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Sample records for ramped magnet current

  1. Simulation of plasma current ramp-up with reduced magnetic flux consumption in JT-60SA

    NASA Astrophysics Data System (ADS)

    Wakatsuki, T.; Suzuki, T.; Hayashi, N.; Shiraishi, J.; Ide, S.; Takase, Y.

    2015-06-01

    Current ramp-up with reduced central solenoid (CS) flux consumption in JT-60SA has been investigated using an integrated modeling code suite (TOPICS) with a turbulent model (CDBM). The plasma current can be ramped-up from 0.6 MA to 2.1 MA with no additional CS flux consumption if the plasma current is overdriven by neutral-beam-driven and bootstrap current. A time duration required for the current ramp-up without CS flux consumption becomes as long as 150 s in the scenario we have examined. In order to achieve a current overdrive condition from 0.6 MA, the current drive by a lower energy neutral beam (85 keV) is effective. A higher energy neutral beam (500 keV) cannot be used in this early phase with a low central electron density (~2 × 1019 m-3) due to large shine through loss, while it can be effectively used in the later phase. Therefore, the main current driver should be switched from the lower energy neutral beam to the higher energy neutral beam during the current ramp-up phase. As a result of an intensive auxiliary heating, plasma beta (the ratio of the plasma pressure to the magnetic pressure) becomes high. Ideal MHD instabilities of such high beta plasmas have been investigated using a linear ideal MHD stability analysis code (MARG2D). External kink modes which might affect the core plasma can be stabilized during the current ramp-up if there is a perfectly conducting wall at the location of the stabilizing plate and the vacuum vessel of JT-60SA and the plasma has a broader pressure profile with the H-mode pedestal and the internal transport barrier.

  2. Dynamical coupling between magnetic equilibrium and transport in tokamak scenario modelling, with application to current ramps

    NASA Astrophysics Data System (ADS)

    Fable, E.; Angioni, C.; Ivanov, A. A.; Lackner, K.; Maj, O.; Medvedev, S. Yu; Pautasso, G.; Pereverzev, G. V.; Treutterer, W.; the ASDEX Upgrade Team

    2013-07-01

    The modelling of tokamak scenarios requires the simultaneous solution of both the time evolution of the plasma kinetic profiles and of the magnetic equilibrium. Their dynamical coupling involves additional complications, which are not present when the two physical problems are solved separately. Difficulties arise in maintaining consistency in the time evolution among quantities which appear in both the transport and the Grad-Shafranov equations, specifically the poloidal and toroidal magnetic fluxes as a function of each other and of the geometry. The required consistency can be obtained by means of iteration cycles, which are performed outside the equilibrium code and which can have different convergence properties depending on the chosen numerical scheme. When these external iterations are performed, the stability of the coupled system becomes a concern. In contrast, if these iterations are not performed, the coupled system is numerically stable, but can become physically inconsistent. By employing a novel scheme (Fable E et al 2012 Nucl. Fusion submitted), which ensures stability and physical consistency among the same quantities that appear in both the transport and magnetic equilibrium equations, a newly developed version of the ASTRA transport code (Pereverzev G V et al 1991 IPP Report 5/42), which is coupled to the SPIDER equilibrium code (Ivanov A A et al 2005 32nd EPS Conf. on Plasma Physics (Tarragona, 27 June-1 July) vol 29C (ECA) P-5.063), in both prescribed- and free-boundary modes is presented here for the first time. The ASTRA-SPIDER coupled system is then applied to the specific study of the modelling of controlled current ramp-up in ASDEX Upgrade discharges.

  3. CABLE DESIGN FOR FAST RAMPED SUPERCONDUCTING MAGNETS (COS-0 DESIGN).

    SciTech Connect

    GHOSH,A.

    2004-03-22

    The new heavy ion synchrotron facility proposed by GSI will have two superconducting magnet rings in the same tunnel, with rigidities of 300 T-m and 100 T-m. Fast ramp times are needed, which can cause significant problems for the magnets, particularly in the areas of ac loss and magnetic field distortion. The development of the low loss Rutherford cable that can be used is described, together with a novel insulation scheme designed to promote efficient cooling. Measurements of contact resistance in the cable are presented and the results of these measurements are used to predict the ac losses, in the magnets during fast ramp operation. For the high energy ring, a lm model dipole magnet was built, based on the RHIC dipole design. This magnet was tested under boiling liquid helium in a vertical cryostat. The quench current showed very little dependence on ramp rate. The ac losses, measured by an electrical method, were fitted to straight line plots of loss/cycle versus ramp rate, thereby separating the eddy current and hysteresis components. These results were compared with calculated values, using parameters which had previously been measured on short samples of cable. Reasonably good agreement between theory and experiment was found, although the measured hysteresis loss is higher than expected in ramps to the highest field levels.

  4. Test results of BM109 magnet field stability during ramping

    SciTech Connect

    Kristalinski, A.

    1992-12-01

    This report presents results of the measured lag between the current ramp and the following magnetic field rise in BM109 magnets. The purpose of these tests is to choose identical ramping programs for PC4AN1, PC4AN2 and PC4AN3 magnets. The lag occurs due to the large eddy currents in the magnets' solid iron cores. The experiment requires a magnetic field stability of 0.1% during beam presence. Using existing equipment and a program slope of 100 Amp/sec starting at Tl yields fields within the 0.05% of set value. Add to this 0.05% for P.S. regulation to meet the required field stability of 0.1%. This program yields annual savings of $200,000 (assuming 100% usage) . Additional savings can be made by using faster slopes, but this requires additional controls.

  5. Test results of BM109 magnet field stability during ramping

    SciTech Connect

    Kristalinski, A.

    1992-12-01

    This report presents results of the measured lag between the current ramp and the following magnetic field rise in BM109 magnets. The purpose of these tests is to choose identical ramping programs for PC4AN1, PC4AN2 and PC4AN3 magnets. The lag occurs due to the large eddy currents in the magnets` solid iron cores. The experiment requires a magnetic field stability of 0.1% during beam presence. Using existing equipment and a program slope of 100 Amp/sec starting at Tl yields fields within the 0.05% of set value. Add to this 0.05% for P.S. regulation to meet the required field stability of 0.1%. This program yields annual savings of $200,000 (assuming 100% usage) . Additional savings can be made by using faster slopes, but this requires additional controls.

  6. Critical mechanical structure of superconducting high current coils for fast ramped accelerator magnets with high repetition rates in long term operation

    NASA Astrophysics Data System (ADS)

    Fischer, E.; Schnizer, P.; Weiss, K.; Nyilas, A.; Mierau, A.; Sikler, G.

    2010-06-01

    The heavy ion synchrotron SIS100 is the core component of the Facility for Antiproton and Ion Research (FAIR) currently under construction at GSI in Darmstadt. It is rapidly cycled with a ramp rate of 4 T/s up to 2 T maximum field and a repetition frequency of 1 Hz. The superconducting coils of the Nuclotron-type magnets utilise a hollow cable cooled with a forced two phase helium flow. These coils must operate reliably over a period of at least 20 years and thus survive 2 · 10 load cycles. Intensive R&D is necessary to find the optimal solution preventing any possible damage of the coils by the fast pulsing loads over the life time taking into account the complex fine structure of the cable and coil designs as well as its sensitive influence on the field quality, AC loss generation and quench protection. We used FEM codes to analyse critical aspects of various design options and had manufactured coils for detailed mechanical tests. These tests on samples extracted from the coil are: thermal expansion measurements in all three directions on the cable package itself and its composite elements, compression tests and investigation of the Inter Laminar Shear Stress (ILSS). The stress strain behaviour of the cable package was measured along the transversal direction; the most important one to sustain the cycling load by Lorentz forces. A second sample was fatigue tested. Successful integral operation test results for the coil mechanics have been obtained within our first experimental runs on the prototype dipole magnets already started at GSI in the end of 2008.

  7. Current ramp-up with rf waves in a tokamak

    SciTech Connect

    Fisch, N.J.; Karney, C.F.F.

    1984-08-01

    The circuit equations for current-drive in a start-up or ramp-up plasma are derived by finding appropriate response functions in the presence of an electric field. The effect of arbitrary wave-induced fluxes on runaway production and current generation can then be determined. An interpretation of the rather remarkable PLT ramp-up efficiencies, difficult to explain using the steady-state efficiency, is now possible. A parameter regime, available also on reactor-grade devices, is identified wherein quick ramp-up by lower-hybrid waves may be efficient.

  8. Current ramp-up with lower hybrid current drive in EAST

    SciTech Connect

    Ding, B. J.; Li, M. H.; Li, J. G.; Kong, E. H.; Zhang, L.; Wei, W.; Li, Y. C.; Wang, M.; Xu, H. D.; Gong, X. Z.; Shen, B.; Liu, F. K.; Shan, J. F.; Fisch, N. J.; Qin, H.; Wilson, J. R.; Collaboration: EAST Team

    2012-12-15

    More economical fusion reactors might be enabled through the cyclic operation of lower hybrid current drive. The first stage of cyclic operation would be to ramp up the plasma current with lower hybrid waves alone in low-density plasma. Such a current ramp-up was carried out successfully on the EAST tokamak. The plasma current was ramped up with a time-averaged rate of 18 kA/s with lower hybrid (LH) power. The average conversion efficiency P{sub el}/P{sub LH} was about 3%. Over a transient phase, faster ramp-up was obtained. These experiments feature a separate measurement of the L/R time at the time of current ramp up.

  9. Ramp compression of a metallic liner driven by a shaped 5 MA current on the SPHINX machine

    NASA Astrophysics Data System (ADS)

    D'Almeida, Thierry; Lassalle, Francis; Morell, Alain; Grunenwald, Julien; Zucchini, Frédéric; Loyen, Arnaud; Maysonnave, Thomas; Chuvatin, Alexandre

    2013-06-01

    SPHINX is a 6MA, 1- μs Linear Transformer Driver operated by the CEA Gramat (France) and primarily used for imploding Z-pinch loads for radiation effects studies. Among the options that are currently being considered for improving the generator performances, there is a compact Dynamic Load Current Amplifier (DLCM). A method for performing magnetic ramp compression experiments, without modifying the generator operation scheme, was developed using the DLCM to shape the initial current pulse. We present the overall experimental configuration chosen for these experiments, based on electrical and hydrodynamic simulations. Initial results obtained over a set of experiments on an aluminum cylindrical liner, ramp-compressed to a peak pressure of 23 GPa, are presented. Details of the electrical and Photonic Doppler Velocimetry (PDV) setups used to monitor and diagnose the ramp compression experiments are provided. Current profiles measured at various locations across the system, particularly the load current, agree with simulated current profile and demonstrate adequate pulse shaping by the DLCM. The liner inner free surface velocity measurements agree with the hydrocode results obtained using the measured load current as the input. Higher ramp pressure levels are foreseen in future experiments with an improved DLCM system.

  10. Ramp compression of a metallic liner driven by a shaped 5 MA current on the SPHINX machine

    NASA Astrophysics Data System (ADS)

    d'Almeida, T.; Lassalle, F.; Morell, A.; Grunenwald, J.; Zucchini, F.; Loyen, A.; Maysonnave, T.; Chuvatin, A.

    2014-05-01

    SPHINX is a 6MA, 1-us Linear Transformer Driver operated by the CEA Gramat (France) and primarily used for imploding Z-pinch loads for radiation effects studies. A method for performing magnetic ramp compression experiments was developed using a compact Dynamic Load Current Multiplier inserted between the convolute and the load, to shape the initial current pulse. We present the overall experimental configuration chosen for these experiments and initial results obtained over a set of experiments on an aluminum cylindrical liner. Current profiles measured at various critical locations across the system, are in good agreement with simulated current profiles. The liner inner free surface velocity measurements agree with the hydrocode results obtained using the measured load current as the input. The potential of the technique in terms of applications and achievable ramp pressure levels lies in the prospects for improving the DLCM efficiency.

  11. Performance of pancake coils of parallel co-wound Ag/BSCCO tape conductors in static and ramped magnetic fields

    SciTech Connect

    Schwenterly, S.W.; Lue, J.W.; Lubell, M.S.; Walker, M.S.; Hazelton, D.W.; Haldar, P.; Rice, J.A.; Hoehn, J.G. Jr.; Motowidlo, L.R.

    1994-12-31

    Critical Currents are reported for several Ag/BSCCO single-pancake coils in static magnetic fields ranging from 0 to 5 T and temperatures from 4.2 K to 105 K. The sample coils were co-wound of one to six tape conductors in parallel. Since the closed loops formed in such an arrangement could lead to eddy current heating or instability in changing fields, one of the coils was also tested in helium gas, in fields ramped at rates of up to 1.5 T/s. For these quasi-adiabatic tests, at each temperature the transport current was set just below the critical value for a preset static field of 3.3 or 4.9 T. The field was then rapidly ramped down to zero, held for 20 sec, and then ramped back up to the original value. The maximum observed temperature transient of about 1.7 K occurred at 9 K, for a field change of 4.75 T. The temperature transients became negligible when the sample was immersed in liquid helium. Above 30 K, the transients were below 1 K. These results give confidence that parallel co-wound HTSC coils are stable in a rapidly-ramped magnetic field, without undue eddy current heating.

  12. Experimental Study of Reversed Shear Alfven Eigenmodes During The Current Ramp In The Alcator C-Mod Tokamak

    SciTech Connect

    Edlund, E. M.; Porkolab, M.; Kramer, G. J.; Lin, L.; Lin, Y.; Tsuji, N.; Wukitch, S. J.

    2010-08-27

    Experiments conducted in the Alcator C-Mod tokamak at MIT have explored the physics of reversed shear Alfven eigenmodes (RSAEs) during the current ramp. The frequency evolution of the RSAEs throughout the current ramp provides a constraint on the evolution of qmin, a result which is important in transport modeling and for comparison with other diagnostics which directly measure the magnetic field line structure. Additionally, a scaling of the RSAE minimum frequency with the sound speed is used to derive a measure of the adiabatic index, a measure of the plasma compressibility. This scaling bounds the adiabatic index at 1.40 ± 0:15 used in MHD models and supports the kinetic calculation of separate electron and ion compressibilities with an ion adiabatic index close to 7~4.

  13. Role of energetic electrons during current ramp-up and production of high poloidal beta plasma in non-inductive current drive on QUEST

    NASA Astrophysics Data System (ADS)

    Tashima, Saya; Zushi, H.; Isobe, M.; Hanada, K.; Idei, H.; Nakamura, K.; Fujisawa, A.; Matsuoka, K.; Hasegawa, M.; Nagashima, Y.; Okamura, S.; Banerjee, S.; Kawasaki, S.; Nakashima, H.; Higashijima, A.

    2014-02-01

    A scenario for non-inductive current ramp-up has been demonstrated using electron cyclotron waves in the spherical tokamak QUEST. The configuration was characterized by a high toroidal magnetic mirror ratio of 2 and a steady vertical magnetic field of more than 10% of the toroidal magnetic field. The generation and confinement of energetic electrons having energy greater than 10 keV were studied using hard x-rays. Because of the energetic electron pressure, a natural divertor formed with an inboard poloidal field null at the high poloidal beta (approximately 3-4).

  14. RAMPING UP THE SNS BEAM CURRENT WITH THE LBNL BASELINE H- SOURCE

    SciTech Connect

    Stockli, Martin P; Han, Baoxi; Murray Jr, S N; Newland, Denny J; Pennisi, Terry R; Santana, Manuel; Welton, Robert F

    2009-01-01

    Over the last two years the Spallation Neutron Source (SNS) has ramped up the repetition rate, pulse length, and the beam current to reach 540 kW, which has challenged many subsystems including the H- source designed and built by Lawrence Berkeley National Laboratory (LBNL). This paper discusses the major modifications of the H- source implemented to consistently and routinely output the beam current required by the SNS beam power ramp up plan. At this time, 32 mA LINAC beam current are routinely produced, which meets the requirement for 690 kW planned for end of 2008. In June 2008, a 14-day production run used 37 mA, which is close to the 38 mA required for 1.44 MW. A medium energy beam transport (MEBT) beam current of 46 mA was demonstrated on September 2, 2008.

  15. Generation and Measurement of Relativistic Electron Bunches Characterized by a Linearly Ramped Current Profile

    SciTech Connect

    England, R. J.; Rosenzweig, J. B.; Travish, G.

    2008-05-30

    We report the first successful attempt to generate ultrashort (1-10 ps) relativistic electron bunches characterized by a ramped longitudinal current profile that rises linearly from head to tail and then falls sharply to zero. Bunches with this type of longitudinal shape may be applied to plasma-based accelerator schemes as an optimized drive beam, and to free-electron lasers as a means of reducing asymmetry in microbunching due to slippage. The scheme used to generate the ramped bunches employs an anisochronous dogleg beam line with nonlinear correction elements to compress a beam having an initial positive time-energy chirp. The beam current profile is measured using a deflecting mode cavity, and a pseudoreconstruction of the beam's longitudinal phase space distribution is obtained by using this diagnostic with a residual horizontal dispersion after the dogleg.

  16. Microsecond ramp compression of a metallic liner driven by a 5 MA current on the SPHINX machine using a dynamic load current multiplier pulse shaping

    SciTech Connect

    D'Almeida, T.; Lassalle, F.; Morell, A.; Grunenwald, J.; Zucchini, F.; Loyen, A.; Maysonnave, T.; Chuvatin, A. S.

    2013-09-15

    SPHINX is a 6 MA, 1-μs Linear Transformer Driver (LTD) operated by the CEA Gramat (France) and primarily used for imploding Z-pinch loads for radiation effects studies. Among the options that are currently being evaluated to improve the generator performances are an upgrade to a 20 MA, 1-μs LTD machine and various power amplification schemes, including a compact Dynamic Load Current Multiplier (DLCM). A method for performing magnetic ramp compression experiments, without modifying the generator operation scheme, was developed using the DLCM to shape the initial current pulse in order to obtain the desired load current profile. In this paper, we discuss the overall configuration that was selected for these experiments, including the choice of a coaxial cylindrical geometry for the load and its return current electrode. We present both 3-D Magneto-hydrodynamic and 1D Lagrangian hydrodynamic simulations which helped guide the design of the experimental configuration. Initial results obtained over a set of experiments on an aluminium cylindrical liner, ramp-compressed to a peak pressure of 23 GPa, are presented and analyzed. Details of the electrical and laser Doppler interferometer setups used to monitor and diagnose the ramp compression experiments are provided. In particular, the configuration used to field both homodyne and heterodyne velocimetry diagnostics in the reduced access available within the liner's interior is described. Current profiles measured at various critical locations across the system, particularly the load current, enabled a comprehensive tracking of the current circulation and demonstrate adequate pulse shaping by the DLCM. The liner inner free surface velocity measurements obtained from the heterodyne velocimeter agree with the hydrocode results obtained using the measured load current as the input. An extensive hydrodynamic analysis is carried out to examine information such as pressure and particle velocity history profiles or magnetic

  17. Microsecond ramp compression of a metallic liner driven by a 5 MA current on the SPHINX machine using a dynamic load current multiplier pulse shaping

    NASA Astrophysics Data System (ADS)

    d'Almeida, T.; Lassalle, F.; Morell, A.; Grunenwald, J.; Zucchini, F.; Loyen, A.; Maysonnave, T.; Chuvatin, A. S.

    2013-09-01

    SPHINX is a 6 MA, 1-μs Linear Transformer Driver (LTD) operated by the CEA Gramat (France) and primarily used for imploding Z-pinch loads for radiation effects studies. Among the options that are currently being evaluated to improve the generator performances are an upgrade to a 20 MA, 1-μs LTD machine and various power amplification schemes, including a compact Dynamic Load Current Multiplier (DLCM). A method for performing magnetic ramp compression experiments, without modifying the generator operation scheme, was developed using the DLCM to shape the initial current pulse in order to obtain the desired load current profile. In this paper, we discuss the overall configuration that was selected for these experiments, including the choice of a coaxial cylindrical geometry for the load and its return current electrode. We present both 3-D Magneto-hydrodynamic and 1D Lagrangian hydrodynamic simulations which helped guide the design of the experimental configuration. Initial results obtained over a set of experiments on an aluminium cylindrical liner, ramp-compressed to a peak pressure of 23 GPa, are presented and analyzed. Details of the electrical and laser Doppler interferometer setups used to monitor and diagnose the ramp compression experiments are provided. In particular, the configuration used to field both homodyne and heterodyne velocimetry diagnostics in the reduced access available within the liner's interior is described. Current profiles measured at various critical locations across the system, particularly the load current, enabled a comprehensive tracking of the current circulation and demonstrate adequate pulse shaping by the DLCM. The liner inner free surface velocity measurements obtained from the heterodyne velocimeter agree with the hydrocode results obtained using the measured load current as the input. An extensive hydrodynamic analysis is carried out to examine information such as pressure and particle velocity history profiles or magnetic

  18. Behavior of a high-temperature superconducting conductor on a round core cable at current ramp rates as high as 67.8 kA s-1 in background fields of up to 19 T

    NASA Astrophysics Data System (ADS)

    Michael, P. C.; Bromberg, L.; van der Laan, D. C.; Noyes, P.; Weijers, H. W.

    2016-04-01

    High temperature superconducting (HTS) conductor-on-round-core (CORC®) cables have been developed for use in power transmission systems and large high-field magnets. The use of high-current conductors for large-scale magnets reduces system inductance and limits the peak voltage needed for ramped field operation. A CORC® cable contains a large number of RE-Ba2Cu3O7-δ (RE = rare earth) (REBCO) coated conductors, helically wound in multiple layers on a thin, round former. Large-scale applications, such as fusion and accelerator magnets, require current ramp rates of several kilo-Amperes per second during pulsed operation. This paper presents results that demonstrate the electromagnetic stability of a CORC® cable during transient conditions. Measurements were performed at 4.2 K using a 1.55 m long CORC® cable in background fields of up to 19 T. Repeated current pulses in a background field of 19 T at current ramp rates of up to 67.8 kA s-1 to approximately 90% of the cable’s quench current at that field, did not show any sign of degradation in cable performance due to excessive ac loss or electromagnetic instability. The very high current ramp rates applied during these tests were used to compensate, to the extent possible, the limited cable length accommodated by the test facility, assuming that the measured results could be extrapolated to longer length cables operated at proportionally lower current ramp rates. No shift of the superconducting transition to lower current was measured when the current ramp rate was increased from 25 A s-1 to 67.8 kA s-1. These results demonstrate the viability of CORC® cables for use in low-inductance magnets that operate at moderate to high current ramp rates.

  19. Meniscal Ramp Lesions

    PubMed Central

    Chahla, Jorge; Dean, Chase S.; Moatshe, Gilbert; Mitchell, Justin J.; Cram, Tyler R.; Yacuzzi, Carlos; LaPrade, Robert F.

    2016-01-01

    Meniscal ramp lesions are more frequently associated with anterior cruciate ligament (ACL) injuries than previously recognized. Some authors suggest that this entity results from disruption of the meniscotibial ligaments of the posterior horn of the medial meniscus, whereas others support the idea that it is created by a tear of the peripheral attachment of the posterior horn of the medial meniscus. Magnetic resonance imaging (MRI) scans have been reported to have a low sensitivity, and consequently, ramp lesions often go undiagnosed. Therefore, to rule out a ramp lesion, an arthroscopic evaluation with probing of the posterior horn of the medial meniscus should be performed. Several treatment options have been reported, including nonsurgical management, inside-out meniscal repair, or all-inside meniscal repair. In cases of isolated ramp lesions, a standard meniscal repair rehabilitation protocol should be followed. However, when a concomitant ACL reconstruction (ACLR) is performed, the rehabilitation should follow the designated ACLR postoperative protocol. The purpose of this article was to review the current literature regarding meniscal ramp lesions and summarize the pertinent anatomy, biomechanics, diagnostic strategies, recommended treatment options, and postoperative protocol. PMID:27504467

  20. Integrated modelling of DEMO-FNS current ramp-up scenario and steady-state regime

    NASA Astrophysics Data System (ADS)

    Dnestrovskij, A. Yu.; Kuteev, B. V.; Bykov, A. S.; Ivanov, A. A.; Lukash, V. E.; Medvedev, S. Yu.; Sergeev, V. Yu.; Sychugov, D. Yu.; Khayrutdinov, R. R.

    2015-06-01

    An approach to the integrated modelling of plasma regimes in the projected neutron source DEMO-FNS based on different codes is developed. The consistency check of the steady-state regime is carried out, namely, the possibility of the plasma current ramp-up, acceptance of growth rates of MHD modes in the steady-state regime, heat loads to the wall and divertor plates and neutron yield value. The following codes are employed for the integrated modelling. ASTRA transport code for calculation of plasma parameters in the steady-state regime, NUBEAM Monte Carlo code for NBI incorporated into the ASTRA code, DINA free boundary equilibrium and evolution code, SPIDER free boundary equilibrium and equilibrium reconstruction code, KINX ideal MHD stability code, TOKSTAB rigid shift vertical stability code, edge and divertor plasma B2SOLPS5.2 code and Semi-analytic Hybrid Model (SHM) code for self-consistent description of the core, edge and divertor plasmas based on the experimental scaling laws. The consistent steady-state regime for the DEMO-FNS plasma and the plasma current ramp-up scenario are developed using the integrated modelling approach. Passive copper coils are suggested to reduce the plasma vertical instability growth rate to below ˜30 s-1.The outer divertor operation in the ‘high-recycling’ regime is numerically demonstrated with a maximal heat flux density of 7-9 MW m-2 that is technically acceptable.

  1. Novel free-boundary equilibrium and transport solver with theory-based models and its validation against ASDEX Upgrade current ramp scenarios

    NASA Astrophysics Data System (ADS)

    Fable, E.; Angioni, C.; Casson, F. J.; Told, D.; Ivanov, A. A.; Jenko, F.; McDermott, R. M.; Medvedev, S. Yu; Pereverzev, G. V.; Ryter, F.; Treutterer, W.; Viezzer, E.; the ASDEX Upgrade Team

    2013-12-01

    Tokamak scenario development requires an understanding of the properties that determine the kinetic profiles in non-steady plasma phases and of the self-consistent evolution of the magnetic equilibrium. Current ramps are of particular interest since many transport-relevant parameters explore a large range of values and their impact on transport mechanisms has to be assessed. To this purpose, a novel full-discharge modelling tool has been developed, which couples the transport code ASTRA (Pereverzev et al 1991 IPP Report 5/42) and the free boundary equilibrium code SPIDER (Ivanov et al 2005 32nd EPS Conf. on Plasma Physics vol 29C (ECA) P-5.063 and http://epsppd.epfl.ch/Tarragona/pdf/P5_063.pdf), utilizing a specifically designed coupling scheme. The current ramp-up phase can be accurately and reliably simulated using this scheme, where a plasma shape, position and current controller is applied, which mimics the one of ASDEX Upgrade. Transport of energy is provided by theory-based models (e.g. TGLF (Staebler et al 2007 Phys. Plasmas 14 055909)). A recipe based on edge-relevant parameters (Scott 2000 Phys. Plasmas 7 1845) is proposed to resolve the low current phase of the current ramps, where the impact of the safety factor on micro-instabilities could make quasi-linear approaches questionable in the plasma outer region. Current ramp scenarios, selected from ASDEX Upgrade discharges, are then simulated to validate both the coupling with the free-boundary evolution and the prediction of profiles. Analysis of the underlying transport mechanisms is presented, to clarify the possible physics origin of the observed L-mode empirical energy confinement scaling. The role of toroidal micro-instabilities (ITG, TEM) and of non-linear effects is discussed.

  2. Magnetic current sensor

    NASA Technical Reports Server (NTRS)

    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.

  3. Low Current Magnet

    NASA Technical Reports Server (NTRS)

    1992-01-01

    Because Goddard Space Flight Center needed a way to cool sensors aboard the AXAF, a low current superconducting magnet was developed under contract by Cryomagnetics, Inc. The magnet, now commercially available, reduced the rate of helium consumption, extending the lifetime of the AXAF's x-ray spectrometer. On Earth, it offers a way to reduce operating costs through smaller, less expensive power supplies and reduced use of coolant. The magnet has particular advantages for MRI systems, as it is safer and has lower maintenance requirements.

  4. Magnetic ramp scale at supercritical perpendicular collisionless shocks: Full particle electromagnetic simulations

    SciTech Connect

    Yang, Zhongwei; Lu, Quanming; Gao, Xinliang; Huang, Can; Yang, Huigen; Hu, Hongqiao; Han, Desheng; Liu, Ying

    2013-09-15

    Supercritical perpendicular collisionless shocks are known to exhibit foot, ramp, and overshoot structures. The shock ramp structure is in a smaller scale in contrast to other microstructures (foot and overshoot) within the shock front. One-dimensional full particle simulations of strictly perpendicular shocks over wide ranges of ion beta β{sub i}, Alfvén Mach number M{sub A}, and ion-to-electron mass ratio m{sub i}/m{sub e} are presented to investigate the impact of plasma parameters on the shock ramp scale. Main results are (1) the ramp scale can be as small as several electron inertial length. (2) The simulations suggest that in a regime below the critical ion beta value, the shock front undergoes a periodic self-reformation and the shock ramp scale is time-varying. At higher ion beta values, the shock front self-reformation is smeared. At still higher ion beta value, the motion of reflected ions is quite diffuse so that they can lead to a quasi-steady shock ramp. Throughout the above three conditions, the shock ramp thickness increases with β{sub i}. (3) The increase (decrease) in Mach number and the decrease (increase) in the beta value have almost equivalent impact on the state (i.e., stationary or nonstationary) of the shock ramp. Both of front and ramp thicknesses are increased with M{sub A}.

  5. Dendritic flux avalanches and the accompanied thermal strain in type-II superconducting films: effect of magnetic field ramp rate

    NASA Astrophysics Data System (ADS)

    Jing, Ze; Yong, Huadong; Zhou, You-He

    2015-07-01

    Dendritic flux avalanches and the accompanying thermal stress and strain in type-II superconducting thin films under transverse magnetic fields are numerically simulated in this paper. The influence of the magnetic field ramp rate, edge defects, and the temperature of the surrounding coolant are considered. Maxwell's equations and the highly nonlinear E-J power-law characteristics of superconductors, coupled with the heat diffusion equation, are adopted to formulate these phenomena. The fast Fourier transform-based iteration scheme is used to track the evolution of the magnetic flux and the temperature in the superconducting film. The finite element method is used to analyze the thermal stress and strain induced in the superconducting film. It is found that the ramp rate has a significant effect on the flux avalanche process. The avalanches nucleate more easily for a film under a large magnetic field ramp rate than for a film under a small one. In addition, the avalanches always initiate from edge defects or areas that experience larger magnetic fields. The superconducting films experience large thermal strain induced by the large temperature gradient during the avalanche process, which may even lead to the failure of the sample.

  6. Self-focusing and self-compression of a laser pulse in the presence of an external tapered magnetized density-ramp plasma

    NASA Astrophysics Data System (ADS)

    Saedjalil, N.; Jafari, S.

    2016-06-01

    In this paper, the effects of external tapered axial magnetic field and plasma density-ramp on the spatiotemporal evolution of the laser pulse in inhomogeneous plasma have been studied. The external magnetic field can modify the refractive index of plasma and consequently intensifies the nonlinear effects. By considering the relativistic nonlinearity effect, self-focusing and self-compression of the laser beam propagating through the magnetized plasma have been investigated, numerically. Numerical results indicate that self-focusing and self-compression are better enhanced in a tapered magnetic field than in a uniform one. Besides, in plasma density-ramp profile, self-focusing and self-compression of the laser beam improve in comparison with no ramp structure. In addition, with increasing both the slope of the density ramp and slope constant parameter of the tapered magnetic field, the laser focusing increases, properly, in short distances of the laser propagation through the plasma.

  7. Generation and Characterization of Electron Bunches with Ramped Current Profiles in a Dual-Frequency Superconducting Linear Accelerator

    NASA Astrophysics Data System (ADS)

    Piot, P.; Behrens, C.; Gerth, C.; Dohlus, M.; Lemery, F.; Mihalcea, D.; Stoltz, P.; Vogt, M.

    2012-01-01

    We report on the successful experimental generation of electron bunches with ramped current profiles. The technique relies on impressing nonlinear correlations in the longitudinal phase space using a superconducing radio frequency linear accelerator operating at two frequencies and a current-enhancing dispersive section. The produced ˜700-MeV bunches have peak currents of the order of a kilo-Ampère. Data taken for various accelerator settings demonstrate the versatility of the method and, in particular, its ability to produce current profiles that have a quasilinear dependency on the longitudinal (temporal) coordinate. The measured bunch parameters are shown, via numerical simulations, to produce gigavolt-per-meter peak accelerating electric fields with transformer ratios larger than 2 in dielectric-lined waveguides.

  8. Generation and Characterization of Electron Bunches with Ramped Current Profiles in a Dual-Frequency Superconducting Linear Accelerator

    DOE PAGESBeta

    Piot, P.; Behrens, C.; Gerth, C.; Dohlus, M.; Lemery, F.; Mihalcea, D.; Stoltz, P.; Vogt, M.

    2011-09-07

    We report on the successful experimental generation of electron bunches with ramped current profiles. The technique relies on impressing nonlinear correlations in the longitudinal phase space using a superconducing radiofrequency linear accelerator operating at two frequencies and a current-enhancing dispersive section. The produced {approx} 700-MeV bunches have peak currents of the order of a kilo-Ampere. Data taken for various accelerator settings demonstrate the versatility of the method and in particular its ability to produce current profiles that have a quasi-linear dependency on the longitudinal (temporal) coordinate. The measured bunch parameters are shown, via numerical simulations, to produce gigavolt-per-meter peak acceleratingmore » electric fields with transformer ratios larger than 2 in dielectric-lined waveguides.« less

  9. Generation and Characterization of Electron Bunches with Ramped Current Profiles in a Dual-Frequency Superconducting Linear Accelerator

    SciTech Connect

    Piot, P.; Behrens, C.; Gerth, C.; Dohlus, M.; Lemery, F.; Mihalcea, D.; Stoltz, P.; Vogt, M.

    2011-09-07

    We report on the successful experimental generation of electron bunches with ramped current profiles. The technique relies on impressing nonlinear correlations in the longitudinal phase space using a superconducing radiofrequency linear accelerator operating at two frequencies and a current-enhancing dispersive section. The produced {approx} 700-MeV bunches have peak currents of the order of a kilo-Ampere. Data taken for various accelerator settings demonstrate the versatility of the method and in particular its ability to produce current profiles that have a quasi-linear dependency on the longitudinal (temporal) coordinate. The measured bunch parameters are shown, via numerical simulations, to produce gigavolt-per-meter peak accelerating electric fields with transformer ratios larger than 2 in dielectric-lined waveguides.

  10. Principal Quasi-Isentropes of Several Materials to Multi-Megabar Pressure from Analysis of Magnetically Driven Ramp Compression Data

    NASA Astrophysics Data System (ADS)

    Davis, Jean-Paul; Martin, Matthew; Knudson, Marcus

    2011-06-01

    Quasi-isentropic ramp-wave experiments promise accurate equation-of-state (EOS) data in the solid phase at relatively low temperatures and multimegabar pressures. In this range of pressure, isothermal diamond-anvil techniques have limited pressure accuracy due to reliance on theoretical EOS of calibration standards, thus accurate quasi-isentropic compression data would help immensely in constraining EOS models. Multi-megabar ramp compression experiments using the Z Machine at Sandia as a magnetic drive with stripline targets have been performed on tantalum, copper, gold, beryllium, molybdenum, and aluminum metals as well as lithium fluoride crystal. Much of the data from these experiments are analyzed using a single-sample inverse Lagrangian approach. This technique, and the quantification of its uncertainties, will be described in detail. Results will be presented for selected materials, with comparisons to independently developed EOS. *Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  11. Experimental observation and theoretical modeling of the effect of magnetic field on the strength of molybdenum under ramp wave compression

    NASA Astrophysics Data System (ADS)

    Ding, Jow; Alexander, C.; Asay, James

    2013-06-01

    A new experimental technique has been developed at Sandia National Labs to study the dynamic material strength at high pressures using ``magnetically applied pressure shear (MAPS)'' ramp waves. In order to apply sufficient shear traction to the test sample, the driver must have substantial strength. Molybdenum was selected for this reason along with its good electrical conductivity. It was observed that an imposed magnetic field of around 10 Tesla induced some annealing on molybdenum. Furthermore, when subjected directly to magnetohydrodynamic loading as encountered for the driver material, molybdenum exhibited an apparently stiff response and did not show a discernible elastic plastic transition. To better understand the experiments and establish a predictive capability for molybdenum, a tentative strength model that incorporates the possible magnetic effects including magnetic diffusion, Joule heating, and the coupling between the magnetic field and material strength has been developed. Experimental observations and the model will be discussed. Sandia National Labs is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corp., for the U.S. Dept. of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  12. Magnetic tape lightning current detectors

    NASA Technical Reports Server (NTRS)

    Crouch, K. E.; Jafferis, W.

    1980-01-01

    Development and application tests of a low cost, passive, peak lightning current detector (LCD) found it to provide measurements with accuracies of + or - 5 percent to + or - 10 percent depending on the readout method employed. The LCD uses magnetic audio recording tape to sense the magnitude of the peak magnetic field around a conductor carrying lightning currents. The test results showed that the length of audio tape erased was linearly related to the peak simulated lightning currents in a round conductor. Accuracies of + or - 10 percent were shown for measurements made using a stopwatch readout technique to determine the amount of tape erased by the lightning current. Where more accurate data are desired, the tape is played and the output recorded on a strip chart, oscilloscope, or some other means so that measurements can be made on that recording. Conductor dimensions, tape holder dimensions, and tape formulation must also be considered to obtain a more accurate result.

  13. Generation and characterization of electron bunches with ramped current profile at the FLASH facility

    SciTech Connect

    Piot, P.; Behrens, C.; Gerth, C.; Lemery, F.; Mihalcea, D.; Vogt, M.; /DESY

    2011-09-01

    We report on the successful generation of electron bunches with current prof les that have a quasi-linear dependency on the longitudinal coordinate. The technique relies on impressing nonlinear correlations in the longitudinal phase space using a linac operating at two frequencies (1.3 and 3.9 GHz) and a bunch compressor. Data taken for various accelerator settings demonstrate the versatility of the method. The produced bunches have parameters well matched to drive high-gradient accelerating field with enhanced transformer ratio in beam-driven accelerators based on sub-mm-sizes dielectric or plasma structures.

  14. Resistors Improve Ramp Linearity

    NASA Technical Reports Server (NTRS)

    Kleinberg, L. L.

    1982-01-01

    Simple modification to bootstrap ramp generator gives more linear output over longer sweep times. New circuit adds just two resistors, one of which is adjustable. Modification cancels nonlinearities due to variations in load on charging capacitor and due to changes in charging current as the voltage across capacitor increases.

  15. Measurements of the persistent current decay and snapback effect in Tevatron dipole magnets

    SciTech Connect

    Velev, G.V.; Bauer, P.; DiMarco, J.; Hanft, R.; Lamm, M.; Schlabach, P.; Sylvester, C.; Tartaglia, M.; Tompkins, J.C.; /Fermilab

    2006-08-01

    A systematic study of the persistent current decay and snapback effect in the fields of Tevatron accelerator dipoles was performed at the Fermilab Magnet Test Facility (MTF). The decay and snapback were measured under a range of conditions including variations of the current ramp parameters and magnet operational history. The study has mostly focused on the dynamic behavior of the normal sextupole component. In addition, the paper presents the persistent current effects observed in the other allowed field harmonics as well. The results provide new information about the previously observed ''excess'' decay during the first several seconds of the sextupole decay during injection and the correlation between the snapback amplitude and its duration.

  16. Simulations towards the achievement of non-inductive current ramp-up and sustainment in the National Spherical Torus Experiment Upgrade

    DOE PAGESBeta

    Poli, F. M.; Andre, R. G.; Bertelli, N.; Gerhardt, S. P.; Mueller, D.; Taylor, G.

    2015-10-30

    One of the goals of the National Spherical Torus Experiment Upgrade (NSTX-U) (Menard et al 2012 Nucl. Fusion 52 083015) is the demonstration of fully non-inductive start-up, current ramp-up and sustainment. This work discusses predictive simulations where the available heating and current drive systems are combined to maximize the non-inductive current and minimize the solenoidal contribution. Radio-frequency waves at harmonics higher than the ion cyclotron resonance (high-harmonic fast waves (HHFW)) and neutral beam injection are used to ramp the plasma current non-inductively starting from an initial Ohmic plasma. An interesting synergy is observed in the simulations between the HHFW andmore » electron cyclotron (EC) wave heating. Furthermore, time-dependent simulations indicate that, depending on the phasing of the HHFW antenna, EC wave heating can significantly increase the effectiveness of the radio-frequency power, by heating the electrons and increasing the current drive efficiency, thus relaxing the requirements on the level of HHFW power that needs to be absorbed in the core plasma to drive the same amount of fast-wave current.« less

  17. Simulations towards the achievement of non-inductive current ramp-up and sustainment in the National Spherical Torus Experiment Upgrade

    SciTech Connect

    Poli, F. M.; Andre, R. G.; Bertelli, N.; Gerhardt, S. P.; Mueller, D.; Taylor, G.

    2015-10-30

    One of the goals of the National Spherical Torus Experiment Upgrade (NSTX-U) (Menard et al 2012 Nucl. Fusion 52 083015) is the demonstration of fully non-inductive start-up, current ramp-up and sustainment. This work discusses predictive simulations where the available heating and current drive systems are combined to maximize the non-inductive current and minimize the solenoidal contribution. Radio-frequency waves at harmonics higher than the ion cyclotron resonance (high-harmonic fast waves (HHFW)) and neutral beam injection are used to ramp the plasma current non-inductively starting from an initial Ohmic plasma. An interesting synergy is observed in the simulations between the HHFW and electron cyclotron (EC) wave heating. Furthermore, time-dependent simulations indicate that, depending on the phasing of the HHFW antenna, EC wave heating can significantly increase the effectiveness of the radio-frequency power, by heating the electrons and increasing the current drive efficiency, thus relaxing the requirements on the level of HHFW power that needs to be absorbed in the core plasma to drive the same amount of fast-wave current.

  18. Simulations towards the achievement of non-inductive current ramp-up and sustainment in the National Spherical Torus Experiment Upgrade

    NASA Astrophysics Data System (ADS)

    Poli, F. M.; Andre, R. G.; Bertelli, N.; Gerhardt, S. P.; Mueller, D.; Taylor, G.

    2015-11-01

    One of the goals of the National Spherical Torus Experiment Upgrade (NSTX-U) (Menard et al 2012 Nucl. Fusion 52 083015) is the demonstration of fully non-inductive start-up, current ramp-up and sustainment. This work discusses predictive simulations where the available heating and current drive systems are combined to maximize the non-inductive current and minimize the solenoidal contribution. Radio-frequency waves at harmonics higher than the ion cyclotron resonance (high-harmonic fast waves (HHFW)) and neutral beam injection are used to ramp the plasma current non-inductively starting from an initial Ohmic plasma. An interesting synergy is observed in the simulations between the HHFW and electron cyclotron (EC) wave heating. Time-dependent simulations indicate that, depending on the phasing of the HHFW antenna, EC wave heating can significantly increase the effectiveness of the radio-frequency power, by heating the electrons and increasing the current drive efficiency, thus relaxing the requirements on the level of HHFW power that needs to be absorbed in the core plasma to drive the same amount of fast-wave current.

  19. Three Magnetic Direct-Current Sensors

    NASA Technical Reports Server (NTRS)

    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.

  20. A VERY FAST RAMPING MUON SYNCHROTRON FOR A NEUTRINO FACTORY.

    SciTech Connect

    SUMMERS,D.J.BERG,J.S.PALMER,R.B.GARREN,A.A.

    2003-05-12

    A 4600 Hz fast ramping synchrotron is studied as an economical way of accelerating muons from 4 to 20 GeV/c for a neutrino factory. Eddy current losses are minimized by the low machine duty cycle plus thin grain oriented silicon steel laminations and thin copper wires. Combined function magnets with high gradients alternating within single magnets form the lattice. Muon survival is 83%.

  1. How to Properly Measure a Current-Voltage Relation?—Interpolation vs. Ramp Methods Applied to Studies of GABAA Receptors

    PubMed Central

    Yelhekar, Tushar D.; Druzin, Michael; Karlsson, Urban; Blomqvist, Erii; Johansson, Staffan

    2016-01-01

    The relation between current and voltage, I-V relation, is central to functional analysis of membrane ion channels. A commonly used method, since the introduction of the voltage-clamp technique, to establish the I-V relation depends on the interpolation of current amplitudes recorded at different steady voltages. By a theoretical computational approach as well as by experimental recordings from GABAA-receptor mediated currents in mammalian central neurons, we here show that this interpolation method may give reversal potentials and conductances that do not reflect the properties of the channels studied under conditions when ion flux may give rise to concentration changes. Therefore, changes in ion concentrations may remain undetected and conclusions on changes in conductance, such as during desensitization, may be mistaken. In contrast, an alternative experimental approach, using rapid voltage ramps, enable I-V relations that much better reflect the properties of the studied ion channels. PMID:26869882

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Current-Produced Magnetic Field Effects on Current Collection

    NASA Technical Reports Server (NTRS)

    Khazanov, George V.; Stone, N. H.; Whitaker, Ann F. (Technical Monitor)

    2002-01-01

    Current collection by an infinitely long, conducting cylinder in a magnetized plasma, taking into account the magnetic field of the collected current, is discussed. A region of closed magnetic surfaces disconnects the cylinder from infinity. Due to this, the collected current depends on the ratio between this region and the plasma sheath region and, under some conditions, current reduction arises. The current collection along a realistic "bare wire" space tether is considered. A number of factors are taken into account, including the resistance of the wire and shielding resulting from the current-induced magnetic field produced by current flow in the tether. The plasma density, tether length and radius, the geomagnetic field strength and angle to the orbital velocity vector were all used as parameters in the study. It is shown that magnetic shielding for certain tether system configurations, when combined with particular values of the governing parameters, significantly reduces the collected current. Specifically, it is shown that an electrodynamic tether in the "thruster" mode suffers greater reduction from magnetic shielding than a tether with the same characteristics deployed in the "generator" mode. We find that, for both modes, current-induced magnetic shielding becomes more significant as plasma density and wire radius increase. The same is true for the dependence on the angle of the geomagnetic field to the orbital velocity vector and the motion-induced electric field for the generator mode For the thruster mode, the effect is larger for smaller angles. In both operating modes, the shielding is more important for smaller angles between the tether and magnetic field. In addition to the above dependencies, the effect for the thruster mode essentially depends on the tether length. In general, any parametric change that increases tether current, relative to the strength of the electric field between the tether and the ambient plasma, will increase the shielding

  4. Ohmic currents and predecoupling magnetism

    SciTech Connect

    Giovannini, Massimo; Nguyen Quynh Lan

    2009-07-15

    Ohmic currents induced prior to decoupling are investigated in a standard transport model accounting both for the expansion of the background geometry as well as of its relativistic inhomogeneities. The relative balance of the Ohmic electric fields in comparison with the Hall and thermoelectric contributions is specifically addressed. The impact of the Ohmic currents on the evolution of curvature perturbations is discussed numerically and it is shown to depend explicitly upon the evolution of the conductivity.

  5. Thinning of current sheets and magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Singh, N.; Deverapalli, C.

    Using three-dimensional particle-in-cell (3DPIC) simulations, we study the formation of a thin current sheet. The processes associated with thin current sheets reported here include its thinning, associated potential well in its central part, ion acceleration into the well, current-driven ion mode instabilities, electron and ion heating, current sheet re- broadening, current disruption in the central part of the current sheet and magnetic reconnection. It is shown that current driven instabilities become explosive when the preferential heating of electrons by the ions make electron temperature higher than that of the ions. This explosive stage is associated with high plasma resistivity, current disruption and bifurcated current sheets. The current disruption is linked to the magnetic reconnection.

  6. Simulating Ramp Compression of Diamond

    NASA Astrophysics Data System (ADS)

    Godwal, B. K.; Gonzàlez-Cataldo, F. J.; Jeanloz, R.

    2014-12-01

    We model ramp compression, shock-free dynamic loading, intended to generate a well-defined equation of state that achieves higher densities and lower temperatures than the corresponding shock Hugoniot. Ramp loading ideally approaches isentropic compression for a fluid sample, so is useful for simulating the states deep inside convecting planets. Our model explicitly evaluates the deviation of ramp from "quasi-isentropic" compression. Motivated by recent ramp-compression experiments to 5 TPa (50 Mbar), we calculate the room-temperature isotherm of diamond using first-principles density functional theory and molecular dynamics, from which we derive a principal isentrope and Hugoniot by way of the Mie-Grüneisen formulation and the Hugoniot conservation relations. We simulate ramp compression by imposing a uniaxial strain that then relaxes to an isotropic state, evaluating the change in internal energy and stress components as the sample relaxes toward isotropic strain at constant volume; temperature is well defined for the resulting hydrostatic state. Finally, we evaluate multiple shock- and ramp-loading steps to compare with single-step loading to a given final compression. Temperatures calculated for single-step ramp compression are less than Hugoniot temperatures only above 500 GPa, the two being close to each other at lower pressures. We obtain temperatures of 5095 K and 6815 K for single-step ramp loading to 600 and 800 GPa, for example, which compares well with values of ~5100 K and ~6300 K estimated from previous experiments [PRL,102, 075503, 2009]. At 800 GPa, diamond is calculated to have a temperature of 500 K along the isentrope; 900 K under multi-shock compression (asymptotic result after 8-10 steps); and 3400 K under 3-step ramp loading (200-400-800 GPa). Asymptotic multi-step shock and ramp loading are indistinguishable from the isentrope, within present uncertainties. Our simulations quantify the manner in which current experiments can simulate the

  7. Dendritic flux instabilities in YB a2C u3O7 -x films: Effects of temperature and magnetic field ramp rate

    NASA Astrophysics Data System (ADS)

    Baruch-El, E.; Baziljevich, M.; Shapiro, B. Ya.; Johansen, T. H.; Shaulov, A.; Yeshurun, Y.

    2016-08-01

    Our recent success in triggering dendritic flux instabilities in YB a2C u3O7 -δ (YBCO) films by applying magnetic fields at ultrahigh rates is followed here by a detailed study of the effect as a function of the field ramp rate, B˙a, and temperature, T . We trace the borderline in the B˙a-T plane separating regions of smooth, gradual flux penetration and dendritic flux avalanches. In addition, we describe the changes in the dendritic morphology in the instability region as a result of changes in either B˙a or T . Our experimental results, showing a monotonic increase of the avalanche threshold field ramp rate with temperature, are discussed in the framework of existing theories. On the basis of these theories we also explain the high stability of YBCO to dendritic avalanches as compared to, e.g., Mg B2 , identifying the flux flow resistivity, rather than any of the thermal parameters, as the main parameter governing the film stability.

  8. How does relativity affect magnetically induced currents?

    PubMed

    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. PMID:26243659

  9. Alternating current driven instability in magnetic junctions.

    PubMed

    Epshtein, E M; Zilberman, P E

    2009-04-01

    An effect is considered of alternating (high-frequency) current on the spin-valve-type magnetic junction configuration. The stability with respect to small fluctuations is investigated in the macrospin approximation. When the current frequency is close to the eigenfrequency (precession frequency) of the free layer, parametric resonance occurs. Both collinear configurations, antiparallel and parallel, can become unstable under resonance conditions. The antiparallel configuration can also become unstable under non-resonant conditions. The threshold current density amplitude is of the order of the dc current density for switching of the magnetic junction. PMID:21825350

  10. Transformer current sensor for superconducting magnetic coils

    DOEpatents

    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.

  11. Validation of Finite-Element Models of Persistent-Current Effects in Nb3Sn Accelerator Magnets

    SciTech Connect

    Wang, X.; Ambrosio, G.; Chlachidze, G.; Collings, E. W.; Dietderich, D. R.; DiMarco, J.; Felice, H.; Ghosh, A. K.; Godeke, A.; Gourlay, S. A.; Marchevsky, M.; Prestemon, S. O.; Sabbi, G.; Sumption, M. D.; Velev, G. V.; Xu, X.; Zlobin, A. V.

    2015-01-06

    Persistent magnetization currents are induced in superconducting filaments during the current ramping in magnets. The resulting perturbation to the design magnetic field leads to field quality degradation, in particular at low field where the effect is stronger relative to the main field. The effects observed in NbTi accelerator magnets were reproduced well with the critical-state model. However, this approach becomes less accurate for the calculation of the persistent-current effects observed in Nb3Sn accelerator magnets. Here a finite-element method based on the measured strand magnetization is validated against three state-of-art Nb3Sn accelerator magnets featuring different subelement diameters, critical currents, magnet designs and measurement temperatures. The temperature dependence of the persistent-current effects is reproduced. Based on the validated model, the impact of conductor design on the persistent current effects is discussed. The performance, limitations and possible improvements of the approach are also discussed.

  12. Magnetic reconnection driven by current repulsion

    NASA Technical Reports Server (NTRS)

    Richard, R. L.; Sydora, R. D.; Ashour-Abdalla, M.

    1990-01-01

    The evolution of an equilibrium consisting of two magnetic islands with oppositely directed currents embedded in a strong magnetic field is investigated, using numerical simulation methods. The rapid development of an ideal magnetohydrodynamic instability is observed, which first rotates and then expels the islands. The growth rate is on the order of the inverse of the Alfven transit time and is much higher than that for magnetic island coalescence. In the nonlinear stage, resistivity becomes important as the reconnection process ensues and dissipates the magnetic energy. The growth rate of the instability is a weak function of the plasma beta and other plasma parameters such as S, the magnetic Reynolds number. An energy principle analysis, based on eigenfunctions obtained from the simulation, confirms the existence of the instability.

  13. Model for RHIC ramp controls

    SciTech Connect

    Kewisch, J.; Mane, V.; Clifford, T.; Hartmann, H.; Kahn, T.; Oerter, B.; Peggs, S.

    1994-08-01

    This paper introduces the hardware and software concepts for the implementation of the ramp controls. The hardware part of the ramp controls consists of a number of multi-purpose Wave Form Generators (WFGS) which control the settings of accelerator hardware directly or indirectly by controlling their WFG. A Real Time Data Link (RTDL) data transfer system connects the WFGs in a three layer architecture. To the usual two layers which generate an independent timing signal and dependent set points, respectively, an intermediate layer is added which produces accelerator parameters such as the magnet strength. The task of the bottom layer is therefore reduced to the function of implementing those parameters. This architecture de-couples two independent functions which axe normally folded together. The function of the hardware becomes modular and easily maintainable. The ramp control software is layered in the same way. Between the top layer (the ramp procedure application program) and the bottom layer (the hardware interface) an additional layer of ``manager`` programs allow operation of accelerator subsystems.

  14. Measurements of the persistent current decay and snapback effect in Nb3Sn Fermilab-built accelerator prototype magnets

    SciTech Connect

    Velev, G.V.; Chlachidze, G.; DiMarco, J.; Kashikhin, V.V.; /Fermilab

    2012-05-01

    In recent years, Fermilab has been performing an intensive R an D program on Nb{sub 3}Sn accelerator magnets. This program has included dipole and quadrupole magnets for different programs and projects, including LARP and VLHC. A systematic study of the persistent current decay and snapback effect in the fields of these magnets was executed at the Fermilab Magnet Test Facility. The decay and snapback were measured under a range of conditions including variations of the current ramp parameters and flattop and injection plateau durations. This study has mostly focused on the dynamic behavior of the normal sextupole and dodecapole components in dipole and quadrupole magnets respectively. The paper summarizes the recent measurements and presents a comparison with previously measured NbTi magnets.

  15. Magnetization switching by current and microwaves

    NASA Astrophysics Data System (ADS)

    Taniguchi, Tomohiro; Saida, Daisuke; Nakatani, Yoshinobu; Kubota, Hitoshi

    2016-01-01

    We propose a theoretical model of magnetization switching in a ferromagnetic multilayer by both electric current and microwaves. The electric current gives a spin transfer torque on the magnetization, while the microwaves induce a precession of the magnetization around the initial state. Based on numerical simulation of the Landau-Lifshitz-Gilbert (LLG) equation, it is found that the switching current is significantly reduced compared with the switching caused solely by the spin transfer torque when the microwave frequency is in a certain range. We develop a theory of switching from the LLG equation averaged over a constant energy curve. It was found that the switching current should be classified into four regions, depending on the values of the microwave frequency. Based on the analysis, we derive an analytical formula of the optimized frequency minimizing the switching current, which is smaller than the ferromagnetic resonance frequency. We also derive an analytical formula of the minimized switching current. Both the optimized frequency and the minimized switching current decrease with increasing the amplitude of the microwave field. The results will be useful to achieve high thermal stability and low switching current in spin torque systems simultaneously.

  16. Primordial magnetic helicity from stochastic electric currents

    NASA Astrophysics Data System (ADS)

    Calzetta, Esteban; Kandus, Alejandra

    2014-04-01

    We study the possibility that primordial magnetic fields generated in the transition between inflation and reheating posses magnetic helicity, HM. The fields are induced by stochastic currents of scalar charged particles created during the mentioned transition. We estimate the rms value of the induced magnetic helicity by computing different four-point scalar quantum electrodynamics Feynman diagrams. For any considered volume, the magnetic flux across its boundaries is in principle not null, which means that the magnetic helicity in those regions is gauge dependent. We use the prescription given by Berger and Field and interpret our result as the difference between two magnetic configurations that coincide in the exterior volume. In this case, the magnetic helicity gives only the number of magnetic links inside the considered volume. We calculate a concrete value of HM for large scales and analyze the distribution of magnetic defects as a function of the scale. Those defects correspond to regular as well as random fields in the considered volume. We find that the fractal dimension of the distribution of topological defects is D=1/2. We also study if the regular fields induced on large scales are helical, finding that they are and that the associated number of magnetic defects is independent of the scale. In this case, the fractal dimension is D=0. We finally estimate the intensity of fields induced at the horizon scale of reheating and evolve them until the decoupling of matter and radiation under the hypothesis of the inverse cascade of magnetic helicity. The resulting intensity is high enough and the coherence length long enough to have an impact on the subsequent process of structure formation.

  17. Eddy current heating in magnetic refrigerators

    NASA Technical Reports Server (NTRS)

    Kittel, Peter

    1990-01-01

    Eddy current heating can be a significant source of parasitic heating in low temperature magnetic refrigerators. To study this problem a technique to approximate the heating due to eddy currents has been developed. A formula is presented for estimating the heating within a variety of shapes commonly found in magnetic refrigerators. These shapes include circular, square, and rectangular rods; cylindrical and split cylindrical shells; wire loops; and 'coil foil. One set of components evaluated are different types of thermal radiation shields. This comparison shows that a simple split shield is almost as effective (only 23 percent more heating) as using a shield, with the same axial thermal conductivity, made of 'coil foil'.

  18. Formation of current sheets in magnetic reconnection

    SciTech Connect

    Boozer, Allen H.

    2014-07-15

    An ideal evolution of magnetic fields in three spatial dimensions tends to cause neighboring field lines to increase their separation exponentially with distance ℓ along the lines, δ(ℓ)=δ(0)e{sup σ(ℓ)}. The non-ideal effects required to break magnetic field line connections scale as e{sup −σ}, so the breaking of connections is inevitable for σ sufficiently large—even though the current density need nowhere be large. When the changes in field line connections occur rapidly compared to an Alfvén transit time, the constancy of j{sub ||}/B along the magnetic field required for a force-free equilibrium is broken in the region where the change occurs, and an Alfvénic relaxation of j{sub ||}/B occurs. Independent of the original spatial distribution of j{sub ||}/B, the evolution is into a sheet current, which is stretched by a factor e{sup σ} in width and contracted by a factor e{sup σ} in thickness with the current density j{sub ||} increasing as e{sup σ}. The dissipation of these sheet currents and their associated vorticity sheets appears to be the mechanism for transferring energy from a reconnecting magnetic field to a plasma. Harris sheets, which are used in models of magnetic reconnection, are shown to break up in the direction of current flow when they have a finite width and are in a plasma in force equilibrium. The dependence of the longterm nature of magnetic reconnection in systems driven by footpoint motion can be studied in a model that allows qualitative variation in the nature of that motion: slow or fast motion compared to the Alfvén transit time and the neighboring footpoints either exponentially separating in time or not.

  19. Modeling of screening currents in coated conductor magnets containing up to 40000 turns

    NASA Astrophysics Data System (ADS)

    Pardo, E.

    2016-08-01

    Screening currents caused by varying magnetic fields degrade the homogeneity and stability of the magnetic fields created by REBCO coated conductor coils. They are responsible for the AC loss; which is also important for other power applications containing windings, such as transformers, motors and generators. Since real magnets contain coils exceeding 10000 turns, accurate modeling tools for this number of turns or above are necessary for magnet design. This article presents a fast numerical method to model coils with no loss of accuracy. We model a 10400-turn coil for its real number of turns and coils of up to 40000 turns with continuous approximation, which introduces negligible errors. The screening currents, the screening current induced field (SCIF) and the AC loss is analyzed in detail. The SCIF is at a maximum at the remnant state with a considerably large value. The instantaneous AC loss for an anisotropic magnetic-field dependent J c is qualitatively different than for a constant J c , although the loss per cycle is similar. Saturation of the magnetization currents at the end pancakes causes the maximum AC loss at the first ramp to increase with J c . The presented modeling tool can accurately calculate the SCIF and AC loss in practical computing times for coils with any number of turns used in real windings, enabling parameter optimization.

  20. 43. VIEW OF THE RAMP ABOVE LOWER PORTAL AND RAMP, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    43. VIEW OF THE RAMP ABOVE LOWER PORTAL AND RAMP, LOOKING NORTHWEST. THE RAMP WAS USED TO GUIDE RUN-OFF FROM THUNDERSTORMS AWAY FROM THE PORTAL. - Independent Coal & Coke Company, Kenilworth, Carbon County, UT

  1. Rare earth magnets resisting eddy currents

    SciTech Connect

    Pan, W.; Li, W.; Cui, L.Y.; Li, X.M.; Guo, Z.H.

    1999-09-01

    Magnets with high electrical resistance were prepared by electrically isolating Sm{sub 2}Co{sub 17} and Nd{sub 2}Fe{sub 14}B powder particles. It is done by a polymer mixture consisting of epoxy polyester-insulant (EPI), polyvinylbutyral (PVB), epoxy resin (ER) and silane coupling (SC). The properties of interest for anisotropic Sm{sub 2}Co{sub 17} and isotropic Nd{sub 2}Fe{sub 14}B magnets respectively are {rho} = 1 x 10{sup 5} {Omega} {minus}cm{sup 2}/m, Br = 6.8 kGs, {sub 1}H{sub c} = 10.0 kOe, (BH){sub max} = 9.2 MGOe in 5% EPI, 4%PVB, 2%ER, 1%SC and {rho} = 9.4 x 10{sup 4} {Omega} {minus}cm{sup 2}/m, Br = 4.5kG, {sub i}H{sub c} = 9.5 kOe, (BH){sub max} = 4.3 MGOe in 4%EPI, 3%PVB, 2% ER, 1%SC. The insulated magnets exhibit far better magnetic stability than those of sintered and bonded magnets after magnetizing in radio frequency. The insulated Sm{sub 2}Co{sub 17} magnet has the best performance in resisting eddy current. In 500 kHz frequency, 830 Oe magnetizing-field and in one minute, the irreversible loss of recoil remanence is 1.47% and 22.2% respectively for insulated Sm{sub 2}Co{sub 17} and Nd{sub 2}Fe{sub 14}B magnets.

  2. Transformer current sensor for superconducting magnetic coils

    DOEpatents

    Shen, S.S.; Wilson, C.T.

    1985-04-16

    The present invention is a current transformer for operating currents larger than 2kA (two kiloamps) that is capable of detecting a millivolt level resistive voltage in the presence of a large inductive voltage. Specifically, the present invention includes substantially cylindrical primary turns arranged to carry a primary current and substantially cylindrical secondary turns arranged coaxially with and only partially within the primary turns, the secondary turns including an active winding and a dummy winding, the active and dummy windings being coaxial, longitudinally separated and arranged to mutually cancel voltages excited by commonly experienced magnetic fields, the active winding but not the dummy winding being arranged within the primary turns.

  3. Casimir Interaction from Magnetically Coupled Eddy Currents

    SciTech Connect

    Intravaia, Francesco; Henkel, Carsten

    2009-09-25

    We study the quantum and thermal fluctuations of eddy (Foucault) currents in thick metallic plates. A Casimir interaction between two plates arises from the coupling via quasistatic magnetic fields. As a function of distance, the relevant eddy current modes cross over from a quantum to a thermal regime. These modes alone reproduce previously discussed thermal anomalies of the electromagnetic Casimir interaction between good conductors. In particular, they provide a physical picture for the Casimir entropy whose nonzero value at zero temperature arises from a correlated, glassy state.

  4. 3-D Magnetic Field Analysis of Permanent Magnet Motor Considering Magnetizing, Demagnetizing and Eddy Current Loss

    NASA Astrophysics Data System (ADS)

    Miyata, Koji; Aoyama, Yasuaki; Yokoyama, Tomonori; Ohashi, Ken; Kondo, Minoru; Matsuoka, Koichi

    Rare-earth magnets, which have high energy product, have been widely used in several industrial applications such as voice coil motors for hard disk drives, MRI for medical devices and motors for electric vehicle. In order to realize a small and high performance device, the magnetic field analysis techniques are required. In this paper, we applied the magnetic field analysis to design the permanent magnet synchronous motors into the rail traction system. In the inverter fed motor drive, the eddy current loss in the permanent magnet increased. We simulated the effect that eddy current was decreased by using a divided permanent magnet. Furthermore, the permanent magnet tends to be demagnetized due to the effect of a demagnetizing field formed at high temperatures. However, according to our analysis, demagnetization does not occur within the range of our design specifications. Also, we performed magnetic field analysis assuming a pulse-type magnetization process and designed an optimal magnetizing coil.

  5. Wind Plant Ramping Behavior

    SciTech Connect

    Ela, E.; Kemper, J.

    2009-12-01

    With the increasing wind penetrations, utilities and operators (ISOs) are quickly trying to understand the impacts on system operations and planning. This report focuses on ramping imapcts within the Xcel service region.

  6. Validation of Finite-Element Models of Persistent-Current Effects in Nb3Sn Accelerator Magnets

    DOE PAGESBeta

    Wang, X.; Ambrosio, G.; Chlachidze, G.; Collings, E. W.; Dietderich, D. R.; DiMarco, J.; Felice, H.; Ghosh, A. K.; Godeke, A.; Gourlay, S. A.; et al

    2015-01-06

    Persistent magnetization currents are induced in superconducting filaments during the current ramping in magnets. The resulting perturbation to the design magnetic field leads to field quality degradation, in particular at low field where the effect is stronger relative to the main field. The effects observed in NbTi accelerator magnets were reproduced well with the critical-state model. However, this approach becomes less accurate for the calculation of the persistent-current effects observed in Nb3Sn accelerator magnets. Here a finite-element method based on the measured strand magnetization is validated against three state-of-art Nb3Sn accelerator magnets featuring different subelement diameters, critical currents, magnet designsmore » and measurement temperatures. The temperature dependence of the persistent-current effects is reproduced. Based on the validated model, the impact of conductor design on the persistent current effects is discussed. The performance, limitations and possible improvements of the approach are also discussed.« less

  7. MUON ACCELERATION WITH A VERY FAST RAMPING SYNCHROTRON FOR A NEUTRINO FACTORY.

    SciTech Connect

    SUMMERS,D.J.BERG,J.S.GARREN,A.A.PALMER,R.B.

    2002-07-01

    A 4600 Hz fast ramping synchrotron is explored as an economical way of accelerating muons from 4 to 20 GeV/c for a neutrino factory. Eddy current losses are minimized by the low machine duty cycle plus thin grain oriented silicon steel laminations and thin copper wires. Combined function magnets with high gradients alternating within single magnets form the lattice we describe. Muon survival is 83%.

  8. Numerical Study of the Role of Magnetic Field Ramping Rate on the Structure Formation in Magnetorheological Fluids

    NASA Astrophysics Data System (ADS)

    Mohebi, M.; Jamasbi, N.; Flores, G. A.; Liu, Jing

    A molecular dynamics model is presented to understand the structural formation of MR fluids by including the thermal motion of the particles. The simulation results indicate that the complexity of the lateral pattern as viewed in the direction of the applied field increases with the rate of the application of external magnetic field. We have also found that the maximum range for attractive interaction (escape distance) for two initially straight chains increases with temperature. These results are relevant to understand the mechanisms and conditions for the formation of labyrinthine and columnar patterns found in MR fluids.

  9. Precision linear ramp function generator

    DOEpatents

    Jatko, W. Bruce; McNeilly, David R.; Thacker, Louis H.

    1986-01-01

    A ramp function generator is provided which produces a precise linear ramp unction which is repeatable and highly stable. A derivative feedback loop is used to stabilize the output of an integrator in the forward loop and control the ramp rate. The ramp may be started from a selected baseline voltage level and the desired ramp rate is selected by applying an appropriate constant voltage to the input of the integrator.

  10. Precision linear ramp function generator

    DOEpatents

    Jatko, W.B.; McNeilly, D.R.; Thacker, L.H.

    1984-08-01

    A ramp function generator is provided which produces a precise linear ramp function which is repeatable and highly stable. A derivative feedback loop is used to stabilize the output of an integrator in the forward loop and control the ramp rate. The ramp may be started from a selected baseline voltage level and the desired ramp rate is selected by applying an appropriate constant voltage to the input of the integrator.

  11. Measuring the Magnetic Force on a Current-Carrying Conductor.

    ERIC Educational Resources Information Center

    Herreman, W.; Huysentruyt, R.

    1995-01-01

    Describes a fast and simple method for measuring the magnetic force acting on a current-carrying conductor using a digital balance. Discusses the influence of current intensity and wire length on the magnetic force on the conductor. (JRH)

  12. Pathfinder Rear Ramp

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Mars Pathfinder's rear rover ramp can be seen successfully unfurled in this image, taken at the end of Sol 2 by the Imager for Mars Pathfinder (IMP). This ramp was later used for the deployment of the microrover Sojourner, which occurred at the end of Sol 2. Areas of a lander petal and deflated airbag are visible at left. The image helped Pathfinder scientists determine that the rear ramp was the one to use for rover deployment. At upper right is the rock dubbed 'Barnacle Bill,' which Sojourner will later study.

    Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C.

  13. Chaotic Scattering In Magnetic Current Sheets

    NASA Astrophysics Data System (ADS)

    Martin, R.; Holland, D.; Matsuoka, H.; Rappa, R.

    We revisit the subject of nonlinear charged particle dynamics and chaos in current sheet magnetic fields using the modified Harris magnetic field. While much has been written on this subject in the last decade we feel there are some as-yet-unanswered fundamental questions as well as some "folklore" which is in need of clarification. We begin by demonstrating that the general behavior of the average exponential di- vergence rate (AEDR) of individual orbits is strongly correlated with the phase space partitions, i.e. the AEDR for integrable orbits goes to zero for long times, the AEDR of stochastic orbits approaches an asymptotic value for long times, and the AEDR of transient orbits (and short lived stochastic orbits) is not well defined. Furthermore, we show that the Lyapunov exponent for a distribution of particles only has well de- fined values at the resonant energy surfaces defined by Burkhart and Chen. Next it is shown that the "chaos" of the system is maximum at = 1 only in the sense that a lot of particles enter the stochastic region of phase space for this energy. The average Lyapunov exponent at = 1 actually approaches zero, and for those energies where the Lyapunov exponent is defined, it increases as the ratio of normal component of the field to the asymptotic field strength increases. Finally, we present particle escape rate and fractal invariant set results corroborating these conclusions and consider the consequences for anomalous transport in these fields.

  14. Current driven dynamics of magnetic domain walls in permalloy nanowires

    NASA Astrophysics Data System (ADS)

    Hayashi, Masamitsu

    The significant advances in micro-fabrication techniques opened the door to access interesting properties in solid state physics. With regard to magnetic materials, geometrical confinement of magnetic structures alters the defining parameters that govern magnetism. For example, development of single domain nano-pillars made from magnetic multilayers led to the discovery of electrical current controlled magnetization switching, which revealed the existence of spin transfer torque. Magnetic domain walls (DWs) are boundaries in magnetic materials that divide regions with distinct magnetization directions. DWs play an important role in the magnetization reversal processes of both bulk and thin film magnetic materials. The motion of DW is conventionally controlled by magnetic fields. Recently, it has been proposed that spin polarized current passed across the DW can also control the motion of DWs. Current in most magnetic materials is spin-polarized, due to spin-dependent scattering of the electrons, and thus can deliver spin angular momentum to the DW, providing a "spin transfer" torque on the DW which leads to DW motion. In addition, owing to the development of micro-fabrication techniques, geometrical confinement of magnetic materials enables creation and manipulation of a "single" DW in magnetic nanostructures. New paradigms for DW-based devices are made possible by the direct manipulation of DWs using spin polarized electrical current via spin transfer torque. This dissertation covers research on current induced DW motion in magnetic nanowires. Fascinating effects arising from the interplay between DWs with spin polarized current will be revealed.

  15. Stable superconducting magnet. [high current levels below critical temperature

    NASA Technical Reports Server (NTRS)

    Boom, R. W. (Inventor)

    1967-01-01

    Operation of a superconducting magnet is considered. A method is described for; (1) obtaining a relatively high current in a superconducting magnet positioned in a bath of a gas refrigerant; (2) operating a superconducting magnet at a relatively high current level without training; and (3) operating a superconducting magnet containing a plurality of turns of a niobium zirconium wire at a relatively high current level without training.

  16. Investigating Ramps and Sliders.

    ERIC Educational Resources Information Center

    Malone, Mark R.

    1986-01-01

    Offers a series of hands-on activities for introducing students to concepts of energy transfer and conversion. Describes how simple devices as marbles, ramps, and sliders can be used to gauge the transfer of energy and assist in the development of investigative skills. (ML)

  17. Crescentic ramp turbine stage

    NASA Technical Reports Server (NTRS)

    Lee, Ching-Pang (Inventor); Tam, Anna (Inventor); Kirtley, Kevin Richard (Inventor); Lamson, Scott Henry (Inventor)

    2007-01-01

    A turbine stage includes a row of airfoils joined to corresponding platforms to define flow passages therebetween. Each airfoil includes opposite pressure and suction sides and extends in chord between opposite leading and trailing edges. Each platform includes a crescentic ramp increasing in height from the leading and trailing edges toward the midchord of the airfoil along the pressure side thereof.

  18. Fold patterns, lateral ramps and seismicity in central Pennsylvania

    USGS Publications Warehouse

    Pohn, H.A.; Coleman, J.L., Jr.

    1991-01-01

    The Susquehanna lateral ramp crosses the entire length of Pennsylvania in a NNE direction and extends into southern New York State. Its presence was first suspected because of a dramatic change in fold wavelength across the Susquehanna River, seen on both side-looking airborne radar (SLAR *) data and the geologic map of Pennsylvania. Seismic reflection profiles confirm the presence of a ramp and show the detailed nature of structures associated with it. These structures include antiformal stacks, juxtaposed anticlines and synclines, and folds beheaded by thrust faults. The change in the fold pattern, which led to recognizing the lateral ramp, occurs above a rapid dropoff in depth to the basement suggesting that the ramp and the basement configuration may somehow be related. In plan view, eleven earthquakes are spatially related to the Susquehanna lateral ramp, although they are in the basement rocks rather than in the cover rocks which contain the lateral ramp itself. The earthquakes are, therefore, not likely directly associated with the ramp, though they may be affiliated with strike-slip faulting in the basement which, itself, appears to be partly responsible for the formation of the ramp. The initial age of the faulting along, and in the vicinity of, the Susquehanna lateral ramp is presumably Early to Middle Paleozoic. However, the presence of a surficially-exposed Mesozoic dike along the ramp and modern seismicity suggest that the Susquehanna lateral ramp may be a zone of protracted, and perhaps repeated, tectonism which is currently being reactivated. A preliminary evaluation of the distribution of modern earthquakes in the Valley and Ridge, Blue Ridge and Appalachian Plateau shows that nearly half of the earthquakes are located under lateral ramps. If this observation is true, the presence of ramps may be a useful geological indicator of areas susceptible to seismicity. ?? 1991.

  19. MEASUREMENTS OF THE FIELD QUALITY IN SUPERCONDUCTING DIPOLES AT HIGH RAMP RATES.

    SciTech Connect

    JAIN, A.; ESCALLIER, J.; GANETIS, G.; LOUIE, W.; MARONE, A.; THOMAS, R.; WANDERER, P.

    2006-09-18

    Several recent applications of superconducting magnets require the magnets to be operated at high ramp rates and at frequencies of several Hertz. Brookhaven National Laboratory (BNL) has recently designed and built prototypes of superconducting dipole magnets that can be ramped at a fairly high rate (1 T/s or more). For accelerator applications, it is also crucial that the magnets maintain good field quality even at high ramp rates. In order to characterize the field quality of magnets at high ramp rates, a measurement system consisting of 16 printed circuit tangential coils has been developed. The coil system is held stationary while the magnet is ramped. This paper describes the techniques used for the measurements and data analysis, and presents the results of measurements at ramp rates of up to 4 T/s in a prototype dipole built at BNL for GSI.

  20. Magnetic field generated by shielding current in high Tc superconducting coils for NMR magnets

    NASA Astrophysics Data System (ADS)

    Amemiya, Naoyuki; Akachi, Ken

    2008-09-01

    Numerical electromagnetic field analyses of high Tc superconducting tape in coils were carried out to calculate the magnetic field generated by the shielding (magnetization) current in superconducting tape. The numerical model employs the power law electric field-current density characteristic and the thin strip approximation, in which the current component normal to the wide face of the tape is neglected. The shielding (magnetization) currents lead to non-uniform current distributions in the superconducting tape in the coils. The magnetic field generated by the shielding (magnetization) current can deteriorate the field quality and could be a concern in insert coils for NMR magnets using high Tc superconducting tape.

  1. Eigenmodes of quasi-static magnetic islands in current sheet

    SciTech Connect

    Li Yi; Cai Xiaohui; Chai Lihui; Wang Shui; Zheng Huinan; Shen Chao

    2011-12-15

    As observation have shown, magnetic islands often appear before and/or after the onset of magnetic reconnections in the current sheets, and they also appear in the current sheets in the solar corona, Earth's magnetotail, and Earth's magnetopause. Thus, the existence of magnetic islands can affect the initial conditions in magnetic reconnection. In this paper, we propose a model of quasi-static magnetic island eigenmodes in the current sheet. This model analytically describes the magnetic field structures in the quasi-static case, which will provide a possible approach to reconstructing the magnetic structures in the current sheet via observation data. This model is self-consistent in the kinetic theory. Also, the distribution function of charged particles in the magnetic island can be calculated.

  2. Current-induced spin torque resonance of a magnetic insulator

    NASA Astrophysics Data System (ADS)

    Schreier, Michael; Chiba, Takahiro; Niedermayr, Arthur; Lotze, Johannes; Huebl, Hans; Geprägs, Stephan; Takahashi, Saburo; Bauer, Gerrit E. W.; Gross, Rudolf; Goennenwein, Sebastian T. B.

    2015-10-01

    We report the observation of current-induced spin torque resonance in yttrium iron garnet/platinum bilayers. An alternating charge current at GHz frequencies in the platinum gives rise to dc spin pumping and spin Hall magnetoresistance rectification voltages, induced by the Oersted fields of the ac current and the spin Hall effect-mediated spin transfer torque. In ultrathin yttrium iron garnet films, we observe spin transfer torque actuated magnetization dynamics which are significantly larger than those generated by the ac Oersted field. Spin transfer torques thus efficiently couple charge currents and magnetization dynamics also in magnetic insulators, enabling charge current-based interfacing of magnetic insulators with microwave devices.

  3. Temperature compensated current sensor using reference magnetic field

    DOEpatents

    Yakymyshyn, Christopher Paul; Brubaker, Michael Allen; Yakymyshyn, Pamela Jane

    2007-10-09

    A method is described to provide temperature compensation and self-calibration of a current sensor based on a plurality of magnetic field sensors positioned around a current carrying conductor. A reference magnetic field generated within the current sensor housing is detected by a separate but identical magnetic field sensor and is used to correct variations in the output signal due to temperature variations and aging.

  4. Current distribution in Cable-In-Conduit Conductors

    SciTech Connect

    Ferri, M.A.

    1994-05-01

    A numerical study of the current distribution in Cable-In-Conduit Conductors (CICC`s) experiencing linearly ramping transport currents and transverse magnetic fields was conducted for both infinitely long, periodic cables and finite length cables terminated in low resistance joints. The goal of the study was to gain insight into the phenomenon known as Ramp Rate Limitation, an as yet unexplained correspondence between maximum attainable current and the ramp time taken to reach that current in CICC superconducting magnets. A discrete geometric model of a 27 strand multiply twisted CICC was developed to effectively represent the flux linkages, mutual inductances, and resistive contact points between the strands of an experimentally tested cable. The results of the numerical study showed that for fully periodic cables, the current imbalances due to ramping magnetic fields and ramping transport currents are negligible in the range of experimentally explored operating conditions. For finite length, joint terminated cables, however, significant imbalances can exist. Unfortunately, quantitative results are limited by a lack of knowledge of the transverse resistance between strands in the joints. Nonetheless, general results are presented showing the dependency of the imbalance on cable length, ramp time, and joint resistance for both ramping transverse magnet fields and ramping transport currents. At the conclusion of the study, it is suggested that calculated current imbalances in a finite length cable could cause certain strands to prematurely ``quench`` -- become non-superconducting --thus leading to an instability for the entire cable. This numerically predicted ``current imbalance instability`` is compared to the experimentally observed Ramp Rate Limitation for the 27 strand CICC sample.

  5. Fast chirality reversal of the magnetic vortex by electric current

    SciTech Connect

    Lim, W. L. Liu, R. H.; Urazhdin, S.; Tyliszczak, T.; Erokhin, S. G.; Berkov, D.

    2014-12-01

    The possibility of high-density information encoding in magnetic materials by topologically stable inhomogeneous magnetization configurations such as domain walls, skyrmions, and vortices has motivated intense research into mechanisms enabling their control and detection. While the uniform magnetization states can be efficiently controlled by electric current using magnetic multilayer structures, this approach has proven much more difficult to implement for inhomogeneous states. Here, we report direct observation of fast reversal of magnetic vortex by electric current in a simple planar structure based on a bilayer of spin Hall material Pt with a single microscopic ferromagnetic disk contacted by asymmetric electrodes. The reversal is enabled by a combination of the chiral Oersted field and spin current generated by the nonuniform current distribution in Pt. Our results provide a route for the efficient control of inhomogeneous magnetization configurations by electric current.

  6. Current density and state density in diluted magnetic semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Pérez Merchancano, S. T.; Paredes Gutiérrez, H.; Zuñiga, J. A.

    2016-02-01

    We study in this paper the spin-polarized current density components in diluted magnetic semiconductor tunnelling diodes with different sample geometries. We calculate the resonant JxV and the density of states. The differential conductance curves are analyzed as functions of the applied voltage and the magnetic potential strength induced by the magnetic ions.

  7. Current methods for synthesis of magnetic nanoparticles.

    PubMed

    Majidi, Sima; Sehrig, Fatemeh Zeinali; Farkhani, Samad Mussa; Goloujeh, Mehdi Soleymani; Akbarzadeh, Abolfazl

    2016-01-01

    The synthesis of different kinds of magnetic nanoparticles (MNPs) has attracted much attention. During the last few years, a large portion of the articles published about MNPs have described efficient routes to attain shape-controlled and highly stable MNPs with narrow size distribution. In this review, we have reported several popular methods including co-precipitation, microemulsion, thermal decomposition, solvothermal, sonochemical, microwave-assisted, chemical vapor deposition, combustion, carbon arc, and laser pyrolysis, for the synthesis of magnetic nanoparticles. PMID:25435409

  8. Instrumentation used to measure residential magnetic fields and currents.

    PubMed

    Lahijanian, H; Yatapanage, K; Rosen, R; Cross, J

    2003-10-01

    The equipment used to measure magnetic fields and electric currents in residences is described. The instrumentation consisted of current transformers, magnetic field probes and locally designed and built signal conditioning modules. The data acquisition system was capable of unattended recording for extended time periods. The complete system was calibrated to verify its response to known physical inputs. PMID:14582878

  9. The effect of Birkeland currents on magnetic field topology

    NASA Technical Reports Server (NTRS)

    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.

  10. How does the edge height of curb ramps obstruct bicycles?

    PubMed

    Hayashi, Masahiro; Uetake, Teruo; Shimoda, Masahiro

    2012-12-01

    The aim of this study is to recommend revisions, based on empirical data, to the current curb ramp standards for keeping bicyclists safe. Four types of curb ramps were tested: (1) concrete with a 50 mm edge height, (2) concrete reinforced by a metal plate with a 50 mm edge height, (3) plastic with a 20 mm edge height, and (4) recycled rubber with a 10 mm edge height. Twenty subjects aged 20-60 years ascended the curbs on a bicycle under various conditions. The angles of approach were 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees and 90 degrees. Experiments were executed under both wet and dry conditions. We found that when approaching from an angle of 45 degrees or more, all subjects could ascend all ramps under both conditions. From a 15 degrees approach under wet conditions, no subjects ascended the concrete ramps. Some could not ascend at a 15 degrees approach on the concrete ramps in dry conditions, and some could not ascend from a 30 degrees approach on the reinforced concrete ramp in wet conditions. Bicyclists riding on roadways cannot easily ascend a curb ramp with a 50 mm edge, even in dry conditions. We thus recommend that curb ramp edge heights be lower than 50 mm. Keywords: friction coefficient; approach angle PMID:25665200

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

    NASA Astrophysics Data System (ADS)

    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.

  12. Current thinking about Jupiter's magnetic anomaly

    NASA Astrophysics Data System (ADS)

    Grodent, D.; Gerard, J.-C.; Gustin, J.; Clarke, J. T.; Connerney, J. E.

    Repeated imaging of Jupiter's aurora has shown that the northern main oval has a distorted 'kidney bean' shape in the general range of 90-150o System III longitude, which appears unchanged since 1994. While it is more difficult to observe the conjugate regions in the southern aurora, no corresponding distortion appears in the south. Recent improved accuracy in locating the auroral footprint emission of Io has provided new information about the geometry of Jupiter's magnetic field in this and other areas. The persistent pattern of the main oval implies a disturbance of the local magnetic field, and the increased latitudinal separation of the locus of the Io footprint from the main oval implies a locally weaker field strength. The most recent images obtained with the Hubble Space Telescope Advance Camera for Surveys (ACS) allow us to complement previous observations with the location of the auroral footprints of Io, Europa, and Ganymede in the region of interest. Their footpaths vary in parallel and form a kink in the 90-150° S3 sector which strongly suggests the presence of a magnetic anomaly in this region.

  13. Design of Current Leads for the MICE Coupling Magnet

    SciTech Connect

    Wang, Li; Li, L.K.; Wu, Hong; Xu, Feng Yu; Liu, X.K.; Jia, Lin X.; Green, Michael A.

    2008-04-02

    A pair of superconducting coupling magnets will be part of the Muon Ionization Cooling Experiment (MICE). They were designed and will be constructed by the Institute of Cryogenics and Superconductivity Technology, Harbin Institute of Technology, in collaboration with Lawrence Berkeley National Laboratory. The coupling magnet is to be cooled by using cryocoolers at 4.2K. In order to reduce the heat leak to the 4.2K cold mass from 300 K, a pair of current leads composed of conventional copper leads and high temperature superconductor (HTS) leads will be used to supply current to the magnet. This paper presents the optimization of the conventional conduction-cooled metal leads for the coupling magnet. Analyses on heat transfer down the leads using theoretical method and numerical simulation were carried out. The stray magnetic field around the HTS leads has been calculated and effects of the magnetic field on the performance of the HTS leads has also been analyzed.

  14. Eddy current characterization of magnetic treatment of materials

    NASA Technical Reports Server (NTRS)

    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.

  15. Multiparametric magnetic resonance imaging: Current role in prostate cancer management.

    PubMed

    Ueno, Yoshiko; Tamada, Tsutomu; Bist, Vipul; Reinhold, Caroline; Miyake, Hideaki; Tanaka, Utaru; Kitajima, Kazuhiro; Sugimura, Kazuro; Takahashi, Satoru

    2016-07-01

    Digital rectal examination, serum prostate-specific antigen screening and transrectal ultrasound-guided biopsy are conventionally used as screening, diagnostic and surveillance tools for prostate cancer. However, they have limited sensitivity and specificity. In recent years, the role of multiparametric magnetic resonance imaging has steadily grown, and is now part of the standard clinical management in many institutions. In multiparametric magnetic resonance imaging, the morphological assessment of T2-weighted imaging is correlated with diffusion-weighted imaging, dynamic contrast-enhanced imaging perfusion and/or magnetic resonance spectroscopic imaging. Multiparametric magnetic resonance imaging is currently regarded as the most sensitive and specific imaging technique for the evaluation of prostate cancer, including detection, staging, localization and aggressiveness evaluation. This article presents an overview of multiparametric magnetic resonance imaging, and discusses the current role of multiparametric magnetic resonance imaging in the different fields of prostate cancer management. PMID:27184019

  16. Magnetically modulated critical current densities of Co/Nb hybrid

    PubMed Central

    Li, Zhigang; Wang, Weike; Zhang, Li; Yang, Zhaorong; Tian, Mingliang; Zhang, Yuheng

    2015-01-01

    By tuning morphology and size of magnetic subsystem, ferromagnet-superconductor (F/S) hybrid system provides an effective way to modulate superconductivity due to the interaction between superconducting and magnetic-order parameters at the mesoscopic length scale. In this work, we report on investigations of critical current density in a large-area Co/Nb hybrid via facile colloidal lithography. Here, Co hexagon shell array as a magnetic template build on Nb film to modulate the critical current density. A novel superconducting transition has been observed in I-V curve with two metastable transition states: double-transition and binary-oscillation-transition states. Importantly, such unusual behavior can be adjusted by temperature, magnetic field and contact area of F/S. Such hybrid film has important implications for understanding the role of magnetic subsystem modulating superconductivity, as well as applied to low-energy electronic devices such as superconducting current fault limiters. PMID:26678595

  17. Magnetically modulated critical current densities of Co/Nb hybrid

    NASA Astrophysics Data System (ADS)

    Li, Zhigang; Wang, Weike; Zhang, Li; Yang, Zhaorong; Tian, Mingliang; Zhang, Yuheng

    2015-12-01

    By tuning morphology and size of magnetic subsystem, ferromagnet-superconductor (F/S) hybrid system provides an effective way to modulate superconductivity due to the interaction between superconducting and magnetic-order parameters at the mesoscopic length scale. In this work, we report on investigations of critical current density in a large-area Co/Nb hybrid via facile colloidal lithography. Here, Co hexagon shell array as a magnetic template build on Nb film to modulate the critical current density. A novel superconducting transition has been observed in I-V curve with two metastable transition states: double-transition and binary-oscillation-transition states. Importantly, such unusual behavior can be adjusted by temperature, magnetic field and contact area of F/S. Such hybrid film has important implications for understanding the role of magnetic subsystem modulating superconductivity, as well as applied to low-energy electronic devices such as superconducting current fault limiters.

  18. Bootstrap current close to magnetic axis in tokamaks

    SciTech Connect

    Shaing, K.C.; Hazeltine, R.D.

    1996-12-01

    It is shown that the bootstrap current density close to the magnetic axis in tokamaks does not vanish in simple electron-ion plasmas because the fraction of the trapped particles is finite. The magnitude of the current density could be comparable to that in the outer core region. This may reduce or even eliminate the need of the seed current.

  19. Development of Interior Permanent Magnet Motors with Concentrated Windings for Reducing Magnet Eddy Current Loss

    NASA Astrophysics Data System (ADS)

    Yamazaki, Katsumi; Kanou, Yuji; Fukushima, Yu; Ohki, Shunji; Nezu, Akira; Ikemi, Takeshi; Mizokami, Ryoichi

    In this paper, we present the development of interior magnet motors with concentrated windings, which reduce the eddy current loss of the magnets. First, the mechanism of the magnet eddy current loss generation is investigated by a simple linear magnetic circuit. Due to the consideration, an automatic optimization method using an adaptive finite element method is carried out to determine the stator and rotor shapes, which decrease the eddy current loss of the magnet. The determined stator and rotor are manufactured in order to proof the effectiveness by the measurement.

  20. 4. INTERIOR VIEW SHOWING CURRENT USE AS MAGNETIC TAPE STORAGE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. INTERIOR VIEW SHOWING CURRENT USE AS MAGNETIC TAPE STORAGE FACILITY; VIEW TO NORTHEAST. - Cape Canaveral Air Station, Launch Complex 17, Facility 36002, East end of Lighthouse Road, Cape Canaveral, Brevard County, FL

  1. The cometary magnetic field and its associated electric currents

    NASA Technical Reports Server (NTRS)

    Ip, W.-H.; Mendis, D. A.

    1975-01-01

    Two different observations of Comet Kohoutek (1973f) seem to suggest the existence of substantial magnetic fields (not less than 100 gammas) in its coma and tail. The effects of the currents and hydromagnetic waves associated with these magnetic fields are considered. It is shown that while the currents closing through the inner coma may represent an important source of ionization in that region, the dissipation of hydromagnetic waves may also be a significant, if not dominant, source of heating there.

  2. Structure of current sheets in magnetic holes at 1 AU

    NASA Technical Reports Server (NTRS)

    Fitzenreiter, R. J.; Burlaga, L. F.

    1978-01-01

    Current density profiles in several types of interplanetary magnetic holes have been calculated using high-resolution Imp 6 magnetic field data (12.5 vector measurements/s), assuming that the currents flow in planar sheets and that the magnetic field varies only in the direction normal to the sheet. The planarity was verified in four holes which were observed by two suitably spaced spacecraft. Four types of simple magnetic holes are discussed, in which B varies nearly monotonically on each side of the hole. In two of the holes, B varies in intensity but not in direction as a result of currents normal to B. In the other two holes, B changes in both magnitude and direction as a result of currents both normal and parallel to B. The observed structures are found to be qualitatively consistent with the models of Burlaga and Lemaire (1978). Examples of complex irregular magnetic holes are also presented, and they are shown to contain multiple current sheets in which currents flow parallel to one another at various angles with respect to B. There is no model of such magnetic holes at present.

  3. Persistent currents in a magnetic bearing with coated conductors

    NASA Astrophysics Data System (ADS)

    Sass, F.; Ramos de Castro, André; Gonçalves Sotelo, Guilherme; de Andrade, R.

    2015-11-01

    Superconducting magnetic bearings are normally built with bulk superconductors. Since coated conductors properties are far superior, we have proposed in a previous work the replacement of bulks for stacks of 2G wires in magnetic levitation devices. A major limitation of this replacement lies in the fact that the induced current is constrained in narrow loops along the available commercial widths of 2G wires. This work presents a technique to achieve wider loops of persistent current without the need of increasing the coated conductors width. As a result, the use of 2G wires in magnetic bearings took a step towards its economical feasibility.

  4. Eddy current characterization of magnetic treatment of nickel 200

    NASA Technical Reports Server (NTRS)

    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.

  5. Current leads cooling for the series-connected hybrid magnets

    NASA Astrophysics Data System (ADS)

    Bai, Hongyu; Marshall, William S.; Bird, Mark D.; Gavrilin, Andrew V.; Weijers, Hubertus W.

    2014-01-01

    Two Series-Connected Hybrid (SCH) magnets are being developed at the National High Magnetic Field Laboratory. Both SCH magnets combine a set of resistive Florida-Bitter coils with a superconducting outsert coil constructed of the cable-in-conduit conductor (CICC). The outsert coils of the two magnets employ 20 kA BSCCO HTS current leads for the power supply although they have different designs and cooling methods. The copper heat exchangers of the HTS current leads for the HZB SCH are cooled with forced flow helium at a supply temperature of 44 K, while the copper heat exchangers of HTS current leads for NHMFL SCH are cooled with liquid nitrogen at a temperature of 78 K in a self-demand boil-off mode. This paper presents the two cooling methods and their impacts on cryogenic systems. Their efficiencies and costs are compared and presented.

  6. Bonded permanent magnets: Current status and future opportunities (invited)

    NASA Astrophysics Data System (ADS)

    Ormerod, John; Constantinides, Steve

    1997-04-01

    Permanent magnets play a vital role in modern society as a component in a wide range of devices utilized by many industries and consumers. In 1995, the world production of permanent magnets was estimated to be valued at 3.6 billion and growing at an annual rate of 12%. Bonded permanent magnets are the fastest growing segment of this market. Bonded magnet technology enables a wide variety of magnetic powders to be combined with several polymer and binder systems to produce magnetic components utilizing several processing options. In this article, we review the development of bonded magnet technology. The major classes of magnetic powders, binder systems, and processing technologies are described. Recent developments in magnetic material grades, e.g., anisotropic NdFeB, rare earth lean NdFeB, SmFe(N,C) are outlined. The current status of processing and binder options aimed at increasing the upper application temperature limit of these materials is highlighted. Finally, the improvements and future opportunities for bonded magnets are discussed.

  7. Currents between tethered electrodes in a magnetized laboratory plasma

    NASA Technical Reports Server (NTRS)

    Stenzel, R. L.; Urrutia, J. M.

    1990-01-01

    This paper describes the experimental setup and measurement techniques used to investigate currents between tethered electodes in a magnetized laboratory plasma. Experimental results include information on current propagation, the formation of wave wings, the limits of current collection, nonlinear effects and instabilities, charging phenomena, and the characteristics of transmission lines in plasma. The results were found to support certain predictions on tethers in space (e.g., the MHD far zone or the motional emf) while contradicting others (e.g., distant current closure), and revealed such new phenomena as current disruptions, current-neutralized beams, and wing spread.

  8. Switching current density reduction in perpendicular magnetic anisotropy spin transfer torque magnetic tunneling junctions

    SciTech Connect

    You, Chun-Yeol

    2014-01-28

    We investigate the switching current density reduction of perpendicular magnetic anisotropy spin transfer torque magnetic tunneling junctions using micromagnetic simulations. We find that the switching current density can be reduced with elongated lateral shapes of the magnetic tunnel junctions, and additional reduction can be achieved by using a noncollinear polarizer layer. The reduction is closely related to the details of spin configurations during switching processes with the additional in-plane anisotropy.

  9. Discontinuous properties of current-induced magnetic domain wall depinning

    PubMed Central

    Hu, X. F.; Wu, J.; Niu, D. X.; Chen, L.; Morton, S. A.; Scholl, A.; Huang, Z. C.; Zhai, Y.; Zhang, W.; Will, I.; Xu, Y. B.; Zhang, R.; van der Laan, G.

    2013-01-01

    The current-induced motion of magnetic domain walls (DWs) confined to nanostructures is of great interest for fundamental studies as well as for technological applications in spintronic devices. Here, we present magnetic images showing the depinning properties of pulse-current-driven domain walls in well-shaped Permalloy nanowires obtained using photoemission electron microscopy combined with x-ray magnetic circular dichroism. In the vicinity of the threshold current density (Jth = 4.2 × 1011 A.m−2) for the DW motion, discontinuous DW depinning and motion have been observed as a sequence of “Barkhausen jumps”. A one-dimensional analytical model with a piecewise parabolic pinning potential has been introduced to reproduce the DW hopping between two nearest neighbour sites, which reveals the dynamical nature of the current-driven DW motion in the depinning regime. PMID:24170087

  10. Beam based measurements of hysteresis effects in Fermilab main injector magnets

    SciTech Connect

    Bruce C. Brown and David P Capista

    2003-05-27

    Operation of the Fermilab Main Injector is sensitive to magnetic field differences due to hysteretic effects. Measurements using the beam are reported with various current ramps. This will provide magnetic field information for accelerator operations with better ramp control than is available from magnet test facility data. This makes possible improved low field reproducibility with mixed 120 GeV and 150 GeV operation of the Main Injector.

  11. Current Sheets Formation in Tangled Coronal Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Rappazzo, A. F.; Parker, E. N.

    2013-08-01

    We investigate the dynamical evolution of magnetic fields in closed regions of solar and stellar coronae. To understand under which conditions current sheets form, we examine dissipative and ideal reduced magnetohydrodynamic models in Cartesian geometry, where two magnetic field components are present: the strong guide field B 0, extended along the axial direction, and the dynamical orthogonal field b. Magnetic field lines thread the system along the axial direction that spans the length L and are line-tied at the top and bottom plates. The magnetic field b initially has only large scales, with its gradient (current) length scale of the order of l b . We identify the magnetic intensity threshold b/B 0 ~ l b /L. For values of b below this threshold, field-line tension inhibits the formation of current sheets, while above the threshold they form quickly on fast ideal timescales. In the ideal case, above the magnetic threshold, we show that current sheets thickness decreases in time until it becomes smaller than the grid resolution, with the analyticity strip width δ decreasing at least exponentially, after which the simulations become underresolved.

  12. CURRENT SHEETS FORMATION IN TANGLED CORONAL MAGNETIC FIELDS

    SciTech Connect

    Rappazzo, A. F.; Parker, E. N. E-mail: parker@oddjob.uchicago.edu

    2013-08-10

    We investigate the dynamical evolution of magnetic fields in closed regions of solar and stellar coronae. To understand under which conditions current sheets form, we examine dissipative and ideal reduced magnetohydrodynamic models in Cartesian geometry, where two magnetic field components are present: the strong guide field B{sub 0}, extended along the axial direction, and the dynamical orthogonal field b. Magnetic field lines thread the system along the axial direction that spans the length L and are line-tied at the top and bottom plates. The magnetic field b initially has only large scales, with its gradient (current) length scale of the order of l{sub b}. We identify the magnetic intensity threshold b/B{sub 0} {approx} l{sub b}/L. For values of b below this threshold, field-line tension inhibits the formation of current sheets, while above the threshold they form quickly on fast ideal timescales. In the ideal case, above the magnetic threshold, we show that current sheets thickness decreases in time until it becomes smaller than the grid resolution, with the analyticity strip width {delta} decreasing at least exponentially, after which the simulations become underresolved.

  13. Magnetic Reconnection Onset and Energy Release at Current Sheets

    NASA Astrophysics Data System (ADS)

    DeVore, C. R.; Antiochos, Spiro K.

    2015-04-01

    Reconnection and energy release at current sheets are important at the Sun (coronal heating, coronal mass ejections, flares, and jets) and at the Earth (magnetopause flux transfer events and magnetotail substorms) and other magnetized planets, and occur also at the interface between the Heliosphere and the interstellar medium, the heliopause. The consequences range from relatively quiescent heating of the ambient plasma to highly explosive releases of energy and accelerated particles. We use the Adaptively Refined Magnetohydrodynamics Solver (ARMS) model to investigate the self-consistent formation and reconnection of current sheets in an initially potential 2D magnetic field containing a magnetic null point. Unequal stresses applied to the four quadrants bounded by the X-line separatrix distort the potential null into a double-Y-type current sheet. We find that this distortion eventually leads to onset of fast magnetic reconnection across the sheet, with copious production, merging, and ejection of magnetic islands due to plasmoid instability. In the absence of a mechanism for ideal instability or loss of equilibrium of the global structure, however, this reconnection leads to minimal energy release. Essentially, the current sheet oscillates about its force-free equilibrium configuration. When the structure is susceptible to a large-scale rearrangement of the magnetic field, on the other hand, the energy release becomes explosive. We identify the conditions required for reconnection to transform rapidly a large fraction of the magnetic free energy into kinetic and other forms of plasma energy, and to restructure the current sheet and its surrounding magnetic field dramatically. We discuss the implications of our results for understanding heliophysical activity, particularly eruptions, flares, and jets in the corona.Our research was supported by NASA’s Heliophysics Supporting Research and Living With a Star Targeted Research and Technology programs.

  14. Analytical model for ramp compression

    NASA Astrophysics Data System (ADS)

    Xue, Quanxi; Jiang, Shaoen; Wang, Zhebin; Wang, Feng; Hu, Yun; Ding, Yongkun

    2016-08-01

    An analytical ramp compression model for condensed matter, which can provide explicit solutions for isentropic compression flow fields, is reported. A ramp compression experiment can be easily designed according to the capability of the loading source using this model. Specifically, important parameters, such as the maximum isentropic region width, material properties, profile of the pressure pulse, and the pressure pulse duration can be reasonably allocated or chosen. To demonstrate and study this model, laser-direct-driven ramp compression experiments and code simulation are performed successively, and the factors influencing the accuracy of the model are studied. The application and simulation show that this model can be used as guidance in the design of a ramp compression experiment. However, it is verified that further optimization work is required for a precise experimental design.

  15. On spontaneous formation of current sheets: Untwisted magnetic fields

    SciTech Connect

    Bhattacharyya, R.; Low, B. C.; Smolarkiewicz, P. K.

    2010-11-15

    This is a study of the spontaneous formation of electric current sheets in an incompressible viscous fluid with perfect electrical conductivity, governed by the magnetohydrodynamic Navier-Stokes equations. Numerical solutions to two initial value problems are presented for a three-dimensional, periodic, untwisted magnetic field evolving, with no change in magnetic topology under the frozen-in condition and at characteristic fluid Reynolds numbers of the order of 500, from a nonequilibrium initial state with the fluid at rest. The evolution converts magnetic free energy into kinetic energy to be all dissipated away by viscosity so that the field settles into a minimum-energy, static equilibrium. The solutions demonstrate that, as a consequence of the frozen-in condition, current sheets must form during the evolution despite the geometric simplicity of the prescribed initial fields. In addition to the current sheets associated with magnetic neutral points and field reversal layers, other sheets not associated with such magnetic features are also in evidence. These current sheets form on magnetic flux surfaces. This property is used to achieve a high degree of the frozen-in condition in the simulations, by describing the magnetic field entirely in terms of the advection of its flux surfaces and integrating the resulting governing equations with a customized version of a general-purpose high-resolution (viz., nonoscillatory) hydrodynamical simulation code EULAG [J. M. Prusa et al., Comput. Fluids 37, 1193 (2008)]. Incompressibility imposes the additional global constraint that the flux surfaces must evolve with no change in the spatial volumes they enclose. In this approach, current sheet formation is demonstrated graphically by the progressive pressing together of suitably selected flux surfaces until their separation has diminished below the minimal resolved distance on a fixed grid. The frozen-in condition then fails in the simulation as the field reconnects through

  16. Magnetic island induced bootstrap current on island dynamics in tokamaks

    SciTech Connect

    Shaing, K.C.; Spong, D.A.

    2006-02-15

    When a magnetic island is embedded in toroidally symmetric tokamaks, the toroidal symmetry in |B| is broken [K. C. Shaing, Phys. Rev. Lett. 87, 245003 (2001)]. Here, B is the magnetic field. This broken symmetry induces an additional bootstrap current density in the vicinity of the island. It is illustrated that this island induced bootstrap current density modifies the island evolution equation and imposes a lower limit on the absolute value of the tearing mode stability parameter {delta}{sup '} for the island to be unstable. This lower limit depends on the local poloidal plasma beta {beta}{sub p}, the ratio of the plasma pressure to the poloidal magnetic field pressure. If {beta}{sub p} is high enough, the magnetic island is stable. This mechanism provides an alternative route to stabilize the island.

  17. Magnetic Island Induced Bootstrap Current on Island Dynamics in Tokamaks

    SciTech Connect

    Spong, Donald A; Shaing, K. C.

    2006-02-01

    When a magnetic island is embedded in toroidally symmetric tokamaks, the toroidal symmetry in |B| is broken [K. C. Shaing, Phys. Rev. Lett. 87, 245003 (2001)] . Here, B is the magnetic field. This broken symmetry induces an additional bootstrap current density in the vicinity of the island. It is illustrated that this island induced bootstrap current density modifies the island evolution equation and imposes a lower limit on the absolute value of the tearing mode stability parameter |{Delta}{prime}| for the island to be unstable. This lower limit depends on the local poloidal plasma beta {beta}{sub p}, the ratio of the plasma pressure to the poloidal magnetic field pressure. If {beta}{sub p} is high enough, the magnetic island is stable. This mechanism provides an alternative route to stabilize the island.

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

    SciTech Connect

    Niknam, A. R.; Taghadosi, M. R.; Majedi, S.; Khorashadizadeh, S. M.

    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.

  19. Mechanisms of spin-polarized current-driven magnetization switching.

    PubMed

    Zhang, S; Levy, P M; Fert, A

    2002-06-10

    The mechanisms of the magnetization switching of magnetic multilayers driven by a current are studied by including exchange interaction between local moments and spin accumulation of conduction electrons. It is found that this exchange interaction leads to two additional terms in the Landau-Lifshitz-Gilbert equation: an effective field and a spin torque. Both terms are proportional to the transverse spin accumulation and have comparable magnitudes. PMID:12059385

  20. Reconfiguring photonic metamaterials with currents and magnetic fields

    SciTech Connect

    Valente, João Ou, Jun-Yu; Plum, Eric; Youngs, Ian J.; Zheludev, Nikolay I.

    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.

  1. Critical current destabilizing perpendicular magnetization by the spin Hall effect

    NASA Astrophysics Data System (ADS)

    Taniguchi, Tomohiro; Mitani, Seiji; Hayashi, Masamitsu

    2015-07-01

    The critical current needed to destabilize the magnetization of a perpendicular ferromagnet via the spin Hall effect is studied. Both the dampinglike and fieldlike torques associated with the spin current generated by the spin Hall effect are included in the Landau-Lifshitz-Gilbert equation to model the system. In the absence of the fieldlike torque, the critical current is independent of the damping constant and is much larger than that of conventional spin torque switching of collinear magnetic systems, as in magnetic tunnel junctions. With the fieldlike torque included, we find that the critical current scales with the damping constant as α0 (i.e., damping independent), α , and α1 /2 depending on the sign of the fieldlike torque and other parameters such as the external field. Numerical and analytical results show that the critical current can be significantly reduced when the fieldlike torque possesses the appropriate sign, i.e., when the effective field associated with the fieldlike torque is pointing opposite to the spin direction of the incoming electrons. These results provide a pathway to reducing the current needed to switch magnetization using the spin Hall effect.

  2. Ring Current Modeling in a Realistic Magnetic Field Configuration

    NASA Technical Reports Server (NTRS)

    Fok, M.-C.; Moore, T. E.

    1997-01-01

    A 3-dimensional kinetic model has been developed to study the dynamics of the storm time ring current in a dipole magnetic field. In this paper, the ring current model is extended to include a realistic, time-varying magnetic field model. The magnetic field is expressed as the cross product of the gradients of two Euler potentials and the bounce-averaged particle drifts are calculated in the Euler potential coordinates. A dipolarization event is modeled by collapsing a tail-like magnetosphere to a dipole-like configuration. Our model is able to simulate the sudden enhancements in the ring current ion fluxes and the corresponding ionospheric precipitation during the substorm expansion.

  3. Bayesian 2D Current Reconstruction from Magnetic Images

    NASA Astrophysics Data System (ADS)

    Clement, Colin B.; Bierbaum, Matthew K.; Nowack, Katja; Sethna, James P.

    We employ a Bayesian image reconstruction scheme to recover 2D currents from magnetic flux imaged with scanning SQUIDs (Superconducting Quantum Interferometric Devices). Magnetic flux imaging is a versatile tool to locally probe currents and magnetic moments, however present reconstruction methods sacrifice resolution due to numerical instability. Using state-of-the-art blind deconvolution techniques we recover the currents, point-spread function and height of the SQUID loop by optimizing the probability of measuring an image. We obtain uncertainties on these quantities by sampling reconstructions. This generative modeling technique could be used to develop calibration protocols for scanning SQUIDs, to diagnose systematic noise in the imaging process, and can be applied to many tools beyond scanning SQUIDs.

  4. Current induced vortex wall dynamics in helical magnetic systems

    NASA Astrophysics Data System (ADS)

    Roostaei, Bahman

    2015-03-01

    Nontrivial topology of interfaces separating phases with opposite chirality in helical magnetic metals result in new effects as they interact with spin polarized current. These interfaces or vortex walls consist of a one dimensional array of vortex lines. We predict that adiabatic transfer of angular momentum between vortex array and spin polarized current will result in topological Hall effect in multi-domain samples. Also we predict that the motion of the vortex array will result in a new damping mechanism for magnetic moments based on Lenz's law. We study the dynamics of these walls interacting with electric current and use fundamental electromagnetic laws to quantify those predictions. On the other hand discrete nature of vortex walls affects their pinning and results in low depinning current density. We predict the value of this current using collective pinning theory.

  5. Calculation of magnetically induced currents in hydrocarbon nanorings.

    PubMed

    Taubert, Stefan; Sundholm, Dage; Jusélius, Jonas; Klopper, Wim; Fliegl, Heike

    2008-12-25

    Magnetically induced current densities, nuclear magnetic shieldings, and electric polarizabilities of planar ring-shaped hydrocarbons have been studied at the density-functional theory level using the Becke-Perdew (BP86) functional. The current densities were calculated using the Gauge-Including Magnetically Induced Current (GIMIC) method employing gauge-including atomic orbitals. The GIMIC calculations yield rules to estimate the global and local ring-current strengths as well as the current pathways for the hydrocarbon nanorings. For the overall antiaromatic molecules, aromatic groups such as benzene, naphthalene, anthracene, and pyrene moieties localize the ring current making the global ring currents vanish. The ability of the edge groups to localize the currents is related to the aromatic character of the molecule as a whole. The local ring current prefers to follow the edges of the group. Phenalenyl corner moieties are found to introduce strong global ring currents, whereas with fused benzene and pyrene corner groups the global ring current vanishes. Fused benzene rings in the corner or along the edge of overall antiaromatic molecules sustain local ring currents of about the same size as for a free benzene molecule. For the overall aromatic molecules, the global ring current is split along the bonds of the edge moieties, but the detailed division fulfilling Kirchhoff's current law is not easily predictable and must be calculated for each individual bond. At the phenalenyl corner moieties, the global ring current follows the innermost route isolating the rest of the group from the main delocalization pathway. A hydrocarbon nanoring sustaining strong ring currents should be large and formally aromatic with many and large aromatic moieties along the edges. A clear correlation between the strength of the global ring currents and the size of the electric polarizabilities is obtained. The calculated 1H NMR shieldings of a proton in immediate contact to the global

  6. Current Sheet Formation and Reconnection at a Magnetic X Line

    NASA Astrophysics Data System (ADS)

    DeVore, C. Richard; Antiochos, S. K.

    2011-05-01

    Phenomena ranging from the quiescent heating of the ambient plasma to the highly explosive release of energy and acceleration of particles in flares are conjectured to result from magnetic reconnection at electric current sheets in the Sun's corona. We are investigating numerically the formation and eventual reconnection of a current sheet in an initially potential 2D magnetic field containing a null. Subjecting this simple configuration to unequal stresses in the four quadrants bounded by the X-line separatrix distorts the potential null into a double-Y-line current sheet. Although the gas pressure is finite in our simulations, so that the plasma beta is infinite at the null, we find that even small distortions of the magnetic field induce the formation of a tangential discontinuity there. This result is well known to occur in the zero-beta, force-free limit; surprisingly, it persists into the high-beta regime where, in principle, a small plasma pressure inhomogeneity could balance all of the magnetic stress. In addition to working to understand the dynamical details of this ideal process, we are examining the effect of resistive dissipation on the development of the current sheet and are seeking to determine the critical condition for fast-reconnection onset in the sheet. Our progress on understanding these issues, and the implications for the dynamic activity associated with current sheets in the solar corona, will be reported at the conference. We gratefully acknowledge NASA sponsorship of our research.

  7. Column buckling of magnetically affected stocky nanowires carrying electric current

    NASA Astrophysics Data System (ADS)

    Kiani, Keivan

    2015-08-01

    Axial load-bearing capacity of current carrying nanowires (CCNWs) acted upon by a longitudinal magnetic field is of high interest. By adopting Gurtin-Murdoch surface elasticity theory, the governing equations of the nanostructure are constructed based on the Timoshenko and higher-order beam models. To solve these equations for critical compressive load, a meshfree approach is exploited and the weak formulations for the proposed models are obtained. The predicted buckling loads are compared with those of assume mode method and a remarkable confirmation is reported. The role of influential factors on buckling load of the nanostructure is carefully addressed and discussed. The obtained results reveal that the surface energy effect becomes important in buckling behavior of slender CCNWs, particularly for high electric currents and magnetic field strengths. For higher electric currents, relative discrepancies between the results of Timoshenko and higher-order beam models increase with a higher rate as the slenderness ratio magnifies. A magnetically affected current-carrying nanowire acted upon by an axial force. Axial buckling of stocky current-carrying nanowires in the presence of a longitudinal magnetic field is of particular interest. Using Timoshenko and higher-order beam theories accounting for surface energy effect, the governing equations are derived and a meshfree methodology is applied to evaluate the buckling load.

  8. A survey on wind power ramp forecasting.

    SciTech Connect

    Ferreira, C.; Gama, J.; Matias, L.; Botterud, A.; Wang, J.

    2011-02-23

    The increasing use of wind power as a source of electricity poses new challenges with regard to both power production and load balance in the electricity grid. This new source of energy is volatile and highly variable. The only way to integrate such power into the grid is to develop reliable and accurate wind power forecasting systems. Electricity generated from wind power can be highly variable at several different timescales: sub-hourly, hourly, daily, and seasonally. Wind energy, like other electricity sources, must be scheduled. Although wind power forecasting methods are used, the ability to predict wind plant output remains relatively low for short-term operation. Because instantaneous electrical generation and consumption must remain in balance to maintain grid stability, wind power's variability can present substantial challenges when large amounts of wind power are incorporated into a grid system. A critical issue is ramp events, which are sudden and large changes (increases or decreases) in wind power. This report presents an overview of current ramp definitions and state-of-the-art approaches in ramp event forecasting.

  9. Directly coupled direct current superconducting quantum interference device magnetometers based on ramp-edge Ag:YBa{sub 2}Cu{sub 3}O{sub 7{minus}x}/PrBa{sub 2}Cu{sub 3}O{sub 7{minus}x}/Ag:YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} junctions

    SciTech Connect

    Jia, Q.X.; Yan, F.; Mombourquette, C.; Reagor, D.

    1998-06-01

    Directly coupled dc superconducting quantum interference device (SQUID) magnetometers on LaAlO{sub 3} substrates were fabricated using ramp-edge superconductor/normal-metal/superconductor junctions, where Ag-doped YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} was used for the electrode and PrBa{sub 2}Cu{sub 3}O{sub 7{minus}x} for the normal-metal barrier. A flux noise of 8{times}10{sup {minus}6}thinsp{Phi}{sub 0}thinspHz{sup {minus}1/2} at 10 kHz measured with a dc bias current was achieved at 75 K, which corresponded to a field sensitivity of 400thinspfTHz{sup {minus}1/2} for a magnetometer with a pick-up loop area of 8.5thinspmm{times}7.5thinspmm. Most significantly, the noise floor increased at lower frequencies with a frequency dependence slightly less than 1/f. The field noise of the SQUID magnetometers increased by only 25{percent} after cycling the devices from zero field to 500 mG. In a static earth{close_quote}s magnetic field background, the field noise of the SQUID magnetometers increased by less than a factor of 2. {copyright} {ital 1998 American Institute of Physics.}

  10. Currents between tethered electrodes in a magnetized laboratory plasma

    NASA Technical Reports Server (NTRS)

    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 sheet oscillations in the magnetic filament approach

    SciTech Connect

    Erkaev, N. V.; Semenov, V. S.; Biernat, H. K.

    2012-06-15

    Magnetic filament approach is applied for modeling of nonlinear 'kink'-like flapping oscillations of thin magnetic flux tubes in the Earth's magnetotail current sheet. A discrete approximation for the magnetic flux tube was derived on a basis of the Hamiltonian formulation of the problem. The obtained system of ordinary differential equations was integrated by method of Rosenbrock, which is suitable for stiff equations. The two-dimensional exact Kan's solution of the Vlasov equations was used to set the background equilibrium conditions for magnetic field and plasma. Boundary conditions for the magnetic filament were found to be dependent on the ratio of the ionospheric conductivity and the Alfven conductivity of the magnetic tube. It was shown that an enhancement of this ratio leads to the corresponding increase of the frequency of the flapping oscillations. For some special case of boundary conditions, when the magnetic perturbations vanish at the boundaries, the calculated frequency of the 'kink'-like flapping oscillations is rather close to that predicted by the 'double gradient' analytical model. For others cases, the obtained frequency of the flapping oscillations is somewhat larger than that from the 'double gradient' theory. The frequency of the nonlinear flapping oscillations was found to be a decreasing function of the amplitude.

  12. Simulations of the bootstrap current in small rotating magnetic islands

    SciTech Connect

    Bergmann, A.; Poli, E.; Peeters, A. G.

    2008-11-01

    The bootstrap current in small magnetic islands of neoclassical tearing modes is studied in numerical simulations whith the guiding center particle code HAGIS. The contributions of both, electrons and ions, are included, as well as the island rotation and its electric field. The case of islands that are smaller than the ion banana orbit width is studied. We find that the size of the bootstrap current in small islands depends strongly on the rotation frequency of the island.

  13. Limiting current mechanisms of Bi2223 wires in magnetic fields

    NASA Astrophysics Data System (ADS)

    Kobayashi, S.; Yamade, S.; Kikuchi, M.; Yamazaki, K.; Fujikami, J.; Ayai, N.; Hayashi, K.; Sato, K.; Hata, R.; Kitaguti, H.

    2008-05-01

    Controlled overpressure (CT-OP) processing eliminates pores and heals cracks, which densifies the Bi2223 filaments and increases the critical current of Ag-sheathed Bi2223 wire. High current capacity wires with critical current values around 210 A at 77 K and self-field have been achieved. The enhancement of the current capacity seems to be due to reducing the weak links between Bi2223 grains and improving the flux pinning. In order to understand the mechanisms for transport critical current in Bi2223 wires, the dependence of the critical current on magnetic field and temperature has been investigated. The critical current is measured as a function of the perpendicular and parallel magnetic fields, up to 12 T, at temperatures ranging from 4.2 to 90 K. These results indicate that higher critical current is associated with highly textured and well connected Bi2223 grains. To further improve a critical current of Bi2223 wires, it is necessary to decrease the misalignment angle and reduce the fraction of Bi2212 and secondary phases.

  14. Tuning Coler Magnetic Current Apparatus with Magneto-Acoustic Resonance

    NASA Astrophysics Data System (ADS)

    Ludwig, Thorsten

    An attempt was made to tune the Coler magnetic current apparatus with the magneto acoustic resonance of the magnetic rods. Measurements with a replica of the famous Coler "Magnetstromapparat" were conducted. In order to tune the acoustic, magnetic and electric resonance circuits of the Coler device the magneto-acoustic resonance was measured with a frequency scan through a function generator and a lock-in amplifier. The frequency generator was powering a driving coil, while the lock-in was connected to a pickup coil. Both coils were placed on a magnetic rod. Resonances were observed up to the 17th harmonic. The quality Q of the observed resonances was 270. To study the magneto-acoustic resonance in the time domain a pair of Permendur rods were employed. The magneto-acoustic resonances of the Permendur rods were observed with an oscilloscope. Spectra of the magneto acoustic resonance were measured for the Permendur rods and for a Coler replica magnet in the frequency range from 25 kHz to 380 kHz. The next step was to bring the resonances of the Permendur rods close together so that they overlap. The 10thharmonic was chosen because it was close to the 180 kHz that Hans Coler related to ferromagnetism. Further more magneto-acoustic coupling between the Permendur rods was studied. Finally the question was explored if Hans Coler converted vacuum fluctuations via magnetic and acoustic resonance into electricity. There is a strong connection between magnetism and quantum field zero point energy (ZPE). An outlook is given on next steps in the experiments to unveil the working mechanism of the Coler magnetic current apparatus.

  15. POLOIDAL MAGNETIC FIELD TOPOLOGY FOR TOKAMAKS WITH CURRENT HOLES

    SciTech Connect

    Puerta, Julio; Martin, Pablo; Castro, Enrique

    2009-07-26

    The appearance of hole currents in tokamaks seems to be very important in plasma confinement and on-set of instabilities, and this paper is devoted to study the topology changes of poloidal magnetic fields in tokamaks. In order to determine these fields different models for current profiles can be considered. It seems to us, that one of the best analytic descriptions is given by V. Yavorskij et al., which has been chosen for the calculations here performed. Suitable analytic equations for the family of magnetic field surfaces with triangularity and Shafranov shift are written down here. The topology of the magnetic field determines the amount of trapped particles in the generalized mirror type magnetic field configurations. Here it is found that the number of maximums and minimums of Bp depends mainly on triangularity, but the pattern is also depending of the existence or not of hole currents. Our calculations allow comparing the topology of configurations of similar parameters, but with and without whole currents. These differences are study for configurations with equal ellipticity but changing the triangularity parameters. Positive and negative triangularities are considered and compared between them.

  16. Dynamic Response of Magnetic Reconnection Due to Current Sheet Variability

    NASA Astrophysics Data System (ADS)

    George, D. E.; Jahn, J. M.; Burch, J. L.; Hesse, M.; Pollock, C. J.

    2014-12-01

    Magnetic reconnection is a process which regulates the interaction between regions of magnetized plasma. While many factors have an impact on the evolution of this process, there still remains a lack of understanding of the key behaviors involved in the triggering of fast reconnection. Despite an abundance of in-situ measurements, indicating the high degree of variability in the thickness, density and composition along the current sheet, no simulation studies exist which account for such current sheet variations. 2D and 3D simulations have a periodic boundary in the dimension along the current sheet and so tend to neglect these variations in the current sheet originating external to the modeled reconnection region. Here we focus on the effects on reconnection due to the variability in the thickness and density of the current sheet. Using 2.5D kinetic simulations of 2-species plasma, we isolate and explore the dynamic effects on reconnection associated with variations in the current sheet originating externally to the reconnection region. While periodic boundary conditions are still used, in the direction along the current sheet, a step-change perturbation in thickness or density of the current sheet is introduced once a stable reconnection rate is reached. The dynamic response of the overall system, after introducing the perturbation, is then evaluated, with a focus on the reconnection rate. When the reconnection rate is slowed significantly over time, loading of the inflow region occurs (a build-up of plasma and magnetic energy/pressure. This state is indicated by an asymptotic behavior in the reconnection rate over time. If a sudden variation in the current sheet is introduced under these conditions, a resultant triggering of fast reconnection may occur, which could lead to an episode of fast reconnection, saw-tooth-crash condition or even act as a trigger for sub-storms.

  17. Calibration tests on magnetic tape lightning current detectors

    NASA Technical Reports Server (NTRS)

    Crouch, K. E.

    1980-01-01

    The low cost, passive, peak lightning current detector (LCD) invented at the NASA/Kennedy Space Center, uses magnetic audio recording tape to sense the magnitude of the peak magnetic field around a conductor carrying lightning currents. Test results show that the length of audio tape erased was linearly related to the peak simulated lightning currents in a round conductor. Accuracies of + or - 10% were shown for measurements made using a stopwatch readout technique to determine the amount of tape erased by the lightning current. The stopwatch technique is a simple, low cost means of obtaining LCD readouts and can be used in the field to obtain immediate results. Where more accurate data are desired, the tape is played and the output recorded on a strip chart, oscilloscope, or some other means so that measurements can be made on that recording. Conductor dimensions, tape holder dimensions, and tape formulation must also be considered to obtain a more accurate result. If the shape of the conductor is other than circular (i.e., angle, channel, H-beam), an analysis of the magnetic field is required to use an LCD, especially at low current levels.

  18. Magnetic nano-oscillator driven by pure spin current

    NASA Astrophysics Data System (ADS)

    Demidov, Vladislav E.; Urazhdin, Sergei; Ulrichs, Henning; Tiberkevich, Vasyl; Slavin, Andrei; Baither, Dietmar; Schmitz, Guido; Demokritov, Sergej O.

    2012-12-01

    With the advent of pure-spin-current sources, spin-based electronic (spintronic) devices no longer require electrical charge transfer, opening new possibilities for both conducting and insulating spintronic systems. Pure spin currents have been used to suppress noise caused by thermal fluctuations in magnetic nanodevices, amplify propagating magnetization waves, and to reduce the dynamic damping in magnetic films. However, generation of coherent auto-oscillations by pure spin currents has not been achieved so far. Here we demonstrate the generation of single-mode coherent auto-oscillations in a device that combines local injection of a pure spin current with enhanced spin-wave radiation losses. Counterintuitively, radiation losses enable excitation of auto-oscillation, suppressing the nonlinear processes that prevent auto-oscillation by redistributing the energy between different modes. Our devices exhibit auto-oscillations at moderate current densities, at a microwave frequency tunable over a wide range. These findings suggest a new route for the implementation of nanoscale microwave sources for next-generation integrated electronics.

  19. A new high-precision current supply for magnets

    SciTech Connect

    Wisnivesky, D. |; Lira, A.C.

    1995-08-01

    A new, high-precision, low-ripple current power supply (CPS) for magnets, based on a combination of an SCR converter and a single transistor switched mode power supply (SMPS) is described. The load power is primarily supplied by the SCR converter. The SMPS handles only a small fraction of the load power, and also, what is more significant, a very small part of the load current. In this paper, the topology and operating principle of the new power supply is discussed. A CPS, rated at 200 A at 45 V, was constructed and tested. The power supply energizes a family of quadrupole magnets at the Brazilian Synchrotron Light Source--LNLS. Making use of the current limit modulation (CLM) control method, magnetic field variations at full current are 5 ppm, with only 8 A passing through the switching transistor. The design and performance of the power supply under different operating conditions ar described. Variations of the proposed topology, suitable for high-current and high-voltage loads, are also discussed.

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

    SciTech Connect

    Zhang, Y.; Klein, J.-O.; Chappert, C.; Ravelosona, D.; Zhao, W. S.

    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.

  1. Ramp-edge structured tunneling devices using ferromagnet electrodes

    DOEpatents

    Kwon, Chuhee; Jia, Quanxi

    2002-09-03

    The fabrication of ferromagnet-insulator-ferromagnet magnetic tunneling junction devices using a ramp-edge geometry based on, e.g., (La.sub.0.7 Sr.sub.0.3) MnO.sub.3, ferromagnetic electrodes and a SrTiO.sub.3 insulator is disclosed. The maximum junction magnetoresistance (JMR) as large as 23% was observed below 300 Oe at low temperatures (T<100 K). These ramp-edge junctions exhibited JMR of 6% at 200 K with a field less than 100 Oe.

  2. High temperature superconducting current leads for fusion magnet systems

    NASA Astrophysics Data System (ADS)

    Wu, J. L.; Dederer, J. T.; Singh, S. K.; Hull, J. R.

    Superconducting magnets for fusion applications typically have very high operating currents. These currents are transmitted from the room temperature power supplies to the low temperature superconducting coils by way of helium-vapor-cooled current leads. Because of the high current magnitude and the resistive characteristics associated with the normal metallic lead conductors, a substantial amount of power is dissipated in the lead. To maintain a stable operation, a high rate of helium vapor flow, generated by the boil-off of liquid helium, is required to cool the lead conductors. This helium boil-off substantially increases both the installation capacity and the operating cost of the helium refrigerator/liquefier. The boil-off of liquid helium can be significantly reduced by employing ceramic high temperature superconductors, such as Y-Ba-Cu-O, in the low temperature part of the lead conductor structure. This concept utilizes the superconducting, as well as the low thermal conductivity properties of the superconductor materials in eliminating power dissipation in part of the current lead and in inhibiting heat conduction into the liquid helium pool, resulting in reduced helium boil-off. This design concept has been conclusively demonstrated by a 2-kA current lead test model using Y-Ba-Cu-O (123) material which, although not optimized in design, has significantly reduced the rate of helium boil-off in comparison to optimized conventional leads. There appear to be no major technological barriers for scaling up this design to higher current levels for applications in fusion magnet systems or in fusion related testing activities. The theoretical basis of the current lead concept, as well as the important design and technology issues are addressed. The potential cost saving derived from employing these leads in fusion magnets is also discussed. In addition, a design concept for a 10-kA lead is presented.

  3. Pulsed currents carried by whistlers. I - Excitation by magnetic antennas

    NASA Technical Reports Server (NTRS)

    Stenzel, R. L.; Urrutia, J. M.; Rousculp, C. L.

    1993-01-01

    Time-varying plasma currents associated with low-frequency whistlers have been investigated experimentally. Pulsed currents are induced in the uniform, boundary-free interior of a large laboratory plasma by means of insulated magnetic antennas. The time-varying magnetic field is measured in three dimensions, and the current density is calculated from del x B(r,t) = mu(0)J, where J includes the displacement current density. Typical fields B(r,t) and J(r,t) induced by a magnetic loop antenna show three-dimensional helices due to linked toroidal and solenoidal field topologies. Constant amplitude and phase surfaces assume conical shapes since the propagation speed along B0 is higher than oblique to B0. The electric field in the wave packet contains both inductive and space-charge contributions, the latter arising from the different dynamics of electrons and ions. The dominant electric field in a whistler packet is a radial space-charge field.

  4. SR-71 on Ramp

    NASA Technical Reports Server (NTRS)

    1990-01-01

    NASA's SR-71A, used for high-speed, high-altitude aeronautical research, is seen here on the ramp outside its main building hangar at the Ames-Dryden Flight Research Facility (later, Dryden Flight Research Center), Edwards, California. NASA operated two of these unique aircraft, an SR-71A and an SR-71B pilot trainer during the decade of the 1990s. The SR-71 was designed and built by the Lockheed Skunk Works, now Lockheed Martin. Studies have shown that less than 20 percent of the total thrust used to fly at Mach 3 is produced by the basic engine itself. The balance of the total thrust is produced by the unique design of the engine inlet and 'moveable spike' system at the front of the engine nacelles, and by the ejector nozzles at the exhaust. Data from the SR-71 high speed research program will be used to aid designers of future supersonic/hypersonic aircraft and propulsion systems. Two SR-71 aircraft have been used by NASA as testbeds for high-speed and high-altitude aeronautical research. The aircraft, an SR-71A and an SR-71B pilot trainer aircraft, have been based here at NASA's Dryden Flight Research Center, Edwards, California. They were transferred to NASA after the U.S. Air Force program was cancelled. As research platforms, the aircraft can cruise at Mach 3 for more than one hour. For thermal experiments, this can produce heat soak temperatures of over 600 degrees Fahrenheit (F). This operating environment makes these aircraft excellent platforms to carry out research and experiments in a variety of areas -- aerodynamics, propulsion, structures, thermal protection materials, high-speed and high-temperature instrumentation, atmospheric studies, and sonic boom characterization. The SR-71 was used in a program to study ways of reducing sonic booms or over pressures that are heard on the ground, much like sharp thunderclaps, when an aircraft exceeds the speed of sound. Data from this Sonic Boom Mitigation Study could eventually lead to aircraft designs that

  5. Rural Alaska Mentoring Project (RAMP)

    ERIC Educational Resources Information Center

    Cash, Terry

    2011-01-01

    For over two years the National Dropout Prevention Center (NDPC) at Clemson University has been supporting the Lower Kuskokwim School District (LKSD) in NW Alaska with their efforts to reduce high school dropout in 23 remote Yup'ik Eskimo villages. The Rural Alaska Mentoring Project (RAMP) provides school-based E-mentoring services to 164…

  6. Visualising Plasma Flow in Current-carrying Magnetic Flux Tubes

    NASA Astrophysics Data System (ADS)

    You, Setthivoine; Bellan, Paul M.

    2003-10-01

    Laboratory experiments at Caltech [1], designed to study the formation and dynamics of spheromaks, solar prominences [2] and astrophysical jets, have motivated a theory for plasma flow within current-carrying magnetic flux tubes [3]. The spheromak and jet plasmas studied are formed by the merging of several plasma-filled magnetic flux tubes. These flux tubes ingest gas puffed in by pulsed gas valves and have current driven along a bias field. The apparatus is now being modified to permit injection of two different gas species into the same flux tube from different ports, corresponding to opposite footpoints of the flux tube. The new gas delivery system allows for simultaneous injection of various combinations of gas species (H, D, He, N, Ne, Ar, Kr) through various gas nozzle locations (inner or outer gun electrodes, left hand side or right hand side series). During the discharge, the multi-species plasmas are to be imaged with high speed, single- and multiple-frame, intensified CCD cameras and will be differentiated by narrow band optical filters. Other diagnostics include a magnetic probe array, soft x-ray diodes and an optical multichannel analyser to monitor the magnetic field evolution, particle velocities and energies. [1] S. C. Hsu and P. M. Bellan, Mon. Not. R. Astron. Soc., 334, 257-261 (2000). [2] J. F. Hansen and P. M. Bellan, Astrophys. J., 563, L183-L186, (2001). [3] P. M. Bellan, Phys. Plasmas, 10, 1999-2008 (2003).

  7. Magnetic and transport eddy-current anomalies in cylinders owing to magnetization rotations

    NASA Astrophysics Data System (ADS)

    Chen, D.-X.; Pascual, L.

    2001-06-01

    For a magnetic conducting cylinder with a coaxial core, where the spontaneous magnetization Ms is helical, the technical magnetization under an axial AC magnetic field or AC transport current is carried out by Ms rotations, which induce normal and lateral eddy currents. The low-frequency eddy-current anomaly factors for the magnetic and the transport case, η, are calculated as functions of the radius ratio of the core to the cylinder, p= rb/ r0, the scalar susceptibility of the shell normalized to the normal susceptibility of the core, q= χs/ χzz or χs/ χφφ, and the helical angle with respect to the z-axis, α. It is shown that for the typical case of α= π/4, the lateral-eddy-current loss is appreciably less and greater than the normal one in the magnetic and transport case, respectively, which is in contrast to the situation of a slab where both losses are equal.

  8. A magnetic persistent current switch at milliKelvin temperatures

    NASA Astrophysics Data System (ADS)

    van Waarde, Bob; Benningshof, Olaf; Oosterkamp, Tjerk

    2016-09-01

    We report the development of a magnetically driven Persistent Current Switch operated in a dilution refrigerator. We show that it can be safely used to charge a 60 mH coil with 0.5 A at 11 mK, which heats up the dilution refrigerator to 60.5 mK. Measurements at 4 K on a 440 μH coil reveal a residual resistance of R ⩽ 3.3 p Ω .

  9. Current understanding of magnetic storms: Storm-substorm relationships

    SciTech Connect

    Kamide, Y.; Gonzalez, W.D.; Baumjohann, W.; Daglis, I.A.; Grande, M.; Joselyn, J.A.; Singer, H.J.; McPherron, R.L.; Phillips, J.L.; Reeves, E.G.; Rostoker, G.; Sharma, A.S.; Tsurutani, B.T.

    1998-08-01

    This paper attempts to summarize the current understanding of the storm/substorm relationship by clearing up a considerable amount of controversy and by addressing the question of how solar wind energy is deposited into and is dissipated in the constituent elements that are critical to magnetospheric and ionospheric processes during magnetic storms. (1) Four mechanisms are identified and discussed as the primary causes of enhanced electric fields in the interplanetary medium responsible for geomagnetic storms. It is pointed out that in reality, these four mechanisms, which are not mutually exclusive, but interdependent, interact differently from event to event. Interplanetary coronal mass ejections (ICMEs) and corotating interaction regions (CIRs) are found to be the primary phenomena responsible for the main phase of geomagnetic storms. The other two mechanisms, i.e., HILDCAA (high-intensity, long-duration, continuous auroral electrojet activity) and the so-called Russell-McPherron effect, work to make the ICME and CIR phenomena more geoeffective. The solar cycle dependence of the various sources in creating magnetic storms has yet to be quantitatively understood. (2) A serious controversy exists as to whether the successive occurrence of intense substorms plays a direct role in the energization of ring current particles or whether the enhanced electric field associated with southward IMF enhances the effect of substorm expansions. While most of the {ital Dst} variance during magnetic storms can be solely reproduced by changes in the large-scale electric field in the solar wind and the residuals are uncorrelated with substorms, recent satellite observations of the ring current constituents during the main phase of magnetic storms show the importance of ionospheric ions. This implies that ionospheric ions, which are associated with the frequent occurrence of intense substorms, are accelerated upward along magnetic field lines, contributing to the energy density of

  10. Repetitive formation and decay of current sheets in magnetic loops: An origin of diverse magnetic structures

    SciTech Connect

    Kumar, Dinesh; Bhattacharyya, R.; Smolarkiewicz, P. K.

    2015-01-15

    In this work, evolution of an incompressible, thermally homogeneous, infinitely conducting, viscous magnetofluid is numerically explored as the fluid undergoes repeated events of magnetic reconnection. The initial magnetic field is constructed by a superposition of two linear force-free fields and has similar morphology as the magnetic loops observed in the solar corona. The results are presented for computations with three distinct sets of footpoint geometries. To onset reconnection, we rely on numerical model magnetic diffusivity, in the spirit of implicit large eddy simulation. It is generally expected that in a high Lundquist number fluid, repeated magnetic reconnections are ubiquitous and hence can lead to a host of magnetic structures with considerable observational importance. In particular, the simulations presented here illustrate formations of magnetic islands, rotating magnetic helices and rising flux ropes—depending on the initial footpoint geometry but through the common process of repeated magnetic reconnections. Further, we observe the development of extended current sheets in two case studies, where the footpoint reconnections generate favorable dynamics.

  11. The bootstrap current in small rotating magnetic islands

    SciTech Connect

    Bergmann, A.; Poli, E.; Peeters, A. G.

    2009-09-15

    The bootstrap current in small magnetic islands of neoclassical tearing modes is studied with guiding center particle simulations including pitch angle scattering. A model for a rotating island and its electric field is used and a new approximation to the electric potential in small islands is derived. Islands with sizes of the order of the ion banana orbit width are studied by means of a two-step model, which allows to treat both ions and electrons kinetically. The bootstrap current in such small islands is found to depend strongly on the direction of rotation of the island. The bootstrap current in small islands rotating in the ion diamagnetic direction is strongly diminished, similarly to what happens in big islands. In small islands rotating in the electron diamagnetic direction, on the contrary, the bootstrap current is almost completely preserved, implying a reduced neoclassical drive of the island growth.

  12. Tailoring of electron flow current in magnetically insulated transmission lines

    NASA Astrophysics Data System (ADS)

    Martin, J. P.; Savage, M. E.; Pointon, T. D.; Gilmore, M. A.

    2009-03-01

    It is desirable to optimize (minimizing both the inductance and electron flow) the magnetically insulated vacuum sections of low impedance pulsed-power drivers. The goal of low inductance is understandable from basic efficiency arguments. The goal of low electron flow results from two observations: (1) flowing electrons generally do not deliver energy to (or even reach) most loads, and thus constitute a loss mechanism; (2) energetic electrons deposited in a small area can cause anode damage and anode plasma formation. Low inductance and low electron flow are competing goals; an optimized system requires a balance of the two. While magnetically insulated systems are generally forgiving, there are times when optimization is crucial. For example, in large pulsed-power drivers used to energize high energy density physics loads, the electron flow as a fraction of total current is small, but that flow often reaches the anode in relatively small regions. If the anode temperature becomes high enough to desorb gas, the resulting plasma initiates a gap closure process that can impact system performance. Magnetic-pressure driven (z pinches and material equation of state) loads behave like a fixed inductor for much of the drive pulse. It is clear that neither fixed gap nor constant-impedance transmission lines are optimal for driving inductive loads. This work shows a technique for developing the optimal impedance profile for the magnetically insulated section of a high-current driver. Particle-in-cell calculations are used to validate the impedance profiles developed in a radial disk magnetically insulated transmission line geometry. The input parameters are the spacing and location of the minimum gap, the effective load inductance, and the desired electron flow profile. The radial electron flow profiles from these simulations are in good agreement with theoretical predictions when driven at relatively high voltage (i.e., V≥2MV).

  13. System and method for magnetic current density imaging at ultra low magnetic fields

    DOEpatents

    Espy, Michelle A.; George, John Stevens; Kraus, Robert Henry; Magnelind, Per; Matlashov, Andrei Nikolaevich; Tucker, Don; Turovets, Sergei; Volegov, Petr Lvovich

    2016-02-09

    Preferred systems can include an electrical impedance tomography apparatus electrically connectable to an object; an ultra low field magnetic resonance imaging apparatus including a plurality of field directions and disposable about the object; a controller connected to the ultra low field magnetic resonance imaging apparatus and configured to implement a sequencing of one or more ultra low magnetic fields substantially along one or more of the plurality of field directions; and a display connected to the controller, and wherein the controller is further configured to reconstruct a displayable image of an electrical current density in the object. Preferred methods, apparatuses, and computer program products are also disclosed.

  14. Pulsed currents carried by whistlers. III. Magnetic fields and currents excited by an electrode

    SciTech Connect

    Urrutia, J.M.; Stenzel, R.L.; Rousculp, C.L.

    1995-04-01

    Detailed measurements and analysis of electromagnetic fields asociated with pulsed plasma currents are reported. The objective is to demonstrate the properties of plasma currents in the electron magnetohydrodynamic regime and their relation to low frequency whistler waves. Short current pulses ({ital f}{sub {ital ce}}{sup {minus}1}{much_lt}{Delta}{ital t}{much_lt}{ital f}{sub {ital ci}}{sup {minus}1}) are injected from an electrode into a large, uniform magnetoplasma. The dynamic fields, B(r,{ital t}), are measured with probes in three-dimensional space and time, and are observed to propagate as wave packets predominantly along the guide magnetic field, B{sub 0}. Four-dimensional fast Fourier transformation of B(r,{ital t}) to B(k,{omega}) verifies that the wave fields fall on the dispersion surface of low-frequency oblique whistlers. The magnetic field topology of the packets consists of linked toroidal and solenoidal contributions in force-free configurations. The wave magnetic helicity is obtained quantitatively. Similarly, the topology of the current density field, J@={bold mc}{times}B/{mu}{sub 0}, is explained by its components, characteristic field lines, and helicity, {integral}J{center_dot}B{ital dV}. It is shown, both theoretically and experimentally, that A, B, and J are nearly parallel to one another. Field energy and helicity decay at the same rate without change in topology. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  15. Magnetic field dependence of critical currents in superconducting polycrystals

    SciTech Connect

    Kugel, K.I.; Lisovskaya, T.Y. ); Mints, R.G. )

    1992-02-10

    The authors study the dependence of critical current j{sub c} on magnetic field H in superconducting polycrystals which are considered as system of superconducting crystallites (isotropic or anisotropic) with Josephson contacts between them. Isotropy or anisotropy of contacts depends on the orientation of their crystallographic axes relatively to edges of contact planes. In this paper it is shown that for a system of randomly oriented isotropic contacts, the dependence j{sub c}(H) in a relatively wide field range has the asymptotic form j{sub c} {approximately} (InH)/H{sup 2}. This differs drastically from j{sub c}(H) for single contacts. Anisotropy effects due to large differences in London penetration depth {lambda} values corresponding to external magnetic field directed along different axes are analyzed in detail. It is shown that for uniaxal crystals with {lambda}{sub 1} = {lambda}{sub 2} {lt} {lambda}{sub 3}, this anisotropy leads to the relation j{sub c} {approximately} {radical}{lambda}{sub 3}/{lambda}{sub 1} for chaotic orientation of crystallites. The form of j{sub c}(H) curves for two different orientations of the magnetic field relatively to the transport current through the sample is found.

  16. Behavior of an eddy-current magnetic bearing

    SciTech Connect

    Ting Leehua.

    1991-01-01

    The perturbation method (PM) in conjunction with the symbolic computing software MATHEMATICA' is employed to solve Maxwell's equations to obtain the theoretical results of forces, stiffness, and damping coefficients for a simplified eddy current magnetic bearing (ECMB). In addition, a finite element method software FLUX2D' and some deliberately designed experiments are employed to check some of the results obtained by the perturbation method. Finally, the results are used to evaluate the dynamic behavior of the ECMB, and are extended to conjecture concerning the prospect of a similar application, Maglev (Magnetically Levitated High-Speed Trains). The theoretical results of forces, stiffness, and damping coefficients obtained by the perturbation method show that such kind of bearing has extremely low damping, probably negative, and moderately low stiffness and forces, compared to ordinary bearings. Data are also obtained by inputting the presumed Maglev features to the perturbation method solutions. It is found that the eddy current type magnetic suspension is more practical in the large scale application (Maglev) than in small scale application (ECMB).

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

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

    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.

  19. Magnetic field and electric current structure in the chromosphere

    NASA Technical Reports Server (NTRS)

    Dravins, D.

    1974-01-01

    The three-dimensional vector magnetic field structure in the chromosphere above an active region is deduced by using high-resolution H-alpha filtergrams together with a simultaneous digital magnetogram. An analog model of the field is made with 400 metal wires representing field lines that outline the H-alpha structure. The height extent of the field is determined from vertical field-gradient observations around sunspots, from observed fibril heights, and from an assumption that the sources of the field are largely local. The computed electric currents (typically 10 mA/sq m) are found to flow in patterns not similar to observed features and not parallel to magnetic fields. Force structures correspond to observed solar features; the dynamics to be expected include: downward motion in bipolar areas in the lower chromosphere, an outflow of the outer chromosphere into the corona with radially outward flow above bipolar plage regions, and motion of arch filament systems.

  20. Studies of time dependence of fields in TEVATRON superconducting dipole magnets

    SciTech Connect

    Hanft, R.W.; Brown, B.C.; Herrup, D.A.; Lamm, M.J.; McInturff, A.D.; Syphers, M.J.

    1988-08-22

    The time variation in the magnetic field of a model Tevatron dipole magnet at constant excitation current has been studied. Variations in symmetry allowed harmonic components over long time ranges show a log t behavior indicative of ''flux creep.'' Both short time range and long time range behavior depend in a detailed way on the excitation history. Similar effects are seen in the remnant fields present in full-scale Tevatron dipoles following current ramping. Both magnitudes and time dependences are observed to depend on details for the ramps, such as ramp rate, flattop duration, and number of ramps. In a few magnets, variations are also seen in symmetry unallowed harmonics. 9 refs., 10 figs.

  1. X-36 on Ramp

    NASA Technical Reports Server (NTRS)

    1997-01-01

    NASA Dryden Flight Fesearch Center, Edwards California is hosting the X-36 program, as well as providing range support for the flight tests. NASA Ames Research Center, Moffett Field, California originated the X- 36 program and is managing the program in a cooperative effort with the McDonnell Douglas Corporation. MDC's responsibilities include flight preparation and testing, data acquisition and analysis. The X-36 is a small, remotely-piloted jet built by MDC and designed to fly without the traditional tail surfaces common on most aircraft. Two 28 percent scale vehicles will be put through fighter aircraft maneuvers during the scheduled 25 flight program. The goal is to gather data on the performance characteristics, especially agility, of tailless, fighter type aircraft. The lack of vertical tails on the X-36 greatly enhances the stealthy characteristics of the airplane, and holds promise for greater agility than is currently available in existing fighter aircraft. The X-36 is 18 feet long with a 10 foot wingspan, is 3 feet high, and weighs 1,270 pounds.

  2. Finite-width currents, magnetic shear, and the current-driven ion-cyclotron instability

    NASA Technical Reports Server (NTRS)

    Bakshi, P.; Ganguli, G.; Palmadesso, P.

    1983-01-01

    Our earlier results that non-local effects due to even a small magnetic shear produce a significant reduction of the growth rate of the ion cyclotron instability driven by a uniform current are now generalized to finite width currents. Externally prescribed as well as self-consistent shears are considered. If the current width Lc exceeds the shear length Ls, the previous results are recovered. Shear becomes less effective with reduction of Lc, and for typical parameters, the growth rate attains its (shearless) local value for Lc/Ls approximately less than 10 to the minus 2. Non-local effects of the finite current width itself come into play if Lc is further reduced to a few ion Larmor radii and can quench the instability. Previously announced in STAR as N83-28996

  3. Magnetic current loop array in a reflector antenna

    NASA Astrophysics Data System (ADS)

    Yung, Edward K. N.; Lee, Wilson W. S.

    1994-04-01

    A magnetic current loop antenna array is designed, implemented, and measured. Radiation pattern, input impedance, and efficiency of the array are presented. The array is intended as a feed in a reflector antenna. Using a 360 mm solid dish, the overall gain of the reflector antenna is 24.6 dB at 9 GHz. The tolerance in placing the feed at the focal point of the dish is high. The present feed is low cost, self-supportive, robust, and easy to manufacture. It is an ideal substitute for the horn in a TVRO (television receive only) or VSAT (very small aperature terminal) antenna.

  4. Renal perfusion evaluation by alternating current biosusceptometry of magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Quini, Caio C.; Matos, Juliana F.; Próspero, André G.; Calabresi, Marcos Felipe F.; Zufelato, Nicholas; Bakuzis, Andris F.; Baffa, Oswaldo; Miranda, José Ricardo A.

    2015-04-01

    Alternating current susceptometry, a simple and affordable technique, was employed to study the sensitivity of this approach to assess rat kidney perfusion by the injection of 200 μL of magnetic nanoparticles with a concentration of 23 mg/mL in the femoral vein and the measurement of the signal above the kidney. The instrument was able to detect the signal and the transit time of the first and second pass were measured in five animals with average values of 13.6±4.3 s and 20.6±7.1 s.

  5. Circular current loops, magnetic dipoles and spherical harmonic analysis.

    USGS Publications Warehouse

    Alldredge, L.R.

    1980-01-01

    Spherical harmonic analysis (SHA) is the most used method of describing the Earth's magnetic field, even though spherical harmonic coefficients (SHC) almost completely defy interpretation in terms of real sources. Some moderately successful efforts have been made to represent the field in terms of dipoles placed in the core in an effort to have the model come closer to representing real sources. Dipole sources are only a first approximation to the real sources which are thought to be a very complicated network of electrical currents in the core of the Earth. -Author

  6. Experimental Study of Current-Driven Turbulence During Magnetic Reconnection

    SciTech Connect

    Porkolab, Miklos; Egedal-Pedersen, Jan; Fox, William

    2010-08-31

    CMPD Final Report Experimental Study of Current-Driven Turbulence During Magnetic Reconnection Miklos Porkolab, PI, Jan Egedal, co-PI, William Fox, graduate student. This is the final report for Grant DE-FC02-04ER54786, MIT Participation in the Center for Multiscale Plasma Dynamics, which was active from 8/1/2004 to 7/31/2010. This Grant supported the thesis work of one MIT graduate student, William Fox, The thesis research consisted of an experimental study of the fluctuations arising during magnetic reconnection in plasmas on the Versatile Toroidal Facility (VTF) at MIT Plasma Science and Fusion Center (PSFC). The thesis was submitted and accepted by the MIT physics Department,. Fox, Experimental Study of Current-Driven Turbulence During Magnetic Reconnection, Ph.D. Thesis, MIT (2009). In the VTF experiment reconnection and current-sheet formation is driven by quickly changing currents in a specially arranged set of internal conductors. Previous work on this device [Egedal, et al, PRL 98, 015003, (2007)] identified a spontaneous reconnection regime. In this work fluctuations were studied using impedance-matched, high-bandwidth Langmuir probes. Strong, broadband fluctuations, with frequencies extending from near the lower-hybrid frequency [fLH = (fcefci)1/2] to the electron cyclotron frequency fce were found to arise during the reconnection events. Based on frequency and wavelength measurements, lower-hybrid waves and Trivelpiece-Gould waves were identified. The lower-hybrid waves are easiest to drive with strong perpendicular drifts or gradients which arise due to the reconnection events; an appealing possibility is strong temperature gradients. The Trivelpiece-Gould modes can result from kinetic, bump-on-tail instability of a runaway electron population energized by the reconnection events. We also observed that the turbulence is often spiky, consisting of discrete positive-potential spikes, which were identified as electron phase-space holes, a class of

  7. Particle Dynamics Discrimination Between Current Sheet Magnetic Field Reversal and Magnetic Neutral Line Fields

    NASA Astrophysics Data System (ADS)

    Martin, R. F., Jr.; Holland, D. L.; Svetich, J.

    2014-12-01

    We consider dynamical signatures of ion motion that discriminate between a current sheet magnetic field reversal and a magnetic neutral line field. These two related dynamical systems have been studied previously as chaotic scattering systems with application to the Earth's magnetotail. Both systems exhibit chaotic scattering over a wide range of parameter values. The structure and properties of their respective phase spaces have been used to elucidate potential dynamical signatures that affect spacecraft measured ion distributions. In this work we consider the problem of discrimination between these two magnetic structures using charged particle dynamics. For example we show that signatures based on the well known energy resonance in the current sheet field provide good discrimination since the resonance is not present in the neutral line case. While both fields can lead to fractal exit region structuring, their characteristics are different and also may provide some field discrimination. Application to magnetotail field and particle parameters will be presented

  8. Ramp-up of CHI Initiated Plasmas on NSTX

    SciTech Connect

    Mueller, D; Bell, R E; LeBlanc, B; Roquemore, A L; Raman, R; Jarboe, T R; Nelson, B A; Soukhanovskii, V

    2009-10-29

    Experiments on the National Spherical Torus (NSTX) have now demonstrated flux savings using transient coaxial helicity injection (CHI). In these discharges, the discharges initiated by CHI are ramped up with an inductive transformer and exhibit higher plasma current than discharges without the benefit of CHI initiation.

  9. Optimal current waveforms for brushless permanent magnet motors

    NASA Astrophysics Data System (ADS)

    Moehle, Nicholas; Boyd, Stephen

    2015-07-01

    In this paper, we give energy-optimal current waveforms for a permanent magnet synchronous motor that result in a desired average torque. Our formulation generalises previous work by including a general back-electromotive force (EMF) wave shape, voltage and current limits, an arbitrary phase winding connection, a simple eddy current loss model, and a trade-off between power loss and torque ripple. Determining the optimal current waveforms requires solving a small convex optimisation problem. We show how to use the alternating direction method of multipliers to find the optimal current in milliseconds or hundreds of microseconds, depending on the processor used, which allows the possibility of generating optimal waveforms in real time. This allows us to adapt in real time to changes in the operating requirements or in the model, such as a change in resistance with winding temperature, or even gross changes like the failure of one winding. Suboptimal waveforms are available in tens or hundreds of microseconds, allowing for quick response after abrupt changes in the desired torque. We demonstrate our approach on a simple numerical example, in which we give the optimal waveforms for a motor with a sinusoidal back-EMF, and for a motor with a more complicated, nonsinusoidal waveform, in both the constant-torque region and constant-power region.

  10. Configuration of Jupiter's magnetic tail and equatorial current sheet

    NASA Technical Reports Server (NTRS)

    Ness, N. F.; Behannon, K. W.; Burlaga, L. F.

    1981-01-01

    Recent research reports by Behannon et al. (1981) and Connerney et al. (1981) are summarized. It is noted that the analysis made of the detailed neutral sheet crossings by the minimum variance method shows a consistent result with regard to the orientation of the neutral sheet in the magnetic tail as a two-dimensional surface rocking back and forth about the Jupiter sun-line as the rotation of the planet leads to a precession of the tilted dipole magnetic axis. The occurrence of neutral sheet crossings is found not to be consistent with any of the axially symmetric theoretical models proposed earlier on the basis of the 1974 Pioneer 10 observations. It is noted that a simple nonaxially symmetric model has been developed on the basis of the Voyager results which indicates the strong control upon orientation by the interaction of the solar wind with the Jovian magnetosphere. The model is described as simple because it improves the fit of theory to observation but uses fewer parameters. A quantitative model of the magnetodisc equatorial current sheet has been developed for the inner magnetosphere region which matches well the in-situ magnetic field observations.

  11. Vibration effect on magnetization and critical current density of superconductors

    NASA Astrophysics Data System (ADS)

    Golovchanskiy, Igor A.; Pan, Alexey V.; George, Jonathan; Wells, Frederick S.; Fedoseev, Sergey A.; Rozenfeld, Anatoly

    2016-07-01

    In this work the effect of vibrations on critical current density (J c ) of superconductors has been studied. The vibrations are shown to affect J c of all types of superconductors during their measurements, employing a vibrating sample magnetometer (VSM). Increasing vibration frequency (f) and/or amplitude (A) leads to progressive reduction of J c as a function of magnetic field (B a ). The effect of vibrations is substantially stronger in thin films. It leads to development of unexpected kinks on {J}c({B}a) curves. Analysis of magnetization loops and relaxation of magnetization in YBCO films revealed that the vibration effect can be treated as the effective reduction of pinning potential. The asymmetry of the vibration effect in ascending and descending B a is observed, indicating differences in free energy of the corresponding vortex structures. Thermal effects induced by vibrations with large f and A are shown to have rather insignificant influence, while the vibrational vortex dynamics exhibit a strong impact. The irreversibility field ({B}{{irr}}) is shown to be instrumentally defined, and its value depends on VSM settings. In addition, the practical importance of {B}{{irr}} for J c modeling is demonstrated.

  12. Rotating magnetic quadrupole current drive for field-reversed configurations

    SciTech Connect

    Milroy, Richard D.; Guo, H.Y.

    2005-07-15

    In the translation, confinement, and sustainment experiment [A. L. Hoffman, H. Y. Guo, J. T. Slough, S. J. Tobin, L. S. Schrank, W. A. Reass, and G. A. Wurden, Fusion Sci. Technol. 41, 92 (2002)], field-reversed configurations (FRCs) are created and sustained using a rotating magnetic field (RMF). The RMF is usually in the form of a rotating dipole, which in vacuum penetrates uniformly to the axis of symmetry. However, plasma conditions in the FRC normally adjust so that the RMF only partially penetrates the plasma column. We have investigated the possibility of using a rotating quadrupole rather than a rotating dipole magnetic field. The vacuum field from a quadrupole is proportional to radius and cannot penetrate to the axis of symmetry; however, this is not a disadvantage if the current drive is confined to the outer region of the FRC. It was found that the quadrupole drive efficiency is comparable to that of a dipole, but the rotating dipole is more effective at stabilizing the n=2 rotational instability. A strong internal oscillation in B{sub {theta}} is often observed in FRCs sustained by a quadrupole field. The spectral content of the signals indicates that an internal n=1 magnetic structure forms and corotates with the electrons. Similar but much lower amplitude structures can form when a rotating dipole is employed (edge-driven mode)

  13. Radial current density effects on rotating magnetic field current drive in field-reversed configurations

    SciTech Connect

    Clemente, R. A.; Gilli, M.; Farengo, R.

    2008-10-15

    Steady state solutions, suitable for field-reversed configurations (FRCs) sustained by rotating magnetic fields (RMFs) are obtained by properly including three-dimensional effects, in the limit of large FRC elongation, and the radial component of Ohm's law. The steady electrostatic potential, necessary to satisfy Ohm's law, is considered to be a surface function. The problem is analyzed at the midplane of the configuration and it is reduced to the solution of two coupled nonlinear differential equations for the real and imaginary parts of the phasor associated to the longitudinal component of the vector potential. Additional constraints are obtained by requesting that the steady radial current density and poloidal magnetic flux vanish at the plasma boundary which is set at the time-averaged separatrix. The results are presented in terms of the degree of synchronism of the electrons with the RMF and compared with those obtained when radial current effects are neglected. Three important differences are observed when compared with the case without radial current density. First, at low penetration of the RMF into the plasma there is a significant increase in the driven azimuthal current. Second, the RMF amplitude necessary to access the high synchronism regime, starting from low synchronism, is larger and the difference appears to increase as the separatrix to classical skin depth ratio increases. Third, the minimum RMF amplitude necessary to sustain almost full synchronism is reduced.

  14. The effect of relay ramps on sediment routes and deposition: A review

    NASA Astrophysics Data System (ADS)

    Athmer, Wiebke; Luthi, Stefan M.

    2011-12-01

    A better understanding of the interplay between rift basin evolution and sediment transport paths can improve the success rate of locating hydrocarbon reservoirs at passive rift margins. This paper reviews the current knowledge and suggests future research directions. Relay ramps at extensional basin margins can form drainage entry points if tectonic activity exceeds sedimentation and incision rates, leading to a diversion of sedimentary flow paths towards the ramp. During base level lowstands, channels and canyons may incise into the relay ramp and provide flow paths from the basin margin into the basin. Their orientation and geometry mainly develops as a response to faulting and fracturing, and their activity is influenced by base level fluctuations. Flow constraints such as channels parallel to the ramp axis direct flows to the foot of the relay ramp where sediment accumulates in response to the basin topography. In subaqueous settings, however, turbidity currents are likely to spill at least partly over channel levees and flow down the fault slope into the basin, depositing its load adjacent to the en-echelon boundary faults. Channels and canyons with oblique and perpendicular orientations to the boundary faults can funnel flows down the hanging wall fault onto the basin floor, by-passing the relay ramp. The prevalent basinward tilt of relay ramps can direct unconstrained subaqueous gravity flows also directly into the basin. In subaerial settings, the duration of channel activity in relation to relay ramp evolution strongly depends on the ratio between flow incision rates and tectonic uplift. Drainage direction on the footwall may revert if footwall uplift exceeds incision rates, and the feeding of former depocentres terminates. In the course of rift margin development relay ramp bounding faults may link, causing the breaching of relay ramps and eventually their burial. The effect of continued rifting on ramp remnants and associated syn-rift deposits, however

  15. Molecular Cardiovascular Magnetic Resonance: Current Status and Future Prospects.

    PubMed

    Bender, Yvonne Y; Pfeifer, Andreas; Ebersberger, Hans U; Diederichs, Gerd; Hoppe, Peter; Hamm, Bernd; Botnar, René M; Makowski, Marcus R

    2016-05-01

    In the Western world and developing countries, the number one causes of mortality and morbidity result from cardiovascular diseases. Cardiovascular diseases represent a wide range of pathologies, including myocardial infarction, peripheral vascular disease, and cerebrovascular disease, which are all linked by a common cause - atherosclerosis. Currently, the diagnosis of atherosclerosis is in most cases established at the end stage of the disease, when patients are administered to the emergency room due to a myocardial infarction or stroke. Even though cardiovascular diseases have an enormous impact on society, there are still limitations in the early diagnosis and the prevention of the disease. Current imaging methods mainly focus on morphological changes that occur at an advanced disease stage, e.g., degree of stenosis. Cardiovascular magnetic resonance imaging and specifically molecular cardiovascular magnetic resonance imaging are capable to reveal pathophysiological changes already occurring during early atherosclerotic plaque formation. This allows for the assessment of cardiovascular disease on a level, which goes beyond morphological or anatomical criteria. In this review, we will introduce promising MR-based molecular imaging strategies for the non-invasive assessment of cardiovascular disease. PMID:27038612

  16. Magnetic particle imaging: current developments and future directions

    PubMed Central

    Panagiotopoulos, Nikolaos; Duschka, Robert L; Ahlborg, Mandy; Bringout, Gael; Debbeler, Christina; Graeser, Matthias; Kaethner, Christian; Lüdtke-Buzug, Kerstin; Medimagh, Hanne; Stelzner, Jan; Buzug, Thorsten M; Barkhausen, Jörg; Vogt, Florian M; Haegele, Julian

    2015-01-01

    Magnetic particle imaging (MPI) is a novel imaging method that was first proposed by Gleich and Weizenecker in 2005. Applying static and dynamic magnetic fields, MPI exploits the unique characteristics of superparamagnetic iron oxide nanoparticles (SPIONs). The SPIONs’ response allows a three-dimensional visualization of their distribution in space with a superb contrast, a very high temporal and good spatial resolution. Essentially, it is the SPIONs’ superparamagnetic characteristics, the fact that they are magnetically saturable, and the harmonic composition of the SPIONs’ response that make MPI possible at all. As SPIONs are the essential element of MPI, the development of customized nanoparticles is pursued with the greatest effort by many groups. Their objective is the creation of a SPION or a conglomerate of particles that will feature a much higher MPI performance than nanoparticles currently available commercially. A particle’s MPI performance and suitability is characterized by parameters such as the strength of its MPI signal, its biocompatibility, or its pharmacokinetics. Some of the most important adjuster bolts to tune them are the particles’ iron core and hydrodynamic diameter, their anisotropy, the composition of the particles’ suspension, and their coating. As a three-dimensional, real-time imaging modality that is free of ionizing radiation, MPI appears ideally suited for applications such as vascular imaging and interventions as well as cellular and targeted imaging. A number of different theories and technical approaches on the way to the actual implementation of the basic concept of MPI have been seen in the last few years. Research groups around the world are working on different scanner geometries, from closed bore systems to single-sided scanners, and use reconstruction methods that are either based on actual calibration measurements or on theoretical models. This review aims at giving an overview of current developments and

  17. Design considerations of a power supply system for fast cycling superconducting accelerator magnets of 2 Tesla b-field generated by a conductor of 100 kA current

    SciTech Connect

    Hays, Steve; Piekarz, Henryk; Pfeffer, Howie; Claypool, Brad; /Fermilab

    2007-06-01

    Recently proposed fast cycling accelerators for proton drivers (SF-SPS, CERN and SF-MR, SF-BOOSTER, FNAL) neutrino sources require development of new magnet technology. In support of this magnet development a power supply system will need to be developed that can support the high current and high rate of power swing required by the fast cycling (1 sec rise and fall in the SF-MR, 5Hz in Booster). This paper will outline a design concept for a +/- 2000 V and 100,000 A fast ramping power supply system. This power supply design is in support of a 6.44 km magnet system at 0.020 H and 330 m 5 Hz, 0.00534 H superconducting loads. The design description will include the layout and plan for extending the present FNAL Main Injector style ramping power supply to the higher currents needed for this operation. This will also include the design for a harmonic filter and power factor corrector that will be needed to control the large power swings caused by the fast cycle time. A conceptual design for the current regulation system and control will also be outlined. The power circuit design will include the bridge, filter and transformer plan based on existing designs.

  18. Buffer influence on magnetic dead layer, critical current, and thermal stability in magnetic tunnel junctions with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Frankowski, Marek; Żywczak, Antoni; Czapkiewicz, Maciej; Zietek, Sławomir; Kanak, Jarosław; Banasik, Monika; Powroźnik, Wiesław; Skowroński, Witold; Checiński, Jakub; Wrona, Jerzy; Głowiński, Hubert; Dubowik, Janusz; Ansermet, Jean-Philippe; Stobiecki, Tomasz

    2015-06-01

    We present a detailed study of Ta/Ru-based buffers and their influence on features crucial from the point of view of applications of Magnetic Tunnel Junctions (MTJs) such as critical switching current and thermal stability. We study buffer/FeCoB/MgO/Ta/Ru and buffer/MgO/FeCoB/Ta/Ru layers, investigating the crystallographic texture, the roughness of the buffers, the magnetic domain pattern, the magnetic dead layer thickness, and the perpendicular magnetic anisotropy fields for each sample. Additionally, we examine the effect of the current induced magnetization switching for complete nanopillar MTJs with lateral dimensions of 270 × 180 nm. Buffer Ta 5/Ru 10/Ta 3 (thicknesses in nm), which has the thickest dead layer, exhibits a much larger thermal stability factor (63 compared to 32.5) while featuring a slightly lower critical current density value (1.25 MA/cm2 compared to 1.5 MA/cm2) than the buffer with the thinnest dead layer Ta 5/Ru 20/Ta 5. We can account for these results by considering the difference in damping which compensates for the difference in the switching barrier heights.

  19. Temperature compensated and self-calibrated current sensor using reference magnetic field

    DOEpatents

    Yakymyshyn, Christopher Paul; Brubaker, Michael Allen; Yakymyshyn, Pamela Jane

    2007-10-09

    A method is described to provide temperature compensation and self-calibration of a current sensor based on a plurality of magnetic field sensors positioned around a current carrying conductor. A reference magnetic field generated within the current sensor housing is detected by the magnetic field sensors and is used to correct variations in the output signal due to temperature variations and aging.

  20. Analyzing Ramp Compression Wave Experiments

    NASA Astrophysics Data System (ADS)

    Hayes, D. B.

    2007-12-01

    Isentropic compression of a solid to 100's of GPa by a ramped, planar compression wave allows measurement of material properties at high strain and at modest temperature. Introduction of a measurement plane disturbs the flow, requiring special analysis techniques. If the measurement interface is windowed, the unsteady nature of the wave in the window requires special treatment. When the flow is hyperbolic the equations of motion can be integrated backward in space in the sample to a region undisturbed by the interface interactions, fully accounting for the untoward interactions. For more complex materials like hysteretic elastic/plastic solids or phase changing material, hybrid analysis techniques are required.

  1. JF-102A on ramp

    NASA Technical Reports Server (NTRS)

    1956-01-01

    Convair JF-102A (54-1374) on the ramp at NACA High-Speed Flight Station , Edwards, California in 1956. The most prominent new feature distinguishing the JF-102A from the YF-102 was a longer fuselage with a pinched or 'coke-bottle' waist. Note wing-fences on both wings. The JF-102A Characteristics are: Wing Span, ft. 38.1 Fuselage length, ft. 63.4 Vertical Tail height, ft. 21.2 Power Plant: Pratt & Whitney J57-P-23 turbojet

  2. A high voltage programmable ramp generator

    SciTech Connect

    Upadhyay, J.; Joshi, M. J.; Deshpande, P. P.; Sharma, M. L.; Navathe, C. P.

    2008-05-15

    In this paper, a ramp generator with programmable slope is presented. It consists of a high voltage step generator, followed by integrator. The capacitor and inductor in the integrator are designed such that they can be varied by a microcontroller. This circuit generates two bipolar ramps with fastest speed <1 ns and provides continuous speed variation from 6 to 30 ns for a ramp of 500 V. This is being developed as a part of automated streak camera for deflection of electron beam.

  3. Launch of a Vehicle from a Ramp

    ERIC Educational Resources Information Center

    Cross, Rod

    2011-01-01

    A vehicle proceeding up an inclined ramp will become airborne if the ramp comes to a sudden end and if the vehicle fails to stop before it reaches the end of the ramp. A vehicle may also become airborne if it passes over the top of a hill at sufficient speed. In both cases, the vehicle becomes airborne if the point of support underneath the…

  4. Spin-polarized currents generated by magnetic Fe atomic chains.

    PubMed

    Lin, Zheng-Zhe; Chen, Xi

    2014-06-13

    Fe-based devices are widely used in spintronics because of high spin-polarization and magnetism. In this work, freestanding Fe atomic chains, the thinnest wires, were used to generate spin-polarized currents due to the spin-polarized energy bands. By ab initio calculations, the zigzag structure was found to be more stable than the wide-angle zigzag structure and had a higher ratio of spin-up and spin-down currents. By our theoretical prediction, Fe atomic chains have a sufficiently long thermal lifetime only at T ≦̸ 150 K, while C atomic chains are very stable even at T = 1000 K. This means that the spintronic devices based on Fe chains could work only at low temperatures. A system constructed by a short Fe chain sandwiched between two graphene electrodes could be used as a spin-polarized current generator, while a C chain could not be used in this way. The present work may be instructive and meaningful to further practical applications based on recent technical developments on the preparation of metal atomic chains (Proc. Natl. Acad. Sci. USA 107 9055 (2010)). PMID:24849670

  5. Low noise charge ramp electrometer

    DOEpatents

    Morgan, J.P.; Piper, T.C.

    1992-10-06

    An electrometer capable of measuring small currents without the use of a feedback resistor which tends to contribute a large noise factor to the measured data. The electrometer eliminates the feedback resistor through the use of a feedback capacitor located across the electrometer amplifier. The signal from the electrometer amplifier is transferred to a electrometer buffer amplifier which serves to transfer the signal to several receptors. If the electrometer amplifier is approaching saturation, the buffer amplifier signals a reset discriminator which energizes a coil whose magnetic field closes a magnetic relay switch which in turn resets or zeros the feedback capacitor. In turn, a reset complete discriminator restarts the measurement process when the electrometer amplifier approaches its initial condition. The buffer amplifier also transmits the voltage signal from the electrometer amplifier to a voltage-to-frequency converter. The signals from the voltage-to-frequency converter are counted over a fixed period of time and the information is relayed to a data processor. The timing and sequencing of the small current measuring system is under the control of a sequence control logic unit. 2 figs.

  6. Low noise charge ramp electrometer

    DOEpatents

    Morgan, John P.; Piper, Thomas C.

    1992-01-01

    An electrometer capable of measuring small currents without the use of a feedback resistor which tends to contribute a large noise factor to the measured data. The electrometer eliminates the feedback resistor through the use of a feedback capacitor located across the electrometer amplifier. The signal from the electrometer amplifier is transferred to a electrometer buffer amplifier which serves to transfer the signal to several receptors. If the electrometer amplifier is approaching saturation, the buffer amplifier signals a reset discriminator which energizes a coil whose magnetic field closes a magnetic relay switch which in turn resets or zeros the feedback capacitor. In turn, a reset complete discriminator restarts the measurement process when the electrometer amplifier approaches its initial condition. The buffer amplifier also transmits the voltage signal from the electrometer amplifier to a voltage-to-frequency converter. The signals from the voltage-to-frequency converter are counted over a fixed period of time and the information is relayed to a data processor. The timing and sequencing of the small current measuring system is under the control of a sequence control logic unit.

  7. Low current linearization of magnetic amplifier for dc transducer

    NASA Technical Reports Server (NTRS)

    Nagano, S. (Inventor)

    1981-01-01

    A magnetic amplifier having two saturable reactor cores with a separate excitation winding on each connected in series opposition, a common control winding, and a common output winding, is adapted for use as a low level signal transducer. The separate excitation windings are excited in push-pull mode through a center tapped transformer, and at least one diode is included in series with a load resistor connected to the output winding. A resistor in series with the output winding and load resistor is connected between the center tap of the excitation transformer and the connection between the two excitation windings of the saturable cores. This series resistor provides a return current path for the output winding and allows the excitation windings of the saturable cores to operate as primary windings of transformers.

  8. Airport ramp safety and crew performance issues

    NASA Technical Reports Server (NTRS)

    Chamberlin, Roy; Drew, Charles; Patten, Marcia; Matchette, Robert

    1995-01-01

    This study examined 182 ramp operations incident reports from the Aviation Safety Reporting System (ASRS) database, to determine which factors influence ramp operation incidents. It was found that incidents occurred more often during aircraft arrival operations than during departure operations; incidents occurred most often at the gate stop area, less so at the gate entry/exit areas, and least on the ramp fringe areas; and reporters cited fewer incidents when more ground crew were present. The authors offer suggestions for both airline management and flight crews to reduce the rate of ramp incidents.

  9. Substantial reduction of critical current for magnetization switching in an exchange-biased spin valve

    NASA Astrophysics Data System (ADS)

    Jiang, Y.; Nozaki, T.; Abe, S.; Ochiai, T.; Hirohata, A.; Tezuka, N.; Inomata, K.

    2004-06-01

    Great interest in current-induced magnetic excitation and switching in a magnetic nanopillar has been caused by the theoretical predictions of these phenomena. The concept of using a spin-polarized current to switch the magnetization orientation of a magnetic layer provides a possible way to realize future 'current-driven' devices: in such devices, direct switching of the magnetic memory bits would be produced by a local current application, instead of by a magnetic field generated by attached wires. Until now, all the reported work on current-induced magnetization switching has been concentrated on a simple ferromagnet/Cu/ferromagnet trilayer. Here we report the observation of current-induced magnetization switching in exchange-biased spin valves (ESPVs) at room temperature. The ESPVs clearly show current-induced magnetization switching behaviour under a sweeping direct current with a very high density. We show that insertion of a ruthenium layer between an ESPV nanopillar and the top electrode effectively decreases the critical current density from about 108 to 107 A cm-2. In a well-designed 'antisymmetric' ESPV structure, this critical current density can be further reduced to 2 × 106 A cm-2. We believe that the substantial reduction of critical current could make it possible for current-induced magnetization switching to be directly applied in spintronic devices, such as magnetic random-access memory.

  10. Electric current and magnetic field effects on bacterial biofilms

    NASA Astrophysics Data System (ADS)

    Sandvik, Elizabeth Louise

    The ability of bacteria to form and grow as biofilm presents a major challenge in clinical medicine. Through this work, two alternative electromagnetic treatment strategies were investigated to combat bacterial biofilms like those that cause chronic infections on indwelling medical devices. Direct electric current (DC) was applied at current densities of 0.7 to 1.8 mA/cm2 alone and in conjunction with antibiotic. Unlike most previous studies, chloride ions were included in the treatment solution at a physiologically-relevant concentration. Using this approach, low levels of DC alone were demonstrated to have a dose-responsive, biocidal effect against Staphylococcus epidermidis and Pseudomonas aeruginosa biofilms with no synergistic enhancement of antibiotic activity. Through a series of experiments using chemical measures, cell viability, and global gene expression, electrolytic generation of chlorine, a potent disinfectant, was identified as the predominant mechanism by which DC kills bacteria in biofilm. The second treatment strategy investigated weak, extremely low-frequency magnetic fields (ELF-MFs) as a noninvasive approach, involving an extension of concepts from well-studied ELF-MF effects observed in eukaryotic systems to bacterial biofilm. S. epidermidis biofilms grown in weak, extremely low-frequency magnetic fields (ELF-MFs) at Ca2+ and K+ ion resonance frequencies were assessed using global gene expression to determine if S. epidermidis in biofilm detect and respond to ELF-MFs. Frequency-dependent changes in gene expression were observed with upregulation of genes involved in transposase activity, signal transduction systems, and membrane transport processes indicating possible effects consistent with theories of ELF-MF induced changes in ion transport reported in eukaryotic cells. This is the first transcriptome study to indentify ELF-MF effects in bacteria. While no direct biocidal effect was observed with ELF-MF treatment, alteration of membrane

  11. Electromagnetic Currents and Magnetic Moments in $\\chi$EFT

    SciTech Connect

    Saori Pastore, Luca Girlanda, Rocco Schiavilla, Michele Viviani, Robert Wiringa

    2009-09-01

    A two-nucleon potential and consistent electromagnetic currents are derived in chiral effective field theory ($\\chi$EFT) at, respectively, $Q^{\\, 2}$ (or N$^2$LO) and $e\\, Q$ (or N$^3$LO), where $Q$ generically denotes the low-momentum scale and $e$ is the electric charge. Dimensional regularization is used to renormalize the pion-loop corrections. A simple expression is derived for the magnetic dipole ($M1$) operator associated with pion loops, consisting of two terms, one of which is determined, uniquely, by the isospin-dependent part of the two-pion-exchange potential. This decomposition is also carried out for the $M1$ operator arising from contact currents, in which the unique term is determined by the contact potential. Finally, the low-energy constants (LEC's) entering the N$^2$LO potential are fixed by fits to the $np$ S- and P-wave phase shifts up to 100 MeV lab energies. Three additional LEC's are needed to completely specify the $M1$ operator at N$^3$L

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  13. Special issue on current research in astrophysical magnetism

    NASA Astrophysics Data System (ADS)

    Kosovichev, Alexander; Lundstedt, Henrik; Brandenburg, Axel

    2012-06-01

    Much of what Hannes Alfvén envisaged some 70 years ago has now penetrated virtually all branches of astrophysical research. Indeed, magnetic fields can display similar properties over a large range of scales. We have therefore been able to take advantage of the transparency of galaxies and the interstellar medium to obtain measurements inside them. On the other hand, the Sun is much closer, allowing us to obtain a detailed picture of the interaction of flows and magnetic fields at the surface, and more recently in the interior by helioseismology. Moreover, the solar timescales are generally much shorter, making studies of dynamical processes more direct. This special issue on current research in astrophysical magnetism is based on work discussed during a one month Nordita program Dynamo, Dynamical Systems and Topology and comprises papers that fall into four different categories (A)-(D). (A) Papers on small-scale magnetic fields and flows in astrophysics 1. E M de Gouveia Dal Pino, M R M Leão, R Santos-Lima, G Guerrero, G Kowal and A Lazarian Magnetic flux transport by turbulent reconnection in astrophysical flows 2. Philip R Goode, Valentyna Abramenko and Vasyl Yurchyshyn New solar telescope in Big Bear: evidence for super-diffusivity and small-scale solar dynamos? 3. I N Kitiashvili, A G Kosovichev, N N Mansour, S K Lele and A A Wray Vortex tubes of turbulent solar convection The above collection of papers begins with a review of astrophysical reconnection and introduces the concept of dynamos necessary to explain the existence of contemporary magnetic fields both on galactic and solar scales (paper 1). This is complemented by observations with the new Big Bear Solar Observatory telescope, allowing us to see magnetic field amplification on small scales (paper 2). This in turn is complemented by realistic simulations of subsurface and surface flow patterns (paper 3). (B) Papers on theoretical approaches to turbulent fluctuations 4. Nathan Kleeorin and Igor

  14. Strain-assisted current-induced magnetization reversal in magnetic tunnel junctions: A micromagnetic study with phase-field microelasticity

    SciTech Connect

    Huang, H. B.; Hu, J. M.; Yang, T. N.; Chen, L. Q.; Ma, X. Q.

    2014-09-22

    Effect of substrate misfit strain on current-induced in-plane magnetization reversal in CoFeB-MgO based magnetic tunnel junctions is investigated by combining micromagnetic simulations with phase-field microelasticity theory. It is found that the critical current density for in-plane magnetization reversal decreases dramatically with an increasing substrate strain, since the effective elastic field can drag the magnetization to one of the four in-plane diagonal directions. A potential strain-assisted multilevel bit spin transfer magnetization switching device using substrate misfit strain is also proposed.

  15. Application of broadband alternating current magnetic susceptibility to the characterization of magnetic nanoparticles in natural materials

    NASA Astrophysics Data System (ADS)

    Kodama, Kazuto

    2013-01-01

    A new method is proposed for characterizing magnetic particles by measuring low-field alternating current magnetic susceptibility at a number of frequency steps spanning four orders of magnitude, from 125 Hz to 512 kHz. This method was tested using natural samples with various grain size distributions, including basalt (Kilauea, Hawaii), loess and paleosol (Luochuan, China), tuff (Yucca Mountain, Nevada), granite (Minnesota Valley, Minnesota), and andesite (Sakurajima, Japan). The resulting frequency spectrum of magnetic susceptibility (FSMS) of the basalt, loess/paleosol, and tuff decreases with increasing frequency, but at different rates of decrease. The FSMS of the basalt is characterized by a monotonic decrease with increasing frequency over the entire range. The FSMS of the loess/paleosol and the tuff decreases more markedly than that of the basalt, which agrees with previous results showing that superparamagnetic particles are dominant in such material. Quantitative estimates using FSMSs allow reconstruction of characteristic grain size distributions and clearly identify differences in the distribution of superparamagnetic particles. The multidomain granite sample has no distinct frequency dependence, which is probably due to the smooth displacement of domain walls in the presence of the external field. In contrast, the FSMSs of the andesite samples exhibit maxima over a limited frequency range, between 16 and 128 kHz. This behavior, together with low-temperature measurements, can be accounted for by magnetic resonance of domain walls in the multidomain phenocrysts.

  16. Magnetic force microscopy method and apparatus to detect and image currents in integrated circuits

    DOEpatents

    Campbell, Ann. N.; Anderson, Richard E.; Cole, Jr., Edward I.

    1995-01-01

    A magnetic force microscopy method and improved magnetic tip for detecting and quantifying internal magnetic fields resulting from current of integrated circuits. Detection of the current is used for failure analysis, design verification, and model validation. The interaction of the current on the integrated chip with a magnetic field can be detected using a cantilevered magnetic tip. Enhanced sensitivity for both ac and dc current and voltage detection is achieved with voltage by an ac coupling or a heterodyne technique. The techniques can be used to extract information from analog circuits.

  17. Magnetic force microscopy method and apparatus to detect and image currents in integrated circuits

    DOEpatents

    Campbell, A.N.; Anderson, R.E.; Cole, E.I. Jr.

    1995-11-07

    A magnetic force microscopy method and improved magnetic tip for detecting and quantifying internal magnetic fields resulting from current of integrated circuits are disclosed. Detection of the current is used for failure analysis, design verification, and model validation. The interaction of the current on the integrated chip with a magnetic field can be detected using a cantilevered magnetic tip. Enhanced sensitivity for both ac and dc current and voltage detection is achieved with voltage by an ac coupling or a heterodyne technique. The techniques can be used to extract information from analog circuits. 17 figs.

  18. Ramp Technology and Intelligent Processing in Small Manufacturing

    NASA Technical Reports Server (NTRS)

    Rentz, Richard E.

    1992-01-01

    To address the issues of excessive inventories and increasing procurement lead times, the Navy is actively pursuing flexible computer integrated manufacturing (FCIM) technologies, integrated by communication networks to respond rapidly to its requirements for parts. The Rapid Acquisition of Manufactured Parts (RAMP) program, initiated in 1986, is an integral part of this effort. The RAMP program's goal is to reduce the current average production lead times experienced by the Navy's inventory control points by a factor of 90 percent. The manufacturing engineering component of the RAMP architecture utilizes an intelligent processing technology built around a knowledge-based shell provided by ICAD, Inc. Rules and data bases in the software simulate an expert manufacturing planner's knowledge of shop processes and equipment. This expert system can use Product Data Exchange using STEP (PDES) data to determine what features the required part has, what material is required to manufacture it, what machines and tools are needed, and how the part should be held (fixtured) for machining, among other factors. The program's rule base then indicates, for example, how to make each feature, in what order to make it, and to which machines on the shop floor the part should be routed for processing. This information becomes part of the shop work order. The process planning function under RAMP greatly reduces the time and effort required to complete a process plan. Since the PDES file that drives the intelligent processing is 100 percent complete and accurate to start with, the potential for costly errors is greatly diminished.

  19. 3D analysis of eddy current loss in the permanent magnet coupling

    NASA Astrophysics Data System (ADS)

    Zhu, Zina; Meng, Zhuo

    2016-07-01

    This paper first presents a 3D analytical model for analyzing the radial air-gap magnetic field between the inner and outer magnetic rotors of the permanent magnet couplings by using the Amperian current model. Based on the air-gap field analysis, the eddy current loss in the isolation cover is predicted according to the Maxwell's equations. A 3D finite element analysis model is constructed to analyze the magnetic field spatial distributions and vector eddy currents, and then the simulation results obtained are analyzed and compared with the analytical method. Finally, the current losses of two types of practical magnet couplings are measured in the experiment to compare with the theoretical results. It is concluded that the 3D analytical method of eddy current loss in the magnet coupling is viable and could be used for the eddy current loss prediction of magnet couplings.

  20. 3D analysis of eddy current loss in the permanent magnet coupling.

    PubMed

    Zhu, Zina; Meng, Zhuo

    2016-07-01

    This paper first presents a 3D analytical model for analyzing the radial air-gap magnetic field between the inner and outer magnetic rotors of the permanent magnet couplings by using the Amperian current model. Based on the air-gap field analysis, the eddy current loss in the isolation cover is predicted according to the Maxwell's equations. A 3D finite element analysis model is constructed to analyze the magnetic field spatial distributions and vector eddy currents, and then the simulation results obtained are analyzed and compared with the analytical method. Finally, the current losses of two types of practical magnet couplings are measured in the experiment to compare with the theoretical results. It is concluded that the 3D analytical method of eddy current loss in the magnet coupling is viable and could be used for the eddy current loss prediction of magnet couplings. PMID:27475575

  1. Alternating current loss of second-generation high-temperature superconducting coils with magnetic and non-magnetic substrate

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Kvitkovic, J.; Kim, Jae-Ho.; Kim, C. H.; Pamidi, S. V.; Coombs, T. A.

    2012-09-01

    It is widely believed that the second-generation high-temperature superconducting (2G HTS) tapes with magnetic substrates suffer higher transport loss compared to those with non-magnetic substrates. To test this, we prepared two identical coils with magnetic and non-magnetic substrates, respectively. The experimental result was rather surprising that they generated roughly the same amount of transport loss. We used finite element method to understand this result. It is found that, unlike in the single tape where the magnetic field-dependent critical current characteristic can be neglected and the effect of magnetic substrate dominates, the magnetic field-dependent critical current characteristic of 2G tape plays as an equally important role as magnetic substrate in terms of HTS coils.

  2. Single expansion ramp nozzle simulations

    NASA Technical Reports Server (NTRS)

    Ruffin, Stephen M.; Venkatapathy, Ethiraj; Lee, Seung-Ho; Keener, Earl R.; Spaid, Frank W.

    1992-01-01

    The single-expansion-ramp-nozzle (SERN) experiment underway at NASA Ames Research Center simulates the National Aerospace Plane propulsive jet-plume flow. Recently, limited experimental data has become available from an experiment with a generic nozzle/afterbody model in a hypersonic wind tunnel. The present paper presents full three-dimensional solutions obtained with the implicit Navier-Stokes solver, FL3D, for the baseline model and a version of the model with side extensions. Analysis of the computed flow clearly shows the complex 3-D nature of the flow, critical flow features, and the effect of side extensions on the plume flow development. Flow schematics appropriate for the conditions tested are presented for the baseline model and the model with side extensions. The computed results show excellent agreement with experimental shadowgraph and with surface pressure measurements. The computed and experimental surface oil-flows show the same features but may be improved by appropriate turbulence modeling.

  3. B-47A on ramp

    NASA Technical Reports Server (NTRS)

    1953-01-01

    Boeing B-47A (NACA 150) shown on the ramp near NACA High-Speed Flight Research Station at South Base of Edwards Air Force Base, California, in 1953. The B-47A Stratojet's wing is mounted high on the fuselage with a sweep back of 36 degrees and a span of 116 feet, with wing vortex generators installed. A two engine pod under each wing, and an additional engine pod at each wing tip using General Electric J-47-GE-23 turbojets. The airplane is fitted with a nose boom for measuring airspeed, altitude, angle-of-attack and angle-of-sideslip, and an optigraph for measuring the movements of target lights on the wing and tail.

  4. Ramp Compression Experiments - a Sensitivity Study

    SciTech Connect

    Bastea, M; Reisman, D

    2007-02-26

    We present the first sensitivity study of the material isentropes extracted from ramp compression experiments. We perform hydrodynamic simulations of representative experimental geometries associated with ramp compression experiments and discuss the major factors determining the accuracy of the equation of state information extracted from such data. In conclusion, we analyzed both qualitatively and quantitatively the major experimental factors that determine the accuracy of equations of state extracted from ramp compression experiments. Since in actual experiments essentially all the effects discussed here will compound, factoring out individual signatures and magnitudes, as done in the present work, is especially important. This study should provide some guidance for the effective design and analysis of ramp compression experiments, as well as for further improvements of ramp generators performance.

  5. GLOBAL DECOUPLING ON THE RHIC RAMP.

    SciTech Connect

    LUO, Y.; CAMERON, P.; DELLA PENNA, A.; FISCHER, W.; ET AL.

    2005-05-16

    The global betatron decoupling on the ramp is an important issue for the operation of the Relativistic Heavy Ion Collider (RHIC), especially in the RHIC polarized proton (pp) run. To avoid the major betatron and spin resonances on the ramp, the betatron tunes are constrained. And the rms value of the vertical closed orbit should be smaller than 0.5mm. Both require the global coupling on the ramp to be well corrected. Several ramp decoupling schemes were found and tested at RHIC, like N-turn map decoupling, three-ramp correction, coupling amplitude modulation, and coupling phase modulation. In this article, the principles of these methods are shortly reviewed and compared. Among them, coupling angle modulation is a robust and fast one. It has been applied to the global decoupling in the routine RHIC operation.

  6. 9 CFR 91.23 - Loading ramps and doors.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... height of not less than 6 feet 6 inches. The incline of the ramps shall not exceed 1:2 (261/2°) between the ramps and the horizontal plane. The ramps shall be fitted with footlocks of approximately...

  7. 9 CFR 91.23 - Loading ramps and doors.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... height of not less than 6 feet 6 inches. The incline of the ramps shall not exceed 1:2 (261/2°) between the ramps and the horizontal plane. The ramps shall be fitted with footlocks of approximately...

  8. 9 CFR 91.23 - Loading ramps and doors.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... height of not less than 6 feet 6 inches. The incline of the ramps shall not exceed 1:2 (261/2°) between the ramps and the horizontal plane. The ramps shall be fitted with footlocks of approximately...

  9. Detecting and characterising ramp events in wind power time series

    NASA Astrophysics Data System (ADS)

    Gallego, Cristóbal; Cuerva, Álvaro; Costa, Alexandre

    2014-12-01

    In order to implement accurate models for wind power ramp forecasting, ramps need to be previously characterised. This issue has been typically addressed by performing binary ramp/non-ramp classifications based on ad-hoc assessed thresholds. However, recent works question this approach. This paper presents the ramp function, an innovative wavelet- based tool which detects and characterises ramp events in wind power time series. The underlying idea is to assess a continuous index related to the ramp intensity at each time step, which is obtained by considering large power output gradients evaluated under different time scales (up to typical ramp durations). The ramp function overcomes some of the drawbacks shown by the aforementioned binary classification and permits forecasters to easily reveal specific features of the ramp behaviour observed at a wind farm. As an example, the daily profile of the ramp-up and ramp-down intensities are obtained for the case of a wind farm located in Spain.

  10. Mars' Magnetic Atmosphere: Ionospheric Currents, Lightning (or Not), E and M Subsurface Sounding, and Future Missions

    NASA Technical Reports Server (NTRS)

    Espley, J. R.; Connerney, J. E. P.

    2014-01-01

    Mars' ionosphere has no obvious magnetic signs of large-scale, dustproduced lightning. However, there are numerous interesting ionospheric currents (some associated with crustal magnetic fields) which would allow for E&M subsurface sounding.

  11. MAGNETIC FIELD MEASUREMENTS FOR FAST-CHANGING MAGNETIC FIELDS.

    SciTech Connect

    JAIN, A.; ESCALLIER, J.; GANETIS, G.; LOUIE, W.; MARONE, A.; THOMAS. R.; WANDERER, P.

    2004-10-03

    Several recent applications for fast ramped magnets have been found that require rapid measurement of the field quality during the ramp. (In one instance, accelerator dipoles will be ramped at 1 T/sec, with measurements needed to the accuracy typically required for accelerators.) We have built and tested a new type of magnetic field measuring system to meet this need. The system consists of 16 stationary pickup windings mounted on a cylinder. The signals induced in the windings in a changing magnetic field are sampled and analyzed to obtain the field harmonics. To minimize costs, printed circuit boards were used for the pickup windings and a combination of amplifiers and ADPs used for the voltage readout system. New software was developed for the analysis. Magnetic field measurements of a model dipole developed for the SIS200 accelerator at GSI are presented. The measurements are needed to insure that eddy currents induced by the fast ramps do not impact the field quality needed for successful accelerator operation.

  12. Ring current-atmosphere interactions model with stormtime magnetic field

    NASA Astrophysics Data System (ADS)

    Vapirev, Alexander Emilov

    An improved version of the ring current-atmosphere interactions kinetic model (RAM) is presented in this thesis. The recent stormtime empirical model T04s and the IGRF model are used to represent the Earth's external and internal magnetic fields respectively. Particle drifts, losses due to charge exchange with geocoronal hydrogen and atmospheric losses are included in the model as they are considered the main mechanisms of ring current development and its following decay. A numerical technique for bounce-averaging along the field lines is introduced and results for the calculated bounce-averaged hydrogen densities and magnetic gradient-curvature drift velocities (general case) for the moderate storm of April 21-25, 2001, are presented. A comparison in the calculations between T04s and a dipole field shows that the bounce-averaged hydrogen density for T04s differs with ˜ 5% from that for a dipole field for quiet time and it may become 30% smaller for disturbed conditions on the nightside for L > 4. The gradient-curvature velocities for T04s at large L-shells are ˜ 20% higher on the nightside and 20% lower on the dayside than those for a dipole field for quiet time. For disturbed conditions they are respectively ˜ 200% higher and 20% lower than the dipole values. The contribution of the cross-B term to the magnetic drift is ˜ 5%. Results for the time evolution of the trapped equatorial flux for H+, He+, and O+ ions for various particle energies and pitch angles obtained by the new model with a non-dipole field (RAM-ND) are presented. The new computations for the April 2001 storm using a Volland-Stern convection model show a slight continued increase in the flux and the total ring current energy for the three ion species even after the storm main phase. A higher increase in the flux is observed towards the dusk side for the RAM-ND model compared to RAM due the difference in the charge exchange rates and the azimuthal drifts for the two different geomagnetic field

  13. Current role of multiparametric magnetic resonance imaging for prostate cancer

    PubMed Central

    Chevallier, Olivier; Moulin, Morgan; Favelier, Sylvain; Genson, Pierre-Yves; Pottecher, Pierre; Crehange, Gilles; Cochet, Alexandre; Cormier, Luc

    2015-01-01

    Multiparametric magnetic resonance imaging (mp-MRI) has shown promising results in diagnosis, localization, risk stratification and staging of clinically significant prostate cancer, and targeting or guiding prostate biopsy. mp-MRI consists of T2-weighted imaging (T2WI) combined with several functional sequences including diffusion-weighted imaging (DWI), perfusion or dynamic contrast-enhanced imaging (DCEI) and spectroscopic imaging. Recently, mp-MRI has been used to assess prostate cancer aggressiveness and to identify anteriorly located tumors before and during active surveillance. Moreover, recent studies have reported that mp-MRI is a reliable imaging modality for detecting local recurrence after radical prostatectomy or external beam radiation therapy. Because assessment on mp-MRI can be subjective, use of the newly developed standardized reporting Prostate Imaging and Reporting Archiving Data System (PI-RADS) scoring system and education of specialist radiologists are essential for accurate interpretation. This review focuses on the current place of mp-MRI in prostate cancer and its evolving role in the management of prostate cancer. PMID:26682144

  14. Dynamic Behaviors of Materials under Ramp Wave Loading on Compact Pulsed Power Generators

    NASA Astrophysics Data System (ADS)

    Zhao, Jianheng; Luo, Binqiang; Wang, Guiji; Chong, Tao; Tan, Fuli; Liu, Cangli; Sun, Chengwei

    The technique using intense current to produce magnetic pressure provides a unique way to compress matter near isentrope to high density without obvious temperature increment, which is characterized as ramp wave loading, and firstly developed by Sandia in 1998. Firstly recent advances on compact pulsed power generators developed in our laboratory, such as CQ-4, CQ-3-MMAF and CQ-7 devices, are simply introduced here, which devoted to ramp wave loading from 50GPa to 200 GPa, and to ultrahigh-velocity flyer launching up to 30 km/s. And then, we show our progress in data processing methods and experiments of isentropic compression conducted on these devices mentioned above. The suitability of Gruneisen EOS and Vinet EOS are validated by isentropic experiments of tantalum, and the parameters of SCG constitutive equation of aluminum and copper are modified to give better prediction under isentropic compression. Phase transition of bismuth and tin are investigated under different initial temperatures, parameters of Helmholtz free energy and characteristic relaxation time in kinetic phase transition equation are calibrated. Supported by NNSF of China under Contract No.11327803 and 11176002

  15. Current status and recent topics of rare-earth permanent magnets

    NASA Astrophysics Data System (ADS)

    Sugimoto, S.

    2011-02-01

    After the development of Nd-Fe-B magnets, rare-earth magnets are now essential components in many fields of technology, because of their ability to provide a strong magnetic flux. There are two, well-established techniques for the manufacture of rare earth magnets: powder metallurgy is used to obtain high-performance, anisotropic, fully dense magnet bodies; and the melt-spinning or HDDR (hydrogenation, disproportionation, desorption and recombination) process is widely used to produce magnet powders for bonded magnets. In the industry of sintered Nd-Fe-B magnets, the total amount of production has increased and their dominant application has been changed to motors. In particular, their use for motors in hybrid cars is one of the most attractive applications. Bonded magnets have also been used for small motors, and the studies of nanocomposite and Sm-Fe-N magnets have become widespread. This paper reviews the current status and future trend in the research of permanent magnets.

  16. Ramp initiation in a thrust wedge.

    PubMed

    Panian, John; Wiltschko, David

    2004-02-12

    Collisional mountain belts are characterized by fold and thrust belts that grow through sequential stacking of thrust sheets from the interior (hinterland) to the exterior (foreland) of the mountain belt. Each of these sheets rides on a fault that cuts up through the stratigraphic section on inclined ramps that join a flat basal fault at depth. Although this stair-step or ramp-flat geometry is well known, there is no consensus on why a particular ramp forms where it does. Perturbations in fault shape, stratigraphy, fluid pressure, folding, and surface slope have all been suggested as possible mechanisms. Here we show that such pre-existing inhomogeneities, though feasible causes, are not required. Our computer simulations show that a broad foreland-dipping plastic strain band forms at the surface near the topographic inflection produced by the previous ramp. This strain band then migrates towards the rigid base, where the plastic strain is preferentially concentrated in a thrust ramp. Subsequent ramps develop toward the foreland in a similar fashion. Syntectonic erosion and deposition may strongly control the location of thrust ramps by enhancing or removing the surface point of initiation. PMID:14961118

  17. Current challenges with understanding greigite (Fe3S4) magnetism

    NASA Astrophysics Data System (ADS)

    Chang, L.; Roberts, A. P.; Winklhofer, M.; Vasiliev, I.; Dekkers, M. J.; Krijgsman, W.

    2014-12-01

    Greigite (Fe3S4) is a widespread authigenic magnetic mineral in anoxic sediments, and is also commonly biosynthesized by magnetotactic bacteria in aqueous environments. Despite the importance of greigite in paleomagnetic and environmental magnetic studies, knowledge of its magnetic properties is at a much lower level than for more common rock-forming magnetic minerals. Much recent progress has been made to develop a more complete understanding of the magnetic properties of greigite and the range of grain sizes in which greigite occurs in nature. We present results of new determinations of a range of fundamental magnetic properties of greigite, including the saturation magnetization, the magnetocrystalline anisotropy, and calculated rock magnetic properties. In addition, we provide evidence for the preservation of greigite magnetofossils in ancient sediments, which has important implications for assessing the reliability of paleomagnetic records carried by greigite. Finally, we present an integrated study from a Messinian former Black Sea sedimentary sequence to unravel environmental controls on diagenetic greigite formation, and demonstrates the usefulness of greigite for studying long-term climate variability in anoxic environments.

  18. Spin current generation and magnetic response in carbon nanotubes by the twisting phonon mode

    NASA Astrophysics Data System (ADS)

    Hamada, Masato; Yokoyama, Takehito; Murakami, Shuichi

    2015-08-01

    We theoretically investigate spin current and magnetic response induced by the twisting phonon mode in carbon nanotubes via the spin-rotation coupling. An effective magnetic field due to the twisting mode induces both spin and orbital magnetizations. The induced spin and orbital magnetizations have both radial and axial components. We show that ac pure spin current is generated by the twisting phonon mode. The magnitude of the spin current and orbital magnetization for a (10,10) armchair nanotube is estimated as an example. We find that the ac pure spin current is detectable in magnitude when the frequency of the twisting mode is of the order of GHz, and that the orbital magnetization is found to be larger than the spin magnetization.

  19. IMPROVEMENTS OF THE RHIC RAMP EFFICIENCY.

    SciTech Connect

    TRBOJEVIC,D.; PTITSYN,V.; FISCHER,W.; AHRENS,L.; BLASKIEWICZ,M.; HAYES,T.; PILAT,F.; ROSER,T.; ET AL

    2002-06-02

    The last nms in both gold-gold and polarized proton-proton required necessary corrections in the ramp as the intensities in the two rings were rising towards design values. Corrections were made with respect to the beam-beam effects, transverse and longitudinal instabilities, transition crossing (for the gold-gold ramps), transverse tune resonances, local and global coupliug problems, aperture restrictions, chromatic effects. Along the ramps we had to use the beam separation, ''Landau'' cavities, chromatic and tune control, orbit correction, special gamma-t quadrupole system for the transition crossing in the gold run, correction octupole circuits, beam position monitor system decoupling etc.

  20. Magnetism in icosahedral quasicrystals: current status and open questions

    SciTech Connect

    Goldman, Alan I.

    2014-07-02

    Progress in our understanding of the magnetic properties of R-containing icosahedral quasicrystals (R = rare earth element) from over 20 years of experimental effort is reviewed. This includes the much studied R-Mg-Zn and R-Mg-Cd ternary systems, as well as several magnetic quasicrystals that have been discovered and investigated more recently including Sc-Fe-Zn, R-Ag-In, Yb-Au-Al, the recently synthesized R-Cd binary quasicrystals, and their periodic approximants. In many ways, the magnetic properties among these quasicrystals are very similar. However, differences are observed that suggest new experiments and promising directions for future research.

  1. Magnetism in icosahedral quasicrystals: current status and open questions

    NASA Astrophysics Data System (ADS)

    Goldman, Alan I.

    2014-08-01

    Progress in our understanding of the magnetic properties of R-containing icosahedral quasicrystals (R = rare earth element) from over 20 years of experimental effort is reviewed. This includes the much studied R-Mg-Zn and R-Mg-Cd ternary systems, as well as several magnetic quasicrystals that have been discovered and investigated more recently including Sc-Fe-Zn, R-Ag-In, Yb-Au-Al, the recently synthesized R-Cd binary quasicrystals, and their periodic approximants. In many ways, the magnetic properties among these quasicrystals are very similar. However, differences are observed that suggest new experiments and promising directions for future research.

  2. Mathematical model for prediction of currents, magnetic fields, melt velocities, melt topography and current efficiency in Hall-Heroult cells

    SciTech Connect

    Evans, J.W.; Zundelevich, Y.; Sharma, D.

    1981-06-01

    The magnetic fields, current densities, metal and electrolyte velocities, current efficiencies and topography of the electrolyte-metal interface within the Hall-Heroult cell used to produce aluminum have been predicted from first principles. The computation of current densities was carried out by solving Ohms law enabling the calculation of magnetic field vectors from the Biot-Savart law. The cross product of the current densities and magnetic fields then yielded the electromagnetic stirring forces acting on the molten metal and electrolyte. By employing a turbulence model and the time averaged Navier-Stokes equations, velocities within these two liquids could be calculated. The solution of the fluid flow equations yielded the pressure distribution within both electrolyte and metal, permitting the calculation of the shape of the interface betweeen these two liquids.

  3. Effective chiral magnetic currents, topological magnetic charges, and microwave vortices in a cavity with an enclosed ferrite disk

    NASA Astrophysics Data System (ADS)

    Sigalov, Michael; Kamenetskii, E. O.; Shavit, Reuven

    2008-01-01

    In microwaves, a TE-polarized rectangular-waveguide resonator with an inserted thin ferrite disk gives an example of a nonintegrable system. The interplay of reflection and transmission at the disk interfaces together with the material gyrotropy effect gives rise to whirlpool-like electromagnetic vortices in the proximity of the ferromagnetic resonance. Based on numerical simulation, we show that a character of microwave vortices in a cavity can be analyzed by means of consideration of equivalent magnetic currents. Maxwell equations allows introduction of a magnetic current as a source of the electromagnetic field. Specifically, we found that in such nonintegrable structures, magnetic gyrotropy and geometrical factors leads to the effect of symmetry breaking resulting in effective chiral magnetic currents and topological magnetic charges. As an intriguing fact, one can observe precessing behavior of the electric-dipole polarization inside a ferrite disk.

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

    NASA Astrophysics Data System (ADS)

    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.

  5. Ramp technique for dc partial discharge testing

    NASA Technical Reports Server (NTRS)

    Bever, R. S.

    1985-01-01

    The partial discharge (PD) data presently obtained by means of a stepwise ramp technique, for the cases of high voltage (HV) components and such resin-packaged HV devices as the Space Telescope's Faint Object Camera, is acquired separately on part-way ramps to rated voltage and on the intermediate voltage plateaus. For test specimens intended for dc service, this ramp method yields more data on insulation integrity than quiescent dc measurements, especially in the case of specimens of high resistivity which causes the discharge frequency to be deceptively low at constant dc voltage. During upward ramping the voltage distribution is capacitive, and the PD behavior resembles that of an ac test. Many more pulses are obtained in the voids without the heat otherwise generated by the application of 60-Hz ac. PD histograms are presented for various materials, with and without intentional defects.

  6. Magnetization reversal induced by in-plane current in Ta/CoFeB/MgO structures with perpendicular magnetic easy axis

    SciTech Connect

    Zhang, C.; Yamanouchi, M. Ikeda, S.; Sato, H.; Fukami, S.; Matsukura, F.; Ohno, H.

    2014-05-07

    We investigate in-plane current-induced magnetization reversal under an in-plane magnetic field in Hall bar shaped devices composed of Ta/CoFeB/MgO structures with perpendicular magnetic easy axis. The observed relationship between the directions of current and magnetization switching and Ta thickness dependence of magnetization switching current are accordance with those for magnetization reversal by spin transfer torque originated from the spin Hall effect in the Ta layer.

  7. Eddy current effects in the magnetization dynamics of ferromagnetic metal nanoparticles

    NASA Astrophysics Data System (ADS)

    Denisov, S. I.; Lyutyy, T. V.; Pedchenko, B. O.; Babych, H. V.

    2014-07-01

    We develop an analytical model for describing the magnetization dynamics in ferromagnetic metal nanoparticles, which is based on the coupled system of the Landau-Lifshitz-Gilbert (LLG) and Maxwell equations. By solving Maxwell's equations in the quasi-static approximation and finding the magnetic field of eddy currents, we derive the closed LLG equation for the magnetization that fully accounts for the effects of conductivity. We analyze the difference between the LLG equations in metallic and dielectric nanoparticles and show that these effects can strongly influence the magnetization dynamics. As an example illustrating the importance of eddy currents, the phenomenon of precessional switching of magnetization is considered.

  8. Current-induced magnetization excitation in a pseudo-spin-valve with in-plane anisotropy

    NASA Astrophysics Data System (ADS)

    Guo, Jie; Jalil, Mansoor Bin Abdul; Tan, Seng Ghee

    2008-05-01

    We study the magnetization dynamics of a pseudo-spin-valve structure with in-plane anisotropy, which is induced by the passage of a perpendicular-to-plane spin-polarized current. The magnetization dynamics is described by a modified Landau-Lifshitz-Gilbert (LLG) equation, which incorporates two spin torque terms. The simulation results reveal two magnetization excitation modes: (a) complete magnetization reversal and (b) persistent spin precession. The existence of these dual modes may be explained in terms of the competition between the four terms of the modified LLG equation. Our results give indications to the optimal operating conditions for current-induced magnetization dynamics for possible device applications.

  9. Current density and poloidal magnetic field for toroidal elliptic plasmas with triangularity

    SciTech Connect

    Martin, P.; Haines, M.G.; Castro, E.

    2005-08-15

    Changes in the poloidal magnetic field around a tokamak magnetic surface due to different values of triangularity and ellipticity are analyzed in this paper. The treatment here presented allows the determination of the poloidal magnetic field from knowledge of the toroidal current density. Different profiles of these currents are studied. Improvements in the analytic forms of the magnetic surfaces have also been found. The treatment has been performed using a recent published system of coordinates. Suitable analytic equations have been used for the elliptic magnetic surfaces with triangularity and Shafranov shift.

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

    NASA Technical Reports Server (NTRS)

    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.

  11. Change in the magnetic moment of a ferromagnetic nanoparticle under polarized current

    NASA Astrophysics Data System (ADS)

    Kozhushner, M. A.; Gatin, A. K.; Grishin, M. V.; Shub, B. R.; Kim, V. P.; Khomutov, G. B.; Trakhtenberg, L. I.

    2016-02-01

    The magnetization reversal of a ferromagnetic Fe3O4 nanoparticle with a volume of the order of several thousands of cubic nanometers under the influence of spin-polarized current has been investigated on a high-vacuum scanning tunneling microscope, where one of the electrodes is a magnetized iron wire needle and the second electrode is a ferromagnetic nanoparticle on a graphite substrate. The measured threshold current of magnetization reversal, i.e., the lowest value of the current corresponding to the magnetization reversal, is found to be I thresh ≈ 9 nA. A change in the magnetization of a nanoparticle is revealed using the giant magnetoresistance effect, i.e., the dependence of the weak polarized current ( I < I thresh) on the relative orientation of the magnetizations of the electrodes.

  12. TOPOLOGICAL MATTER. Observation of chiral currents at the magnetic domain boundary of a topological insulator.

    PubMed

    Wang, Y H; Kirtley, J R; Katmis, F; Jarillo-Herrero, P; Moodera, J S; Moler, K A

    2015-08-28

    A magnetic domain boundary on the surface of a three-dimensional topological insulator is predicted to host a chiral edge state, but direct demonstration is challenging. We used a scanning superconducting quantum interference device to show that current in a magnetized topological insulator heterostructure (EuS/Bi2Se3) flows at the edge when the Fermi level is gate-tuned to the surface band gap. We further induced micrometer-scale magnetic structures on the heterostructure and detected a chiral edge current at the magnetic domain boundary. The chirality of the current was determined by magnetization of the surrounding domain, and its magnitude by the local chemical potential rather than the applied current. Such magnetic structures provide a platform for detecting topological magnetoelectric effects and may enable progress in quantum information processing and spintronics. PMID:26272905

  13. Current-induced Orbital and Spin Magnetizations in Crystals with Helical Structure

    PubMed Central

    Yoda, Taiki; Yokoyama, Takehito; Murakami, Shuichi

    2015-01-01

    We theoretically show that in a crystal with a helical lattice structure, orbital and spin magnetizations along a helical axis are induced by an electric current along the helical axis. We propose a simple tight-binding model for calculations, and the results can be generalized to any helical crystals. The induced magnetizations are opposite for right-handed and left-handed helices. The current-induced spin magnetization along the helical axis comes from a radial spin texture on the Fermi surface. This is in sharp contrast to Rashba systems where the induced spin magnetization is perpendicular to the applied current. PMID:26156643

  14. Effect of high-frequency driving current on magnetization reversal in Co-rich amorphous microwires

    SciTech Connect

    Chizhik, A.; Zhukov, A.; Gonzalez, J.; Blanco, J.M.

    2004-09-20

    Influence of high frequency electric current on the magnetization reversal in Co-rich glass covered amorphous microwires has been studied. The strong correlation between the coercivity and the circular magnetization in the outer shell of the wire has been found. The change of the mechanism of magnetization reversal in the presence of high-frequency circular magnetic field, which is related with the impedance properties, is presented.

  15. Self-Magnetic Field Effects on Electron Emission as the Critical Current is Approached

    SciTech Connect

    Ottinger, P. F.; Cooperstein, G.; Schumer, J. W.; Swanekamp, S. B.

    2001-09-28

    The self-magnetic field associated with the current in a planar diode is shown to reduce electron emission below the Child-Langmuir current density. As the magnetic field increases, the diode current is limited to the critical current. Here, a ID analysis is carried out to calculate the suppressed current density in the presence of a transverse magnetic field. The problem is shown to be similar to that of the limiting current (i.e., Hull current) calculated in a crossed field gap, in which a constant transverse magnetic field is applied across the gap to insulate the electron flow. In the case considered here, the magnetic field is produced by the diode current itself and this self-magnetic field decreases with distance along the gap. It is shown that the emitted current density is only modestly reduced from the Child-Langmuir current density. The 1-D analysis remains valid until critical current is approached, at which point orbit crossing occurs and a 2-D kinetic analysis is required. The minimum diode length required to reach critical current is also derived.

  16. Computer circuit analysis of induced currents in the MFTF-B magnet system

    SciTech Connect

    Magnuson, G.D.; Woods, E.L.

    1981-10-23

    An analysis was made of the induced current behavior of the MFTF-B magnet system. Although the magnet system consists of 22 coils, because of its symmetry we considered only 11 coils in the analysis. Various combinations of the coils were dumped either singly or in groups, with the current behavior in all magnets calculated as a function of time after initiation of the dump.

  17. Finite element analysis of gradient z-coil induced eddy currents in a permanent MRI magnet.

    PubMed

    Li, Xia; Xia, Ling; Chen, Wufan; Liu, Feng; Crozier, Stuart; Xie, Dexin

    2011-01-01

    In permanent magnetic resonance imaging (MRI) systems, pulsed gradient fields induce strong eddy currents in the conducting structures of the magnet body. The gradient field for image encoding is perturbed by these eddy currents leading to MR image distortions. This paper presents a comprehensive finite element (FE) analysis of the eddy current generation in the magnet conductors. In the proposed FE model, the hysteretic characteristics of ferromagnetic materials are considered and a scalar Preisach hysteresis model is employed. The developed FE model was applied to study gradient z-coil induced eddy currents in a 0.5 T permanent MRI device. The simulation results demonstrate that the approach could be effectively used to investigate eddy current problems involving ferromagnetic materials. With the knowledge gained from this eddy current model, our next step is to design a passive magnet structure and active gradient coils to reduce the eddy current effects. PMID:21106418

  18. A microscopic model of current-induced switching of magnetization.

    PubMed

    Sandschneider, N; Nolting, W

    2010-01-20

    The behaviour of the magnetization in a ferromagnetic metal/nonmagnetic insulator/ferromagnetic metal/paramagnetic metal tunnel junction is studied, using the nonequilibrium Keldysh formalism. The two ferromagnets are described using the single-band Hubbard model. The left one is treated in the mean field approximation and the right ferromagnet within a (nonequilibrium) spectral density approach which takes interactions beyond the mean field into account. When a voltage is applied to the junction we observe a change of the relative orientation of the two magnetizations, which can be switched from parallel to antiparallel alignment and vice versa. This switching appears in a self-consistent way, so there is no need to use half-classical methods like the Landau-Lifshitz-Gilbert equation one. The dependence of the critical voltage at which the magnetization changes its sign on the model parameters can be studied in a systematic way. PMID:21386267

  19. The influence of eddy currents on magnetic actuator performance

    NASA Technical Reports Server (NTRS)

    Zmood, R. B.; Anand, D. K.; Kirk, J. A.

    1987-01-01

    The present investigation of the effects of eddy currents on EM actuators' transient performance notes that a transfer function representation encompassing a first-order model of the eddy current influence can be useful in control system analysis. The method can be extended to represent the higher-order effects of eddy currents for actuators that cannot be represented by semiinfinite planes.

  20. A linearly controlled direct-current power source for high-current inductive loads in a magnetic suspension wind tunnel

    NASA Technical Reports Server (NTRS)

    Tripp, John S.; Daniels, Taumi S.

    1990-01-01

    The NASA Langley 6 inch magnetic suspension and balance system (MSBS) requires an independently controlled bidirectional DC power source for each of six positioning electromagnets. These electromagnets provide five-degree-of-freedom control over a suspended aerodynamic test model. Existing power equipment, which employs resistance coupled thyratron controlled rectifiers as well as AC to DC motor generator converters, is obsolete, inefficient, and unreliable. A replacement six phase bidirectional controlled bridge rectifier is proposed, which employs power MOSFET switches sequenced by hybrid analog/digital circuits. Full load efficiency is 80 percent compared to 25 percent for the resistance coupled thyratron system. Current feedback provides high control linearity, adjustable current limiting, and current overload protection. A quenching circuit suppresses inductive voltage impulses. It is shown that 20 kHz interference from positioning magnet power into MSBS electromagnetic model position sensors results predominantly from capacitively coupled electric fields. Hence, proper shielding and grounding techniques are necessary. Inductively coupled magnetic interference is negligible.

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Magnetic field probe for measuring surface current distributions on millimetre wave microstrip antennas

    NASA Astrophysics Data System (ADS)

    Grzybowski, R. R.; Bansal, R.

    1991-01-01

    A magnetic field probe for measuring surface current distributions on millimeter wave microstrip antennas has been designed and fabricated. This current probe was tested by measuring the surface current distributions of printed microstrip dipole antennas. The current distributions obtained compared well with the theoretically expected distributions.

  3. Structure of current sheets in magnetic holes at 1 AU. [regions of low magnetic field intensity in the solar wind

    NASA Technical Reports Server (NTRS)

    Fitzenreiter, R. J.; Burlaga, L. F.

    1978-01-01

    Current density profiles in several types of interplanetary magnetic holes were calculated assuming that the currents flow in planar sheets and that the magnetic field varies only in the direction normal to the sheet. The planarity was verified in four holes which were observed by two suitably spaced spacecraft. The structure of the current sheets ranges from very simple in some holes to very complex in others. The observed structures are found to be qualitatively consistent with models based on self-consistent solutions of Vlasov's equation and Maxwell's equations. Examples of complex, irregular magnetic holes are also presented, and they are shown to contain multiple, current sheets in which currents flow parallel to one another.

  4. Instability of the current sheet in the Earth's magnetotail with normal magnetic field

    SciTech Connect

    Bessho, N.; Bhattacharjee, A.

    2014-10-15

    Instability of a current sheet in the Earth's magnetotail has been investigated by two-dimensional fully kinetic simulations. Two types of magnetic configuration have been studied; those with uniform normal magnetic field along the current sheet and those in which the normal magnetic field has a spatial hump. The latter configuration has been proposed by Sitnov and Schindler [Geophys. Res. Lett. 37, L08102 (2010)] as one in which ion tearing modes might grow. The first type of configuration exhibits electron tearing modes when the normal magnetic field is small. The second type of configuration exhibits an instability which does not tear or change the topology of magnetic field lines. The hump in the initial configuration can propagate Earthward in the nonlinear regime, leading to the formation of a dipolarization front. Secondary magnetic islands can form in regions where the normal magnetic field is very weak. Under no conditions do we find the ion tearing instability.

  5. Direct observation of dynamic modes excited in a magnetic insulator by pure spin current.

    PubMed

    Demidov, V E; Evelt, M; Bessonov, V; Demokritov, S O; Prieto, J L; Muñoz, M; Ben Youssef, J; Naletov, V V; de Loubens, G; Klein, O; Collet, M; Bortolotti, P; Cros, V; Anane, A

    2016-01-01

    Excitation of magnetization dynamics by pure spin currents has been recently recognized as an enabling mechanism for spintronics and magnonics, which allows implementation of spin-torque devices based on low-damping insulating magnetic materials. Here we report the first spatially-resolved study of the dynamic modes excited by pure spin current in nanometer-thick microscopic insulating Yttrium Iron Garnet disks. We show that these modes exhibit nonlinear self-broadening preventing the formation of the self-localized magnetic bullet, which plays a crucial role in the stabilization of the single-mode magnetization oscillations in all-metallic systems. This peculiarity associated with the efficient nonlinear mode coupling in low-damping materials can be among the main factors governing the interaction of pure spin currents with the dynamic magnetization in high-quality magnetic insulators. PMID:27608533

  6. Direct observation of dynamic modes excited in a magnetic insulator by pure spin current

    PubMed Central

    Demidov, V. E.; Evelt, M.; Bessonov, V.; Demokritov, S. O.; Prieto, J. L.; Muñoz, M.; Ben Youssef, J.; Naletov, V. V.; de Loubens, G.; Klein, O.; Collet, M.; Bortolotti, P.; Cros, V.; Anane, A.

    2016-01-01

    Excitation of magnetization dynamics by pure spin currents has been recently recognized as an enabling mechanism for spintronics and magnonics, which allows implementation of spin-torque devices based on low-damping insulating magnetic materials. Here we report the first spatially-resolved study of the dynamic modes excited by pure spin current in nanometer-thick microscopic insulating Yttrium Iron Garnet disks. We show that these modes exhibit nonlinear self-broadening preventing the formation of the self-localized magnetic bullet, which plays a crucial role in the stabilization of the single-mode magnetization oscillations in all-metallic systems. This peculiarity associated with the efficient nonlinear mode coupling in low-damping materials can be among the main factors governing the interaction of pure spin currents with the dynamic magnetization in high-quality magnetic insulators. PMID:27608533

  7. Spin-wave excitation by direct current in obliquely magnetized nanostructures

    NASA Astrophysics Data System (ADS)

    Rodríguez-Suárez, R. L.; Azevedo, A.; de Aguiar, F. M.; Rezende, S. M.

    2009-09-01

    The magnetization dynamics of magnetic nanostructures magnetized at an arbitrary out-of-plane angle is investigated with the spin-wave formalism. The magnetic excitations driven by a spin-polarized direct current are considered to be standing spin-wave modes appropriate for nanopillar structures. The spin waves grow exponentially above a certain critical value of the current density and their post-threshold nonlinear dynamics leads to magnetization oscillations in the microwave range. Due to demagnetizing fields, the current-driven excitation strongly depends on the direction of the applied external magnetic field. In order to calculate the microwave oscillation frequency we derive an equation of motion for the spin-wave amplitude as a function of the out-of-plane angle of the applied field. The results are compared with recent experimental data as well as with another theoretical approach.

  8. Development of forced flow cooled current leads for fusion magnets

    NASA Astrophysics Data System (ADS)

    Heller, R.; Fink, S.; Friesinger, G.; Kienzler, A.; Lingor, A.; Schleinkofer, G.; Süßer, M.; Ulbricht, A.; Wüchner, F.; Zahn, G.

    2001-03-01

    During the past 15 years, the Institut für Technische Physik of the Forschungszentrum Karlsruhe, Germany, has developed current leads cooled by forced-flow supercritical helium in the current range from 20 to 80 kA. The design is based on a separation of the current carrying part and the heat exchanger part as well as the presence of the so-called superconductor inserts made of Nb 3Sn wires inside the conductor in the heat exchanger area which allows the operation of the current lead at minimum helium mass flow in a wide current range. The paper describes the design and construction of the current leads as well as operation results obtained during various tests performed in the coil test facility TOSKA at the Forschungszentrum Karlsruhe.

  9. B-57B on ramp

    NASA Technical Reports Server (NTRS)

    1982-01-01

    A converted Martin B-57B Canberra medium bomber sits on the ramp at the NASA Ames-Dryden Flight Research Facility, Edwards, California. The rugged NASA aircraft was flown by Dryden in the early 1970s to learn more about the atmosphere. Instrumented with a data acquisition system, Dryden pilots measured atmospheric conditions and clear-air turbulence at various altitudes and sampled the upper atmosphere for various aerosols. The research - to give scientists a better understanding of mountain waves, jet streams, convective turbulence, clear-air turbulence, and atmospheric contaminants - was sponsored by NASA's Langley Research Center, the University of Wyoming, and the Department of Transportation. The aircraft was retired from flight status in 1987. In the early 1970s, a Martin B-57B Canberra light bomber was used in several NASA joint flight test programs at the NASA Flight Research Center (now Dryden Flight Research Center) located at Edwards Air Force Base, California. The early 1970s showed a growing interest in continuing atmospheric research. The B-57B was at the NASA Flight Research Center for a joint program with NASA Langley Research Center, Hampton, Virginia and was having a special set of instrumentation installed. Delays in completing the instruments provided an opportunity to support the NASA space program. The B-57B was used in proof-of-concept testing of the Viking Mars landers. The deceleration drop testing part of the program took place at the Joint Parachute Test Facility, El Centro, California. With completion of the Viking parachute tests, the B-57B was flown for measuring and analysis of atmospheric turbulence research in 1974-75 as part of a joint NASA program between the Flight Research Center and Langley Research Center. Additional atmospheric testing provided samples of aerosols for the University of Wyoming and clear-air turbulence data for the Department of Transportation. The aircraft was tested over a span of many years at Edwards Air

  10. Review of Wind Energy Forecasting Methods for Modeling Ramping Events

    SciTech Connect

    Wharton, S; Lundquist, J K; Marjanovic, N; Williams, J L; Rhodes, M; Chow, T K; Maxwell, R

    2011-03-28

    Tall onshore wind turbines, with hub heights between 80 m and 100 m, can extract large amounts of energy from the atmosphere since they generally encounter higher wind speeds, but they face challenges given the complexity of boundary layer flows. This complexity of the lowest layers of the atmosphere, where wind turbines reside, has made conventional modeling efforts less than ideal. To meet the nation's goal of increasing wind power into the U.S. electrical grid, the accuracy of wind power forecasts must be improved. In this report, the Lawrence Livermore National Laboratory, in collaboration with the University of Colorado at Boulder, University of California at Berkeley, and Colorado School of Mines, evaluates innovative approaches to forecasting sudden changes in wind speed or 'ramping events' at an onshore, multimegawatt wind farm. The forecast simulations are compared to observations of wind speed and direction from tall meteorological towers and a remote-sensing Sound Detection and Ranging (SODAR) instrument. Ramping events, i.e., sudden increases or decreases in wind speed and hence, power generated by a turbine, are especially problematic for wind farm operators. Sudden changes in wind speed or direction can lead to large power generation differences across a wind farm and are very difficult to predict with current forecasting tools. Here, we quantify the ability of three models, mesoscale WRF, WRF-LES, and PF.WRF, which vary in sophistication and required user expertise, to predict three ramping events at a North American wind farm.

  11. Bifurcated current sheets produced by magnetic reconnection in the solar wind

    NASA Astrophysics Data System (ADS)

    Gosling, J. T.; Szabo, A.

    2008-10-01

    We report observations from the Wind spacecraft of Petschek-like magnetic reconnection exhausts and thin current sheets in the solar wind on 19 and 20 November 2007, encompassing a solar wind disturbance driven by a magnetic cloud and followed by a corotating high-speed stream. We have identified an unusually large number (11) of reconnection exhausts in this 2-day interval using 3-s plasma and magnetic field data. Despite the relatively smooth large-scale field rotation associated with the magnetic cloud, five of the exhausts occurred within the cloud; three of those exhausts were associated with extremely small (<18°) local field shear angles. All 11 exhausts contained double-step magnetic field rotations; such double-step rotations are called bifurcated current sheets since they result from the splitting of reconnecting current sheets as an after-effect of the reconnection process. We have also identified 27 current sheets in this 2-day interval that were too thin to be adequately resolved by the 3-s plasma measurement cadence. All of these thin current sheets were well resolved by the 92 ms magnetic field measurement. At least three, and possibly six, of these relatively thin current sheets had double-step magnetic field rotations, indicating the underlying current sheets had probably been disrupted by magnetic reconnection. Current sheets thinner than ˜3 ion inertial lengths were not present in this data set. The relative lack of such ultrathin current sheets in the solar wind in general suggests that such current sheets usually are quickly disrupted by magnetic reconnection.

  12. Bifurcated Current Sheets Produced by Magnetic Reconnection in the Solar Wind

    NASA Astrophysics Data System (ADS)

    Gosling, J. T.; Szabo, A.

    2008-12-01

    We report observations from the Wind spacecraft of Petschek-like magnetic reconnection exhausts and thin current sheets in the solar wind on 19 and 20 November 2007, encompassing a solar wind disturbance driven by a magnetic cloud and followed by a corotating high-speed stream. We have identified an unusually large number (11) of reconnection exhausts in this 2-day interval using 3-s plasma and magnetic field data. Despite the relatively smooth, large-scale field rotation associated with the magnetic cloud, 5 of the exhausts occurred within the cloud; 3 of those exhausts were associated with extremely small (less than 18 deg) local field shear angles. All 11 exhausts contained double-step magnetic field rotations; such double-step rotations are called bifurcated current sheets since they result from the splitting of reconnecting current sheets as an after-effect of the reconnection process. We have also identified 27 current sheets in this 2-day interval that were too thin to be adequately resolved by the 3-s plasma measurement cadence. All of these thin current sheets were well resolved by the 92 ms magnetic field measurement. At least 3, and possibly 6, of these relatively thin current sheets had double-step magnetic field rotations, indicating the underlying current sheets had probably been disrupted by magnetic reconnection. Current sheets thinner than about 3 ion inertial lengths were not present in this data set. The relative lack of such ultra-thin current sheets in the solar wind in general suggests that such current sheets usually are quickly disrupted by magnetic reconnection.

  13. Suppression of Collisionless Magnetic Reconnection in Asymmetric Current Sheets

    NASA Technical Reports Server (NTRS)

    Liu, Yi-Hsin; Hesse, Michael

    2016-01-01

    Using fully kinetic simulations, we study the suppression of asymmetric reconnection in the limit where the diamagnetic drift speed >> Alfven speed and the magnetic shear angle is moderate. We demonstrate that the slippage between electrons and the magnetic flux mitigates the suppression and can even result in fast reconnection that lacks one of the outflow jets. Through comparing a case where the diamagnetic drift is supported by the temperature gradient with a companion case that has a density gradient instead, we identify a robust suppression mechanism. The drift of the x-line is slowed down locally by the asymmetric nature of the x-line, and then the x-line is run over and swallowed by the faster-moving following flux.

  14. Clinical applications of magnetic resonance imaging - current status

    SciTech Connect

    Cammoun, D.; Hendee, W.R.; Davis, K.A.

    1985-12-01

    Magnetic resonance imaging has far-reaching real and possible clinical applications. Its usefulness has been best explored and realized in the central nervous system, especially the posterior fossa and brain stem, where most abnormalities are better identified than with computed tomography. Its lack of ionizing radiation and extreme sensitivity to normal and abnormal patterns of myelination make magnetic resonance imaging advantageous for diagnosing many neonatal and pediatric abnormalities. New, reliable cardiac gating techniques open the way for promising studies of cardiac anatomy and function. The ability to image directly in three orthogonal planes gives us new insight into staging and follow-up of pelvic tumors and other pelvic abnormalities. Exquisite soft tissue contrast, far above that attainable by other imaging modalities, has made possible the early diagnosis of traumatic ligamentous knee injury, avascular necrosis of the hip and diagnosis, treatment planning and follow-up of musculoskeletal neoplasms. 59 references, 9 figures.

  15. Variable force, eddy-current or magnetic damper

    NASA Technical Reports Server (NTRS)

    Cunningham, R. E. (Inventor)

    1985-01-01

    An object of the invention is to provide variable damping for resonant vibrations which may occur at different rotational speeds in the range of rpms in which a rotating machine is operated. A variable force damper in accordance with the invention includes a rotating mass carried on a shaft which is supported by a bearing in a resilient cage. The cage is attached to a support plate whose rim extends into an annular groove in a housing. Variable damping is effected by tabs of electrically conducting nonmagnetic material which extend radially from the cage. The tabs at an index position lie between the pole face of respective C shaped magnets. The magnets are attached by cantilever spring members to the housing.

  16. Suppression of collisionless magnetic reconnection in asymmetric current sheets

    NASA Astrophysics Data System (ADS)

    Liu, Yi-Hsin; Hesse, Michael

    2016-06-01

    Using fully kinetic simulations, we study the suppression of asymmetric reconnection in the limit where the diamagnetic drift speed ≫ Alfvén speed and the magnetic shear angle is moderate. We demonstrate that the slippage between electrons and the magnetic flux mitigates the suppression and can even result in fast reconnection that lacks one of the outflow jets. Through comparing a case where the diamagnetic drift is supported by the temperature gradient with a companion case that has a density gradient instead, we identify a robust suppression mechanism. The drift of the x-line is slowed down locally by the asymmetric nature of the x-line, and then the x-line is run over and swallowed by the faster-moving following flux.

  17. Current status and future outlook for bonded neodymium permanent magnets (invited)

    NASA Astrophysics Data System (ADS)

    Croat, J. J.

    1997-04-01

    Bonded neodymium magnets can provide significant size and weight reduction and/or performance enhancement over sintered and, particularly, bonded ferrite permanent magnets and, moreover, provide these benefits at reasonable cost. Primarily for these reasons, these bonded magnets are now used in a wide and growing range of computer peripheral, office automation, and consumer electronic applications and now constitute the fastest growing segment of the permanent magnet market. The current status of these materials will be reviewed. Included is a brief overview of the manufacture of these magnetically isotropic magnets and a discussion of their unique properties and features from the perspective of both bonded magnet producer and user. Major applications are discussed as are some of the factors that will drive the market for these materials in the future. New technical developments, including the status and outlook for anisotropic bonded materials, high remanance isotropic materials and high temperature bonded magnets will also be discussed.

  18. Magnetic structure of nickel nanowires after the high-density current pulse

    NASA Astrophysics Data System (ADS)

    Nurgazizov, N. I.; Bizyaev, D. A.; Bukharaev, A. A.

    2016-05-01

    Changes in the magnetic structure of nickel nanowires formed on a nonconductive surface after the high-density current pulse have been investigated using magnetic force microscopy and voltammetry. Based on the obtained experimental data and results of the computer simulation, it has been concluded that the main reason for the change in the magnetic structure is the heating of the nanowire by a current pulse. It has been shown that, during the subsequent cooling, the newly formed magnetic structure is pinned by surface roughnesses of the relief of the nanowire under investigation.

  19. Meson exchange current effects on magnetic dipole moments of p -shell nuclei

    SciTech Connect

    Booten, J.G.L.; van Hees, A.G.M.; Glaudemans, P.W.M. ); Wervelman, R. )

    1991-01-01

    It is shown that addition of a two-body magnetic dipole operator arising from the exchange of the isovector pion and rho meson to the well-known one-body operator can give important corrections to the magnetic dipole moments of the {ital A}=4--16 nuclei. We performed shell-model calculations in complete 0{h bar}{omega} and (0+2){h bar}{omega} model spaces, thus investigating simultaneously the effects of extension of the model space and meson exchange currents on the magnetic moments. In the enlarged model space a significant improvement on the description of the magnetic moments is obtained by including exchange currents.

  20. Formation of sheet plumes, current coils, and helical magnetic fields in a spherical magnetohydrodynamic dynamo

    NASA Astrophysics Data System (ADS)

    Miyagoshi, Takehiro; Kageyama, Akira; Sato, Tetsuya

    2011-07-01

    Aiming at understanding of magnetic field generation process in rapidly rotating stars and planets represented by the Earth, computer simulations of magnetohydrodynamic (MHD) dynamo were performed in a rotating spherical shell geometry. Thermal convection and dynamo process with Ekman number of the order of 10-7 were studied. New structures of convection motion, dynamo-generated electrical current, and magnetic field are found. The flow is organized as a set of thin, sheet-like plumes. The current is made of small-scale coil structure with magnetic flux tubes within each of the coil. These flux tubes are connected each other to form a large scale helical magnetic field structure.

  1. A Novel Current Angle Control Scheme in a Current Source Inverter Fed Permanent Magnet Synchronous Motor Drive for Automotive Applications

    SciTech Connect

    Tang, Lixin; Su, Gui-Jia

    2011-01-01

    This paper describes a novel speed control scheme to operate a current source inverter (CSI) driven surface-mounted permanent magnet synchronous machine (SPMSM) for hybrid electric vehicles (HEVs) applications. The idea is to use the angle of the current vector to regulate the rotor speed while keeping the two dc-dc converter power switches on all the time to boost system efficiency. The effectiveness of the proposed scheme was verified with a 3 kW CSI-SPMSM drive prototype.

  2. High-beta spherical tokamak startup in TS-4 merging experiment by use of toroidal field ramp-up

    NASA Astrophysics Data System (ADS)

    Kaminou, Yasuhiro; , Toru, II; Kato, Joji; Inomoto, Michiaki; Ono, Yasushi; TS Group Team; National InstituteFusion Science Collaboration

    2014-10-01

    We demonstrated the formation method of an ultrahigh-beta spherical tokamak by use of a field-reversed configuration and a spheromak in TS-4 device (R ~ 0.5 m, A ~ 1.5, Ip ~ 30-100 kA, B ~ 100 mT). This method is composed of the following steps: 1. Two spheromaks are merged together and a high-beta spheromak or FRC is formed by reconnection heating. 2. External toroidal magnetic field is added (current rising time ~50 μs), and spherical tokamak-like configuration is formed. In this way, the ultrahigh-beta ST is formed. The ultrahigh-beta ST formed by FRC has a diamagnetic toroidal field, and it presumed to be in a second-stable state for ballooning stability, and the one formed by spheromak has a weak paramagnetic toroidal magnetic field, while a spheormak has a strong paramagnetic toroidal magnetic field. This diamagnetic current derives from inductive electric field by ramping up the external toroidal magnetic field, and the diamagnetic current sustains high thermal pressure of the ultrahigh-beta spherical tokamak. And the beta of the ultrahigh-beta ST formed by FRC reaches about 50%. To sustain the high-beta state, 0.6 MW neutral beam injection and center solenoid coils are installed to the TS-4 device. In the poster, we report the experimental results of ultrahigh-beta spherical tokamak startup and sustainment by NBI and CS current driving experiment.

  3. Intrinsic magnetic field sensitivities of sensor head housing for all-fiber optic current sensors

    NASA Astrophysics Data System (ADS)

    Zhang, Xuedian; Chang, Min; Mao, Chenfei; Lu, Dunke; Kamagara, Abel

    2014-10-01

    Full-fiber optical current sensors utilize the effects of magnetic-field imposed on the change of polarization azimuth of light in the fibers. Due to the sensitivities to external perturbations, the sensing fiber head in practical applications is usually packed in a fixed metallic housing majorly for protection purposes. However, the housing material itself tends to influence the magnetic field distributions of the current carrying wire in question. In this paper, the intrinsic effect and influence of fiber sensor head housing made of different magnetic materials on the magnetic field distributions around the current-carrying wire have been investigated. Simulation and virtual experimentation was carried out in the COMSOL environment. From the results, the housings made of single magnetic material are found to have magnetic disturbances on the magnetic field distribution around the wire. Housing made of some alloy materials has no influence on the magnetic distributions outside the wire. After experimenting with several materials, the former materials inclusive, steel is preferred as the protective housing and/or casing of fiber sensor head in optical fiber current sensors. This is on the basis of both technical and non-technical consideration of low cost of material though biased toward technical aspect of little or no influence on magnetic distribution around the wire.

  4. Current-driven vortex formation in a magnetic multilayer ring

    NASA Astrophysics Data System (ADS)

    Nam, Chunghee; Ng, B. G.; Castaño, F. J.; Mascaro, M. D.; Ross, C. A.

    2009-02-01

    Current-driven domain wall (DW) motion has been studied in the NiFe layer of a Co/Cu/NiFe thin film ring using giant-magnetoresistance measurements in a four-point contact geometry. The NiFe layer is initially in an onion state configuration with two 180° DWs. An electric current drives the walls around the ring so that they annihilate and the NiFe layer forms a DW-free vortex state. The direction of motion of the two DWs is determined by the current polarity, enabling the vortex chirality to be selected.

  5. Topological currents in neutron stars: kicks, precession, toroidal fields, and magnetic helicity

    SciTech Connect

    Charbonneau, James; Zhitnitsky, Ariel E-mail: arz@phas.ubc.ca

    2010-08-01

    The effects of anomalies in high density QCD are striking. We consider a direct application of one of these effects, namely topological currents, on the physics of neutron stars. All the elements required for topological currents are present in neutron stars: degenerate matter, large magnetic fields, and parity violating processes. These conditions lead to the creation of vector currents capable of carrying momentum and inducing magnetic fields. We estimate the size of these currents for many representative states of dense matter in the neutron star and argue that they could be responsible for the large proper motion of neutron stars (kicks), the toroidal magnetic field and finite magnetic helicity needed for stability of the poloidal field, and the resolution of the conflict between type-II superconductivity and precession. Though these observational effects appear unrelated, they likely originate from the same physics — they are all P-odd phenomena that stem from a topological current generated by parity violation.

  6. Ferromagnetic eddy current probe having eccentric magnetization for detecting anomalies in a tube

    SciTech Connect

    Cecco, V.S.; Carter, J.R.

    1993-08-17

    An eddy current probe is described for detecting anomalies in a tube made of a ferromagnetic material, comprising: a probe housing made of a non-ferromagnetic material and shaped to be introduced into the tube for inspection, said housing having a central axis substantially coinciding with the axis of the tube to be inspected when the probe is in use; at least two eddy current measuring assemblies provided in said housing, each said assembly including magnetization means for generating a magnetic field in the tube under inspection to magnetize said tube, said magnetization means producing a maximum magnetization at an area of said tube and a minimum magnetization at a diametrically opposite area of said tube and at least one eddy current measuring coil associated with said magnetization means to measure the eddy current generated in the said tube and which has a relatively high sensitivity to an anomaly at said maximum magnetization area; and said eddy current measuring assemblies being spaced apart axially within said housing and rotated about said central axis from each other by a predetermined angle so that each assembly is sensitive to anomalies differently depending upon their location in said housing.

  7. Effect of coupling currents on the dynamic inductance during fast transient in superconducting magnets

    NASA Astrophysics Data System (ADS)

    Marinozzi, V.; Sorbi, M.; Manfreda, G.; Bellina, F.; Bajas, H.; Chlachidze, G.

    2015-03-01

    We present electromagnetic models aiming to calculate the variation of the inductance in a magnet due to dynamic effects such as the variation of magnetization or the coupling with eddy currents. The models are studied with special regard to the calculation of the inductance in superconducting magnets which are affected by interfilament coupling currents. The developed models have been compared with experimental data coming from tests of prototype Nb3Sn magnets designed for the new generation of accelerators. This work is relevant for the quench protection study of superconducting magnets: quench is an unwanted event, when part of the magnet becomes resistive; in these cases, the current should be discharged as fast as possible, in order to maintain the resistive zone temperature under a safe limit. The magnet inductance is therefore a relevant term for the description of the current discharge, especially for the high-field new generation superconducting magnets for accelerators, and this work shows how to calculate the correct value during rapid current changes, providing a mean for simulations of the reached temperature.

  8. Finite element modeling of magnetic bias eddy current probe interaction with ferromagnetic materials

    NASA Astrophysics Data System (ADS)

    Lei, J.

    2013-01-01

    Requirements to demonstrate eddy current inspection capabilities for inspection of steam generator tubes in nuclear power generation stations are becoming more rigorous. One method to support qualification of an existing, modified, or new eddy current probe design is to model the probe response to various degradation modes and tube artifacts with a finite element approach. Magnetic-bias probes are used to inspect for defects in conditions where material magnetic permeability effects are a concern, such as in the presence of ferromagnetic tubes, deposits, or supports. In this paper, a transient finite element modeling approach was used to model the interaction of magnetic-bias eddy current probes with ferromagnetic materials.

  9. Geomagnetic Tail and Ring Current Dynamics and Structure during July 6, 2013 magnetic storm

    NASA Astrophysics Data System (ADS)

    Nazarkov, Ilya

    According to THEMIS and POES satellites the structure and spatial dimensions of ring current and geotal current system are restored. Using models of the main magnetic field of Earth (IGRF-11) and a magnetospheric magnetic field (A2000), the magnetic field of the currents other than the tail and the ring currents was subtracted from measurements. The hourly analysis of dynamics and position of current system of a tail was carried out. Evolution of ring current is estimated by data fluxes of STEB particles, measured by POES satellites at low latitudes. Isotropic boundary, determined by data of POES satellites, was projected to equatorial plane and compared with position of the inner edge of geomagnetic tail current, obtained from THEMIS measurements.

  10. Magnetic Resonance Current Density Imaging of Chemical Processes and Reactions

    NASA Astrophysics Data System (ADS)

    Beravs, Katarina; Demš Ar, Alojz; Demsar, Franci

    1999-03-01

    Electric current density imaging was used to image conductivity changes that occur as a chemical process or reaction progresses. Feasibility was assessed in two models representing the dissolving of an ionic solid and the formation of an insoluble precipitate. In both models, temporal and spatial changes in ionic concentrations were obtained on current density images. As expected, the images showed significant signal enhancement along the ionization/dissociation sites.

  11. Ramp Forecasting Performance from Improved Short-Term Wind Power Forecasting: Preprint

    SciTech Connect

    Zhang, J.; Florita, A.; Hodge, B. M.; Freedman, J.

    2014-05-01

    The variable and uncertain nature of wind generation presents a new concern to power system operators. One of the biggest concerns associated with integrating a large amount of wind power into the grid is the ability to handle large ramps in wind power output. Large ramps can significantly influence system economics and reliability, on which power system operators place primary emphasis. The Wind Forecasting Improvement Project (WFIP) was performed to improve wind power forecasts and determine the value of these improvements to grid operators. This paper evaluates the performance of improved short-term wind power ramp forecasting. The study is performed for the Electric Reliability Council of Texas (ERCOT) by comparing the experimental WFIP forecast to the current short-term wind power forecast (STWPF). Four types of significant wind power ramps are employed in the study; these are based on the power change magnitude, direction, and duration. The swinging door algorithm is adopted to extract ramp events from actual and forecasted wind power time series. The results show that the experimental short-term wind power forecasts improve the accuracy of the wind power ramp forecasting, especially during the summer.

  12. Centurion on Ramp with Onlookers

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Onlookers are dwarfed by the 206-foot wingspan of the Centurion flying wing on a hangar ramp at NASA's Dryden Flight Research Center, Edwards, California. The Centurion demonstrated its flying qualities during three battery-powered flights under control of a ground-based pilot at Dryden in late 1998. Centurion was a unique remotely piloted, solar-powered airplane developed under NASA's Environmental Research Aircraft and Sensor (ERAST) Program at the Dryden Flight Research Center, Edwards, California. Dryden joined with AeroVironment, Inc., Monrovia, California, under an ERAST Joint Sponsored Research Agreement, to design, develop, manufacture, and conduct flight development tests for the Centurion. The airplane was believed to be the first aircraft designed to achieve sustained horizontal flight at altitudes of 90,000 to 100,000 feet. Achieving this capability would meet the ERAST goal of developing an ultrahigh-altitude airplane that could meet the needs of the science community to perform upper-atmosphere environmental data missions. Much of the technology leading to the Centurion was developed during the Pathfinder and Pathfinder-Plus projects. However, in the course of its development, the Centurion became a prototype technology demonstration aircraft designed to validate the technology for the Helios, a planned future high-altitude, solar-powered aircraft that could fly for weeks or months at a time on science or telecommunications missions. Centurion had 206-foot-long wings and used batteries to supply power to the craft's 14 electric motors and electronic systems. Centurion first flew at Dryden Nov. 10, 1998, and followed up with a second test flight Nov. 19. On its third and final flight on Dec. 3, the craft was aloft for 31 minutes and reached an altitude of about 400 feet. All three flights were conducted over a section of Rogers Dry Lake adjacent to Dryden. For its third flight, the Centurion carried a simulated payload of more than 600 pounds

  13. R4D on Ramp

    NASA Technical Reports Server (NTRS)

    1956-01-01

    This Photograph taken in 1956 shows the first of three R4D Skytrain aircraft on the ramp behind the NACA High-Speed Flight Station. Note the designation 'United States NACA' on the side of the aircraft. NACA stood for the National Advisory Committee for Aeronautics, which evolved into the National Aeronautics and Space Administration (NASA) in 1958. The R4D Skytrain was one of the early workhorses for NACA and NASA at Edwards Air Force Base, California, from 1952 to 1984. Designated the R4D by the U.S. Navy, the aircraft was called the C-47 by the U.S. Army and U.S. Air Force and the DC-3 by its builder, Douglas Aircraft. Nearly everyone called it the 'Gooney Bird.' In 1962, Congress consolidated the military-service designations and called all of them the C-47. After that date, the R4D at NASA's Flight Research Center (itself redesignated the Dryden Flight Research Center in 1976) was properly called a C-47. Over the 32 years it was used at Edwards, three different R4D/C-47s were used to shuttle personnel and equipment between NACA/NASA Centers and test locations throughout the country and for other purposes. One purpose was landing on 'dry' lakebeds used as alternate landing sites for the X-15, to determine whether their surfaces were hard (dry) enough for the X-15 to land on in case an emergency occurred after its launch and before it could reach Rogers Dry Lake at Edwards Air Force Base. The R4D/C-47 served a variety of needs, including serving as the first air-tow vehicle for the M2-F1 lifting body (which was built of mahogany plywood). The C-47 (as it was then called) was used for 77 tows before the M2-F1 was retired for more advanced lifting bodies that were dropped from the NASA B-52 'Mothership.' The R4D also served as a research aircraft. It was used to conduct early research on wing-tip-vortex flow visualization as well as checking out the NASA Uplink Control System. The first Gooney Bird was at the NACA High-Speed Flight Research Station (now the Dryden

  14. YF-12C on ramp

    NASA Technical Reports Server (NTRS)

    1973-01-01

    The so-called YF-12C on the NASA Flight Research Center ramp. Following the loss of a YF-12A in a non-fatal accident in June 1971, NASA acquired the second production SR-71A (61-7951) from the Air Force. Because the SR-71 program was shrouded in the highest secrecy, the Air Force restricted NASA to using the aircraft solely for propulsion testing with YF-12A inlets and engines. It was designated the YF-12C, and given a bogus tail number (06937). The two YF-12As in the program had actual tail numbers 06935 and 06936. The first NASA flight of the YF-12C took place on 24 May 1972. The Flight Research Center's involvement with the YF-12A, an interceptor version of the Lockheed A-12, began in 1967. Ames Research Center was interested in using wind tunnel data that had been generated at Ames under extreme secrecy. Also, the Office of Advanced Research and Technology (OART) saw the YF-12A as a means to advance high-speed technology, which would help in designing the Supersonic Transport (SST). The Air Force needed technical assistance to get the latest reconnaissance version of the A-12 family, the SR-71A, fully operational. Eventually, the Air Force offered NASA the use of two YF-12A aircraft, 60-6935 and 606936. A joint NASA-USAF program was mapped out in June 1969. NASA and Air Force technicians spent three months readying 935 for flight. On 11 December 1969, the flight program got underway with a successful maiden flight piloted by Col. Joe Rogers and Maj. Gary Heidelbaugh of the SR-71/F-12 Test Force. During the program, the Air Force concentrated on military applications, and NASA pursued a loads research program. NASA studies included inflight heating, skin-friction cooling, 'coldwall' research (a heat transfer experiment), flowfield studies, shaker vane research, and tests in support of the Space Shuttle landing program. Ultimately, 935 became the workhorse of the program, with 146 flights between 11 December 1969 and 7 November 1979. The second YF-12A, 936, made

  15. The Existence Condition for Magnetic Flux-Current Surfaces in Magnetohydrostatic Equilibria

    NASA Astrophysics Data System (ADS)

    Choe, G. S.; No, J.; Kim, S.; Jang, M.

    2014-12-01

    Magnetohydrostatic equilibria, in which the Lorentz force, the plasma pressure force and the gravitational force balance out to zero, are widely adopted as the zeroth order states of many space plasma systems. A magnetic flux-current surface is a surface, whose tangent plane is locally spanned by the magnetic field vector and the current density vector at each point in it; in other words, it is a surface, in which both magnetic field lines and current lines lie. We have derived the necessary and sufficient condition for existence of magnetic flux-current surfaces in magnetohydrostatic equilibria. It is also shown that the existence of flux-current surfaces is a necessary (but not sufficient) condition for the ratio of gravity-aligned components of current density and magnetic field to be constant along each field line. However, its necessary and sufficient condition is found to be very restrictive. This finding gives a significant constraint in modeling solar coronal magnetic fields as force-free fields using photospheric magnetic field observations.

  16. Clinical Applications of Magnetic Resonance Imaging—Current Status

    PubMed Central

    Cammoun, Driss; Davis, Kathleen A.; Hendee, William R.

    1985-01-01

    Magnetic resonance imaging has far-reaching real and possible clinical applications. Its usefulness has been best explored and realized in the central nervous system, especially the posterior fossa and brain stem, where most abnormalities are better identified than with computed tomography. Its lack of ionizing radiation and extreme sensitivity to normal and abnormal patterns of myelination make magnetic resonance imaging advantageous for diagnosing many neonatal and pediatric abnormalities. New, reliable cardiac gating techniques open the way for promising studies of cardiac anatomy and function. The ability to image directly in three orthogonal planes gives us new insight into staging and follow-up of pelvic tumors and other pelvic abnormalities. Exquisite soft tissue contrast, far above that attainable by other imaging modalities, has made possible the early diagnosis of traumatic ligamentous knee injury, avascular necrosis of the hip and diagnosis, treatment planning and follow-up of musculoskeletal neoplasms. ImagesFigure 1.Figure 2.Figure 3.Figure 4.Figure 5.Figure 6.Figure 7.Figure 8.Figure 9. PMID:3911592

  17. Column buckling of doubly parallel slender nanowires carrying electric current acted upon by a magnetic field

    NASA Astrophysics Data System (ADS)

    Kiani, Keivan

    2016-08-01

    Axial buckling of current-carrying double-nanowire-systems immersed in a longitudinal magnetic field is aimed to be explored. Each nanowire is affected by the magnetic forces resulted from the externally exerted magnetic field plus the magnetic field resulted from the passage of electric current through the adjacent nanowire. To study the problem, these forces are appropriately evaluated in terms of transverse displacements. Subsequently, the governing equations of the nanosystem are constructed using Euler-Bernoulli beam theory in conjunction with the surface elasticity theory of Gurtin and Murdoch. Using a meshless technique and assumed mode method, the critical compressive buckling load of the nanosystem is determined. In a special case, the obtained results by these two numerical methods are successfully checked. The roles of the slenderness ratio, electric current, magnetic field strength, and interwire distance on the axial buckling load and stability behavior of the nanosystem are displayed and discussed in some detail.

  18. Manipulation of superparamagnetic beads using on-chip current lines placed on a ferrite magnet

    NASA Astrophysics Data System (ADS)

    Wang, Z. H.; Lew, W. S.; Bland, J. A. C.

    2006-04-01

    Manipulation of superparamagnetic beads in a static solution is demonstrated using on-chip current striplines placed on a ferrite magnet. The ferrite magnet fits the requirement to enhance the bead's magnetic moment while still keeping beads randomly dispersed in the liquid, so allowing easy and selective manipulation of single beads. By applying currents up to hundreds of milliampere, the tapered stripline first attracts the beads to its edge, then the magnetic force along the edge drives the trapped beads moving continuously towards the chip center. On arriving into the chip central area (a square zone which acts as a site to collect the arriving beads), fine manipulation of selected single beads is further performed by switching on/off and/or tuning the current passing through the nearby quadruple striplines. We suggest that the present system may provide a simple but effective platform for handling magnetic tags for biological and biomedical applications.

  19. Start-up and ramp-up of the PLT tokamak by lower hybrid waves

    SciTech Connect

    Jobes, F.C.; Bernabei, S.; Chu, T.K.; Fisch, N.J.; Hooke, W.M.; Karney, C.F.F.; Merservey, E.B.; Motley, R.W.; Stevens, J.E.; von Goeler, S.

    1985-08-01

    Lower hybrid waves have been used on the PLT tokamak both to start the plasma current and to ramp it up from pre-existing levels. The waves, at 800 MHz, were launched from a 6-waveguide grill. The phasing between adjacent guides could be selected electronically, and thus the launched spectrum could be set and changed at will. For start-up, the waveguide phase difference was initially set at 0/sup 0/ in order to create a plasma, then switched to 90/sup 0/ to drive the current. Over 100 kA of plasma current, at a density of 0.5 to 1 x 10/sup 12/ cm/sup -3/, was generated in this manner. Ramp-up experiments were performed under a wide variety of conditions. The most efficient ramp-up was found at the lowest plasma densities and with the fastest launched spectrum (n/sub e/ approx. 2 x 10/sup 12/ cm/sup -3/, N/sub parallel/ approx. 1.6 peak); approx.20% of the launched RF power was converted to (increased) poloidal field energy. All of the ramp-up results are in excellent agreement with a theory which determines the efficiency of ramp-up from the consideration of the relative energy losses of the superthermal current-carrying electrons to collisions and to the opposing inductive E-field.

  20. Critical current density and trapped field in HTS with asymmetric magnetization loops

    NASA Astrophysics Data System (ADS)

    Gokhfeld, D.

    2016-03-01

    Applications of the extended critical state model are considered. The trapped magnetic field, the penetration field and the field dependence of the critical current density are analysed. The critical current density and the trapped field in superconducting grains depend on the grain size. Asymmetry of the hysteresis curves relative to the M = 0 axis is related to the scale of the current circulation.

  1. Loading and Unloading Finishing Pigs: Effects of Bedding Types, Ramp Angle, and Bedding Moisture

    PubMed Central

    Garcia, Arlene; McGlone, John J.

    2014-01-01

    Simple Summary Current guidelines suggest the use of ramps below 20 degrees to load and unload pigs; however, they do not suggest the use of any specific bedding. Bedding types (nothing, feed, sand, wood shavings, and hay) were tested with finishing pigs (70–120 kg) to determine which was most effective in reducing slips, falls, and vocalizations at three ramp angles, two moisture levels, over two seasons. Slips, falls, and vocalizations were summed to establish a scoring system for the types of beddings. Heart rate and the total time it took to load and unload pigs, increased as the slope increased. Bedding, bedding moisture, season, and ramp slope interacted to impact the total time it took for finishing pigs to load and unload the ramp. Selection of the best bedding depends on ramp slope, season, and wetness of bedding. Abstract The use of non-slip surfaces during loading and unloading of finishing pigs plays an important role in animal welfare and economics of the pork industry. Currently, the guidelines available only suggest the use of ramps with a slope below 20 degrees to load and unload pigs. However, the total time it takes to load and unload animals and slips, falls, and vocalizations are a welfare concern. Three ramp angles (0, 10 or 20 degrees), five bedding materials (nothing, sand, feed, wood shavings or wheat straw hay), two moistures (dry or wet bedding, >50% moisture) over two seasons (>23.9 °C summer, <23.9 °C winter) were assessed for slips/falls/vocalizations (n = 2400 pig observations) and analyzed with a scoring system. The use of bedding during summer or winter played a role in the total time it took to load and unload the ramp (p < 0.05). Bedding, bedding moisture, season, and slope significantly interacted to impact the total time to load and unload finishing pigs (p < 0.05). Heart rate and the total time it took to load and unload the ramp increased as the slope of the ramp increased (p < 0.05). Heart rates were higher during the

  2. A magnetic-piezoelectric smart material-structure utilizing magnetic force interaction to optimize the sensitivity of current sensing

    NASA Astrophysics Data System (ADS)

    Yeh, Po-Chen; Chung, Tien-Kan; Lai, Chen-Hung; Wang, Chieh-Min

    2016-01-01

    This paper presents a magnetic-piezoelectric smart material-structure using a novel magnetic-force-interaction approach to optimize the sensitivity of conventional piezoelectric current sensing technologies. The smart material-structure comprises a CuBe-alloy cantilever beam, a piezoelectric PZT sheet clamped to the fixed end of the beam, and an NdFeB permanent magnet mounted on the free end of the beam. When the smart material-structure is placed close to an AC conductor, the magnet on the beam of the smart structure experiences an alternating magnetic attractive and repulsive force produced by the conductor. Thus, the beam vibrates and subsequently generates a strain in the PZT sheet. The strain produces a voltage output because of the piezoelectric effect. The magnetic force interaction is specifically enhanced through the optimization approach (i.e., achieved by using SQUID and machining method to reorient the magnetization to different directions to maximize the magnetic force interaction). After optimizing, the beam's vibration amplitude is significantly enlarged and, consequently, the voltage output is substantially increased. The experimental results indicated that the smart material-structure optimized by the proposed approach produced a voltage output of 4.01 Vrms with a sensitivity of 501 m Vrms/A when it was placed close to a conductor with a current of 8 A at 60 Hz. The optimized voltage output and sensitivity of the proposed smart structure were approximately 316 % higher than those (1.27 Vrms with 159 m Vrms/A) of representative piezoelectric-based current sensing technologies presented in other studies. These improvements can significantly enable the development of more self-powered wireless current sensing applications in the future.

  3. Development of flexible array eddy current probes for complex geometries and inspection of magnetic parts using magnetic sensors

    NASA Astrophysics Data System (ADS)

    Marchand, B.; Decitre, J.-M.; Sergeeva-Chollet, N.; Skarlatos, A.

    2013-01-01

    Eddy Current Technique is a powerful method of inspection of metal parts. When size of flaws decreases, inspection areas become hardly accessible or material is magnetic, traditional winding coil probes are less efficient. Thanks to new CIVA simulation tools, we have designed and optimized advanced EC probes: flexible EC probe based on micro-coil arrays and EC probe with magnetic sensors, including specific electronics.

  4. Mars pathfinder Rover egress deployable ramp assembly

    NASA Technical Reports Server (NTRS)

    Spence, Brian R.; Sword, Lee F.

    1996-01-01

    The Mars Pathfinder Program is a NASA Discovery Mission, led by the Jet Propulsion Laboratory, to launch and place a small planetary Rover for exploration on the Martian surface. To enable safe and successful egress of the Rover vehicle from the spacecraft, a pair of flight-qualified, deployable ramp assemblies have been developed. This paper focuses on the unique, lightweight deployable ramp assemblies. A brief mission overview and key design requirements are discussed. Design and development activities leading to qualification and flight systems are presented.

  5. Programmable Multiple-Ramped-Voltage Power Supply

    NASA Technical Reports Server (NTRS)

    Ajello, Joseph M.; Howell, S. K.

    1993-01-01

    Ramp waveforms range up to 2,000 V. Laboratory high-voltage power-supply system puts out variety of stable voltages programmed to remain fixed with respect to ground or float with respect to ramp waveform. Measures voltages it produces with high resolution; automatically calibrates, zeroes, and configures itself; and produces variety of input/output signals for use with other instruments. Developed for use with ultraviolet spectrometer. Also applicable to control of electron guns in general and to operation of such diverse equipment used in measuring scattering cross sections of subatomic particles and in industrial electron-beam welders.

  6. Current investigations into magnetic nanoparticles for biomedical applications.

    PubMed

    Li, Xiaoming; Wei, Jianrong; Aifantis, Katerina E; Fan, Yubo; Feng, Qingling; Cui, Fu-Zhai; Watari, Fumio

    2016-05-01

    It is generally recognized that nanoparticles possess unique physicochemical properties that are largely different from those of conventional materials, specifically the electromagnetic properties of magnetic nanoparticles (MNPs). These properties have attracted many researchers to launch investigations into their potential biomedical applications, which have been reviewed in this article. First, common types of MNPs were briefly introduced. Then, the biomedical applications of MNPs were reviewed in seven parts: magnetic resonance imaging (MRI), cancer therapy, the delivery of drugs and genes, bone and dental repair, tissue engineering, biosensors, and in other aspects, which indicated that MNPs possess great potentials for many kinds of biomedical applications due to their unique properties. Although lots of achievements have been obtained, there is still a lot of work to do. New synthesis techniques and methods are still needed to develop the MNPs with satisfactory biocompatibility. More effective methods need to be exploited to prepare MNPs-based composites with fine microstructures and high biomedical performances. Other promising research points include the development of more appropriate techniques of experiments both in vitro and in vivo to detect and analyze the biocompatibility and cytotoxicity of MNPs and understand the possible influencing mechanism of the two properties. More comprehensive investigations into the diagnostic and therapeutic applications of composites containing MNPs with "core-shell" structure and deeper understanding and further study into the properties of MNPs to reveal their new biomedical applications, are also described in the conclusion and perspectives part. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1285-1296, 2016. PMID:26779606

  7. The Magnetic and Shielding Effects of Ring Current on Radiation Belt Dynamics

    NASA Technical Reports Server (NTRS)

    Fok, Mei-Ching

    2012-01-01

    The ring current plays many key roles in controlling magnetospheric dynamics. A well-known example is the magnetic depression produced by the ring current, which alters the drift paths of radiation belt electrons and may cause significant electron flux dropout. Little attention is paid to the ring current shielding effect on radiation belt dynamics. A recent simulation study that combines the Comprehensive Ring Current Model (CRCM) with the Radiation Belt Environment (RBE) model has revealed that the ring current-associated shielding field directly and/or indirectly weakens the relativistic electron flux increase during magnetic storms. In this talk, we will discuss how ring current magnetic field and electric shielding moderate the radiation belt enhancement.

  8. Magnetic shielding of large high-power-satellite solar arrays using internal currents

    NASA Technical Reports Server (NTRS)

    Parker, L. W.; Oran, W. A.

    1979-01-01

    Present concepts for solar power satellites involve dimensions up to tens of kilometers and operating internal currents up to hundreds of kiloamperes. A question addressed is whether the local magnetic fields generated by these strong currents during normal operation can shield the array against impacts by plasma ions and electrons (and from thruster plasmas) which can cause possible losses such as power leakage and surface erosion. One of several prototype concepts was modeled by a long narrow rectangular panel 2 km wide and 20 km long. The currents flow in a parallel across the narrow dimension (sheet current) and along the edge (wire currents). The wire currents accumulate from zero to 100 kiloamp and are the dominant sources. The magnetic field is approximated analytically. The equations of motion for charged particles in this magnetic field are analyzed. The ion and electron fluxes at points on the surface are represented analytically for monoenergetic distributions and are evaluated.

  9. Simple Analytic Expressions for the Magnetic Field of a Circular Current Loop

    NASA Technical Reports Server (NTRS)

    Simpson, James C.; Lane, John E.; Immer, Christopher D.; Youngquist, Robert C.; Steinrock, Todd (Technical Monitor)

    2001-01-01

    Analytic expressions for the magnetic induction and its spatial derivatives for a circular loop carrying a static current are presented in Cartesian, spherical and cylindrical coordinates. The solutions are exact throughout all space outside the conductor.

  10. Simulating net particle production and chiral magnetic current in a C P -odd domain

    NASA Astrophysics Data System (ADS)

    Fukushima, Kenji

    2015-09-01

    To address a question of whether the chiral magnetic current is a static polarization or a genuine flow of charged particles, we elucidate the numerical formulation to simulate the net production of right-handed particles and anomalous currents with C P -breaking background fields which cause an imbalance between particles and antiparticles. For a concrete demonstration we numerically impose pulsed electric and magnetic fields to confirm our answer to the question that the produced net particles flow in the dynamical chiral magnetic effect. The rate for the particle production and the chiral magnetic current generation is quantitatively consistent with the axial anomaly, while they appear with a finite response time. We emphasize the importance to quantify the response time that would suppress observable effects of the anomalous current.

  11. LRV-2 vehicle parked on ramp

    NASA Technical Reports Server (NTRS)

    1981-01-01

    The LRV-2 (Low Reynolds Vehicle No. 2), seen here on the ramp at NASA's Dryden Flight Research Center, Edwards, California, was a remotely piloted research vehicle (RPRV) developed to conduct aerodynamic and auto-pilot systems experiments on ultra-light aircraft. The aircraft made its maiden voyage October 20, 1982. The LRV-2 had a 32 ft. wingspan with a 1.5 lb per square foot wing loading. The aluminum tube structure was covered with a lightweight dacron fabric and was powered by a ten horsepower two-stroke engine. The LRV-2 was equipped with a lightweight RPRV system comprised of a radio-control uplink, a nose-mounted television system, a radar transponder for precise tracking and a telemetry system for research data. Wing tip extensions, with experimental wing airfoil sections, were installed and instrumented for surface pressures and wake drag measurements. The very low flying speed of the LRV-2 allowed Reynolds numbers matching those of current and future high altitude lightweight RPRVs. The Reynolds number is a measurement roughly equivalent to 'viscosity' as measured in liquids. The LRV-2 was flown by one of two 'radio-control' pilots. The vehicle could be flown by a 'visual pilot' sitting in the back of a 'chase' pickup truck, or by an 'IFR' pilot watching a television screen and a radar plot board. Landings and take-offs were conducted by either pilot, however, research maneuvers were performed by the IFR pilot having attitude information from the forward looking TV and other data from the telemetry system down-linked from the aircraft. The LRV-2 was flown to 20,000 ft altitude to provide Reynolds number variations and altitude effects on the onboard experiments.

  12. Modelling of eddy currents related to large angle magnetic suspension test fixture

    NASA Technical Reports Server (NTRS)

    Britcher, Colin P.; Foster, Lucas E.

    1994-01-01

    This report presents a preliminary analysis of the mathematical modelling of eddy current effects in a large-gap magnetic suspension system. It is shown that eddy currents can significantly affect the dynamic behavior and control of these systems, but are amenable to measurement and modelling. A theoretical framework is presented, together with a comparison of computed and experimental data related to the Large Angle Magnetic Suspension Test Fixture at NASA Langley Research Center.

  13. Evaluation and Improvement of Eddy Current Position Sensors in Magnetically Suspended Flywheel Systems

    NASA Technical Reports Server (NTRS)

    Dever, Timothy P.; Palazzolo, Alan B.; Thomas, Erwin M., III; Jansen, Ralph H.; McLallin, Kerry (Technical Monitor); Soeder, James (Technical Monitor)

    2001-01-01

    Eddy current position sensor performance is evaluated for use in a high-speed flywheel development system. The flywheel utilizes a five axis active magnetic bearing system. The eddy current sensors are used for position feedback for the bearing controller. Measured characteristics include sensitivity to multiple target materials and susceptibility to noise from the magnetic bearings and from sensor-to-sensor crosstalk. Improvements in axial sensor configuration and techniques for noise reduction are described.

  14. Perseus B Parked on Ramp

    NASA Technical Reports Server (NTRS)

    1999-01-01

    A long, slender wing and a pusher propeller at the rear characterize the Perseus B remotely piloted aircraft, seen here on the ramp at NASA's Dryden Flight Research Center, Edwards, California. Perseus B is a remotely piloted aircraft developed as a design-performance testbed under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) project. Perseus is one of several flight vehicles involved in the ERAST project. A piston engine, propeller-powered aircraft, Perseus was designed and built by Aurora Flight Sciences Corporation, Manassas, Virginia. The objectives of Perseus B's ERAST flight tests have been to reach and maintain horizontal flight above altitudes of 60,000 feet and demonstrate the capability to fly missions lasting from 8 to 24 hours, depending on payload and altitude requirements. The Perseus B aircraft established an unofficial altitude record for a single-engine, propeller-driven, remotely piloted aircraft on June 27, 1998. It reached an altitude of 60,280 feet. In 1999, several modifications were made to the Perseus aircraft including engine, avionics, and flight-control-system improvements. These improvements were evaluated in a series of operational readiness and test missions at the Dryden Flight Research Center, Edwards, California. Perseus is a high-wing monoplane with a conventional tail design. Its narrow, straight, high-aspect-ratio wing is mounted atop the fuselage. The aircraft is pusher-designed with the propeller mounted in the rear. This design allows for interchangeable scientific-instrument payloads to be placed in the forward fuselage. The design also allows for unobstructed airflow to the sensors and other devices mounted in the payload compartment. The Perseus B that underwent test and development in 1999 was the third generation of the Perseus design, which began with the Perseus Proof-Of-Concept aircraft. Perseus was initially developed as part of NASA's Small High-Altitude Science Aircraft (SHASA) program, which

  15. Perseus B Parked on Ramp

    NASA Technical Reports Server (NTRS)

    1999-01-01

    The long, slender wing of the Perseus B remotely piloted research aircraft can be clearly seen in this photo, taken on the ramp of NASA's Dryden Flight Research Center in September 1999. Perseus B is a remotely piloted aircraft developed as a design-performance testbed under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) project. Perseus is one of several flight vehicles involved in the ERAST project. A piston engine, propeller-powered aircraft, Perseus was designed and built by Aurora Flight Sciences Corporation, Manassas, Virginia. The objectives of Perseus B's ERAST flight tests have been to reach and maintain horizontal flight above altitudes of 60,000 feet and demonstrate the capability to fly missions lasting from 8 to 24 hours, depending on payload and altitude requirements. The Perseus B aircraft established an unofficial altitude record for a single-engine, propeller-driven, remotely piloted aircraft on June 27, 1998. It reached an altitude of 60,280 feet. In 1999, several modifications were made to the Perseus aircraft including engine, avionics, and flight-control-system improvements. These improvements were evaluated in a series of operational readiness and test missions at the Dryden Flight Research Center, Edwards, California. Perseus is a high-wing monoplane with a conventional tail design. Its narrow, straight, high-aspect-ratio wing is mounted atop the fuselage. The aircraft is pusher-designed with the propeller mounted in the rear. This design allows for interchangeable scientific-instrument payloads to be placed in the forward fuselage. The design also allows for unobstructed airflow to the sensors and other devices mounted in the payload compartment. The Perseus B that underwent test and development in 1999 was the third generation of the Perseus design, which began with the Perseus Proof-Of-Concept aircraft. Perseus was initially developed as part of NASA's Small High-Altitude Science Aircraft (SHASA) program, which later

  16. Perseus B Parked on Ramp

    NASA Technical Reports Server (NTRS)

    1999-01-01

    The long, slender wing of the Perseus B high-altitude, remotely piloted research aircraft is clearly visible in this photo of the vehicle, taken on the ramp of NASA's Dryden Flight Research Center in September 1999. Perseus B is a remotely piloted aircraft developed as a design-performance testbed under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) project. Perseus is one of several flight vehicles involved in the ERAST project. A piston engine, propeller-powered aircraft, Perseus was designed and built by Aurora Flight Sciences Corporation, Manassas, Virginia. The objectives of Perseus B's ERAST flight tests have been to reach and maintain horizontal flight above altitudes of 60,000 feet and demonstrate the capability to fly missions lasting from 8 to 24 hours, depending on payload and altitude requirements. The Perseus B aircraft established an unofficial altitude record for a single-engine, propeller-driven, remotely piloted aircraft on June 27, 1998. It reached an altitude of 60,280 feet. In 1999, several modifications were made to the Perseus aircraft including engine, avionics, and flight-control-system improvements. These improvements were evaluated in a series of operational readiness and test missions at the Dryden Flight Research Center, Edwards, California. Perseus is a high-wing monoplane with a conventional tail design. Its narrow, straight, high-aspect-ratio wing is mounted atop the fuselage. The aircraft is pusher-designed with the propeller mounted in the rear. This design allows for interchangeable scientific-instrument payloads to be placed in the forward fuselage. The design also allows for unobstructed airflow to the sensors and other devices mounted in the payload compartment. The Perseus B that underwent test and development in 1999 was the third generation of the Perseus design, which began with the Perseus Proof-Of-Concept aircraft. Perseus was initially developed as part of NASA's Small High-Altitude Science Aircraft

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

    NASA Technical Reports Server (NTRS)

    Gary, G. Allen; Rabin, Douglas

    1995-01-01

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

  18. A magnetic bearing based on eddy-current repulsion

    NASA Technical Reports Server (NTRS)

    Nikolajsen, J. L.

    1987-01-01

    This paper describes a new type of electromagnetic bearing, called the Eddy-Current Bearing, which works by repulsion between fixed AC-electromagnets and a conducting rotor. The following advantages are expected: inherent stability, higher load carrying capacity than DC-electromagnetic bearings, simultaneous radial, angular and thrust support, motoring and generating capability, and backup mode of operation in case of primary power failure. A prototype is under construction.

  19. Current control of magnetic anisotropy via stress in a ferromagnetic metal waveguide

    NASA Astrophysics Data System (ADS)

    An, Kyongmo; Ma, Xin; Pai, Chi-Feng; Yang, Jusang; Olsson, Kevin S.; Erskine, James L.; Ralph, Daniel C.; Buhrman, Robert A.; Li, Xiaoqin

    2016-04-01

    We demonstrate that in-plane charge current can effectively control the spin precession resonance in an A l2O3/CoFeB /Ta heterostructure. Brillouin light scattering was used to detect the ferromagnetic resonance field under microwave excitation of spin waves at fixed frequencies. The current control of spin precession resonance originates from modification of the in-plane uniaxial magnetic anisotropy field Hk, which changes symmetrically with respect to the current direction. Numerical simulation suggests that the anisotropic stress introduced by joule heating plays an important role in controlling Hk. These results provide new insight into current manipulation of magnetic properties and have broad implications for spintronic devices.

  20. Sustained chiral magnetic domain wall motion driven by spin-orbit torques under the tilted current

    NASA Astrophysics Data System (ADS)

    He, Peng-Bin; Yan, Han; Cai, Meng-Qiu; Li, Zai-Dong

    2016-06-01

    We theoretically investigate the steady magnetic domain wall driven by spin-orbit torques in the heavy-metal/magnet bilayers with perpendicular anisotropy. Based on collective coordinates method and stability analysis, we analyze the effects of tilted current and Dzyaloshinskii-Moriya interaction on the wall. We find that the wall acquires a sustained motion in the high-current regime by deviating the current from the wall track. Also, a persistent motion can be supported by the competition between spin-orbit torques and Dzyaloshinskii-Moriya interaction in transforming wall type. In the low-current regime, there exist a switching of wall chirality and a reversal of wall motion.

  1. Experimental characterization and constitutive modeling of the mechanical behavior of molybdenum under electromagnetically applied compression-shear ramp loading

    NASA Astrophysics Data System (ADS)

    Alexander, C. S.; Ding, J. L.; Asay, J. R.

    2016-03-01

    Magnetically applied pressure-shear (MAPS) is a new experimental technique that provides a platform for direct measurement of material strength at extreme pressures. The technique employs an imposed quasi-static magnetic field and a pulsed power generator that produces an intense current on a planar driver panel, which in turn generates high amplitude magnetically induced longitudinal compression and transverse shear waves into a planar sample mounted on the drive panel. In order to apply sufficiently high shear traction to the test sample, a high strength material must be used for the drive panel. Molybdenum is a potential driver material for the MAPS experiment because of its high yield strength and sufficient electrical conductivity. To properly interpret the results and gain useful information from the experiments, it is critical to have a good understanding and a predictive capability of the mechanical response of the driver. In this work, the inelastic behavior of molybdenum under uniaxial compression and biaxial compression-shear ramp loading conditions is experimentally characterized. It is observed that an imposed uniaxial magnetic field ramped to approximately 10 T through a period of approximately 2500 μs and held near the peak for about 250 μs before being tested appears to anneal the molybdenum panel. In order to provide a physical basis for model development, a general theoretical framework that incorporates electromagnetic loading and the coupling between the imposed field and the inelasticity of molybdenum was developed. Based on this framework, a multi-axial continuum model for molybdenum under electromagnetic loading is presented. The model reasonably captures all of the material characteristics displayed by the experimental data obtained from various experimental configurations. In addition, data generated from shear loading provide invaluable information not only for validating but also for guiding the development of the material model for

  2. Experimental characterization and constitutive modeling of the mechanical behavior of molybdenum under electromagnetically applied compression-shear ramp loading

    DOE PAGESBeta

    Alexander, C. Scott; Ding, Jow -Lian; Asay, James Russell

    2016-03-09

    Magnetically applied pressure-shear (MAPS) is a new experimental technique that provides a platform for direct measurement of material strength at extreme pressures. The technique employs an imposed quasi-static magnetic field and a pulsed power generator that produces an intense current on a planar driver panel, which in turn generates high amplitude magnetically induced longitudinal compression and transverse shear waves into a planar sample mounted on the drive panel. In order to apply sufficiently high shear traction to the test sample, a high strength material must be used for the drive panel. Molybdenum is a potential driver material for the MAPSmore » experiment because of its high yield strength and sufficient electrical conductivity. To properly interpret the results and gain useful information from the experiments, it is critical to have a good understanding and a predictive capability of the mechanical response of the driver. In this work, the inelastic behavior of molybdenum under uniaxial compression and biaxial compression-shear ramp loading conditions is experimentally characterized. It is observed that an imposed uniaxial magnetic field ramped to approximately 10 T through a period of approximately 2500 μs and held near the peak for about 250 μs before being tested appears to anneal the molybdenum panel. In order to provide a physical basis for model development, a general theoretical framework that incorporates electromagnetic loading and the coupling between the imposed field and the inelasticity of molybdenum was developed. Based on this framework, a multi-axial continuum model for molybdenum under electromagnetic loading is presented. The model reasonably captures all of the material characteristics displayed by the experimental data obtained from various experimental configurations. Additionally, data generated from shear loading provide invaluable information not only for validating but also for guiding the development of the material

  3. Unsteady magnetohydrodynamic free convection flow of a second grade fluid in a porous medium with ramped wall temperature.

    PubMed

    Samiulhaq; Ahmad, Sohail; Vieru, Dumitru; Khan, Ilyas; Shafie, Sharidan

    2014-01-01

    Magnetic field influence on unsteady free convection flow of a second grade fluid near an infinite vertical flat plate with ramped wall temperature embedded in a porous medium is studied. It has been observed that magnitude of velocity as well as skin friction in case of ramped temperature is quite less than the isothermal temperature. Some special cases namely: (i) second grade fluid in the absence of magnetic field and porous medium and (ii) Newtonian fluid in the presence of magnetic field and porous medium, performing the same motion are obtained. Finally, the influence of various parameters is graphically shown. PMID:24785147

  4. Unsteady Magnetohydrodynamic Free Convection Flow of a Second Grade Fluid in a Porous Medium with Ramped Wall Temperature

    PubMed Central

    Samiulhaq; Ahmad, Sohail; Vieru, Dumitru; Khan, Ilyas; Shafie, Sharidan

    2014-01-01

    Magnetic field influence on unsteady free convection flow of a second grade fluid near an infinite vertical flat plate with ramped wall temperature embedded in a porous medium is studied. It has been observed that magnitude of velocity as well as skin friction in case of ramped temperature is quite less than the isothermal temperature. Some special cases namely: (i) second grade fluid in the absence of magnetic field and porous medium and (ii) Newtonian fluid in the presence of magnetic field and porous medium, performing the same motion are obtained. Finally, the influence of various parameters is graphically shown. PMID:24785147

  5. Online Analysis of Wind and Solar Part I: Ramping Tool

    SciTech Connect

    Etingov, Pavel V.; Ma, Jian; Makarov, Yuri V.; Subbarao, Krishnappa

    2012-01-31

    To facilitate wider penetration of renewable resources without compromising system reliability concerns arising from the lack of predictability of intermittent renewable resources, a tool for use by California Independent System Operator (CAISO) power grid operators was developed by Pacific Northwest National Laboratory (PNNL) in conjunction with CAISO with funding from California Energy Commission. This tool predicts and displays additional capacity and ramping requirements caused by uncertainties in forecasts of loads and renewable generation. The tool is currently operational in the CAISO operations center. This is one of two final reports on the project.

  6. Is Knee Magnetic Resonance Imaging Overutilized in Current Practice?

    PubMed Central

    Song, Young Dong; Jain, Nimesh Prakash; Kim, Seok Jin; Kwon, Sae Kwang; Chang, Moon Jong; Chang, Chong Bum

    2015-01-01

    Purpose To determine what proportion of patients visiting a tertiary knee clinic had pre-obtained knee magnetic resonance imaging (MRI) and to assess the impact of pre-obtained knee MRI on the selection of treatment plans. Materials and Methods Six hundred and eighty patients were enrolled from patients who visited our knee clinic during a 6-month period. The proportion of patients with pre-obtained knee MRI was calculated, and associations of sociodemographic factors, disease category, and finally selected treatment options with knee MRI pre-obtainment were investigated. A utility assessment panel of five orthopaedic surgeons was formed and established utility assessment criteria. Two rounds of utility assessment (before and after MRI review) were performed. Results Of the 680 patients, 185 (27%) had pre-obtained knee MRI. In the first round of utility assessment, 39%, 18%, and 43% of the 185 knee MRIs were evaluated as useful, equivocal, and arguably useless, respectively, and almost identical results were obtained in the second round. The proportion of assessed 'useful MRI' was higher in sports related injury (84%) and other conditions (91%) than in degenerative joint disease (18%) and nonspecific knee pain (31%). Utility assessment results among panels varied little for practice patterns and education duration. Conclusions This study suggests clinicians should reconsider and counsel patients the expected utility of knee MRI acquisition. PMID:26060608

  7. A constitutive model for the forces of a magnetic bearing including eddy currents

    NASA Technical Reports Server (NTRS)

    Taylor, D. L.; Hebbale, K. V.

    1993-01-01

    A multiple magnet bearing can be developed from N individual electromagnets. The constitutive relationships for a single magnet in such a bearing is presented. Analytical expressions are developed for a magnet with poles arranged circumferencially. Maxwell's field equations are used so the model easily includes the effects of induced eddy currents due to the rotation of the journal. Eddy currents must be included in any dynamic model because they are the only speed dependent parameter and may lead to a critical speed for the bearing. The model is applicable to bearings using attraction or repulsion.

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

    NASA Technical Reports Server (NTRS)

    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.

  9. Effect of biquadratic coupling on current induced magnetization switching in Co/Cu/Ni-Fe nanopillar

    NASA Astrophysics Data System (ADS)

    Aravinthan, D.; Sabareesan, P.; Daniel, M.

    2016-05-01

    The effect of biquadratic coupling on spin current induced magnetization switching in a Co/Cu/Ni-Fe nanopillar device is investigated by solving the free layer magnetization switching dynamics governed by the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation. The LLGS equation is numerically solved by using Runge-Kutta fourth order procedure for an applied current density of 5 × 1012 Am-2. Presence of biquadratic coupling in the ferromagnetic layers reduces the magnetization switching time of the nanopillar device from 61 ps to 49 ps.

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

    SciTech Connect

    Volkov, Oleksii M. Sheka, Denis D.; Kravchuk, Volodymyr P.; Gaididei, Yuri; Mertens, Franz G.

    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.

  11. Induced fermionic current by a magnetic tube in the cosmic string spacetime

    NASA Astrophysics Data System (ADS)

    Maior de Sousa, M. S.; Ribeiro, R. F.; Bezerra de Mello, E. R.

    2016-02-01

    In this paper, we consider a charged massive fermionic quantum field in the spacetime of an idealized cosmic string, in the presence of a magnetic field confined in a cylindrical tube of finite radius. Three distinct configurations for the magnetic field are taken into account: (i) a cylindrical shell of radius a , (ii) a magnetic field proportional to 1 /r , and (iii) a constant magnetic field. In these three cases, the axis of the infinitely long tube of radius a coincides with the cosmic string. Our main objective is to analyze the induced vacuum fermionic current densities outside the tube. In order to do that, we explicitly construct the wave functions inside and outside the tube for each case. Having the complete set of normalized wave functions, we use the summation method to develop our analysis. We show that, in the region outside the tube, the induced currents are decomposed into parts corresponding to a zero-thickness magnetic flux in addition to core-induced contributions. The latter presents a specific form depending on the magnetic field configuration considered. We also see that the only nonvanishing component of fermionic current corresponds to the azimuthal one. The zero-thickness contribution depends only on the fractional part of the ration of the magnetic flux inside the tube by the quantum one. As to the core-induced contribution, it depends on the total magnetic flux inside the tube and, consequently, it is not, in general, a periodic function of the flux.

  12. A Model for Axial Magnetic Bearings Including Eddy Currents

    NASA Technical Reports Server (NTRS)

    Kucera, Ladislav; Ahrens, Markus

    1996-01-01

    This paper presents an analytical method of modelling eddy currents inside axial bearings. The problem is solved by dividing an axial bearing into elementary geometric forms, solving the Maxwell equations for these simplified geometries, defining boundary conditions and combining the geometries. The final result is an analytical solution for the flux, from which the impedance and the force of an axial bearing can be derived. Several impedance measurements have shown that the analytical solution can fit the measured data with a precision of approximately 5%.

  13. Detectable Warning Surfaces at Curb Ramps.

    ERIC Educational Resources Information Center

    Hauger, J. S.; And Others

    1996-01-01

    Four tests evaluated the need for and effectiveness of detectable warning surfaces at curb ramps for pedestrians with blindness. Results found that the effectiveness of the detectable warning surfaces depended on other aspects of the design of the intersections and on factors such as the density of traffic and the traveler's skills. (CR)

  14. High power fast ramping power supplies

    SciTech Connect

    Marneris,I.; Bajon, E.; Bonati, R.; Sandberg, J.; Roser, T.; Tsoupas, N.

    2009-05-04

    Hundred megawatt level fast ramping power converters to drive proton and heavy ion machines are under research and development at accelerator facilities in the world. This is a leading edge technology. There are several topologies to achieve this power level. Their advantages and related issues will be discussed.

  15. Identifying Wind and Solar Ramping Events: Preprint

    SciTech Connect

    Florita, A.; Hodge, B. M.; Orwig, K.

    2013-01-01

    Wind and solar power are playing an increasing role in the electrical grid, but their inherent power variability can augment uncertainties in power system operations. One solution to help mitigate the impacts and provide more flexibility is enhanced wind and solar power forecasting; however, its relative utility is also uncertain. Within the variability of solar and wind power, repercussions from large ramping events are of primary concern. At the same time, there is no clear definition of what constitutes a ramping event, with various criteria used in different operational areas. Here the Swinging Door Algorithm, originally used for data compression in trend logging, is applied to identify variable generation ramping events from historic operational data. The identification of ramps in a simple and automated fashion is a critical task that feeds into a larger work of 1) defining novel metrics for wind and solar power forecasting that attempt to capture the true impact of forecast errors on system operations and economics, and 2) informing various power system models in a data-driven manner for superior exploratory simulation research. Both allow inference on sensitivities and meaningful correlations, as well as the ability to quantify the value of probabilistic approaches for future use in practice.

  16. Current-Free Plasma Thruster Controlling Cross-Field Diffusion under a Magnetic Nozzle

    NASA Astrophysics Data System (ADS)

    Takahashi, Kazunori; Charles, Christine; Boswell, Rod; Ando, Akira

    A current-free helicon plasma thruster is designed to control cross-field diffusion in a magnetic nozzle while maintaining a constant plasma injection into the nozzle for investigation of the cross-field diffusion effect on the thruster performance. When increasing the magnetic field strength, the cross-field diffusion is inhibited and the higher plasma density in the magnetic nozzle downstream of the thruster is observed. Directly measured thrust also increases with an increase in the field strength, as the Lorentz force arising from the radial magnetic field and the electron diamagnetic drift current is enhanced by the higher electron pressure within the magnetic nozzle. Further, the rf power is increased up to 2 kW and the maximum thrust of about 15 mN is obtained for 20 sccm argon propellant.

  17. Electromagnetic fluctuations due to current sheet instabilities in collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Jain, Neeraj; Büchner, Jörg; Munoz Sepulveda, Patricio Alejandro

    2016-07-01

    In collisionless magnetic reconnection, dissipation region, where frozen-in condition of magnetic field breaks down, develops two scale structure, viz., electron current sheets embedded inside ion current sheets. Instabilities of these current sheets lead to the development of electromagnetic turbulence which can cause anomalous dissipation enhancing the reconnection rate. Laboratory experiments, e.g., Magnetic Reconnection Experiment and VINETA-II have measured fluctuations in electron current sheets in the lower hybrid frequency range. We present simulations of the electromagnetic turbulence generated by current sheet instabilities. The characteristic features of the electromagnetic turbulence, which can be used to identify the unstable modes responsible for the turbulence, will be studied. The results will be compared with the laboratory experiments.

  18. Application of shielding current in bulk HTS to control magnetic field distribution

    NASA Astrophysics Data System (ADS)

    Kii, T.

    2016-03-01

    Superconducting shielding current is excited when external field is applied to superconductor. In case for field cooling of bulk superconductor, shielding current is an origin of strong trapped field. When external field is changed to a properly arranged bulk HTS array, various magnetic field distribution can be formed by an excited shielding current in each bulk HTS. This paper presents a simple intuitively method to design magnetic field distribution using supercurrents in bulk high-temperature superconductor (HTS) array. In this method, an ideal current path for intended field distribution is represented by shielding currents in bulk HTS array. Expected performance can be roughly estimated by using Biot-Savart law. As examples, Maxwell coil pair and helical field generator are designed. This method can be applied to design various magnet devices using bulk HTS array.

  19. Currents induced by magnetic impurities in superconductors with spin-orbit coupling.

    PubMed

    Pershoguba, Sergey S; Björnson, Kristofer; Black-Schaffer, Annica M; Balatsky, Alexander V

    2015-09-11

    We show that superconducting currents are generated around magnetic impurities and ferromagnetic islands proximity coupled to superconductors with finite spin-orbit coupling. Using the Ginzburg-Landau theory, T-matrix calculation, as well as self-consistent numerical simulation on a lattice, we find a strong dependence of the current on the direction and magnitude of the magnetic moment. We establish that in the case of point magnetic impurities, the current is carried by the induced Yu-Shiba-Rusinov (YSR) subgap states. In the vicinity of the phase transition, where the YSR states cross at zero energy, the current increases dramatically. Furthermore, we show that the currents are orthogonal to the local spin polarization and, thus, can be probed by measuring the spin-polarized local density of states. PMID:26406845

  20. Current-induced magnetization switching of a three terminal perpendicular magnetic tunnel junction by spin-orbit torque

    NASA Astrophysics Data System (ADS)

    Cubukcu, Murat; Drouard, Marc; Boulle, Olivier; Garello, Kevin; Miron, Ioan Mihai; Langer, Juergen; Ocker, Berthold; Gambardella, Pietro; Gaudin, Gilles

    2014-03-01

    A current flowing in the plane of a magnetic multilayer with structural inversion asymmetry, such as Pt/Co/AlOx, creates a torque on the magnetization. This torque is due to the strong spin-orbit interaction present in such multilayers and can lead to fast magnetization reversal with a low writing energy.We will present the first proof of concept of a perpendicular spin-orbit torque magnetic random access memory (SOT-MRAM) cell composed of a Ta/FeCoB/MgO/FeCoB magnetic tunnel junction. The basic write and read operations, i.e., the magnetization reversal by current injection in the Ta track and its detection using the high TMR signal, are demonstrated. Our results open a path for the development of a novel class of three terminal MRAM combining fast, reliable and low energy writing. This work was supported by the European Commission under the Seventh Framework Program (Grant Agreement 318144, spot project).

  1. Broadband alternating current magnetic susceptibility: Method and application to the characterization of magnetic particles in igneous rocks

    NASA Astrophysics Data System (ADS)

    Kodama, K.

    2012-12-01

    Low-field alternating current magnetic susceptibility (MS) is among the most commonly used magnetic property, not only in rock and mineral magnetism but also in environmental magnetism studies. This study proposes a new rock magnetic method, Frequency Spectrum of MS (FSM), based on the measurement of the real component of MS over a wide range of frequency (100 Hz to 500 kHz) and the measurement of the imaginary component at high frequencies in the order of 10-102 kHz. This study presents the FSM results at room and low temperatures obtained from a variety of igneous rocks with SP to SD grain sizes, including acidic to basic volcanic rocks in Japan and a basalt in Hawaii. The FSMs from the andesite samples at room temperature unexceptionally show small but anomalous increase, as much as 5%, over a specific frequency interval between 10 kHz and 120 kHz. In contrast, FSMs of basalts from Oshima and Hawaii show no such peak, a typical pattern indicating the presence of SP grain ensembles. The anomalous FSM from the andesites suggests a new rock and mineral magnetic behavior indicating either magnetic resonance or magnetic relaxation. Considering the anomalous FSM patterns and their variations at low temperatures, it is suggested that the hypothetical resonance could be relevant to some magnetoelastic phenomenon, in which magnetic energy could be dissipated through a long-range, magnetostructural coupling, most likely, magnetostriction. The fact that the annealed andesite samples showed less developed FSM anomaly strongly supports this hypothesis, because annealing generally lowers the internal stress leading to the reduction of resistance in a forced oscillation system. Analyses of the low temperature results confirm magnetic relaxation phenomena taking place at low temperatures, and consequently support the above interpretation.

  2. Measurement of the charge and current of magnetic monopoles in spin ice.

    PubMed

    Bramwell, S T; Giblin, S R; Calder, S; Aldus, R; Prabhakaran, D; Fennell, T

    2009-10-15

    The transport of electrically charged quasiparticles (based on electrons or ions) plays a pivotal role in modern technology as well as in determining the essential functions of biological organisms. In contrast, the transport of magnetic charges has barely been explored experimentally, mainly because magnetic charges, in contrast to electric ones, are generally considered at best to be convenient macroscopic parameters, rather than well-defined quasiparticles. However, it was recently proposed that magnetic charges can exist in certain materials in the form of emergent excitations that manifest like point charges, or magnetic monopoles. Here we address the question of whether such magnetic charges and their associated currents-'magnetricity'-can be measured directly in experiment, without recourse to any material-specific theory. By mapping the problem onto Onsager's theory of electrolytes, we show that this is indeed possible, and devise an appropriate method for the measurement of magnetic charges and their dynamics. Using muon spin rotation as a suitable local probe, we apply the method to a real material, the 'spin ice' Dy(2)Ti(2)O(7) (refs 5-8). Our experimental measurements prove that magnetic charges exist in this material, interact via a Coulomb potential, and have measurable currents. We further characterize deviations from Ohm's law, and determine the elementary unit of magnetic charge to be 5 mu(B) A(-1), which is equal to that recently predicted using the microscopic theory of spin ice. Our measurement of magnetic charge and magnetic current establishes an instance of a perfect symmetry between electricity and magnetism. PMID:19829376

  3. Electric current variations and 3D magnetic configuration of coronal jets

    NASA Astrophysics Data System (ADS)

    Schmieder, Brigitte; Harra, Louise K.; Aulanier, Guillaume; Guo, Yang; Demoulin, Pascal; Moreno-Insertis, Fernando, , Prof

    Coronal jets (EUV) were observed by SDO/AIA on September 17, 2010. HMI and THEMIS measured the vector magnetic field from which we derived the magnetic flux, the phostospheric velocity and the vertical electric current. The magnetic configuration was computed with a non linear force-free approach. The phostospheric current pattern of the recurrent jets were associated with the quasi-separatrix layers deduced from the magnetic extrapolation. The large twisted near-by Eiffel-tower-shape jet was also caused by reconnection in current layers containing a null point. This jet cannot be classified precisely within either the quiescent or the blowout jet types. We will show the importance of the existence of bald patches in the low atmosphere

  4. Magnetohydrodynamic Simulations of Current-Sheet Formation and Reconnection at a Magnetic X Line

    NASA Astrophysics Data System (ADS)

    DeVore, C. R.; Antiochos, S. K.; Karpen, J. T.; Black, C.

    2011-12-01

    Phenomena ranging from the quiescent heating of the ambient plasma to the highly explosive release of energy and acceleration of particles in flares are conjectured to result from magnetic reconnection at electric current sheets in the Sun's corona. We are investigating numerically, using a macroscopic magnetohydrodynamic (MHD) model with adaptive mesh refinement, the formation and reconnection of a current sheet in an initially potential 2D magnetic field containing a null. Subjecting this simple configuration to unequal stresses in the four quadrants bounded by the X-line separatrix distorts the potential null into a double-Y-line current sheet. We find that even small distortions of the magnetic field induce the formation of a tangential discontinuity in the high-beta region around the null. A continuously applied stress eventually leads to the onset of fast magnetic reconnection across the sheet, with copious production, merging, and ejection of magnetic islands. We compare the current-sheet development and evolution for three cases: quasi-ideal MHD with numerical resistivity only; uniformly resistive MHD; and MHD with an embedded kinetic reconnection model. Analogous kinetic simulations using particle-in-cell (PIC) methods to investigate the small-scale dynamics of the system also are being pursued (C. Black et al., this meeting). Our progress toward understanding this simple system will be reported, as will the implications of our results for the dynamic activity associated with coronal current sheets and for general multiscale modeling of magnetized plasmas in the Heliosphere. Our research was supported by NASA.

  5. Development of alternating current transmitter of detection system for magnetic material in soil subsurface

    NASA Astrophysics Data System (ADS)

    Indrasari, Widyaningrum; Djamal, Mitra; Srigutomo, Wahyu; Ramli

    2016-03-01

    Generally, detection system for magnetic material in soil subsurface using electromagnetic induction method consists of two parts, they are transmitter and receiver unit. A transmitter must be able to produce a continuous and stable AC current at a certain frequency, meanwhile receiver should be able to catch the secondary magnetic field of magnetic material in soil subsurface. The aim of this study was to develop a new AC current transmitter of detection system for the magnetic material in soil subsurface. This paper will describe the results of the development of AC current transmitter systems, distance characterization of the sensor detection toward horizontal solenoid positions, and characterization of magnetic material in the soil subsurface. It has successfully made the AC current transmitter system, composed of a sinusoidal signal generator, power amplifier, and a source of AC magnetic field. The output of the generator has a frequency varies: 1 kHz, 2 kHz, 5 kHz, and 10 kHz. We found that the AC current transmitter that has been developed able to work properly up to a frequency of 10 kHz.

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

    ERIC Educational Resources Information Center

    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

  7. Fast thermonuclear ignition with two nested high current lower voltage - high voltage lower current magnetically insulated transmission lines

    NASA Astrophysics Data System (ADS)

    Winterberg, F.

    2003-11-01

    Fast thermonuclear ignition with a high gain seems possible with two Marx generators feeding two nested magnetically insulated transmission lines, one delivering a high current lower voltage pulse for compression and confinement, and one delivering a high voltage lower current pulse for fast ignition. With an input energy conceivably as small as 100 kJ the gain can be as large as 10 3. The concept not only would be by orders of magnitude less expensive than laser compression and fast ignition schemes, but because of the large gain with a small yield also be more suitable for a thermonuclear reactor.

  8. Probing the spin polarization of current by soft x-ray imaging of current-induced magnetic vortex dynamics

    SciTech Connect

    Kasai, Shinya; Fischer, Peter; Im, Mi-Young; Yamada, Keisuke; Nakatani, Yoshinobu; Kobayashi, Kensuke; Kohno, Hiroshi; Ono, Teruo

    2008-12-09

    Time-resolved soft X-ray transmission microscopy is applied to image the current-induced resonant dynamics of the magnetic vortex core realized in a micron-sized Permalloy disk. The high spatial resolution better than 25 nm enables us to observe the resonant motion of the vortex core. The result also provides the spin polarization of the current to be 0.67 {+-} 0.16 for Permalloy by fitting the experimental results with an analytical model in the framework of the spin-transfer torque.

  9. Current Transport and Onset-Related Phenomena in an MPD Thruster Modified by Applied Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Moeller, Robert Carlos

    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 determine whether 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. A new MPDT was developed and operated with quasi-steady 1 ms pulses from 36 kW to 3.3 MW with argon propellant. Three magnetic configurations studied included self-field operation (without external electromagnets) and two applied poloidal magnetic fields. One configuration used magnetic field lines tangential to the anode lip (and intersecting the anode further upstream) and the other created a magnetic cusp intersecting the anode downstream. The influence of the applied fields on the discharge current streamlines, current densities, and key plasma properties (electron temperature, number density, and plasma potential) was studied. Key findings included that the current pattern and current densities redistributed to follow the applied magnetic field lines. Also, the anode fall voltage was substantially reduced with both applied fields over a large range of currents (and eliminated at 8 kA). These results occurred because applied magnetic field lines intersecting the anode provided a high conductivity path and reduced the local electric field required to sustain the radial current densities. The applied fields reduced the amplitude and frequency of the terminal voltage fluctuations (up to 49%) over a broad range of currents and also decreased transients in the ion saturation current, which suggest reduction of current filamentation and surface-eroding anode spots. Additionally, the cusp field reduced mean terminal voltages over the entire range of discharge currents (up to 31%), and the tangential

  10. Dynamic response for Dzyaloshinskii–Moriya interaction on bubble-like magnetic solitons driven by spin-polarized current

    NASA Astrophysics Data System (ADS)

    Chen, Shujun; Zhu, Qiyuan; Zhang, Senfu; Jin, Chendong; Song, Chengkun; Wang, Jianbo; Liu, Qingfang

    2016-05-01

    By using micromagnetic simulations, we studied the dynamic response for different bubble-like magnetic solitons in the [CoPt-CoNi]/Cu/CoNi magnetic multilayer with perpendicular magnetic anisotropy. It is found that a localized spin-polarized current can not only nucleate a dissipative magnetic droplet but also excite the in-plane domain wall (DW) oscillation at the edge of bubble-like magnetic solitons. The dependence of oscillation frequency on current for the dissipative magnetic droplet is hysteretic in the absence of the Dzyaloshinskii–Moriya interactions (DMI). In the presence of DMI, three different bubble-like magnetic solitons are excited: (1) singular magnetic droplet, (2) pseudonormal magnetic droplet, (3) dynamical skyrmion. Meanwhile, the oscillation frequencies of these magnetic solitons have different response as current density varies. These results open up new possibilities for the applications of magnetic soliton-based spin transfer nano-oscillators.

  11. Loading and Unloading Finishing Pigs: Effects of Bedding Types, Ramp Angle, and Bedding Moisture.

    PubMed

    Garcia, Arlene; McGlone, John J

    2014-01-01

    The use of non-slip surfaces during loading and unloading of finishing pigs plays an important role in animal welfare and economics of the pork industry. Currently, the guidelines available only suggest the use of ramps with a slope below 20 degrees to load and unload pigs. However, the total time it takes to load and unload animals and slips, falls, and vocalizations are a welfare concern. Three ramp angles (0, 10 or 20 degrees), five bedding materials (nothing, sand, feed, wood shavings or wheat straw hay), two moistures (dry or wet bedding, >50% moisture) over two seasons (>23.9 °C summer, <23.9 °C winter) were assessed for slips/falls/vocalizations (n = 2400 pig observations) and analyzed with a scoring system. The use of bedding during summer or winter played a role in the total time it took to load and unload the ramp (p < 0.05). Bedding, bedding moisture, season, and slope significantly interacted to impact the total time to load and unload finishing pigs (p < 0.05). Heart rate and the total time it took to load and unload the ramp increased as the slope of the ramp increased (p < 0.05). Heart rates were higher during the summer than winter, and summer heart rates increased as the slope increased (p < 0.05). The current study suggests that several factors should be considered in combination to identify the appropriate bedding for the specific occasion. PMID:26479134

  12. 9 CFR 313.1 - Livestock pens, driveways and ramps.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 9 Animals and Animal Products 2 2010-01-01 2010-01-01 false Livestock pens, driveways and ramps... INSPECTION AND CERTIFICATION HUMANE SLAUGHTER OF LIVESTOCK § 313.1 Livestock pens, driveways and ramps. (a) Livestock pens, driveways and ramps shall be maintained in good repair. They shall be free from sharp...

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

    SciTech Connect

    Ivanov, V. V.; Anderson, A. A.; Astanovitskiy, A. L.; Nalajala, V.; Dmitriev, O.; Papp, D.

    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.

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

    NASA Astrophysics Data System (ADS)

    von der Linden, Jens; You, Setthivoine

    2015-11-01

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

  15. On the Role of Global Magnetic Field Configuration in Affecting Ring Current Dynamics

    NASA Technical Reports Server (NTRS)

    Zheng, Y.; Zaharia, S. G.; Fok, M. H.

    2010-01-01

    Plasma and field interaction is one important aspect of inner magnetospheric physics. The magnetic field controls particle motion through gradient, curvature drifts and E cross B drift. In this presentation, we show how the global magnetic field affects dynamics of the ring current through simulations of two moderate geomagnetic storms (20 November 2007 and 8-9 March 2008). Preliminary results of coupling the Comprehensive Ring Current Model (CRCM) with a three-dimensional plasma force balance code (to achieve self-consistency in both E and B fields) indicate that inclusion of self-consistency in B tends to mitigate the intensification of the ring current as other similar coupling efforts have shown. In our approach, self-consistency in the electric field is already an existing capability of the CRCM. The magnetic self-consistency is achieved by computing the three-dimensional magnetic field in force balance with anisotropic ring current ion distributions. We discuss the coupling methodology and its further improvement. In addition, comparative studies by using various magnetic field models will be shown. Simulation results will be put into a global context by analyzing the morphology of the ring current, its anisotropy and characteristics ofthe interconnected region 2 field-aligned currents.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    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 characterising 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.

  17. Current singularities at quasi-separatrix layers and three-dimensional magnetic nulls

    SciTech Connect

    Craig, I. J. D.; Effenberger, Frederic

    2014-11-10

    The open problem of how singular current structures form in line-tied, three-dimensional magnetic fields is addressed. A Lagrangian magneto-frictional relaxation method is employed to model the field evolution toward the final near-singular state. Our starting point is an exact force-free solution of the governing magnetohydrodynamic equations that is sufficiently general to allow for topological features like magnetic nulls to be inside or outside the computational domain, depending on a simple set of parameters. Quasi-separatrix layers (QSLs) are present in these structures and, together with the magnetic nulls, they significantly influence the accumulation of current. It is shown that perturbations affecting the lateral boundaries of the configuration lead not only to collapse around the magnetic null but also to significant QSL currents. Our results show that once a magnetic null is present, the developing currents are always attracted to that specific location and show a much stronger scaling with resolution than the currents that form along the QSL. In particular, the null-point scalings can be consistent with models of 'fast' reconnection. The QSL currents also appear to be unbounded but give rise to weaker singularities, independent of the perturbation amplitude.

  18. Drain Current Modulation of a Single Drain MOSFET by Lorentz Force for Magnetic Sensing Application.

    PubMed

    Chatterjee, Prasenjit; Chow, Hwang-Cherng; Feng, Wu-Shiung

    2016-01-01

    This paper reports a detailed analysis of the drain current modulation of a single-drain normal-gate n channel metal-oxide semiconductor field effect transistor (n-MOSFET) under an on-chip magnetic field. A single-drain n-MOSFET has been fabricated and placed in the center of a square-shaped metal loop which generates the on-chip magnetic field. The proposed device designed is much smaller in size with respect to the metal loop, which ensures that the generated magnetic field is approximately uniform. The change of drain current and change of bulk current per micron device width has been measured. The result shows that the difference drain current is about 145 µA for the maximum applied magnetic field. Such changes occur from the applied Lorentz force to push out the carriers from the channel. Based on the drain current difference, the change in effective mobility has been detected up to 4.227%. Furthermore, a detailed investigation reveals that the device behavior is quite different in subthreshold and saturation region. A change of 50.24 µA bulk current has also been measured. Finally, the device has been verified for use as a magnetic sensor with sensitivity 4.084% (29.6 T(-1)), which is very effective as compared to other previously reported works for a single device. PMID:27589747

  19. Alternating current loss reduction for rectangular busbars by covering their edges with low permeable magnetic caps

    NASA Astrophysics Data System (ADS)

    Sasada, Ichiro

    2014-05-01

    A method to reduce ac conductive losses in a thin rectangular busbar made of copper is presented. The method is based on a technique, which makes the distribution of the ac current in the cross section of a busbar flatter. Edges of a thin busbar are covered with low permeability magnetic thin layers as caps. The magnetic cap makes the impedance experienced by the current flowing near the edge comparatively larger so that currents cannot get crowded near the edges of a busbar. This method is numerically verified.

  20. Alternating current loss reduction for rectangular busbars by covering their edges with low permeable magnetic caps

    SciTech Connect

    Sasada, Ichiro

    2014-05-07

    A method to reduce ac conductive losses in a thin rectangular busbar made of copper is presented. The method is based on a technique, which makes the distribution of the ac current in the cross section of a busbar flatter. Edges of a thin busbar are covered with low permeability magnetic thin layers as caps. The magnetic cap makes the impedance experienced by the current flowing near the edge comparatively larger so that currents cannot get crowded near the edges of a busbar. This method is numerically verified.

  1. Hall current effect on tearing mode instability. [possible cause of magnetic field reconnection in space

    NASA Technical Reports Server (NTRS)

    Terasawa, T.

    1983-01-01

    From a linear 2-D eigenmode analysis, it is found that the Hall current effect on collisional tearing mode instability becomes important for the thin magnetic reversal layer whose width is comparable to the ion inertia length; Hall currents produce a three-dimensional field structure and increase the reconnection (growth) rate. Since the magnetaic reversal layer widths both in the magnetopause and in the magnetotail are reported to become as thin as the ion inertial length (several hundred km) when the reconnection process is supposed to occur, the Hall current effect may explain the appearance of the dawn-dusk component of the magnetic field in the magnetotail reconnection region.

  2. Magnetic Field Observations of Partial Ring Current during Storm Recovery Phase

    NASA Technical Reports Server (NTRS)

    Le, G.; Russell, C. T.; Slavin, J. A.; Lucek, E. A.

    2008-01-01

    We present results of an extensive survey of the magnetic field observations in the inner magnetosphere using 30 years of magnetospheric magnetic field data from Polar, Cluster, ISEE, and AMPTE/CCE missions. The purpose of this study is to understand the magnetic field evolution during the recovery phase of geomagnetic storms, and its implication to the ring current recovery and loss mechanisms of ring current particles. It is now commonly believed that a strong partial ring current is formed during the storm main phase due to the enhanced earthward convection of energetic ions from nightside plasma sheet. But the presence of a strong partial ring current throughout the recovery phase remains controversial. The magnetic field generated by the ring current inflates the inner magnetosphere and causes magnetic field depressions in the equatorial magnetosphere. During the storm recovery phase, we find that the distribution of the equatorial magnetic field depression exhibits similar local time dependence as the ring current distribution obtained from the combined dataset in the earlier study. It shows that a strong partial ring current is a permanent feature throughout the recovery phase. In the early recovery phase, the partial ring current peaks near the dusk terminator as indicated by the peak of the magnetic field depression. As the recovery phase progresses, the partial ring current decays most quickly near the dusk and results in a dusk-to-midnight moving of the peak of the partial ring current. Thus the loss mechanisms work most effectively near the dusk. The magnetic field depression increases the gyroradius of ring current protons to a scale greater or comparable to the thickness of the magnetopause, which increases the chance of ion drift loss near the dusk magnetopause at larger L-shell (L greater than 5). But the drift loss mechanism alone cannot explain the loss of ring current ions especially in the smaller L-shell (L less than 5). The precipitation loss

  3. One-pion exchange current effects on magnetic form factor in the relativistic formalism

    NASA Astrophysics Data System (ADS)

    Zhang, Cun; Liu, Jian; Ren, Zhongzhou

    2016-08-01

    One-pion exchange current effects on the magnetic form factors of some odd nuclei are studied in the relativistic formalism. The Dirac wave functions of nucleons are calculated from the relativistic mean-field theory. After fitting to experimental data by quenching factors, it is found that taking the one-pion exchange currents into account gives a better description of the magnetic form factor. The root-mean-square radii of the valance nucleon orbits are also calculated in RMF model, which coincide with experimental radii extracted with meson exchange current corrections.

  4. Development of internal magnetic probe for current density profile measurement in Versatile Experiment Spherical Torus

    NASA Astrophysics Data System (ADS)

    Yang, J.; Lee, J. W.; Jung, B. K.; Chung, K. J.; Hwang, Y. S.

    2014-11-01

    An internal magnetic probe using Hall sensors to measure a current density profile directly with perturbation of less than 10% to the plasma current is successfully operated for the first time in Versatile Experiment Spherical Torus (VEST). An appropriate Hall sensor is chosen to produce sufficient signals for VEST magnetic field while maintaining the small size of 10 mm in outer diameter. Temperature around the Hall sensor in a typical VEST plasma is regulated by blown air of 2 bars. First measurement of 60 kA VEST ohmic discharge shows a reasonable agreement with the total plasma current measured by Rogowski coil in VEST.

  5. Periodic magnetic structures generated by spin–polarized currents in nanostripes

    SciTech Connect

    Volkov, Oleksii M. Sheka, Denis D.; Kravchuk, Volodymyr P.; Gaididei, Yuri; Mertens, Franz G.

    2013-11-25

    The influence of a transverse spin–polarized current on long ferromagnetic nanostripes is studied numerically. The magnetization behavior is analyzed for all range of the applied currents, up to the saturation. It is shown that the saturation current is a nonmonotonic function of the stripe width. A number of stable periodic magnetization structures are observed below the saturation. Type of the periodical structure depends on the stripe width. Besides the one–dimensional domain structure, typical for narrow wires, and the two–dimensional vortex–antivortex lattice, typical for wide films, a number of intermediate structures are observed, e.g., cross–tie and diamond state.

  6. Global current profile effects on the evolution and saturation of magnetic islands

    SciTech Connect

    Poye, A.; Agullo, O.; Benkadda, S.; Smolyakov, A.; Garbet, X.

    2013-02-15

    The nonlinear evolution of magnetic islands is investigated by means of numerical simulations. The growth and saturation of the island are shown to depend not only on asymptotic tearing mode stability parameter {Delta}{sup Prime} but also on the initial global current profile. Presence of the external current sheets leads to the formation of different island state for the same value of {Delta}{sup Prime }. It is found that the flow vorticity generated by the interacting current sheets is an important feature of nonlocal interactions and nonlocal effects in magnetic islands dynamics.

  7. Island-induced bootstrap current on the saturation of a thin magnetic island in tokamaks

    SciTech Connect

    Shaing, K. C.

    2007-04-15

    It is shown that island-induced bootstrap current density, which results from the symmetry breaking of the vertical bar B vertical bar when an island is embedded in the equilibrium magnetic field B, modifies the evolution equation and the saturation level for a thin magnetic island in tokamaks. This modification is independent of the fraction of the equilibrium bootstrap current density. It is found that island-induced bootstrap current density increases the saturation level for modes with positive values of {delta}{sup '}. Here, {delta}{sup '} is the stability parameter for the linear tearing modes.

  8. Current-induced rotational torques in the skyrmion lattice phase of chiral magnets

    SciTech Connect

    Everschor, Karin; Garst, Markus; Rosch, Achim; Duine, R. A.

    2011-08-01

    In chiral magnets without inversion symmetry, the magnetic structure can form a lattice of magnetic whirl lines, a two-dimensional skyrmion lattice, stabilized by spin-orbit interactions in a small range of temperatures and magnetic fields. The twist of the magnetization within this phase gives rise to an efficient coupling of macroscopic magnetic domains to spin currents. We analyze the resulting spin-transfer effects, and, in particular, focus on the current-induced rotation of the magnetic texture by an angle. Such a rotation can arise from macroscopic temperature gradients in the system as has recently been shown experimentally and theoretically. Here we investigate an alternative mechanism, where small distortions of the skyrmion lattice and the transfer of angular momentum to the underlying atomic lattice play the key role. We employ the Landau-Lifshitz-Gilbert equation and adapt the Thiele method to derive an effective equation of motion for the rotational degree of freedom. We discuss the dependence of the rotation angle on the orientation of the applied magnetic field and the distance to the phase transition.

  9. Dilute plasma coupling currents to a high voltage solar array in weak magnetic fields

    NASA Technical Reports Server (NTRS)

    Grier, N. T.

    1984-01-01

    The plasma coupling current to an approximately 2000 sq cm array was measured for externally biased positive and negative voltages on the array to 1000 V in applied magnetic field strengths from 0 to 0.93 G. The plasma density varied from 2,000 to 1.3 million electrons/cu cm. It was found that the magnetic field primarily increased the plasma coupling current for negative biases. For positive bias, the current could increase or decrease depending on the voltage, field strength, and plasma density. It was also found that the plasma coupling current was not very sensitive to how the plane of the array was oriented relative to the magnetic field.

  10. AC current distribution and losses in multifilamentary superconductors exposed to longitudinal magnetic field

    SciTech Connect

    Le Naour, S.; Lacaze, A.; Laumond, Y.; Estop, P.; Verhaege, T.

    1996-07-01

    The current distribution and also AC losses, in a multifilamentary superconductor carrying a transport current, are influenced by the self and the external magnetic field. By using the Maxwell equations, a model has been developed in order to calculate the temporal evolution of current distribution in a single wire exposed or not to external magnetic field. This model is based on the actual relationship of electrical field E with current density J and takes into account the twist pitch of the wire. AC losses are calculated by adding all local losses through the cross section. This paper presents calculations of the influence of the cable twist coupled with the longitudinal magnetic field, and also gives some ideas how to decrease losses.

  11. Imaging of inhomogeneous magnetization and currents coupled with anomalous transport properties in manganites

    NASA Astrophysics Data System (ADS)

    Tokunaga, M.; Song, H.; Tokunaga, Y.; Tamegai, T.

    2006-05-01

    Using magneto-optical imaging technique, real-space distributions of magnetic fields are visualized in images of a polarized-light microscope. Application of this technique to crystals of (La1-z Prz )0.7Ca0.3MnO3 (z = 0.7) and Nd0.5Ca0.5Mn1-y Cry O3 (y = 0.03) revealed inhomogeneous magnetization and currents in the phase-separated states into ferromagnetic metal and antiferromagnetic insulator. Increase of the transport current switches this inhomogeneous current flow to homogeneous one concomitantly with abrupt increase in resistivity. Using magnetic field dependence of this switching phenomenon, operation fields for colossal magnetoresistance effects can be significantly reduced. Empirical relation between the magnitude of bias currents and transition fields is provided.

  12. Plasma jets subject to adjustable current polarities and external magnetic fields

    NASA Astrophysics Data System (ADS)

    Byvank, Tom; Schrafel, Peter; Gourdain, Pierre; Seyler, Charles; Kusse, Bruce

    2014-12-01

    In the present research, collimated plasma jets form from ablation of a radial foil (Al 20 μm thin disk) using a pulsed power generator (COBRA) with 1 MA peak current and 100 ns rise time. Plasma dynamics of the jet are diagnosed with and without an applied uniform axial magnetic field (1 T) and under a change of current polarities, which correspond to current moving either radially outward or inward from the foil's central axis. Experimental results are compared with numerical simulations (PERSEUS). The influence of the Hall effect on the jet development is observed under opposite current polarities. Additionally, the magnetic field compression within the jet is examined. Further studies will compare the laboratory-generated plasma jets and astrophysical jets with embedded magnetic fields.

  13. Magnetic thin-film split-domain current sensor-recorder

    DOEpatents

    Hsieh, Edmund J.

    1979-01-01

    A sensor-recorder for recording a representation of the direction and peak amplitude of a transient current. A magnetic thin film is coated on a glass substrate under the influence of a magnetic field so that the finished film is magnetically uniaxial and anisotropic. The film is split into two oppositely magnetized contiguous domains with a central boundary by subjecting adjacent portions of the film simultaneously to magnetic fields that are opposed 180.degree.. With the split-domain sensor-recorder placed with the film plane and domain boundary either perpendicular or parallel to the expected conductive path of a transient current, the occurrence of the transient causes switching of a portion of one domain to the direction of the other domain. The amount of the switched domain portion is indicative of the amplitude of the peak current of the transient, while the particular domain that is switched is indicative of the direction of the current. The resulting domain patterns may be read with a passive magnetic tape viewer.

  14. Magnetic Diagnostics for Equilibrium Reconstructions in the Presence of Nonaxisymmetric Eddy Current Distributions in Tokamaks

    SciTech Connect

    Kaita, R.; Kozub, T.; Logan, N.; Majeski, R.; Menard, J.; Zakharov, L.

    2010-12-10

    The lithium tokamak experiment LTX is a modest-sized spherical tokamak R0=0.4 m and a =0.26 m designed to investigate the low-recycling lithium wall operating regime for magnetically confined plasmas. LTX will reach this regime through a lithium-coated shell internal to the vacuum vessel, conformal to the plasma last-closed-flux surface, and heated to 300-400 oC. This structure is highly conductive and not axisymmetric. The three-dimensional nature of the shell causes the eddy currents and magnetic fields to be three-dimensional as well. In order to analyze the plasma equilibrium in the presence of three-dimensional eddy currents, an extensive array of unique magnetic diagnostics has been implemented. Sensors are designed to survive high temperatures and incidental contact with lithium and provide data on toroidal asymmetries as well as full coverage of the poloidal cross-section. The magnetic array has been utilized to determine the effects of nonaxisymmetric eddy currents and to model the start-up phase of LTX. Measurements from the magnetic array, coupled with two-dimensional field component modeling, have allowed a suitable field null and initial plasma current to be produced. For full magnetic reconstructions, a three-dimensional electromagnetic model of the vacuum vessel and shell is under development.

  15. Magnetic diagnostics for equilibrium reconstructions in the presence of nonaxisymmetric eddy current distributions in tokamaks (invited)

    SciTech Connect

    Berzak, L.; Jones, A. D.; Kaita, R.; Kozub, T.; Logan, N.; Majeski, R.; Menard, J.; Zakharov, L.

    2010-10-15

    The lithium tokamak experiment (LTX) is a modest-sized spherical tokamak (R{sub 0}=0.4 m and a=0.26 m) designed to investigate the low-recycling lithium wall operating regime for magnetically confined plasmas. LTX will reach this regime through a lithium-coated shell internal to the vacuum vessel, conformal to the plasma last-closed-flux surface, and heated to 300-400 deg. C. This structure is highly conductive and not axisymmetric. The three-dimensional nature of the shell causes the eddy currents and magnetic fields to be three-dimensional as well. In order to analyze the plasma equilibrium in the presence of three-dimensional eddy currents, an extensive array of unique magnetic diagnostics has been implemented. Sensors are designed to survive high temperatures and incidental contact with lithium and provide data on toroidal asymmetries as well as full coverage of the poloidal cross-section. The magnetic array has been utilized to determine the effects of nonaxisymmetric eddy currents and to model the start-up phase of LTX. Measurements from the magnetic array, coupled with two-dimensional field component modeling, have allowed a suitable field null and initial plasma current to be produced. For full magnetic reconstructions, a three-dimensional electromagnetic model of the vacuum vessel and shell is under development.

  16. A coronal magnetic field model with horizontal volume and sheet currents

    NASA Technical Reports Server (NTRS)

    Zhao, Xuepu; Hoeksema, J. Todd

    1994-01-01

    When globally mapping the observed photospheric magnetic field into the corona, the interaction of the solar wind and magnetic field has been treated either by imposing source surface boundary conditions that tacitly require volume currents outside the source surface or by limiting the interaction to thin current sheets between oppositely directed field regions. Yet observations and numerical Magnetohydrodynamic (MHD) calculations suggest the presence of non-force-free volume currents throughout the corona as well as thin current sheets in the neighborhoods of the interfaces between closed and open field lines or between oppositely directed open field lines surrounding coronal helmet-streamer structures. This work presents a model including both horizontal volume currents and streamer sheet currents. The present model builds on the magnetostatic equilibria developed by Bogdan and Low and the current-sheet modeling technique developed by Schatten. The calculation uses synoptic charts of the line-of-sight component of the photospheric magnetic field measured at the Wilcox Solar Observatory. Comparison of an MHD model with the calculated model results for the case of a dipole field and comparison of eclipse observations with calculations for CR 1647 (near solar minimum) show that this horizontal current-current-sheet model reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces coro nal helmet structures better than the current-sheet model.

  17. On the relationship between morning sector irregular magnetic pulsations and field aligned currents

    NASA Technical Reports Server (NTRS)

    Engebretson, M. J.; Cahill, L. J., Jr.; Potemra, T. A.; Zanetti, L. J.; Arnoldy, R. L.; Mende, S. B.; Rosenberg, T. J.

    1984-01-01

    For three magnetically disturbed days in early 1980, data from south polar masses of the Magsat satellite are compared with data from search coil magnetometer, riometer, and photometer instrumentation at Siple, Antarctica. It is found that during each Magsat polar pass in the morning sector, the level of Pi 1 activity correlates well with the intensities of three-dimensional current systems. Fine structure is often observed in the field-aligned currents during periods of intense Pi activity. Among the Birkeland currents are 2-s to 10-s (16-80 km) structured perturbations; these are evident in the transverse components of the field and are thought to indicate filamentary currents. Pi 1 amplitudes are found to be considerably larger when region 2 Birkeland currents are overhead than when they are not. In one case, detailed features are identified in the high-resolution Magsat magnetic field data that may be current fluctuations related to asymmetric Pi 1.

  18. Magnetic field line reconnection experiments. V - Current disruptions and double layers

    NASA Technical Reports Server (NTRS)

    Stenzel, R. L.; Gekelman, W.; Wild, N.

    1983-01-01

    An investigation is conducted of the stability of a large laboratory plasma current sheet, which has been generated in the process of magnetic field line reconnection, with respect to local current increases. Magnetic flux variations in regions remote from the current sheet generate an inductive voltage in the current loop that drops off inside the plasma in the form of a potential double layer, leading to particle acceleration with velocities much larger than those expected from the steady state electric fields in the plasma. A model for the mechanism of the current disruptions is formulated in which the potential structure leads to ion expulsion, creating a localized density drop. The associated current drop in an inductive circuit drives the potential structure, providing feedback for the disruptive instability. Similarities to, and differences from, magnetospheric substorm phenomena are noted.

  19. Magnetization dynamics under heat current in metallic spin valves and in insulators

    NASA Astrophysics Data System (ADS)

    Yu, Haiming

    Spin caloritronics, an emerging branch of spintronics, studying the addition of thermal effects to the electrical and magnetic properties of nanostructures, has recently seen a rapid development. It has been predicted by Hatami et al. that a heat current can exert a spin torque on the magnetization in a nanostructure, analogous to the well-known spin-transfer torque induced by an electrical current. We provided the experimental evidence for the thermal spin-transfer torque effect in spin valves, showing the switching field change with heat current. I will present measurements of the second harmonic voltage response of Co-Cu-Co pseudo-spinvalves deposited in the middle of Cu nanowires. Both the magnitude of the second harmonic response of the spin valve and the field value of the maximum response are found to be dependent on the heat current. Both effects show that the magnetization dynamics of the pseudo-spinvalves is influenced by the heat current. Thus, the data provide a quantitative estimate of the thermal spin torque exerted on the magnetization of the Co layers. In addition, I will present recent study on the magnetization dynamics in a magnetic insulator YIG film under in-plane heat current. The ferromagnetic resonance linewidth is found to be tuned by the applied temperature gradient, i.e. narrowing and broadening. This suggests that the Gilbert damping parameter is compensated or reinforced by the applied temperature gradient in respective direction. These observations can be understood as a heat-driven spin torque in magnetic insulators.

  20. Continuous critical current measurement of high-temperature superconductor tapes with magnetic substrates using magnetic-circuit method.

    PubMed

    Zou, S N; Gu, C; Qu, T M; Han, Z

    2013-10-01

    The critical current (I(c)) of high-temperature superconductor (HTS) tapes has to be examined not only for short samples, but also for the entire tape, because local weak points can possibly lead to the quenching of the whole HTS device. Some methods were reported for continuous I(c) measurement along the length of a HTS tape, but few of them were applicable to tapes with magnetic substrates represented by YBa2Cu3O(7-δ)(YBCO)-coated conductors based on Ni5W alloy substrate by rolling assisted bi-axially textured substrate process. We previously presented a contact-free method using magnetic circuits to measure I(c) continuously of long HTS tapes, namely the magnetic-circuit (MC) method. This method has been previously applied with high speed and resolution to measure I(c) of HTS tapes with non-magnetic substrates, due to its resistance to noise aroused by mechanical vibration. In this work, its ability to measure HTS tapes with magnetic substrates is demonstrated both theoretically and experimentally. A 100 m long commercial YBCO tape based on Ni5W alloy substrate was measured and regular I(c) fluctuations were discovered. The MC method can be a powerful tool for quality control of HTS tapes, especially for tapes with magnetic substrates. PMID:24182162

  1. High-Resolution SQUID imaging of Magnetic Fields Generated by Propagating Cardiac Action Currents

    NASA Astrophysics Data System (ADS)

    Holzer, Jenny R.; Sidorov, Veniamin; Fong, Luis; Peters, Nicholas; Baudenbacher, Petra; Baudenbacher, Franz

    2004-03-01

    The heart's magnetic field is exquisitely sensitive to anisotropy ratios in the cardiac bidomain model; Therefore, magnetic imaging of cardiac action currents is an ideally suited technique for testing the accuracy of cardiac models and elucidating the effects of anisotropy in the spread of stimulus and action currents. We mapped the magnetocardiogram (MCG) as a function of position over a 10mm x 10mm area of the left ventricle of a Langendorff perfused isolated rabbit heart using high-resolution scanning SQUID microscopy and epi-fluorescent imaging with a high speed CCD camera and the transmembrane voltage sensitive dye di-4-ANEPPS. The combination of these two methods allowed us to map the transmembrane potential, the magnetic field, and consequently the total current, over the same area. The MCGs were combined to produce a time series of 2D field maps that show a clear octupolar pattern during the cathodal current injection, a similar pattern with a reversal of currents immediately after terminating the stimulus, and the generation and propagation of an elliptical action current wave front. The observed patterns are in agreement with predictions using a bidomain model. Our high-resolution SQUID images have confirmed that unequal anisotropies in the intra- and extracellular spaces must be considered to explain the magnetic field associated with action current propagation However, a realistic cardiac bidomain model incorporating fiber rotation, cleavage planes, and tissue heterogeneities are required to reproduce the complete experimental observations.

  2. Dynamics of Dirac strings and monopolelike excitations in chiral magnets under a current drive

    DOE PAGESBeta

    Lin, Shi -Zeng; Saxena, Avadh

    2016-02-10

    Skyrmion lines in metallic chiral magnets carry an emergent magnetic field experienced by the conduction electrons. The inflow and outflow of this field across a closed surface is not necessarily equal, thus it allows for the existence of emergent monopoles. One example is a segment of skyrmion line inside a crystal, where a monopole and antimonopole pair is connected by the emergent magnetic flux line. This is a realization of Dirac stringlike excitations. Here we study the dynamics of monopoles in chiral magnets under an electric current. We show that in the process of creation of skyrmion lines, skyrmion linemore » segments are first created via the proliferation of monopoles and antimonopoles. Then these line segments join and span the whole system through the annihilation of monopoles. The skyrmion lines are destroyed via the proliferation of monopoles and antimonopoles at high currents, resulting in a chiral liquid phase. We also propose to create the monopoles in a controlled way by applying an inhomogeneous current to a crystal. Remarkably, an electric field component in the magnetic field direction proportional to the current squared in the low current region is induced by the motion of distorted skyrmion lines, in addition to the Hall and longitudinal voltage. As a result, the existence of monopoles can be inferred from transport or imaging measurements.« less

  3. Dynamics of Dirac strings and monopolelike excitations in chiral magnets under a current drive

    NASA Astrophysics Data System (ADS)

    Lin, Shi-Zeng; Saxena, Avadh

    2016-02-01

    Skyrmion lines in metallic chiral magnets carry an emergent magnetic field experienced by the conduction electrons. The inflow and outflow of this field across a closed surface is not necessarily equal, thus it allows for the existence of emergent monopoles. One example is a segment of skyrmion line inside a crystal, where a monopole and antimonopole pair is connected by the emergent magnetic flux line. This is a realization of Dirac stringlike excitations. Here we study the dynamics of monopoles in chiral magnets under an electric current. We show that in the process of creation of skyrmion lines, skyrmion line segments are first created via the proliferation of monopoles and antimonopoles. Then these line segments join and span the whole system through the annihilation of monopoles. The skyrmion lines are destroyed via the proliferation of monopoles and antimonopoles at high currents, resulting in a chiral liquid phase. We also propose to create the monopoles in a controlled way by applying an inhomogeneous current to a crystal. Remarkably, an electric field component in the magnetic field direction proportional to the current squared in the low current region is induced by the motion of distorted skyrmion lines, in addition to the Hall and longitudinal voltage. The existence of monopoles can be inferred from transport or imaging measurements.

  4. Spin-polarized current of a transistor in single Mn12 molecular magnets.

    PubMed

    Park, Joonho; Yang, Heok; Park, K S; Lee, Eok-Kyun

    2007-11-01

    Focusing on the framework of how to realize the molecular spintronics in a single molecular magnet, we present theoretical studies on the spin-polarized quantum transport behavior through a single Mn12 molecular magnet. Our theoretical results were obtained by carrying out density functional theoretical calculation within the Keldysh nonequilibrium Green function formalism. The ultimate goal of the molecular spintronics is to develop single molecule transistors which generate spin-polarized currents through the molecular magnet. We obtained the density of states, the transmission coefficients and the characteristic features of the current-voltage (I-V) on the spin-polarized transport properties of Mn12 by the theoretical calculation. These results show the possibility for the realization of molecular spintroinics using single molecular magnets. PMID:18047130

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

    NASA Astrophysics Data System (ADS)

    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.

  6. Pb/InAs nanowire josephson junction with high critical current and magnetic flux focusing.

    PubMed

    Paajaste, J; Amado, M; Roddaro, S; Bergeret, F S; Ercolani, D; Sorba, L; Giazotto, F

    2015-03-11

    We have studied mesoscopic Josephson junctions formed by highly n-doped InAs nanowires and superconducting Ti/Pb source and drain leads. The current-voltage properties of the system are investigated by varying temperature and external out-of-plane magnetic field. Superconductivity in the Pb electrodes persists up to ∼7 K and with magnetic field values up to 0.4 T. Josephson coupling at zero backgate voltage is observed up to 4.5 K and the critical current is measured to be as high as 615 nA. The supercurrent suppression as a function of the magnetic field reveals a diffraction pattern that is explained by a strong magnetic flux focusing provided by the superconducting electrodes forming the junction. PMID:25671540

  7. Enhanced current quantization in high-frequency electron pumps in a perpendicular magnetic field

    SciTech Connect

    Wright, S. J.; Blumenthal, M. D.; Gumbs, Godfrey; Thorn, A. L.; Pepper, M.; Anderson, D.; Jones, G. A. C.; Nicoll, C. A.; Ritchie, D. A.; Janssen, T. J. B. M.; Holmes, S. N.

    2008-12-15

    We present experimental results of high-frequency quantized charge pumping through a quantum dot formed by the electric field arising from applied voltages in a GaAs/AlGaAs system in the presence of a perpendicular magnetic field B. Clear changes are observed in the quantized current plateaus as a function of applied magnetic field. We report on the robustness in the length of the quantized plateaus and improvements in the quantization as a result of the applied B field.

  8. Comparisons of Simulated and Observed Stormtime Magnetic Intensities and Ion Densities in the Ring Current

    NASA Astrophysics Data System (ADS)

    Chen, M. W.; Guild, T. B.; Lemon, C. L.; Schulz, M.

    2008-12-01

    Recent progress in ring current and plasma sheet modeling has shown the importance of a self-consistent treatment of particle transport and magnetic and electric fields in the inner magnetosphere. For example, the feedback of the ring current tends to mitigate the build-up of the asymmetric ring current and associated magnetic depressions during storm main phase. Models with and without self-consistency can lead to significantly different magnitudes and spatial distributions of plasma pressure and magnetic intensity during disturbed times. In this study we compare simulated and observed stormtime magnetic intensities and ion densities at geosynchronous altitude to test how well self-consistent simulations can simultaneously reproduce these quantities. We simulate the ring current and plasma sheet for conditions corresponding to the 12-14 August 2000 storm using the self-consistent Rice Convection Model-Equilibrium (RCM-E) [ Lemon et al., JGR, 2004]. Using the empirical IMF-dependent model of Tsyganenko and Mukai [JGR, 2003], we specify the plasma sheet pressure and density at 10 RE as the plasma boundary location in the RCM- E. We compare the simulated magnetic intensity at geosynchronous altitude (6.6 RE) with the magnetic intensity measured by magnetometers on the GOES G8, G10, and G11 satellites. The simulated ion densities at different magnetic local times are compared with those from the re-analysis model of LANL/MPA densities of O'Brien and Lemon [Space Weather, 2007]. This is a first step towards a more extensive comparison that will include other datasets, such as ion and magnetic field data from Polar, at locations closer to the Earth than geosynchronous altitude.

  9. Fast magnetic reconnection in thin current sheets: effects of different current profiles and electron inertia in Ohm's law.

    NASA Astrophysics Data System (ADS)

    Pucci, Fulvia; Del Sarto, Daniele; Tenerani, Anna; Velli, Marco

    2015-04-01

    By examining sheets with thicknesses scaling as different powers of the Lundquist number S, we previously showed (Pucci and Velli, 2014) that the growth rate of the tearing mode increases as current sheets thin and, once the inverse aspect ratio reaches a scaling a/L = S-1/3, the time-scale for the instability to develop becomes of the order of the Alfvén time. That means that a fast instability sets in well before Sweet-Parker type current sheets can form. In addition, such an instability produces many islands in the sheet, leading to fast nonlinear evolution and most probably a turbulent disruption of the sheet itself. This has fundamental implications for magnetically driven reconnection throughout the corona, and in particular for coronal heating and the triggering of coronal mass ejections. Here we extend the study of reconnection instabilities to magnetic fields of grater complexity, displaying different current structures such as, for example, multiple or asymmetric current layers. We also consider the possibility of a Δ' dependence on wave-number k-p for different values of p, studying analogies and variations of the trigger scaling relation a/L ~ S-1/3 with respect to the Harris current sheet equilibrium. At large Lundquist numbers in typical Heliospheric plasmas kinetic effects become more important in Ohm's law: we consider the effects of electron skin depth reconnection, showing that we can define a trigger relation similar to the resistive case. The results are important to the transition to fast reconnection in the solar corona, solar wind, magnetosphere as well as laboratory plasmas. F. Pucci and M. Velli, "Reconnection of quasi-singular current sheets: the 'ideal" tearing mode" ApJ 780:L19, 2014.

  10. Particle Diffusion in Chaotic Magnetic Fields Generated by Asymmetric Current Configurations

    NASA Astrophysics Data System (ADS)

    Ram, A. K.; Dasgupta, B.

    2008-12-01

    The observed cross-field diffusion of charged particles in cosmic rays is assumed to be due to the chaotic nature of the interplanetary/intergalactic magnetic fields. Among the classic works on this subject have been those of Parker [1] and Jokipii [2]. Parker considered the passage of cosmic ray particles and energetic solar particles in a large scale magnetic field containing small scale irregularities. In the context of cosmic ray propagation, Jokipii considered a small fluctuating component, added on to a uniform magnetic field, to study the spatial transport of particles. In these studies the irregular component of the magnetic field is prescribed in an ad hoc fashion. In contrast, we consider asymmetric, nonlinear, steady-state magnetic fields, in three spatial dimensions, generated by currents flowing in circular loops and straight lines [3]. These magnetic fields are completely deterministic and, for certain range of parameters, chaotic. We will present analytical and numerical studies on the spatial characteristics of these fields. The motion of charged particles in the nonlinear and chaotic magnetic fields is determined using the Lorentz equation. A particle moving in a deterministic chaotic magnetic field superposed on a uniform background magnetic field is found to undergo spatial transport. This shows that chaotic magnetic fields generated by simple current configurations can produce cross-field diffusion. A detailed analysis of particle motion and diffusion along with application to space plasmas will be presented. [1] E.N. Parker, Planet. Space Sci. 13, 9 (1965). [2] J.R. Jokipii, Astrophys. J. 146, 480 (1966), and J.R. Jokipii, Astrophys. J. 149, 405 (1967). [3] A.K. Ram and B. Dasgupta, Eos Trans. AGU 87 (52), Fall Meet. Suppl. Abstract NG31B-1593 (2006); and Eos Trans. AGU 88 (52), Fall Meet. Suppl. Abstract NG21B-0522 (2007).

  11. Engineering Analysis of Characterization Ramps and Platforms

    SciTech Connect

    BOGER, R.M.

    1999-08-25

    The calculations in Appendix A and B determine the adequacy of the ramps and platforms to accomplish two tasks: (1) Core sampling using the modifications imposed by the use of a FDNW foundation at PFP; and (2) Core sampling within the 200E and 200W Tank Farms without the imposed modifications. The calculations in this document determined that the ramps and platforms are adequate for use with core sampling equipment when sampling either tank 241-2-361 or within 200E or 200W Tank Farms. When sampling tank 241-2-361 the modifications made by ECN 651132 must be implemented. These modifications are the addition of diagonal cross bracing on both the lateral and longitudinal sides. Also, a 1 1/4 inch tie rod must connect both bases of each longitudinal side.

  12. Quantitative analysis of the damping of magnet oscillations by eddy currents in aluminum foil

    NASA Astrophysics Data System (ADS)

    Muiznieks, Andris; Dudareva, Inese

    2012-09-01

    This paper considers damped rotational oscillations about the vertical axis of a cylindrical permanent magnet that is horizontally suspended by a vertical inelastic thread. The damping of the oscillations is caused by eddy currents induced in aluminum foil that is placed horizontally below the magnet. A simplified mathematical model of the damped oscillations is proposed and verified by experiment qualitatively and quantitatively. It is shown that the relative energy loss during one oscillation depends linearly on the number of layers of aluminum foil and on the oscillation period. To measure the relative changes of the oscillation amplitude, a magnetic field sensor and data collection interface are used.

  13. Fluxball magnetic field analysis using a hybrid analytical/FEM/BEM with equivalent currents

    NASA Astrophysics Data System (ADS)

    Fernandes, João F. P.; Camilo, Fernando M.; Machado, V. Maló

    2016-03-01

    In this paper, a fluxball electric machine is analyzed concerning the magnetic flux, force and torque. A novel method is proposed based in a special hybrid FEM/BEM (Finite Element Method/Boundary Element Method) with equivalent currents by using an analytical treatment for the source field determination. The method can be applied to evaluate the magnetic field in axisymmetric problems, in the presence of several magnetic materials. Same results obtained by a commercial Finite Element Analysis tool are presented for validation purposes with the proposed method.

  14. Spin-wave activation by spin-polarized current pulse in magnetic nanopillars

    NASA Astrophysics Data System (ADS)

    Montoncello, Federico; Giovannini, Loris; Nizzoli, Fabrizio; Zivieri, Roberto; Consolo, Giancarlo; Gubbiotti, Gianluca

    2010-08-01

    We demonstrate the role of spin-polarized current pulse in activating only a subset of spin-wave normal modes in laterally confined magnetic systems. In order to derive selection rules based on geometrical considerations, the study was carried out by comparing the results of two different micromagnetic frameworks (a classical finite-difference time-domain scheme and the dynamical matrix method) and considering nanopillar devices of elliptical and circular cross-sections in different magnetic ground states (onion, S, and vortex states). The analogies and the differences existing between the mode activation process driven by spin-torque and that obtained by a magnetic field pulse are also addressed.

  15. Finite element simulation of eddy current problems using magnetic scalar potentials

    NASA Astrophysics Data System (ADS)

    Alonso Rodríguez, Ana; Bertolazzi, Enrico; Ghiloni, Riccardo; Valli, Alberto

    2015-08-01

    We propose a new implementation of the finite element approximation of eddy current problems using, as the principal unknown, the magnetic field. In the non-conducting region a scalar magnetic potential is introduced. The method can deal automatically with any topological configuration of the conducting region and, being based on the search of a scalar magnetic potential in the non-conducting region, has the advantage of making use of a reduced number of unknowns. Several numerical tests are presented for illustrating the performance of the proposed method; in particular, the numerical simulation of a new type of transformer of complicated topological shape is shown.

  16. An eddy current-induced magnetic plucking for piezoelectric energy harvesting

    NASA Astrophysics Data System (ADS)

    Do, Nam Ho; Baek, Yoon Su

    2016-04-01

    Frequency up-conversion is a very efficient method of energy harvesting in order to overcome low, non-periodic, or altered ambient vibration. In order to perform frequency up-conversion and transference of mechanical energy without contact, an eddy current-induced magnetic drag force is used. In this paper, we present a novel configuration of eddy current-induced magnetic plucking for piezoelectric energy harvesting. Our method consists of two permanent magnets, a piezoelectric beam, and a copper disk piece. We design our harvesting method to achieve loading, sudden release, and free vibration using the actuation of the piezoelectric beam through the magnetic mutual coupling between the magnet and copper disk piece. We present the principle of magnetic drag force-generation, characterize the energy harvesting performance of our harvesting method, and demonstrate our harvesting method’s capability of frequency up-conversion and transference of mechanical energy without contact under low, non-periodic, or altered ambient vibration. To that end, we describe the calculation of magnetic drag force with various geometric dimensions and material properties, model of the piezoelectric cantilever beam, comparison between estimation response and measured experiment response, and the measured voltage and power responses.

  17. Exploiting the magnetomechanical interaction for cooling magnetic molecular junctions by spin-polarized currents

    NASA Astrophysics Data System (ADS)

    Brüggemann, J.; Weiss, S.; Nalbach, P.; Thorwart, M.

    2016-02-01

    We present a scheme for cooling a vibrational mode of a magnetic molecular nanojunction by a spin-polarized charge current upon exploiting the interaction between its magnetic moment and the vibration. The spin-polarized charge current polarizes the magnetic moment of the nanoisland, thereby lowering its energy. A small but finite coupling between the vibration and the magnetic moment permits a direct exchange of energy such that vibrational energy can be transferred into the magnetic state. For positive bias voltages, this generates an effective cooling of the molecular vibrational mode. We determine parameter regimes for the cooling of the vibration to be optimal. Although the flowing charge current inevitably heats up the vibrational mode via Ohmic energy losses, we show that due to the magnetomechanical coupling, the vibrational energy (i.e, the effective phonon temperature) can be lowered below 50% of its initial value, when the two leads are polarized anti-parallel. In contrast to the cooling effect for positive bias voltages, net heating of the vibrational mode occurs for negative bias voltages. The cooling effect is enhanced for a stronger anti-parallel magnetic polarization of the leads, while the heating is stronger for a larger parallel polarization. Yet, dynamical cooling is also possible with parallel lead alignments when the two tunneling barriers are asymmetric.

  18. Open-loop correction for an eddy current dominated beam-switching magnet

    SciTech Connect

    Koseki, K. Nakayama, H.; Tawada, M.

    2014-04-15

    A beam-switching magnet and the pulsed power supply it requires have been developed for the Japan Proton Accelerator Research Complex. To switch bunched proton beams, the dipole magnetic field must reach its maximum value within 40 ms. In addition, the field flatness should be less than 5 × 10{sup −4} to guide each bunched beam to the designed orbit. From a magnetic field measurement by using a long search coil, it was found that an eddy current in the thick endplates and laminated core disturbs the rise of the magnetic field. The eddy current also deteriorates the field flatness over the required flat-top period. The measured field flatness was 5 × 10{sup −3}. By using a double-exponential equation to approximate the measured magnetic field, a compensation pattern for the eddy current was calculated. The integrated magnetic field was measured while using the newly developed open-loop compensation system. A field flatness of less than 5 × 10{sup −4}, which is an acceptable value, was achieved.

  19. Critical Currents of MgB2 Wire and Tape in Magnetic Field under Bending Deformations

    NASA Astrophysics Data System (ADS)

    Abin, D. A.; Mineev, N. A.; Osipov, M. A.; Pokrovsky, S. V.; Rudnev, I. A.

    Nowadays MgB2 wires are attractive for designing real devices like motors and magnets. The latest production technologies allow to increase critical current value of wires. However, there is a problem of wire performance degradation under bending strain. Thus, there is a problem of manufacturing solenoids with small diameters, especially from ex situ MgB2 wires produced by powder-in-tube (PIT) technology. In this work, influence of bending on critical current Ic multifilament PIT ex situ MgB2 tape and wire has been studied. Critical current dependencies on external magnetic field Ic(H) were measured at liquid helium temperature in the range of fields from 2.5 T up to 8 T. Measurements were carried out in parallel (H||), and perpendicular (H⊥) orientation of external magnetic field to the sample surface. Voltage current characteristics (V-I) on tape samples were measured with bending on diameters D=30; 40; 60; 70; 80; 90;100 mm. It was shown that critical current density (Jc) decreases by 24% and by 28% for tape and wire respectively with decreasing bending diameter from 100 mm to 60 mm. It was found that the tape still had superconductive properties even with bending diameter D=30 mm, but its Jc decreased by 44% in comparison with Jc(D=100 mm). One more feature that was found is the appearance of resistive component in the voltage current characteristics for all bend diameters in magnetic fields H>3.5 T.

  20. Induced electric current-based formulation in computations of low magnetic Reynolds number magnetohydrodynamic flows

    NASA Astrophysics Data System (ADS)

    Smolentsev, S.; Cuevas, S.; Beltrán, A.

    2010-03-01

    We use the induced electric current as the main electromagnetic variable to compute low magnetic Reynolds number magnetohydrodynamic (MHD) flows. The equation for the induced electric current is derived by taking the curl of the induction equation and using Ampère's law. Boundary conditions on the induced electric current are derived at the interface between the liquid and the thin conducting wall by considering the current loop closing in the wall and the adjacent liquid. These boundary conditions at the liquid-solid interface include the Robin boundary condition for the wall-normal component of the current and an additional equation for the wall potential to compute the tangential current component. The suggested formulation (denominated j-formulation) is applied to three common types of MHD wall-bounded flows by implementing the finite-difference technique: (i) high Hartmann number fully developed flows in a rectangular duct with conducting walls; (ii) quasi-two-dimensional duct flow in the entry into a magnet; and (iii) flow past a magnetic obstacle. Comparisons have been performed against the traditional formulation based on the induced magnetic field ( B-formulation), demonstrating very good agreement.

  1. X-ray detection of transient magnetic moments induced by a spin current in Cu

    SciTech Connect

    Kukreja, R.; Bonetti, S.; Chen, Z.; Backes, D.; Acremann, Y.; Katine, J.; Kent, A. D.; Durr, H. A.; Ohldag, H.; Stohr, J.

    2015-08-24

    We have used a MHz lock-in x-ray spectromicroscopy technique to directly detect changes in magnetic moment of Cu due to spin injection from an adjacent Co layer. The elemental and chemical specificity of x rays allows us to distinguish two spin current induced effects. We detect the creation of transient magnetic moments of 3×10–5μB on Cu atoms within the bulk of the 28 nm thick Cu film due to spin accumulation. The moment value is compared to predictions by Mott’s two current model. We also observe that the hybridization induced existing magnetic moments at the Cu interface atoms are transiently increased by about 10% or 4×10–3μB per atom. As a result, this reveals the dominance of spin-torque alignment over Joule heat induced disorder of the interfacial Cu moments during current flow.

  2. RICHTMYER-MESHKOV-TYPE INSTABILITY OF A CURRENT SHEET IN A RELATIVISTICALLY MAGNETIZED PLASMA

    SciTech Connect

    Inoue, Tsuyoshi

    2012-11-20

    The linear stability of a current sheet that is subject to an impulsive acceleration due to shock passage with the effect of a guide magnetic field is studied. We find that a current sheet embedded in relativistically magnetized plasma always shows a Richtmyer-Meshkov-type instability, while the stability depends on the density structure in the Newtonian limit. The growth of the instability is expected to generate turbulence around the current sheet, which can induce the so-called turbulent reconnection, the rate of which is essentially free from plasma resistivity. Thus, the instability can be applied as a triggering mechanism for rapid magnetic energy release in a variety of high-energy astrophysical phenomena such as pulsar wind nebulae, gamma-ray bursts, and active galactic nuclei, where the shock wave is thought to play a crucial role.

  3. X-ray Detection of Transient Magnetic Moments Induced by a Spin Current in Cu.

    PubMed

    Kukreja, R; Bonetti, S; Chen, Z; Backes, D; Acremann, Y; Katine, J A; Kent, A D; Dürr, H A; Ohldag, H; Stöhr, J

    2015-08-28

    We have used a MHz lock-in x-ray spectromicroscopy technique to directly detect changes in magnetic moment of Cu due to spin injection from an adjacent Co layer. The elemental and chemical specificity of x rays allows us to distinguish two spin current induced effects. We detect the creation of transient magnetic moments of 3×10^{-5}μ_{B} on Cu atoms within the bulk of the 28 nm thick Cu film due to spin accumulation. The moment value is compared to predictions by Mott's two current model. We also observe that the hybridization induced existing magnetic moments at the Cu interface atoms are transiently increased by about 10% or 4×10^{-3}μ_{B} per atom. This reveals the dominance of spin-torque alignment over Joule heat induced disorder of the interfacial Cu moments during current flow. PMID:26371670

  4. Time-Resolved AMR measurements of current induced magnetization reversal in ferromagnetic nanowires

    NASA Astrophysics Data System (ADS)

    Guittienne, Ph.; Wegrowe, J.-E.; Kelly, D.; Ansermet, J.-Ph.

    2001-03-01

    Time-resolved detection of the magnetization switching in static magnetic fields was achieved by pulsing current densities of about 107 A/cm2 in single isolated Nickel nanowires (80nm in diameter, 6000 nm in length, electrodeposited in porous membranes), using a Weathstone bridge of a 1GHz bandwidth. This irreversible transition is found to occur in a time of about 10 ns. The time of switching within the pulse, tsw, is measured as a function of applied field and current. The temperature rise due to Joule heating is deduced from the change in resistance. The entire set of data tsw(H,T) are fitted with a simple activation law, with the energy barrier height as the unique fitting parameter. The results show a strong departure from pure thermal activation indicating a current-induced magnetization reversal.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  6. The generation of magnetic fields and electric currents in cometary plasma tails

    NASA Technical Reports Server (NTRS)

    Ip, W.-H.; Mendis, D. A.

    1976-01-01

    Due to the folding of the interplanetary magnetic field into the tail as a comet sweeps through the interplanetary medium, the magnetic field in the tail can be built up to the order of 100 gammas at a heliocentric distance of about 1 AU. This folding of magnetic flux tubes also results in a cross-tail electric current passing through a neutral sheet. When streams of enhanced plasma density merge with the main tail, cross-tail currents as large as 1 billion A may result. A condition could arise which causes a significant fraction of this current to be discharged through the inner coma, resulting in rapid ionization. The typical time scale for such outbursts of ionization is estimated to be of the order of 10,000 sec, which is in reasonable agreement with observation.

  7. X-ray Detection of Transient Magnetic Moments Induced by a Spin Current in Cu

    NASA Astrophysics Data System (ADS)

    Kukreja, R.; Bonetti, S.; Chen, Z.; Backes, D.; Acremann, Y.; Katine, J. A.; Kent, A. D.; Dürr, H. A.; Ohldag, H.; Stöhr, J.

    2015-08-01

    We have used a MHz lock-in x-ray spectromicroscopy technique to directly detect changes in magnetic moment of Cu due to spin injection from an adjacent Co layer. The elemental and chemical specificity of x rays allows us to distinguish two spin current induced effects. We detect the creation of transient magnetic moments of 3 ×10-5μB on Cu atoms within the bulk of the 28 nm thick Cu film due to spin accumulation. The moment value is compared to predictions by Mott's two current model. We also observe that the hybridization induced existing magnetic moments at the Cu interface atoms are transiently increased by about 10% or 4 ×10-3μB per atom. This reveals the dominance of spin-torque alignment over Joule heat induced disorder of the interfacial Cu moments during current flow.

  8. Time-resolved spectroscopy of spin-current emission from a magnetic insulator

    NASA Astrophysics Data System (ADS)

    Tateno, Yuma; Fukami, Masaya; Tashiro, Takaharu; Ando, Kazuya

    2016-05-01

    We demonstrate time-resolved spectroscopy of spin-current emission from a magnetic insulator using the inverse spin Hall effect (ISHE). We measured magnetic field dependence of the spin-current emission in the time domain and found that the spectral shape of the ISHE voltage changes with time. The change in the spectral shape is due to field and power dependent temporal oscillation of the spin pumping driven by parametric magnons. The observed oscillating spin-current emission driven by dipole-exchange magnons is well reproduced by a model calculation based on the S theory. In contrast, the spin-current emission driven by short-wavelength exchange magnons cannot be reproduced with this model, illustrating an important role of higher-order nonlinear effects in the spin-current emission.

  9. An Observational Research on Magnetic Reconnection Current Sheet Occurred in Two Solar Eruptions

    NASA Astrophysics Data System (ADS)

    Cai, Q. W.; Wu, N.; Lin, J.

    2015-11-01

    The coronal magnetic configuration is severely stretched by the disruption in the process of coronal mass ejection (CME), pushing the magnetic fields of opposite polarity to approach one another, and creating a magnetic neutral region (current sheet) behind CME. Magnetic reconnection taking place inside the current sheet converts the magnetic energy into heat and kinetic energy of the plasma, and the kinetic energy of energetic particles. The role of the current sheet in this process is two-fold: the region where reconnection occurs, and connecting the flare to the associated CME. We studied the events of 2003 January 3 and 2003 November 4, respectively. Development of the current sheet was observed in both cases. We investigated the dynamic features of the two events, as well as physical properties of the current sheet, on the basis of analyzing the observational data from LASCO (Large Angle and Spectrometric Coronagraph) and UVCS (Ultraviolet Coronagraph Spectrometer) on board SOHO (Solar and Heliospheric Observatory), and the Hα data from BBSO (Big Bear Solar Observatory) and YNAO (Yunnan Observatories). The existence of ions with high ionization state, such as Fe^{+17} and Si^{+11}, indicated a high temperature up to 3×10^{6}-5×10^{6} K. Direct measurements showed that the apparent thickness of the current sheet varies from 1.3×10^{4} to 1.1×10^{5} km, which increases first and then decreases with time. Using the CHIANTI code (v.7.1), we further calculated the averages of the electron temperature and the corresponding emission measure in the current sheet of the 2003 January 3 event, which were about 3.86× 10^{6} K and 6.1× 10^{24} cm^{-5}, respectively. We also noticed that the current sheet twisted forth and back in a quasi-periodical fashion during the event on 2003 November 4 by analyzing the data from SOHO/UVCS.

  10. Fast magnetic reconnection with plasmoid / current sheet ejection events in laboratory experiments

    NASA Astrophysics Data System (ADS)

    Inomoto, Michiaki; Ono, Yasushi; Hayashi, Yoshinori

    2012-07-01

    Non-steady and fast magnetic reconnections due to plasmoid or current sheet ejection events have been investigated in laboratory experiments using TS-3, TS-4 and UTST plasma merging devices in the University of Tokyo. In these devices, magnetic reconnection is induced by two different schemes, a) push reconnection driven by flux injection from the upstream region, b) pull reconnection driven by flux extraction to the downstream region. Current sheet or plasmoid ejection events are observed in these reconnection experiments particularly with strong guide magnetic field parallel to the reconnection electric field. In push reconnection experiments, anomalous resistivity is induced by the ion's kinetic effect (meandering motion) when the current sheet width is compressed shorter than the ion gyroradius by the strongly injected inflow flux. This fast reconnection regime does not involve plasmoid / current sheet ejection events. On the other hand, the guide field reduces the ion gyroradius and suppresses the onset of the anomalous resistivity, providing slow and steady magnetic reconnection. Impulsive fast reconnection with strong guide field develops, nevertheless, due to plasmoid / current sheet ejection events in pull and push reconnection experiments with extremely large external driving forces. In such a situation, the inflow flux is forcedly pushed into the reconnection region even faster than the maximal reconnection rate, resulting in flux pile up in front of the diffusion region. This piled flux induces large current density inside the current sheet in which plasmoid structure with closed flux surface is formed in pull reconnection case. The induced large current density or plasmoid is then ejected from the diffusion region with significant increase of reconnection electric field. As a result, magnetic reconnection condition with even larger reconnection rate than that obtained by anomalous resistivity was achieved under strong guide field and large external

  11. Rapid Assessment of Marine Pollution (RAMP).

    PubMed

    Bowen, Robert E; Depledge, Michael H

    2006-01-01

    RAMP embraces the integrated use of methods for the rapid measurement, assessment and access to information on the nature, sources and influences of coastal environmental change. It embraces approaches held in the literature, research and programs of RAMP (Rapid Assessment of Marine Pollution) and the emerging work described as RASE (Rapid Assessment of Socio-Economic Indicators). To protect coastal ecosystems and the health of communities effectively, management infrastructure requires the tools and resources necessary to detect damage to coastal ecosystems and their components, identify causative agents, impose remedial action, and demonstrate that measures have been effective. Pragmatic monitoring and prediction capabilities must also be built to provide further confidence that human impacts are being minimized and that threats to human health have been contained. For most of the world, however, the ability to build such capability is a technical challenge and often cost prohibitive. These constraints point to the need to develop and expand the integrated use of simple, robust, cost-effective environmental assessment procedures. This paper suggests that a system built around the Rapid Assessment of Marine Pollution (RAMP) and the Rapid Assessment of Socio-Economic Indicators (RASE) can, should and in some cases already has been effective in meeting such informational and management needs. PMID:17070861

  12. Exchange torque and spin transfer between spin polarized current and ferromagnetic layers

    NASA Astrophysics Data System (ADS)

    Wegrowe, J.-E.; Fábián, A.; Guittienne, Ph.; Hoffer, X.; Kelly, D.; Ansermet, J.-Ph.; Olive, E.

    2002-05-01

    Magnetization reversal triggered by spin injection is measured in electrodeposited Co/Cu/Co pillars (diameter about 60 nm). Two protocols are used. (i) switching of magnetization after a current pulse is monitored as a function of applied field. The maximum offset from the switching field at which irreversible switching occurs is a measure of the strength of the effect; and (ii) irreversible and reversible magnetization changes are observed while the current is ramped at fixed applied field. (i) and (ii) show that irreversible transitions occur only from antiparallel to parallel magnetic configurations and for electrons flow from the polarizer to the analyzer.

  13. The ionospheric current system and its contribution to the Earth's magnetic field

    NASA Astrophysics Data System (ADS)

    Prokhorov, Boris E.; Förster, Matthias; Stolle, Claudia; Lesur, Vincent; Namgalagze, Alexander A.; Holschneider, Matthias

    2016-04-01

    The ionospheric currents are a highly variable part of the coupled Magnetosphere - Ionosphere - Thermosphere (MIT) system. This system is driven by the solar wind and Interplanetary Magnetic Field (IMF) interaction with the Earth's magnetosphere. The solar wind and IMF interactions transfer energy to the MIT system via reconnection processes at the magnetopause. The Field Aligned Currents (FACs) constitute the energetic link between the magnetosphere and the Earth's ionosphere. The system of ionospheric currents depends on the geomagnetic conditions and has significant seasonal and UT variation. The first aim of the present investigation is to model the global dynamic ionospheric current system. For this purpose, we use an improved version of the first-principle, time-dependent, and fully self-consistent numerical global Upper Atmosphere Model (UAM-P). This model describes the thermosphere, ionosphere, plasmasphere and inner magnetosphere as well as the electrodynamics of the coupled MIT system for the altitudinal range from 80 (60) km up to the 15 Earth radii. For this study, the lower latitudinal and equatorial electrodynamics of the UAM-P model was improved. The second aim of this research is to calculate the ionospheric contribution to the Earth's magnetic field. The additional magnetic field is obtained from the global ionospheric current system calculated with the UAM-P model. The ionospheric magnetic field is calculated using the Biot-Savart law. The maximum magnitudes of the ionospheric magnetic field are located close to the areas of the auroral and equatorial electrojets. The contribution of the equatorial electrojet to the magnetic field is significant and comparable to the influence of the high latitude current system.

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  15. Simulations of Sample-Up-The-Ramp for Space-Based Observations of Faint Sources

    NASA Technical Reports Server (NTRS)

    Benford, Dominic J.

    2008-01-01

    We have conducted simulations of a memory-efficient up-the-ramp sampling algorithm for infrared detector arrays. Our simulations use realistic sky models of galaxy brightness, shapes, and distributions, and include the contributions of zodiacal light and cosmic rays. A simulated readout is based on the HAWAII-2RG arrays, and includes read noise, dark current, pedestal, and other effects. The up-the-ramp algorithm rejects cosmic rays and produces a best estimate of the source flux under the assumption of very low signal-to-noise. We present an analysis of the fidelity of image brightness recovery with this algorithm.

  16. Control and readout of current-induced magnetic flux quantization in a superconducting transformer

    NASA Astrophysics Data System (ADS)

    Kerner, C.; Hackens, B.; Golubović, D. S.; Poli, S.; Faniel, S.; Magnus, W.; Schoenmaker, W.; Bayot, V.; Maes, H.

    2009-02-01

    We demonstrate a simple and robust method for inducing and detecting changes of magnetic flux quantization in the absence of an externally applied magnetic field. In our device, an isolated ring is interconnected with two access loops via permalloy cores, forming a superconducting transformer. By applying and tuning a direct current at the first access loop, the number of flux quanta trapped in the isolated ring is modified without the aid of an external field. The flux state of the isolated ring is simply detected by recording the evolution of the critical current of the second access loop.

  17. Eddy Current Analysis and Optimization for Superconducting Magnetic Bearing of Flywheel Energy Storage System

    NASA Astrophysics Data System (ADS)

    Arai, Yuuki; Yamashita, Tomohisa; Hasegawa, Hitoshi; Matsuoka, Taro; Kaimori, Hiroyuki; Ishihara, Terumasa

    Levitation and guidance force is electromagnetic generated between a superconducting coil and zero field cooled bulk superconductors used in our flywheel energy storage system (FESS). Because the magnetic field depends on the configuration of the coil and the bulks, the eccentricity and the vibration of a rotor cause fluctuation in the magnetic field which induces eddy current and consequent Joule heat on electric conductors such as cooling plates. Heat generation in the cryogenic region critically reduces the efficiency of the FESS. In this paper, we will report the result of the electromagnetic analysis of the SMB and propose an optimal divided cooling plate for reducing the eddy current and Joule heat.

  18. Spin-Wave Theory for the Dynamics Induced by Direct Currents in Magnetic Multilayers

    NASA Astrophysics Data System (ADS)

    Rezende, S. M.; de Aguiar, F. M.; Azevedo, A.

    2005-01-01

    A spin-wave theory is presented for the magnetization dynamics in a ferromagnetic film that is traversed by spin-polarized carriers at high direct-current densities. It is shown that nonlinear effects due to four-magnon interactions arising from dipolar and surface anisotropy energies limit the growth of the driven spin wave and produce shifts in the microwave frequency oscillations. The theory explains quantitatively recent experimental results in nanometric point contacts onto magnetic multilayers showing downward frequency shifts (redshifts) with increasing current, if the external field is on the film plane, and upward shifts (blueshifts), if the field is perpendicular to the film.

  19. Final Report Experimental Study of Impulsive Reconnection in a Current Carrying Magnetic Arcade

    SciTech Connect

    Craig, Darren

    2011-10-27

    The Wheaton Impulsive Reconnection Experiment (WIRX) is a new experiment now underway at Wheaton College for the study of magnetic reconnection. The experiment is composed of two parallel electrodes, linked by a magnetic arcade that is generated by a coil surrounding the electrodes. Current is driven along the arcade from one electrode to another. When enough current is driven, the arcade is expected to disrupt or segment by reconnection allowing a study of 3D reconnection. This report is the final report for a three year grant period.

  20. Comparisons of Simulated and Observed Stormtime Magnetic Intensities and Ion Plasma Parameters in the Ring Current

    NASA Astrophysics Data System (ADS)

    Chen, M. W.; Guild, T. B.; Lemon, C.; Roeder, J. L.; Le, G.; Schulz, M.

    2009-12-01

    Recent progress in ring current and plasma sheet modeling has shown the importance of a self-consistent treatment of particle transport and magnetic and electric fields in the inner magnetosphere. Models with and without self-consistency can lead to significantly different magnitudes and spatial distributions of plasma pressure and magnetic intensity during disturbed times. In this study we compare simulated and observed stormtime magnetic intensities (GOES and Polar/MFE) and ion densities (LANL/MPA and Polar/CAMMICE) to test how well self-consistent simulations can simultaneously reproduce these quantities. We simulate the ring current and plasma sheet for conditions corresponding to the 11 August 2000 storm using the self-consistent Rice Convection Model-Equilibrium (RCM-E) [Lemon et al., JGR, 2004] with a constant magnetopause location. Using the empirical IMF-dependent model of Tsyganenko and Mukai [JGR, 2003], we specify the plasma sheet pressure and density at 10 RE as the plasma boundary location in the RCM-E. The simulated ion densities at different magnetic local times agree fairly well with those from the re-analysis model of LANL/MPA densities of O’Brien and Lemon [Space Weather, 2007]. We compare the simulated magnetic intensity with the magnetic intensity measured by magnetometers on the GOES satellites at geosynchronous altitude (6.6 RE) and on the Polar satellite. Agreement between the simulated and observed magnetic intensities tends to agree better on the nightside than on the dayside in the inner magnetosphere. In particular, the model cannot account for observed drops in the dayside magnetic intensity during decreases in the solar wind pressure. We will modify the RCM-E to include a time-varying magnetopause location to simulate compressions and expansions associated with variations in the solar wind pressure. We investigate whether this will lead to improved agreement between the simulated and model magnetic intensities.

  1. The Role of Archives and Records Management in National Information Systems: A RAMP Study.

    ERIC Educational Resources Information Center

    Rhoads, James B.

    Produced as part of the United Nations Educational, Scientific, and Cultural Organization (UNESCO) Records and Archives Management Programme (RAMP), this publication provides information about the essential character and value of archives and about the procedures and programs that should govern the management of both archives and current records,…

  2. Writings on Archives Published by and with the Assistance of UNESCO: A RAMP Study.

    ERIC Educational Resources Information Center

    Evans, Frank B.

    Compiled as part of the United Nations Educational, Scientific and Cultural Organization (UNESCO) Records and Archives Management Programme (RAMP), this document lists 282 writings published by or with the assistance of UNESCO on the subject of archives administration and archival materials (interpreted broadly to include current and semi-current…

  3. Scientific and Technological Information in Transactional Files in Government Records and Archives: A RAMP Study.

    ERIC Educational Resources Information Center

    Wimalaratne, K. D. G.

    This long-term Records and Archives Administration Programme (RAMP) study is designed to assist archivists, records managers, and information specialists in identifying for current use and possible archival selection those transactional or case files that contain scientific and technical information (STI), particularly in those instances where…

  4. Synthesis models of dayside field-aligned currents for strong interplanetary magnetic field By

    NASA Astrophysics Data System (ADS)

    Watanabe, Masakazu; Iijima, Takesi; Rich, Frederick J.

    1996-06-01

    Using particle and magnetic field data acquired with DMSP-F6 and DMSP-F7 satellites, we have investigated interplanetary magnetic field (IMF) By dependence of the global pattern of plasma regime and field-aligned currents (FACs) on dayside high latitudes during strong IMF By (averaged |By|>3.7 nT) and geomagnetically disturbed (mainly IMF Bz<0) periods. From particle data we have identified five plasma regimes: inner plasma sheet, outer plasma sheet, cleft, cusp, and mantle. All the plasma domains except the inner plasma sheet show By dependence in spatial distribution. Region 1 and ``traditional cusp'' currents appear in cusp/mantle domains, which we call midday region 1 and region 0 currents, respectively, in this paper. These currents perfectly reverse their flow directions depending on IMF By polarity. Traditional region 1 currents occurring in cleft and outer plasma sheet almost always flow into the ionosphere in the prenoon sector and flow away from the ionosphere in the postnoon sector regardless of By polarity. Thus the midday region 1 and region 0 current system that appears at local noon is not a simple continuation of flankside region 1/region 2 current system. Midday region 1 and region 0 currents are not necessarily balanced in intensity; region 0 current intensity occasionally exceeds midday region 1 current intensity. Furthermore, intensity imbalance also appears in cleft-associated region 1 currents; that is, region 1 current in the farside cleft from the reconnection site (``downstreamside'' cleft) is larger than region 1 current in the nearside cleft (``upstreamside'' cleft). On the basis of these observational facts we discuss the source mechanisms of the dayside FAC system: (1) directly coupled generation of region 0 and midday region 1 current in the cusp/mantle domains around noon and (2) generation of extra region 0 current in the tail magnetopause which is connected to the extra downstreamside cleft-associated region 1 current.

  5. Quantification and compensation of eddy-current-induced magnetic-field gradients.

    PubMed

    Spees, William M; Buhl, Niels; Sun, Peng; Ackerman, Joseph J H; Neil, Jeffrey J; Garbow, Joel R

    2011-09-01

    Two robust techniques for quantification and compensation of eddy-current-induced magnetic-field gradients and static magnetic-field shifts (ΔB0) in MRI systems are described. Purpose-built 1-D or six-point phantoms are employed. Both procedures involve measuring the effects of a prior magnetic-field-gradient test pulse on the phantom's free induction decay (FID). Phantom-specific analysis of the resulting FID data produces estimates of the time-dependent, eddy-current-induced magnetic field gradient(s) and ΔB0 shift. Using Bayesian methods, the time dependencies of the eddy-current-induced decays are modeled as sums of exponentially decaying components, each defined by an amplitude and time constant. These amplitudes and time constants are employed to adjust the scanner's gradient pre-emphasis unit and eliminate undesirable eddy-current effects. Measurement with the six-point sample phantom allows for simultaneous, direct estimation of both on-axis and cross-term eddy-current-induced gradients. The two methods are demonstrated and validated on several MRI systems with actively-shielded gradient coil sets. PMID:21764614

  6. CURRENT HELICITY OF ACTIVE REGIONS AS A TRACER OF LARGE-SCALE SOLAR MAGNETIC HELICITY

    SciTech Connect

    Zhang, H.; Gao, Y.; Xu, H.; Moss, D.; Kleeorin, N.; Rogachevskii, I.; Kuzanyan, K.; Sokoloff, D.

    2012-05-20

    We demonstrate that the current helicity observed in solar active regions traces the magnetic helicity of the large-scale dynamo generated field. We use an advanced two-dimensional mean-field dynamo model with dynamo saturation based on the evolution of the magnetic helicity and algebraic quenching. For comparison, we also studied a more basic two-dimensional mean-field dynamo model with simple algebraic alpha-quenching only. Using these numerical models we obtained butterfly diagrams both for the small-scale current helicity and also for the large-scale magnetic helicity, and compared them with the butterfly diagram for the current helicity in active regions obtained from observations. This comparison shows that the current helicity of active regions, as estimated by -A {center_dot} B evaluated at the depth from which the active region arises, resembles the observational data much better than the small-scale current helicity calculated directly from the helicity evolution equation. Here B and A are, respectively, the dynamo generated mean magnetic field and its vector potential. A theoretical interpretation of these results is given.

  7. Pressurized heavy water reactor fuel behaviour in power ramp conditions

    NASA Astrophysics Data System (ADS)

    Ionescu, S.; Uţă, O.; Pârvan, M.; Ohâi, D.

    2009-03-01

    In order to check and improve the quality of the Romanian CANDU fuel, an assembly of six CANDU fuel rods has been subjected to a power ramping test in the 14 MW TRIGA reactor at INR. After testing, the fuel rods have been examined in the hot cells using post-irradiation examination (PIE) techniques such as: visual inspection and photography, eddy current testing, profilometry, gamma scanning, fission gas release and analysis, metallography, ceramography, burn-up determination by mass spectrometry, mechanical testing. This paper describes the PIE results from one out of the six fuel rods. The PIE results concerning the integrity, dimensional changes, oxidation, hydriding and mechanical properties of the sheath, the fission-products activity distribution in the fuel column, the pressure, volume and composition of the fission gas, the burn-up, the isotopic composition and structural changes of the fuel enabled the characterization of the behaviour of the Romanian CANDU fuel in power ramping conditions performed in the TRIGA materials testing reactor.

  8. Predictability of wind ramps in the Columbia River Gorge

    NASA Astrophysics Data System (ADS)

    Smith, C.

    2013-12-01

    Wind generation capacity in the Bonneville Power Administration (BPA) system, which stands at 4,500 MW currently, can at time account for 70% of total electricity demand. With 2,500 additional MW of wind generation capacity expected by 2015, increasingly accurate forecasts are required to avoid water quality issues associated with hydropower dam overspill. Wind ramps, or large increases or decreases in wind generation over a short period of time, are particularly difficult to accurately forecast in the Columbia River Gorge area. Industry standard computational resources, combined with turbulence grey-zone issues associated with planetary boundary (PBL) schemes, suggest a leveling off of numerical weather prediction (NWP) model skill score with respect to increasing grid resolution until eddy resolving scales are resolved. However, we show that dispersion errors, which associated with wind ramps, continue to decrease for locations and seasons in which meso-scale and topographically forced diurnal motions account for a significant portion of the power spectral density of hub-height wind speeds.

  9. ALTERNATIVE MATERIALS FOR RAMP-EDGE SNS JUNCTIONS

    SciTech Connect

    Jia, Q.; Fan, Y.

    1999-06-01

    We report on the processing optimization and fabrication of ramp-edge high-temperature superconducting junctions by using alternative materials for both superconductor electrodes and normal-metal barrier. By using Ag-doped YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (Ag:YBCO) as electrodes and a cation-modified compound of (Pr{sub y}Gd{sub 0.6{minus}y})Ca{sub 0.4}Ba{sub 1.6}La{sub 0.4}Cu{sub 3}O{sub 7} (y = 0.4, 0.5, and 0.6) as a normal-metal barrier, high-temperature superconducting Josephson junctions have been fabricated in a ramp-edge superconductor/normal-metal/superconductor (SNS) configuration. By using Ag:YBCO as electrodes, we have found that the processing controllability /reproducibility and the stability of the SNS junctions are improved substantially. The junctions fabricated with these alternative materials show well-defined RSJ-like current vs voltage characteristics at liquid nitrogen temperature.

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

    PubMed Central

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

    2014-01-01

    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. PMID:24753629

  11. Self-organization in space plasma: formation of magnetic shear in current sheets

    NASA Astrophysics Data System (ADS)

    Zelenyi, Lev; Delcourt, Dominique; Mingalev, Oleg; Malova, Helmi; Popov, Victor; Grigorenko, Elena; Petrukovich, Anatoli

    2016-07-01

    Thin current sheets are plasma structures that usually appear near reconnection regions. The presence of the shear magnetic field is characteristic for these structures. Self-consistent kinetic model of magnetotail thin current sheet (TCS) is used to understand the mechanisms of self-organization of sheared thin current sheets in a space plasma. It is shown that these configurations appear as a result of self-consistent evolution of some initial magnetic perturbation at current sheet center. Two general shapes of shear TCS components are found as a function of the transverse coordinate: symmetric and antisymmetric. We show that TCS formation goes together with the emergence of field-aligned currents in the center of the current sheet, as a result of north-south asymmetry of quasi-adiabatic ion motions. Ion drift currents can also contribute to the magnetic shear evolution, but their role is much less significant, their contribution depending upon the normal component Bz and the amplitude of the initial perturbation in TCS. Parametric maps illustrating different types of TCS equilibria are presented.

  12. Determination of the Neutron Lifetime Using Magnetically Trapped Neutrons

    PubMed Central

    Dzhosyuk, S. N.; Copete, A.; Doyle, J. M.; Yang, L.; Coakley, K. J.; Golub, R.; Korobkina, E.; Kreft, T.; Lamoreaux, S. K.; Thompson, A. K.; Yang, G. L.; Huffman, P. R.

    2005-01-01

    We report progress on an experiment to measure the neutron lifetime using magnetically trapped neutrons. Neutrons are loaded into a 1.1 T deep superconducting Ioffe-type trap by scattering 0.89 nm neutrons in isotopically pure superfluid 4He. Neutron decays are detected in real time using the scintillation light produced in the helium by the beta-decay electrons. The measured trap lifetime at a helium temperature of 300 mK and with no ameliorative magnetic ramping is substantially shorter than the free neutron lifetime. This is attributed to the presence of neutrons with energies higher than the magnetic potential of the trap. Magnetic field ramping is implemented to eliminate these neutrons, resulting in an 833−63+74s trap lifetime, consistent with the currently accepted value of the free neutron lifetime. PMID:27308147

  13. Towards a beyond 1 GHz solid-state nuclear magnetic resonance: External lock operation in an external current mode for a 500 MHz nuclear magnetic resonance

    SciTech Connect

    Takahashi, Masato; Maeda, Hideaki; Ebisawa, Yusuke; Tennmei, Konosuke; Yanagisawa, Yoshinori; Nakagome, Hideki; Hosono, Masami; Takasugi, Kenji; Hase, Takashi; Miyazaki, Takayoshi; Fujito, Teruaki; Kiyoshi, Tsukasa; Yamazaki, Toshio

    2012-10-15

    Achieving a higher magnetic field is important for solid-state nuclear magnetic resonance (NMR). But a conventional low temperature superconducting (LTS) magnet cannot exceed 1 GHz (23.5 T) due to the critical magnetic field. Thus, we started a project to replace the Nb{sub 3}Sn innermost coil of an existing 920 MHz NMR (21.6 T) with a Bi-2223 high temperature superconducting (HTS) innermost coil. Unfortunately, the HTS magnet cannot be operated in persistent current mode; an external dc power supply is required to operate the NMR magnet, causing magnetic field fluctuations. These fluctuations can be stabilized by a field-frequency lock system based on an external NMR detection coil. We demonstrate here such a field-frequency lock system in a 500 MHz LTS NMR magnet operated in an external current mode. The system uses a {sup 7}Li sample in a microcoil as external NMR detection system. The required field compensation is calculated from the frequency of the FID as measured with a frequency counter. The system detects the FID signal, determining the FID frequency, and calculates the required compensation coil current to stabilize the sample magnetic field. The magnetic field was stabilized at 0.05 ppm/3 h for magnetic field fluctuations of around 10 ppm. This method is especially effective for a magnet with large magnetic field fluctuations. The magnetic field of the compensation coil is relatively inhomogeneous in these cases and the inhomogeneity of the compensation coil can be taken into account.

  14. Evolution of sunspot activity and inversion of the Sun's polar magnetic field in the current cycle

    NASA Astrophysics Data System (ADS)

    Mordvinov, A. V.; Grigoryev, V. M.; Erofeev, D. V.

    2015-06-01

    A spatiotemporal analysis of the Sun's magnetic field was carried out to study the polar-field inversion in the current cycle in relation to sunspot activity. The causal relationship between these phenomena was demonstrated in a time-latitude aspect. After decay of long-lived activity complexes their magnetic fields were redistributed into the surrounding photosphere and formed unipolar magnetic regions which were transported to high latitudes. Zones of intense sunspot activity during 2011/2012 produced unipolar magnetic regions of the following polarities, whose poleward drift led to the inversion of the Sun's polar fields at the North and South Poles. At the North Pole the polar field reversal was completed by May 2013. It was demonstrated that mixed magnetic polarities near the North Pole resulted from violations of Joy's law at lower latitudes. Later sunspot activity in the southern hemisphere has led to a delay in magnetic polarity reversal at the South Pole. Thus, the north-south asymmetry of sunspot activity resulted in asynchronous polar field reversal in the current cycle.

  15. Numerical experiments of magnetic reconnection in the solar flare and CME current sheet

    NASA Astrophysics Data System (ADS)

    Mei, Zhixing; Lin, Jun; Shen, Chengcai

    2012-07-01

    Magnetic reconnection plays a critical role in the energy conversion in the solar eruption. This paper performs a set of MHD experiments for the magnetic reconnection process in a current sheet formed in a disrupting magnetic configuration. The eruption results from the loss of equilibrium in the magnetic configuration that includes a current-carrying flux rope, which is used to model the filament floating in the corona. In order to study the fine structure and micro process inside the current sheet (CS), the mesh refinement technology is used to depress the numerical diffusion. A uniform physical diffusion is applied and results in a Lundquist number S=10^4 in the vicinity of CS. Because of the advantage of the foregoing setting, some features appear with high resolution, including plasmoids due to the tearing mode and the plasmoid instabilities, turbulence regions, and the slow mode shocks. Inside CS, magnetic reconnection goes through the Sweet-Parker and the fractal fashions, and eventually, it displays a time-dependent Petschek pattern. Our results seem to support the concept of fractal reconnection suggested by Shibata et al. (1995) and Shibata & Tanuma (2001). And our results suggest that the CS evolves through a Sweet-Parker reconnection prior to the fast reconnection stage. For the first time, the detailed features and/or fine structures inside the CME/flare CS in the eruption were investigated in this work.

  16. Magnetic diagnostics for equilibrium reconstructions with eddy currents on the Lithium Tokamak eXperiment.

    PubMed

    Schmitt, J C; Bialek, J; Lazerson, S; Majeski, R

    2014-11-01

    The Lithium Tokamak eXperiment is a spherical tokamak with a close-fitting low-recycling wall composed of thin lithium layers evaporated onto a stainless steel-lined copper shell. Long-lived non-axisymmetric eddy currents are induced in the shell and vacuum vessel by transient plasma and coil currents and these eddy currents influence both the plasma and the magnetic diagnostic signals that are used as constraints for equilibrium reconstruction. A newly installed set of re-entrant magnetic diagnostics and internal saddle flux loops, compatible with high-temperatures and lithium environments, is discussed. Details of the axisymmetric (2D) and non-axisymmetric (3D) treatments of the eddy currents and the equilibrium reconstruction are presented. PMID:25430382

  17. Pulsed currents carried by whistlers. V. Detailed new results of magnetic antenna excitation

    SciTech Connect

    Rousculp, C.L.; Stenzel, R.L.; Urrutia, J.M.

    1995-11-01

    A low frequency, oblique whistler wave packet is excited from a single current pulse applied to a magnetic loop antenna. The magnetic field is mapped in three dimensions. The dominant angle of radiation is determined by the antenna dimensions, not by the resonance cone. Topological properties of the inductive and space charge electric fields and space charge density confirm an earlier physical model. Transverse currents are dominated by Hall currents, while no net current flows in the parallel direction. Electron-ion collisions damp both the energy and the helicity of the wave packet. Landau damping is negligible. The radiation resistance of the loop is a few tenths of an Ohm for the observed frequency range. The loop injects zero net helicity. Rather, oppositely traveling wave packets carry equal amounts of opposite signed helicity. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  18. Magnetic islands and singular currents at rational surfaces in three-dimensional magnetohydrodynamic equilibria

    SciTech Connect

    Loizu, J.; Hudson, S.; Bhattacharjee, A.; Helander, P.

    2015-02-15

    Using the recently developed multiregion, relaxed MHD (MRxMHD) theory, which bridges the gap between Taylor's relaxation theory and ideal MHD, we provide a thorough analytical and numerical proof of the formation of singular currents at rational surfaces in non-axisymmetric ideal MHD equilibria. These include the force-free singular current density represented by a Dirac δ-function, which presumably prevents the formation of islands, and the Pfirsch-Schlüter 1/x singular current, which arises as a result of finite pressure gradient. An analytical model based on linearized MRxMHD is derived that can accurately (1) describe the formation of magnetic islands at resonant rational surfaces, (2) retrieve the ideal MHD limit where magnetic islands are shielded, and (3) compute the subsequent formation of singular currents. The analytical results are benchmarked against numerical simulations carried out with a fully nonlinear implementation of MRxMHD.

  19. Magnetic diagnostics for equilibrium reconstructions with eddy currents on the lithium tokamak experiment

    SciTech Connect

    Schmitt, J. C. Lazerson, S.; Majeski, R.; Bialek, J.

    2014-11-15

    The Lithium Tokamak eXperiment is a spherical tokamak with a close-fitting low-recycling wall composed of thin lithium layers evaporated onto a stainless steel-lined copper shell. Long-lived non-axisymmetric eddy currents are induced in the shell and vacuum vessel by transient plasma and coil currents and these eddy currents influence both the plasma and the magnetic diagnostic signals that are used as constraints for equilibrium reconstruction. A newly installed set of re-entrant magnetic diagnostics and internal saddle flux loops, compatible with high-temperatures and lithium environments, is discussed. Details of the axisymmetric (2D) and non-axisymmetric (3D) treatments of the eddy currents and the equilibrium reconstruction are presented.

  20. Magnetic diagnostics for equilibrium reconstructions with eddy currents on the lithium tokamak experimenta)

    SciTech Connect

    Schmitt, J. C.; Bialek, J.; Lazerson, S.; Majeski, R.

    2014-11-01

    The Lithium Tokamak eXperiment is a spherical tokamak with a close-fitting low-recycling wall composed of thin lithium layers evaporated onto a stainless steel-lined copper shell. Long-lived non-axisymmetric eddy currents are induced in the shell and vacuum vessel by transient plasma and coil currents and these eddy currents influence both the plasma and the magnetic diagnositc signals that are used as constraints for equilibrium reconstruction. A newly installed set of re-entrant magnetic diagnostics and internal saddle flux loops, compatible with high-temperatures and lithium environments, is discussed. Details of the axisymmetric (2D) and non-axisymmetric (3D) treatments of the eddy currents and the equilibrium reconstruction are presented.

  1. Plasma Jets Subject to Adjustable Current Polarities and External Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Byvank, Tom; Schrafel, Peter; Gourdain, Pierre; Seyler, Charles; Kusse, Bruce

    2014-10-01

    In the present research, collimated plasma jets form from ablation of a radial foil (Al 20 μm thin disk) using a pulsed power generator (COBRA) with 1 MA peak current and 100 ns rise time. Plasma dynamics of the jet are diagnosed with and without an applied uniform external field (1-1.5 T) and under a change of current polarities, which correspond to current moving either radially outward or inward from the foil's central axis. Experimental results are compared with numerical simulations (PERSEUS). The influence of the Hall effect on the jet development is observed under opposite current polarities. Additionally, the magnetic field compression within the jet is examined. Further studies will compare the laboratory-generated plasma jets and astrophysical jets with embedded magnetic fields.

  2. Transient analysis and control of bias magnetic state in the transformer of on-line pulse-width-modulation switching full bridge direct current-direct current converter

    NASA Astrophysics Data System (ADS)

    Chen, Jiaxin; Guo, Youguang; Zhu, Jianguo; Wei Lin, Zhi

    2012-04-01

    This paper presents a finite element analysis (FEA) based method for analyzing and controlling the bias magnetic state of the transformer of a pulse-width-modulation (PWM) switching full bridge dc-dc converter. A field-circuit indirect coupling method for predicting the transient bias magnetic state is introduced first. To increase flexibility of the proposed method, a novel transformer model which can address not only its basic input-output characteristic, but also the nonlinear magnetizing inductance, is proposed. Both the asymmetric characteristic and the variable laws of the current flowing through the two secondary windings during the period of PWM switching-off state are highlighted. Finally, the peak magnetizing current controlled method based on the on-line magnetizing current computation is introduced. Analysis results show that this method can address the magnetic saturation at winding ends, and hence many previous difficulties, such as the start-up process and asymmetry of power electronics, can be easily controlled.

  3. Attosecond-magnetic-field-pulse generation by electronic currents in bichromatic circularly polarized UV laser fields

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Bandrauk, André D.

    2015-12-01

    Attosecond-magnetic-field-pulse generation is simulated from numerical solutions of time-dependent Schrödinger equations for oriented H2 +. Two schemes with high frequency co- and counter-rotating bichromatic ω2=2 ω1 circularly polarized UV laser pulses are investigated. Results show that comparing to single color processes, stronger induced localized magnetic fields B at the molecular center O (r =0 ) are obtained with attosecond duration. This is attributed to frequent recollision and to interference effects of two pathways in photoionization. The induced magnetic fields are shown to be sensitive to (i) the helicity of the combined laser pulses due to different recollision laser-induced electron trajectories and currents, and (ii) also the carrier envelope phases of the combined attosecond laser pulses. The sensitivity of recollision to bichromatic pulses thus allows one to control the induced magnetic-field-pulse generation.

  4. Electrodynamics in a Very Thin Current Sheet Leading to Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Singh, Nagendra; Deverapalli, Chakri; Khazanov, George

    2006-01-01

    We study the formation of a very thin current sheet (CS) and associated plasma electrodynamics using three-dimensional (3-D) particle-in-cell simulations with ion to electron mass ratio M/m=1836. The CS is driven by imposed anti-parallel magnetic fields. The noteworthy features of the temporal evolution of the CS are the following: (i) Steepening of the magnetic field profile B,(z) in the central part of the CS, (ii) Generation of three-peak current distribution with the largest peak in the CS center as B,(z) steepens, (iii) Generation of converging electric fields forming a potential well in the CS center in which ions are accelerated. (iv) Electron and ion heating in the central part of the CS by current-driven instabilities (CDI). (v) Re-broadening of the CS due to increased kinetic plasma pressure in the CS center. (vi) Generation of electron temperature anisotropy with temperature perpendicular to the magnetic field being larger than the parallel one. (vii) Current disruption by electron trapping in an explosively growing electrostatic instability (EGEI) and electron tearing instability (ETI). (viii)The onset of EGEI coincides with an increase in the electron temperature above the temperature of the initially hot ions as well as the appearance of new shear in the electron drift velocity. (ix) Bifurcation of the central CS by the current disruption. (x) Magnetic reconnection (MR) beginning near the null in B, and spreading outward. (xi) Generation of highly energized electrons reaching relativistic speeds and having isotropic pitch-angle distribution in the region of reconnected magnetic fields. We compare some of these features of the current sheet with results from laboratory and space experiments.

  5. Structural and magnetic characterization of electro-crystallized magnetite nanoparticles under constant current

    SciTech Connect

    Mosivand, Saba; Kazeminezhad, Iraj

    2015-10-15

    Graphical abstract: Structural and magnetic properties of electro-crystallized magnetite nanoparticles under constant current were studied. All samples were characterized using XRD, SEM, VSM, and Mössbauer spectrometry. - Highlights: • The effect of applied current on morphology and properties of Fe{sub 3}O{sub 4} is studied. • The particle size and morphology are controllable by adjusting the current. • The magnetization depends on particle size, type of surfactant and applied current. • The clear correlation between magnetization and the mean particle size is observed. - Abstract: The effect of applied current on the morphology, particle size, structure, and magnetic properties of magnetite nanoparticles prepared by electro-crystallization method was studied. The synthesis was performed in an electrochemical cell containing two iron electrodes and an aqueous solution of sodium sulfate, and either thiourea, sodium butanoate, or β-cyclodextrine as organic stabilizer. All the samples were characterized by XRD, SEM, VSM, and Mössbauer spectroscopy. X-ray diffraction patterns, clearly confirmed that all products have the cubic spinel Fe{sub 3}O{sub 4} crystal structure. Electron microscope images of the samples showed that their mean particle size is in the range 20–80 nm, and depends critically on the applied current and type of the organic additives. Specific magnetization of the samples at room temperature ranges from 60 to 90 A m{sup 2} kg{sup −1}, depending on the growth conditions. Room temperature Mössbauer spectra are typical of nonstoichiometric Fe{sub 3−δ}O{sub 4}, with a small excess of Fe{sup 3+}, 0.06 ≤ δ ≤ 0.17.

  6. Characteristics of a current sheet shear mode in collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Fujimoto, Keizo

    2016-05-01

    The current study shows the characteristics of the kink-type electromagnetic mode excited in the thin current layer formed around the x-line during the quasi-steady phase of magnetic reconnection. The linear wave analyses are carried out for the realistic current sheet profile which differs significantly from the Harris current sheet. It is found that the peak growth rate is very sensitive to the current sheet width even though the relative drift velocity at the center of the current sheet is fixed. This indicates that the mode is excited by the velocity shear rather than the relative drift velocity. Thus, the mode is termed here a current sheet shear mode. It is also shown that the wavenumber ky has a clear mass ratio dependency as ky λi ∝ (mi /me )1/4, implying the coupling of the ion and electron dynamics, where λi is the ion inertia length.

  7. Anomalous Cross-Field Current and Fluctuating Equilibrium of Magnetized Plasmas

    SciTech Connect

    Rypdal, K.; Garcia, O.E.; Paulsen, J.

    1997-09-01

    It is shown by simple physical arguments and fluid simulations that electrostatic flute-mode fluctuations can sustain a substantial cross-field current in addition to mass and energy transport. The simulations show that this current determines essential features of the fluctuating plasma equilibrium, and explain qualitatively the experimental equilibria and the coherent flute-mode structures observed in a simple magnetized torus. {copyright} {ital 1997} {ital The American Physical Society}

  8. Estimation of localized current anomalies in polymer electrolyte fuel cells from magnetic flux density measurements

    NASA Astrophysics Data System (ADS)

    Nara, Takaaki; Koike, Masanori; Ando, Shigeru; Gotoh, Yuji; Izumi, Masaaki

    2016-05-01

    In this paper, we propose novel inversion methods to estimate defects or localized current anomalies in membrane electrode assemblies (MEAs) in polymer electrolyte fuel cells (PEFCs). One method is an imaging approach with L1-norm regularization that is suitable for estimation of focal anomalies compared to Tikhonov regularization. The second is a complex analysis based method in which multiple pointwise current anomalies can be identified directly and algebraically from the measured magnetic flux density.

  9. Galactic cosmic ray currents and magnetic field irregularity degree in high-speed solar wind streams

    NASA Technical Reports Server (NTRS)

    Kuzmin, A. I.; Samsonov, I. S.; Samsonova, Z. N.

    1985-01-01

    Currents of galactic cosmic rays (GCR) obtained by global survey method are analyzed. The cases of almost total disappearance of GCR currents are compared with the results of direct measurements of the solar wind parameters. The conclusion is made on a restricted application of the convective-diffusive mechanism of the GCR modulation by the solar wind during the occurrence of stationary and regular magnetic fields in the interplanetary medium.

  10. Cold test facility for 1.8 m superconducting model magnets at the SSC

    SciTech Connect

    LaBarge, A.

    1993-07-01

    A new facility has been constructed to measure the characteristic features of superconducting model magnets and cable at cryogenic temperatures -- a function which supports the design and development process for building full-scale accelerator magnets. There are multiple systems operating in concert to test the model magnets, namely: cryogenic, magnet power, data acquisition and system control. A typical model magnet test includes the following items: (1) warm measurements of magnet coils, strain gauges and voltage taps; (2) hipot testing of insulation integrity; (3) cooling with liquid nitrogen and then liquid helium; (4) measuring quench current and magnetic field; (5) magnet warm-up. While the magnet is being cooled to 4.22 K, the mechanical stress is monitored through strain gauges. Current is then ramped into the magnet until it reaches some maximum value and the magnet transitions from the superconducting state to the normal state. Normal-zone propagation is monitored using voltage taps on the magnet coils during this process, thus indicating where the transition began. The current ramp is usually repeated until a plateau current is reached, where the magnet has mechanically settled.

  11. Shearless bifurcation on symplectic maps of magnetic field lines in tokamaks with reversed current

    NASA Astrophysics Data System (ADS)

    Bartoloni, B.; Schelin, A. B.; Caldas, I. L.

    2016-07-01

    We introduce two-dimensional symplectic maps to describe the Poincaré maps of magnetic field lines in large aspect ratio tokamak equilibria with reversed non-monotonic plasma current density profiles. For these maps, we investigate the effect of the symmetry breaking due to the toroidal correction with a peculiar invariant, namely, a magnetic surface with a null rotation number, enclosing a vanishing current. We find that this rotationless invariant surface is surrounded by many small island chains. Furthermore, near such invariant, the symmetry breaking gives rise to two magnetic shearless invariants surrounded by twin island chains. We also find chaotic lines adjacent to all the observed islands created by the considered structurally unstable equilibria.

  12. Neutral current induced {pi}{sup 0} production and neutrino magnetic moment

    SciTech Connect

    Athar, M. Sajjad; Chauhan, S.; Singh, S. K.

    2008-08-01

    We have studied the total cross section, Q{sup 2}, momentum and angular distributions for pions in the {nu}({nu}) induced {pi}{sup 0} production from nucleons. The calculations have been done for the weak production induced by the neutral current in the standard model and the electromagnetic production induced by neutrino magnetic moment. It has been found that with the present experimental limits on the muon neutrino magnetic moment {mu}{sub {nu}{sub {mu}}}, the electromagnetic contribution to the cross section for the {pi}{sup 0} production is small. The neutrino induced neutral current production of {pi}{sup 0}, while giving an alternative method to study the magnetic moment of neutrino {mu}{sub {nu}{sub {mu}}}, does not provide any improvement over the present experimental limit on {mu}{sub {nu}{sub {mu}}} from the observation of this process in future experiments at T2K and NO{nu}A.

  13. Ultrafast proton radiography of the magnetic fields generated by a laser-driven coil current

    NASA Astrophysics Data System (ADS)

    Gao, Lan; Ji, Hantao; Fiksel, Gennady; Fox, William; Evans, Michelle; Alfonso, Noel

    2016-04-01

    Magnetic fields generated by a current flowing through a U-shaped coil connecting two copper foils were measured using ultrafast proton radiography. Two ˜1.25 kJ, 1-ns laser pulses propagated through laser entrance holes in the front foil and were focused to the back foil with an intensity of ˜3 × 1016 W/cm2. The intense laser-solid interaction induced a high voltage between the copper foils and generated a large current in the connecting coil. The proton data show ˜40-50 T magnetic fields at the center of the coil ˜3-4 ns after laser irradiation. The experiments provide significant insight for future target designs that aim to develop a powerful source of external magnetic fields for various applications in high-energy-density science.

  14. Induced vacuum current and magnetic field in the background of a vortex

    NASA Astrophysics Data System (ADS)

    Gorkavenko, Volodymyr M.; Ivanchenko, Iryna V.; Sitenko, Yurii A.

    2016-02-01

    A topological defect in the form of the Abrikosov-Nielsen-Olesen vortex is considered as a gauge-flux-carrying tube that is impenetrable for quantum matter. Charged scalar matter field is quantized in the vortex background with the perfectly reflecting (Dirichlet) boundary condition imposed at the side surface of the vortex. We show that a current circulating around the vortex and a magnetic field directed along the vortex are induced in the vacuum, if the Compton wavelength of the matter field exceeds considerably the transverse size of the vortex. The vacuum current and magnetic field are periodic in the value of the gauge flux of the vortex, providing a quantum-field-theoretical manifestation of the Aharonov-Bohm effect. The total flux of the induced vacuum magnetic field attains notable finite values even for the Compton wavelength of the matter field exceeding the transverse size of the vortex by just three orders of magnitude.

  15. Ultrafast proton radiography of the magnetic fields generated by a laser-driven coil current

    DOE PAGESBeta

    Gao, Lan; Ji, Hantao; Fiksel, Gennady; Fox, William; Evans, Michelle; Alfonso, Noel

    2016-04-15

    Magnetic fields generated by a current flowing through a U-shaped coil connecting two copper foils were measured using ultrafast proton radiography. Two ~ 1.25 kJ, 1-ns laser pulses propagated through laser entrance holes in the front foil and were focused to the back foil with an intensity of ~ 3 x 1016 W/cm2. The intense laser-solid interaction induced a high voltage between the copper foils and generated a large current in the connecting coil. The proton data show ~ 40-50 T magnetic fields at the center of the coil ~ 3-4 ns after laser irradiation. In conclusion, the experiments providemore » significant insight for future target designs that aim to develop a powerful source of external magnetic fields for various applications in high-energy-density science.« less

  16. Critical Current Properties in Longitudinal Magnetic Field of YBCO Superconductor with APC

    NASA Astrophysics Data System (ADS)

    Kido, R.; Kiuchi, M.; Otabe, E. S.; Matsushita, T.; Jha, A. K.; Matsumoto, K.

    The critical current density (Jc) properties of the Artificial Pinning Center (APC) introduced YBa2Cu3O7 (YBCO) films in the longitudinal magnetic field were measured. Y2O3 or Y2BaCuO5 (Y211) was introduced as APCs to YBCO, and YBCO films with APC were fabricated on SrTiO3 single crystal substrate. The sizes of Y2O3 and Y211 were 5-10 nm and 10-20 nm, respectively. As a result, Jc enhancement in the longitudinal magnetic field was observed in Y2O3 introduced YBCO films. However, it was not observed in Y211 introduced YBCO films. Therefore, it was considered that Jc properties in the longitudinal magnetic field were affected by introducing of small size APC, and it was necessary that APC does not disturb the current pathway in the superconductor.

  17. Dynamics of the field-aligned current distribution during a magnetic storm: AMPERE

    NASA Astrophysics Data System (ADS)

    Vassiliadis, D.; Tepke, B. P.

    2015-12-01

    Field-aligned current density in the ionosphere can be used to identify the location and intensity of solar wind-magnetosphere-ionosphere coupling, and help identify the large-scale processes that contribute to this coupling. The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) mission effectively provides high-resolution spatial and temporal measurements of the radial current during magnetic storms. These in situ measurements are complementary to magnetic remote sensing from the ground using magnetometer arrays. Here we examine two storms, on May 29, 2010 and August 5, 2011, using AMPERE and solar wind data. We identify the regions whose radial current density has the greatest correlation with solar wind coupling functions and individual magnetic and plasma variables. We develop a statistical model of the radial current density from the magnetospheric and solar wind data which is then used to represent regions of outflowing and inflowing current in the two hemispheres. While the model is limited in representing high spatial resolution, time series of regional and global field-aligned current are reproduced with relatively large correlation coefficients (0.70-0.90) in each event.

  18. Magnetic field oscillations of the critical current in long ballistic graphene Josephson junctions

    NASA Astrophysics Data System (ADS)

    Rakyta, Péter; Kormányos, Andor; Cserti, József

    2016-06-01

    We study the Josephson current in long ballistic superconductor-monolayer graphene-superconductor junctions. As a first step, we have developed an efficient computational approach to calculate the Josephson current in tight-binding systems. This approach can be particularly useful in the long-junction limit, which has hitherto attracted less theoretical interest but has recently become experimentally relevant. We use this computational approach to study the dependence of the critical current on the junction geometry, doping level, and an applied perpendicular magnetic field B . In zero magnetic field we find a good qualitative agreement with the recent experiment of M. Ben Shalom et al. [Nat. Phys. 12, 318 (2016), 10.1038/nphys3592] for the length dependence of the critical current. For highly doped samples our numerical calculations show a broad agreement with the results of the quasiclassical formalism. In this case the critical current exhibits Fraunhofer-like oscillations as a function of B . However, for lower doping levels, where the cyclotron orbit becomes comparable to the characteristic geometrical length scales of the system, deviations from the results of the quasiclassical formalism appear. We argue that due to the exceptional tunability and long mean free path of graphene systems a new regime can be explored where geometrical and dynamical effects are equally important to understand the magnetic field dependence of the critical current.

  19. Electric Current Filamentation at a Non-potential Magnetic Null-point Due to Pressure Perturbation

    NASA Astrophysics Data System (ADS)

    Jelínek, P.; Karlický, M.; Murawski, K.

    2015-10-01

    An increase of electric current densities due to filamentation is an important process in any flare. We show that the pressure perturbation, followed by an entropy wave, triggers such a filamentation in the non-potential magnetic null-point. In the two-dimensional (2D), non-potential magnetic null-point, we generate the entropy wave by a negative or positive pressure pulse that is launched initially. Then, we study its evolution under the influence of the gravity field. We solve the full set of 2D time dependent, ideal magnetohydrodynamic equations numerically, making use of the FLASH code. The negative pulse leads to an entropy wave with a plasma density greater than in the ambient atmosphere and thus this wave falls down in the solar atmosphere, attracted by the gravity force. In the case of the positive pressure pulse, the plasma becomes evacuated and the entropy wave propagates upward. However, in both cases, owing to the Rayleigh-Taylor instability, the electric current in a non-potential magnetic null-point is rapidly filamented and at some locations the electric current density is strongly enhanced in comparison to its initial value. Using numerical simulations, we find that entropy waves initiated either by positive or negative pulses result in an increase of electric current densities close to the magnetic null-point and thus the energy accumulated here can be released as nanoflares or even flares.

  20. A magnetospheric magnetic field model with flexible current systems driven by independent physical parameters

    NASA Technical Reports Server (NTRS)

    Hilmer, Robert V.; Voigt, Gerd-Hannes

    1995-01-01

    A tilt-dependent magnetic field model of the Earth's magnetosphere with variable magnetopause standoff distance is presented. Flexible analytic representations for the ring and cross-tail currents, each composed of the elements derived from the Tsyganenko and Usmanov (1982) model, are combined with the fully shielded vacuum dipole configurations of Voigt (1981). Although the current sheet does not warp in the y-z plane, changes in the shape and position of the neutral sheet with dipole tilt are consistent with both MHD equilibrium theory and observations. In addition, there is good agreement with observed Delta B profiles and the average equatorial contours of magnetic field magnitude. While the dipole field is rigorously shielded within the defined magnetopause, the ring and cross-tails currents are not similarly confined, consequently, the model's region of validity is limited to the inner magnetosphere. The model depends on four independent external parameters. We present a simple but limited method of simulating several substorm related magnetic field changes associated with the disrupion of the near-Earth cross-tail current sheet and collapse of the midnight magnetotail field region. This feature further facilitates the generation of magnetic field configuration time sequences useful in plasma convection simulations of real magnetospheric events.

  1. Eddy Current, Magnetic Particle and Hardness Testing, Aviation Quality Control (Advanced): 9227.04.

    ERIC Educational Resources Information Center

    Dade County Public Schools, Miami, FL.

    This unit of instruction includes the principles of eddy current, magnetic particle and hardness testing; standards used for analyzing test results; techniques of operating equipment; interpretation of indications; advantages and limitations of these methods of testing; care and calibration of equipment; and safety and work precautions. Motion…

  2. Antiaromatic character of 16 π electron octaethylporphyrins: magnetically induced ring currents from DFT-GIMIC calculations.

    PubMed

    Fliegl, Heike; Pichierri, Fabio; Sundholm, Dage

    2015-03-19

    The magnetically induced current density susceptibility, also called current density, has been calculated for a recently synthesized octaethylporphyrin (OEP) zinc(II) dication with formally 16 π electrons. Numerical integration of the current density passing selected chemical bonds yields the current pathway around the porphyrinoid ring and the strength of the ring current. The current strengths show that the OEP-Zn(II) dication is strongly antiaromatic, as also concluded experimentally. The calculation of the ring current pathway shows that all 24 π electrons participate in the transport of the ring current because the current splits into inner and outer branches of practically equal strengths at the four pyrrolic rings. The corresponding neutral octaethylporphyrinoid without Zn and inner hydrogens is found to be antiaromatic, sustaining a paratropic ring current along the inner pathway with 16 π electrons. The neutral OEP-Zn(II) molecule with formally 18 π electrons is found to be almost as aromatic as free-base porphyrin. However, also in this case, all 26 π electrons contribute to the ring current, as for free-base porphyrin. A comparison of calculated and measured (1)H NMR chemical shifts is presented. The current strength susceptibility under experimental conditions has been estimated by assuming a linear relation between experimental shielding constants and calculated current strengths. PMID:25141236

  3. Rotation of solar magnetic fields for the current solar cycle 24

    SciTech Connect

    Shi, X. J.; Xie, J. L.

    2014-11-01

    The rotation of solar magnetic fields for the current solar cycle 24 is investigated through a cross-correlation analysis of the Carrington synoptic maps of solar photospheric magnetic fields during Carrington rotation numbers 2076-2146 (2008 October to 2014 January). The sidereal rotation rates of positive and negative magnetic fields at some latitudes are shown, and it can be found that the positive (negative) fields generally rotate faster than the negative (positive) fields in the southern (northern) hemisphere at low latitudes. The mean rotation profiles of total, positive, and negative magnetic fields between ±60° latitudes in the time interval are also obtained. It should be noted that both of the mean rotation profiles of the positive and negative magnetic fields, as well as the mean rotation profile of the total magnetic field, exhibit a quasi-rigid rotation at latitudes above about 55°. The mean rotation rates of the positive (negative) polarity reach their maximum values at about 9°(6)° latitude in the southern (northern) hemisphere. The mean rotation profile of the total magnetic field displays an obvious north-south asymmetry, where the rotation seems to be more differential in the northern hemisphere. The latitude variation in the rotation rate differences between positive and negative magnetic fields is further studied, and it is found that magnetic fields with the same polarity as the leading sunspots at a given hemisphere rotate faster than those with the opposite polarity, except for the zones around 52° latitude of the southern hemisphere and around 35° latitude of the northern hemisphere. The implication of these results is discussed. It is clear that the obtained results can provide some observational constraints on the theoretical research of the mechanisms of differential rotation and solar cycle.

  4. Improvement of immunoassay detection system by using alternating current magnetic susceptibility.

    PubMed

    Kawabata, R; Mizoguchi, T; Kandori, A

    2016-03-01

    A major goal with this research was to develop a low-cost and highly sensitive immunoassay detection system by using alternating current (AC) magnetic susceptibility. We fabricated an improved prototype of our previously developed immunoassay detection system and evaluated its performance. The prototype continuously moved sample containers by using a magnetically shielded brushless motor, which passes between two anisotropic magneto resistance (AMR) sensors. These sensors detected the magnetic signal in the direction where each sample container passed them. We used the differential signal obtained from each AMR sensor's output to improve the signal-to-noise ratio (SNR) of the magnetic signal measurement. Biotin-conjugated polymer beads with avidin-coated magnetic particles were prepared to examine the calibration curve, which represents the relation between AC magnetic susceptibility change and polymer-bead concentration. For the calibration curve measurement, we, respectively, measured the magnetic signal caused by the magnetic particles by using each AMR sensor installed near the upper or lower part in the lateral position of the passing sample containers. As a result, the SNR of the prototype was 4.5 times better than that of our previous system. Moreover, the data obtained from each AMR sensor installed near the upper part in the lateral position of the passing sample containers exhibited an accurate calibration curve that represented good correlation between AC magnetic susceptibility change and polymer-bead concentration. The conclusion drawn from these findings is that our improved immunoassay detection system will enable a low-cost and highly sensitive immunoassay. PMID:27036824

  5. Improvement of immunoassay detection system by using alternating current magnetic susceptibility

    NASA Astrophysics Data System (ADS)

    Kawabata, R.; Mizoguchi, T.; Kandori, A.

    2016-03-01

    A major goal with this research was to develop a low-cost and highly sensitive immunoassay detection system by using alternating current (AC) magnetic susceptibility. We fabricated an improved prototype of our previously developed immunoassay detection system and evaluated its performance. The prototype continuously moved sample containers by using a magnetically shielded brushless motor, which passes between two anisotropic magneto resistance (AMR) sensors. These sensors detected the magnetic signal in the direction where each sample container passed them. We used the differential signal obtained from each AMR sensor's output to improve the signal-to-noise ratio (SNR) of the magnetic signal measurement. Biotin-conjugated polymer beads with avidin-coated magnetic particles were prepared to examine the calibration curve, which represents the relation between AC magnetic susceptibility change and polymer-bead concentration. For the calibration curve measurement, we, respectively, measured the magnetic signal caused by the magnetic particles by using each AMR sensor installed near the upper or lower part in the lateral position of the passing sample containers. As a result, the SNR of the prototype was 4.5 times better than that of our previous system. Moreover, the data obtained from each AMR sensor installed near the upper part in the lateral position of the passing sample containers exhibited an accurate calibration curve that represented good correlation between AC magnetic susceptibility change and polymer-bead concentration. The conclusion drawn from these findings is that our improved immunoassay detection system will enable a low-cost and highly sensitive immunoassay.

  6. Calculation of induced current densities for humans by magnetic fields from electronic article surveillance devices.

    PubMed

    Gandhi, O P; Kang, G

    2001-11-01

    This paper illustrates the use of the impedance method to calculate the electric fields and current densities induced in millimetre resolution anatomic models of the human body, namely an adult and 10- and 5-year-old children, for exposure to nonuniform magnetic fields typical of two assumed but representative electronic article surveillance (EAS) devices at 1 and 30 kHz, respectively. The devices assumed for the calculations are a solenoid type magnetic deactivator used at store checkouts and a pass-by panel-type EAS system consisting of two overlapping rectangular current-carrying coils used at entry and exit from a store. The impedance method code is modified to obtain induced current densities averaged over a cross section of 1 cm2 perpendicular to the direction of induced currents. This is done to compare the peak current densities with the limits or the basic restrictions given in the ICNIRP safety guidelines. Because of the stronger magnetic fields at lower heights for both the assumed devices, the peak 1 cm2 area-averaged current densities for the CNS tissues such as the brain and the spinal cord are increasingly larger for smaller models and are the highest for the model of the 5-year-old child. For both the EAS devices, the maximum 1 cm2 area-averaged current densities for the brain of the model of the adult are lower than the ICNIRP safety guideline, but may approach or exceed the ICNIRP basic restrictions for models of 10- and 5-year-old children if sufficiently strong magnetic fields are used. PMID:11720345

  7. Localization of Magnetized Electrons in Current Filaments as a Fundamental Cause of Coulomb Explosion

    SciTech Connect

    Gordeev, A.V.; Losseva, T.V.

    2005-01-15

    Mechanisms for generating current filaments in a dense plasma under the action of focused laser pulses and in a Z-pinch configuration are discussed. The main properties of current filaments with a zero and nonzero electron vorticity {omega}{sub e} = B - (c/e){nabla} x p{sub e} that originate at magnetic fields in the range 4{pi}n{sub e} m{sub e} c{sup 2} << B{sup 2} << 4{pi}n{sub i} m{sub i} c{sup 2} are investigated under the conditions of Coulomb explosion at currents below the ion Alfven current. A study is made of the equilibrium configurations of nonquasineutral current filaments in a purely longitudinal (B{sub z}) and a purely azimuthal (B{sub {theta}}) magnetic field and also in a more general case of a helical magnetic field, having two components, under conditions such that the charge separation occurs on a spatial scale on the order of the magnetic Debye radius r{sub B} {approx_equal} |B |/(4{pi}en{sub e}). It is shown that strong electric fields generated in the current filaments are comparable in magnitude to the atomic field and are capable of accelerating ions to energies of several tens of megaelectronvolts. The ion dynamics in strong electric fields of the filaments is calculated numerically and is shown to lead to the formation of collisionless shock waves on time scales on the order of several inverse ion plasma frequencies {omega}{sup -1}{sub pi}. The possible formation of current filaments on different spatiotemporal scales is considered.

  8. Comparison of current distributions in electroconvulsive therapy and transcranial magnetic stimulation

    NASA Astrophysics Data System (ADS)

    Sekino, Masaki; Ueno, Shoogo

    2002-05-01

    We compared current density distributions in electroconvulsive therapy (ECT) and transcranial magnetic stimulation (TMS) by numerical calculations. The model consisted of an air region and three types of tissues with different conductivities representing the brain, the skull, and the scalp. In the ECT model, electric currents were applied through electrodes with a voltage of 100 V. In the TMS model, a figure-eight coil (6 cm diameter per coil) was placed on the vertex of the head model. An alternating current with a peak intensity of 3.0 kA and a frequency of 4.2 kHz was applied to the coil. The maximum current densities inside the brain in ECT (bilateral electrode position) and TMS were 234 and 322 A/m2, respectively. The results indicate that magnetic stimulators can generate comparable current densities to ECT. While the skull significantly affected current distributions in ECT, TMS efficiently induced eddy currents in the brain. In addition, TMS is more beneficial than ECT because the localized current distribution reduces the risk of adverse side effects.

  9. Spin current valve effect in normal metal/magnetic insulator/normal metal sandwiches

    NASA Astrophysics Data System (ADS)

    Li, Junxue; Xu, Yadong; Aldosary, Mohammed; Tang, Chi; Lin, Zhisheng; Zhang, Shufeng; Lake, Roger; Shi, Jing; Shines Collaboration

    Pure spin current is generated in two common ways. One makes use of the spin Hall effect in normal metals (NM), the other utilizes spin waves with the quasi-particle excitations called magnons. A popular material for the latter is yttrium iron garnet (YIG), a magnetic insulator (MI). Here we demonstrate in NM/MI/NM sandwiches that these two types of spin current are interconvertible, which allows transmitting an electrical signal across the MI, predicted as the magnon-mediated current drag phenomenon. We show experimentally that the spin current can be switched ``on'' or ``off'' by controlling the magnetization orientation of MI, analogous to conventional spin valves for spin-polarized charge current. The transmitted current drag signal scales linearly with the driving current without any threshold and follows the power-law Tn with n ranging from 1.5 to 2.5. Our results indicate that the NM/MI/NM sandwich structure can serve as a scalable pure spin current valve device which is an essential ingredient in spintronics. As part of the SHINES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # SC0012670.

  10. Magnetotail Current Sheet Thinning and Magnetic Reconnection Dynamics in Global Modeling of Substorms

    NASA Technical Reports Server (NTRS)

    Kuznetsova, M. M.; Hesse, M.; Rastaetter, L.; Toth, G.; DeZeeuw, D. L.; Gombosi, T. I.

    2008-01-01

    Magnetotail current sheet thinning and magnetic reconnection are key elements of magnetospheric substorms. We utilized the global MHD model BATS-R-US with Adaptive Mesh Refinement developed at the University of Michigan to investigate the formation and dynamic evolution of the magnetotail thin current sheet. The BATSRUS adaptive grid structure allows resolving magnetotail regions with increased current density up to ion kinetic scales. We investigated dynamics of magnetotail current sheet thinning in response to southwards IMF turning. Gradual slow current sheet thinning during the early growth phase become exponentially fast during the last few minutes prior to nightside reconnection onset. The later stage of current sheet thinning is accompanied by earthward flows and rapid suppression of normal magnetic field component $B-z$. Current sheet thinning set the stage for near-earth magnetic reconnection. In collisionless magnetospheric plasma, the primary mechanism controlling the dissipation in the vicinity of the reconnection site is non-gyrotropic effects with spatial scales comparable with the particle Larmor radius. One of the major challenges in global MHD modeling of the magnetotail magnetic reconnection is to reproduce fast reconnection rates typically observed in smallscale kinetic simulations. Bursts of fast reconnection cause fast magnetic field reconfiguration typical for magnetospheric substorms. To incorporate nongyritropic effects in diffusion regions we developed an algorithm to search for magnetotail reconnection sites, specifically where the magnetic field components perpendicular to the local current direction approaches zero and form an X-type configuration. Spatial scales of the diffusion region and magnitude of the reconnection electric field are calculated self-consistently using MHD plasma and field parameters in the vicinity of the reconnection site. The location of the reconnection sites and spatial scales of the diffusion region are updated

  11. Towards the invisible cryogenic system for Magnetic Resonance Imaging

    NASA Astrophysics Data System (ADS)

    Steinmeyer, F.; Retz, P. W.; White, K.; Lang, A.; Stautner, W.; Smith, P. N.; Gilgrass, G.

    2002-05-01

    With about 10,000 Magnetic Resonance Imaging (MRI) systems installed worldwide, helium cooled magnets have become familiar equipment in hospitals and imaging centers. Patients and operators are only aware of the hissing sound of the Gifford-MacMahon refrigerator. Service technicians, however, still work with cryogenic fluids and cold gases, e.g. for replenishing the helium reservoir, inserting retractable current leads for magnet ramps, or replacing burst disks after a magnet quench. We will describe the steps taken at Oxford Magnet Technology towards the ultimate goal of a superconducting magnet being as simple as a household fridge. Early steps included the development of resealing quench valves, as well as permanently installed transfer siphons that only open when fully cooled to 4K. On recently launched 1.5 Tesla solenoid magnets, 500 A current leads are permanently fixed into the service turret, with hardly any boil-off penalty (40-50 cc/hr total). Ramping of the magnet has been fully automated, including electronic supervision of the gas-cooled current leads. One step ahead, the 1 Tesla High Field Open magnet is refrigerated by a single 4K Gifford MacMahon coldhead, relieving the user from the necessity to refill with helium. Our conduction cooled 0.2 Tesla HTS magnet testbed does not require liquid cryogens at any time in its life, including initial cool-down.

  12. Receptor Activity-Modifying Proteins (RAMPs): New Insights and Roles.

    PubMed

    Hay, Debbie L; Pioszak, Augen A

    2016-01-01

    It is now recognized that G protein-coupled receptors (GPCRs), once considered largely independent functional units, have a far more diverse molecular architecture. Receptor activity-modifying proteins (RAMPs) provide an important example of proteins that interact with GPCRs to modify their function. RAMPs are able to act as pharmacological switches and chaperones, and they can regulate signaling and/or trafficking in a receptor-dependent manner. This review covers recent discoveries in the RAMP field and summarizes the known GPCR partners and functions of RAMPs. We also discuss the first peptide-bound structures of RAMP-GPCR complexes, which give insight into the molecular mechanisms that enable RAMPs to alter the pharmacology and signaling of GPCRs. PMID:26514202

  13. Extending the GMR current measurement range with a counteracting magnetic field.

    PubMed

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

    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 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. PMID:23793022

  14. Magnetic Reconnection Onset via Disruption of a Forming Current Sheet by the Tearing Instability

    NASA Astrophysics Data System (ADS)

    Uzdensky, D. A.; Loureiro, N. F.

    2016-03-01

    The recent realization that Sweet-Parker current sheets are violently unstable to the secondary tearing (plasmoid) instability implies that such current sheets cannot occur in real systems. This suggests that, in order to understand the onset of magnetic reconnection, one needs to consider the growth of the tearing instability in a current layer as it is being formed. Such an analysis is performed here in the context of nonlinear resistive magnetohydrodynamics for a generic time-dependent equilibrium representing a gradually forming current sheet. It is shown that two onset regimes, single-island and multi-island, are possible, depending on the rate of current sheet formation. A simple model is used to compute the criterion for transition between these two regimes, as well as the reconnection onset time and the current sheet parameters at that moment. For typical solar corona parameters, this model yields results consistent with observations.

  15. Magnetic Reconnection Onset via Disruption of a Forming Current Sheet by the Tearing Instability.

    PubMed

    Uzdensky, D A; Loureiro, N F

    2016-03-11

    The recent realization that Sweet-Parker current sheets are violently unstable to the secondary tearing (plasmoid) instability implies that such current sheets cannot occur in real systems. This suggests that, in order to understand the onset of magnetic reconnection, one needs to consider the growth of the tearing instability in a current layer as it is being formed. Such an analysis is performed here in the context of nonlinear resistive magnetohydrodynamics for a generic time-dependent equilibrium representing a gradually forming current sheet. It is shown that two onset regimes, single-island and multi-island, are possible, depending on the rate of current sheet formation. A simple model is used to compute the criterion for transition between these two regimes, as well as the reconnection onset time and the current sheet parameters at that moment. For typical solar corona parameters, this model yields results consistent with observations. PMID:27015487

  16. FPGA-Based Digital Current Switching Power Amplifiers Used in Magnetic Bearing Systems

    NASA Astrophysics Data System (ADS)

    Wang, Yin; Zhang, Kai; Dong, Jinping

    For a traditional two-level current switching power amplifier (PA) used in a magnetic bearing system, its current ripple is obvious. To increase its current ripple performance, three-level amplifiers are designed and their current control is generally based on analog and logical circuits. So the required hardware is complex and a performance increase from the hardware adjustment is difficult. To solve this problem, a FPGA-based digital current switching power amplifier (DCSPA) was designed. Its current ripple was obviously smaller than a two-level amplifier and its control circuit was much simpler than a tri-level amplifier with an analog control circuit. Because of the field-programmable capability of a FPGA chip used, different control algorithms including complex nonlinear algorithms could be easily implemented in the amplifier and their effects could be compared with the same hardware.

  17. Field-Aligned and Ionospheric Current Contributions to Ground Magnetic Perturbations

    NASA Astrophysics Data System (ADS)

    Connors, M. G.; McPherron, R. L.; Anderson, B. J.; Korth, H.; Russell, C. T.; Chu, X.

    2014-12-01

    AMPERE data provides global space-derived radial electric currents on temporal and spatial scales suited to studying magnetic fields at ULF frequencies. It responds little to ionspheric currents, which dominate ground-based measurements, so that AMPERE and ground datasets complement each other to give a comprehensive view of near-Earth electric currents. Connors et al. (GRL, 2014) found that a three-dimensional current system slightly modified from the original substorm current wedge (SCW) concept of McPherron et al. (JGR, 1973) represented substorm midnight sector perturbations well both in the auroral and subauroral regions, if a current equivalent to that found by integrating AMPERE downward current was used, located where clear SCW signatures were indicated by AMPERE, and featuring an ionospheric electrojet. The AMPERE upward current was found to exceed that in the SCW, at least in part since the evening sector electrojet fed into it. We extend these results with a more detailed accounting of field-aligned and ionospheric currents throughout the active period (including growth phase). Ionospheric currents for the study are obtained from ground perturbations through optimization of a simple forward model over regions or on a meridian chain. We also investigate the degree to which subauroral perturbations may be directly calculated from AMPERE results. We further find that auroral zone currents may be very localized, to the extent that the entire SCW ionospheric current flows in a very restricted latitudinal range near onset, possibly corresponding to a single auroral arc.

  18. NASA #801 and NASA 7 on ramp

    NASA Technical Reports Server (NTRS)

    1997-01-01

    NASA N801NA and NASA 7 together on the NASA Dryden ramp. The Beechcraft Beech 200 Super KingAir aircraft N7NA, known as NASA 7, has been a support aircraft for many years, flying 'shuttle' missions to Ames Research Center. It once flew from the Jet Propulsion Laboratory and back each day but now (2001) flies between the Dryden Flight Research Center and Ames. A second Beechcraft Beech 200 Super King Air, N701NA, redesignated N801NA, transferred to Dryden on 3 Oct. 1997 and is used for research missions but substitutes for NASA 7 on shuttle missions when NASA 7 is not available.

  19. Status of the SNS Power Ramp Up

    SciTech Connect

    Plum, Michael A

    2010-01-01

    The Spallation Neutron Source accelerator complex consists of a 2.5 MeV H front-end injector system, a 186 MeV normal-conducting linear accelerator, a 1 GeV superconducting linear accelerator, an accumulator ring, and associated beam transport lines. Since formal operations began in 2006, the beam power has been steadily increasing toward the design goal of 1.4 MW. In September 2009 the power surpassed 1 MW for the first time, and operation at the 1 MW level is now routine. The status of the beam power ramp-up program and present operational limitations will be described.

  20. Enhanced Magnetic Field Perturbations and Electric Currents Observed Downstream of the High Power Helicon

    NASA Astrophysics Data System (ADS)

    Race Roberson, B.; Winglee, Robert; Ziemba, Tim; Prager, James

    2010-11-01

    The high power helicon (HPH) is a compact plasma source that can generate downstream densities of 10^17-10^18 m-3 and directed ion energies greater than 20 eV that continue to increase tens of centimeters downstream of the source. In order to understand the coupling mechanism between the helicon antenna and the plasma outside the immediate source region, measurements were made in the plasma plume downstream from the thruster of the propagating wave magnetic field and the perturbation of the axial bulk field. This magnetic field perturbation (δB) peaks at more than 15 gauss in strength downstream of the plasma source and propagates tens of centimeters downstream, cancelling the base magnetic field as it propagates. Taking the curl of this measured magnetic perturbation and assuming azimuthal symmetry suggests a peak current density of 20 kA m-2. Data will be presented that relates the cancellation of the base magnetic field to the propagation of the helicon wave and the region where the plasma current system closes.

  1. On the linear stability of sheared and magnetized jets without current sheets - non-relativistic case

    NASA Astrophysics Data System (ADS)

    Kim, Jinho; Balsara, Dinshaw S.; Lyutikov, Maxim; Komissarov, Serguei S.

    2016-05-01

    In a prior paper (Kim et al. 2015) we considered the linear stability of magnetized jets that carry no net electric current and do not have current sheets. In this paper, in addition to physically well-motivated magnetic field structures, we also include the effects of jet shear. The jets we study have finite thermal pressure in addition to having realistic magnetic field structures and velocity shear. We find that shear has a strongly stabilizing effect on various modes of jet instability. Increasing shear stabilizes the fundamental pinch modes at long wavelengths and short wavelengths. Increasing shear also stabilizes the first reflection pinch modes at short wavelengths. Increasing shear has only a very modest stabilizing effect on the fundamental kink modes at long wavelengths; however, increasing shear does have a strong stabilizing effect on the fundamental kink modes at short wavelengths. The first reflection kink modes are strongly stabilized by increasing shear at shorter wavelengths. Overall, we find that the combined effect of magnetic field and shear stabilizes jets more than shear alone. In addition to the results from a formal linear stability analysis, we present a novel way of visualizing and understanding jet stability. This gives us a deeper understanding of the enhanced stability of sheared, magnetized jets. We also emphasize the value of our numerical approach in understanding the linear stability of jets with realistic structure.

  2. On the linear stability of sheared and magnetized jets without current sheets - non-relativistic case

    NASA Astrophysics Data System (ADS)

    Kim, Jinho; Balsara, Dinshaw S.; Lyutikov, Maxim; Komissarov, Serguei S.

    2016-09-01

    In a prior paper, we considered the linear stability of magnetized jets that carry no net electric current and do not have current sheets. In this paper, in addition to physically well-motivated magnetic field structures, we also include the effects of jet shear. The jets we study have finite thermal pressure in addition to having realistic magnetic field structures and velocity shear. We find that shear has a strongly stabilizing effect on various modes of jet instability. Increasing shear stabilizes the fundamental pinch modes at long wavelengths and short wavelengths. Increasing shear also stabilizes the first reflection pinch modes at short wavelengths. Increasing shear has only a very modest stabilizing effect on the fundamental kink modes at long wavelengths; however, increasing shear does have a strong stabilizing effect on the fundamental kink modes at short wavelengths. The first reflection kink modes are strongly stabilized by increasing shear at shorter wavelengths. Overall, we find that the combined effect of magnetic field and shear stabilizes jets more than shear alone. In addition to the results from a formal linear stability analysis, we present a novel way of visualizing and understanding jet stability. This gives us a deeper understanding of the enhanced stability of sheared, magnetized jets. We also emphasize the value of our numerical approach in understanding the linear stability of jets with realistic structure.

  3. Current driven magnetization dynamics of a self-polarised synthetic ferrimagnet

    SciTech Connect

    Jenkins, A. S.; Lacoste, B.; Geranton, G.; Gusakova, D.; Dieny, B.; Ebels, U.; Buda-Prejbeanu, L. D.

    2014-02-28

    Spin torque driven excitations in spin valves and tunnel junctions are often investigated for a two magnetic layer system for which a polarizer (fixed magnetization) and a free layer can be distinguished. In the search for improved microwave properties and to understand the role of different coupling mechanisms between the magnetic layers, here, the excitation spectrum of an exchange coupled two layer synthetic ferrimagnet (SyF) system is investigated numerically with spin momentum transfer acting on both layers simultaneously. This self-polarised two layer system does not contain an external polarizer, and excitation of coupled modes arises due to the mutual spin transfer torque and the Ruderman-Kittel-Kasuya-Yosida interlayer exchange coupling. The current-field state diagrams of static and dynamic states are reported as a function of the interlayer exchange coupling strength. The numerically determined critical boundaries are well reproduced by an analytical stability analysis. The dynamic steady states reveal an optic-like mode at low magnetic fields, which becomes progressively acoustic-like for increased magnetic fields and currents. The frequency of these modes can be tuned by the film thickness and the strength of the interlayer exchange interaction. The results presented here will provide an important guide for designing spin torque oscillators that exploit the dynamic coupling between layers and, furthermore, they will provide a basis to test analytical models of spin torque driven coupled excitations.

  4. Magnon excitation by spin-polarized direct currents in magnetic nanostructures

    NASA Astrophysics Data System (ADS)

    Rezende, S. M.; de Aguiar, F. M.; Azevedo, A.

    2006-03-01

    The dynamics of the magnetization in a thin ferromagnetic film traversed by a spin-polarized direct current is studied. In such a system, spin waves (magnons) may be critically driven out of equilibrium by an effective spin-injection field that is proportional to the current density. A direct comparison between the predicted critical current and previous experimental results sheds light on the nature of the excited mode. Beyond the threshold, it is assumed that the spin waves are coupled through nonlinear interactions arising from dipolar and surface anisotropy energies. It is shown that the magnon-magnon interactions play two major roles in the dynamics: (i) They govern and put a limit to the growth in the population of the unstable mode from the thermal level, and (ii) directly contribute to the renormalization of the magnon energy, which manifests itself through a shift in the precession frequency of the magnetic moments with varying current intensity. Numerical results are presented in remarkable quantitative agreement with recent experiments in nanometric magnetic multilayers, where microwave oscillations generated by direct currents have been observed in the postthreshold regime.

  5. Kelvin-Helmholtz instability in a current-vortex sheet at a 3D magnetic null

    SciTech Connect

    Wyper, P. F.; Pontin, D. I.

    2013-03-15

    We report here, for the first time, an observed instability of a Kelvin-Helmholtz nature occurring in a fully three-dimensional (3D) current-vortex sheet at the fan plane of a 3D magnetic null point. The current-vortex layer forms self-consistently in response to foot point driving around the spine lines of the null. The layer first becomes unstable at an intermediate distance from the null point, with the instability being characterized by a rippling of the fan surface and a filamentation of the current density and vorticity in the shear layer. Owing to the 3D geometry of the shear layer, a branching of the current filaments and vortices is observed. The instability results in a mixing of plasma between the two topologically distinct regions of magnetic flux on either side of the fan separatrix surface, as flux is reconnected across this surface. We make a preliminary investigation of the scaling of the system with the dissipation parameters. Our results indicate that the fan plane separatrix surface is an ideal candidate for the formation of current-vortex sheets in complex magnetic fields and, therefore, the enhanced heating and connectivity change associated with the instabilities of such layers.

  6. Nonlinear response of magnetic islands to localized electron cyclotron current injection

    SciTech Connect

    Borgogno, D.; Comisso, L.; Grasso, D.; Lazzaro, E.

    2014-06-15

    The magnetic island evolution under the action of a current generated externally by electron cyclotron wave beams is studied using a reduced resistive magnetohydrodynamics plasma model. The use of a two-dimensional reconnection model shows novel features of the actual nonlinear evolution as compared to the zero-dimensional model of the generalized Rutherford equation. When the radio frequency control is applied to a small magnetic island, the complete annihilation of the island width is followed by a spatial phase shift of the island, referred as “flip” instability. On the other hand, a current-drive injection in a large nonlinear island can be accompanied by the occurrence of a Kelvin-Helmholtz instability. These effects need to be taken into account in designing tearing mode control systems based on radio frequency current-drive.

  7. Ring Current Decay During Northward Turnings of The Interplanetary Magnetic Field

    NASA Astrophysics Data System (ADS)

    Monreal MacMahon, R.; Llop, C.; Miranda, R.

    The ring current formation and energization is thought to be the main consequence of geomagnetic storms and its strength is characterized by the Dst index which evolu- tion satisfies a simple and well-known differential equation introduced by Burton et al. (1975). Since then, several attempts and approaches have been done to study the evolution of the ring current whether introducing discrete values or continuous func- tions for the decay time involved. In this work, we study the character of the recovery phase of magnetic storms in response to well defined northward turnings of the inter- planetary magnetic field using our functional form of the decay time of ring current particles introduced previously.

  8. Method of correcting eddy current magnetic fields in particle accelerator vacuum chambers

    DOEpatents

    Danby, G.T.; Jackson, J.W.

    1990-03-19

    A method for correcting magnetic field aberrations produced by eddy currents induced in a particle accelerator vacuum chamber housing is provided wherein correction windings are attached to selected positions on the housing and the windings are energized by transformer action from secondary coils, which coils are inductively coupled to the poles of electro-magnets that are powered to confine the charged particle beam within a desired orbit as the charged particles are accelerated through the vacuum chamber by a particle-driving rf field. The power inductively coupled to the secondary coils varies as a function of variations in the power supplied by the particle-accelerating rf field to a beam of particles accelerated through the vacuum chamber, so the current in the energized correction coils is effective to cancel eddy current flux fields that would otherwise be induced in the vacuum chamber by power variations (dB/dt) in the particle beam.

  9. Method of correcting eddy current magnetic fields in particle accelerator vacuum chambers

    DOEpatents

    Danby, Gordon T.; Jackson, John W.

    1991-01-01

    A method for correcting magnetic field aberrations produced by eddy currents induced in a particle accelerator vacuum chamber housing is provided wherein correction windings are attached to selected positions on the housing and the windings are energized by transformer action from secondary coils, which coils are inductively coupled to the poles of electro-magnets that are powered to confine the charged particle beam within a desired orbit as the charged particles are accelerated through the vacuum chamber by a particle-driving rf field. The power inductively coupled to the secondary coils varies as a function of variations in the power supplied by the particle-accelerating rf field to a beam of particles accelerated through the vacuum chamber, so the current in the energized correction coils is effective to cancel eddy current flux fields that would otherwise be induced in the vacuum chamber by power variations in the particle beam.

  10. Can we derive the current density from three point LEO measurements of the magnetic field perturbations?

    NASA Astrophysics Data System (ADS)

    Gjerloev, J. W.; Potter, M.; Muhleisen, M.; Friel, M. M.; Martin, P.; Le, G.; Stolle, C.; Luhr, H.

    2014-12-01

    In this paper, we perform critical test of the well-known curlometer technique. The curlometer technique allows a derivation of the current density using measurements of the magnetic field at spatially separated points. At LEO altitudes this generally three dimensionally problem is simplified to a two dimensions by the fact that the current is almost solely flowing along the magnetic field lines. Strictly speaking the current density is derived from integration around a closed loop but in the curlometer technique this integration is simplified to a summation over just three points. In this paper we present a critical analysis of when and to what extend this approximation is valid. We show some simple theoretical considerations, results from a series of simulations, and finally apply the knowledge to ESA SWARM measurements.

  11. Correlation between x-ray reciprocal space maps and magnetic properties of current-induced magnetization switching pseudospin valve structures

    NASA Astrophysics Data System (ADS)

    Siffalovic, P.; Chitu, L.; Halahovets, Y.; Jergel, M.; Senderak, R.; Majkova, E.; Luby, S.

    2007-02-01

    A thorough study of x-ray diffuse scattering from the spin valve structures suitable for current induced magnetization switching is presented. We used complete reciprocal space maps of diffusely scattered x rays to show the effect of bottom Au electrode on the morphology of buried spin valve interfaces. The thickness and roughness of each layer, as well as vertical and lateral roughness correlation lengths, were obtained. The impact of interfaces morphology on the magnetic properties, especially on the increase of spin valve coercivity, was measured and simulated within the frame of Néel magnetostatic coupling model based on the parameters from the x-ray diffuse scattering data. Measurement of x-ray diffuse scattering presents a rapid and nondestructive technique for in-depth and self-contained analysis of spin valve layers and interfaces.

  12. Manipulation of pure spin current in ferromagnetic metals independent of magnetization

    NASA Astrophysics Data System (ADS)

    Tian, Dai; Li, Yufan; Qu, D.; Huang, S. Y.; Jin, Xiaofeng; Chien, C. L.

    2016-07-01

    Upon the injection of a pure spin current, a ferromagnet, similar to a nonmagnetic metal, also exhibits inverse spin Hall effect (ISHE). We show in Co/Cu/YIG, where the thin Cu layer allows transmission of spin current from YIG into Co but decouples the two ferromagnets, that the interaction between ISHE and ferromagnetic ordering in Co can be unambiguously investigated. By switching on and off the pure spin current contribution, we demonstrate that the ISHE in Co is independent of the direction of the Co magnetization, which clearly suggests that the ISHE in Co is dominated not by the extrinsic impurity scatterings, but from the intrinsic origin.

  13. Perpendicular currents and electric fields in fully and partially ionized magnetized plasma

    SciTech Connect

    Rozhansky, V.

    2013-10-15

    Perpendicular currents and self-consistent electric fields in fully and partially ionized plasma in strong magnetic field are analyzed. In fully ionized plasma, the analyses are concentrated on closing of viscosity driven currents. For partially ionized plasma, it is demonstrated that the perpendicular currents could be expressed through the total pressure gradient (including the pressure gradient of neutral particles) and viscosity of neutrals. The self-consistent electric fields and corresponding E(vector sign)×B(vector sign) could be quite large, which is important for various applications, in particular, for the divertor plasma of a tokamak in the detached regime.

  14. Utilizing resonant magnetic perturbations to enhance neoclassical tearing mode stabilization by rf current

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoguang; Zhang, Xiaodong; Yu, Qingquan; Wu, Bin; Zhu, Sizheng; Wang, Jinfang; Zhang, Yang; Wang, Xiaojing

    2015-09-01

    A new method to stabilize the rotating neoclassical tearing mode (NTM) by using both the rf current drive and the static resonant magnetic perturbation (RMP) is investigated. When a non-uniform mode rotation is induced by the RMP, the stabilization of NTM by the rf current is found to be enhanced if the RMP phase has a half period difference from that of the rf wave deposition along the helical angle. The required rf current for mode stabilization is reduced by about one third if an appropriate RMP amplitude is applied.

  15. Ion-Banana-Orbit-Width Effect on Bootstrap Current for Small Magnetic Islands

    NASA Astrophysics Data System (ADS)

    Qu, Hongpeng

    2013-09-01

    A simple and direct theoretical method has been proposed to investigate the so-called ion-banana-orbit-width (IBW) effect on the bootstrap current in the region of magnetic islands generated by the neoclassical tearing mode (NTM). The result shows that, when the IBW approaches the island width, the (ion) bootstrap current can be partly restored inside the island while the pressure profile is flattened. This can lead to the reduction of the bootstrap current drive on the NTM. The strength of the IBW effect on the NTM is related to the safety factor and the inverse aspect ratio on the rational surface.

  16. Spin polarized current controlled dynamics of domain walls in magnetic films with in-plane anisotropy

    NASA Astrophysics Data System (ADS)

    Filippov, B. N.; Dubovik, M. N.; Korzunin, L. G.

    2016-06-01

    We study the dynamic properties of asymmetric vortex Bloch walls and classical 1D Néel walls controlled by a spin-polarized current in magnetic films with in-plane anisotropy. It is shown that fairly high velocities of domain walls (up to 100 m/s) can be obtained for the current density in the range j = 106-108 A/cm2. The nonlinear dependence of the wall velocity on the film thickness and the linear dependence of the velocity on the current density and inverse damping parameter are found.

  17. The influence of the ion polarization current on magnetic island stability in a tokamak plasma

    SciTech Connect

    Fitzpatrick, R.; Waelbroeck, F. L.; Militello, F.

    2006-12-15

    The influence of the ion polarization current on the stability of a constant-{psi} magnetic island in a tokamak plasma is investigated numerically using a reduced two-fluid model in two-dimensional slab geometry. The polarization current is found to be negligibly small when the island is either too narrow or too wide. However, under certain circumstances, there exists an intermediate regime in which the polarization current is appreciable, and has a stabilizing influence on the island. This effect may account for the metastable nature of neoclassical tearing modes in tokamak plasmas.

  18. Analysis of Voltage Signals from Superconducting Accelerator Magnets

    SciTech Connect

    Lizarazo, J.; Caspi, S.; Ferracin, P.; Joseph, J.; Lietzke, A. F.; Sabbi, G. L.; Wang, X.

    2009-10-30

    We present two techniques used in the analysis of voltage tap data collected during recent tests of superconducting magnets developed by the Superconducting Magnet Program at Lawrence Berkeley National Laboratory. The first technique was used on a quadrupole to provide information about quench origins that could not be obtained using the time-of-flight method. The second technique illustrates the use of data from transient flux imbalances occurring during magnet ramping to diagnose changes in the current-temperature margin of a superconducting cable. In both cases, the results of this analysis contributed to make improvements on subsequent magnets.

  19. A synthesis of current knowledge and future directions for soil magnetism research

    NASA Astrophysics Data System (ADS)

    Hannam, Jacqueline A.; Van Dam, Remke L.; Harmon, Russell S.

    2009-05-01

    Magnetic properties of soils have adverse effects on metal detectors, particularly hampering operations during clearance of landmines and unexploded ordnance. Although there is well established research in soil magnetism and modeling electromagnetic induction systems these have tended to exist in disparate disciplines. Hence, a workshop was organized to bring together researchers, academics, stakeholders and manufacturers to discuss key priorities for research and technology in a unique multidisciplinary environment. Key knowledge gaps identified include limited information on the spatial heterogeneity of soil magnetic properties in 2D and 3D, whether current models describing soil responses are appropriate for all soils and the need for compensation mechanisms in detectors to be improved. Several priorities were identified that would maximize future developments for multidisciplinary research in soil magnetism and detector technology. These include acquiring well constrained empirical data on soil electromagnetic properties and detector response over the frequency range of detectors; development of predictive models of soil magnetic properties; investigating variability of soil magnetic properties in two and three dimensions across a range of scales. Improved communication between disciplines is key to effective targeting and realization of research priorities. Possible platforms include a multidisciplinary pilot study at an appropriate site and the development of an online repository to assist dissemination of results and information.

  20. The effect of current-induced spin switching in the presence of quantum tunneling of magnetization

    NASA Astrophysics Data System (ADS)

    Misiorny, Maciej; Barnaś, Józef

    2013-03-01

    Knowledge of transport properties of individual large-spin (S > 1 / 2) atoms/molecules exhibiting magnetic anisotropy is of key importance from the point of view of information processing technologies. The ultimate aim is to incorporate such objects as functional elements of spintronic devices, with the objective of employing spin-polarized currents to control the magnetic state of the system. In particular, for an atom/molecule with the predominant `easy-axis' uniaxial magnetic anisotropy this allows for switching the system's spin between two metastable states. However, the uniaxial component of magnetic anisotropy, underlying the magnetic bistability, is frequently accompanied by the transverse one, whose presence manifests, e.g., as quantum tunneling of magnetization (QTM). Here, we show that not only does QTM induce an effective energy barrier for the spin switching, but also its effect on the transport reveals as an additional signal in transport characteristics. Furthermore, we propose how to experimentally investigate QTM by means of the STM inelastic transport spectroscopy. also at Adam Mickiewicz University

  1. An electrodynamic model of electric currents and magnetic fields in the dayside ionosphere of Venus

    NASA Technical Reports Server (NTRS)

    Cloutier, P. A.; Tascione, T. F.; Danieli, R. E., Jr.

    1981-01-01

    The electric current configuration induced in the ionosphere of Venus by the interaction of the solar wind has been calculated in previous papers (Cloutier and Daniell, 1973; Daniell and Cloutier, 1977; Cloutier and Daniell, 1979) for average steady-state solar wind conditions and interplanetary magnetic field. This model is generalized to include the effects of (1) plasma depletion and magnetic field enhancement near the ionopause, (2) velocity-shear-induced MHD instabilities of the Kelvin-Helmholtz type within the ionosphere, and (3) variations in solar wind parameters and interplanetary magnetic field. It is shown that the magnetic field configuration resulting from the model varies in response to changes in solar wind and interplanetary field conditions, and that these variations produce magnetic field profiles in excellent agreement with those seen by the Pioneer-Venus Orbiter. The formation of flux-ropes by the Kelving-Helmholtz instability is shown to be a natural consequence of the model, with the spatial distribution and size of the flux-ropes determined by the magnetic Reynolds number.

  2. An electrodynamic model of electric currents and magnetic fields in the dayside ionosphere of Venus

    NASA Astrophysics Data System (ADS)

    Cloutier, P. A.; Tascione, T. F.; Daniell, R. E.

    1981-06-01

    The electric current configuration induced in the ionosphere of Venus by the interaction of the solar wind has been calculated in previous papers (Cloutier and Daniell, 1973; Daniell and Cloutier, 1977; Cloutier and Daniell, 1979) for average steady-state solar wind conditions and interplanetary magnetic field. This model is generalized to include the effects of (1) plasma depletion and magnetic field enhancement near the ionopause, (2) velocity-shear-induced MHD instabilities of the Kelvin-Helmholtz type within the ionosphere, and (3) variations in solar wind parameters and interplanetary magnetic field. It is shown that the magnetic field configuration resulting from the model varies in response to changes in solar wind and interplanetary field conditions, and that these variations produce magnetic field profiles in excellent agreement with those seen by the Pioneer-Venus Orbiter. The formation of flux-ropes by the Kelving-Helmholtz instability is shown to be a natural consequence of the model, with the spatial distribution and size of the flux-ropes determined by the magnetic Reynolds number.

  3. Current and future role of magnetically assisted gastric capsule endoscopy in the upper gastrointestinal tract

    PubMed Central

    Ching, Hey-Long; Hale, Melissa Fay; McAlindon, Mark Edward

    2016-01-01

    Capsule endoscopy first captivated the medical world when it provided a means to visualize the small bowel, which was previously out of endoscopic reach. In the subsequent decade and a half we continue to learn of the true potential that capsule endoscopy has to offer. Of particular current interest is whether capsule endoscopy has any reliable investigative role in the upper gastrointestinal tract. Much research has already been dedicated to enhancing the diagnostic and indeed therapeutic properties of capsule endoscopy. Specific modifications to tackle the challenges of the gut have already been described in the current literature. In the upper gastrointestinal tract, the capacious anatomy of the stomach represents one of many challenges that capsule endoscopy must overcome. One solution to improving diagnostic yield is to utilize external magnetic steering of a magnetically receptive capsule endoscope. Notionally this would provide a navigation system to direct the capsule to different areas of the stomach and allow complete gastric mucosal examination. To date, several studies have presented promising data to support the feasibility of this endeavour. However the jury is still out as to whether this system will surpass conventional gastroscopy, which remains the gold standard diagnostic tool in the foregut. Nevertheless, a minimally invasive and patient-friendly alternative to gastroscopy remains irresistibly appealing, warranting further studies to test the potential of magnetically assisted capsule endoscopy. In this article the authors would like to share the current state of magnetically assisted capsule endoscopy and anticipate what is yet to come. PMID:27134661

  4. Depinning probability of a magnetic domain wall in nanowires by spin-polarized currents.

    PubMed

    Fukami, S; Yamanouchi, M; Ikeda, S; Ohno, H

    2013-01-01

    Current-induced magnetic domain wall motion is attractive for manipulating magnetization direction in spintronics devices, which open a new era of electronics. Up to now, in spite of a crucial significance to applications, investigation on a current-induced domain wall depinning probability, especially in sub-nano to a-few-nanosecond range has been lacking. Here we report on the probability of the depinning in perpendicularly magnetized Co/Ni nanowires in this timescale. A high depinning probability was obtained even for 2-ns pulses with a current density of less than 10¹² A m⁻². A one-dimensional Landau-Lifshitz-Gilbert calculation taking into account thermal fluctuations reproduces well the experimental results. We also calculate the depinning probability as functions of various parameters and found that parameters other than the coercive field do not affect the transition width of the probability. These findings will allow one to design high-speed and reliable magnetic devices based on the domain wall motion. PMID:23945735

  5. Current and future role of magnetically assisted gastric capsule endoscopy in the upper gastrointestinal tract.

    PubMed

    Ching, Hey-Long; Hale, Melissa Fay; McAlindon, Mark Edward

    2016-05-01

    Capsule endoscopy first captivated the medical world when it provided a means to visualize the small bowel, which was previously out of endoscopic reach. In the subsequent decade and a half we continue to learn of the true potential that capsule endoscopy has to offer. Of particular current interest is whether capsule endoscopy has any reliable investigative role in the upper gastrointestinal tract. Much research has already been dedicated to enhancing the diagnostic and indeed therapeutic properties of capsule endoscopy. Specific modifications to tackle the challenges of the gut have already been described in the current literature. In the upper gastrointestinal tract, the capacious anatomy of the stomach represents one of many challenges that capsule endoscopy must overcome. One solution to improving diagnostic yield is to utilize external magnetic steering of a magnetically receptive capsule endoscope. Notionally this would provide a navigation system to direct the capsule to different areas of the stomach and allow complete gastric mucosal examination. To date, several studies have presented promising data to support the feasibility of this endeavour. However the jury is still out as to whether this system will surpass conventional gastroscopy, which remains the gold standard diagnostic tool in the foregut. Nevertheless, a minimally invasive and patient-friendly alternative to gastroscopy remains irresistibly appealing, warranting further studies to test the potential of magnetically assisted capsule endoscopy. In this article the authors would like to share the current state of magnetically assisted capsule endoscopy and anticipate what is yet to come. PMID:27134661

  6. Stable explicit coupling of the Yee scheme with a linear current model in fluctuating magnetized plasmas

    SciTech Connect

    Silva, Filipe da; Pinto, Martin Campos; Després, Bruno; Heuraux, Stéphane

    2015-08-15

    This work analyzes the stability of the Yee scheme for non-stationary Maxwell's equations coupled with a linear current model with density fluctuations. We show that the usual procedure may yield unstable scheme for physical situations that correspond to strongly magnetized plasmas in X-mode (TE) polarization. We propose to use first order clustered discretization of the vectorial product that gives back a stable coupling. We validate the schemes on some test cases representative of direct numerical simulations of X-mode in a magnetic fusion plasma including turbulence.

  7. Rolling magnets down a conductive hill: Revisiting a classic demonstration of the effects of eddy currents

    NASA Astrophysics Data System (ADS)

    Tomasel, Fernando G.; Marconi, Mario C.

    2012-09-01

    We re-examine the case of rare-earth magnets rolling down an inclined plane, presenting an approach to conducting quantitative investigations that results in high-quality experimental data connecting simple experiments to a handful of important applications of eddy currents. These include not only magnetic braking but also the characterization of conductive materials, measurement of the thickness of dielectric coatings, and nondestructive evaluation of conductive objects. The simplicity of the proposed experimental setups, which include the use of widely available smart phones to record video that can be post-processed with free software, makes these experiments appealing to high school and college physics students.

  8. MODELING THE SUN'S OPEN MAGNETIC FLUX AND THE HELIOSPHERIC CURRENT SHEET

    SciTech Connect

    Jiang, J.; Cameron, R.; Schmitt, D.; Schuessler, M.

    2010-01-20

    By coupling a solar surface flux transport model with an extrapolation of the heliospheric field, we simulate the evolution of the Sun's open magnetic flux and the heliospheric current sheet (HCS) based on observational data of sunspot groups since 1976. The results are consistent with measurements of the interplanetary magnetic field near Earth and with the tilt angle of the HCS as derived from extrapolation of the observed solar surface field. This opens the possibility for an improved reconstruction of the Sun's open flux and the HCS into the past on the basis of empirical sunspot data.

  9. Linear decomposition method for approximating arbitrary magnetic field profiles by optimization of discrete electromagnet currents

    SciTech Connect

    Tejero, E. M.; Gatling, G.

    2009-03-15

    A method for approximating arbitrary axial magnetic field profiles for a given solenoidal electromagnet coil array is described. The method casts the individual contributions from each coil as a truncated orthonormal basis for the space within the array. This truncated basis allows for the linear decomposition of an arbitrary profile function, which returns the appropriate currents for each coil to best reproduce the desired profile. We present the mathematical details of the method along with a detailed example of its use. The results from the method are used in a simulation and compared with magnetic field measuremen0008.

  10. System overview for the multi-element corrector magnets and controls for the Fermilab Booster

    SciTech Connect

    Drennan, C.; Ball, M.; Franck, A.R.; Harding, D.J.; Kasley, P.A.; Krafczyk, G.E.; Kucera, M.J.; Lackey, J.; McArthur, D.; Misek, J.; Pellico, W.; /Fermilab

    2007-06-01

    To better control the beam position, tune, and chromaticity in the Fermilab Booster synchrotron, a new package of six corrector elements has been designed, incorporating both normal and skew orientations of dipole, quadrupole, and sextupole magnets. The devices are under construction and will be installed in 48 locations in the Booster accelerator. Each of these 288 corrector magnets will be individually powered. Each of the magnets will be individually controlled using operator programmed current ramps designed specifically for each type of Booster acceleration cycle. This paper provides an overview of the corrector magnet installation in the accelerator enclosure, power and sensor interconnections, specifications for the switch-mode power supplies, rack and equipment layouts, controls and interlock electronics, and the features of the operator interface for programming the current ramps and adjusting the timing of the system triggers.

  11. Current Structure and Nonideal Behavior at Magnetic Null Points in the Turbulent Magnetosheath

    NASA Technical Reports Server (NTRS)

    Wendel, D. E.; Adrian, M. L.

    2013-01-01

    The Poincaré index indicates that the Cluster spacecraft tetrahedron entraps a number of 3-D magnetic nulls during an encounter with the turbulent magnetosheath. Previous researchers have found evidence for reconnection at one of the many filamentary current layers observed by Cluster in this region. We find that many of the entrained nulls are also associated with strong currents. We dissect the current structure of a pair of spiral nulls that may be topologically connected. At both nulls, we find a strong current along the spine, accompanied by a somewhat more modest current perpendicular to the spine that tilts the fan toward the axis of the spine. The current along the fan is comparable to the that along the spine. At least one of the nulls manifests a rotational flow pattern in the fan plane that is consistent with torsional spine reconnection as predicted by theory. These results emphasize the importance of examining the magnetic topology in interpreting the nature of currents and reconnection in 3-D turbulence.

  12. Evaluation of Pushback Decision-Support Tool Concept for Charlotte Douglas International Airport Ramp Operations

    NASA Technical Reports Server (NTRS)

    Hayashi, Miwa; Hoang, Ty; Jung, Yoon C.; Malik, Waqar; Lee, Hanbong; Dulchinos, Victoria L.

    2015-01-01

    This paper proposes a new departure pushback decision-support tool (DST) for airport ramp-tower controllers. It is based on NASA's Spot and Runway Departure Advisor (SARDA) collaborative decision-making concept, except with the modification that the gate releases now are controlled by tactical pushback (or gate-hold) advisories instead of strategic pre-assignments of target pushback times to individual departure flights. The proposed ramp DST relies on data exchange with the airport traffic control tower (ATCT) to coordinate pushbacks with the ATCT's flow-management intentions under current operational constraints, such as Traffic Management Initiative constraints. Airlines would benefit in reduced taxi delay and fuel burn. The concept was evaluated in a human-in-the-loop simulation experiment with current ramp-tower controllers at the Charlotte Douglas International Airport as participants. The results showed that the tool helped reduce taxi time by one minute per flight and overall departure flight fuel consumption by 10-12% without reducing runway throughput. Expect Departure Clearance Time (EDCT) conformance also was improved when advisories were provided. These benefits were attained without increasing the ramp-tower controllers' workload. Additionally, the advisories reduced the ATCT controllers' workload.

  13. Quantum Ramp Secret Sharing Scheme and Quantum Operations

    NASA Astrophysics Data System (ADS)

    Xiao, Heling; Wang, Huifeng; Wang, Bin

    2016-05-01

    In order to improve the efficiency of quantum secret sharing, quantum ramp secret sharing schemes were proposed (Ogawa et al., Phys. Rev. A 72, 032318 [2005]), which had a trade-off between security and coding efficiency. In quantum ramp secret sharing, partial information about the secret is allowed to leak to a set of participants, called an intermediate set, which cannot fully reconstruct the secret. This paper revisits the size of a share in the quantum ramp secret scheme based on a relation between the quantum operations and the coherent information. We also propose an optimal quantum ramp secret sharing scheme.

  14. 4. RAMP FOR BENJAMIN FRANKLIN BRIDGE (FOURTH ST.) BETWEEN VINE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. RAMP FOR BENJAMIN FRANKLIN BRIDGE (FOURTH ST.) BETWEEN VINE AND RACE STS., LOOKING NORTHWEST - Independence National Historical Park, Walnut, Sixth, Chestnut & Second Streets, Philadelphia, Philadelphia County, PA

  15. Quantum Ramp Secret Sharing Scheme and Quantum Operations

    NASA Astrophysics Data System (ADS)

    Xiao, Heling; Wang, Huifeng; Wang, Bin

    2016-09-01

    In order to improve the efficiency of quantum secret sharing, quantum ramp secret sharing schemes were proposed (Ogawa et al., Phys. Rev. A 72, 032318 [2005]), which had a trade-off between security and coding efficiency. In quantum ramp secret sharing, partial information about the secret is allowed to leak to a set of participants, called an intermediate set, which cannot fully reconstruct the secret. This paper revisits the size of a share in the quantum ramp secret scheme based on a relation between the quantum operations and the coherent information. We also propose an optimal quantum ramp secret sharing scheme.

  16. ASYMMETRIC MAGNETIC RECONNECTION IN SOLAR FLARE AND CORONAL MASS EJECTION CURRENT SHEETS

    SciTech Connect

    Murphy, N. A.; Miralles, M. P.; Pope, C. L.; Raymond, J. C.; Winter, H. D.; Reeves, K. K.; Van Ballegooijen, A. A.; Lin, J.; Seaton, D. B.

    2012-05-20

    We present two-dimensional resistive magnetohydrodynamic simulations of line-tied asymmetric magnetic reconnection in the context of solar flare and coronal mass ejection current sheets. The reconnection process is made asymmetric along the inflow direction by allowing the initial upstream magnetic field strengths and densities to differ, and along the outflow direction by placing the initial perturbation near a conducting wall boundary that represents the photosphere. When the upstream magnetic fields are asymmetric, the post-flare loop structure is distorted into a characteristic skewed candle flame shape. The simulations can thus be used to provide constraints on the reconnection asymmetry in post-flare loops. More hard X-ray emission is expected to occur at the footpoint on the weak magnetic field side because energetic particles are more likely to escape the magnetic mirror there than at the strong magnetic field footpoint. The footpoint on the weak magnetic field side is predicted to move more quickly because of the requirement in two dimensions that equal amounts of flux must be reconnected from each upstream region. The X-line drifts away from the conducting wall in all simulations with asymmetric outflow and into the strong magnetic field region during most of the simulations with asymmetric inflow. There is net plasma flow across the X-line for both the inflow and outflow directions. The reconnection exhaust directed away from the obstructing wall is significantly faster than the exhaust directed toward it. The asymmetric inflow condition allows net vorticity in the rising outflow plasmoid which would appear as rolling motions about the flux rope axis.

  17. Ramp compression of diamond to five terapascals.

    PubMed

    Smith, R F; Eggert, J H; Jeanloz, R; Duffy, T S; Braun, D G; Patterson, J R; Rudd, R E; Biener, J; Lazicki, A E; Hamza, A V; Wang, J; Braun, T; Benedict, L X; Celliers, P M; Collins, G W

    2014-07-17

    The recent discovery of more than a thousand planets outside our Solar System, together with the significant push to achieve inertially confined fusion in the laboratory, has prompted a renewed interest in how dense matter behaves at millions to billions of atmospheres of pressure. The theoretical description of such electron-degenerate matter has matured since the early quantum statistical model of Thomas and Fermi, and now suggests that new complexities can emerge at pressures where core electrons (not only valence electrons) influence the structure and bonding of matter. Recent developments in shock-free dynamic (ramp) compression now allow laboratory access to this dense matter regime. Here we describe ramp-compression measurements for diamond, achieving 3.7-fold compression at a peak pressure of 5 terapascals (equivalent to 50 million atmospheres). These equation-of-state data can now be compared to first-principles density functional calculations and theories long used to describe matter present in the interiors of giant planets, in stars, and in inertial-confinement fusion experiments. Our data also provide new constraints on mass-radius relationships for carbon-rich planets. PMID:25030170

  18. Chaotic Pattern Dynamics in Spatially Ramped Turbulence

    NASA Astrophysics Data System (ADS)

    Wiener, R. J.; Ashbaker, E.; Olsen, T.; Bodenschatz, E.

    2003-11-01

    In previous experiments(Richard J. Wiener et al), Phys. Rev. E 55, 5489 (1997)., Taylor vortex flow in an hourglass geometry has demonstrated a period-doubling cascade to chaotic pattern dynamics. A spatial ramp exists in the Reynolds number. For low reduced Reynolds numbesr \\varepsilon, supercritical vortex flow occurs between regions of subcritical structureless flow with soft boundaries that allow for pattern dynamics. At \\varepsilon ≈ 0.5, the pattern exhibits phase slips that occur irregularly in time. At \\varepsilon ≈ 1.0 the entire system is supercritical, and the pattern is stabilized against phase slips. At \\varepsilon > 15, shear flow creates a spatial ramp in turbulence. Remarkably, the phase slip instability reoccurs. Vortex pairs are created chaotically, possibly due to the spatial variation of the turbulence. The variance and Fourier spectra of time series of light scattered off Kalliroscope tracer were measured. These indicate that a region of turbulence exists, within which phase slips occur, bounded by regions of laminar flow which may provide soft boundaries that allow for the phase dynamics. Despite the presence of turbulence, the dynamics might be describable by a phase equation.

  19. Rainfall Manipulation Plot Study (RaMPS)

    DOE Data Explorer

    Blair, John [Kansas State University; Fay, Phillip [USDA-ARS; Knapp, Alan [Colorado State University; Collins, Scott [University of New Mexico; Smith, Melinda [Yale University

    Rainfall Manipulation Plots facility (RaMPs) is a unique experimental infrastructure that allows us to manipulate precipitation events and temperature, and assess population community, and ecosystem responses in native grassland. This facility allows us to manipulate the amount and timing of individual precipitation events in replicated field plots at the Konza Prairie Long-Term Ecological Research (LTER) site. Questions we are addressing include: • What is the relative importance of more extreme precipitation patterns (increased climatic variability) vs. increased temperatures (increased climatic mean) with regard to their impact on grassland ecosystem structure and function? Both projected climate change factors are predicted to decrease soil water availability, but the mechanisms by which this resource depletion occurs differ. • Will altered precipitation patterns, increased temperatures and their interaction increase opportunities for invasion by exotic species? • Will long-term (6-10 yr) trajectories of community and ecosystem change in response to more extreme precipitation patterns continue at the same rate as initial responses from years 1-6? Or will non-linear change occur as potential ecological thresholds are crossed? And will increased temperatures accelerate these responses? Data sets are available as ASCII files, in Excel spreadsheets, and in SAS format. (Taken from http://www.konza.ksu.edu/ramps/backgrnd.html

  20. Flyer-Plate-Based Current Diagnostic for Magnetized Liner Inertial Fusion Experiments

    NASA Astrophysics Data System (ADS)

    Reneker, Joseph; Gomez, Matthew; Hess, Mark; Jennings, Christopher

    2015-11-01

    Accurate measurements of the current delivered to Magnetized Liner Inertial Fusion (MagLIF) loads on the Z machine are important for understanding the dynamics of liner implosions. Difficulty acquiring a reliable load current measurement with the standard Z load B-dots has spurred the development of alternative load current diagnostics. Velocimetry of an electromagnetically-accelerated flyer plate can be used to infer the drive current on a flyer surface. A load current diagnostic design is proposed using a cylindrical flyer plate in series with the MagLIF target. Aspects of the flyer plate design were optimized using magnetohydrodynamic simulations. Design and preliminary results will be presented. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.