WorldWideScience

Sample records for current magnetic field

  1. Experimental Study on Current Decay Characteristics of Persistent Current HTS Magnet by Alternating Magnetic Field

    Science.gov (United States)

    Park, Young Gun; Lee, Chang Young; Hwang, Young Jin; Lee, Woo Seung; Lee, Jiho; Jo, Hyun Chul; Chung, Yoon Do; Ko, Tae Kuk

    This paper deals with a current decay characteristics of a high temperature superconducting (HTS) magnet operated in persistent current mode (PCM). In superconducting synchronous machine applications such as linear synchronous motor (LSM), the superconducting coil is designed to operate in the PCM to obtain steady magnetic field with DC transport current. This superconducting magnet operates on a direct current, but it can be exposed to alternating magnetic field due to the armature winding. When the magnet is subjected to an external time-varying magnetic field, it is possible to result in a decay of the current in PCM system due to AC loss. In this research, a PCM system with armature coil which generates time-varying magnetic field was fabricated to verify current decay characteristics by external alternating magnetic field. The current decay rate was measured by using a hall sensor as functions of amplitude and frequency of armature coil.

  2. The effect of Birkeland currents on magnetic field topology

    Science.gov (United States)

    Peroomian, Vahe; Lyons, Larry R.; Schulz, Michael

    1996-01-01

    A technique was developed for the inclusion of large scale magnetospheric current systems in magnetic field models. The region 1 and 2 Birkeland current systems are included in the source surface model of the terrestrial magnetosphere. The region 1 and 2 Birkeland currents are placed in the model using a series of field aligned, infinitely thin wire segments. The normal component of the magnetic field from these currents is calculated on the surface of the magnetopause and shielded using image current carrying wires placed outside of the magnetosphere. It is found that the inclusion of the Birkeland currents in the model results in a northward magnetic field in the near-midnight tail, leading to the closure of previously open flux in the tail, and a southward magnetic field in the flanks. A sunward shift in the separatrix is observed.

  3. Spectral confinement and current for atoms in strong magnetic fields

    DEFF Research Database (Denmark)

    Fournais, Søren

    2007-01-01

    e study confinement of the ground state of atoms in strong magnetic fields to different subspaces related to the lowest Landau band. Using the results on confinement we can calculate the quantum current in the entire semiclassical region B<3......e study confinement of the ground state of atoms in strong magnetic fields to different subspaces related to the lowest Landau band. Using the results on confinement we can calculate the quantum current in the entire semiclassical region B

  4. Streaming current magnetic fields in a charged nanopore

    Science.gov (United States)

    Mansouri, Abraham; Taheri, Peyman; Kostiuk, Larry W.

    2016-11-01

    Magnetic fields induced by currents created in pressure driven flows inside a solid-state charged nanopore were modeled by numerically solving a system of steady state continuum partial differential equations, i.e., Poisson, Nernst-Planck, Ampere and Navier-Stokes equations (PNPANS). This analysis was based on non-dimensional transport governing equations that were scaled using Debye length as the characteristic length scale, and applied to a finite length cylindrical nano-channel. The comparison of numerical and analytical studies shows an excellent agreement and verified the magnetic fields density both inside and outside the nanopore. The radially non-uniform currents resulted in highly non-uniform magnetic fields within the nanopore that decay as 1/r outside the nanopore. It is worth noting that for either streaming currents or streaming potential cases, the maximum magnetic field occurred inside the pore in the vicinity of nanopore wall, as opposed to a cylindrical conductor that carries a steady electric current where the maximum magnetic fields occur at the perimeter of conductor. Based on these results, it is suggested and envisaged that non-invasive external magnetic fields readouts generated by streaming/ionic currents may be viewed as secondary electronic signatures of biomolecules to complement and enhance current DNA nanopore sequencing techniques.

  5. Streaming current magnetic fields in a charged nanopore

    Science.gov (United States)

    Mansouri, Abraham; Taheri, Peyman; Kostiuk, Larry W.

    2016-01-01

    Magnetic fields induced by currents created in pressure driven flows inside a solid-state charged nanopore were modeled by numerically solving a system of steady state continuum partial differential equations, i.e., Poisson, Nernst-Planck, Ampere and Navier-Stokes equations (PNPANS). This analysis was based on non-dimensional transport governing equations that were scaled using Debye length as the characteristic length scale, and applied to a finite length cylindrical nano-channel. The comparison of numerical and analytical studies shows an excellent agreement and verified the magnetic fields density both inside and outside the nanopore. The radially non-uniform currents resulted in highly non-uniform magnetic fields within the nanopore that decay as 1/r outside the nanopore. It is worth noting that for either streaming currents or streaming potential cases, the maximum magnetic field occurred inside the pore in the vicinity of nanopore wall, as opposed to a cylindrical conductor that carries a steady electric current where the maximum magnetic fields occur at the perimeter of conductor. Based on these results, it is suggested and envisaged that non-invasive external magnetic fields readouts generated by streaming/ionic currents may be viewed as secondary electronic signatures of biomolecules to complement and enhance current DNA nanopore sequencing techniques. PMID:27833119

  6. Streaming current magnetic fields in a charged nanopore.

    Science.gov (United States)

    Mansouri, Abraham; Taheri, Peyman; Kostiuk, Larry W

    2016-11-11

    Magnetic fields induced by currents created in pressure driven flows inside a solid-state charged nanopore were modeled by numerically solving a system of steady state continuum partial differential equations, i.e., Poisson, Nernst-Planck, Ampere and Navier-Stokes equations (PNPANS). This analysis was based on non-dimensional transport governing equations that were scaled using Debye length as the characteristic length scale, and applied to a finite length cylindrical nano-channel. The comparison of numerical and analytical studies shows an excellent agreement and verified the magnetic fields density both inside and outside the nanopore. The radially non-uniform currents resulted in highly non-uniform magnetic fields within the nanopore that decay as 1/r outside the nanopore. It is worth noting that for either streaming currents or streaming potential cases, the maximum magnetic field occurred inside the pore in the vicinity of nanopore wall, as opposed to a cylindrical conductor that carries a steady electric current where the maximum magnetic fields occur at the perimeter of conductor. Based on these results, it is suggested and envisaged that non-invasive external magnetic fields readouts generated by streaming/ionic currents may be viewed as secondary electronic signatures of biomolecules to complement and enhance current DNA nanopore sequencing techniques.

  7. Reconfiguring photonic metamaterials with currents and magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Valente, João, E-mail: jpv1f11@orc.soton.ac.uk; Ou, Jun-Yu; Plum, Eric, E-mail: erp@orc.soton.ac.uk [Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton, Southampton SO17 1BJ (United Kingdom); Youngs, Ian J. [Physical Sciences Department, DSTL, Salisbury SP4 0JQ (United Kingdom); Zheludev, Nikolay I., E-mail: niz@orc.soton.ac.uk [Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton, Southampton SO17 1BJ (United Kingdom); Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore 637378 (Singapore)

    2015-03-16

    We demonstrate that spatial arrangement and optical properties of metamaterial nanostructures can be controlled dynamically using currents and magnetic fields. Mechanical deformation of metamaterial arrays is driven by both resistive heating of bimorph nanostructures and the Lorentz force that acts on charges moving in a magnetic field. With electrically controlled transmission changes of up to 50% at sub-mW power levels, our approaches offer high contrast solutions for dynamic control of metamaterial functionalities in optoelectronic devices.

  8. Morphology of the ring current derived from magnetic field observations

    Directory of Open Access Journals (Sweden)

    G. Le

    2004-04-01

    Full Text Available Our examination of the 20 years of magnetospheric magnetic field data from ISEE, AMPTE/CCE and Polar missions has allowed us to quantify how the ring current flows and closes in the magnetosphere at a variety of disturbance levels. Using intercalibrated magnetic field data from the three spacecraft, we are able to construct the statistical magnetic field maps and derive 3-dimensional current density by the simple device of taking the curl of the statistically determined magnetic field. The results show that there are two ring currents, an inner one that flows eastward at ~3 RE and a main westward ring current at ~4–7 RE for all levels of geomagnetic disturbances. In general, the in-situ observations show that the ring current varies as the Dst index decreases, as we would expect it to change. An unexpected result is how asymmetric it is in local time. Some current clearly circles the magnetosphere but much of the energetic plasma stays in the night hemisphere. These energetic particles appear not to be able to readily convect into the dayside magnetosphere. During quiet times, the symmetric and partial ring currents are similar in strength (~0.5MA and the peak of the westward ring current is close to local midnight. It is the partial ring current that exhibits most drastic intensification as the level of disturbances increases. Under the condition of moderate magnetic storms, the total partial ring current reaches ~3MA, whereas the total symmetric ring current is ~1MA. Thus, the partial ring current contributes dominantly to the decrease in the Dst index. As the ring current strengthens the peak of the partial ring current shifts duskward to the pre-midnight sector. The partial ring current is closed by a meridional current system through the ionosphere, mainly the field-aligned current, which maximizes at local times near the dawn and dusk. The closure currents flow in

  9. Magnetic guide field generation in collisionless current sheets

    Directory of Open Access Journals (Sweden)

    W. Baumjohann

    2010-03-01

    Full Text Available In thin (Δ< few λi collisionless current sheets in a space plasma like the magnetospheric tail or magnetopause current layer, magnetic fields can grow from thermal fluctuation level by the action of the non-magnetic Weibel instability (Weibel, 1959. The instability is driven by the counter-streaming electron inflow from the "ion diffusion" (ion inertial Hall region into the inner current (electron inertial region after thermalisation by the two-stream instability. Under magnetospheric tail conditions it takes ~50 e-folding times (~100 s for the Weibel field to reach observable amplitudes |bW|~1 nT. In counter-streaming inflows these fields are of guide field type.

  10. Stray Field Reduction in ALS Eddy Current Septum Magnets

    CERN Document Server

    Shuman, Derek; Prestemon, Soren; Schlüter, Ross D; Steier, Christoph; Stover, Gregory D

    2005-01-01

    Stray field from an eddy current septum magnet adversely affects the circulating beam and can be reduced using several techniques. The stray field time history typically has a fast rise section followed by a long exponential decay section when pulsed with a half sine drive current. Changing the drive current pulse to a full sine has the effect of both reducing peak stray field magnitude by ~3x, and producing a quick decay from this peak to a lower field level which then has a similar long decay time constant as that from the half sine only drive current pulse. A method for tuning the second half sine (reverse) drive current pulse to eliminate the long exponential decay section is given.

  11. A current limiter with superconducting coil for magnetic field shielding

    Science.gov (United States)

    Kaiho, K.; Yamaguchi, H.; Arai, K.; Umeda, M.; Yamaguchi, M.; Kataoka, T.

    2001-05-01

    The magnetic shield type superconducting fault current limiter have been built and successfully tested in ABB corporate research and so on. The device is essentially a transformer in which the secondary winding is the superconducting tube. However, due to the large AC losses and brittleness of the superconducting bulk tube, they have not yet entered market. A current limiter with superconducting coil for the magnetic field shielding is considered. By using the superconducting coil made by the multi-filamentary high Tc superconductor instead of the superconducting bulk tube, the AC losses can be reduced due to the reduced superconductor thickness and the brittleness of the bulk tube can be avoidable. This paper presents a preliminary consideration of the magnetic shield type superconducting fault current limiter with superconducting coil as secondary winding and their AC losses in comparison to that of superconducting bulk in 50 Hz operation.

  12. Formation of current filaments and magnetic field generation in a quantum current-carrying plasma

    Energy Technology Data Exchange (ETDEWEB)

    Niknam, A. R. [Laser and Plasma Research Institute, Shahid Beheshti University, G.C., Tehran (Iran, Islamic Republic of); Taghadosi, M. R.; Majedi, S.; Khorashadizadeh, S. M. [Physics Department, University of Birjand, Birjand (Iran, Islamic Republic of)

    2013-09-15

    The nonlinear dynamics of filamentation instability and magnetic field in a current-carrying plasma is investigated in the presence of quantum effects using the quantum hydrodynamic model. A new nonlinear partial differential equation is obtained for the spatiotemporal evolution of the magnetic field in the diffusion regime. This equation is solved by applying the Adomian decomposition method, and then the profiles of magnetic field and electron density are plotted. It is shown that the saturation time of filamentation instability increases and, consequently, the instability growth rate and the magnetic field amplitude decrease in the presence of quantum effects.

  13. Modified pulsar current analysis: probing magnetic field evolution

    CERN Document Server

    Igoshev, A P

    2014-01-01

    We use a modified pulsar current analysis to study magnetic field decay in radio pulsars. In our approach we analyse the flow, not along the spin period axis as has been performed in previous studies, but study the flow along the direction of growing characteristic age, $\\tau=P/(2\\dot P)$. We perform extensive tests of the method and find that in most of the cases it is able to uncover non-negligible magnetic field decay (more than a few tens of per cent during the studied range of ages) in normal radio pulsars for realistic initial properties of neutron stars. However, precise determination of the magnetic field decay timescale is not possible at present. The estimated timescale may differ by a factor of few for different sets of initial distributions of neutron star parameters. In addition, some combinations of initial distributions and/or selection effects can also mimic enhanced field decay. We apply our method to the observed sample of radio pulsars at distances $<10$ kpc in the range of characteristi...

  14. Modeling the current distribution in HTS tapes with transport current and applied magnetic field

    NARCIS (Netherlands)

    Yazawa, Takashi; Rabbers, Jan-Jaap; Shevchenko, Oleg A.; Haken, ten Bennie; Kate, ten Herman H.J.; Maeda, Hideaki

    1999-01-01

    A numerical model is developed for the current distribution in a high temperature superconducting (HTS) tape, (Bi,Pb)2Sr2 Ca2Cu3Ox-Ag, subjected to a combination of a transport current and an applied magnetic field. This analysis is based on a two-dimensional formulation of Maxwell's equations in te

  15. Relation between magnetic fields and electric currents in plasmas

    Directory of Open Access Journals (Sweden)

    V. M. Vasyliunas

    2005-10-01

    Full Text Available Maxwell's equations allow the magnetic field B to be calculated if the electric current density J is assumed to be completely known as a function of space and time. The charged particles that constitute the current, however, are subject to Newton's laws as well, and J can be changed by forces acting on charged particles. Particularly in plasmas, where the concentration of charged particles is high, the effect of the electromagnetic field calculated from a given J on J itself cannot be ignored. Whereas in ordinary laboratory physics one is accustomed to take J as primary and B as derived from J, it is often asserted that in plasmas B should be viewed as primary and J as derived from B simply as (c/4π∇×B. Here I investigate the relation between ∇×B and J in the same terms and by the same method as previously applied to the MHD relation between the electric field and the plasma bulk flow vmv2001: assume that one but not the other is present initially, and calculate what happens. The result is that, for configurations with spatial scales much larger than the electron inertial length λe, a given ∇×B produces the corresponding J, while a given J does not produce any ∇×B but disappears instead. The reason for this can be understood by noting that ∇×B≠4π/cJ implies a time-varying electric field (displacement current which acts to change both terms (in order to bring them toward equality; the changes in the two terms, however, proceed on different time scales, light travel time for B and electron plasma period for J, and clearly the term changing much more slowly is the one that survives. (By definition, the two time scales are equal at λe. On larger scales, the evolution of B (and hence also of ∇×B is governed by

  16. The effect of toroidal field on the rotating magnetic field current drive in rotamak plasmas

    Institute of Scientific and Technical Information of China (English)

    Zhong Fang-Chuan; Huang Tian-Sen; Petrov Yuri

    2007-01-01

    A rotamak is one kind of compact spherically shaped magnetic-confinement device. In a rotamak the plasma current is driven by means of rotating magnetic field (RMF). The driven current can reverse the original equilibrium field and generate a field-reversed-configuration. In a conventional rotamak, a toroidal field (TF) is not necessary for the RMF to drive plasma current, but it was found that the present of an additional TF can influence the RMF current drive. In this paper the effect of TF on the RMF current drive in a rotamak are investigated in some detail.The experimental results show that addition of TF increases the RMF driven current greatly and enhances the RMF penetration dramatically. Without TF, the RMF can only penetrate into plasma in the edge region. When a TF is added, the RMF can reach almost the whole plasma region. This is an optimal strength of toroidal magnetic field for getting maximum plasma current when Bv and radio frequency generator power are fixed. Besides driving current,the RMF generates high harmonic fields in rotamak plasma. The effect of TF on the harmonic field spectra are also reported.

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

    Science.gov (United States)

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

    2017-01-01

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

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

    Science.gov (United States)

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

    2017-02-23

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

  19. Current induced perpendicular-magnetic-anisotropy racetrack memory with magnetic field assistance

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Y.; Klein, J.-O.; Chappert, C.; Ravelosona, D. [IEF, University of Paris-Sud, Orsay 91405 (France); UMR8622, CNRS, Orsay 91405 (France); Zhao, W. S., E-mail: weisheng.zhao@u-psud.fr [IEF, University of Paris-Sud, Orsay 91405 (France); UMR8622, CNRS, Orsay 91405 (France); Electronics and Information Engineering School, University of Beihang, Beijing 100191 (China)

    2014-01-20

    High current density is indispensable to shift domain walls (DWs) in magnetic nanowires, which limits the using of racetrack memory (RM) for low power and high density purposes. In this paper, we present perpendicular-magnetic-anisotropy (PMA) Co/Ni RM with global magnetic field assistance, which lowers the current density for DW motion. By using a compact model of PMA RM and 40 nm design kit, we perform mixed simulation to validate the functionality of this structure and analyze its density potential. Stochastic DW motion behavior has been taken into account and statistical Monte-Carlo simulations are carried out to evaluate its reliability performance.

  20. Methods of high current magnetic field generator for transcranial magnetic stimulation application

    Science.gov (United States)

    Bouda, N. R.; Pritchard, J.; Weber, R. J.; Mina, M.

    2015-05-01

    This paper describes the design procedures and underlying concepts of a novel High Current Magnetic Field Generator (HCMFG) with adjustable pulse width for transcranial magnetic stimulation applications. This is achieved by utilizing two different switching devices, the MOSFET and insulated gate bipolar transistor (IGBT). Results indicate that currents as high as ±1200 A can be generated with inputs of +/-20 V. Special attention to tradeoffs between field generators utilizing IGBT circuits (HCMFG1) and MOSFET circuits (HCMFG2) was considered. The theory of operation, design, experimental results, and electronic setup are presented and analyzed.

  1. Methods of high current magnetic field generator for transcranial magnetic stimulation application

    Energy Technology Data Exchange (ETDEWEB)

    Bouda, N. R., E-mail: nybouda@iastate.edu; Pritchard, J.; Weber, R. J.; Mina, M. [Department of Electrical and Computer engineering, Iowa State University, Ames, Iowa 50011 (United States)

    2015-05-07

    This paper describes the design procedures and underlying concepts of a novel High Current Magnetic Field Generator (HCMFG) with adjustable pulse width for transcranial magnetic stimulation applications. This is achieved by utilizing two different switching devices, the MOSFET and insulated gate bipolar transistor (IGBT). Results indicate that currents as high as ±1200 A can be generated with inputs of +/−20 V. Special attention to tradeoffs between field generators utilizing IGBT circuits (HCMFG{sub 1}) and MOSFET circuits (HCMFG{sub 2}) was considered. The theory of operation, design, experimental results, and electronic setup are presented and analyzed.

  2. Development of electric currents in a magnetic field configuration containing a magnetic null point

    Science.gov (United States)

    Santos, J. C.; Büchner, J.; Otto, A.

    2011-01-01

    Context. In the past the role of magnetic null points in the generation of electric currents was investigated mainly in the close vicinity of the null, with perturbations being applied at nearby boundaries, or for a magnetic null configuration with a dome-shaped fan. In the solar atmosphere, however, electric currents are generated by perturbations originating at the photosphere, far away from coronal 3D nulls, and the occurence of magnetic nulls with a dome-shaped fan is apparently not common. Aims: We investigate the consequences of photospheric motion for the development of electric currents in a coronal magnetic field configuration containing a null, located far away from the boundaries, and the influence of topological structures on the spatial distribution of the currents. Methods: We use a 3D resistive MHD code to investigate the consequences of photospheric plasma motion for the generation of currents in a coronal magnetic field containing a null. The plasma is considered fully compressible and is initially in hydrostatic equilibrium. The initial magnetic field is potential (current free). Results: The photospheric plasma motion causes magnetic field perturbations that propagate to the corona along the field lines at the local Alfvén speed. The Alfvénic wave perturbations correspond to a propagating current directed mainly parallel to the magnetic field. Perpendicular currents connect to return currents to close the current system. The magnetic perturbations eventually reach the vicinity of the null. However, the currents forming in and around the null, near the fan surface or near the spine field lines, are not always the strongest currents developing in the simulation box. In our simulation, the strongest currents develop close to the bottom boundary, where the plasma is moved, and below the null point, in a region where field line connectivity considerably changes. Conclusions: Our simulation shows that the presence of a magnetic null point does not

  3. Low-noise pulsed current source for magnetic-field measurements of magnets for accelerators

    Science.gov (United States)

    Omelyanenko, M. M.; Borisov, V. V.; Donyagin, A. M.; Khodzhibagiyan, H. G.; Kostromin, S. A.; Makarov, A. A.; Shemchuk, A. V.

    2017-01-01

    The schematic diagram, design, and technical characteristics of the pulsed current source developed and produced for the magnetic-field measurement system of superconducting magnets for accelerators are described. The current source is based on the current regulator with pass transistor bank in the linear mode. Output current pulses (0-100 A) are produced by utilizing the energy of the preliminarily charged capacitor bank (5-40 V), which is additionally charged between pulses. The output current does not have the mains frequency and harmonics ripple. The relative noise level is less than-100 dB (or 10-5) of RMS value (it is defined as the ratio of output RMS noise current to a maximal output current of 100 A within the operating bandwidth, expressed in dB). The work was performed at the Veksler and Baldin Laboratory of High Energy Physics, Joint Institute for Nuclear Research (JINR).

  4. Spontaneous current sheets in magnetic fields with applications to stellar X-rays

    CERN Document Server

    Parker, Eugene N

    1994-01-01

    Expanding upon the ideas first proposed in his seminal book Cosmical Magnetic Fields, Eugene N. Parker here offers the first in-depth treatment of the magnetohydrodynamic theory of spontaneous magnetic discontinuities. In detailing his theory of the spontaneous formation of tangential discontinuities (current sheets) in a magnetic field embedded in highly conducting plasma, Parker shows how it can be used to explain the activity of the external magnetic fields of planets, stars, interstellar gas clouds, and galaxies, as well as the magnetic fields in laboratory plasmas. Provocative and fascinating, Spontaneous Current Sheets in Magnetic Fields presents a bold new theory that will excite interest and discussion throughout the space physics community.

  5. Current and Future Constraints on Primordial Magnetic Fields

    Science.gov (United States)

    Sutton, Dylan R.; Feng, Chang; Reichardt, Christian L.

    2017-09-01

    We present new limits on the amplitude of potential primordial magnetic fields (PMFs) using temperature and polarization measurements of the cosmic microwave background (CMB) from Planck, the BICEP2/Keck Array, Polarbear, and SPTpol. We reduce twofold the 95% confidence upper limit on the CMB anisotropy power due to a nearly scale-invariant PMF, with an allowed B-mode power at ℓ = 1500 of {D}{\\ell =1500}{BB}< 0.071 μ {K}2 for Planck versus {D}{\\ell =1500}{BB}< 0.034 μ {K}2 for the combined data set. We also forecast the expected limits from soon-to-deploy CMB experiments (like SPT-3G, Adv. ACTpol, or the Simons Array) and the proposed CMB-S4 experiment. Future CMB experiments should dramatically reduce the current uncertainties by one order of magnitude for the near-term experiments and two orders of magnitude for the CMB-S4 experiment. The constraints from CMB-S4 have the potential to rule out much of the parameter space for PMFs.

  6. Non-invasively measured cardiac magnetic field maps improve the estimation of the current distribution

    OpenAIRE

    Kosch, Olaf; Steinhoff, Uwe; Trahms, Lutz; Trontelj, Zvonko; Jazbinšek, Vojko

    2015-01-01

    Comprehensive body surface potential mapping (BSPM) and magnetic field mapping (MFM) measurements have been carried out in order to improve the estimation of the current distribution generated by the human heart. Electric and magnetic fields and also the planar gradient of the magnetic field during the QRS complex were imaged as a time series of field maps. A model of the current distribution should explain the features of both BSPM and MFM. Simulated maps generated by a single dipole or a st...

  7. Behavior of magnetic field and eddy current in a magnetostriction based bi-layered composite

    Directory of Open Access Journals (Sweden)

    Kewei Zhang

    2016-12-01

    Full Text Available In this paper, we presented a theoretical method for studying the behavior of magnetic field intensity and eddy current inside a magnetostriction based bi-layered composite. Firstly, the mathematical model for the electromagnetic field in the composite was established. Then, the governing equation for determining the magnetic field intensity and eddy current was solved. Furthermore, the effect of the composite’s conductivity on the magnetic field intensity and eddy current were discussed. Lastly, by comparing with the well known R.L. Stoll’s equation, the magnetic field intensity calculated based on our equation showed a less than 0.5% error.

  8. Behavior of magnetic field and eddy current in a magnetostriction based bi-layered composite

    Science.gov (United States)

    Zhang, Kewei; Zhang, Kehao; Liu, Huifeng; Li, Junlin

    2016-12-01

    In this paper, we presented a theoretical method for studying the behavior of magnetic field intensity and eddy current inside a magnetostriction based bi-layered composite. Firstly, the mathematical model for the electromagnetic field in the composite was established. Then, the governing equation for determining the magnetic field intensity and eddy current was solved. Furthermore, the effect of the composite's conductivity on the magnetic field intensity and eddy current were discussed. Lastly, by comparing with the well known R.L. Stoll's equation, the magnetic field intensity calculated based on our equation showed a less than 0.5% error.

  9. Contribution of the Magnetic Field of Eddy Currents to the Gilbert Damping Parameter

    Directory of Open Access Journals (Sweden)

    S.I. Denisov

    2014-06-01

    Full Text Available We study the role of the magnetic field of eddy currents, which are induced in conducting single-domain particles of spherical form, in the magnetization dynamics. To describe the dynamic behavior of magnetization and electromagnetic field generating by the time-dependent magnetization, we use the coupled system of the Landau-Lifshitz-Gilbert (LLG and Maxwell equations. Assuming that the magnetization direction depends on time in an arbitrary way, we find the solution of the Maxwell equations in the quasi-stationary approximation and calculate the averaged (over the particle volume magnetic field of eddy currents. Considering this field as an extra contribution to the effective magnetic field acting on the particle magnetic moment, we derive the LLG equation in which the influence of eddy currents is completely accounted for by introducing an additional Gilbert damping parameter of electrodynamic origin.

  10. Magnetic Field

    DEFF Research Database (Denmark)

    Olsen, Nils

    2015-01-01

    of the fluid flow at the top of the core. However, what is measured at or near the surface of the Earth is the superposition of the core field and fields caused by magnetized rocks in the Earth’s crust, by electric currents flowing in the ionosphere, magnetosphere, and oceans, and by currents induced......he Earth has a large and complicated magnetic field, the major part of which is produced by a self-sustaining dynamo operating in the fluid outer core. Magnetic field observations provide one of the few tools for remote sensing the Earth’s deep interior, especially regarding the dynamics...... in the Earth by time-varying external fields. These sources have their specific characteristics in terms of spatial and temporal variations, and their proper separation, based on magnetic measurements, is a major challenge. Such a separation is a prerequisite for remote sensing by means of magnetic field...

  11. Magnetic Field Dependence of the Critical Current in S-N Bilayer Thin Films

    Science.gov (United States)

    Sadleir, John E.; Lee, Sang-Jun; Smith, Stephen James; Bandler, Simon; Chervenak, James; Kilbourne, Caroline A.; Finkbeiner, Fred M.; Porter, Frederick S.; Kelley, Richard L.; Adams, Joseph S.; Eckart, Megan E.; Busch, Sarah; Porst, Jan-Patrick

    2013-01-01

    Here we investigate the effects a non-uniform applied magnetic field has on superconducting transition-edge sensors (TESs) critical current. This has implications on TES optimization. It has been shown that TESs resistive transition can be altered by magnetic fields. We have observed critical current rectification effects and explained these effects in terms of a magnetic self-field arising from asymmetric current injection into the sensor. Our TES physical model shows that this magnetic self-field can result in significantly degraded or improved TES performance. In order for this magnetically tuned TES strategy to reach its full potential we are investigating the effect a non-uniform applied magnetic field has on the critical current.

  12. Principal physics of rotating magnetic-field current drive of field reversed configurations

    Science.gov (United States)

    Hoffman, A. L.; Guo, H. Y.; Miller, K. E.; Milroy, R. D.

    2006-01-01

    After extensive experimentation on the Translation, Confinement, and Sustainment rotating magnetic-field (RMF)-driven field reversed configuration (FRC) device [A. L. Hoffman et al., Fusion Sci. Technol. 41, 92 (2002)], the principal physics of RMF formation and sustainment of standard prolate FRCs inside a flux conserver is reasonably well understood. If the RMF magnitude Bω at a given frequency ω is high enough compared to other experimental parameters, it will drive the outer electrons of a plasma column into near synchronous rotation, allowing the RMF to penetrate into the plasma. If the resultant azimuthal current is strong enough to reverse an initial axial bias field Bo a FRC will be formed. A balance between the RMF applied torque and electron-ion friction will determine the peak plasma density nm∝Bω/η1/2ω1/2rs, where rs is the FRC separatrix radius and η is an effective weighted plasma resistivity. The plasma total temperature Tt is free to be any value allowed by power balance as long as the ratio of FRC diamagnetic current, I'dia≈2Be/μo, is less than the maximum possible synchronous current, I'sync=⟨ne⟩eωrs2/2. The RMF will self-consistently penetrate a distance δ* governed by the ratio ζ =I'dia/I'sync. Since the FRC is a diamagnetic entity, its peak pressure pm=nmkTt determines its external magnetic field Be≈(2μopm)1/2. Higher FRC currents, magnetic fields, and poloidal fluxes can thus be obtained, with the same RMF parameters, simply by raising the plasma temperature. Higher temperatures have also been noted to reduce the effective plasma resistivity, so that these higher currents can be supported with surprisingly little increase in absorbed RMF power.

  13. Anomalous current pinch of a toroidal axisymmetric plasma with stochastic magnetic field perturbations

    Science.gov (United States)

    Wang, Shaojie

    2016-07-01

    Anomalous current pinch, in addition to the anomalous diffusion due to stochastic magnetic perturbations, is theoretically found, which may qualitatively explain the recent DIII-D experiment on resonant magnetic field perturbation. The anomalous current pinch, which may resolve the long-standing issue of seed current in a fully bootstrapped tokamak, is also discussed for the electrostatic turbulence.

  14. Effect of the magnetic material on AC losses in HTS conductors in AC magnetic field carrying AC transport current

    Science.gov (United States)

    Wan, Xing-Xing; Huang, Chen-Guang; Yong, Hua-Dong; Zhou, You-He

    2015-11-01

    This paper presents an investigation on the AC losses in several typical superconducting composite conductors using the H-formulation model. A single superconducting strip with ferromagnetic substrate or cores and a stack of coated conductors with ferromagnetic substrates are studied. We consider all the coated conductors carrying AC transport currents and simultaneously exposed to perpendicular AC magnetic fields. The influences of the amplitude, frequency, phase difference and ferromagnetic materials on the AC losses are investigated. The results show that the magnetization losses of single strip and stacked strips have similar characteristics. The ferromagnetic substrate can increase the magnetization loss at low magnetic field, and decrease the loss at high magnetic field. The ferromagnetic substrate can obviously increase the transport loss in stacked strips. The trends of total AC losses of single strip and stacked strips are similar when they are carrying current or exposed to a perpendicular magnetic field. The effect of the frequency on the total AC losses of single strip is related to the amplitude of magnetic field. The AC losses decrease with increasing frequency in low magnetic field region while increase in high magnetic field region. As the phase difference changes, there is a periodic variation for the AC losses. Moreover, when the strip is under only the transport current and magnetic field, the ferromagnetic cores will increase the AC losses for large transport current or field.

  15. Magnetic Field Equivalent Current Analysis-Based Radial Force Control for Bearingless Permanent Magnet Synchronous Motors

    Directory of Open Access Journals (Sweden)

    Huangqiu Zhu

    2015-05-01

    Full Text Available Bearingless permanent magnet synchronous motors (BPMSMs, with all advantages of permanent magnet motors (PMSMs and magnetic bearings, have become an important research direction in the bearingless motor field. To realize a stable suspension for the BPMSM, accurate decoupling control between the electromagnetic torque and radial suspension force is indispensable. In this paper, a concise and reliable analysis method based on a magnetic field equivalent current is presented. By this analysis method, the operation principle is analyzed theoretically, and the necessary conditions to produce a stable radial suspension force are confirmed. In addition, mathematical models of the torque and radial suspension force are established which is verified by the finite element analysis (FEA software ANSYS. Finally, an experimental prototype of a 2-4 poles surface-mounted BPMSM is tested with the customized control strategy. The simulation and experimental results have shown that the motor has good rotation and suspension performance, and validated the accuracy of the proposed analysis method and the feasibility of the control strategy.

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

    OpenAIRE

    J P Silva; Silvestre, A. J.

    2006-01-01

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

  17. Potential Magnetic Field around a Helical Flux-rope Current Structure in the Solar Corona

    CERN Document Server

    Petrie, G J D

    2007-01-01

    We consider the potential magnetic field associated with a helical electric line current flow, idealizing the near-potential coronal field within which a highly localized twisted current structure is embedded. It is found that this field has a significant axial component off the helical magnetic axis where there is no current flow, such that the flux winds around the axis. The helical line current field, in including the effects of flux rope writhe, is therefore more topologically complex than straight line and ring current fields sometimes used in solar flux rope models. The axial flux in magnetic fields around confined current structures may be affected by the writhe of these current structures such that the field twists preferentially with the same handedness as the writhe. This property of fields around confined current structures with writhe may be relevant to classes of coronal magnetic flux rope, including structures observed to have sigmoidal forms in soft X-rays and prominence magnetic fields. For ex...

  18. Reconstruction of conductivity and current density images using only one component of magnetic field measurements.

    Science.gov (United States)

    Seo, Jin Keun; Yoon, Jeong-Rock; Woo, Eung Je; Kwon, Ohin

    2003-09-01

    Magnetic resonance current density imaging (MRCDI) is to provide current density images of a subject using a magnetic resonance imaging (MRI) scanner with a current injection apparatus. The injection current generates a magnetic field that we can measure from MR phase images. We obtain internal current density images from the measured magnetic flux densities via Ampere's law. However, we must rotate the subject to acquire all of the three components of the induced magnetic flux density. This subject rotation is impractical in clinical MRI scanners when the subject is a human body. In this paper, we propose a way to eliminate the requirement of subject rotation by careful mathematical analysis of the MRCDI problem. In our new MRCDI technique, we need to measure only one component of the induced magnetic flux density and reconstruct both cross-sectional conductivity and current density images without any subject rotation.

  19. Currents, magnetization and AC-losses of YBa 2Cu 3O 7 superconductors in rapidly changing magnetic fields

    Science.gov (United States)

    Kwasnitza, K.; Plotzner, V.; Waldmann, M.; Widmer, E.

    1988-06-01

    In YBa 2Cu 3O 7 samples of different shape time dependent magnetization currents were induced at 4.2K by the application of rapid magnetic field changes. This contactless method allows the study of the intergrain and intragrain currents in the resistive flux flow state.

  20. The field line topology of a uniform magnetic field superposed on the field of a distributed ring current

    Energy Technology Data Exchange (ETDEWEB)

    Chance, M.S. (Princeton Univ., NJ (USA). Plasma Physics Lab.); Greene, J.M.; Jensen, T.H. (General Atomics, San Diego, CA (USA))

    1991-07-01

    A magnetic field line topology with nulls, generated by superimposing a uniform magnetic field onto the field from a distributed ring current, is analyzed. This simple model is amenable to substantial analytical progress and also facilitates the visualization of the three dimensional field geometry. Four nulls are seen to exist and representative field lines and tubes of flux found by numerical integration are presented. An infinite number of topologically distinct flux bundles is found. A convenient mapping is defined which proves very useful in distinguishing between and following the paths of the different tubes of flux as they traverse through the null system. The complexities already present in this simple but nontrivial configuration serve to emphasize the difficulties in analyzing more complicated geometries, but the intuition gained from this study proves beneficial in those cases. One such example is the application to a model of plasmoid formations in the earth's magnetotail. 7 refs., 19 figs.

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

    Science.gov (United States)

    G, Ravi; Goyal, Vidhi

    2012-10-01

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

  2. Numerical calculation of superheating magnetic fields and currents for superconducting slabs

    Science.gov (United States)

    Landau, I. L.; Rinderer, L.

    1995-08-01

    Numerical calculations of superheating magnetic fields and superheating currents for superconducting slabs for a wide range of the sample thickness are presented. The calculations were made for low values of Ginzburg-Landau parameter κ, i.e., for type-1 superconductors. We propose also experimental procedures to measure superheating fields and currents in films and bulk samples.

  3. Experimental Measurement of Asymmetric Fluctuations of Poloidal Magnetic Field in Damavand Tokomak at Different Plasma Currents

    Science.gov (United States)

    Moslehi-Fard, Mahmoud; Alinejad, Naser; Rasouli, Chapar; Sadigzadeh, Asghar

    2012-08-01

    Toroidal and Poloidal magnetic fields have an important effect on the tokomak topology. Damavand Tokomak is a small size tokomak characterized with k = 1.2, B t = 1T, R 0 = 36 cm, maximum plasma current is about 35 KA with a discharge time of 21 ms. In this experimental work, the variation of poloidal magnetic field on the torodial cross section is measured and analyzed. In order to measure the polodial magnetic field, 18 probes were installed on the edge of tokomak plasma with ∆θ = 18°, while a limiter was installed inside the torus. Plasma current, I p, induces a polodial magnetic field, B p, smaller than the torodial magnetic field B t. Magnetic lines B produced as a combination of B t and B p, are localized on the nested toroidal magnetic surfaces. The presence of polodial magnetic field is necessary for particles confinement. Mirnov oscillations are the fluctuations of polodial magnetic field, detected by magnetic probes. Disrupted instability in Tokomak typically starts with mirnov oscillations which appear as fluctuations of polodial magnetic field and is detected by magnetic probes. Minor disruptions inside the plasma can contain principal magnetic islands and their satellites can cause the annihilation of plasma confinement. Production of thin layer of turbulent magnetic field lines cause minor disruption. Magnetic limiter may cause the deformation of symmetric equilibrium configuration and chaotic magnetic islands reveal in plasma occurring in thin region of chaotic field lines close to their separatrix. The width of this chaotic layer in the right side of poloidal profile of Damavand Tokomak is smaller than the width in the left side profile because of Shafranov displacement. Ergodic region in the left side of profile develops a perturbation on the magnetic polodial field lines, B p, that are greater in magnitude than that in the right side, although the values of B p on the left side are smaller than that on the right side of the profile. The Left

  4. Near-Earth Magnetic Field Effects of Large-Scale Magnetospheric Currents

    DEFF Research Database (Denmark)

    Lühr, Hermann; Xiong, Chao; Olsen, Nils

    2017-01-01

    Magnetospheric currents play an important role in the electrodynamics of near-Earth space. This has been the topic of many space science studies. Here we focus on the magnetic fields they cause close to Earth. Their contribution to the geomagnetic field is the second largest after the core field...

  5. New theorem of classical electromagnetism: equilibrium magnetic field and current density are zero inside ideal conductors

    CERN Document Server

    Fiolhais, Miguel C N; Providencia, C; Nordmark, Arne B

    2010-01-01

    We prove a theorem on the magnetic energy minimum in a system of perfect, or ideal, conductors. It is analogous to Thomson's theorem on the equilibrium electric field and charge distribution in a system of conductors. We first prove Thomson's theorem using a variational principle. Our new theorem is then derived by similar methods. We find that magnetic energy is minimized when the current distribution is a surface current density with zero interior magnetic field; perfect conductors are perfectly diamagnetic. The results agree with currents in superconductors being confined near the surface. The theorem implies a generalized force that expels current and magnetic field from the interior of a conductor that loses its resistivity. Examples of solutions that obey the theorem are presented.

  6. Currents induced in anatomic models of the human for uniform and nonuniform power frequency magnetic fields.

    Science.gov (United States)

    Gandhi, O P; Kang, G; Wu, D; Lazzi, G

    2001-02-01

    We have used the quasi-static impedance method to calculate the currents induced in the nominal 2 x 2 x 3 and 6 mm resolution anatomically based models of the human body for exposure to magnetic fields at 60 Hz. Uniform magnetic fields of various orientations and magnitudes 1 or 0.417 mT suggested in the ACGIH and ICNIRP safety guidelines are used to calculate induced electric fields or current densities for the various glands and organs of the body including the pineal gland. The maximum 1 cm(2) area-averaged induced current densities for the central nervous system tissues, such as the brain and the spinal cord, were within the reference level of 10 mA/m(2) as suggested in the ICNIRP guidelines for magnetic fields (0.417 mT at 60 Hz). Tissue conductivities were found to play an important role and higher assumed tissue conductivities gave higher induced current densities. We have also determined the induced current density distributions for nonuniform magnetic fields associated with two commonly used electrical appliances, namely a hair dryer and a hair clipper. Because of considerably higher magnetic fields for the latter device, higher induced electric fields and current densities were calculated.

  7. Near-Earth Magnetic Field Effects of Large-Scale Magnetospheric Currents

    Science.gov (United States)

    Luehr, Hermann; Xiong, Chao; Olsen, Nils; Le, Guan

    2016-01-01

    Magnetospheric currents play an important role in the electrodynamics of near- Earth space. This has been the topic of many space science studies. Here we focus on the magnetic fields they cause close to Earth. Their contribution to the geomagnetic field is the second largest after the core field. Significant progress in interpreting the magnetic fields from the different sources has been achieved thanks to magnetic satellite missions like Ørsted, CHAMP and now Swarm. Of particular interest for this article is a proper representation of the magnetospheric ring current effect. Uncertainties in modelling its effect still produce the largest residuals between observations and present-day geomagnetic field models. A lot of progress has been achieved so far, but there are still open issues like the characteristics of the partial ring current. Other currents discussed are those flowing in the magnetospheric tail. Also their magnetic contribution at LEO orbits is non-negligible. Treating them as an independent source is a more recent development, which has cured some of the problems in geomagnetic field modelling. Unfortunately there is no index available for characterizing the tail current intensity. Here we propose an approach that may help to properly quantify the magnetic contribution from the tail current for geomagnetic field modelling. Some open questions that require further investigation are mentioned at the end.

  8. High magnetic field science and its application in the United States current status and future directions

    CERN Document Server

    National Research Council of the National Academies

    2013-01-01

    The Committee to Assess the Current Status and Future Direction of High Magnetic Field Science in the United States was convened by the National Research Council in response to a request by the National Science Foundation. This report answers three questions: (1) What is the current state of high-field magnet science, engineering, and technology in the United States, and are there any conspicuous needs to be addressed? (2) What are the current science drivers and which scientific opportunities and challenges can be anticipated over the next ten years? (3) What are the principal existing and planned high magnetic field facilities outside of the United States, what roles have U.S. high field magnet development efforts played in developing those facilities, and what potentials exist for further international collaboration in this area? A magnetic field is produced by an electrical current in a metal coil. This current exerts an expansive force on the coil, and a magnetic field is "high" if it challenges the str...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-07-01

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

  10. Study of magnetic fields and current in the Z pinch at stagnation

    Energy Technology Data Exchange (ETDEWEB)

    Ivanov, V. V.; Anderson, A. A.; Astanovitskiy, A. L.; Nalajala, V.; Dmitriev, O. [Department of Physics, University of Nevada, Reno, Nevada 89557 (United States); Papp, D. [Department of Physics, University of Nevada, Reno, Nevada 89557 (United States); ELI-ALPS, ELI-Hu Nkft., H-6720 Szeged (Hungary)

    2015-09-15

    The structure of magnetic fields in wire-array Z pinches at stagnation was studied using a Faraday rotation diagnostic at the wavelength of 266 nm. The electron plasma density and the Faraday rotation angle in plasma were calculated from images of the three-channel polarimeter. The magnetic field was reconstructed with Abel transform, and the current was estimated using a simple model. Several shots with wire-array Z pinches at 0.5–1.5 MA were analyzed. The strength of the magnetic field measured in plasma of the stagnated pinch was in the range of 1–2 MG. The magnetic field and current profile in plasma near the neck on the pinch were reconstructed, and the size of the current-carrying plasma was estimated. It was found that current flowed in the large-size trailing plasma near the dense neck. Measurements of the magnetic field near the bulge on the pinch also showed current in trailing plasma. A distribution of current in the large-size trailing plasma can prevent the formation of multi-MG fields in the Z pinch.

  11. Theory of spin current in magnetic nanopillars for zero-field microwave generation

    Energy Technology Data Exchange (ETDEWEB)

    Edwards, D M [Department of Mathematics, Imperial College, London SW7 2BZ (United Kingdom); Mathon, J [Department of Mathematics, City University, London EC1V 0HB (United Kingdom)

    2007-04-23

    In a magnetic nanopillar, microwave oscillations of the magnetization of one magnetic layer can be driven by spin-polarized current emitted from another magnetic layer. The conditions for this to occur in zero applied field are formulated in terms of the two components of the spin-transfer torque. One simple route to achieve microwave generation is to ensure that these components have opposite sign. Quantum-mechanical calculations are presented that show how this may be achieved by a suitable choice of the oscillating magnet thickness.

  12. Effects of a spin-polarized current assisted Ørsted field in magnetization patterning

    Energy Technology Data Exchange (ETDEWEB)

    Volkov, Oleksii M., E-mail: alexey@volkov.ca; Sheka, Denis D. [Taras Shevchenko National University of Kiev, 01601 Kiev (Ukraine); Kravchuk, Volodymyr P.; Gaididei, Yuri [Bogolyubov Institute for Theoretical Physics, 03680 Kiev (Ukraine); Mertens, Franz G. [Physics Institute, University of Bayreuth, 95440 Bayreuth (Germany)

    2015-06-07

    A spin-polarized electrical current leads to a variety of periodical magnetic structures in nanostripes. In the presence of the Ørsted field, which always assists an electrical current, the basic types of magnetic structures, i.e., a vortex-antivortex crystal and cross-tie domain walls, survive. The Ørsted field prevents saturation of the nanostripe and a longitudinal domain wall appears instead. Possible magnetization structures in stripes with different geometrical and material properties are studied numerically and analytically.

  13. Detection of fiber damage in a graphite epoxy composite using current injection and magnetic field mapping

    Science.gov (United States)

    Blalock, T. N.; Yost, W. T.

    1986-01-01

    A novel NDE technique is reported for detecting fiber disruptions in graphite-epoxy composites. The technique involves injecting electric current along the graphite fibers of a composite and measuring the resulting magnetic fields. The disruptions in current paths, which occur in areas of fiber damage, are detectable as perturbations in the magnetic field. The experimental setup, the measurements, and the magnetic images of experimental samples are presented. A resistive model has been developed to be used in the modeling of two-dimensional conductivity patterns in graphite composites. Diagrams of the setup and the circuitry are included.

  14. Near-Earth Magnetic Field Effects of Large-Scale Magnetospheric Currents

    DEFF Research Database (Denmark)

    Lühr, Hermann; Xiong, Chao; Olsen, Nils

    2016-01-01

    . Significant progress in interpreting the magnetic fields from the different sources has been achieved thanks to magnetic satellite missions like Ørsted, CHAMP and now Swarm. Of particular interest for this article is a proper representation of the magnetospheric ring current effect. Uncertainties in modelling...... in the magnetospheric tail. Also their magnetic contribution at LEO orbits is non-negligible. Treating them as an independent source is a more recent development, which has cured some of the problems in geomagnetic field modelling. Unfortunately there is no index available for characterising the tail current intensity...

  15. Research on Proximity Magnetic Field Influence in Measuring Error of Active Electronic Current Transformers

    Directory of Open Access Journals (Sweden)

    Wu Weijiang

    2016-01-01

    Full Text Available The principles of the active electronic current transformer (ECT are introduced, and the mechanism of how a proximity magnetic field can influence the measuring of errors is analyzed from the perspective of the sensor section of the ECT. The impacts on active ECTs created by three-phase proximity magnetic field with invariable distance and variable distance are simulated and analyzed. The theory and simulated analysis indicate that the active ECTs are sensitive to proximity magnetic field under certain conditions. According to simulated analysis, a product structural design and the location of transformers at substation sites are suggested for manufacturers and administration of power supply, respectively.

  16. Charge and spin current oscillations in a tunnel junction induced by magnetic field pulses

    Science.gov (United States)

    Dartora, C. A.; Nobrega, K. Z.; Cabrera, G. G.

    2016-08-01

    Usually, charge and spin transport properties in tunnel junctions are studied in the DC bias regime and/or in the adiabatic regime of time-varying magnetic fields. In this letter, the temporal dynamics of charge and spin currents in a tunnel junction induced by pulsed magnetic fields is considered. At low bias voltages, energy and momentum of the conduction electrons are nearly conserved in the tunneling process, leading to the description of the junction as a spin-1/2 fermionic system coupled to time-varying magnetic fields. Under the influence of pulsed magnetic fields, charge and spin current can flow across the tunnel junction, displaying oscillatory behavior, even in the absence of DC bias voltage. A type of spin capacitance function, in close analogy to electric capacitance, is predicted.

  17. Compensation of the magnetization current induced sextupole error at LHC injection field by short lumped permanent sextupole magnets, incorporated into the end configuration of superconducting dipoles

    CERN Document Server

    Asner, A

    1985-01-01

    Compensation of the magnetization current induced sextupole error at LHC injection field by short lumped permanent sextupole magnets, incorporated into the end configuration of superconducting dipoles

  18. Dissipationless Hall Current in Dense Quark Matter in a Magnetic Field

    CERN Document Server

    Ferrer, E J

    2016-01-01

    We show the realization of axion electrodynamics within the Dual Chiral Density Wave phase of dense quark matter in the presence of a magnetic field. The system exhibits an anomalous dissipantionless Hall current perpendicular to the magnetic field and an anomalous electric charge density. Connection to topological insulators and 3D optical lattices, as well as possible implications for heavy-ion collisions and neutron stars are outlined.

  19. Total AC loss of YBCO coated conductor carrying AC transport current in AC transverse magnetic field with various orientations

    Energy Technology Data Exchange (ETDEWEB)

    Amemiya, Naoyuki [Faculty of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya, Yokohama 240-8501 (Japan); Jiang, Zhenan [Faculty of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya, Yokohama 240-8501 (Japan); Iijima, Yasuhiro [Materials Research Laboratory, Fujikura Ltd, 1-5-1 Kiba, Koto, Tokyo 135-8512 (Japan); Kakimoto, Kazuomi [Materials Research Laboratory, Fujikura Ltd, 1-5-1 Kiba, Koto, Tokyo 135-8512 (Japan); Saitoh, Takashi [Materials Research Laboratory, Fujikura Ltd, 1-5-1 Kiba, Koto, Tokyo 135-8512 (Japan)

    2004-08-01

    Using an electro-magnetic method, we measured the total AC loss of a YBCO coated conductor carrying an AC transport current in an AC transverse magnetic field with various orientations. We measured the magnetization loss (energy flow from the external magnetic field) and the transport loss (energy flow from the transport current circuit) independently during simultaneous application of an AC transverse magnetic field and AC transport current. Their sum gave us the total AC loss. The transport loss increases with increasing AC transverse magnetic field, and the magnetization loss increases with increasing AC transport current. The AC transverse magnetic field and the AC self magnetic field interact with each other at the conductor edges. This nonlinear interaction is a possible cause of the increase in AC loss. Due to the high aspect ratio of YBCO coated conductors, this increase in AC loss due to the interaction between the AC transverse and AC self magnetic fields is observed even when the transverse magnetic field is nearly parallel to the conductor wide-face. When the total AC losses for various transport currents and various field orientations are plotted against a transverse magnetic field component which is perpendicular to the conductor wide-face, the plots with different field angles but identical transport current all agree quite well with each other. The total AC loss is dominated by the self magnetic field and the perpendicular component of the transverse magnetic field, both of which mostly penetrate from the conductor edges.

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

    Science.gov (United States)

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

    2005-09-01

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

  1. Effects of rf current on critical field for magnetization reversal in spin torque devices

    Science.gov (United States)

    Chen, Wenyu; Florez, Sylvia; Katine, Jordan; Carey, Matthew; Folks, Liesl; Terris, Bruce

    2009-03-01

    Current induced switching assisted by rf current has recently been observed in spin torque devices at low temperature [1, 2]. This effect allows control of spin transfer induced magnetization reversal through the frequency of an injected rf current. In this study, the effects of the rf current injection on critical field for magnetization reversal in spin valve junctions have been investigated. Measurements were conducted at room temperature, and the magnetic field was applied along the easy axis of the junction. An rf current was injected into the nanojunction at various frequencies ranging between 1 and 20 GHz. The dynamic resistance, dV/dI, was measured as a function of the rf frequency, power and the dc bias current while ramping the magnetic field. The rf current injection was observed to change the critical field for free layer magnetization reversal when the intrinsic spin-transfer-induced dynamics is frequency-locked with the injected rf. The results will be discussed in the context of macrospin models of spin transfer in metallic spin valve structures. [1] S. H. Florez et al. Phys. Rev. B 78, 184403 (2008) [2] Y.-T. Cui et al. Phys. Rev. B 77, 214440 (2008)

  2. Extended magnetohydrodynamic simulations of field reversed configuration formation and sustainment with rotating magnetic field current drive

    Science.gov (United States)

    Milroy, R. D.; Kim, C. C.; Sovinec, C. R.

    2010-06-01

    Three-dimensional simulations of field reversed configuration (FRC) formation and sustainment with rotating magnetic field (RMF) current drive have been performed with the NIMROD code [C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004)]. The Hall term is a zeroth order effect with strong coupling between Fourier components, and recent enhancements to the NIMROD preconditioner allow much larger time steps than was previously possible. Boundary conditions to capture the effects of a finite length RMF antenna have been added, and simulations of FRC formation from a uniform background plasma have been performed with parameters relevant to the translation, confinement, and sustainment-upgrade experiment at the University of Washington [H. Y. Guo, A. L. Hoffman, and R. D. Milroy, Phys. Plasmas 14, 112502 (2007)]. The effects of both even-parity and odd-parity antennas have been investigated, and there is no evidence of a disruptive instability for either antenna type. It has been found that RMF effects extend considerably beyond the ends of the antenna, and that a large n =0 Bθ can develop in the open-field line region, producing a back torque opposing the RMF.

  3. The Generation of a Large-Scale Galactic Magnetic Field by Electric Currents of Energetic Particles

    Science.gov (United States)

    Dolginov, A. Z.; Toptygin, I. N.

    2003-06-01

    We consider the generation of a magnetic field in the Galaxy by the electric currents excited by cosmic-ray particles in the disk and halo. We assume that the sources of relativistic particles are distributed continuously and uniformly in the Galactic disk, their total power is equal to the observed value, and the particles themselves undergo anisotropic diffusion in a homogeneous medium. We take into account the differential rotation of the Galactic disk but disregard the turbulence gyrotropy (the alpha-effect). The strength of the generated magnetic field in our model is shown to strongly depend on the symmetry of the relativistic proton and thermal electron diffusion tensors, as well as on the relations between the tensor components. In particular, if the diffusion is isotropic, then no magnetic field is generated. For the independent tensor components estimated from observed parameters of the Galactic medium and with a simultaneous allowance made for the turbulent field dissipation processes, the mechanism under consideration can provide an observable magnetic-field strength of the order of several microgauss. This mechanism does not require any seed magnetic field, which leads us to suggest that relativistic particles can give an appreciable and, possibly, determining contribution to the formation of the global Galactic magnetic field. However, a final answer can be obtained only from a nonlinear self-consistent treatment, in which the symmetry and magnitude of the particle diffusion tensor components should be determined together with the calculation of the magnetic field.

  4. Analysis on background magnetic field to generate eddy current by pulsed gradient of permanent-magnet MRI

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    In this paper the analytical expressions for the magnetic field H and induction B in iron-pole plates generated by MRI gradient coil are given using line-current and the multilayer dielectric plate model with the mirror-image method.Eddy current emanates from the magnetic flux in the iron-pole plates.In order to fully suppress the eddy current,this magnetic flux should be fully eliminated.The research results indicate the magnetic permeability of the resist-eddy plate must be bigger than that of magnetic pole material,i.e.pure iron,and that the resist-eddy plate should be thick enough to be far away from its magnetic saturation.

  5. Measurement of weak magnetic field of corrosion current of isolated corrosion center

    Directory of Open Access Journals (Sweden)

    I. V. Bardin

    2015-01-01

    Full Text Available A very small magnetic field of corrosion current, of the order of 10−4 Oe, generated by isolated zinc inclusion in a copper platelet placed in electrolyte has been measured for the first time with a highly sensitive giant magneto-impedance magnetometer. The total corrosion current of the inclusion is estimated comparing the measured magnetic field distribution with corresponding theoretical calculation. The estimated value of the total corrosion current turns out to be in reasonable agreement with that one obtained in the standard gravimetric measurement.

  6. Mapping the earth's magnetic and gravity fields from space Current status and future prospects

    Science.gov (United States)

    Settle, M.; Taranik, J. V.

    1983-01-01

    The principal magnetic fields encountered by earth orbiting spacecraft include the main (core) field, external fields produced by electrical currents within the ionosphere and magnetosphere, and the crustal (anomaly) field generated by variations in the magnetization of the outermost portions of the earth. The first orbital field measurements which proved to be of use for global studies of crustal magnetization were obtained by a series of three satellites launched and operated from 1965 to 1971. Each of the satellites, known as a Polar Orbiting Geophysical Observatory (POGO), carried a rubidium vapor magnetometer. Attention is also given to Magsat launched in 1979, the scalar anomaly field derived from the Magsat measurements, satellite tracking studies in connection with gravity field surveys, radar altimetry, the belt of positive free air gravity anomalies situated along the edge of the Pacific Ocean basin, future technological capabilities, and information concerning data availability.

  7. Current helicity pattern of large-scale magnetic field on the photosphere

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Following Pevtsov and Latushko, we study the current helicity pattern of the large-scale magnetic field on the photosphere. We use the same technique as theirs to derive the vector magnetic field (Br,Bθ,Bφ) from full-disk longitudinal magnetograms based on the assumption that large-scale magnetic fields evolve rather slowly and the variations of the longitudinal magnetic fields within certain time duration are caused by the changing position angles only. Different from their study, we have calculated the current helicity maps directly from the derived vector magnetograms, rather than from obtaining the latitudinal variation of hc by ignoring the role of Bθ component and averaging Br and Bφ over all solar longitudes. This approach significantly strengthens the evidence of the hemispheric rule presented in the reconstructed vector magnetic field. Our study shows that the established hemispheric sign rule, that is, positive helicity sign in the southern hemisphere and negative helicity sign in the northern hemisphere, is applicable everywhere in the global magnetic field, namely, also evident in weak fields outside active regions, and that the obtained sign pattern is independent of the longitudinal magnetograms and the parameters that we have used.

  8. Ring current Atmosphere interactions Model with Self-Consistent Magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    2016-09-09

    The Ring current Atmosphere interactions Model with Self-Consistent magnetic field (B) is a unique code that combines a kinetic model of ring current plasma with a three dimensional force-balanced model of the terrestrial magnetic field. The kinetic portion, RAM, solves the kinetic equation to yield the bounce-averaged distribution function as a function of azimuth, radial distance, energy and pitch angle for three ion species (H+, He+, and O+) and, optionally, electrons. The domain is a circle in the Solar-Magnetic (SM) equatorial plane with a radial span of 2 to 6.5 RE. It has an energy range of approximately 100 eV to 500 KeV. The 3-D force balanced magnetic field model, SCB, balances the JxB force with the divergence of the general pressure tensor to calculate the magnetic field configuration within its domain. The domain ranges from near the Earth’s surface, where the field is assumed dipolar, to the shell created by field lines passing through the SM equatorial plane at a radial distance of 6.5 RE. The two codes work in tandem, with RAM providing anisotropic pressure to SCB and SCB returning the self-consistent magnetic field through which RAM plasma is advected.

  9. Cell death induced by AC magnetic fields and magnetic nanoparticles: current state and perspectives.

    Science.gov (United States)

    Goya, Gerardo F; Asín, Laura; Ibarra, M Ricardo

    2013-12-01

    This review analyses the advances in the field of magnetically induced cell death using intracellular magnetic nanoparticles (MNPs). Emphasis has been given to in vitro research results, discussing the action of radiofrequency (RF) waves on biological systems as well as those results of thermally induced cell death in terms of MNP cell interactions. Our main goal has been to provide a unified depiction of many recent experiments and theoretical models relevant to the effect of applied electromagnetic fields on MNPs after cellular uptake and the cytotoxicity assessment of MNPs. We have addressed the effects of RF waves used for in vitro magnetic hyperthermia on eukaryotic cells regarding physical modifications of the cellular local environment and cell viability.

  10. Conductive shield for ultra-low-field magnetic resonance imaging: Theory and measurements of eddy currents.

    Science.gov (United States)

    Zevenhoven, Koos C J; Busch, Sarah; Hatridge, Michael; Oisjöen, Fredrik; Ilmoniemi, Risto J; Clarke, John

    2014-03-14

    Eddy currents induced by applied magnetic-field pulses have been a common issue in ultra-low-field magnetic resonance imaging. In particular, a relatively large prepolarizing field-applied before each signal acquisition sequence to increase the signal-induces currents in the walls of the surrounding conductive shielded room. The magnetic-field transient generated by the eddy currents may cause severe image distortions and signal loss, especially with the large prepolarizing coils designed for in vivo imaging. We derive a theory of eddy currents in thin conducting structures and enclosures to provide intuitive understanding and efficient computations. We present detailed measurements of the eddy-current patterns and their time evolution in a previous-generation shielded room. The analysis led to the design and construction of a new shielded room with symmetrically placed 1.6-mm-thick aluminum sheets that were weakly coupled electrically. The currents flowing around the entire room were heavily damped, resulting in a decay time constant of about 6 ms for both the measured and computed field transients. The measured eddy-current vector maps were in excellent agreement with predictions based on the theory, suggesting that both the experimental methods and the theory were successful and could be applied to a wide variety of thin conducting structures.

  11. Circulating persistent current and induced magnetic field in a fractal network

    Energy Technology Data Exchange (ETDEWEB)

    Saha, Srilekha [Condensed Matter Physics Division, Saha Institute of Nuclear Physics, Sector-I, Block-AF, Bidhannagar, Kolkata 700 064 (India); Maiti, Santanu K., E-mail: santanu.maiti@isical.ac.in [Physics and Applied Mathematics Unit, Indian Statistical Institute, 203 Barrackpore Trunk Road, Kolkata 700 108 (India); Karmakar, S.N. [Condensed Matter Physics Division, Saha Institute of Nuclear Physics, Sector-I, Block-AF, Bidhannagar, Kolkata 700 064 (India)

    2016-04-29

    We present the overall conductance as well as the circulating currents in individual loops of a Sierpinski gasket (SPG) as we apply bias voltage via the side attached electrodes. SPG being a self-similar structure, its manifestation on loop currents and magnetic fields is examined in various generations of this fractal and it has been observed that for a given configuration of the electrodes, the physical quantities exhibit certain regularity as we go from one generation to another. Also a notable feature is the introduction of anisotropy in hopping causes an increase in magnitude of overall transport current. These features are a subject of interest in this article. - Highlights: • Voltage driven circular current is analyzed in a fractal network. • Current induced magnetic field is strong enough to flip a spin. • Anisotropy in hopping enhances overall transport current.

  12. Photocurrent, rectification, and magnetic field symmetry of induced current through quantum dots.

    Science.gov (United States)

    DiCarlo, L; Marcus, C M; Harris, J S

    2003-12-12

    We report mesoscopic dc current generation in an open chaotic quantum dot with ac excitation applied to one of the shape-defining gates. For excitation frequencies large compared to the inverse dwell time of electrons in the dot (i.e., GHz), we find mesoscopic fluctuations of induced current that are fully asymmetric in the applied perpendicular magnetic field, as predicted by recent theory. Conductance, measured simultaneously, is found to be symmetric in field. In the adiabatic (i.e., MHz) regime, in contrast, the induced current is always symmetric in field, suggesting its origin is mesoscopic rectification.

  13. Photocurrent, Rectification, and Magnetic Field Symmetry of Induced Current Through Quantum Dots

    DEFF Research Database (Denmark)

    DiCarlo, L.; M. Marcus, C.; Harris jr, J.

    2003-01-01

    We report mesoscopic dc current generation in an open chaotic quantum dot with ac excitation applied to one of the shape-defining gates. For excitation frequencies large compared to the inverse dwell time of electrons in the dot (i.e., GHz), we find mesoscopic fluctuations of induced current...... that are fully asymmetric in the applied perpendicular magnetic field, as predicted by recent theory. Conductance, measured simultaneously, is found to be symmetric in field. In the adiabatic (i.e., MHz) regime, in contrast, the induced current is always symmetric in field, suggesting its origin is mesoscopic...

  14. Field-aligned currents during northward interplanetary magnetic field: Morphology and causes

    DEFF Research Database (Denmark)

    Vennerstrøm, Susanne; Moretto, T.; Rastatter, L.

    2005-01-01

    [1] We present the results of a global MHD simulation of solar wind magnetosphere interaction during northward IMF. In particular, we emphasize the effect of the IMF By component on the reconnection geometry and the mapping along field lines to the polar ionosphere, through field-aligned currents....... However, the idea that the NBZ currents rotate to form the two sheets of FACs sandwiching the ionospheric DPY current is only partly confirmed by the simulation....

  15. Conductive shield for ultra-low-field magnetic resonance imaging: Theory and measurements of eddy currents

    Science.gov (United States)

    Zevenhoven, Koos C. J.; Busch, Sarah; Hatridge, Michael; Öisjöen, Fredrik; Ilmoniemi, Risto J.; Clarke, John

    2014-03-01

    Eddy currents induced by applied magnetic-field pulses have been a common issue in ultra-low-field magnetic resonance imaging. In particular, a relatively large prepolarizing field—applied before each signal acquisition sequence to increase the signal—induces currents in the walls of the surrounding conductive shielded room. The magnetic-field transient generated by the eddy currents may cause severe image distortions and signal loss, especially with the large prepolarizing coils designed for in vivo imaging. We derive a theory of eddy currents in thin conducting structures and enclosures to provide intuitive understanding and efficient computations. We present detailed measurements of the eddy-current patterns and their time evolution in a previous-generation shielded room. The analysis led to the design and construction of a new shielded room with symmetrically placed 1.6-mm-thick aluminum sheets that were weakly coupled electrically. The currents flowing around the entire room were heavily damped, resulting in a decay time constant of about 6 ms for both the measured and computed field transients. The measured eddy-current vector maps were in excellent agreement with predictions based on the theory, suggesting that both the experimental methods and the theory were successful and could be applied to a wide variety of thin conducting structures.

  16. Magnetic Field Due to a Finite Length Current-Carrying Wire Using the Concept of Displacement Current

    Science.gov (United States)

    Buschauer, Robert

    2014-01-01

    In undergraduate E&M courses the magnetic field due to a finite length, current-carrying wire can be calculated using the Biot-Savart law. However, to the author's knowledge, no textbook presents the calculation of this field using the Ampere-Maxwell law: ?B [multiplied by] dl = µ[subscript 0] (I + e[subscript 0] dF/dt) [multiplied by] 1

  17. Residual magnetic field profiles and their current density profiles of coated conductors for fast and slow cut-off current operations

    Energy Technology Data Exchange (ETDEWEB)

    Sun, J.; Taillouli, M.; Hamabe, M.; Watanabe, H.; Chikumoto, N.; Yamaguchi, S. [Chubu University, Kasugai, Aichi (Japan); Shyshkin, O. [V. N. Karazin Kharkiv National University, Kharkov (Ukraine)

    2015-03-15

    Coated conductor is an important candidate for power cable applications due to its high current density. Even for DC power cable transmission, we must study the transport properties of HTS tapes after slow and fast discharge. In order to evaluate relation of the magnetic field with applied current we developed a scanning magnetic field measurements system by employing a Hall probe. This work presents the measurements of the magnetic fields above a coated conductor by varying applied current pattern. In the work, a transport current of 100 A, less than the critical current, is applied to YBCO coated conductor. We measured the residual magnetic field distributions after cut off the transport current with slow and fast operations. The results show differences of the magnetic field profiles and the corresponding current profiles by an inverse solution from the magnetic field measurement between these two operations because of the hysteresis of coated conductor excited by the transport current.

  18. Improved Eddy-current Field Loss Model and Scaling Index for Magnets of Permanent Magnet Synchronous Motors

    Directory of Open Access Journals (Sweden)

    Zhang Lei

    2015-01-01

    Full Text Available The paper gives detailed systematic researches on the mechanism and key factors of eddy-current losses in rotor magnets of high power-density permanent magnet synchronous motors(PMSMs. Firstly, this paper establishes quantitative mathematic model of eddy-current losses for surface-mounted PMSM based on eddy current field model and Maxwell equations. Then, a scaling index is put forward to weigh the key factors relevant to the eddy-current losses in magnets. At the same time, the principles of eddy-current losses in prototype PMSM are analyzed by the finite element analysis (FEA software. The contents researched in the paper have practical reference values for design and reliability analysis of PMSMs.

  19. Computation of magnetic fields within source regions of ionospheric and magnetospheric currents

    DEFF Research Database (Denmark)

    Engels, U.; Olsen, Nils

    1998-01-01

    A general method of computing the magnetic effect caused by a predetermined three-dimensional external current density is presented. It takes advantage of the representation of solenoidal vector fields in terms of toroidal and poloidal modes expressed by two independent series of spherical harmon...

  20. Excitation of zero-frequency magnetic field-aligned currents by ionospheric heating

    Directory of Open Access Journals (Sweden)

    A. V. Streltsov

    2011-06-01

    Full Text Available Time-dependent, three-dimensional numerical simulations of the reduced MHD model describing shear Alfvén waves in the magnetosphere provide an interesting prediction superficially similar to results of several ionospheric heating experiments conducted at high altitudes. In these experiments, heating of the ionospheric F-region with a constant/zero-frequency beam of HF waves causes luminous structures in the ionosphere in the form of a ring or a solid spot with a characteristic size comparable to the size of the heated spot. Simulations suggest that spots/rings or similar optical appearance might be associated with a magnetic field-aligned current system produced by the ionospheric heating. Two of the most interesting features of this current system are (1 strong localization across the ambient magnetic field and (2 distinctive non-symmetrical luminous signatures (ring/spot in magnetically conjugate locations in the ionosphere.

  1. Effect of a pinning field on the critical current density for current-induced domain wall motion in perpendicular magnetic anisotropy nanowires.

    Science.gov (United States)

    Ooba, Ayaka; Fujimura, Yuma; Takahashi, Kota; Komine, Takashi; Sugita, Ryuji

    2012-09-01

    In this study, the effect of a pinning field on the critical current density for current-induced domain wall motion in nanowires with perpendicular magnetic anisotropy was investigated using micromagnetic simulations. In order to estimate the pinning field in notched nanowires, we conducted wall energy calculations for nanowires with various saturation magnetizations. The pinning field increased as the notch size increased. The pinning field decreased as the saturation magnetization decreased. As a result, the decreased in the pinning field causes the reduction of the critical current density. Therefore, a significant reduction of the critical current density can be obtained by decreasing the saturation magnetization, even if wall pinning occurs.

  2. Influence of the initial parameters of the magnetic field and plasma on the spatial structure of the electric current and electron density in current sheets formed in helium

    Energy Technology Data Exchange (ETDEWEB)

    Ostrovskaya, G. V., E-mail: galya-ostr@mail.ru [Russian Academy of Sciences, Ioffe Physical Technical Institute (Russian Federation); Markov, V. S.; Frank, A. G., E-mail: annfrank@fpl.gpi.ru [Russian Academy of Sciences, Prokhorov General Physics Institute (Russian Federation)

    2016-01-15

    The influence of the initial parameters of the magnetic field and plasma on the spatial structure of the electric current and electron density in current sheets formed in helium plasma in 2D and 3D magnetic configurations with X-type singular lines is studied by the methods of holographic interferometry and magnetic measurements. Significant differences in the structures of plasma and current sheets formed at close parameters of the initial plasma and similar configurations of the initial magnetic fields are revealed.

  3. The magnetic shear-current effect: generation of large-scale magnetic fields by the small-scale dynamo

    Science.gov (United States)

    Squire, J.; Bhattacharjee, A.

    2016-04-01

    > A novel large-scale dynamo mechanism, the magnetic shear-current effect, is discussed and explored. The effect relies on the interaction of magnetic fluctuations with a mean shear flow, meaning the saturated state of the small-scale dynamo can drive a large-scale dynamo - in some sense the inverse of dynamo quenching. The dynamo is non-helical, with the mean field coefficient zero, and is caused by the interaction between an off-diagonal component of the turbulent resistivity and the stretching of the large-scale field by shear flow. Following up on previous numerical and analytic work, this paper presents further details of the numerical evidence for the effect, as well as an heuristic description of how magnetic fluctuations can interact with shear flow to produce the required electromotive force. The pressure response of the fluid is fundamental to this mechanism, which helps explain why the magnetic effect is stronger than its kinematic cousin, and the basic idea is related to the well-known lack of turbulent resistivity quenching by magnetic fluctuations. As well as being interesting for its applications to general high Reynolds number astrophysical turbulence, where strong small-scale magnetic fluctuations are expected to be prevalent, the magnetic shear-current effect is a likely candidate for large-scale dynamo in the unstratified regions of ionized accretion disks. Evidence for this is discussed, as well as future research directions and the challenges involved with understanding details of the effect in astrophysically relevant regimes.

  4. Effect of longitudinal applied magnetic field on the self-pinched critical current in intense electron beam diode

    Institute of Scientific and Technical Information of China (English)

    Liu Guo-Zhi; Huang Wen-Hua; Shao Hao; Xiao Ren-Zhen

    2006-01-01

    The effect of applied longitudinal magnetic field on the self-pinched critical current in the intense electron beam diode is discussed. The self-pinched critical current is derived and its validity is tested by numerical simulations. The results shows that an applied longitudinal magnetic field tends to increase the self-pinched critical current. Without the effect of anode plasma, the maximal diode current approximately equals the self-pinched critical current with the longitudinal magnetic field applied; when self-pinched occurs, the diode current approaches the self-pinched critical current.

  5. Surface electric current distributions on spheres and spheroids as sources of pure quadrupole magnetic fields

    OpenAIRE

    L. Medina; E. Ley-Koo

    2011-01-01

    Neutral atom magnetic traps and nuclear magnetic resonance imaging require internal regions with constant gradient magnetic induction fields, which are identified as pure quadrupole fields. This contribution starts from such fields in the interior of spheres and spheroids in cartesian coordinates, identifying immediately their respective scalar magnetic potentials. Next, the corresponding potentials inside and outside are constructed using spherical and spheroidal harmonic functions, respecti...

  6. A current filamentation mechanism for breaking magnetic field lines during reconnection.

    Science.gov (United States)

    Che, H; Drake, J F; Swisdak, M

    2011-06-01

    During magnetic reconnection, the field lines must break and reconnect to release the energy that drives solar and stellar flares and other explosive events in space and in the laboratory. Exactly how this happens has been unclear, because dissipation is needed to break magnetic field lines and classical collisions are typically weak. Ion-electron drag arising from turbulence, dubbed 'anomalous resistivity', and thermal momentum transport are two mechanisms that have been widely invoked. Measurements of enhanced turbulence near reconnection sites in space and in the laboratory support the anomalous resistivity idea but there has been no demonstration from measurements that this turbulence produces the necessary enhanced drag. Here we report computer simulations that show that neither of the two previously favoured mechanisms controls how magnetic field lines reconnect in the plasmas of greatest interest, those in which the magnetic field dominates the energy budget. Rather, we find that when the current layers that form during magnetic reconnection become too intense, they disintegrate and spread into a complex web of filaments that causes the rate of reconnection to increase abruptly. This filamentary web can be explored in the laboratory or in space with satellites that can measure the resulting electromagnetic turbulence.

  7. Heating ability of La-Sr-Mn-Cu perovskite spheres under an alternating current magnetic field for magnetic hyperthermia mediators

    Energy Technology Data Exchange (ETDEWEB)

    Horiki, Mayumi [Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Nakagawa, Takashi, E-mail: nakagawa@mit.eng.osaka-u.ac.jp [Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Seino, Satoshi; Yamamoto, Takao A. [Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan)

    2013-03-15

    La{sub 0.666}Sr{sub 0.373}Mn{sub 0.943}Cu{sub 0.018}O{sub 3} spheres (average diameter: 2.4 mm) were used as magnetic hyperthermia mediators. They were prepared by the polymerized complex method and alginate gelation. A starch paste containing nine such spheres (0.1034 g) was maintained at a constant temperature when it was exposed to an alternating current magnetic field (frequency: 1 MHz; magnetic field strength: 20-55 Oe-rms). After exposure to a magnetic field with a field strength of 55 Oe-rms for 60 min, a temperature of T{sub 60}=73.5 Degree-Sign C was obtained. T{sub 60} for field strengths of 40 and 55 Oe-rms differed by only 2.6 Degree-Sign C. La{sub 0.666}Sr{sub 0.373}Mn{sub 0.943}Cu{sub 0.018}O{sub 3} spheres satisfy the following important requirements for heating mediators: their amount can be controlled in tumors, their temperature can be controlled without monitoring, and their heating ability is independent of the field strength and direction. Thus, La{sub 0.666}Sr{sub 0.373}Mn{sub 0.943}Cu{sub 0.018}O{sub 3} spheres are promising heating mediators for inducing magnetic hyperthermia. - Highlights: Black-Right-Pointing-Pointer We prepared La-Sr-Mn-Cu perovskite spheres used as magnetic hyperthermia mediators. Black-Right-Pointing-Pointer Our perovskite spheres were maintained at a constant temperature under AC field. Black-Right-Pointing-Pointer The heating ability is independent of the field strength and direction.

  8. Comparison of empirical magnetic field models and global MHD simulations: The near-tail currents

    Science.gov (United States)

    Pulkkinen, T. I.; Baker, D. N.; Walker, R. J.; Raeder, J.; Ashour-Abdalla, M.

    1995-01-01

    The tail currents predicted by empirical magnetic field models and global MHD simulations are compared. It is shown that the near-Earth currents obtained from the MHD simulations are much weaker than the currents predicted by the Tsyganenko models, primarily because the ring current is not properly represented in the simulations. On the other hand, in the mid-tail and distant tail the lobe field strength predicted by the simulations is comparable to what is observed at about 50 R(sub E) distance, significantly larger than the very low lobe field values predicted by the Tsyganenko models at that distance. Ways to improve these complementary approaches to model the actual magnetospheric configuration are discussed.

  9. Roles of the magnetic field and electric current in thermally activated domain wall motion in a submicrometer magnetic strip with perpendicular magnetic anisotropy.

    Science.gov (United States)

    Emori, Satoru; Beach, Geoffrey S D

    2012-01-18

    We have experimentally studied micrometer-scale domain wall (DW) motion driven by a magnetic field and an electric current in a Co/Pt multilayer strip with perpendicular magnetic anisotropy. The thermal activation energy for DW motion, along with its scaling with the driving field and current, has been extracted directly from the temperature dependence of the DW velocity. The injection of DC current resulted in an enhancement of the DW velocity independent of the current polarity, but produced no measurable change in the activation energy barrier. Through this analysis, the observed current-induced DW velocity enhancement can be entirely and unambiguously attributed to Joule heating.

  10. Magnetic Field Perturbations from Currents in the Dark Polar Regions During Quiet Geomagnetic Conditions

    Science.gov (United States)

    Friis-Christensen, E.; Finlay, C. C.; Hesse, M.; Laundal, K. M.

    2017-02-01

    In the day-side sunlit polar ionosphere the varying and IMF dependent convection creates strong ionospheric currents even during quiet geomagnetic conditions. Observations during such times are often excluded when using satellite data to model the internal geomagnetic main field. Observations from the night-side or local winter during quiet conditions are, however, also influenced by variations in the IMF. In this paper we briefly review the large scale features of the ionospheric currents in the polar regions with emphasis on the current distribution during undisturbed conditions. We examine the distribution of scalar measurements of the magnetic field intensity minus predictions from a geomagnetic field model. These `residuals' fall into two main categories. One category is consistently distributed according to the well-known ionospheric plasma convection and its associated Birkeland currents. The other category represent contributions caused by geomagnetic activity related to the substorm current wedge around local magnetic midnight. A new observation is a strong IMF By control of the residuals in the midnight sector indicating larger ionospheric currents in the substorm current wedge in the northern polar region for By > 0 and correspondingly in the southern hemisphere for By < 0.

  11. Research on zero-sum magnetic field integral technology of optical current sensors

    Science.gov (United States)

    Li, Shen-wang; Yu, Wen-bin; Zhang, Guo-qing; Guo, Zhi-zhong; Shen, Yan

    2013-10-01

    An architecture based on the Faraday effect to minimize the crosstalk effect in optical current sensors (OCSs) is proposed. It was demonstrated that the magnetic field integral along a discrete loop can meet Ampere's law under certain conditions, and the mathematical model of zero-sum points was given. Based on it, a zero-sum OCS (ZOCS) was proposed, which consists of several OCSs forming a symmetrical discrete loop. Ideally, the currents that flow outside the ZOCS do not contribute to the measurement of the currents inside it. The experimental results showed that the magnetic crosstalk-induced errors of ZOCS were less than 0.2%, and the influence of external current was reduced one order compared with conventional OCSs.

  12. Numerical Analysis of Induced Current in Human Head Exposed to Nonuniform Magnetic Field Including Harmonics

    Science.gov (United States)

    Tarao, Hiroo; Hayashi, Noriyuki; Isaka, Katsuo

    In this paper, induced currents in an anatomical head model exposed to a non-uniform ELF magnetic field (B-field) including harmonics are numerically calculated, and are discussed based on the basic restriction established by International Commission on Non-Ionizing Radiation Protection (ICNIRP). A casual hair dryer of 100V and 1.2kW is chosen as a typical source of the non-uniform B-field including both the fundamental and second harmonic components. The B-field distribution around the hair dryer is estimated by using the 3-orthogonal magnetic dipole moments, which are derived from a couple of measured values around it. The high-resolution human head model used is constructed based on the MRI images of a real human, and consists of six kinds of tissues (bone, brain, eyeballs, muscle, skin and blood). So-called impedance method is used for the numerical calculation of the induced current. The numerical results show that the maximum values of the induced current of 17µA/m2, for the 60Hz component, which is about 1/120 of the ICNIRP basic restriction appear in the muscle near the eyeball when the hair dryer is used from the side of the head model, and the averaged current in the eyeballs that have the highest conductivity is the highest among the six tissues. It is also demonstrated that the induced current due to the 120Hz B-field becomes comparable to the 60Hz current although the magnitude of the 120Hz B-field is much smaller than that of the 60Hz B-field.

  13. Amplification of perpendicular and parallel magnetic fields by cosmic ray currents

    Science.gov (United States)

    Matthews, J. H.; Bell, A. R.; Blundell, K. M.; Araudo, A. T.

    2017-08-01

    Cosmic ray (CR) currents through magnetized plasma drive strong instabilities producing amplification of the magnetic field. This amplification helps explain the CR energy spectrum as well as observations of supernova remnants and radio galaxy hotspots. Using magnetohydrodynamic simulations, we study the behaviour of the non-resonant hybrid (NRH) instability (also known as the Bell instability) in the case of CR currents perpendicular and parallel to the initial magnetic field. We demonstrate that extending simulations of the perpendicular case to 3D reveals a different character to the turbulence from that observed in 2D. Despite these differences, in 3D the perpendicular NRH instability still grows exponentially far into the non-linear regime with a similar growth rate to both the 2D perpendicular and 3D parallel situations. We introduce some simple analytical models to elucidate the physical behaviour, using them to demonstrate that the transition to the non-linear regime is governed by the growth of thermal pressure inside dense filaments at the edges of the expanding loops. We discuss our results in the context of supernova remnants and jets in radio galaxies. Our work shows that the NRH instability can amplify magnetic fields to many times their initial value in parallel and perpendicular shocks.

  14. Effects of magnetic field and Hall current to the blood velocity and LDL transfer

    Science.gov (United States)

    Abdullah, I.; Naser, N.; Talib, A. H.; Mahali, S.

    2015-09-01

    The magnetic field and Hall current effects have been considered on blood velocity and concentration of low-density lipoprotein (LDL). It is important to observe those effects to the flowing blood in a stenosed artery. The analysis from the obtained results may be useful to some clinical procedures, such as MRI, where the radiologists may have more information in the investigations before cardiac operations could be done. In this study, the uniform magnetic field and Hall current are applied to the Newtonian blood flow through an artery having a cosine-shaped stenosis. The governing equations are coupled with mass transfer and solved employing a finite difference Marker and Cell (MAC) method with an appropriate initial and boundary conditions. The graphical results of velocity profiles and LDL concentration are presented in this paper and the results show that the velocity increases and concentration decreases as Hall parameter increased.

  15. Analysis of Magnetic Field Intensity and Induced Current under Live Working Based on Charge Simulation Method

    Directory of Open Access Journals (Sweden)

    Luo Yuanxiang

    2015-01-01

    Full Text Available To the problem that safety distance is insufficient for 500 kV substation live working, a magnetic field analysis method for overhead line bus is given based on the charge simulation method. In the method, charge is calculated firstly, and the space field intensity distribution calculation is completed by overlying charge. The space field intensity distribution rule is carried out based on the appropriate analysis, and space field intensity distribution rule of substation is obtained. Then according to the calculation formula of inducing current, the human body induction current under a substation busbar is simulated based on MATLAB. The simulation results have a certain guidance function for actual live working.

  16. Extending the GMR Current Measurement Range with a Counteracting Magnetic Field

    Directory of Open Access Journals (Sweden)

    Tin Yan Poon

    2013-06-01

    Full Text Available Traditionally, current transformers are often used for current measurement in low voltage (LV electrical networks. They have a large physical size and are not designed for use with power electronic circuits. Semiconductor-based current sensing devices such as the Hall sensor and Giant Magnetoresistive (GMR sensor are advantageous in terms of small size, high sensitivity, wide frequency range, low power consumption, and relatively low cost. Nevertheless, the operational characteristics of these devices limit their current measurement range. In this paper, a design based on using counteracting magnetic field is introduced for extending the GMR current measurement range from 9 A (unipolar to ±45 A. A prototype has been implemented to verify the design and the linear operation of the circuit is demonstrated by experimental results. A microcontroller unit (MCU is used to provide an automatic scaling function to optimize the performance of the proposed current sensor.

  17. Influence of Electric, Magnetic, and Electromagnetic Fields on the Circadian System: Current Stage of Knowledge

    Directory of Open Access Journals (Sweden)

    Bogdan Lewczuk

    2014-01-01

    Full Text Available One of the side effects of each electrical device work is the electromagnetic field generated near its workplace. All organisms, including humans, are exposed daily to the influence of different types of this field, characterized by various physical parameters. Therefore, it is important to accurately determine the effects of an electromagnetic field on the physiological and pathological processes occurring in cells, tissues, and organs. Numerous epidemiological and experimental data suggest that the extremely low frequency magnetic field generated by electrical transmission lines and electrically powered devices and the high frequencies electromagnetic radiation emitted by electronic devices have a potentially negative impact on the circadian system. On the other hand, several studies have found no influence of these fields on chronobiological parameters. According to the current state of knowledge, some previously proposed hypotheses, including one concerning the key role of melatonin secretion disruption in pathogenesis of electromagnetic field induced diseases, need to be revised. This paper reviews the data on the effect of electric, magnetic, and electromagnetic fields on melatonin and cortisol rhythms—two major markers of the circadian system as well as on sleep. It also provides the basic information about the nature, classification, parameters, and sources of these fields.

  18. Pulsed remote field eddy current technique applied to non-magnetic flat conductive plates

    Science.gov (United States)

    Yang, Binfeng; Zhang, Hui; Zhang, Chao; Zhang, Zhanbin

    2013-12-01

    Non-magnetic metal plates are widely used in aviation and industrial applications. The detection of cracks in thick plate structures, such as multilayered structures of aircraft fuselage, has been challenging in nondestructive evaluation societies. The remote field eddy current (RFEC) technique has shown advantages of deep penetration and high sensitivity to deeply buried anomalies. However, the RFEC technique is mainly used to evaluate ferromagnetic tubes. There are many problems that should be fixed before the expansion and application of this technique for the inspection of non-magnetic conductive plates. In this article, the pulsed remote field eddy current (PRFEC) technique for the detection of defects in non-magnetic conducting plates was investigated. First, the principle of the PRFEC technique was analysed, followed by the analysis of the differences between the detection of defects in ferromagnetic and non-magnetic plain structures. Three different models of the PRFEC probe were simulated using ANSYS. The location of the transition zone, defect detection sensitivity and the ability to detect defects in thick plates using three probes were analysed and compared. The simulation results showed that the probe with a ferrite core had the highest detecting ability. The conclusions derived from the simulation study were also validated by conducting experiments.

  19. Magnetic Field Perturbations from Currents in the Dark Polar Regions During Quiet Geomagnetic Conditions

    DEFF Research Database (Denmark)

    Friis-Christensen, Eigil; Finlay, Chris; Hesse, M.

    2017-01-01

    In the day-side sunlit polar ionosphere the varying and IMF dependent convection creates strong ionospheric currents even during quiet geomagnetic conditions. Observations during such times are often excluded when using satellite data to model the internal geomagneticmain field. Observations from...... the night-side or local winter during quiet conditions are, however, also influenced by variations in the IMF. In this paper we briefly review the large scale features of the ionospheric currents in the polar regions with emphasis on the current distribution during undisturbed conditions. We examine....... The other category represent contributions caused by geomagnetic activity related to the substorm current wedge around local magnetic midnight. A new observation is a strong IMF By control of the residuals in the midnight sector indicating larger ionospheric currentsin the substorm current wedge...

  20. Dark current, breakdown, and magnetic field effects in a multicell, 805 MHz cavity

    Directory of Open Access Journals (Sweden)

    J. Norem

    2003-07-01

    Full Text Available We present measurements of dark currents and x rays in a six cell 805 MHz cavity, taken as part of an rf development program for muon cooling, which requires high power, high stored energy, low frequency cavities operating in a strong magnetic field. We have done the first systematic study of the behavior of high power rf in a strong (2.5–4 T magnetic field. Our measurements extend over a very large dynamic range in current and provide good fits to the Fowler-Nordheim field emission model assuming mechanical structures produce field enhancements at the surface. The locally enhanced field intensities we derive at the tips of these emitters are very large, (∼10  GV/m, and should produce tensile stresses comparable to the tensile strength of the copper cavity walls and should be capable of causing breakdown events. We also compare our data with estimates of tensile stresses from a variety of accelerating structures. Preliminary studies of the internal surface of the cavity and window are presented, which show splashes of copper with many sharp cone shaped protrusions and wires which can explain the experimentally measured field enhancements. We discuss a “cold copper” breakdown mechanism and briefly review alternatives. We also discuss a number of effects due to the 2.5 T solenoidal fields on the cavity such as altered field emission due to mechanical deformation of emitters, and dark current ring beams, which are produced from the irises by E×B drifts during the nonrelativistic part of the acceleration process.

  1. A Novel High Sensitivity Sensor for Remote Field Eddy Current Non-Destructive Testing Based on Orthogonal Magnetic Field

    Directory of Open Access Journals (Sweden)

    Xiaojie Xu

    2014-12-01

    Full Text Available Remote field eddy current is an effective non-destructive testing method for ferromagnetic tubular structures. In view of conventional sensors’ disadvantages such as low signal-to-noise ratio and poor sensitivity to axial cracks, a novel high sensitivity sensor based on orthogonal magnetic field excitation is proposed. Firstly, through a three-dimensional finite element simulation, the remote field effect under orthogonal magnetic field excitation is determined, and an appropriate configuration which can generate an orthogonal magnetic field for a tubular structure is developed. Secondly, optimized selection of key parameters such as frequency, exciting currents and shielding modes is analyzed in detail, and different types of pick-up coils, including a new self-differential mode pick-up coil, are designed and analyzed. Lastly, the proposed sensor is verified experimentally by various types of defects manufactured on a section of a ferromagnetic tube. Experimental results show that the proposed novel sensor can largely improve the sensitivity of defect detection, especially for axial crack whose depth is less than 40% wall thickness, which are very difficult to detect and identify by conventional sensors. Another noteworthy advantage of the proposed sensor is that it has almost equal sensitivity to various types of defects, when a self-differential mode pick-up coil is adopted.

  2. Unusual dc electric fields induced by a high frequency alternating current in superconducting Nb films under a perpendicular magnetic field

    Science.gov (United States)

    Aliev, F. G.; Levanyuk, A. P.; Villar, R.; Sierra, J. F.; Pryadun, V. V.; Awad, A.; Moshchalkov, V. V.

    2009-06-01

    We report a systematic study of dc electric fields produced by sinusoidal high frequency ac currents in Nb superconducting films subject to a constant magnetic field perpendicular to the film plane. At frequencies in the 100 kHz to MHz range appears a new rectification effect which has not been previously observed at lower frequencies. We have observed the dc electric field generated in this regime in films without intentionally created anisotropic pinning centres, i.e. plain films, both in strip geometry as in cross-shape geometry, and also in films with symmetric periodic pinning centres. The electric field appears in both directions along and transverse to the alternating current and is essentially different at opposite film sides. It depends strongly on the intensity of the magnetic field and may exceed by nearly an order of magnitude the rectified electric fields recently reported at lower frequencies (few kHz) in systems with artificially induced anisotropic vortex pinning. The effect has a non-monotonic dependence on the drive current frequency, being maximum around a few 100 kHz to MHz, and shows a complicated temperature dependence. It is found to be different in long strips and cross shape samples. In the case of films with symmetric periodic pinning centres the rectified voltage shows a lower magnitude than in plain films, and shows an interesting structure when the applied magnetic field crosses the matching fields. We are only able to put forward tentative ideas to explain this phenomenon, which irrespective of its explanation should be taken into account in experimental studies of rectification effects in superconductors.

  3. Effect of External Magnetic Field on Critical Current for the Onset of Virtual Cathode Oscillations in Relativistic Electron Beams

    CERN Document Server

    Hramov, Alexander E; Morozov, Mikhail; Mushtakov, Alexander

    2008-01-01

    In this Letter we research the space charge limiting current value at which the oscillating virtual cathode is formed in the relativistic electron beam as a function of the external magnetic field guiding the beam electrons. It is shown that the space charge limiting (critical) current decreases with growth of the external magnetic field, and that there is an optimal induction value of the magnetic field at which the critical current for the onset of virtual cathode oscillations in the electron beam is minimum. For the strong external magnetic field the space charge limiting current corresponds to the analytical relation derived under the assumption that the motion of the electron beam is one-dimensional [High Power Microwave Sources. Artech House Microwave Library, 1987. Chapter~13]. Such behavior is explained by the characteristic features of the dynamics of electron space charge in the longitudinal and radial directions in the drift space at the different external magnetic fields.

  4. Simulation of the magnetic field generated by wires with stationary current and magnets with constant magnetization applied to the mirror trap, minimum-B and zero-B

    Science.gov (United States)

    Murillo, M. T.; Otero, O.

    2016-02-01

    As a contribution to the computational simulation of magnetic confinement and heating of plasmas ECR (Electron Cyclotron Resonance), this work is dedicated to the calculation and subsequent analysis of the magnetic fields generated by permanent magnets and coils required in magnetic traps between which we can mention the mirror trap, minimum- B and zero-B. To do this, we solved numerically the Biot-Savart law in the case of the coils with stationary current and the Ampere law in the case of the permanent magnets. The study includes the characterization of the ECR areas as well as the display of the vector field all of this applied to the magnetic traps mentioned above. Additionally, in the case of the mirror type trap and minimum-B trap, it is determined the ratio of the mirror, because it is important in the description of confinement.

  5. Resistive current states in wide superconducting films in zero magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Dmitriev, V M [B Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, 61103 Kharkiv (Ukraine); Zolochevskii, I V [B Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, 61103 Kharkiv (Ukraine)

    2006-04-15

    The temperature dependence of the current-voltage characteristics of high-quality thin films of tin from 7 to 50 {mu}m thick are investigated in the absence of an external magnetic field. For the first time, we have experimentally observed phase slip centres (PSCs) and phase slip lines (PSLs) on the same superconducting tin film with known parameters in the temperature intervals corresponding to the mechanisms of their formation and existence. We have shown that the states of a wide film with increasing transport current appear in the following order: the superconducting state for current less than critical; the resistive vortex state for current more than critical, but less than maximum current for the uniform flux flow (instability current); the critical state due to the onset of instability of the steady pattern of viscous motion of the vortices; a vortex-free resistive state with PSLs for current more than instability current, but less than the upper critical current; and the normal state at a current higher than the upper critical current.

  6. Torque analysis and measurements of a permanent magnet type Eddy current brake with a Halbach magnet array based on analytical magnetic field calculations

    Science.gov (United States)

    Park, Min-Gyu; Choi, Jang-Young; Shin, Hyeon-Jae; Jang, Seok-Myeong

    2014-05-01

    This paper presents the torque analysis and measurements of a permanent magnet (PM) type eddy current brake (ECB) with a Halbach magnet array based on analytical magnetic field calculations. On the basis of a magnetic vector potential and using a two-dimensional (2D) polar coordinate system, the analytical solution for magnetic flux density, including the eddy current reaction is evaluated. Based on these solutions, the magnetic torque is also determined analytically. A 2D finite element analysis is employed to validate the method used. Practical issues in the analytical study of the PM type ECBs, such as the maximum braking torque, the required rotor speed, and the segment-dependent, are fully discussed. Finally, the braking torque as a function of the rotor speed is measured to verify the results of the analytical study.

  7. Induced current density in the foetus of pregnant workers in high magnetic field environments.

    Science.gov (United States)

    Xue, C; Wood, A W; Dovan, T

    2004-12-01

    There are moves to limit by legislation the amount of electric and magnetic fields that workers and the general public are exposed to. In work locations near wiring, cables & equipment carrying high electric currents, there are situations in which the proposed magnetic field limits could be exceeded. Since the limits for the general public are more conservative than those for workers and since the foetus or a pregnant worker should be afforded the status of a member of the general public, it is important to assess a worst-case scenario for the purposes of a general code of practice. Three different magnetic field exposures are modelled, which include the worst case - the body of a pregnant woman at a smallest distance of 30 cm to the conductor. All computations were done by using Multiple Multipole Program (MMP), which is based on the Generalized Multipole Technique (GMT) from ETH (Swiss Federal Institute of Technology), Zurich, Switzerland. In a worst-case scenario the proposed basic restrictions would be exceeded slightly in both maternal and foetal tissue. With appropriate pre-placement assessment, these over-exposures can be avoided.

  8. Helicity and alpha-effect by current-driven instabilities of helical magnetic fields

    CERN Document Server

    Gellert, M; Hollerbach, R

    2011-01-01

    Helical magnetic background fields with adjustable pitch angle are imposed on a conducting fluid in a differentially rotating cylindrical container. The small-scale kinetic and current helicities are calculated for various field geometries, and shown to have the opposite sign as the helicity of the large-scale field. These helicities and also the corresponding $\\alpha$-effect scale with the current helicity of the background field. The $\\alpha$-tensor is highly anisotropic as the components $\\alpha_{\\phi\\phi}$ and $\\alpha_{zz}$ have opposite signs. The amplitudes of the azimuthal $\\alpha$-effect computed with the cylindrical 3D MHD code are so small that the operation of an $\\alpha\\Omega$ dynamo on the basis of the current-driven, kink-type instabilities of toroidal fields is highly questionable. In any case the low value of the $\\alpha$-effect would lead to very long growth times of a dynamo in the radiation zone of the Sun and early-type stars of the order of mega-years.

  9. Magnetic current sensor

    Science.gov (United States)

    Black, Jr., William C. (Inventor); Hermann, Theodore M. (Inventor)

    1998-01-01

    A current determiner having an output at which representations of input currents are provided having an input conductor for the input current and a current sensor supported on a substrate electrically isolated from one another but with the sensor positioned in the magnetic fields arising about the input conductor due to any input currents. The sensor extends along the substrate in a direction primarily perpendicular to the extent of the input conductor and is formed of at least a pair of thin-film ferromagnetic layers separated by a non-magnetic conductive layer. The sensor can be electrically connected to a electronic circuitry formed in the substrate including a nonlinearity adaptation circuit to provide representations of the input currents of increased accuracy despite nonlinearities in the current sensor, and can include further current sensors in bridge circuits.

  10. The magnetic shear-current effect: generation of large-scale magnetic fields by the small-scale dynamo

    CERN Document Server

    Squire, Jonathan

    2015-01-01

    A novel large-scale dynamo mechanism, the magnetic shear-current effect, is discussed and explored. The effect relies on the interaction of magnetic fluctuations with a mean shear flow, meaning the saturated state of the small-scale dynamo can drive a large-scale dynamo -- in some sense the inverse of dynamo quenching. The dynamo is nonhelical, with the mean-field $\\alpha$ coefficient zero, and is caused by the interaction between an off-diagonal component of the turbulent resistivity and the stretching of the large-scale field by shear flow. Following up on previous numerical and analytic work, this paper presents further details of the numerical evidence for the effect, as well as an heuristic description of how magnetic fluctuations can interact with shear flow to produce the required electromotive force. The pressure response of the fluid is fundamental to this mechanism, which helps explain why the magnetic effect is stronger than its kinematic cousin, and the basic idea is related to the well-known lack...

  11. Physical and Mechanical Characterization of Electrodeposited Nickel Nanowires -- Influence of Current Density and External Magnetic Field

    Science.gov (United States)

    Samykano, Mahendran

    Magnetic 1-D nanostructures have received great interest due to their various applications including high-density magnetic storage, sensors, drug delivery, and NEMS/MEMS systems. Among different 1-D nanostructures, magnetic nickel (Ni) nanowires with their ferromagnetic properties are of interest in such applications due to their lower cost, and they can be consistently synthesized via electrodeposition. While physical properties are influenced by processing parameters during electrodeposition of Ni nanowires, understanding of their influence on the mechanical properties is still not available. This is primarily due to the following challenges: tediousness involved in experimental techniques for mechanical characterization at nanoscale; sophisticated and careful experimentation required to be performed with advanced microscopy systems (SEM, AFM); robust nanoscale manipulators needed to place a single nanowire within the device; and difficulty in correctly loading and obtaining data for stress-strain within high powered microscopy environments. All of these factors pose significant challenges, limiting the current state of the art in mechanical characterization to its infancy, with wide differences in characterization curves and reported properties in this field. The present research and dissertation focuses on: 1. Experimental synthesis of electrodeposited Ni nanowires at different current densities and external magnetic fields, 2. Physical properties characterization of the synthesized nanowires to understand their morphology, structural and crystallographic properties, 3. Mechanical properties characterization of synthesized Ni nanowires through careful experiments within scanning electron microscope (SEM) based on uni-axial MEMS tensile loading device, 4. Data analysis to understand the process, physical and mechanical property interrelationship and to obtain insights on tensile deformation and failure modes observed in the Ni nanowires studied. Key research

  12. Excessive magnetic field flux density distribution from overhead isolated powerline conductors due to neutral line current.

    Science.gov (United States)

    Netzer, Moshe

    2013-06-01

    Overhead isolated powerline conductors (hereinafter: "OIPLC") are the most compact form for distributing low voltage currents. From the known physics of magnetic field emission from 3-phase power lines, it is expected that excellent symmetry of the 120° shifted phase currents and where compact configuration of the 3-phase+neutral line exist, the phase current vectorial summation of the magnetic field flux density (MFFD) is expected to be extremely low. However, despite this estimation, an unexpectedly very high MFFD was found in at least three towns in Israel. This paper explains the reasons leading to high MFFD emissions from compact OIPLC and the proper technique to fix it. Analysis and measurement results had led to the failure hypothsis of neutral line poor connection design and poor grounding design of the HV-LV utility transformers. The paper elaborates on the low MFFD exposure level setup by the Israeli Environmental Protection Office which adopted a rather conservative precaution principal exposure level (2 mG averaged over 24 h).

  13. Josephson critical current of long SNS junctions in the presence of a magnetic field

    Science.gov (United States)

    Meier, Hendrik; Fal'Ko, Vladimir I.; Glazman, Leonid I.

    We evaluate the Josephson critical current of a long and wide two-dimensional superconductor-normal metal-superconductor (SNS) junction, taking into account the effect of electron reflection off the side edges of the junction. Considering clean junctions, we find that the effect of edges alters the usual Fraunhofer-like dependence of the Josephson critical current Ic on the magnetic flux Φ. At relatively weak fields, B edge effect lifts zeros of the Ic (Φ) dependence and gradually shifts the maxima of that function by Φ0 / 2 . (Here W is the width of the junction and Φ0 the magnetic flux quantum.) At higher fields, B >~Φ0 /W2 , the edge effect leads to an accelerated decay of the critical current Ic (Φ) with increasing Φ. Our results are robust with respect to the roughness of realistic boundaries. Finally, we discuss the role of mesoscopic fluctuations of Ic (Φ) originating from the scattering off the edges, and compare our findings to recent experiments.

  14. Analysis of Magnetic Field Distribution Under Power Lines with Changing Direction and Carrying Different Current%Analysis of Magnetic Field Distribution Under Power Lines with Changing Direction and Carrying Different Current

    Institute of Scientific and Technical Information of China (English)

    T. Matsumoto; H. Hirata; H. Tarao; N. Hayashi; K. Isaka

    2011-01-01

    Transmission power lines are a common source of extremely low frequency (ELF) magnetic fields which are usually analyzed as serial lines in one direction. Overhead vertical-type double-circuit power lines, which are generally used in Japan, sometimes carry different current for each circuit and change direction. In this paper, we focused on both the angle of direction change and the current balance in order to clarify the characteristics of distribution of magnetic fields at a height of 1 m. The magnetic field distributions were analyzed considering both the angle of power lines changing direction and the current balance of each circuit. The total magnetic field under overhead vertical-type double-circuit power lines with same current was generally reduced in comparison with that under a single-circuit power line due to phase difference. The total magnetic fields around the turning point where the change of transmission lines direction increased because each circuit came closer in that area. The component of Bz effect on total magnetic field was greatest around the maximum of total magnetic fields nearby the turning point.

  15. Critical Current Test of Liquid Hydrogen Cooled HTC Superconductors under External Magnetic Field

    Science.gov (United States)

    Shirai, Yasuyuki; Shiotsu, Masahiro; Tatsumoto, Hideki; Kobayashi, Hiroaki; Naruo, Yoshihiro; Nonaka, Satoshi; Inatani, Yoshifumi

    High-Tc (HTC) superconductors including MgB2 will show excellent properties under temperature of Liquid Hydrogen (LH2:20K), which has large latent heat and low viscosity coefficient. In order to design and fabricate the LH2 cooled superconducting energy devices, we must clear the cooling property of LH2 for superconductors, the cooling system and safety design of LH2 cooled superconducting devices and electro-magnetic property evaluation of superconductors (BSCCO, REBCO and MgB2) and their magnets cooled by LH2. As the first step of the study, an experimental setup which can be used for investigating heat transfer characteristics of LH2 in a pool and also in forced flow (circulation loop with a pump), and also for evaluation of electro-magnetic properties of LH2 cooled superconductors under external magnetic field (up to 7 T). In this paper, we will show a short sketch of the experimental set-up, practical experiences in safety operation of liquid hydrogen cooling system and example test results of critical current evaluation of HTC superconductors cooled by LH2.

  16. Temperature and magnetic field dependence of the critical current in polycrystalline Ba2YCu3O(y)

    Science.gov (United States)

    Obara, H.; Yamasaki, H.; Kimura, Y.; Higashida, Y.; Ishihara, T.

    Temperature and magnetic field dependence on the critical current density Jc of polycrystalline high-Tc oxide superconductor, Ba2YCu3O(y), have been measured. In the low magnetic field range, 0.6 to about 7 kOe, the Jc behavior changed at around 70 K. Below 70 K, Jc showed different temperature dependence between field cooling and zero-field cooling, that is, the Jc value measured when the sample was cooled in a fixed magnetic field, was different from that measured when the sample was cooled in zero magnetic field and then a magnetic field was applied. Above 70 K, however, such different temperature dependence on Jc was not observed. These experimental results can be attributed to the effects of anisotropy. A crossover between the two- and three-dimensional superconductivity is considered to occur.

  17. The Onset of Magnetic Reconnection: Tearing Instability in Current Sheets with a Guide Field

    Science.gov (United States)

    Daldorff, Lars K. S.; Klimchuk, James A.; Leake, James E.; Knizhnik, Kalman

    2017-08-01

    Magnetic reconnection is fundamental to many solar phenomena, ranging from coronal heating, to jets, to flares and CMEs. A poorly understood yet crucial aspect of reconnection is that it does not occur until magnetic stresses have built to sufficiently high levels for significant energy release. If reconnection were to happen too soon, coronal heating would be weak and flares would be small. As part of our program to study the onset conditions for magnetic reconnection, we have investigated the instability of current sheets to tearing. Surprisingly little work has been done on this problem for sheets that include a guide field, i.e., for which the field rotates by less than 180 degrees. This is the most common situation on the Sun. We present numerical 3D resistive MHD simulations of several sheets and show how the behavior depends on the shear angle (rotation). We compare our results to the predictions of linear theory and discuss the nonlinear evolution in terms of plasmoid formation and the interaction of different oblique tearing modes. The relevance to the Sun is explained.

  18. Ion motion in the current sheet with sheared magnetic field – Part 1: Quasi-adiabatic theory

    Directory of Open Access Journals (Sweden)

    A. V. Artemyev

    2013-02-01

    Full Text Available We present a theory of trapped ion motion in the magnetotail current sheet with a constant dawn–dusk component of the magnetic field. Particle trajectories are described analytically using the quasi-adiabatic invariant corresponding to averaging of fast oscillations around the tangential component of the magnetic field. We consider particle dynamics in the quasi-adiabatic approximation and demonstrate that the principal role is played by large (so called geometrical jumps of the quasi-adiabatic invariant. These jumps appear due to the current sheet asymmetry related to the presence of the dawn–dusk magnetic field. The analytical description is compared with results of numerical integration. We show that there are four possible regimes of particle motion. Each regime is characterized by certain ranges of values of the dawn–dusk magnetic field and particle energy. We find the critical value of the dawn–dusk magnetic field, where jumps of the quasi-adiabatic invariant vanish.

  19. Analysis of induced electrical currents from magnetic field coupling inside implantable neurostimulator leads

    Directory of Open Access Journals (Sweden)

    Seidman Seth J

    2011-10-01

    Full Text Available Abstract Background Over the last decade, the number of neurostimulator systems implanted in patients has been rapidly growing. Nearly 50, 000 neurostimulators are implanted worldwide annually. The most common type of implantable neurostimulators is indicated for pain relief. At the same time, commercial use of other electromagnetic technologies is expanding, making electromagnetic interference (EMI of neurostimulator function an issue of concern. Typically reported sources of neurostimulator EMI include security systems, metal detectors and wireless equipment. When near such sources, patients with implanted neurostimulators have reported adverse events such as shock, pain, and increased stimulation. In recent in vitro studies, radio frequency identification (RFID technology has been shown to inhibit the stimulation pulse of an implantable neurostimulator system during low frequency exposure at close distances. This could potentially be due to induced electrical currents inside the implantable neurostimulator leads that are caused by magnetic field coupling from the low frequency identification system. Methods To systematically address the concerns posed by EMI, we developed a test platform to assess the interference from coupled magnetic fields on implantable neurostimulator systems. To measure interference, we recorded the output of one implantable neurostimulator, programmed for best therapy threshold settings, when in close proximity to an operating low frequency RFID emitter. The output contained electrical potentials from the neurostimulator system and those induced by EMI from the RFID emitter. We also recorded the output of the same neurostimulator system programmed for best therapy threshold settings without RFID interference. Using the Spatially Extended Nonlinear Node (SENN model, we compared threshold factors of spinal cord fiber excitation for both recorded outputs. Results The electric current induced by low frequency RFID emitter

  20. High magnetic-field scales and critical currents in SmFeAs(O, F) crystals

    Science.gov (United States)

    Moll, Philip J. W.; Puzniak, Roman; Balakirev, Fedor; Rogacki, Krzysztof; Karpinski, Janusz; Zhigadlo, Nikolai D.; Batlogg, Bertram

    2010-08-01

    With the discovery of new superconducting materials, such as the iron pnictides, exploring their potential for applications is one of the foremost tasks. Even if the critical temperature Tc is high, intrinsic electronic properties might render applications difficult, particularly if extreme electronic anisotropy prevents effective pinning of vortices and thus severely limits the critical current density, a problem well known for cuprates. Although many questions concerning microscopic electronic properties of the iron pnictides have been successfully addressed and estimates point to a very high upper critical field, their application potential is less clear. Thus, we focus here on the critical currents, their anisotropy and the onset of electrical dissipation in high magnetic fields up to 65T. Our detailed study of the transport properties of SmFeAsO0.7F0.25 single crystals reveals a promising combination of high (>2×106Acm-2) and nearly isotropic critical current densities along all crystal directions. This favourable intragrain current transport in SmFeAs(O, F), which shows the highest Tc of 54K at ambient pressure, is a crucial requirement for possible applications. Essential in these experiments are four-probe measurements on focused-ion-beam-cut single crystals with a sub-square-micrometre cross-section, with current along and perpendicular to the crystallographic c axis.

  1. Minimum Field Requirements for Spin-Polarized Current Assisted Switching of Magnetization in Nanostructures with Uniaxial Anisotropy

    Directory of Open Access Journals (Sweden)

    GINDULESCU, A.

    2009-03-01

    Full Text Available The present paradigm of magnetic data storage is approaching its fundamental limits for areal storage density, as well as for speed in data processing. As a result, several magnetic recording alternatives, such as spin polarized current assisted recording, precessional switching, toggle switching, heat assisted recording are currently under intense research efforts. This article is aimed at providing a pertinent theoretical analysis of the spin polarized current assisted recording, emphasizing its performance with respect to minimum requirements for switching field. The first analytical derivation of the critical field curve in the presence of spin polarized currents is presented and the results are compared to the classical Stoner-Wohlfarth astroid. The analysis is performed under the framework of the Landau-Lifshitz-Gilbert-Slonczewski equation for describing the magnetization dynamics driven by external magnetic fields and spin polarized currents.

  2. Magnetic-field-induced superconducting state in Zn nanowires driven in the normal state by an electric current.

    Science.gov (United States)

    Chen, Yu; Snyder, S D; Goldman, A M

    2009-09-18

    Four-terminal resistance measurements have been carried out on Zn nanowires formed using electron-beam lithography. When driven resistive by current, these wires reenter the superconducting state upon application of small magnetic fields. The data are qualitatively different from those of previous experiments on superconducting nanowires, which revealed either negative magnetoresistance near T_{c} or high-magnetic-field-enhanced critical currents.

  3. Temperature and Magnetic Field Dependence of Critical Current Density of YBCO with Varying Flux Pinning Additions (POSTPRINT)

    Science.gov (United States)

    2010-03-01

    AFRL-RZ-WP-TP-2010-2083 TEMPERATURE AND MAGNETIC FIELD DEPENDENCE OF CRITICAL CURRENT DENSITY OF YBCO WITH VARYING FLUX PINNING ADDITIONS...MAGNETIC FIELD DEPENDENCE OF CRITICAL CURRENT DENSITY OF YBCO WITH VARYING FLUX PINNING ADDITIONS (POSTPRINT) 5a. CONTRACT NUMBER In-house 5b...20 ‒ 77 K. Films were prepared with pulsed laser deposition by (M/ YBCO )N multilayer or ( YBCO )1-x Mx single-target methods, for different M phases

  4. Influence of Tailored Applied Magnetic Fields on High-Power MPD Thruster Current Transport and Onset-Related Phenomena

    Science.gov (United States)

    Moeller, Robert C.; Polk, James E.

    2013-01-01

    This work investigated the effects of tailored, externally-applied magnetic fields on current transport and near-anode processes in the plasma discharge of a magnetoplasmadynamic thruster (MPDT). Electrical and plasma diagnostics were used to investigate how localized applied magnetic fields could mitigate the effects of the "onset" phenomena, including large-amplitude terminal voltage fluctuations and high anode fall voltages associated with unstable operation and anode erosion. An MPDT with a multi-channel hollow cathode was developed and tested with quasi-steady pulses of 1 millisecond duration at power levels of 36 kilowatts (20 volts, 1800 amperes) to 3.3 milliwatts (255 volts, 13.1 kiloamperes) with argon propellant in three different magnetic configurations: self-field, applied B field tangential to the anode lip near the exit plane, and applied cusp B field. The current pattern and current densities redistributed to follow the applied poloidal magnetic field lines, which created increased conduction paths to the anode. Also, the anode fall voltage was substantially reduced with both applied B field topologies over a large range of currents. For example, at 10.7 kiloamperes, the cusp applied magnetic field decreased anode fall voltages from 45-83 volts down to 15 volts or lower along much of the anode. The amplitude and frequency of the voltage fluctuations were also reduced over a broad range of currents with the applied fields. E.g., the standard deviations of the fluctuations were lowered by 37-49 percent at 8-9 kiloamperes. In addition, decreases in the mean terminal voltages as large as 31 percent were measured with the applied magnetic fields. These effects are shown to be associated with the increased current conduction along the applied magnetic field lines in the near-anode region. These results also suggest a reduction in frequency and intensity of current-concentrating filaments and anode spots, which contribute to erosion. Overall, both applied

  5. Influence of Tailored Applied Magnetic Fields on High-Power MPD Thruster Current Transport and Onset-Related Phenomena

    Science.gov (United States)

    Moeller, Robert C.; Polk, James E.

    2013-01-01

    This work investigated the effects of tailored, externally-applied magnetic fields on current transport and near-anode processes in the plasma discharge of a magnetoplasmadynamic thruster (MPDT). Electrical and plasma diagnostics were used to investigate how localized applied magnetic fields could mitigate the effects of the "onset" phenomena, including large-amplitude terminal voltage fluctuations and high anode fall voltages associated with unstable operation and anode erosion. An MPDT with a multi-channel hollow cathode was developed and tested with quasi-steady pulses of 1 millisecond duration at power levels of 36 kilowatts (20 volts, 1800 amperes) to 3.3 milliwatts (255 volts, 13.1 kiloamperes) with argon propellant in three different magnetic configurations: self-field, applied B field tangential to the anode lip near the exit plane, and applied cusp B field. The current pattern and current densities redistributed to follow the applied poloidal magnetic field lines, which created increased conduction paths to the anode. Also, the anode fall voltage was substantially reduced with both applied B field topologies over a large range of currents. For example, at 10.7 kiloamperes, the cusp applied magnetic field decreased anode fall voltages from 45-83 volts down to 15 volts or lower along much of the anode. The amplitude and frequency of the voltage fluctuations were also reduced over a broad range of currents with the applied fields. E.g., the standard deviations of the fluctuations were lowered by 37-49 percent at 8-9 kiloamperes. In addition, decreases in the mean terminal voltages as large as 31 percent were measured with the applied magnetic fields. These effects are shown to be associated with the increased current conduction along the applied magnetic field lines in the near-anode region. These results also suggest a reduction in frequency and intensity of current-concentrating filaments and anode spots, which contribute to erosion. Overall, both applied

  6. Experimental study of the dependence of beam current on injection magnetic field in 6.4 GHz ECR ion source

    Indian Academy of Sciences (India)

    G S Taki; P R Sarma; D K Chakraborty; R K Bhandari; P K Ray

    2006-09-01

    The ion current from an electron cyclotron resonance (ECR) heavy ion source depends on the confining axial and radial magnetic fields. Some efforts were made by earlier workers to investigate magnetic field scaling on the performance of the ECR source. In order to study the dependence of the ion current on the injection magnetic field in the 6.4 GHz ECR source, we have measured the current by varying the peak injection field and have inferred that the variation of the current is exponential up to our maximum design injection field of 7.5 kG. An attempt has been made to understand this exponential nature on the basis of ion confinement time.

  7. Feasibility assessment of magnetic sensors for measurment of Hall current induced changes to the static magnetic field nearby a Hall thruster

    Science.gov (United States)

    Morozko, Zoe

    A Hall thruster is an electric propulsion device that produces thrust electrostatically by accelerating propellant to velocities 5 to 10 times higher than is achievable using conventional chemical thrusters. This is accomplished through the application of static, crossed electric and magnetic fields that are concentrated in a region close to the exit plane of the thruster. During operation an azimuthal plasma-electron current develops in the region where the electric and magnetic fields are concentrated. This embedded plasma current is referred to as the Hall current. The thrust produced from accelerating the propellant is transferred to a satellite or spacecraft through interaction between the Hall current and the magnetic coils used to produce the static magnetic field within the thruster. The Hall current can be calculated and the thrust can be determined in real time by measuring the magnetic field produced by the Hall current using sensors located external to the thruster. This work investigates the feasibility of placing magnetic sensors in the regions close to the exit of the thruster to measure the external magnetic field and correlate it to the Hall current. A finite element magnetic solver was used to identify several locations outside of the thrust plume and near the pole piece where the magnetic field magnitude changes by several Gauss in a background field level of ˜50 Gauss. Magnetic sensors based on the giant magnetoresistive effect were identified as acceptable with regard to sensitivity, and measurements made with these sensors in a simulated high background magnetic field environment demonstrated that changes of 0.5 Gauss could be easily measured. This work also presents the development of a thrust stand that will be useful in future work to demonstrate the overall concept. Special focus was directed to the design of the data acquisition system and in-vacuum calibration system used to make measurements with the thrust stand.

  8. Three-dimensional evolution of a relativistic current sheet: triggering of magnetic reconnection by the guide field.

    Science.gov (United States)

    Zenitani, S; Hoshino, M

    2005-08-26

    The linear and nonlinear evolution of a relativistic current sheet of pair (e(+/-)) plasmas is investigated by three-dimensional particle-in-cell simulations. In a Harris configuration, it is obtained that the magnetic energy is fast dissipated by the relativistic drift kink instability (RDKI). However, when a current-aligned magnetic field (the so-called "guide field") is introduced, the RDKI is stabilized by the magnetic tension force and it separates into two obliquely propagating modes, which we call the relativistic drift-kink-tearing instability. These two waves deform the current sheet so that they trigger relativistic magnetic reconnection at a crossover thinning point. Since relativistic reconnection produces a lot of nonthermal particles, the guide field is of critical importance to study the energetics of a relativistic current sheet.

  9. Regional estimation of geomagnetically induced currents based on the local magnetic or electric field

    Directory of Open Access Journals (Sweden)

    Viljanen Ari

    2015-01-01

    Full Text Available Previous studies have demonstrated a close relationship between the time derivative of the horizontal geomagnetic field vector (dH/dt and geomagnetically induced currents (GIC at a nearby location in a power grid. Similarly, a high correlation exists between GIC and the local horizontal geoelectric field (E, typically modelled from a measured magnetic field. Considering GIC forecasting, it is not feasible to assume that detailed prediction of time series will be possible. Instead, other measures summarising the activity level over a given period are preferable. In this paper, we consider the 30-min maximum of dH/dt or E as a local activity indicator (|dH/dt|30 or |E|30. Concerning GIC, we use the sum of currents through the neutral leads at substations and apply its 30-min maximum as a regional activity measure (GIC30. We show that |dH/dt|30 at a single point yields a proxy for GIC activity in a larger region. A practical consequence is that if |dH/dt|30 can be predicted at some point then it is also possible to assess the expected GIC level in the surrounding area. As is also demonstrated, |E|30 and GIC30 depend linearly on |dH/dt|30, so there is no saturation with increasing geomagnetic activity contrary to often used activity indices.

  10. The dynamics of field and current-driven magnetic domain wall depinning

    Science.gov (United States)

    Beach, Geoffrey; Knutson, Carl; Tsoi, Maxim; Erskine, James

    2008-03-01

    The depinning of a magnetic domain wall from a well-defined potential well was studied experimentally on timescales ranging from minutes down to tens of nanoseconds. At longer timescales, the behavior follows the classical Neel-Brown model of thermal activation, one of the few observations of this process for the ideal case of a single energy barrier. Below one microsecond, however, the depinning rate becomes independent of the activation volume and assumes a more universal behavior. This transition is due to a vanishing of the energy barrier at a critical field, beyond which the rate of depinning depends primarily on the torque supplied by the field and spin current. A dc spin-polarized current flowing across the domain wall has the effect of lowering the energy barrier by an amount that is predominantly quadratic in current, independent of its direction. This is seen to arise from a shift of the wall in the energy potential due to the adiabatic component of spin-transfer torque.

  11. Magnetar Giant Flares in Multipolar Magnetic Fields --- II. Flux Rope Eruptions With Current Sheets

    CERN Document Server

    Huang, Lei

    2014-01-01

    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 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. Especially, we find two kinds of physical behaviors, i.e., catastrophic state transition and catastrophic escape. Magnetic energy would be released during state transitions. The released magnetic energy is sufficient to drive giant flares. The flux rope would go away from the magnetar quasi-statically, which is ...

  12. Magnetar giant flares in multipolar magnetic fields. II. Flux rope eruptions with current sheets

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Lei [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030 (China); Yu, Cong, E-mail: muduri@shao.ac.cn, E-mail: cyu@ynao.ac.cn [Key Laboratory for the Structure and Evolution of Celestial Object, Chinese Academy of Sciences, Kunming 650011 (China)

    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.

  13. Deformation of the free surface of a conducting fluid in the magnetic field of current-carrying linear conductors

    Science.gov (United States)

    Zubarev, N. M.; Zubareva, O. V.

    2017-06-01

    The magnetic shaping problem is studied for the situation where a cylindrical column of a perfectly conducting fluid is deformed by the magnetic field of a system of linear current-carrying conductors. Equilibrium is achieved due to the balance of capillary and magnetic pressures. Two two-parametric families of exact solutions of the problem are obtained with the help of conformal mapping technique. In accordance with them, the column essentially deforms in the cross section up to its disintegration.

  14. Computation of electrical fields and currents in a plasma flowing in a spatial-periodic magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Gorodzha, L.V.; Krutilin, V.A.; Rashchepkin, A.P.

    1977-01-01

    Electrical processes in a plasma flow in an internal periodically changing magnetic field are studied analytically. The analysis was conducted on the basis of the Riemann boundary problem for automorphic functions. Consequently, evaluations were made of the energy characteristics of the hollow MHD generator with an alternating magnetic field and their relationship to the geometric dimensions of the channel was found.

  15. Influences of a High Frequency Induction Current on the Uniformity of the Magnetic Field in an Electromagnetic Casting Mould

    CERN Document Server

    Zhang, Lintao; Sienz, Johann

    2013-01-01

    An analysis of the influences of a high frequency (30 kHz) alternating current on the uniformity of the magnetic field (B) in an electromagnetic casting (EMC) mould is investigated by means of parametric numerical simulations where the induction current (Js) varies in the range of [1 to 10000 A]. The results show that values of the magnetic flux density along the casting direction (Bz) near the square mould corners are small, compared to those at the other locations where Js < 10000 A, and that the magnitude of Bz increases with an increased induction current (Js). However, it is shown that, for the EMC mould structure investigated in this paper, the variations of Js have no significant influences on the uniformity of the magnetic field, especially for the regions near molten steel level. Moreover, the effective acting region (Rbz) for the critical magnetic field (Bzc) is first introduced in this paper, which opens an interesting topic for future research.

  16. The First Magnetic Fields

    CERN Document Server

    Widrow, Lawrence M; Schleicher, Dominik; Subramanian, Kandaswamy; Tsagas, Christos G; Treumann, Rudolf A

    2011-01-01

    We review current ideas on the origin of galactic and extragalactic magnetic fields. We begin by summarizing observations of magnetic fields at cosmological redshifts and on cosmological scales. These observations translate into constraints on the strength and scale magnetic fields must have during the early stages of galaxy formation in order to seed the galactic dynamo. We examine mechanisms for the generation of magnetic fields that operate prior during inflation and during subsequent phase transitions such as electroweak symmetry breaking and the quark-hadron phase transition. The implications of strong primordial magnetic fields for the reionization epoch as well as the first generation of stars is discussed in detail. The exotic, early-Universe mechanisms are contrasted with astrophysical processes that generate fields after recombination. For example, a Biermann-type battery can operate in a proto-galaxy during the early stages of structure formation. Moreover, magnetic fields in either an early genera...

  17. The Origin and Structure of the Magnetic Fields and Currents of AGN Jets

    Directory of Open Access Journals (Sweden)

    Denise Gabuzda

    2017-02-01

    Full Text Available This paper reviews observational evidence obtained to date about the overall structure of the magnetic fields in the jets of Active Galactic Nuclei (AGN. Because they are sensitive to the line-of-sight magnetic-field component, Faraday rotation observations of AGN jets provide an effective tool for searching for toroidal jet magnetic fields, whose line-of-sight component changes systematically across the jet. Transverse Faraday rotation measure (RM gradients providing direct evidence for helical/toroidal magnetic fields have been reliably detected in nearly 40 AGN on parsec scales. Helical magnetic fields are believed to form due to the combined action of the rotation of the central black hole and accretion disk, and these observations demonstrate that at least some of this helical field survives to distances well beyond the Very Long Baseline Interferometry (VLBI core. Observations of reversals in the direction of the transverse RM gradients in a number of AGN provide evidence for a“return”magnetic field forming a nested helical-field structure with oppositely directed azimuthal components in the inner and outer regions of the helical magnetic field. The collected data now provide firm evidence for a predominance of inward jet currents on parsec scales and outward currents on scales greater than a few tens of parsecs. This suggests a global pattern of magnetic fields and currents with an inward current near the jet axis and an outward current farther from the jet axis, with these currents closing in the accretion disk and far out in the radio lobes, forming a self-consistent set of fields and currents together with the implied nested helical-field structure.

  18. Current-density functional theory study of the H2 molecule evolving under a strong ultrashort magnetic field

    Science.gov (United States)

    Vikas, Hash(0xb7f6e60)

    2012-01-01

    Hydrogen molecule in a strong ultrashort magnetic field is investigated through a current-density functional theory (CDFT) and quantum fluid dynamics (QFD) based approach employing current-density dependent vector exchange-correlation potential and energy density functional derived with a vorticity variable. The numerical computations through the CDFT based approach are performed for the H2 molecule, starting initially from its field-free ground state, in a parallel internuclear axis and magnetic field-axis configuration with the internuclear separation R ranging from 0.1 a.u. to 14.0 a.u., and the strength of the time-dependent (TD) magnetic field varying between 0-1011 G over a few femtoseconds. The numerical results are compared with that obtained using an approach based on the current-density independent approximation under similar computational constraints but employing only scalar exchange-correlation potential dependent on the electronic charge-density alone. The current-density based approach yields exchange- and correlation energy as well as electronic charge-density of the H2 molecule drastically different from that obtained using current-independent approach, in particular, at TD magnetic field-strengths >109 G during a typical time-period of the field when the magnetic-field had attained maximum applied field-strength and is switched to a decreasing ramp function. This nonadiabatic behavior of the TD electronic charge-density is traced to the TD vorticity-dependent vector exchange-correlation potential of the CDFT based approach. The interesting electron dynamics of the H2 molecule in strong TD magnetic field is further elucidated by treating electronic charge-density as an `electron-fluid'. The present work also reveals interesting real-time dynamics on the attosecond time-scale in the electronic charge-density distribution of the hydrogen molecule.

  19. The break of shielding current at pulsed field magnetization of a superconducting annulus (experiment and model simulation)

    Science.gov (United States)

    Korotkov, V. S.; Krasnoperov, E. P.; Kartamyshev, A. A.

    2017-09-01

    During the pulsed field magnetization of a high-T c annulus in liquid nitrogen the shielding current drops abruptly, providing rapid penetration of the magnetic flux into the hole of the superconductor. After the break of current the trapped field in the hole is small and negative although the body of the annulus remains highly magnetized. In the present work the current breaking effect is investigated both experimentally and numerically. The influence of the pulse parameter on the shielding current evolution during the break is researched. A simple model for the qualitative description of this process is proposed. The model shows the development of heating localized on the inhomogeneity of the high-temperature superconductor annulus providing the formation of a high resistive channel with temperature near to T c. The appearance of this hot channel leads to the rapid reduction of the shielding current and presents a new scenario of flux jump at high temperature.

  20. Magnetic Field Dependence of the Critical Current of Planar Geometry Josephson Junctions

    Science.gov (United States)

    Ma, Meng; Cho, Ethan; Huynh, Chuong; Cybart, Shane; Dynes, Robert

    2015-03-01

    We report a study on the magnetic field dependence of the critical current of planar geometry Josephson junctions. We have fabricated Josephson junctions by using a focused helium ion beam to irradiate a narrow barrier in the plane of a 25 nm thick Y-Ba-Cu-O film. The London penetration depth λL is large (~1 μm) because of the ultra-thin thickness of the film. As a result, calculations of the Josephson penetration depth λJ are not realistic nor physical. Therefore in this work, we measure λJ experimentally. We tested devices with bridge widths ranging from 4 to 50 μm, and present measurements of the Fraunhofer quantum diffraction pattern (IC (B)). We observe a crossover from short to long junction behavior, which gives an experimentally measured λJ that ranges between 3 μm to 5 μm. The shape of the IC (B) pattern is strongly affected by the width of the bridge because of self-field effects. As the bridge width increases, Josephson vortices enter the junction and skew the patterns. This work shows that the electronic properties of the planar junctions are very different than those classical ``sandwich'' junctions due to the differences in geometry.

  1. The choice of the concept of magnetic field lines or of electric current lines: Alfvén medal lecture

    Directory of Open Access Journals (Sweden)

    S.-I. Akasofu

    2011-07-01

    Full Text Available In 1967, at the Birkeland Symposium in Sandefjord, Norway, Professor Hannes Alfvén stated that the second approach (in solving unsolved problems by the standard MHD theory to cosmic electrodynamics is to "thaw" the "frozen-in" magnetic field lines. "We can illustrate essential properties of the electromagnetic state of space either by depicting the magnetic field lines or by depicting electric current lines," he said. There has been much progress in space physics since the Birkeland Symposium more than 40 years ago, but unfortunately our scientific community has not really succeeded in thawing the frozen-in field lines. Instead, it has pursued magnetic reconnection, a concept that Alfvén had been critical of. It is shown here that we have to study many unsolved problems and problems thought to be solved in terms of both the magnetic field line concept and the current system concept. In taking Alfvén's approach, we must consider the whole system, including the power supply (dynamo process and its transmission and distribution (electric currents and observed phenomena (power dissipation processes. Such a consideration can provide physical insight into many of our unsolved problems and problems thought to be solved. In this paper, we consider substorm onset processes, the substorm current system, sunspots, solar flares, coronal mass ejections, the interplanetary current sheet, and the magnetic field configuration of the heliosphere in terms of the current system concept. In particular, it is shown that a study of the current system is essential in substorm studies, more than changes of the magnetic field configuration in the magnetotail.

  2. The choice of the concept of magnetic field lines or of electric current lines: Alfvén medal lecture

    Science.gov (United States)

    Akasofu, S.-I.

    2011-07-01

    In 1967, at the Birkeland Symposium in Sandefjord, Norway, Professor Hannes Alfvén stated that the second approach (in solving unsolved problems by the standard MHD theory) to cosmic electrodynamics is to "thaw" the "frozen-in" magnetic field lines. "We can illustrate essential properties of the electromagnetic state of space either by depicting the magnetic field lines or by depicting electric current lines," he said. There has been much progress in space physics since the Birkeland Symposium more than 40 years ago, but unfortunately our scientific community has not really succeeded in thawing the frozen-in field lines. Instead, it has pursued magnetic reconnection, a concept that Alfvén had been critical of. It is shown here that we have to study many unsolved problems and problems thought to be solved in terms of both the magnetic field line concept and the current system concept. In taking Alfvén's approach, we must consider the whole system, including the power supply (dynamo process) and its transmission and distribution (electric currents) and observed phenomena (power dissipation processes). Such a consideration can provide physical insight into many of our unsolved problems and problems thought to be solved. In this paper, we consider substorm onset processes, the substorm current system, sunspots, solar flares, coronal mass ejections, the interplanetary current sheet, and the magnetic field configuration of the heliosphere in terms of the current system concept. In particular, it is shown that a study of the current system is essential in substorm studies, more than changes of the magnetic field configuration in the magnetotail.

  3. Ionospheric conductances and currents of a morning sector auroral arc from Swarm-A electric and magnetic field measurements

    Science.gov (United States)

    Juusola, L.; Archer, W. E.; Kauristie, K.; Burchill, J. K.; Vanhamäki, H.; Aikio, A. T.

    2016-11-01

    We show the first ionospheric Hall and Pedersen conductances derived from Swarm magnetic and electric field measurements during a crossing of a morning sector auroral arc. Only Swarm-A was used, with assumptions of negligible azimuthal gradients and vanishing eastward electric field. We find upward field-aligned current, enhanced Hall and Pedersen conductances, and relatively weak electric field coincident with the arc. Poleward of the arc, the field-aligned current was downward, conductances lower, and the electric field enhanced. The arc was embedded in a westward electrojet, immediately equatorward of the peak current density. The equatorward portion of the electrojet could thus be considered conductance dominant and the poleward portion electric field dominant. Although the electric field measured by Swarm was intense, resulting in conductances lower than those typically reported, comparable electric fields have been observed earlier. These results demonstrate how Swarm data can significantly contribute to our understanding of the ionospheric electrodynamics.

  4. Direct imaging of neural currents using ultra-low field magnetic resonance techniques

    Science.gov (United States)

    Volegov, Petr L.; Matlashov, Andrei N.; Mosher, John C.; Espy, Michelle A.; Kraus, Jr., Robert H.

    2009-08-11

    Using resonant interactions to directly and tomographically image neural activity in the human brain using magnetic resonance imaging (MRI) techniques at ultra-low field (ULF), the present inventors have established an approach that is sensitive to magnetic field distributions local to the spin population in cortex at the Larmor frequency of the measurement field. Because the Larmor frequency can be readily manipulated (through varying B.sub.m), one can also envision using ULF-DNI to image the frequency distribution of the local fields in cortex. Such information, taken together with simultaneous acquisition of MEG and ULF-NMR signals, enables non-invasive exploration of the correlation between local fields induced by neural activity in cortex and more `distant` measures of brain activity such as MEG and EEG.

  5. Influence of bio-membrane on current characteristics induced by ambient ELF magnetic field for spherical tissue model

    Energy Technology Data Exchange (ETDEWEB)

    Hayashi, Noriyuki [Kyushu University, Kasuga (Japan). Graduate School of Engineering Sciences; Tarao, Hiroo; Isaka, Katsuo [University of Tokushima (Japan). Faculty of Engineering

    1999-07-01

    Based on the experimental works using rats and chicken eggs, possible influences of the bio-membrane on the electric field and resultant current induced by the exposure to ambient ELF magnetic field, have been pointed out. Existence of the bio-membrane is, however, rarely implemented in conventional procedures of the induced current examination. The present contribution presents results of the analytical examination on how the thickness and electric conductivity of the bio-membrane affect the induced current profiles, indicating the significant role of the bio-membrane on the exact evaluation of the induced current characteristics. (author)

  6. Method for generating linear current-field characteristics and eliminating charging delay in no-insulation superconducting magnets

    Science.gov (United States)

    Kim, Seokho; Hahn, Seungyong; Kim, Kwangmin; Larbalestier, David

    2017-03-01

    No-insulation (NI) rare-earth barium copper oxide (REBCO) magnets are promising for high field or high temperature superconducting magnets because they simplify quench protection. However, the turn-to-turn leakage current path induced by the absence of insulation introduces nonlinearities into the magnetic fieldcurrent characteristic and significant delay in reaching the desired field. This paper shows that active feedback control can mitigate both the nonlinearity and the charging delay. To verify our approach, simulations and tests were performed with an NI REBCO magnet made of 13 double-pancake coils. A proportional and integral (PI) feedback control of the power supply was adopted which allowed determination of the appropriate PI gains using dynamic simulations of the equivalent circuit of the NI magnet. Feedback control tests were then performed in liquid nitrogen at 77 K. The time to reach 99.5% of the target magnetic field to become essentially steady-state was reduced by more than 2000 times from 850 s without control to 0.4 s with control. The results demonstrate a potential that one of the most significant perceived disadvantages of an NI magnet can essentially be removed by active feedback control of the power supply current.

  7. Optimization of magnetoresistive sensor current for on-chip magnetic bead detection using the sensor self-field

    DEFF Research Database (Denmark)

    Henriksen, Anders Dahl; Rizzi, Giovanni; Østerberg, Frederik Westergaard

    2015-01-01

    , thus the heat conductance is proportional to the sensor area and inversely proportional to the oxide thickness. This simple heat conductance determines the relationship between bias current and sensor temperature, and we show that View the MathML source25μm wide sensor on a View the MathML source1μm......We investigate the self-heating of magnetoresistive sensors used for measurements on magnetic beads in magnetic biosensors. The signal from magnetic beads magnetized by the field due to the sensor bias current is proportional to the bias current squared. Therefore, we aim to maximize the bias....... The measured temperature increase is in good agreement with a finite element model and a simple analytical thermal model. The heat conductance of our system is limited by the View the MathML source1μm thick electrically insulating silicon dioxide layer between the sensor stack and the underlying silicon wafer...

  8. Distortions of the magnetic field by storm-time current systems in Earth's magnetosphere

    Directory of Open Access Journals (Sweden)

    N. Yu. Ganushkina

    2010-01-01

    Full Text Available Magnetic field and current system changes in Earth's inner magnetosphere during storm times are studied using two principally different modeling approaches: on one hand, the event-oriented empirical magnetic field model, and, on the other, the Space Weather Modeling Framework (SWMF built around a global MHD simulation. Two storm events, one moderate storm on 6–7 November 1997 with Dst minimum about −120 nT and one intense storm on 21–23 October 1999 with Dst minimum about −250 nT were modeled. Both modeling approaches predicted a large ring current (first partial, later symmetric contribution to the magnetic field perturbation for the intense storm. For the moderate storm, the tail current plays a dominant role in the event-oriented model results, while the SWMF results showed no strong tail current in the main phase, which resulted in a poorly timed storm peak relative to the observations. These results imply that the the development of a ring current depends on a strong force to inject the particles deep into the inner magnetosphere, and that the tail current is an important external source for the distortions of the inner magnetospheric magnetic field for both storms. Neither modeling approach was able to reproduce all the variations in the Bx and By components observed at geostationary orbit by GOES satellites during these two storms: the magnetopause current intensifications are inadequate, and the field-aligned currents are not sufficiently represented. While the event-oriented model reproduces rather well the Bz component at geostationary orbit, including the substorm-associated changes, the SWMF field is too dipolar at these locations. The empirical model is a useful tool for validation of the first-principle based models such as the SWMF.

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

    Science.gov (United States)

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

    2017-03-01

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

  10. Three-Axis Magnetic Field Measurements in the TCSU RMF Current Drive Experiment

    Science.gov (United States)

    Velas, K. M.; Milroy, R. D.

    2011-10-01

    A 3-axis probe was installed on TCSU shortly before its shutdown. The probe has 90 windings that simultaneously measure Br, Bθ, and Bz at 30 radial positions and is fully translatable. Positioning the probe at multiple axial positions and taking multiple repeatable shots allows for a full r-z map of the magnetic field. Initially, data has been processed with a 10 kHz low pass filter to capture the steady field. Higher frequency content has more shot-to-shot variability; it is difficult to map this axially. Plans include using a band pass filter to isolate the RMF frequency, which is consistent between shots. It is anticipated that the RMF field, in conjunction with the steady field, will yield a map of the full 3D rotating field structure. The 3- axis probe measurements are used to calculate the end-shorting torque, which opposes the RMF torque. Data from even- and odd-parity experiments will be compared. The NIMROD code has been adapted to simulate the TCSU experiment using boundary conditions adjusted to match both even- and odd-parity experimental conditions. A comparison of the n = 0 components of the calculated fields to the 3- axis probe measurements shows agreement in the magnetic field structure of the FRC as well as in the jet region.

  11. Initial results on the correlation between the magnetic and electric fields observed from the DE-2 satellite in the field-aligned current regions

    Science.gov (United States)

    Sugiura, M.; Maynard, N. C.; Farthing, W. H.; Heppner, J. P.; Ledley, B. G.; Cahill, L. J., Jr.

    1982-01-01

    Initial results of the electric and magnetic field observations from the DE-2 satellite show a remarkably good correlation between the north-south component of the electric field and the east-west component of the magnetic field in many passes of the field-aligned current regions. For a dayside cusp pass on August 15, 1981 the coefficient of correlation between these components was 0.996. A preliminary inspection of the available data from the first 6 months of the DE operation indicates that the similarity between the electric and magnetic field signatures of the field-aligned currents is a commonly observed feature at all local times. This high correlation is interpreted to be an indication that the closure of the field-aligned current is essentially meridional. When the correlation between these components is not good, the closure current is likely to be flowing along the auroral belt. When the correlation between the electric and magnetic fields is high, it is possible to estimate the height-integrated Pedersen conductivity from the observed field components.

  12. Acceleration of electric current-carrying string loop near a Schwarzschild black hole immersed in an asymptotically uniform magnetic field

    CERN Document Server

    Tursunov, Arman; Stuchlík, Zdeněk; Ahmedov, Bobomurat

    2014-01-01

    We study the acceleration of an electric current-carrying and axially-symmetric string loop initially oscillating in the vicinity of a Schwarzschild black hole embedded in an external asymptotically uniform magnetic field. The plane of the string loop is orthogonal to the magnetic field lines and the acceleration of the string loop occurs due to the transmutation effect turning in the deep gravitational field the internal energy of the oscillating strings to the energy of their translational motion along the axis given by the symmetry of the black hole spacetime and the magnetic field. We restrict our attention to the motion of string loop with energy high enough, when it can overcome the gravitational attraction and escape to infinity. We demonstrate that for the current-carrying string loop the transmutation effect is enhanced by the contribution of the interaction between the electric current of the string loop and the external magnetic field and we give conditions that have to be fulfilled for an efficien...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-09-07

    We have investigated the shot noise and Fano factor of the dynamic spin-polarized quantum dot under the perturbations of a rotating magnetic field (RMF), and an oscillating magnetic field (OMF) by employing the non-equilibrium Green's function approach. The shot noise is enhanced from sub-Poissonian to super-Poissonian due to the application of RMF and OMF, and it is controlled sensitively by the tilt angle 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.

  14. Relativistic electron's butterfly pitch angle distribution modulated by localized background magnetic field perturbation driven by hot ring current ions

    Science.gov (United States)

    Xiong, Ying; Chen, Lunjin; Xie, Lun; Fu, Suiyan; Xia, Zhiyang; Pu, Zuyin

    2017-05-01

    Dayside modulated relativistic electron's butterfly pitch angle distributions (PADs) from ˜200 keV to 2.6 MeV were observed by Van Allen Probe B at L = 5.3 on 15 November 2013. They were associated with localized magnetic dip driven by hot ring current ion (60-100 keV proton and 60-200 keV helium and oxygen) injections. We reproduce the electron's butterfly PADs at satellite's location using test particle simulation. The simulation results illustrate that a negative radial flux gradient contributes primarily to the formation of the modulated electron's butterfly PADs through inward transport due to the inductive electric field, while deceleration due to the inductive electric field and pitch angle change also makes in part contribution. We suggest that localized magnetic field perturbation, which is a frequent phenomenon in the magnetosphere during magnetic disturbances, is of great importance for creating electron's butterfly PADs in the Earth's radiation belts.

  15. A mechanism for the dynamo terms to sustain closed-flux current, including helicity balance, by driving current which crosses the magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Jarboe, T. R.; Nelson, B. A.; Sutherland, D. A. [University of Washington, Seattle, Washington 98195 (United States)

    2015-07-15

    An analysis of imposed dynamo current drive (IDCD) [T.R. Jarboe et al., Nucl. Fusion 52 083017 (2012)] reveals: (a) current drive on closed flux surfaces seems possible without relaxation, reconnection, or other flux-surface-breaking large events; (b) the scale size of the key physics may be smaller than is often computationally resolved; (c) helicity can be sustained across closed flux; and (d) IDCD current drive is parallel to the current which crosses the magnetic field to produce the current driving force. In addition to agreeing with spheromak data, IDCD agrees with selected tokamak data.

  16. Simulation of bootstrap current in 2D and 3D ideal magnetic fields in tokamaks

    Science.gov (United States)

    Raghunathan, M.; Graves, J. P.; Cooper, W. A.; Pedro, M.; Sauter, O.

    2016-09-01

    We aim to simulate the bootstrap current for a MAST-like spherical tokamak using two approaches for magnetic equilibria including externally caused 3D effects such as resonant magnetic perturbations (RMPs), the effect of toroidal ripple, and intrinsic 3D effects such as non-resonant internal kink modes. The first approach relies on known neoclassical coefficients in ideal MHD equilibria, using the Sauter (Sauter et al 1999 Phys. Plasmas 6 2834) expression valid for all collisionalities in axisymmetry, and the second approach being the quasi-analytic Shaing-Callen (Shaing and Callen 1983 Phys. Fluids 26 3315) model in the collisionless regime for 3D. Using the ideal free-boundary magnetohydrodynamic code VMEC, we compute the flux-surface averaged bootstrap current density, with the Sauter and Shaing-Callen expressions for 2D and 3D ideal MHD equilibria including an edge pressure barrier with the application of resonant magnetic perturbations, and equilibria possessing a saturated non-resonant 1/1 internal kink mode with a weak internal pressure barrier. We compare the applicability of the self-consistent iterative model on the 3D applications and discuss the limitations and advantages of each bootstrap current model for each type of equilibrium.

  17. On the toroidal current density flowing across a poloidal-magnetic-field null in an axisymmetric plasma

    Science.gov (United States)

    Rodrigues, Paulo; Bizarro, João P. S.

    2013-04-01

    The axisymmetry condition and two of Maxwell's equations are used to show that, in general, there are no nested magnetic surfaces around a poloidal-magnetic-field null for a sufficiently small value of the toroidal current density flowing there. Hence, the toroidal current density at the axis of a magnetic configuration with extreme shear reversal cannot continuously approach zero unless nested surfaces are first broken or particular values are assigned to boundary conditions and other plasma parameters. The threshold of the toroidal current-density at which the topology changes is shown to be set by such parameters, and some examples of the predicted topology transition are presented using analytical solutions of the Grad-Shafranov equation.

  18. On the toroidal current density flowing across a poloidal-magnetic-field null in an axisymmetric plasma

    Energy Technology Data Exchange (ETDEWEB)

    Rodrigues, Paulo; Bizarro, Joao P. S. [Associacao Euratom-IST, Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, Universidade Tecnica de Lisboa, 1049-001 Lisboa (Portugal)

    2013-04-15

    The axisymmetry condition and two of Maxwell's equations are used to show that, in general, there are no nested magnetic surfaces around a poloidal-magnetic-field null for a sufficiently small value of the toroidal current density flowing there. Hence, the toroidal current density at the axis of a magnetic configuration with extreme shear reversal cannot continuously approach zero unless nested surfaces are first broken or particular values are assigned to boundary conditions and other plasma parameters. The threshold of the toroidal current-density at which the topology changes is shown to be set by such parameters, and some examples of the predicted topology transition are presented using analytical solutions of the Grad-Shafranov equation.

  19. A distributed equivalent magnetic current based FDTD method for the calculation of E-fields induced by gradient coils.

    Science.gov (United States)

    Liu, Feng; Crozier, Stuart

    2004-08-01

    This paper evaluates a new, low-frequency finite-difference time-domain method applied to the problem of induced E-fields/eddy currents in the human body resulting from the pulsed magnetic field gradients in MRI. In this algorithm, a distributed equivalent magnetic current is proposed as the electromagnetic source and is obtained by quasistatic calculation of the empty coil's vector potential or measurements therein. This technique circumvents the discretization of complicated gradient coil geometries into a mesh of Yee cells, and thereby enables any type of gradient coil modelling or other complex low frequency sources. The proposed method has been verified against an example with an analytical solution. Results are presented showing the spatial distribution of gradient-induced electric fields in a multi-layered spherical phantom model and a complete body model.

  20. Effect of Current Frequency on Droplet Evolution During Magnetic-Field-Controlled Electroslag Remelting Process Via Visualization Method

    Science.gov (United States)

    Wang, Huai; Zhong, Yunbo; Li, Qiang; Fang, Yipeng; Ren, Weili; Lei, Zuosheng; Ren, Zhongming

    2017-02-01

    A transparent physical model was set up to investigate the influence of the remelting current frequencies on droplet evolution during the magnetic-field-controlled electroslag remelting process. Physical simulation experiments were done under the remelting current of 8 A with frequencies ranging from 10 to 500 Hz, and a transverse static magnetic field (TSMF) of 0.7 T was superimposed simultaneously. The high-speed camera was used to record the evolution behavior of the droplet. Representative processes of formation and detachment of the droplets were observed under different conditions. The results showed that there was little influence of the current frequencies on the evolution behavior of the droplet without the external magnetic field. Nevertheless, if a TSMF was introduced, the liquid droplet's neck would be smashed into a lot of smaller droplets when the remelting current frequencies were lower than 100 Hz, while the smashing effect disappeared when the frequencies were higher than 100 Hz. The mechanism of the smashing effect was discussed. Statistical work was done to obtain the quantitative data to give a clear result revealing the influence of the remelting current frequencies on droplet evolution. The decrease in the diameter of the liquid droplets would remarkably increase the interface area and shorten the migrating distance of the inclusions in the droplets, which meant that a higher purifying efficiency could be expected.

  1. Utilisation of the magnetic sensor in a smartphone for facile magnetostatics experiment: magnetic field due to electrical current in straight and loop wires

    Science.gov (United States)

    Septianto, R. D.; Suhendra, D.; Iskandar, F.

    2017-01-01

    This paper reports on the result of a research into the utilisation of a smartphone for the study of magnetostatics on the basis of experiments. The use of such a device gives great measurement result and thus it can replace magnetic sensor tools that are relatively expensive. For the best experimental result, firstly the position of the magnetic sensor in the smartphone has to be considered by way of value mapping of a magnetic field due to permanent magnet. The magnetostatics experiment investigated in this research was the measurement of magnetic field due to electrical currents in two shapes of wire, straight and looped. The current flow, the distance between the observation point and the wire, and the diameter of the loop were the variable parameters investigated to test the smartphone’s capabilities as a measurement tool. To evaluate the experimental results, the measured data were compared with theoretical values that were calculated by using both an analytical and a numerical approach. According to the experiment results, the measured data had good agreement with the results from the analytical and the numerical approach. This means that the use of the magnetic sensor in a smartphone in physics experiments is viable, especially for magnetic field measurement.

  2. A Tailward Moving Current Sheet Normal Magnetic Field Front Followed by an Earthward Moving Dipolarization Front

    Science.gov (United States)

    Hwang, K.-J.; Goldstein, M. L.; Moore, T. E.; Walsh, B. M.; Baishev, D. G.; Moiseyev, A. V.; Shevtsov, B. M.; Yumoto, K.

    2014-01-01

    A case study is presented using measurements from the Cluster spacecraft and ground-based magnetometers that show a substorm onset propagating from the inner to outer plasma sheet. On 3 October 2005, Cluster, traversing an ion-scale current sheet at the near-Earth plasma sheet, detected a sudden enhancement of Bz, which was immediately followed by a series of flux rope structures. Both the local Bz enhancement and flux ropes propagated tailward. Approximately 5 min later, another Bz enhancement, followed by a large density decrease, was observed to rapidly propagate earthward. Between the two Bz enhancements, a significant removal of magnetic flux occurred, possibly resulting from the tailward moving Bz enhancement and flux ropes. In our scenario, this flux removal caused the magnetotail to be globally stretched so that the thinnest sheet formed tailward of Cluster. The thinned current sheet facilitated magnetic reconnection that quickly evolved from plasma sheet to lobe and generated the later earthward moving dipolarization front (DF) followed by a reduction in density and entropy. Ground magnetograms located near the meridian of Cluster's magnetic foot points show two-step bay enhancements. The positive bay associated with the first Bz enhancement indicates that the substorm onset signatures propagated from the inner to the outer plasma sheet, consistent with the Cluster observation. The more intense bay features associated with the later DF are consistent with the earthward motion of the front. The event suggests that current disruption signatures that originated in the near-Earth current sheet propagated tailward, triggering or facilitating midtail reconnection, thereby preconditioning the magnetosphere for a later strong substorm enhancement.

  3. Magnetic fields in diffuse media

    CERN Document Server

    Pino, Elisabete; Melioli, Claudio

    2015-01-01

    This volume presents the current knowledge of magnetic fields in diffuse astrophysical media. Starting with an overview of 21st century instrumentation to observe astrophysical magnetic fields, the chapters cover observational techniques, origin of magnetic fields, magnetic turbulence, basic processes in magnetized fluids, the role of magnetic fields for cosmic rays, in the interstellar medium and for star formation. Written by a group of leading experts the book represents an excellent overview of the field. Nonspecialists will find sufficient background to enter the field and be able to appreciate the state of the art.

  4. Magnetic Field Sensors Based on Giant Magnetoresistance (GMR Technology: Applications in Electrical Current Sensing

    Directory of Open Access Journals (Sweden)

    Càndid Reig

    2009-10-01

    Full Text Available The 2007 Nobel Prize in Physics can be understood as a global recognition to the rapid development of the Giant Magnetoresistance (GMR, from both the physics and engineering points of view. Behind the utilization of GMR structures as read heads for massive storage magnetic hard disks, important applications as solid state magnetic sensors have emerged. Low cost, compatibility with standard CMOS technologies and high sensitivity are common advantages of these sensors. This way, they have been successfully applied in a lot different environments. In this work, we are trying to collect the Spanish contributions to the progress of the research related to the GMR based sensors covering, among other subjects, the applications, the sensor design, the modelling and the electronic interfaces, focusing on electrical current sensing applications.

  5. Magnetic Measurement of the Current Center Line of the Toroidal Field Coil of ITER at Room Temperature

    CERN Document Server

    Deniau, L; Buzio, M; Knaster, J; Savary, F

    2012-01-01

    Geometrical deformations and assembly errors in the ITER Toroidal Field (TF) coils will lead to magnetic field perturbations, which could degrade plasma confinement and eventually lead to disruption. Extensive computational studies of the influence of coil deformations and assembly errors on plasma behavior have given the basis for definition of the geometric tolerance of the Current Centre Line (CCL) of the winding pack of the TF coil. This paper describes an analysis method to establish the feasibility to measure the magnetic CCL locus of the final winding pack (WP) with accuracy better than 1 mm. The proposed method is based on arrays of gradient coils accurately mounted with respect to the WP fiducial marks and datum surfaces. The magnetic measurements will be performed at defined locations around the WP perimeter to characterize accurately the CCL locus. The analysis emphases the robustness and sensitivity of the method versus the measurement location and the TF coil 3D geometrical deformation. The analy...

  6. Charged Particle Dynamics in the Magnetic Field of a Long Straight Current-Carrying Wire

    Science.gov (United States)

    Prentice, A.; Fatuzzo, M.; Toepker, T.

    2015-01-01

    By describing the motion of a charged particle in the well-known nonuniform field of a current-carrying long straight wire, a variety of teaching/learning opportunities are described: 1) Brief review of a standard problem; 2) Vector analysis; 3) Dimensionless variables; 4) Coupled differential equations; 5) Numerical solutions.

  7. Magnetic domain-wall creep driven by field and current in Ta/CoFeB/MgO

    Directory of Open Access Journals (Sweden)

    S. DuttaGupta

    2017-05-01

    Full Text Available Creep motion of magnetic domain wall (DW, thermally activated DW dynamics under subthreshold driving forces, is a paradigm to understand the interaction between driven interfaces and applied external forces. Previous investigation has shown that DW in a metallic system interacts differently with current and magnetic field, manifesting itself as different universality classes for the creep motion. In this article, we first review the experimental determination of the universality classes for current- and field-driven DW creeps in a Ta/CoFeB/MgO wire, and then elucidate the underlying factors governing the obtained results. We show that the nature of torque arising from current in association with DW configuration determines universality class for the current-induced creep in this system. We also discuss the correlation between the field-induced DW creep characteristics and structure observed by a transmission electron microscope. The observed results are expected to provide a deeper understanding for physics of DW motion in various magnetic materials.

  8. Field-dependent critical state of high-Tc superconducting strip simultaneously exposed to transport current and perpendicular magnetic field

    Science.gov (United States)

    Xue, Cun; He, An; Yong, Huadong; Zhou, Youhe

    2013-12-01

    We present an exact analytical approach for arbitrary field-dependent critical state of high-Tc superconducting strip with transport current. The sheet current and flux-density profiles are derived by solving the integral equations, which agree with experiments quite well. For small transport current, the approximate explicit expressions of sheet current, flux-density and penetration depth for the Kim model are derived based on the mean value theorem for integration. We also extend the results to the field-dependent critical state of superconducting strip in the simultaneous presence of applied field and transport current. The sheet current distributions calculated by the Kim model agree with experiments better than that by the Bean model. Moreover, the lines in the Ia-Ba plane for the Kim model are not monotonic, which is quite different from that the Bean model. The results reveal that the maximum transport current in thin superconducting strip will decrease with increasing applied field which vanishes for the Bean model. The results of this paper are useful to calculate ac susceptibility and ac loss.

  9. Field-dependent critical state of high-Tc superconducting strip simultaneously exposed to transport current and perpendicular magnetic field

    Directory of Open Access Journals (Sweden)

    Cun Xue

    2013-12-01

    Full Text Available We present an exact analytical approach for arbitrary field-dependent critical state of high-Tc superconducting strip with transport current. The sheet current and flux-density profiles are derived by solving the integral equations, which agree with experiments quite well. For small transport current, the approximate explicit expressions of sheet current, flux-density and penetration depth for the Kim model are derived based on the mean value theorem for integration. We also extend the results to the field-dependent critical state of superconducting strip in the simultaneous presence of applied field and transport current. The sheet current distributions calculated by the Kim model agree with experiments better than that by the Bean model. Moreover, the lines in the Ia-Ba plane for the Kim model are not monotonic, which is quite different from that the Bean model. The results reveal that the maximum transport current in thin superconducting strip will decrease with increasing applied field which vanishes for the Bean model. The results of this paper are useful to calculate ac susceptibility and ac loss.

  10. Field-dependent critical state of high-Tc superconducting strip simultaneously exposed to transport current and perpendicular magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Xue, Cun; He, An; Yong, Huadong; Zhou, Youhe, E-mail: zhouyh@lzu.edu.cn [Key Laboratory of Mechanics on Disaster and Environment in Western China attached to the Ministry of Education of China, and Department of Mechanics and Engineering Sciences, College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000 (China)

    2013-12-15

    We present an exact analytical approach for arbitrary field-dependent critical state of high-T{sub c} superconducting strip with transport current. The sheet current and flux-density profiles are derived by solving the integral equations, which agree with experiments quite well. For small transport current, the approximate explicit expressions of sheet current, flux-density and penetration depth for the Kim model are derived based on the mean value theorem for integration. We also extend the results to the field-dependent critical state of superconducting strip in the simultaneous presence of applied field and transport current. The sheet current distributions calculated by the Kim model agree with experiments better than that by the Bean model. Moreover, the lines in the I{sub a}-B{sub a} plane for the Kim model are not monotonic, which is quite different from that the Bean model. The results reveal that the maximum transport current in thin superconducting strip will decrease with increasing applied field which vanishes for the Bean model. The results of this paper are useful to calculate ac susceptibility and ac loss.

  11. Evidence of the Relationship between the Emerging Magnetic Fields, Electric Currents, and Solar Flares Observed on May 10, 2012

    CERN Document Server

    Livshits, M A; Myshyakov, I I; Rudenko, G V

    2016-01-01

    We have analyzed multi-wavelength observations and magnetic-field data for the solar flare of May 10, 2012 (04:18 UT) and have detected a sign inversion of the signal in the line-of-sight magnetic measurements in the umbra of a small spot. This effect is associated, at least partly, with the emergence of a new magnetic field. Almost at the same time, a burst of hard X-rays was recorded, and a wave in the vacuum ultraviolet (EUV) range (a "sunquake") was generated due to the impact of the disturbance in the energy release range on the photosphere. At the beginning of the event, a sigmoid flare was recorded, but it did not spread, as it usually does, along the polarity inversion (neutral) line. SDO/HMI full-vector measurements were used to extrapolate the AR 11476 magnetic field to the corona, and the distribution of vertical currents $j_z$ in the photosphere was obtained. The distribution of currents in the active region shows that the relationship between them and the occurrence of flares is very intricate. W...

  12. Probing current-induced magnetic fields in Au|YIG heterostructures with low-energy muon spin spectroscopy

    Science.gov (United States)

    Aqeel, A.; Vera-Marun, I. J.; Salman, Z.; Prokscha, T.; Suter, A.; van Wees, B. J.; Palstra, T. T. M.

    2017-02-01

    We investigated the depth dependence of current-induced magnetic fields in a bilayer of a normal metal (Au) and a ferrimagnetic insulator (Yttrium Iron Garnet—YIG) by using low energy muon spin spectroscopy (LE-μSR). This allows us to explore how these fields vary from the Au surface down to the buried Au|YIG interface, which is relevant to study physics like the spin-Hall effect. We observed a maximum shift of 0.4 G in the internal field of muons at the surface of Au film which is in close agreement with the value expected for Oersted fields. As muons are implanted closer to the Au|YIG interface, the shift is strongly suppressed, which we attribute to the dipolar fields present at the Au|YIG interface. Combining our measurements with modeling, we show that dipolar fields caused by the finite roughness of the Au|YIG interface consistently explain our observations. Our results, therefore, gauge the limits on the spatial resolution and the sensitivity of LE-μSR to the roughness of the buried magnetic interfaces, a prerequisite for future studies addressing current induced fields caused by the spin-accumulations due to the spin-Hall effect.

  13. Empirical compensation function for eddy current effects in pulsed field gradient nuclear magnetic resonance experiments.

    Science.gov (United States)

    Zhu, X X; Macdonald, P M

    1995-05-01

    An empirical compensation function for the correction of eddy current effects in the Stejskal-Tanner pulsed-gradient spin-echo (PGSE) nuclear magnetic resonance (NMR) experiments has been established. Eddy currents may arise as a result of the application of sharp and strong gradient pulses and may cause severe distortion of the NMR signals. In this method, the length of one gradient pulse is altered to compensate for the eddy current effects. The compensation is considered to be ideal when the position and the phase of the spin-echo maximum obtained from an aqueous solution of poly(ethylene glycol) (PEG) is the same in the presence and absence of a gradient pulse in the PGSE pulse sequence. We first characterized the functional dependence of the length of the required compensation on the three principal variables in the PGSE experiment: the gradient strength, the duration of the gradient pulse, and the interval between the two gradient pulses. Subsequently, we derived a model which successfully describes the general relationship between these variables and the size of the induced eddy current. The parameters extracted from fitting the model to the experimental compensation data may be used to predict the correct compensation for any combination of the three principal variables.

  14. AFM nano-plough planar YBCO micro-bridges: critical currents and magnetic field effects.

    Science.gov (United States)

    Elkaseh, A A O; Perold, W J; Srinivasu, V V

    2010-10-01

    The critical current (Ic) of YBa2Cu3O7-x (YBCO) AFM plough micro-constrictions is measured as a function of temperature, width and the magnetic flux density (B), which was applied perpendicular to the YBCO ab-plane and surface of the bridges. C-axis oriented thin films of YBa2Cu3O7-x were deposited on MgO substrates using an inverted cylindrical magnetron (ICM) sputtering technique. The films were then patterned into 8-10 micron size strips, using standard photolithography and dry etching processes. Micro-bridges with widths between 1.9 microm to 4.1 microm were fabricated by using atomic force microscope (AFM) nanolithography techniques. Critical current versus temperature data shows a straight-line behavior, which is typical of constriction type Josephson junctions. The Ic versus B characteristics exhibited a modulation, and a suppression of the critical current of up to 84%. It was also found that the critical current increases with increasing constriction width.

  15. Magnetic Field Calculator

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Magnetic Field Calculator will calculate the total magnetic field, including components (declination, inclination, horizontal intensity, northerly intensity,...

  16. Observation of self-magnetic field relaxations in Bi2223 and Y123 HTS tapes after over-current pulse and DC current operation

    Science.gov (United States)

    Tallouli, M.; Sun, J.; Chikumoto, N.; Otabe, E. S.; Shyshkin, O.; Charfi-Kaddour, S.; Yamaguchi, S.

    2016-07-01

    The development of power transmission lines based on long-length HTS tapes requires the production of high quality tapes. Due to fault conditions, technical mistakes and human errors during the operation of a DC power transmission line, an over-current pulse, several times larger than the rated current, could occur. To study the effect of such over-current pulses on the transport current density distribution in the HTS tapes, we simulated two start-up scenarios for one BSCCO and two YBCO tapes. The first start-up scenario is an initial over-current pulse during which the transport current was turned on rapidly, rising to 900 A during the first milliseconds, then reduced to a 100 A DC current. The second start-up scenario is normal operation, and involved increasing the transport current slowly from 0 A to 100 A at a rate of 1 A/s. For both scenarios, we then measured the vertical component of the self-magnetic field by means of a Hall probe above the tape, and afterward, by solving a linear equation of the inverse problem we obtain the current density profiles. We observe a change of the self-magnetic field above the edge of the BSCCO and YBCO tapes during 30 min after the 5 ms of over-current pulse and during the normal operation. The current density profiles are peaked in the centre for over-current pulse, and more peaked around the edge of the HTS tape for normal operation, which means that the limited time over-current pulse changes the current density profiles of the HTS tapes. We observe also a loop of current for YBCO tapes and we show the role of the HTS tape stabilizer.

  17. MRI detection of weak magnetic fields due to an extended current dipole in a conducting sphere: a model for direct detection of neuronal currents in the brain.

    Science.gov (United States)

    Konn, Daniel; Gowland, Penny; Bowtell, Richard

    2003-07-01

    To investigate the feasibility of direct MR detection of neuronal activity in the brain, neuronal current flow was modeled as an extended current dipole located in a conducting sphere. The spatially varying magnetic field induced within the sphere by such a dipole was calculated, including its form close to and within the current source. The predicted field variation was experimentally verified by measurements of the variation in phase of the MR signal in a sphere containing a model dipole. The effects of the calculated magnetic field distributions on the phase and magnitude of the signal in MR images were explored. The minimum detectable dipole strength under normal experimental conditions was calculated to be about 4.5 nAm, which is similar in magnitude to dipole strengths from evoked neuronal activity, and is an order of magnitude smaller than dipole strengths expected from spontaneous activity. This minimum detectable dipole strength increases with increasing spatial extent of the primary current distribution. In the experimental work, the effects of a field of [1.1 +/- 0.5] x 10(-10) T strength were detected, corresponding to the maximum net field caused by a dipole of 6.3 nAm strength with a spatial extent of 3 x 3 x 2 mm(3). Copyright 2003 Wiley-Liss, Inc.

  18. What Are Electric and Magnetic Fields? (EMF)

    Science.gov (United States)

    ... take for granted. What are electric and magnetic fields? Electric and magnetic fields (EMF) are invisible lines of ... humans. AC electric power produces electric and magnetic fields that create weak electric currents in humans. Being exposed to some kinds ...

  19. He 2++ molecular ion in a strong time-dependent magnetic field: a current-density functional study.

    Science.gov (United States)

    Vikas

    2011-08-01

    The He 2++ molecular ion exposed to a strong ultrashort time-dependent (TD) magnetic field of the order of 10(9) G is investigated through a quantum fluid dynamics (QFD) and current-density functional theory (CDFT) based approach using vector exchange-correlation (XC) potential and energy density functional that depend not only on the electronic charge-density but also on the current density. The TD-QFD-CDFT computations are performed in a parallel internuclear-axis and magnetic field-axis configuration at the field-free equilibrium internuclear separation R = 1.3 au with the field-strength varying between 0 and 10(11) G. The TD behavior of the exchange- and correlation energy of the He 2++ is analyzed and compared with that obtained using a [B-TD-QFD-density functional theory (DFT)] approach based on the conventional TD-DFT under similar computational constraints but using only scalar XC potential and energy density functional dependent on the electronic charge-density alone. The CDFT based approach yields TD exchange- and correlation energy and TD electronic charge-density significantly different from that obtained using the conventional TD-DFT based approach, particularly, at typical magnetic field strengths and during a typical time period of the TD field. This peculiar behavior of the CDFT-based approach is traced to the TD current-density dependent vector XC potential, which can induce nonadiabatic effects causing retardation of the oscillating electronic charge density. Such dissipative electron dynamics of the He 2++ molecular ion is elucidated by treating electronic charge density as an electron-"fluid" in the terminology of QFD.

  20. Computer Calculations of Eddy-Current Power Loss in Rotating Titanium Wheels and Rims in Localized Axial Magnetic Fields

    Energy Technology Data Exchange (ETDEWEB)

    Mayhall, D J; Stein, W; Gronberg, J B

    2006-05-15

    We have performed preliminary computer-based, transient, magnetostatic calculations of the eddy-current power loss in rotating titanium-alloy and aluminum wheels and wheel rims in the predominantly axially-directed, steady magnetic fields of two small, solenoidal coils. These calculations have been undertaken to assess the eddy-current power loss in various possible International Linear Collider (ILC) positron target wheels. They have also been done to validate the simulation code module against known results published in the literature. The commercially available software package used in these calculations is the Maxwell 3D, Version 10, Transient Module from the Ansoft Corporation.

  1. Hysteresis losses in MgB2 superconductors exposed to combinations of low AC and high DC magnetic fields and transport currents

    DEFF Research Database (Denmark)

    Magnusson, N.; Abrahamsen, Asger Bech; Liu, Dawei

    2014-01-01

    a simplified theoretical treatment of the hysteresis losses based on available models in the literature with the aim of setting the basis for estimation of the allowable magnetic fields and current ripples in superconducting generator coils intended for large wind turbine direct drive generators. The resulting...... equations use the DC in-field critical current, the geometry of the superconductor and the magnitude of the AC magnetic field component as parameters. This simplified approach can be valuable in the design of MgB2 DC coils in the 1–4T range with low AC magnetic field and current ripples....

  2. Limits for primordial magnetic fields

    CERN Document Server

    Caprini, Chiara

    2011-01-01

    A possible explanation for the origin of the magnetic fields observed today in matter structures is that they were generated in the primordial universe. After briefly revising the model of a primordial stochastic magnetic field and sketching the main features of its time evolution in the primordial plasma, we illustrate the current upper bounds on the magnetic field amplitude and spectral index from Cosmic Microwave Background observations and gravitational wave production. We conclude that a primordial magnetic field generated by a non-causal process such as inflation with a red spectrum seems to be favoured as a seed for the magnetic fields observed today in structures.

  3. Magnetic field cycling effect on the non-linear current-voltage characteristics and magnetic field induced negative differential resistance in α-Fe1.64Ga0.36O3 oxide

    Directory of Open Access Journals (Sweden)

    R. N. Bhowmik

    2015-06-01

    Full Text Available We have studied current-voltage (I-V characteristics of α-Fe1.64Ga0.36O3, a typical canted ferromagnetic semiconductor. The sample showed a transformation of the I-V curves from linear to non-linear character with the increase of bias voltage. The I-V curves showed irreversible features with hysteresis loop and bi-stable electronic states for up and down modes of voltage sweep. We report positive magnetoresistance and magnetic field induced negative differential resistance as the first time observed phenomena in metal doped hematite system. The magnitudes of critical voltage at which I-V curve showed peak and corresponding peak current are affected by magnetic field cycling. The shift of the peak voltage with magnetic field showed a step-wise jump between two discrete voltage levels with least gap (ΔVP 0.345(± 0.001 V. The magnetic spin dependent electronic charge transport in this new class of magnetic semiconductor opens a wide scope for tuning large electroresistance (∼500-700%, magnetoresistance (70-135 % and charge-spin dependent conductivity under suitable control of electric and magnetic fields. The electric and magnetic field controlled charge-spin transport is interesting for applications of the magnetic materials in spintronics, e.g., magnetic sensor, memory devices and digital switching.

  4. Development of an all-permanent-magnet microwave ion source equipped with multicusp magnetic fields for high current proton beam production.

    Science.gov (United States)

    Tanaka, M; Hara, S; Seki, T; Iga, T

    2008-02-01

    An all-permanent-magnet (APM) microwave hydrogen ion source was developed to reduce the size and to simplify structure of a conventional solenoid coil microwave ion source developed for reliability improvement of high current proton linac application systems. The difficulty in developing the APM source was sensitive dependence of the source performance on axial magnetic field in the microwave discharge chamber. It was difficult to produce high current proton beam stably without precise tuning of the magnetic field using solenoid coils. We lowered the sensitivity using multicusp magnetic fields for plasma confinement at the discharge chamber sidewall of the source. This enabled stable high current proton beam production with the APM microwave ion source with no tuning coil. The water cooling and the power supply for the coils are not necessary for the APM source, which leads to better reliability and system simplification. The outer diameter of the APM source was around 300 mm, which was 20% lower than the coil source. The APM source produced a maximum hydrogen ion beam current of 65 mA (high current density of 330 mA/cm(2), proton ratio of 87%, and beam energy of 30 keV) with a 5 mm diameter extraction aperture, pulse width of 400 micros, and 20 Hz repetition rate at 1.3 kW microwave power. This performance is almost the same as the best performances of the conventional coil sources. The extracted ion beams were focused with electrostatic five-grid lens to match beam to acceptance of radio-frequency quadrupole linacs. The maximum focused beam current through the orifice (5 mm radius) and the lens was 36 mA and the 90% focused beam half-width was 1-2 mm.

  5. Development of an all-permanent-magnet microwave ion source equipped with multicusp magnetic fields for high current proton beam productiona)

    Science.gov (United States)

    Tanaka, M.; Hara, S.; Seki, T.; Iga, T.

    2008-02-01

    An all-permanent-magnet (APM) microwave hydrogen ion source was developed to reduce the size and to simplify structure of a conventional solenoid coil microwave ion source developed for reliability improvement of high current proton linac application systems. The difficulty in developing the APM source was sensitive dependence of the source performance on axial magnetic field in the microwave discharge chamber. It was difficult to produce high current proton beam stably without precise tuning of the magnetic field using solenoid coils. We lowered the sensitivity using multicusp magnetic fields for plasma confinement at the discharge chamber sidewall of the source. This enabled stable high current proton beam production with the APM microwave ion source with no tuning coil. The water cooling and the power supply for the coils are not necessary for the APM source, which leads to better reliability and system simplification. The outer diameter of the APM source was around 300mm, which was 20% lower than the coil source. The APM source produced a maximum hydrogen ion beam current of 65mA (high current density of 330mA/cm2, proton ratio of 87%, and beam energy of 30keV) with a 5mm diameter extraction aperture, pulse width of 400μs, and 20Hz repetition rate at 1.3kW microwave power. This performance is almost the same as the best performances of the conventional coil sources. The extracted ion beams were focused with electrostatic five-grid lens to match beam to acceptance of radio-frequency quadrupole linacs. The maximum focused beam current through the orifice (5mm radius) and the lens was 36mA and the 90% focused beam half-width was 1-2mm.

  6. Enhancement of the high-magnetic-field critical current density of superconducting MgB2 by proton irradiation.

    Science.gov (United States)

    Bugoslavsky, Y; Cohen, L F; Perkins, G K; Polichetti, M; Tate, T J; Gwilliam, R; Caplin, A D

    2001-05-31

    Magnesium diboride, MgB2, has a relatively high superconducting transition temperature, placing it between the families of low- and high-temperature (copper oxide based) superconductors. Supercurrent flow in MgB2 is unhindered by grain boundaries, making it potentially attractive for technological applications in the temperature range 20-30 K. But in the bulk material, the critical current density (Jc) drops rapidly with increasing magnetic field strength. The magnitude and field dependence of the critical current are related to the presence of structural defects that can 'pin' the quantized magnetic vortices that permeate the material, and a lack of natural defects in MgB2 may be responsible for the rapid decline of Jc with increasing field strength. Here we show that modest levels of atomic disorder induced by proton irradiation enhance the pinning of vortices, thereby significantly increasing Jc at high field strengths. We anticipate that either chemical doping or mechanical processing should generate similar levels of disorder, and so achieve performance that is technologically attractive in an economically viable way.

  7. Analysis of the temporal and spatial dependence of the eddy current fields in a 40-cm bore magnet.

    Science.gov (United States)

    Robertson, S; Hughes, D G; Liu, Q; Allen, P S

    1992-05-01

    Eddy current fields, generated in an animal-size superconducting NMR magnet by a nominally rectangular pulsed transverse gradient applied in the vertical direction, have been studied by measuring the offset frequency of the proton NMR signal obtained from a small spherical sample. Measurements were made, after various time delays, at nine different locations in the sample space. Analysis of the data shows that the time-dependent fields at all nine locations are quite well accounted for by the superposition of only four independent exponentially decaying components that have time constants in the range from 9 to 400 ms. Two of these were found to be caused by eddy currents generated in the magnet structure. They generate primarily linear gradients, though one of them also produces a B0 shift, indicating a significant asymmetry about the isocenter of the conducting structure in which the eddy current flows. The other two exponentially decaying components, which had very different time constants from the eddy currents and also initial amplitudes of the opposite sign, were generated by the preemphasis unit. This calls into question the procedure used to adjust the preemphasis unit and an alternative method is proposed.

  8. High Voltage, Fast-Switching Module for Active Control of Magnetic Fields and Edge Plasma Currents

    Science.gov (United States)

    Ziemba, Timothy; Miller, Kenneth; Prager, James; Slobodov, Ilia

    2016-10-01

    Fast, reliable, real-time control of plasma is critical to the success of magnetic fusion science. High voltage and current supplies are needed to mitigate instabilities in all experiments as well as disruption events in large scale tokamaks for steady-state operation. Silicon carbide (SiC) MOSFETs offer many advantages over IGBTs including lower drive energy requirements, lower conduction and switching losses, and higher switching frequency capabilities; however, these devices are limited to 1.2-1.7 kV devices. As fusion enters the long-pulse and burning plasma eras, efficiency of power switching will be important. Eagle Harbor Technologies (EHT), Inc. developing a high voltage SiC MOSFET module that operates at 10 kV. This switch module utilizes EHT gate drive technology, which has demonstrated the ability to increase SiC MOSFET switching efficiency. The module will allow more rapid development of high voltage switching power supplies at lower cost necessary for the next generation of fast plasma feedback and control. EHT is partnering with the High Beta Tokamak group at Columbia to develop detailed high voltage module specifications, to ensure that the final product meets the needs of the fusion science community.

  9. Macroscopic fields in thin ferromagnetic sheets taking into account eddy currents and Landau-Lifshitz magnetization

    Science.gov (United States)

    Dupré, Luc; Olyslager, Frank; Melkebeek, Jan

    2004-05-01

    The paper deals with a numerical model for the evaluation of the electromagnetic behavior in thin magnetic sheets. Therefore, we consider Maxwell's equations together with a nonlinear magnetic constitutive law described by the Landau-Lifshitz equation. We present a suitable numerical approximation based upon a finite element-finite difference method. At each time step in the numerical scheme, the magnetization dynamics is calculated analytically by introducing for each finite element node a transformation towards a local coordinate system.

  10. Algorithms for Computing the Magnetic Field, Vector Potential, and Field Derivatives for a Thin Solenoid with Uniform Current Density

    Energy Technology Data Exchange (ETDEWEB)

    Walstrom, Peter Lowell [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-08-07

    A numerical algorithm for computing the field components Br and Bz and their r and z derivatives with open boundaries in cylindrical coordinates for radially thin solenoids with uniform current density is described in this note. An algorithm for computing the vector potential Aθ is also described. For the convenience of the reader, derivations of the final expressions from their defining integrals are given in detail, since their derivations are not all easily found in textbooks. Numerical calculations are based on evaluation of complete elliptic integrals using the Bulirsch algorithm cel. The (apparently) new feature of the algorithms described in this note applies to cases where the field point is outside of the bore of the solenoid and the field-point radius approaches the solenoid radius. Since the elliptic integrals of the third kind normally used in computing Bz and Aθ become infinite in this region of parameter space, fields for points with the axial coordinate z outside of the ends of the solenoid and near the solenoid radius are treated by use of elliptic integrals of the third kind of modified argument, derived by use of an addition theorem. Also, the algorithms also avoid the numerical difficulties the textbook solutions have for points near the axis arising from explicit factors of 1/r or 1/r2 in the some of the expressions.

  11. High field superconducting magnets

    Science.gov (United States)

    Hait, Thomas P. (Inventor); Shirron, Peter J. (Inventor)

    2011-01-01

    A superconducting magnet includes an insulating layer disposed about the surface of a mandrel; a superconducting wire wound in adjacent turns about the mandrel to form the superconducting magnet, wherein the superconducting wire is in thermal communication with the mandrel, and the superconducting magnet has a field-to-current ratio equal to or greater than 1.1 Tesla per Ampere; a thermally conductive potting material configured to fill interstices between the adjacent turns, wherein the thermally conductive potting material and the superconducting wire provide a path for dissipation of heat; and a voltage limiting device disposed across each end of the superconducting wire, wherein the voltage limiting device is configured to prevent a voltage excursion across the superconducting wire during quench of the superconducting magnet.

  12. Electric field and current density distributions induced in an anatomically-based model of the human head by magnetic fields from a hair dryer.

    Science.gov (United States)

    Tofani, S; Ossola, P; d'Amore, G; Gandhi, O P

    1995-01-01

    We have used the impedance method to calculate the induced electric (E) fields and current densities (J) for the spatially varying vector magnetic fields due to a hair dryer. In this method, applicable for low-frequency exposures where the quasi-static approximation may be made, the biological body or the exposed parts thereof are represented by a three-dimensional (3-D) network of impedances whose individual values are obtained from the electrical properties sigma, epsilon r for the various tissues. We have measured the 3-D variations of the 50-Hz magnetic fields from a typical hair dryer and found that the various components correlate well with those for a helical coil. The non-uniform magnetic fields thus obtained are used to calculate the induced E and J with a resolution of 1.31 cm for the model of the head and neck. The induced E values are compared with the fields endogenous to the body and the minimum detectable E-field limits based on the cellular thermal noise model proposed by Weaver and Astumian (1990, 1992).

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

    Science.gov (United States)

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

    2014-05-01

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

  14. Solar Magnetic Fields

    CERN Document Server

    Hood, Alan W

    2011-01-01

    This review provides an introduction to the generation and evolution of the Sun's magnetic field, summarising both observational evidence and theoretical models. The eleven year solar cycle, which is well known from a variety of observed quantities, strongly supports the idea of a large-scale solar dynamo. Current theoretical ideas on the location and mechanism of this dynamo are presented. The solar cycle influences the behaviour of the global coronal magnetic field and it is the eruptions of this field that can impact on the Earth's environment. These global coronal variations can be modelled to a surprising degree of accuracy. Recent high resolution observations of the Sun's magnetic field in quiet regions, away from sunspots, show that there is a continual evolution of a small-scale magnetic field, presumably produced by small-scale dynamo action in the solar interior. Sunspots, a natural consequence of the large-scale dynamo, emerge, evolve and disperse over a period of several days. Numerical simulation...

  15. Cosmological Magnetic Fields

    CERN Document Server

    Kunze, Kerstin E

    2013-01-01

    Magnetic fields are observed on nearly all scales in the universe, from stars and galaxies upto galaxy clusters and even beyond. The origin of cosmic magnetic fields is still an open question, however a large class of models puts its origin in the very early universe. A magnetic dynamo amplifying an initial seed magnetic field could explain the present day strength of the galactic magnetic field. However, it is still an open problem how and when this initial magnetic field was created. Observations of the cosmic microwave background (CMB) provide a window to the early universe and might therefore be able to tell us whether cosmic magnetic fields are of primordial, cosmological origin and at the same time constrain its parameters. We will give an overview of the observational evidence of large scale magnetic fields, describe generation mechanisms of primordial magnetic fields and possible imprints in the CMB.

  16. The effects of electric and magnetic fields on the current spin polarization and magnetoresistance in a ferromagnetic/organic semiconductor/ferromagnetic (FM/OSC/FM) system

    Institute of Scientific and Technical Information of China (English)

    Wang Yu-Mei; Ren Jun-Feng; Yuan Xiao-Bo; Dou Zhao-Tao; Hu Gui-Chao

    2012-01-01

    From experimental results of spin polarized injection and transport in organic semiconductors (OSCs),we theoretically study the current spin polarization and magnetoresistance under an electric and a magnetic field in a ferromagnetic/organic semiconductor/ferromagnetic (FM/OSC/FM) sandwich structure according to the spin drift-diffusion theory and Ohm's law.From the calculations,it is found that the interfacial current spin polarization is enhanced by several orders of magnitude through tuning the magnetic and electric fields by taking into account the specific characteristics of OSC.Furthermore,the effects of the electric and magnetic fields on the magnetoresistance are also discussed in the sandwich structure.

  17. Magnetic Field Grid Calculator

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Magnetic Field Properties Calculator will computes the estimated values of Earth's magnetic field(declination, inclination, vertical component, northerly...

  18. Algorithms for Computing the Magnetic Field, Vector Potential, and Field Derivatives for Circular Current Loops in Cylindrical Coordinates

    Energy Technology Data Exchange (ETDEWEB)

    Walstrom, Peter Lowell [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-08-24

    A numerical algorithm for computing the field components Br and Bz and their r and z derivatives with open boundaries in cylindrical coordinates for circular current loops is described. An algorithm for computing the vector potential is also described. For the convenience of the reader, derivations of the final expressions from their defining integrals are given in detail, since their derivations (especially for the field derivatives) are not all easily found in textbooks. Numerical calculations are based on evaluation of complete elliptic integrals using the Bulirsch algorithm cel. Since cel can evaluate complete elliptic integrals of a fairly general type, in some cases the elliptic integrals can be evaluated without first reducing them to forms containing standard Legendre forms. The algorithms avoid the numerical difficulties that many of the textbook solutions have for points near the axis because of explicit factors of 1=r or 1=r2 in the some of the expressions.

  19. Analyzing Magnetic Field and Electrical Current Profiles of the Day Side and Terminator of Mars Using Data from Mars Global Surveyor (MGS)

    Science.gov (United States)

    Fogle, A. L.; Ponce, N.; Fillingim, M. O.

    2014-12-01

    Mars does not have a global magnetic field, so the interplanetary magnetic field (IMF) can impact the upper atmosphere and induce currents in the Martian ionosphere. During aerobraking maneuvers, Mars Global Surveyor (MGS) made over 1000 passes through the Martian ionosphere. During the aerobraking phase, MGS measured the local magnetic field in the ionosphere. From measuring changes in the magnetic field, we can calculate the ionospheric currents. By only using measurements where the radial component of the magnetic field is zero and making some assumptions about the gradients in the magnetic field, we are allowed to classify data that meets those conditions as "good" data and calculate horizontal currents in the ionosphere. We focus on data taken over regions of Mars that had negligible crustal magnetic fields to simplify our analysis. The data being analyzed is observed at a maximum altitude of 250 kilometers with a solar zenith angle (SZA) range of 0 degrees to 50 degrees for the day side and 50 to 130 degrees for the terminator. For the day side of Mars, it was found that 24.06% of the data observed was usable data under the initial parameters that were set for "good" data. For the terminator, it was found that 32.08% of the data was usable. The currents that are computed using these "good" magnetic field profiles can give us insights into how the changing solar wind and interplanetary magnetic field can effect the upper atmosphere of mars. For example, induced currents can lead to Joule heating of the atmosphere potentially modifying the neutral dynamics.

  20. The Earth's Magnetic Field

    OpenAIRE

    Edda Lína Gunnarsdóttir 1988

    2012-01-01

    The Earth's magnetic field is essential for life on Earth, as we know it, to exist. It forms a magnetic shield around the planet, protecting it from high energy particles and radiation from the Sun, which can cause damage to life, power systems, orbiting satellites, astronauts and spacecrafts. This report contains a general overview of the Earth's magnetic field. The different sources that contribute to the total magnetic field are presented and the diverse variations in the field are describ...

  1. Extending the GMR Current Measurement Range with a Counteracting Magnetic Field

    OpenAIRE

    Tin Yan Poon; Ricky Wing Hong Lau; Norman Chung Fai Tse

    2013-01-01

    Traditionally, current transformers are often used for current measurement in low voltage (LV) electrical networks. They have a large physical size and are not designed for use with power electronic circuits. Semiconductor-based current sensing devices such as the Hall sensor and Giant Magnetoresistive (GMR) sensor are advantageous in terms of small size, high sensitivity, wide frequency range, low power consumption, and relatively low cost. Nevertheless, the operational characteristics of th...

  2. Photocurrent, Rectification, and Magnetic Field Symmetry of Induced Current Through Quantum Dots

    DEFF Research Database (Denmark)

    DiCarlo, L.; M. Marcus, C.; Harris jr, J.

    2003-01-01

    We report mesoscopic dc current generation in an open chaotic quantum dot with ac excitation applied to one of the shape-defining gates. For excitation frequencies large compared to the inverse dwell time of electrons in the dot (i.e., GHz), we find mesoscopic fluctuations of induced current...

  3. Determination of electric field, magnetic field, and electric current distributions of infrared optical antennas: A nano-optical vector network analyzer

    CERN Document Server

    Olmon, Robert L; Krenz, Peter M; Lail, Brian A; Saraf, Laxmikant V; Boreman, Glenn D; Raschke, Markus B

    2010-01-01

    In addition to the electric field E(r), the associated magnetic field H(r) and current density J(r) characterize any electromagnetic device, providing insight into antenna coupling and mutual impedance. We demonstrate the optical analogue of the radio frequency vector network analyzer implemented in interferometric homodyne scattering-type scanning near-field optical microscopy (s-SNOM) for obtaining E(r), H(r), and J(r). The approach is generally applicable and demonstrated for the case of a linear coupled-dipole antenna in the mid-infrared. The determination of the underlying 3D vector electric near-field distribution E(r) with nanometer spatial resolution and full phase and amplitude information is enabled by the design of probe tips with selectivity with respect to E-parallel and E-perpendicular fabricated by focused ion-beam milling and nano-CVD.

  4. In-vivo Imaging of Magnetic Fields Induced by Transcranial Direct Current Stimulation (tDCS) in Human Brain using MRI

    Science.gov (United States)

    Jog, Mayank V.; Smith, Robert X.; Jann, Kay; Dunn, Walter; Lafon, Belen; Truong, Dennis; Wu, Allan; Parra, Lucas; Bikson, Marom; Wang, Danny J. J.

    2016-10-01

    Transcranial direct current stimulation (tDCS) is an emerging non-invasive neuromodulation technique that applies mA currents at the scalp to modulate cortical excitability. Here, we present a novel magnetic resonance imaging (MRI) technique, which detects magnetic fields induced by tDCS currents. This technique is based on Ampere’s law and exploits the linear relationship between direct current and induced magnetic fields. Following validation on a phantom with a known path of electric current and induced magnetic field, the proposed MRI technique was applied to a human limb (to demonstrate in-vivo feasibility using simple biological tissue) and human heads (to demonstrate feasibility in standard tDCS applications). The results show that the proposed technique detects tDCS induced magnetic fields as small as a nanotesla at millimeter spatial resolution. Through measurements of magnetic fields linearly proportional to the applied tDCS current, our approach opens a new avenue for direct in-vivo visualization of tDCS target engagement.

  5. The magnetic field of cortical current sources: the application of a spatial filtering model to the forward and inverse problems.

    Science.gov (United States)

    Tan, S; Roth, B J; Wikswo, J P

    1990-07-01

    We extend our theoretical model based on spatial filtering to determine the ability of a SQUID magnetometer to resolve 2 localized current sources in the brain. We find that in order to resolve 2 separated but coaxial cortical sources, the source-to-pickup coil distance must be comparable to the distance between the 2 sources. The size of the current sources affects the resolving power of a magnetometer, but an anisotropy of 3 in the cortical tissue does not produce a significant effect. The model also provides a solution of the inverse calculation, either to reconstruct the original current source distribution from the measured magnetic field, or to continue the field at the magnetometer inward towards the sources. Both the inverse and inward calculations are limited by the fact that the inverse filter function serves as a high-pass filter, which leads to instabilities at high spatial frequencies, particularly in the presence of noise. The instabilities can be minimized by choosing an appropriate window to attenuate the noise, but this in turn reduces the spatial resolution.

  6. A low noise modular current source for stable magnetic field control

    Science.gov (United States)

    Biancalana, Valerio; Bevilacqua, Giuseppe; Chessa, Piero; Dancheva, Yordanka; Cecchi, Roberto; Stiaccini, Leonardo

    2017-03-01

    A low cost, stable, programmable, unipolar current source is described. The circuit is designed in view of a modular arrangement, suitable for applications where several DC sources must be controlled at once. A hybrid switching/linear design helps in improving the stability and in reducing the power dissipation and cross-talking. Multiple units can be supplied by a single DC power supply, while allowing for a variety of maximal current values and compliance voltages at the outputs. The circuit is analogically controlled by a unipolar voltage, enabling current programmability and control through commercial digital-to-analogue conversion cards.

  7. Experimental Section: On the magnetic field distribution generated by a dipolar current source situated in a realistically shaped compartment model of the head

    NARCIS (Netherlands)

    Meijs, J.W.H.; Bosch, F.G.C.; Peters, M.J.; Lopes da silva, F.H.

    1987-01-01

    The magnetic field distribution around the head is simulated using a realistically shaped compartment model of the head. The model is based on magnetic resonance images. The 3 compartments describe the brain, the skull and the scalp. The source is represented by a current dipole situated in the

  8. Coronal Magnetic Field Models

    Science.gov (United States)

    Wiegelmann, Thomas; Petrie, Gordon J. D.; Riley, Pete

    2017-09-01

    Coronal magnetic field models use photospheric field measurements as boundary condition to model the solar corona. We review in this paper the most common model assumptions, starting from MHD-models, magnetohydrostatics, force-free and finally potential field models. Each model in this list is somewhat less complex than the previous one and makes more restrictive assumptions by neglecting physical effects. The magnetohydrostatic approach neglects time-dependent phenomena and plasma flows, the force-free approach neglects additionally the gradient of the plasma pressure and the gravity force. This leads to the assumption of a vanishing Lorentz force and electric currents are parallel (or anti-parallel) to the magnetic field lines. Finally, the potential field approach neglects also these currents. We outline the main assumptions, benefits and limitations of these models both from a theoretical (how realistic are the models?) and a practical viewpoint (which computer resources to we need?). Finally we address the important problem of noisy and inconsistent photospheric boundary conditions and the possibility of using chromospheric and coronal observations to improve the models.

  9. Negative differential conductivity induced current instability in two-dimensional electron gas system in high magnetic fields

    Science.gov (United States)

    Lee, Ching-Ping; Komiyama, Susumu; Chen, Jeng-Chung

    2015-03-01

    High mobility two-dimensional electron gas (2DEG) formed in the interface of a GaAs/AlGaAs hetero-structure in high magnetic field (B) exhibits interring nonlinear response either under microwave radiation or to a dc electric field (E). It is general believed that this kind nonlinear behavior is closely related to the occurrence of negative-differential conductance (NDC) in the presence of strong B and E. We observe a new type NDC state driven by a direct current above a threshold value (Ith) applied to a 2DEG as a function of B at relatively high temperatures (T). A current instability is observed in 2DEG system at high B ~6-8 T and at high T ~ 20- 30 K while the applied current is over Ith. The longitudinal voltage Vxx shows sub-linear behavior with the increase of I. As the current exceed Ith, Vxx suddenly drops a ΔVxx and becomes irregular associated with the appearance of hysteresis with sweeping I. We find that Ith increases with the increase of B and of T; meanwhile, ΔVxx is larger at higher B but lower T. Data analysis suggest that the onset of voltage fluctuation can be described by a NDC model proposed by Kurosawa et al. in 1976. The general behaviors of T and B dependence of current instability are analog to those recently reported at lower both T and B. This consistence suggests the same genuine mechanism of NDC phenomena observed in 2DEG system.

  10. Vestibular stimulation by magnetic fields

    Science.gov (United States)

    Ward, Bryan K.; Roberts, Dale C.; Della Santina, Charles C.; Carey, John P.; Zee, David S.

    2015-01-01

    Individuals working next to strong static magnetic fields occasionally report disorientation and vertigo. With the increasing strength of magnetic fields used for magnetic resonance imaging (MRI) studies, these reports have become more common. It was recently learned that humans, mice and zebrafish all demonstrate behaviors consistent with constant peripheral vestibular stimulation while inside a strong, static magnetic field. The proposed mechanism for this effect involves a Lorentz force resulting from the interaction of a strong static magnetic field with naturally occurring ionic currents flowing through the inner ear endolymph into vestibular hair cells. The resulting force within the endolymph is strong enough to displace the lateral semicircular canal cupula, inducing vertigo and the horizontal nystagmus seen in normal mice and in humans. This review explores the evidence for interactions of magnetic fields with the vestibular system. PMID:25735662

  11. Measurement of critical current of superconducting materials at the changing magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Qingrong; Hu Yongchang

    1986-06-01

    In this paper we present a new method for measuring the critical current of superconductor materials. The experimental results indicate the I/sub c/(H) character of the samples rather directly and, comparing with other methods, we can get more data at the same interval.

  12. Effects of Pulsed Current and Pulsed Magnetic Field Complex Pretreatment on Martensite Transformation of Cr5 Steel during Continuous Cooling

    Institute of Scientific and Technical Information of China (English)

    Qing-chun LI; Li-juan LI; Guo-wei CHANG; Qi-jie ZHAI

    2015-01-01

    Carbide precipitation and martensite transformation in Cr5 steel have been observed in situ by high-temper-ature confocal laser-scanning microscopy.In this way,the influences of pulsed current and pulsed magnetic field complex pretreatment on carbide precipitation and martensite transformation during continuous cooling have been studied.The results show that the electropulsing complex pretreatment promotes the precipitation of M7 C3-type car-bides at high temperature,increases the start and finish temperatures of martensite transformation,and extends the phase transformation time.Martensite prefers to nucleate in the austenite with less precipitation of carbides due to the chemically homogeneous distribution of solute atoms.

  13. Electromagnetic analysis of a superconducting transformer for high current characterization of cable in conduit conductors in background magnetic field

    Science.gov (United States)

    Wu, Xiangyang; Tan, Yunfei; Fang, Zhen; Jiang, Donghui; Chen, Zhiyou; Chen, Wenge; Kuang, Guangli

    2017-10-01

    A large cable-in-conduit-conductor (CICC) test facility has been designed and fabricated at the High Magnetic Field Laboratory of the Chinese Academy of Sciences (CHMFL) in order to meet the test requirement of the conductors which are applied to the future fusion reactor. The critical component of the test facility is an 80 kA superconducting transformer which consists of a multi-turn primary coil and a minor-turn secondary coil. As the current source of the conductor samples, the electromagnetic performance of the superconducting transformer determines the stability and safety of the test facility. In this paper, the key factors and parameters, which have much impact on the performance of the transformer, are analyzed in detail. The conceptual design and optimizing principles of the transformer are discussed. An Electromagnetic-Circuit coupled model built in ANSYS Multiphysics is successfully used to investigate the electromagnetic characterization of the transformer under the dynamic operation condition.

  14. Magnetic fields in galaxies

    CERN Document Server

    Beck, Rainer

    2013-01-01

    Most of the visible matter in the Universe is ionized, so that cosmic magnetic fields are quite easy to generate and due to the lack of magnetic monopoles hard to destroy. Magnetic fields have been measured in or around practically all celestial objects, either by in-situ measurements of spacecrafts or by the electromagnetic radiation of embedded cosmic rays, gas or dust. The Earth, the Sun, solar planets, stars, pulsars, the Milky Way, nearby galaxies, more distant (radio) galaxies, quasars and even intergalactic space in clusters of galaxies have significant magnetic fields, and even larger volumes of the Universe may be permeated by "dark" magnetic fields. Information on cosmic magnetic fields has increased enormously as the result of the rapid development of observational methods, especially in radio astronomy. In the Milky Way, a wealth of magnetic phenomena was discovered, which are only partly related to objects visible in other spectral ranges. The large-scale structure of the Milky Way's magnetic fie...

  15. The Juno Magnetic Field Investigation

    DEFF Research Database (Denmark)

    Connerney, J. E. P.; Benn, Mathias; Bjarnø, Jonas Bækby

    2017-01-01

    The Juno Magnetic Field investigation (MAG) characterizes Jupiter’s planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor ...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-04-15

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

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

    CERN Document Server

    Adorno, T C; Shabad, A E

    2014-01-01

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

  18. Forced flow He vapor cooled critical current testing facility for measurements of superconductors in a wide temperature and magnetic field range

    Science.gov (United States)

    Baskys, Algirdas; Hopkins, Simon C.; Bader, Jakob; Glowacki, Bartek A.

    2016-10-01

    As superconducting materials find their way into applications, there is increasing need to verify their performance at operating conditions. Testing of critical current with respect to temperature and magnetic field is of particular importance. However, testing facilities covering a range of temperatures and magnetic fields can be costly, especially when considering the cooling power required in the cryogenic system in the temperature range below 65 K (inaccessible for LN2). Critical currents in excess of 500 A are common for commercial samples, making the testing of such samples difficult in setups cooled via a cryocooler, moreover it often does not represent the actual cooling conditions that the sample will experience in service. This work reports the design and operation of a low-cost critical current testing facility, capable of testing samples in a temperature range of 10-65 K, with magnetic field up to 1.6 T and measuring critical currents up to 900 A with variable cooling power.

  19. Forced vibrations of a current-carrying nanowire in a longitudinal magnetic field accounting for both surface energy and size effects

    Science.gov (United States)

    Kiani, Keivan

    2014-09-01

    Forced vibrations of current-carrying nanowires in the presence of a longitudinal magnetic field are of interest. By considering the surface energy and size effects, the coupled equations of motion describing transverse motions of the nanostructure are derived. By employing Galerkin and Newmark-β approaches, the deflections of the nanowire subjected to transverse dynamic loads are evaluated. The effects of the magnetic field, electric current, pre-tension force, frequency of the applied load, surface and size effects on the maximum transverse displacements are discussed. The obtained results display that for the frequency of the applied load lower than the nanowire's fundamental frequency, by increasing the magnetic field or electric current, the maximum transverse displacements would increase. However, for exciting frequencies greater than that of the nanowire, maximum transverse displacements would increase or decrease with the magnetic field strength or electric current. Additionally, the pre-tension force results in decreasing of the maximum transverse displacements. Such a reduction is more apparent for higher values of the magnetic field strength and electric current. The present study would be useful in the design of the micro- and nano-electro-mechanical systems expected to be one of the most wanted technologies in the near future.

  20. Hysteresis losses in MgB{sub 2} superconductors exposed to combinations of low AC and high DC magnetic fields and transport currents

    Energy Technology Data Exchange (ETDEWEB)

    Magnusson, N., E-mail: niklas.magnusson@sintef.no [SINTEF Energy Research, NO-7465 Trondheim (Norway); Abrahamsen, A.B. [DTU Wind Energy, Technical University of Denmark, DK-4000 Roskilde (Denmark); Liu, D. [Electrical Power Processing Group, TU Delft, Mekelweg 4, NL-2628 CD Delft (Netherlands); Runde, M. [SINTEF Energy Research, NO-7465 Trondheim (Norway); Polinder, H. [Electrical Power Processing Group, TU Delft, Mekelweg 4, NL-2628 CD Delft (Netherlands)

    2014-11-15

    Highlights: • A method for calculating hysteresis losses in the low AC – high DC magnetic field and transport current range has been shown. • The method can be used in the design of wind turbine generators for calculating the losses in the generator DC rotor. • First estimates indicate tolerable current ripple in the 0.1% range for a 4 T DC MgB{sub 2} generator rotor coil. - Abstract: MgB{sub 2} superconductors are considered for generator field coils for direct drive wind turbine generators. In such coils, the losses generated by AC magnetic fields may generate excessive local heating and add to the thermal load, which must be removed by the cooling system. These losses must be evaluated in the design of the generator to ensure a sufficient overall efficiency. A major loss component is the hysteresis losses in the superconductor itself. In the high DC – low AC current and magnetic field region experimental results still lack for MgB{sub 2} conductors. In this article we reason towards a simplified theoretical treatment of the hysteresis losses based on available models in the literature with the aim of setting the basis for estimation of the allowable magnetic fields and current ripples in superconducting generator coils intended for large wind turbine direct drive generators. The resulting equations use the DC in-field critical current, the geometry of the superconductor and the magnitude of the AC magnetic field component as parameters. This simplified approach can be valuable in the design of MgB{sub 2} DC coils in the 1–4 T range with low AC magnetic field and current ripples.

  1. Organic magnetic field sensor

    Energy Technology Data Exchange (ETDEWEB)

    McCamey, Dane; Boehme, Christoph

    2017-01-24

    An organic, spin-dependent magnetic field sensor (10) includes an active stack (12) having an organic material with a spin-dependence. The sensor (10) also includes a back electrical contact (14) electrically coupled to a back of the active stack (12) and a front electrical contact (16) electrically coupled to a front of the active stack (12). A magnetic field generator (18) is oriented so as to provide an oscillating magnetic field which penetrates the active stack (12).

  2. Maximum allowable currents in YBa2Cu3O7 superconducting tapes as a function of the coating thickness, external magnetic field induction, and cooling conditions

    Science.gov (United States)

    Arkharov, A. M.; Dontsova, E. S.; Lavrov, N. A.; Romanovskii, V. R.

    2014-04-01

    Maximum allowable (ultimate) currents stably passing through an YBa2Cu3O7 superconducting current-carrying element are determined as a function of a silver (or copper) coating thickness, external magnetic field induction, and cooling conditions. It is found that if a magnetic system based on yttrium ceramics is cooled by a cryogenic coolant, currents causing instabilities (instability onset currents) are almost independent of the coating thickness. If, however, liquid helium is used as a cooling agent, the ultimate current monotonically grows with the thickness of the stabilizing copper coating. It is shown that depending on cooling conditions, the stable values of the current and electric field strength preceding the occurrence of instability may be both higher and lower than the a priori chosen critical parameters of the superconductor. These features should be taken into account in selecting the stable value of the operating current of YBa2Cu3O7 superconducting windings.

  3. Axial magnetic field and toroidally streaming fast ions in the dense plasma focus are natural consequences of conservation laws in the curved axisymmetric geometry of the current sheath

    CERN Document Server

    Auluck, S K H

    2014-01-01

    Direct measurement of axial magnetic field in the PF-1000 dense plasma focus (DPF), and its reported correlation with neutron emission, call for a fresh look at previous reports of existence of axial magnetic field component in the DPF from other laboratories, and associated data suggesting toroidal directionality of fast ions participating in fusion reactions, with a view to understand the underlying physics. In this context, recent work dealing with application of the hyperbolic conservation law formalism to the DPF is extended in this paper to a curvilinear coordinate system, which reflects the shape of the DPF current sheath. Locally-unidirectional shock propagation in this coordinate system enables construction of a system of 7 one-dimensional hyperbolic conservation law equations with geometric source terms, taking into account all the components of magnetic field and flow velocity. Rankine-Hugoniot jump conditions for this system lead to expressions for the axial magnetic field and three components of ...

  4. Irreversibility line and magnetic field dependence of the critical current in superconducting MgB sub 2 bulk samples

    CERN Document Server

    Gioacchino, D D; Tripodi, P; Grimaldi, G

    2003-01-01

    The third harmonic components of the ac susceptibility of MgB sub 2 bulk samples have been measured as a function of applied magnetic fields, together with standard magnetization cycles. The irreversibility line (IL) of the magnetic field has been extracted from the onset of the third harmonic components. Using a (1 - t) supalpha glass/liquid best fit where alpha 1.27 IL shows a coherent length xi divergence with exponent nu = 0.63, which indicates a 3D behaviour. Moreover, using the numerical solution of the non-linear magnetic diffusion equation, considering the creep model in a 3D vortex glass, a good description of the vortex dynamics has been obtained. The behaviour of the magnetization amplitude (approx Hz) and the ac susceptibility signals (kHz), at different applied magnetic fields, 3.5 T < H sub d sub c < 4.5 T, and at the reduced temperature 0.86 < t < 0.93 (T = 22 K), shows that the superconducting dynamic response of vortices in the MgB sub 2 samples is not evidently dependent on the f...

  5. The mean electro-motive force, current- and cross-helicity under the influence of rotation, magnetic field and shear

    CERN Document Server

    Pipin, V V

    2006-01-01

    The expressions for the mean electromotive force (MEMF) is derived for the case of the stratified magnetohydrodynamical turbulence that is subjected to the influence of rotation, large-scale magnetic field (LSMF) and shear. The derivations were made in the framework of mean-field magnetohydrodynamics. The effect of turbulent flows and fluctuating magnetic fields on the evolution of the large-scale fields is computed within the so-called "minimal tau-approximation" (MTA). The influence of the large-scale fields such as rotation, LSMF and uniform shear (differential rotation) on the different parts of the MEMF (such as $\\alpha$ - effect, turbulent diffusion, turbulent transport and etc.) is explicitly defined via factors describing the efficiency of rotational and LSMF's influence on the turbulent flows. Whenever it possible we make comparison with results obtained earlier within the second order correlation approximation (SOCA). In computing the mean electro-motive force we take into account the influence of t...

  6. Quantum fluid dynamics based current-density functional study of a helium atom in a strong time-dependent magnetic field

    Science.gov (United States)

    Vikas, Hash(0x125f4490)

    2011-02-01

    Evolution of the helium atom in a strong time-dependent (TD) magnetic field ( B) of strength up to 1011 G is investigated through a quantum fluid dynamics (QFD) based current-density functional theory (CDFT). The TD-QFD-CDFT computations are performed through numerical solution of a single generalized nonlinear Schrödinger equation employing vector exchange-correlation potentials and scalar exchange-correlation density functionals that depend both on the electronic charge-density and the current-density. The results are compared with that obtained from a B-TD-QFD-DFT approach (based on conventional TD-DFT) under similar numerical constraints but employing only scalar exchange-correlation potential dependent on electronic charge-density only. The B-TD-QFD-DFT approach, at a particular TD magnetic field-strength, yields electronic charge- and current-densities as well as exchange-correlation potential resembling with that obtained from the time-independent studies involving static (time-independent) magnetic fields. However, TD-QFD-CDFT electronic charge- and current-densities along with the exchange-correlation potential and energy differ significantly from that obtained using B-TD-QFD-DFT approach, particularly at field-strengths >109 G, representing dynamical effects of a TD field. The work concludes that when a helium atom is subjected to a strong TD magnetic field of order >109 G, the conventional TD-DFT based approach differs "dynamically" from the CDFT based approach under similar computational constraints.

  7. Remote field eddy current testing

    Energy Technology Data Exchange (ETDEWEB)

    Cheong, Y. M.; Jung, H. K.; Huh, H.; Lee, Y. S.; Shim, C. M

    2001-03-01

    The state-of-art technology of the remote field eddy current, which is actively developed as an electromagnetic non-destructive testing tool for ferromagnetic tubes, is described. The historical background and recent R and D activities of remote-field eddy current technology are explained including the theoretical development of remote field eddy current, such as analytical and numerical approach, and the results of finite element analysis. The influencing factors for actual applications, such as the effect of frequency, magnetic permeability, receiving sensitivity, and difficulties of detection and classification of defects are also described. Finally, two examples of actual application, 1) the gap measurement between pressure tubes and calandria tube in CANDU reactor and, 2) the detection of defects in the ferromagnetic heat exchanger tubes, are described. The future research efforts are also included.

  8. Behavior of a DC zero-flux current sensor; Magnetic field analysis and comparison with experimental results

    Energy Technology Data Exchange (ETDEWEB)

    Campostrini, P.; Sonato, P. (Istituto Gas Ionizzati del CNR, Padova (IT))

    1991-09-01

    In this paper the magnetic section of the finite-element ANSYS code, and in particular its optimization feature has been used to predict the behaviour of a zero-flux current sensor, briefly described, which is intended to be used in a fusion experiment to measure pulsed currents up to 50 kA, over a bandwidth from DC to 10 k Hz. The computed results fit well with those coming from experimental tests performed on a prototype.

  9. Low Cost Magnetic Field Controller

    CERN Document Server

    Malafronte, Alexandre A

    2005-01-01

    The Physics Institute of the University of São Paulo (IFUSP) is building a continuous wave (cw) racetrack microtron. This machine has several dipole magnets, like the first and second stage recirculators, and a number of smaller ones in the transport line. These magnets must produce very stable magnetic fields to allow the beam to recirculate along very precise orbits and paths. Furthermore, the fields must be reproducible with great accuracy to allow an easier setup of the machine, though the effects of hysteresis tend to jeopardize the reproducibility. If the magnetic field is chosen by setting the current in the coils, temperature effects over the magnet and power supply tend to change the field. This work describes an inexpensive magnetic field controller that allows a direct measure of the magnetic field through an Hall probe. It includes a microcontroller running a feedback algorithm to control the power supply, in order to keep the field stable and reproducible. The controller can also execu...

  10. Influence of Critical Current Density on Guidance Force Decay of HTS Bulk Exposed to AC Magnetic Field Perturbation in a Maglev Vehicle System

    Science.gov (United States)

    Longcai, Zhang; Jianguo, Kong

    2012-07-01

    Superconducting maglev vehicle is one of the most promising applications of HTS bulks. In such a system, the HTS bulks are always exposed to AC external magnetic field, which is generated by the inhomogeneous surface magnetic field of the NdFeB guideway. In our previous work, we studied the guidance force decay of the YBCO bulk over the NdFdB guideway used in the High-temperature superconducting maglev vehicle system with the application of the AC external magnetic field, and calculated the guidance force decay as a function of time based on an analytic model. In this paper, we investigated the influence of the critical current density on the guidance force decay of HTS bulk exposed to AC field perturbation in the maglev vehicle system and try to adopt a method to suppress the decay. From the results, it was found that the guidance force decay rate was higher for the bulk with lower critical current density. Therefore, we could suppress the guidance force decay of HTS bulk exposed to AC external magnetic field perturbation in the maglev vehicle system by improving critical current density of the bulk.

  11. Effects of heat current on magnetization dynamics

    Science.gov (United States)

    Vetro, Francesco Antonio; Brechet, Sylvain; Ansermet, Jean-Philippe

    The work is aimed at investigating the interplay between spin dynamics and heat currents in single-crystal Yttrium Iron Garnet (YIG). The irreversible thermodynamics for a continuous medium predicts that a thermal gradient, in the presence of magnetization waves, produces a magnetic induction field, thus a magnetic analog of the well-known Seebeck effect. Time-resolved transmission measurements revealed a change in the attenuation of magnetization waves propagating along the thermal gradient when the gradient is reversed. This magnetic damping change can be accounted for by the Magnetic Seebeck effect. In order to characterize this effect further, we have conducted studies on magnetization dynamic in YIG single crystal samples placed in various geometrical configurations, e.g. with YIG disks in which magnetic vortices might be present. Various magnetic resonance schemes were used, e.g. local probes and cavities.

  12. Nanometric alternating magnetic field generator.

    Science.gov (United States)

    Espejo, A P; Tejo, F; Vidal-Silva, N; Escrig, J

    2017-07-05

    In this work we introduce an alternating magnetic field generator in a cylindrical nanostructure. This field appears due to the rotation of a magnetic domain wall located at some position, generating a magnetic region that varies its direction of magnetization alternately, thus inducing an alternating magnetic flux in its vicinity. This phenomenon occurs due to the competition between a spin-polarized current and a magnetic field, which allows to control both the angular velocity and the pinning position of the domain wall. As proof of concept, we study the particular case of a diameter-modulated nanowire with a spin-polarized current along its axis and the demagnetizing field produced by its modulation. This inhomogeneous field allows one to control the angular velocity of the domain wall as a function of its position along the nanowire allowing frequencies in the GHz range to be achieved. This generator could be used in telecommunications for devices in the range of radiofrequencies or, following Faraday's induction law, could also induce an electromotive force and be used as a movable alternate voltage source in future nanodevices.

  13. Magnetic field of a combined plasma trap

    Science.gov (United States)

    Kotenko, V. G.; Moiseenko, V. E.; Ågren, O.

    2012-06-01

    This paper presents numerical simulations performed on the structure of a magnetic field created by the magnetic system of a combined plasma trap. The magnetic system includes the stellarator-type magnetic system and one of the mirror-type. For the stellarator type magnetic system the numeric model contains a magnetic system of an l=2 torsatron with the coils of an additional toroidal magnetic field. The mirror-type magnetic system element is considered as being single current-carrying turn enveloping the region of existence of closed magnetic surfaces of the torsatron. The calculations indicate the existence of a vast area of the values of the additional magnetic field magnitude and magnetic field of the single turn where, in principle, the implementation of the closed magnetic surface configuration is quite feasible.

  14. Magnetization reversal in ultrashort magnetic field pulses

    CERN Document Server

    Bauer, M; Fassbender, J; Hillebrands, B

    2000-01-01

    We report the switching properties of a thin magnetic film subject to an ultrashort, laterally localized magnetic field pulse, obtained by numerical investigations. The magnetization distribution in the film is calculated on a grid assuming Stoner-like coherent rotation within the grid square size. Perpendicularly and in-plane magnetized films exhibit a magnetization reversal due to a 4 ps magnetic field pulse. Outside the central region the pulse duration is short compared to the precession period. In this area the evolution of the magnetization during the field pulse does not depend strongly on magnetic damping and/or pulse shape. However, the final magnetization distribution is affected by the magnetic damping. Although the pulse duration is short compared to the precession period, the time needed for the relaxation of the magnetization to the equilibrium state is rather large. The influence of the different magnetic anisotropy contributions and the magnetic damping parameter enters into the magnetization ...

  15. Magnetic Fields at the Center of Coils

    Science.gov (United States)

    Binder, Philippe; Hui, Kaleonui; Goldman, Jesse

    2014-01-01

    In this note we synthesize and extend expressions for the magnetic field at the center of very short and very long current-carrying coils. Elementary physics textbooks present the following equation for the magnetic field inside a very long current-carrying coil (solenoid): B[subscript sol] = µ[subscript 0] (N/L) I, (1) where I is the current, N…

  16. Reconnection of Magnetic Fields

    Science.gov (United States)

    Birn, J.; Priest, E. R.

    2007-01-01

    Preface; Part I. Introduction: 1.1 The Sun E. R. Priest; 1.2 Earth's magnetosphere J. Birn; Part II. Basic Theory of MHD Reconnection: 2.1 Classical theory of two-dimensional reconnection T. G. Forbes; 2.2 Fundamental concepts G. Hornig; 2.3 Three-dimensional reconnection in the absence of magnetic null points G. Hornig; 2.4 Three-dimensional reconnection at magnetic null points D. Pontin; 2.5 Three-dimensional flux tube reconnection M. Linton; Part III. Basic Theory of Collisionless Reconnection: 3.1 Fundamentals of collisionless reconnection J. Drake; 3.2 Diffusion region physics M. Hesse; 3.3 Onset of magnetic reconnection P. Pritchett; 3.4 Hall-MHD reconnection A. Bhattacharjee and J. Dorelli; 3.5 Role of current-aligned instabilities J. Büchner and W. Daughton; 3.6 Nonthermal particle acceleration M. Hoshino; Part IV. Reconnection in the Magnetosphere: 4.1 Reconnection at the magnetopause: concepts and models J. G. Dorelli and A. Bhattacharjee; 4.2 Observations of magnetopause reconnection K.-H. Trattner; 4.3 On the stability of the magnetotail K. Schindler; 4.4 Simulations of reconnection in the magnetotail J. Birn; 4.5 Observations of tail reconnection W. Baumjohann and R. Nakamura; 4.6 Remote sensing of reconnection M. Freeman; Part V. Reconnection in the Sun's Atmosphere: 5.1 Coronal heating E. R. Priest; 5.2 Separator reconnection D. Longcope; 5.3 Pinching of coronal fields V. Titov; 5.4 Numerical experiments on coronal heating K. Galsgaard; 5.5 Solar flares K. Kusano; 5.6 Particle acceleration in flares: theory T. Neukirch; 5.7 Fast particles in flares: observations L. Fletcher; 6. Open problems J. Birn and E. R. Priest; Bibliography; Index.

  17. Molecules in Magnetic Fields

    Science.gov (United States)

    Berdyugina, Svetlana

    2015-08-01

    Molecules probe cool matter in the Universe and various astrophysical objects. Their ability to sense magnetic fields provides new insights into magnetic properties of these objects. During the past fifteen years we have carried out a theoretical study of molecular magnetic effects such as the Zeeman, Paschen-Back and Hanle effects and their applications for inferring magnetic structures and spatial inhomogeneities on the Sun, cool stars, brown dwarfs, and exoplanets from molecular spectro-polarimetry (e.g., Berdyugina 2011). Here, we present an overview of this study and compare our theoretical predictions with recent laboratory measurements of magnetic properties of some molecules. We present also a new web-based tool to compute molecular magnetic effects and polarized spectra which is supported by the ERC Advanced Grant HotMol.

  18. Effect of magnetic field strength in melt-processing on texture development and critical current density of Bi-oxide superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Maeda, H.; Sastry, P.V.P.S.S.; Trociewitz, U.P.; Schwartz, J.; Ohya, K.; Sato, M.; Chen, W.P.; Watanabe, K.; Motokawa, M

    2003-04-15

    Vertical magnetic fields up to 15 T were applied to the magnetic melt-processing (MMP) of Bi2212 bulks and Ag-sheathed tapes with a core thickness above 80 {mu}m, which were set horizontally. Texture with the c-axis along the direction of magnetic field applied during MMP is developed due to the anisotropy in magnetic susceptibility of Bi2212. The degree of texture and the anisotropy factor in magnetization increase almost linearly as the magnetic field strength H{sub a} during MMP is increased. The anisotropy factor in magnetization reaches 6.5 at a H{sub a} of 13 T for Ag-doped Bi2212 bulks, whereas for Bi(Pb)2212 in which Pb partially substitutes for Bi the factor is suppressed to a half of that of Ag-doped Bi2212. The transport critical current I{sub c} and the critical current density J{sub c} of Bi2212 tapes also increase with increasing H{sub a} due to the texture development and I{sub c} reaches above 1000 A in self-filed for the tapes with a core thickness of 180 {mu}m. However, for further thicker tapes, I{sub c} decreases. The suppressions in the I{sub c} for the tapes and in the anisotropy factor in magnetization for Bi(Pb)2212 bulks are due to inhomogeneous melting, and inhomogeneous nucleation and growth of crystals during MMP. When crystal growth is restricted, crystal alignment is suppressed.

  19. An equivalent distributed magnetic current based FDTD method for the calculation of E-fields induced by gradient coils in MRI.

    Science.gov (United States)

    Crozier, S; Liu, F; Wei, Q

    2004-01-01

    This paper evaluates a low-frequency FDTD method applied to the problem of induced E-fields/eddy currents in the human body resulting from the pulsed magnetic field gradients in MRI. In this algorithm, a distributed equivalent magnetic current (DEMC) is proposed as the electromagnetic source and is obtained by quasistatic calculation of the empty coil's vector potential or measurements therein. This technique circumvents the discretizing of complicated gradient coil geometries into a mesh of Yee cells, and thereby enables any type of gradient coil modeling or other complex low frequency sources. The proposed method has been verified against an example with an analytical solution. Results are presented showing the spatial distribution of gradient-induced electric fields in a multilayered spherical phantom model and a complete body model.

  20. Magnetic instability induced by tunnel current in single Co nanoparticles

    OpenAIRE

    Birk, F. Tijiwa; Jiang, W.; Davidović, D.

    2011-01-01

    Measurements of magnetic hysteresis loops in single Co nanoparticles at dilution refrigerator temperatures are presented. The nanoparticles are in electric contact with bulk Al leads via tunnel junctions. The tunnel current versus magnetic field displays a magnetic hysteresis loop. The magnetic switching field is reduced by current, and the magnetization of the nanoparticle can be switched by applying a voltage pulse, demonstrating that the magnetic stability of the nanoparticle is diminished...

  1. Influence of impurity and recycling on high-β steady-state plasmas sustained by rotating magnetic fields current drive

    Science.gov (United States)

    Guo, H. Y.; Grossnickle, J. A.; Hoffman, A. L.; Vlases, G. C.

    2009-06-01

    A new upgrade of the Translation, Confinement, and Sustainment (TCS) device, TCSU, has been built to form and sustain high temperature compact toroids (CT), known as Field Reversed Configurations, using Rotating Magnetic Fields (RMF). In TCS the plasma temperature was limited to several 10s of eV due to high impurity content. These impurities are greatly reduced in TCSU by using advanced plasma chamber and helium glow discharge cleaning. Reducing impurity radiation, when coupled with reduced overall recycling, enabled the plasma to enter into a new, collisionless regime with temperatures well over 200 eV, substantially exceeding the radiation barrier. This is a first for CTs at low input power density. This was achieved using the simple even-parity RMF drive (despite transient opening of field lines by the RMF) because the associated energy loss is sheath-limited, coupled with the low edge density resulting from the RMF pinch effect.

  2. Quantum fluid dynamics based current-density functional study of a helium atom in a strong time-dependent magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Vikas [Quantum Chemistry Group, Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, 160014 Chandigrah (India)

    2011-02-15

    Evolution of the helium atom in a strong time-dependent (TD) magnetic field (B) of strength up to 10{sup 11} G is investigated through a quantum fluid dynamics (QFD) based current-density functional theory (CDFT). The TD-QFD-CDFT computations are performed through numerical solution of a single generalized nonlinear Schroedinger equation employing vector exchange-correlation potentials and scalar exchange-correlation density functionals that depend both on the electronic charge-density and the current-density. The results are compared with that obtained from a B-TD-QFD-DFT approach (based on conventional TD-DFT) under similar numerical constraints but employing only scalar exchange-correlation potential dependent on electronic charge-density only. The B-TD-QFD-DFT approach, at a particular TD magnetic field-strength, yields electronic charge- and current-densities as well as exchange-correlation potential resembling with that obtained from the time-independent studies involving static (time-independent) magnetic fields. However, TD-QFD-CDFT electronic charge- and current-densities along with the exchange-correlation potential and energy differ significantly from that obtained using B-TD-QFD-DFT approach, particularly at field-strengths >10{sup 9} G, representing dynamical effects of a TD field. The work concludes that when a helium atom is subjected to a strong TD magnetic field of order >10{sup 9} G, the conventional TD-DFT based approach differs 'dynamically' from the CDFT based approach under similar computational constraints. (author)

  3. The Vertical-current Approximation Nonlinear Force-free Field Code—Description, Performance Tests, and Measurements of Magnetic Energies Dissipated in Solar Flares

    Science.gov (United States)

    Aschwanden, Markus J.

    2016-06-01

    In this work we provide an updated description of the Vertical-Current Approximation Nonlinear Force-Free Field (VCA-NLFFF) code, which is designed to measure the evolution of the potential, non-potential, free energies, and the dissipated magnetic energies during solar flares. This code provides a complementary and alternative method to existing traditional NLFFF codes. The chief advantages of the VCA-NLFFF code over traditional NLFFF codes are the circumvention of the unrealistic assumption of a force-free photosphere in the magnetic field extrapolation method, the capability to minimize the misalignment angles between observed coronal loops (or chromospheric fibril structures) and theoretical model field lines, as well as computational speed. In performance tests of the VCA-NLFFF code, by comparing with the NLFFF code of Wiegelmann, we find agreement in the potential, non-potential, and free energy within a factor of ≲ 1.3, but the Wiegelmann code yields in the average a factor of 2 lower flare energies. The VCA-NLFFF code is found to detect decreases in flare energies in most X, M, and C-class flares. The successful detection of energy decreases during a variety of flares with the VCA-NLFFF code indicates that current-driven twisting and untwisting of the magnetic field is an adequate model to quantify the storage of magnetic energies in active regions and their dissipation during flares. The VCA-NLFFF code is also publicly available in the Solar SoftWare.

  4. ANALYTIC EXPRESSION OF MAGNETIC FIELD DISTRIBUTION OF RECTANGULAR PERMANENT MAGNETS

    Institute of Scientific and Technical Information of China (English)

    苟晓凡; 杨勇; 郑晓静

    2004-01-01

    From the molecular current viewpoint,an analytic expression exactly describing magnetic field distribution of rectangular permanent magnets magnetized sufficiently in one direction was derived from the Biot-Savart's law. This expression is useful not only for the case of one rectangular permanent magnet bulk, but also for that of several rectangular permanent magnet bulks. By using this expression,the relations between magnetic field distribution and the size of rectangular permanent magnets as well as the magnitude of magnetic field and the distance from the point in the space to the top (or bottom) surface of rectangular permanent magnets were discussed in detail. All the calculating results are consistent with experimental ones. For transverse magnetic field which is a main magnetic field of rectangular permanent magnets,in order to describe its distribution,two quantities,one is the uniformity in magnitude and the other is the uniformity in distribution of magnetic field,were defined. Furthermore, the relations between them and the geometric size of the magnet as well as the distance from the surface of permanent magnets were investigated by these formulas. The numerical results show that the geometric size and the distance have a visible influence on the uniformity in magnitude and the uniformity in distribution of the magnetic field.

  5. Transformer current sensor for superconducting magnetic coils

    Science.gov (United States)

    Shen, Stewart S.; Wilson, C. Thomas

    1988-01-01

    A transformer current sensor having primary turns carrying a primary current for a superconducting coil and secondary turns only partially arranged within the primary turns. The secondary turns include an active winding disposed within the primary turns and a dummy winding which is not disposed in the primary turns and so does not experience a magnetic field due to a flow of current in the primary turns. The active and dummy windings are wound in opposite directions or connected in series-bucking relationship, and are exposed to the same ambient magnetic field. Voltages which might otherwise develop in the active and dummy windings due to ambient magnetic fields thus cancel out. The resultant voltage is purely indicative of the rate of change of current flowing in the primary turns.

  6. Exploring Magnetic Fields with a Compass

    Science.gov (United States)

    Lunk, Brandon; Beichner, Robert

    2011-01-01

    A compass is an excellent classroom tool for the exploration of magnetic fields. Any student can tell you that a compass is used to determine which direction is north, but when paired with some basic trigonometry, the compass can be used to actually measure the strength of the magnetic field due to a nearby magnet or current-carrying wire. In this…

  7. Magnetic Fields of Neutron Stars

    Indian Academy of Sciences (India)

    Sushan Konar

    2017-09-01

    This article briefly reviews our current understanding of the evolution of magnetic fields in neutron stars, which basically defines the evolutionary pathways between different observational classes of neutron stars. The emphasis here is on the evolution in binary systems and the newly emergent classes of millisecond pulsars.

  8. ISR Radial Field Magnet

    CERN Multimedia

    1983-01-01

    There were 37 (normal) + 3 (special) Radial Field magnets in the ISR to adjust vertically the closed orbit. Gap heights and strengths were 200 mm and .12 Tm in the normal magnets, 220 mm and .18 Tm in the special ones. The core length was 430 mm in both types. Due to their small length as compared to the gap heights the end fringe field errors were very important and had to be compensated by suitably shaping the poles. In order to save on cables, as these magnets were located very far from their power supplies, the coils of the normal type magnets were formed by many turns of solid cpper conductor with some interleaved layers of hollow conductor directly cooled by circulating water

  9. Magnetic field of the Earth

    Science.gov (United States)

    Popov, Aleksey

    2013-04-01

    The magnetic field of the Earth has global meaning for a life on the Earth. The world geophysical science explains: - occurrence of a magnetic field of the Earth it is transformation of kinetic energy of movements of the fused iron in the liquid core of Earth - into the magnetic energy; - the warming up of a kernel of the Earth occurs due to radioactive disintegration of elements, with excretion of thermal energy. The world science does not define the reasons: - drift of a magnetic dipole on 0,2 a year to the West; - drift of lithospheric slabs and continents. The author offers: an alternative variant existing in a world science the theories "Geodynamo" - it is the theory « the Magnetic field of the Earth », created on the basis of physical laws. Education of a magnetic field of the Earth occurs at moving the electric charge located in a liquid kernel, at rotation of the Earth. At calculation of a magnetic field is used law the Bio Savara for a ring electric current: dB = . Magnetic induction in a kernel of the Earth: B = 2,58 Gs. According to the law of electromagnetic induction the Faradey, rotation of a iron kernel of the Earth in magnetic field causes occurrence of an electric field Emf which moves electrons from the center of a kernel towards the mantle. So of arise the radial electric currents. The magnetic field amplifies the iron of mantle and a kernel of the Earth. As a result of action of a radial electric field the electrons will flow from the center of a kernel in a layer of an electric charge. The central part of a kernel represents the field with a positive electric charge, which creates inverse magnetic field Binv and Emfinv When ?mfinv = ?mf ; ?inv = B, there will be an inversion a magnetic field of the Earth. It is a fact: drift of a magnetic dipole of the Earth in the western direction approximately 0,2 longitude, into a year. Radial electric currents a actions with the basic magnetic field of a Earth - it turn a kernel. It coincides with laws

  10. Magnetic field structure of Saturn's dayside magnetosphere and its mapping to the ionosphere: Results from ring current modeling

    Science.gov (United States)

    Bunce, E. J.; Arridge, C. S.; Cowley, S. W. H.; Dougherty, M. K.

    2008-02-01

    Ring current modeling in Saturn's magnetosphere using Pioneer-11, Voyager, and Cassini data has shown that the size and strength of the current system grows with the extension of the magnetosphere, governed by the solar wind dynamic pressure. Here we show that the consequent middle magnetosphere field is quasi-dipolar in form when the magnetosphere is strongly compressed, but extends into a magnetodisc when it is strongly expanded. We also show that the region occupied by the modeled ring current corresponds to an essentially fixed shell of field lines that expands and contracts with the size of the system, thus mapping to an almost fixed co-latitude range in Saturn's ionosphere, between ~14° and ~20° in the northern hemisphere, and ~16° and ~22° in the southern hemisphere. The median dayside UV auroral oval is found to map from near the poleward edge of the modeled ring current toward the boundary of open field lines at smaller co-latitudes. In the equatorial plane this corresponds to a layer ~2-5 Saturn radius wide (depending on magnetosphere size), extending from near the outer edge of the ring current to the vicinity of the magnetopause.

  11. Cosmic magnetic fields

    CERN Document Server

    Kronberg, Philipp P

    2016-01-01

    Magnetic fields are important in the Universe and their effects contain the key to many astrophysical phenomena that are otherwise impossible to understand. This book presents an up-to-date overview of this fast-growing topic and its interconnections to plasma processes, astroparticle physics, high energy astrophysics, and cosmic evolution. The phenomenology and impact of magnetic fields are described in diverse astrophysical contexts within the Universe, from galaxies to the filaments and voids of the intergalactic medium, and out to the largest redshifts. The presentation of mathematical formulae is accessible and is designed to add insight into the broad range of topics discussed. Written for graduate students and researchers in astrophysics and related disciplines, this volume will inspire readers to devise new ways of thinking about magnetic fields in space on galaxy scales and beyond.

  12. Azimuthal magnetic fields in Saturn’s magnetosphere: effects associated with plasma sub-corotation and the magnetopause-tail current system

    Directory of Open Access Journals (Sweden)

    E. J. Bunce

    Full Text Available We calculate the azimuthal magnetic fields expected to be present in Saturn’s magnetosphere associated with two physical effects, and compare them with the fields observed during the flybys of the two Voyager spacecraft. The first effect is associated with the magnetosphere-ionosphere coupling currents which result from the sub-corotation of the magnetospheric plasma. This is calculated from empirical models of the plasma flow and magnetic field based on Voyager data, with the effective Pedersen conductivity of Saturn’s ionosphere being treated as an essentially free parameter. This mechanism results in a ‘lagging’ field configuration at all local times. The second effect is due to the day-night asymmetric confinement of the magnetosphere by the solar wind (i.e. the magnetopause and tail current system, which we have estimated empirically by scaling a model of the Earth’s magnetosphere to Saturn. This effect produces ‘leading’ fields in the dusk magnetosphere, and ‘lagging’ fields at dawn. Our results show that the azimuthal fields observed in the inner regions can be reasonably well accounted for by plasma sub-corotation, given a value of the effective ionospheric Pedersen conductivity of ~ 1–2 mho. This statement applies to field lines mapping to the equator within ~ 8 RS (1 RS is taken to be 60 330 km of the planet on the dayside inbound passes, where the plasma distribution is dominated by a thin equatorial heavy-ion plasma sheet, and to field lines mapping to the equator within ~ 15 RS on the dawn side outbound passes. The contributions of the magnetopause-tail currents are estimated to be much smaller than the observed fields in these regions. If, however, we assume that the azimuthal fields observed in these regions are not due to sub-corotation but to some other process, then the above effective conductivities define an upper limit, such that values above ~ 2 mho can definitely be

  13. RANDOM VIBRATION OF A CURRENT CARRYING CIRCULAR PLATE IN MAGNETIC FIELD%载流圆板的磁弹性随机振动

    Institute of Scientific and Technical Information of China (English)

    王平; 李晓靓; 白象忠

    2012-01-01

    The magnetic-elastic random vibration problem of a current-carrying circular plate in a magnetic field is studied. Based on the magneto-elastic theory and the random vibration theory of a continue system with distributed parameters, the magneto-elastic random vibration equation of a current carrying circular plate in a magnetic field was derived. The stochastic response analysis of the circular plate in a magnetic field was finished. The auto-correlation function, power spectral density function and the mean function of the random displacement response of the circular plate in a magnetic field were obtained. In a specific example, the power spectral density function of the displacement response of the circular plate with stationary random current was calculated.%分析载流圆板在磁场中的磁弹性随机振动问题.根据薄板、薄壳体的磁弹性运动方程和连续体的随机振动理论,导出在磁场环境中圆板的磁弹性随机振动方程.对磁场中的载流圆板进行随机响应分析,得到圆板位移响应的自相关函数、功率谱密度函数及均值函数等数字特征.通过具体算例,对处于外加磁场中通入平稳随机电流的导电圆板,计算其位移响应的功率谱密度函数.

  14. Temperature dependence of the critical current of the superconducting microladder in zero magnetic field: Theory and experiment

    Energy Technology Data Exchange (ETDEWEB)

    Fink, H.J. (Department of Electrical Engineering and Computer Science, University of California, Davis, Davis, California 95616 (USA)); Buisson, O.; Pannetier, B. (Centre de Recherches sur les Tres Basses Temperature, Centre National de la Recherche Scientifique, Boite Postale 166X, 38042 Grenoble CEDEX, France (FR))

    1991-05-01

    The largest supercurrent which can be injected into a superconducting microladder was calculated as a function of nodal spacing {ital scrL} and temperature for zero magnetic flux using (i) exact solutions of the Ginzburg-Landau equation in terms of Jacobian elliptic functions and (ii) approximate solutions in terms of hyperbolic functions. The agreement is good for {ital scrL}/{xi}({ital T}){lt}3, where {xi}({ital T}) is the temperature-dependent coherence length. Since solution (ii) is much simpler than solution (i), it is of considerable value when calculating critical currents of micronets with nodal spacings comparable to {xi}({ital T}). We find that the temperature-dependent critical current deviates significantly from the classical 3/2 power law of the Ginzburg-Landau theory. Preliminary experiments on a submicrometer ladder confirm such deviations.

  15. A Deep Analysis of the Magnetic Field Produced by a Current-Carrying Straight Solenoid%长直螺线管磁场的深入分析

    Institute of Scientific and Technical Information of China (English)

    曾晓英; 杨昌虎; 杨昶

    2001-01-01

    将长直螺线管磁场看作直线电流磁场和圆线圈电流磁场迭加。在此基础上,对螺线管磁场进行了深入分析和精确计算,给出了一般情形下近似描述长直螺线管磁场需满足的结构条件。%Decomposing the magnetic filed of a current-carrying strainght solenoid into that of straight current and that of circular curr ent, deep analysis and exact calculation of the field are proposed, and the approximation conditions have been derived for the description of the magnetic field of a straight solenoid in simplified case.

  16. Solar Magnetic Fields

    Indian Academy of Sciences (India)

    J. O. Stenflo

    2008-03-01

    Since the structuring and variability of the Sun and other stars are governed by magnetic fields, much of present-day stellar physics centers around the measurement and understanding of the magnetic fields and their interactions. The Sun, being a prototypical star, plays a unique role in astrophysics, since its proximity allows the fundamental processes to be explored in detail. The PRL anniversary gives us an opportunity to look back at past milestones and try to identify the main unsolved issues that will be addressed in the future.

  17. 柔性涡流阵列传感器的磁场计算分析%Magnetic field computational analysis of flexible eddy current array sensor

    Institute of Scientific and Technical Information of China (English)

    曹青松; 毕彬杰; 周继惠

    2016-01-01

    A flexible eddy current array sensor consists of six array units( spiral coil)is designed,establish electromagnetic field model for flexible eddy current array units based on electromagnetic field theory,the magnetic field strength formula in radial and axial of flexible array unit coil are derived,simulation analysis on relationship between array unit coil magnetic field strength and current,coil gap,inner and outer diameters and other parameters,which have a certain reference value for development of flexible eddy current array sensor.%设计了一种由6个阵列单元(螺旋线圈)所组成的柔性涡流阵列传感器,基于电磁场理论建立柔性涡流阵列单元的电磁场模型,推导出柔性阵列单元线圈径向和轴向的磁场强度计算公式,仿真分析阵列单元线圈磁场强度与电流、线圈间隙、内外径等参数的关系,对柔性涡流阵列传感器的发展具有一定参考价值。

  18. A combined vector and scalar potential method for 3D magnetic fields and transient Eddy current effects in recording head coils

    Energy Technology Data Exchange (ETDEWEB)

    Hrkac, G. [Department of Engineering Materials, University of Sheffield, Western Bank, Sheffield (United Kingdom)]. E-mail: g.hrkac@sheffield.ac.uk; Schrefl, T. [Department of Engineering Materials, University of Sheffield, Western Bank, Sheffield (United Kingdom); Schabes, M. [Hitachi San Jose Research Center, Hitachi Global Storage Technologies, San Jose, CA 95193 (United States)

    2006-10-01

    A mixed 3D finite element vector and scalar potential method was developed to treat inhomogeneities in coils of recording heads. It is assumed that in the yoke of the recording head the change of magnetization, generates a magnetic field that leads to Eddy current effects in the coil. The problem is separated into two regions, a conducting (the coil) and in a non-conducting one. For the conducting region we solve a vector potential diffusion equation with all contributing currents as a source term, including the Eddy currents produced by the yoke and for the non-conducting region a scalar potential partial differential equation is solved. To combine the vector and the scalar potential method special boundary conditions are implemented. The combined system of partial differential equations are solved simultaneously with a finite element/boundary element method.

  19. Magnetic field effects on the vestibular system: calculation of the pressure on the cupula due to ionic current-induced Lorentz force

    Science.gov (United States)

    Antunes, A.; Glover, P. M.; Li, Y.; Mian, O. S.; Day, B. L.

    2012-07-01

    Large static magnetic fields may be employed in magnetic resonance imaging (MRI). At high magnetic field strengths (usually from about 3 T and above) it is possible for humans to perceive a number of effects. One such effect is mild vertigo. Recently, Roberts et al (2011 Current Biology 21 1635-40) proposed a Lorentz-force mechanism resulting from the ionic currents occurring naturally in the endolymph of the vestibular system. In the present work a more detailed calculation of the forces and resulting pressures in the vestibular system is carried out using a numerical model. Firstly, realistic 3D finite element conductivity and fluid maps of the utricle and a single semi-circular canal containing the current sources (dark cells) and sinks (hair cells) of the utricle and ampulla were constructed. Secondly, the electrical current densities in the fluid are calculated. Thirdly, the developed Lorentz force is used directly in the Navier-Stokes equation and the trans-cupular pressure is computed. Since the driving force field is relatively large in comparison with the advective acceleration, we demonstrate that it is possible to perform an approximation in the Navier-Stokes equations that reduces the problem to solving a simpler Poisson equation. This simplification allows rapid and easy calculation for many different directions of applied magnetic field. At 7 T a maximum cupula pressure difference of 1.6 mPa was calculated for the combined ampullar (0.7 µA) and utricular (3.31 µA) distributed current sources, assuming a hair-cell resting current of 100 pA per unit. These pressure values are up to an order of magnitude lower than those proposed by Roberts et al using a simplistic model and calculation, and are in good agreement with the estimated pressure values for nystagmus velocities in caloric experiments. This modeling work supports the hypothesis that the Lorentz force mechanism is a significant contributor to the perception of magnetic field induced vertigo.

  20. Magnetic field effects on the vestibular system: calculation of the pressure on the cupula due to ionic current-induced Lorentz force.

    Science.gov (United States)

    Antunes, A; Glover, P M; Li, Y; Mian, O S; Day, B L

    2012-07-21

    Large static magnetic fields may be employed in magnetic resonance imaging (MRI). At high magnetic field strengths (usually from about 3 T and above) it is possible for humans to perceive a number of effects. One such effect is mild vertigo. Recently, Roberts et al (2011 Current Biology 21 1635-40) proposed a Lorentz-force mechanism resulting from the ionic currents occurring naturally in the endolymph of the vestibular system. In the present work a more detailed calculation of the forces and resulting pressures in the vestibular system is carried out using a numerical model. Firstly, realistic 3D finite element conductivity and fluid maps of the utricle and a single semi-circular canal containing the current sources (dark cells) and sinks (hair cells) of the utricle and ampulla were constructed. Secondly, the electrical current densities in the fluid are calculated. Thirdly, the developed Lorentz force is used directly in the Navier-Stokes equation and the trans-cupular pressure is computed. Since the driving force field is relatively large in comparison with the advective acceleration, we demonstrate that it is possible to perform an approximation in the Navier-Stokes equations that reduces the problem to solving a simpler Poisson equation. This simplification allows rapid and easy calculation for many different directions of applied magnetic field. At 7 T a maximum cupula pressure difference of 1.6 mPa was calculated for the combined ampullar (0.7 µA) and utricular (3.31 µA) distributed current sources, assuming a hair-cell resting current of 100 pA per unit. These pressure values are up to an order of magnitude lower than those proposed by Roberts et al using a simplistic model and calculation, and are in good agreement with the estimated pressure values for nystagmus velocities in caloric experiments. This modeling work supports the hypothesis that the Lorentz force mechanism is a significant contributor to the perception of magnetic field induced vertigo.

  1. High, magnetic-field-insensitive transport critical currents in unoriented polycrystalline thin films of Tl 2CaBa 2Cu 2O y

    Science.gov (United States)

    Kwak, J. F.; Venturini, E. L.; Baughman, R. J.; Morosin, B.; Ginley, D. S.

    1988-08-01

    We report critical current measurements for unoriented polycrystalline films of Tl 2CaBa 2Cu 2O y. At 77 K these films show critical current densities ranging from 10 000 to 110 000 A/cm 2, with a median value of 50 000 A/cm 2. Moreover, the best films' critical currents at 77 K drop less than 50% in an applied magnetic field of 1 T, and less than a factor of 20 at 6 T. At 4 K, critical current densities over 10 6A/cm 2 with less than 15% drop at 6 T have been obtained. The zero-field temperature dependence of the critical current from 4 to 95 K is well described as quadratic. High-field magnetization loops on the films at 76 K show a striking collapse in hysteresis below 0.6 T. Our results indicate that, although the grains in these films are Josephson-coupled, the strength of the coupling is greatly improved over other high- Tc granular systems.

  2. Experiments with Coler magnetic current apparatus

    Science.gov (United States)

    Ludwig, T.

    Experiments with a replica of the famous Coler "Magnetstromapparat" (magnetic current apparatus) were conducted. The replica was built at the same institute at the Technical University of Berlin where the original was tested by Prof. Kloss in 1925. The details of the setup will be presented in this paper. The investigation of the Coler device was done with modern methods. The output was measured with a digital multi meter (DMM) and a digital storage oscilloscope (DSO). The results of the measurements will be presented. Did Coler convert vacuum fluctuations via magnetic, electric and acoustic resonance into electricity? There is a strong connection between magnetism and quantum field radiation energy. The magnetic moment of the electron is in part an energy exchange with the radiation field. The energy output of the Coler apparatus is measured. Furthermore the dynamics of the ferromagnetic magnets that Coler reported as the working principle of his device was investigated with magnetic force microscopy (MFM) and the spectroscopy mode of an atomic force microscope (AFM). The magnetic and acoustic resonance was investigated with magnetic force microscopy (MFM). The connection between ZPE and magnetism will be discussed as well as the perspective of using magnetic systems as a means to convert vacuum fluctuations into usable electricity.

  3. Evolution and structure of the plasma of current sheets forming in two-dimensional magnetic fields with a null line at low initial gas ionization and their interpretation

    Science.gov (United States)

    Ostrovskaya, G. V.; Frank, A. G.

    2012-04-01

    An analysis of the experimental data obtained by holographic interferometry in our work [1] makes it possible to explain most of the observed specific features of the structure and evolution of the plasma sheets developing in a two-dimensional magnetic field with a null line in a plasma with a low initial degree of ionization (≈10-4). The following two processes are shown to play a key role here: additional gas ionization in an electric field and the peculiarities of plasma dynamics in a current sheet expanding in time.

  4. Interaction between Current Imbalance and Magnetization in LHC Cables

    CERN Document Server

    Bottura, L; Kuijper, A; den Ouden, A; ten Haken, B; ten Kate, H H J

    2001-01-01

    The quality of the magnetic field in superconducting accelerator magnets is associated with the properties of the superconducting cable. Current imbalances due to coupling currents DI, as large as 100 A, are induced by spatial variations of the field sweep rate and contact resistances. During injection at a constant field all magnetic field components show a decay behavior. The decay is caused by a diffusion of coupling currents into the whole magnet. This results in a redistribution of the transport current among the strands and causes a demagnetization of the superconducting cable. As soon as the field is ramped up again after the end of injection, the magnetization rapidly recovers from the decay and follows the course of the original hysteresis curve. In order to clarify the interactions between the changes in current and magnetization during injection we performed a number of experiments. A magnetic field with a spatially periodic pattern was applied to a superconducting wire in order to simulate the cou...

  5. Current filaments in turbulent magnetized plasmas

    DEFF Research Database (Denmark)

    Martines, E.; Vianello, N.; Sundkvist, D.;

    2009-01-01

    Direct measurements of current density perturbations associated with non-linear phenomena in magnetized plasmas can be carried out using in situ magnetic measurements. In this paper we report such measurements for three different kinds of phenomena. Current density fluctuations in the edge density...... gradient region of a fusion plasma confined in reversed field pinch configuration and in a density gradient region in the Earth magnetosphere are measured and compared, showing that in both environments they can be attributed to drift-Alfvén vortices. Current structures associated with reconnection events...

  6. Saturn's Periodic Magnetosphere: The Relation Between Periodic Hot Plasma Injections, a Rotating Partial Ring Current, Global Magnetic Field Distortions, Plasmapause Motion, and Radio Emissions

    Science.gov (United States)

    Brandt, P. C.; Mitchell, D. G.; Gurnett, D. A.; Persoon, A. M.; Tsyganenko, N. A.

    2012-04-01

    It has been know for some time that the large-scale energetic particle injections (~3-200 keV) on the nigh side of Saturn observed by Cassini/INCA are closely tracked by the periodic Saturn Kilometric Radiation (SKR). The resulting energetic particle pressure is comparable to that of the colder plasma and it therefore distorts the global magnetic field significantly as the energetic particle population drifts around Saturn. In this presentation we discuss the important consequences this has for the large-scale dynamics and configuration of the entire inner magnetosphere of Saturn. We begin by reviewing the observational correlations between remote, global INCA observations of energetic particles, magnetic field distortions, and radio emissions. We present examples of how the magnetic field measurements and the INCA observations show direct implications of a rotating 3D electrical current system associated with, not only, the energetic particle pressure, but also with an interhemispheric field-aligned current (FAC) system. Recently, we found an intriguing high correlation also between the periodic motion of the high-latitude plasmapause-like boundary reported by Gurnett et al. [2011] and the energetic particles observed remotely by INCA that are periodically injected on the night side and then drift around Saturn according to their energy. In our preliminary analysis we see a direct correlation in at least 75% of the case with the center of drifting energetic particle distribution [Brandt et al., 2010] and the encounter with the rotating plasmapause-like density boundary [Gurnett et al., 2011]. However, the remaining, low-correlation cases suggest that we do not fully understand the global, 3D current system that produces the periodic perturbations in Saturn's magnetosphere. We will use these observations to constrain the underlying 3D current system and in particular, assess the role of interhemispheric FACs in reproducing the observations.

  7. Zero magnetic field type magnetic field sensor. Reijikaigata jikai sensor

    Energy Technology Data Exchange (ETDEWEB)

    Sonoda, T.; Ueda, R. (Kyushu Institute of Technology, Fukuoka (Japan))

    1990-11-20

    It is shown in this paper that a new type of sensor with excellent characteristics can be made by demagnetizing the sensor core toward a zero field state and then detecting an unknown field to be detected by the demagnetizing current. The core operates equivalently in a zero magnetic field so that the detection sensitivity is determined by the coil constant including the number of turns of the solenoid for demagnetization required to offset the field to be detected. Therefore the detection sensitivity does not depend on its configuration and magnetization characteristics and does not depend on the temperature. It is thereby considered that these characteristics can largely reduce such problems at present as the aging deterioration of magnetic materials or the quality control accompanied by manufacturing. In addition, the following points have been clarified: (1) The upper limit of the detectable range does not exist in principle. (2) The accuracy of the detection is 0.02% to the full scale 20kA/m. (3) The magnetization property required to the core used as a sensor is that it has a rectangular B-H loop which is as sharp as possible. 14 refs., 13 figs., 2 tabs.

  8. Effect of the initial plasma parameters on the structure of the current sheets developing in two-dimensional magnetic fields with a null line

    Science.gov (United States)

    Ostrovskaya, G. V.; Frank, A. G.; Bogdanov, S. Yu.

    2010-07-01

    The effect of the initial plasma parameters on the structure of the plasma of the current sheets that form in two-dimensional magnetic fields with a null line is studied by holographic interferometry. The evolution of the plasma sheets that develop in an initial low-density plasma, where a gas is mainly ionized by a pulse current passing through the plasma and initiating the formation of a current sheet, has been comprehensively studied for the first time. At the early stage of evolution, the spatial structure of such a plasma sheet differs substantially from the classic current sheets forming in a dense plasma. Nevertheless, extended plasma sheets with similar parameters form eventually irrespective of the initial plasma density.

  9. 脉冲磁场激励下圆柱导体内瞬态涡流场的快速计算%Fast Calculation of Transient Eddy Current Field in Cylindrical Conductor Excited by Pulsed Magnetic Field

    Institute of Scientific and Technical Information of China (English)

    辛伟

    2013-01-01

    The theoretical model of transient eddy current field is built in cylindrical conductor excited by pulsed magnetic field. Theoretical calculation and experimental measurement of cylindrical conductor in pulsed magnetic field are carried out. The theoretical results are compared with the experimental results in a good agreement, indicate that the fast calculation method of transient eddy current field in cylindrical conductor is effective.%建立了脉冲磁场激励下圆柱导体内瞬态涡流场的理论模型.实现了瞬态涡流场的快速计算.通过实例表明上述圆柱导体内瞬态涡流场的快速计算方法有效.

  10. The HMI Magnetic Field Pipeline

    Science.gov (United States)

    Hoeksema, Jon Todd; Liu, Y.; Schou, J.; Scherrer, P.; HMI Science Team

    2009-05-01

    The Helioseismic and Magnetic Imager (HMI) will provide frequent full-disk magnetic field data after launch of the Solar Dynamics Observatory (SDO), currently scheduled for fall 2009. 16 megapixel line-of-sight magnetograms (Blos) will be recorded every 45 seconds. A full set of polarized filtergrams needed to determine the vector magnetic field requires 90 seconds. Quick-look data will be available within a few minutes of observation. Quick-look space weather and browse products must have identified users, and the list currently includes full disk magnetograms, feature identification and movies, 12-minute disambiguated vector fields in active region patches, time evolution of AR indices, synoptic synchronic frames, potential and MHD model results, and 1 AU predictions. A more complete set of definitive science data products will be offered about a day later and come in three types. "Pipeline” products, such as full disk vector magnetograms, will be computed for all data on an appropriate cadence. A larger menu of "On Demand” products, such as Non-Linear Force Free Field snapshots of an evolving active region, will be produced whenever a user wants them. Less commonly needed "On Request” products that require significant project resources, such as a high resolution MHD simulation of the global corona, will be created subject to availability of resources. Further information can be found at the SDO Joint Science Operations Center web page, jsoc.stanford.edu

  11. Enhancement of the critical current density in FeO-coated MgB2 thin films at high magnetic fields

    Directory of Open Access Journals (Sweden)

    Andrei E. Surdu

    2011-12-01

    Full Text Available The effect of depositing FeO nanoparticles with a diameter of 10 nm onto the surface of MgB2 thin films on the critical current density was studied in comparison with the case of uncoated MgB2 thin films. We calculated the superconducting critical current densities (Jc from the magnetization hysteresis (M–H curves for both sets of samples and found that the Jc value of FeO-coated films is higher at all fields and temperatures than the Jc value for uncoated films, and that it decreases to ~105 A/cm2 at B = 1 T and T = 20 K and remains approximately constant at higher fields up to 7 T.

  12. Magnetic Field Topology in Jets

    Science.gov (United States)

    Gardiner, T. A.; Frank, A.

    2000-01-01

    We present results on the magnetic field topology in a pulsed radiative. jet. For initially helical magnetic fields and periodic velocity variations, we find that the magnetic field alternates along the, length of the jet from toroidally dominated in the knots to possibly poloidally dominated in the intervening regions.

  13. Magnetic fields around black holes

    Science.gov (United States)

    Garofalo, David A. G.

    Active Galactic Nuclei are the most powerful long-lived objects in the universe. They are thought to harbor supermassive black holes that range from 1 million solar masses to 1000 times that value and possibly greater. Theory and observation are converging on a model for these objects that involves the conversion of gravitational potential energy of accreting gas to radiation as well as Poynting flux produced by the interaction of the rotating spacetime and the electromagnetic fields originating in the ionized accretion flow. The presence of black holes in astrophysics is taking center stage, with the output from AGN in various forms such as winds and jets influencing the formation and evolution of the host galaxy. This dissertation addresses some of the basic unanswered questions that plague our current understanding of how rotating black holes interact with their surrounding magnetized accretion disks to produce the enormous observed energy. Two magnetic configurations are examined. The first involves magnetic fields connecting the black hole with the inner accretion disk and the other involves large scale magnetic fields threading the disk and the hole. We study the effects of the former type by establishing the consequences that magnetic torques between the black hole and the inner accretion disk have on the energy dissipation profile. We attempt a plausible explanation to the observed "Deep Minimum" state in the Seyfert galaxy MCG-6- 30-15. For the latter type of magnetic geometry, we study the effects of the strength of the magnetic field threading the black hole within the context of the cherished Blandford & Znajek mechanism for black hole spin energy extraction. We begin by addressing the problem in the non-relativistic regime where we find that the black hole-threading magnetic field is stronger for greater disk thickness, larger magnetic Prandtl number, and for a larger accretion disk. We then study the problem in full relativity where we show that our

  14. Magnetic field switchable dry adhesives.

    Science.gov (United States)

    Krahn, Jeffrey; Bovero, Enrico; Menon, Carlo

    2015-02-01

    A magnetic field controllable dry adhesive device is manufactured. The normal adhesion force can be increased or decreased depending on the presence of an applied magnetic field. If the magnetic field is present during the entire normal adhesion test cycle which includes both applying a preloading force and measuring the pulloff pressure, a decrease in adhesion is observed when compared to when there is no applied magnetic field. Similarly, if the magnetic field is present only during the preload portion of the normal adhesion test cycle, a decrease in adhesion is observed because of an increased stiffness of the magnetically controlled dry adhesive device. When the applied magnetic field is present during only the pulloff portion of the normal adhesion test cycle, either an increase or a decrease in normal adhesion is observed depending on the direction of the applied magnetic field.

  15. Introduction and validation of magnetic field vector analysis method of determining the critical current of HTS magnets%高温超导磁体临界电流的磁矢量分析法及其验证

    Institute of Scientific and Technical Information of China (English)

    焦丰顺; 唐跃进; 周世平; 金涛; 任丽; 何清

    2012-01-01

    Critical current Ic is one of the most important parameters of HTS magnet. The cost of the HTS magnets could be cut down by calculating its Ic correctly. In this paper, a method of determining the Ic of HTS magnets was introduced, named " magnetic field vector analysis method". This method included three steps. Firstly, the anisotropic Ic of the HTS tapes in magnetic field was measured, and then the result was employed as discrete database. Secondly, the distribution of the magnetic field vector inside the HTS magnet was analyzed by means of FEM. Thirdly, the Ic of the HTS magnet was got from interpolation calculation. The reliability of this method was proved by magnet experiment at 77 K.%临界电流是高温超导磁体的关键参数,文中提出了一种名为“磁矢量分析法”的高温超导临界电流计算方法.这种方法以高温超导带材性能测试结果为依据,以有限元仿真软件为手段,通过对计算高温超导磁体内部电磁感应强度矢量的分布,采用插值运算来确定高温超导磁体的临界电流.通过在77K温度下进行1:1的磁体实验,磁矢量分析法的可行性得到了验证.

  16. Effects of magnetic field orientation and injected current density on the output of nano-structured Co/Cu/Fe junctions

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Co/Cu/Fe nano-sized sandwich thin films have been prepared by electron beam evaporation. 5 μm×5 μm Co/Cu/Fe sandwich heterojunction was made using photolithography and lift-off process. The bipolar output signal of Co/Cu/Fe junctions has been measured and analyzed. The effects of applied magnetic field angle (referring to the normal of the junction plane) and injecting spin-polarized current on the output signals have been studied, and the measured results were discussed.

  17. Evolution of Neutron Star Magnetic Fields

    Indian Academy of Sciences (India)

    Dipankar Bhattacharya

    2002-03-01

    This paper reviews the current status of the theoretical models of the evolution of the magnetic fields of neutron stars other than magnetars. It appears that the magnetic fields of neutron stars decay significantly only if they are in binary systems. Three major physical models for this, namely spindown-induced flux expulsion, ohmic evolution of crustal field and diamagnetic screening of the field by accreted plasma, are reviewed.

  18. MDI Synoptic Charts of Magnetic Field: Interpolation of Polar Fields

    Science.gov (United States)

    Liu, Yang; Hoeksema, J. T.; Zhao, X.; Larson, R. M.

    2007-05-01

    In this poster, we compare various methods for interpolation of polar field for the MDI synoptic charts of magnetic field. By examining the coronal and heliospheric magnetic field computed from the synoptic charts based on a Potential Field Source Surface model (PFSS), and by comparing the heliospheric current sheets and footpoints of open fields with the observations, we conclude that the coronal and heliospheric fields calculated from the synoptic charts are sensitive to the polar field interpolation, and a time-dependent interpolation method using the observed polar fields is the best among the seven methods investigated.

  19. Magnetically Guiding Atoms with Current-Carrying Conductors

    Institute of Scientific and Technical Information of China (English)

    刘南春; 高伟建; 印建平

    2002-01-01

    We propose a novel magnetic guide for cold neutral atoms using some current-carrying conductors. The spatial distributions of the magnetic fields from a V-shaped or U-shaped current-carrying conductor are calculated, and the relationship between the resulting magnetic field and the parameters of the current-carrying conductors is analysed in detail. The result shows that these current-carrying conductors can be used to realize a single or a controllable double magnetic guide of cold atoms in the weak-field-seeking state, and to construct various atom-optical elements, and even to realize a single-mode atomic waveguiding under certain conditions.

  20. Solar Force-free Magnetic Fields

    CERN Document Server

    Wiegelmann, Thomas

    2012-01-01

    The structure and dynamics of the solar corona is dominated by the magnetic field. In most areas in the corona magnetic forces are so dominant that all non-magnetic forces like plasma pressure gradient and gravity can be neglected in the lowest order. This model assumption is called the force-free field assumption, as the Lorentz force vanishes. This can be obtained by either vanishing electric currents (leading to potential fields) or the currents are co-aligned with the magnetic field lines. First we discuss a mathematically simpler approach that the magnetic field and currents are proportional with one global constant, the so-called linear force-free field approximation. In the generic case, however, the relation between magnetic fields and electric currents is nonlinear and analytic solutions have been only found for special cases, like 1D or 2D configurations. For constructing realistic nonlinear force-free coronal magnetic field models in 3D, sophisticated numerical computations are required and boundar...

  1. Superhorizon magnetic fields

    CERN Document Server

    Campanelli, Leonardo

    2015-01-01

    [Abridged] We analyze the evolution of superhorizon-scale magnetic fields from the end of inflation till today. Whatever is the mechanism responsible for their generation during inflation, we find that a given magnetic mode with wavenumber $k$ evolves, after inflation, according to the values of $k\\eta_e$, $n_{\\mathbf{k}}$, and $\\Omega_k$, where $\\eta_e$ is the conformal time at the end of inflation, $n_{\\mathbf{k}}$ is the number density spectrum of inflation-produced photons, and $\\Omega_k$ is the phase difference between the two Bogolubov coefficients which characterize the state of that mode at the end of inflation. For any realistic inflationary magnetogenesis scenario, we find that $n_{\\mathbf{k}}^{-1} \\ll |k\\eta_e| \\ll 1$, and three evolutionary scenarios are possible: ($i$) $|\\Omega_k \\mp \\pi| = \\mathcal{O}(1)$, in which case the evolution of the magnetic spectrum $B_k(\\eta)$ is adiabatic, $a^2B_k(\\eta) = \\mbox{const}$, with $a$ being the expansion parameter; ($ii$) $|\\Omega_k \\mp \\pi| \\ll |k\\eta_e|$,...

  2. High magnetic field ohmically decoupled non-contact technology

    Science.gov (United States)

    Wilgen, John [Oak Ridge, TN; Kisner, Roger [Knoxville, TN; Ludtka, Gerard [Oak Ridge, TN; Ludtka, Gail [Oak Ridge, TN; Jaramillo, Roger [Knoxville, TN

    2009-05-19

    Methods and apparatus are described for high magnetic field ohmically decoupled non-contact treatment of conductive materials in a high magnetic field. A method includes applying a high magnetic field to at least a portion of a conductive material; and applying an inductive magnetic field to at least a fraction of the conductive material to induce a surface current within the fraction of the conductive material, the surface current generating a substantially bi-directional force that defines a vibration. The high magnetic field and the inductive magnetic field are substantially confocal, the fraction of the conductive material is located within the portion of the conductive material and ohmic heating from the surface current is ohmically decoupled from the vibration. An apparatus includes a high magnetic field coil defining an applied high magnetic field; an inductive magnetic field coil coupled to the high magnetic field coil, the inductive magnetic field coil defining an applied inductive magnetic field; and a processing zone located within both the applied high magnetic field and the applied inductive magnetic field. The high magnetic field and the inductive magnetic field are substantially confocal, and ohmic heating of a conductive material located in the processing zone is ohmically decoupled from a vibration of the conductive material.

  3. Magnetic field evolution of accreting neutron stars

    CERN Document Server

    Istomin, Ya N

    2016-01-01

    The flow of a matter, accreting onto a magnetized neutron star, is accompanied by an electric current. The closing of the electric current occurs in the crust of a neutron stars in the polar region across the magnetic field. But the conductivity of the crust along the magnetic field greatly exceeds the conductivity across the field, so the current penetrates deep into the crust down up to the super conducting core. The magnetic field, generated by the accretion current, increases greatly with the depth of penetration due to the Hall conductivity of the crust is also much larger than the transverse conductivity. As a result, the current begins to flow mainly in the toroidal direction, creating a strong longitudinal magnetic field, far exceeding an initial dipole field. This field exists only in the narrow polar tube of $r$ width, narrowing with the depth, i.e. with increasing of the crust density $\\rho$, $r\\propto \\rho^{-1/4}$. Accordingly, the magnetic field $B$ in the tube increases with the depth, $B\\propto...

  4. SCUPOL Magnetic Field Analysis

    CERN Document Server

    Poidevin, Frederick; Kowal, Grzegorz; Pino, Elisabete de Gouveia Dal; Magalhaes, Antonio-Mario

    2013-01-01

    We present an extensive analysis of the 850 microns polarization maps of the SCUPOL Catalog produced by Matthews et al. (2009), focusing exclusively on the molecular clouds and star-forming regions. For the sufficiently sampled regions, we characterize the depolarization properties and the turbulent-to-mean magnetic field ratio of each region. Similar sets of parameters are calculated from 2D synthetic maps of dust emission polarization produced with 3D MHD numerical simulations scaled to the S106, OMC-2/3, W49 and DR21 molecular clouds polarization maps. For these specific regions the turbulent MHD regimes retrieved from the simulations, as described by the turbulent Alfv\\`en and sonic Mach numbers, are consistent within a factor 1 to 2 with the values of the same turbulent regimes estimated from the analysis of Zeeman measurements data provided by Crutcher (1999). Constraints on the values of the inclination angle of the mean magnetic field with respect to the LOS are also given. The values obtained from th...

  5. Current leads and magnetic bearings

    Science.gov (United States)

    Hull, J. R.

    1993-10-01

    Since the discovery of high temperature superconductors (HTS's), Argonne National Laboratory (ANL) has been active in a broad spectrum of activities in developing these materials for applications. Work at every stage of development has involved industrial collaboration in order to accelerate commercialization. While most of the development work has been devoted to improving the properties of current-carrying wires, some effort has been devoted to applications that can utilize HTS's with properties available now or in the near future. In this paper, advances made in the area of current leads and magnetic bearings are discussed.

  6. Magnetic Fields: Visible and Permanent.

    Science.gov (United States)

    Winkeljohn, Dorothy R.; Earl, Robert D.

    1983-01-01

    Children will be able to see the concept of a magnetic field translated into a visible reality using the simple method outlined. Standard shelf paper, magnets, iron filings, and paint in a spray can are used to prepare a permanent and well-detailed picture of the magnetic field. (Author/JN)

  7. The Vertical Current Approximation Nonlinear Force-Free Field Code - Description, Performance Tests, and Measurements of Magnetic Energies Dissipated in Solar Flares

    CERN Document Server

    Aschwanden, Markus J

    2016-01-01

    In this work we provide an updated description of the Vertical Current Approximation Nonlinear Force-Free Field (VCA-NLFFF) code, which is designed to measure the evolution of the potential, nonpotential, free energies, and the dissipated magnetic energies during solar flares. This code provides a complementary and alternative method to existing traditional NLFFF codes. The chief advantages of the VCA-NLFFF code over traditional NLFFF codes are the circumvention of the unrealistic assumption of a force-free photosphere in the magnetic field extrapolation method, the capability to minimize the misalignment angles between observed coronal loops (or chromospheric fibril structures) and theoretical model field lines, as well as computational speed. In performance tests of the VCA-NLFFF code, by comparing with the NLFFF code of Wiegelmann (2004), we find agreement in the potential, nonpotential, and free energy within a factor of about 1.3, but the Wiegelmann code yields in the average a factor of 2 lower flare en...

  8. Efficient magnetic fields for supporting toroidal plasmas

    CERN Document Server

    Landreman, Matt

    2016-01-01

    The magnetic field that supports tokamak and stellarator plasmas must be produced by coils well separated from the plasma. However the larger the separation, the more difficult it is to produce a given magnetic field in the plasma region, so plasma configurations should be chosen that can be supported as efficiently as possible by distant coils. The properties of curl-free magnetic fields allow magnetic field distributions to be ranked in order of their difficulty of production from a distance. Plasma shapes with low curvature and spectral width may be difficult to support, whereas plasma shapes with sharp edges may be efficiently supported by distant coils. Two measures of difficulty, which correctly identify such differences in difficulty, will be examined. These measures, which can be expressed as matrices, relate the externally-produced normal magnetic field on the plasma surface to the either the normal field or current on a distant control surface. A singular value decomposition (SVD) of either matrix y...

  9. Measuring the Earth's Magnetic Field in a Laboratory

    Science.gov (United States)

    Cartacci, A.; Straulino, S.

    2008-01-01

    Two methods for measuring the Earth's magnetic field are described. In the former, according to Gauss, the Earth's magnetic field is compared with that of a permanent magnet; in the latter, a well-known method, the comparison is made with the magnetic field generated by a current. As all the used instruments are available off the shelf, both…

  10. Permanent Magnet Eddy Current Loss Analysis of a Novel Motor Integrated Permanent Magnet Gear

    DEFF Research Database (Denmark)

    Zhang, Yuqiu; Lu, Kaiyuan; Ye, Yunyue

    2012-01-01

    In this paper, a new motor integrated permanent magnet gear (MIPMG) is discussed. The focus is on eddy current loss analysis associated to permanent magnets (PMs). A convenient model of MIPMG is provided based on 2-D field-motion coupled time-stepping finite element method for transient eddy...... current analysis. The model takes the eddy current effect of PMs into account in determination of the magnetic field in the air-gap and in the magnet regions. The eddy current losses generated in the magnets are properly interpreted. Design improvements for reducing the eddy current losses are suggested...

  11. Micromagnetic modeling of critical current oscillations in magnetic Josephson junctions

    Science.gov (United States)

    Golovchanskiy, I. A.; Bol'ginov, V. V.; Stolyarov, V. S.; Abramov, N. N.; Ben Hamida, A.; Emelyanova, O. V.; Stolyarov, B. S.; Kupriyanov, M. Yu.; Golubov, A. A.; Ryazanov, V. V.

    2016-12-01

    In this work we propose and explore an effective numerical approach for investigation of critical current dependence on applied magnetic field for magnetic Josephson junctions with in-plane magnetization orientation. This approach is based on micromagnetic simulation of the magnetization reversal process in the ferromagnetic layer with introduced internal magnetic stiffness and subsequent reconstruction of the critical current value using total flux or reconstructed actual phase difference distribution. The approach is flexible and shows good agreement with experimental data obtained on Josephson junctions with ferromagnetic barriers. Based on this approach we have obtained a critical current dependence on applied magnetic field for rectangular magnetic Josephson junctions with high size aspect ratio. We have shown that the rectangular magnetic Josephson junctions can be considered for application as an effective Josephson magnetic memory element with the value of critical current defined by the orientation of magnetic moment at zero magnetic field. An impact of shape magnetic anisotropy on critical current is revealed and discussed. Finally, we have considered a curling magnetic state in the ferromagnetic layer and demonstrated its impact on critical current.

  12. The Earth's magnetosphere is 165 R(sub E) long: Self-consistent currents, convection, magnetospheric structure, and processes for northward interplanetary magnetic field

    Science.gov (United States)

    Fedder, J. A.; Lyon, J. G.

    1995-01-01

    The subject of this paper is a self-consistent, magnetohydrodynamic numerical realization for the Earth's magnetosphere which is in a quasi-steady dynamic equilibrium for a due northward interplanetary magnetic field (IMF). Although a few hours of steady northward IMF are required for this asymptotic state to be set up, it should still be of considerable theoretical interest because it constitutes a 'ground state' for the solar wind-magnetosphere interaction. Moreover, particular features of this ground state magnetosphere should be observable even under less extreme solar wind conditions. Certain characteristics of this magnetosphere, namely, NBZ Birkeland currents, four-cell ionospheric convection, a relatively weak cross-polar potential, and a prominent flow boundary layer, are widely expected. Other characteristics, such as no open tail lobes, no Earth-connected magnetic flux beyond 155 R(sub E) downstream, magnetic merging in a closed topology at the cusps, and a 'tadpole' shaped magnetospheric boundary, might not be expected. In this paper, we will present the evidence for this unusual but interesting magnetospheric equilibrium. We will also discuss our present understanding of this singular state.

  13. Manifestations of Magnetic Field Inhomogeneities

    Indian Academy of Sciences (India)

    Lawrence Rudnick

    2011-12-01

    Both observations and simulations reveal large inhomogeneities in magnetic field distributions in diffuse plasmas. Incorporating these inhomogeneities into various calculations can significantly change the inferred physical conditions. In extragalactic sources, e.g., these can compromise analyses of spectral ageing, which I will illustrate with some current work on cluster relics. I also briefly re-examine the old issue of how inhomogeneous fields affect particle lifetimes; perhaps not surprisingly, the next generation of radio telescopes are unlikely to find many sources that can extend their lifetimes from putting relativistic electrons into a low-field ‘freezer’. Finally, I preview some new EVLA results on the complex relic in Abell 2256, with implications for the interspersing of its relativistic and thermal plasmas.

  14. Interplanetary magnetic field and geomagnetic Dst variations.

    Science.gov (United States)

    Patel, V. L.; Desai, U. D.

    1973-01-01

    The interplanetary magnetic field has been shown to influence the ring current field represented by Dst. Explorer 28 hourly magnetic field observations have been used with the hourly Dst values. The moderate geomagnetic storms of 60 gammas and quiet-time fluctuations of 10 to 30 gammas are correlated with the north to south change of the interplanetary field component perpendicular to the ecliptic. This change in the interplanetary field occurs one to three hours earlier than the corresponding change in the Dst field.

  15. Delayed quarkonium formation in a magnetic field

    CERN Document Server

    Suzuki, Kei

    2016-01-01

    Formation time of heavy quarkonia in a homogeneous magnetic field is analyzed by using a phenomenological ansatz of the vector current correlator. Because the existence of a magnetic field mixes vector quarkonia ($J/\\psi$, $\\psi^\\prime$) and their pseudoscalar partners ($\\eta_c$, $\\eta_c^\\prime$), the properties of the quarkonia can be modified through such a spin mixing. This means that the formation time of quarkonia is also changed by the magnetic field. We show the formation time of vector quarkonia is delayed by an idealized constant magnetic field, where the formation time of the excited state becomes longer than that of the ground state. As a more realistic situation in heavy-ion collisions, effects by a time-dependent magnetic field are also discussed.

  16. Experimental behaviour of a argon plasma, which is passed by a high current intensity, with different magnetic field configurations; Comportamiento experimental de un plasma de argon en diferentes configuraciones de campo magnetico y a elevadas corrientes

    Energy Technology Data Exchange (ETDEWEB)

    Lozano, J.

    1964-07-01

    In a lineal discharge, the longitudinal and azimuthal magnetic fields produced by the current through the tube and the returning conductors, which have 4 different forms, are determined with a magnetic probe, which has a radial and longitudinal displacement. The plasma is produced discharging a 135{mu}F and 9 KV capacitor bank through Argon at 10{sup -}1 Torr. (Author) 5 refs.

  17. Magnetization of a Current-Carrying Superconducting Disk with B-Dependent Critical Current Density

    Science.gov (United States)

    Sohrabi, Mahdi; Babaei-Brojeny, Ali A.

    2010-11-01

    In the frame work of the critical state model (CSM), the magnetic response of a thin type-II superconducting disk that carries a radial transport current and is subjected to an applied magnetic field have been studied. To this end, we have studied the process of the magnetic flux-penetration. For a disk initially containing no magnetic flux but carrying a radial current, when a perpendicular magnetic field is applied, magnetic flux-penetration occurs in three stages: (1) the magnetic flux gradually penetrates from the edges of the disk until an instability occurs, (2) there is a rapid inflow of magnetic flux into the disk’s central region, which becomes resistive, and (3) magnetic flux continues to enter the disk, while persistent azimuthal currents flow in an outer annular region where the net current density is equal to J c . Also the behavior of a current-carrying disk subjected to an AC magnetic field is calculated. The magnetic flux, the current profiles and the magnetization hysteresis loops are calculated for several commonly used J c ( B) dependences. Finally, the results of the applications of the local field-dependent of the critical current density J c ( B) are compared with those obtained from the Bean model.

  18. Introduction to power-frequency electric and magnetic fields.

    OpenAIRE

    1993-01-01

    This paper introduces the reader to electric and magnetic fields, particularly those fields produced by electric power systems and other sources using frequencies in the power-frequency range. Electric fields are produced by electric charges; a magnetic field also is produced if these charges are in motion. Electric fields exert forces on other charges; if in motion, these charges will experience magnetic forces. Power-frequency electric and magnetic fields induce electric currents in conduct...

  19. Magnetization collapse in polycrystalline YBCO under transport current cycles

    Energy Technology Data Exchange (ETDEWEB)

    Giordano, J L [Departamento de Ciencias de la IngenierIa, Universidad de Talca (Chile); Luzuriaga, J [Centro Atomico Bariloche, CNEA, Instituto Balseiro, UNC (Argentina); BadIa-Majos, A [Departamento de Fisica de la Materia Condensada-ICMA, Universidad de Zaragoza (Spain); Nieva, G [Centro Atomico Bariloche, CNEA, Instituto Balseiro, UNC (Argentina); RuIz-Tagle, I [Instituto de QuImica de Recursos Naturales, Universidad de Talca (Chile)

    2006-04-15

    We report measurements of the hysteretic magnetization of YBCO under superimposed transport current cycles, together with numerical simulations of magnetization and current density profiles in the corresponding parallel configuration. Field cooled (FC) and zero-field-cooled (ZFC) experiments were carried out on polycrystalline YBa{sub 2}Cu{sub 3}O{sub 7-x} cylinders, with both the applied magnetic field and transport current in the axial direction, and the current cycled several times, around and above the dissipative threshold. As in previously reported multicomponent field configuration experiments, the magnetization is seen to collapse to a more stable state both in FC and ZFC, because of the interplay between the shielding and transport currents. The results of our numerical simulations are in good qualitative agreement with the measurements, and the competition between shielding and transport due to vortex-pinning interactions and equilibrium magnetization effects are shown to play an important role in the range of our experiments.

  20. Reversals of the Earth's Magnetic Field

    Science.gov (United States)

    Champion, Duene E.

    J.A. Jacobs of Cambridge University has written a concise, authoritative, and up-todate text on reversals of the earth's magnetic field. Chapter 1 is a concise summary of the basic attributes of the geomagnetic field and its behavior in different time frames. It explains spherical harmonic analysis of the field and presents the history of acquisition of the data that best represent the recent field. Lastly, it includes a short summary of the origin and electrodynamics of the magnetic field, outlining the current theoretical basis for its generation.

  1. Experimental Investigation on the Influence of Axial Magnetic Field Distribution on Resisting the Constriction of a High-Current Vacuum Arc

    Institute of Scientific and Technical Information of China (English)

    SHI Zongqian; LIU Zhigang; JIA Shenli; SONG Xiaochuan; WANG Lijun

    2009-01-01

    Effect of the axial magnetic field (AMF) on resisting the constriction of a high-current vacuum arc is studied in this paper. Two typical AMF distributions were investigated, i.e., the traditional bell-shaped AMF, and the saddle-shaped AMF. Experiments were conducted in a detachable vacuum chamber with a rms arc current in the range of 10 kA to 25 kA. The arc column was photographed by a high-speed digital camera with an exposure time of 2 microseconds. The constriction of the vacuum arc was compared by processing the images of the arc column under the two different field configurations and numerically determining the dimensions of the arc column near the electrodes. It was also confirmed that the AMF distribution had a signifcant influence on its effectiveness in resisting arc constriction, Furthermore, the AMF strength near the periphery of the arc is more influential than that at the centre of the electrodes in resisting arc constriction.

  2. NMR in pulsed magnetic field

    KAUST Repository

    Abou-Hamad, Edy

    2011-09-01

    Nuclear magnetic resonance (NMR) experiments in pulsed magnetic fields up to 30.4 T focused on 1H and 93Nb nuclei are reported. Here we discuss the advantage and limitation of pulsed field NMR and why this technique is able to become a promising research tool. © 2011 Elsevier Inc. All Rights Reserved.

  3. The MAVEN Magnetic Field Investigation

    Science.gov (United States)

    Connerney, J. E. P.; Espley, J.; Lawton, P.; Murphy, S.; Odom, J.; Oliversen, R.; Sheppard, D.

    2014-01-01

    The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions ("boomlets"). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a quantization uncertainty of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05%. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers - multiple rotations about the spacecraft x and z axes - to characterize spacecraft fields and/or instrument offsets in flight.

  4. Comparative Study on the Grain Refinement of Al-Si Alloy Solidified under the Impact of Pulsed Electric Current and Travelling Magnetic Field

    Directory of Open Access Journals (Sweden)

    Yunhu Zhang

    2016-07-01

    Full Text Available It is high of commercial importance to generate the grain refinement in alloys during solidification by means of electromagnetic fields. Two typical patterns of electromagnetic fields, pulsed electric currents (ECP and traveling magnetic field (TMF, are frequently employed to produce the finer equiaxed grains in solidifying alloys. Various mechanisms were proposed to understand the grain refinement in alloys caused by ECP and TMF. In this paper, a comparative study is carried out in the same solidification regime to investigate the grain refinement of Al-7 wt. %Si alloy driven by ECP and TMF. Experimental results show that the application of ECP or TMF can cause the same grain refinement occurrence period, during which the refinement of primary Al continuously occurs. In addition, the related grain refinement mechanisms are reviewed and discussed, which shows the most likely one caused by ECP and TMF is the promoted dendrite fragmentation as the result of the ECP-induced or TMF-induced forced flow. It suggests that the same grain refinement process in alloys is provoked when ECP and TMF are applied in the same solidification regime, respectively.

  5. Evolution of the Coronal Magnetic Configurations Including a Current-Carrying Flux Rope in Response to the Change in the Background Field

    CERN Document Server

    Wang, Hong-Juan; Gong, Jian-Cun; Lin, Jun

    2014-01-01

    We investigate equilibrium height of the flux rope, and its internal equilibrium in a realistic plasma environment by carrying out numerical simulations of the evolution of systems including a current-carrying flux rope. We find that the equilibrium height of the flux rope is approximately a power-law function of the relative strength of the background field. Our simulations indicate that the flux rope can escape more easily from a weaker background field. This further confirms the catastrophe in the magnetic configuration of interest can be triggered by decrease of strength of the background field. Our results show that it takes some time to reach internal equilibrium depending on the initial state of the flux rope. The plasma flow inside the flux rope due to the adjustment for the internal equilibrium of the flux rope remains small and does not last very long when the initial state of the flux rope commences from the stable branch of the theoretical equilibrium curve. This work also confirms the influence o...

  6. Critical Current Measurements in Commercial Tapes, Coils, and Magnets.

    Science.gov (United States)

    Gubser, D. U.; Soulen, R. J., Jr.; Fuller-Mora, W. W.; Francavilla, T. L.

    1996-03-01

    We have measured a number of tapes, coils, and magnets produced by commercial vendors and determined their properties as functions of magnetic field and temperature. The tapes were measured at the National High Magnetic Field Laboratory in magnetic fields to 20 tesla and at temperatures of 4.2 K, 27 K, 65 K, and 77 K. For the tapes we report critical currents and current-voltage characteristics. Six inch diameter coils were measured at NRL in zero magnetic field. Critical currents, current-voltage characteristics, and reliability studies are reported for the coils. Larger 10 inch diameter coils, which are to be used in a 200 hp superconducting motor, were also measured and results will be presented. The talk will also review the status of the most recent tests of the superconducting motor.

  7. Polarized radiation diagnostics of stellar magnetic fields

    Science.gov (United States)

    Mathys, Gautier

    geometric structure of these fields. How this can possibly be achieved is briefly discussed. An overview of the current status of polarimetric studies of magnetic fields in non-degenerate stars of other types is presented. The final section is devoted to magnetic fields of white dwarfs. Current knowledge of magnetic fields of isolated white dwarfs is briefly reviewed. Diagnostic techniques are discussed, with particular emphasis on the variety of physical processes to be considered for understanding of spectral line formation over the broad range of magnetic field strengths encountered in these stars.

  8. Magnetic-field-controlled reconfigurable semiconductor logic.

    Science.gov (United States)

    Joo, Sungjung; Kim, Taeyueb; Shin, Sang Hoon; Lim, Ju Young; Hong, Jinki; Song, Jin Dong; Chang, Joonyeon; Lee, Hyun-Woo; Rhie, Kungwon; Han, Suk Hee; Shin, Kyung-Ho; Johnson, Mark

    2013-02-07

    Logic devices based on magnetism show promise for increasing computational efficiency while decreasing consumed power. They offer zero quiescent power and yet combine novel functions such as programmable logic operation and non-volatile built-in memory. However, practical efforts to adapt a magnetic device to logic suffer from a low signal-to-noise ratio and other performance attributes that are not adequate for logic gates. Rather than exploiting magnetoresistive effects that result from spin-dependent transport of carriers, we have approached the development of a magnetic logic device in a different way: we use the phenomenon of large magnetoresistance found in non-magnetic semiconductors in high electric fields. Here we report a device showing a strong diode characteristic that is highly sensitive to both the sign and the magnitude of an external magnetic field, offering a reversible change between two different characteristic states by the application of a magnetic field. This feature results from magnetic control of carrier generation and recombination in an InSb p-n bilayer channel. Simple circuits combining such elementary devices are fabricated and tested, and Boolean logic functions including AND, OR, NAND and NOR are performed. They are programmed dynamically by external electric or magnetic signals, demonstrating magnetic-field-controlled semiconductor reconfigurable logic at room temperature. This magnetic technology permits a new kind of spintronic device, characterized as a current switch rather than a voltage switch, and provides a simple and compact platform for non-volatile reconfigurable logic devices.

  9. Superconducting tapes with critical current density of 10 sup 4 A/cm sup 2 at 77 K and zero magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Narumi, E.; Song, L.W.; Hwa, S.; Ye, J.; Yang, F.; Kao, Y.H.; Patel, S.; Shaw, D.T. (New York State Inst. on Superconductivity, State Univ. of New York at Buffalo, Buffalo, NY (US)); Tkaczyk, J.E. (General Electric Co., Schenectady, NY (United States). Corporate Research and Development Center)

    1991-03-01

    This paper reports on critical current density above 10{sup 4} A/cm{sup 2} at both YBa{sub 2}Cu{sub 3}O{sub 6.8} (YBCO) thin films on metallic substrates and Bi-based superconducting films on silver tapes. A transition buffer, consisting of sub-buffers deposited at different temperatures, was used to enhance the crystallinity and the transport properties of YBCO films on metallic substrates. YBCO films were fabricated, using in-situ laser deposition, and they were strongly c-axis oriented. Critical temperature of 87 K and critical current density of 3 {times} 10{sup 4} A/cm{sup 2} at 77 K were obtained for a 0.5 {mu}m-thick YBCO film. Also, the magnetic field dependence of J{sub c} could be increased by using Pt-coated metallic substrates. For 10 {approximately} 20 {mu}m-thick Bi-based superconducting tape, by using brush-on technique and heat treatment, critical current of 10{sup 4} A/cm{sup 2} at 77 K was obtained.

  10. Electric-field guiding of magnetic skyrmions

    Energy Technology Data Exchange (ETDEWEB)

    Upadhyaya, Pramey; Yu, Guoqiang; Amiri, Pedram Khalili; Wang, Kang L.

    2015-10-01

    We theoretically study equilibrium and dynamic properties of nanosized magnetic skyrmions in thin magnetic films with broken inversion symmetry, where an electric field couples to magnetization via spin-orbit coupling. Based on a symmetry-based phenomenology and micromagnetic simulations we show that this electric-field coupling, via renormalizing the micromagnetic energy, modifies the equilibrium properties of the skyrmion. This change, in turn, results in a significant alteration of the current-induced skyrmion motion. Particularly, the speed and direction of the skyrmion can be manipulated by designing a desired energy landscape electrically, which we describe within Thiele's analytical model and demonstrate in micromagnetic simulations including electric-field-controlled magnetic anisotropy. We additionally use this electric-field control to construct gates for controlling skyrmion motion exhibiting a transistorlike and multiplexerlike function. The proposed electric-field effect can thus provide a low-energy electrical knob to extend the reach of information processing with skyrmions.

  11. Efficient magnetic fields for supporting toroidal plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Landreman, Matt, E-mail: mattland@umd.edu [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States); Boozer, Allen H. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)

    2016-03-15

    The magnetic field that supports tokamak and stellarator plasmas must be produced by coils well separated from the plasma. However, the larger the separation, the more difficult it is to produce a given magnetic field in the plasma region, so plasma configurations should be chosen that can be supported as efficiently as possible by distant coils. The efficiency of an externally generated magnetic field is a measure of the field's shaping component magnitude at the plasma compared to the magnitude near the coils; the efficiency of a plasma equilibrium can be measured using the efficiency of the required external shaping field. Counterintuitively, plasma shapes with low curvature and spectral width may have low efficiency, whereas plasma shapes with sharp edges may have high efficiency. Two precise measures of magnetic field efficiency, which correctly identify such differences in difficulty, will be examined. These measures, which can be expressed as matrices, relate the externally produced normal magnetic field on the plasma surface to the either the normal field or current on a distant control surface. A singular value decomposition (SVD) of either matrix yields an efficiency ordered basis for the magnetic field distributions. Calculations are carried out for both tokamak and stellarator cases. For axisymmetric surfaces with circular cross-section, the SVD is calculated analytically, and the range of poloidal and toroidal mode numbers that can be controlled to a given desired level is determined. If formulated properly, these efficiency measures are independent of the coordinates used to parameterize the surfaces.

  12. Magnetic fields in ring galaxies

    CERN Document Server

    Moss, D; Silchenko, O; Sokoloff, D; Horellou, C; Beck, R

    2016-01-01

    Many galaxies contain magnetic fields supported by galactic dynamo action. However, nothing definitive is known about magnetic fields in ring galaxies. Here we investigate large-scale magnetic fields in a previously unexplored context, namely ring galaxies, and concentrate our efforts on the structures that appear most promising for galactic dynamo action, i.e. outer star-forming rings in visually unbarred galaxies. We use tested methods for modelling $\\alpha-\\Omega$ galactic dynamos, taking into account the available observational information concerning ionized interstellar matter in ring galaxies. Our main result is that dynamo drivers in ring galaxies are strong enough to excite large-scale magnetic fields in the ring galaxies studied. The variety of dynamo driven magnetic configurations in ring galaxies obtained in our modelling is much richer than that found in classical spiral galaxies. In particular, various long-lived transients are possible. An especially interesting case is that of NGC 4513 where th...

  13. Finite element computation of 2-D magnetic field of solenoid with current%通电螺线管2维磁场有限元计算

    Institute of Scientific and Technical Information of China (English)

    彭斓; 杨中海; 胡权; 黄桃; 李斌

    2011-01-01

    Finite element computation of 2-D magnetic field of solenoid with current has been implemented. It adopted first or second order interpolation based finite element method to solve the 2-D magnetic field of the solenoid. The single solenoid model and the periodic structure model were analyzed and simulated. The results were compared with the results of Ansoft Maxwell 2D. It is shown that, compared with the first order interpolation based finite element method, the second order interpolation one has a faster convergence rate and a better accuracy on the axis of symmetry.%通过对通电螺线管磁系统理论分析,实现了通电螺线管2维磁场计算.该算法是采用一次、二次插值函数计算螺线管模型磁场的有限元算法,用于求解螺线管内外任意位置处的磁感应强度分布.实现了螺线管及周期结构的计算,并将结果与Ansoft Maxwell 2-D的计算结果进行了对比.结果表明:较一次插值函数有限元算法相比,二次插值函数算法在对称轴上轴向磁感应强度的分布更准确,体现了该算法的优越性,具有显著的工程应用价值.

  14. Reducing Magnetic Fields Around Power Cables

    Science.gov (United States)

    Sargent, Noel B.; Gitelman, Florida; Pongracz-Bartha, Edward; Spalding, John

    1993-01-01

    Four power conductors arranged symmetrically about fifth grounded conductor. Four current-carrying wires arranged symmetrically around central grounded wire that nominally carries no current. In comparison with other cable configurations, this one results in smaller magnetic fields around cable. Technique for use when size of wires in cable makes twisting impractical.

  15. Probing Magnetic Fields of Early Galaxies

    Science.gov (United States)

    Kohler, Susanna

    2017-06-01

    the magnetic fields in the foreground protogalaxies.Farnes and collaborators were unable to detect either coherent or random magnetic fields in DLAs. LLSs, however, showed some evidence of coherent magnetic fields and significant evidence of incoherent magnetic fields. The observations show that the magnetized gas in LLSs must be highly turbulent on a scale of 520 parsecs similar to turbulence scales in the Milky Way.Support for DynamosWhat do these observations imply? Both support the dynamo theory of magnetic field growth in galaxies!Polarization fraction distributions (top) and their logarithms (bottom) for sources with and without protogalaxies in the foreground (pink for DLAs, blue for LLSs, and grey for no intervenor). Statistical analysis reveals that the distribution for LLSs differs from the control sample, indicating the presence of magnetized gas. [Adapted from Farnes et al. 2017]The DLAs appear to consist of mostly non-turbulent quiescent gas; no dynamo action is currently occurring in these protogalaxies. The LLSs, on the other hand, appear to be growing their random magnetic fields via a turbulent dynamo. Thefields have not yet had enough time to become ordered like the fields of more evolved galaxies, however.Farnes and collaborators data indicate that magnetic fields are indeed being gradually built up in early galaxies by dynamos. They also suggest that DLAs may represent an earlier galactic evolutionary stage than LLSs, as DLAs havent yet had the time to develop their magnetic fields to a detectable level.A future increase in sample size will certainly help improve our understanding of the field formation process. In the meantime, the data in this study provide the first observational picture of magnetic field evolution in galaxies, lending excellent support to theoretical models.CitationJ. S. Farnes et al 2017 ApJ 841 67. doi:10.3847/1538-4357/aa7060

  16. Rotating superconductor magnet for producing rotating lobed magnetic field lines

    Science.gov (United States)

    Hilal, Sadek K.; Sampson, William B.; Leonard, Edward F.

    1978-01-01

    This invention provides a rotating superconductor magnet for producing a rotating lobed magnetic field, comprising a cryostat; a superconducting magnet in the cryostat having a collar for producing a lobed magnetic field having oppositely directed adjacent field lines; rotatable support means for selectively rotating the superconductor magnet; and means for energizing the superconductor magnet.

  17. Current patterns and orbital magnetism in mesoscopic dc transport.

    Science.gov (United States)

    Walz, Michael; Wilhelm, Jan; Evers, Ferdinand

    2014-09-26

    We present ab initio calculations of the local current density j(r) as it arises in dc-transport measurements. We discover pronounced patterns in the local current density, ring currents ("eddies"), that go along with orbital magnetism. Importantly, the magnitude of the ring currents can exceed the (average) transport current by orders of magnitude. We find associated magnetic fields that exhibit drastic fluctuations with field gradients reaching 1  T nm⁻¹ V⁻¹. The relevance of our observations for spin relaxation in systems with very weak spin-orbit interaction, such as organic semiconductors, is discussed. In such systems, spin relaxation induced by bias driven orbital magnetism competes with relaxation induced by the hyperfine interaction and appears to be of similar strength. We propose a NMR-type experiment in the presence of dc-current flow to observe the spatial fluctuations of the induced magnetic fields.

  18. Resonant magnetic fields from inflation

    CERN Document Server

    Byrnes, Christian T; Jain, Rajeev Kumar; Urban, Federico R

    2012-01-01

    We propose a novel scenario to generate primordial magnetic fields during inflation induced by an oscillating coupling of the electromagnetic field to the inflaton. This resonant mechanism has two key advantages over previous proposals. First of all, it generates a narrow band of magnetic fields at any required wavelength, thereby allaying the usual problem of a strongly blue spectrum and its associated backreaction. Secondly, it avoids the need for a strong coupling as the coupling is oscillating rather than growing or decaying exponentially. Despite these major advantages, we find that the backreaction is still far too large during inflation if the generated magnetic fields are required to have a strength of ${\\cal O}(10^{-15}\\, \\Gauss)$ today on observationally interesting scales. We provide a more general no-go argument, proving that this problem will apply to any model in which the magnetic fields are generated on subhorizon scales and freeze after horizon crossing.

  19. Static magnetic fields enhance turbulence

    CERN Document Server

    Pothérat, Alban

    2015-01-01

    More often than not, turbulence occurs under the influence of external fields, mostly rotation and magnetic fields generated either by planets, stellar objects or by an industrial environment. Their effect on the anisotropy and the dissipative behaviour of turbulence is recognised but complex, and it is still difficult to even tell whether they enhance or dampen turbulence. For example, externally imposed magnetic fields suppress free turbulence in electrically conducting fluids (Moffatt 1967), and make it two-dimensional (2D) (Sommeria & Moreau 1982); but their effect on the intensity of forced turbulence, as in pipes, convective flows or otherwise, is not clear. We shall prove that since two-dimensionalisation preferentially affects larger scales, these undergo much less dissipation and sustain intense turbulent fluctuations. When higher magnetic fields are imposed, quasi-2D structures retain more kinetic energy, so that rather than suppressing forced turbulence, external magnetic fields indirectly enha...

  20. High-temperature superconductors in high-field magnets

    NARCIS (Netherlands)

    Weijers, Hubertus Wilhelmus

    2009-01-01

    The properties of both BSCCO conductors and YBCO coated conductors and coils are studied to assess their applicability in high-field magnets. First, the magnetic field dependence of the critical current density in these HTS conductors is measured at 4.2 K in magnetic field conditions ranging from s

  1. Josephson tunnel junctions in a magnetic field gradient

    DEFF Research Database (Denmark)

    Monaco, R.; Mygind, Jesper; Koshelets, V.P.

    2011-01-01

    We measured the magnetic field dependence of the critical current of high-quality Nb-based planar Josephson tunnel junctions in the presence of a controllable nonuniform field distribution. We found skewed and slowly changing magnetic diffraction patterns quite dissimilar from the Fraunhofer-like...... be suppressed by an asymmetric magnetic field profile. © 2011 American Institute of Physics....

  2. Compact low field magnetic resonance imaging magnet: Design and optimization

    Science.gov (United States)

    Sciandrone, M.; Placidi, G.; Testa, L.; Sotgiu, A.

    2000-03-01

    Magnetic resonance imaging (MRI) is performed with a very large instrument that allows the patient to be inserted into a region of uniform magnetic field. The field is generated either by an electromagnet (resistive or superconductive) or by a permanent magnet. Electromagnets are designed as air cored solenoids of cylindrical symmetry, with an inner bore of 80-100 cm in diameter. In clinical analysis of peripheral regions of the body (legs, arms, foot, knee, etc.) it would be better to adopt much less expensive magnets leaving the most expensive instruments to applications that require the insertion of the patient in the magnet (head, thorax, abdomen, etc.). These "dedicated" apparati could be smaller and based on resistive magnets that are manufactured and operated at very low cost, particularly if they utilize an iron yoke to reduce power requirements. In order to obtain good field uniformity without the use of a set of shimming coils, we propose both particular construction of a dedicated magnet, using four independently controlled pairs of coils, and an optimization-based strategy for computing, a posteriori, the optimal current values. The optimization phase could be viewed as a low-cost shimming procedure for obtaining the desired magnetic field configuration. Some experimental measurements, confirming the effectiveness of the proposed approach (construction and optimization), have also been reported. In particular, it has been shown that the adoption of the proposed optimization based strategy has allowed the achievement of good uniformity of the magnetic field in about one fourth of the magnet length and about one half of its bore. On the basis of the good experimental results, the dedicated magnet can be used for MRI of peripheral regions of the body and for animal experimentation at very low cost.

  3. Magnetic Field Control of Combustion Dynamics

    Science.gov (United States)

    Barmina, I.; Valdmanis, R.; Zake, M.; Kalis, H.; Marinaki, M.; Strautins, U.

    2016-08-01

    Experimental studies and mathematical modelling of the effects of magnetic field on combustion dynamics at thermo-chemical conversion of biomass are carried out with the aim of providing control of the processes developing in the reaction zone of swirling flame. The joint research of the magnetic field effect on the combustion dynamics includes the estimation of this effect on the formation of the swirling flame dynamics, flame temperature and composition, providing analysis of the magnetic field effects on the flame characteristics. The results of experiments have shown that the magnetic field exerts the influence on the flow velocity components by enhancing a swirl motion in the flame reaction zone with swirl-enhanced mixing of the axial flow of volatiles with cold air swirl, by cooling the flame reaction zone and by limiting the thermo-chemical conversion of volatiles. Mathematical modelling of magnetic field effect on the formation of the flame dynamics confirms that the electromagnetic force, which is induced by the electric current surrounding the flame, leads to field-enhanced increase of flow vorticity by enhancing mixing of the reactants. The magnetic field effect on the flame temperature and rate of reactions leads to conclusion that field-enhanced increase of the flow vorticity results in flame cooling by limiting the chemical conversion of the reactants.

  4. Origin of cosmic magnetic fields

    Science.gov (United States)

    Rees, M. J.

    2006-06-01

    The first significant cosmic fields, and the seed field for galactic dynamos probably developed after the formation of the first non-linear structures. The history of star formation and the intergalactic medium is controlled, at least in part, by how and when galaxies and their precursors acquired their fields. The amplification of fields behind shocks, and the diffusivity of the magnetic flux, are crucial to the interpretation of radio sources, gamma ray burst afterglows, and other energetic cosmic phenomena. The build-up of magnetic fields is an important aspect of the overall cosmogonic process.

  5. Compensation of Gradient-Induced Magnetic Field Perturbations

    Science.gov (United States)

    Nixon, Terence W.; McIntyre, Scott; Rothman, Douglas L.; de Graaf, Robin A.

    2008-01-01

    Pulsed magnetic field gradients are essential for MR imaging and localized spectroscopy applications. However, besides the desired linear field gradients, pulsed currents in a strong external magnetic field also generate unwanted effects like eddy currents, gradient coil vibrations and acoustic noise. While the temporal magnetic field perturbations associated with eddy currents lead to spectral line shape distortions and signal loss, the vibration-related modulations lead to anti-symmetrical sidebands of any large signal (i.e. water), thereby obliterating the signals from smaller signals (i.e. metabolites). Here the measurement, characterization and compensation of vibrations-related magnetic field perturbations is presented. Following a quantitative evaluation of the various temporal components of the main magnetic field, a digital B0 magnetic field waveform is generated which reduces all temporal variations of the main magnetic field to within the spectral noise level. PMID:18329304

  6. Three Magnetic Direct-Current Sensors

    Science.gov (United States)

    Sullender, Craig C.; Stagg, David A.

    1994-01-01

    Three direct-current-measuring circuits based on magnetic (transformer) coupling, with periodic reset of magnetic flux to reverse saturation. Unidirectional and bidirectional versions demonstrated. Offers greater realibility and lower power consumption.

  7. Detection of the change of a magnetic field in the environment by magnetic fluid

    Science.gov (United States)

    Zyatkov, D.; Yurchenko, A.; Yurchenko, V.

    2017-08-01

    The experimental results of the magnetic field sensor based on various materials are presented. In article the possibility of use of magnetic fluid as a sensitive element of the magnetic field sensor is considered. The importance of current tasks deals with the search of the perspective magnetic substances susceptible to weak magnetic field. The operation principle of the sensor is based on change in the capacity of the condenser with magnetic active medium caused by the magnetic field. The complex organization of magnetic particles into chain aggregates was considered. The principle of measuring the condenser capacity is described. The experimental results are promising for future application.

  8. Field aligned current observations in the polar cusp ionosphere

    Science.gov (United States)

    Ledley, B. G.; Farthing, W. H.

    1973-01-01

    Vector magnetic field measurements made during a sounding rocket flight in the polar cusp ionosphere show field fluctuations in the lower F-region which are interpreted as being caused by the payload's passage through a structured field aligned current system. The field aligned currents have a characteristic horizontal scale size of one kilometer. Analysis of one large field fluctuation gives a current density of 0.0001 amp/m sq.

  9. Field-aligned current observations in the polar cusp ionosphere

    Science.gov (United States)

    Ledley, B. G.; Farthing, W. H.

    1974-01-01

    Vector magnetic field measurements made during a sounding rocket flight in the polar cusp ionosphere show field fluctuations in the lower F region that are interpreted as being caused by the passage of the payload through a structured field-aligned current system. The field-aligned currents have a characteristic horizontal scale size of about 1 km. Analysis of one large field fluctuation gives a current density of .001 A/sq m.

  10. Quantization of edge currents along magnetic barriers and magnetic guides

    CERN Document Server

    Dombrowski, N; Raikov, G D

    2010-01-01

    We investigate the edge conductance of particles submitted to an Iwatsuka magnetic field, playing the role of a purely magnetic barrier. We also consider magnetic guides generated by generalized Iwatsuka potentials. In both cases we prove quantization of the edge conductance. Next, we consider magnetic perturbations of such magnetic barriers or guides, and prove stability of the quantized value of the edge conductance. Further, we establish a sum rule for edge conductances. Regularization within the context of disordered systems is discussed as well.

  11. Measuring Earth's Magnetic Field Simply.

    Science.gov (United States)

    Stewart, Gay B.

    2000-01-01

    Describes a method for measuring the earth's magnetic field using an empty toilet paper tube, copper wire, clear tape, a battery, a linear variable resistor, a small compass, cardboard, a protractor, and an ammeter. (WRM)

  12. ISR split-field magnet

    CERN Multimedia

    1975-01-01

    The experimental apparatus used at intersection 4 around the Split-Field Magnet by the CERN-Bologna Collaboration (experiment R406). The plastic scintillator telescopes are used for precise pulse-height and time-of-flight measurements.

  13. The Juno Magnetic Field Investigation

    Science.gov (United States)

    Connerney, J. E. P.; Benn, M.; Bjarno, J. B.; Denver, T.; Espley, J.; Jorgensen, J. L.; Jorgensen, P. S.; Lawton, P.; Malinnikova, A.; Merayo, J. M.; Murphy, S.; Odom, J.; Oliversen, R.; Schnurr, R.; Sheppard, D.; Smith, E. J.

    2017-02-01

    The Juno Magnetic Field investigation (MAG) characterizes Jupiter's planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor suites, each consisting of a tri-axial Fluxgate Magnetometer (FGM) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. The imaging system sensors are part of a subsystem that provides accurate attitude information (to ˜20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. The two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long magnetometer boom affixed to the outer end of one of 's three solar array assemblies. The magnetometer sensors are controlled by independent and functionally identical electronics boards within the magnetometer electronics package mounted inside Juno's massive radiation shielded vault. The imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. Each magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 Gauss = 1.6 × 106 nT per axis) with a resolution of ˜0.05 nT in the most sensitive dynamic range (±1600 nT per axis). Both magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. The magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. The attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. The system tracks and catalogs objects that pass through the imager field of

  14. The Juno Magnetic Field Investigation

    Science.gov (United States)

    Connerney, J. E. P.; Benna, M.; Bjarno, J. B.; Denver, T.; Espley, J.; Jorgensen, J. L.; Jorgensen, P. S.; Lawton, P.; Malinnikova, A.; Merayo, J. M.; hide

    2017-01-01

    The Juno Magnetic Field investigation (MAG) characterizes Jupiter's planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor suites, each consisting of a tri-axial Fluxgate Magnetometer (FGM) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. The imaging system sensors are part of a subsystem that provides accurate attitude information (to approx. 20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. The two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long magnetometer boom affixed to the outer end of one of 's three solar array assemblies. The magnetometer sensors are controlled by independent and functionally identical electronics boards within the magnetometer electronics package mounted inside Juno's massive radiation shielded vault. The imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. Each magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 Gauss = 1.6 x 10(exp. 6) nT per axis) with a resolution of approx. 0.05 nT in the most sensitive dynamic range (+/-1600 nT per axis). Both magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. The magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. The attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. The system tracks and catalogs objects that pass through

  15. Magnetic-Field Hazards Bibliography.

    Science.gov (United States)

    1985-09-01

    produced during pulsed- magnetic-field therapy for non-union of the tibia." Med. Biol. Eng. Comput., Vol. 20, pp. 501-511 (1982). 32. Miller, D. A...Phenum Publishing Co. (1983). 40. Topper, R. F., "Electromagnetic shielding feasibility study," ASD -TDR-63-194 (Armour Research Foundation, Chicago...mammalian cells by strong magnetic fields (1976). 93. Malins, D. C., and Collier, T. K., "Xenobiotic interactions in aquatic organisms-effects on

  16. Eddy current characterization of magnetic treatment of materials

    Science.gov (United States)

    Chern, E. James

    1992-01-01

    Eddy current impedance measuring methods have been applied to study the effect that magnetically treated materials have on service life extension. Eddy current impedance measurements have been performed on Nickel 200 specimens that have been subjected to many mechanical and magnetic engineering processes: annealing, applied strain, magnetic field, shot peening, and magnetic field after peening. Experimental results have demonstrated a functional relationship between coil impedance, resistance and reactance, and specimens subjected to various engineering processes. It has shown that magnetic treatment does induce changes in a material's electromagnetic properties and does exhibit evidence of stress relief. However, further fundamental studies are necessary for a thorough understanding of the exact mechanism of the magnetic-field processing effect on machine tool service life.

  17. Currents in supersymmetric field theories

    CERN Document Server

    Derendinger, Jean-Pierre

    2016-01-01

    A general formalism to construct and improve supercurrents and source or anomaly superfields in two-derivative N=1 supersymmetric theories is presented. It includes arbitrary gauge and chiral superfields and a linear superfield coupled to gauge fields. These families of supercurrent structures are characterized by their energy-momentum tensors and R currents and they display a specific relation to the dilatation current of the theory. The linear superfield is introduced in order to describe the gauge coupling as a background (or propagating) field. Supersymmetry does not constrain the dependence on this gauge coupling field of gauge kinetic terms and holomorphicity restrictions are absent. Applying these results to an effective (Wilson) description of super-Yang-Mills theory, matching or cancellation of anomalies leads to an algebraic derivation of the all-order NSVZ beta function.

  18. Bootstrapping the Coronal Magnetic Field with STEREO

    Science.gov (United States)

    Aschwanden, Markus J.

    2010-05-01

    The 3D coronal magnetic field obtained from stereoscopically triangulated loops has been compared with standard photospheric magnetogram extrapolations. We found a large misalignment of 20-40 deg, depending on the complexity of an AR (Sandman et al. 2009; DeRosa et al. 2009). These studies prove that the magnetic field in the photosphere is not force-free and fundamentally cannot reproduce the coronal magnetic field. Bootstrapping with coronal loop 3D geometries are required to improve modeling of the coronal field. Such coronal field bootstrapping methods are currently developed using stereoscopically triangulated loops from STEREO/EUVI and preliminary results show already a significantly reduced misalignment of 10-20 deg.

  19. High-Field Superconducting Magnets Supporting PTOLEMY

    Science.gov (United States)

    Hopkins, Ann; Luo, Audrey; Osherson, Benjamin; Gentile, Charles; Tully, Chris; Cohen, Adam

    2013-10-01

    The Princeton Tritium Observatory for Light, Early Universe, Massive Neutrino Yield (PTOLEMY) is an experiment planned to collect data on Big Bang relic neutrinos, which are predicted to be amongst the oldest and smallest particles in the universe. Currently, a proof-of-principle prototype is being developed at Princeton Plasma Physics Laboratory to test key technologies associated with the experiment. A prominent technology in the experiment is the Magnetic Adiabatic Collimation with an Electrostatic Filter (MAC-E filter), which guides tritium betas along magnetic field lines generated by superconducting magnets while deflecting those of lower energies. B field mapping is performed to ensure the magnets produce a minimum field at the midpoint of the configuration of the magnets and to verify accuracy of existing models. Preliminary tests indicate the required rapid decrease in B field strength from the bore of the more powerful 3.35 T magnet, with the field dropping to 0.18 T approximately 0.5 feet from the outermost surface of the magnet.

  20. Levitation forces of a bulk YBCO superconductor in gradient varying magnetic fields

    Science.gov (United States)

    Jiang, J.; Gong, Y. M.; Wang, G.; Zhou, D. J.; Zhao, L. F.; Zhang, Y.; Zhao, Y.

    2015-09-01

    The levitation forces of a bulk YBCO superconductor in gradient varying high and low magnetic fields generated from a superconducting magnet were investigated. The magnetic field intensity of the superconducting magnet was measured when the exciting current was 90 A. The magnetic field gradient and magnetic force field were both calculated. The YBCO bulk was cooled by liquid nitrogen in field-cooling (FC) and zero-field-cooling (ZFC) condition. The results showed that the levitation forces increased with increasing the magnetic field intensity. Moreover, the levitation forces were more dependent on magnetic field gradient and magnetic force field than magnetic field intensity.

  1. Study of current-voltage characteristics of ferromagnetic α-Fe{sub 1.64}Ga{sub 0.36}O{sub 3} oxide under magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Vijayasri, G., E-mail: vsvijiguna.physics@gmail.com; Bhowmik, R. N. [Department of Physics, Pondicherry University, R..Venkataraman Nagar, Kalapet, Puducherry – 605 014 (India)

    2015-06-24

    We report the influence of magnetic field on I-V characteristics of α-Fe{sub 1.64}Ga{sub 0.36}O{sub 3} sample. Synchrotron X-ray diffraction pattern and Raman Spectroscopy have confirmed rhombohedral structure with space group R3C in the sample. The sample exhibits ferromagnetic feature at room temperature and non saturation of magnetization up to 7Tesla suggests the effect of non-collinear structure (canting) of the spins on the ferromagnetic properties. We have recorded I-V characteristics of the sample under magnetic field to study the effect of non-collinear spin structure on the electrical properties. Space charge limited current mechanism controlled the nature of non-linear I-V curves and the curves are significantly affected by magnetic field.

  2. Magnetic field characteristics analysis of a single assembled magnetic medium using ANSYS software

    Institute of Scientific and Technical Information of China (English)

    Ren Liuyi; Zeng Shanglin; Zhang Yimin

    2015-01-01

    The section shape of an assembled magnetic medium is the most important structural parameter of a high gradient magnetic separator, which directly affects the induction distribution and magnetic field gradient of the magnetic separator. In this study, equilateral triangle, square, hexagonal, octagon, dode-cagon, and round shape sections of the assembled magnetic medium are chosen to study their influence on magnetic field distribution characteristics using the ANSYS analysis. This paper utilizes a single assem-bled magnetic medium to understand the relationship between the geometry of the assembled magnetic medium and its magnetic field distribution characteristics. The results show that high magnetic field, regional field, magnetic field gradient, and magnetic force formed by the different sections of the assem-bled magnetic medium in the same background magnetic field reduce in turn based on the triangle, square, hexagonal, octagon, dodecagon, and round. Based on the magnetic field characteristics analytic results, the magnetic separation tests of the ilmenite are carried out. The results indicate that the section shape of the toothed plate compared with the section shape of cylinder can improve the recovery of ilme-nite up to 45%in the same magnetizing current condition of 2 A, which is consistent with magnetic field characteristics analysis of different assembled magnetic medium section shapes.

  3. Magnetic fields and uniformity of radio frequency power deposition in low-frequency inductively coupled plasmas with crossed internal oscillating currents

    DEFF Research Database (Denmark)

    Tsakadze, Erekle; Ostrikov, K.N.; Tsakadze, Z.L.

    2004-01-01

    and equidistant copper litz wires in quartz enclosures and generates three magnetic (H-z, H-r, and H-phi) and two electric (E-phi and E-r) field components at the fundamental frequency. The measurements have been performed in rarefied and dense plasmas generated in the electrostatic (E) and electromagnetic (H......) discharge modes using two miniature magnetic probes. It is shown that the radial uniformity and depth of the rf power deposition can be improved as compared with conventional sources of inductively coupled plasmas with external flat spiral ("pancake") antennas. Relatively deeper rf power deposition...... in the plasma source results in more uniform profiles of the optical emission intensity, which indicates on the improvement of the plasma uniformity over large chamber volumes. The results of the numerical modeling of the radial magnetic field profiles are found in a reasonable agreement with the experimental...

  4. Magnetic fields in spiral galaxies

    Science.gov (United States)

    Beck, Rainer

    2015-12-01

    Radio synchrotron emission, its polarization and Faraday rotation of the polarization angle are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30 \\upmu G) and in central starburst regions (50-100 \\upmu G). Such fields are dynamically important; they affect gas flows and drive gas inflows in central regions. Polarized emission traces ordered fields, which can be regular or anisotropic turbulent, where the latter originates from isotropic turbulent fields by the action of compression or shear. The strongest ordered fields (10-15 \\upmu G) are generally found in interarm regions. In galaxies with strong density waves, ordered fields are also observed at the inner edges of spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies and in central regions. Ordered fields in interacting galaxies have asymmetric distributions and are a tracer of past interactions between galaxies or with the intergalactic medium.—Faraday rotation measures of the diffuse polarized radio emission from galaxy disks reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by mean-field dynamos. "Magnetic arms" between gaseous spiral arms may also be products of dynamo action, but need a stable spiral pattern to develop. Helically twisted field loops winding around spiral arms were found in two galaxies so far. Large-scale field reversals, like the one found in the Milky Way, could not yet be detected in external galaxies. In radio halos around edge-on galaxies, ordered magnetic fields with X-shaped patterns are observed. The origin and evolution of cosmic magnetic fields, in particular their first occurrence in young galaxies and their dynamical importance during galaxy evolution, will be studied with

  5. Interface-enhanced sensitivity of photoconductivity to the electric current and magnetic field in La0.67Ca0.33MnO3/Nb-SrTiO3 p-n junctions

    Science.gov (United States)

    Wang, S.; Ma, Z. Z.; Xiong, J. J.; Li, C. J.; Hou, Y. H.; Ma, T. X.; Xiong, C. M.; Dou, R. F.; Nie, J. C.

    2016-12-01

    The effects of electric current and magnetic field on the photoconductivity (PC) of La0.67Ca0.33MnO3 (LCMO) films have been investigated within a comparative study on LCMO films on an n-type semiconducting Nb-doped SrTiO3 (NSTO) and insulating SrTiO3 (STO) substrates separately. At room temperature, LCMO on NSTO (LCMO/NSTO) was found to show remarkable PC effect than that on STO (LCMO/STO). More attractive is that, compared with that of LCMO/STO, the room-temperature PC of LCMO/NSTO also shows a high sensitivity to the change of current or magnetic field: for LCMO/NSTO under a light illumination with an intensity of 60 mW/cm2, the increment of current yields a decreases of PC at a rate of 7.6%/μA, while an application of magnetic field of 1.2 T can suppress PC by a percentage as high as ˜20%. In contrast, under the same stimulus of current or field, PC of LCMO/STO remains almost unchanged. The phenomena can be explained based on the interface effects correlated with the photocarrier injection, current shunting, and magnetic tunability occurred at the interface. This work demonstrates that manganite-based heterojunctions with interface engineering are promising for developing a new type of photoelectric device with high sensitivity and multifunctionality.

  6. Interaction of Mutually Perpendicular Magnetic Fields in HTSC

    Directory of Open Access Journals (Sweden)

    Vasilyev Aleksandr Fedorovich

    2015-11-01

    Full Text Available In this article a problem of interaction of the crossed magnetic fields in superconductors is considered. Superconducting materials have nonlinear magnetic properties. It allows using a non-linear magnetic susceptibility for measurement of feeble magnetic fields. We place a wire of superconducting material in a constant parallel uniform magnetic field. Then we let through a wire the alternating current leak. Interaction of mutual and perpendicular variation magnetic fields, with adequate accuracy is described by Ginzburg-Landau's equations. Approximate solution of the written equations is received. The component of a magnetic field parallel to a wire contains a variable component. Frequency of a variable component of the magnetic field is equal to the doubled current frequency. Amplitude of the variable component of the magnetic field is proportional to strength of the constant magnetic field. The experimental installation for research of interaction of mutually perpendicular magnetic fields is created. The cylinder from HTSC of ceramics of the YBa2Cu3O7-x was used as a sensor. Dependence of amplitude of the second harmonica of a variation magnetic field on strength of a constant magnetic field is received.

  7. Simultaneous transcranial direct current stimulation (tDCS) and whole-head magnetoencephalography (MEG): Assessing the impact of tDCS on slow cortical magnetic fields

    NARCIS (Netherlands)

    Garcia Cossio, E.; Witkowski, M.; Robinson, S.E.; Cohen, L.G.; Birbaumer, N.; Soekadar, S.R.

    2016-01-01

    Transcranial direct current stimulation (tDCS) can influence cognitive, affective or motor brain functions. Whereas previous imaging studies demonstrated widespread tDCS effects on brain metabolism, direct impact of tDCS on electric or magnetic source activity in task-related brain areas could not b

  8. Cardiac magnetic source imaging based on current multipole model

    Institute of Scientific and Technical Information of China (English)

    Tang Fa-Kuan; Wang Qian; Hua Ning; Lu Hong; Tang Xue-Zheng; Ma Ping

    2011-01-01

    It is widely accepted that the heart current source can be reduced into a current multipole. By adopting three linear inverse methods, the cardiac magnetic imaging is achieved in this article based on the current multipole model expanded to the first order terms. This magnetic imaging is realized in a reconstruction plane in the centre of human heart, where the current dipole array is employed to represent realistic cardiac current distribution. The current multipole as testing source generates magnetic fields in the measuring plane, serving as inputs of cardiac magnetic inverse problem. In the heart-torso model constructed by boundary element method, the current multipole magnetic field distribution is compared with that in the homogeneous infinite space, and also with the single current dipole magnetic field distribution.Then the minimum-norm least-squares (MNLS) method, the optimal weighted pseuDOInverse method (OWPIM), and the optimal constrained linear inverse method (OCLIM) are selected as the algorithms for inverse computation based on current multipole model innovatively, and the imaging effects of these three inverse methods are compared. Besides,two reconstructing parameters, residual and mean residual, are also discussed, and their trends under MNLS, OWPIM and OCLIM each as a function of SNR are obtained and compared.

  9. Magnetostrictive-piezoelectric magnetic sensor with current excitation

    CERN Document Server

    Prieto, J L; López, E; Sanchez, M C; Sanchez, P

    2000-01-01

    A new working configuration for magnetostrictive-piezoelectric magnetic sensors is presented. In this configuration, the excitation is caused using an electrical current flowing through the ferromagnetic sample and the induced signal is sensed in the piezoelectric support as an electrical voltage. This new idea allows a magnetic field detection without any coil and opens a possibility for a future miniaturisation of the sensor.

  10. Magnetic Field Generation in Stars

    CERN Document Server

    Ferrario, Lilia; Zrake, Jonathan

    2015-01-01

    Enormous progress has been made on observing stellar magnetism in stars from the main sequence through to compact objects. Recent data have thrown into sharper relief the vexed question of the origin of stellar magnetic fields, which remains one of the main unanswered questions in astrophysics. In this chapter we review recent work in this area of research. In particular, we look at the fossil field hypothesis which links magnetism in compact stars to magnetism in main sequence and pre-main sequence stars and we consider why its feasibility has now been questioned particularly in the context of highly magnetic white dwarfs. We also review the fossil versus dynamo debate in the context of neutron stars and the roles played by key physical processes such as buoyancy, helicity, and superfluid turbulence,in the generation and stability of neutron star fields. Independent information on the internal magnetic field of neutron stars will come from future gravitational wave detections. Thus we maybe at the dawn of a ...

  11. Magnetic field effect on spoke behaviour

    Science.gov (United States)

    Hnilica, Jaroslav; Slapanska, Marta; Klein, Peter; Vasina, Petr

    2016-09-01

    The investigations of the non-reactive high power impulse magnetron sputtering (HiPIMS) discharge using high-speed camera imaging, optical emission spectroscopy and electrical probes showed that plasma is not homogeneously distributed over the target surface, but it is concentrated in regions of higher local plasma density called spokes rotating above the erosion racetrack. Magnetic field effect on spoke behaviour was studied by high-speed camera imaging in HiPIMS discharge using 3 inch titanium target. An employed camera enabled us to record two successive images in the same pulse with time delay of 3 μs between them, which allowed us to determine the number of spokes, spoke rotation velocity and spoke rotation frequency. The experimental conditions covered pressure range from 0.15 to 5 Pa, discharge current up to 350 A and magnetic fields of 37, 72 and 91 mT. Increase of the magnetic field influenced the number of spokes observed at the same pressure and at the same discharge current. Moreover, the investigation revealed different characteristic spoke shapes depending on the magnetic field strength - both diffusive and triangular shapes were observed for the same target material. The spoke rotation velocity was independent on the magnetic field strength. This research has been financially supported by the Czech Science Foundation in frame of the project 15-00863S.

  12. Low-Power Magnetic Current Sensor

    Science.gov (United States)

    Mclyman, W. T.

    1989-01-01

    Direct current sensed via saturable-core reactor. Transducer senses direct current magnetically, providing isolation between input and output. Detecting-and-isolating element saturable reactor, where input current passes through one-turn control coil. Provides output of 0 to 3 Vdc for input current of 0 to 15 Adc and consumes power of 22 mW at 10 Adc input. Input sensed magnetically, output electrically isolated from input.

  13. Magnetic resonance imaging without field cycling at less than earth's magnetic field

    Science.gov (United States)

    Lee, Seong-Joo; Shim, Jeong Hyun; Kim, Kiwoong; Yu, Kwon Kyu; Hwang, Seong-min

    2015-03-01

    A strong pre-polarization field, usually tenths of a milli-tesla in magnitude, is used to increase the signal-to-noise ratio in ordinary superconducting quantum interference device-based nuclear magnetic resonance/magnetic resonance imaging experiments. Here, we introduce an experimental approach using two techniques to remove the need for the pre-polarization field. A dynamic nuclear polarization (DNP) technique enables us to measure an enhanced resonance signal. In combination with a π / 2 pulse to avoid the Bloch-Siegert effect in a micro-tesla field, we obtained an enhanced magnetic resonance image by using DNP technique with a 34.5 μT static external magnetic field without field cycling. In this approach, the problems of eddy current and flux trapping in the superconducting pickup coil, both due to the strong pre-polarization field, become negligible.

  14. The magnetic fields of Jupiter and Saturn

    Science.gov (United States)

    Ness, N. F.

    1981-01-01

    The magnetic fields of Jupiter and Saturn and the characteristics of their magnetospheres, formed by interaction with the solar wind, are discussed. The origins of both magnetic fields are associated with a dynamo process deep in the planetary interior. The Jovian magnetosphere is analogous to that of a pulsar magnetosphere: a massive central body with a rapid rotation and an associated intense magnetic field. Its most distinctive feature is its magnetodisk of concentrated plasma and particle flux, and reduced magnetic field intensity. The magnetopause near the subsolar point has been observed at radial distances ranging over 50 to 100 Jovian radii, implying a relatively compressible obstacle to solar wind flow. The composition of an embedded current sheet within the magnetic tail is believed to be influenced by volcanic eruptions and emissions from Io. Spectral troughs of the Jovian radiation belts have been interpreted as possible ring particles. The Saturnian magnetosphere appears to be more like the earth in its topology. It is mainly characterized by a dipole axis parallel to the rotational axis of the planet and a magnetic field intensity much less than expected.

  15. Effect of superconductor filament magnetization on the field errors

    CERN Document Server

    Wolf, R

    1999-01-01

    One of the main source of field errors in a superconducting magnet is the magnetization M of the superconducting filaments. Screening currents, of persistent nature, are induced by any. field change during operation of the magnet. This chapter describes the models for the calculation of these effects and the parameters to be defined in ROXIE. (3 refs).

  16. ATLAS Barrel Toroid magnet reached nominal field

    CERN Multimedia

    2006-01-01

     On 9 November the barrel toroid magnet reached its nominal field of 4 teslas, with an electrical current of 21 000 amperes (21 kA) passing through the eight superconducting coils as shown on this graph

  17. Effects of static magnetic fields on plants.

    Science.gov (United States)

    Kuznetsov, O.

    In our recent experiment on STS-107 (MFA-Biotube) we took advantage of the magnetic heterogeneity of the gravity receptor cells of flax roots, namely stronger diamagnetism of starch-filled amyloplasts compared to cytoplasm (Δ ≊ HGMF, grad(H2/2) up to 109-1010 Oe2/cm) of the experimental chambers (MFCs) repelled amyloplasts from the zones of stronger field thus providing a directional stimulus for plant gravisensing system in microgravity, and causing the roots to react. Such reaction was observed in the video downlink pictures. Unfortunately, the ``Columbia'' tragedy caused loss of the plant material and most of the images, thus preventing us from detailed studies of the results. Currently we are looking for a possibility to repeat this experiment. Therefore, it is very important to understand, what other effects (besides displacing amyloplasts) static magnetic fields with intensities 0 to 2.5104 Oe, and with the size of the area of non-uniformity 10-3 to 1 cm. These effects were estimated theoretically and tested experimentally. No statistically significant differences in growth rates or rates of gravicurvature were observed in experiments with Linum, Arabidopsis, Hordeum, Avena, Ceratodon and Chara between the plants grown in uniform magnetic fields of various intensities (102 to 2.5104 Oe) and those grown in the Earth's magnetic field. Microscopic studies also did not detect any structural differences between test and control plants. The magnitudes of possible effects of static magnetic fields on plant cells and organs (including effects on ion currents, magneto-hydrodynamic effects in moving cytoplasm, ponderomotive forces on other cellular structures, effects on some biochemical reactions and biomolecules) were estimated theoretically. The estimations have shown, that these effects are small compared to the thermodynamic noise and thus are insignificant. Both theoretical estimations and control experiments confirm, that intracellular magnetophoresis of

  18. Indoor localization using magnetic fields

    Science.gov (United States)

    Pathapati Subbu, Kalyan Sasidhar

    Indoor localization consists of locating oneself inside new buildings. GPS does not work indoors due to multipath reflection and signal blockage. WiFi based systems assume ubiquitous availability and infrastructure based systems require expensive installations, hence making indoor localization an open problem. This dissertation consists of solving the problem of indoor localization by thoroughly exploiting the indoor ambient magnetic fields comprising mainly of disturbances termed as anomalies in the Earth's magnetic field caused by pillars, doors and elevators in hallways which are ferromagnetic in nature. By observing uniqueness in magnetic signatures collected from different campus buildings, the work presents the identification of landmarks and guideposts from these signatures and further develops magnetic maps of buildings - all of which can be used to locate and navigate people indoors. To understand the reason behind these anomalies, first a comparison between the measured and model generated Earth's magnetic field is made, verifying the presence of a constant field without any disturbances. Then by modeling the magnetic field behavior of different pillars such as steel reinforced concrete, solid steel, and other structures like doors and elevators, the interaction of the Earth's field with the ferromagnetic fields is described thereby explaining the causes of the uniqueness in the signatures that comprise these disturbances. Next, by employing the dynamic time warping algorithm to account for time differences in signatures obtained from users walking at different speeds, an indoor localization application capable of classifying locations using the magnetic signatures is developed solely on the smart phone. The application required users to walk short distances of 3-6 m anywhere in hallway to be located with accuracies of 80-99%. The classification framework was further validated with over 90% accuracies using model generated magnetic signatures representing

  19. Magnetic Fields in Spiral Galaxies

    CERN Document Server

    Beck, Rainer

    2015-01-01

    Radio synchrotron emission is a powerful tool to study the strength and structure of magnetic fields in galaxies. Unpolarized synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30\\mu G) and in central starburst regions (50-100\\mu G). Such fields are dynamically important; they affect gas flows and drive gas inflows in central regions. Polarized emission traces ordered fields, which can be regular or anisotropic turbulent, where the latter originates from isotropic turbulent fields by the action of compression or shear. The strongest ordered fields (10-15\\mu G) are generally found in interarm regions. In galaxies with strong density waves, ordered fields are also observed at the inner edges of spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions. Ordered fields in interacting galaxies have asymmetric distributions and are a tracer of past interactions between galaxies or with the interg...

  20. Eddy current characterization of magnetic treatment of nickel 200

    Science.gov (United States)

    Chern, E. J.

    1993-01-01

    Eddy current methods have been applied to characterize the effect of magnetic treatments on component service-life extension. Coil impedance measurements were acquired and analyzed on nickel 200 specimens that have been subjected to many mechanical and magnetic engineering processes: annealing, applied strain, magnetic field, shot peening, and magnetic field after peening. Experimental results have demonstrated a functional relationship between coil impedance, resistance and reactance, and specimens subjected to various engineering processes. It has shown that magnetic treatment does induce changes in electromagnetic properties of nickel 200 that then exhibit evidence of stress relief. However, further fundamental studies are necessary for a thorough understanding of the exact mechanism of the magnetic field processing effect on machine-tool service life.

  1. Magnetic topology and current channels in plasmas with toroidal current density inversions

    Science.gov (United States)

    Ciro, D.; Caldas, I. L.

    2013-10-01

    The equilibrium magnetic field inside axisymmetric plasmas with inversions on the toroidal current density is considered. Previous works have shown that internal regions with negative current density lead to non-nested magnetic surfaces inside the plasma. Following these results, we derive a general expression relating the positive and negative currents inside the non-nested surfaces. This is done in terms of an anisotropy parameter that is model-independent and is based in very general properties of the magnetic field. We demonstrate that the positive currents in axisymmetric islands screen the negative one in the plasma center by reaching about twice its magnitude. Further, we illustrate these results by developing a family of analytical local solutions for the poloidal magnetic field in a region of interest that contains the inverted current. These local solutions exhibit non-nested magnetic surfaces with a combined current of at least twice the magnitude of the negative one, as prescribed from the topological arguments, and allow to study topological transitions driven by geometrical changes in the current profile. To conclude, we discuss the signatures of internal current density inversions in a confinement device and show that magnetic pitch measurements may be inappropriate to differentiate current reversals and small current holes in plasmas.

  2. Reduction of a Ship's Magnetic Field Signatures

    CERN Document Server

    Holmes, John

    2008-01-01

    Decreasing the magnetic field signature of a naval vessel will reduce its susceptibility to detonating naval influence mines and the probability of a submarine being detected by underwater barriers and maritime patrol aircraft. Both passive and active techniques for reducing the magnetic signatures produced by a vessel's ferromagnetism, roll-induced eddy currents, corrosion-related sources, and stray fields are presented. Mathematical models of simple hull shapes are used to predict the levels of signature reduction that might be achieved through the use of alternate construction materials. Al

  3. Magnetic fields of neutron stars

    CERN Document Server

    Reisenegger, Andreas

    2013-01-01

    Neutron stars contain the strongest magnetic fields known in the Universe. In this paper, I discuss briefly how these magnetic fields are inferred from observations, as well as the evidence for their time-evolution. I show how these extremely strong fields are actually weak in terms of their effects on the stellar structure, as is also the case for magnetic stars on the upper main sequence and magnetic white dwarfs, which have similar total magnetic fluxes. I propose a scenario in which a stable hydromagnetic equilibrium (containing a poloidal and a toroidal field component) is established soon after the birth of the neutron star, aided by the strong compositional stratification of neutron star matter, and this state is slowly eroded by non-ideal magnetohydrodynamic processes such as beta decays and ambipolar diffusion in the core of the star and Hall drift and breaking of the solid in its crust. Over sufficiently long time scales, the fluid in the neutron star core will behave as if it were barotropic, becau...

  4. Magnetic fields during galaxy mergers

    CERN Document Server

    Rodenbeck, Kai

    2016-01-01

    Galaxy mergers are expected to play a central role for the evolution of galaxies, and may have a strong impact on their magnetic fields. We present the first grid-based 3D magneto-hydrodynamical simulations investigating the evolution of magnetic fields during merger events. For this purpose, we employ a simplified model considering the merger event of magnetized gaseous disks in the absence of stellar feedback and without a stellar or dark matter component. We show that our model naturally leads to the production of two peaks in the evolution of the average magnetic field strength within 5 kpc, within 25 kpc and on scales in between 5 and 25 kpc. The latter is consistent with the peak in the magnetic field strength reported by Drzazga et al. (2011) in a merger sequence of observed galaxies. We show that the peak on the galactic scale and in the outer regions is likely due to geometrical effects, as the core of one galaxy enters the outskirts of the other one. In addition, there is a physical enhancement of t...

  5. Magnetic Field Effects on Plasma Plumes

    Science.gov (United States)

    Ebersohn, F.; Shebalin, J.; Girimaji, S.; Staack, D.

    2012-01-01

    Here, we will discuss our numerical studies of plasma jets and loops, of basic interest for plasma propulsion and plasma astrophysics. Space plasma propulsion systems require strong guiding magnetic fields known as magnetic nozzles to control plasma flow and produce thrust. Propulsion methods currently being developed that require magnetic nozzles include the VAriable Specific Impulse Magnetoplasma Rocket (VASIMR) [1] and magnetoplasmadynamic thrusters. Magnetic nozzles are functionally similar to de Laval nozzles, but are inherently more complex due to electromagnetic field interactions. The two crucial physical phenomenon are thrust production and plasma detachment. Thrust production encompasses the energy conversion within the nozzle and momentum transfer to a spacecraft. Plasma detachment through magnetic reconnection addresses the problem of the fluid separating efficiently from the magnetic field lines to produce maximum thrust. Plasma jets similar to those of VASIMR will be studied with particular interest in dual jet configurations, which begin as a plasma loops between two nozzles. This research strives to fulfill a need for computational study of these systems and should culminate with a greater understanding of the crucial physics of magnetic nozzles with dual jet plasma thrusters, as well as astrophysics problems such as magnetic reconnection and dynamics of coronal loops.[2] To study this problem a novel, hybrid kinetic theory and single fluid magnetohydrodynamic (MHD) solver known as the Magneto-Gas Kinetic Method is used.[3] The solver is comprised of a "hydrodynamic" portion based on the Gas Kinetic Method and a "magnetic" portion that accounts for the electromagnetic behaviour of the fluid through source terms based on the resistive MHD equations. This method is being further developed to include additional physics such as the Hall effect. Here, we will discuss the current level of code development, as well as numerical simulation results

  6. Electron holography of magnetic field generated by a magnetic recording head.

    Science.gov (United States)

    Goto, Takayuki; Jeong, Jong Seok; Xia, Weixing; Akase, Zentaro; Shindo, Daisuke; Hirata, Kei

    2013-06-01

    The magnetic field generated by a magnetic recording head is evaluated using electron holography. A magnetic recording head, which is connected to an electric current source, is set on the specimen holder of a transmission electron microscope. Reconstructed phase images of the region around the magnetic pole show the change in the magnetic field distribution corresponding to the electric current applied to the coil of the head. A simulation of the magnetic field, which is conducted using the finite element method, reveals good agreement with the experimental observations.

  7. Lightning Magnetic Field Measurements around Langmuir Laboratory

    Science.gov (United States)

    Stock, M.; Krehbiel, P. R.; Rison, W.; Aulich, G. D.; Edens, H. E.; Sonnenfeld, R. G.

    2010-12-01

    In the absence of artificial conductors, underground lightning transients are produced by diffusion of the horizontal surface magnetic field of a return stroke vertically downward into the conducting earth. The changing magnetic flux produces an orthogonal horizontal electric field, generating a dispersive, lossy transverse electromagnetic wave that penetrates a hundred meters or more into the ground according to the skin depth of the medium. In turn, the electric field produces currents that flow toward or away from the channel to ground depending on the stroke polarity. The underground transients can produce large radial horizontal potential gradients depending on the distance from the discharge and depth below the surface. In this study we focus on the surface excitation field. The goal of the work is to compare measurements of surface magnetic field waveforms B(t) at different distances from natural lightning discharges with simple and detailed models of the return stroke fields. In addition to providing input to the diffusion mechanism, the results should aid in further understanding return stroke field generation processes. The observational data are to be obtained using orthogonal sets of straightened Rogowski coils to measure magnetic field waveforms in N-S and E-W directions. The waveforms are sampled at 500 kS/s over 1.024 second time intervals and recorded directly onto secure digital cards. The instrument operates off of battery power for several days or weeks at a time in remote, unattended locations and measures magnetic field strengths of up to several tens of amperes/meter. The observations are being made in conjunction with collocated slow electric field change measurements and under good 3-D lightning mapping array (LMA) and fast electric field change coverage.

  8. Induced current and redefinition of electric and magnetic fields from non-compact Kaluza-Klein theory: An experimental signature of the fifth dimension

    CERN Document Server

    Liko, T

    2005-01-01

    The field equations for gravitation and electromagnetism with sources in four dimensions can be interpreted as arising from the vacuum Einstein equations in five dimensions. Gauge invariance of the electromagnetic potentials leads to a ``generalized'' electromagnetic field tensor. We use the action principle to derive the equations of motion for free electromagnetic fields in flat spacetime, and isolate an effective electromagnetic current with a source that is purely higher-dimensional in origin. This current provides, at least in principle, a means of detecting extra dimensions experimentally.

  9. High critical current density under magnetic fields in as-grown MgB{sub 2} thin films deposited by molecular-beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Haruta, M [Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan); Fujiyoshi, T [Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan); Kihara, S [Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan); Sueyoshi, T [Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan); Miyahara, K [Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan); Harada, Y [Iwate Industry Promotion Centre, Iioka-shinden 3-35-2, Morioka, Iwate 020-0852 (Japan); Yoshizawa, M [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka, Iwate 020-8551 (Japan); Takahashi, T [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka, Iwate 020-8551 (Japan); Iriuda, H [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka, Iwate 020-8551 (Japan); Oba, T [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka, Iwate 020-8551 (Japan); Awaji, S [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Watanabe, K [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Miyagawa, R [Kumamoto Industrial Research Institute, 3-11-38 Higashi-machi, Kumamoto 862-0901 (Japan)

    2007-01-15

    As-grown MgB{sub 2} thin films were prepared by a MBE method under the conditions of low temperature, low deposition rate and high vacuum for applications in electric devices. The MgB{sub 2} thin films deposited on MgO and Ti buffered ZnO substrates have considerably higher J{sub c} under magnetic fields among MgB{sub 2} thin films reported before. The value of J{sub c} for the MgB{sub 2} thin film deposited on Ti buffered ZnO has been 5.8 x 10{sup 5} A cm{sup -2} at 10 K, 5 T in the magnetic field applied parallel to the c axis. In the angular dependence of J{sub c}, the peak of J{sub c} attributable to c-axis-correlated pinning centres has been observed when the magnetic field was applied parallel to the c axis. (rapid communication)

  10. Solar Flare Magnetic Fields and Plasmas

    CERN Document Server

    Fisher, George

    2012-01-01

    This volume is devoted to the dynamics and diagnostics of solar magnetic fields and plasmas in the Sun’s atmosphere. Five broad areas of current research in Solar Physics are presented: (1) New techniques for incorporating radiation transfer effects into three-dimensional magnetohydrodynamic models of the solar interior and atmosphere, (2) The connection between observed radiation processes occurring during flares and the underlying flare energy release and transport mechanisms, (3) The global balance of forces and momenta that occur during flares, (4) The data-analysis and theoretical tools needed to understand and assimilate vector magnetogram observations and (5) Connecting flare and CME phenomena to the topological properties of the magnetic field in the Solar Atmosphere. The role of the Sun’s magnetic field is a major emphasis of this book, which was inspired by a workshop honoring Richard C. (Dick) Canfield.  Dick has been making profound contributions to these areas of research over a long and pro...

  11. Magnetic fields, special relativity and potential theory elementary electromagnetic theory

    CERN Document Server

    Chirgwin, B H; Kilmister, C W

    1972-01-01

    Magnetic Fields, Special Relativity and Potential Theory is an introduction to electromagnetism, special relativity, and potential theory, with emphasis on the magnetic field of steady currents (magnetostatics). Topics covered range from the origin of the magnetic field and the magnetostatic scalar potential to magnetization, electromagnetic induction and magnetic energy, and the displacement current and Maxwell's equations. This volume is comprised of five chapters and begins with an overview of magnetostatics, followed by a chapter on the methods of solving potential problems drawn from elec

  12. Primordial Magnetic Fields and Causality

    CERN Document Server

    Durrer, R; Durrer, Ruth; Caprini, Chiara

    2003-01-01

    In this letter we discuss the implications of causality on a primordial magnetic field. We show that the residual field on large scales is much stronger suppressed than usually assumed and that a helical component is even suppressed even more than the parity even part. We show that due to this strong suppression, even maximal primordial fields generated at the electroweak phase transition can just marginally seed the fields in galaxies and clusters, but they cannot leave any detectable imprint on the cosmic microwave background.

  13. Reducing blood viscosity with magnetic fields.

    Science.gov (United States)

    Tao, R; Huang, K

    2011-07-01

    Blood viscosity is a major factor in heart disease. When blood viscosity increases, it damages blood vessels and increases the risk of heart attacks. Currently, the only method of treatment is to take drugs such as aspirin, which has, however, several unwanted side effects. Here we report our finding that blood viscosity can be reduced with magnetic fields of 1 T or above in the blood flow direction. One magnetic field pulse of 1.3 T lasting ~1 min can reduce the blood viscosity by 20%-30%. After the exposure, in the absence of magnetic field, the blood viscosity slowly moves up, but takes a couple of hours to return to the original value. The process is repeatable. Reapplying the magnetic field reduces the blood viscosity again. By selecting the magnetic field strength and duration, we can keep the blood viscosity within the normal range. In addition, such viscosity reduction does not affect the red blood cells' normal function. This technology has much potential for physical therapy.

  14. Magnetic fields in Neutron Stars

    CERN Document Server

    Viganò, Daniele; Miralles, Juan A; Rea, Nanda

    2015-01-01

    Isolated neutron stars show a diversity in timing and spectral properties, which has historically led to a classification in different sub-classes. The magnetic field plays a key role in many aspects of the neutron star phenomenology: it regulates the braking torque responsible for their timing properties and, for magnetars, it provides the energy budget for the outburst activity and high quiescent luminosities (usually well above the rotational energy budget). We aim at unifying this observational variety by linking the results of the state-of-the-art 2D magneto-thermal simulations with observational data. The comparison between theory and observations allows to place two strong constraints on the physical properties of the inner crust. First, strong electrical currents must circulate in the crust, rather than in the star core. Second, the innermost part of the crust must be highly resistive, which is in principle in agreement with the presence of a novel phase of matter so-called nuclear pasta phase.

  15. Effect of magnetic field in malaria diagnosis using magnetic nanoparticles

    Science.gov (United States)

    Liu, Quan; Yuen, Clement

    2011-07-01

    The current gold standard method of Malaria diagnosis relies on the blood smears examination. The method is laborintensive, time consuming and requires the expertise for data interpretation. In contrast, Raman scattering from a metabolic byproduct of the malaria parasite (Hemozoin) shows the possibility of rapid and objective diagnosis of malaria. However, hemozoin concentration is usually extremely low especially at the early stage of malaria infection, rendering weak Raman signal. In this work, we propose the sensitive detection of enriched β-hematin, whose spectroscopic properties are equivalent to hemozoin, based on surface enhanced Raman spectroscopy (SERS) by using magnetic nanoparticles. A few orders of magnitude enhancement in the Raman signal of β-hematin can be achieved using magnetic nanoparticles. Furthermore, the effect of magnetic field on SERS enhancement is investigated. Our result demonstrates the potential of SERS using magnetic nanoparticles in the effective detection of hemozoin for malaria diagnosis.

  16. Magnetic Fields in the Interstellar Medium

    Science.gov (United States)

    Clark, Susan

    2017-01-01

    The Milky Way is magnetized. Invisible magnetic fields thread the Galaxy on all scales and play a vital but still poorly understood role in regulating flows of gas in the interstellar medium and the formation of stars. I will present highlights from my thesis work on magnetic fields in the diffuse interstellar gas and in accretion disks. At high Galactic latitudes, diffuse neutral hydrogen is organized into an intricate network of slender linear features. I will show that these neutral hydrogen “fibers” are extremely well aligned with the ambient magnetic field as traced by both starlight polarization (Clark et al. 2014) and Planck 353 GHz polarized dust emission (Clark et al. 2015). The structure of the neutral interstellar medium is more tightly coupled to the magnetic field than previously known. Because the orientation of neutral hydrogen is an independent predictor of the local dust polarization angle, our work provides a new tool in the search for inflationary gravitational wave B-mode polarization in the cosmic microwave background, which is currently limited by dust foreground contamination. Magnetic fields also drive accretion in astrophysical disks via the magnetorotational instability (MRI). I analytically derive the behavior of this instability in the weakly nonlinear regime and show that the saturated state of the instability depends on the geometry of the background magnetic field. The analytical model describes the behavior of the MRI in a Taylor-Couette flow, a set-up used by experimentalists in the ongoing quest to observe MRI in the laboratory (Clark & Oishi 2016a, 2016b).

  17. Chiral transition with magnetic fields

    CERN Document Server

    Ayala, Alejandro; Mizher, Ana Julia; Rojas, Juan Cristobal; Villavicencio, Cristian

    2014-01-01

    We study the nature of the chiral transition for an effective theory with spontaneous breaking of symmetry, where charged bosons and fermions are subject to the effects of a constant external magnetic field. The problem is studied in terms of the relative intensity of the magnetic field with respect to the mass and the temperature. When the former is the smallest of the scales, we present a suitable method to obtain magnetic and thermal corrections up to ring order at high temperature. By these means, we solve the problem of the instability in the boson sector for these theories, where the squared masses, taken as functions of the order parameter, can vanish and even become negative. The solution is found by considering the screening properties of the plasma, encoded in the resummation of the ring diagrams at high temperature. We also study the case where the magnetic field is the intermediate of the three scales and explore the nature of the chiral transition as we vary the field strength, the coupling const...

  18. Resonances of an Oscillating Conductive Pipe Driven by an Alternating Magnetic Field in the Presence of a Static Magnetic Field

    Science.gov (United States)

    Ladera, Celso L.; Donoso, Guillermo

    2011-01-01

    A short conducting pipe that hangs from a weak spring is forced to oscillate by the magnetic field of a surrounding coaxial coil that has been excited by a low-frequency current source in the presence of an additional static magnetic field. Induced oscillating currents appear in the pipe. The pipe motion becomes damped by the dragging forces…

  19. Magnetic Field Effects on Quantum-Dot Spin Valves

    Institute of Scientific and Technical Information of China (English)

    GAO Jin-Hua; SUN Qing-Feng; XIE Xin-Cheng

    2009-01-01

    We study the magnetic field effects on the spin-polarized transport of the quantum dot (QD) spin valve in the sequential tunneling regime. A set of generalized master equation is derived. Based on that, we discuss the collinear and noneollinear magnetic field effects, respectively. In the collinear magnetic field case, we find that the Zeeman splitting can induce a negative differential conductance (NDC), which is quite different from the one found in previous studies. It has a critical polarization in the parallel arrangement and will disappear in the antiparallel configuration. In the noncollinear magnetic field case, the current shows two plateaus and their angular dependence is analyzed. Although sometimes the two current plateaus have similar angular dependence, their mechanisms are different. Our formalism is also suitable for calculating the transport in magnetic molecules, in which the spin splitting is induced not by a magnetic field but by the intrinsic magnetization.

  20. Magnetic fields in spiral galaxies

    Science.gov (United States)

    Krause, Marita

    2015-03-01

    The magnetic field structure in edge-on galaxies observed so far shows a plane-parallel magnetic field component in the disk of the galaxy and an X-shaped field in its halo. The plane-parallel field is thought to be the projected axisymmetric (ASS) disk field as observed in face-on galaxies. Some galaxies addionionally exhibit strong vertical magnetic fields in the halo right above and below the central region of the disk. The mean-field dynamo theory in the disk cannot explain these observed fields without the action of a wind, which also probably plays an important role to keep the vertical scale heights constant in galaxies of different Hubble types and star formation activities, as has been observed in the radio continuum: At λ6 cm the vertical scale heights of the thin disk and the thick disk/halo in a sample of five edge-on galaxies are similar with a mean value of 300 +/- 50 pc for the thin disk and 1.8 +/- 0.2 kpc for the thick disk (a table and references are given in Krause 2011) with our sample including the brightest halo observed so far, NGC 253, with strong star formation, as well as one of the weakest halos, NGC 4565, with weak star formation. If synchrotron emission is the dominant loss process of the relativistic electrons the outer shape of the radio emission should be dumbbell-like as has been observed in several edge-on galaxies like e.g. NGC 253 (Heesen et al. 2009) and NGC 4565. As the synchrotron lifetime t syn at a single frequency is proportional to the total magnetic field strength B t -1.5, a cosmic ray bulk speed (velocity of a galactic wind) can be defined as v CR = h CR /t syn = 2 h z /t syn , where h CR and h z are the scale heights of the cosmic rays and the observed radio emission at this freqnency. Similar observed radio scale heights imply a self regulation mechanism between the galactic wind velocity, the total magnetic field strength and the star formation rate SFR in the disk: v CR ~ B t 1.5 ~ SFR ~ 0.5 (Niklas & Beck 1997).

  1. A Model of Mercury's Magnetospheric Magnetic Field with Dependence on Magnetic Activity

    Science.gov (United States)

    Korth, H.; Tsyganenko, N. A.; Johnson, C. L.; Philpott, L. C.; Anderson, B. J.; Solomon, S. C.; McNutt, R. L., Jr.

    2015-12-01

    Accurate knowledge of Mercury's magnetospheric magnetic field is required to characterize the planet's internal field and the structure of the magnetosphere. We present the first model of Mercury's magnetospheric magnetic field that includes a dependence on magnetic activity. The model consists of individual modules for magnetic fields of internal origin, approximated by a dipole of magnitude 190 nT RM3, where RM is Mercury's radius, offset northward by 479 km along the spin axis, and of external origin resulting from currents flowing on the magnetopause boundary and in the cross-tail current sheet. The magnetic field is confined within a magnetopause shape derived from Magnetometer observations by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft and dependent on magnetic activity. The cross-tail current is prescribed having a disk shape near the planet and extending into a sheet at larger distances. The magnitude of the tail current, which also depends on magnetic activity, is fit to minimize the root-mean-square residual between the model magnetic field and the field within the magnetosphere observed by MESSENGER. The model was fit separately for magnetic field observations within distinct levels of magnetic activity. Linear fits of model parameters versus magnetic activity allows continuous scaling of the model to magnetic activity. The magnetic field contribution from each module is shielded individually by a scalar potential function, which was fit to minimize the root-mean-square normal magnetic field component at the magnetopause. The resulting model reproduces the dependence of the magnetospheric size and tail current intensity on magnetic activity, and allows more accurate characterization of the internal field.

  2. Primordial Magnetic Fields that Last?

    CERN Document Server

    Carroll, S M; Carroll, Sean M.; Field, George B.

    1998-01-01

    The magnetic fields we observe in galaxies today may have their origins in the very early universe. While a number of mechanisms have been proposed which lead to an appreciable field amplitude at early times, the subsequent evolution of the field is of crucial importance, especially whether the correlation length of the field can grow as large as the size of a protogalaxy. This talk is a report on work in progress, in which we consider the fate of one specific primordial field scenario, driven by pseudoscalar effects near the electroweak phase transition. We argue that such a scenario has a number of attractive features, although it is still uncertain whether a field of appropriate size can survive until late times.

  3. Magnetic Properties of Erbium Gallium Gallate under High Magnetic Field

    Institute of Scientific and Technical Information of China (English)

    Zhang Xijuan; Cheng Haiying; Yang Cuihong; Wang Wei

    2004-01-01

    A theoretical investigation on the magnetic properties of rare-earth Er3+ in Er3 Ga5 O12 was reported. The average magnetic moments(M) for applied magnetic field H parallel to the [001 ], [ 100], [ 110], [ 111 ] direction was studied based on the quantum theory. Temperature dependence of the magnetic properties is analyzed for H applied parallel to the [ 100] and [ 111 ] crystallographic directions. The magnetization decreases with increasing temperature,showing good agreement with thermal effect. A strong anisotropy of the magnetization is found under high magnetic field, but when the magnetic field is small, M and H are proportional.

  4. Magnetic Field Observations at Purcell, Oklahoma Field Campaign Report

    Energy Technology Data Exchange (ETDEWEB)

    Chi, P. J. [Univ. of California, Los Angeles, CA (United States); Gibson, J. P. [Univ. of Oklahoma, Norman, OK (United States)

    2017-05-01

    The campaign “Magnetic Field Observations at Purcell, Oklahoma” installed a ground-based magnetometer at Purcell’s U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility boundary installation at the Kessler Atmospheric and Ecological Field Station, University of Oklahoma, to measure local magnetic field variations. It is a part of the nine stations of the Mid-continent MAgnetoseismic Chain (McMAC) placed as close to the 330° magnetic longitude as possible. This is the meridian in the world where land covers the greatest continuous range in magnetic latitude. Figure 1 shows the map of the magnetometer stations along the 330th magnetic meridian, including the Purcell (PCEL) station. The main scientific objective of the campaign is to detect the field line resonance (FLR) frequencies of the magnetic field line connected to the Purcell station. This magnetic field line extends from Purcell to the outer space at distances as far as 2 Earth radii (RE). To accurately identify FLR frequencies, however, simultaneous measurements at slightly different latitudes along the same meridian are necessary to allow the use of the cross-phase technique. This consideration explains the arrangement to operate magnetometers at the Americus (AMER) and Richardson (RICH) stations nearby. The measured resonant frequency can infer the plasma mass density along the field line through the method of normal-mode magnetoseismology. The magnetometer at the Purcell station can detect many other types of magnetic field fluctuations associated with the changes in the electric currents in the ionosphere and the magnetosphere, which by large are affected by the solar activity. In other words, the magnetic field data collected by this campaign are also useful for understanding space weather phenomena. The magnetometer was installed at Purcell’s ARM boundary facility in March 27, 2006. The construction of the triaxial fluxgate magnetometer used by the

  5. Electro-Mechanical Resonant Magnetic Field Sensor

    CERN Document Server

    Temnykh, A B; Temnykh, Alexander B.; Lovelace, Richard V. E.

    2002-01-01

    We describe a new type of magnetic field sensor which is termed an Electro-Mechanical Resonant Sensor (EMRS). The key part of this sensor is a small conductive elastic element with low damping rate and therefore a high Q fundamental mode of frequency $f_1$. An AC current is driven through the elastic element which, in the presence of a magnetic field, causes an AC force on the element. When the frequency of the AC current matches the resonant frequency of the element, maximum vibration of the element occurs and this can be measured precisely by optical means. We have built and tested a model sensor of this type using for the elastic element a length of copper wire of diameter 0.030 mm formed into a loop shape. The wire motion was measured using a light emitting diode photo-transistor assembly. This sensor demonstrated a sensitivity better than 0.001G for an applied magnetic field of $ \\sim 1$G and a good selectivity for the magnetic field direction. The sensitivity can be easily improved by a factor of $\\sim ...

  6. New approaches in the design of magnetic tweezers-current magnetic tweezers

    Science.gov (United States)

    Bessalova, Valentina; Perov, Nikolai; Rodionova, Valeria

    2016-10-01

    The main advantages of the magnetic tweezers are the low price and simplicity of use. However the range of their application is reduced due to shortcomings like, for example, the remanent induction of the core and interaction between ferromagnetic cores. We present the new design of magnetic tweezers-Current Magnetic Tweezers (CMT) that allow particle manipulation by means of the magnetic field generated by the electric currents flowing through the non-magnetic wires. Arranging wires in different geometric shapes allows the particle movement either in two or three dimensions. Forces acting on the magnetic particles with the magnetic moment of 2·10-11 A m2 at distances up to 1 mm had been experimentally measured. It is established that a current of about 1 A at a 1 mm distance generates force of (approximately) 3 pN which is consistent with theoretical estimates.

  7. Modeling and analysis of magnetic dipoles in weak magnetic field

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The magnetic leakage field distribution resulting from linear defects of a tube sample in the geomagnetic field is modeled according to the magnetic dipole theory.The formula to compute the normal component of the weak magnetic field is deduced based on the spatial distribution of the magnetic dipole.The shape and characteristics of the zero line (an important criterion for magnetic memory testing) of the normal field is analyzed under different longitudinal magnetizations.Results show that the characteristics of the zero line should be considered when the metal magnetic memory testing method is used to find and locate the defect.

  8. How does relativity affect magnetically induced currents?

    Science.gov (United States)

    Berger, R J F; Repisky, M; Komorovsky, S

    2015-09-21

    Magnetically induced probability currents in molecules are studied in relativistic theory. Spin-orbit coupling (SOC) enhances the curvature and gives rise to a previously unobserved current cusp in AuH or small bulge-like distortions in HgH2 at the proton positions. The origin of this curvature is magnetically induced spin-density arising from SOC in the relativistic description.

  9. Anchoring Magnetic Field in Turbulent Molecular Clouds

    CERN Document Server

    Li, Hua-bai; Goodman, Alyssa; Hildebrand, Roger; Novak, Giles

    2009-01-01

    One of the key problems in star formation research is to determine the role of magnetic fields. Starting from the atomic inter-cloud medium (ICM) which has density nH ~ 1 per cubic cm, gas must accumulate from a volume several hundred pc across in order to form a typical molecular cloud. Star formation usually occurs in cloud cores, which have linear sizes below 1 pc and densities nH2 > 10^5 per cubic cm. With current technologies, it is hard to probe magnetic fields at scales lying between the accumulation length and the size of cloud cores, a range corresponds to many levels of turbulent eddy cascade, and many orders of magnitude of density amplification. For field directions detected from the two extremes, however, we show here that a significant correlation is found. Comparing this result with molecular cloud simulations, only the sub-Alfvenic cases result in field orientations consistent with our observations.

  10. Theoretical study of in-plane response of magnetic field sensor to magnetic beads magnetized by the sensor self-field

    DEFF Research Database (Denmark)

    Hansen, Troels Borum Grave; Damsgaard, Christian Danvad; Dalslet, Bjarke Thomas

    2010-01-01

    We present a theoretical study of the spatially averaged in-plane magnetic field on square and rectangular magnetic field sensors from a single magnetic bead, a monolayer of magnetic beads, and a half-space filled with magnetic beads being magnetized by the magnetic self-field due to the applied...... bias current through the sensor. The analysis of the single bead response shows that beads always contribute positively to the average magnetic field as opposed to the case for an applied homogeneous magnetic field where the sign of the signal depends on the bead position. General expressions...... and analytical approximations are derived for the sensor response to beads as function of the bead distribution, the bias current, the geometry and size of the sensor, and the bead characteristics. Consequences for the sensor design are exemplified and it is described how the contribution from the self...

  11. Galactic and intergalactic magnetic fields

    CERN Document Server

    Klein, Ulrich

    2014-01-01

    This course-tested textbook conveys the fundamentals of magnetic fields and relativistic plasma in diffuse cosmic media, with a primary focus on phenomena that have been observed at different wavelengths. Theoretical concepts are addressed wherever necessary, with derivations presented in sufficient detail to be generally accessible.In the first few chapters the authors present an introduction to various astrophysical phenomena related to cosmic magnetism, with scales ranging from molecular clouds in star-forming regions and supernova remnants in the Milky Way, to clusters of galaxies. Later c

  12. Magnetic Field Gradient Waveform Monitoring for Magnetic Resonance

    Science.gov (United States)

    Han, Hui

    Linear magnetic field gradients have played a central role in Magnetic Resonance Imaging (MRI) since Fourier Transform MRI was proposed three decades ago. Their primary function is to encode spatial information into MR signals. Magnetic field gradients are also used to sensitize the image contrast to coherent and/or incoherent motion, to selectively enhance an MR signal, and to minimize image artifacts. Modern MR imaging techniques increasingly rely on the implementation of complex gradient waveforms for the manipulation of spin dynamics. However, gradient system infidelities caused by eddy currents, gradient amplifier imperfections and group delays, often result in image artifacts and other errors (e.g., phase and intensity errors). This remains a critical problem for a wide range of MRI techniques on modern commercial systems, but is of particular concern for advanced MRI pulse sequences. Measuring the real magnetic field gradients, i.e., characterizing eddy currents, is critical to addressing and remedying this problem. Gradient measurement and eddy current calibration are therefore a general topic of importance to the science of MRI. The Magnetic Field Gradient Monitor (MFGM) idea was proposed and developed specifically to meet these challenges. The MFGM method is the heart of this thesis. MFGM methods permit a variety of magnetic field gradient problems to be investigated and systematically remedied. Eddy current effects associated with MR compatible metallic pressure vessels were analyzed, simulated, measured and corrected. The appropriate correction of eddy currents may enable most MR/MRI applications with metallic pressure vessels. Quantitative imaging (1D/2D) with model pressure vessels was successfully achieved by combining image reconstruction with MFGM determined gradient waveform behaviour. Other categories of MR applications with metallic vessels, including diffusion measurement and spin echo SPI T2 mapping, cannot be realized solely by MFGM guided

  13. Magnetic fields and density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Salsbury Jr., Freddie [Univ. of California, Berkeley, CA (United States)

    1999-02-01

    A major focus of this dissertation is the development of functionals for the magnetic susceptibility and the chemical shielding within the context of magnetic field density functional theory (BDFT). These functionals depend on the electron density in the absence of the field, which is unlike any other treatment of these responses. There have been several advances made within this theory. The first of which is the development of local density functionals for chemical shieldings and magnetic susceptibilities. There are the first such functionals ever proposed. These parameters have been studied by constructing functionals for the current density and then using the Biot-Savart equations to obtain the responses. In order to examine the advantages and disadvantages of the local functionals, they were tested numerically on some small molecules.

  14. Ideas on DC-DC Converters for Delivery of Low Voltage and High Currents for the SLHC / ILC Detector Electronics in Magnetic field and Radiation environments

    CERN Document Server

    Dhawan, Satish; Neal, H; Sumner, R; Weber, M; Weber, R

    2007-01-01

    For more efficient power transport to the electronics embedded inside large colliding beam detectors, we explore the feasibility of supplying 48 Volts DC and using local DCDC conversion to 2 V (or lower, depending upon on the lithography of the embedded electronics) using switch mode regulators located very close to the front end electronics. These devices will be exposed to high radiation and high magnetic fields, 10 – 100 Mrads and 2 - 4 Tesla at the SLHC, and 20 Krads and 6 Tesla at the ILC.

  15. Collisionless reconnection: magnetic field line interaction

    Directory of Open Access Journals (Sweden)

    R. A. Treumann

    2012-10-01

    Full Text Available Magnetic field lines are quantum objects carrying one quantum Φ0 = 2πh/e of magnetic flux and have finite radius λm. Here we argue that they possess a very specific dynamical interaction. Parallel field lines reject each other. When confined to a certain area they form two-dimensional lattices of hexagonal structure. We estimate the filling factor of such an area. Anti-parallel field lines, on the other hand, attract each other. We identify the physical mechanism as being due to the action of the gauge potential field, which we determine quantum mechanically for two parallel and two anti-parallel field lines. The distortion of the quantum electrodynamic vacuum causes a cloud of virtual pairs. We calculate the virtual pair production rate from quantum electrodynamics and estimate the virtual pair cloud density, pair current and Lorentz force density acting on the field lines via the pair cloud. These properties of field line dynamics become important in collisionless reconnection, consistently explaining why and how reconnection can spontaneously set on in the field-free centre of a current sheet below the electron-inertial scale.

  16. Stress Field of Straight Edge Dislocation in Magnetic Field

    Institute of Scientific and Technical Information of China (English)

    LIU Zhao-long; HU Hai-yun; FAN Tian-you

    2007-01-01

    To study the changes in mechanical properties of materials within magnetic fields and the motion of dislocations,stress fields of dislocation in magnetic field need to be calculated.The straight edge dislocation is of basic importance in various defects.The stress field of straight edge dislocation in an external static magnetic field is determined by the theory of elasticity and electrodynamics according to the Volterra dislocation model for continuous media.This reduces to the known stress field when the magnet field is zero.The results can be used for further study on the strain energy of dislocations and the interactions between dislocations in magnetic fields.

  17. Diagnosis of solar chromospheric magnetic field

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Hongqi(张洪起)

    2002-01-01

    This paper discusses the measurements of the chromospheric magnetic field and the spatial configuration of the field at the lower solar atmosphere inferred by the distribution of the solar photospheric and chromospheric magnetic fields. Some questions in the study of the chromospheric magnetic field are also presented.

  18. Coronal Magnetic Flux Ropes in Quadrupolar Magnetic Fields

    Science.gov (United States)

    Zhang, Yingzhi; Hu, Youqiu; Wang, Jingxiu

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

  19. Magnetic field evolution in magnetar crusts through three dimensional simulations

    CERN Document Server

    Gourgouliatos, Konstantinos N; Hollerbach, Rainer

    2016-01-01

    Current models of magnetars require extremely strong magnetic fields to explain their observed quiescent and bursting emission, implying that the field strength within the star's outer crust is orders of magnitude larger than the dipole component inferred from spin-down measurements. This presents a serious challenge to theories of magnetic field generation in a proto-neutron star. Here, we present detailed modelling of the evolution of the magnetic field in the crust of a neutron star through 3-D simulations. We find that, in the plausible scenario of equipartition of energy between global-scale poloidal and toroidal magnetic components, magnetic instabilities transfer energy to non-axisymmetric, kilometre-sized magnetic features, in which the local field strength can greatly exceed that of the global-scale field. These intense small-scale magnetic features can induce high energy bursts through local crust yielding, and the localised enhancement of Ohmic heating can power the star's persistent emission. Thus...

  20. A Vorticity-Magnetic Field Dynamo Instability

    OpenAIRE

    1997-01-01

    We generalize the mean field magnetic dynamo to include local evolution of the mean vorticity in addition to the mean magnetic field. The coupled equations exhibit a general mean field dynamo instability that enables the transfer of turbulent energy to the magnetic field and vorticity on larger scales. The growth of the vorticity and magnetic field both require helical turbulence which can be supplied by an underlying global rotation. The dynamo coefficients are derived including the backreac...

  1. A Study of Thermocurrent Induced Magnetic Fields in ILC Cavities

    Energy Technology Data Exchange (ETDEWEB)

    Crawford, Anthony C. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Cooley, Victoria [Univ. of Wisconsin, Madison, WI (United States)

    2014-03-31

    The case of axisymmetric ILC-type cavities with titanium helium vessels is investigated. A first-order estimate for magnetic field within the SRF current layer is presented. The induced magnetic field is found to be not more than 1.4x10-8 Tesla = 0.14 milligauss for the case of axial symmetry. Magnetic fields due to symmetry breaking effects are discussed.

  2. A Study of Thermocurrent Induced Magnetic Fields in ILC Cavities

    Energy Technology Data Exchange (ETDEWEB)

    Crawford, Anthony C. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Cooley, Victoria [Univ. of Wisconsin, Madison, WI (United States)

    2014-03-31

    The case of axisymmetric ILC type cavities with titanium helium vessels is investigated. A first order estimate for magnetic field within the SRF current layer is presented. The induced magnetic field is found to be not more than 1.4x10-8 Tesla = 0.14 milligauss for the case of axial symmetry. Magnetic fields due to symmetry breaking effects are discussed.

  3. Permanent Magnet Eddy Current Loss Analysis of a Novel Motor Integrated Permanent Magnet Gear

    DEFF Research Database (Denmark)

    Zhang, Yuqiu; Lu, Kaiyuan; Ye, Yunyue

    2012-01-01

    In this paper, a new motor integrated permanent magnet gear (MIPMG) is discussed. The focus is on eddy current loss analysis associated to permanent magnets (PMs). A convenient model of MIPMG is provided based on 2-D field-motion coupled time-stepping finite element method for transient eddy...

  4. Solar and stellar magnetic fields and atmospheric structures - Theory

    Science.gov (United States)

    Parker, E. N.

    1989-01-01

    Theoretical understanding of the role of magnetic fields in the formation of solar atmospheric structure is reviewed. The origin of the solar magnetic field, the dynamical behavior of the azimuthal field in the convective zone, the fibril state of the field in the photosphere, the formation of sunspots and prominences, and the spontaneous formation of current sheets in the bipolar field above the solar surface are addressed. The relation of the latter to coronal heating and flare formation is considered.

  5. Field and Thermal Characteristics of Magnetizing Fixture

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    This paper describes field modeling and thermal modeling for magnetizing fixture. As the detailed characteristics of magnetizing fixture can be obtained, the efficient design of magnetizer which produce desired magnet will be possible using our modeling. For field modeling finite-element analysis is used as part of the design and analysis process for magnetizing fixture. The thermal modeling method of magnetizing fixture resistor uses multi-lumped model with equivalent thermal resistance and thermal capacitance.

  6. Magnetic fields for fluid motion.

    Science.gov (United States)

    Weston, Melissa C; Gerner, Matthew D; Fritsch, Ingrid

    2010-05-01

    Three forces induced by magnetic fields offer unique control of fluid motion and new opportunities in microfluidics. This article describes magnetoconvective phenomena in terms of the theory and controversy, tuning by redox processes at electrodes, early-stage applications in analytical chemistry, mature applications in disciplines far afield, and future directions for micro total analysis systems. (To listen to a podcast about this article, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html .).

  7. GUIDING OF PLASMA BY ELECTRIC FIELD AND MAGNETIC FIELD

    Institute of Scientific and Technical Information of China (English)

    ZHANG TAO; HOU JUN-DA; TANG BAO-YIN; P. K. CHU; I. G. BROWN

    2001-01-01

    The relationship between the transported ion current and the cathodic arc current is determined in a vacuum arc plasma source equipped with a curved magnetic filter. Our results suggest that the outer and inner walls of the duct interact with the plasma independently. The duct magnetic field is a critical factor of the plasma output. The duct transport efficiency is to maximize at a value of bias plate voltage in the range +10 V to +20 V, and independent (within our limit of measurement) of the magnetic field strength in the duct. The plasma flux is composed of two components:a diffusion flux in the transverse direction due to particle collisions, and a drift flux due to the ion inertia. The inner wall of the magnetic duct sees only the diffusion flux while the outer wall receives both fluxes. Thus, applying a positive potential to the outer duct wall can reflect the ions and increase the output current. Our experimental data also show that biasing both sides of the duct is more effective than biasing the outer wall alone.

  8. Deformation of Water by a Magnetic Field

    Science.gov (United States)

    Chen, Zijun; Dahlberg, E. Dan

    2011-03-01

    After the discovery that superconducting magnets could levitate diamagnetic objects,1,2 researchers became interested in measuring the repulsion of diamagnetic fluids in strong magnetic fields,3-5 which was given the name "The Moses Effect."5 Both for the levitation experiments and the quantitative studies on liquids, the large magnetic fields necessary were produced by superconducting magnets.

  9. Braided magnetic fields: equilibria, relaxation and heating

    CERN Document Server

    Pontin, D I; Russell, A J B; Hornig, G

    2015-01-01

    We examine the dynamics of magnetic flux tubes containing non-trivial field line braiding (or linkage), using mathematical and computational modelling. The key results obtained from recent modelling efforts are summarised, in the context of testable predictions for the laboratory. We discuss the existence of braided force-free equilibria, and demonstrate that for a field anchored at perfectly-conducting plates, these equilibria exist and contain current sheets whose thickness scales inversely with the braid complexity - as measured for example by the topological entropy. By contrast, for a periodic domain braided exact equilibria typically do not exist, while approximate equilibria contain thin current sheets. In the presence of resistivity, reconnection is triggered at the current sheets and a turbulent relaxation ensues. We discuss the properties of this relaxation, and in particular the existence of constraints that may mean that the final state is not the linear force-free field predicted by Taylor's hypo...

  10. Currents between tethered electrodes in a magnetized laboratory plasma

    Science.gov (United States)

    Stenzel, R. L.; Urrutia, J. M.

    1989-01-01

    Laboratory experiments on important plasma physics issues of electrodynamic tethers were performed. These included current propagation, formation of wave wings, limits of current collection, nonlinear effects and instabilities, charging phenomena, and characteristics of transmission lines in plasmas. The experiments were conducted in a large afterglow plasma. The current system was established with a small electron-emitting hot cathode tethered to an electron-collecting anode, both movable across the magnetic field and energized by potential difference up to V approx.=100 T(sub e). The total current density in space and time was obtained from complete measurements of the perturbed magnetic field. The fast spacecraft motion was reproduced in the laboratory by moving the tethered electrodes in small increments, applying delayed current pulses, and reconstructing the net field by a linear superposition of locally emitted wavelets. With this technique, the small-amplitude dc current pattern is shown to form whistler wings at each electrode instead of the generally accepted Alfven wings. For the beam electrode, the whistler wing separates from the field-aligned beam which carries no net current. Large amplitude return currents to a stationary anode generate current-driven microinstabilities, parallel electric fields, ion depletions, current disruptions and time-varying electrode charging. At appropriately high potentials and neutral densities, excess neutrals are ionized near the anode. The anode sheath emits high-frequency electron transit-time oscillations at the sheath-plasma resonance. The beam generates Langmuir turbulence, ion sound turbulence, electron heating, space charge fields, and Hall currents. An insulated, perfectly conducting transmission line embedded in the plasma becomes lossy due to excitation of whistler waves and magnetic field diffusion effects. The implications of the laboratory observations on electrodynamic tethers in space are discussed.

  11. Current-driven filamentation upstream of magnetized relativistic collisionless shocks

    CERN Document Server

    Lemoine, M; Gremillet, L; Plotnikov, I

    2014-01-01

    The physics of instabilities in the precursor of relativistic collisionless shocks is of broad importance in high energy astrophysics, because these instabilities build up the shock, control the particle acceleration process and generate the magnetic fields in which the accelerated particles radiate. Two crucial parameters control the micro-physics of these shocks: the magnetization of the ambient medium and the Lorentz factor of the shock front; as of today, much of this parameter space remains to be explored. In the present paper, we report on a new instability upstream of electron-positron relativistic shocks and we argue that this instability shapes the micro-physics at moderate magnetization levels and/or large Lorentz factors. This instability is seeded by the electric current carried by the accelerated particles in the shock precursor as they gyrate around the background magnetic field. The compensation current induced in the background plasma leads to an unstable configuration, with the appearance of ...

  12. Acceleration of magnetic dipoles by the sequence of current turns

    CERN Document Server

    Dolya, S N

    2014-01-01

    Acceleration of magnetic dipoles is carried out by the running gradient of the magnetic field formed while sequent switching on the current turns. Magnetic dipoles, with a diameter of sixty millimeters and full length one meter, are pre-accelerated by using the gas-dynamic method to speed one kilometer per second, corresponding to the injection rate into the main accelerator. To prevent the turning of the dipoles by one hundred eighty degrees in the field of the accelerating pulse and focus them, the magnetic dipoles are accelerated inside the titanium tube. The magnetic dipoles have mass two kilograms and acquire the finite speed five kilometers per second on the acceleration length three hundreds meters.

  13. Passive Magnetic Shielding in Gradient Fields

    CERN Document Server

    Bidinosti, C P

    2013-01-01

    The effect of passive magnetic shielding on dc magnetic field gradients imposed by both external and internal sources is studied. It is found that for concentric cylindrical or spherical shells of high permeability material, higher order multipoles in the magnetic field are shielded progressively better, by a factor related to the order of the multipole. In regard to the design of internal coil systems for the generation of uniform internal fields, we show how one can take advantage of the coupling of the coils to the innermost magnetic shield to further optimize the uniformity of the field. These results demonstrate quantitatively a phenomenon that was previously well-known qualitatively: that the resultant magnetic field within a passively magnetically shielded region can be much more uniform than the applied magnetic field itself. Furthermore we provide formulae relevant to active magnetic compensation systems which attempt to stabilize the interior fields by sensing and cancelling the exterior fields clos...

  14. Magnetic Field Reentrant Superconductivity in Aluminum Nanowires

    Science.gov (United States)

    Bretz-Sullivan, Terence; Goldman, Allen

    Reentrance to the superconducting state through the application of a magnetic field to quasi-one dimensional superconductors driven resistive by current, is counter to the expected properties of superconductors. It was not until recently that a microscopic mechanism explaining the phenomenon was proposed in which superconductivity and phase slip driven dissipation coexist in a non-equilibrium state. Here we present additional results of magnetic field induced reentrance into the superconducting state in quasi-one-dimensional aluminum nanowires with an in-plane magnetic field both transverse to, and along the wire axis. The reentrant behavior is seen in the magnetic field dependence of the I-V characteristic and resistance vs. temperature, and in the wire's magnetoresistance at 450mK. This work was supported by DOE Basic Energy Sciences Grant DE-FG02-02ER46004. Samples were fabricated at the Minnesota Nanofabrication Center. Parts of this work were carried out in the University of Minnesota Characterization Facility, a member of the Materials Research Facilities Network (www.mrfn.org) funded via the NSF MRSEC program.

  15. Modeling Magnetic Fields with FEMM 3.1

    Science.gov (United States)

    Gumbart, James

    2003-03-01

    FEMM (Finite Element Method Magnetics) 3.1, a freeware program, is useful for modeling problems involving magnets, currents and magnetic fields. The applications of such a program involve both education and upper-level research. The program interface is intuitive and robust. As an educational tool, this program is useful because it handles internally the complicated equations needed to be solved when working with magnetism in matter. Since most elementary applications of magnetism involve permanent magnets, this program enables the user to calculate field energies and forces between magnets and magnetic materials, which would otherwise be impossible to obtain. An analysis of a popular physics demonstration, that of a diamagnetic-assisted levitating magnet, will be used to illustrate these concepts in more detail. The sensitivity of the equilibrium points to the spacing of the diamagnetic plates and the position of the upper attracting magnet is well-reproduced in this simulation.

  16. Effect of axial magnetic field on a 2.45 GHz permanent magnet ECR ion source

    Energy Technology Data Exchange (ETDEWEB)

    Nakamura, T., E-mail: tsubasa@oshima-k.ac.jp; Wada, H.; Furuse, M. [National Institute of Technology, Oshima College, 1091-1 Komatsu, Suouoshima, Oshima, Yamaguchi 742-2193 (Japan); Asaji, T. [National Institute of Technology, Toyama College, 13 Hongo, Toyama 939-8630 (Japan)

    2016-02-15

    Herein, we conduct a fundamental study to improve the generation efficiency of a multi-charged ion source using argon. A magnetic field of our electron cyclotron resonance ion source is composed of a permanent magnet and a solenoid coil. Thereby, the axial magnetic field in the chamber can be tuned. Using the solenoid coil, we varied the magnetic field strength in the plasma chamber and measured the ion beam current extracted at the electrode. We observed an approximately three times increase in the Ar{sup 4+} ion beam current when the magnetic field on the extractor-electrode side of the chamber was weakened. From our results, we can confirm that the multi-charged ion beam current changes depending on magnetic field intensity in the plasma chamber.

  17. Enhanced Cancer Cell (HeLa Killing Efficacy of Mixed Αlpha and Gamma Iron Oxide Superparamagnetic Nanoparticles under Combined AC (Alternating Current Magnetic-Field and Photoexcitation

    Directory of Open Access Journals (Sweden)

    Md. Shariful Islam, Yoshihumi Kusumoto, Md. Abdulla Al-Mamun and Yuji Horie

    2011-12-01

    Full Text Available We synthesized mixed α and γ-Fe2O3 nanoparticles and investigated their toxic effects against HeLa cells under induced AC (alternating current magnetic-fields and photoexcited conditions at room temperature. The findings revealed that the cell-killing percentage was increased with increasing dose for all types of treatments. Finally, 99% cancer cells were destructed at 1.2 mL dose when exposed to combined AC magnetic-field and photoexcited conditions (T3 whereas 89 and 83 % of HeLa cells were killed under only AC magnetic-field induced (T1 or only photoexcited (T2 condition at the same dose.ABSTRAK: Campuran α dan zarah γ-Fe2O3 bersaiz nano disintesiskan dan kesan toksidnya terhadap sel HeLa dikaji dibawah aruhan medan magnet arus ulang-alik (alternating current (AC dan keadaan photoexcited (proses ransangan atom atau molekul suatu bahan dengan penyerapan tenaga sinaran pada suhu bilik. Penemuan mendedahkan bahawa peratusan sel yang musnah bertambah dengan pertambahan dos untuk semua jenis rawatan. Akhirnya, 99% sel kanser dimusnahkan pada kadar dos 1.2mL setelah didedahkan terhadap kombinasi medan magnet AC dan keadaan photoexcited (T3 dimana 89% dan 83% sel HeLa dimusnahkan dengan hanya di bawah aruhan medan magnet AC (T1 atau hanya pada keadaan photoexcited (T2 pada kadar dos yang sama.KEY WORDS : Cancer, Hyperthermia, Iron oxide nanoparticles, Heat dissipation,    Cytotoxicity, HeLa cell.

  18. Relativistic Scott correction in self-generated magnetic fields

    DEFF Research Database (Denmark)

    Erdos, Laszlo; Fournais, Søren; Solovej, Jan Philip

    2012-01-01

    /3}$ and it is unchanged by including the self-generated magnetic field. We prove the first correction term to this energy, the so-called Scott correction of the form $S(\\alpha Z) Z^2$. The current paper extends the result of \\cite{SSS} on the Scott correction for relativistic molecules to include a self......-generated magnetic field. Furthermore, we show that the corresponding Scott correction function $S$, first identified in \\cite{SSS}, is unchanged by including a magnetic field. We also prove new Lieb-Thirring inequalities for the relativistic kinetic energy with magnetic fields....

  19. The free energies of partially open coronal magnetic fields

    Science.gov (United States)

    Low, B. C.; Smith, D. F.

    1993-01-01

    A simple model of the low corona is examined in terms of a static polytropic atmosphere in equilibrium with a global magnetic field. The question posed is whether magnetostatic states with partially open magnetic fields may contain magnetic energies in excess of those in fully open magnetic fields. Based on the analysis presented here, it is concluded that the cross-field electric currents in the pre-eruption corona are a viable source of the bulk of the energies in a mass ejection and its associated flare.

  20. Periodical Plasma Structures Controlled by Oblique Magnetic Field

    CERN Document Server

    Schweigert, Irina

    2016-01-01

    The propulsion type plasma in oblique external magnetic field is studied in 2D3V PIC MCC simulations. A periodical structure with maxima of electron and ion densities appears with an increase of an obliqueness of magnetic field. These ridges of electron and ion densities are aligned with the magnetic field vector and shifted relative each other. As a result the two-dimensional double-layers structure forms in cylindrical plasma chamber. The ion and electron currents on the side wall are essential modulated by the oblique magnetic field.

  1. Toroidal and poloidal magnetic fields at Venus. Venus Express observations

    Science.gov (United States)

    Dubinin, E.; Fraenz, M.; Woch, J.; Zhang, T. L.; Wei, Y.; Fedorov, A.; Barabash, S.; Lundin, R.

    2013-10-01

    Magnetic field and plasma measurements carried out onboard Venus Express during solar minimum conditions suggest the existence of two kinds of magnetic field configuration in the Venusian ionosphere. We interpret these as the manifestation of two different types of generation mechanisms for the induced magnetosphere. A different magnetic field topology (toroidal and poloidal) arises if the induced currents are driven either by the solar wind motional electric field or by the Faraday electric field—a conducting ionosphere sees the magnetic field carried by solar wind as a time-varying field. At the dayside, both driving agents produce a similar draping pattern of the magnetic field. However, different magnetic field signatures inherent to both induction mechanisms appear at lower altitudes in the terminator region. The conditions at low solar EUV flux when the ionosphere of Venus becomes magnetized seem to be favorable to distinguish between two different types of the induced fields. We present cases of both types of the magnetic field topology. The cases when the effects of the Faraday induction become well noticeable are especially interesting since they provide us with an example of solar wind interaction with a tiny induced dipole field immersed into the ionosphere. Another interesting case when poloidal magnetic fields are evidently displayed is observed when the IMF vector is almost aligned with the solar wind velocity. In general case, both mechanisms of induction probably complement each other.

  2. Magnetic field perturbartions in closed-field-line systems with zero toroidal magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Mauel, M; Ryutov, D; Kesner, J

    2003-12-02

    In some plasma confinement systems (e.g., field-reversed configurations and levitated dipoles) the confinement is provided by a closed-field-line poloidal magnetic field. We consider the influence of the magnetic field perturbations on the structure of the magnetic field in such systems and find that the effect of perturbations is quite different from that in the systems with a substantial toroidal field. In particular, even infinitesimal perturbations can, in principle, lead to large radial excursions of the field lines in FRCs and levitated dipoles. Under such circumstances, particle drifts and particle collisions may give rise to significant neoclassical transport. Introduction of a weak regular toroidal magnetic field reduces radial excursions of the field lines and neoclassical transport.

  3. Neutrino-pair emission in a strong magnetic field

    NARCIS (Netherlands)

    van Dalen, ENE; Dieperink, AEL; Sedrakian, A; Timmermans, RGE

    2000-01-01

    We study the neutrino emissivity of strongly magnetized neutron stars due to the charged and neutral current couplings of neutrinos to baryons in strong magnetic fields. The leading order neutral current process is the one-body neutrino-pair bremsstrahlung, which does not have an analogue in the zer

  4. Bats respond to very weak magnetic fields.

    Directory of Open Access Journals (Sweden)

    Lan-Xiang Tian

    Full Text Available How animals, including mammals, can respond to and utilize the direction and intensity of the Earth's magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5th of the natural intensity (i.e., 10 μT; the lowest field strength tested here, the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 μT, despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (P<0.05. Hence, N. plancyi is able to detect the direction of a magnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth's magnetic field strength varied and the polarity reversed tens of times over the past fifty million years.

  5. Hybrid Shielding for Magnetic Fields

    Science.gov (United States)

    Mullins, David; Royal, Kevin

    2017-01-01

    Precision symmetry measurements such as the search for the electric dipole moment of the neutron require magnetic shielding rooms to reduce the ambient field to the pT scale. The massive mu-metal sheets and large separation between layers make these shield rooms bulky and expensive. Active field cancellation systems used to reduce the surrounding field are limited in uniformity of cancellation. A novel approach to reducing the space between shield layers and increasing the effectiveness of active cancellation is to combine the two systems into a hybrid system, with active and passive layers interspersed. We demonstrate this idea in a prototype with an active layer sandwiched between two passive layers of shielding.

  6. Experimental identification of an azimuthal current in a magnetic nozzle of a radiofrequency plasma thruster

    Science.gov (United States)

    Takahashi, Kazunori; Chiba, Aiki; Komuro, Atsushi; Ando, Akira

    2016-10-01

    The azimuthal plasma current in a magnetic nozzle of a radiofrequency plasma thruster is experimentally identified by measuring the plasma-induced magnetic field. The axial plasma momentum increases over about 20 cm downstream of the thruster exit due to the Lorentz force arising from the azimuthal current. The measured current shows that the azimuthal current is given by the sum of the electron diamagnetic drift and \\mathbf{E}× \\mathbf{B} drift currents, where the latter component decreases with an increase in the magnetic field strength; hence the azimuthal current approaches the electron diamagnetic drift one for the strong magnetic field. The Lorentz force calculated from the measured azimuthal plasma current and the radial magnetic field is smaller than the directly measured force exerted to the magnetic field, which indicates the existence of a non-negligible Lorentz force in the source tube.

  7. Effects of magnetic field on fluidization properties of magnetic pearls

    Institute of Scientific and Technical Information of China (English)

    Maoming Fan; Zhenfu Luo; Yuemin Zhao; Qingru Chen; Daniel Tao; Xiuxiang Tao; Zhenqiang Chen

    2007-01-01

    An experimental study of the influence of external magnetic field on the fluidization behavior of magnetic pearls was carried out. Magnetic pearls are a magnetic form of iron oxide that mainly consists of Fe2O3 which are recovered from a high-volume power plant fly ash from pulverized coal combustion. Due to its abundance, low price and particular physical and chemical properties, magnetic pearls can be used as a heavy medium for minerals or solid waste dry separation based on density difference. This paper introduces the properties of magnetic pearls and compares the performance of magnetic pearls fluidised bed operation with or without an external magnetic field. Experimental results show that an external magnetic field significantly improves the fluidization performance of magnetic pearls such as uniformity and stability.

  8. Magnetic Helicity and Large Scale Magnetic Fields: A Primer

    CERN Document Server

    Blackman, Eric G

    2014-01-01

    Magnetic fields of laboratory, planetary, stellar, and galactic plasmas commonly exhibit significant order on large temporal or spatial scales compared to the otherwise random motions within the hosting system. Such ordered fields can be measured in the case of planets, stars, and galaxies, or inferred indirectly by the action of their dynamical influence, such as jets. Whether large scale fields are amplified in situ or a remnant from previous stages of an object's history is often debated for objects without a definitive magnetic activity cycle. Magnetic helicity, a measure of twist and linkage of magnetic field lines, is a unifying tool for understanding large scale field evolution for both mechanisms of origin. Its importance stems from its two basic properties: (1) magnetic helicity is typically better conserved than magnetic energy; and (2) the magnetic energy associated with a fixed amount of magnetic helicity is minimized when the system relaxes this helical structure to the largest scale available. H...

  9. Interaction between two magnetic dipoles in a uniform magnetic field

    Directory of Open Access Journals (Sweden)

    J. G. Ku

    2016-02-01

    Full Text Available A new formula for the interaction force between two magnetic dipoles in a uniform magnetic field is derived taking their mutual magnetic interaction into consideration and used to simulate their relative motion. Results show that when the angle β between the direction of external magnetic field and the centerline of two magnetic dipoles is 0 ° or 90 °, magnetic dipoles approach each other or move away from each other in a straight line, respectively. And the time required for them to contact each other from the initial position is related to the specific susceptibility and the diameter of magnetic particles, medium viscosity and magnetic field strength. When β is between 0 ° and 90 °, magnetic dipole pair performs approximate elliptical motion, and the motion trajectory is affected by the specific susceptibility, diameter and medium viscosity but not magnetic field strength. However, time required for magnetic dipoles to complete the same motion trajectory is shorter when adopting stronger magnetic field. Moreover, the subsequent motion trajectory of magnetic dipoles is ascertained once the initial position is set in a predetermined motion trajectory. Additionally, magnetic potential energy of magnetic dipole pairs is transformed into kinetic energy and friction energy during the motion.

  10. Parafermion Fields Constructed by Current Algebra

    Institute of Scientific and Technical Information of China (English)

    YANGZhan-Ying; SHIKang-Jie; WANGPei; ZHAOLiu

    2004-01-01

    In this letter, the parafermion fields constructed by current algebra are considered. It is proved that there must be a parafermion field with respect to each form of current algebra. We also obtain the corresponding representation and unitary relation of the parafermion field from any current algebra.

  11. Effective magnetic moment of neutrinos in strong magnetic fields

    CERN Document Server

    Pérez, A; Masood, S S; Gaitan, R; Rodríguez, S

    2002-01-01

    In this paper we compute the effective magnetic moment of neutrinos propagating in dense high magnetized medium. Taking typical values of magnetic field and densities of astrophysical objects (such as the cores of supernovae and neutron stars) we obtain an effective type of dipole magnetic moment in agreement with astrophysical and cosmological bounds. (Author)

  12. Stark-induced anapole magnetic fields in n=2 hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, Robert R. [Department of Physics UM, Ann Arbor MI 48109 (United States); Gongora-T, A. [Instituto de Fisica UNAM, 01000 Mexico DF (Mexico)

    1998-08-28

    This paper presents results for the anapole magnetic field moment due to the mixing of states with opposite parity in the n=2 hydrogen atom in an external constant electric field. The evaluation of the current densities of the four n=2 states is carried out to first order in the field strength. These current densities and their associated magnetic fields are expanded in multipoles, including both the ordinary poloidal and the toroidal fields. The dominant contribution to the toroidal dipole (anapole) magnetic field comes from the strong mixing of the degenerate 2S, 2P states within the n=2 shell. A brief discussion is also presented of the electronic scattering from the anapole field of a Rydberg atom. The experimental conditions under which the atomic anapole field could be detected are critically considered, in particular, in terms of the quasi-resonant dependence of the anapole field on the applied electric field. (author)

  13. Magnetic field penetration of erosion switch plasmas

    Science.gov (United States)

    Mason, Rodney J.; Jones, Michael E.; Grossmann, John M.; Ottinger, Paul F.

    1988-10-01

    Computer simulations demonstrate that the entrainment (or advection) of magnetic field with the flow of cathode-emitted electrons can constitute a dominant mechanism for the magnetic field penetration of erosion switch plasmas. Cross-field drift in the accelerating electric field near the cathode starts the penetration process. Plasma erosion propagates the point for emission and magnetic field injection along the cathode toward the load-for the possibility of rapid switch opening.

  14. Magnetic field reversals and galactic dynamos

    OpenAIRE

    2012-01-01

    We argue that global magnetic field reversals similar to those observed in the Milky Way occur quite frequently in mean-field galactic dynamo models that have relatively strong, random, seed magnetic fields that are localized in discrete regions. The number of reversals decreases to zero with reduction of the seed strength, efficiency of the galactic dynamo and size of the spots of the seed field. A systematic observational search for magnetic field reversals in a representative sample of spi...

  15. Current-voltage characteristics of Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+x}/Ag multifilamentary tapes in zero applied magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Crisan, A. [Institute of Cryogenics, University of Southampton, Southampton (United Kingdom); Institute of Physics and Technology of Materials, Bucharest (Romania); Miu, L.; Popa, S. [Institute of Physics and Technology of Materials, Bucharest (Romania); Yang, Y.; Beduz, C. [Institute of Cryogenics, University of Southampton, Southampton (United Kingdom)

    1997-05-01

    Current-voltage characteristics of multifilamentary Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+x}/Ag tapes (short samples) produced by the 'powder in tube' technique were measured at different temperatures close to the mean-field critical temperature, and inzero applied magnetic field. After performing the required corrections due to the current flowing in the silver matrix, the I-V curves were interpreted in terms of current-induced unbinding of the thermally created vortex-antivortex pairs. Two possible mechanisms for appearance of a finite critical current in zero applied magnetic field are discussed: the Jensen-Minnhagen quasi-two-dimensional (2D) approach, that takes into account the interlayer Josephson coupling, and a model of size limitation of vortex fluctuations. From our analysis, it seems that the latter model is more suitable for this kind of superconducting material, due probably to an accentuated intrinsic anisotropy. (author)

  16. Warm Magnetic Field Measurements of LARP HQ Magnet

    Energy Technology Data Exchange (ETDEWEB)

    Caspi, S; Cheng, D; Deitderich, D; Felice, H; Ferracin, P; Hafalia, R; Joseph, J; Lizarazo, J; Martchevskii, M; Nash, C; Sabbi, G L; Vu, C; Schmalzle, J; Ambrosio, G; Bossert, R; Chlachidze, G; DiMarco, J; Kashikhin, V

    2011-03-28

    The US-LHC Accelerator Research Program is developing and testing a high-gradient quadrupole (HQ) magnet, aiming at demonstrating the feasibility of Nb{sub 3}Sn technologies for the LHC luminosity upgrade. The 1 m long HQ magnet has a 120 mm bore with a conductor-limited gradient of 219 T/m at 1.9 K and a peak field of 15 T. HQ includes accelerator features such as alignment and field quality. Here we present the magnetic measurement results obtained at LBNL with a constant current of 30 A. A 100 mm long circuit-board rotating coil developed by FNAL was used and the induced voltage and flux increment were acquired. The measured b{sub 6} ranges from 0.3 to 0.5 units in the magnet straight section at a reference radius of 21.55 mm. The data reduced from the numerical integration of the raw voltage agree with those from the fast digital integrators.

  17. Relation between the ring current and the tail current during magnetic storms

    Directory of Open Access Journals (Sweden)

    V. V. Kalegaev

    2005-02-01

    Full Text Available We study the dynamics of the magnetospheric large-scale current systems during storms by using three different magnetospheric magnetic field models: the paraboloid, event-oriented, and Tsyganenko T01 models. We have modelled two storm events, one moderate storm on 25-26 June 1998, when Dst reached -120nT and one intense storm on 21-23 October 1999, when Dst dropped to -250nT. We compare the observed magnetic field from GOES 8, GOES 9, and GOES 10, Polar and Geotail satellites with the magnetic field given by the three models to estimate their reliability. All models demonstrated quite good agreement with observations. Since it is difficult to measure exactly the relative contributions from different current systems to the Dst index, we compute the contributions from ring, tail and magnetopause currents given by the three magnetic field models. We discuss the dependence of the obtained contributions to the Dst index in relation to the methods used in constructing the models. All models show a significant tail current contribution to the Dst index, comparable to the ring current contribution during moderate storms. The ring current becomes the major Dst source during intense storms.

  18. Slow mode shocks propagating in open and closed magnetic fields

    Institute of Scientific and Technical Information of China (English)

    吕建永; 魏奉思

    1999-01-01

    A 2-D MHD model is used to investigate the propagation of slow mode shocks in the open and closed magnetic fields of the meridional plane near the sun. The solutions demonstrate that a forward slow shock could retain its slow shock characteristics into interplanetary space in the magnetically open region; however, it can evolve into an intermediate shock through the helmet-type current sheet to the open magnetic field.

  19. Exact temporal eddy current compensation in magnetic resonance imaging systems.

    Science.gov (United States)

    Morich, M A; Lampman, D A; Dannels, W R; Goldie, F D

    1988-01-01

    A step-response method has been developed to extract the properties (amplitudes and decay time constants) of intrinsic-eddy-current-sourced magnetic fields generated in whole-body magnetic resonance imaging systems when pulsed field gradients are applied. Exact compensation for the eddy-current effect is achieved through a polynomial rooting procedure and matrix inversion once the 2 N properties of the N-term decay process are known. The output of the inversion procedure yields the required characteristics of the filter for spectrum magnitude and phase equalization. The method is described for the general case along with experimental results for one-, two-, and three-term inversions. The method's usefulness is demonstrated for the usually difficult case of long-term (200-1000-ms) eddy-current compensation. Field-gradient spectral flatness measurements over 30 mHz-100 Hz are given to validate the method.

  20. The origin, evolution and signatures of primordial magnetic fields.

    Science.gov (United States)

    Subramanian, Kandaswamy

    2016-07-01

    The universe is magnetized on all scales probed so far. On the largest scales, galaxies and galaxy clusters host magnetic fields at the micro Gauss level coherent on scales up to ten kpc. Recent observational evidence suggests that even the intergalactic medium in voids could host a weak  ∼  10(-16) Gauss magnetic field, coherent on Mpc scales. An intriguing possibility is that these observed magnetic fields are a relic from the early universe, albeit one which has been subsequently amplified and maintained by a dynamo in collapsed objects. We review here the origin, evolution and signatures of primordial magnetic fields. After a brief summary of magnetohydrodynamics in the expanding universe, we turn to magnetic field generation during inflation and phase transitions. We trace the linear and nonlinear evolution of the generated primordial fields through the radiation era, including viscous effects. Sensitive observational signatures of primordial magnetic fields on the cosmic microwave background, including current constraints from Planck, are discussed. After recombination, primordial magnetic fields could strongly influence structure formation, especially on dwarf galaxy scales. The resulting signatures on reionization, the redshifted 21 cm line, weak lensing and the Lyman-α forest are outlined. Constraints from radio and γ-ray astronomy are summarized. Astrophysical batteries and the role of dynamos in reshaping the primordial field are briefly considered. The review ends with some final thoughts on primordial magnetic fields.

  1. The origin, evolution and signatures of primordial magnetic fields

    Science.gov (United States)

    Subramanian, Kandaswamy

    2016-07-01

    The universe is magnetized on all scales probed so far. On the largest scales, galaxies and galaxy clusters host magnetic fields at the micro Gauss level coherent on scales up to ten kpc. Recent observational evidence suggests that even the intergalactic medium in voids could host a weak  ˜  10-16 Gauss magnetic field, coherent on Mpc scales. An intriguing possibility is that these observed magnetic fields are a relic from the early universe, albeit one which has been subsequently amplified and maintained by a dynamo in collapsed objects. We review here the origin, evolution and signatures of primordial magnetic fields. After a brief summary of magnetohydrodynamics in the expanding universe, we turn to magnetic field generation during inflation and phase transitions. We trace the linear and nonlinear evolution of the generated primordial fields through the radiation era, including viscous effects. Sensitive observational signatures of primordial magnetic fields on the cosmic microwave background, including current constraints from Planck, are discussed. After recombination, primordial magnetic fields could strongly influence structure formation, especially on dwarf galaxy scales. The resulting signatures on reionization, the redshifted 21 cm line, weak lensing and the Lyman-α forest are outlined. Constraints from radio and γ-ray astronomy are summarized. Astrophysical batteries and the role of dynamos in reshaping the primordial field are briefly considered. The review ends with some final thoughts on primordial magnetic fields.

  2. Generation of Cosmic Magnetic Fields at Recombination

    CERN Document Server

    Hogan, C J

    2000-01-01

    It is shown that the standard cosmological model predicts ab initio generation of large-scale cosmic magnetic fields at the epoch of recombination of the primeval plasma. Matter velocities dominated by coherent flows on a scale $L\\approx 50h^{-1}(1+z)^{-1}$ Mpc lead to a dipole of radiation flux in the frame of the moving matter. Thomson scattering of the radiation differentially accelerates the electrons and ions, creating large-scale coherent electric currents and magnetic fields. This process is analyzed using magnetohydrodynamic equations which include a modification of Ohm's law describing the effect of Thomson drag on the electrons. The field strength saturates near equipartition with the baryon kinetic energy density at $B\\simeq 5\\times 10^{-5}$G. Magnetic stresses significantly damp baryonic motions at the epoch of last scattering, reducing the predicted background radiation anisotropy at small angles and changing estimates of fitted cosmological parameters. The field at late times retains its large-s...

  3. Unsteady magnetic reconnection in laboratory experiments with current sheets

    Science.gov (United States)

    Frank, Anna

    2009-11-01

    According to present notion, unsteady magnetic reconnection in current sheets (CS) is basic to dramatic natural phenomena: solar and stellar flares, substorms in the Earth and other planetary magnetospheres, as well as to disruptive instabilities in tokamak plasmas. We present a review of laboratory experiments studying evolution of CS formed in 3D and 2D magnetic configurations with an X line, in the CS-3D device. Usually CS exists during an extended period in a metastable stage, without essential changes of its structure and parameters. Under certain conditions this stage may be suddenly interrupted by unsteady phase of magnetic reconnection, which manifests itself in a rapid change of the magnetic field topology, current redistribution, excitation of pulsed electric fields, and other dynamic effects. The unsteady phase results in effective conversion of magnetic energy into the energy of plasma and accelerated particles, and may finally bring about the CS disruption. In the context of the solar flares, a metastable CS is associated with a pre-flare situation, while CS disruption -- with the flare itself. The physical mechanisms triggering the unsteady magnetic reconnection in the laboratory produced current sheets are discussed. Supported by the Russian Foundation for Basic Research (project # 09-02-00971).

  4. Magnetic Fields Induced in the Solid Earth and Oceans

    DEFF Research Database (Denmark)

    Kuvshinov, Alexei; Olsen, Nils

    Electromagnetic induction in the Earth's interior is an important contributor to the near-Earth magnetic field. Oceans play a special role in the induction, due to their relatively high conductance of large lateral variability. Electric currents that generate secondary magnetic fields are induced...... in the oceans by two different sources: by time varying external magnetic fields, and by motion of the conducting ocean water through the Earth's main magnetic field. Significant progress in the accurate and detailed prediction of magnetic fields induced by these sources has been achieved during the last years......, utilizing realistic 3-D conductivity models of the oceans, crust and mantle. In addition to these improvements in the prediction of 3-D induction effects, much attention has been paid to identifying magnetic signals of oceanic origin in observatory and satellite data. During the talk we will present...

  5. Near-Field Magnetic Dipole Moment Analysis

    Science.gov (United States)

    Harris, Patrick K.

    2003-01-01

    This paper describes the data analysis technique used for magnetic testing at the NASA Goddard Space Flight Center (GSFC). Excellent results have been obtained using this technique to convert a spacecraft s measured magnetic field data into its respective magnetic dipole moment model. The model is most accurate with the earth s geomagnetic field cancelled in a spherical region bounded by the measurement magnetometers with a minimum radius large enough to enclose the magnetic source. Considerably enhanced spacecraft magnetic testing is offered by using this technique in conjunction with a computer-controlled magnetic field measurement system. Such a system, with real-time magnetic field display capabilities, has been incorporated into other existing magnetic measurement facilities and is also used at remote locations where transport to a magnetics test facility is impractical.

  6. Magnetic Fields from the Electroweak Phase Transition

    CERN Document Server

    Törnkvist, O

    1998-01-01

    I review some of the mechanisms through which primordial magnetic fields may be created in the electroweak phase transition. I show that no magnetic fields are produced initially from two-bubble collisions in a first-order transition. The initial field produced in a three-bubble collision is computed. The evolution of fields at later times is discussed.

  7. Topological insulator in a helicoidal magnetization field

    Science.gov (United States)

    Stagraczyński, S.; Chotorlishvili, L.; Dugaev, V. K.; Jia, C.-L.; Ernst, A.; Komnik, A.; Berakdar, J.

    2016-11-01

    A key feature of topological insulators is the robustness of the electron energy spectrum. At a surface of a topological insulator, the Dirac point is protected by the characteristic symmetry of the system. The breaking of the symmetry opens a gap in the energy spectrum. Therefore, topological insulators are very sensitive to magnetic fields, which can open a gap in the electronic spectrum. Concerning "internal" magnetic effects, for example, the situation with doped magnetic impurities, is not trivial. A single magnetic impurity is not enough to open the band gap, while in the case of a ferromagnetic chain of deposited magnetic impurities the Dirac point is lifted. However, a much more interesting case is when localized magnetic impurities form a chiral spin order. Our first principle density functional theory calculations have shown that this is the case for Fe deposited on the surface of a Bi2Se3 topological insulator. But not only magnetic impurities can form a chiral helicoidal spin texture. An alternative way is to use chiral multiferroics (prototype material is LiCu2O2 ) that induce a proximity effect. The theoretical approach we present here is valid for both cases. We observed that opposite to a ferromagnetically ordered case, a chiral spin order does not destroy the Dirac point. We also observed that the energy gap appears at the edges of the new Brillouin zone. Another interesting result concerns the spin dynamics. We derived an equation for the spin density dynamics with a spin current and relaxation terms. We have shown that the motion of the conductance electron generates a magnetic torque and exerts a certain force on the helicoidal texture.

  8. Strong and superstrong pulsed magnetic fields generation

    CERN Document Server

    Shneerson, German A; Krivosheev, Sergey I

    2014-01-01

    Strong pulsed magnetic fields are important for several fields in physics and engineering, such as power generation and accelerator facilities. Basic aspects of the generation of strong and superstrong pulsed magnetic fields technique are given, including the physics and hydrodynamics of the conductors interacting with the field as well as an account of the significant progress in generation of strong magnetic fields using the magnetic accumulation technique. Results of computer simulations as well as a survey of available field technology are completing the volume.

  9. Collisionless Magnetic Reconnection and Dynamo Processes in a Spatially Rotating Magnetic Field

    Science.gov (United States)

    Choe, Gwangson; Lee, Junggi

    2016-04-01

    Spatially rotating magnetic fields have been observed in the solar wind and in the Earth's magnetopause as well as in reversed field pinch (RFP) devices. Such field configurations have a similarity with extended current layers having a spatially varying plasma pressure instead of the spatially varying guide field. It is thus expected that magnetic reconnection may take place in a rotating magnetic field no less than in an extended current layer. We have investigated the spontaneous evolution of a collisionless plasma system embedding a rotating magnetic field with a two-and-a-half-dimensional electromagnetic particle-in-cell (PIC) simulation. It is found that a magnetic-flux-reducing diffusion phase and a magnetic-flux-increasing dynamo phase are alternating with a certain period. The temperature of the system also varies with the same period, showing a similarity to sawtooth oscillations in tokamaks. We have shown that a modified theory of sawtooth oscillations can explain the periodic behavior observed in the simulation. A strong guide field distorts the current layer as was observed in laboratory experiments. This distortion is smoothed out as magnetic islands fade away by the O-line diffusion, but is soon strengthened by the growth of magnetic islands. These processes are all repeating with a fixed period. Our results suggest that a rotating magnetic field configuration continuously undergoes deformation and relaxation in a short time-scale although it might look rather steady in a long-term view.

  10. Discrete Current Control Strategy of Permanent Magnet Synchronous Motors

    Directory of Open Access Journals (Sweden)

    Yan Dong

    2013-01-01

    Full Text Available A control strategy of permanent magnet synchronous motors (PMSMs, which is different from the traditional vector control (VC and direct torque control (DTC, is proposed. Firstly, the circular rotating magnetic field is analyzed on the simplified model and discredited into stepping magnetic field. The stepping magnetomotive force will drive the rotor to run as the stepping motor. Secondly, the stator current orientation is used to build the control model instead of rotor flux orientation. Then, the discrete current control strategy is set and adopted in positioning control. Three methods of the strategy are simulated in computer and tested on the experiment platform of PMSM. The control precision is also verified through the experiment.

  11. Magnetosphere-Ionosphere Coupling and Field-Aligned Currents

    CERN Document Server

    Oliveira, D M

    2015-01-01

    It is presented in this paper a review of one of several interactions between the magnetosphere and the ionosphere through the field-aligned currents (FACs). Some characteristics and physical implications of the currents flowing in a plane perpendicular to the magnetic field at high latitudes are discussed. The behavior of this system as an electric circuit is explained, where momentum and energy are transferred via Poynting flux from the magnetosphere into the ionosphere.

  12. Deformation of Water by a Magnetic Field

    Science.gov (United States)

    Chen, Zijun; Dahlberg, E. Dan

    2011-01-01

    After the discovery that superconducting magnets could levitate diamagnetic objects, researchers became interested in measuring the repulsion of diamagnetic fluids in strong magnetic fields, which was given the name "The Moses Effect." Both for the levitation experiments and the quantitative studies on liquids, the large magnetic fields necessary…

  13. High magnetic field test of bismuth Hall sensors for ITER steady state magnetic diagnostic

    Science.gov (United States)

    Duran, I.; Entler, S.; Kohout, M.; Kočan, M.; Vayakis, G.

    2016-11-01

    Performance of bismuth Hall sensors developed for the ITER steady state magnetic diagnostic was investigated for high magnetic fields in the range ±7 T. Response of the sensors to the magnetic field was found to be nonlinear particularly within the range ±1 T. Significant contribution of the planar Hall effect to the sensors output voltage causing undesirable cross field sensitivity was identified. It was demonstrated that this effect can be minimized by the optimization of the sensor geometry and alignment with the magnetic field and by the application of "current-spinning technique."

  14. Biological Effect of Magnetic Field in Mice

    Institute of Scientific and Technical Information of China (English)

    Zhao-Wei ZENG

    2005-01-01

    Objective: To study the biological effect of magnetic field in mice bodies. Method: With a piece of permanent magnet embeded in mice bodies beside the femoral artery and vein to measure the electrophoretic velocity(um/s). Result: The magnetic field in mice bodies on the experiment group that the electrophoretic velocity is faster more than control and free group.Conclusion:The magnetic field in animal's body can raise the negative electric charges on the surface of erythrocyte to improve the microcirculation, this is the biological effect of magnetic field.

  15. The Magnetic Field Effect on Planetary Nebulae

    Institute of Scientific and Technical Information of China (English)

    A. R. Khesali; K. Kokabi

    2006-01-01

    In our previous work on the 3-dimensional dynamical structure of planetary nebulae the effect of magnetic field was not considered. Recently Jordan et al. have directly detected magnetic fields in the central stars of some planetary nebulae. This discovery supports the hypothesis that the non-spherical shape of most planetary nebulae is caused by magnetic fields in AGB stars. In this study we focus on the role of initially weak toroidal magnetic fields embedded in a stellar wind in altering the shape of the PN. We found that magnetic pressure is probably influential on the observed shape of most PNe.

  16. Maximum trapped field of a ring bulk superconductor by low pulsed field magnetization

    Energy Technology Data Exchange (ETDEWEB)

    Tsuchimoto, M. [Hokkaido Institute of Technology, 7-15 Maeda, Teine-ku, Sapporo 006-8585 (Japan)], E-mail: tsuchi@hit.ac.jp; Kamijo, H. [Railway Technical Research Institute, 2-8-38, Hikari-cho, Kokubunji, Tokyo 185-8540 (Japan)

    2007-10-01

    Pulsed field magnetization is an important technique for a bulk superconducting magnet, which is one practical application of a bulk high T{sub c} superconductor (HTS). Full magnetization of a ring HTS is effective to obtain large trapped field for low pulsed field magnetization. In this study, trapped field in a ring bulk superconductor by the low pulsed field magnetization is numerically analyzed under assumption of variable shielding current by the temperature control. Differences between one-dimensional Bean model and axisymmetric three-dimensional numerical solution are discussed through the analysis. There is maximum trapped field in the axisymmetric three-dimensional model because of finite thickness of the ring HTS. The shielding current density and inner radius of the ring HTS are discussed to obtain the maximum trapped field.

  17. Magnetic field concentrator for probing optical magnetic metamaterials.

    Science.gov (United States)

    Antosiewicz, Tomasz J; Wróbel, Piotr; Szoplik, Tomasz

    2010-12-06

    Development of all dielectric and plasmonic metamaterials with a tunable optical frequency magnetic response creates a need for new inspection techniques. We propose a method of measuring magnetic responses of such metamaterials within a wide range of optical frequencies with a single probe. A tapered fiber probe with a radially corrugated metal coating concentrates azimuthally polarized light in the near-field into a subwavelength spot the longitudinal magnetic field component which is much stronger than the perpendicular electric one. The active probe may be used in a future scanning near-field magnetic microscope for studies of magnetic responses of subwavelength elementary cells of metamaterials.

  18. Pinning features of the magnetic flux trapped by YBCO single crystals in weak constant magnetic fields

    Science.gov (United States)

    Monarkha, V. Yu.; Paschenko, V. A.; Timofeev, V. P.

    2013-02-01

    The dynamics of Abrikosov vortices and their bundles was experimentally investigated in weak constant magnetic fields, in the range of Earth's magnetic field. Characteristics of the isothermal magnetization relaxation in YBCO single-crystal samples with strong pinning centers were studied for different sample-field orientation. The obtained values of normalized relaxation rate S allowed us to estimate the effective pinning potential U in the bulk of the YBCO sample and its temperature dependence, as well as the critical current density Jc. A comparison between the data obtained and the results of similar measurements in significantly higher magnetic fields was performed. To compare different techniques for evaluation of Jc, the magnetization loop measurements M(H), which relate the loop width to the critical current, were carried out. These measurements provided important parameters of the samples under study (penetration field Hp and first critical field Hc1), which involve the geometrical configuration of the samples.

  19. The magnetostriction in a superconductor-magnet system under non-uniform magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Li, Xueyi; Jiang, Lang; Wu, Hao [Key Laboratory of Mechanics on Disaster and Environment in Western China attached to the Ministry of Education of China, Lanzhou University, Lanzhou, Gansu 730000 (China); Gao, Zhiwen, E-mail: gaozhw@lzu.edu.cn [Department of Mechanics and Engineering Science, College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000 (China)

    2017-03-15

    Highlights: • We studied firstly magnetostriction in HTS under non-uniform magnetic field. • The superconductors may be homogeneous and nonhomogeneous. • The magnetostrictions response of the HTS is sensitive to the critical current density and amplitude of the applied magnetic field. • The magnetostriction of nonhomogeneous HTS is larger than that of homogeneous HTS. - Abstract: This paper describes a numerical model to examine the magnetostriction of bulk high-temperature superconductor (HTS) under non-uniform magnetic field in conjunction with finite element analysis. Through this model, the magnetostriction of homogeneous and nonhomogeneous HTS can be implemented under non-uniform magnetic field. Further, the effects of critical current density, applied field frequency and amplitude are also considered. The computational study can provide a fundamental mechanistic understanding the effects of non-uniform magnetic field on magnetostriction of HTS.

  20. Improvement of Main Magnetic Field Power Supply of SFC

    Institute of Scientific and Technical Information of China (English)

    ZhangXianlai; YanHuaihai; XinJunye; ZhangShu

    2003-01-01

    The main magnetic field power supply is used for establishing main magnetic field of SFC, therefore excellent current stability and low ripple are required. Its DC output current range is 0~1300 A and max output voltage is 230 V. The power supply has been put into operation since Sep. in 2000, and was replaced in 033 room from 166 room of No.2 Building. We have improved the performance of power supply in this period.

  1. Planar Josephson tunnel junctions in a transverse magnetic field

    DEFF Research Database (Denmark)

    Monacoa, R.; Aarøe, Morten; Mygind, Jesper

    2007-01-01

    Traditionally, since the discovery of the Josephson effect in 1962, the magnetic diffraction pattern of planar Josephson tunnel junctions has been recorded with the field applied in the plane of the junction. Here we discuss the static junction properties in a transverse magnetic field where...... demagnetization effects imposed by the tunnel barrier and electrodes geometry are important. Measurements of the junction critical current versus magnetic field in planar Nb-based high-quality junctions with different geometry, size, and critical current density show that it is advantageous to use a transverse...

  2. Current-induced magnetic switching of a single molecule magnet on a spin valve

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xiao [Theoretical Condensed Matter Physics and Computational Materials Physics Laboratory, School of Physics, University of Chinese Academy of Sciences, Beijing 100049 (China); Wang, Zheng-Chuan, E-mail: wangzc@ucas.ac.cn [Theoretical Condensed Matter Physics and Computational Materials Physics Laboratory, School of Physics, University of Chinese Academy of Sciences, Beijing 100049 (China); Zheng, Qing-Rong [Theoretical Condensed Matter Physics and Computational Materials Physics Laboratory, School of Physics, University of Chinese Academy of Sciences, Beijing 100049 (China); Zhu, Zheng-Gang [Theoretical Condensed Matter Physics and Computational Materials Physics Laboratory, School of Physics, University of Chinese Academy of Sciences, Beijing 100049 (China); School of Electronics, Electric and Communication Engineering, University of Chinese Academy of Sciences, Beijing 100049 (China); Su, Gang, E-mail: gsu@ucas.ac.cn [Theoretical Condensed Matter Physics and Computational Materials Physics Laboratory, School of Physics, University of Chinese Academy of Sciences, Beijing 100049 (China)

    2015-04-17

    The current-induced magnetic switching of a single-molecule magnet (SMM) attached on the central region of a spin valve is explored, and the condition for the switching current is derived. Electrons flowing through the spin valve will interact with the SMM via the s–d exchange interaction, producing the spin accumulation that satisfies the spin diffusion equation. We further describe the spin motion of the SMM by a Heisenberg-like equation. Based on the linear stability analysis, we obtain the critical current from two coupled equations. The results of the critical current versus the external magnetic field indicate that one can manipulate the magnetic state of the SMM by an external magnetic field. - Highlights: • We theoretically study the current-induced magnetic switching of the SMM. • We describe the spin motion of the SMM by a Heisenberg-like equation. • We describe the spin accumulation by the spin diffusion equation. • We obtain the critical current by the linear stability analysis. • Our approach can be easily extended to other SMMs.

  3. Electrolytic tiltmeters inside magnetic fields: Some observations

    Energy Technology Data Exchange (ETDEWEB)

    Alberdi, J. [CIEMAT, Madrid (Spain); Arce, P. [CIEMAT, Madrid (Spain); Barcala, J.M. [CIEMAT, Madrid (Spain); Calvo, E. [CIEMAT, Madrid (Spain); Ferrando, A. [CIEMAT, Madrid (Spain)]. E-mail: antonio.ferrando@ciemat.es; Josa, M.I. [CIEMAT, Madrid (Spain); Luque, J.M. [CIEMAT, Madrid (Spain); Molinero, A. [CIEMAT, Madrid (Spain); Navarrete, J. [CIEMAT, Madrid (Spain); Oller, J.C. [CIEMAT, Madrid (Spain); Yuste, C. [CIEMAT, Madrid (Spain); Calderon, A. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Garcia-Moral, L.A. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Gomez, G. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Gonzalez-Sanchez, F.J. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Martinez-Rivero, C. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Matorras, F. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Rodrigo, T. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Ruiz-Arbol, P. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Scodellaro, L. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Sobron, M. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Vila, I. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Virto, A.L. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain)

    2007-04-21

    We present observations of the electrolytic clinometers behaviour inside magnetic field environments introducing phenomenological expressions to account for the measured output voltage variations as functions of field gradients and field strengths.

  4. Deriving Potential Coronal Magnetic Fields from Vector Magnetograms

    Science.gov (United States)

    Welsch, Brian T.; Fisher, George H.

    2016-08-01

    The minimum-energy configuration for the magnetic field above the solar photosphere is curl-free (hence, by Ampère's law, also current-free), so can be represented as the gradient of a scalar potential. Since magnetic fields are divergence free, this scalar potential obeys Laplace's equation, given an appropriate boundary condition (BC). With measurements of the full magnetic vector at the photosphere, it is possible to employ either Neumann or Dirichlet BCs there. Historically, the Neumann BC was used with available line-of-sight magnetic field measurements, which approximate the radial field needed for the Neumann BC. Since each BC fully determines the 3D vector magnetic field, either choice will, in general, be inconsistent with some aspect of the observed field on the boundary, due to the presence of both currents and noise in the observed field. We present a method to combine solutions from both Dirichlet and Neumann BCs to determine a hybrid, "least-squares" potential field, which minimizes the integrated square of the residual between the potential and actual fields. We also explore weighting the residuals in the fit by spatially uniform measurement uncertainties. This has advantages both in not overfitting the radial field used for the Neumann BC, and in maximizing consistency with the observations. We demonstrate our methods with SDO/HMI vector magnetic field observations of active region 11158, and find that residual discrepancies between the observed and potential fields are significant, and they are consistent with nonzero horizontal photospheric currents. We also analyze potential fields for two other active regions observed with two different vector magnetographs, and find that hybrid-potential fields have significantly less energy than the Neumann fields in every case - by more than 10^{32} erg in some cases. This has major implications for estimates of free magnetic energy in coronal field models, e.g., non-linear force-free field extrapolations.

  5. 普朗克常数h测定系统中磁场线圈稳流源研究%Special Constant Current Source for Magnetic Field of Measuring System of Planck' s Constant

    Institute of Scientific and Technical Information of China (English)

    王农; 韩冰; 贺青; 张钟华; 李小亭

    2011-01-01

    A constant current source with high stability is required in establishing measuring system of Planck' s constant. The technique based on series compensation type for special constant current source for magnetic field was described. Therewith the constant current source with 4. 5 X 10 ~ /30min stability was constructed through designing the extraordinary sampling resistor, selecting stable voltage reference and operational amplifier with outstanding properties, offsetting the phase shift of inductive load. As a special constant current source for magnetic field, it presently could serve for the measuring system of Planck' s constant.%在建立我国普朗克常数h测定系统中,对高稳定度直流电源提出了新的要求.本文提出一种基于串联补偿型的专用磁场稳流源.通过设计特殊的采样电阻,选用稳定的基准电压,优选性能突出的运放,并针对感性负载进行关键的补偿,搭建了一套稳定度达到4.5×10 -6/30min的稳流源,可用作现阶段普朗克常数h测定系统的磁场稳流源.

  6. Birkeland current effects on high-latitude groundmagnetic field perturbations

    CERN Document Server

    Laundal, K M; Lehtinen, N; Gjerloev, J W; Østgaard, N; Tenfjord, P; Reistad, J P; Snekvik, K; Milan, S E; Ohtani, S; Anderson, B J

    2016-01-01

    Magnetic perturbations on ground at high latitudes are directly associated only with the divergence-free component of the height-integrated horizontal ionospheric current, $\\textbf{J}_{\\perp,df}$. Here we show how $\\textbf{J}_{\\perp,df}$ can be expressed as the total horizontal current $\\textbf{J}_\\perp$ minus its curl-free component, the latter being completely determined by the global Birkeland current pattern. Thus in regions where $\\textbf{J}_\\perp = 0$, the global Birkeland current distribution alone determines the local magnetic perturbation. We show with observations from ground and space that in the polar cap, the ground magnetic field perturbations tend to align with the Birkeland current contribution in darkness but not in sunlight. We also show that in sunlight, the magnetic perturbations are typically such that the equivalent overhead current is anti-parallel to the convection, indicating that the Hall current system dominates. Thus the ground magnetic field in the polar cap relates to different c...

  7. From Inverse to Delayed Magnetic Catalysis in Strong Magnetic Field

    CERN Document Server

    Mao, Shijun

    2016-01-01

    We study magnetic field effect on chiral phase transition in a Nambu--Jona-Lasinio model. In comparison with mean field approximation containing quarks only, including mesons as quantum fluctuations in the model leads to a transition from inverse to delayed magnetic catalysis at finite temperature and delays the transition at finite baryon chemical potential. The location of the critical end point depends on the the magnetic field non-monotonously.

  8. Dynamic shielding of the magnetic fields

    Directory of Open Access Journals (Sweden)

    RAU, M.

    2010-11-01

    Full Text Available The paper presents a comparative study of the methods used to control and compensate the direct and alternative magnetic fields. Two frequently used methods in the electromagnetic compatibility of the complex biomagnetism installations were analyzed. The two methods refer to the use of inductive magnetic field sensors (only for alternative fields and of fluxgate magnetometers as active transducers which measures both the direct and alternative components of the magnetic field. The applications of the dynamic control of the magnetic field are: control of the magnetic field of the military ships, control of parasite magnetic field produced by power transformers and the electrical networks, protection of the mass spectrometers, electronic microscopes, SQUID and optical pumping magnetometers for applications in biomagnetism.

  9. Precise numerical estimation of the magnetic field generated around recombination

    Science.gov (United States)

    Fidler, Christian; Pettinari, Guido; Pitrou, Cyril

    2016-05-01

    We investigate the generation of magnetic fields from nonlinear effects around recombination. As tight-coupling is gradually lost when approaching z ≃1100 , the velocity difference between photons and baryons starts to increase, leading to an increasing Compton drag of the photons on the electrons. The protons are then forced to follow the electrons due to the electric field created by the charge displacement; the same field, following Maxwell's laws, eventually induces a magnetic field on cosmological scales. Since scalar perturbations do not generate any magnetic field as they are curl-free, one has to resort to second-order perturbation theory to compute the magnetic field generated by this effect. We reinvestigate this problem numerically using the powerful second-order Boltzmann code SONG. We show that: (i) all previous studies do not have a high enough angular resolution to reach a precise and consistent estimation of the magnetic field spectrum; (ii) the magnetic field is generated up to z ≃10 ; (iii) it is in practice impossible to compute the magnetic field with a Boltzmann code for scales smaller than 1 Mpc. Finally we confirm that for scales of a few Mpc, this magnetic field is of order 2 ×10-29 G , many orders of magnitude smaller than what is currently observed on intergalactic scales.

  10. Field free line magnetic particle imaging

    CERN Document Server

    Erbe, Marlitt

    2014-01-01

    Marlitt Erbe provides a detailed introduction into the young research field of Magnetic Particle Imaging (MPI) and field free line (FFL) imaging in particular. She derives a mathematical description of magnetic field generation for FFL imaging in MPI. To substantiate the simulation studies on magnetic FFL generation with a proof-of-concept, the author introduces the FFL field demonstrator, which provides the world's first experimentally generated rotated and translated magnetic FFL field complying with the requirements for FFL reconstruction. Furthermore, she proposes a scanner design of consi

  11. High field magnet program at Brookhaven National Laboratory

    CERN Document Server

    Ghosh, A; Muratore, J; Parker, B; Sampson, W; Wanderer, P J; Willen, E

    2000-01-01

    The magnet program at Brookhaven National Laboratory (BNL) is focussed on superconducting magnets for particle accelerators. The effort includes magnet production at the laboratory and in industry, magnet R&D, and test facilities for magnets and superconductors. Nearly 2000 magnets-dipoles, quadrupoles, sextupoles and correctors for the arc and insertion regions-were produced for the Relativistic Heavy Ion Collider (RHIC), which is being commissioned. Currently, production of helical dipoles for the polarized proton program at RHIC, insertion region dipoles for the Large Hadron Collider (LHC) at CERN, and an insertion magnet system for the Hadron-Elektron-Ring- Analage (HERA) collider at Deutsches Elektronen-Synchrotron (DESY) is underway. The R&D effort is exploring dipoles with fields above 10 T for use in post-LHC colliders. Brittle superconductors-Nb/sub 3/Sn or HTS-are being used for these magnets. The superconductor test facility measures short-sample currents and other characteristics of sample...

  12. Are there any stable magnetic fields in barotropic stars?

    CERN Document Server

    Lander, S K

    2012-01-01

    We construct barotropic stellar equilibria, containing magnetic fields with both poloidal and toroidal field components. We extend earlier results by exploring the effect of different magnetic field and current distributions. Our results suggest that the boundary treatment plays a major role in whether the poloidal or toroidal field component is globally dominant. Using time evolutions we provide the first stability test for mixed poloidal-toroidal fields in barotropic stars, finding that all these fields suffer instabilities due to one of the field components: these are localised around the pole for toroidal-dominated equilibria and in the closed-field line region for poloidal-dominated equilibria. Rotation provides only partial stabilisation. There appears to be very limited scope for the existence of stable magnetic fields in barotropic stars. We discuss what additional physics from real stars may allow for stable fields.

  13. Magnetic reconnection at 3D null points: effect of magnetic field asymmetry

    Science.gov (United States)

    Al-Hachami, A. K.; Pontin, D. I.

    2010-03-01

    Context. The magnetic field in many astrophysical plasmas, for example in the solar corona, is known to have a highly complex - and clearly three-dimensional - structure. Turbulent plasma motions in high-β regions where field lines are anchored, such as the solar interior, can store large amounts of energy in the magnetic field. This energy can only be released when magnetic reconnection occurs. Reconnection may only occur in locations where huge gradients of the magnetic field develop, and one candidate for such locations are magnetic null points, known to be abundant for example in the solar atmosphere. Reconnection leads to changes in the topology of the magnetic field, and energy being released as heat, kinetic energy and acceleration of particles. Thus reconnection is responsible for many dynamic processes, for instance flares and jets. Aims: The aim of this paper is to investigate the properties of magnetic reconnection at a 3D null point, with respect to their dependence on the symmetry of the magnetic field around the null. In particular we examine the rate of reconnection of magnetic flux at the null point, as well as how the current sheet forms and its properties. Methods: We use mathematical modelling and finite difference resistive MHD simulations. Results: It is found that the basic structure of the mode of magnetic reconnection considered is unaffected by varying the magnetic field symmetry, that is, the plasma flow is found to cross both the spine and fan of the null. However, the peak intensity and dimensions of the current sheet are dependent on the symmetry/asymmetry of the field lines. As a result, the reconnection rate is also found to be strongly dependent on the field asymmetry. Conclusions: The symmetry/asymmetry of the magnetic field in the vicinity of a magnetic null can have a profound effect on the geometry of any associated reconnection region, and the rate at which the reconnection process proceeds.

  14. Magnetic field mapper based on rotating coils

    CERN Document Server

    AUTHOR|(CDS)2087244; Arpaia, Pasquale

    This thesis presents a magnetic field mapper based on rotating coils. The requirements, the architecture, the conceptual design, and the prototype for straight magnets were shown. The proposed system is made up of a rotating coil transducer and a train-like system for longitudinal motion and positioning inside magnet bore. The mapper allows a localized measurement of magnetic fields and the variation of the harmonic multipole content in the magnet ends. The proof-of-principle demonstration and the experimental characterization of the rotating-coil transducer specifically conceived for mapping validated the main objective of satisfying the magnetic measurement needs of the next generation of compact accelerators.

  15. Magnetic Fields and Star Formation

    CERN Document Server

    Van Loo, S; Falle, S A E G

    2012-01-01

    Research performed in the 1950s and 1960s by Leon Mestel on the roles of magnetic fields in star formation established the framework within which he and other key figures have conducted subsequent investigations on the subject. This short tribute to Leon contains a brief summary of some, but not all, of his ground breaking contributions in the area. It also mentions of some of the relevant problems that have received attention in the last few years. The coverage is not comprehensive, and the authors have drawn on their own results more and touched more briefly on those of others than they would in a normal review. Theirs is a personal contribution to the issue honouring Leon, one of the truly great gentlemen, wits, and most insightful of astrophysicists.

  16. DC-based magnetic field controller

    Energy Technology Data Exchange (ETDEWEB)

    Kotter, Dale K. (Shelley, ID); Rankin, Richard A. (Ammon, ID); Morgan, John P,. (Idaho Falls, ID)

    1994-01-01

    A magnetic field controller for laboratory devices and in particular to dc operated magnetic field controllers for mass spectrometers, comprising a dc power supply in combination with improvements to a hall probe subsystem, display subsystem, preamplifier, field control subsystem, and an output stage.

  17. DC-based magnetic field controller

    Energy Technology Data Exchange (ETDEWEB)

    Kotter, D.K.; Rankin, R.A.; Morgan, J.P.

    1994-05-31

    A magnetic field controller is described for laboratory devices and in particular to dc operated magnetic field controllers for mass spectrometers, comprising a dc power supply in combination with improvements to a Hall probe subsystem, display subsystem, preamplifier, field control subsystem, and an output stage. 1 fig.

  18. High magnetic fields science and technology

    CERN Document Server

    Miura, Noboru

    2003-01-01

    This three-volume book provides a comprehensive review of experiments in very strong magnetic fields that can only be generated with very special magnets. The first volume is entirely devoted to the technology of laboratory magnets: permanent, superconducting, high-power water-cooled and hybrid; pulsed magnets, both nondestructive and destructive (megagauss fields). Volumes 2 and 3 contain reviews of the different areas of research where strong magnetic fields are an essential research tool. These volumes deal primarily with solid-state physics; other research areas covered are biological syst

  19. Trapped magnetic field measurements on HTS bulk by peak controlled pulsed field magnetization

    Energy Technology Data Exchange (ETDEWEB)

    Ida, Tetsuya; Watasaki, Masahiro [Department of Electronic Control Engineering, Hiroshima National College of Maritime Technology, 4272-1, Higashino, Ohsakikamijima-cho, Toyota-gun, Hiroshima 725-0231 (Japan); Kimura, Yosuke [Kawasaki Heavy Industries, Ltd. Technical Institute System Technology Development Centre 1-1, Kawasaki-cho, Akashi-shi, Hyogo 673-8666 (Japan); Miki, Motohiro; Izumi, Mitsuru, E-mail: ida@hiroshima-cmt.ac.j [Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, 2-1-6, Etchu-jima, Koto-ku, Tokyo 135-8533 (Japan)

    2010-06-01

    For the past several years, we have studied the high-temperature superconducting (HTS) synchronous motor assembled with melt-textured Gd-Ba-Cu-O bulk magnets. If the single pulse field magnetizes a bulk effectively, size of electrical motor will become small for the strong magnetic field of the HTS magnets without reducing output power of motor. In the previous study, we showed that the HTS bulk was magnetized to excellent cone-shape magnetic field distribution by using the waveform control pulse magnetization (WCPM) method. The WCPM technique made possible the active control of the waveform on which magnetic flux motion depended. We generated the pulse waveform with controlled risetime for HTS bulk magnetization to suppress the magnetic flux motion which decreases magnetization efficiency. The pulsed maximum magnetic flux density with slow risetime is not beyond the maximum magnetic flux density which is trapped by the static field magnetization. But, as for applying the pulse which has fast risetime, the magnetic flux which exceed greatly the threshold penetrates the bulk and causes the disorder of the trapped magnetic distribution. This fact suggests the possibility that the threshold at pulsed magnetization influences the dynamic magnetic flux motion. In this study, Gd-Ba-Cu-O bulk is magnetized by the controlled arbitrary trapezoidal shape pulse, of which the maximum magnetic flux density is controlled not to exceed the threshold. We will present the trapped magnetic characteristics and the technique to generate the controlled pulsed field.

  20. Anomaly induced effects in a magnetic field

    Science.gov (United States)

    Antoniadis, Ignatios; Boyarsky, Alexey; Ruchayskiy, Oleg

    2008-04-01

    We consider a modification of electrodynamics by an additional light massive vector field, interacting with the photon via Chern-Simons-like coupling. This theory predicts observable effects for the experiments studying the propagation of light in an external magnetic field, very similar to those, predicted by theories of axion and axion-like particles. We discuss a possible microscopic origin of this theory from a theory with non-trivial gauge anomaly cancellation between massive and light particles (including, for example, millicharged fermions). Due to the conservation of the gauge current, the production of the new vector field is suppressed at high energies. As a result, this theory can avoid both stellar bounds (which exist for axions) and the bounds from CMB considered recently, allowing for positive results in experiments like ALPS, LIPPS, OSQAR, PVLAS-2, BMV, Q&A, etc.

  1. Anomaly induced effects in a magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Antoniadis, Ignatios; Boyarsky, Alexey [Department of Physics, CERN, Theory Division, 1211 Geneva 23 (Switzerland); Ruchayskiy, Oleg [Ecole Polytechnique Federale de Lausanne, Institute of Theoretical Physics, FSB/ITP/LPPC, BSP 720, CH-1015 Lausanne (Switzerland)], E-mail: oleg.ruchayskiy@epfl.ch

    2008-04-11

    We consider a modification of electrodynamics by an additional light massive vector field, interacting with the photon via Chern-Simons-like coupling. This theory predicts observable effects for the experiments studying the propagation of light in an external magnetic field, very similar to those, predicted by theories of axion and axion-like particles. We discuss a possible microscopic origin of this theory from a theory with non-trivial gauge anomaly cancellation between massive and light particles (including, for example, millicharged fermions). Due to the conservation of the gauge current, the production of the new vector field is suppressed at high energies. As a result, this theory can avoid both stellar bounds (which exist for axions) and the bounds from CMB considered recently, allowing for positive results in experiments like ALPS, LIPPS, OSQAR, PVLAS-2, BMV, Q and A, etc.

  2. Anomaly induced effects in a magnetic field

    CERN Document Server

    Antoniadis, Ignatios; Ruchayskiy, O

    2008-01-01

    We consider a modification of electrodynamics by an additional light massive vector field, interacting with the photon via Chern-Simons-like coupling. This theory predicts observable effects for the experiments studying the propagation of light in an external magnetic field, very similar to those, predicted by theories of axion and axion-like particles. We discuss a possible microscopic origin of this theory from a theory with non-trivial gauge anomaly cancellation between massive and light particles (including, for example, millicharged fermions). Due to the conservation of the gauge current, the production of the new vector field is suppressed at high energies. As a result, this theory can avoid both stellar bounds (which exist for axions) and the bounds from CMB considered recently, allowing for positive results in experiments like ALPS, LIPPS, OSQAR, PVLAS-2, BMV, Q&A, etc.

  3. Nonlinear spin-wave excitations at low magnetic bias fields

    Science.gov (United States)

    Woltersdorf, Georg

    We investigate experimentally and theoretically the nonlinear magnetization dynamics in magnetic films at low magnetic bias fields. Nonlinear magnetization dynamics is essential for the operation of numerous spintronic devices ranging from magnetic memory to spin torque microwave generators. Examples are microwave-assisted switching of magnetic structures and the generation of spin currents at low bias fields by high-amplitude ferromagnetic resonance. In the experiments we use X-ray magnetic circular dichroism to determine the number density of excited magnons in magnetically soft Ni80Fe20 thin films. Our data show that the common Suhl instability model of nonlinear ferromagnetic resonance is not adequate for the description of the nonlinear behavior in the low magnetic field limit. Here we derive a model of parametric spin-wave excitation, which correctly predicts nonlinear threshold amplitudes and decay rates at high and at low magnetic bias fields. In fact, a series of critical spin-wave modes with fast oscillations of the amplitude and phase is found, generalizing the theory of parametric spin-wave excitation to large modulation amplitudes. For these modes, we also find pronounced frequency locking effects that may be used for synchronization purposes in magnonic devices. By using this effect, effective spin-wave sources based on parametric spin-wave excitation may be realized. Our results also show that it is not required to invoke a wave vector-dependent damping parameter in the interpretation of nonlinear magnetic resonance experiments performed at low bias fields.

  4. Magnetic field evolution in tidal disruption events

    CERN Document Server

    Bonnerot, Clément; Lodato, Giuseppe; Rossi, Elena M

    2016-01-01

    When a star gets tidally disrupted by a supermassive black hole, its magnetic field is expected to be transmitted to the debris. In this paper, we study this process via smoothed particle magnetohydrodynamical simulations of the disruption and early debris evolution including the stellar magnetic field. As the gas stretches into a stream, we show that the magnetic field evolution is strongly dependent on its orientation with respect to the stretching direction. In particular, an alignment of the field lines with the direction of stretching induces an increase of the magnetic energy. For disruptions happening well within the tidal radius, the star compression causes the magnetic field strength to sharply increase by an order of magnitude at the time of pericentre passage. If the disruption is partial, we find evidence for a dynamo process occurring inside the surviving core due to the formation of vortices. This causes an amplification of the magnetic field strength by a factor of $\\sim 10$. However, this valu...

  5. Synchrotron Applications of High Magnetic Fields

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2006-07-01

    This workshop aims at discussing the scientific potential of X-ray diffraction and spectroscopy in magnetic fields above 30 T. Pulsed magnetic fields in the range of 30 to 40 T have recently become available at Spring-8 and the ESRF (European synchrotron radiation facility). This document gathers the transparencies of the 6 following presentations: 1) pulsed magnetic fields at ESRF: first results; 2) X-ray spectroscopy and diffraction experiments by using mini-coils: applications to valence state transition and frustrated magnet; 3) R{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4}: an ideal system to be studied in X-ray under high magnetic field?; 4) high field studies at the Advanced Photon Source: present status and future plans; 5) synchrotron X-ray diffraction studies under extreme conditions; and 6) projects for pulsed and steady high magnetic fields at the ESRF.

  6. Demagnetizing fields in active magnetic regenerators

    DEFF Research Database (Denmark)

    Nielsen, Kaspar Kirstein; Bahl, Christian R.H.; Smith, Anders

    2014-01-01

    is in general both a function of the overall shape of the regenerator and its morphology (packed particles, parallel plates etc.) as well as the magnetization of the material. Due to the pronounced temperature dependence of the magnetization near the Curie temperature, the demagnetization field is also......A magnetic material in an externally applied magnetic field will in general experience a spatially varying internal magnetic field due to demagnetizing effects. When the performance of active magnetic regenerators (AMRs) is evaluated using numerical models the internal field is often assumed...... temperature dependent. We propose a relatively straightforward method to correct sufficiently for the demagnetizing field in AMR models. We discuss how the demagnetizing field behaves in regenerators made of packed spheres under realistic operation conditions....

  7. New knowledge of the Galactic magnetic fields

    CERN Document Server

    Han, J L

    2009-01-01

    The magnetic fields of our Milky Way galaxy are the main agent for cosmic rays to transport. In the last decade, much new knowledge has been gained from measurements of the Galactic magnetic fields. In the Galactic disk, from the RMs of a large number of newly discovered pulsars, the large-scale magnetic fields along the spiral arms have been delineated in a much larger region than ever before, with alternating directions in the arm and interarm regions. The toroidal fields in the Galactic halo were revealed to have opposite directions below and above the Galactic plane, which is an indication of an A0 mode dynamo operating in the halo. The strength of large-scale fields obtained from pulsar RM data has been found to increase exponentially towards the Galactic center. Compared to the steep Kolmogorov spectrum of magnetic energy at small scales, the large-scale magnetic fields show a shallow broken spatial magnetic energy spectrum.

  8. Behaviour of ferrocholesterics under external magnetic fields

    Science.gov (United States)

    Petrescu, Emil; Motoc, Cornelia

    2001-08-01

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

  9. Coulomb crystals in the magnetic field

    CERN Document Server

    Baiko, D A

    2009-01-01

    The body-centered cubic Coulomb crystal of ions in the presence of a uniform magnetic field is studied using the rigid electron background approximation. The phonon mode spectra are calculated for a wide range of magnetic field strengths and for several orientations of the field in the crystal. The phonon spectra are used to calculate the phonon contribution to the crystal energy, entropy, specific heat, Debye-Waller factor of ions, and the rms ion displacements from the lattice nodes for a broad range of densities, temperatures, chemical compositions, and magnetic fields. Strong magnetic field dramatically alters the properties of quantum crystals. The phonon specific heat increases by many orders of magnitude. The ion displacements from their equilibrium positions become strongly anisotropic. The results can be relevant for dusty plasmas, ion plasmas in Penning traps, and especially for the crust of magnetars (neutron stars with superstrong magnetic fields $B \\gtrsim 10^{14}$ G). The effect of the magnetic ...

  10. 3-D Magnetospheric Field and Plasma Containing Thin Current Sheets

    Science.gov (United States)

    Zaharia, S.; Cheng, C. Z.; Maezawa, K.; Wing, S.

    2002-05-01

    In this study we present fully-3D self-consistent solutions of the magnetosphere by using observation-based plasma pressure distributions and computational boundary conditions based on the T96 magnetospheric field model. The pressure profiles we use are either taken directly from observations (GEOTAIL pressure data in the plasma sheet and DMSP ionospheric pressure) or empirical (Spence-Kivelson formula for pressure on the midnight equatorial line). The 3-D solutions involve solving 2 coupled elliptic equations in a flux coordinate systems, with the magnetic field expressed by two Euler potentials and using appropriate boundary conditions for both the closed- and open-field regions derived from the empirical field model. We look into how the self-consistent magnetic field and current structures change under different external conditions, and we discuss the appearance of thin cross-tail current sheets during disturbed magnetospheric times.

  11. Generating the optimal magnetic field for magnetic refrigeration

    DEFF Research Database (Denmark)

    Bjørk, Rasmus; Insinga, Andrea Roberto; Smith, Anders

    2016-01-01

    remanence distribution for any desired magnetic field. The method is based on the reciprocity theorem, which through the use of virtual magnets can be used to calculate the optimal remanence distribution. Furthermore, we present a method for segmenting a given magnet design that always results...

  12. Magnetic field sensor for isotropically sensing an incident magnetic field in a sensor plane

    Science.gov (United States)

    Pant, Bharat B. (Inventor); Wan, Hong (Inventor)

    2001-01-01

    A magnetic field sensor that isotropically senses an incident magnetic field. This is preferably accomplished by providing a magnetic field sensor device that has one or more circular shaped magnetoresistive sensor elements for sensing the incident magnetic field. The magnetoresistive material used is preferably isotropic, and may be a CMR material or some form of a GMR material. Because the sensor elements are circular in shape, shape anisotropy is eliminated. Thus, the resulting magnetic field sensor device provides an output that is relatively independent of the direction of the incident magnetic field in the sensor plane.

  13. Magnetic fields in non-convective regions of stars

    CERN Document Server

    Braithwaite, J

    2015-01-01

    We review the current state of knowledge of magnetic fields inside stars, concentrating on recent developments concerning magnetic fields in stably stratified (zones of) stars, leaving out convective dynamo theories and observations of convective envelopes. We include the observational properties of A, B and O-type main-sequence stars, which have radiative envelopes, and the fossil field model which is normally invoked to explain the strong fields sometimes seen in these stars. Observations seem to show that Ap-type stable fields are excluded in stars with convective envelopes. Most stars contain both radiative and convective zones, and there are potentially important effects arising from the interaction of magnetic fields at the boundaries between them, the solar cycle being one of the better known examples. Related to this, we discuss whether the Sun could harbour a magnetic field in its core. Recent developments regarding the various convective and radiative layers near the surfaces of early-type stars and...

  14. On the origin of cosmic magnetic fields

    Science.gov (United States)

    Kulsrud, Russell M.; Zweibel, Ellen G.

    2008-04-01

    We review the extensive and controversial literature concerning how the cosmic magnetic fields pervading nearly all galaxies and clusters of galaxies actually got started. Some observational evidence supports a hypothesis that the field is already moderately strong at the beginning of the life of a galaxy and its disc. One argument involves the chemical abundance of the light elements Be and B, while a second one is based on the detection of strong magnetic fields in very young high red shift galaxies. Since this problem of initial amplification of cosmic magnetic fields involves important plasma problems it is obvious that one must know the plasma in which the amplification occurs. Most of this review is devoted to this basic problem and for this it is necessary to devote ourselves to reviewing studies that take place in environments in which the plasma properties are most clearly understood. For this reason the authors have chosen to restrict themselves almost completely to studies of dynamos in our Galaxy. It is true that one can get a much better idea of the grand scope of galactic fields in extragalactic systems. However, most mature galaxies share the same dilemma as ours of overcoming important plasma problems. Since the authors are both trained in plasma physics we may be biased in pursuing this approach, but we feel it is justified by the above argument. In addition we feel we can produce a better review by staying close to that which we know best. In addition we have chosen not to consider the saturation problem of the galactic magnetic field since if the original dynamo amplification fails the saturation question does not arise. It is generally accepted that seed fields, whose strength is of order 10-20 G, easily spring up in the era preceding galaxy formation. Several mechanisms have been proposed to amplify these seed magnetic fields to a coherent structure with the microgauss strengths of the currently observed galactic magnetic fields. The standard

  15. Magnetic force of piezo electric cantilever energy harvesting system with an externally applied magnetic field based on magnetizing current metho d%外加磁场压电悬臂梁能量采集系统的磁化电流法磁力研究∗

    Institute of Scientific and Technical Information of China (English)

    谭丹; 冷永刚; 范胜波; 高毓璣

    2015-01-01

    以外加磁场压电悬臂梁能量采集系统结构为研究对象,根据磁化电流方法探讨了具有悬臂梁特征的系统结构的磁场作用力及其计算方法,给出了相应的磁力计算模型,并将计算结果与实验数据进行了对比。研究表明,磁化电流方法导出的磁力计算模型存在偏差,其磁力计算误差随着磁铁间距缩小而增大。通过引入悬臂梁末端磁铁的偏转角度,对磁化电流法计算模型进行改进,得到合理的外加磁场压电悬臂梁能量采集系统的磁力计算模型,为该能量采集系统的进一步研究提供了可靠的磁力计算理论依据。%This paper focuses on the piezoelectric cantilever energy harvesting system with an externally applied magnetic field. The calculation method and model for the magnetic force are proposed from the magnetizing current method, and the calculation results are compared with a set of experimental data. The study shows that there is a deviation in the calculation model derived by the magnetizing current method, which increases as the distance between two magnets decreases. The calculation model is improved by introducing the deflection angle of the magnet at the end of the cantilever beam, and is reliable to calculate the magnetic force of piezoelectric cantilever energy harvesting system with an externally applied magnetic field for further studying this energy harvesting system.

  16. Nonlinear energy dissipation of magnetic nanoparticles in oscillating magnetic fields

    Science.gov (United States)

    Soto-Aquino, D.; Rinaldi, C.

    2015-11-01

    The heating of magnetic nanoparticle suspensions subjected to alternating magnetic fields enables a variety of emerging applications such as magnetic fluid hyperthermia and triggered drug release. Rosensweig (2002) [25] obtained a model for the heat dissipation rate of a collection of non-interacting particles. However, the assumptions made in this analysis make it rigorously valid only in the limit of small applied magnetic field amplitude and frequency (i.e., values of the Langevin parameter that are much less than unity and frequencies below the inverse relaxation time). In this contribution we approach the problem from an alternative point of view by solving the phenomenological magnetization relaxation equation exactly for the case of arbitrary magnetic field amplitude and frequency and by solving a more accurate magnetization relaxation equation numerically. We also use rotational Brownian dynamics simulations of non-interacting magnetic nanoparticles subjected to an alternating magnetic field to estimate the rate of energy dissipation and compare the results of the phenomenological theories to the particle-scale simulations. The results are summarized in terms of a normalized energy dissipation rate and show that Rosensweig's expression provides an upper bound on the energy dissipation rate achieved at high field frequency and amplitude. Estimates of the predicted dependence of energy dissipation rate, quantified as specific absorption rate (SAR), on magnetic field amplitude and frequency, and particle core and hydrodynamic diameter, are also given.

  17. Beam Transport in Toroidal Magnetic Field

    CERN Document Server

    Joshi, N; Meusel, O; Ratzinger, U

    2016-01-01

    The concept of a storage ring with toroidal magnetic field was presented in the two previous EPAC conferences. Here we report the first results of experiments performed with beam transport in toroidal magnetic fields and details of the injection system. The beam transport experiments were carried out with 30 degree toroidal segments with an axial magnetic field of 0.6T. The multi turn injection system relies on a transverse injection coil together with an electric kicker system.

  18. Analytical estimation of the Earth's magnetic field scale

    CERN Document Server

    Bologna, Mauro

    2012-01-01

    In this paper we analytically estimate the magnetic field scale of planets with physical core conditions similar to that of Earth from a statistical point of view. We evaluate the magnetic field on the basis of the physical parameters of the center of the planet, such as density, temperature, and core size. We look at the contribution of the Peltier-Seebeck effect on the magnetic field, showing that an electrical thermal current can exist in a rotating fluid sphere. Finally, we apply our calculations to Earth and Jupiter. In each case we show that the thermal generation of currents leads to a magnetic field scale comparable to the observed fields of the two planets.

  19. Chiral spiral induced by a strong magnetic field

    Directory of Open Access Journals (Sweden)

    Abuki Hiroaki

    2016-01-01

    Full Text Available We study the modification of the chiral phase structure of QCD due to an external magnetic field. We first demonstrate how the effect of magnetic field can systematically be incorporated into a generalized Ginzburg-Landau framework. We then analyze the phase structure in the vicinity of the chiral critical point. In the chiral limit, the effect is found to be so drastic that it brings a “continent” of chiral spiral in the phase diagram, by which the chiral tricritical point is totally washed out. This is the case no matter how small the intensity of magnetic field is. On the other hand, the current quark mass protects the chiral critical point from a weak magnetic field. However, the critical point will eventually be covered by the chiral spiral phase as the magnetic field grows.

  20. Chiral spiral induced by a strong magnetic field

    CERN Document Server

    Abuki, H

    2016-01-01

    We study the modification of the chiral phase structure of QCD due to an external magnetic field. We first demonstrate how the effect of magnetic field can systematically be incorporated into a generalized Ginzburg-Landau framework. We then analyze the phase structure in the vicinity of the chiral critical point. In the chiral limit, the effect is found to be so drastic that it totally washes the tricritical point out of the phase diagram, bringing the continent for the chiral spiral. This is the case no matter how small is the intensity of the magnetic field. On the other hand, the current quark mass protects the chiral critical point from a weak magnetic field. However the critical point will eventually be covered by the chiral spiral phase as the magnetic field grows.