Science.gov

Sample records for simulated main magnetic

  1. ANALYSIS AND SIMULATION OF MAIN MAGNET TRANSMISSION LINE EFFECT

    SciTech Connect

    ZHANG,W.; MARNERIS, I.; SANDBERG, J.

    2007-06-25

    A main magnet chain forms a pair of transmission lines. Pulse-reflection-caused voltage and current differentiation throughout the magnet chain can have adverse effect on main magnet field quality. This effect is associated with magnet system configuration, coupling efficiency, and parasitic parameters. A better understanding of this phenomenon will help us in new design and existing system upgrade. In this paper, we exam the transmission line effect due to different input functions as well as configuration, coupling, and other parameters.

  2. The main magnetic field of Jupiter

    NASA Technical Reports Server (NTRS)

    Acuna, M. H.; Ness, N. F.

    1976-01-01

    The main magnetic field of Jupiter has been measured by the Goddard Space Flight Center flux gate magnetometer on Pioneer 11. Analysis of the data yields a more detailed model than that obtained from Pioneer 10 results. In a spherical harmonic octupole representation the dipole term (with opposite polarity to earth's) has a magnitude of 4.28 G times the radial distance cubed at a tilt angle of 9.6 deg and a system 111 longitude of 232 deg. The quadrupole and octupole moments are 24% and 21% of the dipole, respectively. This leads to a significant deviation of the planetary magnetic field from a simple offset dipole topology at distances of less than three times the radial distance. The north polar field strength is 14 G, and in the Northern Hemisphere the 'footprint' of the Io associated flux tube traverses the magnetic polar region. Associated L shell splitting in the radiation belts, warping of the charged particle equatorial planes, and enhanced absorption effects due to the satellites Amalthea and Io are expected as a result of the field complexity.

  3. Space shuttle main engine hardware simulation

    NASA Technical Reports Server (NTRS)

    Vick, H. G.; Hampton, P. W.

    1985-01-01

    The Huntsville Simulation Laboratory (HSL) provides a simulation facility to test and verify the space shuttle main engine (SSME) avionics and software system using a maximum complement of flight type hardware. The HSL permits evaluations and analyses of the SSME avionics hardware, software, control system, and mathematical models. The laboratory has performed a wide spectrum of tests and verified operational procedures to ensure system component compatibility under all operating conditions. It is a test bed for integration of hardware/software/hydraulics. The HSL is and has been an invaluable tool in the design and development of the SSME.

  4. Simulation of slow extraction in the Main Injector

    SciTech Connect

    Mishra, C.S.; Harfoush, F.A.; Johnstone, J.

    1993-08-01

    Recent modifications to the tracking code TEAPOT have allowed us to simulate both ramp and slow extraction in the Fermilab Main Injector at 120 GeV/c. This calculation includes all the magnetic field and alignment errors. Preliminary results from this calculation are presented here and compared with other calculations. Further studies to optimize the strength and ramp of the extraction elements are in progress.

  5. Magnetic main sequence stars as progenitors of blue supergiants

    NASA Astrophysics Data System (ADS)

    Petermann, I.; Castro, N.; Langer, N.

    2015-01-01

    Blue supergiants (BSGs) to the right the main sequence band in the HR diagram can not be reproduced by standard stellar evolution calculations. We investigate whether a reduced convective core mass due to strong internal magnetic fields during the main sequence might be able to recover this population of stars. We perform calculations with a reduced mass of the hydrogen burning convective core of stars in the mass range 3-30 M ⊙ in a parametric way, which indeed lead to BSGs. It is expected that these BSGs would still show large scale magnetic fields in the order of 10 G.

  6. Main-sequence magnetic CP stars III. Results of magnetic field measurements

    NASA Astrophysics Data System (ADS)

    Romanyuk, I. I.

    2010-10-01

    We present the third part of the survey of magnetic parameters of main-sequence magnetic CP stars. We analyze the main definitions and terminology, basic data on the magnetic fields of CP stars (catalogs, the history of the stellar magnetism research, the main observational results obtained over 60 years of studies). We describe the modern views on the properties of magnetic CP stars, i.e. their geometric structure, distribution of field strengths, magnetic field and rotation, magnetic field and energy distribution anomalies, and the evolutionary status of magnetic CP stars. We conclude that the observational data mostly support the theory of the relict origin and evolution of magnetic fields of CP stars.

  7. Magnetic measurements of the correction and adjustment magnets of the main ring

    SciTech Connect

    Trbojevic, D.

    1986-07-01

    Correction magnets correct the field imperfections and alignment errors of the main quadrupole and bend magnets. For reducing and controlling chromaticity there are 186 sextupoles and 78 octupoles, while for suppressing various resonances there are 12 normal and 18 skew sextupoles and 24 normal and 19 skew quadrupoles. Beam positions are individually controlled by 108 horizontal and 108 skew dipoles. This report includes results of the all Main Ring correction and adjustment magnet harmonic measurements. The measurement principle and basic equations are described.

  8. Simulations of Magnetic Flux Emergence

    NASA Astrophysics Data System (ADS)

    Stein, Robert; Nordlund, Aake

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

  9. Simulations of space charge in the Fermilab Main Injector

    SciTech Connect

    Stern, E.; Amundson, J.; Spentzouris, P.; Qiang, J.; Ryne, R.; /LBL, Berkeley

    2011-03-01

    The Fermilab Project X plan for future high intensity operation relies on the Main Injector as the engine for delivering protons in the 60-120 GeV energy range. Project X plans call for increasing the number of protons per Main Injector bunch from the current value of 1.0 x 10{sup 11} to 3.0 x 10{sup 11}. Space charge effects at the injection energy of 8 GeV have the potential to seriously disrupt operations. We report on ongoing simulation efforts with Synergia, MARYLIE/Impact, and IMPACT, which provide comprehensive capabilities for parallel, multi-physics modeling of beam dynamics in the Main Injector including 3D space-charge effects.

  10. Analysis of the Space Shuttle main engine simulation

    NASA Technical Reports Server (NTRS)

    Deabreu-Garcia, J. Alex; Welch, John T.

    1993-01-01

    This is a final report on an analysis of the Space Shuttle Main Engine Program, a digital simulator code written in Fortran. The research was undertaken in ultimate support of future design studies of a shuttle life-extending Intelligent Control System (ICS). These studies are to be conducted by NASA Lewis Space Research Center. The primary purpose of the analysis was to define the means to achieve a faster running simulation, and to determine if additional hardware would be necessary for speeding up simulations for the ICS project. In particular, the analysis was to consider the use of custom integrators based on the Matrix Stability Region Placement (MSRP) method. In addition to speed of execution, other qualities of the software were to be examined. Among these are the accuracy of computations, the useability of the simulation system, and the maintainability of the program and data files. Accuracy involves control of truncation error of the methods, and roundoff error induced by floating point operations. It also involves the requirement that the user be fully aware of the model that the simulator is implementing.

  11. Main drive selection for the Windstorm Simulation Center

    SciTech Connect

    Lacy, J.M.; Earl, J.S.

    1998-02-01

    Operated by the Partnership for Natural Disaster Reduction, the Windstorm Simulation Center (WSC) will be a structural test center dedicated to studying the performance of civil structural systems subjected to hurricanes, tornadoes, and other storm winds. Within the WSC, a bank of high-power fans, the main drive, will produce the high velocity wind necessary to reproduce these storms. Several options are available for the main drive, each with advantages and liabilities. This report documents a study to identify and evaluate all candidates available, and to select the most promising system such that the best possible combination of real-world performance attributes is achieved at the best value. Four broad classes of candidate were identified: electric motors, turbofan aircraft engines, turboshaft aircraft engines, and turboshaft industrial engines. Candidate systems were evaluated on a basis of technical feasibility, availability, power, installed cost, and operating cost.

  12. Magnetohydrodynamic simulations of turbulent magnetic reconnection

    SciTech Connect

    Fan Quanlin; Feng Xueshang; Xiang Changqing

    2004-12-01

    Turbulent reconnection process in a one-dimensional current sheet is investigated by means of a two-dimensional compressible one-fluid magnetohydrodynamic simulation with spatially uniform, fixed resistivity. Turbulence is set up by adding to the sheet pinch small but finite level of broadband random-phased magnetic field components. To clarify the nonlinear spatial-temporal nature of the turbulent reconnection process the reconnection system is treated as an unforced initial value problem without any anomalous resistivity model adopted. Numerical results demonstrate the duality of turbulent reconnection, i.e., a transition from Sweet-Parker-like slow reconnection to Petschek-like fast reconnection in its nonlinear evolutionary process. The initial slow reconnection phase is characterized by many independent microreconnection events confined within the sheet region and a global reconnection rate mainly dependent on the initially added turbulence and insensitive to variations of the plasma {beta} and resistivity. The formation and amplification of the major plasmoid leads the following reconnection process to a rapid reconnection stage with a fast reconnection rate of the order of 0.1 or even larger, drastically changing the topology of the global magnetic field. That is, the presence of magnetohydrodynamic turbulence in large-scale current sheets can raise the reconnection rate from small values on the order of the Sweet-Parker rate to high values on the order of the Petscheck rate through triggering an evolution toward fast magnetic reconnection. Meanwhile, the backward coupling between the small- and large-scale magnetic field dynamics has been properly represented through the present high resolution simulation. The undriven turbulent reconnection model established here expresses a solid numerical basis for the previous schematic two-step magnetic reconnection models and a possible explanation of two-stage energy release process of solar explosives.

  13. Design and multiparticle simulation of the half integer slow extraction system for the Main Injector

    SciTech Connect

    Trbojevic, D.; Harrison, M.

    1991-05-01

    One of the roles of the new Main Injector ring, in the second phase of the Fermilab upgrade, is to deliver all year around the slow extracted 120 GeV test beams. The half-integer slow extraction system design and results from a Monte-Carlo simulation of fast spill are presented. The simulation was performed with a computer tracking program based on the TEVLAT program with a large number of particles (up to 1000). Particle tracking included the systematic errors produced by the magnetic multipoles within the dipoles and quadrupoles as well as random multipole errors.

  14. Macroscopic simulation of isotropic permanent magnets

    NASA Astrophysics Data System (ADS)

    Bruckner, Florian; Abert, Claas; Vogler, Christoph; Heinrichs, Frank; Satz, Armin; Ausserlechner, Udo; Binder, Gernot; Koeck, Helmut; Suess, Dieter

    2016-03-01

    Accurate simulations of isotropic permanent magnets require to take the magnetization process into account and consider the anisotropic, nonlinear, and hysteretic material behaviour near the saturation configuration. An efficient method for the solution of the magnetostatic Maxwell equations including the description of isotropic permanent magnets is presented. The algorithm can easily be implemented on top of existing finite element methods and does not require a full characterization of the hysteresis of the magnetic material. Strayfield measurements of an isotropic permanent magnet and simulation results are in good agreement and highlight the importance of a proper description of the isotropic material.

  15. Magnetic Helicity in Solar Dynamo Simulations

    NASA Astrophysics Data System (ADS)

    Miesch, Mark; Augustson, Kyle C.; Zhang, Mei

    2015-08-01

    Magnetic helicity is a fundamental agent for magnetic self-organization in magnetohydrodynamic (MHD) dynamos. As a conserved quantity in ideal MHD, it establishes a strict topological coupling between large and small-scale magnetic fields. The generation of magnetic fields on scales larger than the velocity field is linked to an upscale transfer of magnetic helicity, either locally in spectral space as in the inverse cascade of magnetic helicity in MHD turbulence or non-locally, as in the turbulent alpha-effect of mean-field dynamo theory. Thus, understanding the generation, transport, and dissipation of magnetic helicity is an essential prerequisite to understanding manifestations of magnetic self-organization in the solar dynamo, including sunspots, the prominent dipole and quadrupole moments, and the 22-year magnetic activity cycle. Yet, despite its significance, magnetic helicity is often neglected in observational and theoretical studies of solar magnetism. This can be attributed to two factors; First, the calculation of the magnetic helicity is not unique; in general it depends on an electromagnetic guage through the magnetic vector potential. Second, unless it is explicitly calculated as part of the computational algorithm in numerical models, it is not always straightforward to obtain the magnetic vector potential. Here we consider gauge-invariant measures of the magnetic helicity and magnetic helicity flux and we describe how they can be computed from measurable quantities such as the magnetic field, the bulk plasma velocity, and the electrical current density. These measures can be applied to local Cartesian geometries as well as global spherical shells. Here we apply them to two global dynamo simulations, each exhibiting regular magnetic cycles. These include a convective MHD dynamo model and a 3-D Babcock-Leighton dynamo model. Both exhibit patterns of magnetic helicity evolution that reflect the global restructuring of the magnetic field over the

  16. Simulation of magnetophoresis of magnetic nanoparticles in liquids

    NASA Astrophysics Data System (ADS)

    Shi, Zongqian; Sun, Jiajia; Jia, Shenli; Zhang, Pengbo

    2016-08-01

    Magnetophoresis, which is known as a process of driving magnetic particles to depart from the dispersion in the presence of an external inhomogeneous magnetic field, has gained substantial investigations due to its significance in various fields. The main objective of this paper is to analyze the magnetophoretic mechanism of magnetic nanoparticles in fluids with a Lagrangian approach. The equivalent current source method is used to calculate the magnetic field of a cylindrical permanent magnet, which provides a feasible way to simulate the magnetophoresis process. Then the magnetophoretic velocity of particles and the influence of various key factors, e.g. the dimension of a cylindrical permanent magnet, the saturation magnetization of particles and the viscosity of fluid, are investigated. Furthermore, an efficient algorithm is proposed to calculate the trajectory of particles, and to describe the capture efficiency of the particles and the distribution of the captured particles at different times. In addition, the applicability of the Lagrangian approach is also discussed.

  17. Booster main magnet power supply, present operation and potential future upgrades

    SciTech Connect

    Bajon, E.; Bannon, M.; Marneris, I.; Danowski, G.; Sandberg, J.; Savatteri, S.

    2011-03-28

    The Brookhaven Booster Main Magnet Power Supply (MMPS) is a 24 pulse thyristor control supply, rated at 5500 Amps, +/-2000 Volts, or 3000 Amps, +/-6000 Volts. The power supply is fed directly from the power utility and the peak magnet power is 18 MWatts. This peak power is seen directly at the incoming ac line. This power supply has been in operation for the last 18 years. This paper will describe the present topology and operation of the power supply, the feedback control system and the different modes of operation of the power supply. Since the power supply has been in operation for the last 18 years, upgrading this power supply is essential. A new power supply topology has been studied where energy is stored in capacitor banks. DC to DC converters are used to convert the dc voltage stored in the capacitor banks to pulsed DC voltage into the magnet load. This enables the average incoming power from the ac line to be constant while the peak magnet power is pulsed to +/- 18 MWatts. Simulations and waveforms of this power supply will be presented.

  18. Magnetized plasma jets in experiment and simulation

    NASA Astrophysics Data System (ADS)

    Schrafel, Peter; Greenly, John; Gourdain, Pierre; Seyler, Charles; Blesener, Kate; Kusse, Bruce

    2013-10-01

    This research focuses on the initial ablation phase of a thing (20 micron) Al foil driven on the 1 MA-in-100 ns COBRA through a 5 mm diameter cathode in a radial configuration. In these experiments, ablated surface plasma (ASP) on the top of the foil and a strongly collimated axial plasma jet can be observed developing midway through current-rise. Our goal is to establish the relationship between the ASP and the jet. These jets are of interest for their potential relevance to astrophysical phenomena. An independently pulsed 200 μF capacitor bank with a Helmholtz coil pair allows for the imposition of a slow (150 μs) and strong (~1 T) axial magnetic field on the experiment. Application of this field eliminates significant azimuthal asymmetry in extreme ultraviolet emission of the ASP. This asymmetry is likely a current filamentation instability. Laser-backlit shadowgraphy and interferometry confirm that the jet-hollowing is correlated with the application of the axial magnetic field. Visible spectroscopic measurements show a doppler shift consistent with an azimuthal velocity in the ASP caused by the applied B-field. Computational simulations with the XMHD code PERSEUS qualitatively agree with the experimental results.

  19. Thermal conditions on the International Space Station: Effects of operations of the station Main Radiators on the Alpha Magnetic Spectrometer

    NASA Astrophysics Data System (ADS)

    Xie, Min; Burger, Joseph

    2016-04-01

    A thermal model of the Alpha Magnetic Spectrometer on the International Space Station (ISS) has been developed, and Thermal Desktop® (with RadCAD®) and SINDA/FLUINT software have been used to calculate the effects of the operations of the ISS Main Radiators on AMS temperatures. We find that the ISS Starboard Main Radiator has significant influence on temperatures on the port side of AMS. The simulation results are used in AMS thermal control operations.

  20. Geodynamics branch data base for main magnetic field analysis

    NASA Technical Reports Server (NTRS)

    Langel, Robert A.; Baldwin, R. T.

    1991-01-01

    The data sets used in geomagnetic field modeling at GSFC are described. Data are measured and obtained from a variety of information and sources. For clarity, data sets from different sources are categorized and processed separately. The data base is composed of magnetic observatory data, surface data, high quality aeromagnetic, high quality total intensity marine data, satellite data, and repeat data. These individual data categories are described in detail in a series of notebooks in the Geodynamics Branch, GSFC. This catalog reviews the original data sets, the processing history, and the final data sets available for each individual category of the data base and is to be used as a reference manual for the notebooks. Each data type used in geomagnetic field modeling has varying levels of complexity requiring specialized processing routines for satellite and observatory data and two general routines for processing aeromagnetic, marine, land survey, and repeat data.

  1. Nonlinear simulations to optimize magnetic nanoparticle hyperthermia

    SciTech Connect

    Reeves, Daniel B. Weaver, John B.

    2014-03-10

    Magnetic nanoparticle hyperthermia is an attractive emerging cancer treatment, but the acting microscopic energy deposition mechanisms are not well understood and optimization suffers. We describe several approximate forms for the characteristic time of Néel rotations with varying properties and external influences. We then present stochastic simulations that show agreement between the approximate expressions and the micromagnetic model. The simulations show nonlinear imaginary responses and associated relaxational hysteresis due to the field and frequency dependencies of the magnetization. This suggests that efficient heating is possible by matching fields to particles instead of resorting to maximizing the power of the applied magnetic fields.

  2. First-principles simulation and comparison with beam tests for transverse instabilities and damper performance in the Fermilab Main Injector

    SciTech Connect

    Nicklaus, Dennis; Foster, G.William; Kashikhin, Vladimir; /Fermilab

    2005-05-01

    An end-to-end performance calculation and comparison with beam tests was performed for the bunch-by-bunch digital transverse damper in the Fermilab Main Injector. Time dependent magnetic wakefields responsible for ''Resistive Wall'' transverse instabilities in the Main Injector were calculated with OPERA-2D using the actual beam pipe and dipole magnet lamination geometry. The leading order dipole component was parameterized and used as input to a bunch-by-bunch simulation which included the filling pattern and injection errors experienced in high-intensity operation of the Main Injector. The instability growth times, and the spreading of the disturbance due to newly misinjected batches was compared between simulations and beam data collected by the damper system. Further simulation models the effects of the damper system on the beam.

  3. Mini-beta superconducting quadrupole magnet system for the TRISTAN main ring

    SciTech Connect

    Endo, K.; Tsuchiya, K.; Ohuchi, N.; Morita, Y.; Egawa, K.; Sugahara, R.; Fukuma, H.; Kabe, A.; Kubo, T.; Ohsawa, Y. )

    1992-01-01

    After several years of developing a superconducting magnet system (QCS system), including a cryogenic system, mini-beta magnets were installed at all interaction points during the summer of 1990. The final tests were continued until the end of January, 1991, followed immediately by beam operation. In this paper performances of QCS magnets and cryogenic systems are mainly described.

  4. Entropy conservation in simulations of magnetic reconnection

    SciTech Connect

    Birn, J.; Hesse, M.; Schindler, K.

    2006-09-15

    Entropy and mass conservation are investigated for the dynamic field evolution associated with fast magnetic reconnection, based on the 'Newton Challenge' problem [Birn et al., Geophys. Res. Lett. 32, L06105 (2005)]. In this problem, the formation of a thin current sheet and magnetic reconnection are initiated in a plane Harris-type current sheet by temporally limited, spatially varying, inflow of magnetic flux. Using resistive magnetohydrodynamic (MHD) and particle-in-cell (PIC) simulations, specifically the entropy and mass integrated along the magnetic flux tubes are compared between the simulations. In the MHD simulation these should be exactly conserved quantities, when slippage and Ohmic dissipation are negligible. It is shown that there is very good agreement between the conservation of these quantities in the two simulation approaches, despite the effects of dissipation, provided that the resistivity in the MHD simulation is strongly localized. This demonstrates that dissipation is highly localized in the PIC simulation also, and that heat flux across magnetic flux tubes has negligible effect as well, so that the entropy increase on a full flux tube remains small even during reconnection. The mass conservation also implies that the frozen-in flux condition of ideal MHD is a good integral approximation outside the reconnection site. This result lends support for using the entropy-conserving MHD approach not only before and after reconnection but even as a constraint connecting the two phases.

  5. Magnetic Vibration Simulator with Magnetic Levitation for EDS Maglev

    NASA Astrophysics Data System (ADS)

    Murai, Toshiaki; Hasegawa, Hitoshi; Kashiwagi, Takayuki

    A magnetic vibration simulator is one of the most important test tools to evaluate the basic performance of superconducting magnet (SCM) for EDS maglev. In this paper, we propose a new magnetic vibration simulator which can also suspend car and bogie mounted with the SCMs to evaluate the performance of not only SCMs but also vehicle dynamics with levitation. This system is composed of magnetic exciting coils which can simultaneously suspend and vibrate the SCMs and inverters which can simultaneously control 3-phase and zero-phase currents. This paper describes the principle, analytical method and control method of this system, and using numerical example, the vehicle dynamics and the vibration response of SCM are revealed.

  6. Accurate simulation of the electron cloud in the Fermilab Main Injector with VORPAL

    SciTech Connect

    Lebrun, Paul L.G.; Spentzouris, Panagiotis; Cary, John R.; Stoltz, Peter; Veitzer, Seth A.; /Tech-X, Boulder

    2011-01-01

    We present results from a precision simulation of the electron cloud (EC) in the Fermilab Main Injector using the code VORPAL. This is a fully 3d and self consistent treatment of the EC. Both distributions of electrons in 6D phase-space and E.M. field maps have been generated. This has been done for various configurations of the magnetic fields found around the machine have been studied. Plasma waves associated to the fluctuation density of the cloud have been analyzed. Our results are compared with those obtained with the POSINST code. The response of a Retarding Field Analyzer (RFA) to the EC has been simulated, as well as the more challenging microwave absorption experiment. Definite predictions of their exact response are difficult to obtain,mostly because of the uncertainties in the secondary emission yield and, in the case of the RFA, because of the sensitivity of the electron collection efficiency to unknown stray magnetic fields. Nonetheless, our simulations do provide guidance to the experimental program.

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

    SciTech Connect

    Bruce C. Brown and David P Capista

    2003-05-27

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

  8. Accuracy estimates for some global analytical models of the Earth's main magnetic field on the basis of data on gradient magnetic surveys at stratospheric balloons

    NASA Astrophysics Data System (ADS)

    Tsvetkov, Yu. P.; Brekhov, O. M.; Bondar, T. N.; Filippov, S. V.; Petrov, V. G.; Tsvetkova, N. M.; Frunze, A. Kh.

    2014-03-01

    Two global analytical models of the main magnetic field of the Earth (MFE) have been used to determine their potential in deriving an anomalous MFE from balloon magnetic surveys conducted at altitudes of ˜30 km. The daily mean spherical harmonic model (DMSHM) constructed from satellite data on the day of balloon magnetic surveys was analyzed. This model for the day of magnetic surveys was shown to be almost free of errors associated with secular variations and can be recommended for deriving an anomalous MFE. The error of the enhanced magnetic model (EMM) was estimated depending on the number of harmonics used in the model. The model limited by the first 13 harmonics was shown to be able to lead to errors in the main MFE of around 15 nT. The EMM developed to n = m = 720 and constructed on the basis of satellite and ground-based magnetic data fails to adequately simulate the anomalous MFE at altitudes of 30 km. To construct a representative model developed to m = n = 720, ground-based magnetic data should be replaced by data of balloon magnetic surveys for altitudes of ˜30 km. The results of investigations were confirmed by a balloon experiment conducted by Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation of the Russian Academy of Sciences and the Moscow Aviation Institute.

  9. Micromagnetic simulations of thermally activated magnetization reversal of nanoscale magnets

    NASA Astrophysics Data System (ADS)

    Brown, Gregory; Novotny, M. A.; Rikvold, Per Arne

    2000-05-01

    Numerical integration of a stochastic Landau-Lifshitz-Gilbert equation is used to study dynamic processes in single-domain nanoscale magnets at nonzero temperatures. Special attention is given to including thermal fluctuations as a Langevin term, and the fast multipole method is used to calculate dipole-dipole interactions. It is feasible to simulate these dynamics on the nanosecond time scale for spatial discretizations that involve on the order of 104 nodes using a desktop workstation. The nanoscale magnets considered here are single pillars with large aspect ratio. Hysteresis-loop simulations are employed to study the stable and metastable configurations of the magnetization. Each pillar has magnetic end caps. In a time-dependent field the magnetization of the pillars is observed to reverse via nucleation, propagation, and coalescence of the end caps. In particular, the end caps propagate into the magnet and meet near the middle. A relatively long-lived defect is formed when end caps with opposite vorticity meet. Fluctuations are more important in the reversal of the magnetization for fields weaker than the zero-temperature coercive field, where the reversal is thermally activated. In this case, the process must be described by its statistical properties, such as the distribution of switching times, averaged over a large number of independent thermal histories.

  10. Aroostook Sunshine: An Educational Simulation about Life in Maine.

    ERIC Educational Resources Information Center

    Association of Aroostook Indians, Houlton, ME.

    Designed for instruction at the secondary level, this curriculum guide focuses on simulated classroom experiences in prejudice and minority race relations and content materials relative to Northeast Woodland American Indian history and culture. Knowledge of the following are cited as major unit objectives: (1) Indian cultural contributions; (2)…

  11. eRMHD simulations of jets with helical magnetic fields

    NASA Astrophysics Data System (ADS)

    Roca-Sogorb, M.; Perucho, M.; Gómez, J. L.; Martí, J. M.; Antón, L.; Aloy, M. A.; Agudo, I.

    We present numerical magnetohydrodynamic and emission (eRMHD) simulations of relativistic jets in active galactic nuclei. We focus our study on the role played by the magnetic field in the dynamics of the jet, analyzing the balance of the main driving forces which determine the jet evolution. Overpressured jets with different magnetizations are considered in order to study their influence in the jet collimation, confinement and overall stability. Computation of the synchrotron emission from these models allows a direct comparison with actual sources. We find that the relative brightness of the knots associated with the recollimation shocks decreases with increasing magnetization, suggesting that overpressured jets presenting stationary components may have a relatively weak magnetization, with magnetic fields of the order of equipartition or below.

  12. Simulations of the magnetization and magnetoviscosity of dilute magnetic fluids

    NASA Astrophysics Data System (ADS)

    Sanchez Toro, Jorge Hernan

    In this work was studied the rotational Brownian motion of magnetic spherical and tri-axial ellipsoidal particles suspended in a Newtonian fluid, in the dilute suspension limit, under applied shear and magnetic fields by Brownian dynamics simulation to determine the magnetization and magnetoviscosity of the suspension. The algorithm describing the change in the magnetization and magnetoviscosity of the suspension was derived from the stochastic angular momentum equation using the fluctuation-dissipation theorem and a quaternion formulation of orientation space. Results are presented for the response of dilute suspensions of magnetic nanoparticles to constant and transient magnetic fields with and without simple shear flow fields. Simulation results are in agreement with the Langevin function for equilibrium magnetization and with single-exponential relaxation from equilibrium at small fields using Perrin's effective relaxation time. Dynamic susceptibilities for ellipsoidal particles of different aspect ratios were obtained from the response to oscillating magnetic fields of different frequencies and described by Debye's model for the complex susceptibility using Perrin's effective relaxation time. Suspensions of ellipsoidal particles show a significant effect of aspect ratio on the intrinsic magnetoviscosity of the suspension, and this effect is more pronounced as the aspect ratio becomes more extreme. The use of an effective rotational diffusion coefficient Dr,eff collapses the normalized intrinsic magnetoviscosity of all suspensions to a master curve as a function of Peclet number and the Langevin parameter alpha = (mu0muH)/(kBT), up to a critical value of alpha for which the results for suspensions of spherical particles deviate from those of suspensions of ellipsoids. This discrepancy is attributed to the action of the shear-torque on the ellipsoidal particles, which tends to orient the particles in the direction of maximum deformation of the simple shear flow

  13. Magnet reliability in the Fermilab Main Injector and implications for the ILC

    SciTech Connect

    Tartaglia, M.A.; Blowers, J.; Capista, D.; Harding, D.J.; Kiemschies, O.; Rahimzadeh-Kalaleh, S.; Tompkins, J.C.; /Fermilab

    2007-08-01

    The International Linear Collider reference design requires over 13000 magnets, of approximately 135 styles, which must operate with very high reliability. The Fermilab Main Injector represents a modern machine with many conventional magnet styles, each of significant quantity, that has now accumulated many hundreds of magnet-years of operation. We review here the performance of the magnets built for this machine, assess their reliability and categorize the failure modes, and discuss implications for reliability of similar magnet styles expected to be used at the ILC.

  14. SPH simulations of magnetic fields in galaxy clusters

    NASA Astrophysics Data System (ADS)

    Dolag, K.; Bartelmann, M.; Lesch, H.

    1999-08-01

    We perform cosmological, hydrodynamic simulations of magnetic fields in galaxy clusters. The computational code combines the special-purpose hardware Grape for calculating gravitational interaction, and smooth-particle hydrodynamics for the gas component. We employ the usual MHD equations for the evolution of the magnetic field in an ideally conducting plasma. As a first application, we focus on the question what kind of initial magnetic fields yield final field configurations within clusters which are compatible with Faraday-rotation measurements. Our main results can be summarised as follows: (i) Initial magnetic field strengths are amplified by approximately three orders of magnitude in cluster cores, one order of magnitude above the expectation from spherical collapse. (ii) Vastly different initial field configurations (homogeneous or chaotic) yield results that cannot significantly be distinguished. (iii) Micro-Gauss fields and Faraday-rotation observations are well reproduced in our simulations starting from initial magnetic fields of ~ 10(-9) G strength at redshift 15. Our results show that (i) shear flows in clusters are crucial for amplifying magnetic fields beyond simple compression, (ii) final field configurations in clusters are dominated by the cluster collapse rather than by the initial configuration, and (iii) initial magnetic fields of order 10(-9) G are required to match Faraday-rotation observations in real clusters.

  15. The design and manufacture of the Fermilab Main Injector Dipole Magnet

    SciTech Connect

    Brown, B.C.; Chester, N.S.; Harding, D.J.; Martin, P.S.

    1992-03-01

    Fermilab`s new Main Injector Ring (MIR) will replace the currently operating Main Ring to provide 150 GeV Proton and Antiproton beams for Tevetron injection, and rapid cycling, high intensity, 120 GeV Proton beams for Antiproton production. To produce and maintain the required high beam quality, high intensity, and high repetition rate, conventional dipole magnets with laminated iron core and water cooled copper conductor were chosen as the bending magnet. A new magnet design having low inductance, large copper cross section, and field uniformity sufficient for high intensity injection and efficient slow resonant extraction, is required to obtain the needed geometric aperture, dynamic aperture, and operational reliability. The current Main Injector Ring lattice design requires the use of 344 of these magnets. 216 of these magnets are to be 6 m long, and 128 are to be 4 m long.

  16. The design and manufacture of the Fermilab Main Injector Dipole Magnet

    SciTech Connect

    Brown, B.C.; Chester, N.S.; Harding, D.J.; Martin, P.S.

    1992-03-01

    Fermilab's new Main Injector Ring (MIR) will replace the currently operating Main Ring to provide 150 GeV Proton and Antiproton beams for Tevetron injection, and rapid cycling, high intensity, 120 GeV Proton beams for Antiproton production. To produce and maintain the required high beam quality, high intensity, and high repetition rate, conventional dipole magnets with laminated iron core and water cooled copper conductor were chosen as the bending magnet. A new magnet design having low inductance, large copper cross section, and field uniformity sufficient for high intensity injection and efficient slow resonant extraction, is required to obtain the needed geometric aperture, dynamic aperture, and operational reliability. The current Main Injector Ring lattice design requires the use of 344 of these magnets. 216 of these magnets are to be 6 m long, and 128 are to be 4 m long.

  17. Discovery of the Pre-Main Sequence Progenitors of the Magnetic Ap/Bp Stars?

    NASA Astrophysics Data System (ADS)

    Drouin, Dominic; Wade, Gregg; Bagnulo, S.; Landstreet, J. D.; Mason, E.; Monin, D.; Silvester, J.; Alecian, E.; Catala, C.; Bohm, T.; Bouret, J.-C.; Donati, J.-F.

    2005-08-01

    The magnetic Ap/Bp stars represent about 5% of all intermediatemass main sequence stars, and are characterised by strong, globallyordered surface magnetic fields. The physical impact of the presence of these fields is clear: atmospheric structure, photospheric chemical abundances, mass loss, rotation, and ultimately stellar evolution are all modified, to various extents, due to the interaction of the magnetic field with the stellar plasma. Remarkably, the origin of these magnetic fields remains a total mystery. In order to trace the presence of these fields back to the premain sequence (PMS), we have undertaken an extensive search for magnetic fields in the Herbig Ae/Be (HAeBe) stars, the PMS progenitors of the main sequence intermediate-mass stars. Using both the FORS1 spectropolarimeter at the ESO-VLT and the brand-new ESPaDOnS spectropolarimeter at the CFHT, we have surveyed over 50 HAeBe stars for the presence of longitudinal magnetic fields. Here we review the details of our investigation, and announce the detection of magnetic fields and chemical peculiarities in the HAeBe stars HD 72106 and HD 101412. These detections may well represent the identification of the pre-main sequence progenitors of the magnetic Ap/Bp stars. At the same time, we fail to confirm claims by Hubrig et al. (2004) of the presence of magnetic fields in the Herbig Ae star HD 139614.

  18. Evidence of magnetic field decay in massive main-sequence stars

    NASA Astrophysics Data System (ADS)

    Fossati, L.; Schneider, F. R. N.; Castro, N.; Langer, N.; Simón-Díaz, S.; Müller, A.; de Koter, A.; Morel, T.; Petit, V.; Sana, H.; Wade, G. A.

    2016-08-01

    A significant fraction of massive main-sequence stars show strong, large-scale magnetic fields. The origin of these fields, their lifetimes, and their role in shaping the characteristics and evolution of massive stars are currently not well understood. We compile a catalogue of 389 massive main-sequence stars, 61 of which are magnetic, and derive their fundamental parameters and ages. The two samples contain stars brighter than magnitude 9 in the V-band and range in mass between 5 and 100 M⊙. We find that the fractional main-sequence age distribution of all considered stars follows what is expected for a magnitude limited sample, while that of magnetic stars shows a clear decrease towards the end of the main sequence. This dearth of old magnetic stars is independent of the choice of adopted stellar evolution tracks, and appears to become more prominent when considering only the most massive stars. We show that the decreasing trend in the distribution is significantly stronger than expected from magnetic flux conservation. We also find that binary rejuvenation and magnetic suppression of core convection are unlikely to be responsible for the observed lack of older magnetic massive stars, and conclude that its most probable cause is the decay of the magnetic field, over a time span longer than the stellar lifetime for the lowest considered masses, and shorter for the highest masses. We then investigate the spin-down ages of the slowly rotating magnetic massive stars and find them to exceed the stellar ages by far in many cases. The high fraction of very slowly rotating magnetic stars thus provides an independent argument for a decay of the magnetic fields.

  19. Spatial-temporal dynamics of auroras during the magnetic storm main phase

    NASA Astrophysics Data System (ADS)

    Kornilova, T. A.; Kornilov, I. A.

    2009-12-01

    The structure and dynamics of auroras in the midnight sector during substorms, which develop during the magnetic storm main phase as compared to the characteristics of a typical auroral substorm, have been studied using the ground-based and satellite observations. It has been found out that a difference from the classical substorm is observed in auroras during the magnetic storm main phase. At the beginning of the storm main phase, the series of pseudobreakups with the most pronounced jump-like motion toward the equator shifts to lower latitudes. The substorm expansion phase can be observed not only as arc jumps to higher latitudes but also as an explosive expansion of a bright diffuse luminosity in all directions. During the magnetic storm main phase, auroras are mainly characterized by the presence of stable extensive rayed structures and by the simultaneous existence of different auroral forms, typical of different substorm phases, in the TV camera field of view.

  20. Recent electron-cloud simulation results for the main damping rings of the NLC and TESLA linear colliders

    SciTech Connect

    Pivi, M.; Raubenheimer, T.O.; Furman, M.A.

    2003-05-01

    In the beam pipe of the Main Damping Ring (MDR) of the Next Linear Collider (NLC), ionization of residual gases and secondary emission give rise to an electron-cloud which stabilizes to equilibrium after few bunch trains. In this paper, we present recent computer simulation results for the main features of the electron cloud at the NLC and preliminary simulation results for the TESLA main damping rings, obtained with the code POSINST that has been developed at LBNL, and lately in collaboration with SLAC, over the past 7 years. Possible remedies to mitigate the effect are also discussed. We have recently included the possibility to simulate different magnetic field configurations in our code including solenoid, quadrupole, sextupole and wiggler.

  1. MLS, a magnetic logic simulator for magnetic bubble logic design

    NASA Astrophysics Data System (ADS)

    Kinsman, Thomas B.; Cendes, Zoltan J.

    1987-04-01

    A computer program that simulates the logic functions of magnetic bubble devices has been developed. The program uses a color graphics screen to display the locations of bubbles on a chip during operation. It complements the simulator previously developed for modeling bubble devices on the gate level [Smith et al., IEEE Trans. Magn. MAG-19, 1835 (1983); Smith and Kryder, ibid. MAG-21, 1779 (1985)]. This new tool simplifies the design and testing of bubble logic devices, and facilitates the development of complicated LSI bubble circuits. The program operation is demonstrated with the design of an in-stream faulty loop compensator using bubble logic.

  2. Laboratory simulation of astrophysical magnetic turbulence

    NASA Astrophysics Data System (ADS)

    Gattamraju, Ravindra Kumar; Chatterjee, Gourab; Singh, Prahshant; Adak, Amitava; Lad, Amit D.; Schoeffler, K. M.; Silva, L. O.; Sengupta, Sudip; Kaw, P. K.; Das, Amita

    2015-11-01

    Giant magnetic fields (102-103 megagauss) are created when a relativistic intensity (>= 1018 W cm-2), ultrashort laser pulse interacts with plasma created on a solid. Here, we map out the temporal evolution of turbulence in magnetic field. We measure giant magnetic field on a micron scale spatial and femtosecond time resolution using pump-probe Cotton-Mouton polarimetry. The plasma created by an 800 nm laser is probed at density of ~1022 electrons/cc at 266 nm. This density is so far the highest at which plasma probing has been performed. Fourier spectra of the spatial polarigrams show power law behavior indicative of turbulence. Interestingly, the exponent of the power law changes from one value for the initial, fast electron dominated regime to another value at 10s of picoseconds, where ions dominate the behavior. This may be the first time such a transition of the mediation of turbulence has been captured. We present a model and particle-in-cell simulations which reproduce the data very well. Our results mimic observations of kinetic Alfven wave turbulence in earth's magnetosheath, solar flares and solar wind, indicating that we are now opening earth bound laboratory for simulating astrophysical magnetic environments.

  3. Magnetohydrodynamic simulations of global accretion disks with vertical magnetic fields

    SciTech Connect

    Suzuki, Takeru K.; Inutsuka, Shu-ichiro

    2014-04-01

    We report results of three-dimensional magnetohydrodynamical (MHD) simulations of global accretion disks threaded with weak vertical magnetic fields. We perform the simulations in the spherical coordinates with different temperature profiles and accordingly different rotation profiles. In the cases with a spatially constant temperature, because the rotation frequency is vertically constant in the equilibrium condition, general properties of the turbulence excited by magnetorotational instability are quantitatively similar to those obtained in local shearing box simulations. On the other hand, in the cases with a radially variable temperature profile, the vertical differential rotation, which is inevitable in the equilibrium condition, winds up the magnetic field lines in addition to the usual radial differential rotation. As a result, the coherent wound magnetic fields contribute to the Maxwell stress in the surface regions. We obtain nondimensional density and velocity fluctuations ∼0.1-0.2 at the midplane. The azimuthal power spectra of the magnetic fields show shallower slopes, ∼m {sup 0} – m {sup –1}, than those of velocity and density. The Poynting flux associated with the MHD turbulence drives intermittent and structured disk winds as well as sound-like waves toward the midplane. The mass accretion mainly occurs near the surfaces, and the gas near the midplane slowly moves outward in the time domain of the present simulations. The vertical magnetic fields are also dragged inward in the surface regions, while they stochastically move outward and inward around the midplane. We also discuss an observational implication of induced spiral structure in the simulated turbulent disks.

  4. MAGNETIC FIELDS IN COSMOLOGICAL SIMULATIONS OF DISK GALAXIES

    SciTech Connect

    Pakmor, Rüdiger; Marinacci, Federico; Springel, Volker

    2014-03-01

    Observationally, magnetic fields reach equipartition with thermal energy and cosmic rays in the interstellar medium of disk galaxies such as the Milky Way. However, thus far cosmological simulations of the formation and evolution of galaxies have usually neglected magnetic fields. We employ the moving-mesh code AREPO to follow for the first time the formation and evolution of a Milky Way-like disk galaxy in its full cosmological context while taking into account magnetic fields. We find that a prescribed tiny magnetic seed field grows exponentially by a small-scale dynamo until it saturates around z = 4 with a magnetic energy of about 10% of the kinetic energy in the center of the galaxy's main progenitor halo. By z = 2, a well-defined gaseous disk forms in which the magnetic field is further amplified by differential rotation, until it saturates at an average field strength of ∼6 μG in the disk plane. In this phase, the magnetic field is transformed from a chaotic small-scale field to an ordered large-scale field coherent on scales comparable to the disk radius. The final magnetic field strength, its radial profile, and the stellar structure of the disk compare well with observational data. A minor merger temporarily increases the magnetic field strength by about a factor of two, before it quickly decays back to its saturation value. Our results are highly insensitive to the initial seed field strength and suggest that the large-scale magnetic field in spiral galaxies can be explained as a result of the cosmic structure formation process.

  5. Kinetic simulations of magnetized capacitively coupled discharges

    NASA Astrophysics Data System (ADS)

    Trieschmann, Jan; Shihab, Mohammed; Eremin, Denis; Brinkmann, Ralf Peter; Schulze, Julian; Mussenbrock, Thomas

    2012-10-01

    Capacitive high frequency discharges are of crucial importance in the context of plasma etching, deposition and surface modification. As these single or multiple frequency discharges are oftentimes operated at low pressures of less than a few pascal, a high plasma density is commonly achieved with the use of external magnetic fields. In this work kinetic simulations are used to investigate the effect of inhomogeneous external magnetic fields on the discharge dynamics in a strongly nonlocal pressure regime. We found that capacitively coupled discharges can be largely asymmetrized by applying strong magnetic fields in front of a given target electrode. This not only has an effect on the plasma density, but also on the ion energy distribution functions (IEDF) at the electrodes and on the acceleration of fast electrons in the plasma sheath regions. In consequence in the discharge currents a generation of higher harmonics of the driving frequency can be observed. We investigate these scenarios in terms of 1D-3V Particle in Cell simulations.

  6. Exchange interaction energy in magnetic recording simulation

    SciTech Connect

    Igarashi, Masukazu Tonooka, Shun; Katada, Hiroyuki; Maeda, Maki; Hara, Miki; Wood, Roger

    2015-05-07

    Based on a phenomenological theory, micromagnetic simulations and experiments are used to evaluate an improved function for the exchange interaction between magnetic particles in perpendicular recording media. Assuming diluted spin layers in the particle boundary and a gradual rather than abrupt rotation of magnetization between grain cores, the exchange energy is better described by an even power series of θ, rather than a cosine function. The conventional cosine function does not have a restoring torque near θ = π and adjacent grains tend to align strictly antiparallel. In contrast, using a power series of θ, adjacent grains tend to align at a small angle away from θ = π. This gives rise to a small in-plane magnetization component and therefore a distinct peak in in-plane susceptibility is observed around H = 0. From magnetization measurements of a real medium, a peak is observed around H = 0, which matches with an assumption of 2 or 3 spin layers. In some situations, the exchange interaction between discretized cells for numerical calculation is better described by a power series rather than a cosine function.

  7. Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex

    2010-01-01

    Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten-Lan-van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfv enic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond-chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet-Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.

  8. Simulations of Interacting Magnetic Micro-swimmers

    NASA Astrophysics Data System (ADS)

    Keaveny, Eric; Maxey, Martin

    2007-03-01

    Following a recent realization of artificial micro-swimming (Dreyfus et. al., Nature, 437, 862-865), we conduct simulations of a swimmer whose mechanism of propulsion is the magnetically driven undulation of a flagellum-like tail composed of chemically linked paramagnetic beads. In our model, the tail is treated as a series of spheres tied together by inextensible, bendable links. The spheres interact magnetically through mutual dipole interactions, and hydrodynamic interactions are achieved by the force-coupling method. Building on our previous results, we examine the interactions between multiple swimmers employing a flagellum beating strategy as well as those using a rotary propulsion scheme. In addition to swimmer-swimmer interactions, the effects of a nearby surface on the behavior of a micro-swimmer will be discussed.

  9. BOOSTER MAIN MAGNET POWER SUPPLY IMPROVEMENTS FOR NASA SPACE RADIATION LABORATORY AT BNL

    SciTech Connect

    MARNERIS,I.BROWN,K.A.GLENN,J.W.MCNERNEY,A., MORRIS, J., SANDBERG,J., SAVATTERI, S.

    2003-05-12

    The NASA Space Radiation Laboratory (NSRL), constructed at Brookhaven National Laboratory, under contract from NASA, is a new experimental facility, taking advantage of heavy-ion beams from the Brookhaven Alternating Gradient Synchrotron (AGS) Booster accelerator, to study radiation effect on humans, for prolonged space missions beyond the protective terrestrial magnetosphere. This paper describes the modifications and operation of the Booster Main Magnet Power Supply (MMPS) for NSRL applications. The requirement is to run up to 1 sec flattops as high as 5000 Amps with 25% duly cycle. The controls for the Main Magnet Power Supply were modified, including the Booster Main Magnet application program, to enable flattop operation with low ripple and spill control. An active filter (AF) consisting of a {+-}120 volts, {+-}700 Amps power supply transformer coupled through a filter choke, in series with the Main Magnet voltage, was added to the system to enable further ripple reduction during the flattops. We will describe the spill servo system, designed to provide a uniform beam current, during the flattop. Results from system commissioning will be presented.

  10. Multiscale Simulations of Magnetic Island Coalescence

    NASA Technical Reports Server (NTRS)

    Dorelli, John C.

    2010-01-01

    We describe a new interactive parallel Adaptive Mesh Refinement (AMR) framework written in the Python programming language. This new framework, PyAMR, hides the details of parallel AMR data structures and algorithms (e.g., domain decomposition, grid partition, and inter-process communication), allowing the user to focus on the development of algorithms for advancing the solution of a systems of partial differential equations on a single uniform mesh. We demonstrate the use of PyAMR by simulating the pairwise coalescence of magnetic islands using the resistive Hall MHD equations. Techniques for coupling different physics models on different levels of the AMR grid hierarchy are discussed.

  11. Accurate simulation of the electron cloud in the Fermilab Main Injector with VORPAL

    SciTech Connect

    Lebrun, Paul L.G.; Spentzouris, Panagiotis; Cary, John R.; Stoltz, Peter; Veitzer, Seth A.; /Tech-X, Boulder

    2010-05-01

    Precision simulations of the electron cloud at the Fermilab Main Injector have been studied using the plasma simulation code VORPAL. Fully 3D and self consistent solutions that includes E.M. field maps generated by the cloud and the proton bunches have been obtained, as well detailed distributions of the electron's 6D phase space. We plan to include such maps in the ongoing simulation of the space charge effects in the Main Injector. Simulations of the response of beam position monitors, retarding field analyzers and microwave transmission experiments are ongoing.

  12. Magnetic stochasticity in gyrokinetic simulations of plasma microturbulence

    SciTech Connect

    Nevins, W M; Wang, E; Candy, J

    2010-02-12

    Analysis of the magnetic field structure from electromagnetic simulations of tokamak ion temperature gradient turbulence demonstrates that the magnetic field can be stochastic even at very low plasma pressure. The degree of magnetic stochasticity is quantified by evaluating the magnetic diffusion coefficient. We find that the magnetic stochasticity fails to produce a dramatic increase in the electron heat conductivity because the magnetic diffusion coefficient remains small.

  13. Reduction of Marine Magnetic Data for Modeling the Main Field of the Earth

    NASA Technical Reports Server (NTRS)

    Baldwin, R. T.; Ridgway, J. R.; Davis, W. M.

    1992-01-01

    The marine data set archived at the National Geophysical Data Center (NGDC) consists of shipborne surveys conducted by various institutes worldwide. This data set spans four decades (1953, 1958, 1960-1987), and contains almost 13 million total intensity observations. These are often less than 1 km apart. These typically measure seafloor spreading anomalies with amplitudes of several hundred nanotesla (nT) which, since they originate in the crust, interfere with main field modeling. The source for these short wavelength features are confined within the magnetic crust (i.e., sources above the Curie isotherm). The main field, on the other hand, is of much longer wavelengths and originates within the earth's core. It is desirable to extract the long wavelength information from the marine data set for use in modeling the main field. This can be accomplished by averaging the data along the track. In addition, those data which are measured during periods of magnetic disturbance can be identified and eliminated. Thus, it should be possible to create a data set which has worldwide data distribution, spans several decades, is not contaminated with short wavelengths of the crustal field or with magnetic storm noise, and which is limited enough in size to be manageable for the main field modeling. The along track filtering described above has proved to be an effective means of condensing large numbers of shipborne magnetic data into a manageable and meaningful data set for main field modeling. Its simplicity and ability to adequately handle varying spatial and sampling constraints has outweighed consideration of more sophisticated approaches. This filtering technique also provides the benefits of smoothing out short wavelength crustal anomalies, discarding data recorded during magnetically noisy periods, and assigning reasonable error estimates to be used in the least square modeling. A useful data set now exists which spans 1953-1987.

  14. Magnetic Testing, and Modeling, Simulation and Analysis for Space Applications

    NASA Technical Reports Server (NTRS)

    Boghosian, Mary; Narvaez, Pablo; Herman, Ray

    2012-01-01

    The Aerospace Corporation (Aerospace) and Lockheed Martin Space Systems (LMSS) participated with Jet Propulsion Laboratory (JPL) in the implementation of a magnetic cleanliness program of the NASA/JPL JUNO mission. The magnetic cleanliness program was applied from early flight system development up through system level environmental testing. The JUNO magnetic cleanliness program required setting-up a specialized magnetic test facility at Lockheed Martin Space Systems for testing the flight system and a testing program with facility for testing system parts and subsystems at JPL. The magnetic modeling, simulation and analysis capability was set up and performed by Aerospace to provide qualitative and quantitative magnetic assessments of the magnetic parts, components, and subsystems prior to or in lieu of magnetic tests. Because of the sensitive nature of the fields and particles scientific measurements being conducted by the JUNO space mission to Jupiter, the imposition of stringent magnetic control specifications required a magnetic control program to ensure that the spacecraft's science magnetometers and plasma wave search coil were not magnetically contaminated by flight system magnetic interferences. With Aerospace's magnetic modeling, simulation and analysis and JPL's system modeling and testing approach, and LMSS's test support, the project achieved a cost effective approach to achieving a magnetically clean spacecraft. This paper presents lessons learned from the JUNO magnetic testing approach and Aerospace's modeling, simulation and analysis activities used to solve problems such as remnant magnetization, performance of hard and soft magnetic materials within the targeted space system in applied external magnetic fields.

  15. Status of Electron-Cloud Build-Up Simulations for the Main Injector

    SciTech Connect

    Furman, M. A.; Kourbanis, I.; Zwaska, R. M.

    2009-05-04

    We provide a brief status report on measurements and simulations of the electron cloud in the Fermilab Main Injector. Areas of agreement and disagreement are spelled out, along with their possible significance.

  16. Detecting magnetic fields of upper-main-sequence stars with FORS1 at ANTU.

    NASA Astrophysics Data System (ADS)

    Bagnulo, S.; Szeifert, T.; Wade, G. A.; Landstreet, J. D.; Mathys, G.

    2001-06-01

    During the night between 22 and 23 March 2001, the VLT unit telescope ANTU was pointed to a 6th-magnitude A-type star to obtain several low-resolution spectra in circular polarisation with FORS1. Two nights later, the same exercise was repeated selecting a second A-type star of similar magnitude. The outcome of this experiment was the firm detection of a magnetic field in an upper-main-sequence star, HD 94660. It is the first time that a VLT unit telescope was (successfully) used to detect magnetic fields in non degenerate stars.

  17. Main magnetic field of Jupiter and its implications for future orbiter missions

    NASA Technical Reports Server (NTRS)

    Acuna, M. H.; Ness, N. F.

    1975-01-01

    A very strong planetary magnetic field and an enormous magnetosphere with extremely intense radiation belts exist at Jupiter. Pioneer 10 and 11 fly-bys confirmed and extended the earlier ground based estimates of many of these characteristics but left unanswered or added to the list of several important and poorly understood features: the source mechanism and location of decametric emissions, and the absorption effects by the natural satellites Amalthea, Io, Europa and Ganymede. High inclination orbits (exceeding 60 deg) with low periapses (less than 2 Jupiter radii) are required to map the radiation belts and main magnetic field of Jupiter accurately so as to permit full investigation of these and associated phenomena.

  18. Integrated simulation and modeling capability for alternate magnetic fusion concepts

    SciTech Connect

    Cohen, B. I.; Hooper, E.B.; Jarboe, T. R.; LoDestro, L. L.; Pearlstein, L. D.; Prager, S. C.; Sarff, J. S.

    1998-11-03

    This document summarizes a strategic study addressing the development of a comprehensive modeling and simulation capability for magnetic fusion experiments with particular emphasis on devices that are alternatives to the mainline tokamak device. A code development project in this area supports two defined strategic thrust areas in the Magnetic Fusion Energy Program: (1) comprehensive simulation and modeling of magnetic fusion experiments and (2) development, operation, and modeling of magnetic fusion alternate- concept experiment

  19. Kinetic Vlasov simulations of collisionless magnetic reconnection

    SciTech Connect

    Schmitz, H.; Grauer, R.

    2006-09-15

    A fully kinetic Vlasov simulation of the Geospace Environment Modeling Magnetic Reconnection Challenge is presented. Good agreement is found with previous kinetic simulations using particle in cell (PIC) codes, confirming both the PIC and the Vlasov code. In the latter the complete distribution functions f{sub k} (k=i,e) are discretized on a numerical grid in phase space. In contrast to PIC simulations, the Vlasov code does not suffer from numerical noise and allows a more detailed investigation of the distribution functions. The role of the different contributions of Ohm's law are compared by calculating each of the terms from the moments of the f{sub k}. The important role of the off-diagonal elements of the electron pressure tensor could be confirmed. The inductive electric field at the X line is found to be dominated by the nongyrotropic electron pressure, while the bulk electron inertia is of minor importance. Detailed analysis of the electron distribution function within the diffusion region reveals the kinetic origin of the nongyrotropic terms.

  20. Numerical simulation of magnetic compression on a field-reversed configuration plasma

    NASA Astrophysics Data System (ADS)

    Kanki, T.; Suzuki, Y.; Okada, S.; Goto, S.

    1999-12-01

    A two-dimensional magnetohydrodynamic (MHD) simulation of an axial magnetic compression on a field-reversed configuration (FRC) plasma is carried out for the parameter range of a corresponding experiment conducted on the FRC Injection Experiment (FIX) [S. Okada et al., 17th IAEA Fusion Energy Conference 1998 (International Atomic Energy Agency, Vienna) (in press)]. The simulation results show that during the initial stage of the magnetic compression the front part of the FRC plasma is mainly compressed radially, and that after this stage, the compression is primarily axial. Of particular interest is expected that the closed magnetic flux surfaces of the FRC can be retained without any degradation during the magnetic compression process. Further, it is observed in the simulation that the axial magnetic compression enables a transition of the MHD equilibrium from a long and thin to a short and fat FRC. The effects of this magnetic compression on FRC plasmas are discussed.

  1. Characteristics on electodynamic suspension simulator with HTS levitation magnet

    NASA Astrophysics Data System (ADS)

    Lee, J.; Bae, D. K.; Sim, K.; Chung, Y. D.; Lee, Y.-S.

    2009-10-01

    High- Tc superconducting (HTSC) electrodynamic suspension (EDS) system basically consists of the HTSC levitation magnet and the ground conductor. The levitation force of EDS system is forms by the interaction between the moving magnetic field produced by the onboard levitation magnet and the induced magnetic field produced by eddy current in the ground conductor. This paper deals with the characteristics of the EDS simulators with high- Tc superconducting (HTS) levitation magnet. Two EDS simulator systems, rotating type EDS simulator and static type EDS simulator, were studied in this paper. The rotating type EDS simulator consists of a HTS levitation magnet and a 1.5 m diameter rotating ground conductor, a motor, the supporting structure and force measuring devices. In the static type EDS simulator, instead of moving magnetic field, AC current was applied to the fixed HTS levitation magnet to induce the eddy current. The static type EDS simulator consists of a HTS levitation magnet, a ground conductor, force measuring devices and supporting structure. The double-pancake type HTSC levitation magnet was designed, manufactured and tested in the EDS simulator.

  2. Control and performance of the AGS and AGS Booster Main Magnet Power Supplies

    SciTech Connect

    Reece, R.K.; Casella, R.; Culwick, B.; Geller, J.; Marneris, I.; Sandberg, J.; Soukas, A.; Zhang, S.Y.

    1993-06-01

    Techniques for precision control of the main magnet power supplies for the AGS and AGS Booster synchrotron will be discussed. Both synchrotrons are designed to operate in a Pulse-to-Pulse Modulation (PPM) environment with a Supercycle Generator defining and distributing global timing events for the AGS Facility. Details of modelling, real-time feedback and feedforward systems, generation and distribution of real time field data, operational parameters and an overview of performance for both machines are included.

  3. Control and performance of the AGS and AGS Booster Main Magnet Power Supplies

    SciTech Connect

    Reece, R.K.; Casella, R.; Culwick, B.; Geller, J.; Marneris, I.; Sandberg, J.; Soukas, A.; Zhang, S.Y.

    1993-01-01

    Techniques for precision control of the main magnet power supplies for the AGS and AGS Booster synchrotron will be discussed. Both synchrotrons are designed to operate in a Pulse-to-Pulse Modulation (PPM) environment with a Supercycle Generator defining and distributing global timing events for the AGS Facility. Details of modelling, real-time feedback and feedforward systems, generation and distribution of real time field data, operational parameters and an overview of performance for both machines are included.

  4. MHD Simulation Heliospheric Magnetic Fields and Turbulence

    NASA Technical Reports Server (NTRS)

    Roberts, D. Aaron

    2005-01-01

    This talk will present a summary of our results on simulations of heliospheric structure and dynamics. We use a three-dimensional MHD code in spherical coordinates to produce a solar wind containing a rotating, tilted heliospheric current sheet, fast-slow stream and microstream shear layers, waves, 2-D turbulence, and pressure balanced structures that are input to the inner (superAlfvenic) boundary. The evolution of various combinations of these has led to a deeper understanding of sector structure, magnetic holes, fluctuation anisotropies, and general turbulent evolution. We show how the sectors are likely to be connected, how spiral fields can arise, and how field line diffusion can be caused by waves with transverse structure and microstream shears.

  5. Simulating frustrated magnetism with spinor Bose gases

    NASA Astrophysics Data System (ADS)

    Debelhoir, T.; Dupuis, N.

    2016-05-01

    Although there is a broad consensus on the fact that critical behavior in stacked triangular Heisenberg antiferromagnets—an example of frustrated magnets with competing interactions—is described by a Landau-Ginzburg-Wilson Hamiltonian with O(3 )×O(2 ) symmetry, the nature of the phase transition in three dimensions is still debated. We show that spin-one Bose gases provide us with a simulator of the O(3 )×O(2 ) model. Using a renormalization-group approach, we argue that the transition is weakly first order and shows pseudoscaling behavior, and give estimates of the pseudocritical exponent ν in 87Rb, 41K, and 7Li atom gases which can be tested experimentally.

  6. Hierarchical Fast Multipole Simulation of Magnetic Colloids

    NASA Astrophysics Data System (ADS)

    Günal, Yüksel; Visscher, Pieter

    1997-03-01

    We have extended the well-known "fast multipole"footnote L. F. Greengard and V. Rokhlin, J. Comp. Phys. 73 p. 325, 1987. methods for molecular-dynamics simulation of large systems of point charges to continuum systems, such as magnetic films or particulate suspensions. (These methods reduce the computational labor from O(N^2) to O(N log N) or O(N), the number of particles). We apply the method to the particular case of a colloidal dispersion of magnetized cylindrical particles. Our method is fully hierarchical, both upward and downward from the particle size scale. The force on each particle is calculated by grouping distant particles into large clusters, nearer particles into smaller clusters, and dividing the nearest particles into segments. The fineness with which the particles are divided is controlled by an error tolerance parameter. The field of each cluster or segment is computed from a multipole expansion. Distant periodic images are also treated as multipoles - this is much faster than standard Fourier-transform or Ewald summation techniques.

  7. Parallel magnetic field perturbations in gyrokinetic simulations

    SciTech Connect

    Joiner, N.; Hirose, A.; Dorland, W.

    2010-07-15

    At low beta it is common to neglect parallel magnetic field perturbations on the basis that they are of order beta{sup 2}. This is only true if effects of order beta are canceled by a term in the nablaB drift also of order beta[H. L. Berk and R. R. Dominguez, J. Plasma Phys. 18, 31 (1977)]. To our knowledge this has not been rigorously tested with modern gyrokinetic codes. In this work we use the gyrokinetic code GS2[Kotschenreuther et al., Comput. Phys. Commun. 88, 128 (1995)] to investigate whether the compressional magnetic field perturbation B{sub ||} is required for accurate gyrokinetic simulations at low beta for microinstabilities commonly found in tokamaks. The kinetic ballooning mode (KBM) demonstrates the principle described by Berk and Dominguez strongly, as does the trapped electron mode, in a less dramatic way. The ion and electron temperature gradient (ETG) driven modes do not typically exhibit this behavior; the effects of B{sub ||} are found to depend on the pressure gradients. The terms which are seen to cancel at long wavelength in KBM calculations can be cumulative in the ion temperature gradient case and increase with eta{sub e}. The effect of B{sub ||} on the ETG instability is shown to depend on the normalized pressure gradient beta{sup '} at constant beta.

  8. Study of road dust magnetic phases as the main carrier of potentially harmful trace elements.

    PubMed

    Bourliva, Anna; Papadopoulou, Lambrini; Aidona, Elina

    2016-05-15

    Mineralogical and morphological characteristics and heavy metal content of different fractions (bulk, non-magnetic fraction-NMF and magnetic fraction-MF) of road dusts from the city of Thessaloniki (Northern Greece) were investigated. Main emphasis was given on the magnetic phases extracted from these dusts. High magnetic susceptibility values were presented, whereas the MFs content of road dust samples ranged in 2.2-14.7 wt.%. Thermomagnetic analyses indicated that the dominating magnetic carrier in all road dust samples was magnetite, while the presence of hematite and iron sulphides in the investigated samples cannot be excluded. SEM/EDX analyses identified two groups of ferrimagnetic particles: spherules with various surface morphologies and textures and angular/aggregate particles with elevated heavy metal contents, especially Cr. The road dusts (bulk samples) were dominated by calcium, while the mean concentrations of trace elements decreased in the order Zn > Mn > Cu > Pb > Cr > Ni > V > Sn > As > Sb > Co > Mo > W > Cd. MFs exhibited significantly higher concentrations of trace elements compared to NMFs indicating that these potentially harmful elements (PHEs) are preferentially enriched in the MFs and highly associated with the ferrimagnetic particles. Hazard Index (HI) obtained for both adults and children through exposure to bulk dust samples were lower or close to the safe level (=1). On the contrary, the HIs for the magnetic phases indicated that both children and adults are experiencing potential health risk since HI for Cr was significantly higher than safe level. Cancer risk due to road dust exposure is low. PMID:26930312

  9. Main-Sequence CMEs as Magnetic Explosions: Compatibility with Observed Kinematics

    NASA Technical Reports Server (NTRS)

    Moore, Ron; Falconer, David; Sterling, Alphonse

    2004-01-01

    We examine the kinematics of 26 CMEs of the morphological main sequence of CMEs, those having the classic three-part bubble structure of (1) a bright front eveloping (2) a dark cavity within which rides (3) a bright blob/filamentary feature. Each CME is observed in Yohkoh/SXT images to originate from near the limb (> or equal to 0.7 R(sub Sun) from disk center). The basic data (from the SOHO LASCO CME Catalog) for the kinematics of each CME are the sequence of LASCO images of the CME, the time of each image, the measured radial distance of the front edge of the CME in each image, and the measured angular extent of the CME. About half of our CMEs (12) occur with a flare, and the rest (14) occur without a flare. While the average linear-fit speed of the flare CMEs (1000 km/s) is twice that of the non-flare CMEs (510 km/s), the flare CMEs and the non-flare CMEs are similar in that some have nearly flat velocity-height (radial extent) profiles (little acceleration), some have noticeably falling velocity profiles (noticeable deceleration), and the rest have velocity profiles that rise considerably through the outer corona (blatant acceleration). This suggests that in addition to sharing similar morphology, main-sequence CMEs all have basically the same driving mechanism. The observed radial progression of each of our 26 CMEs is fit by a simple model magnetic plasmoid that is in pressure balance with the radial magnetic field in the outer corona and that propels itself outward by magnetic expansion, doing no net work on its surroundings. On average over the 26 CMEs, this model fits the observations as well as the assumption of constant acceleration. This is compatible with main-sequence CMEs being magnetically driven, basically magnetic explosions, with the velocity profile in the outer corona being largely dictated by the initial Alfien speed in the CME (when the front is at approx. 3 (sub Sun), analogous to the mass of a main-sequence star dictating the luminosity.

  10. Microwave Transmission Through the Electron Cloud at the Fermilab Main Injector: Simulation and Comparison with Experiment

    SciTech Connect

    Lebrun, Paul L.G.; Veitzer, Seth Andrew; /Tech-X, Boulder

    2009-04-01

    Simulations of the microwave transmission properties through the electron cloud at the Fermilab Main Injector have been implemented using the plasma simulation code 'VORPAL'. Phase shifts and attenuation curves have been calculated for the lowest frequency TE mode, slightly above the cutoff frequency, in field free regions, in the dipoles and quadrupoles. Preliminary comparisons with experimental results for the dipole case are showed and will guide the next generation of experiments.

  11. Simulation of Electron Cloud Multipacting in Solenoidal Magnetic Field

    SciTech Connect

    Novokhatski, A

    2004-01-27

    A simulation algorithm is based on a numerical solution of the Vlasov equation for the distribution function of an electron cloud density in a cylindrical vacuum chamber with solenoidal magnetic field. The algorithm takes into consideration space charge effects. This approach improves the simulation of multipacting effects as it is free of statistical fluctuations. Simulation studies were carried for the SLAC B-factory vacuum chamber for different bunch patterns and solenoidal field strength. Space charge and the magnetic field limit the maximum density of the electron cloud. Magnetic resonant damping of multipacting was found in special cases of positron beam parameters and magnetic field amplitude.

  12. The MAIN Shirt: A Textile-Integrated Magnetic Induction Sensor Array

    PubMed Central

    Teichmann, Daniel; Kuhn, Andreas; Leonhardt, Steffen; Walter, Marian

    2014-01-01

    A system is presented for long-term monitoring of respiration and pulse. It comprises four non-contact sensors based on magnetic eddy current induction that are textile-integrated into a shirt. The sensors are technically characterized by laboratory experiments that investigate the sensitivity and measuring depth, as well as the mutual interaction between adjacent pairs of sensors. The ability of the device to monitor respiration and pulse is demonstrated by measurements in healthy volunteers. The proposed system (called the MAIN (magnetic induction) Shirt) does not need electrodes or any other skin contact. It is wearable, unobtrusive and can easily be integrated into an individual's daily routine. Therefore, the system appears to be a suitable option for long-term monitoring in a domestic environment or any other unsupervised telemonitoring scenario. PMID:24412900

  13. The MAIN Shirt: a textile-integrated magnetic induction sensor array.

    PubMed

    Teichmann, Daniel; Kuhn, Andreas; Leonhardt, Steffen; Walter, Marian

    2014-01-01

    A system is presented for long-term monitoring of respiration and pulse. It comprises four non-contact sensors based on magnetic eddy current induction that are textile-integrated into a shirt. The sensors are technically characterized by laboratory experiments that investigate the sensitivity and measuring depth, as well as the mutual interaction between adjacent pairs of sensors. The ability of the device to monitor respiration and pulse is demonstrated by measurements in healthy volunteers. The proposed system (called the MAIN (magnetic induction) Shirt) does not need electrodes or any other skin contact. It is wearable, unobtrusive and can easily be integrated into an individual's daily routine. Therefore, the system appears to be a suitable option for long-term monitoring in a domestic environment or any other unsupervised telemonitoring scenario. PMID:24412900

  14. Performance of the cold powered diodes and diode leads in the main magnets of the LHC

    NASA Astrophysics Data System (ADS)

    Willering, G. P.; Giloux, C.; Bajko, M.; Bednarek, M.; Bottura, L.; Charifoulline, Z.; Dahlerup-Petersen, K.; Dib, G.; D'Angelo, G.; Gharib, A.; Grand-Clement, L.; Izquierdo Bermudez, S.; Prin, H.; Roger, V.; Rowan, S.; Savary, F.; Tock, J.-Ph; Verweij, A.

    2015-12-01

    During quench tests in 2011 variations in resistance of an order of magnitude were found in the diode by-pass circuit of the main LHC magnets. An investigation campaign was started to understand the source, the occurrence and the impact of the high resistances. Many tests were performed offline in the SM18 test facility with a focus on the contact resistance of the diode to heat sink contact and the diode wafer temperature. In 2014 the performance of the diodes and diode leads of the main dipole bypass systems in the LHC was assessed during a high current qualification test. In the test a current cycle similar to a magnet circuit discharge from 11 kA with a time constant of 100 s was performed. Resistances of up to 600 μΩ have been found in the diode leads at intermediate current, but in general the high resistances decrease at higher current levels and no sign of overheating of diodes has been seen and the bypass circuit passed the test. In this report the performance of the diodes and in particular the contact resistances in the diode leads are analysed with available data acquired over more than 10 years from acceptance test until the main dipole training campaign in the LHC in 2015.

  15. Numerical simulations of magnetic reversal in layered spring magnets.

    SciTech Connect

    Jiang, J.S.; Kaper, H.G.; Leaf, G.K.

    2001-01-24

    This report summarizes the results of numerical investigations of magnetic reversal in layered spring magnets. A one-dimensional model is used of a film consisting of several atomic layers of soft material on top of several atomic layers of hard material. Each atomic layer is taken to be uniformly magnetized, and spatial inhomogeneities within an atomic layer are neglected. The state of such a system is described by a chain of magnetic spin vectors. Each spin vector behaves like a spinning top driven locally by the effective magnetic field and subject to damping (Landau-Lifshitz-Gilbert equation). A numerical integration scheme for the LLG equation is presented that is unconditionally stable and preserves the magnitude of the magnetization vector at all times. The results of numerical investigations for a bilayer in a rotating in-plane magnetic field show hysteresis with a basic period of 2{pi} at moderate fields and hysteresis with a basic period of {pi} (or any multiple thereof) at strong fields.

  16. Bunch coalescing and bunch rotation in the Fermilab Main Ring: Operational experience and comparison with simulations

    SciTech Connect

    Martin, P.S.; Wildman, D.W.

    1988-07-01

    The Fermilab Tevatron I proton-antiproton collider project requires that the Fermilab Main Ring produce intense bunches of protons and antiprotons for injection into the Tevatron. The process of coalescing a small number of harmonic number h=1113 bunches into a single bunch by bunch-rotating in a lower harmonic rf system is described.The Main Ring is also required to extract onto the antiproton production target bunches with as narrow a time spread as possible. This operation is also discussed. The operation of the bunch coalescing and bunch rotation are compared with simulations using the computer program ESME. 2 refs., 8 figs.

  17. Spherical core-shell magnetic particles constructed by main-chain palladium N-heterocyclic carbenes

    NASA Astrophysics Data System (ADS)

    Zhao, Huaixia; Li, Liuyi; Wang, Jinyun; Wang, Ruihu

    2015-02-01

    The encapsulation of the functional species on magnetic core is a facile approach for the synthesis of core-shell magnetic materials, and surface encapsulating matrices play crucial roles in regulating their properties and applications. In this study, two core-shell palladium N-heterocyclic carbene (NHC) particles (Fe3O4@PNP1 and Fe3O4@PNP2) were prepared by a one-pot reaction of semi-rigid tripodal imidazolium salts and palladium acetate in the presence of magnetite nanoparticles. The magnetite nanoparticles are encapsulated inside the main-chain palladium, which act as cores. The conjugated effects of triphenyltriazine and triphenylbenzene in the imidazolium salts have important influence on their physical properties and catalytic performances. Fe3O4@PNP2 shows better recyclability than Fe3O4@PNP1. Unexpectedly, Pd(ii) is well maintained after six consecutive catalytic runs in Fe3O4@PNP2, and Pd(0) and Pd(ii) coexist in Fe3O4@PNP1 under the same conditions; moreover, the morphologies of these spherical core-shell particles show no significant variation after six consecutive catalytic runs.The encapsulation of the functional species on magnetic core is a facile approach for the synthesis of core-shell magnetic materials, and surface encapsulating matrices play crucial roles in regulating their properties and applications. In this study, two core-shell palladium N-heterocyclic carbene (NHC) particles (Fe3O4@PNP1 and Fe3O4@PNP2) were prepared by a one-pot reaction of semi-rigid tripodal imidazolium salts and palladium acetate in the presence of magnetite nanoparticles. The magnetite nanoparticles are encapsulated inside the main-chain palladium, which act as cores. The conjugated effects of triphenyltriazine and triphenylbenzene in the imidazolium salts have important influence on their physical properties and catalytic performances. Fe3O4@PNP2 shows better recyclability than Fe3O4@PNP1. Unexpectedly, Pd(ii) is well maintained after six consecutive catalytic runs in

  18. Magnetic Null Points in Kinetic Simulations of Space Plasmas

    NASA Astrophysics Data System (ADS)

    Olshevsky, Vyacheslav; Deca, Jan; Divin, Andrey; Peng, Ivy Bo; Markidis, Stefano; Innocenti, Maria Elena; Cazzola, Emanuele; Lapenta, Giovanni

    2016-03-01

    We present a systematic attempt to study magnetic null points and the associated magnetic energy conversion in kinetic particle-in-cell simulations of various plasma configurations. We address three-dimensional simulations performed with the semi-implicit kinetic electromagnetic code iPic3D in different setups: variations of a Harris current sheet, dipolar and quadrupolar magnetospheres interacting with the solar wind, and a relaxing turbulent configuration with multiple null points. Spiral nulls are more likely created in space plasmas: in all our simulations except lunar magnetic anomaly (LMA) and quadrupolar mini-magnetosphere the number of spiral nulls prevails over the number of radial nulls by a factor of 3-9. We show that often magnetic nulls do not indicate the regions of intensive energy dissipation. Energy dissipation events caused by topological bifurcations at radial nulls are rather rare and short-lived. The so-called X-lines formed by the radial nulls in the Harris current sheet and LMA simulations are rather stable and do not exhibit any energy dissipation. Energy dissipation is more powerful in the vicinity of spiral nulls enclosed by magnetic flux ropes with strong currents at their axes (their cross sections resemble 2D magnetic islands). These null lines reminiscent of Z-pinches efficiently dissipate magnetic energy due to secondary instabilities such as the two-stream or kinking instability, accompanied by changes in magnetic topology. Current enhancements accompanied by spiral nulls may signal magnetic energy conversion sites in the observational data.

  19. Preliminary Results of Laboratory Simulation of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Zhang, Shou-Biao; Xie, Jin-Lin; Hu, Guang-Hai; Li, Hong; Huang, Guang-Li; Liu, Wan-Dong

    2011-10-01

    In the Linear Magnetized Plasma (LMP) device of University of Science and Technology of China and by exerting parallel currents on two parallel copper plates, we have realized the magnetic reconnection in laboratory plasma. With the emissive probes, we have measured the parallel (along the axial direction) electric field in the process of reconnection, and verified the dependence of reconnection current on passing particles. Using the magnetic probe, we have measured the time evolution of magnetic flux, and the measured result shows no pileup of magnetic flux, in consistence with the result of numerical simulation.

  20. Precise thermal control test demonstration on simulated space telescope main ring

    NASA Technical Reports Server (NTRS)

    Bettini, R. G.; Wegrich, R. D.

    1983-01-01

    A simulated section of the main ring of the Space Telescope, (ST) the part that holds the primary mirror, was manufactured and tested for thermal stability characteristics in a complex structural assembly. The other telescope subassemblies are also mounted on the main ring, which is constructed of a titanium alloy. The entire ring is wrapped in heater elements around the outside diameter to reduce the external temperature gradient effects by two orders of magnitude. A thermal vacuum test was performed using a stainless steel alloy tailored to represent the titanium ring's thermal characteristics. The tests examined the thermal performance and controllability of the test ring, the effects of a 24-hr slew manuever that produced worst-case environment changes, hot and cold simulation of predicted ST orbital thermal environments, and the effects of heater failure. Pointing and thermal control features were verified, but a heater failure on the 'on' side was found to quickly lead to exceeding the thermal design limits.

  1. Simulations of the electron cloud buildups and suppressions in Tevatron and main injector

    SciTech Connect

    Zhang, Xiaolong; Ostiguy, Jean-Francois; Chou, Weiren; /Fermilab

    2007-06-01

    To assess the effects of the electron cloud on Main Injector intensity upgrades, simulations of the cloud buildup were carried out using POSINST and compared with ECLOUD. Results indicate that even assuming an optimistic 1.3 maximum secondary electron yield, the electron cloud remains a serious concern for the planned future operational mode with 500 bunches, 3e11 proton per bunch. Electron cloud buildup can be mitigated in various ways. We consider a plausible scenario involving solenoids in straight section and a single clearing strip electrode (like SNEG in Tevatron) held at a potential of 500V. Simulations with parameters corresponding to Tevatron and Main Injector operating conditions at locations where special electron cloud detectors have been installed have been carried out and are in satisfactory agreement with preliminary measurements.

  2. Main magnetic focus ion source: Basic principles, theoretical predictions and experimental confirmations

    NASA Astrophysics Data System (ADS)

    Ovsyannikov, V. P.; Nefiodov, A. V.

    2016-03-01

    It is proposed to produce highly charged ions in the local potential traps formed by the rippled electron beam in a focusing magnetic field. In this method, extremely high electron current densities can be attained on short length of the ion trap. The design of very compact ion sources of the new generation is presented. The computer simulations predict that for such ions as, for example, Ne8+ and Xe44+, the intensities of about 109 and 106 ions per second, respectively, can be obtained. The experiments with pilot example of the ion source confirm efficiency of the suggested method. The X-ray emission from Ir59+, Xe44+ and Ar16+ ions was detected. The control over depth of the local ion trap is shown to be feasible.

  3. Simulations of magnetic nanoparticle Brownian motion

    PubMed Central

    Reeves, Daniel B.; Weaver, John B.

    2012-01-01

    Magnetic nanoparticles are useful in many medical applications because they interact with biology on a cellular level thus allowing microenvironmental investigation. An enhanced understanding of the dynamics of magnetic particles may lead to advances in imaging directly in magnetic particle imaging or through enhanced MRI contrast and is essential for nanoparticle sensing as in magnetic spectroscopy of Brownian motion. Moreover, therapeutic techniques like hyperthermia require information about particle dynamics for effective, safe, and reliable use in the clinic. To that end, we have developed and validated a stochastic dynamical model of rotating Brownian nanoparticles from a Langevin equation approach. With no field, the relaxation time toward equilibrium matches Einstein's model of Brownian motion. In a static field, the equilibrium magnetization agrees with the Langevin function. For high frequency or low amplitude driving fields, behavior characteristic of the linearized Debye approximation is reproduced. In a higher field regime where magnetic saturation occurs, the magnetization and its harmonics compare well with the effective field model. On another level, the model has been benchmarked against experimental results, successfully demonstrating that harmonics of the magnetization carry enough information to infer environmental parameters like viscosity and temperature. PMID:23319830

  4. Simulations of magnetic nanoparticle Brownian motion

    NASA Astrophysics Data System (ADS)

    Reeves, Daniel B.; Weaver, John B.

    2012-12-01

    Magnetic nanoparticles are useful in many medical applications because they interact with biology on a cellular level thus allowing microenvironmental investigation. An enhanced understanding of the dynamics of magnetic particles may lead to advances in imaging directly in magnetic particle imaging or through enhanced MRI contrast and is essential for nanoparticle sensing as in magnetic spectroscopy of Brownian motion. Moreover, therapeutic techniques like hyperthermia require information about particle dynamics for effective, safe, and reliable use in the clinic. To that end, we have developed and validated a stochastic dynamical model of rotating Brownian nanoparticles from a Langevin equation approach. With no field, the relaxation time toward equilibrium matches Einstein's model of Brownian motion. In a static field, the equilibrium magnetization agrees with the Langevin function. For high frequency or low amplitude driving fields, behavior characteristic of the linearized Debye approximation is reproduced. In a higher field regime where magnetic saturation occurs, the magnetization and its harmonics compare well with the effective field model. On another level, the model has been benchmarked against experimental results, successfully demonstrating that harmonics of the magnetization carry enough information to infer environmental parameters like viscosity and temperature.

  5. Comparison Of The Global Analytic Models Of The Main Geomagnetic Field With The Stratospheric Balloon Magnetic Data 335

    NASA Astrophysics Data System (ADS)

    Tsvetkov, Yu.; Filippov, S.; Frunze, A.

    2013-12-01

    Three global analytical models of a main geomagnetic field constructed by satellite data are used: model IGRF, Daily Mean Spherical Harmonic Models (DMSHM), and model EMM/2010, and also scalar data of geomagnetic field and its gradients, received in stratospheric balloon gradient magnetic surveys at altitudes of ~30 km. At these altitudes the regional magnetic field is formed from all sources of the Earth's crust. It enables to receive along lengthy routes of surveys the fullest data on regional and longwave-lenght magnetic anomalies. Model DMSHM is used at extracting of magnetic anomalies for elimination of a secular variation up to significant value 0,2 nT. The model can be constructed within the limits of ± 1 months from the moment stratospheric balloon surveys with beneficial day terms with magnetic activity up to Kp <20, that leads to an error of representation of main MFE equal ±5 нТл. It is possible at presence acting for the period of stratospheric balloon magnetic survey of the satellite, for example, Swarm. On stratospheric balloon data it is shown, that model EMM/2010 unsatisfactorily displays MFE at altitude of 30 km. Hence, the qualitative model of the constant (main and anomaly) magnetic field cannot be constructed only with use of satellite and ground data. The improved model constant MFE, constructed according to satellite and stratospheric balloon magnetic surveys, developed up to a degree and the order m=n=720, will have a reliable data about regional crust magnetic field, hence, and about deep magnetic structure of the Earth's crust. The use gradient magnetic surveys aboard stratospheric balloons allows to find the places alternating approximately through 3000 km in which there are no magnetic anomalies. In these places probably to supervise satellite magnetic models for a range of altitude of 20-40 km, timed to stratospheric balloon magnetic surveys.

  6. OVERVIEW OF A RECONFIGURABLE SIMULATOR FOR MAIN CONTROL ROOM UPGRADES IN NUCLEAR POWER PLANTS

    SciTech Connect

    Ronald L. Boring

    2012-10-01

    This paper provides background on a reconfigurable control room simulator for nuclear power plants. The main control rooms in current nuclear power plants feature analog technology that is growing obsolete. The need to upgrade control rooms serves the practical need of maintainability as well as the opportunity to implement newer digital technologies with added functionality. There currently exists no dedicated research simulator for use in human factors design and evaluation activities for nuclear power plant modernization in the U.S. The new research simulator discussed in this paper provides a test bed in which operator performance on new control room concepts can be benchmarked against existing control rooms and in which new technologies can be validated for safety and usability prior to deployment.

  7. Atomistic simulation of static magnetic properties of bit patterned media

    NASA Astrophysics Data System (ADS)

    Arbeláez-Echeverri, O. D.; Agudelo-Giraldo, J. D.; Restrepo-Parra, E.

    2016-09-01

    In this work we present a new design of Co based bit pattern media with out-of-plane uni-axial anisotropy induced by interface effects. Our model features the inclusion of magnetic impurities in the non-magnetic matrix. After the material model was refined during three iterations using Monte Carlo simulations, further simulations were performed using an atomistic integrator of Landau-Lifshitz-Gilbert equation with Langevin dynamics to study the behavior of the system paying special attention to the super-paramagnetic limit. Our model system exhibits three magnetic phase transitions, one due to the magnetically doped matrix material and the weak magnetic interaction between the nano-structures in the system. The different magnetic phases of the system as well as the features of its phase diagram are explained.

  8. Simulations of the anisotropic kinetic and magnetic alpha effects

    NASA Astrophysics Data System (ADS)

    Brandenburg, A.; Subramanian, K.

    2007-07-01

    Using simulations of isotropically forced helical turbulence the contributions to kinetic and magnetic alpha effects are computed. It is shown that for the parameter regimes considered in an earlier publication (Brandenburg & Subramanian 2005), the expressions for isotropic and anisotropic alpha effects give quantitatively similar results. Both kinetic and magnetic alpha effects are proportional to a relaxation time whose value, in units of the turnover time, is shown to be approximately unity and independent of the magnetic Reynolds number.

  9. Numerical simulations of the decay of primordial magnetic turbulence

    SciTech Connect

    Kahniashvili, Tina; Brandenburg, Axel; Tevzadze, Alexander G.; Ratra, Bharat

    2010-06-15

    We perform direct numerical simulations of forced and freely decaying 3D magnetohydrodynamic turbulence in order to model magnetic field evolution during cosmological phase transitions in the early Universe. Our approach assumes the existence of a magnetic field generated either by a process during inflation or shortly thereafter, or by bubble collisions during a phase transition. We show that the final configuration of the magnetic field depends on the initial conditions, while the velocity field is nearly independent of initial conditions.

  10. VERA-CS Modeling and Simulation of PWR Main Steam Line Break Core Response to DNB

    SciTech Connect

    Salko, Robert K; Sung, Yixing; Kucukboyaci, Vefa; Xu, Yiban; Cao, Liping

    2016-01-01

    The Virtual Environment for Reactor Applications core simulator (VERA-CS) being developed by the Consortium for the Advanced Simulation of Light Water Reactors (CASL) includes coupled neutronics, thermal-hydraulics, and fuel temperature components with an isotopic depletion capability. The neutronics capability employed is based on MPACT, a three-dimensional (3-D) whole core transport code. The thermal-hydraulics and fuel temperature models are provided by the COBRA-TF (CTF) subchannel code. As part of the CASL development program, the VERA-CS (MPACT/CTF) code system was applied to model and simulate reactor core response with respect to departure from nucleate boiling ratio (DNBR) at the limiting time step of a postulated pressurized water reactor (PWR) main steamline break (MSLB) event initiated at the hot zero power (HZP), either with offsite power available and the reactor coolant pumps in operation (high-flow case) or without offsite power where the reactor core is cooled through natural circulation (low-flow case). The VERA-CS simulation was based on core boundary conditions from the RETRAN-02 system transient calculations and STAR-CCM+ computational fluid dynamics (CFD) core inlet distribution calculations. The evaluation indicated that the VERA-CS code system is capable of modeling and simulating quasi-steady state reactor core response under the steamline break (SLB) accident condition, the results are insensitive to uncertainties in the inlet flow distributions from the CFD simulations, and the high-flow case is more DNB limiting than the low-flow case.

  11. Magnetic inhibition of convection and the fundamental properties of low-mass stars. II. Fully convective main-sequence stars

    SciTech Connect

    Feiden, Gregory A.; Chaboyer, Brian E-mail: brian.chaboyer@dartmouth.edu

    2014-07-01

    We examine the hypothesis that magnetic fields are inflating the radii of fully convective main-sequence stars in detached eclipsing binaries (DEBs). The magnetic Dartmouth stellar evolution code is used to analyze two systems in particular: Kepler-16 and CM Draconis. Magneto-convection is treated assuming stabilization of convection and also by assuming reductions in convective efficiency due to a turbulent dynamo. We find that magnetic stellar models are unable to reproduce the properties of inflated fully convective main-sequence stars, unless strong interior magnetic fields in excess of 10 MG are present. Validation of the magnetic field hypothesis given the current generation of magnetic stellar evolution models therefore depends critically on whether the generation and maintenance of strong interior magnetic fields is physically possible. An examination of this requirement is provided. Additionally, an analysis of previous studies invoking the influence of star spots is presented to assess the suggestion that star spots are inflating stars and biasing light curve analyses toward larger radii. From our analysis, we find that there is not yet sufficient evidence to definitively support the hypothesis that magnetic fields are responsible for the observed inflation among fully convective main-sequence stars in DEBs.

  12. Efficient Analysis of Simulations of the Sun's Magnetic Field

    NASA Astrophysics Data System (ADS)

    Scarborough, C. W.; Martínez-Sykora, J.

    2014-12-01

    Dynamics in the solar atmosphere, including solar flares, coronal mass ejections, micro-flares and different types of jets, are powered by the evolution of the sun's intense magnetic field. 3D Radiative Magnetohydrodnamics (MHD) computer simulations have furthered our understanding of the processes involved: When non aligned magnetic field lines reconnect, the alteration of the magnetic topology causes stored magnetic energy to be converted into thermal and kinetic energy. Detailed analysis of this evolution entails tracing magnetic field lines, an operation which is not time-efficient on a single processor. By utilizing a graphics card (GPU) to trace lines in parallel, conducting such analysis is made feasible. We applied our GPU implementation to the most advanced 3D Radiative-MHD simulations (Bifrost, Gudicksen et al. 2011) of the solar atmosphere in order to better understand the evolution of the modeled field lines.

  13. A flow simulation study of protein solution under magnetic forces

    NASA Astrophysics Data System (ADS)

    Okada, Hidehiko; Hirota, Noriyuki; Matsumoto, Shinji; Wada, Hitoshi

    2013-02-01

    We have developed a superconducting magnet system generating magnetic forces able to compensate gravity and suppress convection of diamagnetic protein solution from which protein crystals precipitate. A simulation model has been proposed to elucidate the motion of protein solutions and search for the optimal conditions of the crystal formation process. This model incorporates general, non-uniform magnetic forces as external forces, while the previous models involve only simple, uniform magnetic forces. The simulation results indicate that the vertical component can suppress the convection of protein solution, while the horizontal component induces minimal convection. We, therefore, need to take into account the both components when considering the formation of protein crystals under magnetic forces.

  14. Numerical simulation methods of incompressible flows and an application to the space shuttle main engine

    NASA Technical Reports Server (NTRS)

    Chang, J. L. C.; Kwak, D.; Rogers, S. E.; Yang, R.-J.

    1988-01-01

    Incompressible Navier-Stokes solution methods are discussed with an emphasis on the pseudocompressibility method. A steady-state flow solver based on the pseudocompressibility approach is then described. This flow-solver code was used to analyze the internal flow in the Space Shuttle main engine hot-gas manifold. Salient features associated with this three-dimensional realistic flow simulation are discussed. Numerical solutions relevant to the current engine analysis and the redesign effort are discussed along with experimental results. This example demonstrates the potential of computational fluid dynamics as a design tool for aerospace applications.

  15. Non-contact main cable NDE technique for suspension bridge using magnetic flux-based B-H loop measurements

    NASA Astrophysics Data System (ADS)

    Park, Seunghee; Kim, Ju-Won; Moon, Dae-Joong

    2015-04-01

    In this study, a noncontact main cable NDE method has been developed. This cable NDE method utilizes the direct current (DC) magnetization and a searching coil-based total flux measurement. A total flux sensor head prototype was fabricated that consists of an electro-magnet yoke and a searching coil sensor. To obtain a B-H loop, a magnetic field was generated by applying a cycle of low frequency direct current to the electro-magnet yoke. During the magnetization, a search coil sensor measures the electromotive force from magnetized cable. During the magnetization process, a search coil sensor was measured the magnetic flux density. Total flux was calculated by integrating the measured magnetic flux using a fluxmeter. A B-H loop is obtained by using relationship between a cycle of input DC voltage and measured total flux. The B-H loop can reflect the property of the ferromagnetic materials. Therefore, the cross-sectional loss of cable can be detected using variation of features from the B-H curve. To verify the feasibility of the proposed steel cable NDE method, a series of experimental studies using a main-cable mock-up specimen has been performed in this study.

  16. Simulation of magnetization process of Pure-type superconductor magnet undulator based on T-method

    NASA Astrophysics Data System (ADS)

    Deri, Yi; Kawaguchi, Hideki; Tsuchimoto, Masanori; Tanaka, Takashi

    2015-11-01

    For the next generation Free Electron Laser, Pure-type undulator made of high Tc superconductors (HTSs) was considered to achieve a small size and high intensity magnetic field undulator. In general, it is very difficult to adjust the undulator magnet alignment after the HTS magnetization since the entire undulator is installed inside a cryostat. The appropriate HTS alignment has to be determined in the design stage. This paper presents the development of a numerical simulation code for magnetization process of the Pure-type HTS undulator to assist the design of the optimal size and alignment of the HTS magnets.

  17. Simulating functional magnetic materials on supercomputers.

    PubMed

    Gruner, Markus Ernst; Entel, Peter

    2009-07-22

    The recent passing of the petaflop per second landmark by the Roadrunner project at the Los Alamos National Laboratory marks a preliminary peak of an impressive world-wide development in the high-performance scientific computing sector. Also, purely academic state-of-the-art supercomputers such as the IBM Blue Gene/P at Forschungszentrum Jülich allow us nowadays to investigate large systems of the order of 10(3) spin polarized transition metal atoms by means of density functional theory. Three applications will be presented where large-scale ab initio calculations contribute to the understanding of key properties emerging from a close interrelation between structure and magnetism. The first two examples discuss the size dependent evolution of equilibrium structural motifs in elementary iron and binary Fe-Pt and Co-Pt transition metal nanoparticles, which are currently discussed as promising candidates for ultra-high-density magnetic data storage media. However, the preference for multiply twinned morphologies at smaller cluster sizes counteracts the formation of a single-crystalline L1(0) phase, which alone provides the required hard magnetic properties. The third application is concerned with the magnetic shape memory effect in the Ni-Mn-Ga Heusler alloy, which is a technologically relevant candidate for magnetomechanical actuators and sensors. In this material strains of up to 10% can be induced by external magnetic fields due to the field induced shifting of martensitic twin boundaries, requiring an extremely high mobility of the martensitic twin boundaries, but also the selection of the appropriate martensitic structure from the rich phase diagram. PMID:21828528

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

    SciTech Connect

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

    2015-07-01

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

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

    DOE PAGESBeta

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

    2015-07-01

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

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

    SciTech Connect

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

    2015-07-15

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

  1. Magnetic stochasticity in gyrokinetic simulations of plasma microturbulence

    NASA Astrophysics Data System (ADS)

    Wang, Eric

    2010-11-01

    One of the fundamental components of a steady state tokamak or stellerator fusion reactor is the structural integrity of nested magnetic surfaces. The consequences of losing this integrity can have very serious implications, ranging from sawtooth crashes to disruptions. In the present work, we use GYRO to examine the perturbed magnetic field structure generated by electromagnetic gyrokinetic simulations of the CYCLONE base case as β is varied from .1% to .7%, as first investigated in [J. Candy, Phys. Plasmas 12, 072307 (2005)]. By integrating the self-consistent magnetic field lines to produce Poincare surface of section plots, we demonstrate destruction of magnetic surfaces for all nonzero values of β. Despite widespread stochasticity of the perturbed magnetic fields, no significant increase in electron transport is observed. We can quantify the stochastic electron heat transport by using test particles to estimate the magnetic diffusion coefficient Dst [A.B. Rechester and M.N. Rosenbluth, PRL 40, 38 (1978)] for hundreds of time slices in each simulation and find the time-history of Dst to be highly correlated with the electron heat transport due to ``magnetic-flutter'' computed in the simulations. The mechanism that couples electromagnetic turbulence to the linearly damped high-n tearing modes that are responsible for reconnection will be discussed.

  2. Experimental simulation of a magnetic refrigeration cycle in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Dilmieva, E. T.; Kamantsev, A. P.; Koledov, V. V.; Mashirov, A. V.; Shavrov, V. G.; Cwik, J.; Tereshina, I. S.

    2016-01-01

    The complete magnetic refrigeration cycle has been simulated on a sample of gadolinium in magnetic fields of a Bitter coil magnet up to 12 T. The total change of temperature of the sample during the cycle is a consequence of magnetic refrigeration, and the dependence of the magnetization of the sample on the magnetic field exhibits a hysteretic behavior. This makes it possible to determine the work done by the magnetic field on the sample during the magnetic refrigeration cycle and to calculate the coefficient of performance of the process. In a magnetic field of 2 T near the Curie temperature of gadolinium, the coefficient of performance of the magnetic refrigeration is found to be 92. With an increase in the magnetic field, the coefficient of performance of the process decreases sharply down to 15 in a magnetic field of 12 T. The reasons, for which the coefficient of performance of the magnetic refrigeration is significantly below the fundamental limitations imposed by the reversed Carnot theorem, have been discussed.

  3. Simulation of Electromagnetic and Thermal Processes in Fastcycling Magnets for Calculation Parameters of Stability

    NASA Astrophysics Data System (ADS)

    Zubko, V.; Kozub, S.; Tkachenko, L.

    SIS300 fast-cycling superconducting quadrupole magnet is developed at IHEP. Temperature margin and minimum quench energy are main parameters of stability of superconducting magnets. These parameters are important for the design and safe operation of superconducting magnets. But additional understanding for fast-cycling superconducting magnets is needed. To calculate the temperature margin one needs coupled numerical transient simulation of electromagnetic and thermal processes in the coil because critical temperature, operating temperature and AC losses are nonuniform over turns and their magnitudes vary in time during accelerator cycles. For calculation of the minimum quench energy the combination of the network model with thermal analysis is necessary, which allows one to model quench dynamics, including the effects of a current redistribution between strands of cable and spatial inhomogeneity of cable. Results for the temperature margin and the minimum quench energy for the magnet are presented and theirs dependence on various parameters is discussed.

  4. PIC simulation of plasma waves above lunar magnetic anomaly

    NASA Astrophysics Data System (ADS)

    Dokgo, K.; Woo, C. H.; Min, K.; Hwang, J.

    2015-12-01

    We simulated the interaction between solar wind and lunar magnetic anomaly. Reiner Gamma anomaly (7.4°N, 300.9°E) and average solar wind parameters are used for our simulation. To increase spatial resolution for wave analysis, simulation geometry was restricted to 2-dimension. At the top of simulation box, continuous solar wind particle injection was designed to reproduce steady solar wind condition and particles left through the bottom side of simulation box. Mini-magnetosphere was formed above the lunar surface as a result of the interaction between solar wind particle and dipole magnetic field. As it affect incident solar wind particles, electromagnetic field fluctuations were generated and wave structures were observed above mini magnetosphere.

  5. Variations of the ISM Compactness Across the Main Sequence of Star Forming Galaxies: Observations and Simulations

    NASA Astrophysics Data System (ADS)

    Martínez-Galarza, J. R.; Smith, H. A.; Lanz, L.; Hayward, Christopher C.; Zezas, A.; Rosenthal, L.; Weiner, A.; Hung, C.; Ashby, M. L. N.; Groves, B.

    2016-01-01

    The majority of star-forming galaxies follow a simple empirical correlation in the star formation rate (SFR) versus stellar mass (M*) plane, of the form {{SFR}}\\propto {M}*α , usually referred to as the star formation main sequence (MS). The physics that sets the properties of the MS is currently a subject of debate, and no consensus has been reached regarding the fundamental difference between members of the sequence and its outliers. Here we combine a set of hydro-dynamical simulations of interacting galactic disks with state-of-the-art radiative transfer codes to analyze how the evolution of mergers is reflected upon the properties of the MS. We present Chiburst, a Markov Chain Monte Carlo spectral energy distribution (SED) code that fits the multi-wavelength, broad-band photometry of galaxies and derives stellar masses, SFRs, and geometrical properties of the dust distribution. We apply this tool to the SEDs of simulated mergers and compare the derived results with the reference output from the simulations. Our results indicate that changes in the SEDs of mergers as they approach coalescence and depart from the MS are related to an evolution of dust geometry in scales larger than a few hundred parsecs. This is reflected in a correlation between the specific star formation rate, and the compactness parameter { C }, that parametrizes this geometry and hence the evolution of dust temperature ({T}{{dust}}) with time. As mergers approach coalescence, they depart from the MS and increase their compactness, which implies that moderate outliers of the MS are consistent with late-type mergers. By further applying our method to real observations of luminous infrared galaxies (LIRGs), we show that the merger scenario is unable to explain these extreme outliers of the MS. Only by significantly increasing the gas fraction in the simulations are we able to reproduce the SEDs of LIRGs.

  6. Comparisons of Simulated and Observed Stormtime Magnetic Intensities and Ion Densities in the Ring Current

    NASA Astrophysics Data System (ADS)

    Chen, M. W.; Guild, T. B.; Lemon, C. L.; Schulz, M.

    2008-12-01

    Recent progress in ring current and plasma sheet modeling has shown the importance of a self-consistent treatment of particle transport and magnetic and electric fields in the inner magnetosphere. For example, the feedback of the ring current tends to mitigate the build-up of the asymmetric ring current and associated magnetic depressions during storm main phase. Models with and without self-consistency can lead to significantly different magnitudes and spatial distributions of plasma pressure and magnetic intensity during disturbed times. In this study we compare simulated and observed stormtime magnetic intensities and ion densities at geosynchronous altitude to test how well self-consistent simulations can simultaneously reproduce these quantities. We simulate the ring current and plasma sheet for conditions corresponding to the 12-14 August 2000 storm using the self-consistent Rice Convection Model-Equilibrium (RCM-E) [ Lemon et al., JGR, 2004]. Using the empirical IMF-dependent model of Tsyganenko and Mukai [JGR, 2003], we specify the plasma sheet pressure and density at 10 RE as the plasma boundary location in the RCM- E. We compare the simulated magnetic intensity at geosynchronous altitude (6.6 RE) with the magnetic intensity measured by magnetometers on the GOES G8, G10, and G11 satellites. The simulated ion densities at different magnetic local times are compared with those from the re-analysis model of LANL/MPA densities of O'Brien and Lemon [Space Weather, 2007]. This is a first step towards a more extensive comparison that will include other datasets, such as ion and magnetic field data from Polar, at locations closer to the Earth than geosynchronous altitude.

  7. Magnetic fields of chemically peculiar and related stars. 2. Main results of 2015 and near-future prospects

    NASA Astrophysics Data System (ADS)

    Romanyuk, I. I.

    2016-07-01

    We present an analytical survey of key publications concerned with the study of stellar magnetism published in 2015. We considered about 80 publications, the most significant from our point of view, presented brief reviews of them, and made generalizations. The paper considers: instruments, techniques of observations and analysis; large-scale magnetic fields of OBA stars on the Main Sequence (MS) (formation and evolution, field topology, search for new magnetic stars including the projects MiMeS, BOB, and BinaMIcS and observations with the Russian 6-m telescope, rotation and chemical abundance analysis of magnetic CP stars); magnetic fields, chemical abundance and variability of stars related to peculiar, primarily, active cool stars, solar-type stars and white dwarfs; multiple magnetic stars including interferometry data, exoplanets in a system of magnetic stars. We make a conclusion that the accuracy of magnetic field measurements has grown due to universal application of the multilinear method of observations especially with high-resolution spectropolarimeters. Usage of Zeeman-Doppler imaging technique (ZDI) when analyzing the obtained data allows us to confidently search and measure fields of complex topology of the order of 10 Gs. For the first time, a magnetic field has been detected for post-AGB stars and some other types of objects.

  8. Finemet nanocrystalline soft magnetic alloy: Investigation of glass forming ability, crystallization mechanism, production techniques, magnetic softness and the effect of replacing the main constituents by other elements

    NASA Astrophysics Data System (ADS)

    Gheiratmand, T.; Hosseini, H. R. Madaah

    2016-06-01

    Finemet soft magnetic alloy has been in the focus of interest in the last years due to its high saturation magnetization, high permeability and low core loss. The great quantity of papers has been devoted to the study of its structural and magnetic properties, confirms this claim. This paper reviews the different researches performed on Finemet up to now. The criteria that should be satisfied in order to have the high glass forming ability in an alloy and also the techniques applied for production of Finemet ribbons, powders and bulk samples have been explained. In addition, the mechanism of devitrification, nanocrystallization and magnetic softness in this applicable magnetic alloy has been discussed in detail. Finally, the effect of different elements substituted with the main constituents in Finemet has been summarized through the studies on the characterization and magnetic properties of different Finemet-type alloys.

  9. Magnetized laboratory plasma jets: Experiment and simulation

    NASA Astrophysics Data System (ADS)

    Schrafel, Peter; Bell, Kate; Greenly, John; Seyler, Charles; Kusse, Bruce

    2015-01-01

    Experiments involving radial foils on a 1 M A , 100 n s current driver can be used to study the ablation of thin foils and liners, produce extreme conditions relevant to laboratory astrophysics, and aid in computational code validation. This research focuses on the initial ablation phase of a 20 μ m Al foil (8111 alloy), in a radial configuration, driven by Cornell University's COBRA pulsed power generator. In these experiments ablated surface plasma (ASP) on the top side of the foil and a strongly collimated axial plasma jet are observed developing midway through the current rise. With experimental and computational results this work gives a detailed description of the role of the ASP in the formation of the plasma jet with and without an applied axial magnetic field. This ˜1 T field is applied by a Helmholtz-coil pair driven by a slow, 150 μ s current pulse and penetrates the load hardware before arrival of the COBRA pulse. Several effects of the applied magnetic field are observed: (1) without the field extreme-ultraviolet emission from the ASP shows considerable azimuthal asymmetry while with the field the ASP develops azimuthal motion that reduces this asymmetry, (2) this azimuthal motion slows the development of the jet when the field is applied, and (3) with the magnetic field the jet becomes less collimated and has a density minimum (hollowing) on the axis. PERSEUS, an XMHD code, has qualitatively and quantitatively reproduced all these experimental observations. The differences between this XMHD and an MHD code without a Hall current and inertial effects are discussed. In addition the PERSEUS results describe effects we were not able to resolve experimentally and suggest a line of future experiments with better diagnostics.

  10. Magnetized laboratory plasma jets: experiment and simulation.

    PubMed

    Schrafel, Peter; Bell, Kate; Greenly, John; Seyler, Charles; Kusse, Bruce

    2015-01-01

    Experiments involving radial foils on a 1 MA, 100 ns current driver can be used to study the ablation of thin foils and liners, produce extreme conditions relevant to laboratory astrophysics, and aid in computational code validation. This research focuses on the initial ablation phase of a 20 μm Al foil (8111 alloy), in a radial configuration, driven by Cornell University's COBRA pulsed power generator. In these experiments ablated surface plasma (ASP) on the top side of the foil and a strongly collimated axial plasma jet are observed developing midway through the current rise. With experimental and computational results this work gives a detailed description of the role of the ASP in the formation of the plasma jet with and without an applied axial magnetic field. This ∼1 T field is applied by a Helmholtz-coil pair driven by a slow, 150 μs current pulse and penetrates the load hardware before arrival of the COBRA pulse. Several effects of the applied magnetic field are observed: (1) without the field extreme-ultraviolet emission from the ASP shows considerable azimuthal asymmetry while with the field the ASP develops azimuthal motion that reduces this asymmetry, (2) this azimuthal motion slows the development of the jet when the field is applied, and (3) with the magnetic field the jet becomes less collimated and has a density minimum (hollowing) on the axis. PERSEUS, an XMHD code, has qualitatively and quantitatively reproduced all these experimental observations. The differences between this XMHD and an MHD code without a Hall current and inertial effects are discussed. In addition the PERSEUS results describe effects we were not able to resolve experimentally and suggest a line of future experiments with better diagnostics. PMID:25679726

  11. The brain and its main anatomical subdivisions in living hominoids using magnetic resonance imaging.

    PubMed

    Semendeferi, K; Damasio, H

    2000-02-01

    Primary comparative data on the hominoid brain are scarce and major neuroanatomical differences between humans and apes have not yet been described satisfactorily, even at the gross level. Basic questions that involve the evolution of the human brain cannot be addressed adequately unless the brains of all extant hominoid species are analyzed. Contrary to the scarcity of original data, there is a rich literature on the topic of human brain evolution and several debates exist on the size of particular sectors of the brain, e.g., the frontal lobe. In this study we applied a non-invasive imaging technique (magnetic resonance) on living human, great ape and lesser ape subjects in order to investigate the overall size of the hominoid brain. The images were reconstructed in three dimensions and volumetric estimates were obtained for the brain and its main anatomical sectors, including the frontal and temporal lobes, the insula, the parieto-occipital sector and the cerebellum.A remarkable homogeneity is present in the relative size of many of the large sectors of the hominoid brain, but interspecific and intraspecific variation exists in certain parts of the brain. The human cerebellum is smaller than expected for an ape brain of human size. It is suggested that the cerebellum increased less than the cerebrum after the split of the human lineage from the African ancestral hominoid stock. In contrast, humans have a slightly larger temporal lobe and insula than expected, but differences are not statistically significant. Humans do not have a larger frontal lobe than expected for an ape brain of human size and gibbons have a relatively smaller frontal lobe than the rest of the hominoids. Given the fact that the frontal lobe in humans and great apes has similar relative size, it is parsimonious to suggest that the relative size of the whole of the frontal lobe has not changed significantly during hominid evolution in the Plio-Pleistocene. PMID:10656781

  12. MD Simulation of Particle Orientation in Magnetic Inks

    NASA Astrophysics Data System (ADS)

    Visscher; Günal

    1997-03-01

    We have done molecular-dynamics type simulations of particle re-orientation in a magnetic colloid, by a magnetic field during tape and disk manufacture. The model takes into account switching (in a Stoner- Wohlfarth model) as well as particle translation and rotation in response to magnetic, steric, Brownian, and hydrodynamic drag forces and torques. Magnetic interactions are fully included; hysteresis loops with and without magnetic interaction will be displayed, with corresponding Δ M curves. Images of the network structure at various points of the hysteresis loop will be shown. Further information is available at http:// www.mint.ua.edu/colloids/march.html.

  13. Do micromagnetic simulations correctly predict hard magnetic hysteresis properties?

    NASA Astrophysics Data System (ADS)

    Toson, P.; Zickler, G. A.; Fidler, J.

    2016-04-01

    Micromagnetic calculations using the finite element technique describe semi-quantitatively the coercivity of novel rare earth permanent magnets in dependence on grain size, grain shape, grain alignment and composition of grain boundaries and grain boundary junctions and allow the quantitative prediction of magnetic hysteretic properties of rare earth free magnets based on densely packed elongated Fe and Co nanoparticles, which depend on crystal anisotropy, aspect ratio and packing density. The nucleation of reversed domains preferentially takes place at grain boundary junctions in granular sintered and melt-spun magnets independently on the grain size. The microstructure and the nanocompostion of the intergranular regions are inhomogeneous and too complex in order to make an exact model for micromagnetic simulations and to allow a quantitative prediction. The incoherent magnetization reversal processes near the end surfaces reduce and determine the coercive field values of Co- and Fe-based nanoparticles.

  14. A hybrid simulation study of magnetic reconnection in anisotropic plasmas

    NASA Astrophysics Data System (ADS)

    Guo, Jun; Li, Yi; Lu, Quan-ming; Wang, Shui

    2003-10-01

    The process of magnetic reconnection in anisotropic plasmas is studied numerically using a 2-dimensional, 3-component hybrid simulation. The results of the calculation show that, when the plasma pressure in the direction perpendicular to magnetic field is larger than that in the parallel direction (e.g. P ⊥/P ‖ = 1.5 ), instability may greatly increase, speeding up the rate of reconnection. When P⊥ is smaller than P‖, (e.g., when P ⊥/P ‖ = 0.6 ), fire hose instability appears, which will restrain the tearing mode instability and the process of magnetic reconnection.

  15. A mathematical model of a single main rotor helicopter for piloted simulation

    NASA Technical Reports Server (NTRS)

    Talbot, P. D.; Tinling, B. E.; Decker, W. A.; Chen, R. T. N.

    1982-01-01

    A mathematical model, suitable for piloted simulation of the flying qualities of helicopters, is a nonlinear, total force and moment model of a single main rotor helicopter. The model has ten degrees of freedom: six rigid body, three rotor flapping, and the rotor rotational degrees of freedom. The rotor model assumes rigid blades with rotor forces and moments radially integrated and summed about the azimuth. The fuselage aerodynamic model uses a detailed representation over a nominal angle of attack and sideslip range of + or - 15 deg., as well as a simplified curve fit at large angles of attack or sideslip. Stabilizing surface aerodynamics are modeled with a lift curve slope between stall limits and a general curve fit for large angles of attack. A generalized stability and control augmentation system is described. Additional computer subroutines provide options for a simplified engine/governor model, atmospheric turbulence, and a linearized six degree of freedom dynamic model for stability and control analysis.

  16. Properties of Turbulent Dynamics and Oscillations of Main-Sequence Stars Deduced From Numerical Simulations

    NASA Astrophysics Data System (ADS)

    Kitiashvili, Irina N.; Mansour, Nagi N.; Kosovichev, Alexander; Wray, Alan A.

    2015-08-01

    Unique observational data from the Kepler mission open new perspectives for detail investigation of dynamical and internal properties of numerous stars. However, the new observational results require better understand links between the stellar turbulent convection and oscillations. We perform 3D numerical radiative hydrodynamics simulations of convective and oscillation properties of main-sequence stars from the solar-type stars to more massive F- and A-type stars. As the stellar mass increases the convection zone shrinks making it possible to include the whole convection zone in the computational domain. Also in more massive stars the scale and intensity of the turbulent motions dramatically increases, providing more energy for excitation of acoustic and gravity modes. In this talk I will discuss properties of the turbulent dynamics of the stars, interaction between the radiative and convection zones, and excitation of acoustic and gravity modes.

  17. Improvements in the simulation of a main steam line break with steam generator tube rupture

    NASA Astrophysics Data System (ADS)

    Gallardo, Sergio; Querol, Andrea; Verdú, Gumersindo

    2014-06-01

    The result of simultaneous Main Steam Line Break (MSLB) and a Steam Generator Tube Rupture (SGTR) in a Pressurized Water Reactor (PWR) is a depressurization in the secondary and primary system because both systems are connected through the SGTR. The OECD/NEA ROSA-2 Test 5 performed in the Large Scale Test Facility (LSTF) reproduces these simultaneous breaks in a Pressurized Water Reactor (PWR). A simulation of this Test 5 was made with the thermal-hydraulic code TRACE5. Some discrepancies found, such as an underestimation of SG-A secondary pressure during the depressurization and overestimation of the primary pressure drop after the first Power Operated Relief Valve (PORV) opening can be improved increasing the nodalization of the Upper Head in the pressure vessel and meeting the actual fluid conditions of Upper Head during the transient.

  18. Magnetic cycles in global magnetohydrodynamical simulations of solar convection

    NASA Astrophysics Data System (ADS)

    Charbonneau, P.

    2011-12-01

    In this talk I will review some recent advances in our understanding of the solar magnetic cycle through global magnetohydrodynamical simulations of thermally-driven convection in a thick, stratified spherical shell of electrically conducting fluid. I will focus on three related issues: (1) the nature of the turbulent dynamo mechanism; (2) the nature of the mechanism(s) controlling the cycle amplitude; and (3) epochs of strongly suppressed cycle amplitudes, and the existence of possible precursor to such events to be found in the patterns of magnetically-driven torsional oscillations and meridional flow variations arising in the simulations.

  19. Magnetic field simulation of magnetic phase detection sensor for steam generator tube in nuclear power plants

    NASA Astrophysics Data System (ADS)

    Ryu, Kwon-sang; Son, Derac; Park, Duck-gun; Kim, Yong-il

    2010-05-01

    Magnetic phases and defects are partly produced in steam generator tubes by stress and heat, because steam generator tubes in nuclear power plants are used under high temperature, high pressure, and radioactivity. The magnetic phases induce an error in the detection of the defects in steam generator tubes by the conventional eddy current method. So a new method is needed for detecting the magnetic phases in the steam generator tubes. We designed a new U-type yoke which has two kinds of coils and simulated the signal by the magnetic phases and defects in the Inconnel 600 tube.

  20. Magnetic Forces Simulation of Bulk HTS over Permanent Magnetic Railway with Numerical Method

    NASA Astrophysics Data System (ADS)

    Lu, Yiyun; Zhuang, Shujun

    2012-10-01

    Magnetic levitation forces of bulk high temperature superconductor (HTS) above two types permanent magnet railway (PMR) is simulated using finite element method (FEM). The models are formulated by H-formulation and resolving codes is developed using Finite Element Program Generator (FEPG). The E- J power law is used to describe the electrical field vs. current density nonlinear characteristic of HTS. The applied magnetic fields induced by the PMR are calculated by the standard analysis method with the equivalent surface current model. By the method, the calculation formulation of magnetic fields generated by Halbach PMR and symmetrical PMR is derived respectively. The simulation results show that the finite element dynamic mesh rebuilding problem of HTS magnetic levitation transportation system comprised of bulk HTS and PMR can be easily avoided by the methods.

  1. The star formation main sequence and stellar mass assembly of galaxies in the Illustris simulation

    NASA Astrophysics Data System (ADS)

    Sparre, Martin; Hayward, Christopher C.; Springel, Volker; Vogelsberger, Mark; Genel, Shy; Torrey, Paul; Nelson, Dylan; Sijacki, Debora; Hernquist, Lars

    2015-03-01

    Understanding the physical processes that drive star formation is a key challenge for galaxy formation models. In this paper, we study the tight correlation between the star formation rate (SFR) and stellar mass of galaxies at a given redshift, how halo growth influences star formation, and star formation histories of individual galaxies. We study these topics using Illustris, a state-of-the-art cosmological hydrodynamical simulation of galaxy formation. Illustris reproduces the observed relation (the star formation main sequence, SFMS) between SFR and stellar mass at redshifts z = 0 and 4, but at intermediate redshifts of z ≃ 1-2, the simulated SFMS has a significantly lower normalization than reported by observations. The scatter in the relation is consistent with the observed scatter. However, the fraction of outliers above the SFR-stellar mass relation in Illustris is less than that observed. Galaxies with halo masses of ˜1012 M⊙ dominate the SFR density of the Universe, in agreement with the results of abundance matching. Furthermore, more-massive galaxies tend to form the bulk of their stars at high redshift, which indicates that `downsizing' occurs in Illustris. We also studied the star formation histories of individual galaxies, including the use of a principal component analysis decomposition. We find that for fixed stellar mass, galaxies that form earlier have more-massive black holes at z = 0, indicating that star formation and black hole growth are tightly linked processes in Illustris. While many of the properties of normal star-forming galaxies are well reproduced in the Illustris simulation, forming a realistic population of starbursts will likely require higher resolution and probably a more sophisticated treatment of star formation and feedback from stars and black holes.

  2. Thermal conditions on the International Space Station: Heat flux and temperature investigation of main radiators for the Alpha Magnetic Spectrometer

    NASA Astrophysics Data System (ADS)

    Xie, Min; Gao, Jianmin; Wu, Shaohua; Qin, Yukun

    2016-09-01

    The investigation on heat flux can clarify the thermal condition and explain temperature behavior on the main radiators of the Alpha Magnetic Spectrometer (AMS). In this paper, a detailed investigation of heat flux on the AMS main radiators is proposed. The heat transfer process of the AMS main radiators is theoretically analyzed. An updated thermal model of the AMS on the International Space Station (ISS) is developed to calculate the external heat flux density on the AMS main radiators. We conclude the ISS components and operations affect on the solar flux density of the AMS main radiators by reflecting or shading solar illumination. According to the energy conservation on the AMS main radiators, the temperature variation mainly depends on the solar flux change. The investigations are conducive to reference for the long-duration thermal control of the AMS, and knowledge for the thermal conditions on the ISS.

  3. Propulsion simulation for magnetically suspended wind tunnel models

    NASA Technical Reports Server (NTRS)

    Joshi, Prakash B.; Beerman, Henry P.; Chen, James; Krech, Robert H.; Lintz, Andrew L.; Rosen, David I.

    1990-01-01

    The feasibility of simulating propulsion-induced aerodynamic effects on scaled aircraft models in wind tunnels employing Magnetic Suspension and Balance Systems. The investigation concerned itself with techniques of generating exhaust jets of appropriate characteristics. The objectives were to: (1) define thrust and mass flow requirements of jets; (2) evaluate techniques for generating propulsive gas within volume limitations imposed by magnetically-suspended models; (3) conduct simple diagnostic experiments for techniques involving new concepts; and (4) recommend experiments for demonstration of propulsion simulation techniques. Various techniques of generating exhaust jets of appropriate characteristics were evaluated on scaled aircraft models in wind tunnels with MSBS. Four concepts of remotely-operated propulsion simulators were examined. Three conceptual designs involving innovative adaptation of convenient technologies (compressed gas cylinders, liquid, and solid propellants) were developed. The fourth innovative concept, namely, the laser-assisted thruster, which can potentially simulate both inlet and exhaust flows, was found to require very high power levels for small thrust levels.

  4. Simulation of the Magnetic Field Evolution in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Hoyos, J.; Reisenegger, A.; Valdivia, J. A.

    Using a numerical simulation, we study the effects of ambipolar diffusion and ohmic diffusion on the magnetic field evolution in the interior of an isolated neutron star (Goldreich & Reisenegger 1992; Reisenegger et al. 2005; Hoyos et al. 2007). We are interested in the behavior of the magnetic field on a long time scale, over which all Alfven and sound waves have been damped. We model the stellar interior as an electrically neutral plasma composed of neutrons, protons and electrons, which can interact with each other through collisions and electromagnetic forces. Weak interactions convert neutrons and charged particles into each other, erasing chemical imbalances. As a first step, we assume that the magnetic field points in one fixed Cartesian direction but can vary along an orthogonal direction. We start with a uniform-density background threaded by a homogeneous magnetic field and study the evolution of a magnetic perturbation as well as the density fluctuations it induces in the particles. We show that the system evolves through different quasi-equilibrium states and estimate the characteristic time scales on which these quasi-equilibria occur as a function of the magnetic field intensity, the collisional strength between the particles, the weak interaction rate, and the ohmic resistivity. We intend in a near future to extend this simulation to two dimensions in order to study an axially symmetric star geometry.

  5. Magnetic levitation-based Martian and Lunar gravity simulator

    NASA Technical Reports Server (NTRS)

    Valles, J. M. Jr; Maris, H. J.; Seidel, G. M.; Tang, J.; Yao, W.

    2005-01-01

    Missions to Mars will subject living specimens to a range of low gravity environments. Deleterious biological effects of prolonged exposure to Martian gravity (0.38 g), Lunar gravity (0.17 g), and microgravity are expected, but the mechanisms involved and potential for remedies are unknown. We are proposing the development of a facility that provides a simulated Martian and Lunar gravity environment for experiments on biological systems in a well controlled laboratory setting. The magnetic adjustable gravity simulator will employ intense, inhomogeneous magnetic fields to exert magnetic body forces on a specimen that oppose the body force of gravity. By adjusting the magnetic field, it is possible to continuously adjust the total body force acting on a specimen. The simulator system considered consists of a superconducting solenoid with a room temperature bore sufficiently large to accommodate small whole organisms, cell cultures, and gravity sensitive bio-molecular solutions. It will have good optical access so that the organisms can be viewed in situ. This facility will be valuable for experimental observations and public demonstrations of systems in simulated reduced gravity. c2005 Published by Elsevier Ltd on behalf of COSPAR.

  6. Simulation of fluid flow induced by opposing ac magnetic fields in a continuous casting mold

    SciTech Connect

    Chang, F.C.; Hull, J.R.; Beitelman, L.

    1995-07-01

    A numerical simulation was performed for a novel electromagnetic stirring system employing two rotating magnetic fields. The system controls stirring flow in the meniscus region of a continuous casting mold independently from the stirring induced within the remaining volume of the mold by a main electromagnetic stirrer (M-EMS). This control is achieved by applying to the meniscus region an auxiliary electromagnetic field whose direction of rotation is opposite to that of the main magnetic field produced by the M-EMS. The model computes values and spatial distributions of electromagnetic parameters and fluid flow in the stirred pools of mercury in cylindrical and square geometries. Also predicted are the relationships between electromagnetics and fluid flows pertinent to a dynamic equilibrium of the opposing stirring swirls in the meniscus region. Results of the numerical simulation compared well with measurements obtained from experiments with mercury pools.

  7. Electron-Cloud Build-Up Simulations for the FNAL Main Injector

    SciTech Connect

    Furman, Miguel .A.

    2008-08-25

    We present a summary on ongoing simulation results for the electron-cloud (EC) buildup in the context of the proposed FNAL Main Injector (MI) intensity upgrade effort [1]. Most of the results presented here are for the field-free region at the location of the retarding field analyzer (RFA) electron detector [2-4]. The primary input variable we exercise is the peak secondary electron yield (SEY) {delta}{sub max}, which we let vary in the range 1.2 {le} {delta}{sub max} {le} 1.7. By combining our simulated results for the electron flux at the vacuum chamber wall with the corresponding RFA measurements we infer that 1.25 {approx}< {delta}{sub max} {approx}< 1.35 at this location. From this piece of information we estimate features of the EC distribution for various fill patterns, including the average electron number density n{sub e}. We then compare the behavior of the EC for a hypothetical RF frequency f{sub RF} = 212 MHz with the current 53 MHz for a given total beam population N{sub tot}. The density n{sub e} goes through a clear threshold as a function of N{sub tot} in a field-free region. As expected, the higher frequency leads to a weaker EC effect: the threshold in N{sub tot} is a factor {approx} 2 higher for f{sub RF} = 212 MHz than for 53 MHz, and ne is correspondingly lower by a factor {approx} 2 when N{sub tot} is above threshold. We briefly describe further work that needs to be carried out, sensitivities in the calculation, and puzzles in the results that remain to be addressed.

  8. Micromagnetic simulations of magnetic nanowires with constrictions by FIB

    NASA Astrophysics Data System (ADS)

    Long, H. H.; Ong, E. T.; Liu, T.; Li, H. L.; Liu, Z. J.; Li, E. P.; Wu, H. Y.; Adeyeye, A. O.

    2006-08-01

    Magnetic structures and magnetization processes of individual Ni nanowires with constrictions are investigated by means of micromagnetic modeling. The physical problem is modeled with the Landau-Lifshitz-Gilbert (LLG) equation, and the fast Fourier transform on multipoles (FFTM) method is employed to speed up the calculation of the demagnetization field. It is demonstrated that the FFTM algorithm is efficient and accurate for studying magnetization transition configuration in nanowire. The new approach is then used to study the switching phenomenon of the nanowire. And the simulation results show that the switching field increases a little with presence of constriction. The investigation of the magnetization processes illustrates the edge domain forms near constriction region for nanowire with diameter=30 nm and vortex domain for 200 nm case.

  9. High frequency variations of the main magnetic field: convergence of observations and theory (Petrus Peregrinus Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Jault, Dominique

    2013-04-01

    Understanding the main magnetic field variations has been hindered by the discrepancy between the periods (from months to years) of the simplest linear wave phenomena and the relatively long time intervals (10 to 100 years) over which magnetic field changes can be confidently monitored. A theoretical description of short-period waves within the Earth's fluid core is at hand. Quasi-geostrophic inertial waves (akin to Rossby waves in the atmosphere) are slightly modified in the presence of magnetic fields and torsional oscillations consist of differential motion between coaxial rigid cylindrical annuli. Torsional oscillations are sensitive to the whole magnetic field that they shear in the course of their propagation. From their modelling, we have thus gained an estimate for the magnetic field strength in the core interior. There is now ongoing work to extend the theoretical framework to longer times. Furthermore, data collected from the Swarm constellation of three satellites to be launched this year by ESA will permit to better separate the internal and external magnetic signals. We may thus dream to detect quasi-geostrophic inertial waves. As the spectral ranges of theoretical models and observations begin to overlap, we can now go beyond the understanding of the magnetic field variations as the juxtaposition of partial models, arranged as a set of nested Matryoshka dolls. This talk will give illustrations for this statement, among which the question of induction in the lower mantle.

  10. Vlasov simulations of collisionless magnetic reconnection without background density

    NASA Astrophysics Data System (ADS)

    Schmitz, H.; Grauer, R.

    2008-02-01

    A standard starting point for the simulation of collisionless reconnection is the Harris equilibrium which is made up of a current sheet that separates two regions of opposing magnetic field. Magnetohydrodynamic simulations of collisionless reconnection usually include a homogeneous background density for reasons of numerical stability. While, in some cases, this is a realistic assumption, the background density may introduce new effects both due to the more involved structure of the distribution function or due to the fact that the Alfvèn speed remains finite far away from the current sheet. We present a fully kinetic Vlasov simulation of the perturbed Harris equilibrium using a Vlasov code. Parameters are chosen to match the Geospace Environment Modeling (GEM) Magnetic Reconnection Challenge but excluding the background density. This allows to compare with earlier simulations [Schmitz H, Grauer R. Kinetic Vlasov simulations of collisionless magnetic reconnection. Phys Plasmas 2006;13:092309] which include the background density. It is found that the absence of a background density causes the reconnection rate to be higher. On the other hand, the time until the onset of reconnection is hardly affected. Again the off diagonal elements of the pressure tensor are found to be important on the X-line but with modified importance for the individual terms.

  11. Selecting Magnet Laminations Recipes Using the Meth-od of Sim-u-la-ted Annealing

    NASA Astrophysics Data System (ADS)

    Russell, A. D.; Baiod, R.; Brown, B. C.; Harding, D. J.; Martin, P. S.

    1997-05-01

    The Fermilab Main Injector project is building 344 dipoles using more than 7000 tons of steel. Budget and logistical constraints required that steel production, lamination stamping and magnet fabrication proceed in parallel. There were significant run-to-run variations in the magnetic properties of the steel (Martin, P.S., et al., Variations in the Steel Properties and the Excitation Characteristics of FMI Dipoles, this conference). The large lamination size (>0.5 m coil opening) resulted in variations of gap height due to differences in stress relief in the steel after stamping. To minimize magnet-to-magnet strength and field shape variations the laminations were shuffled based on the available magnetic and mechanical data and assigned to magnets using a computer program based on the method of simulated annealing. The lamination sets selected by the program have produced magnets which easily satisfy the design requirements. Variations of the average magnet gap are an order of magnitude smaller than the variations in lamination gaps. This paper discusses observed gap variations, the program structure and the strength uniformity results.

  12. Simulation of a main steam line break with steam generator tube rupture using trace

    SciTech Connect

    Gallardo, S.; Querol, A.; Verdu, G.

    2012-07-01

    A simulation of the OECD/NEA ROSA-2 Project Test 5 was made with the thermal-hydraulic code TRACE5. Test 5 performed in the Large Scale Test Facility (LSTF) reproduced a Main Steam Line Break (MSLB) with a Steam Generator Tube Rupture (SGTR) in a Pressurized Water Reactor (PWR). The result of these simultaneous breaks is a depressurization in the secondary and primary system in loop B because both systems are connected through the SGTR. Good approximation was obtained between TRACE5 results and experimental data. TRACE5 reproduces qualitatively the phenomena that occur in this transient: primary pressure falls after the break, stagnation of the pressure after the opening of the relief valve of the intact steam generator, the pressure falls after the two openings of the PORV and the recovery of the liquid level in the pressurizer after each closure of the PORV. Furthermore, a sensitivity analysis has been performed to know the effect of varying the High Pressure Injection (HPI) flow rate in both loops on the system pressures evolution. (authors)

  13. Numerical simulations of waves in a magnetically structured atmosphere

    NASA Astrophysics Data System (ADS)

    Espinola, Thomas Peter

    A physical model for simulating waves in a stellar atmosphere was developed from a combination of basic fluid mechanics, plasma physics, and electrodynamics. The model was three dimensional and included the effects of gravity, magnetic fields, and viscosity. An algorithm was developed to numerically implement this model. The resulting program used an explicit time integration scheme based on Runge-Kutta and a combination of finite difference and spectral methods to evaluate the spatial derivatives. A number of numerical boundary conditions were developed—the most successful used a modified Sommerfeld radiation condition. The program was written and coded in Fortran on a Vax computer. Additional routines were written to evaluate the required fast fourier transforms and to graph and display the data. The program was tested on a large number of one and two dimensional problems for which the solutions were known. These problems included acoustic waves, Alfvén waves, magnetoacoustic waves, shocks, rarefactions, and contact discontinuities. The numerical results agreed with the analytic solutions of the physical problems to within the precision requested of the simulation. The program proved to be stable and robust for all the problems attempted. This program was then used to simulate three problems for which analytic solutions are not known. All three simulations concerned the propagation of waves in magnetically structured atmospheres and may be applied to outstanding problems in solar physics. First, the interactions of non-linear waves and a flux slab were studied. From the result it is apparent that sources of shocks and rarefactions, such as the solar convection zone, do not concentrate the magnetic field in flux sheaths. Next I used the program to simulate the interaction of non-linear waves with a flux tube. The results suggest that the magnetic fields in flux tubes are also not concentrated by pairs of passing shocks and rarefactions; however, a complete

  14. Magnetic resonance imaging simulator: a teaching tool for radiology.

    PubMed

    Rundle, D; Kishore, S; Seshadri, S; Wehrli, F

    1990-11-01

    The increasing use of magnetic resonance imaging (MRI) as a clinical modality has put an enormous burden on medical institutions to cost effectively teach MRI scanning techniques to technologists and physicians. Since MRI scanner time is a scarce resource, it would be ideal if the teaching could be effectively performed off-line. In order to meet this goal, the radiology Department at the University of Pennsylvania has designed and developed a Magnetic Resonance Imaging Simulator. The simulator in its current implementation mimics the General Electric Signa (General Electric Magnetic Resonance Imaging System, Milwaukee, WI) scanner's user interface for image acquisition. The design is general enough to be applied to other MRI scanners. One unique feature of the simulator is its incorporation of an image-synthesis module that permits the user to derive images for any arbitrary combination of pulsing parameters for spin-echo, gradient-echo, and inversion recovery pulse sequences. These images are computed in 5 seconds. The development platform chosen is a standard Apple Macintosh II (Apple Computer, Inc, Cupertino, CA) computer with no specialized hardware peripherals. The user interface is implemented in HyperCard (Apple Computer Inc, Cupertino, CA). All other software development including synthesis and display functions are implemented under the Macintosh Programmer's Workshop 'C' environment. The scan parameters, demographics, and images are tracked using an Oracle (Oracle Corp, Redwood Shores, CA) data base. Images are currently stored on magnetic disk but could be stored on optical media with minimal effort. PMID:2085559

  15. Simulated magnetic field expulsion in neutron star cores

    NASA Astrophysics Data System (ADS)

    Elfritz, J. G.; Pons, J. A.; Rea, N.; Glampedakis, K.; Viganò, D.

    2016-03-01

    The study of long-term evolution of neutron star (NS) magnetic fields is key to understanding the rich diversity of NS observations, and to unifying their nature despite the different emission mechanisms and observed properties. Such studies in principle permit a deeper understanding of the most important parameters driving their apparent variety, e.g. radio pulsars, magnetars, X-ray dim isolated NSs, gamma-ray pulsars. We describe, for the first time, the results from self-consistent magnetothermal simulations considering not only the effects of the Hall-driven field dissipation in the crust, but also adding a complete set of proposed driving forces in a superconducting core. We emphasize how each of these core-field processes drive magnetic evolution and affect observables, and show that when all forces are considered together in vectorial form, the net expulsion of core magnetic flux is negligible, and will have no observable effect in the crust (consequently in the observed surface emission) on megayear time-scales. Our new simulations suggest that strong magnetic fields in NS cores (and the signatures on the NS surface) will persist long after the crustal magnetic field has evolved and decayed, due to the weak combined effects of dissipation and expulsion in the stellar core.

  16. Design method of the layered active magnetic regenerator (AMR) for hydrogen liquefaction by numerical simulation

    NASA Astrophysics Data System (ADS)

    Park, Inmyong; Kim, Youngkwon; Park, Jiho; Jeong, Sangkwon

    2015-09-01

    The design procedure of an active magnetic regenerator (AMR) operating between liquid nitrogen temperature and liquid hydrogen temperature is discussed with the selected magnetic refrigerants. Selected magnetic refrigerants (GdNi2, Dy0.85Er0.15Al2, Dy0.5Er0.5Al2, and Gd0.1Dy0.9Ni2) that have different transition temperatures are layered in an AMR to widen the temperature span. The optimum volume fraction of the layered refrigerants for the maximum COP with minimum volume is designed in a two-stage active magnetic regenerative refrigerator (AMRR) using one dimensional numerical simulation. The entropy generation in each stage of the AMR is calculated by the numerical simulation to optimize the proposed design. The main sources of the entropy generation in the AMR are pressure drop, convection and conduction heat transfers in the AMR. However, the entropy generation by the convective heat transfer is mostly dominant in the optimized cases. In this paper, the design parameters and the operating conditions such as the distribution of the selected refrigerants in the layered AMR, the intermediate temperature between two stages and the mass flow rate of heat transfer fluid are specifically determined to maximize the performance of the AMR. The proposed design method will facilitate the construction of AMR systems with various magnetic refrigerants and conditions such as AMR size, operating temperature range, and magnetic field variation.

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

    SciTech Connect

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

    2015-09-25

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

  18. Simulations of Filament Channel Formation in a Coronal Magnetic Field

    NASA Astrophysics Data System (ADS)

    Knizhnik, Kalman; DeVore, C. Richard; Antiochos, Spiro K.

    2016-05-01

    A major unanswered problem in solar physics has been explaining the presence of sheared filament channels above photospheric polarity inversion lines (PILs) and the simultaneous lack of structure in the ‘loop’ portion of the coronal magnetic field. The shear inherent in filament channels represents not only a form of magnetic energy, but also magnetic helicity. As a result, models of filament channel formation need to explain not only why helicity is observed above PILs, but also why it is apparently not observed anywhere else in the corona. Previous results (Knizhnik, Antiochos & DeVore, 2015) have suggested that any helicity injected into the coronal field inverse-cascades in scale, a process known as magnetic helicity condensation (Antiochos, 2013). In this work, we present high resolution numerical simulations of photospheric helicity injection into a coronal magnetic field that contains both a PIL and a coronal hole (CH). We show conclusively that the inverse cascade of magnetic helicity terminates at the PIL, resulting in the formation of highly sheared filament channels and a smooth, untwisted corona. We demonstrate that even though magnetic helicity is injected throughout the flux system, it accumulates only at the PIL, where it manifests itself in the form of highly sheared filament channels, while any helicity obtained by the CH is ejected out of the system. We show that the formation of filament channels is both qualitatively and quantitatively in agreement with observations and discuss the implications of our simulations for observations.This work was supported by the NASA Earth and Space Science Fellowship, LWS TR&T and H-SR Programs.

  19. Air quality simulations for North America - MM5-CAMx modelling performance for main gaseous pollutants

    NASA Astrophysics Data System (ADS)

    Ferreira, J.; Rodriguez, A.; Monteiro, A.; Miranda, A. I.; Dios, M.; Souto, J. A.; Yarwood, G.; Nopmongcol, U.; Borrego, C.

    2012-06-01

    In the scope of the Air Quality Model Evaluation International Initiative (AQMEII) the air quality modelling system MM5-CAMx was applied to the North American (NA) domain for calendar year 2006. The simulation domain was defined according to the spatial resolution and the coordinate system of the emission databases provided and the common grid required by AQMEII for ensemble analysis. A Lambert Conformal Projection grid of around 5500 km by 3580 km with 24 × 24 km2 horizontal resolution was defined. Emissions available through AQMEII have been prepared to feed the CAMx model. Meteorological inputs were developed by the application of the meteorological model MM5, which was initialized by 1° resolution NCEP-FNL global data and run for the whole year of 2006. A spatial and temporal analysis of results based on the 2D surface fields and time series for regional monitoring stations was performed for the main gaseous pollutants. A detailed statistical analysis and evaluation against observations was carried out, considering three different sub-domains over North America, in order to comprehend the differences between the East, West and Central part. The exploitation of modelling results was based on the capabilities and analysis tools available through the ENSEMBLE software, developed and upgraded for AQMEII. Results have shown a good agreement between observed and modelled concentrations of O3 (especially regarding peaks) and NO2 and a weaker performance of the air quality model for CO and SO2. However, the model tends to underestimate O3 and overestimate NO2 and CO at night as a consequence of meteorology (weak vertical mixing due to underestimation of the Planetary Boundary Layer (PBL) height). This paper intends to be a valuable contribution to the overall AQMEII exercise since it aims to evaluate the performance of individual models to be used in the ensemble approach for the areas of interest.

  20. Magnetic Braking of the Main Component of θ^{1} Ori C

    NASA Astrophysics Data System (ADS)

    Balega, Yu. Yu.; Leushin, V. V.; Weigelt, G.

    θ^{1} Ori C is the nearest massive O star at the early phase of the evolution. Interferometric study of the star at the 6-m BTA telescope showed that it is a binary system with an orbital period of 11 yr (Weigelt et al., 1999). It was also found that θ^{1} Ori C is an oblique magnetic rotator (Donati et al., 2002; Wade et al., 2006). From high resolution spectra of the binary collected with the 6-m telescope we succeeded to separate week lines of the secondary component and to measure its rotation velocity. It was found that the secondary rotates three times faster than the primary. We discuss the possibility of magnetic braking of the primary star as the mechanism explaining the difference of rotation.

  1. Simulations of Energetic Particles Interacting with Dynamical Magnetic Turbulence

    NASA Astrophysics Data System (ADS)

    Hussein, M.; Shalchi, A.

    2016-02-01

    We explore the transport of energetic particles in interplanetary space by using test-particle simulations. In previous work such simulations have been performed by using either magnetostatic turbulence or undamped propagating plasma waves. In the current paper we simulate for the first time particle transport in dynamical turbulence. To do so we employ two models, namely the damping model of dynamical turbulence and the random sweeping model. We compute parallel and perpendicular diffusion coefficients and compare our numerical findings with solar wind observations. We show that good agreement can be found between simulations and the Palmer consensus range for both dynamical turbulence models if the ratio of turbulent magnetic field and mean field is δB/B0 = 0.5.

  2. Plasma transport in a simulated magnetic-divertor configuration

    SciTech Connect

    Strawitch, C. M.

    1981-03-01

    The transport properties of plasma on magnetic field lines that intersect a conducting plate are studied experimentally in the Wisconsin internal ring D.C. machine. The magnetic geometry is intended to simulate certain aspects of plasma phenomena that may take place in a tokamak divertor. It is found by a variety of measurements that the cross field transport is non-ambipolar; this may have important implications in heat loading considerations in tokamak divertors. The undesirable effects of nonambipolar flow make it preferable to be able to eliminate it. However, we find that though the non-ambipolarity may be reduced, it is difficult to eliminate entirely. The plasma flow velocity parallel to the magnetic field is found to be near the ion acoustic velocity in all cases. The experimental density and electron temperature profiles are compared to the solutions to a one dimensional transport model that is commonly used in divertor theory.

  3. Kinetic simulations of magnetized turbulence in astrophysical plasmas.

    PubMed

    Howes, G G; Dorland, W; Cowley, S C; Hammett, G W; Quataert, E; Schekochihin, A A; Tatsuno, T

    2008-02-15

    This Letter presents the first ab initio, fully electromagnetic, kinetic simulations of magnetized turbulence in a homogeneous, weakly collisional plasma at the scale of the ion Larmor radius (ion gyroscale). Magnetic- and electric-field energy spectra show a break at the ion gyroscale; the spectral slopes are consistent with scaling predictions for critically balanced turbulence of Alfvén waves above the ion gyroscale (spectral index -5/3) and of kinetic Alfvén waves below the ion gyroscale (spectral indices of -7/3 for magnetic and -1/3 for electric fluctuations). This behavior is also qualitatively consistent with in situ measurements of turbulence in the solar wind. Our findings support the hypothesis that the frequencies of turbulent fluctuations in the solar wind remain well below the ion cyclotron frequency both above and below the ion gyroscale. PMID:18352484

  4. Two-dimensional Vlasov code simulation of magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Togano, K.; Umeda, T.; Ogino, T.

    2009-12-01

    There are numerous types of self-consistent simulations that treat plasmas according to some approximations. The fluid codes are used to study global and macroscopic processes in space plasmas. Nonlinear microscopic processes in space plasmas are studied with kinetic simulation codes. Numerical methods for kinetic simulations fall into two groups. One is particle-in-cell (PIC) method which follows motions of individual particles in a self-consistent electromagnetic field. However, a limitation on the number of particles gives rise to numerical thermal fluctuations. Another approach is Vlasov method which follows spatial and temporal development of distribution functions in the position-velocity phase space. In contrast to PIC codes, numerical noise is substantially suppressed. However, Vlasov codes require huge computer resources to represent distribution functions and Vlasov simulation techniques are still developing. Owing to the rapid advancement of recent computer technology, Vlasov code simulation would be more essential in the near future. In the present study, a new two-and-half-dimensional and fully electromagnetic Vlasov simulation code is developed in which phase-space distribution functions are defined in five-dimensional position-velocity phase space (x,y,vx,vy,vz). The Vlasov equation in two-dimensional configuration and three-dimensional velocity spaces is solved with a non-oscillatory and conservative scheme, and the full set of Maxwell’s equations are self-consistently solved based on the implicit Finite Difference Time Domain (FDTD) method. The Geospace Environment Modeling (GEM) magnetic reconnection challenge is chosen as a benchmark test of our two-dimensional Vlasov code. The result is compared with the past simulation results with Darwin-Vlasov, explicit PIC and implicit PIC codes. The present simulation with a very-low spatial resolution gives a high growth rate of magnetic flux, which is in agreement with the results of the GEM

  5. FLASH magnetohydrodynamic simulations of shock-generated magnetic field experiments

    NASA Astrophysics Data System (ADS)

    Tzeferacos, P.; Fatenejad, M.; Flocke, N.; Gregori, G.; Lamb, D. Q.; Lee, D.; Meinecke, J.; Scopatz, A.; Weide, K.

    2012-12-01

    We report the results of benchmark FLASH magnetohydrodynamic (MHD) simulations of experiments conducted by the University of Oxford High Energy Density Laboratory Astrophysics group and its collaborators at the Laboratoire pour l'Utilisation des Lasers Intenses (LULI). In these experiments, a long-pulse laser illuminates a target in a chamber filled with Argon gas, producing shock waves that generate magnetic fields via the Biermann battery mechanism. We first outline the implementation of 2D cylindrical geometry in the unsplit MHD solver in FLASH and present results of verification tests. We then describe the results of benchmark 2D cylindrical MHD simulations of the LULI experiments using FLASH that explore the impact of external fields along with the possibility of magnetic field amplification by turbulence that is associated with the shock waves and that is induced by a grid placed in the gas-filled chamber.

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

    SciTech Connect

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

    2008-11-01

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

  7. Simulating Magnetized Laboratory Plasmas with Smoothed Particle Hydrodynamics

    SciTech Connect

    Johnson, Jeffrey N.

    2009-01-01

    The creation of plasmas in the laboratory continues to generate excitement in the physics community. Despite the best efforts of the intrepid plasma diagnostics community, the dynamics of these plasmas remains a difficult challenge to both the theorist and the experimentalist. This dissertation describes the simulation of strongly magnetized laboratory plasmas with Smoothed Particle Hydrodynamics (SPH), a method born of astrophysics but gaining broad support in the engineering community. We describe the mathematical formulation that best characterizes a strongly magnetized plasma under our circumstances of interest, and we review the SPH method and its application to astrophysical plasmas based on research by Phillips [1], Buerve [2], and Price and Monaghan [3]. Some modifications and extensions to this method are necessary to simulate terrestrial plasmas, such as a treatment of magnetic diffusion based on work by Brookshaw [4] and by Atluri [5]; we describe these changes as we turn our attention toward laboratory experiments. Test problems that verify the method are provided throughout the discussion. Finally, we apply our method to the compression of a magnetized plasma performed by the Compact Toroid Injection eXperiment (CTIX) [6] and show that the experimental results support our computed predictions.

  8. First discovery of a magnetic field in a main-sequence δ Scuti star: the Kepler star HD 188774

    NASA Astrophysics Data System (ADS)

    Neiner, C.; Lampens, P.

    2015-11-01

    The Kepler space mission provided a wealth of δ Sct-γ Dor hybrid candidates. While some may be genuine hybrids, others might be misclassified due to the presence of a binary companion or to rotational modulation caused by magnetism and related surface inhomogeneities. In particular, the Kepler δ Sct-γ Dor hybrid candidate HD 188774 shows a few low frequencies in its light and radial velocity curves, whose origin is unclear. In this work, we check for the presence of a magnetic field in HD 188774. We obtained two spectropolarimetric measurements with an Echelle SpectroPolarimetric Device for the Observation of Stars (ESPaDOnS) at Canada-France-Hawaii Telescope. The data were analysed with the least-squares deconvolution (LSD) method. We detected a clear magnetic signature in the Stokes V LSD profiles. The origin of the low frequencies detected in HD 188774 is therefore most probably the rotational modulation of surface spots possibly related to the presence of a magnetic field. Consequently, HD 188774 is not a genuine hybrid δ Sct-γ Dor star, but the first known magnetic main-sequence δ Sct star. This makes it a prime target for future asteroseismic and spot modelling. This result casts new light on the interpretation of the Kepler results for other δ Sct-γ Dor hybrid candidates.

  9. Simulation of magnetic field line stochasticity at the magnetopause

    NASA Technical Reports Server (NTRS)

    Wang, Zhi; Ashour-Abdalla, Maha

    1994-01-01

    We have conducted a three-dimensional particle simulation to study the magnetic field line stochasticity at the magnetopause current layer. Our results show that the magnetic field lines become stochastic due to the overlap of the destabilized multiple tearing mode islands, which agrees with the percolation model suggested by Galeev et al. (1986). After the field lines become stochastic, these tearing modes grow even 2-3 times faster than in the linear stage and saturate at an amplitude level 3-4 times bigger than the single tearing mode without mode-mode coupling. The field line stochasticity also causes a strong particle diffusion across the current layer. The diffusion coefficient reaches to 10(exp 9) sq m/s for typical magnetopause parameters. Associated with the particle diffusion, the current layer becomes broader in width. As a result, the magnetic energy is dissipated into particle energy by heating parallel to the local magnetic field. The particle energy increases by 60%, while the magnetic helicity, which has always been regarded as a good invariant, changes by 20%.

  10. Simulations of a Detonation Wave in Transverse Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Cole, Lord; Karagozian, Ann; Cambier, Jean-Luc

    2010-11-01

    Numerical simulations of magneto-hydrodynamic (MHD) effects on detonation wave structures are performed, with applications to flow control and MHD power extraction in Pulse Detonation Engines (PDE) and their design variations. In contrast to prior studies of MHD interactions in PDEs,ootnotetextCambier, et al., AIAA-2008-4688 the effects of the finite relaxation length scale for ionization on the stability of the detonation wave are examined. Depending on the coupling parameters, the magnetic field can quench the detonation and effectively act as a barrier to its propagation. Conversely, an applied transient magnetic field can exert a force on a pre-ionized gas and accelerate it. The dynamics are subject to non-linear effects; a propagating transverse magnetic field will initially exert a small force if the gas has a low conductivity and the magnetic Reynolds number (Rem) is low. Nevertheless, the gas accelerated by the "piston" action of the field can pre-heat the ambient gas and increase its conductivity. As the wave progresses, Rem increases and the magnetic field becomes increasingly effective. The dynamics of this process are examined in detail with a high-order shock-capturing method and full kinetics of combustion and ionization. The complex chemical kinetics calculations are ported onto a GPU using the CUDA language, and computational performance is compared with standard CPU-based computations.

  11. Analysing a magnetic molecule detection system--computer simulation.

    PubMed

    Schepper, W; Schotter, J; Brückl, H; Reiss, G

    2004-08-26

    The detection of single molecules, e.g. in biology is possible by marking the interesting molecules with magnetic beads and detect the influence of the beads on giant magnetoresistance (GMR)/tunnel magnetoresistance (TMR)/spin valve (SV) sensors. The development of suitable multilayers has been studied experimentally as well as theoretically in order to optimize the sensor parameters. A finite difference (FD) method including the usually used contributions to the total energy [exchange, antiferromagnetically (af) coupling, anisotropy and magnetostatic] is used for the simulation with additional contributions to the local field according to the stray fields of the beads. In this work, we will show the results of micromagnetic calculations of the magnetization behavior of GMR/TMR sensors considering also the interaction between the domains in the magnetic layers of the sensor and the bead area. We can present first calculations where the bead particles (signal source) and the magnetic layers (sensor device) are considered as a whole magnetic ensemble. PMID:15288939

  12. 3D Relativistic Magnetohydrodynamic Simulations of Magnetized Spine-Sheath Relativistic Jets

    NASA Technical Reports Server (NTRS)

    Mizuno, Yosuke; Hardee, Philip; Nishikawa, Ken-Ichi

    2006-01-01

    Numerical simulations of weakly magnetized and strongly magnetized relativistic jets embedded in a weakly magnetized and strongly magnetized stationary or weakly relativistic (v = c/2) sheath have been performed. A magnetic field parallel to the flow is used in these simulations performed by the new GRMHD numerical code RAISHIN used in its RMHD configuration. In the numerical simulations the Lorentz factor gamma = 2.5 jet is precessed to break the initial equilibrium configuration. In the simulations sound speeds are less than or equal to c/the square root of 3 in the weakly magnetized simulations and less than or equal to 0.56 c in the strongly magnetized simulations. The Alfven wave speed is less than or equal to 0.07 c in the weakly magnetized simulations and less than or equal to 0.56 c in the strongly magnetized simulations. The results of the numerical simulations are compared to theoretical predictions from a normal mode analysis of the linearized relativistic magnetohydrodynamic (RMHD) equations capable of describing a uniform axially magnetized cylindrical relativistic jet embedded in a uniform axially magnetized relativistically moving sheath. The theoretical dispersion relation allows investigation of effects associated with maximum possible sound speeds, Alfven wave speeds near light speed and relativistic sheath speeds. The prediction of increased stability of the weakly magnetized system resulting from c/2 sheath speeds and the stabilization of the strongly magnetized system resulting from c/2 sheath speeds is verified by the numerical simulation results.

  13. MHD Simulations of the Plasma Flow in the Magnetic Nozzle

    NASA Technical Reports Server (NTRS)

    Smith, T. E. R.; Keidar, M.; Sankaran, K.; olzin, K. A.

    2013-01-01

    The magnetohydrodynamic (MHD) flow of plasma through a magnetic nozzle is simulated by solving the governing equations for the plasma flow in the presence of an static magnetic field representing the applied nozzle. This work will numerically investigate the flow and behavior of the plasma as the inlet plasma conditions and magnetic nozzle field strength are varied. The MHD simulations are useful for addressing issues such as plasma detachment and to can be used to gain insight into the physical processes present in plasma flows found in thrusters that use magnetic nozzles. In the model, the MHD equations for a plasma, with separate temperatures calculated for the electrons and ions, are integrated over a finite cell volume with flux through each face computed for each of the conserved variables (mass, momentum, magnetic flux, energy) [1]. Stokes theorem is used to convert the area integrals over the faces of each cell into line integrals around the boundaries of each face. The state of the plasma is described using models of the ionization level, ratio of specific heats, thermal conductivity, and plasma resistivity. Anisotropies in current conduction due to Hall effect are included, and the system is closed using a real-gas equation of state to describe the relationship between the plasma density, temperature, and pressure.A separate magnetostatic solver is used to calculate the applied magnetic field, which is assumed constant for these calculations. The total magnetic field is obtained through superposition of the solution for the applied magnetic field and the self-consistently computed induced magnetic fields that arise as the flowing plasma reacts to the presence of the applied field. A solution for the applied magnetic field is represented in Fig. 1 (from Ref. [2]), exhibiting the classic converging-diverging field pattern. Previous research was able to demonstrate effects such as back-emf at a super-Alfvenic flow, which significantly alters the shape of the

  14. Simulation and Characterization of the MINER{nu}A Dipole Magnets

    SciTech Connect

    Felix, J.; Castorena, J.; Higuera, A.; Urrutia, Z.; Zavala, G.

    2009-12-17

    The MINER{nu}A (Main INjector ExpeRiment for {nu} A) experiment (http://minerva.fnal.gov/) is a neutrino scattering experiment which uses the NuMI beamline at Fermilab. It seeks to measure low energy neutrino interactions both to support neutrino oscillation experiments and to study the strong dynamics of the nucleon and nucleus that affect these interactions. For energy calibration of the main detector, a tertiary test beam line was designed and commissioned. This test beam consisted of target, collimator, two TOF stations and four wire chamber stations. Two dipole trim magnets were used to form a spectrometer. Here we present the simulation and characterization of these dipole magnets.

  15. Propulsion simulator for magnetically-suspended wind tunnel models

    NASA Technical Reports Server (NTRS)

    Joshi, Prakash B.; Goldey, C. L.; Sacco, G. P.; Lawing, Pierce L.

    1991-01-01

    The objective of phase two of a current investigation sponsored by NASA Langley Research Center is to demonstrate the measurement of aerodynamic forces/moments, including the effects of exhaust gases, in magnetic suspension and balance system (MSBS) wind tunnels. Two propulsion simulator models are being developed: a small-scale and a large-scale unit, both employing compressed, liquified carbon dioxide as propellant. The small-scale unit was designed, fabricated, and statically-tested at Physical Sciences Inc. (PSI). The large-scale simulator is currently in the preliminary design stage. The small-scale simulator design/development is presented, and the data from its static firing on a thrust stand are discussed. The analysis of this data provides important information for the design of the large-scale unit. A description of the preliminary design of the device is also presented.

  16. Fokker-Planck formalism in magnetic resonance simulations.

    PubMed

    Kuprov, Ilya

    2016-09-01

    This paper presents an overview of the Fokker-Planck formalism for non-biological magnetic resonance simulations, describes its existing applications and proposes some novel ones. The most attractive feature of Fokker-Planck theory compared to the commonly used Liouville - von Neumann equation is that, for all relevant types of spatial dynamics (spinning, diffusion, stationary flow, etc.), the corresponding Fokker-Planck Hamiltonian is time-independent. Many difficult NMR, EPR and MRI simulation problems (multiple rotation NMR, ultrafast NMR, gradient-based zero-quantum filters, diffusion and flow NMR, off-resonance soft microwave pulses in EPR, spin-spin coupling effects in MRI, etc.) are simplified significantly in Fokker-Planck space. The paper also summarises the author's experiences with writing and using the corresponding modules of the Spinach library - the methods described below have enabled a large variety of simulations previously considered too complicated for routine practical use. PMID:27470597

  17. Fokker-Planck formalism in magnetic resonance simulations

    NASA Astrophysics Data System (ADS)

    Kuprov, Ilya

    2016-09-01

    This paper presents an overview of the Fokker-Planck formalism for non-biological magnetic resonance simulations, describes its existing applications and proposes some novel ones. The most attractive feature of Fokker-Planck theory compared to the commonly used Liouville - von Neumann equation is that, for all relevant types of spatial dynamics (spinning, diffusion, stationary flow, etc.), the corresponding Fokker-Planck Hamiltonian is time-independent. Many difficult NMR, EPR and MRI simulation problems (multiple rotation NMR, ultrafast NMR, gradient-based zero-quantum filters, diffusion and flow NMR, off-resonance soft microwave pulses in EPR, spin-spin coupling effects in MRI, etc.) are simplified significantly in Fokker-Planck space. The paper also summarises the author's experiences with writing and using the corresponding modules of the Spinach library - the methods described below have enabled a large variety of simulations previously considered too complicated for routine practical use.

  18. Experimental study of quantum simulation for quantum chemistry with a nuclear magnetic resonance simulator.

    PubMed

    Lu, Dawei; Xu, Nanyang; Xu, Boruo; Li, Zhaokai; Chen, Hongwei; Peng, Xinhua; Xu, Ruixue; Du, Jiangfeng

    2012-10-13

    Quantum computers have been proved to be able to mimic quantum systems efficiently in polynomial time. Quantum chemistry problems, such as static molecular energy calculations and dynamical chemical reaction simulations, become very intractable on classical computers with scaling up of the system. Therefore, quantum simulation is a feasible and effective approach to tackle quantum chemistry problems. Proof-of-principle experiments have been implemented on the calculation of the hydrogen molecular energies and one-dimensional chemical isomerization reaction dynamics using nuclear magnetic resonance systems. We conclude that quantum simulation will surpass classical computers for quantum chemistry in the near future. PMID:22946038

  19. Terrestrial Microgravity Model and Threshold Gravity Simulation using Magnetic Levitation

    NASA Technical Reports Server (NTRS)

    Ramachandran, N.

    2005-01-01

    What is the threshold gravity (minimum gravity level) required for the nominal functioning of the human system? What dosage is required? Do human cell lines behave differently in microgravity in response to an external stimulus? The critical need for such a gravity simulator is emphasized by recent experiments on human epithelial cells and lymphocytes on the Space Shuttle clearly showing that cell growth and function are markedly different from those observed terrestrially. Those differences are also dramatic between cells grown in space and those in Rotating Wall Vessels (RWV), or NASA bioreactor often used to simulate microgravity, indicating that although morphological growth patterns (three dimensional growth) can be successfully simulated using RWVs, cell function performance is not reproduced - a critical difference. If cell function is dramatically affected by gravity off-loading, then cell response to stimuli such as radiation, stress, etc. can be very different from terrestrial cell lines. Yet, we have no good gravity simulator for use in study of these phenomena. This represents a profound shortcoming for countermeasures research. We postulate that we can use magnetic levitation of cells and tissue, through the use of strong magnetic fields and field gradients, as a terrestrial microgravity model to study human cells. Specific objectives of the research are: 1. To develop a tried, tested and benchmarked terrestrial microgravity model for cell culture studies; 2. Gravity threshold determination; 3. Dosage (magnitude and duration) of g-level required for nominal functioning of cells; 4. Comparisons of magnetic levitation model to other models such as RWV, hind limb suspension, etc. and 5. Cellular response to reduced gravity levels of Moon and Mars. The paper will discuss experiments md modeling work to date in support of this project.

  20. Terrestrial Microgravity Model and Threshold Gravity Simulation sing Magnetic Levitation

    NASA Technical Reports Server (NTRS)

    Ramachandran, N.

    2005-01-01

    What is the threshold gravity (minimum gravity level) required for the nominal functioning of the human system? What dosage is required? Do human cell lines behave differently in microgravity in response to an external stimulus? The critical need for such a gravity simulator is emphasized by recent experiments on human epithelial cells and lymphocytes on the Space Shuttle clearly showing that cell growth and function are markedly different from those observed terrestrially. Those differences are also dramatic between cells grown in space and those in Rotating Wall Vessels (RWV), or NASA bioreactor often used to simulate microgravity, indicating that although morphological growth patterns (three dimensional growth) can be successiblly simulated using RWVs, cell function performance is not reproduced - a critical difference. If cell function is dramatically affected by gravity off-loading, then cell response to stimuli such as radiation, stress, etc. can be very different from terrestrial cell lines. Yet, we have no good gravity simulator for use in study of these phenomena. This represents a profound shortcoming for countermeasures research. We postulate that we can use magnetic levitation of cells and tissue, through the use of strong magnetic fields and field gradients, as a terrestrial microgravity model to study human cells. Specific objectives of the research are: 1. To develop a tried, tested and benchmarked terrestrial microgravity model for cell culture studies; 2. Gravity threshold determination; 3. Dosage (magnitude and duration) of g-level required for nominal functioning of cells; 4. Comparisons of magnetic levitation model to other models such as RWV, hind limb suspension, etc. and 5. Cellular response to reduced gravity levels of Moon and Mars.

  1. Ensemble simulations of the ocean induced magnetic field

    NASA Astrophysics Data System (ADS)

    Irrgang, Christopher; Saynisch, Jan; Hagedoorn, Jan M.; Thomas, Maik

    2016-04-01

    The recent advent of new high-resolution datasets of electromagnetic induction allows novel combinations of observations and models. The ocean induced magnetic field provides the potential to indirectly observe the ocean general circulation and may be utilized by data assimilation techniques. The modelling of the ocean induced magnetic field is affected by various uncertainties that originate from errors in the input data and from the applied model itself. The amount of aggregated uncertainties and their effect on the modelling of electromagnetic induction in the ocean is unknown. However, the knowledge of model uncertainties is essential for many research questions. To investigate the uncertainty in the modelling of motional induction, ensemble simulations with an ocean general circulation model and an electromagnetic induction model are performed on the basis of different error scenarios. This approach allows to estimate both the spatial distribution and temporal variation of the uncertainty. The largest uncertainty in the motionally induced magnetic field occurs in the area of the Antarctic Circumpolar Current. Local maxima reach values of up to 0.7 nano Tesla (nT). The estimated global annual mean uncertainty in the motionally induced magnetic field ranges from 0.1 to 0.4 nT. The relative amount of uncertainty reaches up to 30 % of the induced magnetic signal strength with largest values in regions in the northern hemisphere. The major source of uncertainty is found to be introduced by the wind stress from the atmospheric forcing of the ocean model. In addition, the temporal evolution of the uncertainty in the motionally induced magnetic field shows distinct seasonal variations. Specific regions are identified which are robust with respect to the introduced uncertainties.

  2. Simulations of magnetic hysteresis loops at high temperatures

    SciTech Connect

    Plumer, M. L.; Whitehead, J. P.; Fal, T. J.; Ek, J. van; Mercer, J. I.

    2014-09-28

    The kinetic Monte-Carlo algorithm as well as standard micromagnetics are used to simulate MH loops of high anisotropy magnetic recording media at both short and long time scales over a wide range of temperatures relevant to heat-assisted magnetic recording. Microscopic parameters, common to both methods, were determined by fitting to experimental data on single-layer FePt-based media that uses the Magneto-Optic Kerr effect with a slow sweep rate of 700 Oe/s. Saturation moment, uniaxial anisotropy, and exchange constants are given an intrinsic temperature dependence based on published atomistic simulations of FePt grains with an effective Curie temperature of 680 K. Our results show good agreement between micromagnetics and kinetic Monte Carlo results over a wide range of sweep rates. Loops at the slow experimental sweep rates are found to become more square-shaped, with an increasing slope, as temperature increases from 300 K. These effects also occur at higher sweep rates, typical of recording speeds, but are much less pronounced. These results demonstrate the need for accurate determination of intrinsic thermal properties of future recording media as input to micromagnetic models as well as the sensitivity of the switching behavior of thin magnetic films to applied field sweep rates at higher temperatures.

  3. Fast magnetic reconnection in three-dimensional magnetohydrodynamics simulations

    SciTech Connect

    Pang Bijia; Pen, U.-L.; Vishniac, Ethan T.

    2010-10-15

    A constructive numerical example of fast magnetic reconnection in a three-dimensional periodic box is presented. Reconnection is initiated by a strong, localized perturbation to the field lines. The solution is intrinsically three-dimensional and its gross properties do not depend on the details of the simulations. {approx}30% of the magnetic energy is released in an event which lasts about one Alfven time, but only after a delay during which the field lines evolve into a critical configuration. The physical picture of the process is presented. The reconnection regions are dynamical and mutually interacting. In the comoving frame of these regions, reconnection occurs through a x-like point, analogous to Petschek reconnection. The dynamics appear to be driven by global flows, not local processes.

  4. Simulated imaging properties of a series of magnetic electron lenses

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.

    1995-01-01

    The paraxial lens data were determined for a series of symmetrical magnetic lenses of equal lens diameter but variable air gap width for a wide range of lens excitations using the three-dimensional electrodynamic computer code MAFIA. The results are compared with a similar study done by Liebman and Grad wherein the field distributions within the lenses were measured experimentally with a resistance network analogue. Using these fields the lens data were obtained through numerical trajectory tracing. The utility of using MAFIA, instead of experimental methods for lens design is shown by the excellent agreement of the simulated results compared to experiment. Also demonstrated is the capability of using MAFIA to investigate aberration sources such as higher order off-axis magnetic field and space-charge effects.

  5. Effects of simulated cosmological magnetic fields on the galaxy population

    NASA Astrophysics Data System (ADS)

    Marinacci, Federico; Vogelsberger, Mark

    2016-02-01

    We investigate the effects of varying the intensity of the primordial magnetic seed field on the global properties of the galaxy population in ideal magnetohydrodynamic cosmological simulations performed with the moving-mesh code AREPO. We vary the seed field in our calculations in a range of values still compatible with the current cosmological upper limits. We show that above a critical intensity of ≃10-9 G, the additional pressure arising from the field strongly affects the evolution of gaseous structures, leading to a suppression of the cosmic star formation history, which is stronger for larger seed fields. This directly reflects into a lower total galaxy count above a fixed stellar mass threshold at all redshifts, and a lower galaxy number density at fixed stellar mass and a less massive stellar component at fixed virial mass at all mass scales. These signatures may be used, in addition to the existing methods, to derive tighter constraints on primordial magnetic seed field intensities.

  6. Simulation study of magnetic reconnection in high magnetic Reynolds number plasmas

    NASA Astrophysics Data System (ADS)

    Nakabo, T.; Kusano, K.; Miyoshi, T.; Vekstein, G.

    2013-12-01

    Magnetic reconnection is an important process for dynamics in space and laboratory plasmas. Magnetic reconnection is basically dominated by magnetic diffusion at thin current sheet as proposed by Sweet (1958) and Parker (1963). According to their theory, the reconnection rate must be inversely proportional to the square root of the magnetic Reynolds number (S). In magnetosphere and the solar corona, however, in spite of high magnetic Reynolds number (>10^12), reconnection rate is measured to be about 10^-2 that is much higher than the Sweet and Parker's prediction. Although Petschek proposed that the slow mode shock may accelerate reconnection, numerical simulations suggested that the Petschek's type reconnection cannot be sustained with uniform resistivity. On the other hand, it is pointed out that in high magnetic Reynolds number, the thin current sheet becomes unstable to the so-called secondary tearing instability, which generates many plasmoids and drives a sort of fast reconnection. Although Baty (2012) recently investigated the possibility of Petschek-like structure in relatively high-S (~10^4) regime, it is still unclear whether and how the magnetic reconnection is able to be accelerated in higher-S regime (S>10^5). In this paper, we developed the high-resolution magnetohydrodynamics (MHD) simulation of magnetic reconnection for very high-S (S~10^4-10^6) aiming at revealing the acceleration mechanism of magnetic reconnection. We applied the HLLD Riemann solver, which was developed by Miyoshi and Kusano (2005), to the high resolution two-dimensional MHD simulation of current sheet dynamics. In our model, the initial state is given by the Harris sheet equilibrium plus perturbation. As a result, in the case for S=10^5, multiple X-line reconnection appears as a result of the secondary tearing instability and magnetic reconnection is accelerated through the formation of multiple magnetic islands as pointed out by the previous studies. Furthermore, we found that

  7. Can the earth's magnetic field be simulated in the laboratory?

    PubMed

    Müller, U; Stieglitz, R

    2000-09-01

    Today it is generally accepted that the Earth's magnetic field, as well as that of many other planets, is generated by buoyancy driven convection in the electrically conducting liquid cores of these rotating celestial bodies. The conversion of mechanical energy into electromagnetic energy is known as the dynamo effect. In contrast to technical dynamos, which utilize the rotational motion of a complex arrangement of wire coils and other materials of different electrical and magnetic properties, the geodynamo is based on a freely developing spiral flow in a practically homogeneous, electrically conducting liquid core domain, and is therefore termed a homogeneous dynamo. This report outlines some fundamental properties of the Earth's magnetic field. The structure of the spiral flow in the liquid interior of planets is explained with the help of some model experiments in rapidly rotating spherical shells, which were carried out by Busse and Carrigan (1974). Based on the main ideas of electromagnetism it is shown that spiral motion in well-conducting fluids, like liquid metals, can amplify seed magnetic fields to generate dynamo action. Starting from the conjectured flow structure in the Earth's interior, a conceptional and engineering design is described for a laboratory dynamo experiment. Some details of the construction of the test facility and first experimental results are presented and discussed. PMID:11091960

  8. Theory and simulations of electron vortices generated by magnetic pushing

    NASA Astrophysics Data System (ADS)

    Richardson, A. S.; Angus, J. R.; Swanekamp, S. B.; Ottinger, P. F.; Schumer, J. W.

    2013-08-01

    Vortex formation and propagation are observed in kinetic particle-in-cell (PIC) simulations of magnetic pushing in the plasma opening switch. These vortices are studied here within the electron-magnetohydrodynamic (EMHD) approximation using detailed analytical modeling. PIC simulations of these vortices have also been performed. Strong v ×B forces in the vortices give rise to significant charge separation, which necessitates the use of the EMHD approximation in which ions are fixed and the electrons are treated as a fluid. A semi-analytic model of the vortex structure is derived, and then used as an initial condition for PIC simulations. Density-gradient-dependent vortex propagation is then examined using a series of PIC simulations. It is found that the vortex propagation speed is proportional to the Hall speed vHall≡cB0/4πneeLn. When ions are allowed to move, PIC simulations show that the electric field in the vortex can accelerate plasma ions, which leads to dissipation of the vortex. This electric field contributes to the separation of ion species that has been observed to occur in pulsed-power experiments with a plasma-opening switch.

  9. Progress and Future Directions in Confined Magnetic Fusion Simulation

    NASA Astrophysics Data System (ADS)

    Chan, V. S.

    2004-05-01

    The complexity of fusion plasmas makes the goal of integrated predictive simulation for optimization of fusion systems extremely challenging. Sophisticated computational models are under development for individual features of magnetically confined plasmas, enabled by increased scientific understanding and improvements in computer technology. Simulation codes, particle- and continuum-based, are being developed to elucidate the ability of fusion devices to contain mass, heat and momentum. Rigorous benchmarking among different codes has resulted in increased confidence in the predictive capability. Advances made in extended MHD simulations of actual experiments have led to deeper understanding of the nonlinear evolution of MHD instabilities that set the pressure limit of fusion devices. Simulation of the plasma edge, which controls the overall fusion performance, is especially difficult due to the wide range of spatial and temporal scales involved, as well as the need for a physics model that accurately describes collisionless and collisional plasma. We highlight encouraging progress in plasma microturbulence and extended MHD and a new challenge in simulation of the plasma edge.

  10. Dynamical Evolution of Main-Belt Meteoroids: Numerical Simulations Incorporating Planetary Perturbations and Yarkovsky Drag

    NASA Astrophysics Data System (ADS)

    Burns, J. A.; Bottke, W. F.; Rubincam, D. P.

    2000-05-01

    Using an RMVS N-body integrator, we track meteoroid orbital histories, including planetary perturbations plus the Yarkovsky (radiation-recoil) effect (seasonal and diurnal variants, producing orbital collapse or growth, depending on meteoroid properties and spin); collisions stochastically alter spin rates and directions. Considering two drift rates, we follow -- for tens of Myr -- one hundred bodies started from the positions of each of ten asteroids (e.g., Vesta, Hebe, Maria, Flora, Hestia) scattered across the inner main belt. This region contains the powerful Jovian 3:1 mean-motion resonance and the ν 6 secular resonance, as well as numerous weaker three-body (Jupiter, Saturn, meteoroid) and Martian mean-motion resonances. Once modest eccentricities are achieved, orbits can pass near Mars, which significantly affects them. Dynamical evolution in the main belt can be quite complex. Depending on the speed and direction of orbital evolution as well as the particular resonance, particles may i) be captured, increasing e and/or i while a stays constant; or ii) jump across, kicking e, i and a, but bypassing potential ``escape hatches'' from the main belt. Chaos ensues once resonances overlap. Following convoluted trajectories, which vary with initial conditions and collisional histories, most meteoroids reach Earth-crossing orbits via the 3:1 or ν 6 resonance after tens of Myr in the main belt. These timescales correspond well to the measured cosmic-ray-exposure ages of chondrites and achondrites. Meteorite source are, however, less clear; since Yarkovsky drift allows access to a dense forest of resonant sites, nearly any body in the main belt can add to the cumulate meteoroid flux. Ejecta from small parent bodies will dominate the meteoroid flux if the main- belt size-distribution at sub-km sizes is in collisional equilibrium, while big parent bodies dominate if observed population trends for km-sized bodies persist to smaller radii.

  11. A hybrid model for molecular-dynamics simulations of semiflexible main-chain liquid-crystalline polymer melts

    NASA Astrophysics Data System (ADS)

    Yung, K. L.; He, Lan; Xu, Yan; Shen, Y. W.

    2005-12-01

    This Note proposes a new hybrid model that combines the Gay-Berne/Lennard-Jones (GB/LJ) and bead-spring models to simulate semiflexible main-chain liquid-crystalline polymers (LCPs) for improving simulation efficiency without compromising accuracy. In the new model, one bead and two nonlinear springs are used to describe the flexible spacers between two adjacent rigid units described by ellipsoidal particles. The model is found to be able to describe, with accuracy, detailed structural properties of semiflexible main-chain LCPs, such as the odd-even effects of their thermodynamic properties, where the bead-spring model cannot depict. In our experiments, the speed of simulation for the hybrid model was shown to be up to ten times faster than that for the GB/LJ model when the number of molecular chains exceeded 150.

  12. The IZMIRAN main magnetic field candidate model for IGRF-10, produced by a spherical harmonic-natural orthogonal component method

    NASA Astrophysics Data System (ADS)

    Golovkov, Vadim P.; Zvereva, Tatiana I.; Chernova, Tatiana A.

    2005-12-01

    A simple method is proposed for constructing a space-time model of the main magnetic field based on the high-accuracy satellite survey data. At the first stage, we expand the CHAMP daily mean data into spherical harmonics with constant coefficients. It provides us with a series of the daily mean spherical-harmonic models (DMM) over a survey interval of several years, which are, then, expanded into the natural orthogonal components (NOC). It is shown that the NOC series converges rapidly, and that the accuracy of the space-time model over the time interval under consideration is no worse than the accuracy of the traditional models.

  13. Simulating magnetic nanoparticle behavior in low-field MRI under transverse rotating fields and imposed fluid flow

    NASA Astrophysics Data System (ADS)

    Cantillon-Murphy, P.; Wald, L. L.; Adalsteinsson, E.; Zahn, M.

    2010-09-01

    In the presence of alternating-sinusoidal or rotating magnetic fields, magnetic nanoparticles will act to realign their magnetic moment with the applied magnetic field. The realignment is characterized by the nanoparticle's time constant, τ. As the magnetic field frequency is increased, the nanoparticle's magnetic moment lags the applied magnetic field at a constant angle for a given frequency, Ω, in rad s -1. Associated with this misalignment is a power dissipation that increases the bulk magnetic fluid's temperature which has been utilized as a method of magnetic nanoparticle hyperthermia, particularly suited for cancer in low-perfusion tissue (e.g., breast) where temperature increases of between 4 and 7 °C above the ambient in vivo temperature cause tumor hyperthermia. This work examines the rise in the magnetic fluid's temperature in the MRI environment which is characterized by a large DC field, B0. Theoretical analysis and simulation is used to predict the effect of both alternating-sinusoidal and rotating magnetic fields transverse to B0. Results are presented for the expected temperature increase in small tumors ( ˜1 cm radius) over an appropriate range of magnetic fluid concentrations (0.002-0.01 solid volume fraction) and nanoparticle radii (1-10 nm). The results indicate that significant heating can take place, even in low-field MRI systems where magnetic fluid saturation is not significant, with careful the goal of this work is to examine, by means of analysis and simulation, the concept of interactive fluid magnetization using the dynamic behavior of superparamagnetic iron oxide nanoparticle suspensions in the MRI environment. In addition to the usual magnetic fields associated with MRI, a rotating magnetic field is applied transverse to the main B0 field of the MRI. Additional or modified magnetic fields have been previously proposed for hyperthermia and targeted drug delivery within MRI. Analytical predictions and numerical simulations of the

  14. Reinventing atomic magnetic simulations with spin-orbit coupling

    DOE PAGESBeta

    Perera, Meewanage Dilina N.; Eisenbach, Markus; Nicholson, Don M.; Stocks, George Malcolm; Landau, David P.

    2016-02-10

    We propose a powerful extension to the combined molecular and spin dynamics method that fully captures the coupling between the atomic and spin subsystems via spin-orbit interactions. Moreover, the foundation of this method lies in the inclusion of the local magnetic anisotropies that arise as a consequence of the lattice symmetry breaking due to phonons or crystallographic defects. By using canonical simulations of bcc iron with the system coupled to a phonon heat bath, we show that our extension enables the previously unachievable angular momentum exchange between the atomic and spin degrees of freedom.

  15. Combining micromagnetism and magnetostatic Maxwell equations for multiscale magnetic simulations.

    PubMed

    Bruckner, Florian; Vogler, Christoph; Bergmair, Bernhard; Huber, Thomas; Fuger, Markus; Suess, Dieter; Feischl, Michael; Fuehrer, Thomas; Page, Marcus; Praetorius, Dirk

    2013-10-01

    Magnetostatic Maxwell equations and the Landau-Lifshitz-Gilbert (LLG) equation are combined to a multiscale method, which allows to extend the problem size of traditional micromagnetic simulations. By means of magnetostatic Maxwell equations macroscopic regions can be handled in an averaged and stationary sense, whereas the LLG allows to accurately describe domain formation as well as magnetization dynamics in some microscopic subregions. The two regions are coupled by means of their strayfield and the combined system is solved by an optimized time integration scheme. PMID:24092951

  16. Combining micromagnetism and magnetostatic Maxwell equations for multiscale magnetic simulations

    NASA Astrophysics Data System (ADS)

    Bruckner, Florian; Vogler, Christoph; Bergmair, Bernhard; Huber, Thomas; Fuger, Markus; Suess, Dieter; Feischl, Michael; Fuehrer, Thomas; Page, Marcus; Praetorius, Dirk

    2013-10-01

    Magnetostatic Maxwell equations and the Landau-Lifshitz-Gilbert (LLG) equation are combined to a multiscale method, which allows to extend the problem size of traditional micromagnetic simulations. By means of magnetostatic Maxwell equations macroscopic regions can be handled in an averaged and stationary sense, whereas the LLG allows to accurately describe domain formation as well as magnetization dynamics in some microscopic subregions. The two regions are coupled by means of their strayfield and the combined system is solved by an optimized time integration scheme.

  17. Simulation of the inspection of planar non-magnetic materials with electro magnetic acoustic transducers

    NASA Astrophysics Data System (ADS)

    Prémel, Denis; Reboud, C.; Chatillon, S.; Reverdy, F.; Mahaut, S.

    2012-05-01

    For some specific applications in ultrasonic non destructive evaluation, EMATs (ElectroMagnetic Acoustic Transducers) are very useful for generating and receiving ultrasonic waves. EMAT works without any contact and liquid coupling. Various surface or bulk waves with any arbitrary polarities and orientations may be generated by changing the orientation of the magnets and the coils. Unfortunately, these types of probes show a poor sensitivity as receivers. CEA LIST has developed simulation tools, based on semi-analytical models dedicated to eddy current and ultrasonic testing, in order to predict signals obtained when inspecting planar structures. The first step of these developments concerns the inspection of conducting non-ferromagnetic materials. By combining eddy currents due to coils with the static magnetic field provided by magnets, the 3D Lorentz's force distribution is computed in the time domain and used as input for the semi-analytical ultrasonic models to compute the simulation of ultrasonic bulk waves and flaw interaction in the piece. This communication presents a specific configuration for our first experimental validation. The computation time is sufficiently low to perform parametric studies to improve the performances of the EMAT.

  18. Simulations of Supersonic Turbulence in Magnetized Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Kritsuk, Alexei; Ustyugov, S. D.; Norman, M. L.; Padoan, P.

    2009-01-01

    We report first results from three-dimensional numerical simulations of supersonic magnetohydrodynamic (MHD) turbulence with the Piecewise Parabolic Method on Local Stencil (PPML, Popov & Ustyugov 2008). PPML is a multi-dimensional higher-order Godunov scheme that preserves monotonicity of solutions in the vicinity of strong discontinuities, and maintains zero divergence of the magnetic field through a constrained transport approach. The method is very accurate, extremely low-dissipation, and perfectly stable for super-Alfv'enic turbulence, where many other MHD schemes experience difficulties. We solve the equations of ideal MHD in a periodic domain on Cartesian grids of up to 1024^3 points. Our models describe driven turbulence at Mach 10 and assume an isothermal equation of state to mimic the conditions in molecular clouds. We start with uniform gas density and uniform magnetic field aligned with one of the coordinate directions and apply large-scale solenoidal force to develop a saturated turbulent state in a statistical equilibrium. Depending on the initial field strength, B_0, a saturation is reached within three-to-six dynamical times of driving. We then collect the turbulence statistics and compare those for different models. As predicted by Kritsuk et al. (2007), for weak initial fields we get Kolmogorov spectra for the density-weighted velocities ρ^{1/3}u. With stronger fields, the spectra tend to get shallower, but the -5/3 scaling still appears to hold (even in these highly compressible, magnetized flows) for a combination of kinetic and magnetic variables constructed in the spirit of Politano & Pouquet (1998). We compare PDFs, structure functions, and power spectra from runs with different B_0 and discuss the signature of magnetic field in the statistical properties of molecular cloud turbulence and their role in overall flow dynamics. This research was partially supported by NSF grants AST0607675, AST0808184, and by NRAC allocation MCA07S014. We

  19. Thermo-electromagnetic properties of a magnetically shielded superconductor strip: theoretical foundations and numerical simulations

    NASA Astrophysics Data System (ADS)

    Ma, G. T.; Rauh, H.

    2013-10-01

    Numerical simulations of thermo-electromagnetic properties of a thin type-II superconductor strip surrounded by open cavity soft-magnetic shields and exposed to an oscillating transverse magnetic field are performed by resorting to the quasistatic approximation of a vector potential approach in conjunction with the classical description of conduction of heat. The underlying definition of the superconducting constituent makes use of an extended ‘smoothed’ Bean model of the critical state, which includes the field and temperature dependence of the induced supercurrent as well. The delineation of the magnetic shields exploits the reversible-paramagnet approximation in the Langevin form, as appropriate for magnetizations with narrow Z-type loops, and considers induced eddy currents too. The coolant is envisaged as acting like a bath that instantly takes away surplus heat. Based on the Jacobian-free Newton-Krylov approach and the backward Euler scheme, the numerical analysis at hand is tailored to the problem of a high width/thickness aspect ratio of the superconductor strip. Assigning representative materials characteristics and conditions of the applied magnetic field, the main findings for a practically relevant magnet configuration include: (i) an overall rise of the maximum temperature of the superconductor strip tending to saturation in a superconducting thermo-electromagnetic steady state above the operating temperature, magnetic shielding lending increased stability and smoothing the temperature profile along the width of the superconductor strip; (ii) a washing out of the profile of the magnetic induction and a lowering of its strength, a relaxation of the profile of the supercurrent density and an increase of its strength, a tightening of the power loss density and a reduction of its strength, all inside the superconductor strip. The hysteretic ac loss suffered by the superconductor strip is seen to be cut back or, at most, to converge on that of an

  20. Monte Carlo simulations of kagome lattices with magnetic dipolar interactions

    NASA Astrophysics Data System (ADS)

    Plumer, Martin; Holden, Mark; Way, Andrew; Saika-Voivod, Ivan; Southern, Byron

    Monte Carlo simulations of classical spins on the two-dimensional kagome lattice with only dipolar interactions are presented. In addition to revealing the sixfold-degenerate ground state, the nature of the finite-temperature phase transition to long-range magnetic order is discussed. Low-temperature states consisting of mixtures of degenerate ground-state configurations separated by domain walls can be explained as a result of competing exchange-like and shape-anisotropy-like terms in the dipolar coupling. Fluctuations between pairs of degenerate spin configurations are found to persist well into the ordered state as the temperature is lowered until locking in to a low-energy state. Results suggest that the system undergoes a continuous phase transition at T ~ 0 . 43 in agreement with previous MC simulations but the nature of the ordering process differs. Preliminary results which extend this analysis to the 3D fcc ABC-stacked kagome systems will be presented.

  1. Simulating Magnetic Nanoparticle Behavior in Low-field MRI under Transverse Rotating Fields and Imposed Fluid Flow

    PubMed Central

    Wald, L.L.; Adalsteinsson, E.; Zahn, M.

    2010-01-01

    In the presence of alternating-sinusoidal or rotating magnetic fields, magnetic nanoparticles will act to realign their magnetic moment with the applied magnetic field. The realignment is characterized by the nanoparticle’s time constant, τ. As the magnetic field frequency is increased, the nanoparticle’s magnetic moment lags the applied magnetic field at a constant angle for a given frequency, Ω, in rad/s. Associated with this misalignment is a power dissipation that increases the bulk magnetic fluid’s temperature which has been utilized as a method of magnetic nanoparticle hyperthermia, particularly suited for cancer in low-perfusion tissue (e.g., breast) where temperature increases of between 4°C and 7°C above the ambient in vivo temperature cause tumor hyperthermia. This work examines the rise in the magnetic fluid’s temperature in the MRI environment which is characterized by a large DC field, B0. Theoretical analysis and simulation is used to predict the effect of both alternating-sinusoidal and rotating magnetic fields transverse to B0. Results are presented for the expected temperature increase in small tumors (~1 cm radius) over an appropriate range of magnetic fluid concentrations (0.002 to 0.01 solid volume fraction) and nanoparticle radii (1 to 10 nm). The results indicate that significant heating can take place, even in low-field MRI systems where magnetic fluid saturation is not significant, with careful The goal of this work is to examine, by means of analysis and simulation, the concept of interactive fluid magnetization using the dynamic behavior of superparamagnetic iron oxide nanoparticle suspensions in the MRI environment. In addition to the usual magnetic fields associated with MRI, a rotating magnetic field is applied transverse to the main B0 field of the MRI. Additional or modified magnetic fields have been previously proposed for hyperthermia and targeted drug delivery within MRI. Analytical predictions and numerical simulations

  2. Inter-grain interaction in random magnetic anisotropy simulation in magnetic nanocrystals

    SciTech Connect

    Lee, S.-J.; Yanagihara, Hideto; Kita, Eiji; Inami, Nobuhito; Ono, Kanta; Mitsumata, Chiharu

    2015-05-07

    Effect of inter-grain exchange interaction on the coercive forces was analyzed with a numerical simulation in magnetic materials with random magnetic anisotropy. The magnetization of an assembly of magnetically interacting grains with randomly oriented uniaxial anisotropy was calculated using the Landau-Lifshitz-Gilbert equation. We supposed a single spin model where the magnetizations in a grain were aligned in the same direction, for simplicity. Calculations were carried out for an N×N×N system, where the number of grains on a side, N ranged from 16 to 128. The relation between the coercive forces H{sub C} and the grain size D is represented by H{sub C}∝D{sup k}. With the increase of N, k decreased gradually and tended to reach a saturated value around k = 4.5–5, which dose not correspond to the primitive theory of the random anisotropy model where k = 6. The deviation was discussed in terms of the inter-grain interaction, essentially proportional to the inverse of D.

  3. Inter-grain interaction in random magnetic anisotropy simulation in magnetic nanocrystals

    NASA Astrophysics Data System (ADS)

    Lee, S.-J.; Inami, Nobuhito; Yanagihara, Hideto; Kita, Eiji; Mitsumata, Chiharu; Ono, Kanta

    2015-05-01

    Effect of inter-grain exchange interaction on the coercive forces was analyzed with a numerical simulation in magnetic materials with random magnetic anisotropy. The magnetization of an assembly of magnetically interacting grains with randomly oriented uniaxial anisotropy was calculated using the Landau-Lifshitz-Gilbert equation. We supposed a single spin model where the magnetizations in a grain were aligned in the same direction, for simplicity. Calculations were carried out for an N ×N ×N system, where the number of grains on a side, N ranged from 16 to 128. The relation between the coercive forces HC and the grain size D is represented by HC∝Dk . With the increase of N, k decreased gradually and tended to reach a saturated value around k = 4.5-5, which dose not correspond to the primitive theory of the random anisotropy model where k = 6. The deviation was discussed in terms of the inter-grain interaction, essentially proportional to the inverse of D.

  4. Hybrid simulations of magnetic reconnection with kinetic ions and fluid electron pressure anisotropy

    DOE PAGESBeta

    Le, A.; Daughton, W.; Karimabadi, H.; Egedal, J.

    2016-03-16

    We present the first hybrid simulations with kinetic ions and recently developed equations of state for the electron fluid appropriate for reconnection with a guide field. The equations of state account for the main anisotropy of the electron pressure tensor.Magnetic reconnection is studied in two systems, an initially force-free current sheet and a Harris sheet. The hybrid model with the equations of state is compared to two other models, hybrid simulations with isothermal electrons and fully kinetic simulations. Including the anisotropicequations of state in the hybrid model provides a better match to the fully kinetic model. In agreement with fullymore » kinetic results, the main feature captured is the formation of an electron current sheet that extends several ion inertial lengths. This electron current sheet modifies the Hall magnetic field structure near the X-line, and it is not observed in the standard hybrid model with isotropic electrons. The saturated reconnection rate in this regime nevertheless remains similar in all three models. Here, implications for global modeling are discussed.« less

  5. Simulating physiological conditions to evaluate nanoparticles for magnetic fluid hyperthermia (MFH) therapy applications

    NASA Astrophysics Data System (ADS)

    Chen, Shihwei; Chiang, Chen-li; Hsieh, Shuchen

    2010-01-01

    Magnetite nanoparticles with high self-heating capacity and low toxicity characteristics are a promising candidate for cancer hyperthermia treatment. In order to achieve minimum dosage to a patient, magnetic nanoparticles with high heating capacity are needed. In addition, the influence of physiological factors on the heat capacity of a material should be investigated in order to determine the feasibility. In this study, magnetite nanoparticles coated with lauric acid were prepared by co-precipitation of Fe 3+:Fe 2+ in a ratio of 2:1, 5:3, 3:2, and 4:3, and the pH was controlled using NaOH. Structural and magnetization characterization by means of X-ray diffractometry (XRD) and a superconducting quantum interference device (SQUID) revealed that the main species was Fe 3O 4 and further showed that most of the nanoparticles exhibited superparamagnetic properties. All of the magnetic nanoparticles showed a specific absorption rate (SAR) increase that was linear with the magnetic field strength and frequency of the alternating magnetic field. Among all, the magnetic nanoparticles prepared in a 3:2 ratio showed the highest SAR. To further test the influence of physiological factors on the 3:2 ratio magnetic nanoparticles, we simulated the environment with protein (bovine serum albumin, BSA), blood sugar (dextrose), electrolytes (commercial norm-saline) and viscosity (glycerol) to examine the heating capacity under these conditions. Our results showed that the SAR value was unaffected by the protein and blood sugar environments. On the other hand, the SAR value was significantly reduced in the electrolyte environment, due to precipitation and aggregation with sodium ions. For the simulated viscous environment with glycerol, the result showed that the SAR values reduced with increasing glycerol concentration. We have further tested the heating capacity contribution from the Néel mechanism by trapping the magnetic nanoparticles in a solid form of polydimethylsiloxane

  6. Propulsion simulator for magnetically-suspended wind tunnel models

    NASA Technical Reports Server (NTRS)

    Joshi, P. B.; Malonson, M. R.; Sacco, G. P.; Goldey, C. L.; Garbutt, Keith; Goodyer, M.

    1992-01-01

    In order to demonstrate the measurement of aerodynamic forces/moments, including the effects of exhaust jets in Magnetic Suspension and Balance System (MSBS) wind tunnels, two propulsion simulator models were developed at Physical Sciences Inc. (PSI). Both the small-scale model (1 in. diameter X 8 in. long) and the large-scale model (2.5 in. diameter X 15 in. long) employed compressed, liquefied carbon dioxide as a propellant. The small-scale simulator, made from a highly magnetizable iron alloy, was demonstrated in the 7 in. MSBS wind tunnel at the University of Southampton. It developed a maximum thrust of approximate 1.3 lbf with a 0.098 in. diameter nozzle and 0.7 lbf with a 0.295 in. diameter nozzle. The Southampton MSBS was able to control the simulator at angles-of attack up to 20 deg. The large-scale simulator was demonstrated to operate in both a steady-state and a pulse mode via a miniaturized solinoid valve. It developed a stable and repeatable thrust of 2.75 lbf over a period of 4s and a nozzle pressure ratio (NPR) of 5.

  7. Simulations of the Inspiral and Merger of Magnetized Neutron Stars

    NASA Astrophysics Data System (ADS)

    Motl, Patrick M.; Anderson, M.; Hirschman, E. W.; Lehner, L.; Liebling, S. L.; Neilsen, D.; Palenzuela, C.; Tohline, J. E.

    2008-05-01

    We present simulations of the inspiral, merger and eventual collapse of neutron star binaries calculated in full general relativity. The Einstein equations are solved in a first order reduction of the general harmonic formulation while the matter is evolved in the MHD approximation. Each binary component initially has a dipole magnetic field perpendicular to the orbital plane. We use the adaptive mesh refinement package HAD to resolve the disparate length scales in the problem ranging from the radiation zone down to the internal dynamics of the neutron stars. For aligned fields and our chosen field strength, we find that magnetic effects delay the merger somewhat - thus boosting the gravitational wave signal from the binary. As we will discuss, the magnetic field significantly impacts the distribution of matter and angular momentum in the super-massive, merged object after merger. This work has been supported in part by NSF grants AST 04-07070 and PHY 03-26311, and in part through NASA's ATP program grants NAG5-8497, NAG5-13430 and NNX07AG84G. The computations were performed on computer facilities provided through the Teragrid, LONI, LSU and BYU.

  8. Particle simulation of a magnetized plasma contacting the wall

    SciTech Connect

    Daube, T.; Riemann, K.; Schmitz, H.

    1998-01-01

    One-dimensional particle simulations are performed to study the influence of a strong magnetic field on the plasma boundary layer in front of a completely absorbing wall. The magnetic field lines are parallel to the wall, and the ion transport is provided by charge exchange collisions with cold neutrals. The Debye length is small compared with the ion gyroradius and the electrons are Boltzmann distributed. A modified Particle-in-Cell Monte-Carlo-Collision (PIC-MCC) code is developed to avoid the problem of different time scales of electrons and ions. The self-consistent steady-state simulation is performed for a system with one spatial coordinate and two velocity components (1d, 2v). The results are compared with corresponding results of a self-consistent stationary solution of the ion Boltzmann equation. Although the potential and density profiles are essentially confirmed, the ion velocity distribution functions disagree with analytic solutions in certain singular regions unless certain pertubations in the electric field are suppressed. It is shown that this is due to a microscopic instability of the stationary solution. {copyright} {ital 1998 American Institute of Physics.}

  9. Full Two-Fluid Collisionless Magnetic Reconnection Simulations

    NASA Astrophysics Data System (ADS)

    Gomez, D. O.; Andres, N.; Dmitruk, P.

    2015-12-01

    Magnetic reconnection is an important energy conversion process in space environments such as the solar corona or planetary magnetospheres. At the theoretical level of resistive one-fluid MHD, the Sweet-Parker model leads to extremely low reconnection rates for virtually all space physics applications. Kinetic plasma effects introduce new spatial and temporal scales into the theoretical description, which are expected to increase the reconnection rates. Within the theoretical framework of two-fluid MHD, we retain the effects of the Hall current and electron inertia and neglect dissipative effects such as viscosity and electric resistivity. This level of description brings two new spatial scales into play, namely, the ion and electron inertial scales. In absence of resistive dissipation, reconnection can only be attained by the action of electron inertia. We performed 2.5D two-fluid simulations using a pseudo-spectral code which yields exact conservation (to round-off errors) of the ideal invariants. Our simulations show that when the effects of electron inertia are retained, magnetic reconnection takes place. In a stationary regime, the reconnection rate is simply proportional to the ion inertial length, as also emerges from a scaling law derived from dimensional arguments.

  10. Multiscale dynamics based on kinetic simulation of collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Fujimoto, Keizo; Takamoto, Makoto

    2016-07-01

    Magnetic reconnection is a natural energy converter which allows explosive energy release of the magnetic field energy into plasma kinetic energy. The reconnection processes inherently involve multi-scale process. The breaking of the field lines takes place predominantly in a small region called the diffusion region formed near the x-line, while the fast plasma jets resulting from reconnection extend to a distance far beyond the ion kinetic scales from the x-line. There has been a significant gap in understanding of macro-scale and micro-scale processes. The macro-scale model of reconnection has been developed using the magnetohydrodynamics (MHD) equations, while the micro-scale processes around the x-line have been based on kinetic equations including the ion and electron inertia. The problem is that these two kinds of model have significant discrepancies. It has been believed without any guarantee that the microscopic model near the x-line would connect to the macroscopic model far downstream of the x-line. In order to bridge the gap between the macro and micro-scale processes, we have performed large-scale particle-in-cell simulations with the adaptive mesh refinement. The simulation results suggest that the microscopic processes around the x-line do not connect to the previous MHD model even in the region far downstream of the x-line. The slow mode shocks and the associated plasma acceleration do not appear at the exhaust boundary of kinetic reconnection. Instead, the ions are accelerated due to the Speiser motion in the current layer extending to a distance beyond the kinetic scales. The different acceleration mechanisms between the ions and electrons lead to the Hall current system in broad area of the exhaust. Therefore, the previous MHD model could be inappropriate for collisionless magnetic reconnection. Ref. K. Fujimoto & M. Takamoto, Phys. Plasmas, 23, 012903 (2016).

  11. Electron heating during magnetic reconnection: A simulation scaling study

    SciTech Connect

    Shay, M. A. Haggerty, C. C.; Phan, T. D.; Oieroset, M.; Drake, J. F.; Swisdak, M.; Cassak, P. A.; Wu, P.; Malakit, K.

    2014-12-15

    Electron bulk heating during magnetic reconnection with symmetric inflow conditions is examined using kinetic particle-in-cell simulations. Inflowing plasma parameters are varied over a wide range of conditions, and the increase in electron temperature is measured in the exhaust well downstream of the x-line. The degree of electron heating is well correlated with the inflowing Alfvén speed c{sub Ar} based on the reconnecting magnetic field through the relation ΔT{sub e}=0.033 m{sub i} c{sub Ar}{sup 2}, where ΔT{sub e} is the increase in electron temperature. For the range of simulations performed, the heating shows almost no correlation with inflow total temperature T{sub tot}=T{sub i}+T{sub e} or plasma β. An out-of-plane (guide) magnetic field of similar magnitude to the reconnecting field does not affect the total heating, but it does quench perpendicular heating, with almost all heating being in the parallel direction. These results are qualitatively consistent with a recent statistical survey of electron heating in the dayside magnetopause (Phan et al., Geophys. Res. Lett. 40, 4475, 2013), which also found that ΔT{sub e} was proportional to the inflowing Alfvén speed. The net electron heating varies very little with distance downstream of the x-line. The simulations show at most a very weak dependence of electron heating on the ion to electron mass ratio. In the antiparallel reconnection case, the largely parallel heating is eventually isotropized downstream due a scattering mechanism, such as stochastic particle motion or instabilities. The simulation size is large enough to be directly relevant to reconnection in the Earth's magnetosphere, and the present findings may prove to be universal in nature with applications to the solar wind, the solar corona, and other astrophysical plasmas. The study highlights key properties that must be satisfied by an electron heating mechanism: (1) preferential heating in the parallel direction; (2) heating

  12. Numerical simulations and stability of magnetic structures in the heliosheath

    NASA Astrophysics Data System (ADS)

    Cox, S.; Avinash, K.; Shaikh, D.; Zank, G. P.

    2008-12-01

    We extend the three fluid model of Avinash and Zank [2007] for magnetic structures in the heliosheath to a four fluid model consisting of electrons, pick-up ions (PUIs), solar wind ions (SWI), and neutral hydrogen. The PUIs are generated by neutrals via charge exchange with SWI. Since the kinetic pressure of PUIs is nearly three to four times the pressure of SWI, these are more suited to mediate small scale structures in the heliosheath such as magnetic holes/humps etc. The constant energy exchange between these two fluids drives them non-adiabatic. The PUIs are isothermal while SWI are non adiabatic with an index ~1.25. The four fluid model captures these effects via a modified equation of state for PUI and SWI. The phase space of time independent solutions in terms of the Mach numbers of PUI and SWI is constructed to delineate the parameter space which allows structure formation in the heliosheath. We examine the stability of the time independent solutions by evolving them via a full system of Hall -MHD equations. The simulation results show that these solutions are not quite stable. As the structure propagates it develops growing oscillations in the wings. Concomitantly, there are changes in the amplitude and width of the structure. This instability could be due to local changes in the velocity of the structure and reflects an exchange between the kinetic and magnetic parts of the total energy. Our results showing the presence of growing oscillations in the wings of solitary wave solutions are consistent with the recent analysis of magnetic holes in the heliosheth by Burlaga et al [2007].

  13. Digital simulation for Tristan-AR magnet power supply and control system

    SciTech Connect

    Kubo, T.; Endo, K.; Fukuma, H.; Kabe, A.

    1983-08-01

    The TRISTAN AR Magnet Power Supply is the system for exciting the magnets to accelerate the electron and positron beam from 2.5 GeV to 8 GeV. To estimate its performance the digital simulation was performed using DDS (Digital Dynamics Simulator). The simulation method and the result are described.

  14. Monte Carlo Simulations of the Post-Common-Envelope White-Dwarf Main-Sequence Binary Population

    SciTech Connect

    Camacho, Judit; Torres, Santiago; Garcia-Berro, Enrique; Schreiber, Matthias R.

    2010-12-22

    We present a detailed Monte Carlo simulator of the population of binary systems within the solar neighborhood. We have used the most up-to-date stellar evolutionary models, a complete treatment of the Roche lobe overflow episode, as well as a full implementation of the orbital evolution of the binary system. Preliminary results are presented for the population of white-dwarf main-sequence binaries, resulting from a common envelope episode. We also study the role played by the binding energy parameter, {lambda}, and by the common envelope efficiency, {alpha}{sub CE}. Finally, results are compared with the population of identified white-dwarf main-sequence binaries.

  15. Simulation of interplanetary magnetic field B{sub y} penetration into the magnetotail

    SciTech Connect

    Guo, Jiuling; Shen, Chao; Liu, Zhenxing

    2014-07-15

    Based on our global 3D magnetospheric MHD simulation model, we investigate the phenomena and physical mechanism of the B{sub y} component of the interplanetary magnetic field (IMF) penetrating into the magnetotail. We find that the dayside reconnected magnetic field lines move to the magnetotail, get added to the lobe fields, and are dragged in the IMF direction. However, the B{sub y} component in the plasma sheet mainly originates from the tilt and relative slippage of the south and north lobes caused by plasma convection, which results in the original B{sub z} component in the plasma sheet rotating into a B{sub y} component. Our research also shows that the penetration effect of plasma sheet B{sub y} from the IMF B{sub y} during periods of northward IMF is larger than that during periods of southward IMF.

  16. Rayleigh-Taylor-Unstable Accretion and Variability of Magnetized Stars: Global Three-Dimensional Simulations

    SciTech Connect

    Kulkarni, A. K.; Romanova, M. M.

    2008-10-29

    We present results of 3D simulations of MHD instabilities at the accretion disk-magnetosphere boundary. The instability is Rayleigh-Taylor, and develops for a fairly broad range of accretion rates and stellar rotation rates and magnetic fields. It produces tall, thin tongues of plasma that penetrate the magnetosphere in the equatorial plane. The shape and number of the tongues changes with time on the inner-disk dynamical timescale. In contrast with funnel flows, which deposit matter mainly in the polar region, the tongues deposit matter much closer to the stellar equator. The instability appears for relatively small misalignment angles, {theta} < or approx. 30 deg., between the star's rotation and magnetic axes, and is associated with higher accretion rates. The hot spots and light curves during accretion through instability are generally much more chaotic than during stable accretion. The unstable state of accretion has possible implications for quasi-periodic oscillations and intermittent pulsations from accreting systems.

  17. Simulations of Dynamical Friction Including Spatially-Varying Magnetic Fields

    SciTech Connect

    Bell, G. I.; Bruhwiler, D. L.; Busby, R.; Abell, D. T.; Messmer, P.; Veitzer, S.; Litvinenko, V. N.; Cary, J. R.

    2006-03-20

    A proposed luminosity upgrade to the Relativistic Heavy Ion Collider (RHIC) includes a novel electron cooling section, which would use {approx}55 MeV electrons to cool fully-ionized 100 GeV/nucleon gold ions. We consider the dynamical friction force exerted on individual ions due to a relevant electron distribution. The electrons may be focussed by a strong solenoid field, with sensitive dependence on errors, or by a wiggler field. In the rest frame of the relativistic co-propagating electron and ion beams, where the friction force can be simulated for nonrelativistic motion and electrostatic fields, the Lorentz transform of these spatially-varying magnetic fields includes strong, rapidly-varying electric fields. Previous friction force simulations for unmagnetized electrons or error-free solenoids used a 4th-order Hermite algorithm, which is not well-suited for the inclusion of strong, rapidly-varying external fields. We present here a new algorithm for friction force simulations, using an exact two-body collision model to accurately resolve close interactions between electron/ion pairs. This field-free binary-collision model is combined with a modified Boris push, using an operator-splitting approach, to include the effects of external fields. The algorithm has been implemented in the VORPAL code and successfully benchmarked.

  18. Kinetic simulations of the Chodura and Debye sheaths for magnetic fields with grazing incidence

    NASA Astrophysics Data System (ADS)

    Coulette, David; Manfredi, Giovanni

    2016-02-01

    When an unmagnetized plasma comes in contact with a material surface, the difference in mobility between the electrons and the ions creates a non-neutral layer known as the Debye sheath (DS). However, in magnetic fusion devices, the open magnetic field lines intersect the structural elements of the device with near grazing incidence angles. The magnetic field tends to align the particle flow along its own field lines, thus counteracting the mechanism that leads to the formation of the DS. Recent work using a fluid model (Stangeby 2012 Nucl. Fusion 52 083012) showed that the DS disappears when the incidence angle is smaller than a critical value (around {{5}{^\\circ}} for ITER-like parameters). Here, we study this transition by means of numerical simulations of a kinetic model both in the collisionless and weakly collisional regimes. We show that the main features observed in the fluid model are preserved: for grazing incidence, the space charge density near the wall is reduced or suppressed, the ion flow velocity is subsonic, and the electric field and plasma density profiles are spread out over several ion Larmor radii instead of a few Debye lengths as in the unmagnetized case. As there is no singularity at the DS entrance in the kinetic model, this phenomenon depends smoothly on the magnetic field incidence angle and no particular critical angle arises. The simulation results and the predictions of the fluid model are in good agreement, although some discrepancies subsist, mainly due to the assumptions of isothermal closure and diagonality of the pressure tensor in the fluid model.

  19. Simulation of electromagnetically and magnetically induced transparency in a magnetized plasma

    NASA Astrophysics Data System (ADS)

    Hur, M. S.; Wurtele, J. S.; Shvets, G.

    2003-07-01

    Electromagnetically induced transparency (EIT), a phenomenon well known in atomic systems, has a natural analogy in a classical magnetized plasma. The magnetized plasma has a resonance for right-hand polarized electromagnetic waves at the electron cyclotron frequency Ω0, so that a probe wave with frequency ω1=Ω0 cannot propagate through the plasma. The plasma can be made transparent to such a probe by the presence of a pump wave. The pump may be an electromagnetic wave or magnetostatic wiggler. Simulations and theory show that the physical reason for the transparency is that the beating of the probe wave with the pump wave sets up a plasma oscillation, and the upper sideband of the pump wave cancels the resonant plasma current due to the probe. The theory of plasma EIT derived here extends that found in the earlier work to include the effects of the lower sideband of the pump and renormalization of the plasma frequency and an analysis of the transient response. A detailed comparison of theory to one-dimensional particle-in-cell simulations is presented and estimates for the performance ion accelerator using the EIT interaction are given. The dispersion relation and estimates for the phase velocity and amplitude of the plasma wave are in good agreement with particle-in-cell simulations.

  20. A numerical simulation of the geomagnetic sudden commencement: 2. Plasma processes in the main impulse

    NASA Astrophysics Data System (ADS)

    Fujita, S.; Tanaka, T.; Kikuchi, T.; Fujimoto, K.; Itonaga, M.

    2003-12-01

    A geomagnetic sudden commencement (SC) is studied numerically based on a model of buffeting the magnetosphere by a solar wind density impulse. This paper treats two successive current systems in the main impulse (MI) phase. The two current systems have different current generating mechanisms. The first current generator appears behind the wavefront of a compressional disturbance launched by the impulse. The inertia current of the compressional mode is generated by free energy due to deceleration of plasma flows. A field-aligned current (FAC) is excited through mode conversion from the compressional wave in a VA gradient region. The magnetospheric flows and the ionospheric flows are not connected self-consistently to each other. The second generator is located in the tailward side of the cusp. It is the same as the generator of the region 1 current system. The current generated there is connected with the FAC with the region 1 sense via a diamagnetic current flowing around an isolated enhancement of pressure in the nightside equatorial magnetosphere. The pressure enhancement is induced through compression of the magnetospheric flank due to the solar wind impulse. In this period, plasma convection vortices appear both in the magnetosphere and in the ionosphere, which are correspondent to each other. This is a peculiar convection confined within the magnetosphere (the SC transient cell convection). This convection is driven though compression of the magnetospheric flank due to the solar wind impulse.

  1. Cluster expansion modeling and Monte Carlo simulation of alnico 5–7 permanent magnets

    DOE PAGESBeta

    Nguyen, Manh Cuong; Zhao, Xin; Wang, Cai -Zhuang; Ho, Kai -Ming

    2015-03-05

    The concerns about the supply and resource of rare earth (RE) metals have generated a lot of interests in searching for high performance RE-free permanent magnets. Alnico alloys are traditional non-RE permanent magnets and have received much attention recently due their good performance at high temperature. In this paper, we develop an accurate and efficient cluster expansion energy model for alnico 5–7. Monte Carlo simulations using the cluster expansion method are performed to investigate the structure of alnico 5–7 at atomistic and nano scales. The alnico 5–7 master alloy is found to decompose into FeCo-rich and NiAl-rich phases at lowmore » temperature. The boundary between these two phases is quite sharp (~2 nm) for a wide range of temperature. The compositions of the main constituents in these two phases become higher when the temperature gets lower. Both FeCo-rich and NiAl-rich phases are in B2 ordering with Fe and Al on α-site and Ni and Co on β-site. The degree of order of the NiAl-rich phase is much higher than that of the FeCo-rich phase. In addition, a small magnetic moment is also observed in NiAl-rich phase but the moment reduces as the temperature is lowered, implying that the magnetic properties of alnico 5–7 could be improved by lowering annealing temperature to diminish the magnetism in NiAl-rich phase. Furthermore, the results from our Monte Carlo simulations are consistent with available experimental results.« less

  2. Cluster expansion modeling and Monte Carlo simulation of alnico 5–7 permanent magnets

    SciTech Connect

    Nguyen, Manh Cuong Zhao, Xin; Wang, Cai-Zhuang; Ho, Kai-Ming

    2015-03-07

    The concerns about the supply and resource of rare earth (RE) metals have generated a lot of interests in searching for high performance RE-free permanent magnets. Alnico alloys are traditional non-RE permanent magnets and have received much attention recently due their good performance at high temperature. In this paper, we develop an accurate and efficient cluster expansion energy model for alnico 5–7. Monte Carlo simulations using the cluster expansion method are performed to investigate the structure of alnico 5–7 at atomistic and nano scales. The alnico 5–7 master alloy is found to decompose into FeCo-rich and NiAl-rich phases at low temperature. The boundary between these two phases is quite sharp (∼2 nm) for a wide range of temperature. The compositions of the main constituents in these two phases become higher when the temperature gets lower. Both FeCo-rich and NiAl-rich phases are in B2 ordering with Fe and Al on α-site and Ni and Co on β-site. The degree of order of the NiAl-rich phase is much higher than that of the FeCo-rich phase. A small magnetic moment is also observed in NiAl-rich phase but the moment reduces as the temperature is lowered, implying that the magnetic properties of alnico 5–7 could be improved by lowering annealing temperature to diminish the magnetism in NiAl-rich phase. The results from our Monte Carlo simulations are consistent with available experimental results.

  3. Cluster expansion modeling and Monte Carlo simulation of alnico 5–7 permanent magnets

    SciTech Connect

    Nguyen, Manh Cuong; Zhao, Xin; Wang, Cai -Zhuang; Ho, Kai -Ming

    2015-03-05

    The concerns about the supply and resource of rare earth (RE) metals have generated a lot of interests in searching for high performance RE-free permanent magnets. Alnico alloys are traditional non-RE permanent magnets and have received much attention recently due their good performance at high temperature. In this paper, we develop an accurate and efficient cluster expansion energy model for alnico 5–7. Monte Carlo simulations using the cluster expansion method are performed to investigate the structure of alnico 5–7 at atomistic and nano scales. The alnico 5–7 master alloy is found to decompose into FeCo-rich and NiAl-rich phases at low temperature. The boundary between these two phases is quite sharp (~2 nm) for a wide range of temperature. The compositions of the main constituents in these two phases become higher when the temperature gets lower. Both FeCo-rich and NiAl-rich phases are in B2 ordering with Fe and Al on α-site and Ni and Co on β-site. The degree of order of the NiAl-rich phase is much higher than that of the FeCo-rich phase. In addition, a small magnetic moment is also observed in NiAl-rich phase but the moment reduces as the temperature is lowered, implying that the magnetic properties of alnico 5–7 could be improved by lowering annealing temperature to diminish the magnetism in NiAl-rich phase. Furthermore, the results from our Monte Carlo simulations are consistent with available experimental results.

  4. Cluster expansion modeling and Monte Carlo simulation of alnico 5-7 permanent magnets

    NASA Astrophysics Data System (ADS)

    Nguyen, Manh Cuong; Zhao, Xin; Wang, Cai-Zhuang; Ho, Kai-Ming

    2015-03-01

    The concerns about the supply and resource of rare earth (RE) metals have generated a lot of interests in searching for high performance RE-free permanent magnets. Alnico alloys are traditional non-RE permanent magnets and have received much attention recently due their good performance at high temperature. In this paper, we develop an accurate and efficient cluster expansion energy model for alnico 5-7. Monte Carlo simulations using the cluster expansion method are performed to investigate the structure of alnico 5-7 at atomistic and nano scales. The alnico 5-7 master alloy is found to decompose into FeCo-rich and NiAl-rich phases at low temperature. The boundary between these two phases is quite sharp (˜2 nm) for a wide range of temperature. The compositions of the main constituents in these two phases become higher when the temperature gets lower. Both FeCo-rich and NiAl-rich phases are in B2 ordering with Fe and Al on α-site and Ni and Co on β-site. The degree of order of the NiAl-rich phase is much higher than that of the FeCo-rich phase. A small magnetic moment is also observed in NiAl-rich phase but the moment reduces as the temperature is lowered, implying that the magnetic properties of alnico 5-7 could be improved by lowering annealing temperature to diminish the magnetism in NiAl-rich phase. The results from our Monte Carlo simulations are consistent with available experimental results.

  5. Micromagnetic simulation of the magnetic dispersion angle and effective damping factor for the single-phase soft magnetic films

    NASA Astrophysics Data System (ADS)

    Yuan, Lin; Jiang, Jianjun; Di, Yongjiang; Bie, Shaowei; He, Huahui

    The micromagnetic structure of the single-phase soft magnetic films was simulated using the model of two-dimensional hexagonal lattices by micromagnetic method. The typical micromagnetic ripple structure of magnetic films was obtained. Thus, the magnetic dispersion angle was calculated from the static magnetic structure of the film. Furthermore, the relationship between the magnetic dispersion angles and the corresponding magnetic parameters of the film was discussed. The technique also demonstrated the microwave permeability of the films and the magnetic spectra well fitted by the permeability equation, which was deduced from the Landau-Lifshitz-Gilbert (LLG) function when the film was considered as a single domain. The fitting data of effective damping factor as a function of the magnetic dispersion angle were investigated.

  6. Numerical Simulations on Origin of Galilean Moons' Magnetic Anomalies

    NASA Technical Reports Server (NTRS)

    Jiao, LiQuo; Kuang, WeiJia; Ma, ShiZhuang

    2011-01-01

    Galileo mission detected the magnetic anomalies originated from Galilean moons. These anomalies are likely generated in the moons interiors, under the influence of a strong ambient Jovian field. Among various possible generation mechanisms of the anomalies, we focus on magneto-convection and dynamos in the interiors via numerical simulation. To mimic the electromagnetic environment of the moons, we introduce in our numerical model an external uniform magnetic field B(sub 0) with a fixed orientation but varying field strength. Our results show that a finite B(sub 0) can substantially alter the dynamo processes inside the core. When the ambient field strength B(sub 0) increases to approximately 40% of the field generated by the pure dynamo action, the convective state in the core changes significantly: the convective flow decreases by 80% in magnitude, but the differential rotation becomes stronger in much of the fluid layer, leading to a stronger field generated in the core. The field morphologies inside the core tend to align with the ambient field, while the flow patterns show the symmetry-breaking effect under the influence of B(sub 0). Furthermore, the generated field tends to be temporally more stable.

  7. Quantum Simulation of Frustrated Magnetism with Many Trapped Ions

    NASA Astrophysics Data System (ADS)

    Senko, Crystal

    2013-05-01

    A collection of trapped atomic ions is an excellent system for simulating quantum many-body physics, like magnetism, which may be difficult to access via classical computation or traditional condensed-matter experiments. Our large crystals of 10-20 ions comprise a platform to study a long-range quantum Ising model with tunable couplings in a 1D spin chain. State-dependent optical dipole forces exploit the Coulomb interaction to generate the spin-spin couplings, and fluorescence measurements on a camera are used to read out individual spin states. We investigated the spin order resulting from changing the range of antiferromagnetic interactions or the strength of an axial magnetic field, demonstrating our control over the amount of frustration present. We are turning to the study of dynamics in this system, with the aim of exploring topics including adiabaticity, spectroscopy of the Hamiltonian, the emergence of Kibble-Zurek-like behavior in a finite system, thermalization in an isolated quantum system, and nonequilibrium phase transitions. There is great promise in extending the system to 30+ spins, where computations become classically intractable. Co-authors are R. Islam, P. Richerme, W. C. Campbell, S. Korenblit, J. Smith, A. Lee, E. E. Edwards, C.-C. J. Wang, J. K. Freericks, and C. Monroe. This work is supported by grants from the U.S. Army Research Office with funding from the DARPA OLE program, IARPA, and the MURI program; and the NSF Physics Frontier Center at JQI.

  8. Colloidal Suspensions of Rodlike Nanocrystals and Magnetic Spheres under an External Magnetic Stimulus: Experiment and Molecular Dynamics Simulation.

    PubMed

    May, Kathrin; Eremin, Alexey; Stannarius, Ralf; Peroukidis, Stavros D; Klapp, Sabine H L; Klein, Susanne

    2016-05-24

    Using experiments and molecular dynamics simulations, we explore magnetic field-induced phase transformations in suspensions of nonmagnetic rodlike and magnetic sphere-shaped particles. We experimentally demonstrate that an external uniform magnetic field causes the formation of small, stable clusters of magnetic particles that, in turn, induce and control the orientational order of the nonmagnetic subphase. Optical birefringence was studied as a function of the magnetic field and the volume fractions of each particle type. Steric transfer of the orientational order was investigated by molecular dynamics (MD) simulations; the results are in qualitative agreement with the experimental observations. By reproducing the general experimental trends, the MD simulation offers a cohesive bottom-up interpretation of the physical behavior of such systems, and it can also be regarded as a guide for further experimental research. PMID:27119202

  9. MiR-103 inhibits osteoblast proliferation mainly through suppressing Cav1.2 expression in simulated microgravity.

    PubMed

    Sun, Zhongyang; Cao, Xinsheng; Hu, Zebing; Zhang, Lianchang; Wang, Han; Zhou, Hua; Li, Dongtao; Zhang, Shu; Xie, Manjiang

    2015-07-01

    Emerging evidence indicates that microRNAs (miRNAs) play important roles in modulating osteoblast function and bone formation. However, the influence of miRNA on osteoblast proliferation and the possible mechanisms underlying remain to be defined. In this study, we aimed to investigate whether miR-103 regulates osteoblast proliferation under simulated microgravity condition through regulating Cav1.2, the primary subunit of L-type voltage sensitive calcium channels (LTCCs). We first investigated the effect of simulated microgravity on osteoblast proliferation and the outcomes clearly demonstrated that the mechanical unloading inhibits MC3T3-E1 osteoblast-like cell proliferation. Using quantitative Real-Time PCR (qRT-PCR), we provided data showing that miR-103 was up-regulated in response to simulated microgravity. In addition, we observed that up-regulation of miR-103 inhibited and down-regulation of miR-103 promoted osteoblast proliferation under simulated microgravity condition. Furthermore, knocking-down or over-expressing miR-103, respectively, up- or down-regulated the level of Cav1.2 expression and LTCC currents, suggesting that miR-103 acts as an endogenous attenuator of Cav1.2 in osteoblasts under simulated microgravity condition. More importantly, we showed that the effect of miR-103 on osteoblast proliferation was diminished in simulated microgravity, when co-transfecting miR-103 mimic or inhibitor with Cav1.2 siRNA. Taken together, our data suggest that miR-103 inhibits osteoblast proliferation mainly through suppression of Cav1.2 expression under simulated microgravity condition. This work may provide a novel mechanism of microgravity-induced detrimental effects on osteoblast proliferation, identifying miR-103 as a novel possible therapeutic target in bone remodeling disorders in this mechanical unloading. PMID:25868801

  10. Simulation of electric-field and spin-transfer-torque induced magnetization switching in perpendicular magnetic tunnel junctions

    SciTech Connect

    Zhang, Xiangli; Zhang, Zongzhi; Liu, Yaowen; Jin, Q. Y.

    2015-05-07

    Macrospin simulations are performed to model the magnetization switching driven by the combined action of electric-field and spin-polarized electric current (spin-transfer torque; STT) in MgO/CoFeB based magnetic tunnel junctions with interfacial perpendicular magnetic anisotropy. The results indicate that at low current case, the free layer magnetization shows a fast toggle-like switching, the final parallel or antiparallel magnetization state is determined by the electric-field effect, and the STT just helps or resists it to reach the final state depending on the current direction. However, with the increase of current strength, the contribution of STT effect gradually increases, which eventually achieves a deterministic magnetization switching state. Simulations further demonstrate that by appropriately tuning the parameters of applied electric-field and current the power consumption can be easily reduced by two orders of magnitude.

  11. Simulation of electric-field and spin-transfer-torque induced magnetization switching in perpendicular magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Zhang, Xiangli; Zhang, Zongzhi; Liu, Yaowen; Jin, Q. Y.

    2015-05-01

    Macrospin simulations are performed to model the magnetization switching driven by the combined action of electric-field and spin-polarized electric current (spin-transfer torque; STT) in MgO/CoFeB based magnetic tunnel junctions with interfacial perpendicular magnetic anisotropy. The results indicate that at low current case, the free layer magnetization shows a fast toggle-like switching, the final parallel or antiparallel magnetization state is determined by the electric-field effect, and the STT just helps or resists it to reach the final state depending on the current direction. However, with the increase of current strength, the contribution of STT effect gradually increases, which eventually achieves a deterministic magnetization switching state. Simulations further demonstrate that by appropriately tuning the parameters of applied electric-field and current the power consumption can be easily reduced by two orders of magnitude.

  12. Cold flow simulation of the alternate turbopump development turbine of the Space Shuttle main engine high pressure fuel turbopump

    NASA Astrophysics Data System (ADS)

    Rutkowski, Richard J.

    1994-03-01

    Completion of the installation at the Naval Postgraduate School of a cold-flow test facility for the turbine of the Space Shuttle Main Engine High Pressure Fuel Turbopump is reported. The article to be tested is the first stage of the Alternate Turbopump Development model designed and manufactured by Pratt & Whitney. The purpose of the facility is to enable the development of non-intrusive flow measurements and comparison of those measurements with numerical simulations. Flow field characteristics of the turbine stator were predicted using a three-dimensional viscous flow code. A sensitivity study was conducted to determine the effect of inlet profile to flow field solution. Recommendations are made for future use of the test facility and validation of the numerical simulation scheme.

  13. Magnetic confinement of electron and photon radiotherapy dose: A Monte Carlo simulation with a nonuniform longitudinal magnetic field

    SciTech Connect

    Chen Yu; Bielajew, Alex F.; Litzenberg, Dale W.; Moran, Jean M.; Becchetti, Frederick D.

    2005-12-15

    It recently has been shown experimentally that the focusing provided by a longitudinal nonuniform high magnetic field can significantly improve electron beam dose profiles. This could permit precise targeting of tumors near critical areas and minimize the radiation dose to surrounding healthy tissue. The experimental results together with Monte Carlo simulations suggest that the magnetic confinement of electron radiotherapy beams may provide an alternative to proton or heavy ion radiation therapy in some cases. In the present work, the external magnetic field capability of the Monte Carlo code PENELOPE was utilized by providing a subroutine that modeled the actual field produced by the solenoid magnet used in the experimental studies. The magnetic field in our simulation covered the region from the vacuum exit window to the phantom including surrounding air. In a longitudinal nonuniform magnetic field, it is observed that the electron dose can be focused in both the transverse and longitudinal directions. The measured dose profiles of the electron beam are generally reproduced in the Monte Carlo simulations to within a few percent in the region of interest provided that the geometry and the energy of the incident electron beam are accurately known. Comparisons for the photon beam dose profiles with and without the magnetic field are also made. The experimental results are qualitatively reproduced in the simulation. Our simulation shows that the excessive dose at the beam entrance is due to the magnetic field trapping and focusing scattered secondary electrons that were produced in the air by the incident photon beam. The simulations also show that the electron dose profile can be manipulated by the appropriate control of the beam energy together with the strength and displacement of the longitudinal magnetic field.

  14. Simulation of deformations in magnetic media by the movable cellular automata method

    NASA Astrophysics Data System (ADS)

    Usachev, Victor V.; Andriushchenko, Petr D.; Afremov, Leonid L.

    2015-09-01

    A deformable model of the magnetic medium is considered in the research paper. Simulating algorithms of the impact of the external magnetic field on the deformation of the magnetic medium have been developed on the basis of the movable cellular automata (MCA) method.

  15. Comparison between theory and simulations for the magnetization and the susceptibility of polydisperse ferrofluids.

    PubMed

    Szalai, I; Nagy, S; Dietrich, S

    2013-11-20

    The influence of polydispersity on the magnetization of ferrofluids is studied based on a previously published magnetization equation of state (Szalai and Dietrich, 2011 J. Phys.: Condens. Matter 23 326004) and computer simulations. The polydispersity of the particle diameter is described by the gamma distribution function. Canonical ensemble Monte Carlo simulations have been performed in order to test these theoretical results for the initial susceptibility and the magnetization. The results for the magnetic properties of the polydisperse systems turn out to be in quantitative agreement with our present simulation data. In addition, we find good agreement between our theory and experimental data for magnetite-based ferrofluids. PMID:24153397

  16. Quasi-One-Dimensional Particle-in-Cell Simulation of Magnetic Nozzles

    NASA Technical Reports Server (NTRS)

    Ebersohn, Frans H.; Sheehan, J. P.; Gallimore, Alec D.; Shebalin, John V.

    2015-01-01

    A method for the quasi-one-dimensional simulation of magnetic nozzles is presented and simulations of a magnetic nozzle are performed. The effects of the density variation due to plasma expansion and the magnetic field forces on ion acceleration are investigated. Magnetic field forces acting on the electrons are found to be responsible for the formation of potential structures which accelerate ions. The effects of the plasma density variation alone are found to only weakly affect ion acceleration. Strongly diverging magnetic fields drive more rapid potential drops.

  17. Numerical Simulations of Nanoflares: PDFs of Released Energy, Waiting Times and Quiet- Sun Magnetic Field Elements

    NASA Astrophysics Data System (ADS)

    Egidi, A.; Viticchie`, B.; Berrilli, F.; Del Moro, D.

    2007-12-01

    A numerical model for nanoflares is proposed to describe probability density functions (PDF) and waiting time statistics of the emitted magnetic energy and to guess PDF of quiet-Sun magnetic field strength. In the simulation, footpoints of reconnecting magnetic loops are advected by photospheric flows computed via a n-body algorithm. The model simulates a system whose behavior is characterized by small scale (i.e., granulation) flows that interact to develop large organization scales (i.e., mesogranulation). Such spatio-temporal correlated flows, incessantly supply , remove and convey the passive magnetic footpoints onto the photospheric surface, triggering reconnections and magnetic field reconfigurations.

  18. Three-dimensional Simulation of Magnetic Flux Dynamics and Temperature Rise in HTSC Bulk during Pulsed Field Magnetization

    NASA Astrophysics Data System (ADS)

    Fujishiro, H.; Naito, T.; Oyama, M.

    We have performed a three-dimensional (3D) numerical simulation of the dynamical motion of the magnetic flux and the heat propagation in the superconducting bulk after applying a pulsed magnetic field. An inhomogeneous Jc distribution was supposed in the bulk; the Jc in the growth sector boundary (GSB) is four times higher than that in the growth sector region (GSR). For lower applied pulsed field, magnetic flux was penetrated and trapped in the GSR, and for higher applied pulsed field, the magnetic flux was trapped more preferentially in the GSB. These results of the simulation reproduce the experimental ones and are valuable for the understanding the flux dynamics in the bulk during pulsed field magnetization.

  19. Simulation of systematic errors in the SLC magnets

    SciTech Connect

    Jaeger, J.

    1983-08-08

    The distance (iron to iron) between a focusing and a defocusing magnet in the SLC-arcs is 6.7056 cm and the iron length of each of them is 2.52914 m. To represent these magnets by a hard-edge model in computer codes TRANSPORT or TURTLE the magnetic length rather than the core length of these magnets is of interest. In the present lattice the magnetic length for the field and the gradient of each of these magnets is assumed to be 2.5462 m.

  20. Investigation of magnetic properties of thin films using computer simulation

    NASA Astrophysics Data System (ADS)

    Balakirev, N. A.; Zhikharev, V. A.; Gumarov, G. G.

    2012-03-01

    A two-dimensional dendrite is generated within the diffusion limited aggregation (DLA) model in the presence of an external magnetic field. The magnetic interaction between a grown dendrite and diffusing atoms results in the elongation of the dendrite in the direction of the magnetic field. The dependence is studied of the dendrite elongation on the grid occupation. The energy of the magnetic anisotropy is calculated for an elongated dendrite. The FMR spectra are calculated in geometries when the static magnetic field is either perpendicular or parallel to dendrite plane. It is shown that the FMR signals in latter case depend on the static magnetic field orientation with respect to the elongation direction.

  1. Numerical simulations of magnetohydrodynamic flows driven by a moving permanent magnet

    NASA Astrophysics Data System (ADS)

    Prinz, S.; Bandaru, V.; Kolesnikov, Y.; Krasnov, D.; Boeck, T.

    2016-08-01

    We present results from numerical reconstructions of magnetic obstacle experiments performed in liquid metal flows. The experimental setup consists of an open rectangular container filled with a thin layer of liquid metal (GaInSn). A permanent magnet is installed on a rail beneath the container and is moved with a constant velocity U0, which in turn induces a flow inside the liquid metal due to Lorentz forces. The setup allows experiments in a parameter range that is accessible by direct numerical simulations (DNS). We present results from realizations with four different parameter sets, covering flows with stable stationary vortex structures in the reference system of the moving magnet as well as time-dependent flow regimes. Although the liquid metal layer is very thin, the flow shows a highly three-dimensional character in the near and in the far wake of the magnetic obstacle. We conclude that the streamline visualization in the experiment (using gas bubbles at the surface of the liquid metal layer) is insufficient to picture the flow structure occurring in the liquid metal. To underpin our conclusions, we introduce a modified numerical model which aims to mimic the movement of these gas bubbles. Although this model is a strong simplification of the highly complicated behavior of bubbles at a fluid-fluid interface, it captures the main effects and provides a good reproduction of the experimental results. Furthermore, transient effects are investigated when the flow is initiated, i.e., when the magnet approaches the container and crosses its front wall. We conclude that the process of vortex formation is accompanied by a decrease of the streamwise component of the Lorentz force compared to the time when the fluid is still quiescent. This decrease occurs only for flows with stable vortex structures, which might be of interest for practical applications like Lorentz force velocimetry. The Lorentz forces obtained from our DNS are in good agreement with the values

  2. GLOBAL SIMULATIONS OF THE MAGNETIC FIELD EVOLUTION IN BARRED GALAXIES UNDER THE INFLUENCE OF THE COSMIC-RAY-DRIVEN DYNAMO

    SciTech Connect

    Kulpa-Dybel, K.; Otmianowska-Mazur, K.; Kulesza-Zydzik, B.; Kowal, G.; Hanasz, M.; Woltanski, D.; Kowalik, K.

    2011-06-01

    We present three-dimensional global numerical simulations of the cosmic-ray (CR) driven dynamo in barred galaxies. We study the evolution of the interstellar medium of the barred galaxy in the presence of non-axisymmetric component of the potential, i.e., the bar. The magnetohydrodynamical dynamo is driven by CRs, which are continuously supplied to the disk by supernova (SN) remnants. No magnetic field is present at the beginning of simulations but one-tenth of SN explosions is a source of a small-scale randomly oriented dipolar magnetic field. In all models we assume that 10% of 10{sup 51} erg SN kinetic energy output is converted into CR energy. To compare our results directly with the observed properties of galaxies, we construct realistic maps of polarized radio emission. The main result is that the CR-driven dynamo can amplify weak magnetic fields up to a few {mu}G within a few Gyr in barred galaxies. The obtained e-folding time is equal to 300 Myr and the magnetic field reaches equipartition at time t {approx} 4.0 Gyr. Initially, the completely random magnetic field evolves into large-scale structures. An even (quadrupole-type) configuration of the magnetic field with respect to the galactic plane can be observed. Additionally, the modeled magnetic field configuration resembles maps of the polarized intensity observed in barred galaxies. Polarization vectors are distributed along the bar and between spiral arms. Moreover, the drift of magnetic arms with respect to the spiral pattern in the gas density distribution is observed during the entire simulation time.

  3. Numerical simulation of mass injection for the formation of prominence magnetic field configurations. II - Symmetric injection

    NASA Technical Reports Server (NTRS)

    An, C.-H.; Bao, J. J.; Wu, S. T.; Suess, S. T.

    1988-01-01

    A two-dimensional MHD model simulating the formation of Kippenhahn-Schluter (1957) quiescent prominence (QP) magnetic field configurations is used to explore symmetric mass injection into a dipole magnetic field. An optimum magnetic field strength for QP formation by mass injection is obtained. It is found that a weaker magnetic field strength is more favorable for the condensation of the injected plasma but that a stronger field is more favorable for supporting the condensed plasma against gravity.

  4. 3D Electromagnetic Particle-in-Cell simulations of the solar wind interaction with lunar magnetic anomalies

    NASA Astrophysics Data System (ADS)

    Deca, J.; Lapenta, G.; Divin, A. V.; Lembege, B.; Markidis, S.

    2013-12-01

    Unlike the Earth and Mercury, our Moon has no global magnetic field and is therefore not shielded from the impinging solar wind by a magnetosphere. However, lunar magnetic field measurements made by the Apollo missions provided direct evidence that the Moon has regions of small-scale crustal magnetic fields, ranging up to a few 100km in scale size with surface magnetic field strengths up to hundreds of nanoTeslas. More recently, the Lunar Prospector spacecraft has provided high-resolution observations allowing to construct magnetic field maps of the entire Moon, confirming the earlier results from Apollo, but also showing that the lunar plasma environment is much richer than earlier believed. Typically the small-scale magnetic fields are non-dipolar and rather tiny compared to the lunar radius and mainly clustered on the far side of the moon. Using iPic3D we present the first 3D fully kinetic and electromagnetic Particle-in-Cell simulations of the solar wind interaction with lunar magnetic anomalies. We study the behaviour of a dipole model with variable surface magnetic field strength under changing solar wind conditions and confirm that lunar crustal magnetic fields may indeed be strong enough to stand off the solar wind and form a mini-magnetosphere, as suggested by MHD and hybrid simulations and spacecraft observations. 3D-PIC simulations reveal to be very helpful to analyze the diversion/braking of the particle flux and the characteristics of the resulting particles accumulation. The particle flux to the surface is significantly reduced at the magnetic anomaly, surrounded by a region of enhanced density due to the magnetic mirror effect. Second, the ability of iPic3D to resolve all plasma components (heavy ions, protons and electrons) allows to discuss in detail the electron physics leading to the highly non-adiabatic interactions expected as well as the implications for solar wind shielding of the lunar surface, depending on the scale size (solar wind protons

  5. Object-Oriented Fast Multipole Simulation: Magnetic Colloids

    NASA Astrophysics Data System (ADS)

    Visscher, Pieter; Günal, Yüksel

    1997-08-01

    In simulating a system of N particles, if the interaction is long-ranged all pair interactions must be calculated, requiring CPU time of order N^2. Recently-developed ``fast multipole'' methods (FMM) can reduce this time to order N, at the cost of considerable programming complexity. We have developed an object-oriented approach which uses similar ideas but is conceptually much simpler. The system is represented by a hierarchical tree whose root is the entire system and whose lowest nodes are the particles. The entire calculation of the particle interactions consists of a single call to a recursive function CalculateInteractions(A,B) with A=B=root, which uses a simple opening-angle criterion to choose between multipole expansion and calling itself (subdividing A and B.) The resulting algorithm is essentially equivalent to the FMM, but the choice of when to subdivide (which is laboriously hard-wired in FMM) is made automatically. We will discuss the implementation of periodic BCs and the application of the method to continuum systems (cylindrical magnetic particles).

  6. Role of surfactant molecules in magnetic fluid: comparison of Monte Carlo simulation and electron magnetic resonance.

    PubMed

    Castro, L L; Gonçalves, G R R; Neto, K Skeff; Morais, P C; Bakuzis, A F; Miotto, R

    2008-12-01

    We investigate a magnetic fluid composed of magnetite nanoparticles surfacted with dodecanoic acid molecules and stably dispersed in a hydrocarbon solvent. A comparison between Monte Carlo simulation and different experimental techniques allows us to validate our methodology and investigate the behavior of the surfactant molecules. Our analysis, based on the Langmuir model, suggests that the surfactant grafting number on isolate nanoparticles increases with the nanoparticle concentration, while the grafting on agglomerated nanoparticles presents a more complicated behavior. Our results suggests that, if properly coated and at a certain concentration range, colloids can become stable even in the presence of agglomerates. The role of the Hamaker constant, which controls the van der Waals interaction intensity, was also investigated. We have found that the ratio between grafting and Hamaker constant governs the level of nanoparticle agglomeration. PMID:19256846

  7. Formation Process of the Circumstellar Disk: Long-term Simulations in the Main Accretion Phase of Star Formation

    NASA Astrophysics Data System (ADS)

    Machida, Masahiro N.; Inutsuka, Shu-ichiro; Matsumoto, Tomoaki

    2010-12-01

    The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing cloud cores, the first (adiabatic) core with a size of gsim3 AU forms prior to the formation of the protostar. At its formation, the first core has a thick disk-like structure and is mainly supported by the thermal pressure. After the protostar formation, it decreases the thickness gradually and becomes supported by the centrifugal force. We found that the first core is a precursor of the circumstellar disk with a size of >3 AU. This means that unmagnetized protoplanetary disk smaller than <3 AU does not exist. Reflecting the thermodynamics of the collapsing gas, at the protostar formation epoch, the first core (or the circumstellar disk) has a mass of ~0.005-0.1 M sun, while the protostar has a mass of ~10-3 M sun. Thus, just after the protostar formation, the circumstellar disk is about 10-100 times more massive than the protostar. In the main accretion phase that lasts for ~105 yr, the circumstellar disk mass initially tends to dominate the protostellar mass. Such a massive disk is unstable to gravitational instability and tends to show fragmentation. Our calculations indicate that the low-mass companions may form in the circumstellar disk in the main accretion phase. In addition, the mass accretion rate onto the protostar shows a strong time variability that is caused by the torque from the low-mass companions and/or the spiral arms in the circumstellar disk. Such variability provides an important signature for detecting the substellar mass companion in the circumstellar disk around very young protostars.

  8. FORMATION PROCESS OF THE CIRCUMSTELLAR DISK: LONG-TERM SIMULATIONS IN THE MAIN ACCRETION PHASE OF STAR FORMATION

    SciTech Connect

    Machida, Masahiro N.; Inutsuka, Shu-ichiro; Matsumoto, Tomoaki E-mail: inutsuka@nagoya-u.j

    2010-12-01

    The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing cloud cores, the first (adiabatic) core with a size of {approx}>3 AU forms prior to the formation of the protostar. At its formation, the first core has a thick disk-like structure and is mainly supported by the thermal pressure. After the protostar formation, it decreases the thickness gradually and becomes supported by the centrifugal force. We found that the first core is a precursor of the circumstellar disk with a size of >3 AU. This means that unmagnetized protoplanetary disk smaller than <3 AU does not exist. Reflecting the thermodynamics of the collapsing gas, at the protostar formation epoch, the first core (or the circumstellar disk) has a mass of {approx}0.005-0.1 M{sub sun}, while the protostar has a mass of {approx}10{sup -3} M{sub sun}. Thus, just after the protostar formation, the circumstellar disk is about 10-100 times more massive than the protostar. In the main accretion phase that lasts for {approx}10{sup 5} yr, the circumstellar disk mass initially tends to dominate the protostellar mass. Such a massive disk is unstable to gravitational instability and tends to show fragmentation. Our calculations indicate that the low-mass companions may form in the circumstellar disk in the main accretion phase. In addition, the mass accretion rate onto the protostar shows a strong time variability that is caused by the torque from the low-mass companions and/or the spiral arms in the circumstellar disk. Such variability provides an important signature for detecting the substellar mass companion in the circumstellar disk around very young protostars.

  9. Three-dimensional simulations of the interaction between Type Ia supernova ejecta and their main sequence companions

    NASA Astrophysics Data System (ADS)

    Liu, Z. W.; Pakmor, R.; Röpke, F. K.; Edelmann, P.; Wang, B.; Kromer, M.; Hillebrandt, W.; Han, Z. W.

    2012-12-01

    Context. The identity of the progenitor systems of Type Ia supernovae (SNe Ia) is still uncertain. In the single-degenerate scenario, the interaction between the supernova blast wave and the outer layers of a main sequence companion star strips off hydrogen-rich material which is then mixed into the ejecta. Strong contamination of the supernova ejecta with stripped material could lead to a conflict with observations of SNe Ia. This constrains the single-degenerate progenitor model. Aims: In this work, our previous simulations based on simplified progenitor donor stars have been updated by adopting more realistic progenitor-system models that result from fully detailed, state-of-the-art binary evolution calculations. Methods: We use Eggleton's stellar evolution code including the optically thick accretion wind model and taking into account the possibility of the effects of accretion disk instabilities to obtain realistic models of companion stars for different progenitor systems. The impact of the supernova blast wave on these companion stars is followed in three-dimensional hydrodynamic simulations employing the smoothed particle hydrodynamics code GADGET3. Results: For a suite of main sequence companions, we find that the mass of the material stripped from the companions range from 0.11 M⊙ to 0.18 M⊙. The kick velocity delivered by the impact is between 51 km s-1 and 105 km s-1. We find that the stripped mass and kick velocity depend on the ratio of the orbital separation to the radius of a companion, af/R. They can be fitted in good approximation by a power law for a given companion model. However, we do not find a single power law relation holding for different companion models. This implies that the structure of the companion star is also important for the amount of stripped material. Conclusions: With more realistic companion star models than those employed in previous studies, our simulations show that the hydrogen masses stripped from companions are

  10. Numerical simulation and performance improvement of a multi-polar concentric Halbach cylindrical magnet for magnetic refrigeration

    NASA Astrophysics Data System (ADS)

    You, Yonghua; Guo, Yue; Xiao, Shuifang; Yu, Shen; Ji, Hu; Luo, Xiaobing

    2016-05-01

    Multi-polar concentric Halbach cylinders of magnets could generate the magnetic field varying considerably in the annular gaps, thus were applied in the rotary magnetic refrigerators. In the current investigation, a six-polar concentric Halbach cylinder is developed based on the ideal concentric one by the numerical simulation with COMSOL Multiphysics. Cylinder radii are optimized and magnet material profiles are adjusted for a better overall performance (Λcool). Moreover, the segmentation on the concentric cylinder is conducted for an easy fabrication, and the edge effect of finite-length device is studied. With the present investigation, it is found that a larger external radius of external cylinder facilitates a larger flux density in the high field region (| B | bar high), while Λcool could be worse. Meanwhile, with the removal of magnet materials enclosed by the equipotential lines of magnetic vector potential, the magnetic flux density in low field region (| B | bar low) drops from 0.271 to 0.0136 T, and Λcool rises from 1.36 to 1.85 T0.7. Moreover, a proper segmentation would not degrade the difference between | B | bar high and | B | bar low, on the contrary, Λcool rises by about 20.2% due to magnet materials lack for efficiency replaced by soft irons. Finally, current 3D simulation indicates the edge effect on Λcool could be trivial.

  11. Impeller shroud to casing leakage flow simulations in the Space Shuttle Main Engine high pressure fuel pump

    NASA Technical Reports Server (NTRS)

    Sindir, Munir M.

    1987-01-01

    Quasi-three-dimensional Navier-Stokes calculations were carried out for the Space Shuttle Main Engine high-pressure fuel pump to simulate the impeller shroud to casing leakage flow. This flow geometry was modeled as an axisymmetric cavity flow with a stationary surface representing the casing, and a rotating surface denoting the impeller. A 63 x 81-node mesh provided sufficient resolution in the regions of greatest flow variations and reduced the effects of numerical diffusion. The turbulence field was closed with the high Reynolds number form of the k-epsilon model supplemented with wall functions in the vicinity of the walls. Finally, a parametric study quantified the effects of through mass flow changes on this leakage flow.

  12. Magnetic fields of chemically peculiar and related stars. I. Main results of 2014 and near-future prospects

    NASA Astrophysics Data System (ADS)

    Romanyuk, I. I.

    2015-04-01

    We make a critical analysis of the results of studies of magnetic fields in chemically peculiar and related stars, published mostly in 2014. Methodological matters are discussed, and research results are analyzed. Most of the measurements of magnetic fields were obtained with well-known instruments. In 2014 a large observational project MiMeS was accomplished, the observations of more than 500 objects were performed, magnetic fields were found in 35 of them. Twenty new magnetic stars have been detected from the observations with the SAORAS 6-m telescope. Regular measurements of magnetic fields with an accuracy of units of gauss are conducted on a number of telescopes using the HARPS, ESPaDOnS, and NARVAL spectropolarimeters. The fields of complex topology have been studied, magnetic maps have been built, a connection with the distribution of anomalies of chemical composition has been found. The debate about the existence of a magnetic field of about 1 G in Vega and some other objects is ongoing. Apparently, the absence of a large-scale magnetic field greater than tens of gauss in the mercury-manganese and Am stars is confirmed. First CP stars were detected outside the Galaxy, in the Large Magellanic Cloud. Observations of magnetic fields in solar-type stars are continued, a strong correlation between the field strength and the degree of chromospheric activity was discovered.

  13. Water pollution risk simulation and prediction in the main canal of the South-to-North Water Transfer Project

    NASA Astrophysics Data System (ADS)

    Tang, Caihong; Yi, Yujun; Yang, Zhifeng; Cheng, Xi

    2014-11-01

    The middle route of the South-to-North Water Transfer Project (MRP) will divert water to Beijing Tuancheng Lake from Taocha in the Danjiangkou reservoir located in the Hubei province of China. The MRP is composed of a long canal and complex hydraulic structures and will transfer water in open channel areas to provide drinking water for Beijing, Shijiazhuang and other cities under extremely strict water quality requirements. A large number of vehicular accidents, occurred on the many highway bridges across the main canal would cause significant water pollution in the main canal. To ensure that water quality is maintained during the diversion process, the effects of pollutants on water quality due to sudden pollution accidents were simulated and analyzed in this paper. The MIKE11 HD module was used to calculate the hydraulic characteristics of the 42-km Xishi-to-Beijuma River channel of the MRP. Six types of hydraulic structures, including inverted siphons, gates, highway bridges, culverts and tunnels, were included in this model. Based on the hydrodynamic model, the MIKE11 AD module, which is one-dimensional advection dispersion model, was built for TP, NH3-N, CODMn and F. The validated results showed that the computed values agreed well with the measured values. In accordance with transportation data across the Dianbei Highway Bridge, the effects of traffic accidents on the bridge on water quality were analyzed. Based on simulated scenarios with three discharge rates (ranged from 12 m3/s to 17 m3/s, 40 m3/s, and 60 m3/s) and three pollution loading concentration levels (5 t, 10 t and 20 t) when trucks spill their contents (i.e., phosphate fertilizer, cyanide, oil and chromium solution) into the channel, emergency measures were proposed. Reasonable solutions to ensure the water quality with regard to the various types of pollutants were proposed, including treating polluted water, maintaining materials, and personnel reserves.

  14. Subsolar magnetopause observation and kinetic simulation of a tripolar guide magnetic field perturbation consistent with a magnetic island

    NASA Astrophysics Data System (ADS)

    Eriksson, S.; Cassak, P. A.; Retinò, A.; Mozer, F. S.

    2016-04-01

    The Polar satellite recorded two reconnection exhausts within 6 min on 1 April 2001 across a subsolar magnetopause that displayed a symmetric plasma density, but different out-of-plane magnetic field signatures for similar solar wind conditions. The first magnetopause crossing displayed a bipolar guide field variation in a weak external guide field consistent with a symmetric Hall field from a single X line. The subsequent crossing represents the first observation of a tripolar guide field perturbation at Earth's magnetopause in a strong guide field. This perturbation consists of a significant guide field enhancement between two narrow guide field depressions. A particle-in-cell simulation for the prevailing conditions across this second event resulted in a magnetic island between two simulated X lines across which a tripolar guide field developed consistent with the observation. The simulated island supports a scenario whereby Polar encountered the asymmetric quadrupole Hall magnetic fields between two X lines for symmetric conditions across the magnetopause.

  15. The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Magnetohydrodynamics Simulation Module for the Global Solar Corona

    NASA Astrophysics Data System (ADS)

    Hayashi, K.; Hoeksema, J. T.; Liu, Y.; Bobra, M. G.; Sun, X. D.; Norton, A. A.

    2015-05-01

    Time-dependent three-dimensional magnetohydrodynamics (MHD) simulation modules are implemented at the Joint Science Operation Center (JSOC) of the Solar Dynamics Observatory (SDO). The modules regularly produce three-dimensional data of the time-relaxed minimum-energy state of the solar corona using global solar-surface magnetic-field maps created from Helioseismic and Magnetic Imager (HMI) full-disk magnetogram data. With the assumption of a polytropic gas with specific-heat ratio of 1.05, three types of simulation products are currently generated: i) simulation data with medium spatial resolution using the definitive calibrated synoptic map of the magnetic field with a cadence of one Carrington rotation, ii) data with low spatial resolution using the definitive version of the synchronic frame format of the magnetic field, with a cadence of one day, and iii) low-resolution data using near-real-time (NRT) synchronic format of the magnetic field on a daily basis. The MHD data available in the JSOC database are three-dimensional, covering heliocentric distances from 1.025 to 4.975 solar radii, and contain all eight MHD variables: the plasma density, temperature, and three components of motion velocity, and three components of the magnetic field. This article describes details of the MHD simulations as well as the production of the input magnetic-field maps, and details of the products available at the JSOC database interface. To assess the merits and limits of the model, we show the simulated data in early 2011 and compare with the actual coronal features observed by the Atmospheric Imaging Assembly (AIA) and the near-Earth in-situ data.

  16. Relativistic MHD simulations of core-collapse GRB jets: 3D instabilities and magnetic dissipation

    NASA Astrophysics Data System (ADS)

    Bromberg, Omer; Tchekhovskoy, Alexander

    2016-02-01

    Relativistic jets are associated with extreme astrophysical phenomena, like the core collapse of massive stars in gamma-ray bursts (GRBs) and the accretion on to supermassive black holes in active galactic nuclei. It is generally accepted that these jets are powered electromagnetically, by the magnetized rotation of a central compact object (black hole or neutron star). However, how the jets produce the observed emission and survive the propagation for many orders of magnitude in distance without being disrupted by current-driven instabilities is the subject of active debate. We carry out time-dependent 3D relativistic magnetohydrodynamic (MHD) simulations of relativistic, Poynting-flux-dominated jets. The jets are launched self-consistently by the rotation of a strongly magnetized central object. This determines the natural degree of azimuthal magnetic field winding, a crucial factor that controls jet stability. We find that the jets are susceptible to two types of instability: (i) a global, external kink mode that grows on long time-scales. It bodily twists the jet, reducing its propagation velocity. We show analytically that in flat density profiles, like the ones associated with galactic cores, the external mode grows and may stall the jet. In the steep profiles of stellar envelopes the external kink weakens as the jet propagates outward. (ii) a local, internal kink mode that grows over short time-scales and causes small-angle magnetic reconnection and conversion of about half of the jet electromagnetic energy flux into heat. We suggest that internal kink instability is the main dissipation mechanism responsible for powering GRB prompt emission.

  17. Accretion and Magnetic Reconnection in the Pre-Main Sequence Binary DQ Tau as Revealed through High-Cadence Optical Photometry

    NASA Astrophysics Data System (ADS)

    Tofflemire, Benjamin M.; Mathieu, Robert D.; Ardila, David R.; Akeson, Rachel L.; Ciardi, David R.; Herczeg, Gregory; Johns-Krull, Christopher M.; Vodniza, Alberto

    2016-01-01

    Protostellar disks are integral to the formation and evolution of low-mass stars and planets. A paradigm for the star-disk interaction has been extensively developed through theory and observation in the case of single stars. Most stars, however, form in binaries or higher order systems where the distribution of disk material and mass flows are more complex. Pre-main sequence (PMS) binary stars can have up to three accretion disks: two circumstellar disks and a circumbinary disk separated by a dynamically cleared gap. Theory suggests that mass may periodically flow in an accretion stream from a circumbinary disk across the gap onto circumstellar disks or stellar surfaces.The archetype for this theory is the eccentric, PMS binary DQ Tau. Moderate-cadence broadband photometry (~10 observations per orbital period) has shown pulsed brightening events near most periastron passages, just as numerical simulations would predict for a binary of similar orbital parameters. While this observed behavior supports the accretion stream theory, it is not exclusive to variable accretion rates. Magnetic reconnection events (flares) during the collision of stellar magnetospheres at periastron (when separated by 8 stellar radii) could produce the same periodic, broadband behavior when observed at a one-day cadence. Further evidence for magnetic activity comes from gyrosynchrotron, radio flares (typical of stellar flares) observed near multiple periastron passages. To reveal the physical mechanism seen in DQ Tau's moderate-cadence observations, we have obtained continuous, moderate-cadence, multi-band photometry over 10 orbital periods (LCOGT 1m network), supplemented with 32 nights of minute-cadence photometry centered on 4 separate periastron passages (WIYN 0.9m; APO ARCSAT). With detailed lightcurve morphologies we distinguish between the gradual rise and fall on multi-day time-scales predicted by the accretion stream theory and the hour time-scale, rapid-rise and exponential

  18. Computational fluid dynamics simulation of airflow in the trachea and main bronchi for the subjects with left pulmonary artery sling

    PubMed Central

    2014-01-01

    Background Left pulmonary artery sling (LPAS) is a rare but severe congenital anomaly, in which the stenoses are formed in the trachea and/or main bronchi. Multi-detector computed tomography (MDCT) provides useful anatomical images, but does not offer functional information. The objective of the present study is to quantitatively analyze the airflow in the trachea and main bronchi of LPAS subjects through computational fluid dynamics (CFD) simulation. Methods Five subjects (four LPAS patients, one normal control) aging 6-19 months are analyzed. The geometric model of the trachea and the two main bronchi is extracted from the MDCT images. The inlet velocity is determined based on the body weight and the inlet area. Both the geometric model and personalized inflow conditions are imported into CFD software, ANSYS. The pressure drop, mass flow ratio through two bronchi, wall pressure, flow velocity and wall shear stress (WSS) are obtained, and compared to the normal control. Results Due to the tracheal and/or bronchial stenosis, the pressure drop for the LPAS patients ranges 78.9 - 914.5 Pa, much higher than for the normal control (0.7 Pa). The mass flow ratio through the two bronchi does not correlate with the sectional area ratio if the anomalous left pulmonary artery compresses the trachea or bronchi. It is suggested that the C-shaped trachea plays an important role on facilitating the air flow into the left bronchus with the inertia force. For LPAS subjects, the distributions of velocities, wall pressure and WSS are less regular than for the normal control. At the stenotic site, high velocity, low wall pressure and high WSS are observed. Conclusions Using geometric models extracted from CT images and the patient-specified inlet boundary conditions, CFD simulation can provide vital quantitative flow information for LPAS. Due to the stenosis, high pressure drops, inconsistent distributions of velocities, wall pressure and WSS are observed. The C-shaped trachea may

  19. Galactic ménage à trois: simulating magnetic fields in colliding galaxies

    NASA Astrophysics Data System (ADS)

    Kotarba, H.; Lesch, H.; Dolag, K.; Naab, T.; Johansson, P. H.; Donnert, J.; Stasyszyn, F. A.

    2011-08-01

    We present high-resolution simulations of a multiple merger of three disc galaxies, including the evolution of magnetic fields, performed with the N-body/smoothed particle hydrodynamics (SPH) code GADGET. For the first time, we embed the galaxies in a magnetized, low-density medium, thus modelling an ambient intergalactic medium (IGM). The simulations include radiative cooling and a model for star formation and supernova feedback. Magnetohydrodynamics is followed using the SPH method. The progenitor discs have initial magnetic seed fields in the range 10-9-10-6 G and the IGM has initial fields of 10-12-10-9 G. The simulations are compared to a run excluding magnetic fields. We show that the propagation of interaction-driven shocks depends significantly on the initial magnetic field strength. The shocks propagate faster in simulations with stronger initial field, suggesting that the shocks are supported by magnetic pressure. The Mach numbers of the shocks range from approximately M= 1.5 for the non-magnetized case up to M= 6 for the highest initial magnetization, resulting in higher temperatures of the shock-heated IGM gas. The magnetic field in the system saturates rapidly after the mergers at ˜10-6 G within the galaxies and ˜10-8 G in the IGM independent of the initial value. These field strengths agree with observed values and correspond to the equipartition value of the magnetic pressure with the turbulent pressure in the system. We also present synthetic radio and polarization maps for different phases of the evolution, showing that shocks driven by the interaction produce a high amount of polarized emission. These idealized simulations indicate that magnetic fields play an important role for the hydrodynamics of the IGM during galactic interactions. We also show that even weak seed fields are efficiently strengthened during multiple galactic mergers. This interaction-driven amplification might have been a key process for the magnetization of the Universe.

  20. Comparisons of Simulated and Observed Stormtime Magnetic Intensities and Ion Plasma Parameters in the Ring Current

    NASA Astrophysics Data System (ADS)

    Chen, M. W.; Guild, T. B.; Lemon, C.; Roeder, J. L.; Le, G.; Schulz, M.

    2009-12-01

    Recent progress in ring current and plasma sheet modeling has shown the importance of a self-consistent treatment of particle transport and magnetic and electric fields in the inner magnetosphere. Models with and without self-consistency can lead to significantly different magnitudes and spatial distributions of plasma pressure and magnetic intensity during disturbed times. In this study we compare simulated and observed stormtime magnetic intensities (GOES and Polar/MFE) and ion densities (LANL/MPA and Polar/CAMMICE) to test how well self-consistent simulations can simultaneously reproduce these quantities. We simulate the ring current and plasma sheet for conditions corresponding to the 11 August 2000 storm using the self-consistent Rice Convection Model-Equilibrium (RCM-E) [Lemon et al., JGR, 2004] with a constant magnetopause location. Using the empirical IMF-dependent model of Tsyganenko and Mukai [JGR, 2003], we specify the plasma sheet pressure and density at 10 RE as the plasma boundary location in the RCM-E. The simulated ion densities at different magnetic local times agree fairly well with those from the re-analysis model of LANL/MPA densities of O’Brien and Lemon [Space Weather, 2007]. We compare the simulated magnetic intensity with the magnetic intensity measured by magnetometers on the GOES satellites at geosynchronous altitude (6.6 RE) and on the Polar satellite. Agreement between the simulated and observed magnetic intensities tends to agree better on the nightside than on the dayside in the inner magnetosphere. In particular, the model cannot account for observed drops in the dayside magnetic intensity during decreases in the solar wind pressure. We will modify the RCM-E to include a time-varying magnetopause location to simulate compressions and expansions associated with variations in the solar wind pressure. We investigate whether this will lead to improved agreement between the simulated and model magnetic intensities.

  1. Simulation of turbulent magnetic reconnection in the small-scale solar wind.

    NASA Astrophysics Data System (ADS)

    Wei, Fengsi; Qiang, Hu; Schwen, R.; Feng, Xueshang

    2000-06-01

    Some observational examples for the possible occurrence of the turbulent magnetic reconnection in the solar wind are found by analysing Hellos spacecraft's high resolution data. The phenomena of turbulent magnetic reconnections in small scale solar wind are simulated by introducing a third order accuracy upwind compact difference scheme to the compressible two-dimensional MHD flow. Numerical results verify that the turbulent magnetic reconnection process could occur in small scale interplanetary solar wind, which is a basic feature characterizing the magnetic reconnection in high-magnetic Reynolds number solar wind.

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  3. Effect of Object Orientation Angle on T2* Image and Reconstructed Magnetic Susceptibility: Numerical Simulations

    PubMed Central

    Chen, Zikuan; Calhoun, Vince

    2013-01-01

    The magnetic field resulting from material magnetization in magnetic resonance imaging (MRI) has an object orientation effect, which produces an orientation dependence for acquired T2* images. On one hand, the orientation effect can be exploited for object anisotropy investigation (via multi-angle imaging); on the other hand, it is desirable to remove the orientation dependence using magnetic susceptibility reconstruction. In this report, we design a stick-star digital phantom to simulate multiple orientations of a stick-like object and use it to conduct various numerical simulations. Our simulations show that the object orientation effect is not propagated to the reconstructed magnetic susceptibility distribution. This suggests that accurate susceptibility reconstruction methods should be largely orientation independent. PMID:25114542

  4. Three-dimensional finite element numerical simulation and physical experiment for magnetism-stress detecting in oil casing

    NASA Astrophysics Data System (ADS)

    Meng, Fanshun; Zhang, Jie; Yang, Chaoqun; Yu, Weizhe; Chen, Yuxi

    2015-08-01

    The casing damage has been a big problem in oilfield production. The current detection methods mostly are used after casing damage, which is not very effective. With the rapid development of China's offshore oil industry, the number of offshore oil wells is becoming larger and larger. Because the cost of offshore oil well is very high, the casing damage will cause huge economic losses. What's more, it can also bring serious pollution to marine environment. So the effective methods of detecting casing damage are required badly. The accumulation of stress is the main reason for the casing damage. Magnetic anisotropy technique based on counter magnetostriction effect can detect the stress of casing in real time and help us to find out the hidden dangers in time. It is essential for us to prevent the casing damage from occurring. However, such technique is still in the development stage. Previous studies mostly got the relationship between stress and magnetic signals by physical experiment, and the study of physical mechanism in relative magnetic permeability connecting the stress and magnetic signals is rarely reported. The present paper uses the ANSYS to do the three-dimensional finite element numerical simulation to study how the relative magnetic permeability works for the oil casing model. We find that the quantitative relationship between the stress's variation and magnetic induction intensity's variation is: Δδ = K* Δ B, K = 8.04×109, which is proved correct by physical experiment.

  5. Quantum simulation of magnetic kinks with dipolar lattice gases

    NASA Astrophysics Data System (ADS)

    Cao, Lushuai; Yin, Xiangguo; Schmelcher, Peter

    2015-05-01

    We propose an effective Ising spin chain constructed with dipolar quantum gases confined in a one-dimensional optical superlattice. Mapping the motional degrees of freedom of a single particle in the lattice onto a pseudo-spin results in effective transverse and longitudinal magnetic fields. This effective Ising spin chain exhibits a quantum phase transition from a paramagnetic to a single-kink phase as the dipolar interaction increases. Particularly in the single-kink phase, a magnetic kink arises in the effective spin chain and behaves as a quasi-particle in a pinning potential exerted by the longitudinal magnetic field. Being realizable with current experimental techniques, this effective Ising chain presents a unique platform for emulating the quantum phase transition as well as the magnetic kink effects in the Ising-spin chain and enriches the toolbox for quantum emulation of spin models by ultracold quantum gases.

  6. Numerical simulation of magnetic nanoparticles targeting in a bifurcation vessel

    NASA Astrophysics Data System (ADS)

    Larimi, M. M.; Ramiar, A.; Ranjbar, A. A.

    2014-08-01

    Guiding magnetic iron oxide nanoparticles with the help of an external magnetic field to its target is the principle behind the development of super paramagnetic iron oxide nanoparticles (SPIONs) as novel drug delivery vehicles. The present paper is devoted to study on MDT (Magnetic Drug Targeting) technique by particle tracking in the presence of magnetic field in a bifurcation vessel. The blood flow in bifurcation is considered incompressible, unsteady and Newtonian. The flow analysis applies the time dependent, two dimensional, incompressible Navier-Stokes equations for Newtonian fluids. The Lagrangian particle tracking is performed to estimate particle behavior under influence of imposed magnetic field gradients along the bifurcation. According to the results, the magnetic field increased the volume fraction of particle in target region, but in vessels with high Reynolds number, the efficiency of MDT technique is very low. Also the results showed that in the bifurcation vessels with lower angles, wall shear stress is higher and consequently the risk of the vessel wall rupture increases.

  7. Particle-in-cell simulations of electron energization in laser-driven magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Lu, San; Lu, Quanming; Guo, Fan; Sheng, Zhengming; Wang, Huanyu; Wang, Shui

    2016-01-01

    Electrons can be energized during laser-driven magnetic reconnection, and the energized electrons form three super-Alfvénic electron jets in the outflow region (Lu et al 2014 New J. Phys. 16 083021). In this paper, by performing two-dimensional particle-in-cell simulations, we find that the electrons can also be significantly energized before magnetic reconnection occurs. When two plasma bubbles with toroidal magnetic fields expand and squeeze each other, the electrons in the magnetic ribbons are energized through betatron acceleration due to the enhancement of the magnetic field, and an electron temperature anisotropy {T}{{e}\\perp }\\gt {T}{{e}| | } develops. Meanwhile, some electrons are trapped and bounced repeatedly between the two expanding/approaching bubbles and get energized through a Fermi-like process. The energization before magnetic reconnection is more significant (or important) than that during magnetic reconnection.

  8. Simulation of runaway electrons, transport affected by J-TEXT resonant magnetic perturbation

    NASA Astrophysics Data System (ADS)

    Jiang, Z. H.; Wang, X. H.; Chen, Z. Y.; Huang, D. W.; Sun, X. F.; Xu, T.; Zhuang, G.

    2016-09-01

    The topology of a magnetic field and transport properties of runaway electrons can be changed by a resonant magnetic perturbation field. The J-TEXT magnetic topology can be effectively altered via static resonant magnetic perturbation (SRMP) and dynamic resonant magnetic perturbation (DRMP). This paper studies the effect of resonant magnetic perturbation (RMP) on the confinement of runaway electrons via simulating their drift orbits in the magnetic perturbation field and calculating the orbit losses for different runaway initial energies and different runaway electrons, initial locations. The model adopted is based on Hamiltonian guiding center equations for runaway electrons, and the J-TEXT magnetic turbulences and RMP are taken into account. The simulation indicates that the loss rate of runaway electrons is sensitive to the radial position of electrons. The loss of energetic runaway beam is dominated by the shrinkage of the confinement region. Outside the shrinkage region of the runaway electrons are lost rapidly. Inside the shrinkage region the runaway beam is confined very well and is less sensitive to the magnetic perturbation. The experimental result on the response of runaway transport to the application RMP indicates that the loss of runaway electrons is dominated by the shrinkage of the confinement region, other than the external magnetic perturbation.

  9. Monte Carlo simulation of a cesium atom beam in a magnetic field

    SciTech Connect

    Chen, Jiang Zhu, Hongwei; Ma, Yinguang; Li, Detian; Liu, Zhidong; Wang, Ji

    2015-03-07

    We present Monte Carlo simulations of the deflection of a beam of {sup 133}Cs atoms in a two wire magnetic field. Our results reveal the relationship between transmission rate of the atoms and incident parameters. Incident angle and position of the beam with maximum transmission are obtained from the simulations. The effect of the deflection field on the spatial distribution (beam profile) of {sup 133}Cs is derived. The method will help with the design of magnetic deflection experiments and to extract the magnetic properties from such experiments.

  10. Effects of the magnetic equilibrium on gyrokinetic simulations of tokamak microinstabilities

    SciTech Connect

    Wan, Weigang; Chen, Yang; Parker, Scott E.; Groebner, Richard J.

    2015-06-15

    The general geometry of the experimental tokamak magnetic equilibrium is implemented in the global gyrokinetic simulation code GEM. Compared to the general geometry, the well used Miller parameterization of the magnetic equilibrium is a good approximation in the core region and up to the top of the pedestal. Linear simulations indicate that results with the two geometries agree for r/a ≤ 0.9. However, in the edge region, the instabilities are sensitive to the magnetic equilibrium in both the L-mode and the H-mode plasmas. A small variation of the plasma shaping parameters leads to large changes to the edge instability.