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Sample records for ramped magnet current

  1. Influence of current ramp rate on voltage current measurement of a conduction-cooled HTS magnet

    NASA Astrophysics Data System (ADS)

    Hiltunen, I.; Korpela, A.; Lehtonen, J.; Mikkonen, R.

    2008-06-01

    High-temperature superconductors (HTS) have notably different voltage current characteristic compared to the low-temperature superconductors (LTS). Due to the anisotropy and slanted electric field - current density characteristics the loss of stability in a Bi-2223/Ag magnet is viewed as a global temperature increase inside the coil rather than a local normal zone. Therefore, the quench current depends strongly on the cooling conditions. In this paper a finite element method based analysis method is presented and example runs are carried out in order to explain in detail the influence of the current ramp rate and cooling on the voltage current characteristics of a conduction-cooled Bi-2223/Ag coil at 20 and 45 K. The results show that in certain operation conditions the coil critical current has a maximum value with respect to the ramp rate used in the measurements.

  2. A differential-delay control for ramped magnet current

    SciTech Connect

    Murray, J. . Dept. of Electrical Engineering); Olsen, R. )

    1992-01-01

    A differential-delay control system has been designed and implemented for the main dipole magnet power supply of the booster ring at the National Synchrotron Light Source at Brookhaven National Lab. The control algorithm was implemented on a floating-point digital signal processor; in tests, the use of digital signal-processing techniques gave a factor of ten improvement in the tracking response time, together with a modest improvement in tracking accuracy.

  3. A differential-delay control for ramped magnet current

    SciTech Connect

    Murray, J.; Olsen, R.

    1992-11-01

    A differential-delay control system has been designed and implemented for the main dipole magnet power supply of the booster ring at the National Synchrotron Light Source at Brookhaven National Lab. The control algorithm was implemented on a floating-point digital signal processor; in tests, the use of digital signal-processing techniques gave a factor of ten improvement in the tracking response time, together with a modest improvement in tracking accuracy.

  4. Calculation of eddy-currents induced in a compact synchrotron superconducting magnet structure during a current ramp

    SciTech Connect

    Kalsi, S. . Space and Electronics Systems Div.); Heese, R. )

    1991-01-01

    Under DARPA sponsorship, a compact Superconducting X-Ray Light Source (SXSL) is being designed and built by the Brookhaven National Laboratory (BNL) with industry participation from Grumman Corporation and General Dynamics. The SXLS machine employs two 180{degrees} curved 4 telsa superconducting dipole magnets. These magnets are required to produce a dipole field for bending the beam but at the same time they must produce finite amounts of higher multipoles which are required for conditioning the beam. In fact uniformity of the field to less than 1 part in 10,000 must be maintained under all operating conditions. When a superconducting magnet is ramped from zero to full field, the changing magnetic field produces eddy-currents in the magnet structure which in turn can produce undesirable multipoles. This paper discusses a simple method for estimating these eddy-currents and their effect on the field harmonics. The paper present the analysis basis and its application to the SXLS magnet support structure and to the beam chamber components. 5 figs., 1 tab.

  5. Reduction of poloidal magnetic flux consumption during plasma current ramp-up in DEMO relevant plasma regimes

    NASA Astrophysics Data System (ADS)

    Wakatsuki, T.; Suzuki, T.; Hayashi, N.; Shiraishi, J.; Sakamoto, Y.; Ide, S.; Kubo, H.; Kamada, Y.

    2017-01-01

    The method for reducing a poloidal magnetic flux consumption of external coils is investigated to reduce the size of the central solenoid (CS) in the DEMO reactor. The reduction of the poloidal magnetic flux consumption during a plasma current ramp-up phase by electron cyclotron (EC) heating is investigated using an integrated modeling code suite, TOPICS. A strongly reversed shear q profile tends to be produced if intense off-axis EC heating is applied to obtain a large reduction of the flux consumption. In order to overcome this tendency, we find a method to obtain the optimum temperature profile which minimizes the poloidal flux consumption for a wide range of the q profile. We try to reproduce the optimum temperature profile for a weakly reversed shear q profile using six EC rays of 20 MW. As a result, the resistive flux consumption during the current ramp-up can be reduced by 63% from the estimation using the Ejima constant of 0.45 and the total flux consumption can be reduced by 20% from the conventional estimation. In addition, we find that the resistive flux consumption is closely related to the volume averaged electron temperature and not to the profile shape. Using this relation, the required heating power is estimated to be 31 MW based on a well established global confinement scaling, ITER L-89P. As a result, it is clarified that the poloidal magnetic flux consumption can be reduced by 20% using 20-31 MW of EC heating for a weakly reversed shear q profile. This reduction of the flux consumption accounts for 10% reduction of the CS radius.

  6. 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.

  7. Ramp-rate sensitivity of SSC dipole magnet prototypes

    SciTech Connect

    Devred, A.; Ogitsu, T.

    1994-07-01

    One of the major achievements of the magnet R&D program for the Superconducting Super Collider (SSC) is the fabrication and test of a series of 20 5-cm aperture, 15-m long dipole magnet prototypes. The ramp rate sensitivity of these magnets appears to fall in at least two categories that can be correlated to the manufacturer and production batch of the strands used for the inner-coil cables. The first category, referred to as type-A, is characterized by a strong quench current degradation at high ramp rates, usually accompanied by large distortions of the multipole fields and large energy losses. The second category, referred to as type-B, is characterized by a sudden drop of quench current at low ramp rates, followed by a much milder degradation at larger rates. The multipole fields of the type-B magnets show little ramp-rate sensitivity, and the energy losses are smaller than for the type-A magnets. The behavior of the Type-A magnets can be explained in terms of inter-strand eddy currents arising from low and non-uniform resistances at the crossovers between the strands of the two-layer Rutherford-type cable. Anomalies in the transport-current repartition among the cable strands are suggested as a possible cause for the type-B behavior. The origins of these anomalies have not yet been clearly identified. The SSC project was canceled by decision of the United States Congress on October 21, 1994.

  8. Fast current ramp experiments on TFTR

    SciTech Connect

    Fredrickson, E.D.; McGuire, K.; Goldston, R.J.; Bell, M.; Grek, B.; Johnson, D.; Morris, A.W.; Stauffer, F.J.; Taylor, G.; Zarnstorff, M.C.

    1987-05-01

    Electron heat transport on TFTR and other tokamaks is several orders of magnitude larger than neoclassical calculations would predict. Despite considerable effort, there is still no clear theoretical understanding of this anomalous transport. The electron temperature profile T/sub e/(r), shape has shown a marked consistency on many machines, including TFTR, for a wide range of plasma parameters and heating profiles. This could be an important clue as to the process responsible for this enhanced thermal transport. In this paper 'profile consistency' in TFTR is described and an experiment which uses a fast current ramp to transiently decouple the current density profile J(r), and the T/sub e/(r) profiles is discussed. From this experiment the influence of J(r) on electron temperature profile consistency can be determined.

  9. Lower hybrid assisted plasma current ramp-up in ITER

    NASA Astrophysics Data System (ADS)

    Kim, S. H.; Artaud, J. F.; Basiuk, V.; Bécoulet, A.; Dokuka, V.; Hoang, G. T.; Imbeaux, F.; Khayrutdinov, R. R.; Lister, J. B.; Lukash, V. E.

    2009-06-01

    Lower hybrid (LH) assisted plasma current ramp-up in ITER is demonstrated using a free-boundary full tokamak discharge simulator which combines the DINA-CH and CRONOS codes. LH applied from the initial phase of the plasma current ramp-up increases the safety margins in operating the superconducting poloidal field coils both by reducing resistive ohmic flux consumption and by providing non-inductively driven plasma current. Loss of vertical control associated with high plasma internal inductance is avoided by tailoring the plasma current density profiles. Effects of early LH application on the plasma shape evolution are identified by the free-boundary plasma simulation.

  10. Electron cyclotron heating and current drive studies during current ramp-up in Tore-Supra

    NASA Astrophysics Data System (ADS)

    Rimini, F. G.; Basiuk, V.; Bourdelle, C.; Bucalossi, J.; Fenzi-Bonizec, C.; Giruzzi, G.; Hoang, G. T.; Lennholm, M.; Sabot, R.; Ségui, J. L.; Thomas, P. R.

    2005-06-01

    In a recent series of experiments, electron cyclotron current drive (ECCD) has been successfully used, at a level of 0.75 MW, for current profile tailoring during the current ramp-up in Tore-Supra. The electron cyclotron resonance heating power deposition was varied from on-axis to off-axis and the direction of the driven current from co to counter. In these conditions, the current profile is significantly modified with respect to those typically obtained in pure ohmic scenarios. Central reversed magnetic shear conditions have been achieved with on-axis counter-ECCD, accompanied by high electron temperature gradients, exhibiting internal transport barrier features. This improved electron transport is maintained for some time on the current flat-top when combining ECCD with ion cyclotron resonance heating in a (H)D minority scheme. Integrated interpretative analysis with the CRONOS code confirms that deeply reversed magnetic shear is indeed attained by on-axis counter-ECCD in low density conditions and in combination with a relatively fast controlled current ramp. The high electron temperature gradient is found to be located inside the negative magnetic shear region.

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

    NASA Astrophysics Data System (ADS)

    Ding, B. J.; Li, M. H.; Fisch, N. J.; Qin, H.; Li, J. G.; Wilson, J. R.; 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.

    2012-12-01

    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 Pel/PLH 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.

  12. Guidelines for the Calculation of the Accumulator Magnet Bus Ramps for Fermilab Experiment E835

    SciTech Connect

    McGinnis, Dave; Stancari, Giulio; Werkema, Steve; /Fermilab

    1999-04-15

    This report lists the steps that are required to calculate deceleration ramps for all relevant Accumulator devices. The ramps used for the 1996-97 fixed target run (experiment E835) are saved in files associated with ACNET console application PA1627 (PAUX RAMP DEVELOP). These ramps cannot be re-used because the Accumulator {gamma}{sub t} upgrade has significantly changed the lattice since the last time the ramps were used. Consequently, new deceleration ramps must be calculated and commissioned before the next fixed target run. The deceleration ramp for a particular device is a table that gives the sequence of set values sent to the device as the ramp is executed. The 1997 ramps consist of ramp tables for 100 devices. Appendix 1 gives a list of the devices ramped. Most of these devices will still require ramps for the next fixed target run. Future decelerations will also require ramps for the quadrupole magnet shunts that were installed as part of the {gamma}{sub t} upgrade. Additionally, ramps must be constructed for the two skew-sextupole magnets that will be installed during the summer of 1999.

  13. Generation of Ramped Current Profiles in Relativistic Electron Beams Using Wakefields in Dielectric Structures.

    PubMed

    Andonian, G; Barber, S; O'Shea, F H; Fedurin, M; Kusche, K; Swinson, C; Rosenzweig, J B

    2017-02-03

    Temporal pulse tailoring of charged-particle beams is essential to optimize efficiency in collinear wakefield acceleration schemes. In this Letter, we demonstrate a novel phase space manipulation method that employs a beam wakefield interaction in a dielectric structure, followed by bunch compression in a permanent magnet chicane, to longitudinally tailor the pulse shape of an electron beam. This compact, passive, approach was used to generate a nearly linearly ramped current profile in a relativistic electron beam experiment carried out at the Brookhaven National Laboratory Accelerator Test Facility. Here, we report on these experimental results including beam and wakefield diagnostics and pulse profile reconstruction techniques.

  14. Generation of Ramped Current Profiles in Relativistic Electron Beams Using Wakefields in Dielectric Structures

    NASA Astrophysics Data System (ADS)

    Andonian, G.; Barber, S.; O'Shea, F. H.; Fedurin, M.; Kusche, K.; Swinson, C.; Rosenzweig, J. B.

    2017-02-01

    Temporal pulse tailoring of charged-particle beams is essential to optimize efficiency in collinear wakefield acceleration schemes. In this Letter, we demonstrate a novel phase space manipulation method that employs a beam wakefield interaction in a dielectric structure, followed by bunch compression in a permanent magnet chicane, to longitudinally tailor the pulse shape of an electron beam. This compact, passive, approach was used to generate a nearly linearly ramped current profile in a relativistic electron beam experiment carried out at the Brookhaven National Laboratory Accelerator Test Facility. Here, we report on these experimental results including beam and wakefield diagnostics and pulse profile reconstruction techniques.

  15. 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.

  16. 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.

  17. Effect of Hall Current on Generalized Magneto-Thermoelasticity Micropolar Solid Subjected to Ramp-Type Heating

    NASA Astrophysics Data System (ADS)

    Zakaria, M.

    2014-01-01

    The problem of two-dimensional magnetic micropolar generalized thermoelastic medium in the presence of the combined effect of Hall currents subjected to ramp-type heating is investigated. The medium is permeated by a strong transverse magnetic field imposed perpendicularly on the displacement plane, the induced electric field being neglected. Ohm's law is modified by including two terms, one for the cross product of the current density and the initial magnetic field and the other for the cross product of the velocity and the initial magnetic field. The Laplace and exponential Fourier transform techniques are employed to transform the governing partial differential equations to ODE, which are solved exactly. Comparisons with the previously published work are conducted and the results are found to be in good agreement. The distributions of the temperature, displacement, stress, microrotation, and current density are obtained. The numerical values of these functions are represented graphically

  18. Optimizing the current ramp-up phase for the hybrid ITER scenario

    NASA Astrophysics Data System (ADS)

    Hogeweij, G. M. D.; Artaud, J.-F.; Casper, T. A.; Citrin, J.; Imbeaux, F.; Köchl, F.; Litaudon, X.; Voitsekhovitch, I.; the ITM-TF ITER Scenario Modelling Group

    2013-01-01

    The current ramp-up phase for the ITER hybrid scenario is analysed with the CRONOS integrated modelling suite. The simulations presented in this paper show that the heating systems available at ITER allow, within the operational limits, the attainment of a hybrid q profile at the end of the current ramp-up. A reference ramp-up scenario is reached by a combination of NBI, ECCD (UPL) and LHCD. A heating scheme with only NBI and ECCD can also reach the target q profile; however, LHCD can play a crucial role in reducing the flux consumption during the ramp-up phase. The optimum heating scheme depends on the chosen transport model, and on assumptions of parameters like ne peaking, edge Te,i and Zeff. The sensitivity of the current diffusion on parameters that are not easily controlled, shows that development of real-time control is important to reach the target q profile. A first step in that direction has been indicated in this paper. Minimizing resistive flux consumption and optimizing the q profile turn out to be conflicting requirements. A trade-off between these two requirements has to be made. In this paper it is shown that fast current ramp with L-mode current overshoot is at the one extreme, i.e. the optimum q profile at the cost of increased resistive flux consumption, whereas early H-mode transition is at the other extreme.

  19. Ramping turn-to-turn loss and magnetization loss of a No-Insulation (RE)Ba2Cu3Ox high temperature superconductor pancake coil

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Song, H.; Yuan, W.; Jin, Z.; Hong, Z.

    2017-03-01

    This paper is to study ramping turn-to-turn loss and magnetization loss of a no-insulation (NI) high temperature superconductor (HTS) pancake coil wound with (RE)Ba2Cu3Ox (REBCO) conductors. For insulated (INS) HTS coils, a magnetization loss occurs on superconducting layers during a ramping operation. For the NI HTS coil, additional loss is generated by the "bypassing" current on the turn-to-turn metallic contacts, which is called "turn-to-turn loss" in this study. Therefore, the NI coil's ramping loss is much different from that of the INS coil, but few studies have been reported on this aspect. To analyze the ramping losses of NI coils, a numerical method is developed by coupling an equivalent circuit network model and a H-formulation finite element method model. The former model is to calculate NI coil's current distribution and turn-to-turn loss, and the latter model is to calculate the magnetization loss. A test NI pancake coil is wound with REBCO tapes and the reliability of this model is validated by experiments. Then the characteristics of the NI coil's ramping losses are studied using this coupling model. Results show that the turn-to-turn loss is much higher than the magnetization loss. The NI coil's total ramping loss is much higher than that of its insulated counterpart, which has to be considered carefully in the design and operation of NI applications. This paper also discusses the possibility to reduce NI coil's ramping loss by decreasing the ramping rate of power supply or increasing the coil's turn-to-turn resistivity.

  20. Rapid Current Ramp-Up by Cyclotron-Driving Electrons beyond Runaway Velocity

    SciTech Connect

    Uchida, M.; Yoshinaga, T.; Tanaka, H.; Maekawa, T.

    2010-02-12

    The toroidal current has been rapidly ramped-up after the formation of an initial closed flux surface in an electron cyclotron heated discharge in the low aspect ratio torus experiment device. A current carrying fast electron tail is developed well beyond the runaway velocity against the reverse voltage from self-induction, suggesting a forward driving force on the tail by the cyclotron absorption of high N{sub ||} electron Bernstein waves.

  1. Plasma current ramp-up by lower hybrid wave using innovative antennas on TST-2

    NASA Astrophysics Data System (ADS)

    Takase, Yuichi; Ejiri, Akira; Moeller, Charles; Roidl, Benedikt; Shinya, Takahiro; Tsujii, Naoto; Yajima, Satoru; Yamazaki, Hibiki; Kitayama, Akichika; Matsumoto, Naoki; Sato, Akito; Sonehara, Masateru; Takahashi, Wataru; Tajiri, Yoshiyuki; Takei, Yuki; Togashi, Hiro; Toida, Kazuya; Yoshida, Yusuke

    2016-10-01

    Non-inductive plasma current (Ip) ramp-up by RF power in the lower hybrid frequency range is being studied on the TST-2 spherical tokamak (R = 0.36 m, a = 0.23 m, Bt = 0.3 T, Ip = 0.1 MA). Up to 400 kW of RF power is available at a frequency of 200 MHz. An innovative antenna called the capacitively-coupled combline (CCC) antenna was developed to excite a sharp, highly directional traveling wave with the electric field polarized in the toroidal direction. It is an array of resonant circuit elements made of capacitance and inductance, coupled to neighboring elements by mutual capacitance. Two CCC antennas are installed in TST-2, a 13-element outboard-launch antenna and a 6-element top-launch antenna. The latter was installed in March 2016 to improve accessibility to the core and to achieve single-pass damping. The suspected wave power loss in the scrape-off layer plasma should also be avoided. Ip ramp-up to 25 kA has been achieved so far. An upgrade of the Bt power supply is planned to take advantage of the observed improvement of Ip ramp-up with Bt. Higher Bt for longer pulses should improve the Ip ramp-up efficiency by improving wave accessibility and by reducing prompt orbit losses of energetic electrons.

  2. 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

  3. 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

  4. 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.

  5. 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

  6. Dynamic optimization of open-loop input signals for ramp-up current profiles in tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Ren, Zhigang; Xu, Chao; Lin, Qun; Loxton, Ryan; Teo, Kok Lay

    2016-03-01

    Establishing a good current spatial profile in tokamak fusion reactors is crucial to effective steady-state operation. The evolution of the current spatial profile is related to the evolution of the poloidal magnetic flux, which can be modeled in the normalized cylindrical coordinates using a parabolic partial differential equation (PDE) called the magnetic diffusion equation. In this paper, we consider the dynamic optimization problem of attaining the best possible current spatial profile during the ramp-up phase of the tokamak. We first use the Galerkin method to obtain a finite-dimensional ordinary differential equation (ODE) model based on the original magnetic diffusion PDE. Then, we combine the control parameterization method with a novel time-scaling transformation to obtain an approximate optimal parameter selection problem, which can be solved using gradient-based optimization techniques such as sequential quadratic programming (SQP). This control parameterization approach involves approximating the tokamak input signals by piecewise-linear functions whose slopes and break-points are decision variables to be optimized. We show that the gradient of the objective function with respect to the decision variables can be computed by solving an auxiliary dynamic system governing the state sensitivity matrix. Finally, we conclude the paper with simulation results for an example problem based on experimental data from the DIII-D tokamak in San Diego, California.

  7. ITER-like current ramps in JET with ILW: experiments, modelling and consequences for ITER

    NASA Astrophysics Data System (ADS)

    Hogeweij, G. M. D.; Calabrò, G.; Sips, A. C. C.; Maggi, C. F.; De Tommasi, G. M.; Joffrin, E.; Loarte, A.; Maviglia, F.; Mlynar, J.; Rimini, F. G.; Pütterich, Th.; EFDA Contributors, JET

    2015-01-01

    Since the ITER-like wall in JET (JET-ILW) came into operation, dedicated ITER-like plasma current (Ip) ramp-up (RU) and ramp-down (RD) experiments have been performed and matched to similar discharges with the carbon wall (JET-C). The experiments show that access to H-mode early in the Ip RU phase and maintaining H-mode in the Ip RD as long as possible are instrumental to achieve low internal plasma inductance (li) and to minimize flux consumption. In JET-ILW, at a given current rise rate similar variations in li (0.7-0.9) are obtained as in JET-C. In most discharges no strong W accumulation is observed. However, in some low density cases during the early phase of the Ip RU(n_e/n_e^Gw ˜ 0.2) strong core radiation due to W influx led to hollow electron temperature (Te) profiles. In JET-ILW Zeff is significantly lower than in JET-C. W significantly disturbs the discharge evolution when the W concentration approaches 10-4 this threshold is confirmed by predictive transport modelling using the CRONOS code. Ip RD experiments in JET-ILW confirm the result of JET-C that sustained H-mode and elongation reduction are both instrumental in controlling li.

  8. 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.

  9. Symmetrical dynamics of peak current-mode and valley current-mode controlled switching dc-dc converters with ramp compensation

    NASA Astrophysics Data System (ADS)

    Zhou, Guo-Hua; Xu, Jian-Ping; Bao, Bo-Cheng; Jin, Yan-Yan

    2010-06-01

    The discrete iterative map models of peak current-mode (PCM) and valley current-mode (VCM) controlled buck converters, boost converters, and buck-boost converters with ramp compensation are established and their dynamical behaviours are investigated by using the operation region, parameter space map, bifurcation diagram, and Lyapunov exponent spectrum. The research results indicate that ramp compensation extends the stable operation range of the PCM controlled switching dc-dc converter to D > 0.5 and that of the VCM controlled switching dc-dc converter to D < 0.5. Compared with PCM controlled switching dc-dc converters with ramp compensation, VCM controlled switching dc-dc converters with ramp compensation exhibit interesting symmetrical dynamics. Experimental results are given to verify the analysis results in this paper.

  10. 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.

  11. 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}.

  12. Main Design Principles of the Cold Beam Pipe in the FastRamped Superconducting Accelerator Magnets for Heavy Ion Synchrotron SIS100

    NASA Astrophysics Data System (ADS)

    Mierau, A.; Schnizer, P.; Fischer, E.; Macavei, J.; Wilfert, S.; Koch, S.; Weiland, T.; Kurnishov, R.; Shcherbakov, P.

    SIS100, the world second large scale heavy ion synchrotron using fast ramped superconducting magnets, is to be built at FAIR. Its high current operation of intermediate charge state ions requires stable vacuum pressures < 10-12 mbar under dynamic machine conditions which are only achievable when the whole beam pipe is used as an huge cryopump. In order to find technological feasible design solutions, three opposite requirements have to be met: minimum magnetic field distortion caused by AC losses, mechanical stability and low and stable wall temperatures of the beam pipe. We present the possible design versions of the beam pipe for the high current curved dipole. The pros and cons of these proposed designs were studied using simplified analytical models, FEM calculations and tests on models.

  13. RAMP MANAGEMENT IN RHIC.

    SciTech Connect

    KEWISCH,J.; VAN ZEIJTS,J.; PEGGS,S.; SATOGATA,T.

    1999-03-29

    In RHIC, magnets and RF cavities are controlled by Wave Form Generators (WFGs), simple real time computers which generate the set points. The WFGs are programmed to change set points from one state to another in a synchronized way. Such transition is called a ''Ramp'' and consists of a sequence of ''stepping stones'' which contain the set point of every WFG controlled device at a point in time. An appropriate interpolation defines the set points between these stepping stones. This report describes the implementation of the ramp system. The user interface, tools to create and modify ramps, interaction with modeling tools and measurements and correction programs are discussed.

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

    DOE PAGES

    Piot, P.; Behrens, C.; Gerth, C.; ...

    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

  15. Generation and characterization of electron bunches with ramped current profiles in a dual-frequency superconducting linear accelerator.

    PubMed

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

    2012-01-20

    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.

  16. 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.

  17. Modeling of neutral beam injection heating and current drive during the ramp-up phase in KSTAR

    NASA Astrophysics Data System (ADS)

    Terzolo, L.

    2014-06-01

    For flexible control of the plasma pressure and the current profiles, which are essential for a high performance plasma with long pulse operation, KSTAR is going to implement several heating and current systems, which include Neutral Beam Injection (NBI), Ion Cyclotron Resonant Heting (ICRH)/Fast Wave Current Drive (FWCD), Lower Hybrid Current Drive (LHCD), and Eclectron Cyclotron Heating (ECH)/Electron Cyclotron Current Drive (ECCD). Here, the NBI system is typically used for the central heating and current drive. For the time being, only one NBI device (composed of 3 sources) is available in KSTAR. The first two sources were successfully commissioned in 2010 and 2013. The last source will be installed in 2014. In this work, we present a simulation study of the heating and current drive of the first NBI system (3 sources) during the ramp-up phase. We consider two different NBI configurations (low and high beam energy). The simulation is performed with NUBEAM, a well-recognized Monte-Carlo code. Several different types of KSTAR target equilibria (scan from lower to higher plasma density) are used for the calculation of the current drive, the heating and the different NB losses (shinethrough, charge exchange and bad orbit). The study shows the dependency of those quantities on the plasma density, the position of the NB source and the beam energy. It also shows that because of the shinethrough loss is too high, each NB source cannot be used when the plasma density is under a certain threshold. This study can be used to determine the starting time of the different NB sources during the KSTAR ramp-up phase.

  18. Magnetic resonance imaging of oscillating electrical currents

    PubMed Central

    Halpern-Manners, Nicholas W.; Bajaj, Vikram S.; Teisseyre, Thomas Z.; Pines, Alexander

    2010-01-01

    Functional MRI has become an important tool of researchers and clinicians who seek to understand patterns of neuronal activation that accompany sensory and cognitive processes. However, the interpretation of fMRI images rests on assumptions about the relationship between neuronal firing and hemodynamic response that are not firmly grounded in rigorous theory or experimental evidence. Further, the blood-oxygen-level-dependent effect, which correlates an MRI observable to neuronal firing, evolves over a period that is 2 orders of magnitude longer than the underlying processes that are thought to cause it. Here, we instead demonstrate experiments to directly image oscillating currents by MRI. The approach rests on a resonant interaction between an applied rf field and an oscillating magnetic field in the sample and, as such, permits quantitative, frequency-selective measurements of current density without spatial or temporal cancellation. We apply this method in a current loop phantom, mapping its magnetic field and achieving a detection sensitivity near the threshold required for the detection of neuronal currents. Because the contrast mechanism is under spectroscopic control, we are able to demonstrate how ramped and phase-modulated spin-lock radiation can enhance the sensitivity and robustness of the experiment. We further demonstrate the combination of these methods with remote detection, a technique in which the encoding and detection of an MRI experiment are separated by sample flow or translation. We illustrate that remotely detected MRI permits the measurement of currents in small volumes of flowing water with high sensitivity and spatial resolution. PMID:20421504

  19. GENERAL: Mode shift and stability control of a current mode controlled buck-boost converter operating in discontinuous conduction mode with ramp compensation

    NASA Astrophysics Data System (ADS)

    Bao, Bo-Cheng; Xu, Jian-Ping; Liu, Zhong

    2009-11-01

    By establishing the discrete iterative mapping model of a current mode controlled buck-boost converter, this paper studies the mechanism of mode shift and stability control of the buck-boost converter operating in discontinuous conduction mode with a ramp compensation current. With the bifurcation diagram, Lyapunov exponent spectrum, time-domain waveform and parameter space map, the performance of the buck-boost converter circuit utilizing a compensating ramp current has been analysed. The obtained results indicate that the system trajectory is weakly chaotic and strongly intermittent under discontinuous conduction mode. By using ramp compensation, the buck-boost converter can shift from discontinuous conduction mode to continuous conduction mode, and effectively operates in the stable period-one region.

  20. Investigation of runaway electrons in the current ramp-up by a fully non-inductive lower hybrid current drive on the EAST tokamak

    NASA Astrophysics Data System (ADS)

    Lu, H. W.; Zha, X. J.; Zhong, F. C.; Hu, L. Q.; Zhou, R. J.; EAST Team

    2013-05-01

    The possibility of using a lower hybrid wave (LHW) to ramp up the plasma current (Ip) from a low level to a high enough level required for fusion burn in the EAST (experimental advanced superconducting tokamak) tokamak is examined experimentally. The focus in this paper is on investigating how the relevant plasma parameters evolve during the current ramp-up (CRU) phase driving by a lower hybrid current drive (LHCD) with poloidal field (PF) coil cut-off, especially the behaviors of runaway electrons generated during the CRU phase. It is found that the intensity of runaway electron emission increases first, and then decreases gradually as the discharge goes on under conditions of PF coil cut-off before LHW was launched into plasma, PF coil cut-off at the same time as LHW was launched into plasma, as well as PF coil cut-off after LHW was launched into plasma. The relevant plasma parameters, including Hα line emission (Ha), impurity line emission (UV), soft x-ray emission and electron density n_{\\rm{e}} , increase to a high level. The loop voltage decreases from positive to negative, and then becomes zero because of the cut-off of PF coils. Also, the magnetohydrodynamic activity takes place during the CRU driving by LHCD.

  1. 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.

  2. 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.

  3. Current leads and magnetic bearings

    NASA Astrophysics Data System (ADS)

    Hull, J. R.

    1993-10-01

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

  4. Current leads and magnetic bearings

    SciTech Connect

    Hull, J.R.

    1993-12-31

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

  5. Quantized Chiral Magnetic Current from Reconnections of Magnetic Flux

    DOE PAGES

    Hirono, Yuji; Kharzeev, Dmitri E.; Yin, Yi

    2016-10-20

    We introduce a new mechanism for the chiral magnetic e ect that does not require an initial chirality imbalance. The chiral magnetic current is generated by reconnections of magnetic ux that change the magnetic helicity of the system. The resulting current is entirely determined by the change of magnetic helicity, and it is quantized.

  6. 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.

  7. 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.

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

    DOE PAGES

    Poli, F. M.; Andre, R. G.; Bertelli, N.; ...

    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

  9. 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%.

  10. 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.

  11. Manipulating magnetic moments by superconducting currents

    NASA Astrophysics Data System (ADS)

    Chudnovsky, Eugene M.

    2017-03-01

    We show that the interaction between a superconducting order parameter and the magnetic moment of an atomic cluster in a two-dimensional s -wave superconductor with Rashba spin-orbit coupling generates magnetic anisotropy that can be stronger or comparable to the magnetic anisotropy due to the crystal field and the shape of the cluster. Transport current through the superconductor produces the effective magnetic field acting on the cluster's magnetic moment. The direction of the effective field depends on the direction of the current, thus allowing one to manipulate the magnetic moment by the superconducting current. Due to the large density of the superconducting current this method of magnetization reversal can be more advantageous at low temperatures than the spin-transfer torque method that requires a large spin-polarized current through a normal metal.

  12. Optimization of the Current Ramp-up Phase in DIII-D via Physics-model-based Control of Plasma Safety Factor Profile Dynamics

    NASA Astrophysics Data System (ADS)

    Barton, J. E.; Wehner, W. P.; Schuster, E.; Luce, T. C.; Jackson, G. L.; Ferron, J. R.; Humphreys, D. A.; Hyatt, A. W.

    2014-10-01

    Simulations and experimental results in DIII-D are presented to demonstrate the potential of physics-model-based control of the q profile to improve the reproducibility of plasma startup conditions by achieving a specified target q profile at the end of the current ramp-up. Three different q profiles (qmin of 1.3, 1.65, 2.1 and q95 of 4.4, 5.0, 6.2, respectively) were specified as targets. A feedforward + feedback scheme is utilized to control the q profile and is constructed by embedding a nonlinear, physics-based model of the q profile dynamics into the control design process. A unique characteristic of the feedforward trajectories obtained by solving the optimization problem is the regulation of the plasma current ramp-up rate to achieve the target q profiles. The feedback controller is employed to add robustness to the control scheme and account for drifts due to external plasma disturbances. Supported by the US Department of Energy under DE-SC0001334, DE-SC0010661 and DE-FC02-04ER54698.

  13. 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

  14. Low-Power Magnetic Current Sensor

    NASA Technical Reports Server (NTRS)

    Mclyman, W. T.

    1989-01-01

    Direct current sensed via saturable-core reactor. Transducer senses direct current magnetically, providing isolation between input and output. Detecting-and-isolating element saturable reactor, where input current passes through one-turn control coil. Provides output of 0 to 3 Vdc for input current of 0 to 15 Adc and consumes power of 22 mW at 10 Adc input. Input sensed magnetically, output electrically isolated from input.

  15. Effects of heat current on magnetization dynamics

    NASA Astrophysics Data System (ADS)

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

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

  16. Development of magnetic eddy current testing techniques

    NASA Astrophysics Data System (ADS)

    Tada, Toyokazu; Suetsugu, Hidehiko

    2017-02-01

    IRIS (Internal Rotary Inspection System) has become a major maintenance inspection technique for the heat exchanger and reactor tubes. It is known that IRIS has a high precision of evaluation thickness, however there are a few disadvantages, such as slow inspection speed. Therefore, we have developed a magnetic eddy current flaw testing technique which combines a magnetic array forming a strong magnetic field, 4 coil structures for controlling the generation area of the eddy currents, and a desorption yoke structure to control the magnetizing force. In this presentation, details of this technique and practical application will be elaborated.

  17. Supersonic Elliptical Ramp Inlet

    NASA Technical Reports Server (NTRS)

    Adamson, Eric E. (Inventor); Fink, Lawrence E. (Inventor); Fugal, Spencer R. (Inventor)

    2016-01-01

    A supersonic inlet includes a supersonic section including a cowl which is at least partially elliptical, a ramp disposed within the cowl, and a flow inlet disposed between the cowl and the ramp. The ramp may also be at least partially elliptical.

  18. 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.

  19. Manipulating spin current in the magnetic nanopillar.

    PubMed

    Yang, T; Hirohata, A; Kimura, T; Otani, Y

    2007-01-01

    Because of the capability to switch the magnetization of a nanoscale magnet, the spin transfer effect is critical for the application of magnetic random access memory. For this purpose, it is important to enhance the spin current carried by the charge current. Calculations based on the diffusive spin-dependent transport equations reveal that the magnitude of spin current can be tuned by modifying the ferromagnetic layer and the spin relaxation process in the device. Increasing the ferromagnetic layer thickness is found to enhance both the spin current and the spin accumulation. On the other hand, a strong spin relaxation in the capping layer also increases the spin current but suppresses the spin accumulation. To demonstrate the theoretical results, nanopillar structures with the size of approximately 100 nm are fabricated and the current-induced magnetization switching behaviors are experimentally studied. When the ferromagnetic layer thickness is increased from 3 nm to 20 nm, the critical switching current for the current-induced magnetization switching is significantly reduced, indicating the enhancement of the spin current. When the Au capping layer with a short spin-diffusion length replaces the Cu capping layer with a long spin-diffusion length, the reduction of the critical switching current is also observed.

  20. Effect of Magnetic Fluctuations on Spin Current

    NASA Astrophysics Data System (ADS)

    Niimi, Yasuhiro; Wei, Dahai; Otani, YoshiChika

    2017-01-01

    Spin Hall effect (SHE) and its inverse enable the interconversion between charge current and spin current. It is widely recognized that the SHE occurs in a nonmagnetic material with strong spin-orbit interaction. However, it can be generated even in magnetic materials such as ferromagnets, antiferromagnets, and those mixtures, i.e., spin glass. Here we review the SHEs in two typical magnetic systems. One is the SHE in a weak ferromagnetic metal in the vicinity of the Curie temperature where a nonlinear magnetic susceptibility can be detected. The other is the SHE in a spin glass metal where fluctuations at the magnetic impurity sites can be measured electrically in a very sensitive way. We argue that the spin current could be utilized as a sensor to detect a small magnetic fluctuation.

  1. Multivariable current control for electrically and magnetically coupled superconducting magnets

    SciTech Connect

    Owen, E.W.; Shimer, D.W.

    1985-02-08

    Superconducting magnet systems under construction and projected for the future contain magnets that are magnetically coupled and electrically connected with shared power supplies. A change in one power supply voltage affects all of the magnet currents. A current controller for these systems must be designed as a multivariable system. The paper describes a method, based on decoupling control, for the rational design of these systems. Dynamic decoupling is achieved by cross-feedback of the measured currents. A network of gains at the input decouples the system statically and eliminates the steady-state error. Errors are then due to component variations. The method has been applied to the magnet system of the MFTF-B, at the Lawrence Livermore National Laboratory.

  2. 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.

  3. Experiments with Coler magnetic current apparatus

    NASA Astrophysics Data System (ADS)

    Ludwig, T.

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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. Current Collection in a Magnetic Field

    NASA Technical Reports Server (NTRS)

    Krivorutsky, E. N.

    1997-01-01

    It is found that the upper-bound limit for current collection in the case of strong magnetic field from the current is close to that given by the Parker-Murphy formula. This conclusion is consistent with the results obtained in laboratory experiments. This limit weakly depends on the shape of the wire. The adiabatic limit in this case will be easily surpassed due to strong magnetic field gradients near the separatrix. The calculations can be done using the kinetic equation in the drift approximation. Analytical results are obtained for the region where the Earth's magnetic field is dominant. The current collection can be calculated (neglecting scattering) using a particle simulation code. Dr. Singh has agreed to collaborate, allowing the use of his particle code. The code can be adapted for the case when the current magnetic field is strong. The needed dm for these modifications is 3-4 months. The analytical description and essential part of the program is prepared for the calculation of the current in the region where the adiabatic description can be used. This was completed with the collaboration of Drs. Khazanov and Liemohn. A scheme of measuring the end body position is also proposed. The scheme was discussed in the laboratory (with Dr. Stone) and it was concluded that it can be proposed for engineering analysis.

  11. 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.

  12. Calibrated Faraday Current And Magnetic Field Sensor

    NASA Astrophysics Data System (ADS)

    Neyer, B. T.; Chang, J.; Ruggles, L. E.

    1986-01-01

    We have developed a calibrated optical fiber Faraday rotation current sensor. A strong magnetic field in an optical fiber introduces circular birefringence, causing the plane of polarization of light to rotate by an amount proportional to the magnetic field. Faraday loops used in the past were nonlinear due to the stress-induced linear birefringence caused by bending the loop. This linear birefringence interfered with the Faraday rotation, yielding a complicated relationship between the current and detected light signal. We have found a way to overcome the effects of the unwanted linear birefringence and produce a calibrated current waveform. The calibration is limited only by the accurate knowledge of the Verdet constant of the optical fiber. Results of recent experiments as well as planned measurements will be presented.

  13. 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.

  14. Current distribution and stability criteria for superconducting cables in transient magnetic fields

    NASA Astrophysics Data System (ADS)

    Ferri, Matthew Anthony

    1997-08-01

    A theoretical model of current distribution is developed to explain the performance limitations of superconducting cables in transient magnetic fields. The model self- consistently handles the coupled non-linear electromagnetic and thermal equations which govern the behavior of the cable during both normal operation and quench/recovery events. A two-strand cable is used as an analogy to clarify critical concepts which would be mathematically intractable for larger cable geometries. The model emphasizes the role of 'circulating currents' which are induced by ramping magnetic fields in the vicinity of the low resistance cable terminations. Unlike the fine-scale eddy currents which cause inter-strand coupling losses in cabled superconductors, circulating currents can cause significantly uneven distributions of the net transport current carried by the cable. Since circulating currents have not attracted much attention in the literature, the theoretical model offers unique insights into this important determinant of magnet performance. Characteristic length scales have been identified which differentiate cable designs into one of nine classifications. Analytic formulae characterizing current distribution for each case are presented. Further, the stability criteria for cables in transient magnetic fields is shown to be heavily dependent on cable length. These results have important implications for researchers attempting to model full-scale magnets with lab-scale experiments. The theoretical model is shown to explain some of the more confounding results from previously conducted experiments. The 'Ramp-Rate Limitation' phenomenon first encountered in the United States Demonstration Poloidal Coil (US-DPC) experiment is shown to be a direct result of induced current imbalances within the conductor. The model would need further refinement, however, to accurately predict all features witnessed experimentally. Finally, the findings of the theoretical analysis are used to

  15. 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.

  16. 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%.

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

    DOE PAGES

    Wang, X.; Ambrosio, G.; Chlachidze, G.; ...

    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

  18. Current-Induced Magnetization Dynamics in Magnetic Nanostructures

    NASA Astrophysics Data System (ADS)

    Yan, Peng

    This thesis deals with the study of current-induced magnetization dynamics for both macrospins and magnetic domain walls, driven by the so-called spin transfer torque effect. It consists of three distinct components: (1) a study of spin transfer torque enhancement in dual spin valves in the ballistic regime, (2) a proposal of domain wall propagation due to the synchronization with circularly polarized microwaves, which can be mapped to uniform spin current driven case, and (3) a derivation of an optimal temporally and spatially varying spin current pattern for fast domain wall propagation along nanowires. The spin transfer torque in all-metal dual spin valves, in which two antiparallelly aligned pinned ferromagnetic layers are on the two sides of a free ferromagnetic layer with two thin normal metal spacers in between, is studied in the ballistic regime. It is argued that, similar to the results in the diffusive regime, the spin transfer torque is dramatically enhanced in comparison to that in a conventional spin valve in the ballistic regime. Within the Slonczewski approach, an analytical expression of the torque on the free magnetic layer is obtained, which may serve as a theoretical model for the micromagnetic simulation of the spin dynamics in dual spin valve. Depending on the orientation of free layer and the degree of electron polarization, the spin transfer torque enhancement could be tens of times. The general cases when transmission and reflection probabilities of free layer are different from zero or one are also numerically calculated. Finding a new control parameter for magnetic domain wall motion is important in general and in particular for the spintronics applications. Here, we show that a circularly polarized magnetic field (CPMF) at gigahertz frequency (microwave) can efficiently drive a domain wall to propagate along a magnetic nanowire. Two motion modes are identified: rigid-domain wall propagation at low frequency and oscillatory propagation at

  19. 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.

  20. 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.

  1. 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)

  2. 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.

  3. 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.

  4. 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)

  5. 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.

  6. Laboratory experiments on magnetic reconnection and current systems

    NASA Astrophysics Data System (ADS)

    Stenzel, R. L.; Urrutia, J. M.; Gekelman, W.; Pfister, H.

    After a brief review of laboratory experiments involving magnetic reconnection a series of basic physics experiments on reconnection phenomena is described. These include magnetic annihilation, transport of magnetic energy by waves, stable and unstable current sheets, energy conversion mechanisms, and the role of global current systems vs. local reconnection processes. Current systems driven by electric fields resulting in particle flows are examined. Also, the role of a magnetic field component B(y) along the separator has been investigated.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  8. 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.

  9. Current-induced switching in a magnetic insulator

    NASA Astrophysics Data System (ADS)

    Avci, Can Onur; Quindeau, Andy; Pai, Chi-Feng; Mann, Maxwell; Caretta, Lucas; Tang, Astera S.; Onbasli, Mehmet C.; Ross, Caroline A.; Beach, Geoffrey S. D.

    2016-11-01

    The spin Hall effect in heavy metals converts charge current into pure spin current, which can be injected into an adjacent ferromagnet to exert a torque. This spin-orbit torque (SOT) has been widely used to manipulate the magnetization in metallic ferromagnets. In the case of magnetic insulators (MIs), although charge currents cannot flow, spin currents can propagate, but current-induced control of the magnetization in a MI has so far remained elusive. Here we demonstrate spin-current-induced switching of a perpendicularly magnetized thulium iron garnet film driven by charge current in a Pt overlayer. We estimate a relatively large spin-mixing conductance and damping-like SOT through spin Hall magnetoresistance and harmonic Hall measurements, respectively, indicating considerable spin transparency at the Pt/MI interface. We show that spin currents injected across this interface lead to deterministic magnetization reversal at low current densities, paving the road towards ultralow-dissipation spintronic devices based on MIs.

  10. Current-induced switching in a magnetic insulator.

    PubMed

    Avci, Can Onur; Quindeau, Andy; Pai, Chi-Feng; Mann, Maxwell; Caretta, Lucas; Tang, Astera S; Onbasli, Mehmet C; Ross, Caroline A; Beach, Geoffrey S D

    2017-03-01

    The spin Hall effect in heavy metals converts charge current into pure spin current, which can be injected into an adjacent ferromagnet to exert a torque. This spin-orbit torque (SOT) has been widely used to manipulate the magnetization in metallic ferromagnets. In the case of magnetic insulators (MIs), although charge currents cannot flow, spin currents can propagate, but current-induced control of the magnetization in a MI has so far remained elusive. Here we demonstrate spin-current-induced switching of a perpendicularly magnetized thulium iron garnet film driven by charge current in a Pt overlayer. We estimate a relatively large spin-mixing conductance and damping-like SOT through spin Hall magnetoresistance and harmonic Hall measurements, respectively, indicating considerable spin transparency at the Pt/MI interface. We show that spin currents injected across this interface lead to deterministic magnetization reversal at low current densities, paving the road towards ultralow-dissipation spintronic devices based on MIs.

  11. 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.

  12. The 100 kA current leads for a superconducting transmission line magnet

    SciTech Connect

    Huang, Yuenian; Foster, William; Kim, Seog-Whan; Mazur, Peter; Oleck, Andrew; Piekarz, Henryk; Rabehl, Roger; Wake, Masayoshi; /Fermilab /KEK, Tsukuba

    2005-09-01

    A pair of current leads to power a transmission line magnet cooled at liquid helium temperature has been designed and developed at Fermilab. The leads designed to carry 100 kA dc current. Each lead consists of a warm end, heat exchange section and a cold end. The warm end is a half moon plate and cylinder brazed together. The heat exchange section is made of 202 copper rods arranged in a staggered pattern. Each rod is 6.35 mm in diameter and 1650 mm in length. The rods were soft-soldered into 12.7 mm deep holes at both warm and cold ends. The helium gas flow, guided by anodized aluminum baffles along the lead length, allows for a relatively high heat transfer coefficient between the current carrying rods and cooling helium gas. As a result the current leads were successfully tested with a ramping current of up to 104 kA. The current lead design, assembly work and the test results are presented.

  13. 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.

  14. 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.

  15. Manipulation of magnetic moment using the spin current from magnetic and non-magnetic materials

    NASA Astrophysics Data System (ADS)

    Liu, Luqiao

    This thesis summarizes my studies on the effect of spin transfer torque on metallic ferromagnets. The spin current for generating the spin torque is either from ferromagnetic electrode through the spin filtering effect, or from nonmagnetic material through the spin Hall effect (SHE). In the experiment using the spin filtering effect, the current flows vertically through the nanoscale spin valve geometries. I will describe the fabrication process that I used to make the nanopillar structure and the strategy that I developed to reduce the critical current. In the experiment utilizing the SHE, the current flows within the film plane and the spin current is injected transversely from the non-magnetic (NM) film into the adjacent ferromagnetic (FM) layer. I will present five studies that I made to characterize the properties of the SHE and its influence on the magnetic moment. In the first study, I employed the spin torque ferromagnetic resonance (FMR) technique to determine the spin Hall angle. In this experiment, radio frequency current was applied onto the NM/FM bilayer and FMR was induced by the resultant oscillating spin current. By looking into the amplitude of the FMR signal, I was able to get the value of the spin Hall angle. In the second and third studies, I demonstrated that the SHE could be utilized to switch magnetic moment of both perpendicularly and in-plane magnetized FM films. For the perpendicular case, the spins injected into the FM film exert a torque that is perpendicular to the equilibrium position of the moment and it fights against the restoring anisotropy field and induces switching. For the in-plane case, the spins cause switching through the anti-damping mechanism. In the fourth study, I showed that the SHE could induce persistent magnetic oscillations. DC spin current reduces the magnetic damping to zero and the moment undergoes precession around the applied magnetic field. In the final study, I demonstrated that the SHE switching current can

  16. Measured force/current relations in solid magnetic thrust bearings

    SciTech Connect

    Allaire, P.E.; Fittro, R.L.; Maslen, E.H.; Wakefield, W.C.

    1997-01-01

    When magnetic bearings are employed in a pump, compressor, turbine, or other rotating machine, measurement of the current in the bearing coils provides knowledge of the forces imposed on the bearings. This can be a significant indicator of machine problems. Additionally, magnetic bearings can be utilized as a load cell for measuring impeller forces in test rigs. The forces supported by magnetic bearings are directly related to the currents, air gaps, and other parameters in the bearings. This paper discusses the current/force relation for magnetic thrust bearings. Force versus current measurements were made on a particular magnetic bearing in a test rig as the bearing coil currents were cycled at various time rates of change.d the quasi-static force versus current relations were measured for a variety of air gaps and currents. The thrust bearing exhibits a hysteresis effect, which creates a significant difference between the measured force when the current is increasing as compared to that when the current is decreasing. For design current loops, 0.95 A to 2.55 A, at the time rate of change of 0.1 A/s, the difference between increasing and decreasing current curves due to hysteresis ranged from 4 to 8%. If the bearing is operated in small trajectories about a fixed (nonzero) operation point on the F/I (force/current) curve, the scatter in the measurement error could be expected to be on the order of 4%. A quasi-static nonlinear current/force equation was developed to model the data and curve-fit parameters established for the measured data. The effects of coercive force and iron reluctance, obtained from conventional magnetic materials tests, were included to improve the model, but theoretically calculated values from simple magnetic circuit theory do not produce accurate results. Magnetic fringing, leakage, and other effects must be included.

  17. 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.

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

    PubMed

    Walz, Michael; Wilhelm, Jan; Evers, Ferdinand

    2014-09-26

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

  19. 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.

  20. Charge and current reservoirs for electric and magnetic field enhancement.

    PubMed

    Wang, Dongxing; Yang, Tian; Crozier, Kenneth B

    2010-05-10

    Two optical antenna designs incorporating structures termed charge and current reservoirs are proposed to realize localized high electric and magnetic field enhancement, respectively. Simulation results show that the fan-rod electric antenna design combines the advantages of the rod antenna and the bowtie antenna, and has higher field enhancement than either. The performance of a loop shaped magnetic antenna consisting of a pair of metallic strips with offsets is also verified numerically, with high magnetic field enhancement being observed in the simulation. In both of the designs, the concepts of charge and current reservoirs contribute to high electric and magnetic field enhancement.

  1. 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.

  2. 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.

  3. Calibrated Faraday current and magnetic field sensor

    NASA Astrophysics Data System (ADS)

    Neyer, B. T.; Chang, J.; Lockwood, G. J.; Ruggles, L. E.

    A calibrated optical fiber Faraday rotation current sensor is developed. This sensor has a gigahertz response, is immune to electromagnetic interference, and is constructed entirely of dielectric material. All of these advantages make the sensor ideal for pulsed power measurements.

  4. Magnetization oscillations and waves driven by pure spin currents

    NASA Astrophysics Data System (ADS)

    Demidov, V. E.; Urazhdin, S.; de Loubens, G.; Klein, O.; Cros, V.; Anane, A.; Demokritov, S. O.

    2017-02-01

    Recent advances in the studies of pure spin currents-flows of angular momentum (spin) not accompanied by the electric currents-have opened new horizons for the emerging technologies based on the electron's spin degree of freedom, such as spintronics and magnonics. The main advantage of pure spin current, as compared to the spin-polarized electric current, is the possibility to exert spin transfer torque on the magnetization in thin magnetic films without the electrical current flow through the material. In addition to minimizing Joule heating and electromigration effects, this enables the implementation of spin torque devices based on the low-loss insulating magnetic materials, and offers an unprecedented geometric flexibility. Here we review the recent experimental achievements in investigations of magnetization oscillations excited by pure spin currents in different nanomagnetic systems based on metallic and insulating magnetic materials. We discuss the spectral properties of spin-current nano-oscillators, and relate them to the spatial characteristics of the excited dynamic magnetic modes determined by the spatially-resolved measurements. We also show that these systems support locking of the oscillations to external microwave signals, as well as their mutual synchronization, and can be used as efficient nanoscale sources of propagating spin waves.

  5. Interaction of bootstrap-current-driven magnetic islands

    SciTech Connect

    Hegna, C.C.; Callen, J.D.

    1991-10-01

    The formation and interaction of fluctuating neoclassical pressure gradient driven magnetic islands is examined. The interaction of magnetic islands produces a stochastic region around the separatrices of the islands. This interaction causes the island pressure profile to be broadened, reducing the island bootstrap current and drive for the magnetic island. A model is presented that describes the magnetic topology as a bath of interacting magnetic islands with low to medium poloidal mode number (m {congruent} 3{minus}30). The islands grow by the bootstrap current effect and damp due to the flattening of the pressure profile near the island separatrix caused by the interaction of the magnetic islands. The effect of this sporadic growth and decay of the islands ( magnetic bubbling'') is not normally addressed in theories of plasma transport due to magnetic fluctuations. The nature of the transport differs from statistical approaches to magnetic turbulence since the radial step size of the plasma transport is now given by the characteristic island width. This model suggests that tokamak experiments have relatively short-lived, coherent, long wavelength magnetic oscillations present in the steep pressure-gradient regions of the plasma. 42 refs.

  6. 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

  7. Magnetic topology and current channels in plasmas with toroidal current density inversions

    SciTech Connect

    Ciro, D.; Caldas, I. L.

    2013-10-15

    The equilibrium magnetic field inside axisymmetric plasmas with inversions on the toroidal current density is considered. Previous works have shown that internal regions with negative current density lead to non-nested magnetic surfaces inside the plasma. Following these results, we derive a general expression relating the positive and negative currents inside the non-nested surfaces. This is done in terms of an anisotropy parameter that is model-independent and is based in very general properties of the magnetic field. We demonstrate that the positive currents in axisymmetric islands screen the negative one in the plasma center by reaching about twice its magnitude. Further, we illustrate these results by developing a family of analytical local solutions for the poloidal magnetic field in a region of interest that contains the inverted current. These local solutions exhibit non-nested magnetic surfaces with a combined current of at least twice the magnitude of the negative one, as prescribed from the topological arguments, and allow to study topological transitions driven by geometrical changes in the current profile. To conclude, we discuss the signatures of internal current density inversions in a confinement device and show that magnetic pitch measurements may be inappropriate to differentiate current reversals and small current holes in plasmas.

  8. 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.

  9. Streaming current magnetic fields in a charged nanopore

    PubMed Central

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

    2016-01-01

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

  10. Streaming current magnetic fields in a charged nanopore

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  11. Streaming current magnetic fields in a charged nanopore.

    PubMed

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

    2016-11-11

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

  12. Repair and Maintenance Programs (RAMP)

    SciTech Connect

    Hostetler, D.

    1999-07-01

    The purpose of the paper is to explain in a general way how the development of Komatsu RAMPs can help accomplish the worthy ideal set forth in that theme for all parties involved--the OEM (Original Equipment Manufacturer), the equipment dealer, and the mining company. The goal of the RAMP is to utilize the resources of the OEM, the dealer, and the mining company to minimize the costs, maximize the efficiency, increase the productivity, and improve the profits of all parties. The paper describes how a RAMP works.

  13. New approaches in the design of magnetic tweezers-current magnetic tweezers

    NASA Astrophysics Data System (ADS)

    Bessalova, Valentina; Perov, Nikolai; Rodionova, Valeria

    2016-10-01

    The main advantages of the magnetic tweezers are the low price and simplicity of use. However the range of their application is reduced due to shortcomings like, for example, the remanent induction of the core and interaction between ferromagnetic cores. We present the new design of magnetic tweezers-Current Magnetic Tweezers (CMT) that allow particle manipulation by means of the magnetic field generated by the electric currents flowing through the non-magnetic wires. Arranging wires in different geometric shapes allows the particle movement either in two or three dimensions. Forces acting on the magnetic particles with the magnetic moment of 2·10-11 A m2 at distances up to 1 mm had been experimentally measured. It is established that a current of about 1 A at a 1 mm distance generates force of (approximately) 3 pN which is consistent with theoretical estimates.

  14. 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.

  15. 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.

  16. Critical and supercritical current measurements by a magnetic induction method

    NASA Astrophysics Data System (ADS)

    Harris, E. A.; Bishop, J. E. L.; Havill, R. L.; Ward, P. J.

    1988-10-01

    The temperature dependence of the critical current and current-voltage characteristics at supercritical currents have been measured in the low field limit on toroidal samples of the ceramic high Tc superconductor YBa 2Cu 3O 7- δ by a contactless magnetic induction technique that is sensitive to the transport supercurrent but not to any intragrain current loops. The sample constitutes a tertiary winding on a small ferrite transformer core. The secondary voltage provides a very sensitive indication of when the critical current is exceeded, and when it is integrated it yields the supercritical current-voltage characteristic.

  17. 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

  18. Magnetic Imaging of Superconducting Tapes to Determine Current Flow

    NASA Astrophysics Data System (ADS)

    Mueller, Fred M.; Brown, David J.; Hawley, Marilyn E.; Brown, Geoffrey W.; Yates Coulter, J.

    2000-03-01

    We have developed a magnetic imaging system which yields quantitative information about the magnetic field near the surface of a superconducting tape while it is carrying current at liquid nitrogen temperatures. The imaging system is based on a mechanical scanner with motion coupled into a dewar and uses standard magnetoresistive read heads from computer hard disk drives as the sensor elements. We have numerically inverted the external magnetic field data from silver-coated YBCO tapes to derive the internal tape current densities. Preliminary results are consistent with the expected patterns in the tapes, obey sum rules, and exhibit time reversal symmetry. Preliminary current flow paths suggest that the current density can be non-uniform.

  19. 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.

  20. 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.

  1. 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.

  2. A Management Case Study: The Implementation of the Rapid Acquisition of Manufactured Parts (RAMP) Program

    DTIC Science & Technology

    1993-06-01

    manufacturing needs based on the dollars available to support this new technology. In December 1987, the staif at NAVSUP awarded the current RAMP contract to...describes the implementation of the Navy’s Rapid Acquisition of Manufactured Parts (RAMP) program. The RAMP program was implemented in 1989 by the Naval...time and cost for manufactured spare parts. This management case study concentrates on the examination of how new technology is implemented into current

  3. Unsteady magnetic reconnection in laboratory experiments with current sheets

    NASA Astrophysics Data System (ADS)

    Frank, Anna

    2009-11-01

    According to present notion, unsteady magnetic reconnection in current sheets (CS) is basic to dramatic natural phenomena: solar and stellar flares, substorms in the Earth and other planetary magnetospheres, as well as to disruptive instabilities in tokamak plasmas. We present a review of laboratory experiments studying evolution of CS formed in 3D and 2D magnetic configurations with an X line, in the CS-3D device. Usually CS exists during an extended period in a metastable stage, without essential changes of its structure and parameters. Under certain conditions this stage may be suddenly interrupted by unsteady phase of magnetic reconnection, which manifests itself in a rapid change of the magnetic field topology, current redistribution, excitation of pulsed electric fields, and other dynamic effects. The unsteady phase results in effective conversion of magnetic energy into the energy of plasma and accelerated particles, and may finally bring about the CS disruption. In the context of the solar flares, a metastable CS is associated with a pre-flare situation, while CS disruption -- with the flare itself. The physical mechanisms triggering the unsteady magnetic reconnection in the laboratory produced current sheets are discussed. Supported by the Russian Foundation for Basic Research (project # 09-02-00971).

  4. Current Sheets Formation and Relaxation of Coronal Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Rappazzo, A. F.

    2013-12-01

    We investigate the relaxation of magnetic fields in closed regions of solar and stellar coronae, extending to further topologies our previous work (Rappazzo, A.F. & Parker, E.N., ApJL, 773, L2 (2013)). The dynamical evolution is integrated with the equations of reduced magnetohydrodynamics (RMHD) apt to model a plasma embedded in a strong guide field B0 extended along the axial direction, where the dynamical field is the orthogonal component b. Dissipative and ideal simulations are carried out in Cartesian geometry: 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 in a motionless photosphere. The magnetic field b initially has only large scales, and is not in equilibrium. We show that the magnetic relaxation leads to the formation of current sheets when the intensity of the magnetic field b is beyond a critical value b_c. For values of b below this threshold (b < b_c), line-tying and field-line tension inhibit the formation of current sheets, while above the threshold (b > b_c) 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 under-resolved.

  5. A 3D Current Loop Model of Magnetic Clouds

    NASA Astrophysics Data System (ADS)

    Chen, James

    1992-05-01

    A magnetohydrodynamic (MHD) model is developed to study magnetic clouds (Burlaga et al. 1981). In this model, magnetic clouds observed near 1 AU are treated as a consequence of eruptive solar current loops. It is shown that current loops intially in MHD equilibrium can be triggered to rise rapidly, propelling material of up to 10(16) g at up to ~ 1000 km s(-1) and dissipating ~ 10(32) erg of magnetic energy in tens of minutes. The initial rise profile is consistent with observed height-time profiles of erupting filaments (Kahler et al. 1988). Two triggering mechanisms for eruption are suggested: (1)subphotospheric energy storage and trigger and (2) in situ (coronal) energy storage and trigger. In the former, eruption occurs as a result of changes in the subphotospheric magnetic topology and subsequent relaxation to a new equilibrium. In the latter, the current loop can evolve to exceed a local maximum in the magnetic potential associated with the ambient magnetic fields. The former scenario leads to more energetic and longer-lasting eruption than the latter. Burlaga, L. F., Sittler, E., Mariani, F., and Schwenn, R. 1981, J. Geophys. Res., 86, 6673. Kahler, S. W., Moore, R. L., Kane, S. R., and Zirin, H. 1988, Ap. J., 328, 824.

  6. Explosive magnetic source of current with controllable output voltage

    NASA Astrophysics Data System (ADS)

    Dudai, P. V.; Zimenkov, A. A.; Ivanov, V. A.; Ivanov, E. I.; Karpov, G. V.; Polyushko, S. M.; Skobelev, A. N.; Fevralev, A. Yu.

    2015-01-01

    The paper describes a small-size explosive current source with controllable output voltage shaping a megaampere current pulse. This energy source comprises a helical explosive magnetic generator and an explosive sectionalized current opening switch and is designed to power gas-discharge chambers of the plasma focus type. Control of the output voltage of the pulsed current source is performed in such a manner that in each of the series-connected sections of the explosive current opening switch, voltage is generated with a given time shift relative to the neighboring section.

  7. 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.

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

    PubMed Central

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

    2017-01-01

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

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

    PubMed

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

    2017-02-23

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

  10. Effects of magnetic islands on bootstrap current in toroidal plasmas

    NASA Astrophysics Data System (ADS)

    Dong, G.; Lin, Z.

    2017-03-01

    The effects of magnetic islands on electron bootstrap current in toroidal plasmas are studied using gyrokinetic simulations. The magnetic islands cause little changes of the bootstrap current level in the banana regime because of trapped electron effects. In the plateau regime, the bootstrap current is completely suppressed at the island centers due to the destruction of trapped electron orbits by collisions and the flattening of pressure profiles by the islands. In the collisional regime, small but finite bootstrap current can exist inside the islands because of the pressure gradients created by large collisional transport across the islands. Finally, simulation results show that the bootstrap current level increases near the island separatrix due to steeper local density gradients.

  11. Switchable spin-current source controlled by magnetic domain walls.

    PubMed

    Savero Torres, W; Laczkowski, P; Nguyen, V D; Rojas Sanchez, J C; Vila, L; Marty, A; Jamet, M; Attané, J P

    2014-07-09

    Using nonlocal spin injection, spin-orbit coupling, or spincaloritronic effects, the manipulation of pure spin currents in nanostructures underlies the development of new spintronic devices. Here, we demonstrate the possibility to create switchable pure spin current sources, controlled by magnetic domain walls. When the domain wall is located at a given point of the magnetic circuit, a pure spin current is injected into a nonmagnetic wire. Using the reciprocal measurement configuration, we demonstrate that the proposed device can also be used as a pure spin current detector. Thanks to its simple geometry, this device can be easily implemented in spintronics applications; in particular, a single current source can be used both to induce the domain wall motion and to generate the spin signal.

  12. 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.

  13. 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.

  14. Multivariable current control for electrically and magnetically coupled superconducting magnets. Revision 1

    SciTech Connect

    Owen, E.W.; Shimer, D.W.

    1985-02-08

    Superconducting magnet systems under construction and projected for the future contain magnets that are magnetically coupled and electrically connected with shared power supplies. A change in one power supply voltage affects all of the magnet currents. A current controller for these system must be designed as a multivariable system. The power describes a method, based on decoupling control, for the rational design of these systems. Dynamic decoupling is achieved by cross-feedback of the measured currents. A network of gains at the input decouples the system statically and eliminates the steady-state error. Errors are then due to component variations. The method has been applied to the magnet system of the MFTF-B, at the Lawrence Livermore National Laboratory.

  15. Rapid dissipation of magnetic fields due to the Hall current

    SciTech Connect

    Vainshtein, S. I.; Chitre, S. M.; Olinto, A. V.

    2000-04-01

    We propose a mechanism for the fast dissipation of magnetic fields which is effective in a stratified medium where ion motions can be neglected. In such a medium, the field is frozen into the electrons, and Hall currents prevail. Although Hall currents conserve magnetic energy, in the presence of density gradients they are able to create current sheets which can be sites for efficient dissipation of magnetic fields. We recover the frequency {omega}{sub MH} for Hall oscillations modified by the presence of density gradients. We show that these oscillations can lead to an exchange of energy between different components of the field. We calculate the time evolution, and show that magnetic fields can dissipate on a time scale of order 1/{omega}{sub MH}. This mechanism can play an important role in magnetic dissipation in systems with very steep density gradients, where the ions are static such as those found in the solid crust of neutron stars. (c) 2000 The American Physical Society.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Analytical results of asymmetric exclusion processes with ramps

    NASA Astrophysics Data System (ADS)

    Huang, Ding-Wei

    2005-07-01

    We present the analytical results in a simple traffic model describing a single-lane highway with ramps. Both on-ramps and off-ramps are considered. Complete classification of distinct phases is achieved. Exact phase diagrams are derived. In the case of a single ramp (either on-ramp or off-ramp), the bottleneck effect is absent. The traffic conditions of congestion before the ramp and free-flowing after the ramp cannot be realized. In the case of two consecutive ramps, the bottleneck emerges when the on-ramp is placed before the off-ramp and the flow in between the ramps saturates.

  2. Spin currents and magnon dynamics in insulating magnets

    NASA Astrophysics Data System (ADS)

    Nakata, Kouki; Simon, Pascal; Loss, Daniel

    2017-03-01

    Nambu–Goldstone theorem provides gapless modes to both relativistic and nonrelativistic systems. The Nambu–Goldstone bosons in insulating magnets are called magnons or spin-waves and play a key role in magnetization transport. We review here our past works on magnetization transport in insulating magnets and also add new insights, with a particular focus on magnon transport. We summarize in detail the magnon counterparts of electron transport, such as the Wiedemann–Franz law, the Onsager reciprocal relation between the Seebeck and Peltier coefficients, the Hall effects, the superconducting state, the Josephson effects, and the persistent quantized current in a ring to list a few. Focusing on the electromagnetism of moving magnons, i.e. magnetic dipoles, we theoretically propose a way to directly measure magnon currents. As a consequence of the Mermin–Wagner–Hohenberg theorem, spin transport is drastically altered in one-dimensional antiferromagnetic (AF) spin-1/2 chains; where the Néel order is destroyed by quantum fluctuations and a quasiparticle magnon-like picture breaks down. Instead, the low-energy collective excitations of the AF spin chain are described by a Tomonaga–Luttinger liquid (TLL) which provides the spin transport properties in such antiferromagnets some universal features at low enough temperature. Finally, we enumerate open issues and provide a platform to discuss the future directions of magnonics.

  3. 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.

  4. Ionospheric midlatitude electric current density inferred from multiple magnetic satellites

    NASA Astrophysics Data System (ADS)

    Shore, R. M.; Whaler, K. A.; Macmillan, S.; Beggan, C.; Olsen, N.; Spain, T.; Aruliah, A.

    2013-09-01

    A method for inferring zonal electric current density in the mid-to-low latitude F region ionosphere is presented. We describe a method of using near-simultaneous overflights of the Ørsted and CHAMP satellites to define a closed circuit for an application of Ampère's integral law to magnetic data. Zonal current density from sources in only the region between the two satellites is estimated for the first time. Six years of mutually available vector magnetic data allows overlaps spanning the full 24 h range of local time twice. Solutions are computed on an event-by-event basis after correcting for estimates of main and crustal magnetic fields. Current density in the range ±0.1 μA/m2 is resolved, with the distribution of electric current largely matching known features such as the Appleton anomaly. The currents appear unmodulated at times of either high-negative Dst or high F10.7, which has implications for any future efforts to model their effects. We resolve persistent current intensifications between geomagnetic latitudes of 30 and 50° in the postmidnight, predawn sector, a region typically thought to be relatively free of electric currents. The cause of these unexpected intensifications remains an open issue. We compare our results with current density predictions made by the Coupled Thermosphere-Ionosphere-Plasmasphere model, a self-consistent, first-principles, three-dimensional numerical dynamic model of ionospheric composition and temperatures. This independent validation of our current density estimates highlights good agreement in the broad spatiotemporal trends we identify, which increases confidence in our results.

  5. 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.

  6. Study of Magnetospheric Currents and Resultant Surface Magnetic Variations.

    DTIC Science & Technology

    1980-04-17

    AD-A093 928 RICE 1*319 HOUSTON TX F/6 4/1 STUOT OF MAGNETOSPHERIC URRENTS AND RESULTANT SUR3FACE MAGNETIC-ETC (U) APR A0 C CHEN, R WOLF, N HAREL. J3...KARTY F19628-77-C-0005 UNCLASSIFIED AFGL-TR-60-0139 N -mhmmhhmhhoiu -Ehhhhmhmml 2-81_ _ _ _ AFGL-TR-80-039c Z STUDY OF MAGNETOSPH ERIC CURRENTS AND...RESULTANT SURFACE MAGNETIC VARIATIONS C. -K. Chen R. A. Wolf M. Harel CIZ J. L.Karty R. W.Spiro G. M. Erickson William Marsh Rice University 6100 S

  7. Plasmoid formation in current sheet with finite normal magnetic component.

    PubMed

    Zhu, P; Raeder, J

    2013-06-07

    Current sheet configurations in natural and laboratory plasmas are often accompanied by a finite normal magnetic component that is known to stabilize the two-dimensional resistive tearing instability in the high Lundquist number regime. Recent magnetohydrodynamic simulations indicate that the nonlinear development of ballooning instability is able to induce the formation of X lines and plasmoids in a generalized Harris sheet with a finite normal magnetic component in the high Lundquist number regime where the linear two-dimensional resistive tearing mode is stable.

  8. High temperature superconducting current leads for fusion magnet systems

    SciTech Connect

    Wu, J.L.; Dederer, J.T.; Singh, S.K. . Science and Technology Center); Hull, J.R. )

    1991-01-01

    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.

  9. 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…

  10. Bell 47 #822 on ramp

    NASA Technical Reports Server (NTRS)

    1982-01-01

    Bell 47 #822 on ramp. The helicopter arrived at the NASA Flight Research Center on November 4, 1973 from the NASA Johnson Space Center in Texas. It operated for more than 11 years, before being sent to the Napa City Fire Department on June 21, 1985.

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  12. 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.

  13. Magnetic connection and current distribution in black hole accretion discs

    NASA Astrophysics Data System (ADS)

    Zhao, Cheng-Xuan; Wang, Ding-Xiong; Gan, Zhao-Ming

    2009-10-01

    We discuss one of the possible origins of large-scale magnetic fields based on a continuous distribution of toroidal electric current flowing in the inner region of the disc around a Kerr black hole (BH) in the framework of general relativity. It turns out that four types of configuration of the magnetic connection (MC) are generated, i.e. MC of the BH with the remote astrophysical load (MCHL), MC of the BH with the disc (MCHD), MC of the plunging region with the disc (MCPD) and MC of the inner and outer disc regions (MCDD). It turns out that the Blandford-Znajek process can be regarded as one type of MC, i.e. MCHL. In addition, we propose a scenario for fitting the quasi-periodic oscillations in BH binaries based on MCDD associated with the magnetic reconnection.

  14. Measurement of the magnetic field coefficients of particle accelerator magnets

    SciTech Connect

    Herrera, J.; Ganetis, G.; Hogue, R.; Rogers, E.; Wanderer, P.; Willen, E.

    1989-01-01

    An important aspect in the development of magnets to be used in particle accelerators is the measurement of the magnetic field in the beam aperture. In general it is necessary to measure the harmonic multipoles in the dipole, quadrupole, and sextupole magnets for a series of stationary currents (plateaus). This is the case for the Superconducting Super Collider (SSC) which will be ramped to high field over a long period (/approximately/1000 sec.) and then remain on the flat top for the duration of the particle collision phase. In contrast to this mode of operation, the Booster ring being constructed for the Brookhaven AGS, will have a fast ramp rate of approximately 10 Hz. The multipole fields for these Booster magnets must therefore be determined ''on the ramp.'' In this way the effect of eddy currents will be taken into account. The measurement system which we will describe in this paper is an outgrowth of that used for the SSC dipoles. It has the capability of measuring the field multipoles on both a plateau or during a fast ramp. In addition, the same basic coil assembly is used to obtain the magnetic multipoles in dipole, quadrupole, and sextupole magnets. 2 refs., 3 figs., 1 tab.

  15. 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.

  16. Chaotic behavior of magnetic field lines near simplest current systems

    NASA Astrophysics Data System (ADS)

    Veselovsky, I. S.; Lukashenko, A. T.

    2016-12-01

    In the context of studying the problem of simulation of magnetic fields on the Sun, the structure of the field in the vicinity of two circular current loops with different mutual arrangement in space is considered. When the symmetry in the arrangement is sufficient, a system of magnetic surfaces created by the closed field lines arises. With a reduction in symmetry, isolated closed lines may exist. For the case of two identical current loops coupled perpendicularly, it is shown that the subsystems of these lines may be ordered in space in a complex manner. At large distances, a system of loops is equivalent to a dipole with a high degree of accuracy, while an approximate winding of the lines on the deformed toroids, encircling each of the loops, occurs at small distances. At intermediate distances, there are regions of both ordered and chaotic behavior of field lines. Results were obtained with the use of the numerical simulation method.

  17. 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 .

  18. 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

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

    SciTech Connect

    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.

  20. A current sheet model for the Earth's magnetic field

    NASA Astrophysics Data System (ADS)

    Stump, Daniel R.; Pollack, Gerald L.

    1998-09-01

    As an example in magnetostatics we consider the main magnetic field of the Earth and its current sources. The measured field on the surface is accurately given, in tables of the International Geological Reference Field, in terms of Gaussian coefficients. By applying Maxwell's equations to these data we calculate the extended field, inside the Earth, and give graphical representations of it. We also construct a simple theoretical model of the source of the field, in which the field is the result of currents flowing on the surface of a sphere inside the Earth. The current sources which give the observed field are calculated in terms of vector spherical harmonics. The stream function and currents are displayed on a Mercator projection for a sphere whose radius is half the Earth's radius. Interesting properties of vector operations on the Mercator plane are analytically and graphically described.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Transcranial Magnetic Stimulation in Child Neurology: Current and Future Directions

    PubMed Central

    Frye, Richard E.; Rotenberg, Alexander; Ousley, Molliann; Pascual-Leone, Alvaro

    2008-01-01

    Transcranial magnetic stimulation (TMS) is a method for focal brain stimulation based on the principle of electromagnetic induction, where small intracranial electric currents are generated by a powerful, rapidly changing extracranial magnetic field. Over the past 2 decades TMS has shown promise in the diagnosis, monitoring, and treatment of neurological and psychiatric disease in adults, but has been used on a more limited basis in children. We reviewed the literature to identify potential diagnostic and therapeutic applications of TMS in child neurology and also its safety in pediatrics. Although TMS has not been associated with any serious side effects in children and appears to be well tolerated, general safety guidelines should be established. The potential for applications of TMS in child neurology and psychiatry is significant. Given its excellent safety profile and possible therapeutic effect, this technique should develop as an important tool in pediatric neurology over the next decade. PMID:18056688

  7. Plasma dynamics on current-carrying magnetic flux tubes

    NASA Technical Reports Server (NTRS)

    Swift, Daniel W.

    1992-01-01

    A 1D numerical simulation is used to investigate the evolution of a plasma in a current-carrying magnetic flux tube of variable cross section. A large potential difference, parallel to the magnetic field, is applied across the domain. The result is that density minimum tends to deepen, primarily in the cathode end, and the entire potential drop becomes concentrated across the region of density minimum. The evolution of the simulation shows some sensitivity to particle boundary conditions, but the simulations inevitably evolve into a final state with a nearly stationary double layer near the cathode end. The simulation results are at sufficient variance with observations that it appears unlikely that auroral electrons can be explained by a simple process of acceleration through a field-aligned potential drop.

  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. A statistical model of magnetic islands in a current layer

    SciTech Connect

    Fermo, R. L.; Drake, J. F.; Swisdak, M.

    2010-01-15

    This letter describes a statistical model of the dynamics of magnetic islands in very large current layers that develop in space plasma. Two parameters characterize the island distribution: the flux psi contained in the island and the area A it encloses. The integrodifferential evolution equation for this distribution function is based on rules that govern the small-scale generation of secondary islands, the rates of island growth, and island merging. The numerical solutions of this equation produce island distributions relevant to the magnetosphere and solar corona. The solution of a differential equation for large islands explicitly shows the role merging plays in island growth.

  10. 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

  11. Changes in thickness of magnetized composites due to current flow

    NASA Astrophysics Data System (ADS)

    Bednarek, S.

    1998-02-01

    The pinch magnitude in monolithic metal conductors and ferromagnetics was estimated in this paper. The conditions for the material were formulated so that the pinch which occurs in it could reach the magnitude useful for applications. The way of production of a special composite with a laminar structure was described. The composite consists of sheets of copper foil separating the layers of the elastic ferromagnet which was made by the dispersion of hard magnetic particles in silicon. Using a measuring system containing a Michelson interferometer, measurements of changes were made in the thickness of the produced composite samples during the electric current flow. The obtained results were discussed.

  12. 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

  13. Ramp-induced transitions in traffic dynamics

    NASA Astrophysics Data System (ADS)

    Huang, Ding-Wei

    2006-01-01

    We present the analytical results of ramp effects in asymmetric simple exclusion processes. Both on-ramp and off-ramp are included in between the two open boundaries. The ramps can be taken as the nontrivial boundaries to trigger the phase transitions. Exact phase diagrams are obtained analytically in the full parameter space. We find that the order of the two ramps is crucial. When the on-ramp is placed after the off-ramp along the traffic direction, there are only four distinct phases: free-free-free, free-free-jam, free-jam-jam, and jam-jam-jam. The other four phases from naive expectation cannot be realized, i.e., jam-free-free, jam-jam-free, jam-free-jam, and free-jam-free are all absent. The free flow will not follow the congestion. When the on-ramp is placed before the off-ramp, we observe an interesting phase: jam-max.-free. The bottleneck emerges as the flow in between the two ramps saturates to its maximum. We further show that the roadway configuration is equivalent to a nonstandard intersection. Applications to a traffic rotary are discussed.

  14. 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

  15. 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.

  16. 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.

  17. Multiplicities and thermal runaway of current leads for superconducting magnets

    NASA Astrophysics Data System (ADS)

    Krikkis, Rizos N.

    2017-04-01

    The multiple solutions of conduction and vapor cooled copper leads modeling current delivery to a superconducting magnet have been numerically calculated. Both ideal convection and convection with a finite heat transfer coefficient for an imposed coolant mass flow rate have been considered. Because of the nonlinearities introduced by the temperature dependent material properties, two solutions exist, one stable and one unstable regardless of the cooling method. The limit points separating the stable form the unstable steady states form the blow-up threshold beyond which, any further increase in the operating current results in a thermal runway. An interesting finding is that the multiplicity persists even when the cold end temperature is raised above the liquid nitrogen temperature. The effect of various parameters such as the residual resistivity ratio, the overcurrent and the variable conductor cross section on the bifurcation structure and their stabilization effect on the blow-up threshold is also evaluated.

  18. Measurement of the current sheet during magnetic reconnection in a toroidal plasma.

    PubMed

    Crocker, N A; Fiksel, G; Prager, S C; Sarff, J S

    2003-01-24

    The current and magnetic-field fluctuations associated with magnetic-field-line reconnection have been measured in the reversed field pinch plasma configuration. The current sheet resulting from this reconnection has been measured. The current layer is radially broad, comparable to a magnetic-island width, as may be expected from current transport along magnetic-field lines. It is much larger than that predicted by resistive MHD for linear tearing modes and larger than prediction from two-fluid linear theory.

  19. Magnetic particle imaging: current developments and future directions.

    PubMed

    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 future directions

  20. 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

  1. Current Status and Future Perspective of Magnetic Behavior Analysis for Hard Disc Drive Magnetic Recording Heads

    NASA Astrophysics Data System (ADS)

    Yanagiuchi, Katsuaki; Hirata, Kei; Ishida, Yoichi

    With the increase in the recording density of hard disk drives, the narrower magnetic pole and read-sensor widths in writing and reading heads are required, and techniques used for the magnetic behavior analysis in a nanoscale area is essential. The observation of the in-plane domain structure of the writer pole for a perpendicular recording (PMR) head was performed by electron holography in order to elucidate the mechanism of the pole erasure originating from the instability of the magnetic domain state. The results revealed that the stability of the domain structure is strongly related to the domain wall trapping, and the pole erasure can be suppressed by realizing the stable domain structures. With respect to a current perpendicular to plane (CPP)-giant magneto-resistive (GMR) head, which has been promising candidates of a next-generation reading head element, the insertion of non-magnetic materials, such as Cu, between the ferromagnetic pinned and free layers is known to increase the MR ratio. For realizing the practical use of the CPP-GMR head, effects of the insertion of materials on the increase in the MR ratio were investigated by X-ray magnetic circular dichroism (XMCD). The results revealed that XMCD is a powerful technique to obtain information on electronic states and magnetic moments with the help of the theoretical electronic band calculation. The potential application of secondary cantilever resonance magnetic force microscopy and spin-polarized scanning electron microscope to the in-situ magnetic imaging of PMR heads will be also discussed.

  2. 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.

  3. 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.

  4. 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

  5. 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.

  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 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.

  8. 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…

  9. 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.

  10. Controlled normal and inverse current-induced magnetization switching and magnetoresistance in magnetic nanopillars.

    PubMed

    AlHajDarwish, M; Kurt, H; Urazhdin, S; Fert, A; Loloee, R; Pratt, W P; Bass, J

    2004-10-08

    By combining pairs of ferromagnetic metals with the same or different signs of scattering anisotropies in ferromagnetic-nonmagnetic-ferromagnetic metal nanopillars, we independently invert just the magnetoresistance, just the direction of current-induced magnetization switching, or both together, at room temperature (295 K) and at 4.2 K. In all cases studied, the switching direction is correctly predicted from the net scattering anisotropy of the fixed ferromagnet, including both bulk and interfacial contributions.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Current Noise from a Magnetic Moment in a Helical Edge

    NASA Astrophysics Data System (ADS)

    Väyrynen, Jukka I.; Glazman, Leonid I.

    2017-03-01

    We calculate the two-terminal current noise generated by a magnetic moment coupled to a helical edge of a two-dimensional topological insulator. When the system is symmetric with respect to in-plane spin rotation, the noise is dominated by the Nyquist component even in the presence of a voltage bias V . The corresponding noise spectrum S (V ,ω ) is determined by a modified fluctuation-dissipation theorem with the differential conductance G (V ,ω ) in place of the linear one. The differential noise ∂S /∂V , commonly measured in experiments, is strongly dependent on frequency on a small scale τK-1≪T set by the Korringa relaxation rate of the local moment. This is in stark contrast to the case of conventional mesoscopic conductors where ∂S /∂V is frequency independent and defined by the shot noise. In a helical edge, a violation of the spin-rotation symmetry leads to the shot noise, which becomes important only at a high bias. Uncharacteristically for a fermion system, this noise in the backscattered current is super-Poissonian.

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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...

  4. 9 CFR 91.23 - Loading ramps and doors.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 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...

  5. 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...

  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, 2014 CFR

    2014-01-01

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

    NASA Astrophysics Data System (ADS)

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

    1988-06-01

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

  9. 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.

  10. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  12. 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.

  13. 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.

  14. Detection of current-driven magnetic domains in [Co/Pd] nanowire by tunneling magnetoresistive sensor

    NASA Astrophysics Data System (ADS)

    Okuda, Mitsunobu; Miyamoto, Yasuyoshi; Miyashita, Eiichi; Saito, Nobuo; Hayashi, Naoto; Nakagawa, Shigeki

    2015-05-01

    Current-driven magnetic domain walls in magnetic nanowires have attracted a great deal of interest in terms of both physical studies and engineering applications. The anomalous Hall effect measurement is widely used for detecting the magnetization direction of current-driven magnetic domains in a magnetic nanowire. However, the problem with this measurement is that the detection point for current-driven domain wall motion is fixed at only the installed sensing wire across the specimen nanowire. A potential solution is the magnetic domain scope method, whereby the distribution of the magnetic flux leaking from the specimen can be analyzed directly by contact-scanning a tunneling magnetoresistive field sensor on a sample. In this study, we fabricated specimen nanowires consisting of [Co (0.3)/Pd (1.2)]21/Ta(3) films (units in nm) with perpendicular magnetic anisotropy on Si substrates. A tunneling magnetoresistive sensor was placed on the nanowire surface and a predetermined current pulse was applied. Real-time detection of the current-driven magnetic domain motion was successful in that the resistance of the tunneling magnetoresistive sensor was changed with the magnetization direction beneath the sensor. This demonstrates that magnetic domain detection using a tunneling magnetoresistive sensor is effective for the direct analysis of micro magnetic domain motion.

  15. AC losses in a HTS coil carrying DC current in AC external magnetic field

    NASA Astrophysics Data System (ADS)

    Ogawa, J.; Zushi, Y.; Fukushima, M.; Tsukamoto, O.; Suzuki, E.; Hirakawa, M.; Kikukawa, K.

    2003-10-01

    We electrically measured AC losses in a Bi2223/Ag-sheathed pancake coil excited by a DC current in AC external magnetic field. Losses in the coil contain two kinds of loss components that are the magnetization losses and dynamic resistance losses. In the measurement, current leads to supply a current to the coil were specially arranged to suppress electromagnetic coupling between the coil current and the AC external magnetic field. A double pick-up coils method was used to suppress a large inductive voltage component contained in voltage signal for measuring the magnetization losses. It was observed that the magnetization losses were dependent on the coil current and that a peak of a curve of the loss factor vs. amplitude of the AC external magnetic field shifted to lower amplitude of the AC magnetic field as the coil current increased. This result suggests the full penetration magnetic field of the coil tape decreases as the coil current increases. The dynamic resistance losses were measured by measuring a DC voltage appearing between the coil terminals. It was observed that the DC voltage appearing in the coil subject to the AC external magnetic field was much larger than that in the coil subject to DC magnetic field.

  16. 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.

  17. Ramp technique for dc partial discharge testing

    NASA Astrophysics Data System (ADS)

    Bever, R. S.

    1985-02-01

    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.

  18. 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.

  19. Modeling magnetic perturbation fields associated with ionospheric and geomagnetic-field-aligned currents

    NASA Astrophysics Data System (ADS)

    Richmond, A. D.; Maute, A.

    2003-04-01

    The National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General-Circulation Model calculates ionospheric and geomagnetic-field-aligned electric currents produced by ionospheric wind dynamo action, taking into account magnetospheric sources at high latitudes. The associated magnetic perturbations at the ground and at low-Earth-orbit (LEO) satellite altitudes are calculated by representing the height-integrated horizontal ionospheric current as a current sheet at 110 km, connected to geomagnetic-field-aligned currents flowing into and out of the top. The horizontal sheet current can be divided into two components: a divergence-free equivalent current which, together with the associated induced Earth currents, is responsible for all of the magnetic perturbations below the current sheet, and a divergent (but not irrotational) current that closes the field-aligned currents above. We call the combination of the field-aligned currents and their closing ionospheric currents the ``nonequivalent'' currents. By definition, these produce no magnetic effect at the ground, but they do produce important magnetic effects at LEO altitudes, generally dominating the component of LEO magnetic perturbations perpendicular to the main geomagnetic field. At high magnetic latitudes the nonequivalent LEO magnetic perturbations are largely toroidal, and are associated with the strong field-aligned currents that couple the ionosphere with the outer magnetosphere. At middle and low magnetic latitudes the nonequivalent LEO magnetic perturbations are largely associated with field-aligned currents that flow between the northern and southern hemispheres, and that can produce east-west perturbations of tens of nanoteslas.

  20. Computation of turbulent, separated, unswept compression ramp interactions

    NASA Technical Reports Server (NTRS)

    Marshall, T. A.; Dolling, D. S.

    1992-01-01

    Examination of the literature shows that the comparison between experiment and computation for highly separated unswept compression ramp flows is generally poor, irrespective of the turbulence model used. In general, the upstream influence is not correct, the wall pressure rise through separation is too steep, and the pressures under the separated shear layer are too high. In the current study, the objective is to determine if these discrepancies might be attributed more to other factors such as flowfield unsteadiness or three-dimensionality, rather than to inadequate turbulence modeling. To examine this possibility, multichannel wall pressure fluctuations were measured under the unsteady separation shock wave in a 28-deg unswept compression ramp flow at Mach 5. The results show that the large scale, low frequency separation shock unsteadiness controls the distribution of time-averaged surface properties and that neglect of the unsteadiness is probably the primary cause of the discrepancy between experiment and computation.

  1. 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.

  2. 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.

  3. 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.

  4. Observation of chiral currents at the magnetic domain boundary of a topological insulator

    DOE PAGES

    Wang, Y. H.; Kirtley, J. R.; Katmis, F.; ...

    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. Here, we used a scanning superconducting quantum interference device to show that current in a magnetized EuS/Bi2Se3 heterostructure flows at the edge when the Fermi level is gate-tuned to the surface band gap. We further induced micron-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 rathermore » than the applied current. As a result, such magnetic structures, provide a platform for detecting topological magnetoelectric effects and may enable progress in quantum information processing and spintronics.« less

  5. Observation of chiral currents at the magnetic domain boundary of a topological insulator

    SciTech Connect

    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. Here, we used a scanning superconducting quantum interference device to show that current in a magnetized EuS/Bi2Se3 heterostructure flows at the edge when the Fermi level is gate-tuned to the surface band gap. We further induced micron-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. As a result, such magnetic structures, provide a platform for detecting topological magnetoelectric effects and may enable progress in quantum information processing and spintronics.

  6. 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.

  7. Spin current formation at the graphene/Pt interface for magnetization manipulation in magnetic nanodots

    SciTech Connect

    Shikin, A. M.; Rybkina, A. A.; Rybkin, A. G.; Klimovskikh, I. I.; Skirdkov, P. N.; Zvezdin, K. A.; Zvezdin, A. K.

    2014-07-28

    Spin electronic structure of the Graphene/Pt interface has been investigated. A large induced spin-orbit splitting (∼80 meV) of graphene π states with formation of non-degenerated Dirac-cone spin states at the K{sup ¯}-point of the Brillouin zone crossed with spin-polarized Pt 5d states at Fermi level was found. We show that this spin structure can be used as a spin current source in spintronic devices. By theoretical estimations and micromagnetic modeling based on the experimentally observed spin-orbit splitting, we demonstarte that the induced intrinsic magnetic field in such structure might be effectively used for induced remagnetization of the (Ni-Fe)-nanodots arranged atop the interface.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. Dynamical skyrmion state in a spin current nano-oscillator with perpendicular magnetic anisotropy.

    PubMed

    Liu, R H; Lim, W L; Urazhdin, S

    2015-04-03

    We study the spectral characteristics of spin current nano-oscillators based on the Pt/[Co/Ni] magnetic multilayer with perpendicular magnetic anisotropy. By varying the applied magnetic field and current, both localized and propagating spin wave modes of the oscillation are achieved. At small fields, we observe an abrupt onset of the modulation sidebands. We use micromagnetic simulations to identify this state as a dynamical magnetic skyrmion stabilized in the active device region by spin current injection, whose current-induced dynamics is accompanied by the gyrotropic motion of the core due to the skew deflection. Our results demonstrate a practical route for controllable skyrmion manipulation by spin current in magnetic thin films.

  14. Magnetized direct current microdischarge I. Effect of the gas pressure

    NASA Astrophysics Data System (ADS)

    Levko, Dmitry; Raja, Laxminarayan L.

    2017-03-01

    Following Paschen's law, electrical breakdown of gaps with small pd, where p is the gas pressure and d is the interelectrode gap, requires extremely high voltages. This means that the breakdown voltage for low-pressure microdischarges is of the order of a few kilovolts. This makes impractical the generation of low-pressure dc microdischarges. The application of dc magnetic field confines electrons in the cathode-anode gap. This leads to the significant decrease in the breakdown voltage because each electron experiences many collisions during its diffusion toward the anode. However, as was obtained experimentally, magnetized low-pressure microdischarges experience numerous instabilities whose nature is still not completely understood. In the present paper, we study the influence of the magnetic field on the low-pressure microdischarges. We use the self-consistent one-dimensional Particle-in-Cell Monte Carlo collisions model, which takes into account the electron magnetization while ions remain unmagnetized. We obtain striations in the discharge. We show that these striations appear in both homogeneous and non-homogeneous magnetic fields. We find simple expression for the instability growth rate, which shows that the instability results from ionization processes.

  15. Coronary magnetic resonance imaging: current state-of-the-art.

    PubMed

    Appelbaum, Evan; Botnar, René M; Yeon, Susan B; Manning, Warren J

    2005-09-01

    Over the past decade, coronary magnetic resonance imaging has been transformed from a scientific curiosity to a clinically useful imaging tool for patients with known or suspected anomalous coronary arteries or coronary artery aneurysms and for assessment of coronary artery bypass graft patency. Coronary magnetic resonance imaging also appears to be of clinical value for assessment of native vessel integrity in selected patients, especially those patients with suspected left main/multivessel disease. Among patients referred for X-ray angiography, a normal coronary magnetic resonance imaging strongly suggests the absence of severe multivessel disease. Technical and methodological advances in motion suppression, along with increasing clinical experience will no doubt facilitate improved visualization of the distal and branch vessel.

  16. Ripple filter for the 10,000A superconducting magnet test stand at the magnet test facility

    SciTech Connect

    Drennan, E.

    1991-11-01

    The new 10,000A dumpswitch (1) and dumpresistor (2) system at MTF required a 720Hz filter to eliminate power supply ripple from the load. The new filter, shown in Figure 1, had two requirements: (1) Less then 1/2 Ap-p ripple current with a load current of 10,000A; (2) No or minimal overshoot when the current reaches flattop after it is ramped to 10,000A. MFT magnets are ramped to their final current values at different ramp rates depending on the inductance and type of the magnet under test. The filter design was done with the help of PSPICE simulations. Most of the simulations that will be shown in this write-up were done using a 50mH magnet and a ramprate of 200A/s. In order to study this filter with SPICE, two different simulations had to be done. Due to the relatively high frequency of the ripple when compared with the ramping times, if the ripple current was studied together with the overshoot, the simulations would have taken a very long time to run. Therefore the voltage ripple and the current overshoot were studied separately.

  17. Nonlinear theory of a "shear-current" effect and mean-field magnetic dynamos.

    PubMed

    Rogachevskii, Igor; Kleeorin, Nathan

    2004-10-01

    The nonlinear theory of a "shear-current" effect in a nonrotating and nonhelical homogeneous turbulence with an imposed mean velocity shear is developed. The shear-current effect is associated with the W x J term in the mean electromotive force and causes the generation of the mean magnetic field even in a nonrotating and nonhelical homogeneous turbulence (where W is the mean vorticity and J is the mean electric current). It is found that there is no quenching of the nonlinear shear-current effect contrary to the quenching of the nonlinear alpha effect, the nonlinear turbulent magnetic diffusion, etc. During the nonlinear growth of the mean magnetic field, the shear-current effect only changes its sign at some value B (*) of the mean magnetic field. The magnitude B (*) determines the level of the saturated mean magnetic field which is less than the equipartition field. It is shown that the background magnetic fluctuations due to the small-scale dynamo enhance the shear-current effect and reduce the magnitude B (*) . When the level of the background magnetic fluctuations is larger than 1/3 of the kinetic energy of the turbulence, the mean magnetic field can be generated due to the shear-current effect for an arbitrary exponent of the energy spectrum of the velocity fluctuations.

  18. 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.

  19. 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.

  20. Analysis and experiment of eddy current loss in Homopolar magnetic bearings with laminated rotor cores

    NASA Astrophysics Data System (ADS)

    Jinji, Sun; Dong, Chen

    2013-08-01

    This paper analyses the eddy current loss in Homopolar magnetic bearings with laminated rotor cores produced by the high speed rotation in order to reduce the power loss for the aerospace applications. The analytical model of rotational power loss is proposed in Homopolar magnetic bearings with laminated rotor cores considering the magnetic circuit difference between Homopolar and Heteropolar magnetic bearings. Therefore, the eddy current power loss can be calculated accurately using the analytical model by magnetic field solutions according to the distribution of magnetic fields around the pole surface and boundary conditions at the surface of the rotor cores. The measurement method of rotational power loss in Homopolar magnetic bearing is proposed, and the results of the theoretical analysis are verified by experiments in the prototype MSCMG. The experimental results show the correctness of calculation results.

  1. 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.

  2. Josephson current through a quantum dot coupled to a molecular magnet

    NASA Astrophysics Data System (ADS)

    Stadler, P.; Holmqvist, C.; Belzig, W.

    2013-09-01

    Josephson currents are carried by sharp Andreev states within the superconducting energy gap. We theoretically study the electronic transport of a magnetically tunable nanoscale junction consisting of a quantum dot connected to two superconducting leads and coupled to the spin of a molecular magnet. The exchange interaction between the molecular magnet and the quantum dot modifies the Andreev states due to a spin-dependent renormalization of the quantum dot's energy level and the induction of spin flips. A magnetic field applied to the central region of the quantum dot and the molecular magnet further tunes the Josephson current and starts a precession of the molecular magnet's spin. We use a nonequilibrium Green's function approach to evaluate the transport properties of the junction. Our calculations reveal that the energy level of the dot, the magnetic field, and the exchange interaction between the molecular magnet and the electrons occupying the energy level of the quantum dot can trigger transitions from a 0 to a π state of the Josephson junction. The redistribution of the occupied states induced by the magnetic field strongly modifies the current-phase relation. The critical current exhibits a sharp increase as a function of either the energy level of the dot, the magnetic field, or the exchange interaction.

  3. 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

  4. Superposed Epoch Analysis of Current Systems During Intense Magnetic Storms

    NASA Astrophysics Data System (ADS)

    Liemohn, M. W.; Katus, R. M.

    2013-05-01

    A statistical approach to investigating the intensity and timing of storm-time current systems is conducted and presented. The Hot Electron and Ion Drift Integrator (HEIDI) model was used to simulate all of the intense storms (Dstmin < -100 nT) from solar cycle 23 (1996-2005). Five different HEIDI input combinations were used to create a large collection of numerical results, varying the plasma outer boundary condition and electric field description in the model. The simulation results are then combined with a normalized superposed epoch analysis, where each phase of each storm is prorated to the average duration of that phase and then all of the storms are averaged together. The azimuthal currents in the HEIDI simulation domain are classified as westward and eastward symmetric ring current, partial ring current, banana current, and tail current. The average behavior of these current systems with respect to the HEIDI plasma and electric field boundary conditions are then presented and discussed. It is found that the Volland-Stern electric field produces an earlier increase in the inner magnetospheric current systems because of the usage of the 3-h Kp index. A self-consistent electric field develops the current systems a few hours later, but produces much stronger asymmetric current systems (partial, banana, and tail currents), especially in the main phase of the storm. Applying a nonuniform local time distribution for the plasma outer boundary condition slightly increases the magnitudes of the current systems, but this effect is smaller than the electric field influence.

  5. 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.

  6. Modulation of circular current and associated magnetic field in a molecular junction: A new approach

    PubMed Central

    Patra, Moumita; Maiti, Santanu K.

    2017-01-01

    A new proposal is given to control local magnetic field in a molecular junction. In presence of finite bias a net circular current is established in the molecular ring which induces a magnetic field at its centre. Allowing a direct coupling between two electrodes, due to their close proximity, and changing its strength we can regulate circular current as well as magnetic field for a wide range, without disturbing any other physical parameters. We strongly believe that our proposal is quite robust compared to existing approaches of controlling local magnetic field and can be verified experimentally. PMID:28256548

  7. Current-Driven Magnetization Switching in CoFeB/MgO/CoFeB Magnetic Tunnel Junctions

    NASA Astrophysics Data System (ADS)

    Hayakawa, Jun; Ikeda, Shoji; Lee, Young Min; Sasaki, Ryutaro; Meguro, Toshiyasu; Matsukura, Fumihiro; Takahashi, Hiromasa; Ohno, Hideo

    2005-09-01

    Current-driven magnetization switching in low-resistance Co40Fe40B20/MgO/Co40Fe40B20 magnetic tunnel junctions (MTJs) is reported. The critical-current densities Jc required for current-driven switching in samples annealed at 270 and 300°C are found to be as low as 7.8× 105 and 8.8× 105 A/cm2 with accompanying tunnel magnetoresistance (TMR) ratios of 49 and 73%, respectively. Further annealing of the samples at 350°C increases TMR ratio to 160%, while accompanying Jc increases to 2.5× 106 A/cm2. We attribute the low Jc to the high spin-polarization of tunnel current and small MsV product of the CoFeB single free layer, where Ms is the saturation magnetization and V the volume of the free layer.

  8. 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

  9. 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.

  10. 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.

  11. Generation of magnetic skyrmion bubbles by inhomogeneous spin Hall currents

    DOE PAGES

    Heinonen, Olle; Jiang, Wanjun; Somaily, Hamoud; ...

    2016-03-07

    Recent experiments have shown that magnetic skyrmion bubbles can be generated and injected at room temperature in thin films. In this study, we demonstrate, using micromagnetic modeling, that such skyrmions can be generated by an inhomogeneous spin Hall torque in the presence of Dzyaloshinskii-Moriya interactions (DMIs). In the experimental Ta-Co20Fe60B20 thin films, the DMI is rather small; nevertheless, the skyrmion bubbles are stable, or at least metastable on observational time scales.

  12. 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.

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

    SciTech Connect

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

    2016-01-15

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

  14. 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.

  15. Quantum strongly secure ramp secret sharing

    NASA Astrophysics Data System (ADS)

    Zhang, Paul; Matsumoto, Ryutaroh

    2015-02-01

    Quantum secret sharing is a scheme for encoding a quantum state (the secret) into multiple shares and distributing them among several participants. If a sufficient number of shares are put together, then the secret can be fully reconstructed. If an insufficient number of shares are put together however, no information about the secret can be revealed. In quantum ramp secret sharing, partial information about the secret is allowed to leak to a set of participants, called an unqualified set, that cannot fully reconstruct the secret. By allowing this, the size of a share can be drastically reduced. This paper introduces a quantum analog of classical strong security in ramp secret sharing schemes. While the ramp secret sharing scheme still leaks partial information about the secret to unqualified sets of participants, the strong security condition ensures that qudits with critical information can no longer be leaked.

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

    PubMed

    Emori, Satoru; Beach, Geoffrey S D

    2012-01-18

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

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. Open problems of magnetic island control by electron cyclotron current drive

    NASA Astrophysics Data System (ADS)

    Grasso, D.; Lazzaro, E.; Borgogno, D.; Comisso, L.

    2016-12-01

    This paper reviews key aspects of the problem of magnetic islands control by electron cyclotron current drive in fusion devices. On the basis of the ordering of the basic spatial and time scales of the magnetic reconnection physics, we present the established results, highlighting some of the open issues posed by the small-scale structures that typically accompany the nonlinear evolution of the magnetic islands and constrain the effect of the control action.

  3. Generation of magnetic skyrmion bubbles by inhomogeneous spin Hall currents

    SciTech Connect

    Heinonen, Olle; Jiang, Wanjun; Somaily, Hamoud; te Velthuis, Suzanne G. E.; Hoffmann, Axel

    2016-03-07

    Recent experiments have shown that magnetic skyrmion bubbles can be generated and injected at room temperature in thin films. In this study, we demonstrate, using micromagnetic modeling, that such skyrmions can be generated by an inhomogeneous spin Hall torque in the presence of Dzyaloshinskii-Moriya interactions (DMIs). In the experimental Ta-Co20Fe60B20 thin films, the DMI is rather small; nevertheless, the skyrmion bubbles are stable, or at least metastable on observational time scales.

  4. 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.

  5. 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

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

    DOE PAGES

    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

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

    SciTech Connect

    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 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. Additionally, data generated from shear loading provide invaluable information not only for validating but also for guiding the development of the material model for

  8. 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

  9. 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.

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. A matrix solution for the simulation of magnetic fields with ideal current loops

    NASA Technical Reports Server (NTRS)

    Stankiewicz, N.

    1979-01-01

    A matrix formulation is presented for describing axisymmetric magnetic field data with ideal current loops. A computer program written in APL is used to invert the matrix and hence to solve for the coil strengths which are used to represent the field data. Examples are given of the coil representation for (1) measured magnetic data, (2) refocusing fields, and (3) PPM focusing fields.

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

    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. Our previous work on global ring current distribution [Le et al., 2004] has shown that a significant partial ring current is always present at all Dst levels (regardless of storm phases) even for quiet time ring current. The total current carried by the partial ring current is much stronger than (during stormtime) or at least comparable to (during quiet time) the symmetric ring current. 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

  18. 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.

  19. 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.

  20. Magnetic double-gradient instability and flapping waves in a current sheet.

    PubMed

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

    2007-12-07

    A new kind of magnetohydrodynamic instability and waves are analyzed for a current sheet in the presence of a small normal magnetic field component varying along the sheet. These waves and instability are related to the existence of two gradients of the tangential (B_{tau}) and normal (B_{n}) magnetic field components along the normal (nabla_{n}B_{tau}) and tangential (nabla_{tau}B_{n}) directions with respect to the current sheet. The current sheet can be stable or unstable if the multiplication of two magnetic gradients is positive or negative. In the stable region, the kinklike wave mode is interpreted as so-called flapping waves observed in Earth's magnetotail current sheet. The kink wave group velocity estimated for the Earth's current sheet is of the order of a few tens of kilometers per second. This is in good agreement with the observations of the flapping motions of the magnetotail current sheet.

  1. 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.

  2. Outcomes in spasticity after repetitive transcranial magnetic and transcranial direct current stimulations

    PubMed Central

    Gunduz, Aysegul; Kumru, Hatice; Pascual-Leone, Alvaro

    2014-01-01

    Non-invasive brain stimulations mainly consist of repetitive transcranial magnetic stimulation and transcranial direct current stimulation. Repetitive transcranial magnetic stimulation exhibits satisfactory outcomes in improving multiple sclerosis, stroke, spinal cord injury and cerebral palsy-induced spasticity. By contrast, transcranial direct current stimulation has only been studied in post-stroke spasticity. To better validate the efficacy of non-invasive brain stimulations in improving the spasticity post-stroke, more prospective cohort studies involving large sample sizes are needed. PMID:25206878

  3. 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.

  4. Magnetic Signatures of Ionospheric and Magnetospheric Current Systems During Geomagnetic Quiet Conditions—An Overview

    NASA Astrophysics Data System (ADS)

    Olsen, Nils; Stolle, Claudia

    2017-03-01

    High-precision magnetic measurements taken by LEO satellites (flying at altitudes between 300 and 800 km) allow for studying the ionospheric and magnetospheric processes and electric currents that causes only weak magnetic signature of a few nanotesla during geomagnetic quiet conditions. Of particular importance for this endeavour are multipoint observations in space, such as provided by the Swarm satellite constellation mission, in order to better characterize the space-time-structure of the current systems.

  5. 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.

  6. VISUAL ACCESSIBILITY OF RAMPS AND STEPS

    PubMed Central

    Legge, Gordon E.; Yu, Deyue; Kallie, Christopher S.; Bochsler, Tiana M.; Gage, Rachel

    2010-01-01

    The visual accessibility of a space refers to the effectiveness with which vision can be used to travel safely through the space. For people with low vision, the detection of steps and ramps is an important component of visual accessibility. We used ramps and steps as visual targets to examine the interacting effects of lighting, object geometry, contrast, viewing distance and spatial resolution. Wooden staging was used to construct a sidewalk with transitions to ramps or steps. 48 normally sighted subjects viewed the sidewalk monocularly through acuity-reducing goggles, and made recognition judgments about the presence of the ramps or steps. The effects of variation in lighting were milder than expected. Performance declined for the largest viewing distance, but exhibited a surprising reversal for nearer viewing. Of relevance to pedestrian safety, the step up was more visible than the step down. We developed a probabilistic cue model to explain the pattern of target confusions. Cues determined by discontinuities in the edge contours of the sidewalk at the transition to the targets were vulnerable to changes in viewing conditions. Cues associated with the height in the picture plane of the targets were more robust. PMID:20884503

  7. 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.

  8. 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.

  9. A simple computer-controlled analogue ramp generator for producing multiple ramp-and-hold stimuli.

    PubMed

    Matheson, T; Ditz, F

    1991-08-01

    This report describes an inexpensive ramp generator which produces multiple ramp-and-hold stimuli ("staircase-type" wave forms). The output voltage is analogue and is, therefore, free of stepping artifacts characteristic of digital function generators. When coupled with a standard power amplifier and mechanical vibrator, this system is particularly suitable for stimulation of mechanoreceptive sense organs. Connection to the serial port of an IBM personal computer, or the user port of a BBC computer allows complex ramp-and-hold sequences to be developed and repeated. The number, duration and sign of ramps, and the duration of intervening hold periods can be set using the computer. This system has been used successfully to characterise phasic and tonic neurones in the locust metathoracic femoral chordotonal organ (a leg position and movement detector).

  10. Secondary magnetic islands generated by the Kelvin-Helmholtz instability in a reconnecting current sheet.

    PubMed

    Fermo, R L; Drake, J F; Swisdak, M

    2012-06-22

    Magnetic islands or flux ropes produced by magnetic reconnection have been observed on the magnetopause, in the magnetotail, and in coronal current sheets. Particle-in-cell simulations of magnetic reconnection with a guide field produce elongated electron current layers that spontaneously produce secondary islands. Here, we explore the seed mechanism that gives birth to these islands. The most commonly suggested theory for island formation is the tearing instability. We demonstrate that in our simulations these structures typically start out, not as magnetic islands, but as electron flow vortices within the electron current sheet. When some of these vortices first form, they do not coincide with closed magnetic field lines, as would be the case if they were islands. Only after they have grown larger than the electron skin depth do they couple to the magnetic field and seed the growth of finite-sized islands. The streaming of electrons along the magnetic separatrix produces the flow shear necessary to drive an electron Kelvin-Helmholtz instability and produce the initial vortices. The conditions under which this instability is the dominant mechanism for seeding magnetic islands are explored.

  11. 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.

  12. Current oscillation and chaotic dynamics in superlattices driven by crossed electric and magnetic fields.

    PubMed

    Wang, C; Cao, J C

    2005-03-01

    We have theoretically studied current oscillation and chaotic dynamics in doped GaAsAlAs superlattices driven by crossed electric and magnetic fields. When the superlattice system is driven by a dc voltage, a stationary or dynamic electric-field domain can be obtained. We carefully studied the electric-field-domain dynamics and current self-oscillation which both display different modes with the change of magnetic field. When an ac electric field is also applied to the superlattice, a typical nonlinear dynamic system is constructed with the ac amplitude, ac frequency, and magnetic field as the control parameters. Different nonlinear behaviors show up when we tune the control parameters.

  13. Magnetic Signatures of Ionospheric and Magnetospheric Current Systems During Geomagnetic Quiet Conditions—An Overview

    NASA Astrophysics Data System (ADS)

    Olsen, Nils; Stolle, Claudia

    2016-09-01

    High-precision magnetic measurements taken by LEO satellites (flying at altitudes between 300 and 800 km) allow for studying the ionospheric and magnetospheric processes and electric currents that causes only weak magnetic signature of a few nanotesla during geomagnetic quiet conditions. Of particular importance for this endeavour are multipoint observations in space, such as provided by the Swarm satellite constellation mission, in order to better characterize the space-time-structure of the current systems. Focusing on geomagnetic quiet conditions, we provide an overview of ionospheric and magnetospheric sources and illustrate their magnetic signatures with Swarm satellite observations.

  14. 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.

  15. Hall magnetohydrodynamic effects for current sheet flapping oscillations related to the magnetic double gradient mechanism

    SciTech Connect

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

    2010-06-15

    Hall magnetohydrodynamic model is investigated for current sheet flapping oscillations, which implies a gradient of the normal magnetic field component. For the initial undisturbed current sheet structure, the normal magnetic field component is assumed to have a weak linear variation. The profile of the electric current velocity is described by hyperbolic functions with a maximum at the center of the current sheet. In the framework of this model, eigenfrequencies are calculated as functions of the wave number for the ''kink'' and ''sausage'' flapping wave modes. Because of the Hall effects, the flapping eigenfrequency is larger for the waves propagating along the electric current, and it is smaller for the opposite wave propagation with respect to the current. The asymmetry of the flapping wave propagation, caused by Hall effects, is pronounced stronger for thinner current sheets. This is due to the Doppler effect related to the electric current velocity.

  16. Variation of the ion composition in the ring current during magnetic storms: Van Allen Probes observations

    NASA Astrophysics Data System (ADS)

    Luo, Hao; Du, Aimin; Ge, Yasong; Cao, Xin; Zhang, Ying; Wang, Yuan

    2015-04-01

    It has been reported that the energy density of the oxygen ions in the ring current region will show more enhancements than protons during magnetic storms. Knowing how the ion composition changes during a magnetic storm is important for understanding the dynamic processes in the inner magnetosphere. By using ion flux data from HOPE and RBSPICE instruments on board the Van Allen probes, we study the energy density variation of both protons and oxygen ions during fifteen strong magnetic storms (minimum Dst < -80 nT) happened during year 2013 to 2014. Results provide important details about the ion composition at different storm stages and different magnetic local times. Results also give important indications about the ion acceleration in the inner magnetosphere and the source of the ring current ions during the magnetic storms.

  17. Constant phase uniform current loop for detection of metallic objects using longitudinal magnetic field projection

    NASA Astrophysics Data System (ADS)

    Heinz, Daniel C.; Melber, Adam W.; Brennan, Michael L.

    2013-06-01

    Currents on remote metallic objects such as landmines can be induced by projecting strong magnetic fields. These currents result in electromagnetic fields that can be subsequently detected. The magnetic field varies slowly as it passes from air into the ground and is sufficient to excite currents in buried metallic objects. Traditionally strong magnetic fields are produced using short-range transformer like inductive coupling, or as a component of powerful propagating electromagnetic fields. The strength of the magnetic component of the propagating electromagnetic field is restricted by regulatory limits on the total radiated radio frequency power. There is a need for a means to produce forward projected strong magnetic field at medium ranges with low-level propagation. This paper reports on a non-radiating loop antenna which maintains a constant amplitude and phase current around the loop and projects a strong magnetic field. The radiated field is small and results from the relativistic time-of-flight effect from one side of the loop to the other. The result is that a very strong magnetic field is produced in the near- to mid-field region, up to one wavelength away from the loop. Experiments with a prototype antenna and modeling show that the H-field is very high, radiated electromagnetic fields are negligible, and the drop off in field strength is inversely proportional to the distance squared. This agreement between experiments and modeling allows for a design based on computer simulations.

  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. 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.

  20. Ultrafast magnetization enhancement in metallic multilayers driven by superdiffusive spin current.

    PubMed

    Rudolf, Dennis; La-O-Vorakiat, Chan; Battiato, Marco; Adam, Roman; Shaw, Justin M; Turgut, Emrah; Maldonado, Pablo; Mathias, Stefan; Grychtol, Patrik; Nembach, Hans T; Silva, Thomas J; Aeschlimann, Martin; Kapteyn, Henry C; Murnane, Margaret M; Schneider, Claus M; Oppeneer, Peter M

    2012-01-01

    Uncovering the physical mechanisms that govern ultrafast charge and spin dynamics is crucial for understanding correlated matter as well as the fundamental limits of ultrafast spin-based electronics. Spin dynamics in magnetic materials can be driven by ultrashort light pulses, resulting in a transient drop in magnetization within a few hundred femtoseconds. However, a full understanding of femtosecond spin dynamics remains elusive. Here we spatially separate the spin dynamics using Ni/Ru/Fe magnetic trilayers, where the Ni and Fe layers can be ferro- or antiferromagnetically coupled. By exciting the layers with a laser pulse and probing the magnetization response simultaneously but separately in Ni and Fe, we surprisingly find that optically induced demagnetization of the Ni layer transiently enhances the magnetization of the Fe layer when the two layer magnetizations are initially aligned parallel. Our observations are explained by a laser-generated superdiffusive spin current between the layers.

  1. 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.

  2. 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

  3. Micromagnetic model for studies on Magnetic Tunnel Junction switching dynamics, including local current density

    NASA Astrophysics Data System (ADS)

    Frankowski, Marek; Czapkiewicz, Maciej; Skowroński, Witold; Stobiecki, Tomasz

    2014-02-01

    We present a model introducing the Landau-Lifshitz-Gilbert equation with a Slonczewski's Spin-Transfer-Torque (STT) component in order to take into account spin polarized current influence on the magnetization dynamics, which was developed as an Object Oriented MicroMagnetic Framework extension. We implement the following computations: magnetoresistance of vertical channels is calculated from the local spin arrangement, local current density is used to calculate the in-plane and perpendicular STT components as well as the Oersted field, which is caused by the vertical current flow. The model allows for an analysis of all listed components separately, therefore, the contribution of each physical phenomenon in dynamic behavior of Magnetic Tunnel Junction (MTJ) magnetization is discussed. The simulated switching voltage is compared with the experimental data measured in MTJ nanopillars.

  4. 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.

  5. Non-perturbative calculation of molecular magnetic properties within current-density functional theory.

    PubMed

    Tellgren, E I; Teale, A M; Furness, J W; Lange, K K; Ekström, U; Helgaker, T

    2014-01-21

    We present a novel implementation of Kohn-Sham density-functional theory utilizing London atomic orbitals as basis functions. External magnetic fields are treated non-perturbatively, which enable the study of both magnetic response properties and the effects of strong fields, using either standard density functionals or current-density functionals-the implementation is the first fully self-consistent implementation of the latter for molecules. Pilot applications are presented for the finite-field calculation of molecular magnetizabilities, hypermagnetizabilities, and nuclear magnetic resonance shielding constants, focusing on the impact of current-density functionals on the accuracy of the results. Existing current-density functionals based on the gauge-invariant vorticity are tested and found to be sensitive to numerical details of their implementation. Furthermore, when appropriately regularized, the resulting magnetic properties show no improvement over standard density-functional results. An advantage of the present implementation is the ability to apply density-functional theory to molecules in very strong magnetic fields, where the perturbative approach breaks down. Comparison with high accuracy full-configuration-interaction results show that the inadequacies of current-density approximations are exacerbated with increasing magnetic field strength. Standard density-functionals remain well behaved but fail to deliver high accuracy. The need for improved current-dependent density-functionals, and how they may be tested using the presented implementation, is discussed in light of our findings.

  6. 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%.

  7. 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

  8. Spin current pumped by a rotating magnetic field in zigzag graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Wang, J.; Chan, K. S.

    2010-10-01

    We study electron spin resonance in zigzag graphene nanoribbons by applying a rotating magnetic field on the system without any bias. By using the nonequilibrium Green's function technique, the spin-resolved pumped current is explicitly derived in a rotating reference frame. The pumped spin current density increases with the system size and the intensity of the transverse rotating magnetic field. For graphene nanoribbons with an even number of zigzag chains, there is a nonzero pumped charge current in addition to the pumped spin current owing to the broken spatial inversion symmetry of the system, but its magnitude is much smaller than the spin current. The short-ranged static disorder from either impurities or defects in the ribbon can depress the spin current greatly due to the localization effect, whereas the long-ranged disorder from charge impurities can avoid inter-valley scattering so that the spin current can survive in the strong disorder for the single-energy mode.

  9. Equilibrium configurations of Vlasov plasmas carrying a current component along an external magnetic field.

    NASA Technical Reports Server (NTRS)

    Kan, J. R.

    1972-01-01

    A model of equilibrium configurations of Vlasov plasmas is considered which represents a combination of the models of Harris (1962) and Nicholson (1963). These plasma configurations carry a current component along an external magnetic field. The considered slab model contains a diamagnetic current and a field-aligned current for an arbitrary ratio of particle pressure to magnetic pressure of the applied constant field. For a fixed pressure ratio and field-aligned current, the model admits a family of equilibrium solutions in which the diamagnetic currents range from zero to a maximum value. The amount of diamagnetic current flowing in a machine depends on the width of the machine, the field-aligned current and other plasma parameters.

  10. 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

  11. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2016-01-01

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

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

    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.

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

    PubMed Central

    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

  16. Current-induced magnetization switching with a spin-polarized scanning tunneling microscope

    NASA Astrophysics Data System (ADS)

    Krause, Stefan

    2008-03-01

    In present data storage applications magnetic nanostructures are switched by external magnetic fields. Due to their non-local character, however, cross-talk between adjacent nanomagnets may occur. An elegant method to circumvent this problem is magnetization switching by spin-polarized currents, as observed in GMR,1] as well as in TMR,2] studies. However, the layered structures of these devices do not provide any insight to the details of the spatial distribution of the switching processes. Spin-polarized scanning tunneling microscopy (SP-STM) is a well-established tool to reveal the magnetic structure of surfaces at spatial resolution down to the atomic scale. Besides, SP-STM takes advantage of a perfect TMR junction consisting of an isolating vacuum barrier separating two magnetic electrodes, which are represented by the foremost tip atom and the sample. Our experiments demonstrate that SP-STM serves as a tool to manipulate the switching behavior of uniaxial superparamagnetic nanoislands,3]. Furthermore, we show how SP-STM can be used to switch the magnetization of quasistable magnetic nanoislands at low temperature (T=31,). Besides its scientific relevance to investigate the details of current-induced magnetization switching (CIMS), this technique opens perspectives for future data storage technologies based on SP-STM. [1] J. A. Katine et al., Phys. Rev. Lett. 84, 3149 (2000). [2] Y. Liu et al., Appl. Phys. Lett. 82, 2871 (2003). [3] S. Krause et al., Science 317, 1537 (2007).

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

    NASA Astrophysics Data System (ADS)

    Landau, I. L.; Rinderer, L.

    1995-08-01

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

  18. EVOLUTION OF RELATIVE MAGNETIC HELICITY AND CURRENT HELICITY IN NOAA ACTIVE REGION 11158

    SciTech Connect

    Jing, Ju; Liu, Chang; Lee, Jeongwoo; Xu, Yan; Deng, Na; Wang, Haimin; Park, Sung-Hong; Wiegelmann, Thomas E-mail: chang.liu@njit.edu E-mail: na.deng@njit.edu E-mail: freemler@kasi.re.kr E-mail: wiegelmann@linmpi.mpg.de

    2012-06-10

    Both magnetic and current helicities are crucial ingredients for describing the complexity of active-region magnetic structure. In this Letter, we present the temporal evolution of these helicities contained in NOAA active region 11158 during five days from 2011 February 12 to 16. The photospheric vector magnetograms of the Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory were used as the boundary conditions for the coronal field extrapolation under the assumption of nonlinear force-free field, from which we calculated both relative magnetic helicity and current helicity. We construct a time-altitude diagram in which altitude distribution of the magnitude of current helicity density is displayed as a function of time. This diagram clearly shows a pattern of upwardly propagating current helicity density over two days prior to the X2.2 flare on February 15 with an average propagation speed of {approx}36 m s{sup -1}. The propagation is synchronous with the emergence of magnetic flux into the photosphere, and indicative of a gradual energy buildup for the X2.2 flare. The time profile of the relative magnetic helicity shows a monotonically increasing trend most of the time, but a pattern of increasing and decreasing magnetic helicity above the monotonic variation appears prior to each of two major flares, M6.6 and X2.2, respectively. The physics underlying this bump pattern is not fully understood. However, the fact that this pattern is apparent in the magnetic helicity evolution but not in the magnetic flux evolution makes it a useful indicator in forecasting major flares.

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

    PubMed

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

    2012-09-01

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

  20. 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.

  1. [A rapid method of eddy current compensation in magnetic resonance imaging systems].

    PubMed

    Liu, Zheng-min; Zhou, He-qin; Wu, Hai-cheng

    2005-11-01

    Imaging objects are spatially encoded by gradient magnetic fields in magnetic resonance imaging systems. The eddy current caused by rapid switches of gradient fields will result in artifacts in the images. A method of eddy current compensation based on pre-emphasis of gradient current is presented in this thesis. The compensation parameters are acquired rapidly utilizing Faraday's induction theorem and data fitting method. The experiments prove that the method is efficient for reduction of the debugging time and for the improvement of the image quality.

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

    PubMed

    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.

  3. Linear evolution of current sheets in sheared force-free magnetic fields with discontinuous connectivity

    NASA Technical Reports Server (NTRS)

    Wolfson, Richard

    1990-01-01

    Thin current sheets arising in tenuous, magnetized solar coronal plasmas may constitute an important mechanism for energy buildups and subsequent energy releases; they could arise from the continuous-and-random motion of magnetic footprints associated with photospheric velocity fields. A model is presented for study of the quasi-static evolution of current sheets due to shearing of the footpoints, in a highly idealized geometry that incorporates an abrupt jump in field-line connectivity. The model highlights that formation of thin current layers and allows large shearing motions prior to violation of the linear approximation. Excess energy comparable to that released by solar flares can be stored in a sheared field.

  4. Exact energy principle in magnetic reconnection for current-sheet models.

    PubMed

    Yoon, Peter H; Lui, Anthony T Y

    2005-05-06

    On the basis of an exact nonlinear energy principle, it is shown that the change in magnetic topology (i.e., reconnection) in a finite-domain system leads to the conversion of magnetic field energy to particle energy. However, it is also shown that the conversion efficiency gradually disappears as the system size increases. This principle is demonstrated with model current-sheet equilibria including Harris and Fadeev solutions, as well as a current-sheet equilibrium which contains a singular current layer. The finding that energy conversion in reconnection is highly dependent on the system size may have an important implication for numerical simulations performed under finite geometry.

  5. Exact Energy Principle in Magnetic Reconnection for Current-Sheet Models

    SciTech Connect

    Yoon, Peter H.; Lui, Anthony T.Y.

    2005-05-06

    On the basis of an exact nonlinear energy principle, it is shown that the change in magnetic topology (i.e., reconnection) in a finite-domain system leads to the conversion of magnetic field energy to particle energy. However, it is also shown that the conversion efficiency gradually disappears as the system size increases. This principle is demonstrated with model current-sheet equilibria including Harris and Fadeev solutions, as well as a current-sheet equilibrium which contains a singular current layer. The finding that energy conversion in reconnection is highly dependent on the system size may have an important implication for numerical simulations performed under finite geometry.

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

    PubMed

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

    2010-10-01

    The lithium tokamak experiment (LTX) is a modest-sized spherical tokamak (R(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 °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.

  7. 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.

  8. 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.

  9. 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.

  10. Three-dimensional numerical simulation of current collection by a probe in a magnetized plasma

    NASA Technical Reports Server (NTRS)

    Singh, Nagendra; Vashi, B. I.; Leung, L. C.

    1994-01-01

    A three-dimensional numerical model for current collection in a magnetized plasma is reported. The model is based on an electrostatic particle-in-cell code. The model yields self-consistent sheath structure including distributions of plasma and the electric potential around the body and the collection of electrons. The analytical theory of current collection by a body in a magnetized plasma yields an upper bound for the collected current determined by the conservation of energy and canonical angular momentum. The theory shows that the collected charged particles come from a cylindrical volume aligned with the magnetic shadow of the body; the maximum radius r(sub o) of this volume is determined by the body size, body potential, and the ambient magnetic field. This theory does not deal with the sheath structure around the body. The condition for the actual current to approach the upper-bound value has been a matter of debate. Our simulations reveal when and why the collected current becomes equal to its upper-bound value. Sheath size in the radial direction perpendicular to the axial ambient magnetic field is determined by the current-limiting radius r(sub o). Our simulation yields time-average current in good agreement with its upper bound. This feature of the current collection is explained as follows: Once electrons enter the sheath, some of them are freely accelerated perpendicular to the magnetic field because they are demagnetized by the large gradients in the perpendicular electric fields. Simulations show a large perpendicular acceleration, producing perpendicular energy as large as that determined by the potential on the body, especially in the region where perpendicular electric fields (E perpendicular) are the strongest. An analysis shows that the demagnetization of electrons occurs above a threshold potential on the body. This threshold condition follows from the breakdown of the adiabaticity of the electron dynamics inside the sheath.

  11. Gauge-Origin Independent Calculations of the Anisotropy of the Magnetically Induced Current Densities.

    PubMed

    Fliegl, Heike; Jusélius, Jonas; Sundholm, Dage

    2016-07-21

    Gauge-origin independent current density susceptibility tensors have been computed using the gauge-including magnetically induced current (GIMIC) method. The anisotropy of the magnetically induced current density (ACID) functions constructed from the current density susceptibility tensors are therefore gauge-origin independent. The ability of the gauge-origin independent ACID function to provide quantitative information about the current flow along chemical bonds has been assessed by integrating the cross-section area of the ACID function in the middle of chemical bonds. Analogously, the current strength susceptibility passing a given plane through the molecule is obtained by numerical integration of the current flow parallel to the normal vector of the integration plane. The cross-section area of the ACID function is found to be strongly dependent on the exact location of the integration plane, which is in sheer contrast to the calculated ring-current strength susceptibilities that are practically independent of the chosen position of the integration plane. The gauge-origin independent ACID functions plotted for different isosurface values show that a visual assessment of the current flow and degree of aromaticity depends on the chosen isosurface. The present study shows that ACID functions are not an unambiguous means to estimate the degree of molecular aromaticity according to the magnetic criterion and to determine the current pathway of complex molecular rings.

  12. 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.

  13. 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.

  14. Forward modeling of shock-ramped tantalum

    NASA Astrophysics Data System (ADS)

    Brown, Justin L.; Carpenter, John H.; Seagle, Christopher T.

    2017-01-01

    Dynamic materials experiments on the Z-machine are beginning to reach a regime where traditional analysis techniques break down. Time dependent phenomena such as strength and phase transition kinetics often make the data obtained in these experiments difficult to interpret. We present an inverse analysis methodology to infer the equation of state (EOS) from velocimetry data in these types of experiments, building on recent advances in the propagation of uncertain EOS information through a hydrocode simulation. An example is given for a shock-ramp experiment in which tantalum was shock compressed to 40 GPa followed by a ramp to 80 GPa. The results are found to be consistent with isothermal compression and Hugoniot data in this regime.

  15. Ramp compression of iron to 273 GPa

    DOE PAGES

    Wang, Jue; Smith, Raymond F.; Eggert, Jon H.; ...

    2013-07-11

    Multiple thickness Fe foils were ramp compressed over several nanoseconds to pressure conditions relevant to the Earth’s core. Using wave-profile analysis, the sound speed and the stress-density response were determined to a peak longitudinal stress of 273 GPa. The measured stress-density states lie between shock compression and 300-K static data, and are consistent with relatively low temperatures being achieved in these experiments. Phase transitions generally display time-dependent material response and generate a growing shock. We demonstrate for the first time that a low-pressure phase transformation (α-Fe to ε-Fe) can be overdriven by an initial steady shock to avoid both themore » time-dependent response and the growing shock that has previously limited ramp-wave-loading experiments. Additionally, the initial steady shock pre-compresses the Fe and allows different thermodynamic compression paths to be explored.« less

  16. Ramp compression of iron to 273 GPa

    SciTech Connect

    Wang, Jue; Smith, Raymond F.; Eggert, Jon H.; Braun, Dave G.; Boehly, Thomas R.; Patterson, J. Reed; Celliers, Peter M.; Jeanloz, Raymond; Collins, Gilbert W.; Duffy, Thomas S.

    2013-07-11

    Multiple thickness Fe foils were ramp compressed over several nanoseconds to pressure conditions relevant to the Earth’s core. Using wave-profile analysis, the sound speed and the stress-density response were determined to a peak longitudinal stress of 273 GPa. The measured stress-density states lie between shock compression and 300-K static data, and are consistent with relatively low temperatures being achieved in these experiments. Phase transitions generally display time-dependent material response and generate a growing shock. We demonstrate for the first time that a low-pressure phase transformation (α-Fe to ε-Fe) can be overdriven by an initial steady shock to avoid both the time-dependent response and the growing shock that has previously limited ramp-wave-loading experiments. Additionally, the initial steady shock pre-compresses the Fe and allows different thermodynamic compression paths to be explored.

  17. Calculating Pressure-Driven Current Near Magnetic Islands for 3D MHD Equilibria

    NASA Astrophysics Data System (ADS)

    Radhakrishnan, Dhanush; Reiman, Allan

    2016-10-01

    In general, 3D MHD equilibria in toroidal plasmas do not result in nested pressure surfaces. Instead, islands and chaotic regions appear in the equilibrium. Near small magnetic islands, the pressure varies within the flux surfaces, which has a significant effect on the pressure-driven current, introducing singularities. Previously, the MHD equilibrium current near a magnetic island was calculated, including the effect of ``stellarator symmetry,'' wherein the singular components of the pressure-driven current vanish [A. H. Reiman, Phys. Plasmas 23, 072502 (2016)]. Here we first solve for pressure in a cylindrical plasma from the heat diffusion equation, after adding a helical perturbation. We then numerically calculate the corresponding Pfirsch-Schluter current. At the small island limit, we compare the pressure-driven current with the previously calculated solution, and far from the island, we recover the solution for nested flux surfaces. Lastly, we compute the current for a toroidal plasma for symmetric and non-symmetric geometries.

  18. 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.

  19. Dynamics of Dirac strings and monopolelike excitations in chiral magnets under a current drive

    DOE PAGES

    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

  20. Dynamics of Dirac strings and monopolelike excitations in chiral magnets under a current drive

    SciTech Connect

    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 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. As a result, the existence of monopoles can be inferred from transport or imaging measurements.

  1. Current-induced resonance and mass determination of a single magnetic domain wall.

    PubMed

    Saitoh, Eiji; Miyajima, Hideki; Yamaoka, Takehiro; Tatara, Gen

    2004-11-11

    A magnetic domain wall (DW) is a spatially localized change of magnetization configuration in a magnet. This topological object has been predicted to behave at low energy as a composite particle with finite mass. This particle will couple directly with electric currents as well as magnetic fields, and its manipulation using electric currents is of particular interest with regard to the development of high-density magnetic memories. The DW mass sets the ultimate operation speed of these devices, but has yet to be determined experimentally. Here we report the direct observation of the dynamics of a single DW in a ferromagnetic nanowire, which demonstrates that such a topological particle has a very small but finite mass of 6.6 x 10(-23) kg. This measurement was realized by preparing a tunable DW potential in the nanowire, and detecting the resonance motion of the DW induced by an oscillating current. The resonance also allows low-current operation, which is crucial in device applications; a DW displacement of 10 microm was induced by a current density of 10(10) A m(-2).

  2. Current controlled switching of impedance in magnetic conductor with tilted anisotropy easy axis and its applications

    PubMed Central

    Ipatov, Mihail; Zhukova, Valentina; Zhukov, Arkady; Gonzalez, Julian

    2016-01-01

    We present a concept and prototype of a memory element based on current driven magneto-impedance (MI) effect that stores the binary data (0, 1) as the orientation of the magnetization. The magnetization orientation in the surface layer with tilted anisotropy easy axis can be switched controllably between two stable states by applying current pulses of the appropriate sign, and can be detected by sensing the impedance. We demonstrated the functioning of a non-volatile magnetic memory with a read speed performance up to and above 2 GHz. A prototype of a memory element was realized on a short piece of amorphous microwire, as this material exhibits the highest MI effect, and the required anisotropy can be quite easily obtained. Nevertheless, this concept can be extended to other materials and geometries exhibiting MI effect and possessing a required magnetic anisotropy. PMID:27782190

  3. Current controlled switching of impedance in magnetic conductor with tilted anisotropy easy axis and its applications

    NASA Astrophysics Data System (ADS)

    Ipatov, Mihail; Zhukova, Valentina; Zhukov, Arkady; Gonzalez, Julian

    2016-10-01

    We present a concept and prototype of a memory element based on current driven magneto-impedance (MI) effect that stores the binary data (0, 1) as the orientation of the magnetization. The magnetization orientation in the surface layer with tilted anisotropy easy axis can be switched controllably between two stable states by applying current pulses of the appropriate sign, and can be detected by sensing the impedance. We demonstrated the functioning of a non-volatile magnetic memory with a read speed performance up to and above 2 GHz. A prototype of a memory element was realized on a short piece of amorphous microwire, as this material exhibits the highest MI effect, and the required anisotropy can be quite easily obtained. Nevertheless, this concept can be extended to other materials and geometries exhibiting MI effect and possessing a required magnetic anisotropy.

  4. Axial force imparted by a current-free magnetically expanding plasma

    SciTech Connect

    Takahashi, Kazunori; Lafleur, Trevor; Charles, Christine; Alexander, Peter; Boswell, Rod W.

    2012-08-15

    The axial force imparted from a magnetically expanding, current-free, radiofrequency plasma is directly measured. For an argon gas flow rate of 25 sccm and an effective rf input power of {approx}800W, a maximum force of {approx}6mN is obtained; {approx}3mN of which is transmitted via the expanding magnetic field. The measured forces are reasonably compared with a simple fluid model associated with the measured electron pressure. The model suggests that the total force is the sum of an electron pressure inside the source and a Lorentz force due to the electron diamagnetic drift current and the applied radial magnetic field. It is shown that the Lorentz force is greatest near the magnetic nozzle surface where the radial pressure gradient is largest.

  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. Manipulation of magnetic carriers for drug delivery using pulsed-current high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Cha, Yung; Chen, Lihua; Askew, Thomas; Veal, Boyd; Hull, John

    2007-04-01

    An innovative method of manipulating magnetic carriers is proposed, and its feasibility for drug delivery and therapy is demonstrated experimentally. The proposed method employs pulsed-field solenoid coils with high-critical- temperature ( Tc) superconductor inserts. Pulsed current is used to magnetize and de-magnetize the superconductor insert. The proposed method was demonstrated to be able to (1) move magnetic particles, ranging in size from a few millimeters to 10 μm, with strong enough forces over a substantial distance, (2) hold the particles at a designated position as long as needed, and (3) reverse the processes and retrieve the particles. We further demonstrated that magnetic particles can be manipulated in a stationary environment, in water flow, and in simulated blood (water/glycerol mixture) flow.

  7. Assigning on-ramp flows to maximize capacity of highway with two on-ramps and one off-ramp in between

    NASA Astrophysics Data System (ADS)

    Chen, Jing; Lin, Lan; Jiang, Rui

    2017-01-01

    In this paper, we study the capacity of a highway with two on-ramps and one off-ramp in between by using a cellular automaton traffic flow model. We investigate how to maximize the system capacity by assigning proper traffic flow to the two on-ramps. The system phase diagram is presented and eight different regions are observed under different conditions. It is shown that in region I, in which both on-ramps are in free flow and the main road upstream of the upstream on-ramp is in congestion, assigning proper proportion of the demand to two on-ramps could maximize the system capacity. Two critical values of the off-ramp flow ratio poff have been observed. When poff

    ramp. When poff >p off , c 2, no demand should be assigned to the upstream on-ramp. An analytical investigation has been performed to calculate the critical values. The analytical results are in good agreement with the simulation ones.

  8. Complexing receptor pharmacology: modulation of family B G protein-coupled receptor function by RAMPs.

    PubMed

    Sexton, Patrick M; Morfis, Maria; Tilakaratne, Nanda; Hay, Debbie L; Udawela, Madhara; Christopoulos, George; Christopoulos, Arthur

    2006-07-01

    The most well-characterized subgroup of family B G protein-coupledreceptors (GPCRs) comprises receptors for peptide hormones, such as secretin, calcitonin (CT), glucagon, and vasoactive intestinal peptide (VIP). Recent data suggest that many of these receptors can interact with a novel family of GPCR accessory proteins termed receptor activity modifying proteins (RAMPs). RAMP interaction with receptors can lead to a variety of actions that include chaperoning of the receptor protein to the cell surface as is the case for the calcitonin receptor-like receptor (CLR) and the generation of novel receptor phenotypes. RAMP heterodimerization with the CLR and related CT receptor is required for the formation of specific CT gene-related peptide, adrenomedullin (AM) or amylin receptors. More recent work has revealed that the specific RAMP present in a heterodimer may modulate other functions such as receptor internalization and recycling and also the strength of activation of downstream signaling pathways. In this article we review our current state of knowledge of the consequence of RAMP interaction with family B GPCRs.

  9. 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.

  10. Study of magnetic fields from power-frequency current on water lines.

    PubMed

    Lanera, D; Zapotosky, J E; Colby, J A

    1997-01-01

    The magnetic fields from power-frequency current flowing on water lines were investigated in a new approach that involved an area-wide survey in a small town. Magnetic fields were measured outside the residence under power cables and over water lines, and each residence was characterized as to whether it received water from a private well or the municipal water system. The magnetic field data revealed two statistical modes when they were related to water supply type. The data also showed that in the case of the high mode, the magnetic field remained constant along the line formed by power drop wires, at the back of the house, and the water hookup service, in front of the house, all the way to the street. The patterns are explained by the coincidence of measurement points and the presence of net current flowing on power mains, power drop conductors, residential plumbing, water service hookups, and water mains. These patterns, together with other characteristics of this magnetic field source, such as the gradual spatial fall-off of this field and the presence of a constant component in the time sequence, portray a magnetic field more uniform and constant in the residential environment than has been thought to exist. Such characteristics make up for the weakness of the source and make net current a significant source of exposure in the lives of individuals around the house, when human exposure to magnetic fields is assumed to be a cumulative effect over time. This, together with the bimodal statistical distribution of the residential magnetic field (related to water supply type), presents opportunities for retrospective epidemiological analysis. Water line type and its ability to conduct power-frequency current can be used as the historical marker for a bimodal exposure inference, as Wertheimer et al. have shown.

  11. 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).

  12. Force versus current and air gap calibration of a double acting magnetic thrust bearing

    SciTech Connect

    Baun, D.O.; Fittro, R.L.; Maslen, E.H.

    1995-12-31

    Force versus current and air gap measurements were obtained for a double acting thrust bearing. Static force measurements were made for various air gap settings and bearing current combinations. The resulting data was reduced and an optimized expression representing the force versus current and air gap relationship of the bearing was found. In addition, a theoretical force model was developed using simple magnetic circuit theory and magnetic properties obtained from standard magnetic material tests. The theoretical and the experimentally derived force models were compared. Hysteresis tests were conducted with the thrust disk in the centered position for various current perturbation amplitudes about the design bias current. Hysteresis effects were shown to cause a difference between the measured force as the current was increasing as compared to when the current was decreasing. A second order polynomial expression was developed to express the coercive force as a function of the perturbation current amplitude. The bearing frequency response was examined by injecting sinusoidal currents of varying frequencies into the bearing. A maximum actuator bandwidth of approximately 700 Hz was determined. Above 700 Hz the bearing frequency response could not be distinguished from the test fixture frequency response.

  13. Eddy current effects in plain and hollow cylinders spinning inside homogeneous magnetic fields: Application to magnetic resonance

    NASA Astrophysics Data System (ADS)

    Aubert, G.; Jacquinot, J.-F.; Sakellariou, D.

    2012-10-01

    We present a thorough analysis of eddy currents that develop in a rectangular cross section toroid rotating in a uniform magnetic field. The slow rotation regime is assumed. Compact expressions for the current density, the total dissipated power, and the braking torque are given. Examination of the topology of current lines reveals that depending upon the relative dimensions of the side and length of the toroid two different regimes exist. The conditions of existence of the two regimes are analytically established. In view of nuclear magnetic resonance (NMR) applications, we derive the angular variation of the magnetic field created by eddy currents and lay down the formalism necessary for calculating the effect of this field on the NMR spectra of the conductor itself or of a sample co-rotating with the conductor, a situation encountered when dealing with rotating detectors. Examples of calculations for cases of practical interest are presented. The theory is confronted with available data, and we give guidelines for the design of optimized rotating micro-coils.

  14. Public transit bus ramp slopes measured in situ.

    PubMed

    Bertocci, Gina; Frost, Karen; Smalley, Craig

    2014-05-02

    Abstract Purpose: The slopes of fixed-route bus ramps deployed for wheeled mobility device (WhMD) users during boarding and alighting were assessed. Measured slopes were compared to the proposed Americans with Disabilities Act (ADA) maximum allowable ramp slope. Methods: A ramp-embedded inclinometer measured ramp slope during WhMD user boarding and alighting on a fixed-route transit bus. The extent of bus kneeling was determined for each ramp deployment. In-vehicle video surveillance cameras captured ramp deployment level (street versus sidewalk) and WhMD type. Results: Ramp slopes ranged from -4° to 15.5° with means of 4.3° during boarding (n = 406) and 4.2° during alighting (n = 405). Ramp slope was significantly greater when deployed to street level. During boarding, the proposed ADA maximum allowable ramp slope (9.5°) was exceeded in 66.7% of instances when the ramp was deployed to street level, and in 1.9% of instances when the ramp was deployed to sidewalk level. During alighting, the proposed ADA maximum allowable slope was exceeded in 56.8% of instances when the ramp was deployed to street level and in 1.4% of instances when the ramp was deployed to sidewalk level. Conclusions: Deployment level, built environment and extent of bus kneeling can affect slope of ramps ascended/descended by WhMD users when accessing transit buses. Implications for Rehabilitation Since public transportation services are critical for integration of wheeled mobility device (WhMD) users into the community and society, it is important that they, as well as their therapists, are aware of conditions that may be encountered when accessing transit buses. Knowledge of real world ramp slope conditions that may be encountered when accessing transit buses will allow therapists to better access capabilities of WhMD users in a controlled clinical setting. Real world ramp slope conditions can be recreated in a clinical setting to allow WhMD users to develop and practice necessary

  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. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Drift velocity of charged particles in magnetic fields and its relation to the direction of the source current

    NASA Astrophysics Data System (ADS)

    Essén, Hanno; Nordmark, Arne B.

    2016-10-01

    Integrable motion of charged particles in magnetic fields produced by stationary current distributions is investigated. We treat motion in the magnetic field from an infinite flat current sheet, a Harris current sheath, an infinite rectilinear current, and a dipole in its equatorial plane. We find that positively charged particles as a rule will drift in the same direction as the current that is the source of the magnetic field in question. The conclusion is that charged particles moving under the influence of current distributions tend to enhance the current and that this indicates current self-amplification.

  2. Observation of a periodic pattern in the persistent-current fields of the superconducting HERA magnets

    SciTech Connect

    Brueck, H.; Gall, D.; Krzywinski, J.; Meinke, R.; Preissner, H. , Hamburg ); Halemeyer, M.; Schmueser, P.; Stolzenburg, C. . 2. Inst. fuer Experimentalphysik); Stiening, R. ); ter Avest, D.; van de Klundert, L.J.M. (Technische Hogeschool Twente, Enschede (Netherlands

    1991-05-01

    The time dependence of persistent current multipoles in superconducting magnets is still unexplained. The decay is too large to be accounted for by flux creep and it does not show the expected dependence on temperature. Furthermore the decay is influenced by a preceding field sweep in the magnet, it becomes more pronounced if the magnet was previously excited to its maximum field. For a detailed study of the decay mechanism a special sensor has been developed which allows to record small sexupole components in superconducting dipole magnets. During an experimental study of the time dependence of a HERA dipole it was found that the sextupole field exhibits a sinusoidal structure along the axis of the magnet. A similar periodic structure was found for the main dipole field with the help of a nuclear magnetic resonance probe. The wavelength of the periodic pattern is compatible with the transposition pitch of the Rutherford-type cable in the magnet coils. The structure was found to exist in all HERA dipoles measured afterwards and also in a superconducting coil without iron yoke. With a specially developed 2 cm long pickup coil it was found that all accessible multipole components in dipole and quadrupole magnets are modulated along their axis. 3 refs., 6 figs.

  3. On the Lévy-Nature of Magnetic Field Fluctuations During Magnetospheric Tail Current Disruption

    NASA Astrophysics Data System (ADS)

    Consolini, G.; Lui, A. T.; Zimbardo, G.

    2002-12-01

    One of the most relevant phenomena occurring at the substorm onset is the development of a current wedge, which is responsible for the magnetosphere-ionosphere coupling during magnetic substorms. This current wedge is generally associated with the diversion or disruption of the near cross-tail current system [Lui, 1996]. In the last years this near-Earth dipolarization phenomenon has been the subject of several observation, as well as, simulation studies, which suggested a multiscale and a non-MHD nature of the phenomenon [Sitnov et al., 2000; Malova et al., 2000; Zelenyi et al., 2000; Miura, 2000]. Here, using magnetic field data relative to 3 current disruption (CD) events as observed by AMPTEE/CCE spacecraft, we investigate the statistical features of magnetic field fluctuations. In the kinetic domain (i.e. above the ion cyclotron frequency during CD) the distribution function of magnetic field fluctuations shows non Gaussian tails and the probability of return Pt(0) scales as t-α with α !=q 1/2 which is compatible with a Lévy-statistics. Conversely, in the magnetohydrodynamic (MHD) region CD magnetic fluctuations are compatible with a classical Brownian motion. These findings seem to indicate that the near-Earth dipolarization process, associated with CD, is a non-MHD phenomenon, during which fast kinetic processes in collisionless plasmas take place.

  4. 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.

  5. Conversion of electronic to magnonic spin current at a heavy-metal magnetic-insulator interface

    NASA Astrophysics Data System (ADS)

    Wang, Xi-guang; Li, Zhi-xiong; Zhou, Zhen-wei; Nie, Yao-zhuang; Xia, Qing-lin; Zeng, Zhong-ming; Chotorlishvili, L.; Berakdar, J.; Guo, Guang-hua

    2017-01-01

    Electronic spin current is convertible to magnonic spin current via the creation or annihilation of thermal magnons at the interface of a magnetic insulator and a metal with a strong spin-orbital coupling. So far this phenomenon was evidenced in the linear regime. Based on analytical and full-fledged numerical results for the nonlinear regime we demonstrate that the generated thermal magnons or magnonic spin current in the insulator is asymmetric with respect to the charge current direction in the metal and exhibits a nonlinear dependence on the charge current density, which is explained by the tuning effect of the spin Hall torque and the magnetization damping. The results are also discussed in light of, and are in line with, recent experiments pointing to a new way of nonlinear manipulation of spin with electrical means.

  6. 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.

  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. 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

    NASA Astrophysics Data System (ADS)

    Takahashi, Masato; Ebisawa, Yusuke; Tennmei, Konosuke; Yanagisawa, Yoshinori; Hosono, Masami; Takasugi, Kenji; Hase, Takashi; Miyazaki, Takayoshi; Fujito, Teruaki; Nakagome, Hideki; Kiyoshi, Tsukasa; Yamazaki, Toshio; Maeda, Hideaki

    2012-10-01

    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 Nb3Sn 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 7Li 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.

  10. The effect of the magnetic field stretching on the development of the ring current

    NASA Astrophysics Data System (ADS)

    Ilie, R.; Toth, G.; Liemohn, M. W.; Skoug, R. M.

    2010-12-01

    While the dipolar solution for the geomagnetic field during quiet times represents a reasonable assumption, during storm activity this assumption becomes invalid. Theoretical and numerical modifications to an inner magnetosphere - Hot Electron Ion Drift Integrator (HEIDI)- model are implemented, in order to accommodate for a non-dipolar arbitrary magnetic field. HEIDI solves the time dependent, gyration and bounced averaged kinetic equation for the phase space density of one or more ring current species. In this study the effect of the magnetic field stretching on the build-up of the ring current is examined for both real and idealized input conditions.

  11. 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.

  12. ac current generation in chiral magnetic insulators and Skyrmion motion induced by the spin Seebeck effect.

    PubMed

    Lin, Shi-Zeng; Batista, Cristian D; Reichhardt, Charles; Saxena, Avadh

    2014-05-09

    We show that a temperature gradient induces an ac electric current in multiferroic insulators when the sample is embedded in a circuit. We also show that a thermal gradient can be used to move magnetic Skyrmions in insulating chiral magnets: the induced magnon flow from the hot to the cold region drives the Skyrmions in the opposite direction via a magnonic spin transfer torque. Both results are combined to compute the effect of Skyrmion motion on the ac current generation and demonstrate that Skyrmions in insulators are a promising route for spin caloritronics applications.

  13. 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.

  14. Magnetization Dynamics in a Current-Driven Magnetic Nano-Pillar with Dipole-Dipole Coupling between Magnetic Layers (PREPRINT)

    DTIC Science & Technology

    2009-09-25

    gyromagnetic ratio. The structure of He! !,j will be clarified bellow. The second term a"( TD,j = M [Mj x [ Hef !,j x Mjll is dissipative torque that...nano-pillar looks as fol- lows: 8M· 8/ = "( [ Hef !,j x Mj ], j = 1,2. (2) The effective magnetic field Hef !,j for j-th layer, which enters the LLGS...equation, consists of the external bias magnetic field Hext and magnetodipolar fields, created by each of the two layers: 2 Hef !,j = Hext + L Hj,k

  15. Mechanism of orientation of stimulating currents in magnetic brain stimulation (abstract)

    NASA Astrophysics Data System (ADS)

    Ueno, S.; Matsuda, T.

    1991-04-01

    We made a functional map of the human motor cortex related to the hand and foot areas by stimulating the human brain with a focused magnetic pulse. We observed that each functional area in the cortex has an optimum direction for which stimulating currents can produce neural excitation. The present report focuses on the mechanism which is responsible for producing this anisotropic response to brain stimulation. We first obtained a functional map of the brain related to the left ADM (abductor digiti minimi muscles). When the stimulating currents were aligned in the direction from the left to the right hemisphere, clear EMG (electromyographic) responses were obtained only from the left ADM to magnetic stimulation of both hemisphere. When the stimulating currents were aligned in the direction from the right to the left hemisphere, clear EMG signals were obtained only from the right ADM to magnetic stimulation of both hemisphere. The functional maps of the brain were sensitive to changes in the direction of the stimulating currents. To explain the phenomena obtained in the experiments, we developed a model of neural excitation elicited by magnetic stimulation. When eddy currents which are induced by pulsed magnetic fields flow in the direction from soma to the distal part of neural fiber, depolarized area in the distal part are excited, and the membrane excitation propagates along the nerve fiber. In contrast, when the induced currents flow in the direction from the distal part to soma, hyperpolarized parts block or inhibit neural excitation even if the depolarized parts near the soma can be excited. The model explains our observation that the orientation of the induced current vectors reflect both the functional and anatomical organization of the neural fibers in the brain.

  16. SQUID Measurements of the Magnetic Field Distribution from Ionic Currents in Plants

    NASA Astrophysics Data System (ADS)

    Jazbinsek, Vojko; Thiel, Gerhard; Zorec, Robert; Mueller, Wolfgang; Baudenbacher, Franz; Fong, Luis; Holzer, Jenny; Wikswo, John; Trontelj, Zvonko

    2001-03-01

    SQUIDs, the most sensitive magnetic flux sensor, are often a useful tool in the biophysical and biomedical research. Our aim was to use a multi-channel SQUID system and a SQUID microscope in a magnetically shielded room to obtain the noninvasive information on (i) ionic currents in green algae Chara corallina under either electric field excitation or illumination with visible light, and (ii) injury-induced ionic currents in the higher-developed plant Vicia faba. For the green algae Chara corallina, we found that the action potential spread with the velocity of 3-4 cm/s, that the intracellular current was up to 1 μ A and that the magnetic field distribution was altered by the ifluence of light. For the wounded bean plant Vicia faba, the measured magnetic field distribution adjacent to the injury demonstrated that the injury-related ionic current decays with τ of 10 min. These results demonstrate the value od SQUID-based measuring systems for noninvasive research of ionic currents in the slowest cells and living tissues in nature.

  17. 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.

  18. Current disruption and its spreading in collision-less magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Jain, Neeraj; Buechner, Joerg; Dorfman, Seth; Ji, Hantao; Sharma, A. Surjalal; Max-Planck/Princeton CenterPlasma Physics Collaboration

    2013-10-01

    Recent magnetic reconnection experiments (MRX) [Dorfman et al., Geophys. Res. Lett. 40, 233 (2012)] have disclosed current disruption in the absence of guide field. During current disruption in MRX, current density and total out-of-reconnection-plane current drop simultaneous with a rise in out-of-reconnection-plane electric field. Here we show that current disruption is an intrinsic property of dynamic formation of X-point configuration of magnetic field in magnetic reconnection, independent of the model used for plasma description and of dimensionality (2-D or 3-D) of reconnection. An analytic expression for the current drop is derived from Ampere's equation and its predictions are verified by 2-D and 3-D electron-magnetohydrodynamic (EMHD) simulations. Three dimensional EMHD simulations show that the current disruption due to localized reconnection spreads along the direction of electron flow with a speed which depends on the wave number of the perturbation. The implications of these results for MRX and other reconnection experiments will be presented. This work was partially funded by the Max-Planck/Princeton Center for Plasma Physics.

  19. 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

  20. Spin-polarized current injection induced magnetic reconstruction at oxide interface

    DOE PAGES

    Fang, F.; Yin, Y. W.; Li, Qi; ...

    2017-01-04

    Electrical manipulation of magnetism presents a promising way towards using the spin degree of freedom in very fast, low-power electronic devices. Though there has been tremendous progress in electrical control of magnetic properties using ferromagnetic (FM) nanostructures, an opportunity of manipulating antiferromagnetic (AFM) states should offer another route for creating a broad range of new enabling technologies. Here we selectively probe the interface magnetization of SrTiO3/La0.5Ca0.5MnO3/La0.7Sr0.3MnO3 heterojunctions and discover a new spin-polarized current injection induced interface magnetoelectric (ME) effect. The accumulation of majority spins at the interface causes a sudden, reversible transition of the spin alignment of interfacial Mn ionsmore » from AFM to FM exchange-coupled, while the injection of minority electron spins alters the interface magnetization from C-type to A-type AFM state. In contrast, the bulk magnetization remains unchanged. We attribute the current-induced interface ME effect to modulations of the strong double-exchange interaction between conducting electron spins and local magnetic moments. As a result, the effect is robust and may serve as a viable route for electronic and spintronic applications.« less

  1. Spin-polarized current injection induced magnetic reconstruction at oxide interface

    PubMed Central

    Fang, F.; Yin, Y. W.; Li, Qi; Lüpke, G.

    2017-01-01

    Electrical manipulation of magnetism presents a promising way towards using the spin degree of freedom in very fast, low-power electronic devices. Though there has been tremendous progress in electrical control of magnetic properties using ferromagnetic (FM) nanostructures, an opportunity of manipulating antiferromagnetic (AFM) states should offer another route for creating a broad range of new enabling technologies. Here we selectively probe the interface magnetization of SrTiO3/La0.5Ca0.5MnO3/La0.7Sr0.3MnO3 heterojunctions and discover a new spin-polarized current injection induced interface magnetoelectric (ME) effect. The accumulation of majority spins at the interface causes a sudden, reversible transition of the spin alignment of interfacial Mn ions from AFM to FM exchange-coupled, while the injection of minority electron spins alters the interface magnetization from C-type to A-type AFM state. In contrast, the bulk magnetization remains unchanged. We attribute the current-induced interface ME effect to modulations of the strong double-exchange interaction between conducting electron spins and local magnetic moments. The effect is robust and may serve as a viable route for electronic and spintronic applications. PMID:28051142

  2. Spin-polarized current injection induced magnetic reconstruction at oxide interface

    NASA Astrophysics Data System (ADS)

    Fang, F.; Yin, Y. W.; Li, Qi; Lüpke, G.

    2017-01-01

    Electrical manipulation of magnetism presents a promising way towards using the spin degree of freedom in very fast, low-power electronic devices. Though there has been tremendous progress in electrical control of magnetic properties using ferromagnetic (FM) nanostructures, an opportunity of manipulating antiferromagnetic (AFM) states should offer another route for creating a broad range of new enabling technologies. Here we selectively probe the interface magnetization of SrTiO3/La0.5Ca0.5MnO3/La0.7Sr0.3MnO3 heterojunctions and discover a new spin-polarized current injection induced interface magnetoelectric (ME) effect. The accumulation of majority spins at the interface causes a sudden, reversible transition of the spin alignment of interfacial Mn ions from AFM to FM exchange-coupled, while the injection of minority electron spins alters the interface magnetization from C-type to A-type AFM state. In contrast, the bulk magnetization remains unchanged. We attribute the current-induced interface ME effect to modulations of the strong double-exchange interaction between conducting electron spins and local magnetic moments. The effect is robust and may serve as a viable route for electronic and spintronic applications.

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

    SciTech Connect

    Jordanova, Vania; Jeffery, Christopher; Welling, Daniel

    2016-09-09

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

  4. Spin-polarized current injection induced magnetic reconstruction at oxide interface.

    PubMed

    Fang, F; Yin, Y W; Li, Qi; Lüpke, G

    2017-01-04

    Electrical manipulation of magnetism presents a promising way towards using the spin degree of freedom in very fast, low-power electronic devices. Though there has been tremendous progress in electrical control of magnetic properties using ferromagnetic (FM) nanostructures, an opportunity of manipulating antiferromagnetic (AFM) states should offer another route for creating a broad range of new enabling technologies. Here we selectively probe the interface magnetization of SrTiO3/La0.5Ca0.5MnO3/La0.7Sr0.3MnO3 heterojunctions and discover a new spin-polarized current injection induced interface magnetoelectric (ME) effect. The accumulation of majority spins at the interface causes a sudden, reversible transition of the spin alignment of interfacial Mn ions from AFM to FM exchange-coupled, while the injection of minority electron spins alters the interface magnetization from C-type to A-type AFM state. In contrast, the bulk magnetization remains unchanged. We attribute the current-induced interface ME effect to modulations of the strong double-exchange interaction between conducting electron spins and local magnetic moments. The effect is robust and may serve as a viable route for electronic and spintronic applications.

  5. Surface barrier effect on magnetization of a current-carrying type-II superconductor

    NASA Astrophysics Data System (ADS)

    Genenko, Yu. A.; Freyhardt, H. C.

    2000-10-01

    Vortex penetration in and exit from ideal flux-filled current-carrying superconductors are studied in the frame of the modified Meissner state model accounting for the vortex interactions with the sample surface, transport current, external field and the other vortices inside the sample. The generalized Silsbee's rule is first formulated and the M- H diagram of ideal current-carrying superconductors in a parallel field is estimated which is irreversible due to the surface effect alone. In general, magnetic behaviour of superconductors is shown to be more reversible in the presence of a transport current.

  6. Magnetic field orientation dependence of critical current in industrial Nb 3Sn strands

    NASA Astrophysics Data System (ADS)

    Schild, T.; Cloez, H.

    In usual superconducting devices such as magnets for NMR, the magnetic field is perpendicular to the superconducting strand axis. But in some special devices, such as magnets for the toroidal field system of fusion machines, the strands can experience any field orientation. For NbTi strands, the pinning force is dependent on the field orientation because of the drawing process (Takacs, S., Polak, M. and Krempasky, L., Critical currents of NbTi tapes with differently oriented anisotropic defects, Cryogenics, 1983, 23, 153-159). In the case of Nb 3Sn strands, the draw and react process suggests that the pinning force is isotropic. In fact, preliminary experiments have shown the contrary, which is why the magnetic field orientation dependence of the critical current for two types of industrial Nb 3Sn strands has been measured. These measurements have been performed for seven field orientations at field strengths up to 20 T. A clear anisotropic effect has been observed, which cannot be explained by Kramer's pinning law. The results are in very good agreement with an empirical law proposed in a recent study by Takayasu et al. (Takayasu, M., Montgomery, D.B. and Minervini, J.V., Effect of magnetic field direction on the critical current of twisted multifilamentary superconducting wires, Inst. of Phys. Conf. Ser., 1997, 158, 917-920). The parameters to be used in this law could be specific to the manufacturing process.

  7. Current driven domain wall motion in rare-earth transition metal alloys with perpendicular magnetic anisotropy.

    PubMed

    Li, Songtian; Liu, Xiaoxi; Morisako, Akimistu

    2012-09-01

    The domain wall movement behaviors under current combining with magnetic field in perpendicularly magnetized TbFeCo wire were studied by a polar magneto-optical Kerr effect microscope. The velocity for domain wall creeping along electrons flowing direction was found to be apparently higher than that of domain wall creeping against electrons flowing, which is the signature of the spin transfer torque effect. By employing the modified field-driven creep motion law, a spin transfer efficiency of 2.7 Oe cm2/10(6) A was determined for TbFeCo wire by treating the spin transfer torque as an effective field adding to the external field. The high spin transfer efficiency suggests that perpendicularly magnetized system with sharp domain walls in TbFeCo film shows high superiorities for applications in spin transfer torque based devices compared with in-plane magnetized systems.

  8. Effect of an axial magnetic field and arc current on the anode current density in diffuse vacuum arcs

    NASA Astrophysics Data System (ADS)

    Ma, Hui; Geng, Yingsan; Liu, Zhiyuan; Wang, Jianhua; Wang, Zhenxing; Zhang, Zaiqin

    2016-09-01

    The objective of this paper is to measure the effect of an axial magnetic field (AMF) BAMF and arc current on the anode current density in diffuse vacuum arcs. The experimental geometry included a split anode and a butt-type cathode, both with a diameter of 60 mm. The anode surface was divided into a central area and three symmetrically disposed peripheral annular areas. The central area of the split anode had a diameter of 20 mm. The contact material was CuCr25 (25% Cr). The arc current IARC ranged from 4 to 14 kA (rms) at 50 Hz. The opening velocity was 2.4 m/s. The currents of the four areas on the anode contact were measured using four Rogowski coils situated outside the vacuum chamber. An external uniform AMF BAMF ranging from 0 to 110 mT was applied during the experiment. The observed arc modes were recorded by a high-speed charge-coupled device video camera. The experimental results quantitatively reveal that the current density distribution on the anode surface in the diffuse arc mode was not uniform but concentrated in the central area. The current density in the central anode area at the current peak JPeakArea I decreased with increasing BAMF following a power law. For BAMF of 0-110 mT and IARC of 4-14 kA, JPeakArea I = (2.2 IARC + 0.069 IARC2) BAMF-0.22, where JPeakArea I is in A/mm2, BAMF is in mT, and IARC is in kA. Moreover, the current distribution was uneven in the three peripheral areas.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Electric toothbrushes induce electric current in fixed dental appliances by creating magnetic fields.

    PubMed

    Kameda, Takashi; Ohkuma, Kazuo; Ishii, Nozomu; Sano, Natsuki; Ogura, Hideo; Terada, Kazuto

    2012-01-01

    Magnetic fields can represent a health problem, especially low frequency electromagnetic fields sometimes induced by electric current in metallic objects worn or used in or on the body (as opposed to high frequency electromagnetic fields that produce heat). Electric toothbrushes are widely used because of their convenience, but the electric motors that power them may produce electromagnetic waves. In this study, we showed that electric toothbrushes generate low frequency (1-2000 Hz) magnetic fields and induce electric current in dental appliances (e. g. orthodontic and prosthetic appliances and dental implants). Current induced by electric toothbrushes might be dependent on the quantity and types of metals used, and the shape of the appliances. Furthermore, these induced currents in dental appliances could impact upon human oral health, producing pain and discomfort.

  14. 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.

  15. 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}.

  16. 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.

  17. Generalized magnetotail equilibria: Effects of the dipole field, thin current sheets, and magnetic flux accumulation

    NASA Astrophysics Data System (ADS)

    Sitnov, M. I.; Merkin, V. G.

    2016-08-01

    Generalizations of the class of quasi-1-D solutions of the 2-D Grad-Shafranov equation, first considered by Schindler in 1972, are investigated. It is shown that the effect of the dipole field, treated as a perturbation, can be included into the original 1972 class solution by modification of the boundary conditions. Some of the solutions imply the formation of singularly thin current sheets. Equilibrium solutions for such sheets resolving their singular current structure on the scales comparable to the thermal ion gyroradius can be obtained assuming anisotropic and nongyrotropic plasma distributions. It is shown that one class of such equilibria with the dipole-like boundary perturbation describes bifurcation of the near-Earth current sheet. Another class of weakly anisotropic equilibria with thin current sheets embedded into a thicker plasma sheet helps explain the formation of thin current sheets in a relatively distant tail, where such sheets can provide ion Landau dissipation for spontaneous magnetic reconnection. The free energy for spontaneous reconnection can be provided due to accumulation of the magnetic flux at the tailward end of the closed field line region. The corresponding hump in the normal magnetic field profile Bz(x,z = 0) creates a nonzero gradient along the tail. The resulting gradient of the equatorial magnetic field pressure is shown to be balanced by the pressure gradient and the magnetic tension force due to the higher-order correction of the latter in the asymptotic expansion of the tail equilibrium in the ratio of the characteristic tail current sheet variations across and along the tail.

  18. 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.

  19. Ultrafast proton radiography of the magnetic fields generated by a laser-driven coil current

    DOE PAGES

    Gao, Lan; Ji, Hantao; Fiksel, Gennady; ...

    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

  20. Ultrafast proton radiography of the magnetic fields generated by a laser-driven coil current

    SciTech Connect

    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 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.

  1. Optimal current control strategies for surface-mounted permanent-magnet synchronous machine drives

    SciTech Connect

    Chapman, P.L.; Sudhoff, S.D.; Whitcomb, C.A.

    1999-12-01

    The current waveforms for optimal excitation of surface-mounted permanent-magnet synchronous machines are set forth. Four different modes are considered, involving varying degrees of minimization of rms current and torque ripple. The optimized waveforms are markedly different than the traditional sinusoidal or rectangular excitation schemes. Inclusion of cogging torque and arbitrary degree of torque ripple minimization generalize this work over that of previous authors. An experimental drive and a detailed computer simulation verify the proposed control schemes.

  2. Calculation of the induced currents and forces for a hybrid magnetic levitation system

    SciTech Connect

    Albertz, D.; Dappen, S.; Henneberger, G.

    1997-03-01

    This paper presents the calculation of the induced currents and forces for a 3D non-linear eddy current field problem with ferromagnetic moving conductors. The {rvec A}, V-{rvec A} formulation is used in combination with four different gauging methods to stabilize the solution process. To consider non-rectangular shapes of geometries tetrahedral elements were employed. The computation procedure is applied to a hybrid magnetic levitation system of a contactless and frictionless conveyance system.

  3. 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}

  4. 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.

  5. Observational Study on Current Sheet of Magnetic Reconnection in Two Solar Eruptions

    NASA Astrophysics Data System (ADS)

    Qiang-wei, Cai; Ning, Wu; Jun, Lin

    2016-07-01

    The coronal magnetic configuration behind coronal mass ejections (CMEs) can commonly be stretched severely, thus to push the magnetic fields with opposite polarities to approach each other, and to form a current sheet of magnetic reconnection. The current sheet in solar eruptions is not only an important region to convert the magnetic free energy into thermal energy, plasma kinetic energy, and energetic particle beams, but also plays a role to connect CMEs and flares. In the CME events of 2003 January 3 and 2003 November 4, the development of current sheet has been observed in both cases. We have investigated the dynamic features and physical properties of current sheet in the two events, based on the data of LASCO (Large Angle and Spectrometric Coronagraph) and UVCS (Ultraviolet Coronagraph Spectrometer) on board of SOHO (Solar and Heliospheric Observatory), and the Hα data from BBSO (Big Bear Solar Observatory) and YNAO (Yunnan Astronomical Observatory). The existence of ions with a high degree of ionization, such as Fe+17 and Si+11, indicates a high temperature up to 3×106 ∼5×106 K in the region of current sheet. A direct measurement shows that the thickness of current sheet varies between 1.3×104 and 1.1×105 km, which increases first and then decreases with time. Using the CHIANTI code (v.7.1), we have further calculated the average values of electron temperature and corresponding emission measure (EM) respectively to be 3.86×106 K and 6.1×1024 cm-5 in the current sheet of the 2003 January 3 event. We also find that the current sheet twisted forth and back quasi-periodically during the eruption event on 2003 November 4 by analyzing the observational data from SOHO/UVCS.

  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. 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…

  8. ELECTRIC CURRENT FILAMENTATION AT A NON-POTENTIAL MAGNETIC NULL-POINT DUE TO PRESSURE PERTURBATION

    SciTech Connect

    Jelínek, P.; Karlický, M.; Murawski, K.

    2015-10-20

    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.

  9. 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.

  10. Exploring how sand ramps respond to Quaternary environmental change in Southern Africa

    NASA Astrophysics Data System (ADS)

    Rowell, Alex; Thomas, David; Bailey, Richard

    2014-05-01

    The current climate of southern Africa is particularly complex and interesting due to the interaction of several climatic systems. However, reconstructions of how these systems behaved in the past, and how the environment responded, have been hampered by a general paucity of records and poor chronological control. Sand ramps may provide the potential to improve palaeoenvironmental reconstructions of southern Africa (and beyond). Formed against a topographic barrier, sand ramps include a combination of aeolian, fluvial and colluvial deposits in varying proportions. Therefore, they have the potential to record changes in moisture availability, circulation patterns and sediment supply which can be independently dated using luminescence dating. Nevertheless relatively little attention has been paid to these features and thus the environmental controls on their formation are not yet fully understood. In particular, there is debate as to whether they reflect deposition during a 'window of opportunity' in which high-magnitude, low-frequency events are recorded (Bateman et al. 2012) or whether they record more gradual, cyclic climate change (Bertram, 2003) or even if there is a uniform control on their formation. This research aims to investigate how sand ramps respond to environmental change and what they can tell us about the paleoenvironment of southern Africa. This poster displays preliminary results based on initial field investigation. This confirmed sand ramps to be ubiquitous in southern Africa and that they record a complex interaction of aeolian, fluvial and colluvial deposits which appears to differ between sand ramps. Preliminary luminescence dating results and sedimentology are displayed for two sand ramps, one from south west Namibia the other from the Karoo region of South Africa.

  11. 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.

  12. 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.

  13. Magnetic Double-Gradient Instability and Flapping Waves in a Current Sheet

    SciTech Connect

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

    2007-12-07

    A new kind of magnetohydrodynamic instability and waves are analyzed for a current sheet in the presence of a small normal magnetic field component varying along the sheet. These waves and instability are related to the existence of two gradients of the tangential (B{sub {tau}}) and normal (B{sub n}) magnetic field components along the normal ({nabla}{sub n}B{sub {tau}}) and tangential ({nabla}{sub {tau}}B{sub n}) directions with respect to the current sheet. The current sheet can be stable or unstable if the multiplication of two magnetic gradients is positive or negative. In the stable region, the kinklike wave mode is interpreted as so-called flapping waves observed in Earth's magnetotail current sheet. The kink wave group velocity estimated for the Earth's current sheet is of the order of a few tens of kilometers per second. This is in good agreement with the observations of the flapping motions of the magnetotail current sheet.

  14. Magnetic properties and texture of NdFeB magnets fabricated by current-applied-pressure-assisted process

    NASA Astrophysics Data System (ADS)

    Kim, H. T.; Kim, Y. B.; Kim, H. S.

    2001-03-01

    The current-applied-pressure-assisted (CAPA) process has been applied to obtain full dense isotropic and anisotropic NdFeB magnets from melt spun NdFeB alloy (MQP-A). The energy product of isotropic magnets obtained by this process was 120-135 kJ/m 3(15-17 MGOe) and the remanence was 0.8-0.9 T(8-9 kG). These isotropic magnets were deformed with different thickness reduction ratio by CAPA process. The energy product obtained by this procedure was in excess of 320 kJ/m 3(40 MGOe), and the best magnetic properties obtained were B r=1.36 T(13.6 kG) , iH c=868 kA/m(10.9 kOe) and (BH) max=352 kJ/m 3(44.2 MGOe) . The effect of deformation by CAPA process on texture was examined using pole figures. The (1 0 5) texture was dominant up to the thickness reduction ratio of 74%, whereas the (0 0 6) texture was dominant at the thickness reduction ratio of 81%.

  15. 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.

  16. 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.

  17. INITIAL TEST OF A FAST RAMPED SUPERCONDUCTING MODEL DIPOLE FOR GSIS PROPOSED SIS200 ACCELERATOR.

    SciTech Connect

    WANDERER,P.; ANERELLA,M.; GANETIS,G.; GHOSH,A.; JOSHI,P.; MARONE,A.; MURATORE,J.; SCHMALZLE,J.; SOIKA,R.; THOMAS,R.; KAUGERTS,J.; MORITZ,G.; HASSENZAHL,W.; WILSON,N.M.

    2003-05-12

    Gesellschaft fur Schwerionenforschung (GSI) has proposed a large expansion of the existing facility in Darmstadt, Germany. The proposal includes an accelerator, SIS200, with rigidity of 200 Tam that utilizes 4 T superconducting dipoles ramped at 1 T/s. An R&D program including both the superconductor and the magnet is directed at achieving the desired ramp rate with minimal energy loss. The RHIC arc dipoles, with 8 cm aperture, possess adequate aperture and field strength but are ramped at only 1/20 of the desired rate. However, for reasons of speed and economy, the RHIC dipole is being used as the basis for this work. The superconductor R&D has progressed far enough to permit the manufacture of an initial cable with satisfactory properties. This cable has been used in the construction of a I m model magnet, appropriately modified from the RHIC design. The magnet has been tested successfully at 2 T/s to 4.38 T.

  18. 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.

  19. 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.

  20. 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.

  1. Characterization of Prototype Superconducting Magnetic Quadrupolesfor the High Current Transport Experiment

    SciTech Connect

    Lund, Steven M.; Sabbi, GianLuca; Seidl, Peter

    2001-02-22

    Later phases of the High Current Transport Experiment (HCX) at LBNL will employ superconducting magnetic quadrupole lenses to focus an intense, heavy-ion beam over approximately 50 lattice periods (100 quadrupoles). Here they present a characterization of a baseline quadrupole design suitable for transporting a single, low-energy ({approx} 2 MeV), high-current ({approx} 800 mA) heavy-ion (K{sup +}) beam that will be provided from an existing injector and beam matching section. For optimal performance in this application, a compact quadrupole magnet providing high focusing strength and high field quality is required. The reference parameters that they have chosen take into account magnet development work by AML, LLNL, and MIT and result in a transport lattice well matched to programmatic needs with a lattice period of approximately 50 cm. The goal of this note is to introduce a common framework where the magnetic performance of different designs can be compared. In that regard, they try to avoid the details of an earlier parameter note [1] where provisions for tweaks in magnet excitation, cryostat assembly, etc. were discussed in fairly general terms. This note is not intended to be a final specification for the HCX quadrupoles to be constructed or to be the sole basis on which competing magnet designs will be compared. Other aspects such as prototype test results, economic considerations, and attractiveness within the context of ultimate applications in multi-beam drivers for heavy-ion fusion (i.e, compatibility with magnet arrays, etc.) will all factor in the selection of the appropriate design option. This note is organized as follows. Magnet characterizations including geometric and conductor parameters are given in Sec II. Performance parameters to be reported that quantify the magnet properties are outlined in Sec III. Supporting information is included in appendices. A reference coordinate system to be employed in field calculations is defined in Appendix A

  2. Effect of perpendicular magnetic field on bubble-like magnetic solitons driven by spin-polarized current with Dzyaloshinskii-Moriya interaction

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    The topological properties of bubble-like magnetic solitons can be modified by interfacial Dzyaloshinskii-Moriya interaction (DMI). In this paper, the dynamic responses of bubble-like magnetic solitons nucleated in the free layer of the spin-torque nano-oscillators (STNOs) are investigated in the presence of DMI and the perpendicular magnetic field by using micromagnetic simulations. We observed that the oscillation frequency of bubble-like magnetic solitons can be manipulated by the perpendicular magnetic field. Moreover, the magnetic structures keep stable in small DMI. With an increase in the DMI strength, rich kinds of bubble-like magnetic solitons appear at different spin-polarized current and perpendicular magnetic field. These results provide a further understanding of bubble-like magnetic solitons structures and direct applications in STNOs.

  3. Stability of vortex rotation around a mesoscopic square superconducting ring under radially injected current and an external magnetic field.

    PubMed

    Xue, Cun; He, An; Li, Chun; Zhou, Youhe

    2017-04-05

    We present the stability of vortex rotation around a mesoscopic square superconducting ring under radially injected currents and external magnetic fields based on time-dependent Ginzburg-Landau equations. We demonstrate that the vortex rotation around a square ring can lead to voltage oscillations as the vortices periodically pass by the corners. The amplitude of the time evolution of the voltage oscillations as a function of external current is studied at different magnetic fields, and the effect of thermal noise on the voltage oscillations is discussed. The rotation frequency depends linearly on external current at lower magnetic fields, whereas it is a nonlinear function of external current at higher magnetic fields. The stable vortex rotation appears in a certain range of injected currents under magnetic fields, but it is unstable at high injected currents. It is found that such a transition from stability to instability can lead to an abrupt jump in current-voltage characteristics.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. Magnetic probe measurements of the current sheath on the PF-3 facility

    SciTech Connect

    Krauz, V. I.; Mitrofanov, K. N.; Myalton, V. V.; Vinogradov, V. P.; Vinogradova, Yu. V.; Grabovski, E. V.; Zukakishvili, G. G.; Koidan, V. S.; Mokeev, A. N.

    2010-11-15

    Results are presented from experimental studies of the dynamics of the current sheath (CS) on the PF-3 plasma focus facility. The parameters of the sheath, including the current distribution in it, were measured using absolutely calibrated magnetic probes installed at different positions with respect to the facility axis and the anode surface. The CS dynamics in discharges operating in argon and neon was investigated, and the skin depth in different stages of the discharge was determined. One of the probes was installed at a distance of {approx}2 cm from the facility axis, which made it possible to estimate the efficiency of current transfer to the region of pinch formation. Operating modes were obtained in which the current dynamics detected by magnetic probes at different distances from the axis agreed well with the dynamics of the total discharge current until the instant of singularity in the current time derivative. It is shown that shunting breakdowns can lead to the formation of closed current loops. The shunting of the discharge current by the residual plasma is directly related to the efficiency of snowplowing of the working gas by the CS as it propagates from the insulator toward the facility axis.

  9. 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.

  10. Dynamics and instability of current-carrying microbeams in a longitudinal magnetic field

    NASA Astrophysics Data System (ADS)

    Wang, Lin; Liu, Wen-Bo; Dai, Hu-Liang

    2015-02-01

    The dynamics and instability of current-carrying slender microbeams immersed in a longitudinal magnetic field is investigated by considering the material length scale effect of the microbeam. On the basis of modified couple stress theory, a theoretical model considering the effect of Lorentz forces is developed to analyze the free vibration and possible instability of the microbeam. Using the differential quadrature method, the governing equations of motion are solved and the lowest three natural frequencies are determined. The obtained results reveal that the electric current and the longitudinal magnetic field tend to reduce the microbeam's flexural stiffness. It is therefore shown that the lowest natural frequencies would decrease with increasing magnetic field parameter. The mode shapes of the microbeam are found to be generally three-dimensional spatial in the presence of the longitudinal magnetic field. It is interesting that buckling instability would concurrently occur in the first mode or in the higher-order modes when the magnetic field parameter becomes sufficiently large.

  11. Lateral Vibration Attenuation by the Dynamic Adjustment of Bias Currents in Magnetic Suspension System

    NASA Astrophysics Data System (ADS)

    Mizuno, Takeshi; Takasaki, Masaya; Ishino, Yuji

    2016-09-01

    Switching stiffness control is applied to attenuate vibration in the lateral directions in an active magnetic suspension system with electromagnets operated in differential mode. The magnetic suspension system using the attractive force between magnetized bodies is inherently unstable in the normal direction so that feedback control is necessary to achieve stable suspension. In contrast, it can be stable in the lateral directions due to the edge effects in the magnetic circuits. In several applications, such passive suspension is used in combination with the active one to reduce cost and space. However, damping in the lateral directions is generally small. As a result, induced vibrations in these directions are hardly attenuated. To suppress such vibration without any additional actuator (electromagnet), switching stiffness control is applied to an magnetic suspension system operated in the differential mode. The stiffness in the lateral direction is adjusted by varying the bias currents of an opposed pair of electromagnets located in the normal direction simultaneously according to the motion of the suspended object. When the varied bias currents are adjusted for the additive normal forces cancel each other, such control does not affect the suspension in the normal direction. The effectiveness of the proposed control methods is confirmed experimentally.

  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. Magnetic reconnection onset via disruption of a forming current sheet by the tearing instability

    NASA Astrophysics Data System (ADS)

    Loureiro, Nuno; Uzdensky, Dmitri

    2016-10-01

    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.

  14. Extending the GMR current measurement range with a counteracting magnetic field.

    PubMed

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

    2013-06-21

    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.

  15. Current Bypassing Properties by Thermal Switch for PCS Application on NMR/MRI HTS Magnets

    NASA Astrophysics Data System (ADS)

    Kim, S. B.; Takahashi, M.; Saito, R.; Park, Y. J.; Lee, M. W.; Oh, Y. K.; Ann, H. S.

    We develop the compact NMR/MRI device using high temperature superconducting (HTS) wires with the persistent current mode operating. So, the joint techniques between 2G wires are very important issue and many studies have been carried out. Recently, the Kbigdot JOINS, Inc. has developed successfully the high performance superconducting joints between 2G wires by partial melting diffusion and oxygenation annealing process [1]. In this study, the current bypassing properties in a loop-shaped 2G wire are measured experimentally to develop the permanent current switch (PSC). The current bypassing properties of loop-shaped test coil wound with 2G wire (GdBCO) are evaluated by measured the self-magnetic field due to bypassed current by Hall sensors. The strain gauge was used as heater for persistent current switch, and thermal properties against various thermal inputs were investigated experimentally.

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

    PubMed Central

    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

  17. 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.

  18. 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.

  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. 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.

  1. Current Control of Magnetic Anisotropy via Strain in a CoFeB Waveguide

    NASA Astrophysics Data System (ADS)

    An, Kyongmo; Ma, Xin; Pai, Chi-Feng; Yang, Jusang; Olsson, Kevin; Erskine, James; MacDonald, Allan; Ralph, Daniel; Buhrman, Robert; Li, Xiaoqin

    We demonstrate that in-plane charge current can effectively control the spin precession resonance in an Al2O3/CoFeB/Ta heterostructure. Brillouin Light Scattering (BLS) was used to detect the ferromagnetic resonance field under microwave excitation of spin waves at fixed frequencies. Such control originates from the modified in-plane uniaxial magnetic anisotropy field Hk, which changes symmetrically with respect to the current direction. Numerical simulation suggests that the anisotropic stressintroduced by Joule heating plays an important role in controlling Hk. The results provide new insights into current manipulation of magnetic properties and have broad implications on spintronic devices. This work is supported by SHINES, an Energy Frontier Research Center funded by the U.S. Department of Energy (DoE), Office of Science, Basic Energy Science (BES) under Award # DE-SC0012670.

  2. 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.

  3. 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.

  4. 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.

  5. Transient Magnetic Fields and Current Distributions in an Electric Vehicle Caused by a Lightning Stroke

    NASA Astrophysics Data System (ADS)

    Yamamoto, Kazuo; Kanata, Jun; Ametani, Akihiro

    An electric vehicle includes more electronic parts than a gasoline-powered vehicle. Not only control but also driving circuits of electric vehicles are electrical at variance with those of gasoline-powered vehicles. It means that there is higher possibility of malfunctions on an electric vehicle due to electromagnetic disturbances caused by a lightning stroke. Therefore, it is important to establish lightning protection methodologies for electric vehicles. To solve the mechanisms that the lightning current following through the vehicle body and some other parts causes the malfunctions, it is important to clarify transient magnetic fields and current distributions in electric vehicles. In this paper, the transient magnetic fields and the current distributions in an electric vehicle are simulated using the FDTD method, and the probability of lightning damages is discussed.

  6. 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

  7. 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.

  8. Investigation of current-density modification during magnetic reconnection by analysis of hydrogen-pellet deflection.

    PubMed

    Waller, V; Pégourié, B; Giruzzi, G; Huysmans, G T A; Garzotti, L; Géraud, A

    2003-11-14

    A pellet penetrating the inner region of a tokamak discharge, where the safety factor drops below unity, triggers an instability analogous to a sawtooth crash. Because of the simultaneity of the crash and pellet crossing, the latter is an appropriate probe for investigating the current distribution during reconnection. In this Letter, pellet deflection is used to characterize the associated electron distribution function. The perturbation compatible with the observed trajectory requires a negative current layer on the q=1 magnetic surface between 3 and 12 times the equilibrium current density and an expulsion of high energy electrons from the plasma core.

  9. Current-Driven Motion of Magnetic Domain Wall with Many Bloch Lines

    NASA Astrophysics Data System (ADS)

    Iwasaki, Junichi; Nagaosa, Naoto

    2015-08-01

    The current-driven motion of a domain wall (DW) in a ferromagnet with many Bloch lines (BLs) via the spin transfer torque is studied theoretically. It is found that the motion of BLs changes the current-velocity (j-v) characteristic considerably. In particular, the critical current density for overcoming the pinning force is even lower than that of a skyrmion by the factor of the Gilbert damping coefficient α. This is in sharp contrast to the case of magnetic-field-driven motion, where the existence of BLs reduces the mobility of the DW.

  10. 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.

  11. 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

  12. Formation of a bifurcated current layer by the collision of supersonic magnetized plasmas

    NASA Astrophysics Data System (ADS)

    Suttle, Lee; Hare, Jack; Lebedev, Sergey; Ciardi, Andrea; Loureiro, Nuno; Burdiak, Guy; Chittenden, Jerry; Clayson, Thomas; Ma, Jiming; Niasse, Nicolas; Robinson, Timothy; Smith, Roland; Stuart, Nicolas; Suzuki-Vidal, Francisco

    2016-10-01

    We present detailed experimental data showing the formation and structure of a current layer produced by the collision of two supersonic and well magnetized plasma flows. The pulsed-power driven setup provides two steady and continuous flows, whose embedded magnetic fields mutually annihilate inside the interaction region giving rise to the current layer. Spatially resolved measurements with Faraday rotation polarimetry, Thomson scattering and laser interferometry diagnostics show the detailed distribution of the magnetic field and other plasma parameters throughout the system. We show that the pile-up of magnetic field ahead of the annihilation gives rise to the multi-layered / bi-directional nature of the current sheet, and we discuss pressure balance and energy exchange mechanisms within the system. This work was supported in part by the Engineering and Physical Sciences Research Council (EPSRC) Grant No. EP/G001324/1, and by the U.S. Department of Energy (DOE) Awards No. DE-F03-02NA00057 and No. DE-SC-0001063.

  13. Measurement of current density fluctuations and ambipolar particle flux due to magnetic fluctuations in MST

    SciTech Connect

    Shen, Weimin.

    1992-08-01

    Studies of magnetic fluctuation induced particle transport on Reversed Field Pinch plasmas were done on the Madison Symmetric Torus. Plasma current density and current density fluctuations were measured using a multi-coil magnetic probes. The low frequency (f<50 kHz) current density fluctuations are consistent with the global resistive tearing instabilities predicted by 3-D MHD simulations. At frequencies above 50 kHz, the magnetic fluctuations were detected to be localized with a radial correlation length of about 1--2 cm. These modes are locally resonant modes since the measured dominant mode number spectra match the local safety factor q. The net charged particle flux induced by magnetic fluctuations was obtained by measuring the correlation term <{tilde j}{sub {parallel}} {tilde B}{sub r}>. The result of zero net charged particle loss was obtained, meaning the flux is ambipolar. The ambipolarity of low frequency global tearing modes is satisfied through the phase relations determined by tearing instabilities. The ambipolarity of high frequency localized modes could be partially explained by the simple model of Waltz based on the radial average of small scale turbulence.

  14. [Magnetic helicity and current drive in fusion devices]. Final technical report

    SciTech Connect

    1998-02-02

    The research program focused on two main themes: (i) magnetic helicity and (ii) current drive by low-frequency waves. At first these themes seemed unrelated, but as time progressed, they became interwoven, and ultimately closely connected. A sub-theme is that while the MHD model of a plasma stimulates many intriguing counter-intuitive ideas for creating and sustaining magnetic confinement configurations, usually the crux of these schemes involves some sort of breakdown of MHD, i.e., involves physics which transcends MHD.

  15. 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.

  16. 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.

  17. 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.

  18. Cretaceous tide-dominated carbonate ramp: Comparison of reservoir hetergeneity in tide-versus wave-dominated carbonate ramp systems

    SciTech Connect

    Kerans, C.

    1995-08-01

    Cretaceous (upper Albian) carbonate ramp strata, Pecos River Canyon, Texas, provide a uniquely continuous exposure of a tide-dominated ramp reservoir analog. The continuous 100-km shelf-to-basin outcrop begins in inner ramp mud-rich facies that record both high-frequency (20-100 ky) and intermediate frequency (>200 ky) cyclicity. The ramp-crest is up to 40 km across depositional dip. Intermediate-scale cycles in the ramp crest include basal oyster and toucasid wackestones, chondrodontid-rudist packstones, rudist-skeletal grainstones, and caprinid biostromes. Ramp-crest grainstones are 4-23 m in thickness and extend more than 20 km in a shelf to basin direction. Rudist biostromes are 3-7 m in thickness and are up to several kilometers in dip continuity except in deeper outer ramp settings where 100-200 m wide mounds are more common. The ramp crest is dominated by grain-rich facies with moderate to high permeability. Toucasid wackestones and oyster marls are 1-5 m in thickness and extend tens of kilometers in a dip direction, representing potential fluid flow barriers. Wave-dominated ramp systems of the Permian of West Texas provide a contrast to the Cretaceous tide-dominated setting. Low-permeability high-frequency cycle base mudstones and high-permeability cycle-top grainstones are preserved in both inner ramp and ramp crest settings. Fluid-flow modeling of these Permian wave-dominated reservoir strata illustrates that the intercalation of thin high- and low-permeability layers result in crossflow trapping and thief zones controlling the position and amount of remaining oil saturation. The depositional homogeneity of the Cretaceous tide-dominated ramp indicates that diagenetic heterogeneities and gravitational effects are potentially dominant controls on reservoir performance for these strata.

  19. 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.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  3. Sedimentary structures formed by upper-regime flows on a Pleistocene carbonate ramp (Favignana Calcarenite, Sicily, Italy)

    NASA Astrophysics Data System (ADS)

    Slootman, Arnoud; Moscariello, Andrea; Cartigny, Matthieu; de Boer, Poppe

    2015-04-01

    Antidune, chute-and-pool and cyclic step deposits are found in the outcrops of the Pleistocene calcarenite wedge of Favignana Island. These deposits were formed on a prograding carbonate ramp. Three zones are identified: inner-mid ramp (shoreface), ramp slope, and outer ramp (offshore). The ramp slope dips 3° to 10° and drops 30-40 m over 400-600 m. The ramp slope and outer ramp show a succession of bioturbated dune cross beds with up to 10 m-thick, intercalated event beds containing supercritical-flow structures. Grain sizes range from coarse sand to granules, with large rhodoliths (algal balls) and shells as gravel-sized clasts. It is our aim to provide insight into the processes that create upper-regime flow structures and the hydraulic parameters of their generating flows. During normal storms, wind-driven currents generated submarine dunes that migrated across the sea floor. During exceptional high-energy events (megastorms, tsunamis), large amounts of skeletal debris from the carbonate factory were transported towards the top of the ramp slope, where under the effect of gravity sustained supercritical sediment gravity flows were generated. In a case study of bedform evolution, we present the formation of a large downstream-asymmetric bedform with two antidunes superimposed on its upstream flank. A stepwise flow reconstruction reveals the progressive steepening of the antidunes until critical steepness is reached, and the first and, shortly after, the second antidune wave breaks. The two hydraulic jumps thus formed, developed a temporary cyclic step morphology (i.e. hydraulic jump, accelerating subcritical flow, supercritical chute, hydraulic jump etc.). The bedform geometries are used to reconstruct the nature of the catastrophic events that were active on the ramp slope. The wave length of the antidunes is measured from outcrop, which, through hydraulic equations, allows for estimation of mean flow velocity as a function of sediment concentration in the

  4. Stability of vortex rotation around a mesoscopic square superconducting ring under radially injected current and an external magnetic field

    NASA Astrophysics Data System (ADS)

    Xue, Cun; He, An; Li, Chun; Zhou, Youhe

    2017-04-01

    We present the stability of vortex rotation around a mesoscopic square superconducting ring under radially injected currents and external magnetic fields based on time-dependent Ginzburg–Landau equations. We demonstrate that the vortex rotation around a square ring can lead to voltage oscillations as the vortices periodically pass by the corners. The amplitude of the time evolution of the voltage oscillations as a function of external current is studied at different magnetic fields, and the effect of thermal noise on the voltage oscillations is discussed. The rotation frequency depends linearly on external current at lower magnetic fields, whereas it is a nonlinear function of external current at higher magnetic fields. The stable vortex rotation appears in a certain range of injected currents under magnetic fields, but it is unstable at high injected currents. It is found that such a transition from stability to instability can lead to an abrupt jump in current–voltage characteristics.

  5. Current-induced spin-orbit torque magnetization switching in a MnGa/Pt film with a perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Ranjbar, Reza; Suzuki, Kazuya Z.; Sasaki, Yuta; Bainsla, Lakhan; Mizukami, Shigemi

    2016-12-01

    Current-induced magnetization switching is demonstrated in a micron sized Hall bar consisting of Pt-capped ultrathin ferrimagnetic MnGa films. The films showed a low magnetization M s ≃ 150 kA/m and a large perpendicular magnetic anisotropy (PMA) field μ 0HK\\text{eff} ≃ 2.5 T, indicating a PMA thickness t product K\\text{u}\\text{eff}t ≃ 0.47 mJ/m2, which is relatively larger than those reported for other material films with PMA. Magnetization switching induced by an in-plane electrical current was examined with the application of an in-plane magnetic field. The phase diagram of the switching current vs the in-plane magnetic field is qualitatively consistent with that of the torque due to the spin-Hall effect in the Pt layer.

  6. Current density filaments measured by electrostatic, magnetic and optical diagnostics in RFX-mod

    NASA Astrophysics Data System (ADS)

    Vianello, N.; Spolaore, M.; Agostini, M.; Antoni, V.; Cavazzana, R.; Martines, E.; Serianni, G.; Scarin, P.; Spada, E.; Zuin, M.

    2008-11-01

    Edge turbulence is ubiquitous in fusion devices and characterized by the formation of coherent structures which are believed to play a relevant role in driving particle losses. These structures have been observed also in the edge region of the RFX-mod Reversed Field Pinch device. In order to gain insight into their origin and features an original probe system has been used measuring both magnetic and electrostatic fluctuations simultaneously and on the same location with a high time resolution. This insertable probe head allows the direct measurements of several plasma parameters including local vorticity patterns and current density fluctuations. An array of toroidally distributed sensors allows following the structures along the main flow direction. It is found that in the cross-field plane bursts correspond to pressure structures and are related to current density filaments mainly oriented along the magnetic field. These results are compared with those provided by the measured relationship between structures on HeI emitted radiation observed by the Gas Puffing Imaging system and magnetic fluctuations. The presence and features of the current density filaments are assessed at different plasma current regimes.

  7. Design and Application of Hybrid Magnetic Field-Eddy Current Probe

    NASA Technical Reports Server (NTRS)

    Wincheski, Buzz; Wallace, Terryl; Newman, Andy; Leser, Paul; Simpson, John

    2013-01-01

    The incorporation of magnetic field sensors into eddy current probes can result in novel probe designs with unique performance characteristics. One such example is a recently developed electromagnetic probe consisting of a two-channel magnetoresistive sensor with an embedded single-strand eddy current inducer. Magnetic flux leakage maps of ferrous materials are generated from the DC sensor response while high-resolution eddy current imaging is simultaneously performed at frequencies up to 5 megahertz. In this work the design and optimization of this probe will be presented, along with an application toward analysis of sensory materials with embedded ferromagnetic shape-memory alloy (FSMA) particles. The sensory material is designed to produce a paramagnetic to ferromagnetic transition in the FSMA particles under strain. Mapping of the stray magnetic field and eddy current response of the sample with the hybrid probe can thereby image locations in the structure which have experienced an overstrain condition. Numerical modeling of the probe response is performed with good agreement with experimental results.

  8. Childhood cancer in relation to indicators of magnetic fields from ground current sources

    SciTech Connect

    Wertheimer, N.; Leeper, E.; Savitz, D.A.

    1995-06-01

    This study examines childhood cancer risk in relation to certain factors likely to indicate magnetic field exposure from ground currents in the home. Substantial ground currents are most often found in homes having conductive plumbing, in which an uninterrupted metallic path in the water pipes and water main connects the grounding systems of neighboring houses. Information on plumbing conductivity was obtained from water suppliers for the homes of 347 cases and 277 controls identified in an earlier study of magnetic field exposure and childhood cancer in the Denver area. An increased cancer risk was observed for children in homes with conductive plumbing: the matched odds ratio was 1.72 and increased to 3.00 when analysis was limited to cases and controls who were residentially stable from the reference date to the study date. A measurement metric likely to indicate active ground currents (measurements having above-median intensity and a nonvertical orientation of < 55{degree} from the horizontal) was identified. In contrast to measured field intensity alone, for which only modest associations with cancer have been reported, this metric shows a high and significant cancer risk consistent over a range of intensity and angle cutpoints. Such elevated nonvertical fields were also associated with cancer in an independent data set, which was gathered to study adult nonlymphocytic leukemia in the Seattle area. The associations of cancer with conductive plumbing and with this exposure metric both suggest that cancer risk is increased among persons with elevated magnetic field exposure from residential ground currents.

  9. THE ROTATING MAGNETIC FIELD OSCILLATOR SYSTEM FOR CURRENT DRIVE IN THE TRANSLATION, CONFINEMENT AND SUSTAINMENT EXPERIMENT

    SciTech Connect

    S. TOBIN; ET AL

    2000-12-01

    The experimental setup and test results for the {approximately}125 MW rotating magnetic field current drive system of the Translation, Confinement and Sustainment Experiment at the University of Washington are described. The oscillator system, constructed at Los Alamos National Laboratory, drives two tank circuits (15 kV{sub peak} potential, 8.5 kA{sub peak} maximum circulating current in each tank to date) operated 90{degree} out of phase to produce a 54 G rotating magnetic field with a frequency of 163 kHz ({omega} = 1.02{sup x} 10{sup {minus}6} s{sup {minus}1}). Programmable waveform generators control ''hot deck'' totem pole drivers that are used to control the grid of 12 Machlett 8618 magnetically beamed triode tubes. This setup allows the current to be turned on or off in less than 100 ns ({approximately}6{degree}). Both tank circuits are isolated from the current source by a 1:1 air core, transmission line transformer. Each tank circuit contains two saddle coils (combined inductance of 1.6 {micro}H) and radio frequency capacitors (580 nF). Test results are presented for three conditions: no external load, a resistive external load and a plasma load. A SPICE model of the oscillator system was created. Comparisons between this model and experimental data are given.

  10. Current induced magnetization switching in Co/Cu/Ni-Fe nanopillar with orange peel coupling

    SciTech Connect

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

    2015-07-15

    The impact of orange peel coupling on spin current induced magnetization switching in a Co/Cu/Ni-Fe nanopillar device is investigated by solving the switching dynamics of magnetization of the free layer governed by the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation. The value of the critical current required to initiate the magnetization switching is calculated analytically by solving the LLGS equation and verified the same through numerical analysis. Results of numerical simulation of the LLGS equation using Runge-Kutta fourth order procedure shows that the presence of orange peel coupling between the spacer and the ferromagnetic layers reduces the switching time of the nanopillar device from 67 ps to 48 ps for an applied current density of 4 × 10{sup 12}Am{sup −2}. Also, the presence of orange peel coupling reduces the critical current required to initiate switching, and in this case, from 1.65 × 10{sup 12}Am{sup −2} to 1.39 × 10{sup 12}Am{sup −2}.

  11. Intergrain magnetic properties and critical currents of T1-1223 bulk and tape superconductors

    NASA Astrophysics Data System (ADS)

    Zalecki, R.; Kolodziejczyk, A.; Chmist, J.; König, W.; Gritzner, G.

    2000-11-01

    The magnetic field and the temperature dependencies of the dispersive and the absorption components of the low frequency ac magnetic susceptibility for Pb and Bi single doped bulk superconductors as well as for Pb and Bi co-doped Ag-sheathed superconducting T1-1223 tapes have been measured and analyzed. The studies were accompanied by optical and electron microscopic observations of the microstructure. The ac susceptibility measured at various ac magnetic field amplitudes showed both intergrain and intragrain features. The temperature dependencies of the intergrain critical current densities were extracted from the absorption susceptibility via a modified Bean model. They were at relevant temperatures one order of magnitude larger for the tape than for the bulk specimens.

  12. Fits combining hyperon semileptonic decays, magnetic moments, and the conserved-vector-current hypothesis

    SciTech Connect

    Bohm, A.; Kielanowski, P.

    1983-06-01

    We have performed a test of the conserved-vector-current hypothesis (CVC) by determining the baryon charges and magnetic moments from the hyperon semileptonic data. Then CVC was applied in order to make a joint fit of all baryon semileptonic decay data and baryon magnetic moments for the spectrum-generating-group (SG) model as well as for the conventional (Cabibbo and magnetic moments in nuclear magnetons) model. The SG model gives a very good fit with chi/sup 2//n/sub D/ = 25/20/sup triangle-open//sub 21% C.L. whereas the conventional model gives a fit with chi/sup 2//n/sub D/approx. =244/20.

  13. Chiral ground-state currents of interacting photons in a synthetic magnetic field

    NASA Astrophysics Data System (ADS)

    Roushan, P.; Neill, C.; Megrant, A.; Chen, Y.; Babbush, R.; Barends, R.; Campbell, B.; Chen, Z.; Chiaro, B.; Dunsworth, A.; Fowler, A.; Jeffrey, E.; Kelly, J.; Lucero, E.; Mutus, J.; O’Malley, P. J. J.; Neeley, M.; Quintana, C.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T.; Kapit, E.; Neven, H.; Martinis, J.

    2016-10-01

    The intriguing many-body phases of quantum matter arise from the interplay of particle interactions, spatial symmetries, and external fields. Generating these phases in an engineered system could provide deeper insight into their nature. Using superconducting qubits, we simultaneously realize synthetic magnetic fields and strong particle interactions, which are among the essential elements for studying quantum magnetism and fractional quantum Hall phenomena. The artificial magnetic fields are synthesized by sinusoidally modulating the qubit couplings. In a closed loop formed by the three qubits, we observe the directional circulation of photons, a signature of broken time-reversal symmetry. We demonstrate strong interactions through the creation of photon vacancies, or `holes’, which circulate in the opposite direction. The combination of these key elements results in chiral ground-state currents. Our work introduces an experimental platform for engineering quantum phases of strongly interacting photons.

  14. Ionospheric magnetic fields and currents at Mars and Venus. Perspectives from MEX and VEX observations.

    NASA Astrophysics Data System (ADS)

    Dubinin, E.; Fraenz, M.; Zhang, T.-L.; Wei, Y.; Woch, J.; Fedorov, A.; Barabash, S.; Lundin, R.; Duru, F.

    2012-09-01

    Mars Express and Venus Express spacecrafts have provided us a wealth of in-situ observations of characteristics of induced magnetospheres of Mars and Venus at low altitudes during solar minimum conditions. At such conditions large-scale magnetic fields are observed deeply in the ionospheres (magnetized ionospheres). The observations again raise a long-standing question about the origin of these fields. The problem is intimately related to issue of electric current system and their closure. Analysis of ASPERA-3, ASPERA-4, MARSIS and MAG data reveals a lot of features which require a more sophisticated view at the origin and topology of the ionospheric magnetic fields. Differing perspectives at this problem are widely discussed.

  15. Current collection by a long conducting cylinder in a flowing magnetized plasma

    NASA Technical Reports Server (NTRS)

    Singh, Nagendra; Vashi, Bharat I.

    1990-01-01

    The numerical techniques, the definitions, and the normalizations used in the simulations of plasma flow past a long conducting cylinder with a magnetic field along the cylinder axis are described. The effect of cross-field plasma transport on the current collection without any contribution to the current from the field-aligned motion of the plasma particles is highlighted. The electric fields in the structure create a two-cell circulation of the electrons near the cylinder. The cell in the wake region has negative potentials. A fan-shaped circulation cell forms around the cylinder and in this cell the potential is generally positive. The geometry and the size of this positive cell affect the current collection. The potential structure around the cylinder is examined, along with its effect on the current collection and its oscillatory behavior. The variation of the time-average current as a function of the relative motion between the plasma and the cylinder is also investigated.

  16. Magnetic Reconnection Onset via Disruption of a Forming Current Sheet by the Plasmoid Instability

    NASA Astrophysics Data System (ADS)

    Loureiro, Nuno; Uzdensky, Dmitri

    The recent realization that Sweet-Parker reconnection current sheets are violently unstable to the secondary tearing (plasmoid) instability implies that such current sheets are unlikely to be realized 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 just being formed. We present such an analysis in the context of nonlinear resistive MHD for a generic time-dependent equilibrium representing a gradually forming current sheet. It is shown that, under most conditions, the longest-wavelength mode dominates, resulting in just one or two big plasmoids produced in the immediate aftermath of current sheet formation. Specific examples pertaining to solar flares and to parasitic modes of the magnetorotational instability are provided.

  17. Magnetization stability analysis of the Stoner-Wohlfarth model under a spin-polarized current with a tilted polarization

    SciTech Connect

    Wang, Zhiyuan; Sun, Z. Z.

    2014-02-14

    The stationary-state solutions of magnetization dynamics under a spin-polarized current that was polarized in an arbitrary direction were investigated by solving the Landau-Lifshitz-Gilbert-Slonczewski equation for a single-domain magnet. Taking into consideration the uniaxial magnetic anisotropy, the equilibrium directions of the magnetization vectors were analytically obtained by solving an algebraic cubic equation. It was found that one to three pairs of magnetization equilibrium states existed, depending on the current intensity and the direction of the spin polarization. By numerically analyzing the stabilities of these equilibrium states, the threshold switching current for the reversing the magnetic vector was obtained under different current polarization configurations, which may be useful for use in future spintronics devices.

  18. Observed nonpotential magnetic fields and the inferred flow of electric currents at a location of repeated flaring

    NASA Technical Reports Server (NTRS)

    Hagyard, M. J.

    1988-01-01

    The vector magnetic field of an active region at a location of repeated flaring is studied in order to explore the nature of the currents flowing in the areas where the flares initiated. The observed transverse component of the magnetic field is used to obtain the component of electric current density crossing the photosphere along the line-of-sight. It is found that currents flow out of an area of positive magnetic polarity and across the magnetic inversion line into two areas of negative polarity. Characteristics of the calculated source field are discussed.

  19. Observation of chiral currents at the magnetic domain boundary of a topological insulator

    NASA Astrophysics Data System (ADS)

    Wang, Yihua

    2015-03-01

    The broken time-reversal symmetry (TRS) states on the surface of a three-dimensional topological insulator (3D-TI) promise many exotic quantum phenomena. Breaking TRS opens a band gap on the surface Dirac cone and transforms the metallic surface into a Chern insulator. The TRS-broken surface states coupled to a superconductor are predicted to lead to Majorana fermions, which are the fundamental ingredients of topological quantum computation. Just as the surface Dirac cone is a signature of the non-trivial topological bulk band structure of a time-reversal invariant 3D-TI, bulk-boundary correspondence dictates that the TRS-broken surface states with a nonzero Chern number is manifested by a gapless chiral edge state (CES) at the domain boundary. In the special case where the domain boundary is the edge of the sample surface, CES along the edge leads to a quantized anomalous Hall conductance, which was recently measured in a magnetically doped 3D-TI. More generally, a magnetic domain boundary on the surface of TI hosts a CES, which is yet to be directly demonstrated because any local change of conductivity due to the CES does not affect conductance globally. Here we use a scanning superconducting quantum interference device (SQUID) to show that in a uniformly magnetized topological insulator - ferromagnetic insulator (TI-FMI) heterostructure current flows at the edge of the surface of the topological insulator when the Fermi level is gate-tuned to the surface band gap. We further induce micron-scale magnetic structures using the field coil of the SQUID and show that there emerges a chiral edge current at the magnetic domain boundary. In both cases the magnitude of the chiral edge current depends on the chemical potential rather than the applied current. Such magnetic nano-structures, which can be readily created on a TI in an arbitrary geometry, provide a versatile platform for detecting topological magnetoelectric effects and may allow the engineering of

  20. Optimal Temporal Evolution of the Magnet Currents of the Ignitor Machine

    NASA Astrophysics Data System (ADS)

    Coletti, A.; Coletti, R.; Ramogida, M.; Roccella, M.; Santinelli, M.

    2003-10-01

    The Ignitor Magnet System is comprised of 24 Toroidal Field Coils (TFC) and 12+2 pairs of Poloidal Field Coils (PFC), including the Central Solenoid and the EM Press. Currents in the TFC and each of the PFC are regulated by dedicated thyristor converter units. Starting from a first possible scenario for the magnet currents and voltages evolution, an iterative optimization process of the total installed electrical power has been performed, by taking into account several elements: smoothing of the current evolution, reduction of the voltage step variations by switching on proper resistors, modifying the coil turns and the coil current consequently, connecting in series coils with similar current behaviour, eliminating coils if poorly effective on the plasma, using converter schemes (sequential control or internal feedback control) suitable to reduce the reactive power requirements and ac current harmonics. In this way the total installed power in the Ignitor Power Supply System is about 2200 MVA instead of about 3400 MVA calculated before the optimization process. In addition the power requirements (max active power, max reactive power, max active power negative/positive steps) result compatible to the 400 kV Grid operational requirements.

  1. Study of Current Sheath Velocity and Its Distribution Using Tridimensional Magnetic Probe in Sahand Plasma Focus

    NASA Astrophysics Data System (ADS)

    A. Mohammadi, M.; Hedyeh, S.

    2015-05-01

    The current sheath velocity in 0.25 Torr gas pressure of Filippov type plasma focus is studied experimentally. By using two tridimensional magnetic probes on top of the anode surface, the current sheath velocity is measured for argon, oxygen and nitrogen. Additionally, the effect of charging voltage on the current sheath velocity is studied in both axial and radial phases. We found that, the maximum current sheath velocities at both radial and axial phases are respectively 4.33 ± 0.28 (cm/μs) and 3.92 ± 0.75 (cm/μs) with argon as the working gas at 17 kV. Also, the minimum values of current sheath velocity are 1.48 ± 0.15 (cm/μs) at the radial phase and 1.14 ± 0.09 (cm/μs) at the axial phase with oxygen at 12 kV. The current sheath velocity at the radial phase is higher than that at the axial phase for all gases and voltages. In this study, variation of the full width half maximum (FWHM) of magnetic probe signals with voltage is investigated for different gases at radial and axial phases.

  2. Structural properties of the solar flare-producing coronal current system developed in an emerging magnetic flux tube

    NASA Astrophysics Data System (ADS)

    Magara, Tetsuya

    2017-02-01

    The activity of a magnetic structure formed in the solar corona depends on a coronal current system developed in the structure, which determines how an electric current flows in the corona. To investigate structural properties of the coronal current system responsible for producing a solar flare, we perform magnetohydrodynamic simulation of an emerging magnetic flux tube which forms a coronal magnetic structure. Investigation using fractal dimensional analysis and electric current streamlines reveals that the flare-producing coronal current system relies on a specific coronal current structure of two-dimensional spatiality, which has a sub-region where a nearly anti-parallel magnetic field configuration is spontaneously generated. We discuss the role of this locally generated anti-parallel magnetic field configuration in causing the reconnection of a three-dimensional magnetic field, which is a possible mechanism for producing a flare. We also discuss how the twist of a magnetic flux tube affects structural properties of a coronal current system, showing how much volume current flux is carried into the corona by an emerging flux tube. This gives a way to evaluate the activity of a coronal magnetic structure.

  3. High-field, high-current-density, stable superconducting magnets for fusion machines

    SciTech Connect

    Lue, J.W.; Dresner, L.; Lubell, M.S.

    1989-01-01

    Designs for large fusion machines require high-performance superconducting magnets to reduce cost or increase machine performance. By employing force-flow cooling, cable-in-conduit conductor configuration, and NbTi superconductor, it is now possible to design superconducting magnets that operate a high fields (8-12 T) with high current densities (5-15 kA/cm/sup 2/ over the winding pack) in a stable manner. High current density leads to smaller, lighter, and thus less expensive coils. The force-flow cooling provides confined helium, full conductor insulation, and a rigid winding pack for better load distribution. The cable-in-conduit conductor configuration ensures a high stability margin for the magnet. The NbTi superconductor has reached a good engineering material standard. Its strain-insensitive critical parameters are particularly suitable for complex coil windings of a stellarator machine. The optimization procedure for such a conductor design, developed over the past decade, is summarized here. If desired a magnet built on the principles outlines in this paper can be extended to a field higher than the design value without degrading its stability by simply lowering the operating temperature below 4.2 K. 11 refs., 3 figs.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  5. The current status and future direction of high magnetic field science in the United States

    SciTech Connect

    Lancaster, James

    2013-11-01

    This grant provided partial support for the National Research Council (NRC) study that assesses the current status of high magnetic field research in the United States and provides recommendations to guide the future of research and technology development for this area given the needs of user communities and in the context of other programs worldwide. A pdf version of the report is available for download, for free, at http://www.nap.edu/catalog.php?record_id=18355. The science drivers fall into 4 broad areas—(1) condensed matter and materials physics; (2) chemistry, biochemistry, and biology; (3) medical and life science studies; and (4) other fields such as high-energy physics, plasma physics, and particle astrophysics. Among the topics covered in the report’s findings, conclusions, and recommendations are a recognition that there is a continuing need for a centralized facility but also that clear benefits will flow to research communities from decentralized facilities. According to the report, support agencies should evaluate whether to establish such facilities when 32 Tesla superconducting magnets become available. The report also recommends the provision of facilities that combine magnetic fields with scattering facilities and THz radiation sources, and sets out specific magnet goals for magnets needed in several areas of research.

  6. 14. VIEW OF THE MODERN CONCRETE RAMP THAT CONNECTED THE ...

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

    14. VIEW OF THE MODERN CONCRETE RAMP THAT CONNECTED THE UPPER AND LOWER MINE ROADS. TRUCKS USED THIS RAMP AND THE ROADS TO HAUL SLAG TO THE MINE DUMP. - Tower Hill No. 2 Mine, Approximately 0.47 mile Southwest of intersection of Stone Church Road & Township Route 561, Hibbs, Fayette County, PA

  7. 9 CFR 313.1 - Livestock pens, driveways and ramps.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 9 Animals and Animal Products 2 2013-01-01 2013-01-01 false Livestock pens, driveways and ramps. 313.1 Section 313.1 Animals and Animal Products FOOD SAFETY AND INSPECTION SERVICE, DEPARTMENT OF... INSPECTION AND CERTIFICATION HUMANE SLAUGHTER OF LIVESTOCK § 313.1 Livestock pens, driveways and ramps....

  8. 9 CFR 313.1 - Livestock pens, driveways and ramps.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 9 Animals and Animal Products 2 2012-01-01 2012-01-01 false Livestock pens, driveways and ramps. 313.1 Section 313.1 Animals and Animal Products FOOD SAFETY AND INSPECTION SERVICE, DEPARTMENT OF... INSPECTION AND CERTIFICATION HUMANE SLAUGHTER OF LIVESTOCK § 313.1 Livestock pens, driveways and ramps....

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

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 9 Animals and Animal Products 2 2014-01-01 2014-01-01 false Livestock pens, driveways and ramps. 313.1 Section 313.1 Animals and Animal Products FOOD SAFETY AND INSPECTION SERVICE, DEPARTMENT OF... INSPECTION AND CERTIFICATION HUMANE SLAUGHTER OF LIVESTOCK § 313.1 Livestock pens, driveways and ramps....

  10. 40 CFR 1033.520 - Alternative ramped modal cycles.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 34 2012-07-01 2012-07-01 false Alternative ramped modal cycles. 1033.520 Section 1033.520 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS CONTROL OF EMISSIONS FROM LOCOMOTIVES Test Procedures § 1033.520 Alternative ramped...

  11. 40 CFR 1033.520 - Alternative ramped modal cycles.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 32 2010-07-01 2010-07-01 false Alternative ramped modal cycles. 1033.520 Section 1033.520 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS CONTROL OF EMISSIONS FROM LOCOMOTIVES Test Procedures § 1033.520 Alternative ramped...

  12. 40 CFR 1033.520 - Alternative ramped modal cycles.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 33 2011-07-01 2011-07-01 false Alternative ramped modal cycles. 1033.520 Section 1033.520 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS CONTROL OF EMISSIONS FROM LOCOMOTIVES Test Procedures § 1033.520 Alternative ramped...

  13. 40 CFR 1033.520 - Alternative ramped modal cycles.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 33 2014-07-01 2014-07-01 false Alternative ramped modal cycles. 1033.520 Section 1033.520 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS CONTROL OF EMISSIONS FROM LOCOMOTIVES Test Procedures § 1033.520 Alternative ramped...

  14. 40 CFR 1033.520 - Alternative ramped modal cycles.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 34 2013-07-01 2013-07-01 false Alternative ramped modal cycles. 1033.520 Section 1033.520 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS CONTROL OF EMISSIONS FROM LOCOMOTIVES Test Procedures § 1033.520 Alternative ramped...

  15. DETAIL VIEW OF THREE CONCENTRATION TABLES, LOADING RAMP, AND CLASSIFIER, ...

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

    DETAIL VIEW OF THREE CONCENTRATION TABLES, LOADING RAMP, AND CLASSIFIER, LOOKING EST. THE RAKE THAT WAS ORIGINALLY INSIDE THE CLASSIFIER IS AT CENTER RIGHT ON TOP OF THE LOADING RAMP. - Gold Hill Mill, Warm Spring Canyon Road, Death Valley Junction, Inyo County, CA

  16. Efficient calculation of integrals in mixed ramp-Gaussian basis sets.

    PubMed

    McKemmish, Laura K

    2015-04-07

    Algorithms for the efficient calculation of two-electron integrals in the newly developed mixed ramp-Gaussian basis sets are presented, alongside a Fortran90 implementation of these algorithms, RampItUp. These new basis sets have significant potential to (1) give some speed-up (estimated at up to 20% for large molecules in fully optimised code) to general-purpose Hartree-Fock (HF) and density functional theory quantum chemistry calculations, replacing all-Gaussian basis sets, and (2) give very large speed-ups for calculations of core-dependent properties, such as electron density at the nucleus, NMR parameters, relativistic corrections, and total energies, replacing the current use of Slater basis functions or very large specialised all-Gaussian basis sets for these purposes. This initial implementation already demonstrates roughly 10% speed-ups in HF/R-31G calculations compared to HF/6-31G calculations for large linear molecules, demonstrating the promise of this methodology, particularly for the second application. As well as the reduction in the total primitive number in R-31G compared to 6-31G, this timing advantage can be attributed to the significant reduction in the number of mathematically complex intermediate integrals after modelling each ramp-Gaussian basis-function-pair as a sum of ramps on a single atomic centre.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  18. Universal charge and current on magnetic domain walls in Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Araki, Yasufumi; Yoshida, Akihide; Nomura, Kentaro

    2016-09-01

    Domain walls in three-dimensional Weyl semimetals, formed by localized magnetic moments, are investigated. There appear bound states around the domain wall with the discrete spectrum, among which we find "Fermi arc" states with the linear dispersion. The Fermi arc modes contribute to the electric charge and current localized at the domain wall, which reveal a universal behavior depending only on chemical potential and the splitting of the Weyl nodes. This equilibrium current can be traced back to the chiral magnetic effect, or the edge counterpart of the anomalous Hall effect in the bulk. We propose a way to manipulate the motion of the domain wall, accompanied with the localized charge, by applying an external electric field.

  19. Current sheet flapping motions in the tailward flow of magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Wu, Mingyu; Lu, Quanming; Volwerk, Martin; Vörös, Zoltán.; Ma, Xuanye; Wang, Shui

    2016-08-01

    The feature and origin of current sheet flapping motions are one of most interesting issues of magnetospheric dynamics. In this paper we report the flapping motion of the current sheet detected in the tailward flow of a magnetic reconnection event on 7 February 2009. This flapping motion with frequency about 12 mHz was accompanied by magnetic turbulence. The observations by the tail-elongated fleet of five Time History of Events and Macroscale Interactions during Substorms probes indicate that these flapping oscillations were rather confined within the tailward flow than were due to a global process. This flapping motion could be due to the instability driven by the free energy associated with the ion temperature anisotropy in the tailward flow. Our observations indicate that the flapping motion in the tailward flow could have a different generation mechanism with that in the earthward flow.

  20. The effects of direct-current magnetic fields on turtle retinas vitro

    SciTech Connect

    Raybourn, M.S.

    1983-05-13

    Direct-current magnetic fields of 10 to 100 gauss cause a significant short-term reduction of the in vitro electroretinographic b-wave response in turtle retina. This response compression is not accompanied by the usual reduction in retinal sensitivity that occurs with background illumination. Furthermore, this effect is obtained only briefly after the offset of ambient lighting in the diurnal light-dark cycle of nonhibernating animals.