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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, lnω, ω-1/2, and ω-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. Magnetic flux noise in copper oxide superconductors

    SciTech Connect

    Ferrari, M.J.

    1991-11-01

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

  3. Magnetic flux noise in dc SQUIDs: temperature and geometry dependence.

    PubMed

    Anton, S M; Birenbaum, J S; O'Kelley, S R; Bolkhovsky, V; Braje, D A; Fitch, G; Neeley, M; Hilton, G C; Cho, H-M; Irwin, K D; Wellstood, F C; Oliver, W D; Shnirman, A; Clarke, John

    2013-04-01

    The spectral density S(Φ)(f) = A(2)/(f/1 Hz)(α) of magnetic flux noise in ten dc superconducting quantum interference devices (SQUIDs) with systematically varied geometries shows that α increases as the temperature is lowered; in so doing, each spectrum pivots about a nearly constant frequency. The mean-square flux noise, inferred by integrating the power spectra, grows rapidly with temperature and at a given temperature is approximately independent of the outer dimension of a given SQUID. These results are incompatible with a model based on the random reversal of independent, surface spins. PMID:25167026

  4. 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.

  5. Measurement of the Magnetic Flux Noise Spectrum in Superconducting Xmon Transmon Quantum Bits

    NASA Astrophysics Data System (ADS)

    Chiaro, Ben; Sank, D.; Kelly, J.; Chen, Z.; Campbell, B.; Dunsworth, A.; O'Malley, P.; Neill, C.; Quintana, C.; Vainsencher, A.; Wenner, J.; Barends, R.; Chen, Y.; Fowler, A.; Jeffrey, E.; Migrant, A.; Mutus, J.; Roushan, P.; White, T.; Martinis, J. M.

    Dephasing induced by magnetic flux noise limits the performance of modern superconducting quantum processors. We measure the flux noise power spectrum in planar, frequency-tunable, Xmon transmon quantum bits (qubits), with several SQUID loop geometries. We extend the Ramsey Tomography Oscilloscope (RTO) technique by rapid sampling up to 1 MHz, without state reset, to measure the flux noise power spectrum between 10-2 and 105 Hz. The RTO measurements are combined with idle gate randomized benchmarking and Ramsey decay to give a more complete picture of dephasing in SQUID-based devices.

  6. 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.

  7. Suppression of magnetic flux noise in YBa sub 2 Cu sub 3 O sub 7-x flux transformers

    SciTech Connect

    Ferrari, M.; Wellstood, F.C.; Kingston, J.J.; Johnson, M.; Clarke, J.

    1991-08-01

    We have constructed hybrid magnetometers by coupling a flux transformer of YBa{sub 2}Cu{sub 3}O{sub 7-x} to a Nb-PbIn SQUID. The low frequency (1/f) noise is dominated by fluctuations in the supercurrent circulating in the transformer, driven by vortex motion. The application of a small static magnetic field induces a supercurrent that reversibly suppresses the noise, in quantitative agreement with a model of thermally activated vortex hopping between symmetrical pairs of pinning sites. A persistent current can be used to reduce the low frequency noise power of high-{Tc} flux transformers by at least one order of magnitude. 11 refs., 4 figs., 1 tab.

  8. Suppression of magnetic flux noise in YBa{sub 2}Cu{sub 3}O{sub 7-x} flux transformers

    SciTech Connect

    Ferrari, M.; Wellstood, F.C.; Kingston, J.J.; Johnson, M.; Clarke, J.

    1991-08-01

    We have constructed hybrid magnetometers by coupling a flux transformer of YBa{sub 2}Cu{sub 3}O{sub 7-x} to a Nb-PbIn SQUID. The low frequency (1/f) noise is dominated by fluctuations in the supercurrent circulating in the transformer, driven by vortex motion. The application of a small static magnetic field induces a supercurrent that reversibly suppresses the noise, in quantitative agreement with a model of thermally activated vortex hopping between symmetrical pairs of pinning sites. A persistent current can be used to reduce the low frequency noise power of high-{Tc} flux transformers by at least one order of magnitude. 11 refs., 4 figs., 1 tab.

  9. Gamma-magnetic normalization - new effect to reduce flux-gate magnetometer noise level

    NASA Astrophysics Data System (ADS)

    Korepanov, V.

    2012-04-01

    It is the author's opinion confirmed by numerous experiments, that the FGM noise level (NL) is determined not by Barkhausen jumps during the core remagnetization from positive to negative state as the majority of designers believe, but by non-repeatability of the magnetic domains transition from negative to positive states and back. This shows the way how to reduce the magnetic noise: to manufacture the magnetic material with a structure which will create conditions for magnetic domain walls to glide easily and uniformly when changing their orientation leading to minimal efforts at cyclic remagnetization. Ideally, such a material may be represented as a solid "liquid" with freely floating uniform magnetic domains without walls friction. To reduce the specific NL of the materials, several post-melting processing technologies were developed. A set of experiments made by many investigators has shown that the best results gives the magnetic materials annealing in vacuum or in any inert gas applying by this during all annealing time the alternative magnetic field, imitating core excitation field during FGM operation. If to accept the "solid liquid" model, this mechanism of NL decreasing has clear physical explanation: permanent re-magnetization of domains leads to the structural improvements favorable namely for the homogenization of transitions, rise of temperature gives necessary energy for the impurities liquidation. Probably, M. Acuna was the first who reported that during FGM operation in space its NL is decreasing with time and attributed this to the relaxation of mechanical stresses in the core material in weightlessness conditions [1]. We studied in details the conditions in which the core material is in space: weightlessness, vacuum and radiation. Mechanical stresses relaxation hypothesis was rejected because the internal forces in any solid body are much stronger as those to which a gravity force might have influence. Also the tests of FGM sensor in vacuum chamber both in operation and switched off conditions showed any influence of this parameter on NL. And radiation influence, the dose of which was selected approximately equal to yearly dose at near-Earth orbit (~10 krad), revealed interesting facts: the magnetic material itself and the FGM sensor in non-operation state showed any dependence on radiation, whereas this dose applied to the operating FGM sensor lead to the marked NL reducing. This new effect was named "gamma-magnetic normalization" and also can be explained by the accepted model: the mechanism is the same as above, but, because γ-quantum have much greater energy as thermal one, more "rigid" impurities are eliminated at γ-radiation action. The experimental results confirming this hypothesis are presented in the report. This work was partially supported by NASU Contract 1-71/11/1531. [1] Acuna M M, 2002. Space based magnetometers. Rev. Sci. Instr. 73(11) pp. 3717-36.

  10. Flux noise due to magnetic impurities in superconducting circuits: Optimal spin texture and role of phase transition

    NASA Astrophysics Data System (ADS)

    de Sousa, Rogério

    Superconducting quantum interference devices (SQUIDs) and other superconducting circuits are limited by intrinsic flux noise with spectral density 1 /fα with α < 1 whose origin is believed to be due to spin impurities. We present a theory of flux noise in the presence of phase transitions and arbitrary spin textures in the impurity spin system. At higher temperatures we find that the spin-spin correlation length scale (describing, e.g., the average size of ferromagnetic spin clusters) greatly impacts the scaling of flux noise with wire geometry. At lower temperatures we find that flux noise is quite sensitive to the particular spin texture realized by the spin system ground state. Remarkably, we show that flux-noise is exactly equal to zero when the spins form a poloidal texture. Flux noise is nonzero for other spin textures, but gets reduced in the presence of correlated ferromagnetic fluctuations between the top and bottom wire surfaces, where the flux vectors are antiparallel. This demonstrates the idea of engineering spin textures and/or intersurface correlation as a method to reduce flux noise in superconducting circuits. This research was supported by the Natural Sciences and Engineering Research Council of Canada (RGPIN/342982-2010, EGP/429649-2012) through its Discovery and Engage programs.

  11. Investigation of weldments in Victoria-class submarine pressure-hull using magnetic flux leakage and Barkhausen noise

    NASA Astrophysics Data System (ADS)

    Samimi, A. A.; Babbar, V.; Krause, T. W.; Clapham, L.

    2014-02-01

    Evaluation of the stress state within submarine hulls can contribute to risk assessments, which provide assurance that in-service induced stresses will not adversely affect the service life of the naval structure. The purpose of this study was to evaluate the feasibility of using magnetic NDE techniques for identification of stresses associated with weldments in two original pressure hulls of Canada's Victoria class submarines. Magnetic Flux Leakage (MFL) and flux-controlled Barkhausen Noise measurements were investigated for identification of patch boundaries and welds in two sections of Victoria-class submarine-hull steel. While MFL showed clear demarcation of weld boundaries, Barkhausen measurements did not provide sufficiently clear response to identify these features in submarine hull samples. For a better understanding of Barkhausen response, uniaxial tensile stress was investigated on separate samples of submarine steel. A nonlinear dependence of Barkhausen response was observed, with a weaker sensitivity to tensile stresses below 200 MPa. This behavior, combined with the presence of substantial surface compressive stresses, was used to explain the observed insensitivity of Barkhausen measurements to the presence of welds.

  12. Candidate Source of Flux Noise in SQUIDs: Adsorbed Oxygen Molecules

    NASA Astrophysics Data System (ADS)

    Wang, Hui; Shi, Chuntai; Hu, Jun; Han, Sungho; Yu, Clare C.; Wu, R. Q.

    2015-08-01

    A major obstacle to using superconducting quantum interference devices (SQUIDs) as qubits is flux noise. We propose that the heretofore mysterious spins producing flux noise could be O2 molecules adsorbed on the surface. Using density functional theory calculations, we find that an O2 molecule adsorbed on an α-alumina surface has a magnetic moment of ˜1.8 μB . The spin is oriented perpendicular to the axis of the O-O bond, the barrier to spin rotations is about 10 mK. Monte Carlo simulations of ferromagnetically coupled, anisotropic X Y spins on a square lattice find 1 /f magnetization noise, consistent with flux noise in Al SQUIDs.

  13. Solar Magnetic Flux Ropes

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  14. Flux Compression Magnetic Nozzle

    NASA Technical Reports Server (NTRS)

    Thio, Y. C. Francis; Schafer, Charles (Technical Monitor)

    2001-01-01

    In pulsed fusion propulsion schemes in which the fusion energy creates a radially expanding plasma, a magnetic nozzle is required to redirect the radially diverging flow of the expanding fusion plasma into a rearward axial flow, thereby producing a forward axial impulse to the vehicle. In a highly electrically conducting plasma, the presence of a magnetic field B in the plasma creates a pressure B(exp 2)/2(mu) in the plasma, the magnetic pressure. A gradient in the magnetic pressure can be used to decelerate the plasma traveling in the direction of increasing magnetic field, or to accelerate a plasma from rest in the direction of decreasing magnetic pressure. In principle, ignoring dissipative processes, it is possible to design magnetic configurations to produce an 'elastic' deflection of a plasma beam. In particular, it is conceivable that, by an appropriate arrangement of a set of coils, a good approximation to a parabolic 'magnetic mirror' may be formed, such that a beam of charged particles emanating from the focal point of the parabolic mirror would be reflected by the mirror to travel axially away from the mirror. The degree to which this may be accomplished depends on the degree of control one has over the flux surface of the magnetic field, which changes as a result of its interaction with a moving plasma.

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

    NASA Technical Reports Server (NTRS)

    Groom, Nelson J. (Inventor)

    1991-01-01

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

  16. Fast Flux Test Facility noise data management

    SciTech Connect

    Not Available

    1987-01-01

    An extensive collection of spectra from an automated data collection system at the Fast Flux Test Facility has features from neutron data extracted and managed by database software. Inquiry techniques, including screening, applied to database results show the influences of control rods on wideband noise and, more generally, abilities to detect diverse types of off-normal noise. Uncovering a temporary 0.1-Hz resonance shift gave additional diagnostic information on a 13-Hz mechanical motion characterized by the interference of two resonances. The latter phenomenon is discussed generically for possible application to other reactor types.

  17. Fast Ion Transport by Magnetic Flux Ropes

    NASA Astrophysics Data System (ADS)

    Preiwisch, Adam; Heidbrink, William; Boehmer, Heinrich; McWilliams, Roger; Carter, Troy; Gekelman, Walter; Tripathi, Shreekrishna; Compernolle, Bart; Vincena, Steven

    2014-10-01

    Energetic Lithium test ions (500 <= Efast/Ti <= 1000) are launched in a Helium plasma in the presence of current-produced magnetic flux ropes at the upgraded Large Plasma Device (LAPD) at UCLA. Perturbing flux ropes are introduced via a hot, biased LaB6 cathode in the main chamber. Ion beam broadening up to fifty percent above background levels is observed in the radial direction after passing through the flux rope region (Te,max = 7 eV, Bperp = 7G, ?V = 160 V). Density, temperature, and magnetic fluctuation profiles are also obtained. A noise model has been developed to assess the quality of ion signals during the flux rope discharge period. The enhancement to transport may be a result of increased Coulomb scattering, magnetic fluctuations, or electric fields. Further analysis to determine the primary mechanism is ongoing.

  18. Magnetic balltracking: Tracking the photospheric magnetic flux

    NASA Astrophysics Data System (ADS)

    Attie, R.; Innes, D. E.

    2015-02-01

    Context. One aspect of understanding the dynamics of the quiet Sun is to quantify the evolution of the flux within small-scale magnetic features. These features are routinely observed in the quiet photosphere and were given various names, such as pores, knots, magnetic patches. Aims: This work presents a new algorithm for tracking the evolution of the broad variety of small-scale magnetic features in the photosphere, with a precision equal to the instrumental resolution. Methods: We have developed a new technique to track the evolution of the individual magnetic features from magnetograms, called "magnetic balltracking". It quantifies the flux of the tracked features, and it can track the footpoints of magnetic field lines inferred from magnetic field extrapolation. The algorithm can detect and quantify flux emergence, as well as flux cancellation. Results: The capabilities of magnetic balltracking are demonstrated with the detection and the tracking of two cases of magnetic flux emergence that lead to the brightening of X-ray loops. The maximum emerged flux ranges from 1018 Mx to 1019 Mx (unsigned flux) when the X-ray loops are observed. Movies associated to Figs. 6 and 18 are available in electronic form at http://www.aanda.org

  19. Magnetic Flux and Helicity of Magnetic Clouds

    NASA Astrophysics Data System (ADS)

    Démoulin, P.; Janvier, M.; Dasso, S.

    2016-02-01

    Magnetic clouds (MCs) are formed by flux ropes (FRs) launched from the Sun as part of coronal mass ejections (CMEs). They carry away a large amount of magnetic flux and helicity. The main aim of this study is to quantify these amounts from in situ measurements of MCs at 1 AU. The fit of these data by a local FR model provides the axial magnetic field strength, the radius, the magnetic flux, and the helicity per unit length along the FR axis. We show that these quantities are statistically independent of the position along the FR axis. We then derive the generic shape and length of the FR axis from two sets of MCs. These results improve the estimation of magnetic helicity. Next, we evaluate the total magnetic flux and helicity that cross the sphere of radius of 1 AU, centred at the Sun, per year and during a solar cycle. We also include in the study two sets of small FRs that do not have all the typical characteristics of MCs. While small FRs are at least ten times more numerous than MCs, the magnetic flux and helicity are dominated by the contribution from the larger MCs. In one year they carry away the magnetic flux of about 25 large active regions and the magnetic helicity of 200 of them. MCs carry away an amount of unsigned magnetic helicity similar to the amount estimated for the solar dynamo and that measured in emerging active regions.

  20. Magnetic Flux and Helicity of Magnetic Clouds

    NASA Astrophysics Data System (ADS)

    Démoulin, P.; Janvier, M.; Dasso, S.

    2015-12-01

    Magnetic clouds (MCs) are formed by flux ropes (FRs) launched from the Sun as part of coronal mass ejections (CMEs). They carry away a large amount of magnetic flux and helicity. The main aim of this study is to quantify these amounts from in situ measurements of MCs at 1 AU. The fit of these data by a local FR model provides the axial magnetic field strength, the radius, the magnetic flux, and the helicity per unit length along the FR axis. We show that these quantities are statistically independent of the position along the FR axis. We then derive the generic shape and length of the FR axis from two sets of MCs. These results improve the estimation of magnetic helicity. Next, we evaluate the total magnetic flux and helicity that cross the sphere of radius of 1 AU, centred at the Sun, per year and during a solar cycle. We also include in the study two sets of small FRs that do not have all the typical characteristics of MCs. While small FRs are at least ten times more numerous than MCs, the magnetic flux and helicity are dominated by the contribution from the larger MCs. In one year they carry away the magnetic flux of about 25 large active regions and the magnetic helicity of 200 of them. MCs carry away an amount of unsigned magnetic helicity similar to the amount estimated for the solar dynamo and that measured in emerging active regions.

  1. Magnetic noise from Kondo charge traps (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Dias da Silva, Luis G.; de Sousa, Rogério

    2015-09-01

    Magnetic noise impacts a wide variety of solid-state devices, from quantum bits in superconductor and semiconductor-based quantum computer architectures to spintronic devices made of metals and semiconductors. Developing a theory of magnetic noise will have great impact in minimizing fluctuations in these devices. Magnetic noise is commonly detected as flux noise in superconducting quantum interference devices (SQUIDs). At low frequencies, SQUID flux noise spectral density decreases with frequency as 1/f^{α} with α=0.5-0.8 in a wide variety of devices. However, at higher frequencies (above 1 GHZ) flux noise was found to be Ohmic, i.e. increasing linearly with frequency. This puzzling behavior is not explained by any model of magnetic fluctuations. Here we present a theory for the magnetic noise produced by local charge traps, elucidating the kind of noise that the majority of defects produce in a typical solid-state device. Our numerical renormalization group calculations reveal a deviation from 1/f behavior in the magnetic noise of charge traps in the Kondo regime over a wide range of frequencies. Remarkably, such behavior is not present in the charge noise, which is dominated by single-particle processes, consistent with a mean-field picture. The results show that, when Kondo correlations are present, magnetic noise originating from charge traps has a many-particle character, while charge noise does not. Since Kondo temperatures can be relatively high in charge traps, these findings indicate that electron-electron interactions can lead to a strong contribution to the magnetic noise that has not been captured by current models.

  2. 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.

  3. 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.

  4. 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 μB. 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).

  5. Imaging magnetic noise sources in magnetic recording heads (Invited Paper)

    NASA Astrophysics Data System (ADS)

    Yuan, Lu; Shen, Jian-Xiang; Pant, Bharat B.; Liou, Sy-Hwang

    2005-05-01

    A detailed understanding of noise characteristics is essential for the design of a high signal-to-noise ratio (SNR) reader sensor. We intend to correlate the microstructure to the source of magnetic noises for improving the magnetic stability of the recording heads. A dynamic magnetic sensitivity mapping (MSM) system is designed to image the magnetic noise sources in sub-micrometer sized recording heads. A nanometer sized magnetic force microscopy (MFM) tip was used to apply a well-defined, localized magnetic field on the air bearing surface (ABS) of the head. For a certain area position of the free layer with incoherent rotation of the magnetic moment, this localized magnetic field will cause magnetic instability in the head, and this instability will show up as electrical noise on the output signal. Because most of the noise related to magnetic domain fluctuation is dominated at the low frequency region, our study concentrates on the spatial characterization of the noise source in a frequency range of 20 kHz to 60 kHz. Recording the average amplitude of the noise spectrum due to the excitation in the measured frequency range as a function of the tip's position, the location of the magnetic noise source can be identified. Magnetic noise images have been obtained by our system for some recording giant magnetoresistance (GMR) and tunnel magnetoresistance (TMR) recording heads. Noise MSM images of some unstable recording heads clearly show the spatially uneven noise.

  6. Noise and nonlinearities in digital magnetic recording systems

    NASA Astrophysics Data System (ADS)

    Xing, Xinzhi

    1998-11-01

    Various types of noise and nonlinearities in digital magnetic recording systems are investigated in this dissertation. Measurement techniques and analyzing methods are developed to understand each phenomenon. The nonlinearities due to the replay process using MR sensors are studied in Chapter 4. The nonlinearities are determined by comparing the measured signal with that obtained from a linear analysis. A characterization method of transition noise is developed in Chapter 5. Approximating transition noise by several leading 'modes' allows the noise parameters to be determined experimentally. Chapter 6 covers the investigation of disk substrate texture induced noise. The noise mechanism and characteristics are systematically studied. An analytical noise correlation function that directly relates the noise with the fluctuations of the textured disk surface is also developed in this chapter. An error rate model including colored and nonstationary noise is developed to further understand the impact of noise on system performance in Chapter 7. Noise with different characteristics is shown to influence the system performance differently. In addition, the influence of texture noise is examined in term of each noise parameter based upon the noise model developed in Chapter 6. Finally, in Chapter 8, the effect of finite write field rise time on recording performance is studied. Recording performance predicted by a simplified analytical model is compared with the measurements. It is shown that a slow flux rise time causes a degraded field gradient during writing, which results in a broader written transition, a larger NLTS, and noisier transition boundaries.

  7. Force sensor using changes in magnetic flux

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

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

  8. Measurement of Integrated Low Frequency Flux Noise in Superconducting Flux/Phase Qubits

    SciTech Connect

    Mao Bo; Qiu Wei; Han Siyuan

    2008-11-07

    We measured the integrated low frequency flux noise ({approx}1 m{phi}{sub 0}) of an rf SQUID as a flux qubit by fitting the resonant peaks from photon assistant tunneling (PAT). The energy relaxation time Tl between the ground and first excited states in the same potential well, measured directly in time domain, is 3 ns. From these results we identified low frequency flux noise as the dominant source of decoherence. In addition, we found that the measured values of integrated flux noise in three qubits of various sizes differ more than an order of magnitude.

  9. Chaos in Magnetic Flux Ropes

    NASA Astrophysics Data System (ADS)

    Gekelman, W. N.; DeHaas, T.; Van Compernolle, B.

    2013-12-01

    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 using correlation techniques. The permutation entropy1 ,which is related to the Lyapunov exponent, 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 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, Gissinger and Henon 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. The entropy and complexity change in space and time which reflects the change and possibly type of chaos associated with the ropes. The maps give insight as to the type of chaos (deterministic chaos, fractional diffusion , Levi flights..) and underlying dynamical process. The power spectra of much of the magnetic and flow data is exponential and Lorentzian structures in the time domain are embedded in them. Other quantities such as the Hurst exponent are evaluated for both magnetic fields and plasma flow. Work Supported by a UC-LANL Lab fund and the Basic Plasma Science Facility which is funded by DOE and NSF. 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, 55, 085015 (2013)

  10. Annihilation of Quantum Magnetic Fluxes

    NASA Astrophysics Data System (ADS)

    Gonzalez, W. D.

    After introducing the concepts associated with the Aharonov and Bohm effect and with the existence of a quantum of magnetic flux (QMF), we briefly discuss the Ginzburg-Landau theory that explains its origin and fundamental consequences. Also relevant observations of QMFs obtained in the laboratory using superconducting systems (vortices) are mentioned. Next, we describe processes related with the interaction of QMFs with opposite directions in terms of the gauge field geometry related to the vector potential. Then, we discuss the use of a Lagrangian density for a scalar field theory involving radiation in order to describe the annihilation of QMFs, claimed to be responsible for the emission of photons with energies corresponding to that of the annihilated magnetic fields. Finally, a possible application of these concepts to the observed variable dynamics of neutron stars is briefly mentioned.

  11. Flux qubit as a sensor of magnetic flux

    NASA Astrophysics Data System (ADS)

    Il'ichev, E.; Greenberg, Ya. S.

    2007-03-01

    A magnetometer based on the quantum properties of a superconducting flux qubit is proposed. The main advantage of this device is that its sensitivity can be below the so-called "standard quantum limit" (for an oscillator this is half of the Plank constant). Moreover its transfer functions relative to the measured flux can be made to be about 10 mV/Φ0, which is an order of magnitude more than the best value for a conventional DC SQUIDs with a direct readout. We analyze here the voltage-to-flux, the phase-to-flux transfer functions and the main noise sources. We show that the experimental characteristics of a flux qubit, obtained in recent experiments, allow the use of a flux qubit as magnetometer with energy resolution close to the Planck constant.

  12. 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)

  13. Flux emergence in a magnetized convection zone

    NASA Astrophysics Data System (ADS)

    Pinto, Rui; Brun, Allan Sacha

    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 and analysed the dynamical evolution of such buoyant flux-ropes from the bottom of the convection zone until the post-emergence phases. The actual flux-emergence episode is preceded by a localised increase of radial velocity, density and current density at the top of the convection zone. During the buoyant rise, the flux-rope's magnetic field strength and density scale as B~rho(alpha) , with alpha≤sssim 1. The properties of initial phases of the buoyant rise are determined essentially by the flux-rope's properties and the convective flows and are, in consequence, in good agreement with previous studies. However, the effects of the interaction of the background dynamo field become increasingly stronger as the flux-ropes evolve. The threshold for the initial magnetic field amplitude is slightly increased by the presence of the background dynamo field, even if it is on average much weaker than the flux-rope's field. The geometry and relative orientation of the magnetic field in the flux-ropes with respect to that in the background magnetic field influences the resulting rise speeds, zonal flows amplitudes (which develop within the flux-ropes) and surface signatures of magnetic flux emergence. This strongly influences the morphology, duration and amplitude of the surface shearing and Poynting flux associated with magnetic flux-rope emergence, which are key ingredients to the current coronal eruption triggering scenarios. The actual magnetic flux emergence is consistently preceded by strong and localised radial velocity enhancements at the place where the flux rope will emerge. The emerged magnetic flux is in most of the cases studied enough to influence the global surface magnetic field. In some cases, the emergence reinforces the system's global polarity reversal while in some others it inhibits the background dynamo from doing so. The fraction of magnetic flux which remains attached to the flux-rope is slowly spread out in latitude, diffused and assimilated by the background dynamo field.

  14. How the Saturnian Magnetosphere Conserves Magnetic Flux

    NASA Astrophysics Data System (ADS)

    Powell, R. L.; Wei, H.; Russell, C. T.; Arridge, C. S.; Dougherty, M. K.

    2012-12-01

    The magnetospheric dynamics at Saturn are driven by the centrifugal force of near co-rotating water group ions released at a rate of hundreds of kilograms per second by Saturn's moon Enceladus. The plasma is accelerated up to co-rotation speed by the magnetospheric magnetic field coupled to the Saturnian ionosphere. The plasma is lost ultimately through the process of magnetic reconnection in the tail. Conservation of magnetic flux requires that plasma-depleted, "empty" flux tubes return magnetic flux to the inner magnetosphere. After completion of the initial inrush of the reconnected and largely emptied flux tubes inward of the reconnection point, the flux tubes face the outflowing plasma and must move inward against the flow. Observations of such flux tubes have been identified in the eight years of Cassini magnetometer data. The occurrence of these tubes is observed at all local times indicating slow inward transport of the tubes relative to the co-rotation speed. Depleted flux tubes observed in the equatorial region appear as an enhancement in the magnitude of the magnetic field, whereas the same flux tubes observed at higher latitudes appear as decreased field strength. The difference in appearance of the low latitude and the high latitude tubes is due to the plasma environment just outside the tube. Warm low-density plasma fills the inside of the flux tube at all latitudes. This flux tube thus will expand in the less dense regions away from the magnetic equator and will be observed as a decrease in the magnitude of the magnetic field from the background. These flux tubes near the equator, where the plasma density outside of the flux tube is much greater, will be observed as an enhancement in the magnitude of the magnetic field. Cassini magnetometer and CAPS data are examined to understand the properties of these flux tubes and their radial and latitudinal evolution throughout the Saturnian magnetospheric environment.

  15. 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.

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

    SciTech Connect

    Yamamoto, Tetsuya T.; Kataoka, R.; Inoue, S.

    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.

  17. 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.

  18. Strongly magnetized accretion discs require poloidal flux

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  19. Microscopic analysis of low-frequency flux noise in YBa2Cu3O7 direct current superconducting quantum interference devices

    NASA Astrophysics Data System (ADS)

    Doenitz, D.; Straub, R.; Kleiner, R.; Koelle, D.

    2004-12-01

    We use low-temperature scanning electron microscopy combined with superconducting quantum interference device (SQUID) detection of magnetic flux to image vortices and to investigate low-frequency flux noise in YBa2Cu3O7 thin film SQUIDs. The low-frequency flux noise shows a nonlinear increase with magnetic cooling field up to 60μT. This effect is explained by the surface potential barrier at the SQUID hole. By correlating flux noise data with the spatial distribution of vortices, we obtain information on spatial fluctuations of vortices on a microscopic scale, e.g., an average vortex hopping length of ˜10nm.

  20. FLUX EMERGENCE IN A MAGNETIZED CONVECTION ZONE

    SciTech Connect

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

    2013-07-20

    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 B{proportional_to}{rho}{sup {alpha}}, with {alpha} {approx}< 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.

  1. 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 Bvpropρα, with α <~ 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.

  2. Magnetic flux tubes and the dynamo problem

    NASA Astrophysics Data System (ADS)

    Schssler, Manfred; Ferriz-Mas, Antonio

    The observed properties of the magnetic field in the solar photosphere and theoretical studies of magneto-convection in electrically well-conducting fluids suggest that the magnetic field in stellar convection zones is quite inhomogeneous: magnetic flux is concentrated into magnetic flux tubes embedded in significantly less magnetized plasma. Such a state of the magnetic field potentially has strong implications for stellar dynamo theory since the dynamics of an ensemble of flux tubes is rather different from that of a more uniform field and new phenomena like magnetic buoyancy appear. If the diameter of a magnetic flux tube is much smaller than any other relevant length scale, the MHD equations governing its evolution can be considerably simplified in terms of the thin-flux-tube approximation. Studies of thin flux tubes in comparison with observed properties of sunspot groups have led to far-reaching conclusions about the nature of the dynamo-generated magnetic field in the solar interior. The storage of magnetic flux for periods comparable to the amplification time of the dynamo requires the compensation of magnetic buoyancy by a stably stratified medium, a situation realized in a layer of overshooting convection at the bottom of the convection zone. Flux tubes stored in mechanical force equilibrium in this layer become unstable with respect to an undular instability once a critical field strength is exceeded, flux loops rise through the convection zone and erupt as bipolar magnetic regions at the surface. For parameter values relevant for the solar case, the critical field strength is of the order of 105 G. A field of similar strength is also required to prevent the rising unstable flux loops from being strongly deflected poleward by the action of the Coriolis force and also from `exploding' in the middle of the convection zone. The latter process is caused by the superadiabatic stratification. The magnetic energy density of a field of 105 G is two orders of magnitude larger than the kinetic energy density of the convective motions in the lower solar convection zone. This raises serious doubts whether the conventional turbulent dynamo process based upon cyclonic convection can work on the basis of such a strong field. Moreover, it is unclear whether solar differential rotation is capable of generating a toroidal magnetic field of 105 G; it is conceivable that thermal processes like an entropy-driven outflow from exploded flux tubes leads to the large field strength required. The instability of magnetic flux tubes stored in the overshoot region suggests an alternative dynamo mechanism based upon growing helical waves propagating along the tubes. Since this process operates only for field strengths exceeding a critical value, such a dynamo can fall into a `grand minimum' once the field strength is globally driven below this value, for instance by magnetic flux pumped at random from the convection zone into the dynamo region in the overshoot layer. The same process may act as a (re-)starter of the dynamo operation. Other non-conventional dynamo mechanisms based upon the dynamics of magnetic flux tubes are also conceivable.

  3. Vector Magnetic Field in Emerging Flux Regions

    NASA Astrophysics Data System (ADS)

    Schmieder, B.; Pariat, E.

    A crucial phase in magnetic flux emergence is the rise of magnetic flux tubes through the solar photosphere, which represents a severe transition between the very different environments of the solar interior and corona. Multi-wavelength observations with Flare Genesis, TRACE, SoHO, and more recently with the vector magnetographs at THEMIS and Hida (DST) led to the following conclusions. The fragmented magnetic field in the emergence region - with dipped field lines or bald patches - is directly related with Ellerman bombs, arch filament systems, and overlying coronal loops. Measurements of vector magnetic fields have given evidence that undulating "serpentine" fields are present while magnetic flux tubes cross the photosphere. See the sketch below, and for more detail see Pariat et al. (2004, 2007); Watanabe et al. (2008):

  4. Magnetic refrigeration using flux compression in superconductors

    NASA Technical Reports Server (NTRS)

    Israelsson, U. E.; Strayer, D. M.; Jackson, H. W.; Petrac, D.

    1990-01-01

    The feasibility of using flux compression in high-temperature superconductors to produce the large time-varying magnetic fields required in a field cycled magnetic refrigerator operating between 20 K and 4 K is presently investigated. This paper describes the refrigerator concept and lists limitations and advantages in comparison with conventional refrigeration techniques. The maximum fields obtainable by flux compression in high-temperature supercoductor materials, as presently prepared, are too low to serve in such a refrigerator. However, reports exist of critical current values that are near usable levels for flux pumps in refrigerator applications.

  5. Ising-Glauber spin cluster model for temperature-dependent magnetization noise in SQUIDs.

    PubMed

    De, Amrit

    2014-11-21

    Clusters of interacting two-level-systems, likely due to Farbe+(F(+)) centers at the metal-insulator interface, are shown to self-consistently lead to 1/f(?) magnetization noise [with ?(T)?1] in SQUIDs. Model calculations, based on a new method of obtaining correlation functions, explains various puzzling experimental features. It is shown why the inductance noise is inherently temperature dependent while the flux noise is not, despite the same underlying microscopics. Magnetic ordering in these systems, established by three-point correlation functions, explains the observed flux-inductance-noise cross correlations. Since long-range ferromagnetic interactions are shown to lead to a more weakly temperature dependent flux noise when compared to short-range interactions, the time reversal symmetry of the clusters is also not likely broken by the same mechanism which mediates surface ferromagnetism in nanoparticles and thin films of the same insulator materials. PMID:25479516

  6. 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.

  7. Heat flux viscosity in collisional magnetized plasmas

    SciTech Connect

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

    2015-05-15

    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.

  8. Solar cycle of magnetic flux spectrum

    NASA Astrophysics Data System (ADS)

    Wang, Jingxiu; Jin, Chunlan

    2015-08-01

    Solar cycle has not only presented fascinating scientific challenges but also left massive footprints on our living environments. To get better understanding on the magnetic cycle, we have made efforts to extend the knowledge by examining the cyclic behavior of Sun’s small-scale magnetic elements with SOHO/MDI and Hinode/SP observations (Jin et al. 2011, Jin and Wang 2012, 2014). The work has been made on the basic of identity of tens Million magnetic elements in the flux range from current detection limit (1.5x1016 Mx) to times of 1019 Mx. We find that from the detective limit to the large end of the magnetic flux spectrum, the variation of magnetic element numbers show no correlation, anti-correlation and correlation with sunspot number, respectively. The magnetic elements with flux less than 2.9x1018 Mx display behavior of some local dynamo that is independent of the sunspot cycle, while the enhanced network magnetic elements with flux larger a few times of 1019 Mx are likely to be the debris of decayed sunspots. Possibilities are considered to explain the anti-correlated magnetic elements in term of the interplay of local and global dynamos. We will report our new efforts and results in exploring the solar cycle in term of Sun’s magnetic flux spectrum by combining the SOHO/MDI, SDO/HMI and Hinode/SP observations. All efforts will help with learning which component of solar magnetism has responsibility for the change of solar total irradiance.

  9. Magnetic topology of emerging flux regions

    NASA Astrophysics Data System (ADS)

    Pariat, Etienne

    Coronal magnetic fields structure and governs the dynamics of the solar atmosphere. These magnetic fields are often complex, composed of multiples domains of magnetic-field-lines connectivity. The topology of the magnetic field allows a synthetic description of these complex magnetic field by highlighting the structural elements that are important for the dynamic and the activity of the corona. Topology identifies the key elements where magnetic reconnection will preferentially occurs, and allows to explain and predict the evolution of the coronal plasma. However the topological elements - such as null points, separatrices, separators - do not appear out of thin air. Along with energy, and helicity, the magnetic topology of an active region is build up as the consequence of flux emergence. Some topological elements, such as bald-patches, are even fully part of the mechanism of flux emergence mechanism and drive the evolution and the structuration of the coronal magnetic field as it crosses the lower layer of the solar atmosphere. In the present talk I will therefore review our current understanding of the formation of active region in terms of magnetic topology. I will speak on how the topological structures which are key to solar activity are formed. Meanwhile I'll also discus the topological properties of emerging active region and how topology influences the very process of flux emergence.

  10. Tuning magnetic nanostructures and flux concentrators for magnetoresistive sensors

    NASA Astrophysics Data System (ADS)

    Yin, Xiaolu; Liu, Yen-Fu; Ewing, Dan; Ruder, Carmen K.; De Rego, Paul J.; Edelstein, A. S.; Liou, Sy-Hwang

    2015-09-01

    The methods for the optimization of the magnetoresistive (MR) sensors are to reduce sources of noises, to increase the signal, and to understand the involved fundamental limitations. The high-performance MR sensors result from important magnetic tunnel junction (MTJ) properties, such as tunneling magnetoresistance ratio (TMR), coercivity (Hc), exchange coupling field (He), domain structures, and noise properties as well as the external magnetic flux concentrators. All these parameters are sensitively controlled by the magnetic nanostructures, which can be tuned by varying junction free layer nanostructures, geometry, and magnetic annealing process etc. In this paper, we discuss some of efforts that an optimized magnetic sensor with a sensitivity as high as 5,146 %/mT. This sensitivity is currently the highest among all MR-type sensors that have been reported. The estimated noise of our magnetoresistive sensor is 47 pT/Hz1/2 at 1 Hz. This magnetoresistance sensor dissipates only 100 μW of power while operating under an applied voltage of 1 V at room temperature.

  11. Magnetic flux density in the heliosphere

    NASA Astrophysics Data System (ADS)

    Balogh, André; Erdös, Géza

    2013-04-01

    Recently it was shown that the evaluation of the open magnetic flux in the heliosphere is strongly affected by the fluctuations of the field. A new method of data analysis has been developed which effectively reduces the bias introduced by the fluctuations (Erdős, G., & Balogh, A., Ap. J. 753:130, 2012). As a result, the magnetic flux density has been shown to be highly uniform in the heliosphere with respect to latitude and longitude. Also, a regular R-2 form decay by heliospheric distance of the flux density was established. In the present paper these results are further investigated by analysing magnetic field measurements by spacecraft in various heliospheric locations. The main data sources are from observations by ACE, STEREO A and B, and Ulysses; these observations cover a large range of latitude and longitude in location and almost two complete solar cycles in time. Special focus is devoted to the search for any possible longitudinal variations of the magnetic flux density in the ecliptic, in particular as related to CIRs and CMEs and the way these affect the observed relationship between the open solar magnetic field and the heliospheric flux density.

  12. Crossed Flux Tubes Magnetic Reconnection Experiment

    NASA Astrophysics Data System (ADS)

    Tobin, Zachary; Bellan, Paul

    2012-10-01

    The dynamics of arched, plasma-filled flux tubes have been studied in experiments at Caltech. These flux tubes expand, undergo kink instabilities, magnetically reconnect, and are subject to magnetohydrodynamic forces. An upgraded experiment will arrange for two of these flux tubes to cross over each other. It is expected then that the flux tubes will undergo magnetic reconnection at the crossover point, forming one long flux tube and one short flux tube. This reconnection should also result in a half-twist in the flux tubes at the crossover point, which will propagate along each tube as Alfv'en waves. The control circuitry requires two independent floating high energy capacitor power supplies to power the plasma loops, which will be put in series when the plasma loops reconnect. Coordinating these two power supplies requires the building of new systems for controlling plasma generation. Unlike with previous designs, all timing functions are contained on a single printed circuit board, allowing the design to be easily replicated for use with each independent capacitor involved. The control circuit sequencing has been tested successfully in generating a single flux tube. The plasma gun is currently under construction, with its installation pending completion of prior experiments.

  13. Geometrical Effects in Noise Spectra of Superconducting Flux Qubits

    NASA Astrophysics Data System (ADS)

    Petukhov, Andre; Smelyanskiy, Vadim; Martinis, John

    We present theoretical study of geometrical effects related to spin diffusion in superconducting flux qubits. We adopt a model of a long superconducting wire surrounded by a thin oxide layer with spins distributed uniformly over cross-sectional area of the oxide layer. Using a continuous transformation from a round cylinder to a flat wire strip, we demonstrate that the noise spectral density tends to a power law S (ω) ~(ω / Γ) - s with s 3 / 4 , approaching s = 3 / 4 for very thin wires. The ω-s dependence is valid in a broad frequency range above ωΓ stretching up to four orders of magnitude in units of characteristic diffusion decay rate Γ ~ 1 -102 Hz. The effect is highly sensitive to a cross-sectional aspect ratio of a thin wire thus revealing its geometrical origin. We substantiate our findings by detailed comparison with available experimental data and conclude that 3 / 4 power law distinguishes spin diffusion flux noise from generic `` 1 / f '' family. Supported by the AFRL Information Directorate under Grant F4HBKC4162G001.

  14. Magnetic flux reconstruction methods for shaped tokamaks

    SciTech Connect

    Tsui, Chi-Wa

    1993-12-01

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

  15. Magnetic Flux Supplement to Coronal Bright Points

    NASA Astrophysics Data System (ADS)

    Mou, Chaozhou; Huang, Zhenghua; Xia, Lidong; Madjarska, Maria S.; Li, Bo; Fu, Hui; Jiao, Fangran; Hou, Zhenyong

    2016-02-01

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

  16. Magnetic Flux Tube Interchange at the Heliopause

    NASA Astrophysics Data System (ADS)

    Florinski, V.

    2015-11-01

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

  17. Photospheric Magnetic Flux Transport - Supergranules Rule

    NASA Technical Reports Server (NTRS)

    Hathaway, David H.; Rightmire-Upton, Lisa

    2012-01-01

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

  18. Magnetic Flux Transients during Solar Flares

    NASA Astrophysics Data System (ADS)

    Balasubramaniam, K. S.; Delgado, F.; Hock, R. A.

    2013-12-01

    Solar flares result from the sudden release of energy stored in the magnetic field of the solar atmosphere, attributed to magnetic reconnection. In this work, we use line-of-sight magnetograms to study the changes in photospheric magnetic field during large solar flares. The magnetograms are derived from observations using NASA's Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory, and have a cadence of 3 minutes at a 0.5 arcsecond spatial resolution. We studied the inferred magnetic flux changes in 11 X-class flares from (2011-2012) and 26 M-class flares (2011). Of the 37 flares, 32 exhibited short-lived (less than 30 minutes) magnetic flux transients (MFTs) during the progress of the flare, similar to those by Maurya et al. (2012). We note that MFTs were co-temporal with GOES X-ray peaks. Flares with rapid rises (impulsive flares) had stronger transients while those with slower rises (gradual flares) had weak or no MFTs. Finally, flares with stronger GOES X-ray peaks (flare class) showed stronger MFTs. We believe that these changes are non-physical because the changes in the magnetic field are transient (the magnetic field returns to the pre-flare state) and coincide with the impulsive phase of the flare. This work supported by the US Airforce Office of Scientific Research and the AFRL/RV Space Scholar Program.

  19. Synthetic magnetic fluxes on the honeycomb lattice

    SciTech Connect

    Gorecka, Agnieszka; Gremaud, Benoit; Miniatura, Christian

    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.

  20. Synthetic magnetic fluxes on the honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Górecka, Agnieszka; Grémaud, Benoît; Miniatura, Christian

    2011-08-01

    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.

  1. The Invariance of Open Solar Magnetic Flux

    NASA Astrophysics Data System (ADS)

    Smith, E. J.; Zhou, X.

    2005-12-01

    A major finding of Ulysses has been the relative invariance of the open magnetic flux transported into the heliosphere from the Sun by the solar wind. The measure of open flux, r- squared Br, where r is heliocentric distance and Br is the radial field component, was found to be independent of both heliolatitude and phase of the solar cycle, being essentially the same (to within much less than a factor of two) at the recent sunspot minimum and maximum (cycle #23). Although such an invariance is generally not a feature of models of the solar-heliospheric field, it was predicted by L. Fisk and N. Schwadron who proposed that newly created open flux is the result of merging of already open flux with adjacent magnetic loops so that reconnecting field lines result in another open field and another loop with the total number of each unchanged. Thus, studying the open flux in the solar wind is a test of this hypothesis. The preceding study of open flux by Smith and Balogh ended shortly after solar maximum in 2001 when the polar cap magnetic fields had just reversed and were still relatively weak. Since then, the polar cap fields have strengthened and are now about one-half their value during the previous two sunspot cycles (#21, 22). We now present further evidence regarding this important question in Ulysses data acquired over the past 4 years. The radial components at Ulysses and in-ecliptic spacecraft are compared since the latter measurements are potentially a measure of open flux extending back to previous sunspot cycles.

  2. Magnetic flux concentrations in a polytropic atmosphere

    NASA Astrophysics Data System (ADS)

    Losada, I. R.; Brandenburg, A.; Kleeorin, N.; Rogachevskii, I.

    2014-04-01

    Context. Strongly stratified hydromagnetic turbulence has recently been identified as a candidate for explaining the spontaneous formation of magnetic flux concentrations by the negative effective magnetic pressure instability (NEMPI). Much of this work has been done for isothermal layers, in which the density scale height is constant throughout. Aims: We now want to know whether earlier conclusions regarding the size of magnetic structures and their growth rates carry over to the case of polytropic layers, in which the scale height decreases sharply as one approaches the surface. Methods: To allow for a continuous transition from isothermal to polytropic layers, we employ a generalization of the exponential function known as the q-exponential. This implies that the top of the polytropic layer shifts with changing polytropic index such that the scale height is always the same at some reference height. We used both mean-field simulations (MFS) and direct numerical simulations (DNS) of forced stratified turbulence to determine the resulting flux concentrations in polytropic layers. Cases of both horizontal and vertical applied magnetic fields were considered. Results: Magnetic structures begin to form at a depth where the magnetic field strength is a small fraction of the local equipartition field strength with respect to the turbulent kinetic energy. Unlike the isothermal case where stronger fields can give rise to magnetic flux concentrations at larger depths, in the polytropic case the growth rate of NEMPI decreases for structures deeper down. Moreover, the structures that form higher up have a smaller horizontal scale of about four times their local depth. For vertical fields, magnetic structures of super-equipartition strengths are formed, because such fields survive downward advection that causes NEMPI with horizontal magnetic fields to reach premature nonlinear saturation by what is called the "potato-sack" effect. The horizontal cross-section of such structures found in DNS is approximately circular, which is reproduced with MFS of NEMPI using a vertical magnetic field. Conclusions: Results based on isothermal models can be applied locally to polytropic layers. For vertical fields, magnetic flux concentrations of super-equipartition strengths form, which supports suggestions that sunspot formation might be a shallow phenomenon.

  3. SYNOPTIC MAPPING OF CHROMOSPHERIC MAGNETIC FLUX

    SciTech Connect

    Jin, C. L.; Harvey, J. W.; Pietarila, A. E-mail: jharvey@nso.edu

    2013-03-10

    We used daily full-disk Ca II 854.2 nm magnetograms from the Synoptic Optical Long Term Investigations of the Sun (SOLIS) facility to study the chromospheric magnetic field from 2006 April through 2009 November. We determined and corrected previously unidentified zero offsets in the SOLIS magnetograms. By tracking the disk passages of stable unipolar regions, the measured net flux densities were found to systematically decrease from the disk center to the limb by a factor of about two. This decrease was modeled using a thin flux tube model with a difference in signal formation height between the center and limb sides. Comparison of photospheric and chromospheric observations shows that their differences are largely due to horizontal spreading of magnetic flux with increasing height. The north polar magnetic field decreased nearly linearly with time during our study period while the south polar field was nearly constant. We used the annual change in the viewing angle of the polar regions to estimate the radial and meridional components of the polar fields and found that the south polar fields were tilted away from the pole. Synoptic maps of the chromospheric radial flux density distribution were used as boundary conditions for extrapolation of the field from the chromosphere into the corona. A comparison of modeled and observed coronal hole boundaries and coronal streamer positions showed better agreement when using the chromospheric rather than the photospheric synoptic maps.

  4. Stochastic flux freezing and magnetic dynamo.

    PubMed

    Eyink, Gregory L

    2011-05-01

    Magnetic flux conservation in turbulent plasmas at high magnetic Reynolds numbers is argued neither to hold in the conventional sense nor to be entirely broken, but instead to be valid in a statistical sense associated to the "spontaneous stochasticity" of Lagrangian particle trajectories. The latter phenomenon is due to the explosive separation of particles undergoing turbulent Richardson diffusion, which leads to a breakdown of Laplacian determinism for classical dynamics. Empirical evidence is presented for spontaneous stochasticity, including numerical results. A Lagrangian path-integral approach is then exploited to establish stochastic flux freezing for resistive hydromagnetic equations and to argue, based on the properties of Richardson diffusion, that flux conservation must remain stochastic at infinite magnetic Reynolds number. An important application of these results is the kinematic, fluctuation dynamo in nonhelical, incompressible turbulence at magnetic Prandtl number (Pr(m)) equal to unity. Numerical results on the Lagrangian dynamo mechanisms by a stochastic particle method demonstrate a strong similarity between the Pr(m)=1 and 0 dynamos. Stochasticity of field-line motion is an essential ingredient of both. Finally, some consequences for nonlinear magnetohydrodynamic turbulence, dynamo, and reconnection are briefly considered. PMID:21728673

  5. Stochastic flux freezing and magnetic dynamo

    SciTech Connect

    Eyink, Gregory L.

    2011-05-15

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

  6. Magnetic Flux Compression Experiments Using Plasma Armatures

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  7. The structure of untwisted magnetic flux tubes

    NASA Astrophysics Data System (ADS)

    Browning, P. K.; Priest, E. R.

    1982-10-01

    While most previous investigations have concentrated on slender flux tubes, the present study of the equilibrium structure of an axisymmetric magnetic flux tube, confined by an external pressure that varies along the length of the tube, explores the properties of thick tubes in order to establish the degree to which slender tube theory is valid. It is found that slender flux tube results may in some cases give no indication of thick tube behavior in a nonuniform atmosphere. Depending on boundary conditions applied at the ends of the tube, it may expand or contract upon entering a region of increasing pressure. Rather than expanding indefinitely, the tube surface may form a cusped shape when a point of external pressure on the tube surface falls to equality with the internal pressure. Numerical solutions for an initially uniform tube give smaller expansions than would be expected from slender tube theory.

  8. Magnetic flux concentrations from turbulent stratified convection

    NASA Astrophysics Data System (ADS)

    Käpylä, P. J.; Brandenburg, A.; Kleeorin, N.; Käpylä, M. J.; Rogachevskii, I.

    2016-04-01

    Context. The formation of magnetic flux concentrations within the solar convection zone leading to sunspot formation is unexplained. Aims: We study the self-organization of initially uniform sub-equipartition magnetic fields by highly stratified turbulent convection. Methods: We perform simulations of magnetoconvection in Cartesian domains representing the uppermost 8.5-24 Mm of the solar convection zone with the horizontal size of the domain varying between 34 and 96 Mm. The density contrast in the 24 Mm deep models is more than 3 × 103 or eight density scale heights, corresponding to a little over 12 pressure scale heights. We impose either a vertical or a horizontal uniform magnetic field in a convection-driven turbulent flow in set-ups where no small-scale dynamos are present. In the most highly stratified cases we employ the reduced sound speed method to relax the time step constraint arising from the high sound speed in the deep layers. We model radiation via the diffusion approximation and neglect detailed radiative transfer in order to concentrate on purely magnetohydrodynamic effects. Results: We find that super-equipartition magnetic flux concentrations are formed near the surface in cases with moderate and high density stratification, corresponding to domain depths of 12.5 and 24 Mm. The size of the concentrations increases as the box size increases and the largest structures (20 Mm horizontally near the surface) are obtained in the models that are 24 Mm deep. The field strength in the concentrations is in the range of 3-5 kG, almost independent of the magnitude of the imposed field. The amplitude of the concentrations grows approximately linearly in time. The effective magnetic pressure measured in the simulations is positive near the surface and negative in the bulk of the convection zone. Its derivative with respect to the mean magnetic field, however, is positive in most of the domain, which is unfavourable for the operation of the negative effective magnetic pressure instability (NEMPI). Simulations in which a passive vector field is evolved do not show a noticeable difference from magnetohydrodynamic runs in terms of the growth of the structures. Furthermore, we find that magnetic flux is concentrated in regions of converging flow corresponding to large-scale supergranulation convection pattern. Conclusions: The linear growth of large-scale flux concentrations implies that their dominant formation process is a tangling of the large-scale field rather than an instability. One plausible mechanism that can explain both the linear growth and the concentration of the flux in the regions of converging flow pattern is flux expulsion. A possible reason for the absence of NEMPI is that the derivative of the effective magnetic pressure with respect to the mean magnetic field has an unfavourable sign. Furthermore, there may not be sufficient scale separation, which is required for NEMPI to work. Movies associated to Figs. 4 and 5 are available in electronic form at http://www.aanda.org

  9. 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

  10. 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 ěc{J}×ěc{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

  11. 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.

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

    NASA Technical Reports Server (NTRS)

    Studer, P. A. (Inventor)

    1982-01-01

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

  13. Harmonic Fluxes and Electromagnetic Forces of Concentric Winding Brushless Permanent Magnet Motor

    NASA Astrophysics Data System (ADS)

    Ishibashi, Fuminori; Takemasa, Ryo; Matsushita, Makoto; Nishizawa, Takashi; Noda, Shinichi

    Brushless permanent magnet motors have been widely used in home applications and industrial fields. These days, high efficiency and low noise motors are demanded from the view point of environment. Electromagnetic noise and iron loss of the motor are produced by the harmonic fluxes and electromagnetic forces. However, order and space pattern of these have not been discussed in detail. In this paper, fluxes, electromagnetic forces and magneto-motive forces of brushless permanent magnet motors with concentric winding were analyzed analytically, experimentally and numerically. Time harmonic fluxes and time electromagnetic forces in the air gap were measured by search coils on the inner surface of the stator teeth and analyzed by FEM. Space pattern of time harmonic fluxes and time electromagnetic forces were worked out with experiments and FEM. Magneto motive forces due to concentric winding were analyzed with equations and checked by FEM.

  14. On turbulent diffusion of magnetic fields and the loss of magnetic flux from stars

    NASA Technical Reports Server (NTRS)

    Vainshtein, Samuel I.; Rosner, Robert

    1991-01-01

    The turbulent diffusion of magnetic fields in astrophysical objects, and the processes leading to magnetic field flux loss from such objects are discussed with attention to the suppression of turbulent diffusion by back-reaction of magnetic fields on small spatial scales, and on the constraint imposed on magnetic flux loss by flux-freezing within stars. Turbulent magnetic diffusion can be suppressed even for very weak large-scale magnetic fields, so that 'standard' turbulent diffusion is incapable of significant magnetic flux destruction within a star. Finally, magnetic flux loss via winds is shown to be generally ineffective, no matter what the value of the effective magnetic Reynolds number is.

  15. 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.

  16. 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.

  17. Permanent-magnet switched-flux machine

    SciTech Connect

    Trzynadlowski, Andrzej M.; Qin, Ling

    2012-02-21

    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.

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

    DOEpatents

    Preston, Mark A.; King, Robert D.

    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.

  19. 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.

  20. Noise analysis in fast magnetic resonance electrical impedance tomography (MREIT) based on spoiled multi gradient echo (SPMGE) pulse sequence

    NASA Astrophysics Data System (ADS)

    In Oh, Tong; Jeong, Woo Chul; Kim, Ji Eun; Sajib, Saurav Z. K.; Kim, Hyung Joong; In Kwon, Oh; Woo, Eung Je

    2014-08-01

    Magnetic resonance electrical impedance tomography (MREIT) is a promising non-invasive method to visualize a static cross-sectional conductivity and/or current density image by injecting low frequency currents. MREIT measures one component of the magnetic flux density caused by the injected current using a magnetic resonance (MR) scanner. For practical in vivo implementations of MREIT, especially for soft biological tissues where the MR signal rapidly decays, it is crucial to develop a technique for optimizing the magnetic flux density signal by the injected current while maintaining spatial-resolution and contrast. We design an MREIT pulse sequence by applying a spoiled multi-gradient-echo pulse sequence (SPMGE) to the injected current nonlinear encoding (ICNE), which fully injects the current at the end of the read-out gradient. The applied ICNE-SPMGE pulse sequence maximizes the duration of injected current almost up to a repetition time by measuring multiple magnetic flux density data. We analyze the noise level of measured magnetic flux density with respect to the pulse width of injection current and T_{2}^{*} relaxation time. In due consideration of the ICNE-SPMGE pulse sequence, using a reference information of T_{2}^{*} values in a local region of interest by a short pre-scan data, we predict the noise level of magnetic flux density to be measured for arbitrary repetition time TR. Results from phantom experiment demonstrate that the proposed method can predict the noise level of magnetic flux density for an appropriate TR = 40 ms using a reference scan for TR = 75 ms. The predicted noise level was compared with the noise level of directly measured magnetic flux density data.

  1. Multiplicative noise effects on electroconvection in controlling additive noise by a magnetic field

    NASA Astrophysics Data System (ADS)

    Huh, Jong-Hoon

    2015-12-01

    We report multiplicative noise-induced threshold shift of electroconvection (EC) in the presence of a magnetic field H . Controlling the thermal fluctuation (i.e., additive noise) of the rodlike molecules of nematic liquid crystals by H , the EC threshold is examined at various noise levels [characterized by their intensity and cutoff frequency (fc) ]. For a sufficiently strong H (i.e., ignorable additive noise), a modified noise sensitivity characterizing the shift problem is in good agreement with experimental results for colored as well as white noise (fc→∞ ) ; until now, there was a large deviation for (sufficiently) colored noises. The present study shows that H provides us with ideal conditions for studying the corresponding Carr-Helfrich theory considering pure multiplicative noise.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  3. NONLINEAR THREE-DIMENSIONAL MAGNETOCONVECTION AROUND MAGNETIC FLUX TUBES

    SciTech Connect

    Botha, G. J. J.; Rucklidge, A. M.; Hurlburt, N. E. E-mail: A.M.Rucklidge@leeds.ac.uk

    2011-04-20

    Magnetic flux in the solar photosphere forms concentrations from small scales, such as flux elements, to large scales, such as sunspots. This paper presents a study of the decay process of large magnetic flux tubes, such as sunspots, on a supergranular scale. Three-dimensional nonlinear resistive magnetohydrodynamic numerical simulations are performed in a cylindrical domain, initialized with axisymmetric solutions that consist of a well-defined central flux tube and an annular convection cell surrounding it. As the nonlinear convection evolves, the annular cell breaks up into many cells in the azimuthal direction, allowing magnetic flux to slip between cells away from the central flux tube (turbulent erosion). This lowers magnetic pressure in the central tube, and convection grows inside the tube, possibly becoming strong enough to push the tube apart. A remnant of the central flux tube persists with nonsymmetric perturbations caused by the convection surrounding it. Secondary flux concentrations form between convection cells away from the central tube. Tube decay is dependent on the convection around the tube. Convection cells forming inside the tube as time-dependent outflows will remove magnetic flux. (This is most pronounced for small tubes.) Flux is added to the tube when flux caught in the surrounding convection is pushed toward it. The tube persists when convection inside the tube is sufficiently suppressed by the remaining magnetic field. All examples of persistent tubes have the same effective magnetic field strength, consistent with the observation that pores and sunspot umbrae all have roughly the same magnetic field strength.

  4. Magnetic Flux Pileup and Magnetic Field Dipolarization During Substorm

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Pu, Z.; Cao, X.; Fu, S.; Xiao, C.; Zong, Q.; Liu, Z.; Cao, J.; Korth, A.; Frazen, M.; Carr, C.; Reme, H.; Glassmeier, K.

    2005-12-01

    During the period from July to October in 2004, the orbit apogee of Double Star TC-1 of 13Re located in the magnetotail, which made it possible to survey some basic features of substorm processes in the magnetotail. In the present paper we make a case study of substorm occurring on Sep. 17, 2004. At about 0117 UT FUV WIC on board IMAGE observed an aurora breakup. Almost at the same time the LANL-01A and 90-085 at the geosynchronous altitude detected dispersionless injection of energetic electrons. About 2-3 minutes later a weak dipolarization was seen by NOAA geosynchronous satellite GOES 12. Interestingly, ten minutes before substorm onset, Cluster observed an earthward flow at (-15.00, 2.05, 3.50) Re(GSM). At 0116 UT (one min before onset) TC-1 saw a beginning of magnetic flux pile-up at its position (-10.26, -1.36, 1.01) REGSM, characterized by an increasing of Bz component with almost constant Bx and thermal pressure. At about 0126 UT (9 minutes after onset) TC-1 observed a local dipolarization of the magnetic field which was characterized by a rapid decrease of Bx component and a sharp jump in the thermal pressure, together with a continuous increase of Bz. In the literature, some authors treated the flux pile-up and dipolarization in the tail as a single process named `dipolarization'. However, as TC-1 measurements show in this event, flux pile-up and dipolarization are characterized by completely different signatures. The same feature holds for many other events. Detailed inspections of TC-1 data in this event show that the beginning of flux pile-up was about 10 minutes preceding the dipolarization. Besides, the latter lasted only for about two minutes, whereas the former kept for almost one hour. All these aforementioned differences imply that flux pile-up and dipolarization are two different dynamical processes. Nevertheless, further studies indicate that they are `cause-effect' related: The magnetic flux pileup may lead the field lines with `good' curvature to change to the `bad' ones, further compresses the magnetic field and yields disturbances. These can set up appropriate conditions for development of instabilities and then trigger substorm expansion onset. In summary, this case study seems consistent with the synthesis substorm model of near-Earth neutral line (NENL) and near-Earth current disruption (NECD).

  5. Forecasting the Solar Photosphere's Magnetic Flux with Local Data Assimilation

    NASA Astrophysics Data System (ADS)

    Hickmann, K. S.; Godinez, H. C.; Henney, C. J.; Arge, C. N.

    2014-12-01

    Accurate forecasts of the photospheric magnetic flux are important since the photosphere provides the driving bound-ary conditions for the Corona and Solar wind which impact near Earth space weather. These space weather phenomenaeffect satellite trajectories and communication systems as well as safety on manned space missions. In this presen-tation we detail our recent improvements to the data assimilation mechanisms in the Air Force Data AssimilativePhotospheric flux Transport (ADAPT) model. These include implementation of the local ensemble transform Kalmanfilter (LETKF) for the assimilation of satellite observations. In the past non-local ensemble methods have been usedto assimilate data into photosphere models. Due to the small ensemble sizes allowed for Solar forecasts spuriouscorrelations were introduced in the sample covariance, causing model divergence from observations. With our imple-mentation of the LETKF in ADAPT this ensemble divergence has been reduced. In addition multi-scale techniqueshave been implemented in ADAPT to deal with the lack of active region creation in the photosphere model. Lackof large scale active region creation in the ADAPT model caused ensemble bias when assimilating observations ofnewly created regions using ensemble Kalman methods. Separating the scales at which active regions occur allowsobservational noise for such regions to be controlled independently. We show that our consideration of the multi-scalenature of photosphere flux transport has allowed more accurate assimilation of large active regions.

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

    SciTech Connect

    Bai, Xue-Ning; Stone, James M.

    2014-11-20

    Accretion disks are likely threaded by external vertical magnetic flux, which enhances the level of turbulence via the magnetorotational instability (MRI). Using shearing-box simulations, we find that such external magnetic flux also strongly enhances the amplitude of banded radial density variations known as zonal flows. Moreover, we report that vertical magnetic flux is strongly concentrated toward low-density regions of the zonal flow. Mean vertical magnetic field can be more than doubled in low-density regions, and reduced to nearly zero in high-density regions in some cases. In ideal MHD, the scale on which magnetic flux concentrates can reach a few disk scale heights. In the non-ideal MHD regime with strong ambipolar diffusion, magnetic flux is concentrated into thin axisymmetric shells at some enhanced level, whose size is typically less than half a scale height. We show that magnetic flux concentration is closely related to the fact that the turbulent diffusivity of the MRI turbulence is anisotropic. In addition to a conventional Ohmic-like turbulent resistivity, we find that there is a correlation between the vertical velocity and horizontal magnetic field fluctuations that produces a mean electric field that acts to anti-diffuse the vertical magnetic flux. The anisotropic turbulent diffusivity has analogies to the Hall effect, and may have important implications for magnetic flux transport in accretion disks. The physical origin of magnetic flux concentration may be related to the development of channel flows followed by magnetic reconnection, which acts to decrease the mass-to-flux ratio in localized regions. The association of enhanced zonal flows with magnetic flux concentration may lead to global pressure bumps in protoplanetary disks that helps trap dust particles and facilitates planet formation.

  7. 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.

  8. Transport of magnetic flux in Saturn’s inner magnetosphere

    NASA Astrophysics Data System (ADS)

    Russell, Christopher T.; Lai, H. R.; Wei, H. Y.; Jia, Y. D.; Dougherty, M. K.

    2015-11-01

    The dynamics of the Saturnian magnetosphere, which rotates rapidly with an internal plasma source provided by Enceladus, qualitatively resembles those of the jovian magnetosphere powered by Io. The newly added plasma is accelerated to the corotation speed and moves outward together with the magnetic flux. In the near tail region, reconnection cuts the magnetic flux, reconnects it into plasma-depleted inward moving flux tubes and outward moving massive plasmoids. The buoyant empty tubes then convect inward against the outward flow to conserve the total magnetic flux established by the internal dynamo. In both jovian and saturnian magnetospheres, flux tubes with enhanced field strength relative to their surroundings are detected in the equatorial region. Recent observations show that there are flux tubes with reduced field strength off the equator in the saturnian magnetosphere. To understand the formation mechanism of both types of flux tubes, we have surveyed all the available 1-sec magnetic field data from Cassini. The systematic statistical study confirms the different latitudinal distributions of the two types of flux tubes. In addition, enhanced-field flux tubes are closer to the planet while reduced-field flux tubes can be detected at larger distances; both types of flux tubes become indistinguishable from the background magnetic flux inside an L-value of about 4; the local time distribution of both types of flux tubes are similar and they contain about the same amount of magnetic flux. Therefore, the two types of flux tubes are the same phenomena with different manifestations in different plasma environments. When the surrounding plasma density is high (near the equator and closer to the plasma source region), the flux tubes are compressed and have enhanced field strength inside; while in the low-plasma density region (off the equator and further from the plasma source region), the flux tubes expand and have reduced field strength inside.

  9. 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.

  10. Magnetic Flux Pileup and Magnetic Field Dipolarization during Substorm

    NASA Astrophysics Data System (ADS)

    Zhanghui, H.; Pu, Z. Y.; Liu, Z. X.; Korth, A.; Frazen, M.; Friedel, R.; Zong, Q. G.; Reme, H.; Glassmeier, K. H.

    During the period from July to October in 2004 the orbit apogee of Double Star TC-1 of 13RE located in the magnetotail which made it possible to survey some basic features of substorm processes in the magnetotail In the present paper we make a case study of substorm occurring on Sep 17 2004 At about 0117 UT FUV WIC on board IMAGE observed an aurora breakup Almost at the same time the LANL-01A and 90-085 at the geosynchronous altitude detected dispersionless injection of energetic electrons About 2-3 minutes later a weak dipolarization was seen by NOAA geosynchronous satellite GOES 12 Interestingly ten minutes before substorm onset Cluster observed an earthward flow at -15 00 2 05 3 50 REGSM At 0116 UT one min before onset TC-1 saw a beginning of magnetic flux pile-up at its position -10 26 -1 36 1 01 REGSM characterized by an increasing of Bz component with almost constant Bx and thermal pressure At about 0126 UT 9 minutes after onset TC-1 observed a local dipolarization of the magnetic field which was characterized by a rapid decrease of Bx component and a sharp jump in the thermal pressure together with a continuous increase of Bz In the literature some authors treated the flux pile-up and dipolarization in the tail as a single process named odipolarization - However as TC-1 measurements show in this event flux pile-up and dipolarization are characterized by completely different signatures The same feature holds for many other events Detailed inspections of TC-1 data in this event show that the beginning of flux pile-up was 10 minutes

  11. The noise main characteristic for magnetic microsensors structures

    NASA Astrophysics Data System (ADS)

    Panait, Cornel; Srbu, Vasile; C?runtu, George

    2009-01-01

    The noise-signal at the output of a Hall magnetic sensor can be interpreted as a result of an equivalent magnetic induction, acting on a noiseless Hall device. In this paperwork based on the adequate models it is analysed the operating conditions, and are established the noise main characteristic for three magnetic microsensor structures, realized in the bipolar and the MOS integrated circuits technology. By using the numerical simulation the values of the signal-to-noise ratio and the noise-equivalent magnetic induction spectral density for different structure devices are compared and it is also emphasized the way in which choosing the geometry and the material features allows getting high-performance sensors. (properties influence on the device performances.)

  12. Detection of spin torque magnetization dynamics through low frequency noise

    NASA Astrophysics Data System (ADS)

    Cascales, Juan Pedro; Herranz, David; Ebels, Ursula; Katine, Jordan A.; Aliev, Farkhad G.

    2015-08-01

    We present a comparative study of high frequency dynamics and low frequency noise in elliptical magnetic tunnel junctions with lateral dimensions under 100 nm presenting current-switching phenomena. The analysis of the high frequency oscillation modes with respect to the current reveals the onset of a steady-state precession regime for negative bias currents above J = 10 7 A / cm 2 , when the magnetic field is applied along the easy axis of magnetization. By the study of low frequency noise for the same samples, we demonstrate the direct link between changes in the oscillation modes with the applied current and the normalised low frequency (1/f) noise as a function of the bias current. These findings prove that low frequency noise studies could be a simple and powerful technique to investigate spin-torque based magnetization dynamics.

  13. Magnetic flux ropes in 3-dimensional MHD simulations

    NASA Technical Reports Server (NTRS)

    Ogino, Tatsuki; Walker, Raymond J.; Ashour-Abdalla, Maha

    1990-01-01

    The interaction of the solar wind and the earth's magnetosphere is presently simulated by a 3D, time-dependent, global MHD method in order to model the magnetopause and magnetotail generation of magnetic flux ropes. It is noted that strongly twisted and localized magnetic flux tubes simular to magnetic flux ropes appear at the subpolar magnetopause when the IMF has a large azimuthal component, as well as a southward component. Plasmoids are generated in the magnetotail after the formation of a near-earth magnetic neutral line; the magnetic field lines have a helical structure that is connected from dawn to dusk.

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

    SciTech Connect

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

    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.

  15. Transport of magnetic flux and mass in Saturn's inner magnetosphere

    NASA Astrophysics Data System (ADS)

    Lai, H. R.; Russell, C. T.; Jia, Y. D.; Wei, H. Y.; Dougherty, M. K.

    2016-04-01

    It is well accepted that cold plasma sourced by Enceladus is ultimately lost to the solar wind, while the magnetic flux convecting outward with the plasma must return to the inner magnetosphere. However, whether the interchange or reconnection, or a combination of the two processes is the dominant mechanism in returning the magnetic flux is still under debate. Initial Cassini observations have shown that the magnetic flux returns in the form of flux tubes in the inner magnetosphere. Here we investigate those events with 10 year Cassini magnetometer data and confirm that their magnetic signatures are determined by the background plasma environments: inside (outside) the plasma disk, the returning magnetic field is enhanced (depressed) in strength. The distribution, temporal variation, shape, and transportation rate of the flux tubes are also characterized. The flux tubes break into smaller ones as they convect in. The shape of their cross section is closer to circular than fingerlike as produced in the simulations based on the interchange mechanism. In addition, no sudden changes in any flux tube properties can be found at the "boundary" which has been claimed to separate the reconnection and interchange-dominant regions. On the other hand, reasonable cold plasma loss rate and outflow velocity can be obtained if the transport rate of the magnetic flux matches the reconnection rate, which supports reconnection alone as the dominant mechanism in unloading the cold plasma from the inner magnetosphere and returning the magnetic flux from the tail.

  16. Effect of uncertainties in solar synoptic magnetic flux maps in modeling of solar wind

    NASA Astrophysics Data System (ADS)

    Pevtsov, Alexei A.; Bertello, Luca; MacNeice, Peter

    2015-12-01

    Recently, the NSO/SOLIS team developed variance (error) maps that represent uncertainties in magnetic flux synoptic charts. These uncertainties are determined by the spatial variances of the magnetic flux distribution from full disk magnetograms that contribute to each bin in the synoptic chart. Here we present a study of the effects of variances on solar wind parameters (wind speed, density, magnetic field, and temperature) derived using the WSA-ENLIL model and ensemble modeling approach. We compare the results of the modeling with near-Earth solar wind magnetic field and plasma data as extracted from NASA/GSFC's OMNI data set. We show that analysis of uncertainties may be useful for understanding the sensitivity of the model predictions to short-term evolution of magnetic field and noise in the synoptic magnetograms.

  17. PROTOSTELLAR ACCRETION FLOWS DESTABILIZED BY MAGNETIC FLUX REDISTRIBUTION

    SciTech Connect

    Krasnopolsky, Ruben; Shang, Hsien; Li Zhiyun; Zhao Bo

    2012-09-20

    Magnetic flux redistribution lies at the heart of the problem of star formation in dense cores of molecular clouds that are magnetized to a realistic level. If all of the magnetic flux of a typical core were to be dragged into the central star, the stellar field strength would be orders of magnitude higher than the observed values. This well-known magnetic flux problem can in principle be resolved through non-ideal MHD effects. Two-dimensional (axisymmetric) calculations have shown that ambipolar diffusion, in particular, can transport magnetic flux outward relative to matter, allowing material to enter the central object without dragging the field lines along. We show through simulations that such axisymmetric protostellar accretion flows are unstable in three dimensions to magnetic interchange instability in the azimuthal direction. The instability is driven by the magnetic flux redistributed from the matter that enters the central object. It typically starts to develop during the transition from the prestellar phase of star formation to the protostellar mass accretion phase. In the latter phase, the magnetic flux is transported outward mainly through advection by strongly magnetized low-density regions that expand against the collapsing inflow. The tussle between the gravity-driven infall and magnetically driven expansion leads to a highly filamentary inner accretion flow that is more disordered than previously envisioned. The efficient outward transport of magnetic flux by advection lowers the field strength at small radii, making the magnetic braking less efficient and the formation of rotationally supported disks easier in principle. However, we find no evidence for such disks in any of our rotating collapse simulations. We conclude that the inner protostellar accretion flow is shaped to a large extent by the flux redistribution-driven magnetic interchange instability. How disks form in such an environment is unclear.

  18. Unresolved Magnetic Flux Removal Process in the Photosphere

    NASA Astrophysics Data System (ADS)

    Kubo, Masahito; Chye Low, Boon; Lites, Bruce

    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. An Ω-loop submerging below the surface or a U-loop rising through the photosphere is the usual idea to explain the magnetic flux cancellation. Magnetic reconnection may be crucial for the forma-tion of these loops, especially for the submerging -loop. In fact, chromospheric and coronal activities are often observed at the cancellation sites. We investigate the evolution of 5 cancel-lation events of the opposite-polarity magnetic elements at granular scales by using accurate spectropolarimetric measurements with the Solar Optical Telescope aboard Hinode. We find that the horizontal magnetic field, which is expected in both submerging Ω-loop model and emerging U-loop model, does not appear between the canceling magnetic elements in 4 of the 5 events. The approaching magnetic elements in these events are more concentrated rather than gradually diffused, and they have nearly vertical fields even while they are in contact each other. We thus imply that the actual flux cancellation is highly time dependent event near the solar surface at scales less than a pixel of Hinode/SOT (about 200 km). At the polarity inversion line formed by the canceling magnetic elements, highly asymmetric Stokes-V profiles are observed. We confirm that such asymmetric profile can be made by the sum of the profiles at the opposite-polarity magnetic elements next to the polarity inversion line. This means that the approaching bipolar flux tubes still keep their nature within the pixel where they come in contact with each other, and thus supports the unresolved flux removal process within the pixel at the polarity inversion line.

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

    NASA Technical Reports Server (NTRS)

    Hathaway, David H.

    2010-01-01

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

  20. Helicity charging and eruption of magnetic flux from the Sun

    NASA Technical Reports Server (NTRS)

    Rust, David M.; Kumar, A.

    1994-01-01

    The ejection of helical toroidal fields from the solar atmosphere and their detection in interplanetary space are described. The discovery that solar magnetic fields are twisted and that they are segregated by hemisphere according to their chirality has important implications for the escape process. The roles played by erupting prominences, coronal mass ejections (CME's) and active region (AR) loops in expressing the escape of magnetic flux and helicity are discussed. Sporadic flux escape associated with filament eruptions accounts for less than one-tenth the flux loss. Azimuthal flux loss by CME's could account for more, but the major contributor to flux escape may be AR loop expansion. It is shown how the transfer of magnetic helicity from the sun's interior into emerged loops ('helicity charging') could be the effective driver of solar eruptions and of flux loss from the sun.

  1. Magnetic flux circulation in the rotationally driven giant magnetospheres

    NASA Astrophysics Data System (ADS)

    Delamere, P. A.; Otto, A.; Ma, X.; Bagenal, F.; Wilson, R. J.

    2015-06-01

    The giant-planet magnetodiscs are shaped by the radial transport of plasma originating in the inner magnetosphere. Magnetic flux transport is a key aspect of the stretched magnetic field configuration of the magnetodisc. While net mass transport is outward (ultimately lost to the solar wind), magnetic flux conservation requires a balanced two-way transport process. Magnetic reconnection is a critical aspect of the balanced flux transport. We present a comprehensive analysis of current sheet crossings in Saturn's magnetosphere using Cassini magnetometer data from 2004 to 2012 in an attempt to quantify the circulation of magnetic flux, emphasizing local time dependence. A key property of flux transport is the azimuthal bend forward or bend back of the magnetic field. The bend back configuration is an expected property of the magnetodisc with net mass outflow, but the bend forward configuration can be achieved with the rapid inward motion of mostly empty flux tubes following reconnection. We find a strong local time dependence for the bend forward cases, localized mostly in the postnoon sector, indicating that much of the flux-conserving reconnection occurs in the subsolar and dusk sector. We suggest that the reconnection occur in a complex and patchy network of reconnection sites, supporting the idea that plasma can be lost on small scales through a "drizzle"-like process. Auroral implications for the observed flux circulation will also be presented.

  2. Signal photon flux and background noise in a coupling electromagnetic detecting system for high-frequency gravitational waves

    NASA Astrophysics Data System (ADS)

    Li, Fangyu; Yang, Nan; Fang, Zhenyun; Baker, Robert M. L., Jr.; Stephenson, Gary V.; Wen, Hao

    2009-09-01

    A coupling system among Gaussian-type microwave photon flux, a 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 the pure inverse Gertsenshtein effect (G effect) caused by the HFGWs in the gigahertz band, the electromagnetic (EM) detecting scheme proposed by China and the U.S. HFGW groups is based on the composite effect of the synchroresonance effect and the inverse G effect. The key parameter in the scheme is the 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 ˜103-105 seconds for the typical laboratory condition and parameters of hrms˜10-26-10-30/Hz at 5 GHz with bandwidth ˜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.

  3. 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.

  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. 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.

  6. Spin noise explores local magnetic fields in a semiconductor

    NASA Astrophysics Data System (ADS)

    Ryzhov, Ivan I.; Kozlov, Gleb G.; Smirnov, Dmitrii S.; Glazov, Mikhail M.; Efimov, Yurii P.; Eliseev, Sergei A.; Lovtcius, Viacheslav A.; Petrov, Vladimir V.; Kavokin, Kirill V.; Kavokin, Alexey V.; Zapasskii, Valerii S.

    2016-02-01

    Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new - magnetometric - potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This “optical field” is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates.

  7. Spin noise explores local magnetic fields in a semiconductor.

    PubMed

    Ryzhov, Ivan I; Kozlov, Gleb G; Smirnov, Dmitrii S; Glazov, Mikhail M; Efimov, Yurii P; Eliseev, Sergei A; Lovtcius, Viacheslav A; Petrov, Vladimir V; Kavokin, Kirill V; Kavokin, Alexey V; Zapasskii, Valerii S

    2016-01-01

    Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new - magnetometric - potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This "optical field" is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates. PMID:26882994

  8. Spin noise explores local magnetic fields in a semiconductor

    PubMed Central

    Ryzhov, Ivan I.; Kozlov, Gleb G.; Smirnov, Dmitrii S.; Glazov, Mikhail M.; Efimov, Yurii P.; Eliseev, Sergei A.; Lovtcius, Viacheslav A.; Petrov, Vladimir V.; Kavokin, Kirill V.; Kavokin, Alexey V.; Zapasskii, Valerii S.

    2016-01-01

    Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new – magnetometric – potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This “optical field” is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates. PMID:26882994

  9. MAGNETIC HELICITY FLUX IN THE PRESENCE OF SHEAR

    SciTech Connect

    Hubbard, Alexander; Brandenburg, Axel

    2011-01-20

    Magnetic helicity has risen to be a major player in dynamo theory, with the helicity of the small-scale field being linked to the dynamo saturation process for the large-scale field. It is a nearly conserved quantity, which allows its evolution equation to be written in terms of production and flux terms. The flux term can be decomposed in a variety of fashions. One particular contribution that has been expected to play a significant role in dynamos in the presence of mean shear was isolated by Vishniac and Cho. Magnetic helicity fluxes are explicitly gauge dependent however, and the correlations that have come to be called the Vishniac-Cho flux were determined in the Coulomb gauge, which turns out to be fraught with complications in shearing systems. While the fluxes of small-scale helicity are explicitly gauge dependent, their divergences can be gauge independent. We use this property to investigate magnetic helicity fluxes of the small-scale field through direct numerical simulations in a shearing-box system and find that in a numerically usable gauge the divergence of the small-scale helicity flux vanishes, while the divergence of the Vishniac-Cho flux remains finite. We attribute this seeming contradiction to the existence of horizontal fluxes of small-scale magnetic helicity with finite divergences.

  10. Amplitude and phase noise of magnetic tunnel junction oscillators

    NASA Astrophysics Data System (ADS)

    Quinsat, M.; Gusakova, D.; Sierra, J. F.; Michel, J. P.; Houssameddine, D.; Delaet, B.; Cyrille, M.-C.; Ebels, U.; Dieny, B.; Buda-Prejbeanu, L. D.; Katine, J. A.; Mauri, D.; Zeltser, A.; Prigent, M.; Nallatamby, J.-C.; Sommet, R.

    2010-11-01

    The microwave emission linewidth of spin transfer torque nano-oscillators is closely related to their phase and amplitude noise that can be extracted from the magnetoresistive voltage signal V(t ) using single shot time domain techniques. Here we report on phase and amplitude noise studies for MgO based magnetic tunnel junction oscillators. The analysis of the power spectral densities allows one to separate the linear and nonlinear contributions to the phase noise, the nonlinear contribution being due to the coupling between phase and amplitude. The coupling strength as well as the amplitude relaxation rate can be directly extracted.

  11. Magnetic Field Noise Changes Effect of Combined Magnetic Field on Gravitropic Reaction of Cress Roots.

    NASA Astrophysics Data System (ADS)

    Bogatina, Nina; Kordyum, Elizabeth; Sheykina, Nadezhda

    The gravitropic reaction of cress roots in combined magnetic field was studied in details. It was shown that the negative roots gravitropism observed at the frequency of alternating component of combined magnetic field adjusted to the Ca ion cyclotron frequency could be observed only at Nayquist magnetic field noise level under 5 nT/Hz. While the magnetic noise level was increasing the negative gravitropism was disappearing. The inhibition of gravitropic reaction was observed in all cases. The effect was accompanied by the changes in the noise spectrum generated by cress roots.

  12. A novel high temperature superconducting magnetic flux pump for MRI magnets

    NASA Astrophysics Data System (ADS)

    Bai, Zhiming; Yan, Guo; Wu, Chunli; Ding, Shufang; Chen, Chuan

    2010-10-01

    This paper presents a kind of minitype magnetic flux pump made of high temperature superconductor. This kind of novel high temperature superconducting (HTS) flux pump has not any mechanical revolving parts or thermal switches. The excitation current of copper coils in magnetic pole system is controlled by a singlechip. The structure design and operational principle have been described. The operating performance of the new model magnetic flux pump has been preliminarily tested. The experiments show that the maximum pumping current is approximately 200 A for Bi2223 flux pump and 80 A for MgB 2 flux pump operating at 20 K. By comparison, it is discovered that the operating temperature range is wider, the ripple is smaller and the pumping frequency is higher in Bi2223 flux pump than those in MgB 2 flux pump. These results indicate that the newly developed Bi2223 magnetic flux pump may efficiently compensate the magnetic field decay in HTS magnet and make the magnet operate in persistent current mode, this point is significant to the magnetic resonance imaging (MRI) magnets. This new flux pump is under construction presently. It is expected that the Bi2223 flux pump would be applied to the superconducting MRI magnets by further optimizing structure and improving working process.

  13. Flux-vector model of spin noise in superconducting circuits: Electron versus nuclear spins and role of phase transition

    NASA Astrophysics Data System (ADS)

    LaForest, S.; de Sousa, Rogério

    2015-08-01

    Superconducting quantum interference devices (SQUIDs) and other superconducting circuits are limited by intrinsic flux noise with spectral density 1 /fα with α <1 whose origin is believed to be due to spin impurities. Here, we present a theory of flux noise that takes into account the vectorial nature of the coupling of spins to superconducting wires. We present explicit numerical calculations of the flux-noise power (spectral density integrated over all frequencies) for electron impurities and lattice nuclear spins under several different assumptions. The noise power is shown to be dominated by surface electron spins near the wire edges, with bulk lattice nuclear spins contributing ˜5 % of the noise power in aluminum and niobium wires. We consider the role of electron spin phase transitions, showing that the spin-spin correlation length (describing, e.g., the average size of ferromagnetic spin clusters) greatly impacts the scaling of flux noise with wire geometry. Remarkably, the flux-noise power is exactly equal to zero when the spins are polarized along the flux-vector direction, forming what we call a poloidal state. Flux noise is nonzero for other spin textures, but gets reduced in the presence of correlated ferromagnetic fluctuations between the top and bottom wire surfaces, where the flux vectors are antiparallel. This demonstrates that engineering spin textures and/or intersurface correlation provides a method to reduce flux noise in superconducting devices.

  14. Acoustic emission from magnetic flux tubes in the solar network

    NASA Astrophysics Data System (ADS)

    Vigeesh, G.; Hasan, S. S.

    2013-06-01

    We present the results of three-dimensional numerical simulations to investigate the excitation of waves in the magnetic network of the Sun due to footpoint motions of a magnetic flux tube. We consider motions that typically mimic granular buffeting and vortex flows and implement them as driving motions at the base of the flux tube. The driving motions generates various MHD modes within the flux tube and acoustic waves in the ambient medium. The response of the upper atmosphere to the underlying photospheric motion and the role of the flux tube in channeling the waves is investigated. We compute the acoustic energy flux in the various wave modes across different boundary layers defined by the plasma and magnetic field parameters and examine the observational implications for chromospheric and coronal heating.

  15. A correlative study of magnetic flux transfer in the magnetosphere

    NASA Technical Reports Server (NTRS)

    Holzer, R. E.; Slavin, J. A.

    1979-01-01

    The applied magnetic flux of the southward component of the IMF in GSM coordinates (Bz-) which impinges upon the sunward magnetopause is compared to the time integral of the auroral AL index during 56 intervals within a 3-month period in 1969 when interplanetary records from Heos 1 and Explorer 35 were available. The periods of magnetic activity were those for which Bz was greater than 0 and AL was less than 20gamma at the beginning and end of the interval. It was found that for these intervals, the time integral of the AL index was proportional to the applied magnetic flux with a correlation coefficient of 0.94. In addition, the empirical relationships between magnetic flux transfer, applied southward flux, and the time integral of AL arrived at by Holzer and Slavin (1978) on the basis of expansion and contractions of the forward magnetosphere observed with OGO 5 are reexamined and improved.

  16. Force-Free Magnetic Flux Ropes in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Wolfson, R.

    2003-05-01

    In the course of an ongoing investigation of force-free magnetic fields in the spherical geometry appropriate to the solar corona, we have found solutions that represent magnetic flux ropes. The magnetic energy stored in these ropes and the surrounding field is larger than that which can be stored in simple magnetic arcades with the same boundary conditions, and in some cases exceeds slightly the Aly-Sturrock limit on the energy of a closed force-free magnetic field with all its magnetic flux connected to the coronal base. Flux-rope solutions with the highest energies tend to arise when a strong potential field overlies a region of sheared field containing field-aligned currents. These flux-rope solutions have an unusual topology; instead of a single twisted, disconnected flux system, there are two distinct rope structures. A two-dimensional slice through each rope contains an O-type magnetic neutral point, and the overall solution therefore correspondingly contains two X-type neutral points. We speculate on the relation of this unusual topology to observations of magnetic clouds as interplanetary signatures of coronal mass ejections. This work was supported by NASA grant NAG5-9733 to Middlebury College.

  17. 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

  18. Evolution of the magnetic helicity flux during the formation and eruption of flux ropes

    SciTech Connect

    Romano, P.; Zuccarello, F. P.; Guglielmino, S. L.; Zuccarello, F.

    2014-10-20

    We describe the evolution and the magnetic helicity flux for two active regions (ARs) since their appearance on the solar disk: NOAA 11318 and NOAA 11675. Both ARs hosted the formation and destabilization of magnetic flux ropes. In the former AR, the formation of the flux rope culminated in a flare of C2.3 GOES class and a coronal mass ejection (CME) observed by Large Angle and Spectrometric Coronagraph Experiment. In the latter AR, the region hosting the flux rope was involved in several flares, but only a partial eruption with signatures of a minor plasma outflow was observed. We found a different behavior in the accumulation of the magnetic helicity flux in the corona, depending on the magnetic configuration and on the location of the flux ropes in the ARs. Our results suggest that the complexity and strength of the photospheric magnetic field is only a partial indicator of the real likelihood of an AR producing the eruption of a flux rope and a subsequent CME.

  19. Optimization of multiply acquired magnetic flux density Bz using ICNE-Multiecho train in MREIT

    NASA Astrophysics Data System (ADS)

    Nam, Hyun Soo; In Kwon, Oh

    2010-05-01

    The aim of magnetic resonance electrical impedance tomography (MREIT) is to visualize the electrical properties, conductivity or current density of an object by injection of current. Recently, the prolonged data acquisition time when using the injected current nonlinear encoding (ICNE) method has been advantageous for measurement of magnetic flux density data, Bz, for MREIT in the signal-to-noise ratio (SNR). However, the ICNE method results in undesirable side artifacts, such as blurring, chemical shift and phase artifacts, due to the long data acquisition under an inhomogeneous static field. In this paper, we apply the ICNE method to a gradient and spin echo (GRASE) multi-echo train pulse sequence in order to provide the multiple k-space lines during a single RF pulse period. We analyze the SNR of the measured multiple Bz data using the proposed ICNE-Multiecho MR pulse sequence. By determining a weighting factor for Bz data in each of the echoes, an optimized inversion formula for the magnetic flux density data is proposed for the ICNE-Multiecho MR sequence. Using the ICNE-Multiecho method, the quality of the measured magnetic flux density is considerably increased by the injection of a long current through the echo train length and by optimization of the voxel-by-voxel noise level of the Bz value. Agarose-gel phantom experiments have demonstrated fewer artifacts and a better SNR using the ICNE-Multiecho method. Experimenting with the brain of an anesthetized dog, we collected valuable echoes by taking into account the noise level of each of the echoes and determined Bz data by determining optimized weighting factors for the multiply acquired magnetic flux density data.

  20. 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 μΦ(0)/(Hz)(1/2) at B = 0 to 2.3 μΦ(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(μ)(1/2) = 62 μ(B)/(Hz))(1/2) at B = 0 and 110 μ(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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  2. Longitudinal variations of the magnetic flux in the heliosphere

    NASA Astrophysics Data System (ADS)

    Dósa, Melinda; Erdős, 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.

  3. Sudden flux change studies in high field superconducting accelerator magnets

    SciTech Connect

    Feher, S.; Bordini, B.; Carcagno, R.; Makulski, A.; Orris, D.F.; Pischalnikov, Y.M.; Sylvester, C.; Tartaglia, M.; Tompkins, J.C.; Zlobin, A.V.; /Fermilab

    2004-10-01

    As part of the High Field Magnet Program at Fermilab many magnets have been tested which utilize multi strand Rutherford type cable made of state-of-the art Nb{sub 3}Sn strands. During these magnet tests we observed sudden flux changes by monitoring coil voltages and the magnetic field close to the magnets. These flux changes might be linked to magnet instabilities. The voltage spike signals were correlated with quench antenna signals, a strong indication that these are magnet phenomena. With a new high resolution voltage spike detection system, we were able to observe the detailed structure of the spikes. Two fundamentally different signal shapes were distinguished, most likely generated by different mechanisms.

  4. Electron heat flux dropouts in the solar wind: evidence for interplanetary magnetic field reconnection

    SciTech Connect

    McComas, D. J.; Gosling, J. T.; Phillips, J. L.; Bame, S. J.; Luhmann, J. G.; Smith, E. J.

    1989-06-01

    Electron heat flux dropout events have been observed in the solar wind using the ISEE 3 plasma electron data set. These events manifest themselves as dropouts of the solar wind halo electrons which are normally found streaming outward along the local magnetic field. These dropouts leave nearly isotropic distributions of solar wind halo electrons, and consequently, the heat flux in these events is reduced to near the observational noise level. We have examined ISEE 3 data from shortly after launch (August 16, 1978) through the end of 1978 and identified 25 such events ranging in duration from 20 min to over 11 hours. Comparison with the ISEE 3 magnetometer data indicates that these intervals nearly always occur in conjunction with large rotations of the interplanetary magnetic field. Statistical analyses of the plasma and magnetic field data for the 25 dropout intervals indicate that heat flux dropouts generally occur in association with high plasma densities low plasma velocities, low ion and electron temperatures, and low magnetic field magnitudes. A second set of 25 intervals chosen specifically to lie at large field rotations, but at times at which not heat flux dropouts were observed, do not show these characteristic plalsma variations. This suggests that the dropout intervals comprise a unique set of events. Since the hot halo electrons normally found streaming outward from the Sun along the interplanetary magnetic field (the solar wind electron heat flux) are a result of direct magnetic connection to the hot solar corona, heat flux dropout intervals may indicate that the spacecraft is sampling plasma regimes which are magnetically disconnected from the Sun and instead are connected to the outer heliosphere at both ends.

  5. Superpoissonian shot noise in organic magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Cascales, Juan Pedro; Hong, Jhen-Yong; Martinez, Isidoro; Lin, Minn-Tsong; Szczepański, Tomasz; Dugaev, Vitalii K.; Barnaś, Józef; Aliev, Farkhad G.

    2014-12-01

    Organic molecules have recently revolutionized ways to create new spintronic devices. Despite intense studies, the statistics of tunneling electrons through organic barriers remains unclear. Here, we investigate conductance and shot noise in magnetic tunnel junctions with 3,4,9,10-perylene-teracarboxylic dianhydride (PTCDA) barriers a few nm thick. For junctions in the electron tunneling regime, with magnetoresistance ratios between 10% and 40%, we observe superpoissonian shot noise. The Fano factor exceeds in 1.5-2 times the maximum values reported for magnetic tunnel junctions with inorganic barriers, indicating spin dependent bunching in tunneling. We explain our main findings in terms of a model which includes tunneling through a two level (or multilevel) system, originated from interfacial bonds of the PTCDA molecules. Our results suggest that interfaces play an important role in the control of shot noise when electrons tunnel through organic barriers.

  6. Superpoissonian shot noise in organic magnetic tunnel junctions

    SciTech Connect

    Cascales, Juan Pedro; Martinez, Isidoro; Aliev, Farkhad G.; Hong, Jhen-Yong; Lin, Minn-Tsong; Szczepański, Tomasz; Dugaev, Vitalii K.; Barnaś, Józef

    2014-12-08

    Organic molecules have recently revolutionized ways to create new spintronic devices. Despite intense studies, the statistics of tunneling electrons through organic barriers remains unclear. Here, we investigate conductance and shot noise in magnetic tunnel junctions with 3,4,9,10-perylene-teracarboxylic dianhydride (PTCDA) barriers a few nm thick. For junctions in the electron tunneling regime, with magnetoresistance ratios between 10% and 40%, we observe superpoissonian shot noise. The Fano factor exceeds in 1.5–2 times the maximum values reported for magnetic tunnel junctions with inorganic barriers, indicating spin dependent bunching in tunneling. We explain our main findings in terms of a model which includes tunneling through a two level (or multilevel) system, originated from interfacial bonds of the PTCDA molecules. Our results suggest that interfaces play an important role in the control of shot noise when electrons tunnel through organic barriers.

  7. Magnetic flux density reconstruction using interleaved partial Fourier acquisitions in MREIT.

    PubMed

    Park, Hee Myung; Nam, Hyun Soo; Kwon, Oh In

    2011-04-01

    Magnetic resonance electrical impedance tomography (MREIT) has been introduced as a non-invasive modality to visualize the internal conductivity and/or current density of an electrically conductive object by the injection of current. In order to measure a magnetic flux density signal in MREIT, the phase difference approach in an interleaved encoding scheme cancels the systematic artifacts accumulated in phase signals and also reduces the random noise effect. However, it is important to reduce scan duration maintaining spatial resolution and sufficient contrast, in order to allow for practical in vivo implementation of MREIT. The purpose of this paper is to develop a coupled partial Fourier strategy in the interleaved sampling in order to reduce the total imaging time for an MREIT acquisition, whilst maintaining an SNR of the measured magnetic flux density comparable to what is achieved with complete k-space data. The proposed method uses two key steps: one is to update the magnetic flux density by updating the complex densities using the partially interleaved k-space data and the other is to fill in the missing k-space data iteratively using the updated background field inhomogeneity and magnetic flux density data. Results from numerical simulations and animal experiments demonstrate that the proposed method reduces considerably the scanning time and provides resolution of the recovered B(z) comparable to what is obtained from complete k-space data. PMID:21386139

  8. Magnetic flux density reconstruction using interleaved partial Fourier acquisitions in MREIT

    NASA Astrophysics Data System (ADS)

    Park, Hee Myung; Nam, Hyun Soo; In Kwon, Oh

    2011-04-01

    Magnetic resonance electrical impedance tomography (MREIT) has been introduced as a non-invasive modality to visualize the internal conductivity and/or current density of an electrically conductive object by the injection of current. In order to measure a magnetic flux density signal in MREIT, the phase difference approach in an interleaved encoding scheme cancels the systematic artifacts accumulated in phase signals and also reduces the random noise effect. However, it is important to reduce scan duration maintaining spatial resolution and sufficient contrast, in order to allow for practical in vivo implementation of MREIT. The purpose of this paper is to develop a coupled partial Fourier strategy in the interleaved sampling in order to reduce the total imaging time for an MREIT acquisition, whilst maintaining an SNR of the measured magnetic flux density comparable to what is achieved with complete k-space data. The proposed method uses two key steps: one is to update the magnetic flux density by updating the complex densities using the partially interleaved k-space data and the other is to fill in the missing k-space data iteratively using the updated background field inhomogeneity and magnetic flux density data. Results from numerical simulations and animal experiments demonstrate that the proposed method reduces considerably the scanning time and provides resolution of the recovered Bz comparable to what is obtained from complete k-space data.

  9. 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.

  10. Localization of Metal-Induced Gap States at the Metal-Insulator Interface: Origin of Flux Noise in SQUIDs and Superconducting Qubits

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

    The origin of magnetic flux noise in dc Superconducting Quantum Interference Devices (SQUIDs) with a power spectrum scaling as 1/f (f is frequency) has been a puzzle for over 25 years. This noise limits both the low frequency performance of SQUIDs and the decoherence time of flux-sensitive superconducting qubits, making scaling-up for quantum computing problematic. Recent calculations and experiments indicate that the noise is generated by electrons that randomly reverse their spin directions. Their areal density of ˜ 5 x 10^17 m-2 is relatively insensitive to the nature of the superconductor and substrate. Here, we propose that the local magnetic moments originate in metal-induced gap states (MIGSs) localized by potential disorder at the metal-insulator interface. MIGSs are particularly sensitive to such disorder, so that the localized states have a Coulomb repulsion sufficiently large to make them singly occupied. Our calculations demonstrate that a modest level of disorder generates the required areal density of localized moments. This result suggests that magnetic flux noise could be reduced by fabricating superconductor-insulator interfaces with less disorder. Support: NSF DMR07-05941, US DOE De-AC02-05CH11231, Samsung Foundation, Teragrid, NERSC.

  11. SIGNATURES OF MAGNETIC RECONNECTION AT BOUNDARIES OF INTERPLANETARY SMALL-SCALE MAGNETIC FLUX ROPES

    SciTech Connect

    Tian Hui; Yao Shuo; Zong Qiugang; Qi Yu; He Jiansen

    2010-09-01

    The interaction between interplanetary small-scale magnetic flux ropes and the magnetic field in the ambient solar wind is an important topic in the understanding of the evolution of magnetic structures in the heliosphere. Through a survey of 125 previously reported small flux ropes from 1995 to 2005, we find that 44 of them reveal clear signatures of Alfvenic fluctuations and thus classify them as Alfven wave trains rather than flux ropes. Signatures of magnetic reconnection, generally including a plasma jet of {approx}30 km s{sup -1} within a magnetic field rotational region, are clearly present at boundaries of about 42% of the flux ropes and 14% of the wave trains. The reconnection exhausts are often observed to show a local increase in the proton temperature, density, and plasma beta. About 66% of the reconnection events at flux rope boundaries are associated with a magnetic field shear angle larger than 90{sup 0} and 73% of them reveal a decrease of 20% or more in the magnetic field magnitude, suggesting a dominance of anti-parallel reconnection at flux rope boundaries. The occurrence rate of magnetic reconnection at flux rope boundaries through the years 1995-2005 is also investigated and we find that it is relatively low around the solar maximum and much higher when approaching solar minima. The average magnetic field depression and shear angle for reconnection events at flux rope boundaries also reveal a similar trend from 1995 to 2005. Our results demonstrate for the first time that boundaries of a substantial fraction of small-scale flux ropes have properties similar to those of magnetic clouds, in the sense that both of them exhibit signatures of magnetic reconnection. The observed reconnection signatures could be related either to the formation of small flux ropes or to the interaction between flux ropes and the interplanetary magnetic fields.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

    Gošić, 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.

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

    SciTech Connect

    Gošić, M.; Rubio, L. R. Bellot; Del Toro Iniesta, J. C.; Orozco Suárez, D.; Katsukawa, Y.

    2014-12-10

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

  15. Magnetic flux quantization effects in disordered bismuth

    SciTech Connect

    Rajasekharan, K.; Boughton, R.I.; Yin, F.F.; Sumanasekera, G. . Dept. of Physics)

    1988-10-01

    Measurements have been carried out on the oscillatory part of the low field magnetoresistance of thin disordered bismuth films. Observations of the flux quantization oscillations and their harmonics yield values for the electron diffusion length in this material, L/sub phi/. The results are discussed in terms of the implications of the weak localization theory of Altshuler, Aronov and Spivak.

  16. 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 ɛ 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 ɛ 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.

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

    NASA Astrophysics Data System (ADS)

    Erdős, 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.

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

    SciTech Connect

    Erdős, G.; Balogh, A.

    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.

  19. Correlated low-frequency electric and magnetic noise along the auroral field lines

    NASA Technical Reports Server (NTRS)

    Gurnett, D. A.; Huff, R. L.; Menietti, J. D.; Burch, J. L.; Winningham, J. D.; Shawhan, S. D.

    1984-01-01

    Dynamics Explorer 1 measurements of intense low-frequency electric and magnetic noise observed at low altitudes over the auroral zone are described. The intensity of both the electric and magnetic fields decreases rapidly with increasing frequency. Most of the energy is at frequencies below the O(+) cyclotron frequency, and some evidence is found for a cutoff or change in spectral slope near that frequency. The magnetic to electric field ratio decreases rapidly with increasing radial distance and also decreases with increasing frequency. The polarization of the electric field in a plane perpendicular to the earth's magnetic field is essentially random. The transverse electric and magnetic fields are closely correlated, with the average Poynting flux directed toward the earth. The total electromagnetic power flow associated with the noise is substantial. Two general models are discussed to interpret these observations, one based on static electric and magnetic fields imbedded in the ionosphere and the other based on Alfven waves propagating along the auroral field lines.

  20. Measurements of EUV coronal holes and open magnetic flux

    SciTech Connect

    Lowder, C.; Qiu, J.; Leamon, R.; Liu, Y.

    2014-03-10

    Coronal holes are regions on the Sun's surface that map the footprints of open magnetic field lines. We have developed an automated routine to detect and track boundaries of long-lived coronal holes using full-disk extreme-ultraviolet (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 potential field source surface (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)× 10{sup 22} Mx. The solar cycle dependence of these measurements is 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 measured much enhanced open magnetic flux in the range of (2-4)× 10{sup 22} Mx, which is about twice the flux measured by EIT, and matches with the PFSS calculated open flux, with discrepancies in the location and strength of coronal holes. A detailed comparison between the three measurements (by EIT, AIA-EUVI, and PFSS) indicates that coronal holes in low latitudes contribute significantly to the total open magnetic flux. These low-latitude coronal holes are not well measured with either the He I 10830 line in previous studies, or EIT EUV images; neither are they well captured by the static PFSS model. The enhanced observations from AIA/EUVI allow a more accurate measure of these low-latitude coronal holes and their contribution to open magnetic flux.

  1. Controlling the motion of magnetic flux quanta.

    PubMed

    Zhu, B Y; Marchesoni, F; Nori, Franco

    2004-05-01

    We study the transport of vortices in superconductors with triangular arrays of boomerang- or V-shaped asymmetric pinning wells, when applying an alternating electrical current. The asymmetry of the pinning landscape induces a very efficient "diode" effect, that allows the sculpting at will of the magnetic field profile inside the sample. We present the first quantitative study of magnetic "lensing" of fluxons inside superconductors. Our proposed vortex lens provides a near threefold increase of the vortex density at its "focus" regions. The main numerical features have been derived analytically. PMID:15169477

  2. Magnetic clouds, helicity conservation, and intrinsic scale flux ropes

    NASA Technical Reports Server (NTRS)

    Kumar, A.; Rust, D. M.

    1995-01-01

    An intrinsic-scale flux-rope model for interplanetary magnetic clouds, incorporating conservation of magnetic helicity, flux and mass is found to adequately explain clouds' average thermodynamic and magnetic properties. In spite their continuous expansion as they balloon into interplanetary space, magnetic clouds maintain high temperatures. This is shown to be due to magnetic energy dissipation. The temperature of an expanding cloud is shown to pass through a maximum above its starting temperature if the initial plasma beta in the cloud is less than 2/3. Excess magnetic pressure inside the cloud is not an important driver of the expansion as it is almost balanced by the tension in the helical field lines. It is conservation of magnetic helicity and flux that requires that clouds expand radially as they move away from the Sun. Comparison with published data shows good agreement between measured cloud properties and theory. Parameters determined from theoretical fits to the data, when extended back to the Sun, are consistent with the origin of interplanetary magnetic clouds in solar filament eruptions. A possible extension of the heating mechanism discussed here to heating of the solar corona is discussed.

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  4. A generalized flux function for three-dimensional magnetic reconnection

    SciTech Connect

    Yeates, A. R.; Hornig, G.

    2011-10-15

    The definition and measurement of magnetic reconnection in three-dimensional magnetic fields with multiple reconnection sites is a challenging problem, particularly in fields lacking null points. We propose a generalization of the familiar two-dimensional concept of a magnetic flux function to the case of a three-dimensional field connecting two planar boundaries. In this initial analysis, we require the normal magnetic field to have the same distribution on both boundaries. Using hyperbolic fixed points of the field line mapping, and their global stable and unstable manifolds, we define a unique flux partition of the magnetic field. This partition is more complicated than the corresponding (well-known) construction in a two-dimensional field, owing to the possibility of heteroclinic points and chaotic magnetic regions. Nevertheless, we show how the partition reconnection rate is readily measured with the generalized flux function. We relate our partition reconnection rate to the common definition of three-dimensional reconnection in terms of integrated parallel electric field. An analytical example demonstrates the theory and shows how the flux partition responds to an isolated reconnection event.

  5. Magnetic flux cancellation and Doppler shifts in flaring active regions

    NASA Astrophysics Data System (ADS)

    Burtseva, Olga; Petrie, Gordon

    2016-05-01

    Flux cancellation plays an important role in some theories of solar eruptions. The mechanism of flux cancellation is suggested by many models to be a necessary condition of flare initiation as a part of slow reconnection processes in the lower atmosphere. In our earlier work we analyzed flux cancellation events during major flares using GONG line-of-sight magnetograms. In this work we use vector magnetic field data from SDO/HMI for better interpretation of the longitudinal field changes. We also compute Doppler velocity shifts at the cancellation sites in attempt to distinguish between the three physical processes that could stand behind flux removal from the photosphere: submergence of U-shaped loops, emergence of Ω-shaped loops and magnetic reconnection.

  6. The magnetotail and substorms. [magnetic flux transport model

    NASA Technical Reports Server (NTRS)

    Russell, C. T.; Mcpherron, R. L.

    1973-01-01

    The tail plays a very active and important role in substorms. Magmetic flux eroded from the dayside magnetosphere is stored here. As more and more flux is transported to the magnetotail and stored, the boundary flares more, the field strength in the tail increases, and the currents strengthen and move closer to the earth. Further, the plasma sheet thins and the magnetic flux crossing the neutral sheet lessens. The experimental evidence for these processes is discussed and a phenomenological or qualitative model of the substorm sequence is presented. In this model, the flux transport is driven by the merging of the magnetospheric and interplanetary magnetic fields. During the growth phase of substorms the merging rate on the dayside magnetosphere exceeds the reconnection rate in the neutral sheet.

  7. The origin of noise and magnetic hysteresis in crystalline permalloy ring-core fluxgate sensors

    NASA Astrophysics Data System (ADS)

    Narod, B. B.

    2014-09-01

    Developed in the 1960s for use in high-performance ring-core fluxgate sensors, 6-81.3 Mo permalloy remains the state of the art for permalloy-cored fluxgate magnetometers. The magnetic properties of 6-81.3, namely magnetocrystalline and magnetoelastic anisotropies and saturation induction, are all optimum in the Fe-Ni-Mo system. In such polycrystalline permalloy fluxgate sensors, a single phenomenon may cause both fluxgate noise and magnetic hysteresis; explain Barkhausen jumps, remanence and coercivity; and avoid domain denucleation. This phenomenon, domain wall reconnection, is presented as part of a theoretical model. In the unmagnetized state a coarse-grain high-quality permalloy foil ideally forms stripe domains, which present at the free surface as parallel, uniformly spaced domain walls that cross the entire thickness of the foil. Leakage flux "in" and "out" of alternating domains is a requirement of the random orientation, grain by grain, of magnetic easy axes' angles with respect to the foil free surface. Its magnetostatic energy together with domain wall energy determines an energy budget to be minimized. Throughout the magnetization cycle the free-surface domain pattern remains essentially unchanged, due to the magnetostatic energy cost such a change would elicit. Thus domain walls are "pinned" to free surfaces. Driven to saturation, domain walls first bulge then reconnect via Barkhausen jumps to form a new domain configuration that I have called "channel domains", which are attached to free surfaces. The approach to saturation now continues as reversible channel domain compression. Driving the permalloy deeper into saturation compresses the channel domains to arbitrarily small thickness, but will not cause them to denucleate. Returning from saturation the channel domain structure will survive through zero H, thus explaining remanence. The Barkhausen jumps, being irreversible exothermic events, are sources of fluxgate noise powered by the energy available from domain wall reconnection. A simplified domain energy model can then provide a predictive relation between ring-core magnetic properties and fluxgate sensor noise power. Four properties are predicted to affect noise power, two of which are well known: saturation total magnetic flux density and magnetic anisotropy. The two additional properties are easy axes alignment and foil thickness. Flux density and magnetic anisotropy are primary magnetic properties determined by an alloy's chemistry and crystalline lattice properties. Easy axes alignment and foil thickness are secondary, geometrical properties related to an alloy's polycrystalline fabric and manufacture. Improvements to fluxgate noise performance can in principle be achieved by optimizing any of these four properties in such a way as to minimize magnetostatic energy. Fluxgate signal power is proportional to B - H loop curvature [d2B/dH2]. The degree to which Barkhausen jumps coincide with loop curvature is a measure of noise that accompanies the fluxgate signal. B - H loops with significant curvature beyond the open hysteresis loop may be used to advantage to acquire the fluxgate signal with reduced noise.

  8. The origin of noise and magnetic hysteresis in crystalline permalloy ring-core fluxgate sensors

    NASA Astrophysics Data System (ADS)

    Narod, B. B.

    2014-06-01

    6-81.3 Mo permalloy, developed in the 1960s for use in high performance ring-core fluxgate sensors, remains the state-of-the-art for permalloy-cored fluxgate magnetometers. The magnetic properties of 6-81.3, namely magnetocrystalline and magnetoelastic anisotropies and saturation induction are all optimum in the Fe-Ni-Mo system. In such polycrystalline permalloy fluxgate sensors a single phenomenon may cause both fluxgate noise and magnetic hysteresis, explain Barkhausen jumps, remanence and coercivity, and avoid domain denucleation. The phenomenon, domain wall reconnection, is presented as part of a theoretical model. In the unmagnetized state a coarse-grain high-quality permalloy foil ideally forms stripe domains, which present at the free surface as parallel, uniformly spaced domain walls that cross the entire thickness of the foil. Leakage flux "in" and "out" of alternating domains is a requirement of the random orientation, grain-by-grain, of magnetic easy axes' angles with respect to the foil free surface. Its magnetostatic energy together with domain wall energy determines an energy budget to be minimized. Throughout the magnetization cycle the free surface domain pattern remains essentially unchanged, due to the magnetostatic energy cost such a change would elicit. Thus domain walls are "pinned" to free surfaces. Driven to saturation, domain walls first bulge then reconnect via Barkhausen jumps to form a new domain configuration this author has called "channel domains", that are attached to free surfaces. The approach to saturation now continues as reversible channel domain compression. Driving the permalloy deeper into saturation compresses the channel domains to arbitrarily small thickness, but will not cause them to denucleate. Returning from saturation the channel domain structure will survive through zero H, thus explaining remanence. The Barkhausen jumps being irreversible exothermic events are sources of fluxgate noise, powered by the energy available from domain wall reconnection. A simplified domain energy model can then provide a predictive relation between ring core magnetic properties and fluxgate sensor noise power. Four properties are predicted to affect noise power, two of which, are well known: saturation total magnetic flux density and magnetic anisotropy. The two additional properties are easy axes alignment and foil thickness. Flux density and magnetic anisotropy are primary magnetic properties determined by an alloy's chemistry and crystalline lattice properties. Easy axes alignment and foil thickness are secondary, geometrical properties related to an alloy's polycrystalline fabric and manufacture. Improvements to fluxgate noise performance can in principle be achieved by optimizing any of these four properties in such a way as to minimize magnetostatic energy. Fluxgate signal power is proportional to B-H loop curvature (d2B/dH2). The degree to which Barkhausen jumps coincide with loop curvature is a measure of noise that accompanies fluxgate signal. B-H loops with significant curvature beyond the open hysteresis loop may be used to advantage to acquire fluxgate signal with reduced noise.

  9. 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.

  10. Temperature coefficient improvement for low noise magnetic measurements in LISA

    NASA Astrophysics Data System (ADS)

    Mateos, I.; Diaz-Aguiló, M.; Gibert, F.; Lloro, I.; Lobo, A.; Nofrarias, M.; Ramos-Castro, J.

    2012-06-01

    Previous research with Anisotropic Magnetoresistive sensors (AMR) have shown significant improvements for weak magnetic field applications using dedicated noise reduction techniques in the signal conditioning circuit. However, an important source of error that must be addressed is the thermal dependence of the sensor system, more significant in the AMR sensitivity. The external temperature fluctuations affect the output of the sensors due to the temperature coefficient of the magnetoresistors, which may cause an increase of the estimation of the noise spectral density at low frequencies. Ongoing research using a low noise/low temperature coefficient current source to supply the sensor's bridge enhances the thermal performance of the sensors at the lower end of the LISA bandwidth. Preliminary results are shown in this paper.

  11. Modeled ground magnetic signatures of flux transfer events

    NASA Technical Reports Server (NTRS)

    Mchenry, Mark A.; Clauer, C. Robert

    1987-01-01

    The magnetic field on the ground due to a small (not greater than 200 km scale size) localized field-aligned current (FAC) system interacting with the ionosphere is calculated in terms of an integral over the ionospheric distribution of FAC. Two different candidate current systems for flux transfer events (FTEs) are considered: (1) a system which has current flowing down the center of a cylindrical flux tube with a return current uniformly distributed along the outside edge; and (2) a system which has upward current on one half of the perimeter of a cylindrical flux tube with downward current on the opposite half. The peak magnetic field on the ground is found to differ by a factor of 2 between the two systems, and the magnetic perturbations are in different directions depending on the observer's position.

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

    SciTech Connect

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

    2008-10-15

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

  13. Theory and Application of Magnetic Flux Leakage Pipeline Detection

    PubMed Central

    Shi, Yan; Zhang, Chao; Li, Rui; Cai, Maolin; Jia, Guanwei

    2015-01-01

    Magnetic flux leakage (MFL) detection is one of the most popular methods of pipeline inspection. It is a nondestructive testing technique which uses magnetic sensitive sensors to detect the magnetic leakage field of defects on both the internal and external surfaces of pipelines. This paper introduces the main principles, measurement and processing of MFL data. As the key point of a quantitative analysis of MFL detection, the identification of the leakage magnetic signal is also discussed. In addition, the advantages and disadvantages of different identification methods are analyzed. Then the paper briefly introduces the expert systems used. At the end of this paper, future developments in pipeline MFL detection are predicted. PMID:26690435

  14. Theory and Application of Magnetic Flux Leakage Pipeline Detection.

    PubMed

    Shi, Yan; Zhang, Chao; Li, Rui; Cai, Maolin; Jia, Guanwei

    2015-01-01

    Magnetic flux leakage (MFL) detection is one of the most popular methods of pipeline inspection. It is a nondestructive testing technique which uses magnetic sensitive sensors to detect the magnetic leakage field of defects on both the internal and external surfaces of pipelines. This paper introduces the main principles, measurement and processing of MFL data. As the key point of a quantitative analysis of MFL detection, the identification of the leakage magnetic signal is also discussed. In addition, the advantages and disadvantages of different identification methods are analyzed. Then the paper briefly introduces the expert systems used. At the end of this paper, future developments in pipeline MFL detection are predicted. PMID:26690435

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

    NASA Astrophysics Data System (ADS)

    Owens, M. J.

    2016-02-01

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

  16. Properties of magnetic helicity flux in turbulent dynamos

    SciTech Connect

    Vishniac, Ethan T.; Shapovalov, Dmitry E-mail: dmsh@jhu.edu

    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.

  17. Hamiltonian magnetic reconnection with parallel electron heat flux dynamics

    NASA Astrophysics Data System (ADS)

    Grasso, D.; Tassi, E.

    2015-10-01

    > We analyse, both analytically and numerically, a two-dimensional six-field fluid model for collisionless magnetic reconnection, accounting for temperature and heat flux fluctuations along the direction of the magnetic guide field. We show that the model possesses a Hamiltonian structure with a non-canonical Poisson bracket. This bracket is characterized by the presence of six infinite families of Casimirs, associated with Lagrangian invariants. This reveals that the model can be reformulated as a system of advection equations, thus generalizing previous results obtained for Hamiltonian isothermal fluid models for reconnection. Numerical simulations indicate that the presence of heat flux and temperature fluctuations yields slightly larger growth rates and similar saturated island amplitudes, with respect to the isothermal models. For values of the sonic Larmor radius much smaller than the electron skin depth, heat flux fluctuations tend to be suppressed and temperature fluctuations follow density fluctuations. Increasing the sonic Larmor radius results in an increasing fraction of magnetic energy converted into heat flux, at the expense of temperature fluctuations. In particular, heat flux fluctuations tend to become relevant along the magnetic island separatrices. The qualitative structures associated with the electron field variables are also reinterpreted in terms of the rotation of the Lagrangian invariants of the system.

  18. The magnetic flux in the quiet sun network

    NASA Technical Reports Server (NTRS)

    Labonte, B. J.; Howard, R.

    1982-01-01

    Direct magnetic measurements are used to confirm that the Ca II K line emission from the quiet sun network does not vary with the 11 year cycle (White and Livingston, 1981). As the K emission intensity is correlated with magnetic field strength, magnetic flux measurements are valid for comparison. Data were taken from the full-disk Mount Wilson daily magnetograms, and the aperture was decreased from 17.5 to 12.5 during the interval 1970 through 1980. Measurements are restricted to the latitude zones centered on + or - 1.7 degrees. The mean total flux in the + or - 15.3 degree zones increased by a factor of 10 between activity minimum and maximum, and the quiet sun flux shows no variation, thus confirming White and Livingston's (1981) result. In order for the amplitude of the quiet sun magnetic flux to remain constant, a balance between increasing and decreasing factors must exist, and the primary factor in this balance is the rate of destruction of the quiet sun flux.

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

    SciTech Connect

    Leake, James E.; Linton, Mark G.; Török, Tibor

    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.

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

    SciTech Connect

    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{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}

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

    SciTech Connect

    Xia, C.; Keppens, R.; Guo, Y.

    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.

  2. Explosive instability and erupting flux tubes in a magnetized plasma

    PubMed Central

    Cowley, S. C.; Cowley, B.; Henneberg, S. A.; Wilson, H. R.

    2015-01-01

    The eruption of multiple flux tubes in a magnetized plasma is proposed as a mechanism for explosive release of energy in plasmas. A significant fraction of the linearly stable isolated flux tubes are shown to be metastable in a box model magnetized atmosphere in which ends of the field lines are embedded in conducting walls. The energy released by destabilizing such field lines can be a large proportion of the gravitational energy stored in the system. This energy can be released in a fast dynamical time. PMID:26339193

  3. Sausage Mode Propagation in a Thick Magnetic Flux Tube

    NASA Astrophysics Data System (ADS)

    Pardi, A.; Ballai, I.; Marcu, A.; Orza, B.

    2014-04-01

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

  4. 1/f noise and susceptibility-magnetization correlation in disordered ferromagnets

    NASA Astrophysics Data System (ADS)

    Kechedzhi, Kostyantyn

    2011-03-01

    We consider a strongly disordered ferromagnet modeled by Ising spins placed at random in 2D with ferromagnetic interactions decaying exponentially with inter-site distance. Ferromagnetic phase in this model arises due to formation of infinite percolation cluster of strongly interacting spins. Fractal nature of the percolation cluster manifests itself in the dynamics of the system in the vicinity of the percolation transition. Simulating the dynamics with single spin flip Monte Carlo algorithm we observe 1/f power spectra of magnetization noise in a wide temperature range near the transition. Subjected to external AC magnetic field the system shows significant cross-correlation between susceptibility and magnetization in the ferromagnetic phase. This results suggest a possible explanation of the inductance-flux cross-correlation recently observed in SQUIDs. This work is done in collaboration with Lara Faoro and Lev B. Ioffe.

  5. Inference of physical phenomena from FFTF (Fast Flux Test Facility) noise analysis

    SciTech Connect

    Thie, J.A.; Damiano, B.; Campbell, L.R.

    1989-01-01

    The source of features observed in noise spectra collected by an automated data collection system operated by the Oak Ridge National Laboratory at the Fast Flux Test Facility (FFTF) can be identified using a methodology based on careful data observation and intuition. When a large collection of data is available, as in this case, automatic pattern recognition and parameter storage and retrieval using a data base can be used to extract useful information. However, results can be limited to empirical signature comparison monitoring unless an effort is made to determine the noise sources. This paper describes the identification of several FFTF noise data phenomena and suggests how this understanding may lead to new or enhanced monitoring. 13 refs., 4 figs.

  6. 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.

  7. Magnetic flux generation and transport in cool stars

    NASA Astrophysics Data System (ADS)

    Işık, 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 αΩ 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 αΩ 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

  8. MESSENGER Observations of Magnetic Flux Ropes in Mercury's Plasma Sheet

    NASA Astrophysics Data System (ADS)

    DiBraccio, Gina A.; Slavin, James A.; Imber, Suzanne M.; Gershman, Daniel J.; Raines, Jim M.; Boardsen, Scott A.; Anderson, Brian J.; Korth, Haje; Zurbuchen, Thomas H.; McNutt, Ralph L., Jr.; Solomon, Sean C.

    2014-05-01

    MESSENGER orbital observations provide a new opportunity to investigate magnetic reconnection in the cross-tail current sheet of Mercury's magnetotail. Here we use measurements collected by the Magnetometer and Fast Imaging Plasma Spectrometer (FIPS) during 'hot seasons,' when the orbital periapsis is on Mercury's dayside and MESSENGER crosses the plasma sheet at distances of ~1.5 to 3 RM (where RM is Mercury's radius, or 2440 km). These data frequently contain signatures of large-scale magnetic reconnection in the form of plasmoid-type magnetic flux ropes and southward magnetic fields in the post-plasmoid plasma sheet. In the cross-tail current sheet, which separates the north and south lobes of the magnetotail, flux ropes are formed by reconnection at two or more X-lines and are then transported either toward or away from the planet by the Alfvénic flow emanating from the X-lines. Here we present a survey of 49 plasmoid-type flux ropes identified during seven MESSENGER 'hot seasons,' for which minimum variance analysis indicates that the spacecraft passed near the central axis of the structure. The locations of the selected flux ropes range between 1.7 and 2.8 RM down the tail from the center of the planet. With FIPS measurements, we determined an average proton density of 2.55 cm-3 in the adjacent plasma sheet surrounding the flux ropes, implying an Alfvén speed of ~450 km s-1. Under the assumption that the flux ropes are moving at the local Alfvén speed, we used the mean duration of 0.74 ± 0.15 s to calculate a typical diameter of ~0.14 RM, or ~340 km. We have modeled the plasmoids as force-free flux ropes in order to confirm this result. A superposed epoch analysis demonstrates that the magnetic structure of the flux ropes is similar to what is observed at Earth, but the timescales are 40 times faster at Mercury. The results of this flux rope survey indicate that intense magnetic reconnection occurs frequently in the cross-tail current layer of this small but extremely dynamic magnetosphere.

  9. Magnetic flux-load current interactions in ferrous conductors

    NASA Astrophysics Data System (ADS)

    Cannell, Michael J.; McConnell, Richard A.

    1992-06-01

    A modeling technique has been developed to account for interactions between load current and magnetic flux in an iron conductor. Such a conductor would be used in the active region of a normally conducting homopolar machine. This approach has been experimentally verified and its application to a real machine demonstrated. Additionally, measurements of the resistivity of steel under the combined effects of magnetic field and current have been conducted.

  10. 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 Φ0/Hz1 /2 in the thermal white-noise limit, which yields spin sensitivities of a few μB/Hz1 /2 (Φ0 is the magnetic flux quantum, and μB 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.

  11. Simulation of magnetic hysteresis loops and magnetic Barkhausen noise of α-iron containing nonmagnetic particles

    SciTech Connect

    Li, Yi; Xu, Ben; Hu, Shenyang Y.; Li, Yulan; Li, Qiulin; Liu, Wei

    2015-09-25

    Hysteresis loops and Magnetic Barkhausen Noise in a single crystal α-iron containing a nonmagnetic particle were simulated based on the Laudau-Lifshitz-Gilbert equation. The analyses of domain morphologies and hysteresis loops show that reversal magnetization process is control by nucleation of reversed domains at nonmagnetic particle when the particle size reaches a particle value. In such a situation, the value of nucleation field is determined by the size of nonmagnetic particles, and moreover, coercive field and Magnetic Barkhausen Noise signal are strongly affected by the nucleation field of reversed domains.

  12. 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.

  13. DISTRIBUTION OF MAGNETIC HELICITY FLUX WITH SOLAR CYCLES

    SciTech Connect

    Zhang, Hongqi; Yang, Shangbin

    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.

  14. Enhanced solar antineutrino flux in random magnetic fields

    NASA Astrophysics Data System (ADS)

    Miranda, O. G.; Rashba, T. I.; Rez, A. I.; Valle, J. W.

    2004-12-01

    We discuss the impact of the recent KamLAND constraint on the solar antineutrino flux on the analysis of solar neutrino data in the presence of Majorana neutrino transition magnetic moments and solar magnetic fields. We consider different stationary solar magnetic field models, both regular and random, highlighting the strong enhancement in the antineutrino production rates that characterize turbulent solar magnetic field models. Moreover, we show that for such magnetic fields inside the Sun, one can constrain the intrinsic neutrino magnetic moment down to the level of μν≲few×10-12μB irrespective of details of the underlying turbulence model. This limit is more stringent than all current experimental sensitivities, and similar to the most stringent bounds obtained from stellar cooling. We also comment on the robustness of this limit and show that at most it might be weakened by 1 order of magnitude, under very unlikely circumstances.

  15. 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.

    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.

  16. Mean square value of noise equivalent magnetic induction for magnetic microsensors

    NASA Astrophysics Data System (ADS)

    Panait, Cornel; Tama?, Razvan; C?runtu, George

    2010-11-01

    The noise-signal at the output of a Hall magnetic sensor can be interpreted as a results of an equivalent magnetic induction, acting on a noiseless Hall device. In the paperwork is defined this characteristic for two Hall devices realised in the bipolar and the MOS integrated circuits technology. The influence of geometry and material properties on these essential parameters in the characterisation of magnetic sensors performances, can be emphasised by simulating a few Hall devices structures.

  17. Calculation of magnetic field noise from high-permeability magnetic shields and conducting objects with simple geometry

    NASA Astrophysics Data System (ADS)

    Lee, S.-K.; Romalis, M. V.

    2008-04-01

    High-permeability magnetic shields generate magnetic field noise that can limit the sensitivity of modern precision measurements. We show that calculations based on the fluctuation-dissipation theorem allow quantitative evaluation of magnetic field noise, either from current or magnetization fluctuations, inside enclosures made of high-permeability materials. Explicit analytical formulas for the noise are derived for a few axially symmetric geometries, which are compared with results of numerical finite element analysis. Comparison is made between noises caused by current and magnetization fluctuations inside a high-permeability shield and also between current-fluctuation-induced noises inside magnetic and nonmagnetic conducting shells. A simple model is suggested to predict power-law decay of noise spectra beyond a quasi-static regime. Our results can be used to assess noise from existing shields and to guide design of new shields for precision measurements.

  18. Noise-induced bifurcations in magnetization dynamics of uniaxial nanomagnets

    SciTech Connect

    Serpico, C. Perna, S.; Quercia, A.; Bertotti, G.; D'Aquino, M.; Mayergoyz, I. D.

    2015-05-07

    Stochastic magnetization dynamics in uniformly magnetized nanomagnets is considered. The system is assumed to have rotational symmetry as the anisotropy axis, the applied field, and the spin polarization are all aligned along an axis of symmetry. By appropriate integration of the Fokker-Planck equation associated to the problem, the stochastic differential equation governing the evolution of the angle between the magnetization orientation and the symmetry axis is derived. The drift terms present in this equation contain a noise-induced drift term, which, in combination with drift terms of deterministic origin, can be written as the derivative of an effective potential. Superparamagnetic-like transitions are studied in connections with the bifurcations of the effective potential as temperature and excitation conditions are varied.

  19. An Emerging Magnetic Flux Catalog for SOHO/MDI

    NASA Astrophysics Data System (ADS)

    Lamb, Derek; Munoz-Jaramillo, Andres; DeForest, Craig

    2016-05-01

    We present a catalog of emerging magnetic flux events covering the entirety of the 15-year-long SOHO/MDI 96-minute magnetogram dataset. Such a catalog has myriad uses in studies of the solar dynamo and solar cycle. Our catalog is designed to mimic as nearly as possible the Emerging Flux region catalog produced for SDO/HMI, allowing continuity across missions and solar cycles. We will present details of the algorithm for identifying emerging flux events, special considerations for MDI as opposed to HMI, detailed examples of some detected emerging flux regions, and a brief overview of statistics of the entire catalog. The catalog will be available for querying through the Heliophysics Event Knowledgebase, as well as for direct downloading from Southwest Research Institute. This work has been supported by NASA Grant NNX14AJ67G through the Heliophysics Data Environment Enhancements program.

  20. Plasmas fluxes to surfaces for an oblique magnetic field

    SciTech Connect

    Pitcher, C.S. ); Stangeby, P.C.; Elder, J.D. ); Bell, M.G.; Kilpatrick, S.J.; Manos, D.M.; Medley, S.S.; Owens, D.K.; Ramsey, A.T.; Ulrickson, M. . Plasma Physics Lab.)

    1992-07-01

    The poloidal and toroidal spatial distributions of D{sub {alpha}}, He I and C II emission have been obtained in the vicinity of the TFTR bumper limiter and are compared with models of ion flow to the surface. The distributions are found not to agree with a model (the Cosine'' model) which determines the incident flux density using only the parallel fluxes in the scrape-off layer and the projected area of the surface perpendicular to the field lines. In particular, the Cosine model is not able to explain the significant fluxes observed at locations on the surface which are oblique to the magnetic field. It is further shown that these fluxes cannot be explained by the finite Larmor radius of impinging ions. Finally, it is demonstrated, with the use of Monte Carlo codes, that the distributions can be explained by including both parallel and cross-field transport onto the limiter surface.

  1. Plasmas fluxes to surfaces for an oblique magnetic field

    SciTech Connect

    Pitcher, C.S.; Stangeby, P.C.; Elder, J.D.; Bell, M.G.; Kilpatrick, S.J.; Manos, D.M.; Medley, S.S.; Owens, D.K.; Ramsey, A.T.; Ulrickson, M.

    1992-07-01

    The poloidal and toroidal spatial distributions of D{sub {alpha}}, He I and C II emission have been obtained in the vicinity of the TFTR bumper limiter and are compared with models of ion flow to the surface. The distributions are found not to agree with a model (the ``Cosine`` model) which determines the incident flux density using only the parallel fluxes in the scrape-off layer and the projected area of the surface perpendicular to the field lines. In particular, the Cosine model is not able to explain the significant fluxes observed at locations on the surface which are oblique to the magnetic field. It is further shown that these fluxes cannot be explained by the finite Larmor radius of impinging ions. Finally, it is demonstrated, with the use of Monte Carlo codes, that the distributions can be explained by including both parallel and cross-field transport onto the limiter surface.

  2. Testing the magnetic flux paradigm of AGN jets

    NASA Astrophysics Data System (ADS)

    O'Sullivan, Shane; Gaensler, Bryan; Banfield, Julie; Stil, Jeroen; Croom, Scott; Farnes, Jamie

    2014-04-01

    Recent theoretical work has proposed the 'magnetic-flux paradigm', where the accumulation of magnetic flux around the black hole is the dominant factor in determining the power and radio-loudness of AGN jets (eg. Sikora et al. 2013). From analysis of a large sample of polarized sources from the NVSS, with optical host galaxy identifications, we have found that the 1.4 GHz fractional linear polarization is greater for sources whose accretion-mode favours large accumulation of magnetic flux close to the black hole. However, from the current data, we cannot determine whether this relation is due to greater ordering of the magnetic field in the source or less Faraday depolarisation caused by the surrounding environment. Therefore, we propose broadband (1 to 10 GHz), high angular resolution (6 km config), spectropolarimetric ATCA observations (108 hrs total) to unambiguously determine the Faraday rotation measure environment as well as the intrinsic fractional polarization of the 162 sources in our sample. This will enable the first comprehensive study of the magnetic properties of radio-loud AGN in relation to their host galaxy accretion properties, while also producing the largest dataset to date of high angular-resolution, broadband radio polarization measurements of AGN.

  3. Flux Pileup Magnetic Reconnection at the Terrestrial Magnetopause

    NASA Astrophysics Data System (ADS)

    Dorelli, John; Hesse, Michael; Raeder, Joachim; Rastaetter, Lutz; Kuznetsova, Masha

    2003-10-01

    The physics of flux pileup magnetic reconnection at the subsolar terrestrial magnetopause is addressed. Analytical results for 3D ``fan type'' reconnection are reviewed and compared with global magnetohydrodynamics simulations of subsolar magnetopause reconnection under steady, southward IMF conditions. The scaling of the magnetic flux pileup and the reconnection electric field with plasma resistivity are shown to be consistent with scalings predicted by the 3D stagnation point flow annihilation model of Sonnerup and Priest (J. Plasma Phys., 14, 283-294, 1975) and Craig et al. (ApJ, 485, 383-388, 1997), implying that the reconnection rate should vanish in the infinite Lundquist number limit. Effects of Hall electric fields are addressed using an analytical 2D stagnation point annihilation model which allows flux pileup to saturate well before the reconnection rate begins to drop; nevertheless, our resistive Hall MHD results predict significant pileup at the subsolar magnetopause even for a purely southward IMF orientation. This result is puzzling, since spacecraft observations typically show no significant pileup of magnetic energy at the magnetopause when the IMF is southward. It thus appears that Hall-induced pileup saturation alone cannot account for the lack of observed magnetic energy pileup during subsolar magnetic reconnection under southward IMF conditions.

  4. Materials for efficient high-flux magnetic bearing actuators

    NASA Technical Reports Server (NTRS)

    Williams, M. E.; Trumper, D. L.

    1994-01-01

    Magnetic bearings have demonstrated the capability for achieving positioning accuracies at the nanometer level in precision motion control stages. This makes possible the positioning of a wafer in six degrees of freedom with the precision necessary for photolithography. To control the position of an object at the nanometer level, a model of the magnetic bearing actuator force-current-airgap relationship must be accurately obtained. Additionally, to reduce thermal effects the design of the actuator should be optimized to achieve maximum power efficiency and flux density. Optimization of the actuator is accomplished by proper pole face sizing and utilizing a magnetic core material which can be magnetized to the highest flux density with low magnetic loss properties. This paper describes the construction of a magnetic bearing calibration fixture designed for experimental measurement of the actuator force characteristics. The results of a material study that review the force properties of nickel-steel, silicon-steel, and cobalt-vanadium-iron, as they apply to magnetic bearing applications are also presented.

  5. Magnetic flux leakage inspection of tailor-welded blanks

    NASA Astrophysics Data System (ADS)

    O'Connor, S.; Clapham, L.; Wild, P.

    2002-02-01

    A feasibility study was conducted on the application of magnetic flux leakage (MFL) inspection to the evaluation of weld quality in automotive tailor-welded blanks (TWB). Using a permanent magnet configuration, magnetic flux was directed through the weld region of a TWB. A Hall effect sensor was coupled to the movement of a digital plotter and was, thereby, scanned around the weld region. Signals from the Hall effect sensor were processed and correlated with defects to determine corresponding MFL signatures. Simulated through-hole defects as small as 0.34 mm in diameter were readily detected. Furthermore, there was a reasonably linear relationship between the MFL signals associated with these defects and the diameter of the defect hole. Preliminary tests with specimens having naturally occurring defects such as concavity, pinholes, and undercutting, indicate that the MFL technique has excellent potential as an inspection method in this application.

  6. Coalescence of magnetic flux ropes in the ion diffusion region of magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Wang, Rongsheng; Lu, Quanming; Nakamura, Rumi; Huang, Can; Du, Aimin; Guo, Fan; Teh, Waileong; Wu, Mingyu; Lu, San; Wang, Shui

    2016-03-01

    Magnetic reconnection is an important process in space and laboratory plasmas that effectively converts magnetic energy into plasma kinetic energy within a current sheet. Theoretical work suggested that reconnection occurs through the growth and overlap of magnetic flux ropes that deconstruct magnetic surfaces in the current sheet and enable the diffusion of the magnetic field lines between two sides of the sheet. This scenario was also proposed as a primary mechanism for accelerating energetic particles during reconnection, but experimental evidence has remained elusive. Here, we identify a total of 19 flux ropes during reconnection in the magnetotail. We found that the majority of the ropes are embedded in the Hall magnetic field region and 63% of them are coalescing. These observations show that the diffusion region is filled with flux ropes and that their interaction is intrinsic to the reconnection dynamics, leading to turbulence.

  7. GRANULAR-SCALE MAGNETIC FLUX CANCELLATIONS IN THE PHOTOSPHERE

    SciTech Connect

    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.

  8. Resolving Magnetic Flux Patches at the Surface of the Core

    NASA Technical Reports Server (NTRS)

    OBrien, Michael S.

    1996-01-01

    The geomagnetic field at a given epoch can be used to partition the surface of the liquid outer core into a finite number of contiguous regions in which the radial component of the magnetic flux density, B (sub r), is of one sign. These flux patches are instrumental in providing detail to surface fluid flows inferred from the changing geomagnetic field and in evaluating the validity of the frozen-flux approximation on which such inferences rely. Most of the flux patches in models of the modem field are small and enclose little flux compared to the total unsigned flux emanating from the core. To demonstrate that such patches are not required to explain the most spatially complete and accurate data presently available, those from the Magsat mission, I have constructed a smooth core field model that fits the Magsat data but does not possess small flux patches. I conclude that our present knowledge of the geomagnetic field does not allow us to resolve these features reliably at the core-mantle boundary; thus we possess less information about core flow than previously believed.

  9. SIMULATIONS OF TURBULENT DYNAMOS DRIVEN BY THE MAGNETIC HELICITY FLUX

    SciTech Connect

    Shapovalov, Dmitry S.; Vishniac, Ethan T. E-mail: ethan@mcmaster.ca

    2011-09-01

    We present results of numerical simulations of driven magnetohydrodynamic turbulence in a periodic box with an imposed large-scale sinusoidal shear. We produce strong large-scale magnetic fields through dynamo action. This dynamo action is highly dependent on the spectral properties of the forcing function. In particular, we can produce either dynamo or antidynamo action by choosing particular forcing functions for the small-scale turbulence. Our results show that the large-scale electromotive force is well correlated with the local accumulation of eddy-scale magnetic helicity. Conversely, the electromotive force is very weakly correlated with the large-scale magnetic field strength or its product with kinetic helicity. We argue that in these simulations large-scale dynamo action is driven by an inverse cascade of magnetic helicity, ultimately caused by the tendency of anisotropic turbulence to create a magnetic helicity flux.

  10. Simulation of magnetic hysteresis loops and magnetic Barkhausen noise of α-iron containing nonmagnetic particles

    SciTech Connect

    Li, Yi; Xu, Ben; Hu, Shenyang; Li, Yulan; Li, Qiulin; Liu, Wei

    2015-07-01

    The magnetic hysteresis loops and Barkhausen noise of a single α-iron with nonmagnetic particles are simulated to investigate into the magnetic hardening due to Cu-rich precipitates in irradiated reactor pressure vessel (RPV) steels. Phase field method basing Landau-Lifshitz-Gilbert (LLG) equation is used for this simulation. The results show that the presence of the nonmagnetic particle could result in magnetic hardening by making the nucleation of reversed domains difficult. The coercive field is found to increase, while the intensity of Barkhausen noise voltage is decreased when the nonmagnetic particle is introduced. Simulations demonstrate the impact of nucleation field of reversed domains on the magnetization reversal behavior and the magnetic properties.

  11. Simulation of magnetic hysteresis loops and magnetic Barkhausen noise of α-iron containing nonmagnetic particles

    DOE PAGESBeta

    Li, Yi; Xu, Ben; Hu, Shenyang; Li, Yulan; Li, Qiulin; Liu, Wei

    2015-07-01

    The magnetic hysteresis loops and Barkhausen noise of a single α-iron with nonmagnetic particles are simulated to investigate into the magnetic hardening due to Cu-rich precipitates in irradiated reactor pressure vessel (RPV) steels. Phase field method basing Landau-Lifshitz-Gilbert (LLG) equation is used for this simulation. The results show that the presence of the nonmagnetic particle could result in magnetic hardening by making the nucleation of reversed domains difficult. The coercive field is found to increase, while the intensity of Barkhausen noise voltage is decreased when the nonmagnetic particle is introduced. Simulations demonstrate the impact of nucleation field of reversed domainsmore » on the magnetization reversal behavior and the magnetic properties.« less

  12. C 4 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 4 wavelength 1548 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 C 4 wavelength 1551 rasters of plages and C 4 1548 rasters of the quiet sun. The sample contains 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 4 wavelength 1548 line can be neglected in the conversion from intensity to flux density. As expected for the nearly optically thin situation, the C 4 1548 line is twice as bright as the C 4 wavelength 1551 line. The average C 4 wavelength 1548 flux density for a quiet is 2700 erg/cm/s and, with surprisingly little scatter, 18,000 erg/cm/s for plages. The intensity histograms of rasters obtained at disk centers can be separated into characteristic plage and quiet-sun contributions with variable relative filling factors. The disk-averaged flux density in the C 4 doublet and the disk-averaged magnitude of the magnetic flux density are related. The relationship between the C 4 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.

  13. Convective Radial Energy Flux Due To Resonant Magnetic Perturbations

    NASA Astrophysics Data System (ADS)

    Marcus, Francisco Alberto; Beyer, Peter; Fuhr, Guillaume; Monnier, Arnaud; Benkadda, Sadruddin

    2014-10-01

    With the resonant magnetic perturbations (RMPs) consolidating as an important tool to control the transport barrier relaxation, the mechanism on how they work is still a subject to be clearly understood. In this work we investigate the equilibrium states in the presence of RMPs for a reduced MHD model using 3D electromagnetic fluid numerical code (EMEDGE3D) with a single harmonic RMP (single magnetic island chain) and multiple harmonics RMPs in cylindrical and toroidal geometry. Two different equilibrium states were found in the presence of the RMPs with different characteristics for each of the geometries used. For the cylindrical geometry in the presence of a single RMP, the equilibrium state is characterized by a strong convective radial thermal flux and the generation of a mean poloidal velocity shear. In contrast, for toroidal geometry the thermal flux is dominated by the magnetic flutter. For multiple RMPs, the high amplitude of the convective flux and poloidal rotation are basically the same in cylindrical geometry, but in toroidal geometry the convective thermal flux and the poloidal rotation appear only with the islands overlapping of the linear coupling between neighbouring poloidal wavenumbers m, m - 1 , m + 1 . French agency CNRS and Brazilian agencies CNPq and FAPESP. Projects Numbers: ANR2010-BLAN-940-01, 560491/2010-7 and 201119296-1.

  14. Magnetic flux submergence in the photosphere: A target for DKIST

    NASA Astrophysics Data System (ADS)

    Martinez Pillet, Valentin

    2016-05-01

    While magnetic flux emergence is ubiquitous on the Sun and relatively well observed, the opposite process, flux submergence, is elusive. In the absence of large-scale submergence processes, it has always been assumed that submergence occurs at granular or smaller scales. Models that explain flux rope and filament formation near neutral lines, specifically need small-scale submergence. The same is true for dynamo models that propose the repair of the large-scale toroidal tubes after they have emerged to the surface. However, the detection of field lines being pulled back down into the solar photosphere has escaped clear detection. In this work, I demonstrate that DKIST capabilities are uniquely tailored to observe and characterize small-scale flux submergence, if it indeed happens on the Sun. By searching for transverse fields at small scales and studying their Doppler shifts, an understanding of the nature of flux submergence can be achieved. Such studies are particularly relevant near magnetic neutral lines where filaments are formed though poorly understood processes.

  15. Contagious Coronal Heating from Recurring Emergence of Magnetic Flux

    NASA Technical Reports Server (NTRS)

    Moore, Ronald L.; Falconer, David; Sterling, Alphonse; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    For each of six old bipolar active regions, we present and interpret Yohkoh/SXT and SOHO/MDI observations of the development, over several days, of enhanced coronal heating in and around the old bipole in response to new magnetic flux emerge= within the old bipole. The observations show: 1. In each active region, new flux emerges in the equatorward side of the old bipole, around a lone remaining leading sunspot and/or on the equatorward end of the neutral line of the old bipole. 2. The emerging field is marked by intense internal coronal heating, and enhanced coronal heating occurs in extended loops stemming from the emergence site. 3. In five of the six cases, a "rooster tail" of coronal loops in the poleward extent of the old bipole also brightens in response to the flux emergence. 4. There are episodes of enhanced coronal heating in surrounding magnetic fields that are contiguous with the old bipole but are not directly connected to the emerging field. From these observations, we suggest that the accommodation of localized newly emerged flux within an old active region entails far reaching adjustments in the 3D magnetic field throughout the active region and in surrounding fields in which the active region is embedded, and that these adjustments produce the extensive enhanced coronal heating. We also note that the reason for the recurrence of flux emergence in old active regions may be that active region flux tends to emerge in giant-cell convection downflows. If so, the poleward "rooster tail" is a coronal flag of a long-lasting downflow in the convection zone. This work was funded by NASA's Office of Space Science through the Solar Physics Supporting Research and Technology Program and the Sun-Earth Connection Guest Investigator Program.

  16. Contagious Coronal Heating from Recurring Emergence of Magnetic Flux

    NASA Astrophysics Data System (ADS)

    Moore, R. L.; Falconer, D. A.; Sterling, A. C.

    2002-01-01

    For each of six old bipolar active regions, we present and interpret Yohkoh/SXT and SOHO/MDI observations of the development, over several days, of enhanced coronal heating in and around the old bipole in response to new magnetic flux emergence within the old bipole. The observations show: 1. In each active region, new flux emerges in the equatorward side of the old bipole, around a lone remaining leading sunspot and/or on the equatorward end of the neutral line of the old bipole. 2. The emerging field is marked by intense internal coronal heating, and enhanced coronal heating occurs in extended loops stemming from the emergence site. 3. In five of the six cases, a "rooster tail" of coronal loops in the poleward extent of the old bipole also brightens in response to the flux emergence. 4. There are episodes of enhanced coronal heating in surrounding magnetic fields that are contiguous with the old bipole but are not directly connected to the emerging field. From these observations, we suggest that the accommodation of localized newly emerged flux within an old active region entails far reaching adjustments in the 3D magnetic field throughout the active region and in surrounding fields in which the active region is embedded, and that these adjustments produce the extensive enhanced coronal heating. We Also Note That The Reason For The recurrence of flux emergence in old active regions may be that active-region flux tends to emerge in giant-cell convection downflows. If so, the poleward "rooster tail" is a coronal flag of a long-lasting downflow in the convection zone. This work was funded by NASA's Office of Space Science through the Solar Physics Supporting Research and Technology Program and the Sun-Earth Connection Guest Investigator Program.

  17. 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.

  18. TWISTED MAGNETIC FLUX TUBES IN THE SOLAR WIND

    SciTech Connect

    Zaqarashvili, Teimuraz V.; Vörös, Zoltán; Narita, Yasuhito; Bruno, Roberto

    2014-03-01

    Magnetic flux tubes in the solar wind can be twisted as they are transported from the solar surface, where the tubes are twisted due to photospheric motions. It is suggested that the twisted magnetic tubes can be detected as the variation of total (thermal+magnetic) pressure during their passage through the observing satellite. We show that the total pressure of several observed twisted tubes resembles the theoretically expected profile. The twist of the isolated magnetic tube may explain the observed abrupt changes of magnetic field direction at tube walls. We have also found some evidence that the flux tube walls can be associated with local heating of the plasma and elevated proton and electron temperatures. For the tubes aligned with the Parker spiral, the twist angle can be estimated from the change of magnetic field direction. Stability analysis of twisted tubes shows that the critical twist angle of the tube with a homogeneous twist is 70°, but the angle can further decrease due to the motion of the tube with respect to the solar wind stream. The tubes with a stronger twist are unstable to the kink instability, therefore they probably cannot reach 1 AU.

  19. Injection of magnetic flux and helicity in the solar atmosphere

    NASA Astrophysics Data System (ADS)

    Pariat, E.

    2006-09-01

    This thesis is related to the mechanisms of emergence into the solar atmosphere, of two quantities playing key roles in solar activity: magnetic flux and magnetic helicity. Helicity, which is a topological measure of twist and shear, is believed to be a conserved quantity for solar conditions, in the frame of magnetohydrodynamics (MHD). A crucial phase in the emergence process of these quantities, which are generated and amplified in the solar interior, are their injection through the solar photosphere, the transition region between the solar interior and atmosphere. The first part of my work provided new answers to questions unsolved by the classical scenario of emergence. I have analyzed multi-wavelength observations (FGE, TRACE, SoHO, THEMIS) of an emerging active region. I demonstrated that magnetic flux tubes emerge with a flat undulated shape and that small scale magnetic reconnection events, are necessary to this emergence process. Then, using a 3D MHD numerical simulation, I studied the mechanism of magnetic reconnection and in particular the natural formation of current layers where regions of strong variations of magnetic connectivity, called quasi-separatrix layers, are present. Finally, I demonstrated that the classical definition of helicity flux density is biased and proposed a more accurate definition. I applied my new definition to observations of active regions and showed that the photospheric injection pattern of magnetic helicity is unipolar and homogenous. This study allows to link the generation of helicity in the solar atmosphere, its injection and its distribution in the solar corona and its ejection in the interplanetary medium.

  20. Weak localization in a distribution of magnetic flux tubes

    SciTech Connect

    Bending, S.J.; von Klitzing, K.; Ploog, K. )

    1990-08-20

    Thin gates of type-II superconducting materials have been prepared on top of the two-dimensional electron gas in a GaAs/AlGaAs heterostructure. In an applied magnetic field the flux distribution at the electron gas takes the form of flux tubes which are much narrower than an electron phase coherence length. We observe a qualitatively new weak-localization magnetoconductance for small fields proportional to {vert bar}{ital B}{vert bar}, in contrast to the {ital B}{sup 2} homogeneous result and in semiquantitative agreement with the theory of Rammer and Shelankov.

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

    NASA Technical Reports Server (NTRS)

    Hollweg, Joseph V.

    1990-01-01

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

  2. Variation of Magnetic Flux Ropes With Heliocentric Distance

    NASA Astrophysics Data System (ADS)

    Russell, C. T.; Mulligan, T.; Anderson, B. J.

    As the magnetic flux ropes in interplanetary coronal mass ejections move away from the Sun, their thickness expands and the field strength drops. This radial variation has been measured statistically by Bothmer and Schwenn with Helios. On occasion spacecraft are sufficiently radially aligned during the passage of an ICME that this expansion can be determined for a single structure. Two such occasions occurred with ACE and NEAR on July 12-16, 2000 and August 13-15, 2000. In accord with the statistical results from Helios, we find that the axial field for the first rope (the Bastille Day event) decreased as R^-1.4 and the poloidal field as R^-1.2 and as R^-1.8 and R^- 1.3 for the second rope. The thickness of the ropes increased from 0.50 to 0.86 AU over a distance of 0.76 AU and from 0.34 to 0.58 AU over 0.72 AU respectively. These results confirm that even when in quasi force-free magnetic balance magnetic ropes expand with heliocentric distance. Such an evolution is a natural consequence of the motion of the flux tube if it is rooted to the Sun even if the twist and magnetic flux content of the tube remain constant since the poloidal field must decrease as the tube moves outward.

  3. Numerical Simulations of Magnetic Flux Emergence in Active Regions

    NASA Astrophysics Data System (ADS)

    Abbett, W. P.

    2002-05-01

    Understanding the sub-photospheric structure and dynamics of emerging active region magnetic fields, and how these fields are coupled to structures observed above the photosphere, is important to a variety of ongoing research projects in both the solar physics and space science communities (for example, the effort to predict the onset of intense episodes of solar activity such as CMEs and flares). Over the past decade, much progress has been made by using 2-D MHD codes and the 1-D ``thin flux tube'' approximation to describe the evolution of buoyant magnetic flux tubes in the solar interior. However, in recent years, the rapid evolution of computer technology, coupled with advances in computational algorithms, have made it possible to use physically self-consistent, 3-D MHD numerical simulations to model the evolution of strong magnetic fields through stratified model convection zones without the restrictive assumptions of earlier models. This review will summarize efforts to use modern 3-D codes as tools to test predictions of earlier theoretical models and to interpret observational data. The emphasis will be on the progress made in modeling emerging magnetic flux in the solar interior; however, a brief overview of recent efforts to couple sub-photospheric simulations to models of the solar atmosphere and corona will also be presented.

  4. Thermal magnetic field noise limits resolution in transmission electron microscopy.

    PubMed

    Uhlemann, Stephan; Müller, Heiko; Hartel, Peter; Zach, Joachim; Haider, Max

    2013-07-26

    The resolving power of an electron microscope is determined by the optics and the stability of the instrument. Recently, progress has been obtained towards subångström resolution at beam energies of 80 kV and below but a discrepancy between the expected and achieved instrumental information limit has been observed. Here we show that magnetic field noise from thermally driven currents in the conductive parts of the instrument is the root cause for this hitherto unexplained decoherence phenomenon. We demonstrate that the deleterious effect depends on temperature and at least weakly on the type of material. PMID:23931384

  5. Open Magnetic Flux and Magnetic Reconnection During Steady Magnetic Convection Intervals.

    NASA Astrophysics Data System (ADS)

    Hubert, B.; Milan, S. E.; Cowley, S. W.

    2009-05-01

    The Imager for Magnetopause to Aurora Global Exploration (IMAGE) spacecraft was launched in 2000 with several imaging instruments onboard. The Far UltraViolet (FUV) experiment imaged the N2 LBH (Wideband Imaging Camera - WIC-), OI 135.6 nm (Spectrographic Imager -SI13-) and Doppler-shifted Lyman alpha auroral emission (SI12). The Doppler-shifted Lyman-alpha emission allows to monitor the auroral oval both on the day and night sides. Remote sensing of the polar aurora is completed by ground based data of the Super Dual Auroral Radar Network (SuperDARN) that monitors the ionospheric convection flow pattern in the polar region. In the present study, SI12 images are used to estimate the open/closed (o/c) field line boundary location, and monitor its movement. The SuperDARN data are used to compute the electric field of the polar cap at the location of the o/c boundary. The total electric field is then computed along the boundary accounting for its movement applying Faraday's law, so that the dayside and nightside reconnection voltages can be retrieved. We apply this method to the study of several intervals of steady magnetic convection (SMC). SMC events are intervals of enhanced convection without classical substorm signatures. During these intervals, it is expected that the amount of open magnetic flux remains fairly constant, and it has been suggested that the rate of opening (at the magnetopause) and closure (in the magnetotail) of magnetic flux balance each other. These rates can be expressed as voltages with a positive sign for the opening and a negative sign for closure. The net reconnection voltage then represents the net rate of accumulation of open flux by the magnetosphere. We find that, during SMC intervals, the open magnetic flux varies only slowly, and sometimes remains stationary during several hours. As a consequence, the net voltage often remains close to zero during SMC intervals. Occasionally, we find that an increase in the opening voltage is followed by a similar intensification of the closure voltage after downtail convection of the newly created open flux. The convection time can be roughly estimated and ranges between 20 and 40 minutes, i.e. the typical order of magnitude of the convection time in the magnetosphere.

  6. Magnetic Flux Conservation in the Heliosheath Including Solar Cycle Variations of Magnetic Field Intensity

    NASA Astrophysics Data System (ADS)

    Michael, A. T.; Opher, M.; Provornikova, E.; Richardson, J. D.; Tóth, G.

    2015-04-01

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

  7. Anisotropy study of grain oriented steels with Magnetic Barkhausen Noise

    NASA Astrophysics Data System (ADS)

    de Campos, M. F.; Campos, M. A.; Landgraf, F. J. G.; Padovese, L. R.

    2011-07-01

    Grain oriented electrical steels present strong anisotropy, due to a {110} <001> texture (Goss), with [100] direction parallel to rolling direction (RD) and [110] direction parallel to transverse direction (TD). MBN (Magnetic Barkhausen Noise) were employed to measure magnetic properties in several angles towards RD using a 15° step. For 90° to the rolling direction (i.e., TD), the MBN signal changes, decreasing the MBNrms. It is found a connection between initial permeability and MBNrms. The lower initial permeability for the TD is related to a larger contribution of irreversible rotation in the hysteresis. The MBN procedure is non-destructive and provides rapid understanding of the anisotropy of the material, without the use of laborious methods like Epstein frame or toroidal coils.

  8. Magnetic Flux Compression Concept for Aerospace Propulsion and Power

    NASA Technical Reports Server (NTRS)

    Litchford, Ron J.; Robertson, Tony; Hawk, Clark W.; Turner, Matt; Koelfgen, Syri

    2000-01-01

    The objective of this research is to investigate system level performance and design issues associated with magnetic flux compression devices for aerospace power generation and propulsion. The proposed concept incorporates the principles of magnetic flux compression for direct conversion of nuclear/chemical detonation energy into electrical power. Specifically a magnetic field is compressed between an expanding detonation driven diamagnetic plasma and a stator structure formed from a high temperature superconductor (HTSC). The expanding plasma cloud is entirely confined by the compressed magnetic field at the expense of internal kinetic energy. Electrical power is inductively extracted, and the detonation products are collimated and expelled through a magnetic nozzle. The long-term development of this highly integrated generator/propulsion system opens up revolutionary NASA Mission scenarios for future interplanetary and interstellar spacecraft. The unique features of this concept with respect to future space travel opportunities are as follows: ability to implement high energy density chemical detonations or ICF microfusion bursts as the impulsive diamagnetic plasma source; high power density system characteristics constrain the size, weight, and cost of the vehicle architecture; provides inductive storage pulse power with a very short pulse rise time; multimegajoule energy bursts/terawatt power bursts; compact pulse power driver for low-impedance dense plasma devices; utilization of low cost HTSC material and casting technology to increase magnetic flux conservation and inductive energy storage; improvement in chemical/nuclear-to-electric energy conversion efficiency and the ability to generate significant levels of thrust with very high specific impulse; potential for developing a small, lightweight, low cost, self-excited integrated propulsion and power system suitable for space stations, planetary bases, and interplanetary and interstellar space travel; potential for attaining specific impulses approaching 10 (exp 6) seconds, which would enable missions to the outer planets within ten years and missions at interstellar distances within fifty years.

  9. Solving the problem of magnetic flux transport during star formation

    NASA Astrophysics Data System (ADS)

    Santos de Lima, Reinaldo; de Gouveia Dal Pino, Elisabete; Guerrero, Gustavo; Leao, Marcia; Lazarian, Alex

    2015-08-01

    Fast magnetic reconnection is an omnipresent process in turbulent astrophysical flows. It allows the magnetic flux to diffuse through the gas even when the electrical conductivity is very high. Recently we have tested this diffusive mechanism (termed Reconnection Diffusion, RD) for solving two intriguing problems related to star formation: (i) the removal of magnetic flux from collapsing molecular clouds in order to explain the observed magnetic field intensities in protostars, and (ii) the formation of rotationally sustained protostellar disks in the presence of the magnetic fields, which tend to remove all the angular momentum. Using 3D MHD simulations we have demonstrated successfully the efficiency of the RD in both problems. More recently, we have also identified the conditions under which RD is able to produce supercritical cores from self-gravitating subcritical molecular cloud clumps. In this presentation we review the RD theory and the results of our numerical studies in different phases of star formation. We also derive the RD coefficient from the numerical simulations and compare with the theoretical predictions

  10. Fractional flux plateau in magnetization curve of multicomponent superconductor loop

    NASA Astrophysics Data System (ADS)

    Huang, Zhao; Hu, Xiao

    2015-12-01

    Time-reversal symmetry (TRS) may be broken in superconductors with three or more condensates interacting repulsively, yielding two degenerate states specified by chirality of gap functions. We consider a loop of such a superconductor with two halves occupied by the two states with opposite chiralities. Fractional flux plateaus are found in a magnetization curve associated with free-energy minima, where the two domain walls between the two halves of loop accommodate different intercomponent phase kinks leading to finite winding numbers around the loop only in a part of all condensates. Fractional flux plateaus form pairs related by the flux quantum Φ0=h c /2 e , although they individually take arbitrary values depending on material parameters and temperature. This phenomenon is a clear evidence of TRS broken superconductivity, and in a general point of view it provides a novel chance to explore relative phase difference, phase kink and soliton in ubiquitous multicomponent superconductivity such as that in iron pnicitides.

  11. Alternative magnetic flux leakage modalities for pipeline inspection

    SciTech Connect

    Katragadda, G.; Lord, W.; Sun, Y.S.; Udpa, S.; Udpa, L.

    1996-05-01

    Increasing quality consciousness is placing higher demands on the accuracy and reliability of inspection systems used in defect detection and characterization. Nondestructive testing techniques often rely on using multi-transducer approaches to obtain greater defect sensitivity. This paper investigates the possibility of taking advantage of alternative modalities associated with the standard magnetic flux leakage tool to obtain additional defect information, while still using a single excitation source.

  12. Application of the flux noise reducing filter for CO2 inverse modelling

    NASA Astrophysics Data System (ADS)

    Maksyutov, Shamil; Yaremchuk, Alexey

    2010-05-01

    Recent atmospheric remote sensing products from AIRS and GOSAT provide large volume of the observations but with larger errors and variance as compared to in-situ measurements, so efficient noise reduction techniques are required for inverse modeling of the surface fluxes. Inverse models of the atmospheric transport optimize regional or grid resolving surface CO2 fluxes to fit transport model simulation optimally to the observations. The optimization problem appears to be ill-posed so it is usually solved by applying regularization techniques. Most widely used regularization methods apply constraints on flux deviation from prior and/or from adjacent regions of same surface type (land-ocean, vegetation type), and from adjacent time periods. Convenient method for solving the problem of limited dimension is based on singular value decomposition (SVD) of the transport matrix, because it can decompose the solution space into a combination of the independent singular vectors. Introducing a simple constraint on fluxes limits amplitude of the corresponding singular vectors with larger reduction for smaller singular values. However this amplitude reduction is not sufficient in practice for inverse modeling of the regional CO2 fluxes, when we have large underconstrained regions in tropics. Alternatively other means of the amplitude reduction are also used, such as truncation, when all amplitudes below threshold singular value are set to zero. We apply a filter which is less abrupt is less abrupt compared to truncation but still suppressing strongly small singular value related vectors. Setting strength of a constraint is often done empirically. To decide a proper value of the cut-off singular value we suggest analyzing a dependence of the singular vector amplitude vs the singular value and set the cut-off value aiming at retaining most of useful information from observation. A graphical tool based on a plot of amplitude spectra is proposed. Advantage of the technique is demonstrated by applying it to optimization of the model-simulated CO2 seasonality at the Globalview observation network using Transcom-3 simulated transport matrixes. As compared to using a Transcom-3 constraint our filter produces smoother seasonal variations for fluxes with a minor impact on model fit with the observations. At the same time, retrieved flux variability at the regions with weak signal at observation sites is strongly suppressed. Applying a filter combined with iterative optimization procedure leads to faster convergence to the optimal flux solution compared to use of the SVD for larger size problems such as batch inversion of the interannually varying regional fluxes. The approach is extended to iterative optimization of the large dimension problems involving use of the adjoint operator of the atmospheric transport instead of precalculated transport matrix.

  13. 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.

  14. Enhanced magnetic flux density mapping using coherent steady state equilibrium signal in MREIT

    NASA Astrophysics Data System (ADS)

    Jeong, Woo Chul; Lee, Mun Bae; Sajib, Saurav Z. K.; Kim, Hyung Joong; Kwon, Oh In; Woo, Eung Je

    2016-03-01

    Measuring the z-component of magnetic flux density B = (Bx, By, Bz) induced by transversally injected current, magnetic resonance electrical impedance tomography (MREIT) aims to visualize electrical property (current density and/or conductivity distribution) in a three-dimensional imaging object. For practical implementations of MREIT technique, it is critical to reduce injection of current pulse within safety requirements. With the goal of minimizing the noise level in measured Bz data, we propose a new method to enhance the measure Bz data using steady-state coherent gradient multi-echo (SSC-GME) MR pulse sequence combining with injection current nonlinear encoding (ICNE) method in MREIT, where the ICNE technique injects current during a readout gradient to maximize the signal intensity of phase signal including Bz. The total phase offset in SSC-GME includes additional magnetic flux density due to the injected current, which is different from the phase signal for the conventional spoiled MR pulse sequence. We decompose the magnetization precession phase from the total phase offset including Bz and optimize Bz data using the steady-state equilibrium signal. Results from a real phantom experiment including different kinds of anomalies demonstrated that the proposed method enhanced Bz comparing to a conventional spoiled pulse sequence.

  15. Magnetic flux transport of decaying active regions and enhanced magnetic network. [of solar supergranulation

    NASA Technical Reports Server (NTRS)

    Wang, Haimin; Zirin, Harold; Ai, Guoxiang

    1991-01-01

    Several series of coordinated observations on decaying active regions and enhanced magnetic network regions on the sun were carried out jointly at Big Bear Solar Observatory and at the Huairou Solar Observing Station of the Bejing Astronomical Observatory in China. The magnetic field evolution in several regions was followed closely for three to seven days. The magnetic flux transport from the remnants of decayed active regions was studied, along with the evolution and lifetime of the magnetic network which defines the boundaries of supergranules. The magnetic flux transport in an enhanced network region was studied in detail and found to be negative. Also briefly described are some properties of moving magnetic features around a sunspot. Results of all of the above studies are presented.

  16. Magnetic flux concentrations from dynamo-generated fields

    NASA Astrophysics Data System (ADS)

    Jabbari, S.; Brandenburg, A.; Losada, I. R.; Kleeorin, N.; Rogachevskii, I.

    2014-08-01

    Context. The mean-field theory of magnetized stellar convection gives rise to two distinct instabilities: the large-scale dynamo instability, operating in the bulk of the convection zone and a negative effective magnetic pressure instability (NEMPI) operating in the strongly stratified surface layers. The latter might be important in connection with magnetic spot formation. However, as follows from theoretical analysis, the growth rate of NEMPI is suppressed with increasing rotation rates. On the other hand, recent direct numerical simulations (DNS) have shown a subsequent increase in the growth rate. Aims: We examine quantitatively whether this increase in the growth rate of NEMPI can be explained by an α2 mean-field dynamo, and whether both NEMPI and the dynamo instability can operate at the same time. Methods: We use both DNS and mean-field simulations (MFS) to solve the underlying equations numerically either with or without an imposed horizontal field. We use the test-field method to compute relevant dynamo coefficients. Results: DNS show that magnetic flux concentrations are still possible up to rotation rates above which the large-scale dynamo effect produces mean magnetic fields. The resulting DNS growth rates are quantitatively reproduced with MFS. As expected for weak or vanishing rotation, the growth rate of NEMPI increases with increasing gravity, but there is a correction term for strong gravity and large turbulent magnetic diffusivity. Conclusions: Magnetic flux concentrations are still possible for rotation rates above which dynamo action takes over. For the solar rotation rate, the corresponding turbulent turnover time is about 5 h, with dynamo action commencing in the layers beneath.

  17. Magnetic Flux Circulation During Dawn-Dusk Oriented Interplanetary Magnetic Field

    NASA Technical Reports Server (NTRS)

    Mitchell, E. J.; Lopez, R. E.; Fok, M.-C.; Deng, Y.; Wiltberger, M.; Lyon, J.

    2010-01-01

    Magnetic flux circulation is a primary mode of energy transfer from the solar wind into the ionosphere and inner magnetosphere. For southward interplanetary magnetic field (IMF), magnetic flux circulation is described by the Dungey cycle (dayside merging, night side reconnection, and magnetospheric convection), and both the ionosphere and inner magnetosphere receive energy. For dawn-dusk oriented IMF, magnetic flux circulation is not well understood, and the inner magnetosphere does not receive energy. Several models have been suggested for possible reconnection patterns; the general pattern is: dayside merging; reconnection on the dayside or along the dawn/dusk regions; and, return flow on dayside only. These models are consistent with the lack of energy in the inner magnetosphere. We will present evidence that the Dungey cycle does not explain the energy transfer during dawn-dusk oriented IMF. We will also present evidence of how magnetic flux does circulate during dawn-dusk oriented IMF, specifically how the magnetic flux reconnects and circulates back.

  18. Nonlinear evolution of magnetic flux ropes. 2: Finite beta plasma

    NASA Technical Reports Server (NTRS)

    Osherovich, V. A.; Farrugia, C. J.; Burlaga, L. F.

    1995-01-01

    In this second paper on the evolution of magnetic flux ropes we study the effects of gas pressure. We assume that the energy transport is described by a polytropic relationship and reduce the set of ideal MHD equations to a single, second-order, nonlinear, ordinary differential equation for the evolution function. For this conservative system we obtain a first integral of motion. To analyze the possible motions, we use a mechanical analogue -- a one-dimensional, nonlinear oscillator. We find that the effective potential for such an oscillator depends on two parameters: the polytropic index gamma and a dimensionless quantity kappa the latter being a function of the plasma beta, the strength of the azimuthal magnetic field relative to the axial field of the flux rope, and gamma. Through a study of this effective potential we classify all possible modes of evolution of the system. In the main body of the paper, we focus on magnetic flux ropes whose field and gas pressure increase steadily towards the symmetry axis. In this case, for gamma greater than 1 and all values of kappa, only oscillations are possible. For gamma less than 1, however, both oscillations and expansion are allowed. For gamma less than 1 and kappa below a critical value, the energy of the nonlinear oscillator determines whether the flux rope will oscillate or expand to infinity. For gamma less than 1 and kappa above critical, however, only expansion occurs. Thus by increasing kappa while keeping gamma fixed (less than 1), a phase transition occurs at kappa = kappa(sub critical) and the oscillatory mode disappears. We illustrate the above theoretical considerations by the example of a flux rope of constant field line twist evolving self-similarly. For this example, we present the full numerical MHD solution. In an appendix to the paper we catalogue all possible evolutions when (1) either the magnetic field or (2) the gas pressure decreases monotonically toward the axis. We find that in these cases critical conditions can occur for gamma greater than 1. While in most cases the flux rope collapses, there are notable exceptions when, for certain ranges of kappa and gamma, collapse may be averted.

  19. Dilation of force-free magnetic flux tubes. [solar magnetic field profiles

    NASA Technical Reports Server (NTRS)

    Frankenthal, S.

    1977-01-01

    A general study is presented of the mapping functions which relate the magnetic-field profiles across a force-free rope in segments subjected to various external pressures. The results reveal that if the external pressure falls below a certain critical level (dependent on the flux-current relation which defines the tube), the magnetic profile consists of an invariant core sheathed in a layer permeated by an azimuthal magnetic field.

  20. Potential micrometeoroid and orbital debris protection system using a gradient magnetic field and magnetic flux compression

    NASA Astrophysics Data System (ADS)

    Giffin, A.; Shneider, M. N.; Miles, R. B.

    2010-08-01

    A system for using a magnetic field in conjunction with conventional shielding configurations to protect against micrometeoroid and orbital debris is presented. Analytical, numerical, and experimental studies of a conductor moving through a gradient magnetic field have been performed. The results show that in the high magnetic Reynolds number regime a conducting object will experience large forces that tend to deform it while moving through the gradient field. Additionally a configuration using magnetic flux compression is introduced to act as a magnetic shock absorber. Separately or together, this technology may augment or replace current protection designs for space systems.

  1. A dynamo effect due to instability of magnetic flux tubes

    NASA Astrophysics Data System (ADS)

    Ferriz-Mas, A.; Schmitt, D.; Schuessler, M.

    1994-09-01

    We show that a non-axisymmetric instability of toroidal magnetic flux tubes in a rotating star provides a dynamo effect. The instability occurs in the form of propagating helical waves; their growth in amplitude causes a phase shift between the perturbations of magnetic field and velocity, which leads to an electric field (anti)parallel to the direction of the unperturbed field. Together with differential rotation, this effects is capable of driving a dynamo of the alpha omega-type. In contrast to the conventional alpha-effect in cyclonic convention, this dynamo effect operates in strong (super-equipartition) magnetic fields which resist against distortion by convective flows. We calculate the induced electric field using results from linear stability and a model of the solar convection zone which consistently includes an overshoot layer. We find that for growing magnetic field the dynamo effect occurs first in high latitudes (near the poles) in a region of weak instability which moves towards the equator as the field strength increases further. The dependence of the dynamo effect on the location of the flux tubes (in depth and latitude) and on the rotation rate is discussed.

  2. Nonlinear Parker instability of isolated magnetic flux in a plasma

    NASA Technical Reports Server (NTRS)

    Shibata, K.; Tajima, T.; Matsumoto, R.; Hanawa, T.; Horiuchi, T.

    1989-01-01

    The nonlinear evolution of the Parker instability in an isolated horizontal magnetic-flux sheet embedded in a two-temperature layer atmosphere is studied by using a two-dimensional MHD code. In the solar case, this two-layer model is regarded as a simplified abstraction of the sun's photosphere/chromosphere and its overlying much hotter (coronal) envelope. The horizontal flux sheet is initially located in the lower temperature atmosphere so as to satisfy magnetostatic equilibrium under a constant gravitational acceleration. Ideal MHD is assumed, and only perturbations with k parallel to the magnetic-field lines are investigated. As the instability develops, the gas slides down the expanding loop, and the evacuated loop rises as a result of enhanced magnetic buoyancy. In the nonlinear regime of the instability, both the rise velocity of a magnetic loop and the local Alfven velocity at the top of the loop increase linearly with height and show self-similar behavior with height as long as the wavelength of the initial perturbation is much smaller than the horizontal size of the computing domain.

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

    SciTech Connect

    Sharma, Raghav; Dürrenfeld, P.; Iacocca, E.; Heinonen, O. G.; Åkerman, J.; Muduli, P. K.

    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.

  4. A magnetohydrodynamic simulation of the formation of magnetic flux tubes at the earth's dayside magnetopause

    NASA Technical Reports Server (NTRS)

    Ogino, Tatsuki; Walker, Raymond J.; Ashour-Abdalla, Maha

    1989-01-01

    Dayside magnetic reconnection was studied by using a three-dimensional global magnetohydrodynamic simulation of the interaction between the solar wind and the magnetosphere. Two different mechanisms were found for the formation of magnetic flux tubes at the dayside magnetopause, which depend on the orientation of the interplanetary magnetic field (IMF). The dayside magnetic flux tubes occur only when the IMF has a southward component. A strongly twisted and localized magnetic flux tube similar to magnetic flux ropes appears at the subsolar magnetopause when the IMF has a large B(y) component. When the B(y) component is small, twin flux tubes appear at the dayside magnetopause. Both types of magnetic flux tube are consistent with several observational features of flux transfer events and are generated by antiparallel magnetic reconnection.

  5. Magnetic Flux Compression Concept for Nuclear Pulse Propulsion and Power

    NASA Technical Reports Server (NTRS)

    Litchford, Ronald J.

    2000-01-01

    The desire for fast, efficient interplanetary transport requires propulsion systems having short acceleration times and very high specific impulse attributes. Unfortunately, most highly efficient propulsion systems which are within the capabilities of present day technologies are either very heavy or yield very low impulse such that the acceleration time to final velocity is too long to be of lasting interest, One exception, the nuclear thermal thruster, could achieve the desired acceleration but it would require inordinately large mass ratios to reach the range of desired final velocities. An alternative approach, among several competing concepts that are beyond our modern technical capabilities, is a pulsed thermonuclear device utilizing microfusion detonations. In this paper, we examine the feasibility of an innovative magnetic flux compression concept for utilizing microfusion detonations, assuming that such low yield nuclear bursts can be realized in practice. In this concept, a magnetic field is compressed between an expanding detonation driven diamagnetic plasma and a stationary structure formed from a high temperature superconductor (HTSC). In general, we are interested in accomplishing two important functions: (1) collimation of a hot diamagnetic plasma for direct thrust production; and (2) pulse power generation for dense plasma ignition. For the purposes of this research, it is assumed that rnicrofusion detonation technology may become available within a few decades, and that this approach could capitalize on recent advances in inertial confinement fusion ICF) technologies including magnetized target concepts and antimatter initiated nuclear detonations. The charged particle expansion velocity in these detonations can be on the order of 10 (exp 6)- 10 (exp 7) meters per second, and, if effectively collimated by a magnetic nozzle, can yield the Isp and the acceleration levels needed for practical interplanetary spaceflight. The ability to ignite pure fusion micro-bursts with reasonable levels of input energy is an equally challenging scientific problem. It remains to be seen, however, whether an effective ignition driver can be developed which meets the requirements for practical spaceflight application (namely high power density, compactness, low weight, and low cost). In this paper, system level performance and design issues are examined including generator performance, magnetic flux compression processes, magnetic diffusion processes, high temperature superconductor (HTSC) material properties, plasmadynamic processes, detonation plasma expansion processes, magnetohydrodynamic instabilities, magnetic nozzle performance, and thrust production performance. Representative generator performance calculations based on a simplified skin layer formulation are presented as well as the results of exploratory small-scale laboratory experiments on magnetic flux diffusion in HTSC materials. In addition, planned follow-on scientific feasibility experiments are described which utilize high explosive detonations and high energy gas discharges to simulate the plasma conditions associated with thermonuclear micro-detonations.

  6. 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.

  7. The distribution mechanism of noise fluxes between three oscillating modes of a free-running class-A laser

    NASA Astrophysics Data System (ADS)

    Khalilzadeh, E.; Jahanpanah, J.

    2016-03-01

    In the present work, we have extended the noise features of a class-A laser from the single-mode state with one oscillating freedom to the three-mode state with three oscillating freedoms. The laser noise is modeled by the cavity Langevin force in the absence of other two atomic population inversion and dipole moment Langevin forces. The Maxwell-Bloch equations of motion are thus solved in the presence of three cavity Langevin forces associated with the simultaneous oscillations of cavity central mode and its left and right adjacent modes. Therefore, the phase and amplitude fluctuations of electric field components that are oscillating at the three consecutive longitudinal modes have analytically been calculated in frequency domain. The results of our calculations indicate that the cavity Langevin force of each of three oscillating modes makes a direct contribution in producing the noise fluxes of other two oscillating modes. We have also determined the exact share of each oscillating mode in the total output intensity noise spectra of a three-mode laser. It is finally demonstrated that the input noise flux of laser pumping is distributed between the output noise fluxes of spontaneous and stimulated emission radiations of three oscillating modes according to the flux conservation law.

  8. 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.

  9. Stochastic Flux-Freezing and Turbulent Magnetic Dynamo

    NASA Astrophysics Data System (ADS)

    Eyink, G. L.

    2010-12-01

    “Spontaneous stochasticity” of Lagrangian particle trajectories is a long-overlooked consequence of the explosive separation of particles undergoing turbulent Richardson diffusion. The effect implies a breakdown of Laplacian determinism for classical dynamics, with infinitely many (random) trajectories for the same initial particle position. We discuss the theoretical basis and empirical evidence for the phenomenon. Spontaneous stochasticity implies that magnetic field-lines cannot be ``frozen-in’’ to a turbulent MHD fluid (plasma or liquid metal) in the original sense of Alfvén, even at infinite conductivity if also the kinetic Reynolds number is large. We show that systems described by resistive nonlinear hydromagnetic equations (MHD, Hall MHD, etc.) satisfy a stochastic Alfvén Theorem and we use this result to argue that flux-conservation must remain stochastic at infinite Reynolds numbers. The predictions of standard flux-freezing are thus found to be wrong---by many orders of magnitude---in high-Reynolds-number MHD turbulence. Stochastic flux-freezing has fundamental consequences for many astrophysical problems, such as planetary and solar dynamos, star formation, solar flares, etc. As one example, we present numerical results on the kinematic, fluctuation dynamo in non-helical, incompressible turbulence at magnetic Prandtl number Pr=1, using a Lagrangian particle method with a hydrodynamic turbulence database at Re_λ=433. We find that Richardson diffusion and stochasticity of field-line motion play an essential role in magnetic energy growth. The Lagrangian mechanisms of small-scale dynamo are found to be very similar to those in the soluble Kazantsev model at Pr=0. We also discuss briefly the application of stochastic flux-freezing to the problem of fast magnetic reconnection. We use the phenomenological Goldreich-Sridhar 1995 theory to estimate the dispersion of particle-pairs in strong MHD turbulence with an imposed magnetic field. We then recover the Lazarian-Vishniac 1999 theory of fast reconnection as a natural generalization of the laminar Sweet-Parker model to high-Reynolds-number MHD turbulence.

  10. Laser-driven magnetic flux compression simulation with Nautilus

    NASA Astrophysics Data System (ADS)

    Zhou, C. D.; Loverich, J.; Hakim, A.

    2010-11-01

    The Tech-X fluid and MHD framework, Nautilus, is a finite-volume and finite-element shock-capturing code supporting both structured and unstructured meshes. Nautilus is an easy-to-access, parallel, 3D code available to the ICF community. It is incorporated with features relevant to magneto-inertial confinement fusion (MIF) simulations. Laser-driven magnetic-flux compression is an innovative approach to achieve MIF. A cylindrical target with initial seed magnetic field is compressed by energetic laser beams. The magnetic field that is ``frozen-in'' plasma gets compressed with the target. The resulting high magnetic field reduces electron thermal conductivity and improves alpha particle confinement, thus providing an additional thermal insulation of the fuel forming the hot spot. It reduces the energy and driver symmetry requirements for ignition. Features for MIF simulations, such as anisotropic heat conduction , laser ray tracing and energy deposition, have been demonstrated with Nautilus. We discuss our approach to determine the best algorithms for properly modeling laser-driven shock implosions with magnetic fields in conditions relevant to cylindrical MIF.

  11. The effect of an interaction of magnetic flux and supergranulation on the decay of magnetic plages

    NASA Technical Reports Server (NTRS)

    Schrijver, C. J.

    1989-01-01

    This paper studies how the properties of large-scale convection affect the decay of plages. The plage decay, caused by the random-walk dispersion of flux tubes, is suggested to be severely affected by differences between the mean size of cellular openings within and around plages. The smaller cell size within a plage largely explains the smaller diffusion coefficient within plages as compared to that of the surrounding regions. The semipermeability of the plage periphery, together with the dependence of the diffusion coefficient on the flux-tube density, can explain the observed slow decay of plages (predicting a typical life time of about a month for a medium-sized plage), the existence of a well-defined plage periphery, and the observed characteristic mean magnetic flux density of about 100 G. One effect of the slowed decay of the plage by the semipermeability of the plage periphery is the increase of the fraction of the magnetic flux that can cancel with flux of the opposite polarity along the neutral line to as much as 80 percent as compared to at most 50 percent in the case of nonuniform diffusion. This may explain why only a small fraction of the magnetic flux is observed to escape from the plage into the surrounding network.

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

    NASA Astrophysics Data System (ADS)

    Palacios, J.; Cid, C.; Guerrero, A.; Saiz, E.; Cerrato, Y.

    2015-11-01

    Aims: Here we report evidence of a large solar filament eruption on 2013, September 29. This smooth eruption, which passed without any previous flare, formed after a two-ribbon flare and a coronal mass ejection towards Earth. The coronal mass ejection generated a moderate geomagnetic storm on 2013, October 2 with very serious localized effects. The whole event passed unnoticed to flare-warning systems. Methods: We have conducted multi-wavelength analyses of the Solar Dynamics Observatory through Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) data. The AIA data on 304, 193, 211, and 94 Å sample the transition region and the corona, respectively, while HMI provides photospheric magnetograms, continuum, and linear polarization data, in addition to the fully inverted data provided by HMI. Results: This flux emergence happened very close to a filament barb that was very active in mass motion, as seen in 304 Å images. The observed flux emergence exhibited hectogauss values. The flux emergence extent appeared just beneath the filament, and the filament rose during the following hours. The emergence acquired a size of 33'' in ~12 h, about ~0.16 km s-1. The rate of signed magnetic flux is around 2 × 1017 Mx min-1 for each polarity. We have also studied the eruption speed, size, and dynamics. The mean velocity of the rising filament during the ~40 min previous to the flare is 115 ± 5 km s-1, and the subsequent acceleration in this period is 0.049 ± 0.001 km s-2. Conclusions: We have observed a supergranular-sized emergence close to a large filament in the boundary of the active region NOAA11850. Filament dynamics and magnetogram results suggest that the magnetic flux emergence takes place in the photospheric level below the filament. Reconnection occurs underneath the filament between the dipped lines that support the filament and the supergranular emergence. The very smooth ascent is probably caused by this emergence and torus instability may play a fundamental role, which is helped by the emergence. Movies associated to Figs. 1 and 2 are available in electronic form at http://www.aanda.org

  13. System having unmodulated flux locked loop for measuring magnetic fields

    DOEpatents

    Ganther, Jr., Kenneth R.; Snapp, Lowell D.

    2006-08-15

    A system (10) for measuring magnetic fields, wherein the system (10) comprises an unmodulated or direct-feedback flux locked loop (12) connected by first and second unbalanced RF coaxial transmission lines (16a, 16b) to a superconducting quantum interference device (14). The FLL (12) operates for the most part in a room-temperature or non-cryogenic environment, while the SQUID (14) operates in a cryogenic environment, with the first and second lines (16a, 16b) extending between these two operating environments.

  14. Influence of the maximum applied magnetic field on the angular dependence of Magnetic Barkhausen Noise in API5L steels

    NASA Astrophysics Data System (ADS)

    Martnez-Ortiz, P.; Prez-Bentez, J. A.; Espina-Hernndez, J. H.; Caleyo, F.; Mehboob, N.; Grssinger, R.; Hallen, J. M.

    2016-03-01

    This work studies the influence of the maximum applied magnetic field on the angular dependence of the energy of the Magnetic Barkhausen Noise signal in three different API5L pipeline steels. The results show that the shape of the angular dependence of the Magnetic Barkhausen Noise energy changes with the increase of the amplitude of the applied magnetic field. This phenomenon is a consequence of the presence of unlike magnetization processes at different magnitudes of the applied magnetic field. The outcomes reveal the importance of controlling the value of the maximum applied field as parameter for the improvement of the MBN angular dependence measurements.

  15. 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

  16. 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

  17. Investigation of the influence of magnetostriction and magnetic forces on transformer core noise and vibration

    NASA Astrophysics Data System (ADS)

    Phophongviwat, Teeraphon

    Transformer noise is of increasing environmental concern so continued efforts are being made by electrical steel and transformer producers to satisfy users by reducing the noise. Magnetostriction and magnetic forces are the main causes of transformer core noise and vibration. Understanding of the relationship from the core material to core structure and core vibration to core noise can help the design of low noise transformer cores. The most appropriate parameter for investigating the relationship between noise and vibration is sound pressure (in the unit of Pascals) in the frequency domain because it is not A-weighted. In this study, the side surfaces of transformer cores were found to emit higher noise than front and top surfaces at low magnetic induction. When the magnetic induction was increased, the effect of magnetic force increased and caused the front surfaces to emit higher noise. For three phase three limb transformer cores, the front surface of the middle limb generated higher noise than the outer limbs due to the effect of T-joint. However this does not translate higher noise level because of the phase difference of the vibration between the limbs. Due to this A-weighted sound power level of three phase, three limb transformer cores were shown to be lower than single phase transformer cores, although at the same cross sectional area and core window size the three phase cores has larger size.. A model, developed to separate the effects of magnetostriction and magnetic forces on transformer core vibration, showed that at low induction, magnetostriction is more significant than magnetic forces. The magnetic forces become more significant than magnetostriction when the induction is increased. Magnetostriction primarily depends on material and stress but magnetic forces principally depend on core building. Louder noise can be generated from a core built with low magnetostriction material than higher magnetostriction if the building tolerances are worse. The effect of magnetic forces on transformer core vibration can be reduced by using a bonding technique..

  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. Magnetically coupled quantum-flux-latch with wide operation margins

    NASA Astrophysics Data System (ADS)

    Tsuji, Naoki; Takeuchi, Naoki; Narama, Tatsuya; Ortlepp, Thomas; Yamanashi, Yuki; Yoshikawa, Nobuyuki

    2015-11-01

    We have been developing adiabatic quantum-flux-parametron (AQFP) circuits as an ultra-low-power superconductor logic for energy-efficient computing. In a previous study, we proposed and demonstrated a quantum-flux-latch (QFL), which is a compact and compatible latch for AQFP logic. The QFL is composed of an AQFP buffer gate and a storage loop, which are directly connected to each other. However, the operation margins were not sufficiently wide due to a trade-off between the operation margins of the storage loop and that of the buffer gate. In this present study, we propose a magnetically coupled QFL (MC-QFL), where the storage loop and the buffer gate are physically separated and magnetically coupled to each other to eliminate the trade-off in the operation margins. The simulation results showed that the critical parameter margin of the MC-QFL is twice as large as that of the previously designed QFL. For comparison, we fabricated and demonstrated both the previously designed QFL and the newly designed MC-QFL. The measurement results showed that the MC-QFL has wider operation margins compared with the previously designed QFL.

  20. Counterstreaming electrons in small interplanetary magnetic flux ropes

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  1. Emerging Magnetic Flux as a Trigger of a Confined Flare

    NASA Astrophysics Data System (ADS)

    Titov, Viacheslav; Wang, Yuming; Liu, Kai; Liu, Rui; Wang, Haimin; Gou, Tingyu

    We present the observation of an X-class long-duration confined flare and the analysis of its magnetic structure evolution. Although it appears as a compact-loop flare in the traditional EUV passbands (171 and 195 {Å}), in the passbands sensitive to flare plasmas (94 and 131 {Å}; ˜6-10 MK), it exhibits a cusp-shaped structure above an arcade of loops like other long-duration events. Inspecting images in a running difference approach, we find that the seemingly diffuse, quasi-static cusp-shaped structure actually consists of multiple nested loops that repeatedly rise upward and disappear approaching the cusp point. Over the gradual phase of the flare, we detect numerous episodes of loop rising, each lasting tens of seconds to minutes. A differential emission measure analysis reveals that the temperature is highest at the top of the arcade and becomes cooler at higher altitudes within the cusp-shaped structure. These features are opposite to what the standard flare model predicts. To understand the actual scenario of this event, we make first a nonlinear force-free reconstruction of the active region for a sequence of vector magnetograms that covers the time period of the event’s duration and then investigate the structure of the resulting sequence of configurations, using our field-line mapping technique based on the so-called squashing factor Q. Our analysis shows that the configurations have locally a tri-polar structure, in the middle of which the negative photospheric polarity is divided in half by a high-Q line. The respective halves belong to two adjacent sheared arcades, one of which harbors a magnetic flux rope. The indicated high-Q line is a footprint of a hyperbolic flux tube (HFT) where two quasi-separatrix layers adjoin each other at a T-type junction passing through the joint arcades’ apex. Comparing UV 1600 {Å} images of the Sun's disk with photospheric Q-maps at close times, we conclude that the emergence of a new magnetic flux within one of the arcades triggers the flare, while the preexisting T-type HFT and flux rope dictate the structure and dynamics of the observed flare loops and ribbons in this event.

  2. Plasma Flows Observed in Magnetic Flux Concentrations and Sunspot Fine Structure Using Adaptive Optics

    NASA Astrophysics Data System (ADS)

    Rimmele, Thomas R.

    2004-04-01

    We present diffraction-limited observations of magnetic flux concentrations and penumbral and umbral fine structure within an active region observed at disk center. We recorded G-band images, magnetograms, Dopplergrams, and narrowband filtergrams, using the Universal Birefringent Filter (UBF) at the Dunn Solar Telescope (DST). The National Solar Observatory (NSO) adaptive optics system at the DST was used to achieve diffraction-limited long-exposure imaging with a high signal-to-noise ratio. The main results can be summarized as follows: Strong and spatially narrow downflows are observed at the edge of magnetic structures, such as small flux concentrations (sometimes also referred to as flux tubes), pores, a light bridge, and the sunspot umbrae. For the particular sunspot observed, we find strong evidence for what appear to be vigorous, small-scale convection patterns in a light bridge. We observe extremely narrow (<0.2") channels or sheets of downflowing plasma. Flux concentrations as seen in intensity expand from a height close to where the continuum is formed to the height of formation for the G band. These observations indicate that the G band forms in the mid-photosphere. We are able to identify individual penumbral fibrils in our data and find a bright (hot) upflow and a more vertical field structure at the filament footpoint near the umbral boundary. The observations are consistent with a filament geometry in which the field and flow turn to a nearly horizontal, dark structure over a distance of about 0.2". In the deep photosphere we observe strong upflows of the order of 1 km s-1 in umbral dots. We compare our results with theoretical model predictions.

  3. Noise-reduction and fast-startup induced in magnetrons by magnetic priming

    NASA Astrophysics Data System (ADS)

    Neculaes, V. B.; Gilgenbach, R. M.; Lau, Y. Y.; Jones, M. C.; White, W. M.; Luginsland, J. W.

    2004-11-01

    Azimuthally-varying-axial magnetic fields (Â"magnetic primingÂ") in magnetrons yield fast startup and low noise. Optimal magnetic priming of N-cavity magnetrons uses N/2 azimuthal magnetic periods, to pre-bunch electrons in N/2 spokes. Magnetic priming experiments on DC oven magnetrons show rapid mode growth and (-30 dB) noise reduction in sidebands and close-to-carrier noise. Azimuthally-varying-axial magnetic fields in 10-vane oven magnetrons add five perturbing magnets on the existing upper annular magnet. Simulations by 3D ICEPIC confirm magnetic priming experimental results: fast startup and lower noise. By adding five perturbing magnets on both annular permanent magnets of the magnetron, an axially-symmetric, azimuthally-varying, magnetic field is created, causing (-20 dB) noise reduction close to carrier. This research was supported by AFOSR and DUST (S) under the Innovative Microwave Vacuum Electronics MURI Program managed by AFOSR under Grant F49620-99-1-1297. 1. V. B. Neculaes et al., Appl. Phys. Lett. 83, 1938 (2003); IEEE T-PS (6/2004). 2. M. C. Jones et al., Appl. Phys. Lett. 84, 1016 (2003); J. W. Luginsland et al., ibid, 84, 5425 (2004).

  4. Low-frequency noise in serial arrays of MgO-based magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Zhang, Wenzhe; Hao, Qiang; Xiao, Gang

    2011-09-01

    We have studied the low-frequency noise in MgO-based magnetic tunnel junctions (MTJs) in serial configurations. Two types of junctions were compared: MTJ Wheatstone bridges and MTJ discrete resistors closely packed on a wafer die. We have characterized each individual junction to ensure that they have uniform parameters such as linear field sensitivity and noise level. In the array of bridges, the low-frequency noise decreases with an increasing number (N) of bridges, but does not scale with 1/N, as expected from noise theory. The deviation is likely due to the statistical dispersions in MTJ bridge resistance and normalized voltage noise. The total noise of the discrete resistor series does not scale with 1/N either, but rather exhibits a sinusoidal-like variation with N. We attribute it to the possible enhancement of noise from magnetic coupling among the tightly spaced MTJ elements.

  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. Diffusion of Magnetic Field and Removal of Magnetic Flux from Clouds Via Turbulent Reconnection

    NASA Astrophysics Data System (ADS)

    Santos-Lima, R.; Lazarian, A.; de Gouveia Dal Pino, E. M.; Cho, J.

    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.

  7. Emergence of undulatory magnetic flux tubes by small scale reconnections

    NASA Astrophysics Data System (ADS)

    Pariat, E.; Aulanier, G.; Schmieder, B.; Georgoulis, M. K.; Rust, D. M.; Bernasconi, P. N.

    2006-01-01

    With Flare Genesis Experiment (FGE), a balloon borne observatory launched in Antarctica on January 2000, series of high spatial resolution vector magnetograms, Dopplergrams, and Hα filtergrams have been obtained in an emerging active region (AR 8844). Previous analyses of this data revealed the occurence of many short-lived and small-scale H α brightenings called 'Ellerman bombs' (EBs) within the AR. We performed an extrapolation of the field above the photosphere using the linear force-free field approximation. The analysis of the magnetic topology reveals a close connexion between the loci of EBs and the existence of "Bald patches" (BP) regions (BPs are regions where the vector magnetic field is tangential to the photosphere). Some of these EBs/BPs are magnetically connected by low-lying field lines, presenting a serpentine shape. This results leads us to conjecture that arch filament systems and active regions coronal loops do not result from the smooth emergence of large scale Ω-loops, but rather from the rise of flat undulatory flux tubes which get released from their photospheric anchorage by reconnection at BPs, which observational signature is Ellerman bombs.

  8. An investigation into the torque density capabilities of flux-focusing magnetic gearboxes

    NASA Astrophysics Data System (ADS)

    Uppalapati, Krishna Kiran

    Wind and many rotary based ocean energy conversion devices rely on a mechanical gearbox to increase their speed so as to match the requirements of the electromagnetic generator. However, mechanical gearboxes have a number of disadvantages such as the need for gear lubrication, no overload protection and the creation of acoustic noise. Frequently direct-drive generators are employed to overcome these issues, wherein the gearbox is removed and the shaft of the turbine is directly connected to the synchronous generator, either with an electrically excited or permanent magnet rotor. If the input speed to the generator is very low the torque must be very high in order to generate the necessary power. However, as the electrical loading of a synchronous generator is thermally limited, the size of the generator will become excessively large at high power levels. An alternative to these technologies is to consider replacing the mechanical gearbox with a magnetic gear. A magnetic gear can create speed change without any physical contact. It has inherent overload protection, and its non-contact operation offers the potential for high reliability. Despite significant progress, existing magnetic gear designs do not achieve torque densities that are competitive with mechanical gearboxes. This research has focused on designing a coaxial magnetic gear that can operate at a volumetric torque density that is comparable to a mechanical gearbox. A flux-focusing rotor topology also called spoke-type rotor magnet arrangement was adopted to improve the air-gap magnetic flux density which in turn improves the torque transferred between the rotors. Finite element analysis was utilized to conduct a parameter sweep analysis of the different geometric parameters of the magnetic gear. A sub-scale magnetic gear with a diameter of 110 mm and a scaled-up magnetic gear with a diameter of 228 mm was designed, constructed and experimentally evaluated. The torque and torque density of sub-scale design was measured to be 115 Nm and 151.2 Nm/L respectively and that of the scaled-up model was measured to be 731 Nm and 239 Nm/L respectively. An iterative magnetomechanical analysis technique was developed to study the deflection of the magnetic gear steel rotor bars due to the magnetic forces coming from the inner and outer rotor permanent magnets. The accuracy of the technique was validated by using an experimental test-stand. It was shown that the deflection is an important issue to consider especially if the air-gaps are small. A 2-D analytical based model was derived for the flux-focusing coaxial magnetic gear by using the separation of variables method to solve the Laplace and Poisson equation in each region. After applying the applicable Dirchlet and Neumann boundary conditions a set of 16 equations with 16 unknown Fourier coefficients was obtained. The 16 unknowns were solved numerically by putting the equations in a matrix form. It was shown that the analytical based model immensely reduced the torque and field computational time when compared to using finite element analysis. However, the analytical model does not take into consideration the non-linear properties of the steel. The benefits of using the analytical model was demonstrated by conducting a radial scaling and gear-ratio analysis.

  9. A new stator-flux orientation strategy for flux-switching permanent magnet motor based on current-hysteresis control

    NASA Astrophysics Data System (ADS)

    Hua, Wei; Cheng, Ming; Lu, Wei; Jia, Hongyun

    2009-04-01

    A stator-flux orientation strategy based on current hysteresis for the flux-switching permanent magnet (FSPM) motor is proposed, in which the stator-PM FSPM motor is considered as a conventional rotor-PM surface-mounted motor and an equivalent rotor-orientated dq-axes synchronous reference frame is built although there are actually no rotary magnetic motive force produced by the stator magnets in the FSPM motor. Based on the proposed model, a vector-control strategy with current hysteresis for the FSPM motor drive is investigated and implemented on a dSPACE-based platform, and both the simulated and experimental results validate the effectiveness. It should be emphasized that the proposed stator-flux orientation strategy can be applied to other stator-PM machines (including doubly salient and flux-reversal PM machines) and other control methods (including space-vector pulsed-width-modification and direct torque control).

  10. Results of railgun experiments powered by magnetic flux compression generators

    SciTech Connect

    Hawke, R.S.; Brooks, A.L.; Deadrick, F.J.; Scudder, J.K.; Fowler, C.M.; Caird, R.S.; Peterson, D.R.

    1980-10-24

    Researchers from LLNL and LANSL initiated a joint railgun research and development program to explore the potential of electromagnetic railguns to accelerate projectiles to hypervelocities. The effort was intended to determine experimentally the limits of railgun operation, to verify calculations of railgun performance, and to establish a data base at megampere currents. The program has led to the selection of a particular magnetic flux compression generator (MFCG) design for a set of initial experiments and to the design of small- and large-square bore railguns to match the expected MFCG power profile. The bore sizes are 12.7 and 50 mm, respectively. The design of the railguns and the diagnostic and data reduction techniques, followed by the results of eight experiments with the two railgun types are presented.

  11. Results of railgun experiments powered by magnetic flux compression generators

    SciTech Connect

    Hawke, R.S.; Brooks, A.L.; Deadrick, J.; Scudder, J.K.; Fowler, C.M.; Caird, R.S.; Peterson, D.R.

    1981-03-16

    Researchers from the Lawrence Livermore National Laboratory and the Los Alamos National Laboratory initiated a joint railgun research and development program to explore the potential of electromagnetic railguns to accelerate projectiles to hypervelocities. The effort was intended to (1) determine experimentally the limits of railgun operation; (2) verify calculations of railgun performance; and (3) establish a data base at megampere currents. The program has led to the selection of a particular magnetic flux compression generator (MFCG) design for a set of initial experiments and the design of small- and large-square-bore railguns to match the expected MFCG power profile. The bore sizes are 12.7 and 50 mm, respectively. In this paper, the design of the railguns and the diagnostic and data reduction techniques, followed by the results of eight experiments with the two railgun types, are presented.

  12. Validation Tests of Data Driven Magnetic Flux Emergence

    NASA Astrophysics Data System (ADS)

    Linton, Mark; Lukin, Vyacheslav; Leake, James Edward; Schuck, Peter W.

    2014-06-01

    The emergence of magnetic flux through the solar photosphere into the corona is a key problem to understanding the energization of the solar corona. With the advent of high spatial and temporal resolution solar vector magnetic field measurements, it may now be possible to simulate the dynamical evolution of the corona by using these measurements as the driving boundary condition for magnetohydrodynamical (MHD) simulations of the corona. First, however, methods for using this data to drive simulations must be validated via quantitative tests. We report here on a series of such tests wherein the driving inputs are taken from self-consistent simulations of the emergence of flux ropes from the upper convection zone through the photosphere and chromosphere into the low corona. Photospheric MHD output from these simulations is then used to drive new simulations, and the driven results are compared against the original results for a variety of driving assumptions and algorithms. We will focus here on the relative advantages and disadvantages of data driving a higher order finite-element-based MHD code (HiFi) versus data driving a lower order Lagrangian remap-based MHD code (LARE3D). For each code, we will report on the necessary input conditions (spatial and temporal resolution, specification of MHD variables, and specification of vertical gradients) needed to reproduce a high level of agreement between the original and the driven simulations. Finally, we will report on the level of agreement achieved when using driving input equivalent to that of current solar observations. Based on these tests, we will address the prospects for using high time and spatial resolution vector magnetogram observations to drive MHD simulations of the solar chromosphere and corona.This work was supported by the ONR 6.1 and the NASA LWS programs.

  13. Evidence for globally coherent variability in solar magnetic flux emergence

    NASA Technical Reports Server (NTRS)

    Golub, L.; Vaiana, G. S.

    1980-01-01

    We examine the large-scale spatial and temporal variations in the emergence of X-ray bright points on the sun, in order to study the global properties of magnetic flux emergence. Major variations in the rate of flux emergence are observed at all solar latitudes, on a time scale of 3-5 months. The most economical explanation of the observations is that the full sun participated in a single large eruptive event during the available 8 month observing period from Skylab in 1973. The peak of this global event corresponds in time to the eruption of a major complex of activity. Moreover, it appears that the only portion of the solar surface which deviates from the above pattern of behavior is the low latitude region in the vicinity of the AR complex; this area shows a temporary depletion immediately following the AR outburst. The high-latitude regions in both hemispheres show the same variation and appear to lead the low-latitude emergence by approximately 1 month.

  14. Inertia Wheel on Low-Noise Active Magnetic Suspension

    NASA Astrophysics Data System (ADS)

    Carabelli, S.; Genta, G.; Silvagni, M.; Tonoli, A.

    2002-01-01

    Magnetic bearings are particularly suited for space applications for a number of reasons: - they are ideally suited for vacuum applications; - the lack of lubrication and wear enhances the reliability and guaranties a long maintenance-free operation - the low drag torque decreases power consumption and reduces the torque exerted on the stator of the machine. - the possibility of insulating actively the spacecraft from the excitation due to unbalance of the rotating system In the case of reaction wheels, a well designed magnetic suspension allows high speed operation with a very low power consumption and vibration level. Conversely, microgravity (and possibly vacuum) operation is an advantage for magnetic bearings. The absence of static forces allows to operate with low current levels, thus reducing electrical noise and allowing to reach even lower vibration levels than in Earth applications of magnetic bearings. Active magnetic bearings (AMB) allow to adapt the working characteristics of the system to the operating needs: it is possible to use the actuators to lock the system during launch (absence of grabbers) and to stiffen the suspension when the spacecraft is accelerated (impulsive phases), while working in conditions optimised for microgravity when this is needed. Magnetic suspension systems designed for microgravity environment cannot be correctly tested on the ground. Testing in ground conditions results in the need of grossly overdesigning the levitation device; furthermore, in some cases ground testing is completely impossible, if not by introducing devices which compensate for the Earth gravitational field. If the compensation for the gravitational force is supplied by the same actuators used for microgravity operation, the actuators and the power amplifiers must be overdesigned and in some cases the suspension can be altogether impossible. They work in conditions which are much different from nominal ones and, above all, it is impossible to reach the precision in force measuring or vibration isolation which are required. Note that the stiffness of a magnetic suspension usually increases when it must compensate for a large static force and the increase of stiffness changes drastically the vibration isolation characteristics. It is also possible to support the rotor using a separate controlled electromagnet, but the latter will introduce disturbances which make impossible to evaluate the performances of the magnetic levitation system. Moreover, the sensitivity of the device to the operating conditions makes testing in conditions so different from the actual ones of very little significance. This is particularly true when accurate force measuring or vibration isolation is required or when low power consumption is one of the design specifications. Finally, if an external electromagnetic device is used for compensating for weight, its presence changes the stiffness of the system, to the point of altering drastically its stability characteristics. Parabolic flight is not a solution for this problem: the duration of low gravity conditions during parabolic flights is too short to perform significant experiments on magnetic suspension systems, particularly if the natural frequency of the suspension is very low as is typical of devices aimed at the isolation from low frequency vibrations. The environment in which parabolic flight testing is performed is also too rough for accurate testing. The availability of the space station changes deeply this situation: magnetic levitation systems built for space application can be tested in conditions which are very close to the operating ones. Although the space station environment is not vibrationally so clean as it would be necessary for some application, it is nevertheless far better than any simulated environment on the ground. The present paper deals with the design and construction of an engineering model of an inertia wheel on AMB. The aim of the project is to test the performance of the inertia wheel, particularly for what the disturbances caused by the rotor on the supporting structure are concerned, in actual microgravity conditions and to validate different control strategies. At present the engineering model is completed for what the mechanical subsystems and the electromechanical parts of the bearings are concerned. The drive motor is at an advanced design stage and the control electronics is almost completed. The construction phase will be completed within four to six months. A number of ground tests aimed to verifying that the device is able to operate satisfactorily are planned to be completed within the end of year 2002.

  15. Emergence of undulatory magnetic flux tubes by small scale reconnections

    NASA Astrophysics Data System (ADS)

    Pariat, E.; Aulanier, G.; Schmieder, B.; Georgoulis, M. K.; Rust, D. M.; Bernasconi, P. N.

    With Flare Genesis Experiment (FGE), a balloon borne observatory launched in Antarctica on January 2000, series of high spatial resolution vector magnetograms, Dopplergrams, and Hα filtergrams have been obtained in an emerging active region (AR 8844). Previous analyses of this data revealed the occurence of many short-lived and small-scale Hα brightenings called 'Ellerman bombs' (EBs) within the AR. We performed an extrapolation of the field above the photosphere using the linear force-free field approximation. The analysis of the magnetic topology reveals a close connexion between the loci of EBs and the existence of ``Bald patches'' regions (BPs are regions where the vector magnetic field is tangential to the photosphere). Among 47 identified EBs, we found that 23 are co-spatial with a BP, while 19 are located at the footpoint of very flat separatrix field lines passing throught a distant BP. We reveal for the first time that some of these EBs/BPs are magneticaly connected by low-lying lines, presenting a 'sea-serpent' shape. This results leads us to conjecture that arch filament systems and active regions coronal loops do not result from the smooth emergence of large scale Ω loops, but rather from the rise of flat undulatory flux tubes which get released from their photospheric anchorage by reconnection at BPs, whose observational signature is Ellerman bombs.

  16. Flux-coherent series SQUID array magnetometers operating above 77 K with superior white flux noise than single-SQUIDs at 4.2 K

    NASA Astrophysics Data System (ADS)

    Chesca, Boris; John, Daniel; Mellor, Christopher J.

    2015-10-01

    A very promising direction to improve the sensitivity of magnetometers based on superconducting quantum interference devices (SQUIDs) is to build a series-array of N non-interacting SQUIDs operating flux-coherently, because in this case their voltage modulation depth, ΔV, linearly scales with N whereas the white flux noise SΦ1/2 decreases as 1/N1/2. Here, we report the realization of both these improvements in an advanced layout of very large SQUID arrays made of YBa2Cu3O7. Specially designed with large area narrow flux focusers for increased field sensitivity and improved flux-coherency, our arrays have extremely low values for SΦ1/2 between (0.25 and 0.44) μΦ0/Hz1/2 for temperatures in the range (77-83) K. In this respect, they outperform niobium/aluminium trilayer technology-based single-SQUIDs operating at 4.2 K. Moreover, with values for ΔV and transimpedance in the range of (10-17) mV and (0.3-2.5) kΩ, respectively, a direct connection to a low-noise room temperature amplifier is allowed, while matching for such readout is simplified and the available bandwidth is greatly increased. These landmark performances suggest such series SQUID arrays are ideal candidates to replace single-SQUIDs operating at 4.2 K in many applications.

  17. 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. This work is supported by LPS-NSA-CMTC, IARPA-MQCO and CNAM.

  18. Testing a solar coronal magnetic field extrapolation code with the Titov-Démoulin magnetic flux rope model

    NASA Astrophysics Data System (ADS)

    Jiang, Chao-Wei; Feng, Xue-Shang

    2016-01-01

    In the solar corona, the magnetic flux rope is believed to be a fundamental structure that accounts for magnetic free energy storage and solar eruptions. Up to the present, the extrapolation of the magnetic field from boundary data has been the primary way to obtain fully three-dimensional magnetic information about the corona. As a result, the ability to reliably recover the coronal magnetic flux rope is important for coronal field extrapolation. In this paper, our coronal field extrapolation code is examined with an analytical magnetic flux rope model proposed by Titov & Démoulin, which consists of a bipolar magnetic configuration holding a semi-circular line-tied flux rope in force-free equilibrium. By only using the vector field at the bottom boundary as input, we test our code with the model in a representative range of parameter space and find that the model field can be reconstructed with high accuracy. In particular, the magnetic topological interfaces formed between the flux rope and the surrounding arcade, i.e., the “hyperbolic flux tube” and “bald patch separatrix surface,” are also reliably reproduced. By this test, we demonstrate that our CESE-MHD-NLFFF code can be applied to recovering the magnetic flux rope in the solar corona as long as the vector magnetogram satisfies the force-free constraints.

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

    NASA Technical Reports Server (NTRS)

    Hollweg, Joseph V.; Lee, Martin A.

    1989-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Hollweg, Joseph V.; Lee, Martin A.

    1989-08-01

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

  1. 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.

  2. 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.; Linton, Mark G.; Antiochos, Spiro K.

    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.

  3. Enhancement of magnetic flux distribution in a DC superconducting electric motor

    NASA Astrophysics Data System (ADS)

    Hamid, N. A.; Ewe, L. S.; Chin, K. M.

    2013-06-01

    Most motor designs require an air gap between the rotor and stator to enable the armature to rotate freely. The interaction of magnetic flux from rotor and stator within the air gap will provide the thrust for rotational motion. Thus, the understanding of magnetic flux in the vicinity of the air gap is very important to mathematically calculate the magnetic flux generated in the area. In this work, a finite element analysis was employed to study the behavior of the magnetic flux in view of designing a synchronous DC superconducting electric motor. The analysis provides an ideal magnetic flux distribution within the components of the motor. From the flux plot analysis, it indicates that flux losses are mainly in the forms of leakage and fringe effect. The analysis also shows that the flux density is high at the area around the air gap and the rotor. The high flux density will provide a high force area that enables the rotor to rotate. In contrast, the other parts of the motor body do not show high flux density indicating low distribution of flux. Consequently, a bench top model of a DC superconducting motor was developed where by motor with a 2-pole type winding was chosen. Each field coil was designed with a racetrack-shaped double pancake wound using DI-BSCCO Bi-2223 superconducting tapes. The performance and energy efficiency of the superconducting motor was superior when compared to the conventional motor with similar capacity.

  4. Fine resolution soil water fluxes measured with a small Smart Field Lysimeter: The noise removal and further interpretation

    NASA Astrophysics Data System (ADS)

    Dolezal, Frantisek; Bekere Mekonnen, Getu; Matula, Svatopluk; Mihalikova, Marketa; Fisak, Jaroslav; Teressa Chala, Ayele; Hrkalova, Marketa; Moreira Barradas, Joao Manuel

    2014-05-01

    A weighable Smart Field Lysimeter (30 cm diameter, 30 cm depth) with an adaptively regulated suction at its bottom was used to measure soil water fluxes at the surface and at the 30 cm depth of a short grass stand. No overland flow or accumulation of water at the surface were observed and there was no groundwater table within the soil profile. Appropriate distinction between the fluxes of different directions made it possible to separately estimate actual evapotranspiration (upward surface flux), precipitation and condensation (downward surface flux and dew on grass leaves), percolation (downward flux at 30 cm) and capillary rise (upward flux at 30 cm). The primary data were collected at 1 minute intervals but required digital filtering to remove the information noise. Various methods of filtering were tested, with a special regard to intensive rain events. The resulting data have a 10-minute resolution. The lysimeter is capable of self-recovery after a period of drought but the noise of percolation and capillary rise estimates is enhanced for some time during, before and after this period. In these situations, it is important that a porous matrix sensor measures the suction in parallel to the reference tensiometer. Both the precipitation and the actual evapotranspiration derived from the lysimeter data alone are in absolute values higher than the analogous quantities obtained with the help of the directly measured tipping bucket precipitation. These discrepancies are probably due to the rain gauge underestimating true precipitation, but partly also due to numerical noise, however smoothed. If the rain gauge data are used only to distinguish the periods of rain from the rainless periods, than the condensation of water in the soil and on the grass leaves can be estimated. The actual evapotranspiration measured by the lysimeter has a diurnal patterns depending on actual weather. The maximum occurs, on average, shortly after the noon. The percolation curves after rain events make it possible to estimate the soil hydraulic properties on the principle of the outflow method.

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

    SciTech Connect

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

    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.

  6. 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.; Erdlyi, 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.

  7. Empirical relationships between interplanetary conditions, magnetospheric flux transfer, and the AL index. [auroral zone magnetic index

    NASA Technical Reports Server (NTRS)

    Slavin, J. A.; Holzer, R. E.

    1979-01-01

    Holzer and Slavin (1978) have found that the transfer of magnetic flux to and from the dayside magnetosphere as inferred from observed displacements of the magnetopause surface is correlated with both the magnitude of the auroral zone magnetic index AL and the incident flux of southward IMF. Empirical expressions specifying the rate at which magnetic flux is eroded in terms of interplanetary parameters and the rate of magnetic flux return as a function of AL have been developed. These relations are then used to predict magnetotail magnetic field enhancements from interplanetary and ground based data during an interval of substorm activity. The total magnetic flux in the tail is increased during intervals when the amount of flux transferred into its volume by dayside erosion exceeds the flux lost to the dayside by magnetospheric convection. Using Ogo-5 tail observations it is found for the sample events considered that these magnetic field enhancements can be described by empirical expressions for the magnetic flux transfer rates.

  8. Pulsating Reconnection in the interaction of two magnetic flux ropes

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    Two flux ropes (dia = 7 cm, ds = 3 cm, L = 10m, Irope = 300 A/rope) are generated by using a mask in front of a high emissivity cathode (n = 4X1012 cm3, Te-rope = 8.5 eV) in a background magnetoplasma (He, Boz = 330 G, n =1.0X1012cm3, Te = 4 eV) in the LAPD device at UCLA. The ropes are kink unstable (I >250 A) but not violently so. All three components of the magnetic field were measured with small (1 mm dia) 3-axis probes sensitive to ∂/B-> ∂ t and the plasma potential measured with an emissive probe. These were measured at 42,075 locations in the volume containing the ropes and 7000 time steps (δτ = .33 μs). The total electric field E-> = - ∇ ϕ -∂/A-> ∂ t and parallel resistivity as well as the Quasi Seperatrix layer (QSL) were derived from the data. The flux ropes periodically collide as they kink. Each time this happens a strong QSL (Q<400) forms and the resistivity jumps to over a hundred times the classical value at locations within the QSL and also on the gradient of the rope current. The reconnection rate is directly evaluated by integrating the electric field along field lines as well as the energy deposition J-> . E-> . The data indicate that there is more than one process causing the enhanced resistivity. The reconnection rate cannot be explained by conventional 2D theories. Work done at the BaPSF which is supported by NSF/DOE. project supported by DOE and a LANL research grant.

  9. 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 β, 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, Φ0 = 2π/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.

  10. BUILDUP OF MAGNETIC SHEAR AND FREE ENERGY DURING FLUX EMERGENCE AND CANCELLATION

    SciTech Connect

    Fang Fang; Manchester, Ward IV; Van der Holst, Bart; Abbett, William P.

    2012-07-20

    We examine a simulation of flux emergence and cancellation, which shows a complex sequence of processes that accumulate free magnetic energy in the solar corona essential for the eruptive events such as coronal mass ejections, filament eruptions, and flares. The flow velocity at the surface and in the corona shows a consistent shearing pattern along the polarity inversion line (PIL), which together with the rotation of the magnetic polarities, builds up the magnetic shear. Tether-cutting reconnection above the PIL then produces longer sheared magnetic field lines that extend higher into the corona, where a sigmoidal structure forms. Most significantly, reconnection and upward-energy-flux transfer are found to occur even as magnetic flux is submerging and appears to cancel at the photosphere. A comparison of the simulated coronal field with the corresponding coronal potential field graphically shows the development of non-potential fields during the emergence of the magnetic flux and formation of sunspots.

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

    SciTech Connect

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

    2007-12-14

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

  12. Low frequency noise peak near magnon emission energy in magnetic tunnel junctions

    SciTech Connect

    Liu, Liang; Xiang, Li; Guo, Huiqiang; Wei, Jian; Li, D. L.; Yuan, Z. H.; Feng, J. F. Han, X. F.; Coey, J. M. D.

    2014-12-15

    We report on the low frequency (LF) noise measurements in magnetic tunnel junctions (MTJs) below 4 K and at low bias, where the transport is strongly affected by scattering with magnons emitted by hot tunnelling electrons, as thermal activation of magnons from the environment is suppressed. For both CoFeB/MgO/CoFeB and CoFeB/AlO{sub x}/CoFeB MTJs, enhanced LF noise is observed at bias voltage around magnon emission energy, forming a peak in the bias dependence of noise power spectra density, independent of magnetic configurations. The noise peak is much higher and broader for unannealed AlO{sub x}-based MTJ, and besides Lorentzian shape noise spectra in the frequency domain, random telegraph noise (RTN) is visible in the time traces. During repeated measurements the noise peak reduces and the RTN becomes difficult to resolve, suggesting defects being annealed. The Lorentzian shape noise spectra can be fitted with bias-dependent activation of RTN, with the attempt frequency in the MHz range, consistent with magnon dynamics. These findings suggest magnon-assisted activation of defects as the origin of the enhanced LF noise.

  13. Magnetic Flux Concentrations in Stratified Turbulent Plasma Due to Negative Effective Magnetic Pressure Instability

    NASA Astrophysics Data System (ADS)

    Jabbari, S.; Brandenburg, A.

    2014-12-01

    Recent studies have suggested a new mechanism that can be used to explain the formation of magnetic spots or bipolar regions in highly stratified turbulent plasmas. According to this model, a large-scale magnetic field suppresses the turbulent pressure, which leads to a negative contribution of turbulence to the effective magnetic pressure. Direct numerical simulations (DNS) have confirmed that the negative contribution is large enough so that the effective magnetic pressure becomes negative and leads to a large-scale instability, which we refer to as negative effective magnetic pressure Instability (NEMPI). NEMPI was used to explain the formation of active regions and sunspots on the solar surface. One step toward improving this model was to combine dynamo in- stability with NEMPI. The dynamo is known to be responsible for the solar large-scale magnetic field and to play a role in solar activity. In this context, we studied stratified turbulent plasmas in spherical geometry, where the background field was generated by alpha squared dynamo. For NEMPI to be excited, the initial magnetic field should be in a proper range, so we used quenching function for alpha. Using the Pencil Code and mean field simulations (MFS), we showed that in the presence of dynamo-generated magnetic fields, we deal with a coupled system, where both instabilities, dynamo and NEMPI, work together and lead to the formation of magnetic structures (Jabbari et al. 2013). We also studied a similar system in plane geometry in the presence of rotation and confirmed that for slow rotation NEMPI works, but as the Coriolis number increases, the rotation suppresses NEMPI. By increasing the Coriolis number even further, the combination of fast rotation and high stratification excites a dynamo, which leads again to a coupled system of dynamo and NEMPI (Jabbari et al. 2014). Another important finding concerning NEMPI is the case where the instability is excited by a vertical magnetic field (Brandenburg et al. 2013). When the field is vertical, the resulting magnetic flux concentrations lead to the magnetic spots and can be of equipartition field strength. DNS, MFS, and implicit large eddy simulations (ILES) confirm that in a proper parameter regime, vertical imposed fields lead to the formation of circular magnetic spots (Brandenburg et al. 2014).

  14. On the evolution of a magnetic flux rope: Two-dimensional MHD simulation results

    NASA Astrophysics Data System (ADS)

    Teh, W.-L.; Nakamura, T. K. M.; Nakamura, R.; Baumjohann, W.; Abdullah, M.

    2015-10-01

    We use the time-dependent, two-dimensional (2-D), ideal MHD equations to simulate and investigate the evolution of magnetic field and plasma profiles of the typical (T) and crater (C) magnetic flux ropes (FRs). The T-FR has a magnetic pressure peak at the center of the flux rope, while the C-FR has a local dip instead. The simulation starts with a 2-D magnetic flux rope in magnetohydrostatic equilibrium, where pressure gradient forces are balanced by Lorentz forces. The magnetic field and plasma pressure profiles for the initial flux rope are derived from the analytical solutions by Zhang et al. (2010). The initial flux rope starts to evolve when the force balance is broken by imposing pressure or magnetic field perturbations onto the equilibrium system. The pressure perturbations are produced by increasing/decreasing the internal plasma pressure of the flux rope, while the magnetic field perturbations are produced by increasing/decreasing the transverse magnetic fields across the flux rope. We conclude that a T-FR can be evolved into a C-FR and vice versa, if the perturbation strength is sufficient, and that the plasma pressure and density in the new equilibrium state could be either increased or decreased for the evolution of C-FR to T-FR and also for the evolution of T-FR to C-FR.

  15. How Well Can a Footpoint Tracking Method Estimate the Magnetic Helicity Influx during Flux Emergence?

    NASA Astrophysics Data System (ADS)

    Choe, Gwangson; Kim, Sunjung; Kim, Kap-Sung; No, Jincheol

    2015-08-01

    As shown by Démoulin and Berger (2003), the magnetic helicity flux through the solar surface into the solar atmosphere can be exactly calculated if we can trace the motion of footpoints with infinite temporal and spatial resolutions. When there is a magnetic flux transport across the solar surface, the horizontal velocity of footpoints becomes infinite at the polarity inversion line, although the surface integral yielding the helicity flux does not diverge. In practical application, a finite temporal and spatial resolution causes an underestimate of the magnetic helicity flux when a magnetic flux emerges from below the surface, because there is an observational blackout area near a polarity inversion line whether it is pre-existing or newly formed. In this paper, we consider emergence of simple magnetic flux ropes and calculate the supremum of the magnitude of the helicity influx that can be estimated from footpoint tracking. The results depend on the ratio of the resolvable length scale and the flux rope diameter. For a Gold-Hoyle flux rope, in which all field lines are uniformly twisted, the observationally estimated helicity influx would be about 90% of the real influx when the flux rope diameter is one hundred times the spatial resolution (for a large flux rope), and about 45% when it is ten times (for a small flux rope). For Lundquist flux ropes, the errors incurred by observational estimation are smaller than the case of the Gold-Hoyle flux rope, but could be as large as 30% of the real influx. Our calculation suggests that the error in the helicity influx estimate is at least half of the real influx or even larger when small scale magnetic structures (less than 10,000 km) emerge into the solar atmosphere.

  16. Numerical dynamos with outer boundary heat flux inferred from probabilistic tomography—consequences for latitudinal distribution of magnetic flux

    NASA Astrophysics Data System (ADS)

    Amit, Hagay; Deschamps, Frédéric; Choblet, Gaël

    2015-11-01

    Mantle control on the geodynamo is often simulated using numerical dynamos with imposed outer boundary heat flux inferred from lower mantle tomography, assuming that seismic and thermal anomalies in the lowermost mantle are highly correlated. However, non-thermal effects might perturb this idealized linear seismic-thermal mapping. Here we use a probabilistic tomography model to isolate the thermal part of the seismic anomaly in order to impose a more realistic core-mantle boundary heat flux pattern on the outer boundary of numerical dynamo simulations. We demonstrate that on time average these dynamo models have more low-latitude convective and magnetic activity than corresponding models with conventional tomographic heat flux. In addition, the low-latitude magnetic flux and kinetic energy contributions are more time-dependent in the dynamo models with a probabilistic tomography heat flux, and thus may recover the observed latitudinal distribution of geomagnetic flux on the core-mantle boundary, which we propose as a morphological criterion for Earth-like dynamo models.

  17. Numerical dynamos with outer boundary heat flux inferred from probabilistic tomography - Consequences for latitudinal distribution of magnetic flux

    NASA Astrophysics Data System (ADS)

    Amit, Hagay; Deschamps, Frédéric; Choblet, Gaël

    2015-04-01

    Mantle control on the geodynamo is often simulated using numerical dynamos with imposed outer boundary heat flux inferred from lower mantle tomography, assuming that seismic and thermal anomalies in the lowermost mantle are highly correlated. However, non-thermal effects might perturb this idealized linear seismic-thermal mapping. Here we use a probabilistic tomography model to isolate the thermal part of the seismic anomaly in order to impose a more realistic core-mantle boundary heat flux pattern on the outer boundary of numerical dynamo simulations. We demonstrate that on time-average these dynamo models have more low-latitudes convective and magnetic activity than corresponding models with conventional tomographic heat flux. In addition, the low-latitudes magnetic flux and kinetic energy contributions are more time-dependent in the dynamo models with a probabilistic tomography heat flux, and thus may recover the observed latitudinal distribution of geomagnetic flux on the core-mantle boundary, which we propose as a morphological criterion for Earth-like dynamo models.

  18. Mechanism of a high-Tc superconducting flux pump: Using alternating magnetic field to trigger flux flow

    NASA Astrophysics Data System (ADS)

    Geng, Jianzhao; Coombs, T. A.

    2015-10-01

    High-Tc Superconducting (HTS) magnets operating in persistent current mode suffer a current decay due to flux creep of superconductor and joint resistance. Flux pumps are able to inject direct current into superconducting circuit to compensate the current decay, without the thermal loss caused by current leads. In this work, we proposed a flux pumping mechanism for HTS coils, with an experimental verification and an analytical model. The basic principle we have used is that flux flow can be triggered when the superconductor carrying a direct current is subjected to a perpendicular AC magnetic field. Low frequency alternating current is induced in a loop of YBCO tape using an AC field. A portion of the tape which we refer to as the "bridge" shorts a superconducting coil. A high frequency AC field is applied perpendicular to the bridge tape when alternating current in the tape reaches one polarity. This triggers a net flux flow and results in a current increase in the coil. The proposed flux pump has clear physics and is easily controllable, which may make it promising in practical use.

  19. The magnetic, basal, and radiative-equilibrium components in Mount Wilson Ca II H + K fluxes

    NASA Technical Reports Server (NTRS)

    Schrijver, C. J.; Dobson, Andrea K.; Radick, Richard R.

    1989-01-01

    Mount Wilson Ca II H + K flux measurements of cool dwarf stars are analyzed and compared with stellar Mg II h + k fluxes, variability amplitudes, rotation rates, and solar data. It is concluded that the Mount Wilson Ca II H + K fluxes comprise three principal parts: (1) a photospheric contribution in the line wings, (2) a basal chromospheric component that appears to be unrelated to stellar magnetic activity and is, therefore, possibly nonmagnetic in origin, and (3) a chromospheric component which is associated with magnetically active regions and the (quiet and active) network. The basal chromosphere appears to cover the entire surface of magnetically inactive stars. The basal Ca II H + K flux density for solar-type stars equals the average emission observed in the centers of solar supergranulation cells, where the magnetic flux density is small.

  20. Asymmetric planar gradiometer for rejection of uniform ambient magnetic noise

    DOEpatents

    Dantsker, Eugene; Clarke, John

    2000-01-01

    An asymmetric planar gradiometer for use in making biomagnetic measurements. The gradiometer is formed from a magnetometer which is inductively-coupled to the smaller of two connected loops patterned in a superconducting film which form a flux transformer. The magnetometer is based on a SQUID formed from a high T.sub.c superconducting material. The flux transformer and magnetometer may be formed on separate substrates, allowing the baseline to be increased relative to presently available devices.

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

    NASA Astrophysics Data System (ADS)

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

    2007-05-01

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

  2. A high-speed induction motor making use of the third harmonic of the magnetic flux

    NASA Astrophysics Data System (ADS)

    Goleman, Ryszard

    1994-05-01

    This paper indicates some possibilities of construction of high-speed induction motors taking advantage of the magnetic flux third harmonic due to a process of magnetization of nonlinear magnetic circuits. Configurations of magnetic frequency triplers, which can be used as basic stator structures and generate a distorted flux, are presented. The paper also describes an experimental high-speed induction motor supplied from a single-phase source via a magnetic frequency tripler that make possible to obtain a rotating field having a synchronous speed equal to 9000 rpm at a supply voltage angular frequency of 314 rd.

  3. An Experimental Determination of Static Magnetic Fields Induced Noise in Living Systems

    NASA Astrophysics Data System (ADS)

    Brady, Megan; Laramee, Craig

    2013-03-01

    Living systems are constantly exposed to static magnetic fields (SMFs) from both natural and man-made sources. Exposures vary in dose and duration ranging from geomagnetic (~50 ?T) to residential and industrial (~10s of mT) fields. Efforts to characterize responses to SMFs have yielded conflicting results, showing a dependence on experimental variables used. Here we argue that low to moderate SMF exposure is a sub-threshold perturbation operating below thermal noise, and assays that evaluate statistical characteristics of a single cell may identify responses not consistently found by population averaging approaches. Recent studies of gene expression show that it is a stochastic process capable of producing bursting dynamics. Moreover, theoretical and experimental methods have also been developed to allow quantitative estimates of the associated biophysical parameters. These developments provide a new way to assess responses of living systems to SMFs. In this work, we report on our efforts to use single molecule fluorescence in situ hybridization to assess responses of NIH-3T3 cells to SMF exposure at flux densities ranging from 1 to 440 mT for 48 hours. Results will contribute to determining mechanisms by which SMF exposure influences gene expression.

  4. Structures of interplanetary magnetic flux ropes and comparison with their solar sources

    SciTech Connect

    Hu, Qiang; Dasgupta, B.; Khare, A.; Webb, G. M. E-mail: qiu@physics.montana.edu

    2014-09-20

    Whether a magnetic flux rope is pre-existing or formed in situ in the Sun's atmosphere, there is little doubt that magnetic reconnection is essential to release the flux rope during its ejection. During this process, the question remains: how does magnetic reconnection change the flux-rope structure? In this work, we continue with the original study of Qiu et al. by using a larger sample of flare-coronal mass ejection (CME)-interplanetary CME (ICME) events to compare properties of ICME/magnetic cloud (MC) flux ropes measured at 1 AU and properties of associated solar progenitors including flares, filaments, and CMEs. In particular, the magnetic field-line twist distribution within interplanetary magnetic flux ropes is systematically derived and examined. Our analysis shows that, similar to what was found before, for most of these events, the amount of twisted flux per AU in MCs is comparable with the total reconnection flux on the Sun, and the sign of the MC helicity is consistent with the sign of the helicity of the solar source region judged from the geometry of post-flare loops. Remarkably, we find that about half of the 18 magnetic flux ropes, most of them associated with erupting filaments, have a nearly uniform and relatively low twist distribution from the axis to the edge, and the majority of the other flux ropes exhibit very high twist near the axis, up to ≳ 5 turns per AU, which decreases toward the edge. The flux ropes are therefore not linearly force-free. We also conduct detailed case studies showing the contrast of two events with distinct twist distribution in MCs as well as different flare and dimming characteristics in solar source regions, and discuss how reconnection geometry reflected in flare morphology may be related to the structure of the flux rope formed on the Sun.

  5. Resistive noise of YBCO high- Tc granular superconductors in magnetic field

    NASA Astrophysics Data System (ADS)

    Celasco, M.; Cone, G.; Popescu, V.; Masoero, A.; Stepanescu, A.

    1995-02-01

    Resistance and resistance-noise experimental results, obtained in the transition region of two YBCO bulk superconductors submitted to a DC magnetic field are reported. The magnetic field was found to influence only the second stage of the transition, enlarging the transition-temperature interval and determining a shift of the noise peak towards lower temperatures. The sample is modelled as a precolating network formed by Josephson junctions and resistance noise is ascribed to the random switching of certain junctions (p-noise) [L.B. Kiss et al. Physica C 207(1993)318]. A junction may be enable to switch either by thermal fluctuations or by random motion of intergranular vortices. The square of the temperature derivative of the resistance was used to control the thermal-fluctuations effect in producing the noise. The magnetic field is believed to influence the resistance and resistance noise via a parameter p (percentage of phase-locked junctions) and p-noise behavior is considered an intrinsic property of the network.

  6. The Evolution of the Sun's Open Magnetic Flux - II. Full Solar Cycle Simulations

    NASA Astrophysics Data System (ADS)

    Mackay, D. H.; Priest, E. R.; Lockwood, M.

    2002-10-01

    In this paper the origin and evolution of the Sun's open magnetic flux is considered by conducting magnetic flux transport simulations over many solar cycles. The simulations include the effects of differential rotation, meridional flow and supergranular diffusion on the radial magnetic field at the surface of the Sun as new magnetic bipoles emerge and are transported poleward. In each cycle the emergence of roughly 2100 bipoles is considered. The net open flux produced by the surface distribution is calculated by constructing potential coronal fields with a source surface from the surface distribution at regular intervals. In the simulations the net open magnetic flux closely follows the total dipole component at the source surface and evolves independently from the surface flux. The behaviour of the open flux is highly dependent on meridional flow and many observed features are reproduced by the model. However, when meridional flow is present at observed values the maximum value of the open flux occurs at cycle minimum when the polar caps it helps produce are the strongest. This is inconsistent with observations by Lockwood, Stamper and Wild (1999) and Wang, Sheeley, and Lean (2000) who find the open flux peaking 1-2 years after cycle maximum. Only in unrealistic simulations where meridional flow is much smaller than diffusion does a maximum in open flux consistent with observations occur. It is therefore deduced that there is no realistic parameter range of the flux transport variables that can produce the correct magnitude variation in open flux under the present approximations. As a result the present standard model does not contain the correct physics to describe the evolution of the Sun's open magnetic flux over an entire solar cycle. Future possible improvements in modeling are suggested.

  7. Single image signal-to-noise ratio estimation for magnetic resonance images.

    PubMed

    Sim, K S; Lai, M A; Tso, C P; Teo, C C

    2011-02-01

    A novel technique to quantify the signal-to-noise ratio (SNR) of magnetic resonance images is developed. The image SNR is quantified by estimating the amplitude of the signal spectrum using the autocorrelation function of just one single magnetic resonance image. To test the performance of the quantification, SNR measurement data are fitted to theoretically expected curves. It is shown that the technique can be implemented in a highly efficient way for the magnetic resonance imaging system. PMID:20703587

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  9. 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.

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

    SciTech Connect

    Sipahi, L.B. Iowa State Univ., Ames, IA . 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.

  11. Magnetic Flux Transport and the Long-term Evolution of Solar Active Regions

    NASA Astrophysics Data System (ADS)

    Ugarte-Urra, Ignacio; Upton, Lisa; Warren, Harry P.; Hathaway, David H.

    2015-12-01

    With multiple vantage points around the Sun, Solar Terrestrial Relations Observatory (STEREO) and Solar Dynamics Observatory imaging observations provide a unique opportunity to view the solar surface continuously. We use He ii 304 Å data from these observatories to isolate and track ten active regions and study their long-term evolution. We find that active regions typically follow a standard pattern of emergence over several days followed by a slower decay that is proportional in time to the peak intensity in the region. Since STEREO does not make direct observations of the magnetic field, we employ a flux-luminosity relationship to infer the total unsigned magnetic flux evolution. To investigate this magnetic flux decay over several rotations we use a surface flux transport model, the Advective Flux Transport model, that simulates convective flows using a time-varying velocity field and find that the model provides realistic predictions when information about the active region's magnetic field strength and distribution at peak flux is available. Finally, we illustrate how 304 Å images can be used as a proxy for magnetic flux measurements when magnetic field data is not accessible.

  12. 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.

  13. 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.

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

    SciTech Connect

    Omidi, Mahboubeh Faizabadi, Edris

    2015-03-21

    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.

  15. LARGE-SCALE MAGNETIC HELICITY FLUXES ESTIMATED FROM MDI MAGNETIC SYNOPTIC CHARTS OVER THE SOLAR CYCLE 23

    SciTech Connect

    Yang Shangbin; Zhang Hongqi

    2012-10-10

    To investigate the characteristics of large-scale and long-term evolution of magnetic helicity with solar cycles, we use the method of Local Correlation Tracking to estimate the magnetic helicity evolution over solar cycle 23 from 1996 to 2009 using 795 MDI magnetic synoptic charts. The main results are as follows: the hemispheric helicity rule still holds in general, i.e., the large-scale negative (positive) magnetic helicity dominates the northern (southern) hemisphere. However, the large-scale magnetic helicity fluxes show the same sign in both hemispheres around 2001 and 2005. The global, large-scale magnetic helicity flux over the solar disk changes from a negative value at the beginning of solar cycle 23 to a positive value at the end of the cycle, while the net accumulated magnetic helicity is negative in the period between 1996 and 2009.

  16. Magnetic background noise cancellation in a biomagnetometer system for unshielded environments

    NASA Astrophysics Data System (ADS)

    Wltgens, P. J. M.; Koch, R. H.; Brown, S. L.; Altman, R. A.; Gallagher, W. J.; Matthews, R.; Haupt, S. G.; Lathrop, D. K.

    1996-03-01

    We are presently building a 7-channel high-Tc SQUID-based biomagnetometer system to measure magnetocardiograms in an unshielded environment. The main challenge in such a system is to resolve the very small magnetic signals originating from the human heart in the noisy magnetic background of a real-world environment. In this biomagnetometer setup, the SQUID sensors are being used in a three-SQUID gradiometer arrangement. The sensors are configured as first-order gradiometers, and at each sensor a common magnetic field is applied to cancel out the background field as measured by a reference sensor. To investigate the limits of magnetic background noise cancellation, the frequency dependence of the correlation between the magnetic backgrounds at two positions was measured as a function of distance between these positions. Furthermore, a study was made of how eddy currents induced in nearby metallic objects affect these correlations and the background noise cancellation.

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

    SciTech Connect

    Thomas, James

    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.

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

    NASA Astrophysics Data System (ADS)

    Thomas, James

    2014-02-01

    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&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.

  19. 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. This work is supported by LPS-NSA-CMTC, IARPA-MQCO and CNAM.

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

    PubMed

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

    2013-01-01

    To predict the performance of flux trapping cascaded flux compression generators, a calculation model based on an equivalent circuit is investigated. The system circuit is analyzed according to its operation characteristics in different steps. Flux conservation coefficients are added to the driving terms of circuit differential equations to account for intrinsic flux losses. To calculate the currents in the circuit by solving the circuit equations, a simple zero-dimensional model is used to calculate the time-varying inductance and dc resistance of the generator. Then a fast computer code is programmed based on this calculation model. As an example, a two-staged flux trapping generator is simulated by using this computer code. Good agreements are achieved by comparing the simulation results with the measurements. Furthermore, it is obvious that this fast calculation model can be easily applied to predict performances of other flux trapping cascaded flux compression generators with complex structures such as conical stator or conical armature sections and so on for design purpose. PMID:23387675

  1. Characterization and compensation of systematic noise in functional magnetic resonance imaging

    NASA Astrophysics Data System (ADS)

    Peltier, Scott James

    Functional magnetic resonance imaging (fMRI) has emerged as an important tool for noninvasive neuroscientific research. A limit to its effectiveness, however, is the presence of systematic noise that can obscure neuronal activation. Systematic noise in fMRI has a temporal and/or spatial structure, as opposed to additive random Gaussian white noise (e.g. thermal fluctuations). Several examples are low frequency signal drifts, head motion, physiological noise, and spontaneous neuronal events. These systematic noise sources are generally multiplicative and depend on the signal strength. As the fMRI signal is increased, by increasing voxel size or field strength, these noise sources may dominate the thermal noise, and determine the effective signal-to-noise ratio of a functional imaging experiment. Thus, understanding these noise sources and how to mitigate their effects is an important step in maximizing the potential of functional MRI as a neuro-imaging tool. This dissertation investigates characterization and compensation techniques for several types of systematic noise in fMRI. First, mitigation techniques for signal drift in single cycle MRI studies and physiological noise (caused by the respiratory and cardiac rhythms) are investigated, with functional contrast increased using appropriate noise compensation. Then, the effect of physiological noise in multi-shot imaging is explored. It is seen that the effective repetition time (TR) combines with the frequency of the physiological noise to modulate the level of physiological noise variance induced in a multi-shot study. A noise compensation process is next applied to a rapid, multi-slice acquisition and is shown to reduce noise variance down to the level of the associated single-slice case. Finally, resting state low frequency functional connectivity patterns are examined. Using a multi-echo sequence, they are shown to have the same T2* and echo time dependence as "normal" task activation. A data-driven method of detecting functional connectivity patterns using a clustering algorithm is also investigated, and compared to the standard reference-based approach.

  2. Magnetic field enhancement of generation-recombination and shot noise in organic light emitting diodes

    SciTech Connect

    Djidjou, T. K.; Basel, Tek; Rogachev, A.; Chen, Ying; Shinar, J.

    2015-03-21

    We have studied the effect of magnetic field on noise in series of 2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene-based organic light emitting diodes with dominant hole injection, dominant electron injection, and balanced electron and hole injection. The noise spectra of the balanced devices revealed the generation-recombination (g-r) noise term, which we associated with bimolecular electron-hole recombination. The presence of the g-r noise term is correlated with the strong organic magnetoresistance (up to 25%) observed in the balanced devices. The noise spectra also have the shot noise contribution with the Fano factor 0.25–0.4. We found that time constant of the g-r term decreases and the magnitude of shot noise increases when magnetic field is applied. This behavior can be consistently explained within the polaron-polaron model of organic magnetoresistance. We have not found any evidence that the magnetoresistance in studied devices is affected by traps.

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

    SciTech Connect

    O`Connor, T.; The BaBar Collaboration

    1995-03-01

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

  4. Morphology and magnetic flux distribution in superparamagnetic, single-crystalline Fe3O4 nanoparticle rings

    NASA Astrophysics Data System (ADS)

    Takeno, Yumu; Murakami, Yasukazu; Sato, Takeshi; Tanigaki, Toshiaki; Park, Hyun Soon; Shindo, Daisuke; Ferguson, R. Matthew; Krishnan, Kannan M.

    2014-11-01

    This study reports on the correlation between crystal orientation and magnetic flux distribution of Fe3O4 nanoparticles in the form of self-assembled rings. High-resolution transmission electron microscopy demonstrated that the nanoparticles were single-crystalline, highly monodispersed, (25 nm average diameter), and showed no appreciable lattice imperfections such as twins or stacking faults. Electron holography studies of these superparamagnetic nanoparticle rings indicated significant fluctuations in the magnetic flux lines, consistent with variations in the magnetocrystalline anisotropy of the nanoparticles. The observations provide useful information for a deeper understanding of the micromagnetics of ultrasmall nanoparticles, where the magnetic dipolar interaction competes with the magnetic anisotropy.

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

    SciTech Connect

    Ginzburg, S. L.; Nakin, A. V.; Savitskaya, N. E.

    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.

  6. Modeling Barkhausen Noise in magnetic glasses with dipole-dipole interactions

    NASA Astrophysics Data System (ADS)

    Dubey, Awadhesh K.; Hentschel, H. George E.; Jaiswal, Prabhat K.; Mondal, Chandana; Procaccia, Itamar; Gupta, Bhaskar Sen

    2015-10-01

    Long-ranged dipole-dipole interactions in magnetic glasses give rise to magnetic domains having labyrinthine patterns on the scale of about 1 micron. Barkhausen Noise then results from the movement of domain boundaries which is modeled by the motion of elastic membranes with random pinning. Here we propose that on the nanoscale new sources of Barkhausen Noise can arise. We propose an atomistic model of magnetic glasses in which we measure the Barkhausen Noise which results from the creation of new domains and the movement of domain boundaries on the nanoscale. The statistics of the Barkhausen Noise found in our simulations is in striking disagreement with the expectations in the literature. In fact we find exponential statistics without any power law, stressing the fact that Barkhausen Noise can belong to very different universality classes. In the present model the essence of the phenomenon is the fact that the spin response Green's function is decaying too rapidly for having sufficiently large magnetic jumps. A theory is offered in excellent agreement with the measured data without any free parameter.

  7. Reducing media noise of perpendicular magnetic recording tape for over-50 TB class data cartridge

    NASA Astrophysics Data System (ADS)

    Matsunuma, S.; Inoue, T.; Watanabe, T.; Doi, T.; Gomi, S.; Mashiko, Y.; Hirata, K.; Nakagawa, S.

    2011-04-01

    To reduce medium noise inherent in a perpendicular magnetic recording tape, which is deposited by facing targets sputtering, we have examined an epitaxial double-layered structure consisting of a soft magnetic underlayer (SUL), bcc-FeCoB/fcc-NiFe/Si/bcc-FeCoB, on a 4.5 μm para-aromatic polyamide (aramid) film. An epitaxial soft magnetic bilayer reduces broadband noise by 5.6 dB at 337 kilo fluxchanges per inch (kfci) compared to a single SUL medium (Tape S). This is due to the reduction in the low-frequency noise, which originates from the domain walls of the SUL. Improvement of the crystal orientation of the magnetic layer hcp-CoPtCr-SiO2 and the intermediate layer hcp-Ru by inserting a fcc-NiFe spacer in laminated SULs extends the roll-off curve toward high linear density. When each SUL layer of the bilayer was made thinner, from 25 nm (Tape D2) to 10 nm (Tape D1), the medium noise decreased, improving the signal-to-noise ratio by 8.6 dB at 337 kfci compared to Tape S. In a high resolution playback test of Tape D1, an areal density of 45.0 gigabits per square inch (Gb/in.2) was confirmed. Achieved areal density means the capability of an over-50 terabyte (TB) capacity for a typical linear-formatted data cartridge.

  8. 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

  9. Cluster electric current density measurements within a magnetic flux rope in the plasma sheet

    NASA Technical Reports Server (NTRS)

    Slavin, J. A.; Lepping, R. P.; Gjerloev, J.; Goldstein, M. L.; Fairfield, D. H.; Acuna, M. H.; Balogh, A.; Dunlop, M.; Kivelson, M. G.; Khurana, K.

    2003-01-01

    On August 22, 2001 all 4 Cluster spacecraft nearly simultaneously penetrated a magnetic flux rope in the tail. The flux rope encounter took place in the central plasma sheet, Beta(sub i) approx. 1-2, near the leading edge of a bursty bulk flow. The "time-of-flight" of the flux rope across the 4 spacecraft yielded V(sub x) approx. 700 km/s and a diameter of approx.1 R(sub e). The speed at which the flux rope moved over the spacecraft is in close agreement with the Cluster plasma measurements. The magnetic field profiles measured at each spacecraft were first modeled separately using the Lepping-Burlaga force-free flux rope model. The results indicated that the center of the flux rope passed northward (above) s/c 3, but southward (below) of s/c 1, 2 and 4. The peak electric currents along the central axis of the flux rope predicted by these single-s/c models were approx.15-19 nA/sq m. The 4-spacecraft Cluster magnetic field measurements provide a second means to determine the electric current density without any assumption regarding flux rope structure. The current profile determined using the curlometer technique was qualitatively similar to those determined by modeling the individual spacecraft magnetic field observations and yielded a peak current density of 17 nA/m2 near the central axis of the rope. However, the curlometer results also showed that the flux rope was not force-free with the component of the current density perpendicular to the magnetic field exceeding the parallel component over the forward half of the rope, perhaps due to the pressure gradients generated by the collision of the BBF with the inner magnetosphere. Hence, while the single-spacecraft models are very successful in fitting flux rope magnetic field and current variations, they do not provide a stringent test of the force-free condition.

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

    NASA Astrophysics Data System (ADS)

    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.

  11. Direct control of air gap flux in permanent magnet machines

    DOEpatents

    Hsu, John S. (Oak Ridge, TN)

    2000-01-01

    A method and apparatus for field weakening in PM machines uses field weakening coils (35, 44, 45, 71, 72) to produce flux in one or more stators (34, 49, 63, 64), including a flux which counters flux normally produced in air gaps between the stator(s) (34, 49, 63, 64) and the rotor (20, 21, 41, 61) which carries the PM poles. Several modes of operation are introduced depending on the magnitude and polarity of current in the field weakening coils (35, 44, 45, 71, 72). The invention is particularly useful for, but not limited to, the electric vehicle drives and PM generators.

  12. Suppression of weak localization due to magnetic flux in few-channel ballistic microstructures

    SciTech Connect

    Pluhar, Z.; Weidenmueller, H.A.; Zuk, J.A. ); Lewenkopf, C.H. )

    1994-10-10

    Using a random-matrix model for the Hamiltonian of a ballistic microstructure, which is chaotic in the classical limit, maximizing the coupling to the external leads, and employing Landauer's formula and Efetov's supersymmetry technique, we derive an expression for the magnetic-flux dependence of weak localization. This expression describes the crossover from orthogonal to unitary symmetry, depends only on the number of channels and on the magnetic flux through the structure, and is expected to apply universally.

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

    NASA Astrophysics Data System (ADS)

    He, Jianliang; Rote, D. M.

    The magnetic force computations in a null-flux suspension system using dynamic circuit theory are discussed. 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.

  14. 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.

  15. 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.

  16. Line-of-sight magnetic flux imbalances caused by electric currents

    NASA Technical Reports Server (NTRS)

    Gary, G. Allen; Rabin, Douglas

    1995-01-01

    Several physical and observational effects contribute to the significant imbalances of magnetic flux that are often observed in active regions. We consider an effect not previously treated: the influence of electric currents in the photosphere. Electric currents can cause a line-of-sight flux imbalance because of the directionality of the magnetic field they produce. Currents associated with magnetic flux tubes produce larger imbalances than do smoothly-varying distributions of flux and current. We estimate the magnitude of this effect for current densities, total currents, and magnetic geometry consistent with observations. The expected imbalances lie approximately in the range 0-15%, depending on the character of the current-carying fields and the angle from which they are viewed. Observationally, current-induced flux imbalances could be indicated by a statistical dependence of the imbalance on angular distance from disk center. A general study of magnetic flux balance in active regions is needed to determine the relative importance of other- probably larger- effects such as dilute flux (too weak to measure or rendered invisible by radiative transfer effects), merging with weak background fields, and long-range connections between active regions.

  17. Changes in magnetic flux density around fatigue crack tips of carbon tool steels

    NASA Astrophysics Data System (ADS)

    Honda, Takashi; Kida, Katsuyuki; Santos, Edson C.; Tanabe, Hirotaka

    2010-03-01

    Fatigue failure of steel occurs when small cracks form in a component and then continue to grow to a size large enough to cause failure. In order to understand the strength of steel components it is important to find the cracks which eventually grow to cause failures. However, at present, it is not easy to distinguish, in the early stages of growth, the cracks which will grow fast and cause failure. We hypothesized that it may be possible to distinguish them by comparing changes in the magnetic flux density around the tips of those cracks that grew large enough to cause failure. In order to measure these changes in magnetic flux density, we developed a scanning Hall probe microscope and observed the fatigue cracks growing from artificial slits in carbon tool steels (JIS SKS93). We also compared the changes in magnetic flux density around crack tips which grew under different loads and found that there is a strong correlation between the magnetic flux density, crack growth and stress intensity factors. In order to understand this relation, we measured the changes in the magnetic flux density and residual tensile stress by using an X-ray system, and found that the magnetic flux density changes not only in the plastic deformation area but also in the area of elastic stress field with increased stress.

  18. Changes in magnetic flux density around fatigue crack tips of carbon tool steels

    NASA Astrophysics Data System (ADS)

    Honda, Takashi; Kida, Katsuyuki; Santos, Edson C.; Tanabe, Hirotaka

    2009-12-01

    Fatigue failure of steel occurs when small cracks form in a component and then continue to grow to a size large enough to cause failure. In order to understand the strength of steel components it is important to find the cracks which eventually grow to cause failures. However, at present, it is not easy to distinguish, in the early stages of growth, the cracks which will grow fast and cause failure. We hypothesized that it may be possible to distinguish them by comparing changes in the magnetic flux density around the tips of those cracks that grew large enough to cause failure. In order to measure these changes in magnetic flux density, we developed a scanning Hall probe microscope and observed the fatigue cracks growing from artificial slits in carbon tool steels (JIS SKS93). We also compared the changes in magnetic flux density around crack tips which grew under different loads and found that there is a strong correlation between the magnetic flux density, crack growth and stress intensity factors. In order to understand this relation, we measured the changes in the magnetic flux density and residual tensile stress by using an X-ray system, and found that the magnetic flux density changes not only in the plastic deformation area but also in the area of elastic stress field with increased stress.

  19. 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

  20. AN ANALYSIS OF MAGNETOHYDRODYNAMIC INVARIANTS OF MAGNETIC FLUCTUATIONS WITHIN INTERPLANETARY FLUX ROPES

    SciTech Connect

    Telloni, D.; Perri, S.; Carbone, V.; Bruno, R.; D Amicis, R.

    2013-10-10

    A statistical analysis of magnetic flux ropes, identified by large-amplitude, smooth rotations of the magnetic field vector and a low level of both proton density and temperature, has been performed by computing the invariants of the ideal magnetohydrodynamic (MHD) equations, namely the magnetic helicity, the cross-helicity, and the total energy, via magnetic field and plasma fluctuations in the interplanetary medium. A technique based on the wavelet spectrograms of the MHD invariants allows the localization and characterization of those structures in both scales and time: it has been observed that flux ropes show, as expected, high magnetic helicity states (|σ{sub m}| in [0.6: 1]), but extremely variable cross-helicity states (|σ{sub c}| in [0: 0.8]), which, however, are not independent of the magnetic helicity content of the flux rope itself. The two normalized MHD invariants observed within the flux ropes tend indeed to distribute, neither trivially nor automatically, along the √(σ{sub m}{sup 2}+σ{sub c}{sup 2})=1 curve, thus suggesting that some constraint should exist between the magnetic and cross-helicity content of the structures. The analysis carried out has further showed that the flux rope properties are totally independent of their time duration and that they are detected either as a sort of interface between different portions of solar wind or as isolated structures embedded in the same stream.

  1. Second Order Magnetic Barriers in Tokamaks, Noble Tori, and Topological Noise

    NASA Astrophysics Data System (ADS)

    Ali, Halima; Punjabi, Alkesh

    2007-11-01

    Second order perturbation method of creating invariant manifold inside chaos in Hamiltonian systems [1-4] is applied to tokamak to build magnetic barriers inside the region of magnetic chaos created by resonant magnetic perturbations. Different safety factor profiles are used to represent tokamaks such as the ohmically heated tokamaks (OHT), the DIII-D and the ASDEX UG. In OHT, a magnetic barrier is created at about midway between two resonant magnetic surfaces. The barrier reduces the diffusion of magnetic field lines by about half. The barrier is fortified by adding up to third order magnetic perturbation. Beyond a maximum value of magnetic perturbation, the barrier is not sustainable. However, if a barrier is created at noble value of safety factor, then it is found to be much more robust. For the DIII-D, the robustness of magnetic barrier is tested for topological noise, and the barrier is found to be robust up to some maximum value of noise. This work is supported by US DOE OFES DE-FG02-01ER54624 and DE-FG02-04ER54793. [1] Ciraolo G et al. 2004, J. Phys. A: Math Gen 37 3589. [2] Ciraolo G et al. 2004, Phys. Rev. E 69 056213. [3] Vittot M 2004, Phys. A: Math Gen 37 6337. [4] Chandre C et al. 2005, Phys. Rev. Lett.94 074101.

  2. Magnetic flux and heat losses by diffusive, advective, and Nernst effects in magnetized liner inertial fusion-like plasma

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    The magnetized liner inertial fusion (MagLIF) approach to inertial confinement fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010); Cuneo et al., IEEE Trans. Plasma Sci. 40, 3222 (2012)] involves subsonic/isobaric compression and heating of a deuterium-tritium plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion, and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstrates that the heat loss from the hot compressed magnetized plasma to the cold liner is dominated by transverse heat conduction and advection, and the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter ( ωeτe≫1 ), the effective diffusion coefficients determining the losses of heat and magnetic flux to the liner wall are both shown to decrease with ωeτe as does the Bohm diffusion coefficient c T /(16 e B ) , which is commonly associated with low collisionality and two-dimensional transport. We demonstrate how this family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics.

  3. Magnetic flux and heat losses by diffusive, advective, and Nernst effects in magnetized liner inertial fusion-like plasma

    SciTech Connect

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

    2015-04-15

    The magnetized liner inertial fusion (MagLIF) approach to inertial confinement fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010); Cuneo et al., IEEE Trans. Plasma Sci. 40, 3222 (2012)] involves subsonic/isobaric compression and heating of a deuterium-tritium plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion, and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstrates that the heat loss from the hot compressed magnetized plasma to the cold liner is dominated by transverse heat conduction and advection, and the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter (ω{sub e}τ{sub e}≫1), the effective diffusion coefficients determining the losses of heat and magnetic flux to the liner wall are both shown to decrease with ω{sub e}τ{sub e} as does the Bohm diffusion coefficient cT/(16eB), which is commonly associated with low collisionality and two-dimensional transport. We demonstrate how this family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics.

  4. Electron heat flux dropouts in the solar wind - Evidence for interplanetary magnetic field reconnection?

    NASA Technical Reports Server (NTRS)

    Mccomas, D. J.; Gosling, J. T.; Phillips, J. L.; Bame, S. J.; Luhmann, J. G.; Smith, E. J.

    1989-01-01

    An examination of ISEE-3 data from 1978 reveal 25 electron heat flux dropout events ranging in duration from 20 min to over 11 hours. The heat flux dropouts are found to occur in association with high plasma densities, low plasma velocities, low ion and electron temperatures, and low magnetic field magnitudes. It is suggested that the heat flux dropout intervals may indicate that the spacecraft is sampling plasma regimes which are magnetically disconnected from the sun and instead are connected to the outer heliosphere at both ends.

  5. In situ observations of flux rope at the separatrix region of magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Huang, S. Y.; Retino, A.; Phan, T. D.; Daughton, W.; Vaivads, A.; Karimabadi, H.; Zhou, M.; Sahraoui, F.; Li, G. L.; Yuan, Z. G.; Deng, X. H.; Fu, H. S.; Fu, S.; Pang, Y.; Wang, D. D.

    2016-01-01

    We present the first in situ observations of a small-scale flux rope locally formed at the separatrix region of magnetic reconnection without large guide field. Bidirectional electron beams (cold and hot beams) and density cavity accompanied by intense wave activity substantiate the crossing of the separatrix region. Density compression and one parallel electron beam are detected inside the flux rope. We suggest that this flux rope is locally generated at the separatrix region due to the tearing instability within the separatrix current layer. This observation sheds new light on the 3-D picture of magnetic reconnection in space plasma.

  6. Structure, Stability, and Evolution of Magnetic Flux Ropes from the Perspective of Magnetic Twist

    NASA Astrophysics Data System (ADS)

    Liu, Rui; Kliem, Bernhard; Titov, Viacheslav S.; Chen, Jun; Wang, Yuming; Wang, Haimin; Liu, Chang; Xu, Yan; Wiegelmann, Thomas

    2016-02-01

    We investigate the evolution of NOAA Active Region (AR) 11817 during 2013 August 10-12, when it developed a complex field configuration and produced four confined, followed by two eruptive, flares. These C-and-above flares are all associated with a magnetic flux rope (MFR) located along the major polarity inversion line, where shearing and converging photospheric flows are present. Aided by the nonlinear force-free field modeling, we identify the MFR through mapping magnetic connectivities and computing the twist number {{ T }}w for each individual field line. The MFR is moderately twisted (| {{ T }}w| \\lt 2) and has a well-defined boundary of high squashing factor Q. We found that the field line with the extremum | {{ T }}w| is a reliable proxy of the rope axis, and that the MFR's peak | {{ T }}w| temporarily increases within half an hour before each flare while it decreases after the flare peak for both confined and eruptive flares. This pre-flare increase in | {{ T }}w| has little effect on the AR's free magnetic energy or any other parameters derived for the whole region, due to its moderate amount and the MFR's relatively small volume, while its decrease after flares is clearly associated with the stepwise decrease in the whole region's free magnetic energy due to the flare. We suggest that {{ T }}w may serve as a useful parameter in forewarning the onset of eruption, and therefore, the consequent space weather effects. The helical kink instability is identified as the prime candidate onset mechanism for the considered flares.

  7. Adaptive cancellation of geomagnetic background noise for magnetic anomaly detection using coherence

    NASA Astrophysics Data System (ADS)

    Liu, Dunge; Xu, Xin; Huang, Chao; Zhu, Wanhua; Liu, Xiaojun; Yu, Gang; Fang, Guangyou

    2015-01-01

    Magnetic anomaly detection (MAD) is an effective method for the detection of ferromagnetic targets against background magnetic fields. Currently, the performance of MAD systems is mainly limited by the background geomagnetic noise. Several techniques have been developed to detect target signatures, such as the synchronous reference subtraction (SRS) method. In this paper, we propose an adaptive coherent noise suppression (ACNS) method. The proposed method is capable of evaluating and detecting weak anomaly signals buried in background geomagnetic noise. Tests with real-world recorded magnetic signals show that the ACNS method can excellently remove the background geomagnetic noise by about 21 dB or more in high background geomagnetic field environments. Additionally, as a general form of the SRS method, the ACNS method offers appreciable advantages over the existing algorithms. Compared to the SRS method, the ACNS algorithm can eliminate the false target signals and represents a noise suppressing capability improvement of 6.4 dB. The positive outcomes in terms of intelligibility make this method a potential candidate for application in MAD systems.

  8. lower ionosphere cosmic noise absorption responses to the interplanetary magnetic field behavior in the south atlantic magnetic anomaly and sub-auroral regions

    NASA Astrophysics Data System (ADS)

    Brum, C. G. M.; Abdu, M. A.; Batista, I. S.; Santos, P. M. T.; Barros, L. P.

    The interplanetary magnetic field (IMF) plays an important role in the cosmic ray flux modulation that reaches the lower ionosphere, which is one of the main sources of the ionization in these regions. In this work, it is presented data analysis results obtained from riometers operating at 30 MHz over Cachoeira Paulista (located at South Atlantic Magnetic Anomaly (SAMA) - connected to an antenna pointed to the zenith direction, 22.50°S; 45.00°W) and the Brazilian Antarctic Station - EACF (connected to an antenna pointed to the zenith and geomagnetic west directions, 62.56°S; 58.39°W) during almost one complete solar cycle (1989-1996). Previous results have shown that there is a strong correlation between the cosmic noise absorption (CNA) behavior and the IMF. Basically, the sub-auroral region presents a decrease in the CNA with the increase of the IMF intensity, while in the SAMA region, for the same IMF conditions, it was registered an increase. Related to the IMF direction, the greater values of CNA are present when the IMF is pointed to the south and to the east for EACF and AMAS regions, respectively. The results of these data analysis are discussed and the galactic cosmic noise absorption is computed by using the geomagnetic activity (geomagnetic field values) to show the relationship between CNA and IMF behavior.

  9. A Numerical Study of the Response of the Coronal Magnetic Field to Flux Emergence

    NASA Astrophysics Data System (ADS)

    Jacobs, C.; Poedts, S.

    2012-10-01

    Large-scale solar eruptions, known as coronal mass ejections (CMEs), are regarded as the main drivers of space weather. The exact trigger mechanism of these violent events is still not completely clear; however, the solar magnetic field indisputably plays a crucial role in the onset of CMEs. The strength and morphology of the solar magnetic field are expected to have a decisive effect on CME properties, such as size and speed. This study aims to investigate the evolution of a magnetic configuration when driven by the emergence of new magnetic flux in order to get a better insight into the onset of CMEs and their magnetic structure. The three-dimensional, time-dependent equations for ideal magnetohydrodynamics are numerically solved on a spherical mesh. New flux emergence in a bipolar active region causes destabilisation of the initial stationary structure, finally resulting in an eruption. The initial magnetic topology is suitable for the `breakout' CME scenario to work. Although no magnetic flux rope structure is present in the initial condition, highly twisted magnetic field lines are formed during the evolution of the system as a result of internal reconnection due to the interaction of the active region magnetic field with the ambient field. The magnetic energy built up in the system and the final speed of the CME depend on the strength of the overlying magnetic field, the flux emergence rate, and the total amount of emerged flux. The interaction with the global coronal field makes the eruption a large-scale event, involving distant parts of the solar surface.

  10. SCATTERING OF THE f-MODE BY SMALL MAGNETIC FLUX ELEMENTS FROM OBSERVATIONS AND NUMERICAL SIMULATIONS

    SciTech Connect

    Felipe, T.; Braun, D.; Crouch, A.; Birch, A.

    2012-10-01

    The scattering of f-modes by magnetic tubes is analyzed using three-dimensional numerical simulations. An f-mode wave packet is propagated through a solar atmosphere embedded with three different flux tube models that differ in radius and total magnetic flux. A quiet-Sun simulation without a tube present is also performed as a reference. Waves are excited inside the flux tube and propagate along the field lines, and jacket modes are generated in the surroundings of the flux tube, carrying 40% as much energy as the tube modes. The resulting scattered wave is mainly an f-mode composed of a mixture of m = 0 and m = {+-}1 modes. The amplitude of the scattered wave approximately scales with the magnetic flux. A small amount of power is scattered into the p{sub 1}-mode. We have evaluated the absorption and phase shift from a Fourier-Hankel decomposition of the photospheric vertical velocities. They are compared with the results obtained from the ensemble average of 3400 small magnetic elements observed in high-resolution MDI Doppler datacubes. The comparison shows that the observed dependence of the phase shift with wavenumber can be matched reasonably well with the simulated flux tube model. The observed variation of the phase shifts with the azimuthal order m appears to depend on details of the ensemble averaging, including possible motions of the magnetic elements and asymmetrically shaped elements.

  11. MAGNETAR GIANT FLARES-FLUX ROPE ERUPTIONS IN MULTIPOLAR MAGNETOSPHERIC MAGNETIC FIELDS

    SciTech Connect

    Yu Cong

    2012-09-20

    We address a primary question regarding the physical mechanism that triggers the energy release and initiates the onset of eruptions in the magnetar magnetosphere. Self-consistent stationary, axisymmetric models of the magnetosphere are constructed based on force-free magnetic field configurations that contain a helically twisted force-free flux rope. Depending on the surface magnetic field polarity, there exist two kinds of magnetic field configurations, inverse and normal. For these two kinds of configurations, variations of the flux rope equilibrium height in response to gradual surface physical processes, such as flux injections and crust motions, are carefully examined. We find that equilibrium curves contain two branches: one represents a stable equilibrium branch, and the other an unstable equilibrium branch. As a result, the evolution of the system shows a catastrophic behavior: when the magnetar surface magnetic field evolves slowly, the height of the flux rope would gradually reach a critical value beyond which stable equilibriums can no longer be maintained. Subsequently, the flux rope would lose equilibrium and the gradual quasi-static evolution of the magnetosphere will be replaced by a fast dynamical evolution. In addition to flux injections, the relative motion of active regions would give rise to the catastrophic behavior and lead to magnetic eruptions as well. We propose that a gradual process could lead to a sudden release of magnetosphere energy on a very short dynamical timescale, without being initiated by a sudden fracture in the crust of the magnetar. Some implications of our model are also discussed.

  12. Plasma diagnosis from thermal noise and limits on dust flux or mass in comet Giacobini-Zinner

    NASA Technical Reports Server (NTRS)

    Meyer-Vernet, N.; Couturier, P.; Hoang, S.; Perche, C.; Steinberg, J. L.; Fainberg, J.

    1986-01-01

    Thermal noise spectroscopy was used to measure the density and temperature of the main (cold) electron plasma population during two hours around the point of closest approach of the International Cometary Explorer (ICE) to comet Giacobini-Zinner. The time resolution was 18 seconds in the plasma tail and 54 seconds elsewhere. Near the tail axis, the maximum plasma density was 670/cu cm and the temperature slightly above one volt. Away from the axis, the plasma density dropped to 100/cu cm over 2000 km, then decreased to 10/cu cm over 15,000 km; at the plasma tail, the density fluctuated between 10 and 30/cu cm, and the temperature, between 100,000 and 400,000 K. No evidence was found of grain impact on the spacecraft or antennas in the plasma tail. This yields an upper limit for the dust flux or particle mass, indicating either fluxes or masses in the tail smaller than those implied by models or an anomalous grain structure. Outside the tail, and particularly near 100,000 km from its axis, impulsive noises indicating plasma turbulence were observed.

  13. 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

  14. Induced fermionic current by a magnetic flux in a cosmic string spacetime at finite temperature

    NASA Astrophysics Data System (ADS)

    Bezerra de Mello, Eugênio R.; Saharian, Aram A.; Mohammadi, Azadeh

    2016-01-01

    Here we analyze the finite temperature expectation values of the charge and current densities for a massive fermionic quantum field with nonzero chemical potential μ, induced by a magnetic flux running along the axis of an idealized cosmic string. These densities are decomposed into the vacuum expectation values and contributions coming from the particles and antiparticles. Specifically the charge density is an even periodic function of the magnetic flux with the period equal to the quantum flux and an odd function of the chemical potential. The only nonzero component of the current density corresponds to the azimuthal current and it is an odd periodic function of the magnetic flux and an even function of the chemical potential. Both analyzed are developed for the cases where |μ| is smaller than the mass of the field quanta m.

  15. An Optimized Air-Core Coil Sensor with a Magnetic Flux Compensation Structure Suitable to the Helicopter TEM System

    PubMed Central

    Chen, Chen; Liu, Fei; Lin, Jun; Zhu, Kaiguang; Wang, Yanzhang

    2016-01-01

    The air-core coil sensor (ACS) is widely used as a transducer to measure the variation in magnetic fields of a helicopter transient electromagnetic (TEM) system. A high periodic emitting current induces the magnetic field signal of the underground medium. However, such current also generates a high primary field signal that can affect the received signal of the ACS and even damage the receiver. To increase the dynamic range of the received signal and to protect the receiver when emitting current rises/falls, the combination of ACS with magnetic flux compensation structure (bucking coil) is necessary. Moreover, the optimized ACS, which is composed of an air-core coil and a differential pre-amplifier circuit, must be investigated to meet the requirements of the helicopter TEM system suited to rapid surveying for shallow buried metal mine in rough topography. Accordingly, two ACSs are fabricated in this study, and their performance is verified and compared inside a magnetic shielding room. Using the designed ACSs, field experiments are conducted in Baoqing County. The field experimental data show that the primary field response can be compensated when the bucking coil is placed at an appropriate point in the range of allowed shift distance beyond the center of the transmitting coil and that the damage to the receiver induced by the over-statured signal can be solved. In conclusion, a more suitable ACS is adopted and is shown to have better performance, with a mass of 2.5 kg, resultant effective area of 11.6 m2 (i.e., diameter of 0.496 m), 3 dB bandwidth of 66 kHz, signal-to-noise ratio of 4 (i.e., varying magnetic field strength of 0.2 nT/s), and normalized equivalent input noise of 3.62 nV/m2. PMID:27077862

  16. An Optimized Air-Core Coil Sensor with a Magnetic Flux Compensation Structure Suitable to the Helicopter TEM System.

    PubMed

    Chen, Chen; Liu, Fei; Lin, Jun; Zhu, Kaiguang; Wang, Yanzhang

    2016-01-01

    The air-core coil sensor (ACS) is widely used as a transducer to measure the variation in magnetic fields of a helicopter transient electromagnetic (TEM) system. A high periodic emitting current induces the magnetic field signal of the underground medium. However, such current also generates a high primary field signal that can affect the received signal of the ACS and even damage the receiver. To increase the dynamic range of the received signal and to protect the receiver when emitting current rises/falls, the combination of ACS with magnetic flux compensation structure (bucking coil) is necessary. Moreover, the optimized ACS, which is composed of an air-core coil and a differential pre-amplifier circuit, must be investigated to meet the requirements of the helicopter TEM system suited to rapid surveying for shallow buried metal mine in rough topography. Accordingly, two ACSs are fabricated in this study, and their performance is verified and compared inside a magnetic shielding room. Using the designed ACSs, field experiments are conducted in Baoqing County. The field experimental data show that the primary field response can be compensated when the bucking coil is placed at an appropriate point in the range of allowed shift distance beyond the center of the transmitting coil and that the damage to the receiver induced by the over-statured signal can be solved. In conclusion, a more suitable ACS is adopted and is shown to have better performance, with a mass of 2.5 kg, resultant effective area of 11.6 m² (i.e., diameter of 0.496 m), 3 dB bandwidth of 66 kHz, signal-to-noise ratio of 4 (i.e., varying magnetic field strength of 0.2 nT/s), and normalized equivalent input noise of 3.62 nV/m². PMID:27077862

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

    SciTech Connect

    Zhao, Hong-Kang Zou, Wei-Ke; Chen, Qiao

    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 θ of RMF. The magnitude of shot noise increases as the photon energy ℏω 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 μ{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. 1/f noise in magnetic tunnel junctions with MgO tunnel barriers

    NASA Astrophysics Data System (ADS)

    Gokce, Aisha; Nowak, E. R.; Yang, See Hun; Parkin, S. S. P.

    2006-04-01

    Electrical noise measurements are reported for magnetic tunnel junctions having magnesium oxide tunnel barriers. These junctions have resistance-area products (RAPs) of order 10-100 MΩ μm2 and exhibit zero-bias tunneling magnetoresistance ratios (TMRs) as high as 120% at room temperature. The TMR is bias dependent and decreases to half its maximum value for biases near 300 mV. The dominant low-frequency electrical noise is due to resistance fluctuations having a 1/f-like power spectral dependence and a nonmagnetic origin. The normalized 1/f noise parameter, α, is found to be of order 10-7 to 10-6 which compares favorably to magnetic tunnel junctions consisting of an aluminum oxide barrier with comparable RAPs but lower TMR. At high biases, α is found to decrease which we attribute to defect-assisted tunneling mechanisms.

  19. Mean-field and direct numerical simulations of magnetic flux concentrations from vertical field

    NASA Astrophysics Data System (ADS)

    Brandenburg, A.; Gressel, O.; Jabbari, S.; Kleeorin, N.; Rogachevskii, I.

    2014-02-01

    Context. Strongly stratified hydromagnetic turbulence has previously been found to produce magnetic flux concentrations if the domain is large enough compared with the size of turbulent eddies. Mean-field simulations (MFS) using parameterizations of the Reynolds and Maxwell stresses show a large-scale negative effective magnetic pressure instability and have been able to reproduce many aspects of direct numerical simulations (DNS) regarding growth rate, shape of the resulting magnetic structures, and their height as a function of magnetic field strength. Unlike the case of an imposed horizontal field, for a vertical one, magnetic flux concentrations of equipartition strength with the turbulence can be reached, resulting in magnetic spots that are reminiscent of sunspots. Aims: We determine under what conditions magnetic flux concentrations with vertical field occur and what their internal structure is. Methods: We use a combination of MFS, DNS, and implicit large-eddy simulations (ILES) to characterize the resulting magnetic flux concentrations in forced isothermal turbulence with an imposed vertical magnetic field. Results: Using DNS, we confirm earlier results that in the kinematic stage of the large-scale instability the horizontal wavelength of structures is about 10 times the density scale height. At later times, even larger structures are being produced in a fashion similar to inverse spectral transfer in helically driven turbulence. Using ILES, we find that magnetic flux concentrations occur for Mach numbers between 0.1 and 0.7. They occur also for weaker stratification and larger turbulent eddies if the domain is wide enough. Using MFS, the size and aspect ratio of magnetic structures are determined as functions of two input parameters characterizing the parameterization of the effective magnetic pressure. DNS, ILES, and MFS show magnetic flux tubes with mean-field energies comparable to the turbulent kinetic energy. These tubes can reach a length of about eight density scale heights. Despite being ≤1% equipartition strength, it is important that their lower part is included within the computational domain to achieve the full strength of the instability. Conclusions: The resulting vertical magnetic flux tubes are being confined by downflows along the tubes and corresponding inflow from the sides, which keep the field concentrated. Application to sunspots remains a viable possibility.

  20. Noise temperature improvement for magnetic fusion plasma millimeter wave imaging systems.

    PubMed

    Lai, J; Domier, C W; Luhmann, N C

    2014-03-01

    Significant progress has been made in the imaging and visualization of magnetohydrodynamic and microturbulence phenomena in magnetic fusion plasmas [B. Tobias et al., Plasma Fusion Res. 6, 2106042 (2011)]. Of particular importance have been microwave electron cyclotron emission imaging and microwave imaging reflectometry systems for imaging T(e) and n(e) fluctuations. These instruments have employed heterodyne receiver arrays with Schottky diode mixer elements directly connected to individual antennas. Consequently, the noise temperature has been strongly determined by the conversion loss with typical noise temperatures of ~60,000 K. However, this can be significantly improved by making use of recent advances in Monolithic Microwave Integrated Circuit chip low noise amplifiers to insert a pre-amplifier in front of the Schottky diode mixer element. In a proof-of-principle design at V-Band (50-75 GHz), significant improvement of noise temperature from the current 60,000 K to measured 4000 K has been obtained. PMID:24689579

  1. Line-Tied Magnetic Flux Ropes in the Laboratory: Equilibrium Force Balance and Eruptive Instabilities

    NASA Astrophysics Data System (ADS)

    Myers, Clayton E.; Yamada, M.; Belova, E. V.

    2013-07-01

    Flux-rope-based models of solar eruptions rely on the formation of a line-tied flux rope equilibrium that persists until an ideal instability or a breakdown in force balance triggers an eruption. In this paper, we present a quantitative study of equilibrium force balance in solar-relevant flux ropes, focusing primarily on the role of the potential magnetic field in controlling the flux rope behavior. This study was conducted using a newly constructed laboratory experiment in conjunction with supporting three-dimensional MHD simulations that directly model the experimental geometry. The flux ropes studied here, which are produced in the Magnetic Reconnection Experiment (MRX), evolve quasi-statically over many Alfvén times and have footpoints that are line-tied to two fixed electrodes [E. Oz, C. E. Myers, M. Yamada, et al., Phys. Plasmas 18, 102107 (2011)]. They are formed within a solar-relevant potential magnetic field configuration that can be systematically modified between discharges. Detailed in situ magnetic measurements from the experiments are compared directly to results from the simulations in order to quantitatively evaluate the various contributions to the equilibrium force balance. We find that forces derived from the applied toroidal guide field contribute significantly to the equilibrium—so much so that the flux ropes are often well confined even in the absence of a "strapping" arcade. These observed guide field forces arise from changes in the toroidal magnetic pressure and tension that result from a combination of effects within the expanding flux rope. With regard to eruptions, the aforementioned guide field forces supplement the well-known strapping field forces to largely prevent the flux ropes from erupting. In particular, many regimes were explored where the strapping field configuration is predicted to be "torus unstable" and yet the flux ropes do not erupt. Eruptions are observed in some regimes, however, and we will discuss the physical mechanisms that may explain this behavior.

  2. Effect of the proximity of the Heliospheric Current Sheet on the heliospheric magnetic flux density

    NASA Astrophysics Data System (ADS)

    Erdös, Géza; Balogh, André

    2014-05-01

    In recent work (Erdős & Balogh, ApJ., 781, 50, 2014) it has been shown that the magnetic flux density measured by the Ulysses probe around its solar polar orbit from 1990 to 2009 matches that calculated from the OMNI in-ecliptic, 1 AU data set over the same interval. This result has shown that the sun's magnetic flux is generally distributed uniformly in the heliosphere and depends only on the total open magnetic flux of the sun. We have nevertheless examined those two intervals in the nearly 20-year long observations, when the flux density measured at Ulysses appears to be greater than that observed at 1 AU. The two intervals are near the minima in solar activity in 1995-96 and 2007-08, with the difference in the first interval noticeably larger than in the second. We show that the difference between the Ulysses and the OMNI results are strongly correlated to the distance between the Heliospheric Current Sheet (HCC) and the 1 AU observation point, with the flux density smaller at the in ecliptic observation point than at Ulysses which during those intervals was generally well north or south of the HCC. A corresponding result can also be identified as a longitude dependence in the magnetic flux density when comparing the observations by the STEREO-A and -B spacecraft which are close to 1 AU in the ecliptic, but are widely separated in heliolongitude. We discuss possible causes of the reduced flux density near the HCC in terms of the geometric effects on the uniform spreading of the solar magnetic flux and the possible effect of magnetic reconnection associated with the HCC and the properties of the slow wind in which it is embedded.

  3. A noise-rejecting current amplifier for surface atmospheric ion flux measurements

    NASA Astrophysics Data System (ADS)

    Harrison, R. G.

    1997-09-01

    Large area electrodes are required to determine atmospheric charge fluxes at the earth's surface. These also act as antennas for power line hum, swamping the small atmospheric electric signals. A battery-powered head-amplifier resolving 0.025 pA is described here, which uses active compensation to substantially cancel the interference, allowing the atmospheric charge fluxes to be resolved in the presence of the interference. The overall response is nominally -100 mV/pA, with 30 dB of 50 Hz rejection. The head amplifier can drive a low impedance line.

  4. Magnetic flux trapping during field reversal in the formation of a field-reversed configuration

    NASA Astrophysics Data System (ADS)

    Steinhauer, Loren C.

    1985-11-01

    The flow of plasma and magnetic flux toward a wall is examined in a slab geometry where the magnetic field is parallel to the wall. Magnetohydrodynamic (MHD) flow with a quasisteady approximation is assumed that reduces the problem to three coupled ordinary differential equations. The calculated behavior shows that a thin current sheath is established at the wall in which a variety of phenomena appear, including significant resistive heating and rapid deceleration of the plasma flow. The sheath physics determines the speed at which flux and plasma flow toward the wall. The model has been applied to the field-reversal phase of a field-reversed theta pinch, during which the reduced magnetic field near the wall drives an outward flow of plasma and magnetic flux. The analysis leads to approximate expressions for the instantaneous flow speed, the loss of magnetic flux during the field reversal phase, the integrated heat flow to the wall, and the highest possible magnetic flux retained after reversal. Predictions from this model are compared with previous time-dependent MHD calculations and with experimental results from the TRX-1 [Proceedings of the 4th Symposium on the Physics and Technology of Compact Toroids, 27-29 October 1981 (Lawrence Livermore National Laboratory, Livermore, CA, 1982), p. 61] and TRX-2 [Proceedings of the 6th U.S. Symposium on Compact Toroid Research, 20-23 February, 1984 (Princeton Plasma Physics Laboratory, Princeton, NJ, 1984), p. 154] experiments.

  5. Embedding Circular Force-Free Flux Ropes in Potential Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Titov, V. S.; Torok, T.; Mikic, Z.; Linker, J.

    2013-12-01

    We propose a method for constructing approximate force-free equilibria in active regions that locally have a potential bipolar-type magnetic field with a thin force-free flux rope embedded inside it. The flux rope has a circular-arc axis and circular cross-section in which the interior magnetic field is predominantly toroidal (axial). Its magnetic pressure is balanced outside by that of the poloidal (azimuthal) field created at the boundary by the electric current sheathing the flux rope. To facilitate the implementation of the method in our numerical magnetohydrodynamic (MHD) code, the entire solution is described in terms of the vector potential of the magnetic field. The parameters of the flux rope can be chosen so that a subsequent MHD relaxation of the constructed configuration under line-tied conditions at the boundary provides a numerically exact equilibrium. Such equilibria are an approximation for the magnetic configuration preceding solar eruptions, which can be triggered in our model by imposing suitable photospheric flows beneath the flux rope. The proposed method is a useful tool for constructing pre-eruption magnetic fields in data-driven simulations of solar active events. Research supported by NASA's Heliophysics Theory and LWS Programs, and NSF/SHINE and NSF/FESD.

  6. Dynamics of local isolated magnetic flux tubes in a fast-rotating stellar atmosphere

    SciTech Connect

    Chou, W.; Tajima, C.T.; Matsumoto, R. |; Shibata, K.

    1998-01-01

    Dynamics of magnetic flux tubes in the fast rotating stellar atmosphere is studied. We focus on the effects and signatures of the instability of the flux tube emergence influenced by the Coriolis force. We present the result from a linear stability analysis and discuss its possible signatures in the course of the evolution of G-type and M-type stars. We present a three dimensional magnetohydrodynamical simulation of local isolated magnetic flux tubes under a magnetic buoyancy instability in co-rotating Cartesian coordinates. We find that the combination of the buoyancy instability and the Coriolis effect gives rise to a mechanism, to twist the emerging magnetic flux tube into a helical structure. The tilt angle, east-west asymmetry and magnetic helicity of the Twisted flux tubes in the simulations are studied in detail. The linear and nonlinear analyses provide hints as to what kind of pattern of large spots in young M-type main-sequence stars might be observed. We find that young and old G-type stars may have different distributions of spots while M-type stars may always have low latitudes spots. The size of stellar spots may decrease when a star becomes older, due to the decreasing of magnetic field. A qualitative comparison with solar observations is also presented.

  7. Photospheric Injection of Magnetic Helicity: Connectivity-Based Flux Density Method

    NASA Astrophysics Data System (ADS)

    Dalmasse, K.; Pariat, E.; Dmoulin, P.; Aulanier, G.

    2014-01-01

    Magnetic helicity quantifies the degree to which the magnetic field in a volume is globally sheared and/or twisted. This quantity is believed to play a key role in solar activity due to its conservation property. Helicity is continuously injected into the corona during the evolution of active regions (ARs). To better understand and quantify the role of magnetic helicity in solar activity, the distribution of magnetic helicity flux in ARs needs to be studied. The helicity distribution can be computed from the temporal evolution of photospheric magnetograms of ARs such as the ones provided by SDO/HMI and Hinode/SOT. Most recent analyses of photospheric helicity flux derived a proxy to the helicity-flux density based on the relative rotation rate of photospheric magnetic footpoints. Although this proxy allows a good estimate of the photospheric helicity flux, it is still not a true helicity flux density because it does not take into account the connectivity of the magnetic field lines. For the first time, we implement a helicity density that takes this connectivity into account. To use it for future observational studies, we tested the method and its precision on several types of models involving different patterns of helicity injection. We also tested it on more complex configurations - from magnetohydrodynamics (MHD) simulations - containing quasi-separatrix layers. We demonstrate that this connectivity-based proxy is best-suited to map the true distribution of photospheric helicity injection.

  8. CONDITIONS FOR TRANSVERSE WAVES PROPAGATION ALONG THIN MAGNETIC FLUX TUBES ON THE SUN

    SciTech Connect

    Lopin, Igor; Nagorny, Ivan

    2013-09-10

    The propagation of kink waves in the thin gravity stratified flux tubes with a generalized magnetic field distribution model is considered in cylindrical geometry. The new kink wave equations for both wave variables are obtained. It is shown that the inclusion of the radial component of an unperturbed tube magnetic field sufficiently transforms the conditions for the propagation of transverse waves. It is demonstrated that, for the models of isothermal and polytropic atmosphere in the tube and its environment, the propagation of kink waves along thin magnetic flux tubes is cutoff-free.

  9. 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 Miyamoto, Yasuyoshi; Miyashita, Eiichi; Hayashi, Naoto

    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 μm 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.

  10. Plasma diagnosis from thermal noise and limits on dust flux or mass in comet giacobini-zinner.

    PubMed

    Meyer-Vernet, N; Couturier, P; Hoang, S; Perche, C; Steinberg, J L; Fainberg, J; Meetre, C

    1986-04-18

    Thermal noise spectroscopy was used to measure the density and temperature of the main (cold) electron plasma population during 2 hours (1.5x10(5) kilometers perpendicular to the tail axis) around the point of closest approach of the International Cometary Explorer (ICE) to Comet Giacobini-Zinner. The time resolution was 18 seconds (370 kilometers) in the plasma tail and 54 seconds (1100 kilometers) elsewhere. Near the tail axis, the maximum plasma density was 670 per cubic centimeter and the temperature slightly above 1 electron volt. Away from the axis, the plasma density dropped to 100 per cubic centimeter (temperature, 2x 10(4) K) over 2000 kilometers, then decreased to 10 (1.5x 10(5)K) over 15,000 kilometers; outside that region (plasma tail), the density fluctuated between 10 and 30 per cubic centimeter and the temperature between 1x 10(5) and 4 x10(5) K. The relative density of the hot population rarely exceeded a few percent. The tail was highly asymmetrical and showed much structure. On the other antenna, shot noise was recorded from the plasma particle impacts on the spacecraft body. No evidence was found of grain impacts on the antennas or spacecraft in the plasma tail. This yields an upper limit for the dust flux or particle mass, indicating either fluxes or masses in the tail smaller than implied by the models or an anomalous grain structure. This seems to support earlier suggestions that these grains are featherlike. Outside the tail, and particularly near 10(5) kilometers from its axis, impulsive noises indicating plasma turbulence were observed. PMID:17792147

  11. Equilibrium features and eruptive instabilities in laboratory magnetic flux rope plasmas

    NASA Astrophysics Data System (ADS)

    Myers, Clayton E; Yamada, Masaaki; Belova, Elena V; Ji, Hantao; Yoo, Jongsoo; Fox, William

    2014-06-01

    One avenue for connecting laboratory and solar plasma studies is to carry out laboratory plasma experiments that serve as a well-diagnosed model for specific solar phenomena. In this paper, we present the latest results from one such laboratory experiment that is designed to address ideal instabilities that drive flux rope eruptions in the solar corona. The experiment, which utilizes the existing Magnetic Reconnection Experiment (MRX) at Princeton Plasma Physics Laboratory, generates a quasi-statically driven line-tied magnetic flux rope in a solar-relevant potential field arcade. The parameters of the potential field arcade (e.g., its magnitude, orientation, and vertical profile) are systematically scanned in order to study their influence on the evolution and possible eruption of the line-tied flux rope. Each flux rope discharge is diagnosed using a combination of fast visible light cameras and an in situ 2D magnetic probe array that measures all three components of the magnetic field over a large cross-section of the plasma. In this paper, we present the first results obtained from this new 2D magnetic probe array. With regard to the flux rope equilibrium, non-potential features such as the formation of a characteristic sigmoid shape and the generation of core toroidal field within the flux rope are studied in detail. With regard to instabilities, the onset and evolution of two key eruptive instabilities—the kink and torus instabilities—are quantitatively assessed as a function of the potential field arcade parameters and the amount of magnetic energy stored in the flux rope.This research is supported by DoE Contract Number DE-AC02-09CH11466 and by the NSF/DoE Center for Magnetic Self-Organization (CMSO).

  12. Energetic protons, alpha particles, and electrons in magnetic flux transfer events

    NASA Technical Reports Server (NTRS)

    Scholer, M.; Hovestadt, D.; Ipavich, F. M.; Gloeckler, G.

    1982-01-01

    Energetic proton, alpha particle, and electron data are presented for two magnetopause crossings, which show magnetic field signatures characteristic of flux transfer events (FTEs). Energetic proton and alpha particles are observed streaming along the magnetic field within the magnetosheath in all events showing magnetic signatures characteristic of the FTEs. Flux ratios as high as about 180 parallel and antiparallel to the magnetic field are observed, which means that ions of about 30 keV per charge are at times streaming almost scatter-free from the magnetopause into the magnetosheath. Energetic ion bursts with signatures equal to those observed in FTEs are reduced by more than an order of magnitude as compared to the trapped particle flux.

  13. 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.

  14. Magnetic damping forces in figure-eight-shaped null-flux coil suspension systems

    SciTech Connect

    He, Jianliang; Coffey, H.

    1997-08-01

    This paper discusses magnetic damping forces in figure-eight-shaped null-flux coil suspension systems, focusing on the Holloman maglev rocket system. The paper also discusses simulating the damping plate, which is attached to the superconducting magnet by two short-circuited loop coils in the guideway. Closed-form formulas for the magnetic damping coefficient as functions of heave-and-sway displacements are derived by using a dynamic circuit model. These formulas are useful for dynamic stability studies.

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

    SciTech Connect

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

    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.

  16. Formation processes of flux ropes downstream from Martian crustal magnetic fields inferred from Grad-Shafranov reconstruction

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    We applied the Grad-Shafranov reconstruction (GSR) technique to Martian magnetic flux ropes observed downstream from strong crustal magnetic fields in the southern hemisphere. The GSR technique can provide a two-dimensional axial magnetic field map as well as the axial orientation of flux ropes from single-spacecraft data under assumptions that the structure is magnetohydrostatic and time independent. The reconstructed structures, including their orientation, allowed us to evaluate possible formation processes for the flux ropes. We reconstructed 297 magnetic flux ropes observed by Mars Global Surveyor between April 1999 and November 2006. Based on characteristics of their geometrical axial orientation and transverse magnetic field topology, we found that they can be mainly distinguished according to whether draped interplanetary magnetic fields overlaying the crustal magnetic fields are involved or not. Approximately two thirds of the flux ropes can be formed by magnetic reconnection between neighboring crustal magnetic fields attached to the surface. The remaining events seem to require magnetic reconnection between crustal and overlaid draped magnetic fields. The latter scenario should allow planetary ions to be transferred from closed magnetic flux tube to flux tubes connected to interplanetary space, allowing atmospheric ions to escape from Mars. We quantitatively evaluate lower limits on potential ion escape rates from Mars owing to magnetic flux ropes.

  17. A tubular flux-switching permanent magnet machine

    NASA Astrophysics Data System (ADS)

    Wang, J.; Wang, W.; Clark, R.; Atallah, K.; Howe, D.

    2008-04-01

    The paper describes a novel tubular, three-phase permanent magnet brushless machine, which combines salient features from both switched reluctance and permanent magnet machine technologies. It has no end windings and zero net radial force and offers a high power density and peak force capability, as well as the potential for low manufacturing cost. It is, therefore, eminently suitable for a variety of applications, ranging from free-piston energy converters to active vehicle suspensions.

  18. Exact scattering matrix of graphs in magnetic field and quantum noise

    SciTech Connect

    Caudrelier, Vincent; Mintchev, Mihail; Ragoucy, Eric

    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.

  19. On Polar Magnetic Field Reversal and Surface Flux Transport During Solar Cycle 24

    NASA Astrophysics Data System (ADS)

    Sun, Xudong; Hoeksema, J. Todd; Liu, Yang; Zhao, Junwei

    2015-01-01

    As each solar cycle progresses, remnant magnetic flux from active regions (ARs) migrates poleward to cancel the old-cycle polar field. We describe this polarity reversal process during Cycle 24 using four years (2010.33-2014.33) of line-of-sight magnetic field measurements from the Helioseismic and Magnetic Imager. The total flux associated with ARs reached maximum in the north in 2011, more than two years earlier than the south; the maximum is significantly weaker than Cycle 23. The process of polar field reversal is relatively slow, north-south asymmetric, and episodic. We estimate that the global axial dipole changed sign in 2013 October; the northern and southern polar fields (mean above 60° latitude) reversed in 2012 November and 2014 March, respectively, about 16 months apart. Notably, the poleward surges of flux in each hemisphere alternated in polarity, giving rise to multiple reversals in the north. We show that the surges of the trailing sunspot polarity tend to correspond to normal mean AR tilt, higher total AR flux, or slower mid-latitude near-surface meridional flow, while exceptions occur during low magnetic activity. In particular, the AR flux and the mid-latitude poleward flow speed exhibit a clear anti-correlation. We discuss how these features can be explained in a surface flux transport process that includes a field-dependent converging flow toward the ARs, a characteristic that may contribute to solar cycle variability.

  20. ON POLAR MAGNETIC FIELD REVERSAL AND SURFACE FLUX TRANSPORT DURING SOLAR CYCLE 24

    SciTech Connect

    Sun, Xudong; Todd Hoeksema, J.; Liu, Yang; Zhao, Junwei

    2015-01-10

    As each solar cycle progresses, remnant magnetic flux from active regions (ARs) migrates poleward to cancel the old-cycle polar field. We describe this polarity reversal process during Cycle 24 using four years (2010.33-2014.33) of line-of-sight magnetic field measurements from the Helioseismic and Magnetic Imager. The total flux associated with ARs reached maximum in the north in 2011, more than two years earlier than the south; the maximum is significantly weaker than Cycle 23. The process of polar field reversal is relatively slow, north-south asymmetric, and episodic. We estimate that the global axial dipole changed sign in 2013 October; the northern and southern polar fields (mean above 60° latitude) reversed in 2012 November and 2014 March, respectively, about 16 months apart. Notably, the poleward surges of flux in each hemisphere alternated in polarity, giving rise to multiple reversals in the north. We show that the surges of the trailing sunspot polarity tend to correspond to normal mean AR tilt, higher total AR flux, or slower mid-latitude near-surface meridional flow, while exceptions occur during low magnetic activity. In particular, the AR flux and the mid-latitude poleward flow speed exhibit a clear anti-correlation. We discuss how these features can be explained in a surface flux transport process that includes a field-dependent converging flow toward the ARs, a characteristic that may contribute to solar cycle variability.

  1. 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.

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

    NASA Astrophysics Data System (ADS)

    Li, Ting; Zhang, Jun; Ji, Haisheng

    2015-06-01

    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.

  3. Study on formation processes of Martian magnetic flux ropes observed downstream from crustal magnetic fields based on the Grad-Shafranov reconstruction technique

    NASA Astrophysics Data System (ADS)

    Hara, T.; Seki, K.; Hasegawa, H.; Brain, D. A.

    2014-12-01

    Magnetic flux ropes have been observed even in unmagnetized planets' ionosphere, such as Venus and Mars. In the case of Mars, the origin of Martian flux ropes is owing to not only the interplanetary magnetic field and associated draped magnetic fields, but also crustal magnetic fields. Planetary ions are energized through the direct interaction of the solar wind with the upper atmosphere, resulting in ion escape into interplanetary space. Hence magnetic flux ropes can contribute to the ion escape rates, because they may confine large amounts of ionospheric plasma. Here, we investigated formation processes of Martian magnetic flux ropes observed downstream from strong crustal magnetic fields in the southern hemisphere based on the Grad-Shafranov reconstruction (GSR) technique. The GSR technique can provide a two-dimensional axial magnetic field map as well as flux ropes axial orientation from single spacecraft data under assumptions that the structure is magneto-hydrostatic and time-independent. We reconstructed the 297 magnetic flux ropes from Mars Global Surveyor measurements between April 1999 and November 2006. Based on characteristics of their geometrical axial orientation and transverse magnetic field topology, we found that they can be mainly distinguished according to whether draped interplanetary magnetic fields overlaying on the crustal magnetic fields are involved or not. For approximately two-thirds of the events, they can be formed by magnetic reconnection between neighboring crustal magnetic fields attached to the surface. For the remaining events, however, magnetic reconnection between the crustal and overlaid draping magnetic fields seems to be necessary. Since the overlaid draping magnetic field connects to interplanetary space, planetary ions included inside those flux ropes can be easy to escape from Mars. We also quantitatively evaluate lower limits on potential ion escape rates from Mars owing to the magnetic flux ropes based on the GSR results, and discuss the contribution of magnetic flux ropes to the ion escape rate from Mars.

  4. Vacuum currents induced by a magnetic flux around a cosmic string with finite core

    NASA Astrophysics Data System (ADS)

    Bezerra de Mello, E. R.; Bezerra, V. B.; Saharian, A. A.; Harutyunyan, H. H.

    2015-03-01

    We evaluate the Hadamard function and the vacuum expectation value of the current density for a massive complex scalar field in the generalized geometry of a straight cosmic string with a finite core enclosing an arbitrary distributed magnetic flux along the string axis. For the interior geometry, a general cylindrically symmetric static metric tensor is used with finite support. In the region outside the core, both the Hadamard function and the current density are decomposed into the idealized zero-thickness cosmic string and core-induced contributions. The only nonzero component corresponds to the azimuthal current. The zero-thickness part of the latter is a periodic function of the magnetic flux inside the core, with the period equal to the quantum flux. As a consequence of the direct interaction of the quantum field with the magnetic field inside the penetrable core, the core-induced contribution, in general, is not a periodic function of the flux. In addition, the vacuum current, in general, is not a monotonic function of the distance from the string and may change the sign. For a general model of the core interior, we also evaluate the magnetic fields generated by the vacuum current. As applications of the general results, we have considered an impenetrable core modeled by Robin boundary condition, a core with the Minkowski-like interior and a core with a constant positive curvature space. Various exactly solvable distributions of the magnetic flux are discussed.

  5. ABSORPTION OF p MODES BY THIN MAGNETIC FLUX TUBES

    SciTech Connect

    Jain, Rekha; Hindman, Bradley W.; Braun, Doug C.; Birch, Aaron C.

    2009-04-10

    We study the interaction between p modes and the many magnetic fibrils that lace the solar convection zone. In particular, we investigate the resulting absorption of p-mode energy by the fibril magnetic field. Through mechanical buffeting, the p modes excite tube waves on the magnetic fibrils-in the form of longitudinal sausage waves and transverse kink waves. The tube waves propagate up and down the magnetic fibrils and out of the p-mode cavity, thereby removing energy from the incident acoustic waves. We compute the absorption coefficient associated with this damping mechanism and model the absorption that would be observed for magnetic plage. We compare our results to the absorption coefficient that is measured using the local-helioseismic technique of ridge-filtered holography. We find that, depending on the mode order and the photospheric boundary conditions, we can achieve absorption coefficients for simulated plage that exceed 50%. The observed increase of the absorption coefficient as a function of frequency is reproduced for all model parameters.

  6. Colliding Magnetic Flux Ropes and Quasi-Separatrix Layers in a Laboratory Plasma

    NASA Astrophysics Data System (ADS)

    Lawrence, Eric Eugene

    An experimental study of the dynamics of colliding magnetic flux ropes and the magnetic reconnection that occurs during these collisions is presented. A magnetic flux rope is a bundle of twisted magnetic field lines that is ubiquitous in space and solar plasmas. The flux ropes are created in the Large Plasma Device (LAPD) using two heated lanthanum hexaboride (LaB6) cathodes that inject currents into the background plasma. The currents are initially parallel to the background magnetic field. The azimuthal field of each current together with the background axial field create helical twisted flux ropes. It is found that the flux ropes rotate in time (corkscrew) and collide with each other. During a collision, antiparallel magnetic fields can undergo magnetic reconnection. When these collisions occur, we observe current layers flowing in the opposite direction of the injected current, a signatuare of reconnection. Analysis of the three-dimensional magnetic field lines shows the existence of quasi-separatrix layers (QSLs). These are regions in the magnetic configuration where there are large spatial gradients in the connectivity of field line footpoints in the boundary surfaces. QSLs are thought to be favorable sites for magnetic reconnection. It is shown that the location and shape of the QSL is similar to what is seen in simulations of merging flux ropes. Furthermore, the field line structure of the QSL is similar to that of a twisted hyperbolic flux tube (HFT). An HFT is a type of QSL that has been shown to be a preferred site for current sheet formation in simulations of interacting coronal loops. The HFT in this experiment is found to be generally near the reverse current layers, although the agreement is not perfect. Looking at the time evolution of the QSL, we find that the QSL cross-sectional area grows and contracts at the same time that the flux ropes collide and that the reverse current layers appear. Analysis of the field line motion shows that, during reconnection, bundles of field lines rapidly flip across the QSLs. This is analagous to the way that field lines are pushed across a separatrix in 2D reconnection.

  7. MHD simulation of direct laser-driven magnetic-flux compression with Nautilus

    NASA Astrophysics Data System (ADS)

    Zhou, C. D.; Loverich, J.; Hakim, A.

    2011-10-01

    Direct laser-driven magnetic-flux compression is an innovative approach to achieve magneto-inertial fusion (MIF). A cylindrical target with initial seed magnetic field is compressed by energetic laser beams. The magnetic field that is ``frozen-in'' the plasma gets compressed with the target. The resulting high magnetic field reduces electron thermal conductivity and improves alpha particle confinement, thus providing an additional thermal insulation of the fuel forming the hot spot. Numerical simulations of magneto-inertial fusion implosions require realistic equation of states, thermonuclear fusion energy generation and laser energy deposition coupling with MHD equations. These simulations are important in stability and scaling studies of MIF implosions. Nautilus is a multidimensional shock-capturing MHD simulation framework developed at Tech-X. Incorporated with PROPACEOS equation of states, fusion reaction and laser ray tracing modules, it is utilized to perform direct laser-driven magnetic-flux compression implosions. Simulation results and relevant Nautilus features are discussed.

  8. Estimation of the spatial structure of a detached magnetic flux rope at Mars based on simultaneous MAVEN plasma and magnetic field observations

    NASA Astrophysics Data System (ADS)

    Hara, Takuya; Mitchell, David L.; McFadden, James P.; Seki, Kanako; Brain, David A.; Halekas, Jasper S.; Harada, Yuki; Espley, Jared R.; DiBraccio, Gina A.; Connerney, John E. P.; Andersson, Lailla; Mazelle, Christian; Jakosky, Bruce M.

    2015-11-01

    Simultaneous Mars Atmosphere and Volatile EvolutioN mission (MAVEN) plasma and magnetic field observations reveal a detached magnetic flux rope in the Martian induced magnetosphere. The flux rope was identified by an increase in the magnetic field amplitude accompanied by smooth vector rotations. In addition, MAVEN observed a pronounced ion composition change across the structure, with solar wind ions dominating outside and planetary ions dominating within. Grad-Shafranov reconstruction is applied to determine the two-dimensional spatial structure of the flux rope. The event occurred near the dusk terminator, downstream from strong crustal magnetic fields. One possibility is that the flux rope was created by magnetic reconnection associated with interplanetary and/or crustal magnetic fields. A weak interplanetary coronal mass ejection (ICME) arrived at Mars a few hours before the event. A pressure pulse and turbulent magnetic fields due to the ICME might be responsible for driving magnetic reconnection to detach the flux rope from the crustal source.

  9. Evidence for the core field polarity of magnetic flux ropes against the reconnection guide field

    NASA Astrophysics Data System (ADS)

    Teh, W.-L.; Abdullah, M.; Hasbi, A. M.

    2014-11-01

    We present the observational evidence by Time History of Events and Macroscale Interactions during Substorms (THEMIS)-D spacecraft to demonstrate that magnetic flux rope can have a core field polarity opposite to the guide field during asymmetric reconnection with a high magnetic shear across the magnetopause. In the presented event, a bipolar reconnection outflow was observed at the magnetopause, across which the magnetic shear was ~149° corresponding to a predicted guide field BG = -15.6 nT. The ratios for magnetic field strength and ion density between the magnetospheric and magnetosheath sides of the magnetopause were ~1.6 and ~0.15, respectively. During the event, the component of magnetic field along the M axis (the intermediate variance direction) remained negative and stable for most of the time, and its mean value agreed with the BG. Two magnetic flux ropes with a strong core field were identified, but one flux rope had a core field polarity against the guide field BG. Our finding differs from current theoretical simulations that the core field polarity of the flux ropes inherits from the guide field.

  10. White noise response of turbine blades subjected to heat flux and thermal gradient

    SciTech Connect

    Karadag, V.; Aba, E.; Morguel, O.K.

    1997-07-01

    Design and production of the complex mechanical structures rarely result in an optimal solution. A typical example for this is a turbine blade design. Fatigue failures of the turbine blades is one of the most vexing problems of turbo-machine manufacturers, ever since the steam turbine became the main stay for power generating equipment and the gas turbines are increasingly used in air transport. Turbine blade failures due to fatigue are predominantly vibration related. The dynamic loads on the blading can arise from many different sources such as the high rotational speed, the high operating temperatures, the asymmetric aerofil tapered form of the turbine blade etc. Therefore, vibratory analysis is one of the most important stage in the designing of the turbine blades. In this study, the random response of the turbine blade to white noise excitation has been consistently calculated, including the internal damping mechanisms of the blade. Beside the damping effects, the rotational speed and the linear thermal gradient along the turbine blade are incorporated into the analysis. Pressure difference between the two surfaces of the turbine blades are modelled as white noise excitation along all over the turbine blade. The system dynamic equation of motion are derived and solved by using the combined Finite Element-Modal Analysis Method.

  11. Noise annoyance caused by magnetic levitation train passbys

    NASA Astrophysics Data System (ADS)

    Vos, Joos

    2001-05-01

    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 the same, (1) the annoyance was independent of the driving speed of the maglev train, (2) the annoyance caused by the maglev train was considerably higher than that caused by intercity trains, (3) the annoyance caused by the maglev train was hardly different from that caused by road traffic (passenger cars and trucks), and (4) the results (1)-(3) held true both for open or closed windows. On the basis of the present results, it might be expected that the sounds are equally annoying if the ASELs of the maglev-train passbys are at least 5 dB lower than those of the intercity train passbys. Consequently, the results of the present experiment do not support application of a railway bonus to the maglev-train sounds. Issues for future research, such as exploring further contributions of nonacoustic factors, will be discussed.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

    Birn, J.; Hesse, M.

    On the basis of a 3D MHD simulation, 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 y N is discussed. As a consequence of B sub y N not equalling 0, the plasmoid assumes a helical flux rope structure rather than an isolated island or bubble structure. Initially all field lines of the plasmoid 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 an ad hoc plasmoid model.

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

    NASA Astrophysics Data System (ADS)

    Birn, J.; Hesse, M.

    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 plasmoid gets a helical flux rope structure rather than an isolated island or bubble structure. Initially all field lines of the plasmoid flux rope remain connected with the Earth, while at later times a gradually increasing number 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 plasmoid models.

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

    NASA Astrophysics Data System (ADS)

    Birn, J.; Hesse, M.

    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 ByN. As a consequence of ByN ≠ 0 the plasmoid assumes a helical flux rope structure rather than an isolated island or bubble structure. Initially all field lines of the plasmoid 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 an ad-hoc plasmoid model.

  16. A flux-mnemonic permanent magnet brushless machine for wind power generation

    NASA Astrophysics Data System (ADS)

    Yu, Chuang; Chau, K. T.; Jiang, J. Z.

    2009-04-01

    In this paper, the concept of flux mnemonics is newly extended to the wind power generator. By incorporating a small magnetizing winding into an outer-rotor doubly salient AlNiCo permanent magnet (PM) machine, a new flux-mnemonic PM brushless wind power generator is proposed and implemented. This generator can offer effective and efficient air-gap flux control. First, the characteristics of the proposed generator are analyzed by using the finite element method. Second, the closed-loop flux control is devised to achieve a constant generated voltage under time-varying wind speeds. Finally, the experimental results are given to verify the validity of the proposed generator and control system.

  17. Plasma β scaling of anisotropic magnetic field fluctuations in the solar wind flux tube

    SciTech Connect

    Sarkar, Aveek; Bhattacharjee, Amitava; Ebrahimi, Fatima E-mail: amitava@princeton.edu

    2014-03-10

    Based on various observations, it has been suggested that at 1 AU, solar wind consists of 'spaghetti'-like magnetic field structures that have the magnetic topology of flux tubes. It is also observed that the plasma fluctuation spectra at 1 AU show a plasma β dependence. Reconciling these two sets of observations and using the Invariance Principle, Bhattacharjee et al. suggested that the plasma inside every flux tube may become unstable with respect to pressure-driven instabilities and gives rise to fluctuation spectra that depend on the local plasma β. The present work is the first direct numerical simulation of such a flux tube. We solve the full magnetohydrodynamic equations using the DEBS code and show that if the plasma inside the flux tube is driven unstable by spatial inhomogeneities in the background plasma pressure, the observed nature of the fluctuating power spectra agrees reasonably well with observations, as well as the analytical prediction of Bhattacharjee et al.

  18. An accurate symplectic calculation of the inboard magnetic footprint from statistical topological noise and field errors in the DIII-D

    NASA Astrophysics Data System (ADS)

    Punjabi, Alkesh; Ali, Halima

    2011-02-01

    Any canonical transformation of Hamiltonian equations is symplectic, and any area-preserving transformation in 2D is a symplectomorphism. Based on these, a discrete symplectic map and its continuous symplectic analog are derived for forward magnetic field line trajectories in natural canonical coordinates. The unperturbed axisymmetric Hamiltonian for magnetic field lines is constructed from the experimental data in the DIII-D [J. L. Luxon and L. E. Davis, Fusion Technol. 8, 441 (1985)]. The equilibrium Hamiltonian is a highly accurate, analytic, and realistic representation of the magnetic geometry of the DIII-D. These symplectic mathematical maps are used to calculate the magnetic footprint on the inboard collector plate in the DIII-D. Internal statistical topological noise and field errors are irreducible and ubiquitous in magnetic confinement schemes for fusion. It is important to know the stochasticity and magnetic footprint from noise and error fields. The estimates of the spectrum and mode amplitudes of the spatial topological noise and magnetic errors in the DIII-D are used as magnetic perturbation. The discrete and continuous symplectic maps are used to calculate the magnetic footprint on the inboard collector plate of the DIII-D by inverting the natural coordinates to physical coordinates. The combination of highly accurate equilibrium generating function, natural canonical coordinates, symplecticity, and small step-size together gives a very accurate calculation of magnetic footprint. Radial variation of magnetic perturbation and the response of plasma to perturbation are not included. The inboard footprint from noise and errors are dominated by m =3, n =1 mode. The footprint is in the form of a toroidally winding helical strip. The width of stochastic layer scales as 1/2 power of amplitude. The area of footprint scales as first power of amplitude. The physical parameters such as toroidal angle, length, and poloidal angle covered before striking, and the safety factor all have fractal structure. The average field diffusion near the X-point for lines that strike and that do not strike differs by about three to four orders of magnitude. The magnetic footprint gives the maximal bounds on size and heat flux density on collector plate.

  19. An accurate symplectic calculation of the inboard magnetic footprint from statistical topological noise and field errors in the DIII-D

    SciTech Connect

    Punjabi, Alkesh; Ali, Halima

    2011-02-15

    Any canonical transformation of Hamiltonian equations is symplectic, and any area-preserving transformation in 2D is a symplectomorphism. Based on these, a discrete symplectic map and its continuous symplectic analog are derived for forward magnetic field line trajectories in natural canonical coordinates. The unperturbed axisymmetric Hamiltonian for magnetic field lines is constructed from the experimental data in the DIII-D [J. L. Luxon and L. E. Davis, Fusion Technol. 8, 441 (1985)]. The equilibrium Hamiltonian is a highly accurate, analytic, and realistic representation of the magnetic geometry of the DIII-D. These symplectic mathematical maps are used to calculate the magnetic footprint on the inboard collector plate in the DIII-D. Internal statistical topological noise and field errors are irreducible and ubiquitous in magnetic confinement schemes for fusion. It is important to know the stochasticity and magnetic footprint from noise and error fields. The estimates of the spectrum and mode amplitudes of the spatial topological noise and magnetic errors in the DIII-D are used as magnetic perturbation. The discrete and continuous symplectic maps are used to calculate the magnetic footprint on the inboard collector plate of the DIII-D by inverting the natural coordinates to physical coordinates. The combination of highly accurate equilibrium generating function, natural canonical coordinates, symplecticity, and small step-size together gives a very accurate calculation of magnetic footprint. Radial variation of magnetic perturbation and the response of plasma to perturbation are not included. The inboard footprint from noise and errors are dominated by m=3, n=1 mode. The footprint is in the form of a toroidally winding helical strip. The width of stochastic layer scales as (1/2) power of amplitude. The area of footprint scales as first power of amplitude. The physical parameters such as toroidal angle, length, and poloidal angle covered before striking, and the safety factor all have fractal structure. The average field diffusion near the X-point for lines that strike and that do not strike differs by about three to four orders of magnitude. The magnetic footprint gives the maximal bounds on size and heat flux density on collector plate.

  20. Emergent 1/f noise in collections of individually oscillating magnetic dots

    NASA Astrophysics Data System (ADS)

    Costanzi, Barry; Dahlberg, E. Dan

    We experimentally demonstrate an emergent 1/f spectrum from a superposition of the noise from random telegraph noise (RTN) oscillators. The system consists of individual square magnetic permalloy dots with dimensions on the order of 200nm x 200nm x 10nm that exhibit RTN in their magnetization at appropriate applied fields. The magnetization fluctuations are measured by the anisotropic magnetoresistance (AMR). AMR is used to find applied fields necessary to exhibit RTN, which result in Lorentizan spectra in the power spectral density of the measurement. A composite AMR measurement of multiple oscillating dots at once, however, shows an emergent 1/f spectrum in the power spectral density. This agrees with the prediction of Van Der Ziel that, for an appropriate distribution of oscillators showing Lorentzian spectra, the composite spectrum will have a 1/f character. This experimental demonstration of 1/f noise from a system of two-state oscillators indicates a possible mechanism for the origin of 1/f spectra observed in both other magnetic systems, and potentially in other, more disparate systems. This work was supported by ONR Grant N00014-11-1-0850. Samples were fabricated in the Minnesota Nano Center, which receives funding from the NSF through the NNIN program.

  1. Improving the signal amplitude of meandering coil EMATs by using ribbon soft magnetic flux concentrators (MFC).

    PubMed

    Dhayalan, R; Satya Narayana Murthy, V; Krishnamurthy, C V; Balasubramaniam, Krishnan

    2011-08-01

    This paper presents a new method of improving the ultrasonic signal amplitude from a meander line EMAT by using soft magnetic alloy ribbon (Fe₆₀Ni₁₀V₁₀B₂₀) as a magnetic flux concentrator (MFC). The flux concentrator is a thin soft amorphous magnetic material (Fe₆₀Ni₁₀V₁₀B₂₀) which is very sensitive to a small flux change. The MFC is used with the EMAT to improve the signal amplitude and it was observed that the peak signal amplitude increases by a factor of two compared to the signal without MFC. Two dimensional numerical models have been developed for the EMAT with MFC to quantify the improvement of the received signal amplitudes. Model calculations and experiments have been carried out for a wide range of ultrasonic frequencies (500 kHz-1 MHz) in different materials. PMID:21376358

  2. Numerical simulations of magnetic Kelvin-Helmholtz instability at a twisted solar flux tube

    NASA Astrophysics Data System (ADS)

    Murawski, K.; Chmielewski, P.; Zaqarashvili, T. V.; Khomenko, E.

    2016-04-01

    The paper aims to study the response of a solar small-scale and weak magnetic flux tube to photospheric twisting motions. We numerically solve three-dimensional ideal magnetohydrodynamic equations to describe the evolution of the perturbation within the initially static flux tube, excited by twists in the azimuthal component of the velocity. These twists produce rotation of the magnetic field lines. Perturbation of magnetic field lines propagates upwardly, driving vertical and azimuthal flow as well as plasma compressions and rarefactions in the form of eddies. We conclude that these eddies result from the sheared azimuthal flow which seeds Kelvin-Helmholtz instability (KHI) between the flux tube and the ambient medium. Numerically obtained properties of the KHI confirm the analytical predictions for the occurrence of the instability.

  3. Parallel heat flux and flow acceleration in open field line plasmas with magnetic trapping

    SciTech Connect

    Guo, Zehua; Tang, Xian-Zhu; McDevitt, Chris

    2014-10-15

    The magnetic field strength modulation in a tokamak scrape-off layer (SOL) provides both flux expansion next to the divertor plates and magnetic trapping in a large portion of the SOL. Previously, we have focused on a flux expander with long mean-free-path, motivated by the high temperature and low density edge anticipated for an absorbing boundary enabled by liquid lithium surfaces. Here, the effects of magnetic trapping and a marginal collisionality on parallel heat flux and parallel flow acceleration are examined. The various transport mechanisms are captured by kinetic simulations in a simple but representative mirror-expander geometry. The observed parallel flow acceleration is interpreted and elucidated with a modified Chew-Goldberger-Low model that retains temperature anisotropy and finite collisionality.

  4. NUMERICAL EXPERIMENTS ON THE TWO-STEP EMERGENCE OF TWISTED MAGNETIC FLUX TUBES IN THE SUN

    SciTech Connect

    Toriumi, S.; Yokoyama, T.

    2011-07-10

    We present the new results of the two-dimensional numerical experiments on the cross-sectional evolution of a twisted magnetic flux tube rising from the deeper solar convection zone (-20,000 km) to the corona through the surface. The initial depth is 10 times deeper than most of the previous calculations focusing on the flux emergence from the uppermost convection zone. We find that the evolution is illustrated by the following two-step process. The initial tube rises due to its buoyancy, subject to aerodynamic drag due to the external flow. Because of the azimuthal component of the magnetic field, the tube maintains its coherency and does not deform to become a vortex roll pair. When the flux tube approaches the photosphere and expands sufficiently, the plasma on the rising tube accumulates to suppress the tube's emergence. Therefore, the flux decelerates and extends horizontally beneath the surface. This new finding owes to our large-scale simulation, which simultaneously calculates the dynamics within the interior as well as above the surface. As the magnetic pressure gradient increases around the surface, magnetic buoyancy instability is triggered locally and, as a result, the flux rises further into the solar corona. We also find that the deceleration occurs at a higher altitude than assumed in our previous experiment using magnetic flux sheets. By conducting parametric studies, we investigate the conditions for the two-step emergence of the rising flux tube: field strength {approx}> 1.5 x 10{sup 4} G and the twist {approx}> 5.0 x 10{sup -4} km{sup -1} at -20,000 km depth.

  5. Performance comparison of three-phase flux reversal permanent magnet motors in BLDC and BLAC operation mode

    NASA Astrophysics Data System (ADS)

    Štumberger, B.; Štumberger, G.; Hadžiselimović, M.; Hamler, A.; Goričan, V.; Jesenik, M.; Trlep, M.

    The paper presents a comparison of torque capability and flux-weakening performance of three-phase flux reversal permanent magnet motors with surface and inset permanent magnets. Finite element analysis is employed to determine the performance of each motor in BLDC and BLAC operation mode. It is shown that the torque capability and flux-weakening performance of surface or inset permanent magnet configuration is strongly dependent on the stator teeth number/rotor pole number combination.

  6. Disc formation in turbulent cloud cores: is magnetic flux loss necessary to stop the magnetic braking catastrophe or not?

    NASA Astrophysics Data System (ADS)

    Santos-Lima, R.; de Gouveia Dal Pino, E. M.; Lazarian, A.

    2013-03-01

    Recent numerical analysis of Keplerian disc formation in turbulent, magnetized cloud cores by Santos-Lima et al. demonstrated that reconnection diffusion is an efficient process to remove the magnetic flux excess during the buildup of a rotationally supported disc. This process is induced by fast reconnection of the magnetic fields in a turbulent flow. In a similar numerical study, Seifried et al. concluded that reconnection diffusion or any other non-ideal magnetohydrodynamic effects would not be necessary and turbulence shear alone would provide a natural way to build up a rotating disc without requiring magnetic flux loss. Their conclusion was based on the fact that the mean mass-to-flux ratio (μ) evaluated over a spherical region with a radius much larger than the disc is nearly constant in their models. In this paper, we compare the two sets of simulations and show that this averaging over large scales can mask significant real increases of μ in the inner regions where the disc is built up. We demonstrate that turbulence-induced reconnection diffusion of the magnetic field happens in the initial stages of the disc formation in the turbulent envelope material that is accreting. Our analysis is suggestive that reconnection diffusion is present in both sets of simulations and provides a simple solution for the `magnetic braking catastrophe' which is discussed in the literature in relation to the formation of protostellar accretion discs.

  7. Cross-tail magnetic flux ropes as observed by the GEOTAIL spacecraft

    SciTech Connect

    Leppintg, R.P.; Fairfield, D.H.

    1995-05-15

    Ten transient magnetic structures in Earth`s magnetotail, as observed in GEOTAIL measurements, selected for early 1993 [at({minus}) X{sub GSM}=90-130 R{sub E}], are shown to have helical magnetic field configurations similar to those of interplanetary magnetic clouds at 1 AU but smaller in size by a factor of {approx} 700. Such structures are shown to be well approximated by a comprehensive magnetic force-free flux-rope model. For this limited set of 10 events the rope axes and the average diameter of these structures is {approx} 15 R{sub E}. 18 refs., 2 figs., 1 tab.

  8. Cross-tail magnetic flux ropes as observed by the GEOTAIL spacecraft

    NASA Technical Reports Server (NTRS)

    Lepping, R. P.; Fairfield, D. H.; Jones, J.; Frank, L. A.; Paterson, W. R.; Kokubun, S.; Yamamoto, T.

    1995-01-01

    Ten transient magnetic structures in Earth's magnetotail, as observed in GEOTAIL measurements, selected for early 1993 (at (-) X(sub GSM) = 90 - 130 Earth radii), are shown to have helical magnetic field configurations similar to those of interplanetary magnetic clouds at 1 AU but smaller in size by a factor of approximately = 700. Such structures are shown to be well approximated by a comprehensive magnetic force-free flux-rope model. For this limited set of 10 events the rope axes are seen to be typically aligned with the Y(sub GSM) axis and the average diameter of these structures is approximately = 15 Earth radii.

  9. Aurora and open magnetic flux during isolated substorms, sawteeth, and SMC events

    NASA Astrophysics Data System (ADS)

    Dejong, A. D.; Cai, X.; Clauer, R. C.; Spann, J. F.

    2007-08-01

    Using Polar UVI LBHl and IMAGE FUV WIC data, we have compared the auroral signatures and polar cap open flux for isolated substorms, sawteeth oscillations, and steady magnetospheric convection (SMC) events. First, a case study of each event type is performed, comparing auroral signatures and open magnetic fluxes to one another. The latitude location of the auroral oval is similar during isolated substorms and SMC events. The auroral intensity during SMC events is similar to that observed during the expansion phase of an isolated substorm. Examination of an individual sawtooth shows that the auroral intensity is much greater than the SMC or isolated substorm events and the auroral oval is displaced equatorward making a larger polar cap. The temporal variations observed during the individual sawtooth are similar to that observed during the isolated substorm, and while the change in polar cap flux measured during the sawtooth is larger, the percent change in flux is similar to that measured during the isolated substorm. These results are confirmed by a statistical analysis of events within these three classes. The results show that the auroral oval measured during individual sawteeth contains a polar cap with, on average, 150% more magnetic flux than the oval measured during isolated substorms or during SMC events. However, both isolated substorms and sawteeth show a 30% decrease in polar cap magnetic flux during the dipolarization (expansion) phase.

  10. Magnetic flux expulsions and secular acceleration pulses at the core surface: is there a link? (Invited)

    NASA Astrophysics Data System (ADS)

    Chulliat, A.

    2010-12-01

    Recent observational studies based upon satellite data have shown that magnetic flux is being expelled from the core in several regions of the core surface. This phenomenon is observed below the South Atlantic Anomaly, where at least two reversed flux patches have been growing for several decades, including one under St Helena Island, and below the North polar region, where a small reversed flux patch has emerged in the 1990s, contributing to the acceleration of the North magnetic pole over the same time interval. Secular acceleration pulses are rapid surges in the second order derivative of the radial magnetic field at the core surface. The most recent pulse occurred in 2005 and was at the origin of the 2003 and 2007 geomagnetic jerks, defined as sudden changes in the field second derivative at the Earth’s surface. It was largest under St Helena and Cocos Islands. The simultaneous occurrences in the 2000s of a flux expulsion and an acceleration pulse under the St Helena region are intriguing. Both phenomena were also simultaneously observed under the North polar region in the 1990s. This presentation will (a) briefly review recent evidence in favor of the existence of magnetic flux expulsions and secular acceleration pulses at the core surface, and (b) discuss possible kinematic and dynamical links between both phenomena.

  11. Dynamic analysis of a magnetic bearing system with flux control

    NASA Technical Reports Server (NTRS)

    Knight, Josiah; Walsh, Thomas; Virgin, Lawrence

    1994-01-01

    Using measured values of two-dimensional forces in a magnetic actuator, equations of motion for an active magnetic bearing are presented. The presence of geometric coupling between coordinate directions causes the equations of motion to be nonlinear. Two methods are used to examine the unbalance response of the system: simulation by direct integration in time; and determination of approximate steady state solutions by harmonic balance. For relatively large values of the derivative control coefficient, the system behaves in an essentially linear manner, but for lower values of this parameter, or for higher values of the coupling coefficient, the response shows a split of amplitudes in the two principal directions. This bifurcation is sensitive to initial conditions. The harmonic balance solution shows that the separation of amplitudes actually corresponds to a change in stability of multiple coexisting solutions.

  12. Vector magnetic field observations of flux tube emergence

    NASA Astrophysics Data System (ADS)

    Schmieder, B.; Aulanier, G.; Pariat, E.; Georgoulis, M. K.; Rust, D. M.; Bernasconi, P. N.

    2002-10-01

    With Flare Genesis Experiment (FGE), a balloon borne Observatory high spatial and temporal resolution vector magnetograms have been obtained in an emerging active region. The comparison of the observations (FGE and TRACE) with a linear force-free field analysis of the region shows where the region is non-force-free. An analysis of the magnetic topology furnishes insights into the existence of "bald patches" regions (BPs are regions where the vector field is tangential to the boundary (photosphere) along an inversion line). Magnetic reconnection is possible and local heating of the chromopshere is predicted near the BPs. Ellerman bombs (EBs) were found to coincide with few BPs computed from a linear force-free extrapolation of the observed longitudinal field. But when the actual observations of transverse fields were used to identify BPs, then the correspondence with EB positions improved significantly. We conclude that linear force-free extrapolations must be done with the true observed vertical fields, which require the measurement of the three components of the magnetic field.

  13. Theoretical Noise Analysis on a Position-sensitive Metallic Magnetic Calorimeter

    NASA Technical Reports Server (NTRS)

    Smith, Stephen J.

    2007-01-01

    We report on the theoretical noise analysis for a position-sensitive Metallic Magnetic Calorimeter (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 and investigate the correlations between the noise measured at each MMC coupled by the absorber. We then calculate, using the optimal filter concept, the theoretical energy and position resolution across the detector and discuss the trade-offs involved in optimizing the detector design for energy resolution, position resolution and count rate. The results show, theoretically, the position-sensitive MMC concept offers impressive spectral and spatial resolving capabilities compared to pixel arrays and similar position-sensitive cryogenic technologies using Transition Edge Sensor (TES) read-out.

  14. The stretching of magnetic flux tubes in the convective overshoot region

    NASA Technical Reports Server (NTRS)

    Fisher, George H.; Mcclymont, Alexander N.; Chou, Dean-Yi

    1991-01-01

    The present study examines the fate of a magnetic flux tube initially lying at the bottom of the solar convective overshoot region. Stretching of the flux tube, e.g., by differential rotation, reduces its density, causing it to rise quasi-statically (a process referred to as vertical flux drift) until it reaches the top of the overshoot region and enters the buoyantly unstable convection region, from which a portion of it may ultimately protrude to form an active region on the surface. It is suggested that vertical flux drift and flux destabilization are inevitable consequences of field amplification, and it is surmised that these phenomena should be considered in self-consistent models of solar and stellar dynamos operating in the overshoot region.

  15. Kondo-induced electric polarization modulated by magnetic flux through a triangular triple quantum dot

    NASA Astrophysics Data System (ADS)

    Koga, M.; Matsumoto, M.; Kusunose, H.

    2015-03-01

    The Kondo effect plays an important role in emergence of electric polarization in a triangular triple-quantum-dot system, where one of the three dots is point-contacted with a single lead, and a magnetic flux penetrates through the triangular loop. The Kondo-induced electric polarization exhibits an Aharonov-Bohm type oscillation as a function of the magnetic flux. Our theoretical study shows various oscillation patterns associated with the field-dependent mixing of twofold orbitally degenerate ground states and their sensitivity to the point contact.

  16. Axisymmetric and non-axisymmetric modulated MHD waves in magnetic flux tubes

    NASA Astrophysics Data System (ADS)

    Chargeishvili, B. B.; Japaridze, D. R.

    2016-02-01

    Nonlinear modulated both axisymmetric and non-axisymmetric MHD wave propagation in magnetic flux tubes is studied. In the cylindrical coordinates, ordinary differential equation with cubic nonlinearity is derived. In both cases of symmetry, the equation has solitary solutions. Modulation stability of the solutions is studied. The results of the study show that the propagation of axisymmetric soliton causes rising of plasma temperature in peripheral regions of a magnetic flux tube. In the non-axisymmetric case, it gives also temperature rising effect. Results of theoretical study are examined on idealized model of chromospheric spicule.

  17. 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.

    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.

  18. Evidence in Magnetic Clouds for Systematic Open Flux Transport on the Sun

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

    Most magnetic clouds encountered by spacecraft at 1 AU display a mix of unidirectional suprathermal electrons signaling open field lines and counterstreaming electrons signaling loops connected to the Sun at both ends. Assuming the open fields were originally loops that underwent interchange reconnection with open fields at the Sun, we determine the sense of connectedness of the open fields found in 72 of 97 magnetic clouds identified by the Wind spacecraft in order to obtain information on the location and sense of the reconnection and resulting flux transport at the Sun. The true polarity of the open fields in each magnetic cloud was determined from the direction of the suprathermal electron flow relative to the magnetic field direction. Results indicate that the polarity of all open fields within a given magnetic cloud is the same 89% of the time, implying that interchange reconnection at the Sun most often occurs in only one leg of a flux rope loop, thus transporting open flux in a single direction, from a coronal hole near that leg to the foot point of the opposite leg. This pattern is consistent with the view that interchange reconnection in coronal mass ejections systematically transports an amount of open flux sufficient to reverse the polarity of the heliospheric field through the course of the solar cycle. Using the same electron data, we also find that the fields encountered in magnetic clouds are only a third as likely to be locally inverted as not. While one might expect inversions to be equally as common as not in flux rope coils, consideration of the geometry of spacecraft trajectories relative to the modeled magnetic cloud axes leads us to conclude that the result is reasonable.

  19. Fabrication issues in optimizing YBa{sub 2}Cu{sub 3}O{sub 7-x} flux transformers for low l/f noise

    SciTech Connect

    Ludwig, F.; Dantsker, E.; Nemeth, D.T.; Koelle, D.; Miklich, A.H.; Clarke, J.; Knappe, S.; Koch, H.; Thomson, R.E.

    1993-11-01

    We describe an improved interconnect technology for the fabrication of multiturn flux transformers from YBa{sub 2}Cu{sub 3}O{sub 7-x}-SrTiO{sub 3}-YBa{sub 2}Cu{sub 3}O{sub 7-x} multilayers. The essential improvements arc reductions in the thicknesses of the trilayer films, typically to 100 nm 250 nm and 250 mn respectively, and in the deposition rate, to 0.07 nm/laser pulse. This process yields crossovers in which the critical current density in the upper YBa{sub 2}Cu{sub 3}O{sub 7-x} film at 77K is (2-3) {times} 10{sup 6} A cm{sup {minus}2}. In situ trilayers exhibited 1/f flux noise levels at lHz below the measurement sensitivity of 15{mu}{Phi}{sub 0} Hz{sup {minus}1/2}, where {Phi}{sub 0} is the flux quantum. However, the flux noise of trilayers in which each layer had been patterned was significantly higher. The best flip-chip magnetometer had a white noise of 40 fT Hz{sup {minus}1/2} increasing to 340 fT Hz{sup {minus}1/2} at lHz; the corresponding flux noise levels were 9 {mu}{Phi}{sub 0} Hz{sup {minus}l/2} and 75 {mu}{Phi}{sub 0} Hz{sup {minus}l/2}, respectively.

  20. SOLAR MAGNETIC TRACKING. III. APPARENT UNIPOLAR FLUX EMERGENCE IN HIGH-RESOLUTION OBSERVATIONS

    SciTech Connect

    Lamb, D. A.; DeForest, C. E.; Hagenaar, H. J.; Parnell, C. E.; Welsch, B. T.

    2010-09-10

    Understanding the behavior of weak magnetic fields near the detection limit of current instrumentation is important for determining the flux budget of the solar photosphere at small spatial scales. Using 0.''3-resolution magnetograms from the Solar Optical Telescope's Narrowband Filter Imager (NFI) on the Hinode spacecraft, we confirm that the previously reported apparent unipolar magnetic flux emergence seen in intermediate-resolution magnetograms is indeed the coalescence of previously existing flux. We demonstrate that similar but smaller events seen in NFI magnetograms are also likely to correspond to the coalescence of previously existing weak fields. The uncoalesced flux, detectable only in the ensemble average of hundreds of these events, accounts for 50% of the total flux within 3 Mm of the detected features. The spatial scale at which apparent unipolar emergence can be directly observed as coalescence remains unknown. The polarity of the coalescing flux is more balanced than would be expected given the imbalance of the data set, however without further study we cannot speculate whether this implies that the flux in the apparent unipolar emergence events is produced by a granulation-scale dynamo or is recycled from existing field.

  1. Competition between electric field and magnetic field noise in the decoherence of a single spin in diamond

    NASA Astrophysics Data System (ADS)

    Jamonneau, P.; Lesik, M.; Tetienne, J. P.; Alvizu, I.; Mayer, L.; Dréau, A.; Kosen, S.; Roch, J.-F.; Pezzagna, S.; Meijer, J.; Teraji, T.; Kubo, Y.; Bertet, P.; Maze, J. R.; Jacques, V.

    2016-01-01

    We analyze the impact of electric field and magnetic field fluctuations in the decoherence of the electronic spin associated with a single nitrogen-vacancy (NV) defect in diamond. To this end, we tune the amplitude of a magnetic field in order to engineer spin eigenstates protected either against magnetic noise or against electric noise. The competition between these noise sources is analyzed quantitatively by changing their relative strength through modifications of the host diamond material. This study provides significant insights into the decoherence of the NV electronic spin, which is valuable for quantum metrology and sensing applications.

  2. Morphology and magnetic flux distribution in superparamagnetic, single-crystalline Fe3O4 nanoparticle rings

    PubMed Central

    Takeno, Yumu; Murakami, Yasukazu; Sato, Takeshi; Tanigaki, Toshiaki; Park, Hyun Soon; Shindo, Daisuke; Ferguson, R. Matthew

    2014-01-01

    This study reports on the correlation between crystal orientation and magnetic flux distribution of Fe3O4 nanoparticles in the form of self-assembled rings. High-resolution transmission electron microscopy demonstrated that the nanoparticles were single-crystalline, highly monodispersed, (25 nm average diameter), and showed no appreciable lattice imperfections such as twins or stacking faults. Electron holography studies of these superparamagnetic nanoparticle rings indicated significant fluctuations in the magnetic flux lines, consistent with variations in the magnetocrystalline anisotropy of the nanoparticles. The observations provide useful information for a deeper understanding of the micromagnetics of ultrasmall nanoparticles, where the magnetic dipolar interaction competes with the magnetic anisotropy. PMID:25422526

  3. Laboratory Measurement of 3D Magnetic Reconnection of Arched Flux Tubes

    NASA Astrophysics Data System (ADS)

    Haw, Magnus; Bellan, Paul M.

    2015-11-01

    An experiment has been constructed to collide two arched magnetic flux tubes at different angles with fully 3D, non-symmetric geometry. The configuration is designed to mimic sheared solar arcades and evaluate the importance of magnetic reconnection in such systems. Time resolved (1MHz) 3D magnetic measurements are taken with a multi-channel 3D magnetic probe. Preliminary analysis shows good agreement between calculated current density and external current diagnostics. Additional simultaneous diagnostics include voltage probes, fast camera imaging, and a 12-channel spectrometer. The spectrometer measures temperature, density, velocity, while the camera provides a view of global plasma behavior. Fast camera images indicate that the topology of the flux tubes evolves such that two equally sized, overlapping loops reconnect to form a small underlying loop and a large overarching loop.

  4. Magnetic x-ray microscopy at low temperatures - Visualization of flux distributions in superconductors

    NASA Astrophysics Data System (ADS)

    Stahl, Claudia; Ruoß, Stephen; Weigand, Markus; Bechtel, Michael; Schütz, Gisela; Albrecht, Joachim

    2016-01-01

    X-ray Magnetic Circular Dichroism (XMCD) microscopy at liquid nitrogen temperature has been performed on bilayers of high-Tc superconducting YBCO (YBa2Cu3O7-δ) and soft-magnetic Co40Fe40B20. This should allow us to map the magnetic flux density distribution in the current-carrying state of the superconductor with high spatial resolution. For that purpose the UHV scanning X-ray microscope MAXYMUS has been upgraded by a MMR Micro Miniature Joule-Thompson cryostat capable of temperatures between 75 K and 580 K. Resulting XMCD images of the magnetic flux density in the superconductor with a field of view ranging from millimeters to micrometers are presented. The microscope's unique combination of total electron yield (TEY) measurements together with low temperatures offers novel possibilities concerning the current transport in superconductors on small length scales.

  5. Large-Scale Coronal Heating, Clustering of Coronal Bright Points, and Concentration of Magnetic Flux

    NASA Technical Reports Server (NTRS)

    Falconer, D. A.; Moore, R. L.; Porter, J. G.; Hathaway, D. H.

    1998-01-01

    By combining quiet-region Fe XII coronal images from SOHO/EIT with magnetograms from NSO/Kitt Peak and from SOHO/MDI, we show that on scales larger than a supergranule the population of network coronal bright points and the magnetic flux content of the network are both markedly greater under the bright half of the quiet corona than under the dim half. These results (1) support the view that the heating of the entire corona in quiet regions and coronal holes is driven by fine-scale magnetic activity (microflares, explosive events, spicules) seated low in the magnetic network, and (2) suggest that this large-scale modulation of the magnetic flux and coronal heating is a signature of giant convection cells.

  6. 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.

  7. Thermal noise of mechanical oscillators in steady states with a heat flux.

    PubMed

    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. PMID:25314407

  8. Nonlinear fast sausage waves in homogeneous magnetic flux tubes

    NASA Astrophysics Data System (ADS)

    Mikhalyaev, Badma B.; Ruderman, Michael S.

    2015-12-01

    > We consider fast sausage waves in straight homogeneous magnetic tubes. The plasma motion is described by the ideal magnetohydrodynamic equations in the cold plasma approximation. We derive the nonlinear Schrödinger equation describing the nonlinear evolution of an envelope of a carrier wave. The coefficients of this equation are expressed in terms Bessel and modified Bessel functions. They are calculated numerically for various values of parameters. In particular, we show that the criterion for the onset of the modulational or Benjamin-Fair instability is satisfied. The implication of the obtained results for solar physics is discussed.

  9. A very low noise preamplifier for extremely low frequency magnetic antenna

    NASA Astrophysics Data System (ADS)

    Shimin, Feng; Suihua, Zhou; Zhiyi, Chen

    2013-07-01

    Besides the electrode-pair antenna, the magnetic antenna is also used for the extremely low frequency (ELF) submarine communication. To receive the weak ELF signals, the structure of a small sized magnetic antenna determines its specific electrical characteristics. The ELF magnetic antenna shows high internal resistance, alternating-current impedance, and a resonance frequency near the operating bandwidth. In accordance with the electrical characteristics of ELF magnetic antenna, a low noise preamplifier and frequency compensation circuit were designed and realized. The preamplifier is a three-stage negative feedback circuit, which is composed of parallel JFET, common-emitter amplifier with a Darlington structure and a common-collector amplifier in push-pull connection. And a frequency compensation circuit is cascaded to compensate the characteristic in low frequency range. In the operating bandwidth f = 30-200 Hz, the circuit has a gain of 39.4 dB. The equivalent input noise is 1.97 nV/√Hz and the frequency response keeps flat in operating bandwidth. The proposed preamplifier of the ELF magnetic antenna performs well in receiving ELF signals.

  10. Numerical Study of Magnetic Reconnection in Merging Flux Tubes

    NASA Astrophysics Data System (ADS)

    Breslau, Joshua; Jardin, Stephen

    2001-06-01

    A comprehensive 2D numerical study of magnetic reconnection in merging magnetic islands has been conducted using a parallel resistive MHD/two-fluid code developed for the purpose. The code's variable resolution and parallel scalability make it possible to resolve both the narrow reconnection boundary layer and the global plasma, and to follow the evolution of both from triple-island to single-island equilibrium. An initial resistive MHD study showed slow reconnection in strong agreement with the Sweet-Parker model. Subsequent studies were conducted to compare two proposed mechanisms for increasing the reconnection rate: anomalous localized enhanced resistivity and two-fluid effects, which enter the fluid equations via the Hall term in Ohm's law. Both anomalous resistivity and the Hall term showed a clear tendency to increase the reconnection rate significantly and to eliminate its dependence on the resistivity. In both cases, this effect is associated with a broadening of the toroidal current sheet and consequently with an opening of the angle of the X-point at the field null. These faster reconnection rates are in better agreement with observational and experimental data.

  11. Numerical study of magnetic reconnection in merging flux tubes

    NASA Astrophysics Data System (ADS)

    Breslau, Joshua Adam

    2001-09-01

    A comprehensive 2D numerical study of magnetic reconnection in merging magnetic islands has been conducted using a new parallel resistive MHD/two-fluid code developed for the purpose. The code's variable resolution and parallel scalability make it possible to resolve both the narrow reconnection boundary layer and the global plasma, and to follow the evolution of both from triple-island to single-island equilibrium. An initial resistive MHD study showed slow reconnection in strong agreement with the Sweet-Parker model. Subsequent studies were conducted to compare two proposed mechanisms for increasing the reconnection rate: anomalous localized enhanced resistivity and two-fluid effects, which enter the fluid equations via the Hall term in Ohm's law. Both anomalous resistivity and the Hall term showed a clear tendency to increase the reconnection rate significantly and to eliminate its dependence on the resistivity. In both cases, this effect is associated with a broadening of the toroidal current sheet and consequently with an opening of the angle of the X-point at the field null. These faster reconnection rates are in better agreement with observational and experimental data.

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

    SciTech Connect

    Ruoß, S. Stahl, C.; Weigand, M.; Schütz, G.; Albrecht, J.

    2015-01-12

    The penetration of magnetic flux into high-temperature superconductors has been observed using a high-resolution technique based on x-ray magnetic circular dichroism. Superconductors coated with thin soft-magnetic layers are observed in a scanning x-ray microscope under the influence of external magnetic fields. Resulting electric currents in the superconductor create an inhomogeneous magnetic field distribution above the superconductor and lead to a local reorientation of the ferromagnetic layer. Measuring the local magnetization of the ferromagnet by x-ray absorption microscopy with circular-polarized radiation allows the analysis of the magnetic flux distribution in the superconductor with a spatial resolution on the nanoscale.

  13. A flux extraction device to measure the magnetic moment of large samples; application to bulk superconductors.

    PubMed

    Egan, R; Philippe, M; Wera, L; Fagnard, J F; Vanderheyden, B; Dennis, A; Shi, Y; Cardwell, D A; Vanderbemden, P

    2015-02-01

    We report the design and construction of a flux extraction device to measure the DC magnetic moment of large samples (i.e., several cm(3)) at cryogenic temperature. The signal is constructed by integrating the electromotive force generated by two coils wound in series-opposition that move around the sample. We show that an octupole expansion of the magnetic vector potential can be used conveniently to treat near-field effects for this geometrical configuration. The resulting expansion is tested for the case of a large, permanently magnetized, type-II superconducting sample. The dimensions of the sensing coils are determined in such a way that the measurement is influenced by the dipole magnetic moment of the sample and not by moments of higher order, within user-determined upper bounds. The device, which is able to measure magnetic moments in excess of 1 A m(2) (1000 emu), is validated by (i) a direct calibration experiment using a small coil driven by a known current and (ii) by comparison with the results of numerical calculations obtained previously using a flux measurement technique. The sensitivity of the device is demonstrated by the measurement of flux-creep relaxation of the magnetization in a large bulk superconductor sample at liquid nitrogen temperature (77 K). PMID:25725888

  14. Magnetic flux distortion in two-phase liquid metal flow: Model experiment

    NASA Astrophysics Data System (ADS)

    Kumar, M.; Bergez, W.; Tordjeman, Ph.; Arinero, R.; Paumel, K.

    2016-05-01

    In this paper, we present the model experiments in order to study the magnetic flux distortion of a two-phase liquid metal flow excited by an AC magnetic field in a range of pulsation where Faraday induction and Lorentz force effects are significant. These experiments realized with solid aluminum rods allow to characterize the effects of flow velocity ( 0 ≲ U ≤1 ms-1 ), void fraction ( 0 ≤α≤6.9 % ), pulsation of the AC magnetic field ( 1.5 ×103≤ω≤12.5 ×103 rad s-1 ), and of two different void geometries. The results are analyzed on the basis of a first order expansion of magnetic flux in U and α. Despite the strong coupling between Faraday induction and Lorentz force effects, the results show that the contributions of U and α on a magnetic flux distortion can be well separated at both low magnetic Reynolds number and α values. These results are independent of void geometry.

  15. A flux extraction device to measure the magnetic moment of large samples; application to bulk superconductors

    NASA Astrophysics Data System (ADS)

    Egan, R.; Philippe, M.; Wera, L.; Fagnard, J. F.; Vanderheyden, B.; Dennis, A.; Shi, Y.; Cardwell, D. A.; Vanderbemden, P.

    2015-02-01

    We report the design and construction of a flux extraction device to measure the DC magnetic moment of large samples (i.e., several cm3) at cryogenic temperature. The signal is constructed by integrating the electromotive force generated by two coils wound in series-opposition that move around the sample. We show that an octupole expansion of the magnetic vector potential can be used conveniently to treat near-field effects for this geometrical configuration. The resulting expansion is tested for the case of a large, permanently magnetized, type-II superconducting sample. The dimensions of the sensing coils are determined in such a way that the measurement is influenced by the dipole magnetic moment of the sample and not by moments of higher order, within user-determined upper bounds. The device, which is able to measure magnetic moments in excess of 1 A m2 (1000 emu), is validated by (i) a direct calibration experiment using a small coil driven by a known current and (ii) by comparison with the results of numerical calculations obtained previously using a flux measurement technique. The sensitivity of the device is demonstrated by the measurement of flux-creep relaxation of the magnetization in a large bulk superconductor sample at liquid nitrogen temperature (77 K).

  16. Observation of the magnetic flux and three-dimensional structure of skyrmion lattices by electron holography.

    PubMed

    Park, Hyun Soon; Yu, Xiuzhen; Aizawa, Shinji; Tanigaki, Toshiaki; Akashi, Tetsuya; Takahashi, Yoshio; Matsuda, Tsuyoshi; Kanazawa, Naoya; Onose, Yoshinori; Shindo, Daisuke; Tonomura, Akira; Tokura, Yoshinori

    2014-05-01

    Skyrmions are nanoscale spin textures that are viewed as promising candidates as information carriers in future spintronic devices. Skyrmions have been observed using neutron scattering and microscopy techniques. Real-space imaging using electrons is a straightforward way to interpret spin configurations by detecting the phase shifts due to electromagnetic fields. Here, we report the first observation by electron holography of the magnetic flux and the three-dimensional spin configuration of a skyrmion lattice in Fe(0.5)Co(0.5)Si thin samples. The magnetic flux inside and outside a skyrmion was directly visualized and the handedness of the magnetic flux flow was found to be dependent on the direction of the applied magnetic field. The electron phase shifts φ in the helical and skyrmion phases were determined using samples with a stepped thickness t (from 55 nm to 510 nm), revealing a linear relationship (φ = 0.00173 t). The phase measurements were used to estimate the three-dimensional structures of both the helical and skyrmion phases, demonstrating that electron holography is a useful tool for studying complex magnetic structures and for three-dimensional, real-space mapping of magnetic fields. PMID:24727689

  17. Characterization of magnetic degradation mechanism in a high-neutron-flux environment

    NASA Astrophysics Data System (ADS)

    Samin, Adib; Qiu, Jie; Hattrick-Simpers, Jason; Dai-Hattrick, Liyang; Zheng, Yuan F.; Cao, Lei

    2014-09-01

    Radiation-induced demagnetization of permanent magnets can result in the failure of magnet-based devices operating in high-radiation environments. To understand the mechanism underlying demagnetization, Nd-Fe-B magnets were irradiated with fast and fast plus thermal neutrons at fluences of 1012, 1013, 1014, and 1015 n/cm2, respectively. After irradiation, magnetic flux losses were shown to increase with the fluence. Compared with samples irradiated only with fast neutrons, the samples exposed to the fast plus thermal neutrons have higher magnetic flux losses, which is attributed to the thermal neutron capture reaction of boron. Hysteresis loops of the Nd-Fe-B magnets reveal a slightly increase in the coercivity after irradiation. Full remagnetization of the samples after irradiation was possible, which indicates that structural damage is unlikely an important factor in the demagnetization process at these levels of neutron flux and fluence. Finally, we performed a preliminary Molecular Dynamic (MD) simulation on a cube of ions to obtain a better understanding of the thermal spike mechanism.

  18. Slipping Magnetic Reconnection Triggering a Solar Eruption of a Triangle-shaped Flag Flux Rope

    NASA Astrophysics Data System (ADS)

    Li, Ting; Zhang, Jun

    2014-08-01

    We report the first simultaneous activities of the slipping motion of flare loops and a slipping eruption of a flux rope in 131 Å and 94 Å channels on 2014 February 2. The east hook-like flare ribbon propagated with a slipping motion at a speed of about 50 km s-1, which lasted about 40 minutes and extended by more than 100 Mm, but the west flare ribbon moved in the opposite direction with a speed of 30 km s-1. At the later phase of flare activity, there was a well developed "bi-fan" system of flare loops. The east footpoints of the flux rope showed an apparent slipping motion along the hook of the ribbon. Simultaneously, the fine structures of the flux rope rose up rapidly at a speed of 130 km s-1, much faster than that of the whole flux rope. We infer that the east footpoints of the flux rope are successively heated by a slipping magnetic reconnection during the flare, which results in the apparent slippage of the flux rope. The slipping motion delineates a "triangle-shaped flag surface" of the flux rope, implying that the topology of a flux rope is more complex than anticipated.

  19. Slipping Magnetic Reconnection Triggering a Solar Eruption of a Triangle-Shaped Flag Flux Rope

    NASA Astrophysics Data System (ADS)

    Li, Ting

    2015-08-01

    We report the first simultaneous activities of the slipping motion of flare loops and a slipping eruption of a flux rope in 131Å and 94Å channels on 2014 February 2. The east hook-like flare ribbon propagated with a slipping motion at a speed of about 50 km/s, which lasted about 40 minutes and extended by more than 100 Mm, but the west flare ribbon moved in the opposite direction with a speed of 30 km/s. At the later phase of flare activity, there was a well developed “bi-fan” system of flare loops. The east footpoints of the flux rope showed an apparent slipping motion along the hook of the ribbon. Simultaneously, the fine structures of the flux rope rose up rapidly at a speed of 130 km/s, much faster than that of the whole flux rope. We infer that the east footpoints of the flux rope are successively heated by a slipping magnetic reconnection during the flare, which results in the apparent slippage of the flux rope. The slipping motion delineates a “triangle-shaped flag surface” of the flux rope, implying that the topology of a flux rope is more complex than anticipated.

  20. SLIPPING MAGNETIC RECONNECTION TRIGGERING A SOLAR ERUPTION OF A TRIANGLE-SHAPED FLAG FLUX ROPE

    SciTech Connect

    Li, Ting; Zhang, Jun E-mail: zjun@nao.cas.cn

    2014-08-10

    We report the first simultaneous activities of the slipping motion of flare loops and a slipping eruption of a flux rope in 131 Å and 94 Å channels on 2014 February 2. The east hook-like flare ribbon propagated with a slipping motion at a speed of about 50 km s{sup –1}, which lasted about 40 minutes and extended by more than 100 Mm, but the west flare ribbon moved in the opposite direction with a speed of 30 km s{sup –1}. At the later phase of flare activity, there was a well developed ''bi-fan'' system of flare loops. The east footpoints of the flux rope showed an apparent slipping motion along the hook of the ribbon. Simultaneously, the fine structures of the flux rope rose up rapidly at a speed of 130 km s{sup –1}, much faster than that of the whole flux rope. We infer that the east footpoints of the flux rope are successively heated by a slipping magnetic reconnection during the flare, which results in the apparent slippage of the flux rope. The slipping motion delineates a ''triangle-shaped flag surface'' of the flux rope, implying that the topology of a flux rope is more complex than anticipated.

  1. DYNAMIC COUPLING OF CONVECTIVE FLOWS AND MAGNETIC FIELD DURING FLUX EMERGENCE

    SciTech Connect

    Fang Fang; Manchester IV, Ward; Van der Holst, Bart; Abbett, William P.

    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.

  2. A method for embedding circular force-free flux ropes in potential magnetic fields

    SciTech Connect

    Titov, V. S.; Török, T.; Mikic, Z.; Linker, J. A.

    2014-08-01

    We propose a method for constructing approximate force-free equilibria in pre-eruptive configurations in which a thin force-free flux rope is embedded into a locally bipolar-type potential magnetic field. The flux rope is assumed to have a circular-arc axis, a circular cross-section, and electric current that is either concentrated in a thin layer at the boundary of the rope or smoothly distributed across it with a maximum of the current density at the center. The entire solution is described in terms of the magnetic vector potential in order to facilitate the implementation of the method in numerical magnetohydrodynamic (MHD) codes that evolve the vector potential rather than the magnetic field itself. The parameters of the flux rope can be chosen so that its subsequent MHD relaxation under photospheric line-tied boundary conditions leads to nearly exact numerical equilibria. To show the capabilities of our method, we apply it to several cases with different ambient magnetic fields and internal flux-rope structures. These examples demonstrate that the proposed method is a useful tool for initializing data-driven simulations of solar eruptions.

  3. Three-dimensional observations of magnetic flux density around fatigue crack tips of bearing steels

    NASA Astrophysics Data System (ADS)

    Kida, Katsuyuki; Santos, Edson C.; Honda, Takashi; Tanabe, Hirotaka

    2009-12-01

    Fatigue failure of steel occurs when small cracks form in a component and then continue to grow to a size large enough to cause failure. In order to understand the strength of steel components it is important to find these cracks. However, at present, it is not easy to distinguish the cracks that will grow fast and cause failure. We developed a three-dimensional scanning Hall probe microscope (3D-SHPM) and observed fatigue cracks at room temperature while they were growing. Four-point-bending fatigue tests were carried out using pre-cracked specimens (JIS-SUJ2, bearing steel). We observed the two-dimensional magnetic flux density distributions around the crack tips and found that there is a strong correlation between the changes in the magnetic flux densities and the crack growth. In order to understand this, we looked into all the three components of the magnetic flux densities, and found that they shape an arched bridge around a crack. We also found that the magnetic flux density moves in front of the crack tip along the crack growth direction.

  4. Three-dimensional observations of magnetic flux density around fatigue crack tips of bearing steels

    NASA Astrophysics Data System (ADS)

    Kida, Katsuyuki; Santos, Edson C.; Honda, Takashi; Tanabe, Hirotaka

    2010-03-01

    Fatigue failure of steel occurs when small cracks form in a component and then continue to grow to a size large enough to cause failure. In order to understand the strength of steel components it is important to find these cracks. However, at present, it is not easy to distinguish the cracks that will grow fast and cause failure. We developed a three-dimensional scanning Hall probe microscope (3D-SHPM) and observed fatigue cracks at room temperature while they were growing. Four-point-bending fatigue tests were carried out using pre-cracked specimens (JIS-SUJ2, bearing steel). We observed the two-dimensional magnetic flux density distributions around the crack tips and found that there is a strong correlation between the changes in the magnetic flux densities and the crack growth. In order to understand this, we looked into all the three components of the magnetic flux densities, and found that they shape an arched bridge around a crack. We also found that the magnetic flux density moves in front of the crack tip along the crack growth direction.

  5. Convective radial energy flux due to resonant magnetic perturbations and magnetic curvature at the tokamak plasma edge

    SciTech Connect

    Marcus, F. A.; Beyer, P.; Fuhr, G.; Monnier, A.; Benkadda, S.

    2014-08-15

    With the resonant magnetic perturbations (RMPs) consolidating as an important tool to control the transport barrier relaxation, the mechanism on how they work is still a subject to be clearly understood. In this work, we investigate the equilibrium states in the presence of RMPs for a reduced MHD model using 3D electromagnetic fluid numerical code with a single harmonic RMP (single magnetic island chain) and multiple harmonics RMPs in cylindrical and toroidal geometry. Two different equilibrium states were found in the presence of the RMPs with different characteristics for each of the geometries used. For the cylindrical geometry in the presence of a single RMP, the equilibrium state is characterized by a strong convective radial thermal flux and the generation of a mean poloidal velocity shear. In contrast, for toroidal geometry, the thermal flux is dominated by the magnetic flutter. For multiple RMPs, the high amplitude of the convective flux and poloidal rotation are basically the same in cylindrical geometry, but in toroidal geometry the convective thermal flux and the poloidal rotation appear only with the islands overlapping of the linear coupling between neighbouring poloidal wavenumbers m, m – 1, and m + 1.

  6. Turbulent transport of Small-scale magnetic flux elements on Solar Photosphere

    NASA Astrophysics Data System (ADS)

    Agrawal, Piyush; Rempel, Matthias; Bellot Rubio, Luis; Rast, Mark

    2016-05-01

    We study the transport of small-scale magnetic elements on the solar photosphere using both observations and simulations. Observational data was obtained from Hinode - Solar Optical Telescope (SOT/SP) instrument and simulations from MURaM code. The magnetic flux elements were tracked in both data sets and statistics were obtained. We compute the probability density of the Eulerian distances traveled by the flux elements along Lagrangian trajectories. For a two-dimensional random walk process this distribution should be Rayleigh. Preliminary results show that the measured probability distribution in both the observed and simulated data approximates a random walk, on time scale close to the lifetime of granules, but deviates from it for longer times. This implies that diffusion may not be an appropriate framework for transport in the solar photosphere. We explore the roles of flux cancelation and element trapping in producing this result. Work is ongoing.

  7. Comparison of simulated and observed trapped and precipitating electron fluxes during a magnetic storm

    NASA Astrophysics Data System (ADS)

    Chen, Margaret W.; Lemon, Colby L.; Orlova, Ksenia; Shprits, Yuri; Hecht, James; Walterscheid, R. L.

    2015-10-01

    The ability to accurately model precipitating electron distributions is crucial for understanding magnetosphere-ionosphere-thermosphere coupling processes. We use the magnetically and electrically self-consistent Rice Convection Model-Equilibrium (RCM-E) of the inner magnetosphere to assess how well different electron loss models can account for observed electron fluxes during the large 10 August 2000 magnetic storm. The strong pitch angle scattering rate produces excessive loss on the morning and dayside at geosynchronous orbit (GEO) compared to what is observed by a Los Alamos National Laboratory satellite. RCM-E simulations with parameterized scattering due to whistler chorus outside the plasmasphere and hiss inside the plasmasphere are able to account simultaneously for trapped electron fluxes at 1.2 keV to ~100 keV observed at GEO and for precipitating electron fluxes and electron characteristic energies in the ionosphere at 833 km measured by the NOAA 15 satellite.

  8. Magnetic forces and magnetized biomaterials provide dynamic flux information during bone regeneration.

    PubMed

    Russo, Alessandro; Bianchi, Michele; Sartori, Maria; Parrilli, Annapaola; Panseri, Silvia; Ortolani, Alessandro; Sandri, Monica; Boi, Marco; Salter, Donald M; Maltarello, Maria Cristina; Giavaresi, Gianluca; Fini, Milena; Dediu, Valentin; Tampieri, Anna; Marcacci, Maurilio

    2016-03-01

    The fascinating prospect to direct tissue regeneration by magnetic activation has been recently explored. In this study we investigate the possibility to boost bone regeneration in an experimental defect in rabbit femoral condyle by combining static magnetic fields and magnetic biomaterials. NdFeB permanent magnets are implanted close to biomimetic collagen/hydroxyapatite resorbable scaffolds magnetized according to two different protocols . Permanent magnet only or non-magnetic scaffolds are used as controls. Bone tissue regeneration is evaluated at 12 weeks from surgery from a histological, histomorphometric and biomechanical point of view. The reorganization of the magnetized collagen fibers under the effect of the static magnetic field generated by the permanent magnet produces a highly-peculiar bone pattern, with highly-interconnected trabeculae orthogonally oriented with respect to the magnetic field lines. In contrast, only partial defect healing is achieved within the control groups. We ascribe the peculiar bone regeneration to the transfer of micro-environmental information, mediated by collagen fibrils magnetized by magnetic nanoparticles, under the effect of the static magnetic field. These results open new perspectives on the possibility to improve implant fixation and control the morphology and maturity of regenerated bone providing "in site" forces by synergically combining static magnetic fields and biomaterials. PMID:26758898

  9. MAGNETIC FLUX DENSITY MEASURED IN FAST AND SLOW SOLAR WIND STREAMS

    SciTech Connect

    Erdos, G.; Balogh, A.

    2012-07-10

    The radial component of the heliospheric magnetic field vector is used to estimate the open magnetic flux density of the Sun. This parameter has been calculated using observations from the Ulysses mission that covered heliolatitudes from 80 Degree-Sign S to 80 Degree-Sign N, from 1990 to 2009 and distances from 1 to 5.4 AU, the Advanced Composition Explorer mission at 1 AU from 1997 to 2010, the OMNI interplanetary database from 1971, and the Helios 1 and 2 missions that covered the distance range from 0.3 to 1 AU. The flux density was found to be much affected by fluctuations in the magnetic field which make its calculated value dependent on heliospheric location, type of solar wind (fast or slow), and the level of solar activity. However, fluctuations are distributed symmetrically perpendicular to the average Parker direction. Therefore, distributions of the field vector in the two-dimensional plane defined by the radial and azimuthal directions in heliospheric coordinates provide a way to reduce the effects of the fluctuations on the measurement of the flux density. This leads to a better defined flux density parameter; the distributions modified by removing the effects of fluctuations then allow a clearer assessment of the dependence of the flux density on heliospheric location, solar wind type, and solar activity. This assessment indicates that the flux density normalized to 1 AU is independent of location and solar wind type (fast or slow). However, there is a residual dependence on solar activity which can be studied using the modified flux density measurements.

  10. Magnetic Flux Density Measured in Fast and Slow Solar Wind Streams

    NASA Astrophysics Data System (ADS)

    Erdős, G.; Balogh, A.

    2012-07-01

    The radial component of the heliospheric magnetic field vector is used to estimate the open magnetic flux density of the Sun. This parameter has been calculated using observations from the Ulysses mission that covered heliolatitudes from 80°S to 80°N, from 1990 to 2009 and distances from 1 to 5.4 AU, the Advanced Composition Explorer mission at 1 AU from 1997 to 2010, the OMNI interplanetary database from 1971, and the Helios 1 and 2 missions that covered the distance range from 0.3 to 1 AU. The flux density was found to be much affected by fluctuations in the magnetic field which make its calculated value dependent on heliospheric location, type of solar wind (fast or slow), and the level of solar activity. However, fluctuations are distributed symmetrically perpendicular to the average Parker direction. Therefore, distributions of the field vector in the two-dimensional plane defined by the radial and azimuthal directions in heliospheric coordinates provide a way to reduce the effects of the fluctuations on the measurement of the flux density. This leads to a better defined flux density parameter; the distributions modified by removing the effects of fluctuations then allow a clearer assessment of the dependence of the flux density on heliospheric location, solar wind type, and solar activity. This assessment indicates that the flux density normalized to 1 AU is independent of location and solar wind type (fast or slow). However, there is a residual dependence on solar activity which can be studied using the modified flux density measurements.

  11. Spatial configuration of a flux rope observed downstream from the Martian crustal magnetic fields

    NASA Astrophysics Data System (ADS)

    Hara, T.; Seki, K.; Hasegawa, H.; Brain, D. A.; Saito, M. H.

    2012-12-01

    Mars is a unique planet since 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 (IMF) embedded in the solar wind interacts with the Martian crustal magnetic field. 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 Earth often in association with substorms. 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 magnetic field. Recently, Brain et al. [2010] found a large-scale isolated flux rope filled with Martian atmospheric plasma located downstream from the crustal magnetic fields with respect to the solar wind flow based on their analyses of the magnetic field and suprathermal electron measurements from the Mars Global Surveyor (MGS) spacecraft. They suggested that the flux rope can intermittently carry significant amounts of atmosphere away from Mars by a bulk removal process such as magnetic reconnection between the IMF and the crustal magnetic fields. They supposed that this process occurs frequently and may account for as much as 10 % of the total present-day ion escape from Mars. We here attempt to reconstruct the spatial configuration of the reported flux rope using the Grad-Shafranov (GS) reconstruction technique, assuming that it has a magnetohydrostatic, two-dimensional magnetic field structure [Hu and Sonnerup, 2002]. The GS reconstruction technique is capable of recovering a two-dimensional field structure from single spacecraft data. Since there is no ion detector onboard MGS, we assumed a typical density and temperature of the Martian ionosphere at the spacecraft altitude in order to calculate the input thermal pressure for the model. It is also assumed that the spacecraft velocity is the dominant component causing apparent movement of the flux rope relative to the MGS spacecraft. The reconstructed structure of the flux rope indicates stretching in the anti-sunward direction, which is consistent with Brain et al. [2010]. We also find that the stretching of the reconstructed structure has a significant component in the dawn-dusk direction in the Mars-centered, Solar Orbital (MSO) coordinate system. The result provides a reliable observational restriction on the spatial scales of the flux rope. In the presentation, we will also discuss the effects of the flux rope on the atmospheric escape from Mars.

  12. Magnetic flux penetration in Nb superconducting films with lithographically defined microindentations

    NASA Astrophysics Data System (ADS)

    Brisbois, J.; Adami, O.-A.; Avila, J. I.; Motta, M.; Ortiz, W. A.; Nguyen, N. D.; Vanderbemden, P.; Vanderheyden, B.; Kramer, R. B. G.; Silhanek, A. V.

    2016-02-01

    We present a thorough investigation by magneto-optical imaging of the magnetic flux penetration in Nb thin films with lithographically defined border indentations. We demonstrate that discontinuity lines (d lines), caused by the abrupt bending of current streamlines around the indentations, depart from the expected parabolic trend close to the defect and depend on the shape and size of the indentation as well as on the temperature. These findings are backed up and compared with theoretical results obtained by numerical simulations and analytical calculations highlighting the key role played by demagnetization effects and the creep exponent n . In addition, we show that the presence of nearby indentations and submicrometer random roughness of the sample border can severely modify the flux front topology and dynamics. Strikingly, in contrast to what has been repeatedly predicted in the literature, we do not observe that indentations act as nucleation spots for flux avalanches, but they instead help to release the flux pressure and avoid thermomagnetic instabilities.

  13. Dynamics of an Erupting Arched Magnetic Flux Rope in a Laboratory Plasma Experiment

    NASA Astrophysics Data System (ADS)

    Tripathi, S. K. P.; Gekelman, W.

    2013-09-01

    A laboratory plasma experiment has been built to study the eruption of arched magnetic flux ropes (AMFRs) in the presence of a large magnetized plasma. This experiment simulates the eruption of solar AMFRs in two essential steps: i) it produces an AMFR ( n=6.0×1012 cm-3, T_e = 14~eV, B≈1 kilo-gauss, L=0.51 m) with a persistent appearance that lasts several Alfvén transit times using a lanthanum hexaboride (LaB6) plasma source, and ii) it generates controlled plasma flows from the footpoints of the AMFR using laser beams. An additional LaB6 plasma source generates a large magnetized plasma in the background. The laser-generated flows trigger the eruption by injecting dense plasma and magnetic flux into the AMFR. The experiment is highly reproducible and runs continuously with a 0.5 Hz repetition rate; hence, several thousand identical loop eruptions are routinely generated and their spatio-temporal evolution is recorded in three-dimensions using computer-controlled movable probes. Measurements demonstrate striking similarities between the erupting laboratory and solar arched magnetic flux ropes.

  14. Eruption of an arched magnetic flux rope in an ambient magnetoplasma

    NASA Astrophysics Data System (ADS)

    Tripathi, Shreekrishna; Gekelman, Walter

    2012-10-01

    Arched magnetic flux ropes (AMFRs) are arch-shaped, current-carrying, magnetized plasma structures that ubiquitously exist in the solar atmosphere. A laboratory plasma experiment [Tripathi and Gekelman, PRL 105, 075005 (2010)] has been built to study the eruption of AMFRs in two essential steps: (i) production of an AMFR (n˜ 10^19 m-3, Te˜14 eV, B˜1 kG, L˜0.5 m) with a persistent appearance lasting several Alfven transit times using a Lanthnum Hexaboride (LaB6) plasma source, and (ii) generation of controlled plasma flows from the foot-points of the AMFR using two laser beams (1064 nm, 1 J/pulse). An additional LaB6 source produces a large magnetoplasma in the background. The laser generated flows drive the eruption by injecting plasma and magnetic flux in the AMFR. The experiment is highly reproducible and runs continuously with a 0.5 Hz repetition rate, hence evolution of the AMFR is recorded using computer-controlled movable probes in 3D. High-speed imaging, Langmuir and 3-axis magnetic-loop probes are the main diagnostic tools. New results from this experiment on global kink-mode oscillations of the AMFR, excitation of fast waves, and ejection of a large magnetic flux rope from the apex of the AMFR will be presented.

  15. Magnetic Field Reconnection and the quasi-seperatrix layer of three interacting flux ropes

    NASA Astrophysics Data System (ADS)

    Gekelman, Walter; van Compernolle, Bart; Vincena, Stephen

    2010-11-01

    Three magnetic flux ropes are created in a background magnetoplasma (L = 16 m, nbackgnd=2x10^12cm-3,nrope=1x10^13cm-3,B0z330G, He, plasma diameter = 60 cm). The ropes are made using a masked LaB6 , 8 cm diameter cathode and remote anode. Each rope carries 40 A of current. Magnetic field data is acquired in 16 perpendicular planes (size lx=ly=15cm, 3mm sampling) with axial spacing of 64 cm. The magnetic field lines generated from the data reveal that the flux ropes twist about themselves and each other in a complicated fashion in space and time and there are spatial locations at which transverse magnetic fields of opposite polarity are forced towards each other and reconnect. Fast photography of the light from a He II line shows similar structure. The magnetic field data is used to compute the quasi-seperatrix layer (QSL) much as it was in the case of two interacting flux ropes[1]. The QSL is a 3D region in which reconnection activity is likely to occur. This is shown in movies that illustrate the space-time evolution. [4pt] [1] E. Lawrence, W. Gekelman, Identification of a quasi-seperatrix layer in a reconnecting laboratory magnetoplasma, Phys. Rev. Lett., 103, 105002 (2009)

  16. 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.

  17. Direct observation of closed magnetic flux trapped in the high-latitude magnetosphere.

    PubMed

    Fear, R C; Milan, S E; Maggiolo, R; Fazakerley, A N; Dandouras, I; Mende, S B

    2014-12-19

    The structure of Earth's magnetosphere is poorly understood when the interplanetary magnetic field is northward. Under this condition, uncharacteristically energetic plasma is observed in the magnetotail lobes, which is not expected in the textbook model of the magnetosphere. Using satellite observations, we show that these lobe plasma signatures occur on high-latitude magnetic field lines that have been closed by the fundamental plasma process of magnetic reconnection. Previously, it has been suggested that closed flux can become trapped in the lobe and that this plasma-trapping process could explain another poorly understood phenomenon: the presence of auroras at extremely high latitudes, called transpolar arcs. Observations of the aurora at the same time as the lobe plasma signatures reveal the presence of a transpolar arc. The excellent correspondence between the transpolar arc and the trapped closed flux at high altitudes provides very strong evidence of the trapping mechanism as the cause of transpolar arcs. PMID:25525244

  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. High-latitude Poynting flux measured by DMSP satellites during magnetic storms

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Huang, C. Y.; Su, Y. J.

    2014-12-01

    Previous studies have shown strong enhancement of Poynting flux in the polar cap from observations during magnetic storms, which was comparable to or even larger than that in the auroral zones. We investigate the high-latitude Poynting flux enhancement measured by DMSP satellites (F15, F16, F17 and F18) for quiet and main phases of several storm events in this study. The distribution of Poynting Flux enhancement in the polar region is illustrated with a bin size of 2.5 MLAT and 1 hour MLT. Also the horizontal component of ion drift velocity is used to define the Convection Reversal Boundaries (CRBs), which indicate the area of polar cap. The analysis of two storms on August 6, 2011 and September 26, 2011 shows clear enhancement of nightside Poynting flux that is pole-ward of 80 MLAT and well inside CRBs. It is also found that the polar cap can extend equator-ward to 60 MLAT during main phases. Moreover, the track-integrated Poynting flux shows enhancement in both auroral zone and polar cap during main phases, and the Poynting flux in the polar cap can reach above 90% of the total Poynting flux integrated along the track.

  20. The quasi-periodic behavior of recurrent jets caused by emerging magnetic flux

    NASA Astrophysics Data System (ADS)

    Li, H. D.; Jiang, Y. C.; Yang, J. Y.; Bi, Y.; Liang, H. F.

    2015-10-01

    A series of recurring jets occurred at the edge of an active region NOAA 11459 on 2012 April 20, and they were observed simultaneously at EUV and soft X-ray wavelengths. They also were sometimes associated with a hard X-ray source at the base region. The jets might have resulted from magnetic reconnection between the newly emerging flux and the preexisting magnetic field that corresponded to the footpoint region of large-scale coronal loops. We obtained two periods of 171 Å intensity variations at the jet footpoint region, which were about 5 and 13 min. At the jet base, the short and long periodic brightenings might have originated from magneto-acoustic waves and magnetic reconnection. It is plausible that the p-modes might possibly trigger magnetic reconnection, and that reconnection might release stored magnetic energy to produce the jets.

  1. Torsional Alfvén waves in solar magnetic flux tubes of axial symmetry

    NASA Astrophysics Data System (ADS)

    Murawski, K.; Solov'ev, A.; Musielak, Z. E.; Srivastava, A. K.; Kraśkiewicz, J.

    2015-05-01

    Aims: Propagation and energy transfer of torsional Alfvén 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 formulas for the equilibrium mass density and 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 numerically simulate the propagation of nonlinear Alfvén 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, the 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 Alfvén waves, as well as energy transfer to the magnetoacoustic waves that are triggered by the Alfvén waves and are akin to the vertical jet flows. Alfvén waves experience about 5% amplitude reflection at the transition region. Magnetic (velocity) field perturbations that experience attenuation (growth) with height agree with analytical findings. The kinetic energy of magnetoacoustic waves consists of 25% of the total energy of Alfvén waves. The energy transfer may lead to localized mass transport in the form of vertical jets, as well as to localized heating because slow magnetoacoustic waves are prone to dissipation in the inner corona.

  2. Modelling the Initiation of Coronal Mass Ejections by Magnetic Flux Emergence

    NASA Astrophysics Data System (ADS)

    Zuccarello, F. P.; Soenen, A.; Poedts, S.

    2008-09-01

    The possible role of magnetic flux emergence as triggering mechanism for the initiation of Coronal Mass Ejections (CMEs) is studied in the framework of the ideal magnetohydrodynamics (MHD) model. The full MHD equations are solved numerically on a spherical, axisymmetric (2.5D) domain. All simulations are performed with a modified version of the Versatile Advection Code (VAC) (Toth 1996). The magnetic field of the solution is maintained divergence-free at machine precision by exploiting an approach similar to that of Balsara and Spicer (1999): instead of storing the magnetic field components on a staggered mesh, we use the vector potential components in the nodes. In order to get satisfactorily solar wind properties, the Manchester et al. (2004) source term is implemented in the energy equation and gravity is taken into account as well in the model. Finally, a magnetic vector potential is superimposed at the inlet boundary of the Parker wind solution so that, when the steady state is reached, the Antiochos et al. (1999) triple arcade 'break out' magnetic field configuration (symmetric with respect to the equator) of a helmet streamers is obtained. When the steady state has been reached, we impose a magnetic flux emergence at the inlet boundary that is linearly growing in time during a time interval of ? t = 24 hours. After this time the vector potential at the solar base is again fixed. Due to the magnetic flux emergence at the solar base, extra radial magnetic field, is built up near the neutral line of the central arcade that expands outward. This generates an extra upward magnetic pressure force. As a consequence, the central flux system expands outward. Also the overlying field expands and, therefore, the downward magnetic tension increases. As a result, the X-point is flattened. When the distance between the central expanding arcade field and the overlying streamer field is of the order of the grid resolution, the (numerical) reconnection between these fields sets in. A flux rope is formed and, later, accelerated. Height-time and velocity-height plots of the ejected material are produced. The obtained eruption corresponds to a slow CME. The time evolution of the magnetic energy, kinetic energy and internal energy in the entire domain shows that magnetic energy is converted into kinetic energy, as expected. The energy evolution plots show, however, that only a small amount of magnetic energy is released in the system, so that the system evolves to a higher energy state. We think that the explanation of this behavior lies in the role of the magnetic helicity, which we neglected by only emerging radial magnetic field. In conclusion, we stress that by imposing a reasonable (Romano et al. (2007)) flux emergence rate, in a large but realistic active region (with, of course, model dimensionality limitations), quite realistic velocity profiles and energetics of slow CMEs are obtained.

  3. Noise temperature improvement for magnetic fusion plasma millimeter wave imaging systems

    SciTech Connect

    Lai, J.; Domier, C. W.; Luhmann, N. C.

    2014-03-15

    Significant progress has been made in the imaging and visualization of magnetohydrodynamic and microturbulence phenomena in magnetic fusion plasmas [B. Tobias et al., Plasma Fusion Res. 6, 2106042 (2011)]. Of particular importance have been microwave electron cyclotron emission imaging and microwave imaging reflectometry systems for imaging T{sub e} and n{sub e} fluctuations. These instruments have employed heterodyne receiver arrays with Schottky diode mixer elements directly connected to individual antennas. Consequently, the noise temperature has been strongly determined by the conversion loss with typical noise temperatures of ∼60 000 K. However, this can be significantly improved by making use of recent advances in Monolithic Microwave Integrated Circuit chip low noise amplifiers to insert a pre-amplifier in front of the Schottky diode mixer element. In a proof-of-principle design at V-Band (50–75 GHz), significant improvement of noise temperature from the current 60 000 K to measured 4000 K has been obtained.

  4. Development of a low-cost double rotor axial flux motor with soft magnetic composite and ferrite permanent magnet materials

    NASA Astrophysics Data System (ADS)

    Liu, Chengcheng; Zhu, Jianguo; Wang, Youhua; Guo, Youguang; Lei, Gang; Liu, Xiaojing

    2015-05-01

    This paper proposes a low-cost double rotor axial flux motor (DRAFM) with low cost soft magnetic composite (SMC) core and ferrite permanent magnets (PMs). The topology and operating principle of DRAFM and design considerations for best use of magnetic materials are presented. A 905 W 4800 rpm DRAFM is designed for replacing the high cost NdFeB permanent magnet synchronous motor (PMSM) in a refrigerator compressor. By using the finite element method, the electromagnetic parameters and performance of the DRAFM operated under the field oriented control scheme are calculated. Through the analysis, it is shown that that the SMC and ferrite PM materials can be good candidates for low-cost electric motor applications.

  5. Flux jumps in high-J c MgB2 bulks during pulsed field magnetization

    NASA Astrophysics Data System (ADS)

    Fujishiro, H.; Mochizuki, H.; Naito, T.; Ainslie, M. D.; Giunchi, G.

    2016-03-01

    Pulsed field magnetization (PFM) of a high-J c MgB2 bulk disk has been investigated at 20 K, in which flux jumps frequently occur for high pulsed fields. Using a numerical simulation of the PFM procedure, we estimated the time dependence of the local magnetic field and temperature during PFM. We analyzed the electromagnetic and thermal instability of the high-J c MgB2 bulk to avoid flux jumps using the time dependence of the critical thickness, d c(t), which shows the upper safety thickness to stabilize the superconductor magnetically, and the minimum propagation zone length, l m(t), to obtain dynamical stability. The values of d c(t) and l m(t) change along the thermally-stabilized direction with increasing temperature below the critical temperature, T c. However, the flux jump can be qualitatively understood by the local temperature, T(t), which exceeds T c in the bulk. Finally, possible solutions to avoid flux jumps in high-J c MgB2 bulks are discussed.

  6. Twisted versus braided magnetic flux ropes in coronal geometry. I. Construction and relaxation

    NASA Astrophysics Data System (ADS)

    Prior, C.; Yeates, A. R.

    2016-03-01

    We introduce a technique for generating tubular magnetic fields with arbitrary axial geometry and internal topology. As an initial application, this technique is used to construct two magnetic flux ropes that have the same sigmoidal tubular shape, but have different internal structures. One is twisted, the other has a more complex braided magnetic field. The flux ropes are embedded above the photospheric neutral line in a quadrupolar linear force-free background. Using resistive-magnetohydrodynamic simulations, we show that both fields can relax to stable force-free equilibria whilst maintaining their tubular structure. Both end states are nonlinear force-free; the twisted field contains a single sign of alpha (the force-free parameter), indicating a twisted flux rope of a single dominant chirality, the braided field contains both signs of alpha, indicating a flux rope whose internal twisting has both positive and negative chirality. The electric current structures in these final states differ significantly between the braided field, which has a diffuse structure, and the twisted field, which displays a clear sigmoid. This difference might be observable.

  7. Permanent magnet online magnetization performance analysis of a flux mnemonic double salient motor using an improved hysteresis model

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaoyong; Quan, Li; Chen, Yunyun; Liu, Guohai; Shen, Yue; Liu, Hui

    2012-04-01

    The concept of the memory motor is based on the fact that the magnetization level of the AlNiCo permanent magnet in the motor can be regulated by a temporary current pulse and memorized automatically. In this paper, a new type of memory motor is proposed, namely a flux mnemonic double salient motor drive, which is particularly attractive for electric vehicles. To accurately analyze the motor, an improved hysteresis model is employed in the time-stepping finite element method. Both simulation and experimental results are given to verify the validity of the new method.

  8. Two Types of Magnetic Flux Cancellation in the Solar Eruption of 2007 May 20

    NASA Technical Reports Server (NTRS)

    Sterlin, Alphonse C.; Moore, Ronald L.; Mason, Helen

    2010-01-01

    We 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-alpha 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 approximately 10^{21} 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 approximately 1 kilometer per second 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.

  9. Magnetar giant flares in multipolar magnetic fields. II. Flux rope eruptions with current sheets

    SciTech Connect

    Huang, Lei; Yu, Cong E-mail: cyu@ynao.ac.cn

    2014-11-20

    We propose a physical mechanism to explain giant flares and radio afterglows in terms of a magnetospheric model containing both a helically twisted flux rope and a current sheet (CS). With the appearance of a CS, we solve a mixed boundary value problem to get the magnetospheric field based on a domain decomposition method. We investigate properties of the equilibrium curve of the flux rope when the CS is present in background multipolar fields. In response to the variations at the magnetar surface, it quasi-statically evolves in stable equilibrium states. The loss of equilibrium occurs at a critical point and, beyond that point, it erupts catastrophically. New features show up when the CS is considered. In particular, we find two kinds of physical behaviors, i.e., catastrophic state transition and catastrophic escape. Magnetic energy would be released during state transitions. This released magnetic energy is sufficient to drive giant flares, and the flux rope would, therefore, go away from the magnetar quasi-statically, which is inconsistent with the radio afterglow. Fortunately, in the latter case, i.e., the catastrophic escape, the flux rope could escape the magnetar and go to infinity in a dynamical way. This is more consistent with radio afterglow observations of giant flares. We find that the minor radius of the flux rope has important implications for its eruption. Flux ropes with larger minor radii are more prone to erupt. We stress that the CS provides an ideal place for magnetic reconnection, which would further enhance the energy release during eruptions.

  10. Dual-spacecraft reconstruction of a three-dimensional magnetic flux rope at the Earth's magnetopause

    DOE PAGESBeta

    Hasegawa, H.; Sonnerup, B. U. Ö.; Eriksson, S.; Nakamura, T. K. M.; Kawano, H.

    2015-02-03

    We present the first results of a data analysis method, developed by Sonnerup and Hasegawa (2011), for reconstructing three-dimensional (3-D), magnetohydrostatic structures from data taken as two closely spaced satellites traverse the structures. The method is applied to a magnetic flux transfer event (FTE), which was encountered on 27 June 2007 by at least three (TH-C, TH-D, and TH-E) of the five THEMIS probes near the subsolar magnetopause. The FTE was sandwiched between two oppositely directed reconnection jets under a southward interplanetary magnetic field condition, consistent with its generation by multiple X-line reconnection. The recovered 3-D field indicates that amore » magnetic flux rope with a diameter of ~ 3000 km was embedded in the magnetopause. The FTE flux rope had a significant 3-D structure, because the 3-D field reconstructed from the data from TH-C and TH-D (separated by ~ 390 km) better predicts magnetic field variations actually measured along the TH-E path than does the 2-D Grad–Shafranov reconstruction using the data from TH-C (which was closer to TH-E than TH-D and was at ~ 1250 km from TH-E). Such a 3-D nature suggests that the field lines reconnected at the two X-lines on both sides of the flux rope are entangled in a complicated way through their interaction with each other. The generation process of the observed 3-D flux rope is discussed on the basis of the reconstruction results and the pitch-angle distribution of electrons observed in and around the FTE.« less

  11. Dual-spacecraft reconstruction of a three-dimensional magnetic flux rope at the Earth's magnetopause

    SciTech Connect

    Hasegawa, H.; Sonnerup, B. U. Ö.; Eriksson, S.; Nakamura, T. K. M.; Kawano, H.

    2015-02-03

    We present the first results of a data analysis method, developed by Sonnerup and Hasegawa (2011), for reconstructing three-dimensional (3-D), magnetohydrostatic structures from data taken as two closely spaced satellites traverse the structures. The method is applied to a magnetic flux transfer event (FTE), which was encountered on 27 June 2007 by at least three (TH-C, TH-D, and TH-E) of the five THEMIS probes near the subsolar magnetopause. The FTE was sandwiched between two oppositely directed reconnection jets under a southward interplanetary magnetic field condition, consistent with its generation by multiple X-line reconnection. The recovered 3-D field indicates that a magnetic flux rope with a diameter of ~ 3000 km was embedded in the magnetopause. The FTE flux rope had a significant 3-D structure, because the 3-D field reconstructed from the data from TH-C and TH-D (separated by ~ 390 km) better predicts magnetic field variations actually measured along the TH-E path than does the 2-D Grad–Shafranov reconstruction using the data from TH-C (which was closer to TH-E than TH-D and was at ~ 1250 km from TH-E). Such a 3-D nature suggests that the field lines reconnected at the two X-lines on both sides of the flux rope are entangled in a complicated way through their interaction with each other. The generation process of the observed 3-D flux rope is discussed on the basis of the reconstruction results and the pitch-angle distribution of electrons observed in and around the FTE.

  12. Confined partial filament eruption and its reformation within a stable magnetic flux rope

    SciTech Connect

    Joshi, Navin Chandra; Kayshap, Pradeep; Uddin, Wahab; Srivastava, Abhishek K.; Dwivedi, B. N.; Filippov, Boris; Chandra, Ramesh; Choudhary, Debi Prasad E-mail: njoshi98@gmail.com

    2014-05-20

    We present observations of a confined partial eruption of a filament on 2012 August 4, which restores its initial shape within ≈2 hr after eruption. From the Global Oscillation Network Group Hα observations, we find that the filament plasma turns into dynamic motion at around 11:20 UT from the middle part of the filament toward the northwest direction with an average speed of ≈105 km s{sup –1}. A little brightening underneath the filament possibly shows the signature of low-altitude reconnection below the filament eruptive part. In Solar Dynamics Observatory/Atmospheric Imaging Assembly 171 Å images, we observe an activation of right-handed helically twisted magnetic flux rope that contains the filament material and confines it during its dynamical motion. The motion of cool filament plasma stops after traveling a distance of ≈215 Mm toward the northwest from the point of eruption. The plasma moves partly toward the right foot point of the flux rope, while most of the plasma returns after 12:20 UT toward the left foot point with an average speed of ≈60 km s{sup –1} to reform the filament within the same stable magnetic structure. On the basis of the filament internal fine structure and its position relative to the photospheric magnetic fields, we find filament chirality to be sinistral, while the activated enveloping flux rope shows a clear right-handed twist. Thus, this dynamic event is an apparent example of one-to-one correspondence between the filament chirality (sinistral) and the enveloping flux rope helicity (positive). From the coronal magnetic field decay index, n, calculation near the flux rope axis, it is evident that the whole filament axis lies within the domain of stability (i.e., n < 1), which provides the filament stability despite strong disturbances at its eastern foot point.

  13. Noise-Sustained Convective Instability in a Magnetized Taylor-Couette Flow

    SciTech Connect

    W. Liu

    2009-02-20

    The helical magnetorotational instability of the magnetized Taylor-Couette flow is studied numerically in a finite cylinder. A distant upstream insulating boundary is shown to stabilize the convective instability entirely while reducing the growth rate of the absolute instability. The reduction is less severe with larger height. After modeling the boundary conditions properly, the wave patterns observed in the experiment turn out to be a noise-sustained convective instability. After the source of the noise resulted from unstable Ekman and Stewartson layers is switched off, a slowly-decaying inertial oscillation is observed in the simulation. We reach the conclusion that the experiments completed to date have not yet reached the regime of absolute instability.

  14. Noise-sustained convective instability in a magnetized Taylor-Couette flow

    SciTech Connect

    Liu, Wei

    2008-01-01

    The helical magnetorotational instability of the magnetized Taylor-Couette flow is studied numerically in a finite cylinder. A distant upstream insulating boundary is shown to stabilize the convective instability entirely while reducing the growth rate of the absolute instability. The reduction is less severe with larger height. After modeling the boundary conditions properly, the wave patterns observed in the experiment turn out to be a noise-sustained convective instability. After the source of the noise resulted from unstable Ekman and Stewartson layers is switched off, a slowly-decaying inertial oscillation is observed in the simulation. We reach the conclusion that the experiments completed to date have not yet reached the regime of absolute instability.

  15. 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.

  16. Numerical Investigations of Capabilities and Limits of Photospheric Data Driven Magnetic Flux Emergence

    NASA Astrophysics Data System (ADS)

    Linton, Mark; Leake, James; Schuck, Peter W.

    2016-05-01

    The magnetic field of the solar atmosphere is the primary driver of solar activity. Understanding the magnetic state of the solar atmosphere is therefore of key importance to predicting solaractivity. One promising means of studying the magnetic atmosphere is to dynamically build up and evolve this atmosphere from the time evolution of the magnetic field at the photosphere, where it can be measured with current solar vector magnetograms at high temporal and spatial resolution.We report here on a series of numerical experiments investigating the capabilities and limits of magnetohydrodynamical simulations of such a process, where a magnetic corona is dynamically built up and evolved from a time series of synthetic photospheric data. These synthetic data are composed of photospheric slices taken from self consistent convection zone to corona simulations of flux emergence. The driven coronae are then quantitatively compared against the coronae of the original simulations. We investigate and report on the fidelity of these driven simulations, both as a function of the emergence timescale of the magnetic flux, and as a function of the driving cadence of the input data.This work was supported by the Chief of Naval Research and the NASA Living with a Star and Heliophysics Supporting Research programs.

  17. 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.; MartInez Pillet, V.; Bonet, J. A.; Del Toro Iniesta, J. C.; Domingo, V.; Knoelker, M.; Title, A. M.

    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.

  18. Quantum measurement and the Aharonov-Bohm effect with superposed magnetic fluxes

    NASA Astrophysics Data System (ADS)

    Bradonjić, Kaća; Swain, John D.

    2013-10-01

    We consider the magnetic flux in a quantum mechanical superposition of two values and find that the Aharonov-Bohm effect interference pattern contains information about the nature of the superposition, allowing information about the state of the flux to be extracted without disturbance. The information is obtained without transfer of energy or momentum and by accumulated nonlocal interactions of the vector potential \\varvec{A} with many charged particles forming the interference pattern, rather than with a single particle. We suggest an experimental test using already experimentally realized superposed currents in a superconducting ring and discuss broader implications.

  19. 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.

  20. Catastrophe versus instability for the eruption of a toroidal solar magnetic flux rope

    SciTech Connect

    Kliem, B.; Lin, J.; Forbes, T. G.; Priest, E. R.; Török, T.

    2014-07-01

    The onset of a solar eruption is formulated here as either a magnetic catastrophe or as an instability. Both start with the same equation of force balance governing the underlying equilibria. Using a toroidal flux rope in an external bipolar or quadrupolar field as a model for the current-carrying flux, we demonstrate the occurrence of a fold catastrophe by loss of equilibrium for several representative evolutionary sequences in the stable domain of parameter space. We verify that this catastrophe and the torus instability occur at the same point; they are thus equivalent descriptions for the onset condition of solar eruptions.

  1. Are subsurface flows evidence of hidden magnetic flux during cycle minimum?

    NASA Astrophysics Data System (ADS)

    Komm, Rudolf; Howe, Rachel; Hill, Frank

    2016-05-01

    Subsurface flows vary during the course of a solar cycle showing bands of faster- and slower-than-average rotation and bands of converging meridional flow. These flow patterns migrate with latitude; they first appear during the declining phase of a solar cycle and are present during cycle minimum. They appear several years before the magnetic pattern of a new cycle is apparent in synoptic maps and the values of magnetic flux at these locations are comparable to other quiet-Sun locations without such flow patterns. Do the precursory flow patterns thus indicate the presence of magnetic flux that is too small-scale or short-lived to be noticed in synoptic maps? How much flux would be required to generate these flow patterns?We quantify the relationship between subsurface flow patterns and magnetic activity during Cycles 23 and 24 and address these questions. We have analyzed GONG and SDO/HMI Dopplergrams using a dense-pack ring-diagram analysis and determined flows in the near-surface layers of the solar convection zone to a depth of about 16 Mm.

  2. Relationship Between the Magnetic Flux of Solar Eruptions and the Ap Index of Geomagnetic Storms

    NASA Astrophysics Data System (ADS)

    Chertok, I. M.; Abunina, M. A.; Abunin, A. A.; Belov, A. V.; Grechnev, V. V.

    2015-02-01

    Solar coronal mass ejections (CMEs) are the main drivers of the most powerful non-recurrent geomagnetic storms. In the extreme-ultraviolet range, CMEs are accompanied by bright post-eruption arcades and dark dimmings. The analysis of events of Solar Cycle 23 (Chertok et al. in Solar Phys. 282, 175, 2013) revealed that the summarized unsigned magnetic flux in the arcades and dimming regions at the photospheric level, Φ, is significantly related to the intensity (Dst index) of geomagnetic storms. This provides the basis for the earliest diagnostics of geoefficiency of solar eruptions. In the present article, using the same data set, we find that a noticeable correlation also exists between the eruptive magnetic flux, Φ, and another geomagnetic index, Ap. As the magnetic flux increases from some tens to ≈ 500 (in units of 1020 Mx), the geomagnetic storm intensity measured by the three-hour Ap index increases on average from Ap ≈ 50 to a formal upper limit of 400 (in units of 2 nT). The established relationship shows that the real value of the Ap index is not limited and during the most severe magnetic storms may significantly exceed 400.

  3. MODELING OF STOCHASTIC MAGNETIC FLUX LOSS FROM THE EDGE OF A POOIDALLY DIVERTED TOKAMAK

    SciTech Connect

    EVANS, TE,; MOYER, RA; MONAT, P

    2002-06-01

    OAK A271 MODELING OF STOCHASTIC MAGNETIC FLUX LOSS FROM THE EDGE OF A POOIDALLY DIVERTED TOKAMAK. A field line integration code is used to study the loss of edge poloidal magnetic flux due to stochastic magnetic fields produced by an error field correction coil (C-coil) in DIII-D for various plasma shapes, coil currents and edge magnetic shear profiles. The authors find that the boundary of a diverted tokamak is more sensitive to stochastic flux loss than a nondiverted tokamak. The C-coil has been used to produce a stochastic layer in an ohmic diverted discharge with characteristics similar to those seen in stochastic boundary experiments in circular limiter ohmic plasmas, including: (1) an overall increase in recycling, (2) a broadening of the recycling profile at the divertor, and (3) a flattening of the boundary profiles over the extent of the stochastic layer predicted by the field line integration code. Profile flattening consistent with field line integration results is also seen in some high performance discharges with edge transport barriers. The prediction of a significant edge stochastic layer even in discharges with high performance and edge radial transport barriers indicates that either the self-consistent plasma response heals the stochastic layer or that edge stochastic layers are compatible with edge radial transport barriers.

  4. 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.

  5. Magnetar giant flares in multipolar magnetic fields. I. Fully and partially open eruptions of flux ropes

    SciTech Connect

    Huang, Lei; Yu, Cong E-mail: cyu@ynao.ac.cn

    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.

  6. Non-contact main cable NDE technique for suspension bridge using magnetic flux-based B-H loop measurements

    NASA Astrophysics Data System (ADS)

    Park, Seunghee; Kim, Ju-Won; Moon, Dae-Joong

    2015-04-01

    In this study, a noncontact main cable NDE method has been developed. This cable NDE method utilizes the direct current (DC) magnetization and a searching coil-based total flux measurement. A total flux sensor head prototype was fabricated that consists of an electro-magnet yoke and a searching coil sensor. To obtain a B-H loop, a magnetic field was generated by applying a cycle of low frequency direct current to the electro-magnet yoke. During the magnetization, a search coil sensor measures the electromotive force from magnetized cable. During the magnetization process, a search coil sensor was measured the magnetic flux density. Total flux was calculated by integrating the measured magnetic flux using a fluxmeter. A B-H loop is obtained by using relationship between a cycle of input DC voltage and measured total flux. The B-H loop can reflect the property of the ferromagnetic materials. Therefore, the cross-sectional loss of cable can be detected using variation of features from the B-H curve. To verify the feasibility of the proposed steel cable NDE method, a series of experimental studies using a main-cable mock-up specimen has been performed in this study.

  7. Pb/InAs nanowire josephson junction with high critical current and magnetic flux focusing.

    PubMed

    Paajaste, J; Amado, M; Roddaro, S; Bergeret, F S; Ercolani, D; Sorba, L; Giazotto, F

    2015-03-11

    We have studied mesoscopic Josephson junctions formed by highly n-doped InAs nanowires and superconducting Ti/Pb source and drain leads. The current-voltage properties of the system are investigated by varying temperature and external out-of-plane magnetic field. Superconductivity in the Pb electrodes persists up to ∼7 K and with magnetic field values up to 0.4 T. Josephson coupling at zero backgate voltage is observed up to 4.5 K and the critical current is measured to be as high as 615 nA. The supercurrent suppression as a function of the magnetic field reveals a diffraction pattern that is explained by a strong magnetic flux focusing provided by the superconducting electrodes forming the junction. PMID:25671540

  8. The role of the ejecta magnetic flux on the two-step Forbush decreases

    NASA Astrophysics Data System (ADS)

    Masías Meza, Jimmy; Dasso, Sergio

    A Forbush Decrease (FD) is a depression in the Galactic Cosmic Ray (GCR) background intensity, and are usually associated to the passage of an Interplanetary Coronal Mass Ejection (ICME). Magnetic Clouds (MCs) are a subset of ICMEs that are well studied, and are known to cause the deepest FDs. Usually, FDs present two steps in the depression profile, one associated to the shock arrival, and a steeper one restricted to the duration of the ejecta passage. There is a wide variety of processes responsible for the GCR depressions. For instance: the enhanced solar wind (SW) convection, reduced diffusion coefficients, enhanced adiabatic cooling, increase of the coherent magnetic field, etc. Our aim is to make a selection of FD events filtering those associated to well studied magnetic structures, such as Magnetic Clouds (MCs), in order to minimize the mixing processes involved in the ICME-GCR interactions in the resulting sample, and to study statistical properties. We determine the parameters of each FD profile and look for correlations with the associated MC parameters. We propose a method to decompose the FD profile into shock and ejecta components, and investigate correlations with the associated amplitudes of the ejecta components. We introduce the parameter, ``magnetic flux per unit length F/L'', and investigate its importance in the context of a simple ``diffusive barrier'' model. According to the correlations found, the two-step events are better represented by the ``diffusive barrier'' model, and the flux F/L is the parameter that better correlates with these events.

  9. Low temperature X-ray imaging of magnetic flux patterns in high temperature superconductors

    NASA Astrophysics Data System (ADS)

    Stahl, Claudia; Ruoß, Stephen; Weigand, Markus; Bechtel, Michael; Schütz, Gisela; Albrecht, Joachim

    2015-05-01

    We present X-ray magnetic circular dichroism (XMCD) microscopy results obtained at liquid nitrogen temperatures on the high-Tc superconductor YBCO (YBa2Cu3O7-δ). The magnetic flux distribution arising from electric currents in the superconductor is detected and visualized using soft-magnetic Co40Fe40B20 (CoFeB) as sensor layer and XMCD as contrast mechanism. It has been shown that the XMCD contrast in the sensor layer directly corresponds to magnetic flux distribution of the superconductor and hence can be used to image magnetic structures in superconductors [Stahl et al., Phys. Rev. B 90, 104515 (2014)]. The existing scanning UHV X-ray microscopy setup MAXYMUS at the synchrotron BESSY II in Berlin has been upgraded for that purpose: we use a nitrogen based MMR Micro Miniature Joule-Thompson Cryostat with temperature range from 75 K to 580 K. The capability of the method is demonstrated on two different superconducting samples, an optimally doped thin film and a melt-textured block.

  10. Influence of magnetic domain landscape on the flux dynamics in superconductor/ferromagnet bilayers

    NASA Astrophysics Data System (ADS)

    Adamus, Z.; Cieplak, Marta Z.; Kończykowski, M.; Zhu, L. Y.; Chien, C. L.

    2016-02-01

    We use a line of miniature Hall sensors to study the influence of the magnetic domain distribution on the flux dynamics in superconductor/ferromagnet bilayers. Two bilayers are built of a ferromagnetic Co/Pt multilayer with perpendicular magnetic anisotropy and a superconducting Nb layer, with the insulating layer in-between to avoid proximity effect. The magnetic domain patterns of various geometries are reversibly predefined in the Co/Pt multilayers using the appropriate magnetization procedure. The Pt thickness is different in the two bilayers, resulting in different width and length of the domains, which profoundly affects vortex dynamics. We show that narrow short domains lead to strong confinement of vortices at the sample edge, while narrow elongated domains of uniform width induce smaller confinement and easy vortex entry. Large enhancement of flux pinning and critical current density, by a factor of more than 7, is observed in the last case, while the former results in smaller enhancement. When domains are wide, the disorder in the domain widths becomes beneficial for larger enhancement of pinning, while more uniform distribution of domain widths results in a precipitous drop of the enhancement. The analysis of these results suggests that with increasing domain width, a transition occurs from vortex chains pinned by narrow domains to disordered triangular vortex lattice pinned by a maze of multiply interconnected magnetic domains.

  11. 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

  12. Seeding magnetic fields for laser-driven flux compression in high-energy-density plasmas

    NASA Astrophysics Data System (ADS)

    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 Ω) 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.

  13. 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.

  14. Flux Shunts for Temperature Compensation and Tuning in Ferrite Hybrid Permanent Magnets

    NASA Astrophysics Data System (ADS)

    Bertsche, K. J.; Brown, B. C.; Glass, H. D.

    1996-05-01

    When constructing large systems using hybrid permanent magnets, such as the proposed Fermilab Recycler Ring, stringent field strength and strength stability requirements suggest that inovative stabilizing and tuning schemes are useful. Thermal stability limits cannot be easily met with temperature control alone. This is a special concern for magnet structures based on ferrites, which have large temperature coefficients of Br. We will discuss flux shunting temperature compensation in such structures using FeNi alloys. Simple expressions for the material used and spacing required, which apply to useful geometries, will be presented for strength tuning and temperature compensation via flux shunting. Data showing the effectiveness of compensation will be presented. *Operated by Universities Research Association, Inc., under contract with the US. Department of Energy.

  15. Extracting, Tracking, and Visualizing Magnetic Flux Vortices in 3D Complex-Valued Superconductor Simulation Data.

    PubMed

    Guo, Hanqi; Phillips, Carolyn L; Peterka, Tom; Karpeyev, Dmitry; Glatz, Andreas

    2016-01-01

    We propose a method for the vortex extraction and tracking of superconducting magnetic flux vortices for both structured and unstructured mesh data. In the Ginzburg-Landau theory, magnetic flux vortices are well-defined features in a complex-valued order parameter field, and their dynamics determine electromagnetic properties in type-II superconductors. Our method represents each vortex line (a 1D curve embedded in 3D space) as a connected graph extracted from the discretized field in both space and time. For a time-varying discrete dataset, our vortex extraction and tracking method is as accurate as the data discretization. We then apply 3D visualization and 2D event diagrams to the extraction and tracking results to help scientists understand vortex dynamics and macroscale superconductor behavior in greater detail than previously possible. PMID:26529730

  16. A novel double-sided flux-switching permanent magnet linear motor

    NASA Astrophysics Data System (ADS)

    Xiao, Feng; Du, Yi; Sun, Yuxin; Zhu, Huangqiu; Zhao, Wenxiang; Li, Wenlong; Ching, T. W.; Qiu, Chun

    2015-05-01

    This paper proposes a novel double-sided flux-switching permanent magnet (PM) linear (DS-FSPML) motor which is suitable for low speed and high thrust force applications. In order to balance the normal force, the motor adopts double-sided arrangement in which the mover is sandwiched between two stators. The mover teeth alternately located on both sides of the mover are composed of laminated iron core segments between which the axially magnetized PMs of alternate polarity are inserted. Similar to conventional flux-switching PM (FSPM) motor, the 3-phase concentrated windings are employed. And the stator is designed as a double-sided simple iron core with salient teeth so that it is very robust to transmit high thrust force. By using the finite element method, the characteristics and performances of the proposed motor are analyzed and compared with the conventional single-sided FSPM linear motor.

  17. 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.

  18. An axial-flux permanent-magnet generator for a gearless wind energy system

    SciTech Connect

    Chalmers, B.J.; Wu, W.; Spooner, E.

    1999-06-01

    The paper discusses the development of an axial-flux permanent-magnet generator for a gearless wind energy system which aims to demonstrate the feasibility of integrating wind and photovoltaic energy converters for the generation of electricity and to achieve optimum exploitation of the two energy sources. The merits of an axial-flux generator topology are discussed with reference to the particular requirements of an electrical generator for a direct-coupled wind turbine application. The design, construction and test results of a 5 kW, 200 rev/min permanent-magnet generator, to form a 10 kW pilot power plant with a 5 kW photovoltaic array, are presented.

  19. The appearance of magnetic flux on the surfaces of the early main-sequence F stars

    NASA Technical Reports Server (NTRS)

    Giampapa, M. S.; Rosner, R.

    1984-01-01

    Available chromospheric, transition region, and coronal observations of the early main-sequence F stars are examined in order to find that while these objects exhibit enhanced levels of magnetic field-related radiative emissions, significant inhomogeneities in surface activity are not present. This phenomenon is discussed within the context of the calculations published by Schmitt and Rosner (1983) for the production of flux ropes of various spatial scales at a given rotation rate at the bottom of a stellar convection zone. It is found that the spatial scales and area contrast of emergent magnetic flux in these stars that, as a class, are characterized by rapid rotation and thin convection zones are substantially reduced relative to that of the sun.

  20. Basic properties of magnetic flux tubes and restrictions on theories of solar activity

    NASA Technical Reports Server (NTRS)

    Parker, E. N.

    1976-01-01

    It is shown that the mean longitudinal field in a magnetic flux tube is reduced, rather than enhanced, by twisting the tube to form a rope. It is shown that there is no magnetohydrostatic equilibrium when one twisted rope is wound around another. Instead there is rapid line cutting (neutral point annihilation). It is shown that the twisting increases, and the field strength decreases, along a flux tube extending upward through a stratified atmosphere. These facts are at variance with Piddington's (1975) recent suggestion that solar activity is to be understood as the result of flux tubes which are enormously concentrated by twisting, which consist of several twisted ropes wound around each other, and which came untwisted where they emerge through the photosphere.