D analogue of a 2D x line with a guide field, and is defined by the line corresponding to the intersection of the separatrix surfaces associated with the magnetic nulls. A separator in the magnetosphere represents the intersection of four distinct magnetic topologies: solar wind, closed, open connected to the northern hemisphere, and open connected to the southern hemisphere. The integral of the parallel electric field along the separator defines the rate of open flux production, and is one measure of the reconnection rate. We present three methods for locating magnetic separators and apply them to 3D resistive MHD simulations of the Earth's magnetosphere using the BATS-R-US code. The techniques for finding separators and determining the reconnection rate are insensitive to IMF clock angle and can in principle be applied to any magnetospheric model. The present work examines cases of high and low resistivity, for two clock angles. We also examine the separator during Flux Transfer Events (FTEs) and Kelvin-Helmholtz instability.

  15. Modeling of an Electronic Noise and Media in a Magnetic Recording Read Channel Using VHDL

    Microsoft Academic Search

    R. Bogdan Staszewski

    2007-01-01

    This paper presents a modeling and simulation methodology of two challenging aspects of a partial response maximum likelihood (PRML) magnetic recording read channel: electronic noise and magnetic media. The methodology is based on an event-driven simulator that supports real-valued signals, such as standard VHDL. A few examples are presented for the noise source, PLL jitter\\/wander modeling, and magnetic media waveform

  16. Original superconducting quantum interference device (SQUID) design and measurement technique for flux noise source localization in SQUID systems

    Microsoft Academic Search

    M. Lam Chok Sing; S. Flament; X. Ridereau; C. Gunther; L. Méchin; D. Bloyet

    2003-01-01

    We present an original method for studying the low frequency flux noise due to vortices in superconducting quantum interference device (SQUID) systems. We use two SQUIDs connected to the same washer in order to study the correlation of their outputs. A dedicated electronic system has been built so as to operate both SQUIDs at the same time. It was thus

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

    SciTech Connect

    Gent, F. A.; Erdélyi, R. [SP"2RC, School of Mathematics and Statistics, University of Sheffield, S3 7RH (United Kingdom); Fedun, V., E-mail: f.gent@shef.ac.uk [Space Systems Laboratory, Department of Automatic Control and Systems Engineering, University of Sheffield, S1 3JD (United Kingdom)

    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.

  18. OBSERVATIONAL CONSEQUENCES OF A MAGNETIC FLUX ROPE EMERGING INTO THE CORONA S. E. Gibson,1

    E-print Network

    Demoulin, Pascal

    OBSERVATIONAL CONSEQUENCES OF A MAGNETIC FLUX ROPE EMERGING INTO THE CORONA S. E. Gibson,1 Y. Fan,1 predicts solar structures and dynamics consistent with observations. We first consider the structure twisting motions along the magnetic flux surfaces. Observations of rotating sunspots may provide better

  19. MODELS OF THE LARGE-SCALE CORONA. I. FORMATION, EVOLUTION, AND LIFTOFF OF MAGNETIC FLUX ROPES

    E-print Network

    Mackay, Duncan

    and thread through the solar atmosphere. Observations show that within the solar corona, magnetic fields such eruptions, we need to determine how flux ropes are formed and evolve in the solar corona in additionMODELS OF THE LARGE-SCALE CORONA. I. FORMATION, EVOLUTION, AND LIFTOFF OF MAGNETIC FLUX ROPES D. H

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

    NASA Astrophysics Data System (ADS)

    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.

  1. Speed control of interior permanent magnet synchronous motor drive for the flux weakening operation

    Microsoft Academic Search

    Jang-Mok Kim; Seung-Ki Sul

    1997-01-01

    A novel flux-weakening scheme for the interior permanent magnet synchronous motor (IPMSM) is proposed. This is implemented based on the output of the synchronous PI current regulator-reference voltage to the PWM inverter. The onset of flux weakening and the flux level are adjusted inherently by the outer voltage regulation loop to prevent saturation of the current regulator. Attractive features of

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

    Microsoft Academic Search

    J. P. Silva; A. J. Silvestre

    2005-01-01

    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

  3. Assessing electron heat flux dropouts as signatures of magnetic field line disconnection from the Sun

    NASA Astrophysics Data System (ADS)

    Pagel, C.; Crooker, N. U.; Larson, D. E.

    2005-07-01

    Suprathermal electrons focused along magnetic field lines, called the strahl, carry heat flux away from the Sun. Various factors can cause heat flux dropouts (HFDs), including times when the strahl almost vanishes. HFDs are a necessary but insufficient condition for detecting magnetic flux disconnected from the Sun. To quantitatively assess the fraction of HFDs which might be due to disconnected fields, we use four years of suprathermal electron data from the Wind spacecraft to perform a comprehensive survey of heat flux dropouts with durations greater than an hour. Eliminating periods within interplanetary coronal mass ejections or containing counterstreaming electrons, we find that only ~10% of HFDs have signatures consistent with disconnected flux.

  4. Landau-Lifshitz magnetization dynamics driven by a random jump-noise process (invited)

    NASA Astrophysics Data System (ADS)

    Mayergoyz, I.; Bertotti, G.; Serpico, C.

    2011-04-01

    In the paper, a jump-noise process is introduced in magnetization dynamics equations in order to account for random thermal effects. It is demonstrated that in the case of small noise, Landau-Lifshitz and Gilbert damping terms emerge as average effects caused by the jump-noise process. This approach leads to simple formulas for the damping constant in terms of the scattering rate of the jump-noise process. These formulas also reveal the dependence of the damping constant on magnetization. The analysis of random switching of magnetization caused by the jump-noise process is presented. It is shown that the switching rate at very low temperatures may appreciably deviate from the predictions of thermal activation theory, which is consistent with experimental observations of low temperature switchings and is usually attributed to the phenomenon of "macroscopic tunneling" of magnetization.

  5. Anthropogenic electromagnetic noise disrupts magnetic compass orientation in a migratory bird.

    PubMed

    Engels, Svenja; Schneider, Nils-Lasse; Lefeldt, Nele; Hein, Christine Maira; Zapka, Manuela; Michalik, Andreas; Elbers, Dana; Kittel, Achim; Hore, P J; Mouritsen, Henrik

    2014-05-15

    Electromagnetic noise is emitted everywhere humans use electronic devices. For decades, it has been hotly debated whether man-made electric and magnetic fields affect biological processes, including human health. So far, no putative effect of anthropogenic electromagnetic noise at intensities below the guidelines adopted by the World Health Organization has withstood the test of independent replication under truly blinded experimental conditions. No effect has therefore been widely accepted as scientifically proven. Here we show that migratory birds are unable to use their magnetic compass in the presence of urban electromagnetic noise. When European robins, Erithacus rubecula, were exposed to the background electromagnetic noise present in unscreened wooden huts at the University of Oldenburg campus, they could not orient using their magnetic compass. Their magnetic orientation capabilities reappeared in electrically grounded, aluminium-screened huts, which attenuated electromagnetic noise in the frequency range from 50?kHz to 5?MHz by approximately two orders of magnitude. When the grounding was removed or when broadband electromagnetic noise was deliberately generated inside the screened and grounded huts, the birds again lost their magnetic orientation capabilities. The disruptive effect of radiofrequency electromagnetic fields is not confined to a narrow frequency band and birds tested far from sources of electromagnetic noise required no screening to orient with their magnetic compass. These fully double-blinded tests document a reproducible effect of anthropogenic electromagnetic noise on the behaviour of an intact vertebrate. PMID:24805233

  6. Induced vacuum bosonic current by magnetic flux in a higher dimensional compactified cosmic string spacetime

    NASA Astrophysics Data System (ADS)

    Bragança, E. A. F.; Mota, H. F. Santana; de Mello, E. R. Bezerra

    2015-05-01

    In this paper, we analyze the bosonic current densities induced by a magnetic flux running along an idealized cosmic string in a high-dimensional spacetime, admitting that the coordinate along the string's axis is compactified. Additionally we admit the presence of a magnetic flux enclosed by the compactification axis. In order to develop this analysis we calculate the complete set of normalized bosonic wave functions obeying a quasiperiodicity condition, with arbitrary phase ?, along the compactified dimension. In this context, only azimuthal and axial currents densities take place. As to the azimuthal current, two contributions appear. The first contribution corresponds to the standard azimuthal current in a cosmic string spacetime without compactification, while the second contribution is a new one, induced by the compactification itself. The latter is an even function of the magnetic flux enclosed by the string axis and is an odd function of the magnetic flux along its core with period equal to quantum flux, ?0 = 2?/e. On the other hand, the nonzero axial current density is an even function of the magnetic flux along the core of the string and an odd function of the magnetic flux enclosed by it. We also find that the axial current density vanishes for untwisted and twisted bosonic fields in the absence of the magnetic flux enclosed by the string axis. Some asymptotic expressions for the current density are provided for specific limiting cases of the physical parameter of the model.

  7. Evaluation of Ductile Cast Iron Microstructure by Magnetic Hysteresis and Barkhausen Noise Methods

    Microsoft Academic Search

    Oleksandr STUPAKOV; Tetsuya UCHIMOTO; Toshiyuki TAKAGI; Seyed Ali SANAEE; Ivan TOM

    The work investigates applicability of the magnetic hystere- sis and Barkhausen noise techniques for testing of ductile cast iron mi- crostructure. The measurements were performed on 4 series of difier- ent matrix structures with 5 samples in each series of difierent size of spheroidal graphite. The samples were magnetized by a single yoke at quasi-static regime; their magnetic fleld was

  8. A mechanism of magnetic flux rope formation in the ionosphere of Venus

    NASA Astrophysics Data System (ADS)

    Kleeorin, N.; Rogachevskii, I.; Eviatar, A.

    1994-04-01

    Magnetic field observations in the dayside ionosphere of Venus revealed the existence of magnetic flux ropes. The general properties of these small-scale magnetic field structures can be explained by a theory of magnetic fluctuations excited by random magnetohydrodynamic flows of ionospheric plasma. The local spatial distribution of the magnetic field is random: the field is concentrated inside flux tubes separated by regions with weak fields. A mechanism of amplification of magnetic fluctuations in the presence of zero mean field, proposed by Zeldovich, is applied to the nonlinear theory of flux rope formation by means of a nonlinear equation derived from the induction equation; the nonlinearity is associated with the Hall effect. The equation describes the evolution of the correlation function of the magnetic field and resembles the Schroedinger equation except for a variable mass and the absence of the imaginary unit in the time-derivative term. In the limit of large Reynolds number the formulation is amenable to treatment by a modified WKB method. On the basis of this theory it is possible to explain why flux ropes are not observed if there is a strong regular large-scale magnetic field caused by the lowering of the ionopause. The theory predicts correctly the cross section of the flux ropes in the ionosphere of Venus and the maximum value of the magnetic field inside the flux rope.

  9. Control of magnetic flux and eddy currents in magnetic films for on-chip radio frequency inductors: Role of the magnetic vias

    NASA Astrophysics Data System (ADS)

    Wu, Hao; Gardner, Donald S.; Zhao, Shirong; Huang, Hai; Yu, Hongbin

    2014-05-01

    In this paper, the role of the magnetic vias for magnetic flux and eddy current control is investigated using both simulations and experiments that used different patterning techniques and by altering the magnetic via width. Improved finger-shaped magnetic vias have been designed and integrated into on-chip radio frequency inductors improving the peak quality factor from 400 MHz to 800 MHz without sacrificing the inductance enhancement. The eddy currents and magnetic flux density in different areas of the magnetic vias are analyzed by 3D electromagnetic simulation. With optimized magnetic vias, the high frequency response of up to 2 GHz has been achieved.

  10. Evidence for submergencew of magnetic flux in a growing active region

    NASA Technical Reports Server (NTRS)

    Rabin, D. M.; Moore, R. L.; Hagyard, M. J.

    1985-01-01

    In NOAA Active Region 2372 (April 1980), 4 x 10 to the 20th power maxwell of magnetic flux concentrated within a 30" circular area disappeared overnight. Vector magnetograms show that all components of the magnetic field weakened together. If the field had weakened through diffusion or fluid flow, 80% of the original flux would still have been detected by the magnetograph within a suitably enlarged area. In fact there was at least a threefold decrease in detected flux. Evidently, magnetic field was removed from the photosphere. Since the disappearing flux was located in a region of low magnetic shear and low activity, it is unlikely that the field dissipated through reconnection. The most likely possibility is that flux submerged. Observations suggest that even in the growth phase of active regions, submergence is a strong process comparable in magnitude to emergence.

  11. A case for submergence of magnetic flux in a solar active region

    NASA Technical Reports Server (NTRS)

    Rabin, D.; Moore, R.; Hagyard, M. J.

    1984-01-01

    In NOAA Active Region 2372 (April 1980), 4 x 10 to the 20th maxwells of magnetic flux concentrated in an area 30 arcsec across disappeared overnight. Vector magnetograms show that all components of the magnetic field weakened together. If the field had weakened through diffusion or fluid flow, 90 percent of the original flux would still have been detected by the magnetograph within a suitably enlarged area. In fact there was a threefold decrease in detected flux. Evidently, magnetic field was removed from the photosphere. Since the disappearing flux was located in a region of low magnetic shear and low activity in H-alpha and Ly-alpha, it is unlikely that the field dissipated through reconnection. It is argued that the most likely possibility is that flux submerged. The observations suggest that even during the growth phase of active regions, submergence is a strong process comparable in magnitude to emergence.

  12. Magnetic flux emergence in granular convection: Radiative MHD simulations and observational signatures

    E-print Network

    Mark Chun Ming Cheung; Manfred Schuessler; Fernando Moreno-Insertis

    2007-02-25

    We study the emergence of magnetic flux from the near-surface layers of the solar convection zone into the photosphere. 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. 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 $10^{19}$ 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.

  13. Comparison of Magnetic Flux Distribution between a Coronal Hole and a Quiet Region

    E-print Network

    Jun Zhang; Jun Ma; Haimin Wang

    2007-05-04

    Employing Big Bear Solar Observatory (BBSO) deep magnetograms and H${\\alpha}$ images in a quiet region and a coronal hole, observed on September 14 and 16, 2004, respectively, we have explored the magnetic flux emergence, disappearance and distribution in the two regions. The following results are obtained: (1) The evolution of magnetic flux in the quiet region is much faster than that in the coronal hole, as the flux appeared in the form of ephemeral regions in the quiet region is 4.3 times as large as that in the coronal hole, and the flux disappeared in the form of flux cancellation, 2.9 times as fast as in the coronal hole. (2) More magnetic elements with opposite polarities in the quiet region are connected by arch filaments, estimating from magnetograms and H${\\alpha}$ images. (3) We measured the magnetic flux of about 1000 magnetic elements in each observing region. The flux distribution of network and intranetwork (IN) elements is similar in both polarities in the quiet region. For network fields in the coronal hole, the number of negative elements is much more than that of positive elements. However for the IN fields, the number of positive elements is much more than that of negative elements. (4) In the coronal hole, the fraction of negative flux change obviously with different threshold flux density. 73% of the magnetic fields with flux density larger than 2 Gauss is negative polarity, and 95% of the magnetic fields is negative, if we only measure the fields with their flux density larger than 20 Gauss. Our results display that in a coronal hole, stronger fields is occupied by one predominant polarity; however the majority of weaker fields, occupied by the other polarity.

  14. Optimal Control of a Magnetic Bearing without Bias Flux Using Finite Voltage Charles Yang *, Research Assistant

    E-print Network

    Knospe, Carl

    Optimal Control of a Magnetic Bearing without Bias Flux Using Finite Voltage Charles Yang, Sterling Heights, MI 48314 SUMMARY Conventional Active Magnetic Bearings (AMB) are operated using a bias. In this paper, optimal control of a magnetic bearing without bias is investigated. A single degree

  15. Stator-flux-based vector control of induction machines in magnetic saturation

    SciTech Connect

    Hofmann, H.; Sanders, S.R.; Sullivan, C. [Univ. of California, Berkeley, CA (United States). Dept. of Electrical Engineering and Computer Sciences

    1995-12-31

    In many variable-torque applications of induction machines it is desirable to operate the machine in magnetic saturation, thus allowing the machine to produce higher torques. Stator-flux-based control schemes have been developed as a possible alternative method of control of induction machines. Stator-flux-based control schemes need not depend on the magnetic characteristics of the machine, and hence are potentially more robust and easier to implement in magnetic saturation than rotor-flux-based control. The authors analyze the induction machine in saturation using a nonlinear {pi}-model of the machine`s magnetics, and develop a control scheme in the stator flux reference frame that is independent of magnetics. Experiments carried out on a 3 hp, 1,800 rpm wound rotor induction machine show smooth operation of the control scheme at torque levels up to at least 4 times rated torque.

  16. Flux penetration into superconducting Nb3Sn in oblique magnetic fields Diana G. Gheorghe, Mariela Menghini, and Rinke J. Wijngaarden

    E-print Network

    Wijngaarden, Rinke J.

    Flux penetration into superconducting Nb3Sn in oblique magnetic fields Diana G. Gheorghe, Mariela; published 14 June 2006 Penetration of magnetic flux into a rectangular platelet of superconducting Nb3Sn of the applied magnetic field Ha consid- erably exceeds the field of full-flux penetration into the sample, Hp

  17. Analysis and Design of a High Power Density Axial Flux Permanent Magnet Linear Synchronous Machine Used for Stirling System

    Microsoft Academic Search

    Ping Zheng; Xuhui Gan; Lin Li

    2010-01-01

    A high power density axial flux permanent magnet linear synchronous machine and the stirling system will be introduced. This machine is a tubular axial flux permanent magnet machine. It comprises two parts: stator and mover. With the 2D finite-element method (FEM), the high power density axial flux permanent magnet linear synchronous machine will be analyzed and designed. To get the

  18. Analytical modelling of the magnetic field in axial flux permanent magnet machines with semi-closed slots at no load

    Microsoft Academic Search

    A. Bellara; Y. Amara; G. Barakat; P. Reghem

    2010-01-01

    This paper presents an analytical solution for prediction of the no-load magnetic field in slotted semi-closed permanent magnet axial flux synchronous machines. The technique is based on 2-D solution of the Maxwell's equations using the separation of variables method, this technique is validated for two different machines. The magnetic field expressions are developed in slots regions, magnetic airgap region, slot

  19. Spin Quantum Tunneling in Single Molecular Magnets: Fingerprints in Transport Spectroscopy of Current and Noise

    E-print Network

    of Current and Noise C. Romeike, M. R. Wegewijs, and H. Schoeller Institut fu¨r Theoretische Physik A, RWTH. We find current and noise oscillations as a function of bias voltage due to a weak violation of spin in the nonequilibrium occupations of the magnetic states since they allow for a violation of spin-selection rules

  20. The signal photon flux, background photons and shot noise in electromagnetic response of high-frequency relic gravitational waves

    Microsoft Academic Search

    Jin Li; Kai Lin; Fangyu Li; Yuanhong Zhong

    2011-01-01

    On the basis of the electromagnetic response of high frequency relic gravitational waves (HFRGWs), we research on more accurate\\u000a calculation of signal (i.e. transverse perturbative photon flux (PPF)) and background photons flux (BPF) in the sycro-resonance\\u000a electromagnetic system, which consists of Gaussian beam (GB), a static magnetic field and fractal membranes. According to\\u000a the relationship between frequency of gravitational waves

  1. Reducing magnetic field induced noise in broad-band seismic recordings

    Microsoft Academic Search

    Thomas Forbriger

    2007-01-01

    Seismic broad-band sensors are known to be sensitive to the magnetic field. Magnetic storms and man-made disturbances of the magnetic field can produce significant noise in seismic recordings. I show that variations in the magnetic field translate directly into apparent acceleration of the seismic sensor within the period range from 60 to 1200s for all leaf-spring sensors under investigation. For

  2. Fermionic condensate in a conical space with a circular boundary and magnetic flux

    SciTech Connect

    Bellucci, S. [INFN, Laboratori Nazionali di Frascati, Via Enrico Fermi 40, 00044 Frascati (Italy); Bezerra de Mello, E. R. [Departamento de Fisica, Universidade Federal da Paraiba 58.059-970, Caixa Postal 5.008, Joao Pessoa, PB (Brazil); Saharian, A. A. [Department of Physics, Yerevan State University, Alex Manoogian Street, 0025 Yerevan (Armenia)

    2011-04-15

    The fermionic condensate is investigated in a (2+1)-dimensional conical spacetime in the presence of a circular boundary and a magnetic flux. It is assumed that on the boundary the fermionic field obeys the MIT bag boundary condition. For irregular modes, we consider a special case of boundary conditions at the cone apex, when the MIT bag boundary condition is imposed at a finite radius, which is then taken to zero. The fermionic condensate is a periodic function of the magnetic flux with the period equal to the flux quantum. For both exterior and interior regions, the fermionic condensate is decomposed into boundary-free and boundary-induced parts. Two integral representations are given for the boundary-free part for arbitrary values of the opening angle of the cone and magnetic flux. At distances from the boundary larger than the Compton wavelength of the fermion particle, the condensate decays exponentially, with the decay rate depending on the opening angle of the cone. If the ratio of the magnetic flux to the flux quantum is not a half-integer number for a massless field the boundary-free part in the fermionic condensate vanishes, whereas the boundary-induced part is negative. For half-integer values of the ratio of the magnetic flux to the flux quantum, the irregular mode gives a nonzero contribution to the fermionic condensate in the boundary-free conical space.

  3. Distribution of magnetic flux density at the solar surface. Formulation and results from simulations

    NASA Astrophysics Data System (ADS)

    Steiner, O.

    2003-08-01

    A formal description of the distribution of magnetic flux density in a quiet Sun region supplemented by an example and an application is presented. We define a flux-based probability density, which is useful to reveal the presence of any strong-field component in the region. The corresponding flux-based probability distribution gives the fraction of the total absolute magnetic flux with a given field-strength limit. Application to the simulations of convective field intensification of Grossmann-Doerth et al. (1998) shows, that, depending on the strength of the initial homogeneous vertical field, 1-50% of the total magnetic flux within the computational domain of 3 arcsec width is concentrated into flux fibrils with a flux density exceeding 0.1 T. It is shown that a low efficiency of the flux-concentration process is compatible with new observations that suggest a large fraction of the surface magnetic field to have a flux density below 0.1 T.

  4. Magnetic flux conversion and relaxation toward a minimum-energy state in S-1 spheromak plasmas

    SciTech Connect

    Janos, A.

    1985-09-01

    S-1 Spheromak currents and magnetic fluxes have been measured with Rogowski coils and flux loops external to the plasma. Toroidal plasma currents up to 350 kA and spheromak configuration lifetimes over 1.0 msec have been achieved at moderate power levels. The plasma formation in the S-1 Spheromak device is based on an inductive transfer of poloidal and toroidal magnetic flux from a toroidal ''flux core'' to the plasma. Formation is programmed to guide the configuration into a force-free, minimum-energy Taylor state. Properly detailed programming of the formation process is found not to be essential since plasmas adjust themselves during formation to a final equilibrium near the Taylor state. After formation, if the plasma evolves away from the stable state, then distinct relaxation oscillation events occur which restore the configuration to that stable state. The relaxation process involves reconnection of magnetic field lines, and conversion of poloidal to toroidal magnetic flux (and vice versa) has been observed and documented. The scaling of toroidal plasma current and toroidal magnetic flux in the plasma with externally applied currents is consistent with the establishment of a Taylor state after formation. In addition, the magnetic helicity is proportional to that injected from the flux core, independent of how that helicity is generated.

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

    PubMed

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

    2011-07-01

    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 ? ? 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)/?) while the peak rate remains nearly independent of island size. For the largest islands (? = 100d(i)), reconnection is bursty and nearly shuts off after the first bounce, reconnecting ~20% of the available flux. PMID:21797613

  6. Expulsion of magnetic flux in a type-I superconducting strip

    NASA Astrophysics Data System (ADS)

    Jung, G.; Girard, T. A.; Valko, P.; Gomes, M. R.; Jeudy, V.; Limagne, D.; Waysand, G.

    2002-08-01

    Flux expulsion in a type-I superconducting strip, induced by decrease of a perpendicular magnetic field following field increase-induced flux penetration, is observed by real time detection of the flux-induced voltage pulses. Three different expulsion regimes are identified, corresponding in general to the three initial regimes of flux penetration. The crossover field between two expulsion regimes is found to be associated with the change of nucleation mechanism at Hc2. Possible association of the expulsion onset with surface superconductivity and Hc3 is discussed. The results support the idea of existence of an energy barrier against flux expulsion.

  7. Controlling the magnetic susceptibility in an artificial elliptical quantum ring by magnetic flux and external Rashba effect

    NASA Astrophysics Data System (ADS)

    Omidi, Mahboubeh; Faizabadi, Edris

    2015-03-01

    Magnetic susceptibility is investigated in a man-made elliptical quantum ring in the presence of Rashba spin-orbit interactions and the magnetic flux. It is shown that magnetic susceptibility as a function of magnetic flux changes between negative and positive signs periodically. The periodicity of the Aharonov-Bohm oscillations depends on the geometry of the region where magnetic field is applied, the eccentricity, and number of sites in each chain ring (the elliptical ring is composed of chain rings). The magnetic susceptibility sign can be reversed by tuning the Rashba spin-orbit strength as well. Both the magnetic susceptibility strength and sign can be controlled via external spin-orbit interactions, which can be exploited in spintronics and nanoelectronics.

  8. Granular Scale Magnetic Flux Cancellations as Observed with the Hinode/SOT

    NASA Astrophysics Data System (ADS)

    Kubo, M.; Low, B.; Lites, B. W.

    2009-12-01

    The mutual loss of magnetic flux due to the apparent collision of opposite-polarity magnetic elements is called ``magnetic flux cancellation'' as a descriptive term. The flux cancellation is essential to understand the dissipation of magnetic flux from the solar surface. We investigate the evolution of 5 granular-scale flux cancellations just outside the moat region of a sunspot by using accurate spectropolarimetric measurements with the Solar Optical Telescope aboard Hinode. We find that the opposite-polarity magnetic elements approach a junction of the intergranular lanes and then they collide with each other there. The intergranular junction has Doppler red shifts, darker intensities than the regular intergranular lanes, and surface converging flows. We also find that the horizontal magnetic field appears between the canceling elements in only one event. The horizontal fields are observed along the intergranular lanes with red shifts. This cancellation is most probably a result of the submergence of low-lying photospheric magnetic flux. In the other 4 events, the horizontal field is not observed between the opposite-polarity magnetic elements at any time when they approach and cancel each other. These canceling elements have nearly vertical fields even while they are in contact each other. These events are more interesting because in the usual idea of the submergence of a low lying ?-loop or the buoyant rise of a U-loop, the appearance of a horizontal field is the observational signature of the loop top (or bottom) passing across the photosphere. Our observational results suggest the possibility that the actual flux cancellation is highly time dependent events near the solar surface at scales less than a pixel of Hinode/SOT (about 200 km). Observations with a spatial resolution higher than Hinode/SOT are essential to reveal physical process of the dissipation of magnetic flux on the Sun.

  9. Erupting Solar Magnetic Flux Ropes: Theory and Observation

    Microsoft Academic Search

    J. Krall; J. Chen; R. T. Duffin; R. A. Howard; B. J. Thompson

    2001-01-01

    Measurements of coronograph (LASCO) and extreme-ultraviolet (EIT) images are presented for 11 coronal mass ejection (CME) events. Detailed measurements of these events, selected because they have flux-rope-like morphological features, show excellent agreement with results from a theoretical model of erupting flux-rope dynamics. Here, data are used to provide inputs and constraints on the model wherever possible. We conclude that flux

  10. A possible interplay between electron beams and magnetic fluxes in the Aharonov-Bohm effect

    NASA Astrophysics Data System (ADS)

    Wang, Rui-Feng

    2015-04-01

    Most studies on the magnetic Aharonov-Bohm (A-B) effect focus on the action exerted by the magnetic flux on the electron beam, but neglect the back-action exerted by the electron beam on the magnetic flux. This paper focuses on the latter, which is the electromotive force ?U across the solenoid induced by the time-dependent magnetic field of the electron beam. Based on the back-action analysis, we observe that the magnetic A-B effect arises owing to the interaction energy between the magnetic field of the electron beam and the magnetic field of the solenoid. We also demonstrate that the interpretation attributing the magnetic A-B effect to the vector potential violates the uncertainty principle.

  11. Comparison of an axial flux and a radial flux permanent magnet motor for solar race cars

    Microsoft Academic Search

    R. Al Zaher; S. de Groot; H. Polinder; P. Wieringa

    2010-01-01

    This paper provides analyses, models and a new frame design for the Csiro electric drive for solar cars. The main objective is to determine whether the axial flux Csiro motor (CM) is more efficient than the radial flux Biel motor (BM). To do that, performance tests were conducted and both drives were compared. Results showed that the CM is more

  12. Avalanche dynamics of magnetic flux in a two-dimensional discrete superconductor

    SciTech Connect

    Ginzburg, S. L.; Nakin, A. V.; Savitskaya, N. E. [Russian Academy of Sciences, Petersburg Nuclear Physics Institute (Russian Federation)], E-mail: savitska@thd.pnpi.spb.ru

    2006-11-15

    The critical state of a two-dimensional discrete superconductor in an external magnetic field is studied. This state is found to be self-organized in the generalized sense, i.e., is a set of metastable states that transform to each other by means of avalanches. An avalanche is characterized by the penetration of a magnetic flux to the system. The sizes of the occurring avalanches, i.e., changes in the magnetic flux, exhibit the power-law distribution. It is also shown that the size of the avalanche occurring in the critical state and the external magnetic field causing its change are statistically independent quantities.

  13. Electrical resistance of gases in explosive magnetic flux compression generator environments 

    E-print Network

    Dorsey, Daniel John

    2000-01-01

    the electrical properties of several gases in the FCG environment. The hydrodynamics in a helical explosive magnetic flux compression generator (FCG) are modeled using the Gurney method and a shock physics code, CTH, developed at Sandia National Laboratory...

  14. Magnetic Effects in Nanomaterials Flux Closure in Self-Assembled Cobalt

    E-print Network

    Dunin-Borkowski, Rafal E.

    -axis electron holography to visualize magnetic flux with nanometer spatial resolution.[6] These bracelet, then deposited onto carbon-coated copper grids and dried in air using a standardized procedure.[7

  15. Electrical resistance of gases in explosive magnetic flux compression generator environments

    E-print Network

    Dorsey, Daniel John

    2000-01-01

    the electrical properties of several gases in the FCG environment. The hydrodynamics in a helical explosive magnetic flux compression generator (FCG) are modeled using the Gurney method and a shock physics code, CTH, developed at Sandia National Laboratory...

  16. Modeling effects of adding a flux channel to a planar magnet-coil actuator

    E-print Network

    Bourgeois, Jacob

    2005-01-01

    Planar magnet-coil actuators are used in many different MEMS devices. This report describes one way to improve the actuator range per current input of planar coil actuators. This is accomplished by adding a flux channel ...

  17. Maximization of No-Load Flux Density in Surface Mounted Permanent Magnet Motors Frdric DUBAS, Christophe ESPANET & Abdellatif MIRAOUI.

    E-print Network

    Paris-Sud XI, Université de

    Maximization of No-Load Flux Density in Surface Mounted Permanent Magnet Motors Frédéric DUBAS mounted permanent magnet motors having a direction of parallel or radial magnetization [1]. I expression of the optimal thickness of the magnet which make it possible to maximize the no-load flux density

  18. Modeling magnetic fields measured by surface probes embedded in a cylindrical flux conserver.

    PubMed

    Golingo, R P

    2007-03-01

    Calculating magnetic fields at the surface of a flux conserver, perfect conductor, for displaced plasma currents is useful for understanding modes of a Z-pinch. The magnetic fields measured at the flux conserver are a sum of the magnetic fields from the plasma current and the eddy currents which form in the walls to keep the flux constant. While the magnetic field at the wall from the plasma current alone is easily calculated using the Biot-Savart law, finding the eddy currents in the flux conserver which satisfy the boundary conditions can be a tedious process. A simple method of calculating the surface magnetic field for a given Z-pinch displacement off-axis is derived for a cylindrical flux conserver. This relationship does not require the explicit calculation of the eddy currents, saving time when analyzing surface magnetic probe measurements. Analytic expressions can be used to describe the surface magnetic field which increase the understanding of the magnetic probe measurements. PMID:17411182

  19. Composite multi-qubit gates dynamically corrected against charge noise and magnetic field noise for singlet-triplet qubits

    NASA Astrophysics Data System (ADS)

    Kestner, Jason; Barnes, Edwin; Wang, Xin; Bishop, Lev; Das Sarma, Sankar

    2013-03-01

    We use previously described single-qubit SUPCODE pulses on both intra-qubit and inter-qubit exchange couplings, integrated with existing strategies such as BB1, to theoretically construct a CNOT gate that is robust against both charge noise and magnetic field gradient fluctuations. We show how this allows scalable, high-fidelity implementation of arbitrary multi-qubit operations using singlet-triplet spin qubits in the presence of experimentally realistic noise. We use previously described single-qubit SUPCODE pulses on both intra-qubit and inter-qubit exchange couplings, integrated with existing strategies such as BB1, to theoretically construct a CNOT gate that is robust against both charge noise and magnetic field gradient fluctuations. We show how this allows scalable, high-fidelity implementation of arbitrary multi-qubit operations using singlet-triplet spin qubits in the presence of experimentally realistic noise. This work is supported by LPS-NSA-CMTC, IARPA-MQCO and CNAM.

  20. High noise suppression using magnetically isotropic (CoFe-AlN)/(AlN) multilayer films

    NASA Astrophysics Data System (ADS)

    Kijima, Hanae; Ohnuma, Shigehiro; Masumoto, Hiroshi; Shimada, Yutaka; Endo, Yasushi; Yamaguchi, Masahiro

    2015-05-01

    Magnetically isotropic (CoFe-AlN)n/(AlN)n+1 multilayer films, in which the number of CoFe-AlN magnetic layers n ranged from 1 to 27, were prepared by radio frequency sputtering to achieve noise suppression at gigahertz frequencies. The soft CoFe-AlN magnetic layers consisted of nanometer-sized CoFe ferromagnetic grains embedded in an insulating AlN amorphous matrix, while the insulating AlN layers comprised AlN columnar crystals. All films showed a similar frequency dependence of permeability and ferromagnetic resonance of 1.7 GHz. Noise suppression was evaluated using a microstrip line as a noise source by determining the in-line conductive loss and the near-field intensity picked up by magnetic field detective probes. High noise suppression effects were observed in every direction in the film plane. Maximum noise suppression values amounted to 60% for the in-line conductive loss and -20 dB for the magnetic near-field intensity at around 1.7 GHz in the 27-layer film. These high-frequency noise suppression levels may be attributed to eddy current losses and ferromagnetic resonance.

  1. Evidence for Sterilization of Saccharomyces Cerevisiae K 7 by an External Magnetic Flux

    NASA Astrophysics Data System (ADS)

    Ito, Tatsuya; Murayama, Yuzo; Suzuki, Masafumi; Yoshimura, Noboru; Iwano, Kimio; Kudo, Kozo

    1992-06-01

    A new process of sterilization on Saccharomyces cerevisiae proposed and experimentally demonstrated. This process consists of external magnetic flux and ferrite. Consequently, an alteration of yeast cells, caused by treatment with 2000 G magnetic flux and 6 g of ferrite, was detected through observation of the release of materials from yeast cells absorbing at 260 nm and microscopy of disrupted cells, cell debris, ghost cells and intracellular components. The same results were seen at 28°C and 4°C.

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

    SciTech Connect

    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.

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

    SciTech Connect

    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.

  4. Electric and magnetic flux compression theory for arbitrary large liner velocities

    Microsoft Academic Search

    H. E. Wilhelm

    1986-01-01

    Theoretical analyses of the compression of axial (i) magnetic and (ii) electric fluxes by means of cylindrical liners are presented for arbitrary large implosion velocities vmagnetic and (ii) electric flux compression are given, which are good approximations for nonrelativistic liner speeds v≪c0. For relativistic liner velocities, significant amounts of electromagnetic radiation would be

  5. Electromagnetic Analysis of Axial-Flux Permanent Magnet Synchronous Machines With Fractional Windings With Experimental Validation

    Microsoft Academic Search

    Roberto Di Stefano; Fabrizio Marignetti

    2012-01-01

    Axial-flux permanent magnet (PM) synchronous machines are suitable for direct drive applications. Axial-flux PM synchronous machines with fractional windings provide high power density, low torque ripple, and sinusoidal phase voltages, but suffer from high rotor losses due to stator field harmonics and slotting. This paper formulates an electromagnetic model based on the polar coordinate representation of the air-gap magnetic field.

  6. Flux-Weakening Control of IPM Motors With Significant Effect of Magnetic Saturation and Stator Resistance

    Microsoft Academic Search

    Cheol Jo; Ji-Yun Seol; In-Joong Ha

    2008-01-01

    In this paper, we propose a systematic optimization approach to flux-weakening control of interior permanent-magnet (IPM) motors, which operate in magnetic saturation. The current commands are chosen to be optimal so as to minimize power loss not only in the constant-torque region but also in the constant-power region. Our approach aims at the same objective as the previously known flux-weakening

  7. A MTPA control scheme for an IPM synchronous motor considering magnet flux variation caused by temperature

    Microsoft Academic Search

    Gubae Rang; Jaesang Lim; Kwanghee Nam; Hyung-Bin Ihm; Ho-Gi Kim

    2004-01-01

    In a hybrid electric vehicle (HEV), an interior permanent magnet (Nd-Fe-B) synchronous motor is widely used. However, the flux density of the Nd-Fe-B magnet is sensitive to the temperature variation. Particularly, in a HEV, the heat coming from internal combustion engine causes high temperature rise of the motor. It degrades the flux density and output torque. In this paper, a

  8. Photospheric Magnetic Field: Relationship Between North-South Asymmetry and Flux Imbalance

    NASA Astrophysics Data System (ADS)

    Vernova, E. S.; Tyasto, M. I.; Baranov, D. G.

    2014-08-01

    Photospheric magnetic fields were studied using the Kitt Peak synoptic maps for 1976 - 2003. Only strong magnetic fields ( B>100 G) of the equatorial region were taken into account. The north-south asymmetry of the magnetic fluxes was considered as well as the imbalance between positive and negative fluxes. The north-south asymmetry displays a regular alternation of the dominant hemisphere during the solar cycle: the northern hemisphere dominated in the ascending phase, the southern one in the descending phase during Solar Cycles 21 - 23. The sign of the imbalance did not change during the 11 years from one polar-field reversal to the next and always coincided with the sign of the Sun's polar magnetic field in the northern hemisphere. The dominant sign of leading sunspots in one of the hemispheres determines the sign of the magnetic-flux imbalance. The sign of the north-south asymmetry of the magnetic fluxes and the sign of the imbalance of the positive and the negative fluxes are related to the quarter of the 22-year magnetic cycle where the magnetic configuration of the Sun remains constant (from the minimum where the sunspot sign changes according to Hale's law to the magnetic-field reversal and from the reversal to the minimum). The sign of the north-south asymmetry for the time interval considered was determined by the phase of the 11-year cycle (before or after the reversal); the sign of the imbalance of the positive and the negative fluxes depends on both the phase of the 11-year cycle and on the parity of the solar cycle. The results obtained demonstrate the connection of the magnetic fields in active regions with the Sun's polar magnetic field in the northern hemisphere.

  9. Novel axial flux interior PM synchronous motor realized with powdered soft magnetic materials

    Microsoft Academic Search

    F. Profumo; A. Tenconi; Z. Zhang; A. Cavagnino

    1998-01-01

    A novel axial flux interior PM (AFIPM) synchronous motor for wheel-motor applications is presented. Due to the new anisotropic rotor structure, the AFIPM motor can deliver constant power with flux weakening operation. The rotor construction is feasible only using powdered soft magnetic materials. The proposed design procedure uses the finite element method (FEM) in addition to the classical electric motor

  10. A Novel Axial Flux Permanent-Magnet Machine for Flywheel Energy Storage System: Design and Analysis

    Microsoft Academic Search

    Trong Duy Nguyen; King-Jet Tseng; Shao Zhang; Hoan Thong Nguyen

    2011-01-01

    This paper presents the design and analysis of a novel axial flux permanent-magnet (AFPM) machine for a flywheel energy storage system (FESS). Its design and control facilitate significant reduction in axial bearing stress and losses. Due to the unconventional flux distribution in this machine, a 3-D finite element method was employed for its design and analysis, in- cluding its electromagnetic

  11. Table of Contents flux a publication of the national high magnetic field laboratory

    E-print Network

    Weston, Ken

    for Management and Administration Brian Fairhurst Director of Public Affairs Susan Ray Flux Editor Amy Mast#12;Table of Contents flux a publication of the national high magnetic field laboratory research as "fundamental" or "curiosity-based" research. Its motivation is knowledge of still unanswered

  12. Position sensorless control for interior permanent magnet synchronous motors using H? flux observer

    Microsoft Academic Search

    Tomonobu Senjyu; Yohei Noguchi; Naomitsu Urasaki; Abdul Motin Howlader; Atsushi Yona; H. Sekine

    2008-01-01

    Generally, a back electro-motive-force or flux observer is used for position sensorless drive of permanent magnet synchronous motors from middle to high speed range. Thus, the estimation accuracy of the observer influences position sensorless drive performance. This paper proposes a position sensorless drive system using the Hinfin flux observer in which the observer gain is designed by using the Hinfin

  13. Catastrophic Eruption of Magnetic Flux Rope in the Corona and Solar Wind With and Without Magnetic Reconnection

    Microsoft Academic Search

    Y. Chen; Y. Q. Hu; S. J. Sun

    2007-01-01

    It is generally believed that the magnetic free energy accumulated in the corona serves as a main energy source for solar explosions such as coronal mass ejections (CMEs). In the framework of the flux rope catastrophe model for CMEs, the energy may be abruptly released either by an ideal magnetohydrodynamic (MHD) catastrophe, which belongs to a global magnetic topological instability

  14. Physiological noise in oxygenation-sensitive magnetic resonance imaging

    Microsoft Academic Search

    Gunnar Krueger; Gary H. Glover

    2001-01-01

    The physiological noise in the resting brain, which arises from fluctuations\\u000ain metabolic-linked brain physiology and subtle brain pulsations,\\u000awas investigated in six healthy volunteers using oxygenation-sensitive\\u000adual-echo spiral MRI at 3.0 T. In contrast to the system and thermal\\u000anoise, the physiological noise demonstrates a signal strength dependency\\u000aand, unique to the metabolic-linked noise, an echo-time dependency.\\u000aVariations of

  15. PLASTIC VERSUS ELASTIC DEFORMATION EFFECTS ON MAGNETIC BARKHAUSEN NOISE IN STEEL

    E-print Network

    Clapham, Lynann

    PLASTIC VERSUS ELASTIC DEFORMATION EFFECTS ON MAGNETIC BARKHAUSEN NOISE IN STEEL C.-G. STEFANITA, D) AbstractÐA study was performed to dierentiate the eects of elastic and plastic deformation on magnetic samples subjected to varying degrees of uniaxial elastic and plastic deformation up to H40% strain

  16. The Effect of Plastic Deformation and Residual Stress on Magnetic Barkhausen Noise Signals in Mild Steel

    Microsoft Academic Search

    Thana Rahim; Lynann Clapham

    2003-01-01

    This study was conducted to investigate the effects of plastic deformation on magnetic Barkhausen noise (MBN) signals in mild steel. A number of mild steel samples were subjected to different degrees of uniaxial plastic deformation up to 30% strain. Angular MBN measurements were done on those samples. The results indicated that plastic deformation introduces a magnetic easy axis depending on

  17. Effect of an azimuthally varying magnetic field on the noise level in a multicavity magnetron

    NASA Astrophysics Data System (ADS)

    Baiburin, V. B.; Kaminskii, K. V.

    2009-06-01

    A mathematical model of a multicavity magnetron with an azimuthally varying magnetic field is considered. It is demonstrated that the magnetic field of this type decreases the time of charge occurrence in the interaction space and reduces the level of noise in the magnetron.

  18. Low frequency noise in arrays of magnetic tunnel junctions connected in series and parallel

    Microsoft Academic Search

    R. Guerrero; M. Pannetier-Lecoeur; C. Fermon; S. Cardoso; R. Ferreira; P. P. Freitas

    2009-01-01

    Low frequency noise and small output voltage are the strongest limitations to the use of magnetic tunnel junctions (MTJs) for magnetic sensor applications, replacing giant magnetoresistance (GMR) and anisotropic magnetoresistance sensors. In this paper, we explore the possibility of using arrays with a large number of MTJs connected in parallel\\/series to overcome these limitations. MTJ's sensor arrays of more than

  19. Generalized H-theorems for magnetization dynamics driven by a jump-noise process

    NASA Astrophysics Data System (ADS)

    Mayergoyz, I.; Bertotti, G.; Serpico, C.

    2011-04-01

    In this paper, stochastic magnetization dynamics driven by a jump-noise process is discussed and, under the condition of "detailed balance," generalized H-theorems for this dynamics are established. These H-theorems reveal the existence of a class of functionals that monotonically decrease in time during stochastic magnetization dynamics.

  20. Defect Profile Estimation from Magnetic Flux Leakage Signal via Efficient Managing Particle Swarm Optimization

    PubMed Central

    Han, Wenhua; Xu, Jun; Wang, Ping; Tian, Guiyun

    2014-01-01

    In this paper, efficient managing particle swarm optimization (EMPSO) for high dimension problem is proposed to estimate defect profile from magnetic flux leakage (MFL) signal. In the proposed EMPSO, in order to strengthen exchange of information among particles, particle pair model was built. For more efficient searching when facing different landscapes of problems, velocity updating scheme including three velocity updating models was also proposed. In addition, for more chances to search optimum solution out, automatic particle selection for re-initialization was implemented. The optimization results of six benchmark functions show EMPSO performs well when optimizing 100-D problems. The defect simulation results demonstrate that the inversing technique based on EMPSO outperforms the one based on self-learning particle swarm optimizer (SLPSO), and the estimated profiles are still close to the desired profiles with the presence of low noise in MFL signal. The results estimated from real MFL signal by EMPSO-based inversing technique also indicate that the algorithm is capable of providing an accurate solution of the defect profile with real signal. Both the simulation results and experiment results show the computing time of the EMPSO-based inversing technique is reduced by 20%–30% than that of the SLPSO-based inversing technique. PMID:24926693

  1. Observation of an evolving magnetic flux rope before and during a solar eruption.

    PubMed

    Zhang, Jie; Cheng, Xin; Ding, Ming-de

    2012-01-01

    Explosive energy release is a common phenomenon occurring in magnetized plasma systems ranging from laboratories, Earth's magnetosphere, the solar corona and astrophysical environments. Its physical explanation is usually attributed to magnetic reconnection in a thin current sheet. Here we report the important role of magnetic flux rope structure, a volumetric current channel, in producing explosive events. The flux rope is observed as a hot channel before and during a solar eruption from the Atmospheric Imaging Assembly telescope on board the Solar Dynamic Observatory. It initially appears as a twisted and writhed sigmoidal structure with a temperature as high as 10 MK, and then transforms toward a semi-circular shape during a slow-rise phase, which is followed by fast acceleration and onset of a flare. The observations suggest that the instability of the magnetic flux rope triggers the eruption, thus making a major addition to the traditional magnetic-reconnection paradigm. PMID:22434190

  2. Flux growth and magnetic properties of FeVO{sub 4} single crystals

    SciTech Connect

    He Zhangzhen [Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581 (Japan)], E-mail: hezz@fjirsm.ac.cn; Yamaura, Jun-Ichi; Ueda, Yutaka [Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581 (Japan)

    2008-09-15

    FeVO{sub 4} (I) single crystals are grown by the flux method using V{sub 2}O{sub 5} as the self-flux. The grown crystals exhibit a characteristic morphology with natural facets. The quality of the crystals is confirmed by X-ray diffraction and EPMA techniques. Magnetic properties are investigated by means of magnetic susceptibility, magnetization, and heat capacity measurements. Two magnetic phase transitions are observed at {approx}13 and {approx}20 K. Such unusual magnetic behaviors are suggested to originate from two different Fe ligand environments of octahedral FeO{sub 6} and trigonal bipyramidal FeO{sub 5} in a six-column doubly bent chain. - Graphical abstract: FeVO{sub 4} (I) single crystals are grown by the flux method using V{sub 2}O{sub 5} as the self-flux. Magnetic properties are investigated by means of magnetic susceptibility, magnetization, and heat capacity measurements, showing two magnetic phase transitions at {approx}13 and {approx}20 K.

  3. CHARACTERIZATION OF ACOUSTIC NOISE AND MAGNETIC FIELD FLUCTUATIONS IN A 4 T WHOLE-BODY MRI SCANNER

    Microsoft Academic Search

    CHRIS K. MECHEFSKE; Yuhua Wu; Brian Rutt

    2002-01-01

    High-field, high-speed magnetic resonance imaging (MRI) can generate high levels of sound within and around the scanner. The process that produces the gradient magnetic field is the primary cause of this noise. With the push to greater background magnetic field strength and gradient field switching speed, in order to improve image quality and resolution, the noise situation is becoming worse.

  4. Magnetic Relaxation of a Long Cylinder in the Flux Creep Regime

    NASA Astrophysics Data System (ADS)

    Nader, A.

    2000-09-01

    The magnetic relaxation of a long cylinder in the flux creep regime was analyzed numerically when the energy barrier U depends logarithmically on the current density J. A method to extract ?=U0/kT from short time interval magnetization decay is suggested.

  5. Flux Jumps” in Cable-in-Conduit Conductors Induced by Transient Magnetic Field

    Microsoft Academic Search

    V. E. Keilin; I. A. Kovalev; S. L. Kruglov; S. A. Lelekhov; P. G. Naumov; V. I. Shcherbakov

    2006-01-01

    A jump-like temperature increase that can not be explained only by AC losses was observed during the tests of Nb-Ti CICC model samples in transient magnetic fields. The samples were placed between two racetracks that generate background transient magnetic field (TMF). The flux jumps occurred in CICC samples even during the slow discharge of racetrack coils. A physical model was

  6. A Study of an Absolute Determination of the Magnetic Flux Quantum Using a Superconducting Levitation System

    Microsoft Academic Search

    Fuyuhiko Shiota; Ko Hara; Takaaki Hirata

    1983-01-01

    A study on a new method of determining the magnetic flux quantum phi0 possibly at subppm level using a superconducting levitation system is described with some data from a preliminary experiment. The method employs a superconducting levitation system to substitute the gravitational potential energy of the floating body for the magnetic energy. The estimation of the expected accuracy and methods

  7. Three-Dimensional Force Measurement and Control of a Flux-Path Control Magnetic Suspension

    Microsoft Academic Search

    Munehiro Furutachi; Shunsuke Inaba; Yuji Ishino; Masaya Takasaki; Takeshi Mizuno

    2008-01-01

    In the flux-path control magnetic suspension system, the force acting on a floator is controlled by moving a control plate made of ferromagnetic material, which is located between the permanent magnet and the floator. In this paper, the three-dimensional attractive forces acting on the floator were measured with a manufactured force sensor. The force actuating in the vertical direction is

  8. A permanent magnet flux switching motor for low energy axial fans

    Microsoft Academic Search

    Yi Cheng; Charles Pollock; Helen Pollock

    2005-01-01

    In this paper, a permanent magnet flux switching motor (PMFSM) is presented as an alternative to the more familiar brushless DC motor (BDC) used in low energy consumption axial fans. The PMFSM has permanent magnets as a part of the stator structure which also contains an armature winding. The rotor is a simple steel, salient pole structure. Simulated and experimental

  9. A Magnetic Flux Leakage and Magnetostrictive Guided Wave Hybrid Transducer for Detecting Bridge Cables

    PubMed Central

    Xu, Jiang; Wu, Xinjun; Cheng, Cheng; Ben, Anran

    2012-01-01

    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. PMID:22368483

  10. Dynamical evolution of twisted magnetic flux tubes. I - Equilibrium and linear stability

    NASA Technical Reports Server (NTRS)

    Mikic, Zoran; Schnack, Dalton D.; Van Hoven, Gerard

    1990-01-01

    The three-dimensional dynamical evolution of twisted magnetic flux tubes is studied using a time-dependent magnetohydrodynamic (MHD) model. The flux tubes are intended to model solar coronal loops, and include the stabilizing effect of photospheric line tying. The model permits the complete evolution of flux tubes to be followed self-consistently, including the formation, equilibrium, linear instability, and nonlinear behavior. Starting from an initial uniform background magnetic field, a twisted flux tube is created by the application of slow, localized photospheric vortex flows. The flux tube evolves quasi-statically through sequences of equilibria with increasing twist, until it becomes linearly unstable to an ideal MHD kink mode. In this paper, the equilibrium properties and the linear stability behavior are discussed. The application of the method to the uniform-twist, Gold-Hoyle field confirms the previous stability threshold for kink instability and provides estimates of the resulting growth rate.

  11. Magneto-optical study of magnetic-flux penetration into a current-carrying high-temperature-superconductor strip

    E-print Network

    Johansen, Tom Henning

    Magneto-optical study of magnetic-flux penetration into a current-carrying high-carrying state, reasonable agreement is found. However, there is a systematic deviation--the flux penetration of magnetic-flux penetration into high-temperature superconductor HTSC films have been extensively performed

  12. Evaluation of magnetic flux distribution from magnetic domains in [Co/Pd] nanowires by magnetic domain scope method using contact-scanning of tunneling magnetoresistive sensor

    SciTech Connect

    Okuda, Mitsunobu, E-mail: okuda.m-ky@nhk.or.jp; Miyamoto, Yasuyoshi; Miyashita, Eiichi; Hayashi, Naoto [NHK Science and Technology Research Laboratories, 1-10-11 Kinuta Setagaya, Tokyo 157-8510 (Japan)

    2014-05-07

    Current-driven magnetic domain wall motions in magnetic nanowires have attracted great interests for physical studies and engineering applications. The magnetic force microscope (MFM) is widely used for indirect verification of domain locations in nanowires, where relative magnetic force between the local domains and the MFM probe is used for detection. However, there is an occasional problem that the magnetic moments of MFM probe influenced and/or rotated the magnetic states in the low-moment nanowires. To solve this issue, the “magnetic domain scope for wide area with nano-order resolution (nano-MDS)” method has been proposed recently that could detect the magnetic flux distribution from the specimen directly by scanning of tunneling magnetoresistive field sensor. In this study, magnetic domain structure in nanowires was investigated by both MFM and nano-MDS, and the leakage magnetic flux density from the nanowires was measured quantitatively by nano-MDS. Specimen nanowires consisted from [Co (0.3)/Pd (1.2)]{sub 21}/Ru(3) films (units in nm) with perpendicular magnetic anisotropy were fabricated onto Si substrates by dual ion beam sputtering and e-beam lithography. The length and the width of the fabricated nanowires are 20??m and 150?nm. We have succeeded to obtain not only the remanent domain images with the detection of up and down magnetizations as similar as those by MFM but also magnetic flux density distribution from nanowires directly by nano-MDS. The obtained value of maximum leakage magnetic flux by nano-MDS is in good agreement with that of coercivity by magneto-optical Kerr effect microscopy. By changing the protective diamond-like-carbon film thickness on tunneling magnetoresistive sensor, the three-dimensional spatial distribution of leakage magnetic flux could be evaluated.

  13. Electric Charge and Magnetic Flux on Rotating Black Holes in a Force-Free Magnetosphere

    E-print Network

    Hyun Kyu Lee; Chul H. Lee; Maurice H. P. M. van Putten

    2001-02-13

    The electric charge on rotating black holes is calculated to be ~ BJ in the force-free configuration of Ghosh (2000), with a horizon flux of ~ BM^2. This charge is gravitationally weak for B ~ 10^{15} G, so that the Kerr metric applies. Being similar to the electric charge of a magnetar, both electric charge and magnetic flux should be, in sign and order of magnitude, continuous during stellar collapse into a black hole. Extraction of the rotational energy from newly formed black holes may proceed by interaction with the magnetic field. Keywords:black hole physics --magnetic fields

  14. RMHD simulations of collision-induced magnetic dissipations in Poynting flux dominated jets

    NASA Astrophysics Data System (ADS)

    Deng, Wei; Li, Hui; Zhang, Bing; Li, Shengtai

    2015-01-01

    We perform a 3D relativistic ideal MHD simulation to study the collision between high-? magnetic blobs which contain both poloidal and toroidal magnetic field components, which can mimic the interactions inside a highly variable Poynting flux dominated jet. We discover a significant Poynting flux energy dissipation component in addition to the dissipation due to the evolution of the blob without collision. We identify this additional Poynting flux energy dissipation as being mainly facilitated by the collision driven magnetic reconnections, through both observing the reconnection events in the simulations and quantitative calculations of the energy dissipation rate. Additional resolution and parameter studies show a robust result that our results are nearly independent of the numerical resolution or most physical parameters in the relevant parameter range. Our results give a good support to some theories in astrophysical systems, such as the internal collision-induced magnetic reconnection and turbulence (ICMART) model for GRBs, and some reconnection triggered mini-jet model for AGNs.

  15. Computer Simulations and Observations of Solar Magnetic Flux Ropes and Eruptions

    NASA Astrophysics Data System (ADS)

    Kosovichev, Alexander; Kitiashvili, Irina; Mansour, Nagi; Wray, Alan

    2012-10-01

    Solar observations reveal a great variety of plasma eruptions of different scales and energetics, from small-scale jets and spicules to giant coronal mass ejections. The magnetic flux ropes observed in the solar atmosphere and corona are formed in the turbulent convection zone by a dynamo process, which is poorly understood. We present 3D radiative MHD simulations of the upper convective boundary layer and the chromosphere, which capture the basic physics of magnetic self-organization and dynamics of the turbulent solar plasma, formation of magnetic flux ropes and spontaneous small-scale spicule-like eruptions. The simulations show that the key mechanism of the flux-rope formation and eruptions is in the generation of compact vortex tubes and their interaction with magnetic field. The simulation results are compared with observations from the Solar Dynamics Observatory and large ground-based telescopes.

  16. Acoustic and magnetic wave heating in stars . I. Theoretical chromospheric models and emerging radiative fluxes

    Microsoft Academic Search

    D. Fawzy; W. Rammacher; P. Ulmschneider; Z. E. Musielak; K. Stepien

    2002-01-01

    We describe a method to construct theoretical, time-dependent, two-component and wave heated chromosphere models for late-type dwarfs. The models depend only on four basic stellar parameters: effective temperature, gravity, metallicity and filling factor, which determines the coverage of these stars by surface magnetic fields. They consist of non-magnetic regions heated by acoustic waves and vertically oriented magnetic flux tubes heated

  17. Twist accumulation and topology structure of a solar magnetic flux rope

    SciTech Connect

    Guo, Y.; Ding, M. D.; Cheng, X. [School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China); Zhao, J. [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China); Pariat, E., E-mail: guoyang@nju.edu.cn [LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris Diderot, 5 place Jules Janssen, F-92190 Meudon (France)

    2013-12-20

    To study the buildup of a magnetic flux rope before a major flare and coronal mass ejection (CME), we compute the magnetic helicity injection, twist accumulation, and topology structure of the three-dimensional (3D) magnetic field, which is derived by the nonlinear force-free field model. The Extreme-ultraviolet Imaging Telescope on board the Solar and Heliospheric Observatory observed a series of confined flares without any CME before a major flare with a CME at 23:02 UT on 2005 January 15 in active region NOAA 10720. We derive the vector velocity at eight time points from 18:27 UT to 22:20 UT with the differential affine velocity estimator for vector magnetic fields, which were observed by the Digital Vector Magnetograph at Big Bear Solar Observatory. The injected magnetic helicity is computed with the vector magnetic and velocity fields. The helicity injection rate was (– 16.47 ± 3.52) × 10{sup 40} Mx{sup 2} hr{sup –1}. We find that only about 1.8% of the injected magnetic helicity became the internal helicity of the magnetic flux rope, whose twist increasing rate was –0.18 ± 0.08 Turns hr{sup –1}. The quasi-separatrix layers (QSLs) of the 3D magnetic field are computed by evaluating the squashing degree, Q. We find that the flux rope was wrapped by QSLs with large Q values, where the magnetic reconnection induced by the continuously injected magnetic helicity further produced the confined flares. We suggest that the flux rope was built up and heated by the magnetic reconnection in the QSLs.

  18. Formation of Intensive Magnetic Flux Tubes in a Converging Flow of Partially Ionized Solar Photospheric Plasma

    Microsoft Academic Search

    M. L. Khodachenko; V. V. Zaitsev

    2002-01-01

    Theoretical model, explaining a phenomenon of formation of Intensive Magnetic Flux Tube (IMFT) in a converging flow of partially\\u000a ionized solar photospheric plasma is considered. Special attention is paid to the fact of weak ionization (n\\/n\\u000a n ? 10-4) of plasma in the photosphere. The cases of 2D magnetic slab and cylindric magnetic tube are considered. It was shown that

  19. Twist Accumulation and Topology Structure of a Solar Magnetic Flux Rope

    NASA Astrophysics Data System (ADS)

    Guo, Y.; Ding, M. D.; Cheng, X.; Zhao, J.; Pariat, E.

    2013-12-01

    To study the buildup of a magnetic flux rope before a major flare and coronal mass ejection (CME), we compute the magnetic helicity injection, twist accumulation, and topology structure of the three-dimensional (3D) magnetic field, which is derived by the nonlinear force-free field model. The Extreme-ultraviolet Imaging Telescope on board the Solar and Heliospheric Observatory observed a series of confined flares without any CME before a major flare with a CME at 23:02 UT on 2005 January 15 in active region NOAA 10720. We derive the vector velocity at eight time points from 18:27 UT to 22:20 UT with the differential affine velocity estimator for vector magnetic fields, which were observed by the Digital Vector Magnetograph at Big Bear Solar Observatory. The injected magnetic helicity is computed with the vector magnetic and velocity fields. The helicity injection rate was (- 16.47 ± 3.52) × 1040 Mx2 hr-1. We find that only about 1.8% of the injected magnetic helicity became the internal helicity of the magnetic flux rope, whose twist increasing rate was -0.18 ± 0.08 Turns hr-1. The quasi-separatrix layers (QSLs) of the 3D magnetic field are computed by evaluating the squashing degree, Q. We find that the flux rope was wrapped by QSLs with large Q values, where the magnetic reconnection induced by the continuously injected magnetic helicity further produced the confined flares. We suggest that the flux rope was built up and heated by the magnetic reconnection in the QSLs.

  20. Correlated magnetic noise in global networks of gravitational-wave detectors: Observations and implications

    NASA Astrophysics Data System (ADS)

    Thrane, E.; Christensen, N.; Schofield, R. M. S.

    2013-06-01

    One of the most ambitious goals of gravitational-wave astronomy is to observe the stochastic gravitational-wave background. Correlated noise in two or more detectors can introduce a systematic error, which limits the sensitivity of stochastic searches. We report on measurements of correlated magnetic noise from Schumann resonances at the widely separated LIGO and Virgo detectors. We investigate the effect of this noise on a global network of gravitational-wave detectors and derive a constraint on the allowable coupling of environmental magnetic fields to test mass motion in gravitational-wave detectors. We find that while correlated noise from global electromagnetic fields could be safely ignored for initial LIGO stochastic searches, it could severely impact Advanced LIGO, Advanced Virgo, KAGRA, as well as third-generation detectors.

  1. Effects of creep damage, shot peening, and case hardening on magnetic Barkhausen noise analysis

    SciTech Connect

    Sipahi, L.B. (Ames Lab., IA (United States) Iowa State Univ., Ames, IA (United States). Inst. for Physical Research and Technology)

    1994-11-01

    The micromagnetic emissions, commonly known as Barkhausen noise, are very sensitive to variations in the microstructure and sub-surface stress states of magnetic materials. Steel pipelines at power plants often have creep damage due to microstructural changes in their service life. Early detection of this damage will prevent costly failures. There is also an increasing demand to characterize the sub-surface stress states in structural materials such as high strength materials used in landing gear components in the aerospace industry. Shot peening is used to improve the fatigue strength of these components by the introduction of residual compressive stresses to the surface. Because the magnitude of Barkhausen noise varies with the magnitude of compressive stress, these noise measurements can be used for in-situ evaluation of the effectiveness of the shot peening process. Furthermore, surface modification such as case hardened magnetic samples can be easily observed using micromagnetic Barkhausen noise (MBE) to determine further modification needs.

  2. Diffusion of magnetic flux elements on a fractal geometry

    Microsoft Academic Search

    J. K. Lawrence

    1991-01-01

    Recent observations have indicated that magnetic field elements are distributed on the Sun in fractal patterns with dimension D < 2. We suggest that the transport of magnetic field elements across the solar surface should be treated as diffusion on a fractal geometry. We review a semi-analytical, theoretical treatment of fractal diffusion. Comparison with observations of small-scale motions of solar

  3. A moving hum filter to suppress rotor noise in high-resolution airborne magnetic data

    USGS Publications Warehouse

    Xia, J.; Doll, W.E.; Miller, R.D.; Gamey, T.J.; Emond, A.M.

    2005-01-01

    A unique filtering approach is developed to eliminate helicopter rotor noise. It is designed to suppress harmonic noise from a rotor that varies slightly in amplitude, phase, and frequency and that contaminates aero-magnetic data. The filter provides a powerful harmonic noise-suppression tool for data acquired with modern large-dynamic-range recording systems. This three-step approach - polynomial fitting, bandpass filtering, and rotor-noise synthesis - significantly reduces rotor noise without altering the spectra of signals of interest. Two steps before hum filtering - polynomial fitting and bandpass filtering - are critical to accurately model the weak rotor noise. During rotor-noise synthesis, amplitude, phase, and frequency are determined. Data are processed segment by segment so that there is no limit on the length of data. The segment length changes dynamically along a line based on modeling results. Modeling the rotor noise is stable and efficient. Real-world data examples demonstrate that this method can suppress rotor noise by more than 95% when implemented in an aeromagnetic data-processing flow. ?? 2005 Society of Exploration Geophysicists. All rights reserved.

  4. Theoretical noise analysis on a position-sensitive Metallic Magnetic Calorimeter

    Microsoft Academic Search

    S. J. Smith

    2007-01-01

    We report on the theoretical noise analysis for a position-sensitive Metallic Magnetic Calorimter (MMC), consisting of MMC read-out at both ends of a large X-ray absorber. Such devices are under consideration as alternatives to other cryogenic technologies for future X-ray astronomy missions. We use a finite-element model (FEM) to numerically calculate the signal and noise response at the detector outputs

  5. Equilibrium force balance and eruptive instabilities in solar-relevant laboratory magnetic flux ropes

    NASA Astrophysics Data System (ADS)

    Myers, C. E.; Yamada, M.; Belova, E. V.; Ji, H.; Yoo, J.; Jara-Almonte, J.

    2013-10-01

    Quasi-statically driven line-tied magnetic flux ropes are studied in the context of storage-and-release eruptions in the solar corona. The Magnetic Reconnection Experiment (MRX) facility is utilized to produce these arched low- ? flux ropes. Detailed in situ magnetic measurements and supporting MHD simulations permit quantitative analysis of the plasma behavior. We find that the orientation of the applied potential magnetic field arcade with respect to the flux rope footpoints (i.e., the electrodes) is key. With an arcade that is aligned parallel to the footpoints, force free currents induced in the expanding flux rope modify the pressure and tension in the arcade to produce a confined, quiescent discharge and a saturated kink instability. In an obliquely aligned arcade, on the other hand, a sigmoidal equilibrium forms that can dynamically erupt. Both the kink instability and the torus instability are studied as candidate eruptive mechanisms--the latter by varying the vertical gradient of the potential field arcade. New 2D magnetic measurements of these equilibrium and eruptive features facilitate comparisons to solar observations and modeling. Quasi-statically driven line-tied magnetic flux ropes are studied in the context of storage-and-release eruptions in the solar corona. The Magnetic Reconnection Experiment (MRX) facility is utilized to produce these arched low- ? flux ropes. Detailed in situ magnetic measurements and supporting MHD simulations permit quantitative analysis of the plasma behavior. We find that the orientation of the applied potential magnetic field arcade with respect to the flux rope footpoints (i.e., the electrodes) is key. With an arcade that is aligned parallel to the footpoints, force free currents induced in the expanding flux rope modify the pressure and tension in the arcade to produce a confined, quiescent discharge and a saturated kink instability. In an obliquely aligned arcade, on the other hand, a sigmoidal equilibrium forms that can dynamically erupt. Both the kink instability and the torus instability are studied as candidate eruptive mechanisms--the latter by varying the vertical gradient of the potential field arcade. New 2D magnetic measurements of these equilibrium and eruptive features facilitate comparisons to solar observations and modeling. This research is supported by DoE Contract Number DE-AC02-09CH11466 and by the Center for Magnetic Self-Organization (CMSO).

  6. Hybrid Magnetic Tunnel Junction-MEMS High Frequency Field Modulator for 1\\/f Noise Suppression

    Microsoft Academic Search

    André Guedes; Samadhan B. Patil; Piotr Wisniowski; Virginia Chu; JoÃo P. Conde; Paulo P. Freitas

    2008-01-01

    A dc to ac magnetic field transformer was developed using a magnetic tunnel junction (MTJ)\\/microelectromechanical system (MEMS) mixed device. A MEMS torsionator was fabricated with an incorporated magnetic flux guide, that when actuated by a gate electrode, modulates an external dc field into the same frequency of the micro-torsionator oscillation. Attached to it a MgO based MTJ was fabricated, performing

  7. On the role of crystal and stress anisotropy in magnetic Barkhausen noise

    NASA Astrophysics Data System (ADS)

    Sheikh Amiri, Meisam; Thielen, Matthias; Rabung, Madalina; Marx, Michael; Szielasko, Klaus; Boller, Christian

    2014-12-01

    The article describes the micromagnetic behavior of non- and pre-plastically deformed high strength steel samples under applied stress using different magnetic nondestructive methods such as magnetic Barkhausen noise analysis and hysteresis measurements. It was found that the maximum amplitude of Barkhausen noise (MMAX) increases with applied stress up to a certain point and then decreases again (so-called MMAX(?)-curve). Changes of magnetostriction, hysteresis curves and magnetic domain structures have been measured and have been further investigated to find out the reasons with respect to macro- and microscopic material behavior. The results obtained are mainly discussed on the basis of the Villari effect and the relation between applied stress and the Barkhausen noise parameters is described. It is concluded that the interaction between crystal and stress anisotropy is the main reason of the specific MMAX(?)-curve observed.

  8. Noise reduction for magnetic resonance images via adaptive multiscale products thresholding.

    PubMed

    Bao, Paul; Zhang, Lei

    2003-09-01

    Edge-preserving denoising is of great interest in medical image processing. This paper presents a wavelet-based multiscale products thresholding scheme for noise suppression of magnetic resonance images. A Canny edge detector-like dyadic wavelet transform is employed. This results in the significant features in images evolving with high magnitude across wavelet scales, while noise decays rapidly. To exploit the wavelet interscale dependencies we multiply the adjacent wavelet subbands to enhance edge structures while weakening noise. In the multiscale products, edges can be effectively distinguished from noise. Thereafter, an adaptive threshold is calculated and imposed on the products, instead of on the wavelet coefficients, to identify important features. Experiments show that the proposed scheme better suppresses noise and preserves edges than other wavelet-thresholding denoising methods. PMID:12956264

  9. The application of wavelet shrinkage denoising to magnetic Barkhausen noise measurements

    SciTech Connect

    Thomas, James [American Stress Technologies, Inc., 540 Alpha Drive, Pittsburgh, PA 15238 (United States)

    2014-02-18

    The application of Magnetic Barkhausen Noise (MBN) as a non-destructive method of defect detection has proliferated throughout the manufacturing community. Instrument technology and measurement methodology have matured commensurately as applications have moved from the R and D labs to the fully automated manufacturing environment. These new applications present a new set of challenges including a bevy of error sources. A significant obstacle in many industrial applications is a decrease in signal to noise ratio due to (i) environmental EMI and (II) compromises in sensor design for the purposes of automation. The stochastic nature of MBN presents a challenge to any method of noise reduction. An application of wavelet shrinkage denoising is proposed as a method of decreasing extraneous noise in MBN measurements. The method is tested and yields marked improvement on measurements subject to EMI, grounding noise, and even measurements in ideal conditions.

  10. Flux penetration measurements and the harmonic magnetic response of hot isostatically pressed ,,Pb,Gd...Mo6S8

    E-print Network

    Hampshire, Damian

    Flux penetration measurements and the harmonic magnetic response of hot isostatically pressed ,,Pb penetration measurements and the harmonic magnetic response have been measured from 4.2 K up to the critical In this article, we present detailed flux penetration measurements made in high magnetic fields and investigate

  11. Magnetic flux rotation and two types of additional maxima in magnetization curves of LaSrCuO single crystals in tilted magnetic field

    Microsoft Academic Search

    Yu. V. Bugoslavsky; A. L. Ivanov; V. A. Kovalsky; A. A. Minakov

    1996-01-01

    Magnetic hysteresis loops of LaSrCuO superconducting single crystals were studied by means of a vibrating sample magnetometer at T = 4.2 K. It was directly confirmed that two types of secondary maxima are present in the magnetization curves. By means of vector magnetization measurements we proved that low-field secondary maxima in tilted magnetic field are caused by the flux line

  12. Comparing Poynting flux dominated magnetic towers with kinetic-energy dominated jets

    E-print Network

    Huarte-Espinosa, Martín; Blackman, Eric G; Ciardi, Andrea; Hartigan, Patrick M; Lebedev, Sergey; Chittenden, Jeremy P

    2012-01-01

    Modern theoretical models of astrophysical jets combine accretion, rotation, and magnetic fields to launch and collimate supersonic flows from a central source. Near the source, magnetic field strengths must be large enough to collimate the jet requiring that the Poynting flux exceeds the kinetic-energy flux. The extent to which the Poynting flux dominates kinetic energy flux at large distances from the engine distinguishes two classes of models. In magneto-centrifugal launch (MCL) models, magnetic fields dominate only at scales of order 100 engine radii or less, after which the jets become hydrodynamically dominated (HD). By contrast, in Poynting flux dominated (PFD) magnetic tower models, the field dominates even out to much larger scales. To compare the large distance propagation differences of these two paradigms, we perform 3-D ideal MHD AMR simulations of both HD and PFD jets formed via the same energy flux. We also compare how thermal energy losses and rotation of the jet base affects the stability in ...

  13. The spatial structure of Martian magnetic flux ropes recovered by the Grad-Shafranov reconstruction technique

    NASA Astrophysics Data System (ADS)

    Hara, Takuya; Seki, Kanako; Hasegawa, Hiroshi; Brain, David A.; Matsunaga, Kazunari; Saito, Miho H.

    2014-02-01

    We applied the Grad-Shafranov (GS) reconstruction technique to Martian magnetic flux ropes observed by Mars Global Surveyor in order to estimate their spatial structures. This technique can provide a magnetic field map of their cross section from single spacecraft data, under the assumption that the structure is two-dimensional, magnetohydrostatic, and time independent. We succeeded in recovering the spatial structure for 70 events observed between April 1999 and November 2006. The reconstruction results indicate that the flux rope axes were mostly oriented horizontal to the Martian surface and were randomly distributed with respect to the typical plasma streamline. A subset of events with duration longer than 240 s was observed at solar zenith angles larger than 75°. These events all occur downstream from strong crustal magnetic field in the southern hemisphere, indicating an association between the crustal fields and the detected flux ropes. Using the shape and size of the flux ropes obtained from the GS reconstruction, we estimate lower limits on their volume that span 2-3 orders of magnitude, with larger flux ropes observed downstream from strong crustal magnetic fields. Estimated ion escape rates associated with flux ropes are of the order of 1022-1023 ion/s, being approximately 10% of previously estimated escape rates during solar minimum.

  14. ELF-magnetic flux densities measured in a city environment in summer and winter.

    PubMed

    Straume, Aksel; Johnsson, Anders; Oftedal, Gunnhild

    2008-01-01

    Epidemiological studies have indicated a connection between extremely low frequency magnetic flux densities above 0.4 microT (time weighted average) and childhood leukemia risks. This conclusion is based mainly on indoor exposure measurements. We therefore regarded it important to map outdoor magnetic flux densities in public areas in Trondheim, Norway. Because of seasonal power consumption variations, the fields were measured during both summer and winter. Magnetic flux density was mapped 1.0 m above the ground along 17 km of pavements in downtown Trondheim. The spectrum was measured at some spots and the magnetic flux density emanated mainly from the power frequency of 50 Hz. In summer less than 4% of the streets showed values exceeding 0.4 microT, increasing to 29% and 34% on cold and on snowy winter days, respectively. The average levels were 0.13 microT (summer), 0.85 microT (winter, cold), and 0.90 microT (winter, snow), with the highest recorded value of 37 microT. High spot measurements were usually encountered above underground transformer substations. In winter electric heating of pavements also gave rise to relatively high flux densities. There was no indication that the ICNIRP basic restriction was exceeded. It would be of interest to map the flux density situation in other cities and towns with a cold climate. PMID:17786926

  15. Influence of magnetic field on 1/f noise in GaAs resistors without surface effects

    SciTech Connect

    Song, M.H.; Birbas, A.N.; van der Ziel, A.; van Rheenen, A.D.

    1988-07-15

    The influence on magnetic field on 1/f noise in a planar GaAs resistor grown by molecular-beam epitaxy and without surface effects was investigated experimentally. The experimental results can be explained by the number fluctuation model but not by the mobility fluctuation model. Previously, experimental results indicating number fluctuation type of 1/f noise were mostly attributed to the surface effects associated with the particular structures used for the experiments. In our device the surface effects were diminished so that the fluctuations of the bulk current could be considered to produce the 1/f noise.

  16. Spin torque in the framework of random magnetization dynamics driven by a jump-noise process

    NASA Astrophysics Data System (ADS)

    Bertotti, G.; Serpico, C.; Liu, Z.; Lee, A.; Mayergoyz, I.

    2014-02-01

    It is demonstrated that the Slonczewski spin-torque term can be naturally derived from the equation for magnetization dynamics driven by a jump-noise process. The central point of the derivation is the modification of transition probability rate of the jump-noise process caused by spin-polarized current injection. This modification results in two distinct terms in the expected value of the jump-noise process: the traditional one corresponding to the Landau-Lifshitz damping and another one representing the Slonczewski spin-torque term.

  17. Filament Activation in Response to Magnetic Flux Emergence and Cancellation in Filament Channels

    NASA Astrophysics Data System (ADS)

    Li, Ting; Zhang, Jun; Ji, Haisheng

    2015-05-01

    We conducted a comparative analysis of two filaments that showed a 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) were made to analyze the two filaments on 2013 August 17 - 20 (SOL2013-08-17) and September 29 (SOL2013-09-29). 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 6.4×1021 Mx underlying the filament. The close neighborhood and common direction of the bright threads in the filament and the open AR fan loops suggest a similar magnetic connectivity of these two flux systems. The equilibrium of the filament was not destroyed three 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 4.2×1020 Mx, about one order of magnitude lower than that of the first event. Two patches of parasitic polarity in the vicinity of the barb merged, then cancelled with nearby network fields. About 20 hours after the onset of the emergence, the filament erupted. Our findings imply that the location of emerging flux within the filament channel is probably crucial to filament evolution. If the flux emergence appears nearby the barbs, it is highly likely that the emerging flux and the filament magnetic fields will cancel, which may lead to the eruption of the filament. The comparison of the two events shows that the emergence of a small AR may still not be enough to disrupt the stability of a filament system, and the actual eruption only occurs after the flux cancellation sets in.

  18. Long-range field effects on magnetic Barkhausen noise

    NASA Astrophysics Data System (ADS)

    Pérez-Benitez, J. A.; Capó-Sánchez, J.; Padovese, L. R.

    2007-07-01

    We present findings related to the effect of long-range fields on the Barkhausen effect. The results show an internal demagnetizing effect that comes from the magnetic long-range interactions. This demagnetizing effect induces the appearance of a magnetic pattern in the region of magnetic avalanches. The produced magnetic pattern represents long three-dimensional branches located either parallel or diagonal to the applied field. The current model also reveals the presence of three different magnetization stages, in coincidence with previous experimental reports. The simulations of Barkhausen effect using long-range field is performed using a method that includes dipole-dipole interactions with boundary conditions. Finally, we analyze the critical exponents of the simulated Barkhausen jumps.

  19. Negative differential conductance and super-Poissonian shot noise in single-molecule magnet junctions

    PubMed Central

    Xue, Hai-Bin; Liang, Jiu-Qing; Liu, Wu-Ming

    2015-01-01

    Molecular spintroinic device based on a single-molecule magnet is one of the ultimate goals of semiconductor nanofabrication technologies. It is thus necessary to understand the electron transport properties of a single-molecule magnet junction. Here we study the negative differential conductance and super-Poissonian shot noise properties of electron transport through a single-molecule magnet weakly coupled to two electrodes with either one or both of them being ferromagnetic. We predict that the negative differential conductance and super-Poissonian shot noise, which can be tuned by a gate voltage, depend sensitively on the spin polarization of the source and drain electrodes. In particular, the shot noise in the negative differential conductance region can be enhanced or decreased originating from the different formation mechanisms of negative differential conductance. The effective competition between fast and slow transport channels is responsible for the observed negative differential conductance and super-Poissonian shot noise. In addition, we further discuss the skewness and kurtosis properties of transport current in the super-Poissonian shot noise regions. Our findings suggest a tunable negative differential conductance molecular device, and the predicted properties of high-order current cumulants are very interesting for a better understanding of electron transport through single-molecule magnet junctions. PMID:25736094

  20. Analysis of flux-switching permanent-magnet machine by nonlinear magnetic network model with bypass-bridges

    Microsoft Academic Search

    Gan Zhang; Ming Cheng; Wei Hua

    2010-01-01

    In this paper, a nonlinear magnetic circuit network model for the analysis of a three-phase 12-stator-slot\\/10-rotor-pole flux-switching permanent-magnet (FSPM) motor is proposed considering localized saturation effect, which enables the predictions of open-circuit air-gap field distributions, phase flux-linkage, phase back-electro-motive-force (back-EMF) and winding inductances waveforms. Further, a developed model with bypass-bridges is also proposed, which enables the winding inductances to be

  1. Qualities of Cosmic Rays Flux, Crossing the Boundary between Magnetic Cloud and Solar Wind

    NASA Astrophysics Data System (ADS)

    Petukhov, Ivan; Petukhov, Stanislav

    The model of cosmic ray (CR) Forbush-decrease is researched in a magnetic cloud propagating in interplanetary space. The magnetic cloud is presented as the part of a torus in initial time. The characteristic type of the cloud magnetic field is taken into consideration in the calculation. The change of the torus shape in the following time depends on radial distribution of flow velocity and is described by the kinematic model. The magnetic field is determined from the condition of the freezing-in. The kinetic method of CR flux calculation crossing the boundary between the magnetic cloud and solar wind in view of magnetic field properties is developed. The CR flux arriving in the cloud from interplanetary space and escaping from it, depending on particle energy, magnetic cloud properties and cloud orientation in interplanetary space is determined. It is found: 1) the spectrum value of CR flux coming into the magnetic cloud is higher than the spectrum value of CR existing in interplanetary space; 2) the fastest escaping occurs through the front part of the torus surface; 3) the considerable part of the particles come to its butt-ends during propagation inside the torus.

  2. The role of stationarity in magnetic crackling noise

    Microsoft Academic Search

    Gianfranco Durin; Stefano Zapperi

    2006-01-01

    We discuss the effect of stationarity on the avalanche statistics of Barkhausen noise signals. We perform experimental measurements on an Fe85B15 amorphous ribbon and compare the avalanche distributions measured around the coercive field, where the signal is stationary, with those sampled through the entire hysteresis loop. In the first case, we recover scaling exponents (tau ~ 1.38, alpha ~ 1.65)

  3. The magnetic topology of the plasmoid flux rope in a MHD simulation of magnetotail reconnection

    SciTech Connect

    Birn, J.; Hesse, M.

    1989-01-01

    On the basis of a three-dimensional MHD simulation we discuss the magnetic topology of a plasmoid that forms by a localized reconnection process in a magnetotail configuration including a net dawn-dusk magnetic field component B/sub yN/. As a consequence of b/sub yN/ /ne/ 0 the plasmid gets a helical flux rope structure rather than an isolated island or bubble structure. Initially all field lines of the plasmid flux rope remain connected with the Earth, while at later times a gradually increasing amount of flux tubes becomes separated, connecting to either the distant boundary or to the flank boundaries. In this stage topologically different flux tubes become tangled and wrapped around each other, consistent with predictions on the basis of ad-hoc plasmid models. 10 refs., 8 figs.

  4. Accurate periodicity measurement of superconducting quantum interference device magnetic flux response

    NASA Astrophysics Data System (ADS)

    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 (?) and its period is a flux quantum (?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 ? with a period of ?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 4300?o. Its flux dependence was periodic below about 3400?o.

  5. Catastrophic eruption of magnetic flux rope in the corona and solar wind with and without magnetic reconnection

    Microsoft Academic Search

    Y. Chen; Y. Q. Hu; S. J. Sun

    2007-01-01

    It is generally believed that the magnetic free energy accumulated in the\\u000acorona serves as a main energy source for solar explosions such as coronal mass\\u000aejections (CMEs). In the framework of the flux rope catastrophe model for CMEs,\\u000athe energy may be abruptly released either by an ideal magnetohydrodynamic\\u000a(MHD) catastrophe, which belongs to a global magnetic topological instability

  6. Dynamic roughening of the magnetic flux landscape in YBa2Cu3O7-x

    Microsoft Academic Search

    C. M. Aegerter; M. S. Welling; R. J. Wijngaarden

    2005-01-01

    We study the magnetic flux landscape in YBa2Cu3O7-x thin films as a two dimensional rough surface. The vortex density in the superconductor forms a self-affine structure in both space and time. It is characterized by a roughness exponent alpha=0.76(3) and a growth exponent beta=0.57(6). The roughening is caused by flux avalanches in a self-organized critical state, which is formed in

  7. Influence of specimen velocity on the leakage signal in magnetic flux leakage type nondestructive testing

    E-print Network

    Lintao Zhang; Fawzi Belblidia; Ian Cameron; Johann Sienz; Matthew Boat; Neil Pearson

    2014-12-05

    We investigate the influence of the specimen velocity on the magnetic flux leakage with the aim of selecting the optimum sensor locations. Parametric numerical simulations where the specimen velocity was in the range [0.1-20] m$\\cdot$s$^{-1}$ were carried out. As the specimen velocity is increased, the magnetic field varies from being symmetrical to being asymmetric. For the radial magnetic induction, the peak to peak value moves from the centre of the bridge towards the direction of the specimen movement. For the axial magnetic induction, the specimen velocity influence is dependent on the sensor location and a signal-velocity independent region was discussed.

  8. Influence of specimen velocity on the leakage signal in magnetic flux leakage type nondestructive testing

    E-print Network

    Zhang, Lintao; Cameron, Ian; Sienz, Johann; Boat, Matthew; Pearson, Neil

    2015-01-01

    We investigate the influence of the specimen velocity on the magnetic flux leakage with the aim of selecting the optimum sensor locations. Parametric numerical simulations where the specimen velocity was in the range [0.1-20] m$\\cdot$s$^{-1}$ were carried out. As the specimen velocity is increased, the magnetic field varies from being symmetrical to being asymmetric. For the radial magnetic induction, the peak to peak value moves from the centre of the bridge towards the direction of the specimen movement. For the axial magnetic induction, the specimen velocity influence is dependent on the sensor location and a signal-velocity independent region was discussed.

  9. Detection of leakage magnetic flux from near-side and far-side defects in carbon steel plates using a giant magneto-resistive sensor

    NASA Astrophysics Data System (ADS)

    Sharatchandra Singh, W.; Rao, B. P. C.; Vaidyanathan, S.; Jayakumar, T.; Raj, Baldev

    2008-01-01

    Giant magneto-resistive (GMR) sensors are attractive for magnetic flux leakage measurements, especially for the detection of shallow near-side cracks and deeply located defects. An optimized measurement system with magnetic yoke, GMR sensor and selective amplifier has been devised to detect the tangential component of leakage flux from various near-side notches and far-side notches (widths 0.5 mm and 1.0 mm, respectively) in 12 mm thick carbon steel plates. Far-side notches located at nearly 11 mm below the measurement surface have been detected with a good signal-to-noise ratio. The performance of the GMR sensor with lift off has also been studied for possible non-contact examination of hot surfaces and a lift off of 2 mm is expected to ensure the saturation-free detection of near-side as well as far-side notches.

  10. Measurement of irradiation effects in a RPV steel by ball indentation technique and magnetic Barkhausen noise

    Microsoft Academic Search

    In-Sup Kim; Duck-Gun Park; Thak-Sang Byun; Jun-Hwa Hong

    1999-01-01

    Effects of neutron dose on the mechanical and magnetic properties of a SA508-3 nuclear pressure vessel steel were investigated by using ball indentation test technique and magnetic Barkhausen noise (BN) measurements. The samples were irradiated in a research reactor up to 1018 n\\/cm2 (E>1 MeV) at 70 °C. The yield strength and flow curve were evaluated from the indentation load-depth

  11. The structure and dynamics of a three-dimensional magnetic flux rope flanked by two active magnetic reconnection X-lines at the Earth's magnetopause

    NASA Astrophysics Data System (ADS)

    Oieroset, M.; Phan, T.; Mozer, F.; Eastwood, J. P.; Fujimoto, M.; Daughton, W. S.; Shay, M. A.; Angelopoulos, V.; Sundkvist, D. J.; Drake, J. F.; McFadden, J. P.; Larson, D. E.; Glassmeier, K.

    2012-12-01

    We report the direct detection by three THEMIS spacecraft of a magnetic flux rope flanked by two active X-lines producing colliding plasma jets near the center of the flux rope. The observed density depletion and open magnetic field topology inside the flux rope reveal important three dimensional effects. There was also evidence for non-thermal electron energization within the flux rope core where the fluxes of 1 - 4 keV super-thermal electrons were higher than those in the converging reconnection jets. The flux rope core where the jets collide is an active region characterized by the presence of large amplitude parallel electric fields and solitary waves.

  12. Magnetic energy fluxes in sub-Alfvénic planet star and moon planet interactions

    NASA Astrophysics Data System (ADS)

    Saur, J.; Grambusch, T.; Duling, S.; Neubauer, F. M.; Simon, S.

    2013-04-01

    Context. Electromagnetic coupling of planetary moons with their host planets is well observed in our solar system. Similar couplings of extrasolar planets with their central stars have been studied observationally on an individual as well as on a statistical basis. Aims: We aim to model and to better understand the energetics of planet star and moon planet interactions on an individual and as well as on a statistical basis. Methods: We derived analytic expressions for the Poynting flux communicating magnetic field energy from the planetary obstacle to the central body for sub-Alfvénic interaction. We additionally present simplified, readily useable approximations for the total Poynting flux for small Alfvén Mach numbers. These energy fluxes were calculated near the obstacles and thus likely present upper limits for the fluxes arriving at the central body. We applied these expressions to satellites of our solar system and to HD 179949 b. We also performed a statistical analysis for 850 extrasolar planets. Results: Our derived Poynting fluxes compare well with the energetics and luminosities of the satellites' footprints observed at Jupiter and Saturn. We find that 295 of 850 extrasolar planets are possibly subject to sub-Alfvénic plasma interactions with their stellar winds, but only 258 can magnetically connect to their central stars due to the orientations of the associated Alfvén wings. The total energy fluxes in the magnetic coupling of extrasolar planets vary by many orders of magnitude and can reach values larger than 1019 W. Our calculated energy fluxes generated at HD 179949 b can only explain the observed energy fluxes for exotic planetary and stellar magnetic field properties. In this case, additional energy sources triggered by the Alfvén wave energy launched at the extrasolar planet might be necessary. We provide a list of extrasolar planets where we expect planet star coupling to exhibit the largest energy fluxes. As supplementary information we also attach a table of the modeled stellar wind plasma properties and possible Poynting fluxes near all 850 extrasolar planets included in our study. Conclusions: The orders of magnitude variations in the values for the total Poynting fluxes even for close-in extrasolar planets provide a natural explanation why planet star coupling might have been only observable on an individual basis but not on a statistical basis. Estimated plasma parameters and their associated Poynting fluxes are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/552/A119

  13. A TORSIONAL ALFVEN WAVE EMBEDDED WITHIN A SMALL MAGNETIC FLUX ROPE IN THE SOLAR WIND

    SciTech Connect

    Gosling, J. T.; Teh, W.-L.; Eriksson, S., E-mail: jack.gosling@lasp.colorado.ed [Laboratory for Atmospheric and Space Physics, University of Colorado, 1234 Innovation Drive, Boulder, CO 80303 (United States)

    2010-08-10

    We describe and use novel techniques to analyze a striking and distinct solar wind event observed by two spacecraft. We show that the event is consistent with an interpretation as a torsional Alfven wave embedded within a small, nearly radially aligned, magnetic flux rope of total width {approx}10{sup 6} km. It seems likely that the torsional wave was generated by distortions produced within a pre-existing flux rope that erupted from the Sun. Our examination of many events previously identified as flux ropes in the solar wind indicates that torsional Alfven waves are extremely rare in such events.

  14. Composite pulses robust against charge noise and magnetic field noise for universal control of a singlet-triplet qubit

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Barnes, Edwin; Kestner, Jason P.; Bishop, Lev S.; Das Sarma, Sankar

    2013-03-01

    We generalize our SUPCODE pulse sequences for singlet-triplet qubits to correct errors from imperfect control. This yields gates that are simultaneously corrected for both charge noise and magnetic field gradient fluctuations, addressing the two dominant T2* processes. By using this more efficient version of SUPCODE, we are able to introduce this capability while also substantially reducing the overall pulse time compared to the previous sequence. We show that our sequence remains realistic under experimental constraints such as finite bandwidth. We generalize our SUPCODE pulse sequences for singlet-triplet qubits to correct errors from imperfect control. This yields gates that are simultaneously corrected for both charge noise and magnetic field gradient fluctuations, addressing the two dominant T2* processes. By using this more efficient version of SUPCODE, we are able to introduce this capability while also substantially reducing the overall pulse time compared to the previous sequence. We show that our sequence remains realistic under experimental constraints such as finite bandwidth. This work is supported by LPS-NSA-CMTC, IARPA-MQCO and CNAM.

  15. Fabrication and Characterization of Nano-Sized Magnetic Structures and Their Flux-Pinning Effects on Superconducting Thin Films 

    E-print Network

    Lee, Han Gil

    2011-02-22

    This dissertation describes experimental studies of how a spatially alternating magnetic field can effectively pin the magnetic flux in a superconducting thin film (Pb 82 Bi18), thereby enhancing the superconductivity. The ...

  16. Torsional Alfven Waves in Solar Magnetic Flux Tubes of Axial Symmetry

    E-print Network

    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...

  17. Shot noise of charge current in a quantum dot responded by rotating and oscillating magnetic fields

    SciTech Connect

    Zhao, Hong-Kang, E-mail: zhaohonk@yahoo.com; Zou, Wei-Ke [School of Physics, Beijing Institute of Technology, Beijing 100081 (China); Chen, Qiao [Department of Maths and Physics, Hunan Institute of Engineering, Xiangtan 411104 (China)

    2014-09-07

    We have investigated the shot noise and Fano factor of the dynamic spin-polarized quantum dot under the perturbations of a rotating magnetic field (RMF), and an oscillating magnetic field (OMF) by employing the non-equilibrium Green's function approach. The shot noise is enhanced from sub-Poissonian to super-Poissonian due to the application of RMF and OMF, and it is controlled sensitively by the tilt angle ? of RMF. The magnitude of shot noise increases as the photon energy ?? of OMF increases, and its valley eventually is reversed to peaks as the photon energy is large enough. Double-peak structure of Fano factor is exhibited as the frequency of OMF increases to cover a large regime. The Zeeman energy ?{sub 0}B{sub 0} acts as an effective gate bias to exhibit resonant behavior, and novel peak emerges associated with the applied OMF.

  18. Signal to noise ratio scaling and density limit estimates in longitudinal magnetic recording

    Microsoft Academic Search

    H. N. Bertram; H. Zhou; R. Gustafson

    1998-01-01

    A simplified general expression is given for SNR for digital magnetic recording for transition noise dominant systems. High density media are assumed in which the transition parameter scales with the in-plane grain diameter. At a fixed normalized code density, the SNR varies as the square of the bit spacing times the read track width divided by the grain diameter cubed.

  19. A model for the influence of microstructural defects on magnetic Barkhausen noise in plain steels

    NASA Astrophysics Data System (ADS)

    Pérez-Benitez, J. A.; Capó-Sánchez, J.; Anglada-Rivera, J.; Padovese, L. R.

    2005-03-01

    This study presents a model of the microstructural defect influence on the magnetic Barkhausen noise in plain steels. The comparison of the theoretical and experimental results reveals an excellent agreement between them. We show that both model and experimental approach can be very useful, particularly, for the carbon content characterization in commercial steels.

  20. Anatomy of field effects on magnetization dynamics and spin transfer noise

    Microsoft Academic Search

    L. Wang; G. C. Han; Y. K. Zheng

    2006-01-01

    Spin transfer-related phenomena in nanomagnets have attracted extensive studies. In this paper we shall focus on analysis of individual and combined effects of the external, anisotropy, and demagnetization fields on magnetization dynamics and spin transfer noise. It is found that individual roles of the external, anisotropy, and demagnetization fields, as well as the combined roles of external plus anisotropy fields

  1. Correlated magnetic noise in global networks of gravitational-wave detectors: Observations and implications

    E-print Network

    Christensen, Nelson

    coupling of environmental magnetic fields to test mass motion in gravitational- wave detectors. We find noise artifacts, such as a 1 Hz comb from similar electronics components at each site, have previously be reduced through integration. To the extent that it cannot be mitigated through instrumental (re)design and

  2. Studying the Effect of the Local Thunderstorm Cells on the Background ULF Magnetic Noise Parameter Spectra

    NASA Astrophysics Data System (ADS)

    Ermakova, E. N.; Kotik, D. S.; Ryabov, A. V.; Panyutin, A. A.

    2015-04-01

    We study the effect of the masking factor from the local thunderstorm cells on ULF magnetic field spectra with the inhomogeneous electron-density structures existing in the local ionosphere (ionospheric and lower ionospheric Alfvén resonators). Using an original data-processing technique for recording of horizontal magnetic components at the midlatitude reception point Novaya Zhizn', we have examined the contribution of the sources located at different distances from the reception point to the formation of the background noise spectra. The ULF signal processing technique permitted us to reduce the pulse component of magnetic noise in amplitude above a certain threshold and thus rule out the effect of a local thunderstorm activity. Frequency dependences of the azimuthal angle of the principal axis of the magnetic noise polarization ellipse are also analyzed. It is shown that the presence of the lower ionospheric Alfvén resonator leads to a nonmonotonic dependence of the azimuthal angle on the frequency. It was found that the local thunderstorms within 60 -80 km from the reception point completely mask the manifestation of the lower ionospheric Alfvén resonator in the ULF noise polarization parameters. To spot the local thunderstorm cells, we used the data from the meteorological radar facility MRL-4 in Nizhny Novgorod.

  3. The effect of a transverse magnetic field on 1/f noise in graphene S. L. Rumyantsev,1,2,a)

    E-print Network

    of the 1/f noise has also been established for Si, GaAs, and metals. In bulk Si and GaAs, the 1/f noiseThe effect of a transverse magnetic field on 1/f noise in graphene S. L. Rumyantsev,1,2,a) D; accepted 10 October 2013; published online 25 October 2013) The low frequency 1/f noise in graphene devices

  4. Active control of the volume acquisition noise in functional magnetic resonance imaging: method and psychoacoustical evaluation.

    PubMed

    Chambers, J; Akeroyd, M A; Summerfield, A Q; Palmer, A R

    2001-12-01

    Functional magnetic resonance imaging (fMRI) provides a noninvasive tool for observing correlates of neural activity in the brain while a subject listens to sound. However, intense acoustic noise is generated in the process of capturing MR images. This noise stimulates the auditory nervous system, limiting the dynamic range available for displaying stimulus-driven activity. The noise is potentially damaging to hearing and is distracting for the subject. In an active noise control (ANC) system, a reference sample of a noise is processed to form a sound which adds destructively with the noise at the listener's ear. We describe an implementation of ANC in the electromagnetically hostile and physically compact MRI scanning environment. First, a prototype system was evaluated psychoacoustically in the laboratory, using the electrical drive to a noise-generating loudspeaker as the reference. This system produced 10-20 dB of subjective noise-reduction between 250 Hz and 1 kHz, and smaller amounts at higher frequencies. The system was modified to operate in a real MR scanner where the reference was obtained by recording the acoustic scanner noise. Objective reduction by 30-40 dB of the most intense component in scanner noises was realized between 500 Hz and 3500 Hz, and subjective reduction of 12 dB and 5 dB in tests at frequencies of 600 Hz and at 1.9 kHz, respectively. Although the benefit of ANC is limited by transmission paths to the cochlea other than air-conduction routes from the auditory meatus, ANC achieves worthwhile attenuation even in the frequency range of maximum bone conduction (1.5-2 kHz). ANC should, therefore, be generally useful during auditory fMRI. PMID:11785805

  5. Automatic estimation of the noise variance from the histogram of a magnetic resonance image

    NASA Astrophysics Data System (ADS)

    Sijbers, Jan; Poot, Dirk; den Dekker, Arnold J.; Pintjens, Wouter

    2007-03-01

    Estimation of the noise variance of a magnetic resonance (MR) image is important for various post-processing tasks. In the literature, various methods for noise variance estimation from MR images are available, most of which however require user interaction and/or multiple (perfectly aligned) images. In this paper, we focus on automatic histogram-based noise variance estimation techniques. Previously described methods are reviewed and a new method based on the maximum likelihood (ML) principle is presented. Using Monte Carlo simulation experiments as well as experimental MR data sets, the noise variance estimation methods are compared in terms of the root mean squared error (RMSE). The results show that the newly proposed method is superior in terms of the RMSE.

  6. Plasma PhysicsUnivMaryland 19-21Apr2004 Intrator 3D flux tubes 1 Magnetic reconnection, merging flux ropes,

    E-print Network

    Sitnov, Mikhail I.

    Plasma PhysicsUnivMaryland 19-21Apr2004 Intrator 3D flux tubes 1 Magnetic reconnection, merging flux ropes, 3D effects in RSX T. Intrator P-24 Plasma Physics I. Furno, E. Hemsing, S. Hsu, + many students G.Lapenta, P.Ricci T-15 Plasma Theory Second Workshop on Thin Current Sheets University

  7. Modeling of electromagnetic phenomena in soft magnetic materials under unidirectional time periodic flux excitations

    Microsoft Academic Search

    L. R. Dupre; Oriano Bottauscio; M. Chiampi; M. Repetto; J. A. A. Melkebeek

    1999-01-01

    We report on recent advances in the modeling of magnetic losses in steel laminations used in electromagnetic devices. The integrated-lamination moving dynamic Preisach model, used to evaluate the dynamic magnetization loops under distorted unidirectional flux patterns, is described. The main goal is the comparison of two numerical procedures, using the finite element-finite difference technique and the finite element-fixed point technique,

  8. Current measurement system utilizing cryogenic techniques for the absolute measurement of the magnetic flux quantum

    SciTech Connect

    Endo, T.; Murayama, Y.; Sakamoto, Y.; Sakuraba, T. (Electrotechnical Lab., Tsukuba-shi, Ibaraki (JP)); Shiota, F. (National Research Lab. of Metrology, 1-1-4 Umezono, Tsukuba-shi, Ibaraki 305 (JP))

    1989-04-01

    A series of systems composed of cryogenic devices such as a Josephson potentiometer and a cryogenic current comparator has been proposed and developed to precisely measure a current with any value up to 1 A. These systems will be used to measure the injected electrical energy with an uncertainty of the order of 0.01 ppm or less in the absolute measurement of the magnetic flux quantum by superconducting magnetic levitation. Some preliminary experiments are described.

  9. Flux Pumping and Magnetic Fields in the Outer Penumbra of a Sunspot

    NASA Astrophysics Data System (ADS)

    Brummell, Nicholas H.; Tobias, Steven M.; Thomas, John H.; Weiss, Nigel O.

    2008-10-01

    The filamentary structure of a sunspot penumbra is believed to be magnetoconvective in origin. In the outer penumbra there is a difference in inclination of up to 30°-40° between the magnetic fields associated with bright and dark filaments, and the latter fields plunge downward below the surface toward the edge of the spot. We have proposed that these fields are dragged downward by magnetic pumping caused by the external granular convection. In this paper we model this process in a more elaborate idealized configuration that includes the curvature force exerted by an arched magnetic field in addition to magnetic buoyancy, and demonstrate that magnetic pumping remains an efficient mechanism for holding flux submerged. We discuss the implications of these results for the magnetic structure of the outer penumbra.

  10. Downward pumping of magnetic flux as the cause of filamentary structures in sunspot penumbrae

    NASA Astrophysics Data System (ADS)

    Thomas, John H.; Weiss, Nigel O.; Tobias, Steven M.; Brummell, Nicholas H.

    2002-11-01

    The structure of a sunspot is determined by the local interaction between magnetic fields and convection near the Sun's surface. The dark central umbra is surrounded by a filamentary penumbra, whose complicated fine structure has only recently been revealed by high-resolution observations. The penumbral magnetic field has an intricate and unexpected interlocking-comb structure and some field lines, with associated outflows of gas, dive back down below the solar surface at the outer edge of the spot. These field lines might be expected to float quickly back to the surface because of magnetic buoyancy, but they remain submerged. Here we show that the field lines are kept submerged outside the spot by turbulent, compressible convection, which is dominated by strong, coherent, descending plumes. Moreover, this downward pumping of magnetic flux explains the origin of the interlocking-comb structure of the penumbral magnetic field, and the behaviour of other magnetic features near the sunspot.

  11. Downward pumping of magnetic flux as the cause of filamentary structures in sunspot penumbrae.

    PubMed

    Thomas, John H; Weiss, Nigel O; Tobias, Steven M; Brummell, Nicholas H

    2002-11-28

    The structure of a sunspot is determined by the local interaction between magnetic fields and convection near the Sun's surface. The dark central umbra is surrounded by a filamentary penumbra, whose complicated fine structure has only recently been revealed by high-resolution observations. The penumbral magnetic field has an intricate and unexpected interlocking-comb structure and some field lines, with associated outflows of gas, dive back down below the solar surface at the outer edge of the spot. These field lines might be expected to float quickly back to the surface because of magnetic buoyancy, but they remain submerged. Here we show that the field lines are kept submerged outside the spot by turbulent, compressible convection, which is dominated by strong, coherent, descending plumes. Moreover, this downward pumping of magnetic flux explains the origin of the interlocking-comb structure of the penumbral magnetic field, and the behaviour of other magnetic features near the sunspot. PMID:12459777

  12. Precise measurement of a magnetic field generated by the electromagnetic flux compression technique.

    PubMed

    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. PMID:23635215

  13. Assessing the Impact of Magnetic Flux Erosion on Coronal Mass Ejection Geo-effectiveness

    NASA Astrophysics Data System (ADS)

    Lavraud, B.; Ruffenach, A.

    2012-12-01

    We investigate the magnetic flux erosion that occurred due to magnetic reconnection at the front of several magnetic clouds (MC) observed near Earth. For some MCs the erosion process may be enhanced thanks to a significant magnetic shear at the front of the MC, in particular if the MC has a south-north magnetic polarity while the slow solar wind ahead of it has a predominantly northward orientation. Using a standard MC model, a semi-empirical model of the Dst index and an observational estimate of the magnetic flux erosion we find that the strength of the ensuing storm for these MCs are significantly lower than if no erosion had occurred. We further study and discuss the competitive interplay between adiabatic compression and magnetic erosion at the front of the MC. We conclude that the most geo-effective configuration for a south-north polarity MC is to be preceded by a slow solar wind with southward IMF. However, this stems not only from the formation of a geo-effective sheath region with southward IMF ahead of it, but also from the fact that adiabatic compression and reduced (or lack thereof) magnetic erosion constructively conspire for the structure to be more geo-effective.

  14. TWO-STEP EMERGENCE OF THE MAGNETIC FLUX SHEET FROM THE SOLAR CONVECTION ZONE

    SciTech Connect

    Toriumi, S.; Yokoyama, T., E-mail: toriumi@eps.s.u-tokyo.ac.j [Department of Earth and Planetary Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2010-05-01

    We perform two-dimensional magnetodydrodynamic simulations of the flux emergence from the solar convection zone to the corona. The flux sheet is initially located moderately deep in the adiabatically stratified convection zone (-20,000 km) and is perturbed to trigger the Parker instability. The flux rises through the solar interior due to the magnetic buoyancy, but suffers a gradual deceleration and a flattening in the middle of the way to the surface since the plasma piled on the emerging loop cannot pass through the convectively stable photosphere. As the magnetic pressure gradient enhances, the flux becomes locally unstable to the Parker instability so that the further evolution to the corona occurs. The second-step nonlinear emergence is well described by the expansion law by Shibata et al. To investigate the condition for this 'two-step emergence' model, we vary the initial field strength and the total flux. When the initial field is too strong, the flux exhibits the emergence to the corona without a deceleration at the surface and reveals an unrealistically strong flux density at each footpoint of the coronal loop, while the flux either fragments within the convection zone or cannot pass through the surface when the initial field is too weak. The condition for the 'two-step emergence' is found to be 10{sup 21}-10{sup 22} Mx with 10{sup 4} G at z = -20,000 km. We present some discussions in connection with recent observations and the results of the thin-flux-tube model.

  15. Filament Activation in Response to Magnetic Flux Emergence and Cancellation in Filament Channels

    E-print Network

    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 ...

  16. Noise annoyance caused by magnetic levitation train passbys

    Microsoft Academic Search

    Joos Vos

    2001-01-01

    In a laboratory study, the annoyance caused by the passby sounds from a magnetic levitation (maglev) train was investigated. The outdoor A-weighted sound exposure level (ASEL) of the maglev sounds varied from 65 to 90 dB. The driving speed of the maglev train varied from 100 to 400 km\\/h. Four important results were obtained. Provided that the outdoor ASELs were

  17. Exact scattering matrix of graphs in magnetic field and quantum noise

    SciTech Connect

    Caudrelier, Vincent, E-mail: v.caudrelier@city.ac.uk [Department of Mathematical Science, City University London, Northampton Square, London EC1V 0HB (United Kingdom); Mintchev, Mihail, E-mail: mintchev@df.unipi.it [Istituto Nazionale di Fisica Nucleare and Dipartimento di Fisica dell’Università di Pisa, Largo Pontecorvo 3, 56127 Pisa (Italy); Ragoucy, Eric, E-mail: eric.ragoucy@lapth.cnrs.fr [LAPTh, Laboratoire d’Annecy-le-Vieux de Physique Théorique, CNRS, Université de Savoie, BP 110, 74941 Annecy-le-Vieux Cedex (France)

    2014-08-15

    We consider arbitrary quantum wire networks modelled by finite, noncompact, connected quantum graphs in the presence of an external magnetic field. We find a general formula for the total scattering matrix of the network in terms of its local scattering properties and its metric structure. This is applied to a quantum ring with N external edges. Connecting the external edges of the ring to heat reservoirs, we study the quantum transport on the graph in ambient magnetic field. We consider two types of dynamics on the ring: the free Schrödinger and the free massless Dirac equations. For each case, a detailed study of the thermal noise is performed analytically. Interestingly enough, in presence of a magnetic field, the standard linear Johnson-Nyquist law for the low temperature behaviour of the thermal noise becomes nonlinear. The precise regime of validity of this effect is discussed and a typical signature of the underlying dynamics is observed.

  18. New power supply method for soft magnetic material characterization at high flux density values

    Microsoft Academic Search

    A. Boglietti; P. Ferraris; M. Lazzari; M. Pastorelli; F. Profumo

    1992-01-01

    A novel power supply is proposed to improve the characterization of soft magnetic materials at high flux density. The power supply consists of a high-frequency switching power supply (PWM inverter) with a voltage regulator to control the distortion of the electromotive force induced in the device under test (Epstein yoke, wound, core, etc.). Experimental results confirm the good features of

  19. PARTICLE MOTION ON MAGNETIC FLUX SURFACES IN STABILIZED AND HARDCORE PINCHES

    Microsoft Academic Search

    D. H. Birdsall; S. A. Colgate; H. P. Furth; C. W. Hartman; R. L. Spoerlein

    1962-01-01

    High-power stabilized pinches are subject to magnetic disturbances and ; leakage of energetic particles. A diffusion theory describing the leakage in ; terms of interconnection of flux surfaces is consistent with the experimental ; data. Direct observation of the leakage phenomenon was realized in a 4-in., 100-; kamp linear pinch tube, along which is passed a 200-kv, 10-mamp electron beam

  20. Development of magnetic flux leakage pipe inspection robot using Hall sensors

    Microsoft Academic Search

    Jin Tao; Que Peiwen; Tao Zhengsu

    2004-01-01

    Pipeline safety evaluation is an important problem of industry, and this paper presents an automated pipe inspection robot to inspect pipeline defects. Based on magnetic flux leakage (MFL) method, the robot utilizes established mechatronic principles to produce a low-cost device capable of detecting inner pipe defects. The pipe inspection robot's design mainly includes its mechanical design, electronic design and data

  1. Rotor Yoke Thickness of Coreless High-Speed Axial-Flux Permanent Magnet Generator

    Microsoft Academic Search

    M. Sadeghierad; A. Darabi; H. Lesani; H. Monsef

    2009-01-01

    Recently, high-speed axial flux generator (HSAFG) has come to attention because of its some advantages such as high power density and efficiency. This paper presents a modeling and designing procedure of HSAFG with some details. The back iron of the permanent magnet is the main design subject investigated in this paper. Optimized thickness of the back-iron used in the rotor

  2. Influence of design parameters on output torque of flux-switching permanent magnet machines

    Microsoft Academic Search

    Z. Q. Zhu; Y. Pang; J. T. Chen; Z. P. Xia; D. Howe

    2008-01-01

    The influence of design parameters of a flux-switching PM (FSPM) machine for maximum output torque has been investigated by finite element analyses and validated by measurements made on a prototype FSPM motor. These parameters include the split ratio of the inner diameter to outer diameter of the stator, the stator tooth width, the stator magnet thickness, the stator back-iron thickness,

  3. ACRIM-gap and TSI trend issue resolved using a surface magnetic flux TSI proxy model

    E-print Network

    Scafetta, Nicola

    of solar magnetic flux. `Mixed' versions of ACRIM and PMOD TSI composites are constructed, frequent observations and precise solar pointing. The Nimbus7/ERB and ERBS/ ERBE were lower precision solar observational opportunities and were not solar pointed. [4] The single greatest challenge

  4. Delocking of flux-flow states in dc-driven magnetically coupled Josephson junctions E. Goldobin

    E-print Network

    Wallraff, Andreas

    Delocking of flux-flow states in dc-driven magnetically coupled Josephson junctions E. Goldobin , A with different damping parameters are con- sidered. An analytical model of the delocking is developed for dense coupled oscillators with enhanced power and frequency yield [1]. Spectral char- acteristics of the two

  5. Optimal control of a flywheel energy storage system with a radial flux hybrid magnetic bearing

    Microsoft Academic Search

    Jr-Yi Shen; Brian C. Fabien

    2002-01-01

    This paper describes the design and implementation of digital controllers for a flywheel energy storage device that incorporates a radial flux hybrid permanent magnetic bearing. Although the uncontrolled device is asymptotically stable, active control is required to: (i) ensure that a finite radial air gap is maintained at all times, and (ii) attenuate the oscillations of the flywheel which reduce

  6. Modeling Solar Spectral Irradiance and Total Magnetic Flux Using Sunspot Areas

    Microsoft Academic Search

    Dora G. Preminger; Stephen R. Walton

    2006-01-01

    We show that daily sunspot areas can be used in a simple, single parameter model to reconstruct daily variations in several other solar parameters, including solar spectral irradiance and total magnetic flux. The model assumes that changes in any given parameter can be treated mathematically as the response of the system to the emergence of a sunspot. Using cotemporal observational

  7. DYNAMIC COUPLING OF CONVECTIVE FLOWS AND MAGNETIC FIELD DURING FLUX EMERGENCE

    SciTech Connect

    Fang Fang; Manchester IV, Ward; Van der Holst, Bart [Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48109 (United States); Abbett, William P. [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)

    2012-01-20

    We simulate the buoyant rise of a magnetic flux rope from the solar convection zone into the corona to better understand the energetic coupling of the solar interior to the corona. The magnetohydrodynamic model addresses the physics of radiative cooling, coronal heating, and ionization, which allow us to produce a more realistic model of the solar atmosphere. The simulation illustrates the process by which magnetic flux emerges at the photosphere and coalesces to form two large concentrations of opposite polarities. We find that the large-scale convective motion in the convection zone is critical to form and maintain sunspots, while the horizontal converging flows in the near-surface layer prevent the concentrated polarities from separating. The footpoints of the sunspots in the convection zone exhibit a coherent rotation motion, resulting in the increasing helicity of the coronal field. Here, the local configuration of the convection causes the convergence of opposite polarities of magnetic flux with a shearing flow along the polarity inversion line. During the rising of the flux rope, the magnetic energy is first injected through the photosphere by the emergence, followed by energy transport by horizontal flows, after which the energy is subducted back to the convection zone by the submerging flows.

  8. On the designing procedure of a permanent magnet transverse flux generator (PMTFG) with specific topology

    Microsoft Academic Search

    Larisa Strete; I.-A. Viorel; A. C. Viorel

    2008-01-01

    The permanent magnet transverse flux (PMTF) machine operates at low speed and is capable of producing power densities larger than the ones produced by conventional machines. The PMTF machine has the advantage of modularity, since each phase is an independent module. Due to these features, a PMTF machine can be an excellent option for low and medium power, low speed

  9. Optimal design of a rotating transverse flux motor (TFM) with permanent magnets in rotor

    Microsoft Academic Search

    Larisa Strete; L. Tutelea; I. Boldea; Claudia Martis; I.-A. Viorel

    2010-01-01

    An optimal design procedure, based on Hooke-Jeeves method, applied to a permanent magnet transverse flux motor (PMTFM) is presented in the paper. Different objective functions, as minimum cost, minimum cogging torques and maximum efficiency were considered. The results obtained for a low power sample PMTFM are given and commented.

  10. Effects of Core Characteristics on Detection Performances in Zero Flux Type Magnetic Sensor

    Microsoft Academic Search

    T. Sonoda; R. Ueda

    1987-01-01

    To verify the lack of dependence of a proposed zero flux type magnetic sensor on the material and shape of the core used, the authors constructed sensors using amorphous and supermalloy ribbons, and studied the detection characteristics. Detection levels were found to be unaffected by the type of ribbon core used and by the core shape, and an accuracy to

  11. A Flux Tube Tectonics Model for Solar Coronal Heating Driven by the Magnetic Carpet.

    E-print Network

    Priest, Eric

    A Flux Tube Tectonics Model for Solar Coronal Heating Driven by the Magnetic Carpet. Eric R. Priest heating. The dissipation of energy along sharp boundaries we call, by analogy with geophysi- cal plate tectonics, the tectonics model of coronal heating. Similar to the case on Earth, the relative motions

  12. Temperature Evolution of a Magnetic Flux Rope in a Failed Solar Eruption

    NASA Astrophysics Data System (ADS)

    Song, H. Q.; Zhang, J.; Cheng, X.; Chen, Y.; Liu, R.; Wang, Y. M.; Li, B.

    2014-03-01

    In this paper, we report for the first time the detailed temperature evolution process of the magnetic flux rope in a failed solar eruption. Occurring on 2013 January 05, the flux rope was impulsively accelerated to a speed of ~400 km s-1 in the first minute, then decelerated and came to a complete stop in two minutes. The failed eruption resulted in a large-size high-lying (~100 Mm above the surface), high-temperature "fire ball" sitting in the corona for more than two hours. The time evolution of the thermal structure of the flux rope was revealed through the differential emission measure analysis technique, which produced temperature maps using observations of the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory. The average temperature of the flux rope steadily increased from ~5 MK to ~10 MK during the first nine minutes of the evolution, which was much longer than the rise time (about three minutes) of the associated soft X-ray flare. We suggest that the flux rope is heated by the energy release of the continuing magnetic reconnection, different from the heating of the low-lying flare loops, which is mainly produced by the chromospheric plasma evaporation. The loop arcade overlying the flux rope was pushed up by ~10 Mm during the attempted eruption. The pattern of the velocity variation of the loop arcade strongly suggests that the failure of the eruption was caused by the strapping effect of the overlying loop arcade.

  13. The characteristics of trapped magnetic flux inside bulk HTS in the Mixed-? levitation system

    NASA Astrophysics Data System (ADS)

    Ghodsi, M.; Ueno, T.; Teshima, H.; Hirano, H.; Higuchi, T.

    2006-10-01

    In this paper we propose a new experimental method to investigate the principle of ‘Mixed-?’ levitation systems. To confirm our claim, we measured the attractive force and the variation of flux passing through both, the HTS sample and the face surface of iron yoke, when the yoke is approached/retreated to the surface of field-cooled HTS sample. It is revealed that when the diameter of the yoke is less than the diameter of the HTS, in the small gap by reducing the gap, the flux which passes through the face surface of the yoke and consequently the attractive force will decrease. Therefore, stable levitation is achievable. However, when the diameter of yoke is equal to the diameter of the HTS, the magnetic flux will not decrease for a reducing gap and stable levitation is unfeasible. Briefly, stable levitation is achievable when the yoke diameter is less than the HTS’s diameter. Additionally, as the yoke is approached to the HTS the flux variation of the HTS in 77 K is negligible compare to the flux variation of the HTS in the room temperature. Therefore, in superconductivity state the pinned fluxes in the HTS samples remain approximately constant and the HTS acts as a ‘magnetic isolator’. This specification can be used to simulate the behavior of field-cooled HTS by the FEM software.

  14. Temperature evolution of a magnetic flux rope in a failed solar eruption

    SciTech Connect

    Song, H. Q.; Chen, Y.; Li, B. [Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment and Institute of Space Sciences, Shandong University, Weihai, Shandong 264209 (China); Zhang, J. [School of Physics, Astronomy and Computational Sciences, George Mason University, Fairfax, Virginia 22030 (United States); Cheng, X. [School of Astronomy and Space Science, Nanjing University, Nanjing, Jiangsu 210093 (China); Liu, R.; Wang, Y. M., E-mail: jzhang7@gmu.edu [CAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Sciences, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2014-03-20

    In this paper, we report for the first time the detailed temperature evolution process of the magnetic flux rope in a failed solar eruption. Occurring on 2013 January 05, the flux rope was impulsively accelerated to a speed of ?400 km s{sup –1} in the first minute, then decelerated and came to a complete stop in two minutes. The failed eruption resulted in a large-size high-lying (?100 Mm above the surface), high-temperature 'fire ball' sitting in the corona for more than two hours. The time evolution of the thermal structure of the flux rope was revealed through the differential emission measure analysis technique, which produced temperature maps using observations of the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory. The average temperature of the flux rope steadily increased from ?5 MK to ?10 MK during the first nine minutes of the evolution, which was much longer than the rise time (about three minutes) of the associated soft X-ray flare. We suggest that the flux rope is heated by the energy release of the continuing magnetic reconnection, different from the heating of the low-lying flare loops, which is mainly produced by the chromospheric plasma evaporation. The loop arcade overlying the flux rope was pushed up by ?10 Mm during the attempted eruption. The pattern of the velocity variation of the loop arcade strongly suggests that the failure of the eruption was caused by the strapping effect of the overlying loop arcade.

  15. Quantitative Imaging of the Solar Wind: CME Mass Evolution and the Interplanetary Magnetic Flux Balance

    NASA Astrophysics Data System (ADS)

    DeForest, Craig

    2012-05-01

    We recently developed post-processing techniques for heliospheric images from the STEREO spacecraft; the new data sets enable, for the first time, quantitative photometric studies of evolving wind features at distances up to 1 A.U. from the Sun. We have used the new data to trace several CMEs and magnetic disconnection events to their origins in the solar corona, and to infer the force balance and entrained magnetic flux in those features. We present recent results showing the relationship between ICME and CME anatomy, in particular the origin of an observed interplanetary flux rope and the relationship between original launched solar material and piled-up sheath material and flux in the storm at 1. A.U. We discuss implications for understanding space weather physics and predicting individual events, and point out the importance of future imaging technologies such as polarized heliospheric imaging.

  16. Laser-Driven Magnetic-Flux Compression in High-Energy-Density Plasmas O. V. Gotchev,1,2,3

    E-print Network

    Laser-Driven Magnetic-Flux Compression in High-Energy-Density Plasmas O. V. Gotchev,1,2,3 P. Y velocity, minimizing the effect of resistive flux diffusion. The magnetic fields in the compressed core density. In such systems, thermal conduction losses are a major factor in the energy balance

  17. Laboratory Simulation of Arched Magnetic Flux Rope Eruptions in the Solar Atmosphere S. K. P. Tripathi* and W. Gekelman

    E-print Network

    California at Los Angles, University of

    Laboratory Simulation of Arched Magnetic Flux Rope Eruptions in the Solar Atmosphere S. K. P loops, prominences, and filaments are arched magnetic flux rope (AMFR) structures in the solar atmo] and spacecraft observations, however, ubiquitously show solar AMFRs with stable appearances suspended for longer

  18. Effect of trapped magnetic flux on the threshold curves of three-junction superconducting quantum interference devices

    SciTech Connect

    Chang, W.H.

    1982-12-01

    Thin-film Josephson-junction quantum-interference devices require only a small amount of magnetic flux to switch them between the voltage state and the superconducting state. They are sensitive to any spurious magnetic flux present at the device. The magnetic flux may be trapped in the superconducting ground plane, particularly in ground plane holes. This paper analyzes the effects of the trapped magnetic flux on the threshold curves of three-junction Josephson interferometers. The threshold curves of the interferometer are calculated automatically by using a circuit optimization program. The automatic procedure of calculating the threshold curves of an interferometer can be applied to any Josephson-junction interferometer device. The threshold curves of both symmetric and asymmetric interferometers are calculated. We find that the threshold curves of a symmetric three-junction interferometer changes periodically as a function of the effective coupled trapped magnetic flux with a period of Phi/sub 0/. The threshold curves are shifted and severely distorted in shape by the presence of the coupled trapped magnetic flux. The degeneracy of the threshold curves of a symmetric interferometer makes the unique quantitative determination of the trapped magnetic flux difficult. However, the degeneracy is removed in an asymmetric interferometer. The presence of the unbalanced trapped magnetic flux greatly shifts the entire threshold curve of an asymmetric interferometer.

  19. Gaussian approximation and single-spin measurement in magnetic resonance force microscopy with spin noise

    SciTech Connect

    Raghunathan, Shesha; Brun, Todd A. [Center for Quantum Information Science and Technology, Communication Sciences Institute, Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089 (United States); Goan, Hsi-Sheng [Department of Physics and Center for Theoretical Sciences, National Taiwan University, Taipei 10617, Taiwan (China); Center for Quantum Science and Engineering, National Taiwan University, Taipei 10617, Taiwan (China)

    2010-11-15

    A promising technique for measuring single electron spins is magnetic resonance force microscopy (MRFM), in which a microcantilever with a permanent magnetic tip is resonantly driven by a single oscillating spin. The most effective experimental technique is the oscillating cantilever-driven adiabatic reversals (OSCAR) protocol, in which the signal takes the form of a frequency shift. If the quality factor of the cantilever is high enough, this signal will be amplified over time to the point where it can be detected by optical or other techniques. An important requirement, however, is that this measurement process occurs on a time scale that is short compared to any noise which disturbs the orientation of the measured spin. We describe a model of spin noise for the MRFM system and show how this noise is transformed to become time dependent in going to the usual rotating frame. We simplify the description of the cantilever-spin system by approximating the cantilever wave function as a Gaussian wave packet and show that the resulting approximation closely matches the full quantum behavior. We then examine the problem of detecting the signal for a cantilever with thermal noise and spin with spin noise, deriving a condition for this to be a useful measurement.

  20. Dynamical Process of Liner Implosion in the Electromagnetic Flux Compression for Ultra-high Magnetic Fields

    E-print Network

    Nakamura, Daisuke; Matsuda, Yasuhiro H; Takeyama, Shojiro

    2013-01-01

    The spatial distribution of magnetic fields that are generated by the electromagnetic flux compression technique is investigated, with emphasis on the dynamical processes of an imploding liner. By comparing with the results of computer simulations, we found that the non-uniform implosion of a liner is important in order to explain the magnetic field's distribution during the liner's implosion. In addition, our results suggest that the initial inwards compressing spool-like motion of the liner subsequently turns out to be outwards stretching barrel-like motion along the magnetic field axis.

  1. Feasibility study on 3 axis magnetic sensor for flux leakage method

    NASA Astrophysics Data System (ADS)

    Sasamoto, Akira

    2014-04-01

    Most of NDT system by magnetic field sensing has employed coil or semiconductor as sensor which has one axis sensitivity. Recent development of semiconductor technology can makes a chip that enable us to measure 3 axis magnetic field in a 1mm square. This vector information is expected to show a new insight in NDT testing. This presentation will show a basic experimental feasibility study for application of magnetic sensor to flux leakage and eddy current testing method by using a sensing system with the chip.

  2. Small-Scale Magnetic-Flux Emergence Observed with Hinode Solar Optical Telescope

    NASA Astrophysics Data System (ADS)

    Otsuji, Kenichi; Shibata, Kazunari; Kitai, Reizaburo; Ueno, Satoru; Nagata, Shin'ichi; Matsumoto, Takuma; Nakamura, Tahei; Watanabe, Hiroko; Tsuneta, Saku; Suematsu, Yoshinori; Ichimoto, Kiyoshi; Shimizu, Toshifumi; Katsukawa, Yukio; Tarbell, Theodore D.; Lites, Bruce; Shine, Richard A.; Title Alan M.

    2007-11-01

    We observed small-scale magnetic-flux emergence in a sunspot moat region by the Solar Optical Telescope (SOT) aboard the Hinode satellite. We analyzed filtergram images observed at wavelengths of Fe 6302Å, G band, and CaII H. In Stokes I images of Fe 6302Å, emerging magnetic flux was recognized as dark lanes. In the G band, they showed to be their shapes almost the same as in Stokes I images. These magnetic fluxes appeared as dark filaments in CaII H images. Stokes V images of Fe 6302Å showed pairs of opposite polarities at footpoints of each filament. These magnetic concentrations were identified to correspond to bright points in G band/CaII H images. From an analysis of time-sliced diagrams, we derived the following properties of emerging flux, which are consistent with those of previous studies: (1) Two footpoints separate each other at a speed of 4.2kms-1 during the initial phase of evolution, and decrease to about 1kms-1 10minutes later. (2) CaII H filaments appear almost simultaneously with the formation of dark lanes in Stokes I in an observational cadence of 2minutes. (3) The lifetime of the dark lanes in the Stokes I and G band is 8minutes, while that of Ca filament is 12minutes. An interesting phenomena was observed, that an emerging flux tube expanded laterally in the photosphere with a speed of 3.8kms-1. A discussion on the horizontal expansion of the flux tube is given with refernce to previous simulation studies.

  3. The pecular magnetic field morphology of the white dwarf WD 1953-011: evidence for a large-scale magnetic flux tube?

    E-print Network

    -scale magnetic flux tube? G. Valyavin1 , G.A. Wade2 , S. Bagnulo3 , T. Szeifert4 , J.D. Landstreet5 , Inwoo Han1 a geometry similar to a magnetic flux tube. 1 Korea Astronomy and Space Science Institute, 61-1, Whaam, London, Canada 6 Special Astrophysical Observatory, Russian Academy of Sciences, Nizhnii Arkhyz, Karachai

  4. The structure of an earthward propagating magnetic flux rope early in its evolution: comparison of methods

    NASA Astrophysics Data System (ADS)

    Möstl, C.; Farrugia, C. J.; Biernat, H. K.; Kiehas, S. A.; Nakamura, R.; Ivanova, V. V.; Khotyaintsev, Y.

    2009-05-01

    We analyze a magnetic signature associated with the leading edge of a bursty bulk flow observed by Cluster at -19 RE downtail on 22 August 2001. A distinct rotation of the magnetic field was seen by all four spacecraft. This event was previously examined by Slavin et al. (2003b) using both linear force-free modeling as well as a curlometer technique. Extending this work, we apply here single- and multi-spacecraft Grad-Shafranov (GS) reconstruction techniques to the Cluster observations and find good evidence that the structure encountered is indeed a magnetic flux rope and contains helical magnetic field lines. We find that the flux rope has a diameter of approximately 1 RE, an axial field of 26.4 nT, a velocity of ?650 km/s, a total axial current of 0.16 MA and magnetic fluxes of order 105 Wb. The field line twist is estimated as half a turn per RE. The invariant axis is inclined at 40° to the ecliptic plane and 10° to the GSM equatorial plane. The flux rope has a force-free core and non-force-free boundaries. When we compare and contrast our results with those obtained from minimum variance, single-spacecraft force-free fitting and curlometer techniques, we find in general fair agreement, but also clear differences such as a higher inclination of the axis to the ecliptic. We further conclude that single-spacecraft methods have limitations which should be kept in mind when applied to THEMIS observations, and that non-force-free GS and curlometer techniques are to be preferred in their analysis. Some properties we derived for this earthward- moving structure are similar to those inferred by Lui et al. (2007), using a different approach, for a tailward-moving flux rope observed during the expansion phase of the same substorm.

  5. Heat flux effects on magnetic field dynamics in solid density plasmas traversed by relativistic electron beams

    NASA Astrophysics Data System (ADS)

    Williams, B. E. R.; Kingham, R. J.; Bissell, J. J.

    2013-09-01

    Relativistic electron beam propagation through solid density plasma is a rich area for magnetic field dynamics. It is well known that Ohmic heating of the background plasma caused by the beam significantly affects magnetic field generation, primarily through changes in the resistivity. In particular, temperature changes in the background plasma leads to the generation of a magnetic field that acts to deflect relativistic electrons from the beam axis. This ‘beam hollowing’ field could have disastrous implications for the fast ignitor scheme. In this paper, the effects of background heat flow on magnetic field generation are considered, first with a simple analytic investigation, and then with 1D Vlasov Fokker-Planck and classical transport simulations using a rigid beam for the fast electrons. It is shown that the thermal conduction of the background plasma acts to diffuse the temperature, reducing both the temperature gradients and the beam hollowing field. This gives rise to the re-emergence of a collimating magnetic field. The influence of the background heat flux is also investigated in the context of solids with imposed resistivity gradients, and is shown to significantly enhance the magnetic field present. More exotic transport effects, such as an enhanced Nernst velocity (due to non-local heat flux) and double peaked temperature profiles (due to distortion of the heating and heat-flow profiles by the magnetic field), are also reported.

  6. Iron loss in permanent-magnet brushless AC machines under maximum torque per ampere and flux weakening control

    Microsoft Academic Search

    Z. Q. Zhu; Y. S. Chen; D. Howe

    2002-01-01

    The airgap flux density distribution, flux density loci in the stator core, and the associated iron loss in two topologies of brushless AC motor, having a surface-mounted magnet rotor and an interior-mounted magnet rotor, respectively, are investigated when operated under maximum torque per ampere control in the constant torque mode and maximum power control in the flux-weakening mode. It is

  7. Direct evidence for a three-dimensional magnetic flux rope flanked by two active magnetic reconnection X lines at Earth's magnetopause.

    PubMed

    Øieroset, M; Phan, T D; Eastwood, J P; Fujimoto, M; Daughton, W; Shay, M A; Angelopoulos, V; Mozer, F S; McFadden, J P; Larson, D E; Glassmeier, K-H

    2011-10-14

    We report the direct detection by three THEMIS spacecraft of a magnetic flux rope flanked by two active X lines producing colliding plasma jets near the center of the flux rope. The observed density depletion and open magnetic field topology inside the flux rope reveal important three-dimensional effects. There was also evidence for nonthermal electron energization within the flux rope core where the fluxes of 1-4 keV superthermal electrons were higher than those in the converging reconnection jets. The observed ion and electron energizations differ from current theoretical predictions. PMID:22107399

  8. Depinning of flux lines and AC losses in magnet-superconductor levitation system

    SciTech Connect

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

    1999-11-29

    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 {approx}2Oe, 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.

  9. Hybrid magnetoresistive\\/microelectromechanical devices for static field modulation and sensor 1\\/f noise cancellation

    Microsoft Academic Search

    A. Guedes; S. B. Patil; S. Cardoso; V. Chu; J. P. Conde; P. P. Freitas

    2008-01-01

    Low frequency 1\\/f noise in magnetoresistive (MR) spin valve sensors was suppressed by modulating an external dc magnetic field at high frequency microelectromechanical system using a (MEMS) microcantilever structure with an integrated magnetic flux guide. With this hybrid MR\\/MEMS device, direct detection of dc magnetic fields in the sensor high frequency thermal noise regime was achieved. The microcantilever was actuated

  10. Investigation of Surface Magnetic Noise by Shallow Spins in Diamond

    NASA Astrophysics Data System (ADS)

    Rosskopf, T.; Dussaux, A.; Ohashi, K.; Loretz, M.; Schirhagl, R.; Watanabe, H.; Shikata, S.; Itoh, K. M.; Degen, C. L.

    2014-04-01

    We present measurements of spin relaxation times (T1, T1?, T2) on very shallow (?5 nm) nitrogen-vacancy centers in high-purity diamond single crystals. We find a reduction of spin relaxation times up to 30 times compared to bulk values, indicating the presence of ubiquitous magnetic impurities associated with the surface. Our measurements yield a density of 0.01-0.1?B/nm2 and a characteristic correlation time of 0.28(3) ns of surface states, with little variation between samples and chemical surface terminations. A low temperature measurement further confirms that fluctuations are thermally activated. The data support the atomistic picture where impurities are associated with the top carbon layers, and not with terminating surface atoms or adsorbate molecules. The low spin density implies that the presence of a single surface impurity is sufficient to cause spin relaxation of a shallow nitrogen-vacancy center.

  11. Asymmetric magnetic flux generation, m = 1 activity, and edge phenomena on a reversed-field pinch. [ZT-40M

    SciTech Connect

    Howell, R.B.; Ingraham, J.C.; Wurden, G.A.; Weber, P.G.; Buchenauer, C.J.

    1987-06-01

    The ZT-40M (Fusion Tech. 8, 1571 (1985)) reversed-field pinch has been used to study magnetic flux perturbations during high-theta (theta = B/sub theta/(a)/>1.6) discharges. Asymmetric toroidal magnetic flux perturbations are found to be associated with magnetic flux emerging through the toroidal shell gap and with m = 0 magnetic disturbances moving toroidally. Ramping current discharges, which are a special case of high-theta operation, show the most robust self-generation of toroidal flux. The electron density fluctuations on the inside major radius and associated m = 1 and m = 0 fluctuations seen on edge magnetic field probes provide a clearer picture of activity during a soft x-ray sawtooth crash. During the sawtooth crash, significant magnetic energy is apparently converted into kinetic energy of the particles.

  12. Influence of growth and annealing conditions on low-frequency magnetic 1/f noise in MgO magnetic tunnel junctions

    SciTech Connect

    Feng Jiafeng; Diao Zhu; Kurt, Huseyin; Singh, A.; Coey, J. M. D. [CRANN and School of Physics, Trinity College, Dublin 2 (Ireland); Stearrett, Ryan; Nowak, Edmund R. [Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States)

    2012-11-01

    Magnetic 1/f noise is compared in magnetic tunnel junctions with electron-beam evaporated and sputtered MgO tunnel barriers in the annealing temperature range 350 - 425 Degree-Sign C. The variation of the magnetic noise parameter ({alpha}{sub mag}) of the reference layer with annealing temperature mainly reflects the variation of the pinning effect of the exchange-bias layer. A reduction in {alpha}{sub mag} with bias is associated with the bias dependence of the tunneling magnetoresistance. The related magnetic losses are parameterized by a phase lag {epsilon}, which is nearly independent of bias especially below 100 mV. The similar changes in magnetic noise with annealing temperature and barrier thickness for two types of MgO magnetic tunnel junctions indicate that the barrier layer quality does not affect the magnetic losses in the reference layer.

  13. Tidal disruption and magnetic flux capture: powering a jet from a quiescent black hole

    NASA Astrophysics Data System (ADS)

    Kelley, Luke Zoltan; Tchekhovskoy, Alexander; Narayan, Ramesh

    2014-12-01

    The transient Swift J1644+57 is believed to have been produced by an unlucky star wandering too close to a supermassive black hole (BH) leading to a tidal disruption event. This unusual flare displayed highly super-Eddington X-ray emission which likely originated in a relativistic, collimated jet. This presents challenges to modern accretion and jet theory as upper limits of prior BH activity, which we obtain from the radio afterglow of this event, imply that both the pre-disruption BH and stellar magnetic fluxes fall many orders of magnitude short of what is required to power the observed X-ray luminosity. We argue that a pre-existing, `fossil' accretion disc can contain a sufficient reservoir of magnetic flux and that the stellar debris stream is capable of dragging this flux into the BH. To demonstrate this, we perform local, 3D magnetohydrodynamic simulations of the disc-stream interaction and demonstrate that the interface between the two is unstable to mixing. This mixing entrains a sufficient amount of fossil disc magnetic flux into the infalling stellar debris to power the jet. We argue that the interaction with the fossil disc can have a pronounced effect on the structure and dynamics of mass fallback and likely the resulting transient. Finally, we describe possible ramifications of these interactions on unresolved problems in tidal disruption dynamics, in particular, the efficiency of debris circularization, and effects of the disruption on the pre-existing BH system.

  14. Magnetic Activity in Thick Accretion Disks and Associated Observable Phenomena: II. Flux Storage

    E-print Network

    Sydney D'Silva; Sandip K. Chakrabarti

    1993-11-02

    In paper I, we have studied the conditions under which flux tubes are expelled from adiabatic thick accretion disks. In the present paper, we explore a few other models of thick disks, where flux tubes could be stored. We show that flux tubes with sufficiently weak fields are not expelled out if they move adiabatically inside an isothermal disk; they continue to oscillate around mean equipotential surfaces inside the disk. If the field in the flux tube is amplified due to the shear, they are eventually expelled away. We explore a `toy' model also, where the entropy increase outwards from the center of the thick disk and find a similar behavior. Flux storage in the disk, as in the case of the sun, in general, enhances the possibility of sustained magnetic activity formation of coronae in the chimney region. The existence of coronae on the disk surface may explain the short-time variability in the spectra of Blazars and the emission of energetic particles from AGNs and Quasars. It may also supply matter to the cosmic jets through magnetized winds.

  15. Topological Invariant and Quantum Spin Models from Magnetic ? Fluxes in Correlated Topological Insulators

    E-print Network

    F. F. Assaad; M. Bercx; M. Hohenadler

    2013-02-28

    The adiabatic insertion of a \\pi flux into a quantum spin Hall insulator gives rise to localized spin and charge fluxon states. We demonstrate that \\pi fluxes can be used in exact quantum Monte Carlo simulations to identify a correlated Z_2 topological insulator using the example of the Kane-Mele-Hubbard model. In the presence of repulsive interactions, a \\pi flux gives rise to a Kramers doublet of spinon states with a Curie law signature in the magnetic susceptibility. Electronic correlations also provide a bosonic mode of magnetic excitons with tunable energy that act as exchange particles and mediate a dynamical interaction of adjustable range and strength between spinons. \\pi fluxes can therefore be used to build models of interacting spins. This idea is applied to a three-spin ring and to one-dimensional spin chains. Due to the freedom to create almost arbitrary spin lattices, correlated topological insulators with \\pi fluxes represent a novel kind of quantum simulator potentially useful for numerical simulations and experiments.

  16. Formation of Intensive Magnetic Flux Tubes in a Converging Flow of Partially Ionized Solar Photospheric Plasma

    NASA Astrophysics Data System (ADS)

    Khodachenko, M. L.; Zaitsev, V. V.

    Theoretical model, explaining a phenomenon of formation of Intensive Magnetic Flux Tube (IMFT) in a converging flow of partially ionized solar photospheric plasma is considered. Special attention is paid to the fact of weak ionization (n/n ~ 10^-4) of plasma in the photosphere. The cases of 2D magnetic slab and cylindric magnetic tube are considered. It was shown that in a converging flow of photospheric plasma thin magnetic tubes, or slabs with the characteristic scale L_0 ~ (1 ÷ 5) ? 10^7 cm and magnetic field 1000 ÷ 2000 G can be generated. By this 2D magnetic slabs could be unstable with respect to an exchange instability and appear as an intermediate step during IMFT formation on the boundary of two supergranulation cells. Formation of compact strong magnetic field structures, and their energy balance are discussed. Stationary Joule energy dissipation taking place on the photospheric levels in the models of magnetic slab or IMFT under consideration increases towards the periphery of these objects and can exceed radiation looses. This can cause the occurrence of magnetic tubes with hot external envelopes, and modification of plasma temperature and density distribution, with respect to ones in a quiet atmosphere.

  17. ON THE CAUSES OF PLASMOID ACCELERATION AND CHANGES IN MAGNETIC FLUX IN A RESISTIVE MAGNETOHYDRODYNAMIC PLASMA

    SciTech Connect

    Yu, H. S.; Lyu, L. H. [Institute of Space Science, National Central University, Chung-Li 32001, Taiwan (China); Wu, S. T., E-mail: hsyu@jupiter.ss.ncu.edu.t, E-mail: Lyu@jupiter.ss.ncu.edu.t [Center for Space Plasma and Aeronomic Research, Department of Mechanical and Aerospace Engineering, University of Alabama in Huntsville, Huntsville, AL 35899 (United States)

    2011-01-10

    Observationally, the change of acceleration of coronal mass ejections is commonly attributed to the change of the reconnection rate. In this study, we use a two-dimensional magnetohydrodynamic simulation with finite resistivity to study: (1) the forces that lead to the acceleration of the plasma and plasmoid and (2) the time evolution of the topological change of the magnetic flux across the current sheet. Our results show that the fast flows are not limited to the direction perpendicular to the local magnetic field. The fast parallel flows are accelerated by the parallel component of the pressure gradient force. The net force perpendicular to the magnetic field can accelerate the plasma and the plasmoid along the current sheet. The acceleration of the plasmoid is also controlled by the mass contained in the plasmoid. We find that the fast ejection of the plasmoid can stretch the current sheet and consequently reduce the magnetic reconnection/reconfiguration rate temporally before a new plasmoid is formed. We show that the topological change of the magnetic flux is due to the non-uniform magnetic annihilation rate along the current sheet. Therefore, the reconnection/reconfiguration site does not necessarily stay at the neutral point. It can move with the Y-line next to the bifurcated current sheets.

  18. FULLY RESOLVED QUIET-SUN MAGNETIC FLUX TUBE OBSERVED WITH THE SUNRISE/IMAX INSTRUMENT

    SciTech Connect

    Lagg, A.; Solanki, S. K.; Riethmueller, T. L.; Schuessler, M.; Hirzberger, J.; Feller, A.; Borrero, J. M.; Barthol, P.; Gandorfer, A. [Max-Planck-Institut fuer Sonnensystemforschung, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau (Germany); MartInez Pillet, V.; Bonet, J. A. [Instituto de Astrofisica de Canarias, C/Via Lactea s/n, 38200 La Laguna, Tenerife (Spain); Schmidt, W.; Berkefeld, T. [Kiepenheuer-Institut fuer Sonnenphysik, Schoeneckstrasse 6, 79104 Freiburg (Germany); Del Toro Iniesta, J. C. [Instituto de Astrofisica de AndalucIa (CSIC), Apartado de Correos 3004, 18080 Granada (Spain); Domingo, V. [Grupo de AstronomIa y Ciencias del Espacio, Universidad de Valencia, 46980 Paterna, Valencia (Spain); Knoelker, M. [High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000 (United States); Title, A. M., E-mail: lagg@mps.mpg.d [Lockheed Martin Solar and Astrophysics Laboratory, Bldg. 252, 3251 Hanover Street, Palo Alto, CA 94304 (United States)

    2010-11-10

    Until today, the small size of magnetic elements in quiet-Sun areas has required the application of indirect methods, such as the line-ratio technique or multi-component inversions, to infer their physical properties. A consistent match to the observed Stokes profiles could only be obtained by introducing a magnetic filling factor that specifies the fraction of the observed pixel filled with magnetic field. Here, we investigate the properties of a small magnetic patch in the quiet Sun observed with the IMaX magnetograph on board the balloon-borne telescope SUNRISE with unprecedented spatial resolution and low instrumental stray light. We apply an inversion technique based on the numerical solution of the radiative transfer equation to retrieve the temperature stratification and the field strength in the magnetic patch. The observations can be well reproduced with a one-component, fully magnetized atmosphere with a field strength exceeding 1 kG and a significantly enhanced temperature in the mid to upper photosphere with respect to its surroundings, consistent with semi-empirical flux tube models for plage regions. We therefore conclude that, within the framework of a simple atmospheric model, the IMaX measurements resolve the observed quiet-Sun flux tube.

  19. Integrated Hall-effect magnetic sensors

    Microsoft Academic Search

    R. S Popovic; Z Randjelovic; D Manic

    2001-01-01

    Integrated Hall magnetic sensors are used in automotive and computer industry. Their farther penetration into other applications is mainly hampered by the problems of switching noise and of offset and drift related to the packaging stress. The equivalent magnetic noise and offset can be dramatically reduced by integrating magnetic flux concentrators on the sensor chip. A promising way to eliminate

  20. Fast Solar Wind from Slowly Expanding Magnetic Flux Tubes (P54)

    NASA Astrophysics Data System (ADS)

    Srivastava, A. K.; Dwivedi, B. N.

    2006-11-01

    aks.astro.itbhu@gmail.com We present an empirical model of the fast solar wind, emanating from radially oriented slowly expanding magnetic flux tubes. We consider a single-fluid, steady state model in which the flow is driven by thermal and non-thermal pressure gradients. We apply a non-Alfvénic energy correction at the coronal base and find that specific relations correlate solar wind speed and non-thermal energy flux with the aerial expansion factor. The results are compared with the previously reported ones.

  1. Theory of equilibrium flux lattice in UPt3 under magnetic field parallel to hexagonal crystal axis.

    PubMed

    Champel, T; Mineev, V P

    2001-05-21

    We investigate Abrikosov lattice structures in the unconventional superconductor UPt (3) under magnetic field parallel to the hexagonal crystal axis. Only the two-dimensional E2 superconducting state among the many other states of different symmetry is compatible with the recent observation [A. Huxley et al., Nature (London) 406, 160 (2000)] of the flux lattice in the A phase misaligned with crystallographic directions. It is shown that the inequality of the London penetration depths in the basal plane directions resulting from the superposition of hexagonal crystal and superconducting state anisotropies leads for E2 to a slightly distorted triangular flux lattice. PMID:11384377

  2. Trapped Field and Flux Dynamics in MgB2 Superconducting Bulks Magnetized by Pulsed Field

    NASA Astrophysics Data System (ADS)

    Fujishiro, H.; Naito, T.; Ujiie, T.; Albisetti, A. Figini; Giunchi, G.

    Pulsed field magnetization (PFM) was performed at Ts=14 K for the MgB2 bulk of 55 mm diameter fabricated by a reactive liquid Mg infiltration (Mg-RLI) method. The time dependence of the local field BLC(t) and temperature change T(t) and the trapped field profiles were measured. The numerical simulation of the flux dynamics and heat propagation in the bulk was also performed. The experimental results can be qualitatively explained by the model analyses. We discuss about the characteristic differences of the flux dynamics and heat propagation during PFM between MgB2 and REBaCuO bulks.

  3. Gauge coupling unification in SO(32) heterotic string theory with magnetic fluxes

    E-print Network

    Abe, Hiroyuki; Otsuka, Hajime; Takano, Yasufumi; Tatsuishi, Takuya H

    2015-01-01

    We study $SO(32)$ heterotic string theory on torus with magnetic fluxes. Non-vanishing fluxes can lead to non-universal gauge kinetic functions for $SU(3) \\times SU(2) \\times U(1)_Y$ which is the important features of $SO(32)$ heterotic string theory in contrast to the $E_8\\times E_8$ theory. It is found that the experimental values of gauge couplings are realized with ${\\cal O}(1)$ values of moduli fields based on the realistic models with the $SU(3) \\times SU(2) \\times U(1)_Y$ gauge symmetry and three chiral generations of quarks and leptons without chiral exotics.

  4. Electronic delocalization and persistent currents in nonsymmetric-dimer mesoscopic rings threaded by magnetic flux

    NASA Astrophysics Data System (ADS)

    Hu, X. F.; Peng, Z. H.; Peng, R. W.; Liu, Y. M.; Qiu, F.; Huang, X. Q.; Hu, A.; Jiang, S. S.

    2004-06-01

    We investigate electronic delocalization and magnetic-flux-induced persistent current in the mesoscopic ring, which is constructed according to the nonsymmetric-dimer (NSD) model. The flux-dependent energy spectra, electronic wavefunctions, and persistent currents are theoretically obtained. It is demonstrated that due to the localization-delocalization transition of electrons, the electronic state in the NSD ring can be localized, extended, and the intermediate case between extended states and localized ones. The persistent current (PC) approaches the behavior of free electrons if the Fermi level is around the near-resonant energy. Otherwise, the PC is depressed dramatically. This conclusion could be generalized to other correlated-disordered systems.

  5. Dynamic roughening of the magnetic flux landscape in YBa2Cu3O7-x

    NASA Astrophysics Data System (ADS)

    Aegerter, C. M.; Welling, M. S.; Wijngaarden, R. J.

    2005-03-01

    We study the magnetic flux landscape in YBa2Cu3O7-x thin films as a two dimensional rough surface. The vortex density in the superconductor forms a self-affine structure in both space and time. It is characterized by a roughness exponent ?=0.76(3) and a growth exponent ?=0.57(6). The roughening is caused by flux avalanches in a self-organized critical state, which is formed in the vortex matter of the superconductor. We discuss our results in the context of other roughening systems in the presence of quenched disorder.

  6. Finite-frequency-dependent noise of a quantum dot in a magnetic field

    NASA Astrophysics Data System (ADS)

    Moca, C. P.; Simon, P.; Chung, Chung-Hou; Zaránd, G.

    2014-04-01

    We present a detailed study for the finite-frequency current noise of a Kondo quantum dot in the presence of a magnetic field by using a recently developed real-time functional renormalization group approach [C. P. Moca, P. Simon, C. H. Chung, and G. Zaránd, Phys. Rev. B 83, 201303(R) (2011), 10.1103/PhysRevB.83.201303]. The scaling equations are modified in an external magnetic field; the couplings and nonlocal current vertices become strongly anisotropic, and develop new singularities. Consequently, in addition to the natural emission threshold frequency, ?? =|eV|, a corresponding singular behavior is found to emerge in the noise spectrum at frequencies ?? ?|eV±B|. The predicted singularities are measurable with present-day experimental techniques.

  7. Magnetar Giant Flares in Multipolar Magnetic Fields. I. Fully and Partially Open Eruptions of Flux Ropes

    NASA Astrophysics Data System (ADS)

    Huang, Lei; Yu, Cong

    2014-04-01

    We propose a catastrophic eruption model for the enormous energy release of magnetars 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, 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 fields. Nevertheless, it is hard to generate fully open magnetic eruptions for multipolar background fields. Given the observational importance of the multipolar magnetic fields in the vicinity of the magnetar surface, it would be worthwhile to explore the possibility of the alternative eruption approach in multipolar background fields. Fortunately, we find that flux ropes may give rise to partially open eruptions in the multipolar fields, which involve only partial opening of background fields. The energy release fractions are greater for cases with central-arcaded multipoles than those with central-caved multipoles that emerged in background fields. Eruptions would fail only when the centrally caved multipoles become extremely strong.

  8. Microstructural dependence of Barkhausen noise and magnetic relaxation in the weld HAZ of an RPV steel

    Microsoft Academic Search

    Duck-Gun Park; Cheol Gi Kim; Jun-Hwa Hong

    2000-01-01

    Magnetic Barkhausen noise and permeability spectra have been measured to characterize different microstructure regions such as coarse-grain region, fine-grain region, intercritical structure (composed of tempered martensite and bainite) within the heat-affected zone (HAZ) of SA508-3 steel weldments using simulated HAZ microstructure sample. The intercritical region and coarse-grained region can be distinguished from the BNE and relaxation frequency. The BNE was

  9. Magnetic Barkhausen noise indications of stress concentrations near pits of various depths

    NASA Astrophysics Data System (ADS)

    Mandal, K.; Loukas, M. E.; Corey, A.; Atherton, D. L.

    1997-11-01

    The presence of a defect in a material under stress, changes the local stress distribution around it. This local stress distributions around three circular pits in line pipe steel with depths of 30, 50 and 80% wall thickness were studied nondestructively by magnetic Barkhausen noise measurements and in the presence of different bending stresses. The results show stress concentration factors ˜ 1.5, 1.7 and 2.05, respectively, and are consistent with theoretical predictions.

  10. Thermal noise of mechanical oscillators in steady states with a heat flux

    NASA Astrophysics Data System (ADS)

    Conti, Livia; Lazzaro, Claudia; Karapetyan, Gagik; Bonaldi, Michele; Pegoraro, Matteo; Thakur, Ram-Krishna; De Gregorio, Paolo; Rondoni, Lamberto

    2014-09-01

    We present an experimental investigation of the statistical properties of the position fluctuations of low-loss oscillators in nonequilibrium steady states. The oscillators are coupled to a heat bath, and a nonequilibrium steady state is produced by flowing a constant heat flux, setting a temperature difference across the oscillators. We investigated the distribution of the measurements of the square of the oscillator position and searched for signs of changes with respect to the equilibrium case. We found that, after normalization by the mean value, the second, third, and fourth standardized statistical moments are not modified by the underlying thermodynamic state. This differs from the behavior of the absolute, i.e., not normalized, second moment, which is strongly affected by temperature gradients and heat fluxes. We illustrate this with a numerical experiment in which we study via molecular dynamics the fluctuations of the length of a one-dimensional chain of identical particles interacting via anharmonic interparticle potentials, with the extremes thermostated at different temperatures: we use the variance of the length in correspondence to its first elastic mode of resonance to define an effective temperature which we observe to depart from the thermodynamic one in the nonequilibrium states. We investigate the effect of changing the interparticle potential and show that the qualitative behavior of the nonequilibrium excess is unchanged. Our numerical results are consistent with the chain length being Gaussian distributed in the nonequilibrium states. Our experimental investigation reveals that the position variance is the only, and crucially easily accessible, observable for distinguishing equilibrium from nonequilibrium steady states. The consequences of this fact for the design of interferometric gravitational wave detectors are discussed.

  11. Single-sided mobile NMR apparatus using the transverse flux of a single permanent magnet.

    PubMed

    Chang, Wei-Hao; Chen, Jyh-Horng; Hwang, Lian-Pin

    2010-01-01

    This study presents a simple design for a mobile, single-sided nuclear magnetic resonance (NMR) apparatus which uses the magnetic flux parallel to the magnetization direction of a single, disc-shaped permanent magnet polarized in radial direction. The stray magnetic field above the magnet is approximately parallel to the magnetization direction of the magnet and is utilized as the B(0) magnetic field of the apparatus. The apparatus weighs 1.8 kg, has a compact structure and can be held in one's palm. The apparatus generates a B(0) field strength of about 0.279 T at the center of apparatus surface and can acquire a clear Hahn echo signal of a pencil eraser block lying on the RF coil in one shot. Moreover, a strong static magnetic field gradient exists in the direction perpendicular to the apparatus surface. The strength of the static magnetic field gradient near the center of the apparatus surface is about 10.2 T/m; one-dimensional imaging of thin objects and liquid self-diffusion coefficient measurements can be performed therein. The available spatial resolution of the one-dimensional imaging experiments using a 5 x 5 mm horizontal sample area is about 200 mum. Several nondestructive inspection applications of the apparatus, including distinguishing between polyethylene grains of different densities, characterizing epoxy putties of distinct set times and evaluating the fat content percentages of milk powders, are also demonstrated. Compared with many previously published designs, the proposed design bears a simple structure and generates a B(0) magnetic field parallel to the apparatus surface, simplifying apparatus construction and simultaneously rendering the selection of the radiofrequency coil relatively flexible. PMID:19577401

  12. Anatomy of field effects on magnetization dynamics and spin transfer noise

    NASA Astrophysics Data System (ADS)

    Wang, L.; Han, G. C.; Zheng, Y. K.

    2006-08-01

    Spin transfer-related phenomena in nanomagnets have attracted extensive studies. In this paper we shall focus on analysis of individual and combined effects of the external, anisotropy, and demagnetization fields on magnetization dynamics and spin transfer noise. It is found that individual roles of the external, anisotropy, and demagnetization fields, as well as the combined roles of external plus anisotropy fields and anisotropy plus demagnetization fields, do not change the behavior of current induced magnetization switching. Such magnetization reversal procedures are of low noise. Our dynamics and power spectral density calculations show that it is the demagnetization field that plays a major role in inducing spin transfer noise: the demagnetization field itself or in combination with the anisotropy field will result in wave-like switching; moreover, the demagnetization field, together with the external field (not too small), will lead to precession and hence the system would be in noisy states. Our modeling work for an elliptical Py alloy is qualitatively consistent with Cornell's experiment and simulation [Science 307 (2005) 228].

  13. Thermal-Electromagnetic Analysis of a Fault-Tolerant Dual Star Flux-Switching Permanent Magnet Motor for Critical

    E-print Network

    Paris-Sud XI, Université de

    of a fault-tolerant dual star Flux-Switching Permanent Magnet (FSPM) motor. The analytical results in terms permanent magnet motors have attracted increasing attentions in safety critical applications such as Hybrid, the phases of the motors are magnetically and physically separated. Thus, the phase failures (short

  14. Comparing Poynting flux dominated magnetic tower jets with kinetic-energy dominated jets

    NASA Astrophysics Data System (ADS)

    Huarte-Espinosa, M.; Frank, A.; Blackman, E. G.; Ciardi, A.; Hartigan, P.; Lebedev, S. V.; Chittenden, J. P.

    2013-06-01

    Magnetic towers represent one of two fundamental forms of MHD outflows. Driven by magnetic pressure gradients, these flows have been less well studied than magneto-centrifugally launched jets even though magnetic towers may well be as common. Here we present new results exploring the behavior and evolution of magnetic tower outflows and demonstrate their connection with pulsed power experimental studies and purely hydrodynamic jets which might represent the asymptotic propagation regimes of magneto-centrifugally launched jets. High-resolution AMR MHD simulations (using the AstroBEAR code) provide insights into the underlying physics of magnetic towers and help us constrain models of their propagation. Our simulations have been designed to explore the effects of thermal energy losses and rotation on both tower flows and their hydro counterparts. We find these parameters have significant effects on the stability of magnetic towers, but mild effects on the stability of hydro jets. Current-driven perturbations in the Poynting Flux Dominated (PDF) towers are shown to be amplified in both the cooling and rotating cases. Our studies of the long term evolution of the towers show that the formation of weakly magnetized central jets within the tower are broken up by these instabilities becoming a series of collimated clumps which magnetization properties vary over time. In addition to discussing these results in light of laboratory experiments, we address their relevance to astrophysical observations of young star jets and outflow from highly evolved solar type stars.

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

    PubMed

    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. PMID:20366046

  16. Methods of reducing audible noise caused by magnetic components in variable-frequency-controlled switch-mode converters

    Microsoft Academic Search

    Laszlo Huber; Milan M. Jovanovic

    2011-01-01

    Methods and a circuit implementation of audible noise reduction in switch-mode converters with variable switching frequency are presented. The audible noise caused by magnetic components is reduced by controlling the switching frequency so that it stays above the audible range as the load decreases. This is accomplished by decreasing the peak value of the main switch current pulses in discrete

  17. Acoustic Noise of Switched Reluctance and Permanent Magnet Motors: A Comparison in the Context of Electric Brakes

    Microsoft Academic Search

    Avoki M. Omekanda; Suresh Gopalakrishnan; Harald Klode

    2007-01-01

    It is held as fact that Permanent Magnet (PM) brushless motors are less noisy than Switched Reluctance (SR) motors, and many methods have been published to reduce the noise of SR drives. This paper provides a systematic experimental comparison of both drives, and of proposed noise- mitigation strategies, in the context of a specific mass-market application: Automotive Electro Mechanical Brakes

  18. Seeding magnetic fields for laser-driven flux compression in high-energy-density plasmas.

    PubMed

    Gotchev, O V; Knauer, J P; Chang, P Y; Jang, N W; Shoup, M J; Meyerhofer, D D; Betti, R

    2009-04-01

    A compact, self-contained magnetic-seed-field generator (5 to 16 T) is the enabling technology for a novel laser-driven flux-compression scheme in laser-driven targets. A magnetized target is directly irradiated by a kilojoule or megajoule laser to compress the preseeded magnetic field to thousands of teslas. A fast (300 ns), 80 kA current pulse delivered by a portable pulsed-power system is discharged into a low-mass coil that surrounds the laser target. A >15 T target field has been demonstrated using a <100 J capacitor bank, a laser-triggered switch, and a low-impedance (<1 Omega) strip line. The device has been integrated into a series of magnetic-flux-compression experiments on the 60 beam, 30 kJ OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. The initial application is a novel magneto-inertial fusion approach [O. V. Gotchev et al., J. Fusion Energy 27, 25 (2008)] to inertial confinement fusion (ICF), where the amplified magnetic field can inhibit thermal conduction losses from the hot spot of a compressed target. This can lead to the ignition of massive shells imploded with low velocity-a way of reaching higher gains than is possible with conventional ICF. PMID:19405657

  19. Dual-rotor, radial-flux, toroidally-wound, permanent-magnet machine

    DOEpatents

    Qu, Ronghai; Lipo, Thomas A.

    2005-08-02

    The present invention provides a novel dual-rotor, radial-flux, toroidally-wound, permanent-magnet machine. The present invention improves electrical machine torque density and efficiency. At least one concentric surface-mounted permanent magnet dual-rotor is located inside and outside of a torus-shaped stator with back-to-back windings, respectively. The machine substantially improves machine efficiency by reducing the end windings and boosts the torque density by at least doubling the air gap and optimizing the machine aspect ratio.

  20. Chains with loops - synthetic magnetic fluxes and topological order in one-dimensional spin systems

    E-print Network

    Tobias Grass; Christine Muschik; Alessio Celi; Ravindra Chhajlany; Maciej Lewenstein

    2015-06-04

    Engineering topological quantum order has become a major field of physics. Many advances have been made by synthesizing gauge fields in cold atomic systems. Here, we carry over these developments to other platforms which are extremely well suited for quantum engineering, namely trapped ions and nano-trapped atoms. Since these systems are typically one-dimensional, the action of artificial magnetic fields has so far received little attention. However, exploiting the long-range nature of interactions, loops with non-vanishing magnetic fluxes become possible even in one-dimensional settings. This gives rise to intriguing phenomena, such as fractal energy spectra, flat bands with localized edge states, and topological many-body states. We elaborate on a simple scheme for generating the required artificial fluxes by periodically driving an XY spin chain. Concrete estimates demonstrating the experimental feasibility for trapped ions and atoms in waveguides are given.

  1. Detailed Review and Application of the 3-Phase Self-Limiting Transformer with Magnetic Flux Applied

    NASA Astrophysics Data System (ADS)

    Kosa, Janos

    The paper describes in detail the 3-phase self-limiting transformer with magnetic flux applied and contains measured results. The solution includes two independent iron cores. I applied two pieces of iron cores with 3 limbs on each. One of the iron cores contains the 3 primary coils on the limbs respectively and the other iron core also contains 3 secondary coils. As I use two iron cores the loss, the size, the weight and the cost are higher compared to the conventional transformers but this solution has several advantages. For example, the fault power is less, switching is fast. In the case, when there is no load on the secondary side and primary voltage increases, the arrangement is able to break coupling between the primary and secondary sides. The work has been carried out by me as a novel possibility of application of the principle of magnetic flux constancy in the closed loop.

  2. Synthetic magnetic fluxes and topological order in one-dimensional spin systems

    NASA Astrophysics Data System (ADS)

    Graß, Tobias; Muschik, Christine; Celi, Alessio; Chhajlany, Ravindra W.; Lewenstein, Maciej

    2015-06-01

    Engineering topological quantum order has become a major field of physics. Many advances have been made by synthesizing gauge fields in cold atomic systems. Here we carry over these developments to other platforms which are extremely well suited for quantum engineering, namely, trapped ions and nano-trapped atoms. Since these systems are typically one-dimensional, the action of artificial magnetic fields has so far received little attention. However, exploiting the long-range nature of interactions, loops with nonvanishing magnetic fluxes become possible even in one-dimensional settings. This gives rise to intriguing phenomena, such as fractal energy spectra, flat bands with localized edge states, and topological many-body states. We elaborate on a simple scheme for generating the required artificial fluxes by periodically driving an XY spin chain. Concrete estimates demonstrating the experimental feasibility for trapped ions and atoms in wave guides are given.

  3. High Frequency Magnetization Dynamics and Popcorn Noise in Thin Film Heads.

    NASA Astrophysics Data System (ADS)

    Liu, Francis H.

    As the areal density and data rates in magnetic recording continue to increase, it is important to limit the occurrences of popcorn noise in thin film inductive recording heads, especially in disk drives utilizing sector servo schemes. In this dissertation, the mechanisms of popcorn noise are described. In particular, the effects of thermal transients after write, changes in stress-magnetostriction products, dynamic domain structures and dynamic domain instabilities on popcorn noise probabilities in thin film heads are discussed. A new and simple inductance fluctuation measurement technique using DC bias current to the head is shown to be useful in quickly detecting heads that are susceptible to popcorn noise. Finally, based upon the improved understanding of popcorn noise mechanisms, various criteria for head design, processing, and operating conditions are suggested to ensure low probabilities of popcorn noise in thin film heads. Delayed-relaxation Barkhausen wall jumps which cause popcorn noise have been modelled by Klaassen and van Peppen (IEEE Trans. Magn. MAG-5, 3212 (1989)) as Poisson processes. However, it has been found that additional factors, such as external stress gradients, dynamic domain structures and domain instabilities, also can strongly affect the occurrences of popcorn noise in thin film heads. In the cases where the stress-magnetostriction products in the top yokes are negative, popcorn noise probabilities were observed to increase as functions of applied stress gradients in micro Flexhead^{rm TM} components. On the other hand, applied stress gradients have negligible effect when the resultant stress-magnetostriction products in the top yokes are positive. This sign-dependent effect has been explained to be caused by negative-magnetoelastic-energy induced Bloch domain wall instabilities. Thin film heads with unstable domain structures near the backgap closure of top yokes, either in the configuration of edge closure domains of spike-like domains, have also been found to be particular noisy. Using a 0.5-nsec exposure time wide-field Kerr effect microscope, occurrences of delayed-relaxation Barkhausen wall jumps were actually imaged after specific write current excitations in noisy heads. A quantitative correlation between the probabilities of popcorn noise and dynamic domain instabilities was also observed in a noisy head. In addition to the improved understanding of popcorn noise mechanisms, it has also been found that the susceptibilities of thin film heads to Barkhausen wall jumps, thus to popcorn noise, can be measured electrically as inductance fluctuations under DC bias current. A quantitative correlation was found between the peak popcorn noise probabilities and peak inductance fluctuations of 12 different thin film heads. This inductance characterization technique was thus shown to be useful in quickly detecting heads that are susceptible to popcorn noise. Finally, several criteria in head design, processing and operating conditions were proposed to ensure low probabilities of popcorn noise in thin film heads.

  4. The magnetic flux excess effect as a consequence of non-Parker radial evolution of interplanetary magnetic field

    NASA Astrophysics Data System (ADS)

    Khabarova, Olga

    2015-04-01

    The “magnetic flux excess” effect is exceeding of magnetic flux Fs=4?|Br|r2 measured by distant spacecraft over the values obtained through measurements at the Earth’s orbit (Owens et al., JGR, 2008). Theoretically, its conservation should take place at any heliocentric distance r further than 10 solar radii, which means that the difference between the flux measured at 1 AU and Fs observed in another point in the heliosphere should be zero. However, the difference is negative closer to the Sun and increasingly positive at larger heliocentric distances. Possible explanations of this effect are continuously discussed, but the consensus is yet not reached.It is shown that a possible source of this effect is the solar wind expansion not accordingly with the Parker solution at least at low heliolatitudes. The difference between the experimentally found (r?5/3) and commonly used (r?2) radial dependence of the radial component of the IMF Br may lead to mistakes in the IMF point-to-point recalculations (Khabarova & Obridko, ApJ, 2012; Khabarova, Astronomy Reports, 2013). Using the observed Br (r) dependence, it is easy to find the variation of difference between the magnetic flux Fs(r) at certain heliocentric distance r and Fs_1AU at 1 AU, which can be calculated as Fs(r)-Fs_1AU =4?·(B1AU /[1AU]-5/3) (r2-5/3 –[1AU]2-5/3) (Khabarova, Astronomy Reports, 2013).The possible influence of presence of the heliospheric current sheet near the ecliptic plane on the picture of magnetic field lines and consequent deviation from the Parker's model is discussed.- Khabarova Olga, and Obridko Vladimir, Puzzles of the Interplanetary Magnetic Field in the Inner Heliosphere, 2012, Astrophysical Journal, 761, 2, 82, doi:10.1088/0004-637X/761/2/82, http://arxiv.org/pdf/1204.6672v2.pdf- Olga V. Khabarova, The interplanetary magnetic field: radial and latitudinal dependences. Astronomy Reports, 2013, Vol. 57, No. 11, pp. 844–859, http://arxiv.org/ftp/arxiv/papers/1305/1305.1204.pdf

  5. Construction of Lur'e type Lyapunov function with effect of magnetic flux decay

    Microsoft Academic Search

    N. Kakimoto; Y. Ohsawa; M. Hayashi

    1979-01-01

    In this paper a generalized stability criterion for a system with multi-argument nonlinearities is derived. The new criterion is based on Pai's work, and is proved along with Anderson's criterion. The new criterion makes it possible to construct a Lur'e type Liapunov function in a systematic way. The new criterion is applied to a multi-machine power system with magnetic flux

  6. Photon-assisted tunneling through open mesoscopic rings threaded by time-periodic magnetic fluxes

    Microsoft Academic Search

    Cong Hua Yan; Lian Fu Wei

    2010-01-01

    Quantum waveguide theories have been successfully applied to various time-independent ballistic transports in mesoscopic structures, including typically the Aharonov-Bohm rings. Here, we consider the quantum transport along the one-dimensional electron structures driven by time-dependent external fields, typical the open mesoscopic rings threaded by time-periodic magnetic fluxes. Based on the well-known Floquet theorem we effectively separate the time and space variables

  7. Photon-assisted tunneling through open mesoscopic rings threaded by time-periodic magnetic fluxes

    Microsoft Academic Search

    Cong Hua Yan; Lian Fu Wei

    2010-01-01

    Quantum waveguide theories have been successfully applied to various time-independent ballistic transports in mesoscopic structures, including typically the Aharonov–Bohm rings. Here, we consider the quantum transport along the one-dimensional electron structures driven by time-dependent external fields, typical the open mesoscopic rings threaded by time-periodic magnetic fluxes. Based on the well-known Floquet theorem we effectively separate the time and space variables

  8. Modeling Solar Spectral Irradiance and Total Magnetic Flux Using Sunspot Areas

    Microsoft Academic Search

    Dora G. Preminger; Stephen R. Walton

    2006-01-01

    We show that daily sunspot areas can be used in a simple, single parameter model to reconstruct daily variations in several\\u000a other solar parameters, including solar spectral irradiance and total magnetic flux. The model assumes that changes in any\\u000a given parameter can be treated mathematically as the response of the system to the emergence of a sunspot. Using cotemporal\\u000a observational

  9. THREE-DIMENSIONAL SIMULATIONS OF VERTICAL MAGNETIC FLUX IN THE IMMEDIATE VICINITY OF BLACK HOLES

    SciTech Connect

    Punsly, Brian [4014 Emerald Street No.116, Torrance, CA 90503 (United States); Igumenshchev, Igor V. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, NY 14623 (United States); Hirose, Shigenobu, E-mail: brian.punsly@verizon.ne [Earth Simulator Center, JAMSTEC 3173-25 Showamachi, Kanazawa-ku, Yokohama, Kanagawa 236-0001 (Japan)

    2009-10-20

    This article reports on three-dimensional MHD simulations of non-rotating and rapidly rotating black holes and the adjacent black hole accretion disk magnetospheres. A particular emphasis is placed on the vertical magnetic flux that is advected inward from large radii and threads the equatorial plane near the event horizon. In both cases of non-rotating and rotating black holes, the existence of a significant vertical magnetic field in this region is like a switch that creates powerful jets. There are many similarities in the vertical flux dynamics in these two cases in spite of the tremendous enhancement of azimuthal twisting of the field lines and enhancement of the jet power because of an 'ergospheric disk' in the Kerr metric. A three-dimensional approach is essential because two-dimensional axisymmetric flows are incapable of revealing the nature of the vertical flux near a black hole. Poloidal field lines from the ergospheric accretion region have been visualized in three dimensions and much of the article is devoted to a formal classification of the different manifestations of the vertical flux in the Kerr case.

  10. Kelvin-Helmholtz Waves/Vortices and Magnetic Flux Ropes at Earth's Magnetopause

    NASA Astrophysics Data System (ADS)

    Hasegawa, H.; Nakamura, T.

    2014-12-01

    Kelvin-Helmholtz (KH) waves/vortices and magnetic flux ropes at Earth's magnetopause are important ingredients in the solar wind-magnetosphere interaction. KH instabilities are excited in a velocity shear layer, leading to an undulation of the magnetopause or inner edge of its boundary layer and eventually to the formation of flow vortices, while flux ropes are generated in a current sheet through a time-dependent form of magnetic reconnection, which interconnect the field lines on both sides of the magnetopause. Because of their two- or three-dimensional nature, in-depth observational studies have become possible only with the advent of multi-spacecraft missions such as Cluster and THEMIS. We discuss similarities/differences of these two phenomena and the roles of these processes in the transfer of mass, momentum, and energy across the magnetopause, in particular with regard to the formation of the low-latitude boundary layer. Recent advances in studies of three-dimensional effects on these phenomena, effects of nonlinear evolution of the KH instability on magnetic reconnection and flux rope generation, and dawn-dusk symmetry/asymmetry in and IMF dependence of the occurrence of nonlinear (overturned) KH waves are also presented.

  11. Peculiarities of Alfven wave propagation along a nonuniform magnetic flux tube

    SciTech Connect

    Erkaev, N.V.; Shaidurov, V.A.; Semenov, V.S.; Langmayr, D.; Biernat, H.K. [Intitute of Computational Modelling, Russian Academy of Sciences, Krasnoyarsk 660036 (Russian Federation); State University of Krasnoyarsk, Krasnoyarsk 660041 (Russian Federation); Institute of Physics, State University, St. Petersburg 198504 (Russian Federation); Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz (Austria)

    2005-01-01

    Within the framework of the assumption of large azimuthal wave numbers, the equations for Alfven and slow magnetosonic waves are obtained using frozen-in material coordinates. These equations are specified for the case of a nonuniform magnetic field with axial symmetry. Assuming a meridional polarization of the magnetic field and velocity perturbations, the effects of Alfven wave propagation are analyzed which are related to geometric characteristics of a nonuniform magnetic field: (a) A finite curvature radius of the magnetic field lines and (b) convergence of magnetic field lines. The interaction between the Alfven and magnetosonic waves is found to be strongly dependent on the curvature radius of the magnetic tube and the local plasma {beta} parameter. The electric field amplitude and the length scale of a wave front are found to increase very strongly in the course of the Alfven wave propagation along a converging magnetic flux tube. Also studied is a temporal decrease of the wave perturbations which is caused by dissipation at the conducting boundary.

  12. Particle Simulations of Magnetic Field Reconnection and Applications to Flux Transfer Events

    NASA Astrophysics Data System (ADS)

    Ding, Da-Qing

    1990-01-01

    Basic plasma processes associated with driven collisionless magnetic reconnection at the Earth's dayside magnetopause are studied on the basis of particle simulations. A two-and-one-half-dimensional (21over2 -D) electromagnetic particle simulation model with a driven inflow boundary and an open outflow boundary is developed for the present study. The driven inflow boundary is featured with a driving electric field for the vector potential, while the open outflow boundary is characterized by a vacuum force free condition for the electrostatic potential. The major findings are as follows. (1) The simulations exhibit both quasi-steady single X-line reconnection (SXR) and intermittent multiple X line reconnection (MXR). The MXR process is characterized by repeated formation and convection of magnetic islands (flux tubes or plasmoids). (2) Particle acceleration in the MXR process occurs mainly in O line regions as particles are trapped within magnetic islands, not in X line regions. The MXR process results in a power law particle energy spectrum of f(E)~ E ^{-4}. (3) Field-aligned particle heat fluxes and intense plasma waves associated with the collisionless magnetic reconnection process are also observed. (4) When applied to the dayside magnetopause, simulation results show that the MXR process tends to generate a simultaneous magnetic field perturbation on both sides of the dayside magnetopause, resembling the observed features of two-regime flux transfer events (FTEs). (5) An intrusion of magnetosheath plasma bulge into the magnetosphere due to the formation of magnetic islands may lead to the layered structures observed in magnetospheric FTEs. (6) In the current sheet, the enhanced tearing mode instability caused by the driving force applied at the driven inflow boundary creates an energy source at a specific wavenumber range with k zL~ 0.3 in the modal spectrum of the magnetic field B_{x } component. An inverse cascade of the modal spectrum of Bx<=ads to the formation of the large-scale ordered magnetic island structures observed in the simulations. (7) In addition, the results of a theoretical study show that the tearing mode instability, and hence the magnetic reconnection at the dayside magnetopause, do not exhibit strong dependence on the magnetosheath beta values.

  13. Geodesic dynamo chaotic flows and non-Anosov maps in twisted magnetic flux tubes

    E-print Network

    Garcia de Andrade

    2008-11-21

    Recently Tang and Boozer [{\\textbf{Phys. Plasmas (2000)}}], have investigated the anisotropies in magnetic field dynamo evolution, from local Lyapunov exponents, giving rise to a metric tensor, in the Alfven twist in magnetic flux tubes (MFTs). Thiffeault and Boozer [\\textbf{Chaos}(2001)] have investigated the how the vanishing of Riemann curvature constrained the Lyapunov exponential stretching of chaotic flows. In this paper, Tang-Boozer-Thiffeault differential geometric framework is used to investigate effects of twisted magnetic flux tube filled with helical chaotic flows on the Riemann curvature tensor. When Frenet torsion is positive, the Riemann curvature is unstable, while the negative torsion induces an stability when time $t\\to{\\infty}$. This enhances the dynamo action inside the MFTs. The Riemann metric, depends on the radial random flows along the poloidal and toroidal directions. The Anosov flows has been applied by Arnold, Zeldovich, Ruzmaikin and Sokoloff [\\textbf{JETP (1982)}] to build a uniformly stretched dynamo flow solution, based on Arnold's Cat Map. It is easy to show that when the random radial flow vanishes, the magnetic field vanishes, since the exponential Lyapunov stretches vanishes. This is an example of the application of the Vishik's anti-fast dynamo theorem in the magnetic flux tubes. Geodesic flows of both Arnold and twisted MFT dynamos are investigated. It is shown that a constant random radial flow can be obtained from the geodesic equation. Throughout the paper one assumes, the reasonable plasma astrophysical hypothesis of the weak torsion. Pseudo-Anosov dynamo flows and maps have also been addressed by Gilbert [\\textbf{Proc Roy Soc A London (1993)}

  14. The Revised Electromagnetic Fields Directive and Worker Exposure in Environments With High Magnetic Flux Densities

    PubMed Central

    Stam, Rianne

    2014-01-01

    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. PMID:24557933

  15. Reducing magnetic field induced noise in broad-band seismic recordings

    NASA Astrophysics Data System (ADS)

    Forbriger, Thomas

    2007-04-01

    Seismic broad-band sensors are known to be sensitive to the magnetic field. Magnetic storms and man-made disturbances of the magnetic field can produce significant noise in seismic recordings. I show that variations in the magnetic field translate directly into apparent acceleration of the seismic sensor within the period range from 60 to 1200s for all leaf-spring sensors under investigation. For a Streckeisen STS-1V this is shown even for periods down to 1s. The sensitivity is quantified in magnitude and direction. Both are quite stable over many time windows and signal periods. The sensitivities obtained by linear regression of the acceleration signal on magnetic field recordings during a magnetic storm can effectively be applied to reduce noise in seismic signals. The sensitivity varies in magnitude from sensor to sensor but all are in the range from 0.05 to 1.2ms-2T-1. Seismograms from sensors at Black Forest Observatory (BFO) and stations of the German Regional Seismic Network were investigated. Although these are mainly equipped with leaf-spring sensors, the problem is not limited to this type of instrument. The effect is not observable on the horizontal component STS-1s at BFO while it is significant in the recordings of the vertical STS-1. The main difference between these instruments is the leaf-spring suspension in the vertical component that appears to be the source of the trouble. The suspension springs are made of temperature compensated Elinvar alloys that inherently are ferromagnetic and may respond to the magnetic field in various ways. However, the LaCoste Romberg ET-19 gravimeter at BFO, which uses this material too, does not respond to magnetic storms at a similar magnitude neither do the Invar-wire strainmeters. An active shielding, composed of three Helmholtz coils and a feedback system, is installed at station Stuttgart and provides an improvement of signal-to-noise ratio by almost a factor of 20 at this particular station. The passive Permalloy shielding commonly installed with STS-1V sensors performs similarly well.

  16. Magnetic properties of high-T(sub c) superconductors: Rigid levitation, flux pinning, thermal depinning, and fluctuation

    NASA Technical Reports Server (NTRS)

    Brandt, E. H.

    1990-01-01

    The levitation of high-T(sub c) superconductors is quite conspicuous: Above magnets of low symmetry a disk of these ceramics floats motionless, without vibration or rotation; it has a continuous range of stable positions and orientations as if it were stuck in sand. Some specimens may even be suspended above or below the same magnet. This fascinating stability, inherent to no other type of levitation, is caused by the pinning of magnetic flux lines by inhomogeneities inside these extreme type-2 superconductors. The talk deals with pinning of magnetic flux in these materials, with flux flow, flux creep, thermally activated depinning, and the thermal fluctuation of the vortex positions in the flux line lattice (often called flux lattice melting). Also discussed are the fluctuations of the (nearly periodic) magnetic field inside these superconductors which are caused by random pinning sites and by the finite temperature. These fluctuations broaden the van-Hove singularities observed in the density of the magnetic field by nuclear magnetic resonance and by muon spin rotation.

  17. Pinning features of the magnetic flux trapped by YBCO single crystals in weak constant magnetic fields

    NASA Astrophysics Data System (ADS)

    Monarkha, V. Yu.; Paschenko, V. A.; Timofeev, V. P.

    2013-02-01

    The dynamics of Abrikosov vortices and their bundles was experimentally investigated in weak constant magnetic fields, in the range of Earth's magnetic field. Characteristics of the isothermal magnetization relaxation in YBCO single-crystal samples with strong pinning centers were studied for different sample-field orientation. The obtained values of normalized relaxation rate S allowed us to estimate the effective pinning potential U in the bulk of the YBCO sample and its temperature dependence, as well as the critical current density Jc. A comparison between the data obtained and the results of similar measurements in significantly higher magnetic fields was performed. To compare different techniques for evaluation of Jc, the magnetization loop measurements M(H), which relate the loop width to the critical current, were carried out. These measurements provided important parameters of the samples under study (penetration field Hp and first critical field Hc1), which involve the geometrical configuration of the samples.

  18. Reducing the Effects of Background Noise during Auditory Functional Magnetic Resonance Imaging of Speech Processing: Qualitative and Quantitative Comparisons between Two Image Acquisition Schemes and Noise Cancellation

    ERIC Educational Resources Information Center

    Blackman, Graham A.; Hall, Deborah A.

    2011-01-01

    Purpose: The intense sound generated during functional magnetic resonance imaging (fMRI) complicates studies of speech and hearing. This experiment evaluated the benefits of using active noise cancellation (ANC), which attenuates the level of the scanner sound at the participant's ear by up to 35 dB around the peak at 600 Hz. Method: Speech and…

  19. Source mapping analysis, a multi-source method for the interpretation and analysis of magnetic Barkhausen noise signals

    NASA Astrophysics Data System (ADS)

    Pérez-Benitez, J. A.; Espina-Hernández, J. H.

    2013-01-01

    This work proposes a method to study multiple sources in the magnetic Barkhausen noise signal. The method is termed source mapping analysis and is based on the generation of a map of signals using a set of elementary sources. The evolution of Barkhausen noise signals as a function of two microstructural features, i.e. carbon content and level of plastic deformation, is studied by placing the input signal on the map. The position of the magnetic Barkhausen noise signal in the map follows a trajectory depending on these microstructural features, which could be used to simultaneously estimate their values.

  20. Flux-Path Control Magnetic Suspension System Using Voice Coil Motors

    NASA Astrophysics Data System (ADS)

    Mizuno, Takeshi; Hirai, Yuzo; Ishino, Yuji; Takasaki, Masaya

    A novel magnetic suspension system with three flux-path control modules was developed. The module consists of a ferromagnetic plate, a voice coil motor (VCM) for driving the plate and a displacement sensor for detecting the position of the plate; the sensor is comprised of a V-shape plate spring and four strain gauges pasted on it. The ferromagnetic plate is inserted into the gap between a permanent magnet and a suspended object (floator). The lateral position of the plate is controlled by using the VCM and the sensor. Since the flux from the permanent magnet to the floator varies according to the position, the amplitude and direction of the attractive force acting on the floator can be adjusted with multiple modules. Stable suspension was achieved by applying PD control. A fluctuation was observed in the position of the floator. It was reduced by feeding back the lateral motions of the floator. The two-dimensional and three-dimensional noncontact manipulation of the floator was also achieved in the developed magnetic suspension system.

  1. Resolving the 180° Ambiguity in Solar Vector Magnetic Field Data: Evaluating the Effects of Noise, Spatial Resolution, and Method Assumptions

    NASA Astrophysics Data System (ADS)

    Leka, K. D.; Barnes, Graham; Crouch, A. D.; Metcalf, Thomas R.; Gary, G. Allen; Jing, Ju; Liu, Y.

    2009-11-01

    The objective testing of algorithms for performing ambiguity resolution in vector magnetic field data is continued, with an examination of the effects of noise in the data. Through the use of analytic magnetic field models, two types of noise are “added” prior to resolving: noise to simulate Poisson photon noise in the observed polarization spectra, and a spatial binning to simulate the effects of unresolved structure. The results are compared through the use of quantitative metrics and performance maps. We find that while no algorithm severely propagates the effects of Poisson noise beyond very local influences, some algorithms are more robust against high photon-noise levels than others. In the case of limited spatial resolution, loss of information regarding fine-scale structure can easily result in erroneous solutions. Our tests imply that photon noise and limited spatial resolution can act so as to make assumptions used in some ambiguity resolution algorithms no longer consistent with the observed magnetogram. We confirm a finding of the earlier comparison study that results can be very sensitive to the details of the treatment of the observed boundary and the assumptions governing that treatment. We discuss the implications of these findings, given the relative sensitivities of the algorithms to the two sources of noise tested here. We also touch on further implications for interpreting observational vector magnetic field data for general solar physics research.

  2. Fermionic current densities induced by magnetic flux in a conical space with a circular boundary

    SciTech Connect

    Bezerra de Mello, E. R.; Bezerra, V. B. [Departamento de Fisica, Universidade Federal da Paraiba 58.059-970, Caixa Postal 5.008, Joao Pessoa, PB (Brazil); Saharian, A. A. [Departamento de Fisica, Universidade Federal da Paraiba 58.059-970, Caixa Postal 5.008, Joao Pessoa, PB (Brazil); Department of Physics, Yerevan State University, Alex Manoogian Street, 0025 Yerevan (Armenia); Bardeghyan, V. M. [Department of Physics, Yerevan State University, Alex Manoogian Street, 0025 Yerevan (Armenia)

    2010-10-15

    We investigate the vacuum expectation value of the fermionic current induced by a magnetic flux in a (2+1)-dimensional conical spacetime in the presence of a circular boundary. On the boundary the fermionic field obeys the MIT bag boundary condition. For irregular modes, a special case of boundary conditions at the cone apex is considered, when the MIT bag boundary condition is imposed at a finite radius, which is then taken to zero. We observe that the vacuum expectation values for both the charge density and azimuthal current are periodic functions of the magnetic flux with the period equal to the flux quantum whereas the expectation value of the radial component vanishes. For both exterior and interior regions, the expectation values of the current are decomposed into boundary-free and boundary-induced parts. For a massless field the boundary-free part in the vacuum expectation value of the charge density vanishes, whereas the presence of the boundary induces nonzero charge density. Two integral representations are given for the boundary-free part in the case of a massive fermionic field for arbitrary values of the opening angle of the cone and magnetic flux. The behavior of the induced fermionic current is investigated in various asymptotic regions of the parameters. At distances from the boundary larger than the Compton wavelength of the fermion particle, the vacuum expectation values decay exponentially with the decay rate depending on the opening angle of the cone. We make a comparison with the results already known from the literature for some particular cases.

  3. Two types of magnetic flux cancelation in the solar eruption of 2007 May 20

    NASA Astrophysics Data System (ADS)

    Sterling, Alphonse; Moore, Ronald; Mason, Helen

    We study a solar eruption on 2007 May 20, in an effort to understand the cWe study a solar eruption of 2007 May 20, in an effort to understand the cause of the eruption's onset. The event produced a GOES class B6.7 flare peaking at 05:56 UT, while ejecting a surge/filament and producing a coronal mass ejection (CME). We examine several data sets, including H? images from the Solar Optical Telescope (SOT) on Hinode, EUV images from TRACE, and line-of-sight magnetograms from SoHO/MDI. Flux cancelation occurs among two different sets of flux elements inside of the erupting active region: First, for several days prior to eruption, opposite-polarity sunspot groups inside the region move toward each other, leading to the cancelation of ˜ 1021 Mx of flux over three days. Second, within hours prior to the eruption, positive-polarity moving magnetic features (MMFs) flowing out of the positive-flux spots at ˜ 1 km/s repeatedly cancel with field inside a patch of negative-polarity flux located north of the sunspots. The filament erupts as a surge whose base is rooted in the location where the MMF cancelation occurs, while during the eruption that filament flows out along the polarity inversion line between the converging spot groups. We conclude that a plausible scenario is that the converging spot fields brought the magnetic region to the brink of instability, and the MMF cancelation pushed the system "over the edge," triggering the eruption. This work was funded by NASA's Science Mission Directorate thought the Living With a Star Targeted Research and Technology Program, the Supporting Research and Program, and the Hinode project.

  4. The dynamics of fibril magnetic fields. I - Effect of flux tubes on convection. II - The mean field equations

    NASA Technical Reports Server (NTRS)

    Parker, E. N.

    1982-01-01

    Observations have established the general fibril state of the magnetic field at the visible surface of the sun. This extraordinary state of the field, in separate intense flux tubes, implies that the convection has a relatively permanent, closed topology, in spite of the large Reynolds number. This paper explores some of the effects of the separate flux tubes on the convective motions, generally pushing the convective cells toward aligning their downdrafts with the flux tubes so as to minimize the dissipation.

  5. Development of Large-Scale Data Visualization System for Magnetic Flux Tracing in Global MHD Simulations

    NASA Astrophysics Data System (ADS)

    Murata, K. T.; Watari, S.; Kubota, Y.; Fukazawa, K.; Tsubouchi, K.; Fujita, S.; Tanaka, T.; Den, M.; Murayama, Y.

    2011-12-01

    At NICT (National Institute of Information and Communications Technology) we have been developing a new research environment named "OneSpaceNet". The OneSpaceNet is a cloud-computing environment to provide the researchers rich resources for research studies, such as super-computers, large-scale disk area, licensed applications, database and communication devices. The large-scale disk area is rovided via Gfarm, which is one of the distributed file systems. This paper first proposes a distributed data-type and/or data-intensive processing system that are provided via Gfarm as a solution to large-scale data processing in the context of distributed data management and data processing environments in the field of solar-terrestrial physics. The usefulness of a system composed of many file system nodes was examined using large-scale computer simulation data. In the parallel 3D visualization of computer simulation data varying in terms of data processing granularity, optimized load balancing through FIFO scheduling or pipe-line scheduling yielded parallelization efficacy. Using the large-scale data processing system, we have developed a magnetic flux tracing system of global MHD simulations. Under the assumption of magnetic field frozen-in theory of ideal MHD plasma, we trace an element (or elements) of plasma at all steps of global MHD simulation, and visualize magnetic flux (magnetic field lines) penetrating the element(s). Since this system depends on the frozen-in theory, we need to examine when and where this assumption breaks before we apply it for physical data analyses. Figure (a) and Figure (b) show magnetic field lines in the vicinity of the Earth's magnetopause visualized via present system. Both figures show that the magnetic field lines are scattered as they advance downward. In the present talk we discuss the error in the tracings and the restrictions to apply for this technique.

  6. Modeling and Results for Creating Oblique Fields in a Magnetic Flux Leakage Survey Tool

    NASA Astrophysics Data System (ADS)

    Simek, James C.

    2010-02-01

    Integrity management programs designed to maintain safe pipeline systems quite often will use survey results from In line inspection (ILI) tools in addition to data from other sources. Commonly referred to a "smart pigs," one of the most widely used types are those based upon the magnetic flux leakage technique, typically used to detect and quantify metal loss zones. The majority of pipelines surveyed to date have used tools with the magnetic field direction axially aligned with the length of the pipeline. In order to enable detection and quantification of extremely narrow metal loss features or certain types of weld zone anomalies, tools employing magnetic circuits directing the magnetic fields around the pipe circumference have been designed and are use in segments where these feature categories are a primary concern. Modeling and laboratory test data of metal loss features will be used to demonstrate the response of extremely narrow metal loss zones as the features are rotated relative to the induced field direction. Based upon these results, the basis for developing a magnetizer capable of creating fields oblique to either pipeline axis will be presented along with the magnetic field profile models of several configurations.

  7. Decreasing Sunspot Magnetic Fields Explain Unique 10.7cm Radio Flux

    NASA Astrophysics Data System (ADS)

    Penn, Matthew J.; Livingston, W.; Svalgaard, L.

    2012-05-01

    Infrared spectral observations of sunspots from 1998-2011 have shown that on average sunspots changed; the magnetic fields weakened and the temperatures rose. The data also show that sunspots or dark pores can only form at the solar surface only if the magnetic field strength exceeds 1500 Gauss. Sunspots appear at the solar surface with a variety of field strengths, and during the period from 1998-2002 a histogram of the sunspot magnetic fields shows a normal distribution with a mean near 2400 Gauss and a width of about 340 Gauss. During this observing period the mean of the magnetic field distribution decreased by about 64 Gauss per year, and we assume that as the 1500 Gauss threshold was approached, magnetic fields appeared at the solar surface which could not form dark sunspots or pores With this assumption we propose a quantity called the sunspot formation fraction and give an analytical form derived from the magnetic field distribution. We show this fraction can quantitatively explain the changing elationship between sunspot number and solar radio flux measured at 10.7cm wavelengths.

  8. Decreasing Sunspot Magnetic Fields Explain Unique 10.7 cm Radio Flux

    NASA Astrophysics Data System (ADS)

    Livingston, W.; Penn, M. J.; Svalgaard, L.

    2012-09-01

    Infrared spectral observations of sunspots from 1998 to 2011 have shown that on average sunspots changed, the magnetic fields weakened, and the temperatures rose. The data also show that sunspots or dark pores can only form at the solar surface if the magnetic field strength exceeds about 1500 G. Sunspots appear at the solar surface with a variety of field strengths, and during the period from 1998 to 2002 a histogram of the sunspot magnetic fields shows a normal distribution with a mean of 2436 ± 26 G and a width of 323 ± 20 G. During this observing period the mean of the magnetic field distribution decreased by 46 ± 6 G per year, and we assume that as the 1500 G threshold was approached, magnetic fields appeared at the solar surface which could not form dark sunspots or pores. With this assumption we propose a quantity called the sunspot formation fraction and give an analytical form derived from the magnetic field distribution. We show that this fraction can quantitatively explain the changing relationship between sunspot number and solar radio flux measured at 10.7 cm wavelengths.

  9. DECREASING SUNSPOT MAGNETIC FIELDS EXPLAIN UNIQUE 10.7 cm RADIO FLUX

    SciTech Connect

    Livingston, W.; Penn, M. J. [National Solar Observatory, 950 North Cherry Avenue, Tucson, AZ 85718 (United States); Svalgaard, L. [HEPL, Via Ortega, Stanford University, Stanford, CA 94305 (United States)

    2012-09-20

    Infrared spectral observations of sunspots from 1998 to 2011 have shown that on average sunspots changed, the magnetic fields weakened, and the temperatures rose. The data also show that sunspots or dark pores can only form at the solar surface if the magnetic field strength exceeds about 1500 G. Sunspots appear at the solar surface with a variety of field strengths, and during the period from 1998 to 2002 a histogram of the sunspot magnetic fields shows a normal distribution with a mean of 2436 {+-} 26 G and a width of 323 {+-} 20 G. During this observing period the mean of the magnetic field distribution decreased by 46 {+-} 6 G per year, and we assume that as the 1500 G threshold was approached, magnetic fields appeared at the solar surface which could not form dark sunspots or pores. With this assumption we propose a quantity called the sunspot formation fraction and give an analytical form derived from the magnetic field distribution. We show that this fraction can quantitatively explain the changing relationship between sunspot number and solar radio flux measured at 10.7 cm wavelengths.

  10. Simulating rare switching events of magnetic nanostructures with forward flux sampling

    NASA Astrophysics Data System (ADS)

    Vogler, Christoph; Bruckner, Florian; Bergmair, Bernhard; Huber, Thomas; Suess, Dieter; Dellago, Christoph

    2013-10-01

    Predicting the thermal stability of magnetic storage devices is an important and challenging task. Here, we demonstrate how the forward flux sampling method (FFS) can be used to determine the thermal stability of magnets with general microstructures for time scales ranging from picoseconds to years. To apply FFS to magnetic systems, we first use the nudged elastic band (NEB) method to determine a minimum energy path connecting the initial with the final state of the magnetic transition. Interfaces defined based on this minimum energy path then provide the basis for the FFS procedure in which dynamical trajectories are generated by integrating a stochastic version of the fundamental equation of motion of the magnetization (Landau-Lifshitz-Gilbert equation) at finite temperature. This approach allows to determine average lifetimes for incoherent reversal processes and it can be applied for any value of the damping constant. We validate the method for a single-grain particle by comparison with the results of direct Langevin simulations carried out and demonstrate its capabilities and efficiency by computing the lifetime of a graded media grain, a magnetic structure with a tailored magnetocrystalline spatial anisotropy profile.

  11. Electron and Positron Fluxes in Primary Cosmic Rays Measured with the Alpha Magnetic Spectrometer on the International Space Station

    E-print Network

    Becker, Ulrich J.

    Precision measurements by the Alpha Magnetic Spectrometer on the International Space Station of the primary cosmic-ray electron flux in the range 0.5 to 700 GeV and the positron flux in the range 0.5 to 500 GeV are presented. ...

  12. ERUPTION OF A BUOYANTLY EMERGING MAGNETIC FLUX ROPE W. Manchester IV, T. Gombosi, and D. DeZeeuw

    E-print Network

    De Zeeuw, Darren L.

    Zeeuw Center for Space Environment Modeling, University of Michigan, Ann Arbor, MI 48109 and Y. Fan HAO motions transport axial flux and energy to the expanding portion of the magnetic field, driving, the same shearing process has been demonstrated in buoyantly emerging flux ropes (Fan 2001; Magara

  13. The magnetic structure of an earthward-moving flux rope observed by Cluster in the near-tail

    NASA Astrophysics Data System (ADS)

    Zhang, Y. C.; Liu, Z. X.; Shen, C.; Fazakerley, A.; Dunlop, M.; Réme, H.; Lucek, E.; Walsh, A. P.; Yao, L.

    2007-07-01

    We investigate the magnetic structure of a small earthward-moving flux rope observed by Cluster in the near-Earth plasma sheet through application of the Grad-Shafranov (GS) technique to reconstruct the transverse magnetic field distribution perpendicular to the flux rope axis at X=-14.75 RE. We find that the principal axis of the flux rope lies approximately along the dawn-dusk direction and that the diameter of the flux rope is about 1.5 RE. There is a strong duskward core magnetic field in the center of the flux rope. According to the AE index, there is no obvious substorm associated with the magnetic flux rope. Recent studies indicate that the formation of the flux rope in the plasma sheet can be understood in terms of simultaneous reconnection at multiple X-line points in the near-tail. The distribution of the transverse magnetic field on the cross section is the asymmetric circles, which requires that the reconnections at multiple X-line points occur. So our results also provide additional evidence for the occurrence of multiple-X line reconnection in the magnetotail.

  14. On the estimation of the magnetic easy axis in pipeline steels using magnetic Barkhausen noise

    NASA Astrophysics Data System (ADS)

    Martínez-Ortiz, P.; Pérez-Benitez, J. A.; Espina-Hernández, J. H.; Caleyo, F.; Hallen, J. M.

    2015-01-01

    A method for determination of the magnetic easy axis of the Roll Magnetic Anisotropy in API-5L steels is proposed. The method is based on the fact that the angular dependence of the energy corresponding to the main peak of the Magnetic Barkhausen signal presents uniaxial anisotropy with its easy axis parallel to the rolling direction, independently of the angular dependence of the magnetocrystalline energy in the materials. The proposal is also justified based on the analysis of the influence of microstructural changes, produced by hot-rolling on the domain wall dynamics.

  15. The dynamic evolution of active-region-scale magnetic flux tubes in the turbulent solar convective envelope

    NASA Astrophysics Data System (ADS)

    Weber, Maria Ann

    The Sun exhibits cyclic properties of its large-scale magnetic field on the order of sigma22 years, with a ˜11 year frequency of sunspot occurrence. These sunspots, or active regions, are the centers of magnetically driven phenomena such as flares and coronal mass ejections. Volatile solar magnetic events directed toward the Earth pose a threat to human activities and our increasingly technological society. As such, the origin and nature of solar magnetic flux emergence is a topic of global concern. Sunspots are observable manifestations of solar magnetic fields, thus providing a photospheric link to the deep-seated dynamo mechanism. However, the manner by which bundles of magnetic field, or flux tubes, traverse the convection zone to eventual emergence at the solar surface is not well understood. To provide a connection between dynamo-generated magnetic fields and sunspots, I have performed simulations of magnetic flux emergence through the bulk of a turbulent, solar convective envelope by employing a thin flux tube model subject to interaction with flows taken from a hydrodynamic convection simulation computed through the Anelastic Spherical Harmonic (ASH) code. The convective velocity field interacts with the flux tube through the drag force it experiences as it traverses through the convecting medium. Through performing these simulations, much insight has been gained about the influence of turbulent solar-like convection on the flux emergence process and resulting active region properties. I find that the dynamic evolution of flux tubes change from convection dominated to magnetic buoyancy dominated as the initial field strength of the flux tubes increases from 15 kG to 100 kG. Additionally, active-region-scale flux tubes of 40 kG and greater exhibit properties similar to those of active regions on the Sun, such as: tilt angles, rotation rates, and morphological asymmetries. The joint effect of the Coriolis force and helical motions present in convective upflows help tilt the apex of rising flux tubes toward the equator in accordance with Joys Law. Utilizing these simulations, I find that rotationally aligned, columnar convective structures called giant cells present near the equatorial regions of the ASH simulation organizes flux emergence into a large-scale longitudinal pattern similar to the active longitude trend on the Sun and other solar-like stars. The effect of radiative diffusion across the radiation zone-convection zone interface on the buoyant rise of magnetic flux tubes is also studied. Incorporating this effect into the flux tube model, flux tubes with magnetic field strengths of 60 kG or less no longer anchor in the stably stratified overshoot region. These flux tubes still have average emergence properties that agree with observations of solar active regions, although tilt angles have a larger scatter about the mean value. Finally, I will discuss possible future research problems that can be investigated through the thin flux tube approach, such as convection-induced twisting of the flux tube magnetic field lines and flux emergence properties on a young Sun rotating at 5 times the current solar rate.

  16. Coil Designs for Novel Magnetic Geometries to Cure the Divertor Heat Flux Problem for Reactors

    NASA Astrophysics Data System (ADS)

    Pekker, M.; Valanju, P.; Kotschenreuther, M.; Wiley, J. C.; Strickler, D.

    2004-11-01

    Coil designs are developed for novel magnetic divertor geometries with a second axi-symmetric x-point and flux expansion region along the separatrix. Adjacent posters describe how these lead to spreading of heat flux and the possibility of stable, complete detachment to overcome serious physics and engineering problems in reactors. The principal feasibility issue is creating, with simple coils, additional X-points on the separatrix without extensively deforming the magnetic field in the main plasma. For the spherical tokamak NSTX, we show that adding one or two poloidal coils suffices to create a divergent flux at the divertor, i.e., a new x-point. The currents and forces for the extra coils are small. We also modify ARIES ST design to show reactor feasibility. Optimized coil designs for PEGASUS, ARIES RS/AT, and a modular ITER retrofit are also being developed. For our calculations we used self consistent code FBEQ, which was used to design NSTX. We also use NCSX tools for optimization of designs with competing physics and engineering constraints.

  17. Noise in the processing and application of magnetic gradients Leon Foks, Kristofer Davis, and Yaoguo Li, Center for Gravity, Electrical, and Magnetics, Colorado School of Mines,

    E-print Network

    , and Yaoguo Li, Center for Gravity, Electrical, and Magnetics, Colorado School of Mines, Golden, Colorado calculations coupled with statistical analysis to observe the distribution of noise within gradient; Hardwick, 1999) in both spatial and wavenumber domains. Current processing of airborne magnetic data

  18. Electron and Positron Fluxes in Primary Cosmic Rays Measured with the Alpha Magnetic Spectrometer on the International Space Station

    NASA Astrophysics Data System (ADS)

    Aguilar, M.; Aisa, D.; Alvino, A.; Ambrosi, G.; Andeen, K.; Arruda, L.; Attig, N.; Azzarello, P.; Bachlechner, A.; Barao, F.; Barrau, A.; Barrin, L.; Bartoloni, A.; Basara, L.; Battarbee, M.; Battiston, R.; Bazo, J.; Becker, U.; Behlmann, M.; Beischer, B.; Berdugo, J.; Bertucci, B.; Bigongiari, G.; Bindi, V.; Bizzaglia, S.; Bizzarri, M.; Boella, G.; de Boer, W.; Bollweg, K.; Bonnivard, V.; Borgia, B.; Borsini, S.; Boschini, M. J.; Bourquin, M.; Burger, J.; Cadoux, F.; Cai, X. D.; Capell, M.; Caroff, S.; Casaus, J.; Cascioli, V.; Castellini, G.; Cernuda, I.; Cervelli, F.; Chae, M. J.; Chang, Y. H.; Chen, A. I.; Chen, H.; Cheng, G. M.; Chen, H. S.; Cheng, L.; Chikanian, A.; Chou, H. Y.; Choumilov, E.; Choutko, V.; Chung, C. H.; Clark, C.; Clavero, R.; Coignet, G.; Consolandi, C.; Contin, A.; Corti, C.; Coste, B.; Cui, Z.; Dai, M.; Delgado, C.; Della Torre, S.; Demirköz, M. B.; Derome, L.; Di Falco, S.; Di Masso, L.; Dimiccoli, F.; Díaz, C.; von Doetinchem, P.; Du, W. J.; Duranti, M.; D'Urso, D.; Eline, A.; Eppling, F. J.; Eronen, T.; Fan, Y. Y.; Farnesini, L.; Feng, J.; Fiandrini, E.; Fiasson, A.; Finch, E.; Fisher, P.; Galaktionov, Y.; Gallucci, G.; García, B.; García-López, R.; Gast, H.; Gebauer, I.; Gervasi, M.; Ghelfi, A.; Gillard, W.; Giovacchini, F.; Goglov, P.; Gong, J.; Goy, C.; Grabski, V.; Grandi, D.; Graziani, M.; Guandalini, C.; Guerri, I.; Guo, K. H.; Habiby, M.; Haino, S.; Han, K. C.; He, Z. H.; Heil, M.; Hoffman, J.; Hsieh, T. H.; Huang, Z. C.; Huh, C.; Incagli, M.; Ionica, M.; Jang, W. Y.; Jinchi, H.; Kanishev, K.; Kim, G. N.; Kim, K. S.; Kirn, Th.; Kossakowski, R.; Kounina, O.; Kounine, A.; Koutsenko, V.; Krafczyk, M. S.; Kunz, S.; La Vacca, G.; Laudi, E.; Laurenti, G.; Lazzizzera, I.; Lebedev, A.; Lee, H. T.; Lee, S. C.; Leluc, C.; Li, H. L.; Li, J. Q.; Li, Q.; Li, Q.; Li, T. X.; Li, W.; Li, Y.; Li, Z. H.; Li, Z. Y.; Lim, S.; Lin, C. H.; Lipari, P.; Lippert, T.; Liu, D.; Liu, H.; Lomtadze, T.; Lu, M. J.; Lu, Y. S.; Luebelsmeyer, K.; Luo, F.; Luo, J. Z.; Lv, S. S.; Majka, R.; Malinin, A.; Mañá, C.; Marín, J.; Martin, T.; Martínez, G.; Masi, N.; Maurin, D.; Menchaca-Rocha, A.; Meng, Q.; Mo, D. C.; Morescalchi, L.; Mott, P.; Müller, M.; Ni, J. Q.; Nikonov, N.; Nozzoli, F.; Nunes, P.; Obermeier, A.; Oliva, A.; Orcinha, M.; Palmonari, F.; Palomares, C.; Paniccia, M.; Papi, A.; Pedreschi, E.; Pensotti, S.; Pereira, R.; Pilo, F.; Piluso, A.; Pizzolotto, C.; Plyaskin, V.; Pohl, M.; Poireau, V.; Postaci, E.; Putze, A.; Quadrani, L.; Qi, X. M.; Rancoita, P. G.; Rapin, D.; Ricol, J. S.; Rodríguez, I.; Rosier-Lees, S.; Rozhkov, A.; Rozza, D.; Sagdeev, R.; Sandweiss, J.; Saouter, P.; Sbarra, C.; Schael, S.; Schmidt, S. M.; Schuckardt, D.; von Dratzig, A. Schulz; Schwering, G.; Scolieri, G.; Seo, E. S.; Shan, B. S.; Shan, Y. H.; Shi, J. Y.; Shi, X. Y.; Shi, Y. M.; Siedenburg, T.; Son, D.; Spada, F.; Spinella, F.; Sun, W.; Sun, W. H.; Tacconi, M.; Tang, C. P.; Tang, X. W.; Tang, Z. C.; Tao, L.; Tescaro, D.; Ting, Samuel C. C.; Ting, S. M.; Tomassetti, N.; Torsti, J.; Türko?lu, C.; Urban, T.; Vagelli, V.; Valente, E.; Vannini, C.; Valtonen, E.; Vaurynovich, S.; Vecchi, M.; Velasco, M.; Vialle, J. P.; Wang, L. Q.; Wang, Q. L.; Wang, R. S.; Wang, X.; Wang, Z. X.; Weng, Z. L.; Whitman, K.; Wienkenhöver, J.; Wu, H.; Xia, X.; Xie, M.; Xie, S.; Xiong, R. Q.; Xin, G. M.; Xu, N. S.; Xu, W.; Yan, Q.; Yang, J.; Yang, M.; Ye, Q. H.; Yi, H.; Yu, Y. J.; Yu, Z. Q.; Zeissler, S.; Zhang, J. H.; Zhang, M. T.; Zhang, X. B.; Zhang, Z.; Zheng, Z. M.; Zhuang, H. L.; Zhukov, V.; Zichichi, A.; Zimmermann, N.; Zuccon, P.; Zurbach, C.; AMS Collaboration

    2014-09-01

    Precision measurements by the Alpha Magnetic Spectrometer on the International Space Station of the primary cosmic-ray electron flux in the range 0.5 to 700 GeV and the positron flux in the range 0.5 to 500 GeV are presented. The electron flux and the positron flux each require a description beyond a single power-law spectrum. Both the electron flux and the positron flux change their behavior at ˜30 GeV but the fluxes are significantly different in their magnitude and energy dependence. Between 20 and 200 GeV the positron spectral index is significantly harder than the electron spectral index. The determination of the differing behavior of the spectral indices versus energy is a new observation and provides important information on the origins of cosmic-ray electrons and positrons.

  19. Application of Barkhausen noise and ferromagnetic hysteresis for magnetic non-destructive evaluation of multiphase composites and structures

    NASA Astrophysics Data System (ADS)

    Prabhu Gaunkar, Neelam; Kypris, Orfeas; Nlebedim, Cajetan; Jiles, David

    2015-03-01

    Composite ferromagnetic materials with multiple magnetic phases are increasingly being used in applications such as magnetic data storage, magnetic sensors and actuators and exchange-spring magnets. These materials occur in single or multiphase conditions and can undergo phase changes over time or during processing. For these materials, we examine the interrelation between ferromagnetic hysteresis, Barkhausen noise and the material microstructure. We observe that the presence of a second phase in these materials can be detected with the help of Barkhausen noise signals due to the occurrence of additional peaks in the magnetization envelope. This behavior in the magnetic response can serve as a tool for non-destructive evaluation of ferromagnetic materials for which phase constitution and phase changes affect the structural performance.

  20. The Dynamic Evolution of Active-Region-Scale Magnetic Flux Tubes in the Turbulent Solar Convective Envelope

    NASA Astrophysics Data System (ADS)

    Weber, Maria A.; Fan, Yuhong; Miesch, Mark S.

    2014-06-01

    The manner by which bundles of magnetic field, or flux tubes, traverse the convection zone to eventual emergence at the solar surface is not well understood. To provide a connection between dynamo-generated magnetic fields and sunspots, I have performed simulations of magnetic flux emergence through the bulk of a turbulent, solar convective envelope by employing a thin flux tube model subject to interaction with flows taken from a hydrodynamic convection simulation computed through the Anelastic Spherical Harmonic (ASH) code. Through performing these simulations, much insight has been gained about the influence of turbulent solar-like convection on the flux emergence process and resulting active region properties. I find that the dynamic evolution of flux tubes change from convection dominated to magnetic buoyancy dominated as the initial field strength of the flux tubes increases from 15 kG to 100 kG. Additionally, active-region-scale flux tubes of 40 kG and greater exhibit properties similar to those of active regions on the Sun, such as: tilt angles, rotation rates, and morphological asymmetries. The joint effect of the Coriolis force and helical motions present in convective upflows help tilt the apex of rising flux tubes toward the equator in accordance with Joy’s Law. Additionally, rotationally aligned, columnar convective structures called giant cells present in the ASH simulation organizes flux emergence into a large-scale longitudinal pattern similar to the active longitude trend on the Sun and other solar-like stars. The effect of radiative diffusion across the radiation zone-convection zone interface on the buoyant rise of magnetic flux tubes is also studied, as well as the possibility of an induced twist of flux tube magnetic fields lines due to the Coriolis force induced tilting of the flux tube apex, presence of turbulent convection, and the conservation of helicity. Flux emergence simulations through the convection zone of a Sun rotating at 5 times the current solar rate are also conducted to explore the rotation-convection relationship as it relates to flux emergence.

  1. Cosmic strings with twisted magnetic flux lines and wound-strings in extra dimensions

    SciTech Connect

    Lake, Matthew; Yokoyama, Jun'ichi, E-mail: lake@resceu.s.u-tokyo.ac.jp, E-mail: yokoyama@resceu.s.u-tokyo.ac.jp [Research Center for the Early Universe, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2012-09-01

    We consider a generalization of the Nielsen-Olesen ansatz, in the abelian-Higgs model, which describes strings with twisted magnetic flux lines in the vortex core. The solution does not possess cylindrical symmetry, which leads to the existence of components of conserved momentum, both around the core-axis and along the length of the string. In addition, we consider a model of F-strings with rotating, geodesic windings in the compact space of the Klebanov-Strassler geometry and determine matching conditions which ensure energy and momentum conservation when loops chop off from the long-string network. We find that the expressions for the constants of motion, which determine the macroscopic string dynamics, can be made to coincide with those for the twisted flux line string, suggesting that extra-dimensional effects for F-strings may be mimicked by field-theoretic structure in topological defects.

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Vacuum current and magnetic field induced by an impenetrable flux tube. Dirichlet problem

    E-print Network

    Volodymyr M. Gorkavenko; Iryna V. Ivanchenko

    2015-05-10

    We consider the vacuum polarization effects created by a finite radius magnetic-flux-carrying tube that is impenetrable for quantum matter. The vacuum polarization depends on the choice of a boundary condition at the edge of the tube. We impose a perfectly reflecting (Dirichlet) boundary condition at the edge of the tube on the charged massive scalar matter field which is quantized outside the tube. We find that a current is induced in the vacuum of the quantized scalar field and it circulates around the tube. As a consequence of the Maxwell equation, a magnetic field strength is also induced in the vacuum and is directed along the tube. We restrict our consideration to a plane case. The behavior of the current and the field strength is comprehensively analyzed. In contrast to the model of singular magnetic filament, magnetic field strength is finite at the edge of the string. Induced vacuum effects strongly depend on the tube radius $r_0$. They are quite negligible at $mr_0 > 1$, whereas it becomes noticeable at $mr_0\\ll1$. Induced vacuum effects are less than in the case of singular magnetic filament.

  4. EFFECT OF POLARIMETRIC NOISE ON THE ESTIMATION OF TWIST AND MAGNETIC ENERGY OF FORCE-FREE FIELDS

    SciTech Connect

    Tiwari, Sanjiv Kumar; Venkatakrishnan, P.; Gosain, Sanjay; Joshi, Jayant [Udaipur Solar Observatory, Physical Research Laboratory, Dewali, Bari Road, Udaipur-313 001 (India)], E-mail: stiwari@prl.res.in, E-mail: pvk@prl.res.in, E-mail: sgosain@prl.res.in, E-mail: jayant@prl.res.in

    2009-07-20

    The force-free parameter {alpha}, also known as helicity parameter or twist parameter, bears the same sign as the magnetic helicity under some restrictive conditions. The single global value of {alpha} for a whole active region gives the degree of twist per unit axial length. We investigate the effect of polarimetric noise on the calculation of global {alpha} value and magnetic energy of an analytical bipole. The analytical bipole has been generated using the force-free field approximation with a known value of constant {alpha} and magnetic energy. The magnetic parameters obtained from the analytical bipole are used to generate Stokes profiles from the Unno-Rachkovsky solutions for polarized radiative transfer equations. Then we add random noise of the order of 10{sup -3} of the continuum intensity (I {sub c}) in these profiles to simulate the real profiles obtained by modern spectropolarimeters such as Hinode (SOT/SP), SVM (USO), ASP, DLSP, POLIS, and SOLIS etc. These noisy profiles are then inverted using a Milne-Eddington inversion code to retrieve the magnetic parameters. Hundred realizations of this process of adding random noise and polarimetric inversion is repeated to study the distribution of error in global {alpha} and magnetic energy values. The results show that (1) the sign of {alpha} is not influenced by polarimetric noise and very accurate values of global twist can be calculated, and (2) accurate estimation of magnetic energy with uncertainty as low as 0.5% is possible under the force-free condition.

  5. The Flux of Open and Toroidal Interplanetary Magnetic Field as a Function of Heliolatitude and Solar Cycle

    Microsoft Academic Search

    David E. Connick; Charles W. Smith; Nathan A. Schwadron

    2009-01-01

    We examine 45 years of near-Earth interplanetary observations as recorded in the National Space Science Data Center OMNI data set and 18 years of observations by the Ulysses spacecraft. We find that recent claims for a 50+ year low in interplanetary magnetic field intensity are substantiated, that the low flux levels can be attributed to open magnetic field lines, and

  6. IEEE TRANSACTIONSON APPLIED SUPERCONDUCTIVITY,VOL. I I, NO. I, MARCH 2001 I223 Magnetic Flux Controlled Josephson Array

    E-print Network

    Orlando, Terry P.

    and frequency of the array are controlled by the independent variables of magnetic field and current bias. WeIEEE TRANSACTIONSON APPLIED SUPERCONDUCTIVITY,VOL. I I, NO. I, MARCH 2001 I223 Magnetic Flux Controlled Josephson Array Oscillators Donald S. Crankshaw, Enrique Trias, and Terry P. Orlando Abstruct- One

  7. IEEE TRANSACTIONS ON MAGNETICS, VOL. 49, NO. 4, APRIL 2013 1493 Comparison of Complementary and Modular Linear Flux-Switching

    E-print Network

    Mi, Chunting "Chris"

    switched reluctance (LSR) motors, and high power density of linear synchronous PM (LSPM) motors, which and Modular Linear Flux-Switching Motors With Different Mover and Stator Pole Pitch Ruiwu Cao , Ming Cheng-switching permanent magnet (LFSPM) motors with both permanent magnets and armature windings on the short pri- mary

  8. Analytical prediction of the inductance of slotless axial flux permanent magnet synchronous generator using Quasi3D method

    Microsoft Academic Search

    Qamaruzzaman; A. Pradikta; P. A. Dahono

    2009-01-01

    The inductance in a generator is an important parameter to determine the generator operating point. Synchronous inductance consists of magnetization and leakage inductance. In this paper, an analytic method, Quasi-3D, has been proposed to predict inductance in an axial flux permanent magnet slot less synchronous generator. Analytic calculation was done using MATLAB. Then analytical prediction was compared to experiment result.

  9. Measurement of irradiation effects in a RPV steel by ball indentation technique and magnetic Barkhausen noise

    NASA Astrophysics Data System (ADS)

    Kim, In-Sup; Park, Duck-Gun; Byun, Thak-Sang; Hong, Jun-Hwa

    1999-12-01

    Effects of neutron dose on the mechanical and magnetic properties of a SA508-3 nuclear pressure vessel steel were investigated by using ball indentation test technique and magnetic Barkhausen noise (BN) measurements. The samples were irradiated in a research reactor up to 1018n/cm2 (E>1 MeV) at 70 °C. The yield strength and flow curve were evaluated from the indentation load-depth curves. The change of mechanical properties showed characteristic trend with respect to neutron dose, namely near plateau, rapid increase and slow increase. On the other hand, the BN varied in a reverse manner, a slow decrease up to a neutron dose of 1016n/cm2, followed by a rapid decrease up to a dose of 1018n/cm2.

  10. Barkhausen noise in the Random Field Ising Magnet NdFeB

    NASA Astrophysics Data System (ADS)

    Xu, Jian; Silevitch, Daniel; Rosenbaum, Thomas

    2015-03-01

    With the application of a magnetic field transverse to the magnetic easy axis, sintered blocks of the rare-earth ferromagnet Nd2Fe14B form a realization of the Random-Field Ising Model at room temperature. We study domain reversal and avalanche dynamics through an analysis of the Barkhausen noise. Power-law behavior with a cutoff is observed in the avalanche energy spectrum, consistent with theoretical predictions for disordered materials. Two regimes of behavior are found, one at low temperature and high transverse field where the system shows behavior consistent with randomness-dominated dynamics, and a high-temperature, low-transverse-field regime in which thermal fluctuations dominate the dynamics. In the randomness-dominated regime, the critical exponents are consistent with mean-field predictions for heavily disordered system, whereas in the thermal-fluctuation regime, the critical exponents differ substantially from the mean-field predictions.

  11. Improvements of measuring system on magnetic levitation system for the determination of magnetic flux quantum

    Microsoft Academic Search

    F. Shiota; T. Morokuma

    2002-01-01

    A development of a video frame synchronized data sampling system is in progress for superconducting magnetic levitation system parameters to correct an error of vertical displacement reading due to attitude change of floating body using real time movement analysis in equilibrium condition.

  12. KELVIN-HELMHOLTZ INSTABILITY IN CORONAL MAGNETIC FLUX TUBES DUE TO AZIMUTHAL SHEAR FLOWS

    SciTech Connect

    Soler, R.; Terradas, J.; Oliver, R.; Ballester, J. L. [Departament de Fisica, Universitat de les Illes Balears, E-07122, Palma de Mallorca (Spain); Goossens, M., E-mail: roberto.soler@uib.e [Centre for Plasma Astrophysics and Leuven Mathematical Modeling and Computational Science Centre, K. U. Leuven, Celestijnenlaan 200B, 3001 Heverlee (Belgium)

    2010-04-01

    Transverse oscillations of coronal loops are often observed and have been theoretically interpreted as kink magnetohydrodynamic (MHD) modes. Numerical simulations by Terradas et al. suggest that shear flows generated at the loop boundary during kink oscillations could give rise to a Kelvin-Helmholtz instability (KHI). Here, we investigate the linear stage of the KHI in a cylindrical magnetic flux tube in the presence of azimuthal shear motions. We consider the basic, linearized MHD equations in the beta = 0 approximation and apply them to a straight and homogeneous cylindrical flux tube model embedded in a coronal environment. Azimuthal shear flows with a sharp jump of the velocity at the cylinder boundary are included in the model. We obtain an analytical expression for the dispersion relation of the unstable MHD modes supported by the configuration, and compute analytical approximations of the critical velocity shear and the KHI growth rate in the thin tube limit. A parametric study of the KHI growth rates is performed by numerically solving the full dispersion relation. We find that fluting-like modes can develop a KHI in timescales comparable to the period of kink oscillations of the flux tube. The KHI growth rates increase with the value of the azimuthal wavenumber and decrease with the longitudinal wavenumber. However, the presence of a small azimuthal component of the magnetic field can suppress the KHI. Azimuthal motions related to kink oscillations of untwisted coronal loops may trigger a KHI, but this phenomenon has not been observed to date. We propose that the azimuthal component of the magnetic field is responsible for suppressing the KHI in a stable coronal loop. The required twist is small enough to prevent the development of the pinch instability.

  13. Evolution of a Magnetic Flux Tube in a Sunspot K. Jahn 1;2 , R. Schlichenmaier 3 , H.U. Schmidt 1

    E-print Network

    Jahn, Krzysztof

    Evolution of a Magnetic Flux Tube in a Sunspot Penumbra K. Jahn 1;2 , R. Schlichenmaier 3 , H, Germany. (Received ............. ) The motion of an individual magnetic flux tube inside the penumbra of a sunspot is studied numerically. Here, we present preliminary results. The thin flux tube approximation

  14. Interplanetary Electric Field and Solar Open Magnetic Flux: no Increase Since 1926.

    NASA Astrophysics Data System (ADS)

    Le Sager, P.; Svalgaard, L.

    2003-12-01

    A correlation analysis between the interplanetary electric field and the magnetograms recorded at Godhavn (Qeqertarsuaq), a polar cap geomagnetic observatory, is performed. A direction, along which the latitudinal dependence of the geomagnetic perturbation is minimum, is found, and allows us to apply the correlation results to pre-satelitte data, back to 1926. The findings indicate no secular trend in the cross-polar cap electric field, in the interplanetary electric field, and by inference in the sun's open magnetic flux, since 1926. The result is independent of the aa geomagnetic index.

  15. Noise correlation in fundamental mode orthogonal fluxgate

    NASA Astrophysics Data System (ADS)

    Butta, M.; Sasada, I.

    2012-04-01

    One of the key issues to reduce noise in a flux gate is the knowledge of how the noise is originated within the sensor. In this paper we measured the noise of an orthogonal flux gate operated in the fundamental mode in narrow regions of the magnetic wire used as a core, and we show how the correlation between the noise measured in two different sections drops when the distance between the sections is increased. This indicates that the noise is originated locally in the magnetic wire and then spread thought the wire due to its high permeability. This was confirmed by the measurement with a longer wire that yields higher correlation than those observed with shorter ones. Therefore, uncorrelated noise generated in sections of the wire far enough can be compensated. Finally, we show how the noise from two different wires is totally uncorrelated even if excited by the same current source, confirming that the noise is originated within the magnetic core. Such results can be used to design sensors with lower noise.

  16. Three-Dimensional Force Measurement and Control of a Flux-Path Control Magnetic Suspension

    NASA Astrophysics Data System (ADS)

    Furutachi, Munehiro; Inaba, Shunsuke; Ishino, Yuji; Takasaki, Masaya; Mizuno, Takeshi

    In the flux-path control magnetic suspension system, the force acting on a floator is controlled by moving a control plate made of ferromagnetic material, which is located between the permanent magnet and the floator. In this paper, the three-dimensional attractive forces acting on the floator were measured with a manufactured force sensor. The force actuating in the vertical direction is measured with the load cell built in the sensor. The force actuating in the horizontal direction is measured with the plate springs with strain gauges. These measurements clarify the relations between the positions of the control plates and the three-dimensional attractive forces. In addition, stable suspension and three-dimensional positioning were achieved by applying PD control. Several dynamic characteristics were measured in both the vertical and horizontal directions.

  17. A twisted flux tube model for solar prominences. III. Magnetic support

    SciTech Connect

    Ridgway, C.; Priest, E.R.; Amari, T. (Saint Andrews Univ. (Scotland))

    1991-01-01

    The model for the support of a solar prominence in a twisted flux tube by Priest et al. (1989) is here extended to consider large deviations of the tube from cylindrical symmetry. The prominence is modeled as a finite current sheet with mass which is locally free from singularities in the magnetic field. Analytical solutions are found to the nonlinear force-free equations for the structure around the prominence for two functional forms of the field component parallel to the prominence axis. An associated mixed boundary-value problem is also solved in which the prominence is connected at its base to the photosphere, and the normal magnetic field components along the prominence and the photosphere are imposed. 21 refs.

  18. Heating of coronal plasma by anomalous current dissipation. [induced by solar magnetic flux

    NASA Technical Reports Server (NTRS)

    Rosner, R.; Golub, L.; Coppi, B.; Vaiana, G. S.

    1978-01-01

    It is shown that there exist heating mechanisms which connect the observed radiative properties of the inner corona in a simple way to the underlying solar magnetic field. The mechanisms considered involve the generation and consequent dissipation of coronal currents. It is argued that the spatially and temporally inhomogeneous nature of the erupting solar magnetic field is an essential element of coronal heating. Unlike heating theories conceived in the context of the 'homogeneous' corona, this class of current heating models incorporates the observed stochastic coronal structuring at the onset, and does not view it as a complication of an otherwise straightforward model. Attention is given to the generation of coronal currents, the flux-tube emergence, the gradual growth and decay of active regions, the energetics of current dissipation, current sheath geometry and heat transport, and anomalous current dissipation.

  19. Magnetohydrodynamic waves in a compressible magnetic flux tube with elliptical cross-section

    NASA Astrophysics Data System (ADS)

    Erdélyi, R.; Morton, R. J.

    2009-01-01

    Aims: The propagation of magnetohydrodynamic (MHD) waves in a finite, compressible magnetic flux tube with an elliptical cross-section embedded in a magnetic environment is investigated. Methods: We present the derivation of the general dispersion relation of linear magneto-acoustic wave propagation for a compressible magnetic flux tube with elliptical cross-section in a plasma with finite beta. The wave modes of propagation for the n=0 (symmetric) sausage and n=1 (anti-symmetric) kink oscillations are then examined within the limit of the thin flux tube approximation. Results: It is shown that a compressible magnetic tube with elliptical cross-section supports slow and fast magneto-acoustic waves. In the thin tube approximation, the slow sausage mode and the slow and fast kink modes are found in analogue to a circular cross-section. However, the kink modes propagate with different phase speeds depending on whether the axial displacement takes place along the major or minor axis of the ellipse. This feature is present in both the slow and the fast bands, providing two infinite sets of slow kink modes and two infinite sets of fast kink modes, i.e. each corresponding cylindrical mode splits into two sets of modes due to the ellipticity. The difference between the phase speeds along the different axis is dependent on the ratio of the lengths of the two axes. Analytical expressions for the phase speeds are found. We show that the sausage modes do not split due to the introduced ellipticity and only the phase speed is modified when compared to the appropriate cylindrical counterpart. The percentage difference between the periods of the circular and elliptical cross-sections is also calculated, which reaches up to 21% for oscillations along the major axis. The level of difference in period could be very important in magneto-seismological applications, when observed periods are inverted into diagnostic properties (e.g. magnetic field strength, gravitational scale height, tube expansion parameter). Also shown is the perturbation of focal points of the elliptical cross-section for different modes. It is found that the focal points are unperturbed for the sausage mode, but are perturbed for all higher modes.

  20. Magnetic structures of an emerging flux region in the solar photosphere and chromosphere

    NASA Astrophysics Data System (ADS)

    Xu, Z.; Lagg, A.; Solanki, S. K.

    2010-09-01

    Aims: We investigate the vector magnetic field and Doppler velocity in the photosphere and upper chromosphere of a young emerging flux region of the sun close to disk center. Methods: Spectropolarimetric scans of a young active region made using the second generation Tenerife Infrared Polarimeter (TIP II) on the German Vacuum Tower Telescope (VTT) are analyzed. The scanned area contained multiple sunspots and an emerging flux region. An inversion based on the Milne-Eddington approximation was performed on the full Stokes vector of the chromospheric He I 10 830 Å and the photospheric Si I 10 827.1 Å lines. This provided the magnetic vector and line-of-sight velocity at each spatial point in both atmospheric layers. Results: A clear difference is seen between the complex magnetic structure of the emerging flux region (EFR) in the photosphere and the much simpler structure in the upper chromosphere. The upper chromospheric structure is consistent with a set of emerging loops following elongated dark structures seen in the He I 10 830 Å triplet, similar to arch filament systems (AFS), while in the photosphere we infer the presence of U-loops within the emergence zone. Nonetheless, in general the upper chromospheric field has a similar linear relationship between inclination angle and field strength as the photospheric field: the field is weak (?300 G) and horizontal in the emergence zone, but strong (up to 850 G) and more vertical near its edges. The field strength decreases from the photosphere to the upper chromosphere by approximately 0.1-0.2 G km-1 (or even less) within the emergence zone and by 0.3-0.6 G km-1 in sunspots located at its edge. We reconstructed the magnetic field in 3D based on the chromospheric vector field under the assumption that the He I 10 830 Å triplet forms along the magnetic field loops. The reconstructed loops are quite flat with supersonic downflows at both footpoints. Arguments and evidence for an enhanced formation height of He I 10 830 Å in arch-filaments seen in this line are provided, which support the validity of the reconstructed loops. Conclusions: The main chromospheric properties of EFRs previously deduced for a single region NOAA 9451 are shown to be valid for another region as well, suggesting that the main original results may have a wider application. The main exception is that only the first region displayed a current sheet in the chromosphere. We propose a scenario in which the relatively complex photospheric structure evolves into the simpler chromospheric one.

  1. STRUCTURE OF NON-FORCE-FREE MAGNETIC FLUX ROPES IN AN AMBIENT MEDIUM

    SciTech Connect

    Chen, James, E-mail: James.Chen@nrl.navy.mil [Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375 (United States)

    2012-12-20

    The structure of non-force-free equilibrium magnetic flux ropes in an ambient medium of specified pressure p{sub a} is studied. A flux rope is a self-organized magnetized plasma structure consisting of a localized channel of electric current and the magnetic field arising from this current. An analytic method is developed to obtain one-dimensional equilibrium solutions satisfying c {sup -1} J Multiplication-Sign B - {nabla}p = 0 subject to the requirements that (1) all physical quantities be nonsingular and continuous, (2) pressure p(r) be physically admissible-real and non-negative, and (3) the magnetic field profile have ''minimum complexity''. The solutions are shown to be characterized by two parameters, B{sup *}{sub t}{identical_to} B-bar{sub t}/(8{pi}p{sub a}){sup 1/2} and B*{sub p} {identical_to} B{sub pa} /(8{pi}p{sub a} ){sup 1/2}, where B-bar{sub t} is the toroidal (axial) field averaged over the cross-sectional radius a and B{sub pa} is the poloidal (azimuthal) field at the edge of the current channel (r = a). The physical constraint on pressure defines equilibrium boundaries in the B*{sub t}-B*{sub p} space beyond which no physical solutions exist. The method is illustrated with a number of families of solutions governed by distinct physical constraints. The force-free limit with p{sub a} {ne} 0 is investigated and is found to be characterized by plasma {beta} = {infinity}. The local Alfven speed V{sub A} and plasma {beta} are computed. The results are scale-invariant.

  2. Very low 1\\/f noise at room temperature in fully epitaxial Fe\\/MgO\\/Fe magnetic tunnel junctions

    Microsoft Academic Search

    F. G. Aliev; R. Guerrero; D. Herranz; R. Villar; F. Greullet; C. Tiusan; M. Hehn

    2007-01-01

    We report on room temperature 1\\/f noise in fully epitaxial Fe (45 nm)\\/MgO (2.6 nm)\\/Fe (10 nm) magnetic tunnel junctions (MTJs) with and without carbon doping of the Fe\\/MgO bottom interface. We have found that the normalized noise (Hooge factor) asymmetry between parallel and antiparallel states may strongly depend on the applied bias and its polarity. Both types of MTJs

  3. Dynamics of the formation of intense magnetic flux tubes on the sun by a converging plasma flow

    NASA Astrophysics Data System (ADS)

    Kruglov, A. A.

    2013-03-01

    We study the dynamics of the formation of an intense magnetic flux tube (IMFT) from the background magnetic field by a converging plasma flow with nonlinear magnetic diffusion due to the Cowling conductivity. We confirm the formation of a stationary profile of the magnetic field that was obtained earlier and estimate its onset time. We also consider relaxation of the background field inhomogeneities in the course of their advection into the magnetic flux tube. In the case of nonzero projection of the electrical current on the magnetic field, we found a new mode of the field inhomogeneity relaxation in plasmas with a highly anisotropic resistivity tensor. In this mode, unlike the case of absence of currents along the magnetic flux tube axis, which was studied earlier, an impulsive component of the magnetic energy release is observed, and the magnetic field outside the impulsive component is nearly force-free. A qualitative description of this phenomenon is proposed, analytical estimates are given, and the results of numerical calculations are presented.

  4. Effects of different magnetic flux densities on microstructure and magnetic properties of molecular-beam-vapor-deposited nanocrystalline Fe64Ni36 thin films

    NASA Astrophysics Data System (ADS)

    Cao, Yongze; Wang, Qiang; Li, Guojian; Ma, Yonghui; Du, Jiaojiao; He, Jicheng

    2015-04-01

    The nanocrystalline Fe64Ni36 thin films were prepared by molecular-beam-vapor deposition under different magnetic flux densities. The microstructure and magnetic properties of thin films were examined by AFM, TEM, HRTEM and VSM. The results show that with the increase of magnetic flux densities, the changing trend of the average particle size is the same as the coercive force except 6 T. Under 6 T condition, the thin film became the mixture of bcc and fcc phases, which leads to slight increase of the coercive force. In addition, the HRTEM result shows the short-range ordered clusters (embryos) or nucleation rate of thin films increase with increasing magnetic flux densities.

  5. Characteristics of the spatial structure of Martian magnetic flux ropes recovered by the Grad-Shafranov reconstruction technique

    NASA Astrophysics Data System (ADS)

    Hara, T.; Seki, K.; Hasegawa, H.; Brain, D. A.; Matsunaga, K.; Saito, M. H.

    2013-12-01

    Mars is a unique planet because it locally possesses strong crustal magnetic fields mainly located in the southern hemisphere [e.g., Acuna et al., 1999]. The Martian electromagnetic environment can thus become highly complicated and variable, since the interplanetary magnetic field embedded in the solar wind interacts with the Martian crustal magnetic fields. Whereas it is known that the Martian upper atmosphere is escaping to interplanetary space due to the interaction with the solar wind [e.g., Lundin et al., 1989; Barabash et al., 2007], the contribution of crustal magnetic fields to atmospheric escape from Mars has not yet been well understood. Flux ropes are characteristic magnetic field structures seen throughout the solar system, e.g., at the Sun, in the interplanetary space, and at the terrestrial magnetosphere. Flux ropes are also observed at planets such as at Venus and Mars [e.g., Russell and Elphic, 1979; Vignes et al., 2004], which do not possess a global intrinsic magnetic field. Brain et al. [2010] found a large-scale isolated magnetic flux rope filled with Martian atmospheric plasma located downstream from the crustal magnetic fields with respect to the solar wind flow based on the Mars Global Surveyor (MGS) measurements. They suggested that the magnetic flux rope could be intermittently detached from Mars, and remove significant amounts of atmosphere away from Mars. They proposed that this process might occur frequently and account for as much as 10% of the total present-day ion escape from Mars. However, this estimation of the ion escape rate is somewhat ambiguous, because it is difficult to infer the spatial structure of them from the single spacecraft data. We here investigated characteristics of the Martian magnetic flux ropes based on the Grad-Shafranov (GS) reconstruction technique using the MGS magnetic field data. This technique is capable of recovering the two-dimensional spatial structure of the magnetic flux ropes from single spacecraft data [e.g., Hu and Sunnerup, 2002]. The resultant structure allows us to provide a reliable observational restriction on the spatial scales of magnetic flux ropes. We applied the GS reconstruction technique to 135 obvious magnetic flux rope events observed by MGS. As a result, their spatial structures were successfully recovered for 70 events. The reconstruction results indicated that magnetic flux rope axes are mostly oriented horizontally with respect to the Martian surface. We demonstrated that the events, which have solar zenith angle larger than 75 deg and duration longer than 240 sec, are mostly in the region where the upstream crustal magnetic field strength is larger than the other events. Using the shape and size of the flux ropes obtained from the GS reconstruction technique, we are able to calculate lower limits on their volume and the potential ion escape rates. The volumes can vary by factors of 2--3 orders of magnitude. Ion escape rates via the flux ropes based on the GS reconstruction technique turn out to attain to the order of 10^22 -- 10^23 ion/sec. This result could be comparable to the global ion escape rate obtained from the ion mass analyzer onboard the Mars Express orbiter at solar minimum [e.g., Barabash et al., 2007].

  6. Magnetic flux emergence from the convective zone into the solar atmosphere

    NASA Astrophysics Data System (ADS)

    Title, Alan

    2012-07-01

    The flight of the Solar Dynamics Observatory (SDO) with its three instruments the Atmospheric Imaging Assembly (AIA), the Helioseismic and Magnetic Imager (HMI), and the Extreme ultraviolet Variability Experiment (EVE) has started a revolution in our understanding the role of flux emergence on the heating and stability of the solar atmosphere. Because the imaging instruments, AIA and HM, operate 24/7 and take data at high temporal cadence and high spatial resolution over the entire Sun, there now exists a data set that can track the magnetic field from the solar convection zone to its appearance on the solar surface and then follow the consequences of the emergence on the outer atmosphere. EVE provides a major contribution with a second by second recording of the solar irradiance in the EUV with high spectral resolution. The complete data allows determination of the rate that the atmosphere is heating and cooling in different temperature domains.. The breath and completeness of the data sets that these three instruments produce provides modelers exciting new challenges. Supercomputers are now beginning to produce increasingly convincing simulations of both flux emergence and the associated heating processes in the outer atmosphere. Movies of many of the effects of emerging solar fields with be presented.

  7. Three-dimensional magnetic flux rope structure formed by multiple sequential X-line reconnection at the magnetopause

    NASA Astrophysics Data System (ADS)

    Zhong, J.; Pu, Z. Y.; Dunlop, M. W.; Bogdanova, Y. V.; Wang, X. G.; Xiao, C. J.; Guo, R. L.; Hasegawa, H.; Raeder, J.; Zhou, X. Z.; Angelopoulos, V.; Zong, Q. G.; Fu, S. Y.; Xie, L.; Taylor, M. G. G. T.; Shen, C.; Berchem, J.; Zhang, Q. H.; Volwerk, M.; Eastwood, J. P.

    2013-05-01

    On 14 June 2007, four Time History of Events and Macroscale Interactions during Substorms spacecraft observed a flux transfer event (FTE) on the dayside magnetopause, which has been previously proved to be generated by multiple, sequential X-line reconnection (MSXR) in a 2-D context. This paper reports a further study of the MSXR event to show the 3-D viewpoint based on additional measurements. The 3-D structure of the FTE flux rope across the magnetospheric boundary is obtained on the basis of multipoint measurements taken on both sides of the magnetopause. The flux rope's azimuthally extended section is found to lie approximately on the magnetopause surface and parallel to the X-line direction; while the axis of the magnetospheric branch is essentially along the local unperturbed magnetospheric field lines. In the central region of the flux rope, as distinct from the traditional viewpoint, we find from the electron distributions that two types of magnetic field topology coexist: opened magnetic field lines connecting the magnetosphere and the magnetosheath and closed field lines connecting the Southern and Northern hemispheres. We confirm, therefore, for the first time, the characteristic feature of the 3-D reconnected magnetic flux rope, formed through MSXR, through a determination of the field topology and the plasma distributions within the flux rope. Knowledge of the complex geometry of FTE flux ropes will improve our understanding of solar wind-magnetosphere interaction.

  8. A study on the radiation damage and recovery of neutron irradiated vessel steel using magnetic Barkhausen noise

    NASA Astrophysics Data System (ADS)

    Park, Duck-Gun; Jeong, Hee-Tae; Hong, Jun-Hwa

    1999-04-01

    The radiation damage and thermal recovery characteristic of neutron irradiated SA508-3 reactor pressure vessel steel specimens have been investigated. Two recovery stages were identified from the results of hardness measurements during isochronal annealing and the mechanism responsible for the two stages was explained by using the results of Barkhausen noise measurement on the basis of the interaction between radiation induced defects and the magnetic domain wall. The coercivity was not changed by neutron irradiation, whereas the maximum magnetic induction increased. Barkhausen noise parameters associated with the domain wall motion were decreased by neutron irradiation and recovered with subsequent heat treatments.

  9. Shipboard magnetic field "noise" reveals shallow heavy mineral sediment concentrations in Chesapeake Bay

    USGS Publications Warehouse

    Shah, Anjana K.; Vogt, Peter R.; Rosenbaum, Joseph G.; Newell, Wayne; Cronin, Thomas M.; Willard, Debra A.; Hagen, Rick A.; Brozena, John; Hofstra, Albert

    2012-01-01

    Shipboard magnetic field data collected over Chesapeake Bay exhibit low-amplitude, short-wavelength anomalies that most likely indicate shallow concentrations of heavy mineral sediments. Piston core layers and black sand beach samples exhibit enhanced magnetic susceptibilities and carry remanent magnetization, with mineralogical analyses indicating ilmenite and trace magnetite and/or maghemite and hematite. The anomalies are subtle and would be filtered as noise using traditional approaches, but can instead be highlighted using spectral methods, thus providing nearly continuous coverage along survey tracks. The distribution of the anomalies provides constraints on relevant sorting mechanisms. Comparisons to sonar data and previous grab samples show that two of three areas surveyed exhibit short-wavelength anomalies that are clustered over sand-covered areas, suggesting initial sorting through settling mechanisms. This is supported by a correlation between core magnetic susceptibility and grain size. Near the Choptank River, where sediment resuspension is wave-dominated, anomalies show a sharp decrease with seafloor depth that cannot be explained by signal attenuation alone. In Pocomoke Sound, where both tidal currents and wave-action impact sediment resuspension, anomalies show a more gradual decrease with depth. Near the mouth of the bay, where there is a higher influx of sediments from the continental shelf, short-wavelength anomalies are isolated and do not appear to represent heavy mineral sand concentrations. These combined observations suggest the importance of further sorting by erosional processes in certain parts of the bay. Additionally, comparisons of these data to cores sampling pre-Holocene sediments suggest that the sorting of heavy minerals in higher energy, shallow water environments provides a mechanism for correlations between core magnetic susceptibility and sea-level changes.

  10. Stopping frequency of type III solar radio bursts in expanding magnetic flux tubes

    NASA Astrophysics Data System (ADS)

    Reid, Hamish A. S.; Kontar, Eduard P.

    2015-05-01

    Aims: Understanding the properties of type III radio bursts in the solar corona and interplanetary space is one of the best ways to remotely deduce the characteristics of solar accelerated electron beams and the solar wind plasma. One feature of all type III bursts is the lowest frequency they reach (or stopping frequency). This feature reflects the distance from the Sun that an electron beam can drive the observable plasma emission mechanism. The stopping frequency has never been systematically studied before from a theoretical perspective. Methods: Using numerical kinetic simulations, we explore the different parameters that dictate how far an electron beam can travel before it stops inducing a significant level of Langmuir waves, responsible for plasma radio emission. We use the quasilinear approach to model the resonant interaction between electrons and Langmuir waves self-consistently in inhomogeneous plasma, and take into consideration the expansion of the guiding magnetic flux tube and the turbulent density of the interplanetary medium. Results: We find that the rate of radial expansion has a significant effect on the distance an electron beam travels before enhanced levels of Langmuir waves, hence radio waves, cease. Radial expansion of the guiding magnetic flux tube rarefies the electron stream to the extent that the density of non-thermal electrons is too low to drive Langmuir wave production. The initial conditions of the electron beam have a significant effect, where decreasing the beam density or increasing the spectral index of injected electrons would cause higher type III stopping frequencies. We also demonstrate how the intensity of large-scale density fluctuations increases the highest frequency to which Langmuir waves can be driven by the beam and how the magnetic field geometry can be the cause of type III bursts that are only observed at high coronal frequencies.

  11. Ion flux from vacuum arc cathode spots in the absence and presence of a magnetic field

    SciTech Connect

    Anders, Andre; Yushkov, George Yu.

    2001-10-02

    Because plasma production at vacuum cathode spots is approximately proportional to the arc current, arc current modulation can be used to generate ion current modulation that can be detected far from the spot using a negatively biased ion collector. The drift time to the ion detector can used to determine kinetic ion energies. A very wide range of cathode materials have been used. It has been found that the kinetic ion energy is higher at the beginning of each discharge and approximately constant after 150 {micro}s. The kinetic energy is correlated with the arc voltage and the cohesive energy of the cathode material. The ion erosion rate has in inverse relation to the cohesive energy, enhancing the effect that the power input per plasma particle correlates with the cohesive energy of the cathode material. The influence of three magnetic field configurations on the kinetic energy has been investigated. Generally, a magnetic field increases the plasma impedance, arc burning voltage, and kinetic ion energy. However, if the plasma is produced in a region of low field strength and streaming into a region of higher field strength, the velocity may decrease due to the mirror effect. A magnetic field can increase the plasma temperature but may reduce the density gradients by preventing free expansion into vacuum. Therefore, depending on the configuration, a magnetic field may increase or decrease the kinetic energy of ions. Additionally, the angular distribution of the ion flux and ion kinetic energy has been investigated in the absence of an external magnetic field. The result can be fitted by a superposition of an isotropic and a cosine distribution.

  12. Low-noise pulsed pre-polarization magnet system for ultra-low field NMR

    SciTech Connect

    Sims, James R [Los Alamos National Laboratory; Schilling, Josef B [Los Alamos National Laboratory; Swenson, Charles A [Los Alamos National Laboratory; Gardner, David L [Los Alamos National Laboratory; Matlashov, Andrei N [Los Alamos National Laboratory; Ammerman, Curti N [Los Alamos National Laboratory

    2009-01-01

    A liquid cooled, pulsed electromagnet of solenoid configuration suitable for duty in an ultra-low field nuclear magnetic resonance system has been designed, fabricated and successfully operated. The magnet design minimizes Johnson noise, minimizes the hydrogen signal and incorporates minimal metal and no ferromagnetic materials. In addition, an acoustically quiet cooling system permitting 50% duty cycle operation was achieved by designing for single-phase, laminar flow, forced convection cooling. Winding, conductor splicing and epoxy impregnation techniques were successfully developed to produce a coil winding body with integral cooling passageways and adequate structural integrity. Issues of material compatibility, housing, coolant flow system and heat rejection system design will be discussed. Additionally, this pulsed electromagnet design has been extended to produce a boiling liquid cooled version in a paired solenoid configuration suitable for duty in an ultra-low field nuclear magnetic resonance system. This pair of liquid nitrogen cooled coils is currently being tested and commissioned. Issues of material compatibility, thermal insulation, thermal contraction, housing and coolant flow design are discussed.

  13. Influence of applied magnetic field strength and frequency response of pick-up coil on the magnetic barkhausen noise profile

    NASA Astrophysics Data System (ADS)

    Vashista, M.; Moorthy, V.

    2013-11-01

    The influence of applied magnetic field strength and frequency response of the pick-up coil on the shape of Magnetic Barkhausen Noise (MBN) profile have been studied. The low frequency MBN measurements have been carried out using 5 different MBN pick-up coils at two different ranges of applied magnetic field strengths on quenched and tempered (QT) and case-carburised and tempered (CT) 18CrNiMo7 steel bar samples. The MBN pick-up coils have been designed to obtain different frequency response such that the peak frequency response varies from ˜4 kHz to ˜32 kHz and the amplitude of low frequency signals decreases gradually. At lower applied magnetic field strength of ±14,000 A/m, all the pick-up coils produced a single peak MBN profile for both QT and CT sample. However, at higher applied magnetic field strength of ±22,000 A/m, the MBN profile showed two peaks for both QT and CT samples for pick-up coils with peak frequency response up to ˜17 kHz. Also, there is systematic reduction in peak 2 for QT sample and asymmetric reduction in the heights of peak 1 and peak 2 for CT sample with increase in peak frequency response of the pick-up coils. The decreasing sensitivity of pick-up coils with increasing peak frequency response to MBN signal generation is indicated by the gradual reduction in width of MBN profile and height of peak 2 in the QT sample. The drastic reduction in peak 1 as compared to peak 2 in the CT sample shows the effect of decreasing low frequency response of the pick-up coils on lowering skin-depth of MBN signal detection. This study clearly suggests that it is essential to optimise both maximum applied magnetic field strength and frequency response of the MBN pick-up coil for maximising the shape of the MBN profile for appropriate correlation with the magnetisation process and hence the material properties.

  14. Magnetic Flux-Trapping of Anisotropic-Grown Y-Ba-Cu-O Bulk Superconductors during and after Pulsed-Field Magnetizing Processes

    NASA Astrophysics Data System (ADS)

    Oka, T.; Yamada, Y.; Horiuchi, T.; Ogawa, J.; Fukui, S.; Sato, T.; Yokoyama, K.; Langer, M.

    2014-05-01

    The magnetic flux penetration into the melt-textured Y-Ba-Cu-O high temperature superconducting bulk magnets were precisely evaluated during and after the pulsed field magnetization processes operated at 30 K. The bulk magnets were carefully fabricated by the cold seeding method with use of a single and a pair of seed crystals composed of the Nd-Ba-Cu-O thin films. These seed crystals were put on the top surfaces of the precursors to let the large grains grow during the heat treatments. We observed the flux penetrations which occurred in the lower applied-field regions at around 3.1 T for the samples bearing the twin seeds than those of the single-seeded crystals at around 3.8 T. This means that the magnetic fluxes are capable of invading into the twin-seeded samples more easily than the single-seeds. It suggests that the anisotropic grain growths of parallel and normal to the rows of seed crystals affects the variations of Jc values with different distributions of the pinning centers, results in the preferential paths for the invading magnetic fluxes.

  15. Magnetic twin boundaries and flux pinning in the antiferromagnetic superconductor ErNi2B2C R. Surdeanu,2

    E-print Network

    Wijngaarden, Rinke J.

    Magnetic twin boundaries and flux pinning in the antiferromagnetic superconductor ErNi2B2C N. Saha that in the antiferromagnetic superconductor ErNi2B2C, the increase in flux pinning below TN coincides with the appearance of antiferromagnetic super- conductors has made a remarkable revival since the discov- ery of the (R)Ni2B2C, where R

  16. Disintegration of Magnetic Flux in Decaying Sunspots as Observed with the Hinode/SOT

    NASA Astrophysics Data System (ADS)

    Kubo, M.; Lites, B. W.; Ichimoto, K.; Shimizu, T.; Suematsu, Y.; Katsukawa, Y.; Tarbell, T. D.; Shine, R. A.; Title, A. M.; Nagata, S.; Tsuneta, S.

    2008-05-01

    Continuous observations of sunspot penumbrae with the Solar Optical Telescope aboard Hinode clearly show that the outer boundary of the penumbra fluctuates around its averaged position. The penumbral outer boundary moves inward when granules appear in the outer penumbra. We discover that such granules appear one after another while moving magnetic features (MMFs) are separating from the penumbral "spines" (penumbral features having fields that are stronger and more vertical than their surroundings). These granules that appear in the outer penumbra often merge with bright features inside the penumbra that move with spines as they elongate toward the moat region. This suggests that convective motions around the penumbral outer boundary are related to disintegration of magnetic flux in the sunspot. We also find that dark penumbral filaments frequently elongate into the moat region in the vicinity of MMFs that detach from penumbral spines. Such elongating dark penumbral filaments correspond to nearly horizontal fields extending from the penumbra. Pairs of MMFs with positive and negative polarities are sometimes observed along the elongating dark penumbral filaments. This strongly supports the notion that such elongating dark penumbral filaments have magnetic fields with a "sea serpent"-like structure. Evershed flows, which are associated with the penumbral horizontal fields, may be related to detachment of the MMFs from the penumbral spines, as well as to the formation of the MMFs along the dark penumbral filaments that elongate into the moat region.

  17. Disintegration of Magnetic Flux in Decaying Sunspots as Observed with the Hinode SOT

    NASA Astrophysics Data System (ADS)

    Kubo, M.; Lites, B. W.; Ichimoto, K.; Shimizu, T.; Suematsu, Y.; Katsukawa, Y.; Tarbell, T. D.; Shine, R. A.; Title, A. M.; Nagata, S.; Tsuneta, S.

    2008-07-01

    Continuous observations of sunspot penumbrae with the Solar Optical Telescope aboard Hinode clearly show that the outer boundary of the penumbra fluctuates around its averaged position. The penumbral outer boundary moves inward when granules appear in the outer penumbra. We discover that such granules appear one after another while moving magnetic features (MMFs) are separating from the penumbral ``spines'' (penumbral features that have fields that are stronger and more vertical than those of their surroundings). These granules that appear in the outer penumbra often merge with bright features inside the penumbra that move with the spines as they elongate toward the moat region. This suggests that convective motions around the penumbral outer boundary are related to the disintegration of magnetic flux in the sunspot. We also find that dark penumbral filaments frequently elongate into the moat region in the vicinity of MMFs that detach from penumbral spines. Such elongating dark penumbral filaments correspond to nearly horizontal fields extending from the penumbra. Pairs of MMFs with positive and negative polarities are sometimes observed along the elongating dark penumbral filaments. This strongly supports the notion that such elongating dark penumbral filaments have magnetic fields with a ``sea serpent''-like structure. Evershed flows, which are associated with the penumbral horizontal fields, may be related to the detachment of the MMFs from the penumbral spines, as well as to the formation of the MMFs along the dark penumbral filaments that elongate into the moat region.

  18. Low-noise microwave oven magnetrons with fast start-oscillation by azimuthally varying axial magnetic fields

    Microsoft Academic Search

    V. Bogdan Neculaes; Ronald M. Gilgenbach; Yue Ying Lau; Michael C. Jones; William M. White

    2004-01-01

    A technique has been proven to significantly reduce the noise and to hasten the startup in microwave signals from dc operating oven magnetrons. The technique is based on imposition of an azimuthally varying axial magnetic field in magnetrons. For an N-cavity magnetron operating in pi-mode, the optimal number of periods of azimuthal variations in the axial magnetic field is N\\/2.

  19. Signal-to-noise ratio mismatch for low-density parity-check coded magnetic recording channels

    Microsoft Academic Search

    Weijun Tan; J. R. Cruz

    2004-01-01

    Signal-to-noise ratio (SNR) mismatch is found in simulations to have great influence on the performance of low-density parity-check coded magnetic recording channels. While an inappropriate SNR mismatch degrades the performance dramatically, a properly selected optimum SNR mismatch can improve it significantly. In this paper we analyze the causes of this phenomenon and find optimum SNR mismatch values for specific magnetic

  20. Microstructural dependence of Barkhausen noise and magnetic relaxation in the weld HAZ of an RPV steel

    NASA Astrophysics Data System (ADS)

    Park, Duck-Gun; Kim, Cheol Gi; Hong, Jun-Hwa

    2000-06-01

    Magnetic Barkhausen noise and permeability spectra have been measured to characterize different microstructure regions such as coarse-grain region, fine-grain region, intercritical structure (composed of tempered martensite and bainite) within the heat-affected zone (HAZ) of SA508-3 steel weldments using simulated HAZ microstructure sample. The intercritical region and coarse-grained region can be distinguished from the BNE and relaxation frequency. The BNE was decreased in the martensite regions and increased in the bainite regions by the post-weld heat treatment (PWHT). The change of relaxation frequency also showed similar trends, but the rate of change was less than that of BNE. The behavior of BNE and permeability spectra on the corresponding microstructure can be explained in terms of carbide morphology and residual stress related with domain wall motion.