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1

Drift Instabilities in General Magnetic Field Configurations  

Microsoft Academic Search

A theory of low-frequency drift (universal) instabilities in a nonuniform collisionless plasma is developed for general magnetic field configurations including trapped particle effects, rather than the plane geometry which has previously received most attention. A type of energy principle shows that the special equilibrium distribution F(?, ?), of interest in minimum-B mirror configurations, is absolutely stable to these modes provided

P. H. Rutherford; E. A. Frieman

1968-01-01

2

Stable magnetic field configurations in stars  

NASA Astrophysics Data System (ADS)

Long-lived, large-scale magnetic field configurations with similar total fluxes exist in at least three very different, although related kind of stars: upper main sequence stars, white dwarfs, and neutron stars (e.g. Reisenegger 2001). Much or all of the volume of these stars is stably stratified, so there is no convection that could maintain these fields through dynamo processes (except in the cores of upper main sequence stars). Magnetohydrodynamic simulations of stably stratified stars (Braithwaite & Spruit 2004, 2006; Braithwaite & Nordlund 2006) suggest that configurations with linked poloidal and toroidal fields get spontaneously established and might be stable over long times. Physical arguments show that such configurations are in fact natural and that the stable stratification is likely to play a crucial role in their stability. Thus, contrary to assumptions in recent papers, the field is not force-free, and the fluid cannot be taken to be barotropic. Work is in progress to represent these fields analytically and investigate the conditions for their stability. In the case of neutron stars with strong enough fields, the stable stratification can be overcome by long-term, dissipative processes such as beta decays and ambipolar diffusion (Goldreich & Reisenegger 1992; Reisenegger et al. 2005), leading to the release of magnetic energy and potentially explaining the energy source for the "magnetar" phenomenon (Thompson & Duncan 1993, 1996).

Reisenegger, Andreas; Munoz, Francisco; Santos, Raul

3

Configurational sensitivity of multipoint magnetic field measurements  

NASA Astrophysics Data System (ADS)

A computational calibration model which can access the error budget for these measurements at all system levels is reported. The model is parametric since the total error contribution can be treated as an error function for the derived quantity, dependent on the various error sources. The possible measurement errors for the derived quantities to be critical at current mission specifications are found. Typical hard error sources, which are likely to remain following standard interspacecraft calibration, are identified. Orbit strategy, in particular, imposes constraints at the four spacecraft level. The sensitivity of the error functions to spacecraft configuration is investigated. The determination of the vector curl of the magnetic field is taken as a model measurement and the role of the divergence of the field for this quantity is discussed.

Dunlop, M. W.; Balogh, A.; Southwood, D. J.; Elphic, R. C.; Glassmeier, K.-H.; Neubauer, F. M.

1990-05-01

4

Simplest magnetometer configuration scheme to measure magnetic field gradient tensor  

Microsoft Academic Search

Due to geomagnetic anomaly strength can't be separated from magnetic field data, underwater vehicle localization based on geomagnetic anomaly needs vehicle draft depth information. For this localization method, we conclude that the simplest configuration be seven single-axis vector magnetometers to measure magnetic dipole gradients. The essential conditions and optimal measurement matrix of magnetic gradient tensor are analyzed, and a kind

Huang Yu; Sun Feng; Hao Yan-ling

2010-01-01

5

Revealing the Magnetic Field Configuration in M17-SO1  

NASA Astrophysics Data System (ADS)

We present near-infrared imaging polarimetry of the silhouette young stellar object M17-SO1. When the continuum and the scattering components are separated, the 2.17-?m Br? image reveals the absorptive polarization vectors (i.e., magnetic field lines) exiting the mid-plane of the circumstellar envelope at relatively wide angles. Such a configuration may imply a slightly pulled-in, co-rotating frozen-in poloidal magnetic field.

Fujiyoshi, T.; Yamashita, T.; Sako, S.; Hough, J. H.; Lucas, P. W.

2011-11-01

6

Influence of initial magnetic field configuration on spheromak evolution  

NASA Astrophysics Data System (ADS)

The influence of the initial magnetic field distribution on spheromak formation and closed flux generation upon decay is studied using the NIMROD code. Previous spheromak simulations using the NIMROD code have demonstrated the formation of axisymmetric closed flux surfaces with decay of the magnetic field. The q profile within the closed flux region was non-monotonic with values q0˜0.8 and qmin˜0.5. As the configuration evolved, a m=1, n=2 mode led to localized magnetic field chaos resulting in a degradation of thermal energy confinement. Given the limited ability to control the evolution of the q profile within the closed flux region of a spheromak, we investigate the possibility of forming spheromak plasmas that avoid this deleterious mode by tailoring the initial magnetic field profile appropriately. Poloidal flux amplification during the formation process involves conversion of injected toroidal flux via a line-tied kink mode. By strengthening or weakening the initial magnetic field along the geometric axis of the flux conserver, we attempt to control the amount of flux amplification to produce higher or lower values of q throughout the closed flux surface region. Simulations are performed using a finite element grid that approximates the geometry of the Sustained Spheromak Physics Experiment. In collaboration with Bick Hooper and Bruce Cohen, Lawrence Livermore National Laboratories.

Cone, Giovanni

2005-10-01

7

Residential magnetic fields predicted from wiring configurations: I. Exposure model.  

PubMed

A physically based model for residential magnetic fields from electric transmission and distribution wiring was developed to reanalyze the Los Angeles study of childhood leukemia by London et al. For this exposure model, magnetic field measurements were fitted to a function of wire configuration attributes that was derived from a multipole expansion of the Law of Biot and Savart. The model parameters were determined by nonlinear regression techniques, using wiring data, distances, and the geometric mean of the ELF magnetic field magnitude from 24-h bedroom measurements taken at 288 homes during the epidemiologic study. The best fit to the measurement data was obtained with separate models for the two major utilities serving Los Angeles County. This model's predictions produced a correlation of 0.40 with the measured fields, an improvement on the 0.27 correlation obtained with the Wertheimer-Leeper (WL) wire code. For the leukemia risk analysis in a companion paper, the regression model predicts exposures to the 24-h geometric mean of the ELF magnetic fields in Los Angeles homes where only wiring data and distances have been obtained. Since these input parameters for the exposure model usually do not change for many years, the predicted magnetic fields will be stable over long time periods, just like the WL code. If the geometric mean is not the exposure metric associated with cancer, this regression technique could be used to estimate long-term exposures to temporal variability metrics and other characteristics of the ELF magnetic field which may be cancer risk factors. PMID:10495305

Bowman, J D; Thomas, D C; Jiang, L; Jiang, F; Peters, J M

1999-10-01

8

Stochastic Ion Heating in a Field-reversed Configuration Geometry by Rotating Magnetic Fields.  

National Technical Information Service (NTIS)

Ion heating by application of rotating magnetic fields (RMF) to a prolate field-reversed configuration(FRC) is explored by analytical and numerical techniques. For odd-parity RMF (RMFo), perturbation analysis shows ions in figure-8 orbits gain energy at r...

A. S. Landsman S. A. Cohen

2007-01-01

9

Resonance and Chaotic Trajectories in Magnetic Field Reversed Configuration  

SciTech Connect

The nonlinear dynamics of a single ion in a field-reversed configuration (FRC) were investigated. FRC is a toroidal fusion device which uses a specific type of magnetic field to confine ions. As a result of angular invariance, the full three-dimensional Hamiltonian system can be expressed as two coupled, highly nonlinear oscillators. Due to the high nonlinearity in the equations of motion, the behavior of the system is extremely complex, showing different regimes, depending on the values of the conserved canonical angular momentum and the geometry of the fusion vessel. Perturbation theory and averaging were used to derive the unperturbed Hamiltonian and frequencies of the two degrees of freedom. The derived equations were then used to find resonances and compare to Poincar{copyright} surface-of-section plots. A regime was found where the nonlinear resonances were clearly separated by KAM [Kolmogorov-Arnold-Mosher] curves. The structure of the observed island chains was explained. The condition for the destruction of KAM curves and the onset of strong chaos was derived, using Chirikov island overlap criterion, and shown qualitatively to depend both on the canonical angular momentum and geometry of the device. After a brief discussion of the adiabatic regime the paper goes on to explore the degenerate regime that sets in at higher values of angular momenta. In this regime, the unperturbed Hamiltonian can be approximated as two uncoupled linear oscillators. In this case, the system is near-integrable, except in cases of a universal resonance, which results in large island structures, due to the smallness of nonlinear terms, which bound the resonance. The linear force constants, dominant in this regime, were derived and the geometry for a large one-to-one resonance identified. The above analysis showed good agreement with numerical simulations and was able to explain characteristic features of the dynamics.

A.S. Landsman; S.A. Cohen; M. Edelman; G.M. Zaslavsky

2005-04-13

10

A field-reversed magnetic configuration and applications of high-temperature FRC plasma  

SciTech Connect

As applied to a tokomak, a magnetic trap for confinement of a plasma with an inverted field or a magnetic field reversed configuration (FRC) is one of the most promising alternatives of the systems with high {beta}. A brief review of the latest data on FRC and potential directions of using such configurations in addition to energy generation in thermonuclear reactors (TNRs) is proposed.

Ryzhkov, S. V., E-mail: ryzhkov@power.bmstu.ru [Bauman Moscow State Technical University (Russian Federation)

2011-12-15

11

Internal magnetic field measurement on C-2 field-reversed configuration plasmas.  

PubMed

A long-lived field-reversed configuration (FRC) plasma has been produced in the C-2 device by dynamically colliding and merging two oppositely directed, highly supersonic compact toroids (CTs). The reversed-field structure of the translated CTs and final merged-FRC state have been directly verified by probing the internal magnetic field structure using a multi-channel magnetic probe array near the midplane of the C-2 confinement chamber. Each of the two translated CTs exhibits significant toroidal fields (B(t)) with opposite helicity, and a relatively large B(t) remains inside the separatrix after merging. PMID:23126880

Gota, H; Thompson, M C; Knapp, K; Van Drie, A D; Deng, B H; Mendoza, R; Guo, H Y; Tuszewski, M

2012-10-01

12

Internal magnetic field measurement on C-2 field-reversed configuration plasmas  

NASA Astrophysics Data System (ADS)

A long-lived field-reversed configuration (FRC) plasma has been produced in the C-2 device by dynamically colliding and merging two oppositely directed, highly supersonic compact toroids (CTs). The reversed-field structure of the translated CTs and final merged-FRC state have been directly verified by probing the internal magnetic field structure using a multi-channel magnetic probe array near the midplane of the C-2 confinement chamber. Each of the two translated CTs exhibits significant toroidal fields (Bt) with opposite helicity, and a relatively large Bt remains inside the separatrix after merging.

Gota, H.; Thompson, M. C.; Knapp, K.; Van Drie, A. D.; Deng, B. H.; Mendoza, R.; Guo, H. Y.; Tuszewski, M.

2012-10-01

13

The Magnetic Field Configuration of Magnetic Clouds and iCMEs: Writhe Vs. Twist  

NASA Astrophysics Data System (ADS)

Magnetic clouds are the most regular type of interplanetary coronal mass ejections (iCMEs), the counterparts in the interplanetary space of solar eruptions. Among other features, magnetic clouds are characterized by the smooth rotation of the magnetic field inside them. This has resulted in the current paradigm of associating magnetic clouds with twisted flux ropes. In this poster, we test this assumption by using a new model of solar eruption. Using results from a MHD simulation, we perform a ``blind'' reconstruction of the magnetic structure of the iCME using simulated satellite data and codes used for real observations of iCMEs. The 3-D structure of the iCME, in the simulation, does not exhibit much magnetic twist but when reconstructed from synthetic satellite data, it appears to have some characteristics of a magnetic cloud, due in particular to a writhe in the magnetic field lines. We eventually show that magnetic clouds do not necessarily have twisted magnetic field configuration.

Al-Haddad, Nada; Roussev, Ilia I.; Jacobs, Carla; Moestl, Christian; Lynch, Benjamin; Farrugia, Charles J.

2010-05-01

14

Twisted field configurations in magnetically linked star-disk systems  

NASA Astrophysics Data System (ADS)

A large-scale stellar magnetic field that threads a surrounding accretion disk can mediate a torque that regulates the stellar rotation rate, can channel some of the inflowing matter to polar regions, and may play a role in the transfer of angular momentum from the disk to the surrounding interstellar medium, possibly in the form of a centrifugally driven wind. These processes have originally been studied in the context of X-ray pulsars but have more recently been recognized as possibly playing a central role also in young stellar objects. Motivated by these applications and guided by recent numerical simulations and by related work in solar flare research, we have begun to develop analytic and semianalytic tools for analyzing the complex phenomena involved in the magnetic star-disk interaction. In this contribution we report on preliminary results on the time evolution of the magnetic field structure brought about by the relative rotation between the disk and the star. Although the magnetic field has a negligible dynamical effect on the disk over a rotation period, its structure in the magnetosphere outside the disk can change drastically on this time scale. Specifically, as the disk rotates, the field in the magnetosphere evolves through a sequence of sheared force-free equilibria. To determine this sequence, we first model the situation where the field lines are frozen into both the star and the disk and where the medium outside the disk is perfectly conducting. Subsequently, however, we relax these assumptions and consider the effects of finite resistivity both inside and outside the disk. This research is supported in part by NASA grants NAG 5-3687 and NAG 5-1485.

Uzdensky, D. A.; Litwin, C.; Konigl, A.

1999-05-01

15

Equilibrium configuration of the 1u state of hydrogen molecular ion in a magnetic field  

NASA Astrophysics Data System (ADS)

Using the variational method based on the Gaussian basis set, the authors investigate the 1u state of hydrogen molecular ion in a non-parallel magnetic field with respect to the fixed molecular axis. At sufficiently small field strength, the equilibrium configuration prefers the perpendicular orientation, in which the (relative) orientation ? between the magnetic field and the molecular axis is 90°. With increasing field strength, the orientation ? of the equilibrium configuration decreases, and is neither the parallel orientation nor the perpendicular orientation at field strength between 109 G and 2.35 × 1010 G. Meanwhile, more and more configurations with large orientations become unstable with respect to the dissociation H + p.

Song, Xuanyu; Gong, Cheng; Wang, Xiaofeng; Qiao, Haoxue

2013-08-01

16

Investigating Tx coils and magnetic field Rx sensor configurations for underwater geo-location  

Microsoft Academic Search

In this work, new configurations of magnetic field transmitter coils (Tx) and receiver sensors (Rx) are studied for underwater (UW) geo-locations. The geo-location system, based on low frequency magnetic fields, uses measured vector magnetic fields at a given set of points in space. It contains an active pulsed direct current transmitter, tri-axial field receivers, and a global positioning system unit

Fridon Shubitidze; Alex Bijamov; Gregory Schultz; Jon Miller; Irma Shamatava

2011-01-01

17

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

NASA Astrophysics Data System (ADS)

Context. In the past the role of magnetic null points in the generation of electric currents was investigated mainly in the close vicinity of the null, with perturbations being applied at nearby boundaries, or for a magnetic null configuration with a dome-shaped fan. In the solar atmosphere, however, electric currents are generated by perturbations originating at the photosphere, far away from coronal 3D nulls, and the occurence of magnetic nulls with a dome-shaped fan is apparently not common. Aims: We investigate the consequences of photospheric motion for the development of electric currents in a coronal magnetic field configuration containing a null, located far away from the boundaries, and the influence of topological structures on the spatial distribution of the currents. Methods: We use a 3D resistive MHD code to investigate the consequences of photospheric plasma motion for the generation of currents in a coronal magnetic field containing a null. The plasma is considered fully compressible and is initially in hydrostatic equilibrium. The initial magnetic field is potential (current free). Results: The photospheric plasma motion causes magnetic field perturbations that propagate to the corona along the field lines at the local Alfvén speed. The Alfvénic wave perturbations correspond to a propagating current directed mainly parallel to the magnetic field. Perpendicular currents connect to return currents to close the current system. The magnetic perturbations eventually reach the vicinity of the null. However, the currents forming in and around the null, near the fan surface or near the spine field lines, are not always the strongest currents developing in the simulation box. In our simulation, the strongest currents develop close to the bottom boundary, where the plasma is moved, and below the null point, in a region where field line connectivity considerably changes. Conclusions: Our simulation shows that the presence of a magnetic null point does not necessarily mean that the strongest currents will form in or around the null, at the fan surface or at the spine. Our results indicate that regions of considerable change in field line connectivity are fundamental for the development of strong and thin current sheets. Regions of connectivity change are important because they combine perturbations that are generated at different locations on the Sun. Our results also suggest that it is more important how the perturbations are mapped and combined in regions of considerable connectivity change than what is the driver of the perturbations itself. The driver does not necessarily need to create strong currents where it is applied. However, when the perturbations produced by the driver combine in the regions of considerable connectivity change, they can increase the current in regions for which the length scale is much smaller than the characteristic length scale of the system. The location of regions of connectivity change, combined with the mapping of the perturbations to those regions, can be a useful tool to predict where and when solar flares will occur.

Santos, J. C.; Büchner, J.; Otto, A.

2011-01-01

18

An Electron Cyclotron Resonance Ion Source with Cylindrically Comb-Shaped Magnetic Field Configuration  

SciTech Connect

A new concept on magnetic field of plasma production and confinement has been proposed to enhance efficiency of an electron cyclotron resonance (ECR) plasma for broad and dense ion beam source under the low pressure. The magnetic field configuration is constructed by a pair of comb-shaped magnet which has opposite polarity each other, and which cylindrically surrounds the plasma chamber. This magnetic configuration suppresses the loss due to ExB drift, and then plasma confinement is enhanced. The resonance zones of the fundamental and the second harmonics for 2.45GHz microwaves detach from the wall of the chamber. The connection length of the magnetic field lines through the resonance zone is elongated, and the confinement is better than that of the simple multipole magnetic field. The 2.45 GHz microwaves are fed from the side wall by the rod antenna. The electron density attained to about four times cutoff density for the 2.45GHz microwave at the low Ar pressure below 0.08Pa and also the low microwave power below 300W. We compare profiles of the electron density and temperature in the comb-shaped magnetic field configuration with those in the simple multipole magnetic field.

Kato, Yushi; Sasaki, Hiroshi; Kubo, Takashi; Sato, Fuminobu; Iida, Toshiyuki [Devision of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka Univ., 2-1 Yamada-oka, Suita-shi, Osaka 565-0871 (Japan); Asaji, Toyohisa [Devision of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka Univ., 2-1 Yamada-oka, Suita-shi, Osaka 565-0871 (Japan); Tateyama Machine Co., Ltd., 30 Shimonoban, Toyama 930-1305 (Japan)

2006-11-13

19

Experimental Study on the Effects of Magnetic Field Configuration near the Channel Exit on the Plume Divergence of Hall Thrusters  

Microsoft Academic Search

Experimental investigations into the effects of the magnetic field configuration near the channel exit on the plume of Hall thrusters were conducted. The magnetic field configuration near the channel exit is characterized by the inclination angle between the magnetic field lines and the thruster radial direction. Different inclination angles were obtained by varying the current ratio in the coils. The

Daren Yu; Jie Li; Hong Li; Yong Li; Binhao Jiang

2009-01-01

20

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

SciTech Connect

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

Clemente, R. A.; Gilli, M. [Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas, 13083-970 Campinas, SP (Brazil); Farengo, R. [Centro Atomico Bariloche and Instituto Balseiro, San Carlos de Bariloche (8400), RN (Argentina)

2008-10-15

21

Characteristics of RF Wave Propagation in Large-Diameter Plasma with Cusp Magnetic Field Configurations  

NASA Astrophysics Data System (ADS)

RF wave propagation, in the large-diameter (45 cm) plasma produced by a planar, spiral antenna, was investigated with the cusp magnetic field configurations. Measurements of the excited magnetic field amplitude and the phase were examined by a helicon wave dispersion relation, and the obtained results were consistent with the calculated ones by Transport Analyzing System for tokamaK/Wave analysis by Finite element method (TASK/WF) code. The wave characteristics depended on the gradient and the magnitude of the magnetic field near the line cusp position, and in the neighborhood of this position, this wave showed different behavior from the helicon wave observed in a uniform field.

Takechi, Seiji; Shinohara, Shunjiro; Fukuyama, Atsushi

1999-06-01

22

Effect of magnetic field configuration on parallel plasma flow during neutral beam injection in Heliotron J  

NASA Astrophysics Data System (ADS)

The effect of magnetic field configurations on plasma flow velocity was investigated by measuring the parallel flow velocity (v?) using a charge-exchange recombination spectroscopy during neutral beam injection in three different toroidal mirror configurations of Heliotron J: high, standard and reversed mirror configurations. The magnetic ripple strengths, ?, for these mirror configurations were ? = 0.073 m-1, 0.031 m-1 and 0.027 m-1, respectively, at the normalized averaged minor radius ? = 0.07. The magnetic ripple strength is defined as ? = {<(?B/?l)2/B2>}1/2, where <…> is the flux surface averaged value and l is the length along the magnetic field line. At ? = 0.07, the parallel flow velocity in the high mirror configuration (v? ˜ 4 km s-1) was 2-3 times smaller than those in the standard and reversed mirror configurations (v? ˜ 10-12 km s-1). An anticipated interpretation is that the difference in the neoclassical damping force contributes to the difference in v? among the three mirror configurations.

Lee, H.; Kobayashi, S.; Yokoyama, M.; Mizuuchi, T.; Minami, T.; Harada, T.; Nagasaki, K.; Okada, H.; Minami, T.; Yamamoto, S.; Murakami, S.; Nakamura, Y.; Konoshima, S.; Ohshima, S.; Zang, L.; Sano, F.

2013-03-01

23

Equilibrium configuration of the 1u state of hydrogen molecular ion in a magnetic field.  

PubMed

Using the variational method based on the Gaussian basis set, the authors investigate the 1u state of hydrogen molecular ion in a non-parallel magnetic field with respect to the fixed molecular axis. At sufficiently small field strength, the equilibrium configuration prefers the perpendicular orientation, in which the (relative) orientation ? between the magnetic field and the molecular axis is 90°. With increasing field strength, the orientation ? of the equilibrium configuration decreases, and is neither the parallel orientation nor the perpendicular orientation at field strength between 10(9) G and 2.35 × 10(10) G. Meanwhile, more and more configurations with large orientations become unstable with respect to the dissociation H + p. PMID:23947853

Song, Xuanyu; Gong, Cheng; Wang, Xiaofeng; Qiao, Haoxue

2013-08-14

24

A MAGNETOHYDRODYNAMIC MODEL FOCUSED ON THE CONFIGURATION OF MAGNETIC FIELD RESPONSIBLE FOR A SOLAR PENUMBRAL MICROJET  

SciTech Connect

In order to understand the configuration of magnetic field producing a solar penumbral microjet that was recently discovered by Hinode, we performed a magnetohydrodynamic simulation reproducing a dynamic process of how that configuration is formed in a modeled solar penumbral region. A horizontal magnetic flux tube representing a penumbral filament is placed in a stratified atmosphere containing the background magnetic field that is directed in a relatively vertical direction. Between the flux tube and the background field there forms the intermediate region in which the magnetic field has a transitional configuration, and the simulation shows that in the intermediate region magnetic reconnection occurs to produce a clear jet-like structure as suggested by observations. The result that a continuous distribution of magnetic field in three-dimensional space gives birth to the intermediate region producing a jet presents a new view about the mechanism of a penumbral microjet, compared to a simplistic view that two field lines, one of which represents a penumbral filament and the other the background field, interact together to produce a jet. We also discuss the role of the intermediate region in protecting the structure of a penumbral filament subject to microjets.

Magara, T., E-mail: magara@khu.ac.k [Department of Astronomy and Space Science, School of Space Research, Kyung Hee University, 1 Seocheon-dong, Giheung-gu, Yongin, Gyeonggi-do 446-701 (Korea, Republic of)

2010-05-20

25

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

NASA Astrophysics Data System (ADS)

After extensive experimentation on the Translation, Confinement, and Sustainment rotating magnetic-field (RMF)-driven field reversed configuration (FRC) device [A. L. Hoffman et al., Fusion Sci. Technol. 41, 92 (2002)], the principal physics of RMF formation and sustainment of standard prolate FRCs inside a flux conserver is reasonably well understood. If the RMF magnitude B? at a given frequency ? is high enough compared to other experimental parameters, it will drive the outer electrons of a plasma column into near synchronous rotation, allowing the RMF to penetrate into the plasma. If the resultant azimuthal current is strong enough to reverse an initial axial bias field Bo a FRC will be formed. A balance between the RMF applied torque and electron-ion friction will determine the peak plasma density nm~B?/?1/2?1/2rs, where rs is the FRC separatrix radius and ? is an effective weighted plasma resistivity. The plasma total temperature Tt is free to be any value allowed by power balance as long as the ratio of FRC diamagnetic current, I'dia~2Be/?o, is less than the maximum possible synchronous current, I'sync=e?rs2/2. The RMF will self-consistently penetrate a distance ?* governed by the ratio ?=I'dia/I'sync. Since the FRC is a diamagnetic entity, its peak pressure pm=nmkTt determines its external magnetic field Be~(2?opm)1/2. Higher FRC currents, magnetic fields, and poloidal fluxes can thus be obtained, with the same RMF parameters, simply by raising the plasma temperature. Higher temperatures have also been noted to reduce the effective plasma resistivity, so that these higher currents can be supported with surprisingly little increase in absorbed RMF power.

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

2006-01-01

26

Penetration and radial force balance in field-reversed configuration with large rotating magnetic field  

SciTech Connect

A field-reversed configuration (FRC) is formed by applying a rotating magnetic field (RMF) much larger than the axial magnetic field to a cylindrical glass vacuum chamber filled with 10 Pa argon gas without a preionization. The FRC with the plasma density 2.2x10{sup 19} m{sup -3}, the temperature 8.0 eV, the separatrix length 0.45 m, and the separatrix radius 0.035 m is sustained for the notably long period of 40 ms. It is observed that the antenna current which produces the RMF is reduced by about half after the FRC is formed. The interaction between the plasma and the antenna circuit increases the antenna resistance and changes the inductance of the antenna so that the circuit becomes nonresonant. The RMF is sufficiently large to fully penetrate to the center during the period and drive the current with a rigid rotor profile. The RMF is shown to play a major role in sustaining the plasma pressure.

Ohnishi, M.; Fukuhara, M.; Masaki, T.; Osawa, H.; Chikano, T. [Department of Electrical Engineering and Computer Science, Kansai University, 3-3-35 Yamate-cho, Suita-shi, Osaka 564-8680 (Japan); Hugrass, W. [School of Computing, University of Tasmania, Locked Bag 1359, Launceston, Tasmania 7250 (Australia)

2008-10-15

27

The Star Thrust Experiment, rotating magnetic field current drive in the field reversed configuration  

NASA Astrophysics Data System (ADS)

The Star Thrust Experiment (STX) has formed and sustained the Field Reversed Configuration (FRC) with a Rotating Magnetic Field (RMF) operated at a strength of 25 G and a frequency of 350 kHz. The RMF was generated with two IGBT switched solid state power supplies capable of delivering 2 MW each. Plasmas were typically 2 m long by 0.2m in radius and consisted of fully ionized deuterium at temperatures of 60 eV and peak densities of 5 × 1018m- 3. The primary diagnostic was an extremely small 24 channel berylia jacketed internal magnetic probe that was used to make measurements as a function of time, radius, and axial position. These measurements when combined with the FRC's unique geometry and equilibrium relationships determined many other important plasma parameters. Axial confining fields of 100 G maintained a true vacuum boundary around the plasma and allowed for the study of FRC RMF equilibrium interactions. Key findings are that the RMF maintained a near zero separatrix pressure, penetrated only partially, and drove strong radial and axial flows. Issues discussed include the importance of the RMF driving an axial current distribution consistent with that of the FRC, possible benefits of varying the average beta condition, and potential RMF antenna length limits set by the tendency of driven axial flows to screen the RMF from the plasma.

Miller, Kenneth Elric

2001-11-01

28

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

Microsoft Academic Search

Context. In the past the role of magnetic null points in the generation of electric currents was investigated mainly in the close vicinity of the null, with perturbations being applied at nearby boundaries, or for a magnetic null configuration with a dome-shaped fan. In the solar atmosphere, however, electric currents are generated by perturbations originating at the photosphere, far away

J. C. Santos; J. Büchner; A. Otto

2011-01-01

29

Configuration of the magnetic field and reconstruction of Pangaea in the Permian period  

Microsoft Academic Search

THE virtual geomagnetic poles of Laurasia and Gondwanaland in the Carboniferous and Permian periods diverge significantly when these continents are reassembled according to the fit calculated by Bullard et al.1. Two interpretations have been offered: Briden et al.2 explain these divergences by a magnetic field configuration very different from that of a geocentric axial dipole; Irving3 (and private communication), Van

M. Westphal

1977-01-01

30

RF Wave Propagation in Bounded Plasma under Divergent and Convergent Magnetic Field Configurations  

NASA Astrophysics Data System (ADS)

Radio frequency (RF) wave propagation in a bounded plasma (cylindrical shape with a large diameter of 45 cm) produced by a planar, spiral antenna was investigated under divergent and convergent magnetic field configurations. The measured excited magnetic field amplitude and the phase were examined based on helicon wave characteristics, and were consistent with the computed results using the Transport Analyzing System for tokamaK/Wave analysis by Finite element method (TASK/WF) code. The wave propagation region was broadened (focused) in the radial direction with increasing distance from the antenna under the divergent (convergent) field.

Takechi, Seiji; Shinohara, Shunjiro

1999-11-01

31

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

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

32

3-D Magnetic Field Configuration Late in a Large Two-Ribbon Flare  

NASA Astrophysics Data System (ADS)

We present H-alpha and coronal X-ray images of the large two-ribbon flare of 25/26 June 1992 during its long-lasting gradual decay phase. From these observations we deduce that the 3-D magnetic field configuration late in this flare was similar to that at and before the onset of such large eruptive bipolar flares: the sheared core field running under and out of the flare arcade was S-shaped, and at least one elbow of the S looped into the low corona. From previous observations of filament-eruption flares, we infer that such core-field coronal elbows, though rarely observed, are probably a common feature of the 3-D magnetic field configuration late in large two-ribbon flares. The rare circumstance that apparently resulted in a coronal elbow of the core field being visible in H-alpha in our flare was the occurrence of a series of subflares low in the core field under the late-phase arcade of the large flare; these subflares probably produced flaring arches in the northern coronal elbow, thereby rendering this elbow visible in H-alpha. The observed late-phase 3-D field configuration presented here, together with the recent sheared-core bipolar magnetic field model of Antiochos, Dahlburg, and Klimchuk (1994) and recent Yohkoh SXT observations of the coronal magnetic field configuration at and before the onset of large eruptive bipolar flares, supports the seminal 3-D model for eruptive two-ribbon flares proposed by Hirayama (1974), with three modifications: (1) the preflare magnetic field is closed over the filament-holding core field; (2) the preflare core field has the shape of an S (or backward S) with coronal elbows; (3) a lower part of the core field does not erupt and open, but remains closed throughout flare, and can have prominent coronal elbows. In this picture, the rest of the core field, the upper part, does erupt and open along with the preflare arcade envelope field in which it rides; the flare arcade is formed by reconnection that begins in the middle of the core field at the start of the eruption and progresses from reconnecting closed core field early in the flare to reconnecting "opened" envelope field late in the flare.

Moore, R. L.; Schmieder, B.; Hathaway, D. H.; Tarbell, T. D.

1997-05-01

33

Particle Confinement in Axisymmetric Poloidal Magnetic Field Configurations with Zeros of B: Methodological Note  

SciTech Connect

Collisionless particle confinement in axisymmetric configurations with magnetic field nulls is analyzed. The existence of an invariant of motion--the generalized azimuthal momentum--makes it possible to determine in which of the spatial regions separated by magnetic separatrices passing through the magnetic null lines the particle occurs after it leaves the vicinity of a magnetic null line. In particular, it is possible to formulate a sufficient condition for the particle not to escape through the separatrix from the confinement region to the external region. In the configuration under analysis, the particles can be lost from a separatrix layer with a thickness on the order of the Larmor radius because of the nonconservation of the magnetic moment {mu}. In this case, the variations in {mu} are easier to describe in a coordinate system associated with the magnetic surfaces. An analysis is made of the applicability of expressions for the single-pass change {delta}{mu} in the magnetic moment that were obtained in different magnetic field models for a confinement system with a divertor (such that there is a circular null line)

Arsenin, V.V.; Skovoroda, A.A. [Nuclear Fusion Institute, Russian Research Centre Kurchatov Institute, pl. Kurchatova 1, Moscow, 123182 (Russian Federation)

2005-12-15

34

The use of time-dependent magnetic fields for control of convective flows in melt growth configurations  

Microsoft Academic Search

The influence of a rotating magnetic field on buoyancy driven convection in a Rayleigh–Bénard configuration (vertical cylinder) and on Marangoni convection in a floating zone configuration was investigated experimentally and numerically. The main result of our study is that temperature fluctuations caused by time-dependent buoyancy and Marangoni convection can be damped by using a rotating magnetic field with relatively small

B. Fischer; J Friedrich; H Weimann; G Müller

1999-01-01

35

Investigating Tx coils and magnetic field Rx sensor configurations for underwater geo-location  

NASA Astrophysics Data System (ADS)

In this work, new configurations of magnetic field transmitter coils (Tx) and receiver sensors (Rx) are studied for underwater (UW) geo-locations. The geo-location system, based on low frequency magnetic fields, uses measured vector magnetic fields at a given set of points in space. It contains an active pulsed direct current transmitter, tri-axial field receivers, and a global positioning system unit (GPS). The GPS is coupled with the EMI system and provides continuous geo-referencing of the UW system's position. UW geolocations are estimated using a) closed form solution, that uses the total vector magnetic field tensor's gradient, and b) nonlinear optimization technique based of the differential evolution (DE) algorithm. In this work we first investigated the advantages and disadvantages of the proposed UW low frequency magnetic field geo-location system. Namely, we present systematic studies on: a) magnetic field transmitter configurations to determine the best compromise between size, shape and practical implementation to achieve maximum transmitter range in the UW environment, b) the placements of tri-axial receiver sensors with respect to the Tx to accurately estimate the UW geo-location from the measured magnetic fields; c) different sources of noise (such as the air-water interface, coupling between targets' EMI responses and the geo-location system's signals, water conductivity), to estimate how these noises influence the system's performance and localization precision. Finally, we assessed the capabilities of the closed-form solution and the DE technique to predict the location of an underwater interrogation system by comparing their corresponding estimated results to the true value. We found that for realistic water conductivities, the frequency should be less than 100 Hz. We showed that when the primary magnetic field is contaminated with random noises due to the presence of underwater metallic targets, water conductivity/frequency changes, and finite size of the transmitter, the performance of the full vector magnetic field tensor gradient approach degrades significantly compared to that of the DE method. In addition, the number of receivers required by the vector magnetic field tensor gradient technique and its sensitivity with respect to the sensor separation prevented us from further considering this technique for UW geo-location, leaving the non-linear approach, that uses only three vector Rx, as our technique of choice for tracking the location of underwater interrogation sensors with centimeter-level accuracy.

Shubitidze, Fridon; Bijamov, Alex; Schultz, Gregory; Miller, Jon; Shamatava, Irma

2011-05-01

36

Paramagnetic spin-up of a field-reversed configuration with rotating magnetic field current drive  

NASA Astrophysics Data System (ADS)

A transverse Rotating Magnetic Field (RMF) can drive toroidal current and sustain the poloidal flux of a Field Reversed Configuration (FRC) through the application of a Lorentz force on the electrons, where vz is the axial screening current and Br is the radial component of the RMF. The torque applied by the RMF will eventually be transferred to the ions through resistive collisions. In the absence of any drag force, the plasma will rapidly spin up in the ion paramagnetic direction, negating the current drive and possibly becoming rotationally unstable. A multi-chord Intensified Charge-Coupled Device (ICCD) spectrometer has measured the ion rotation profile via the Doppler shift of impurity line radiation in the Translation, Confinement, and Sustainment (TCS) experiment. The plasma is observed to rapidly spin up in the ion paramagnetic direction to a rigid rotation frequency of about oi ? 7 x 104 s-1, less than 15% of the typical RMF frequency o ? 0.5 x 106 s-1 . Neutral deuterium is observed to have no rotational velocity, and had been proposed as a mechanism for preventing synchronous spin-up of the ions. The neutral density and resulting charge-exchange and ionization rates have been calculated from an array of absolutely calibrated Dalpha detectors. The typical neutral fraction of about 2% of the plasma density is several times too low for ion-neutral collisions to balance the applied torque. Other possible braking mechanisms are shorting of the radial electric field needed to confine paramagnetic ions, and viscous drag. Assuming axial and azimuthal symmetry and pure deuterium, viscous wall drag is found to be insufficient to slow the plasma as well. Viscous drag could be significant if the edge plasma has high impurity content or is spatially non-uniform.

Peter, Andrew Maxwell

37

Onset and Saturation of Ion Heating by Odd-parity Rotating-magnetic-fields in a Field-reversed Configuration  

SciTech Connect

Heating of figure-8 ions by odd-parity rotating magnetic fields (RMF?) applied to an elongated field-reversed configuration (FRC) is investigated. The largest energy gain occurs at resonances (s ? ?(sub)R??) of the RMF? frequency, ?(sub)R, with the figure-8 orbital frequency, ?, and is proportional to s^2 for s – even resonances and to s for s – odd resonances. The threshold for the transition from regular to stochastic orbits explains both the onset and saturation of heating. The FRC magnetic geometry lowers the threshold for heating below that in the tokamak by an order of magnitude.

A.S. Landsman, S.A. Cohen, A.H. Glasser

2005-11-01

38

Configuration of the magnetic field and reconstruction of Pangaea in the Permian period.  

PubMed

The virtual geomagnetic poles of Laurasia and Gondwanaland in the Carboniferous and Permian periods diverge significantly when these continents are reassembled according to the fit calculated by Bullard et al. Two interpretations have been offered: Briden et al. explain these divergences by a magnetic field configuration very different from that of a geocentric axial dipole; Irving (and private communication), Van der Voo and French(4) suggest a different reconstruction and it is shown here that these two interpretations are not incompatible and that the first may help the second. PMID:16073416

Westphal, M

1977-05-12

39

The ion distribution in a field-reversed configuration heated by odd-parity rotating magnetic field  

NASA Astrophysics Data System (ADS)

The ion heating effect of odd-parity rotating magnetic field (oRMF) in a field-reversed magnetic configuration (FRC) is studied by a single particle Hamiltonian code. By varying the particle initial condition and assuming the ergodic hypothesis, we obtain a particle distribution on both configuration space and velocity space. The simulation shows that strong enough RMF will give high energy betatron orbit particles a strong concentration effect in the frame rotating with the RMF. Moreover, the RMF will accelerate the particles to form a double bump distribution rather than a Maxwellian. Both of those effect will improve the nuclear fusion efficiency and will increase the energy ratio of charged particles to neutrons when D-He^3 is used as fuel, which is good to future FRC-based nuclear fusion plant.

Liu, Chang; Cohen, Samuel

2012-10-01

40

Improvement of the magnetic configuration in the reversed field pinch through successive bifurcations  

NASA Astrophysics Data System (ADS)

The reversed field pinch (RFP) is a magnetic configuration alternative to the tokamak that can be considered for a second generation of reactors. In this paper new remarkable results obtained in the RFP experiment RFX-mod are presented, showing that an internal transport barrier delimitates a large fraction of the plasma volume in a RFP when the current is raised to ~1.5 MA. The formation of this transport barrier is related to a profound, spontaneous modification of the magnetic topology. Due to the occurrence of a saddle node bifurcation the plasma enters in the single helical axis state, which is theoretically known to be more resilient to chaos. This bifurcation is driven by the amplitude of the helical perturbation which dominates the mode spectrum.

Lorenzini, R.; Agostini, M.; Alfier, A.; Antoni, V.; Apolloni, L.; Auriemma, F.; Barana, O.; Baruzzo, M.; Bettini, P.; Bonfiglio, D.; Bolzonella, T.; Bonomo, F.; Brombin, M.; Buffa, A.; Canton, A.; Cappello, S.; Carraro, L.; Cavazzana, R.; Chitarin, G.; Dal Bello, S.; de Lorenzi, A.; de Masi, G.; Escande, D. F.; Fassina, A.; Franz, P.; Gaio, E.; Gazza, E.; Giudicotti, L.; Gnesotto, F.; Gobbin, M.; Grando, L.; Guo, S. C.; Innocente, P.; Luchetta, A.; Manduchi, G.; Marchiori, G.; Marcuzzi, D.; Marrelli, L.; Martin, P.; Martini, S.; Martines, E.; Milani, F.; Moresco, M.; Novello, L.; Ortolani, S.; Paccagnella, R.; Pasqualotto, R.; Peruzzo, S.; Piovan, R.; Piovesan, P.; Piron, L.; Pizzimenti, A.; Pomaro, N.; Predebon, I.; Puiatti, M. E.; Rostagni, G.; Sattin, F.; Scarin, P.; Serianni, G.; Sonato, P.; Spada, E.; Soppelsa, A.; Spagnolo, S.; Spizzo, G.; Spolaore, M.; Taliercio, C.; Terranova, D.; Toigo, V.; Valisa, M.; Veltri, P.; Vianello, N.; Zaccaria, P.; Zaniol, B.; Zanotto, L.; Zilli, E.; Zuin, M.

2009-05-01

41

Magnetic diagnostic suite of the C-2 field-reversed configuration experiment confinement vessel  

NASA Astrophysics Data System (ADS)

Magnetic measurements are a fundamental part of determining the size and shape of field-reversed configuration (FRC) plasmas in the C-2 device. The magnetic probe suite consists of 44 in-vessel and ex-vessel probes constructed using various technologies: ultra-high vacuum compatible mineral-insulated cable, nested triple axis coils hand-wound on ceramic bobbins, and commercial chip inductors mounted on printed circuit boards. Together, these probes measure the three-dimensional excluded flux profile of the FRC, which approximates the shape of the separatrix between the confined plasma volume and the scrape-off layer. High accuracy is achieved by using the extensive probe measurements to compensate for non-ideal effects such as flux leakage through the vacuum vessel and bulk motion of the FRC towards the wall. A subset of the probes is also used as a set of Mirnov arrays that provide sensitive detection of perturbations and oscillations of the FRC.

Thompson, M. C.; Douglass, J. D.; Feng, P.; Knapp, K.; Luo, Y.; Mendoza, R.; Patel, V.; Tuszewski, M.; Van Drie, A. D.

2012-10-01

42

Effect of Magnetic Field Configuration on n = 1 Instabilities in Rotamak  

NASA Astrophysics Data System (ADS)

The n = 1 tilt/radial shift modes are observed in rotating magnetic field (RMF) driven FRC plasmas. Experiments studying on the response of n = 1 instabilities to the changes of magnetic field structure have been conducted in 40 ms Rotamak discharges. In one series of experiments the axial current Iz (which produces toroidal field) ramps linearly in time from 0 to 2 kA, leading to transition from FRC to ST configuration. The amplitude of the tilt mode is suddenly doubled when Iz reaches 0.5 kA (compare to 2 kA plasma current); the amplitude remains at this level when Iz is in the range of 0.5-1 kA. The tilt instability disappears when Iz exceeds 1 kA. In other series of experiments, by using a middle shaping coil with a moderate current of 0.25-0.5 kA, the doublet-FRCs are formed which are completely free from both the tilt and radial shift modes.

Yang, Xiaokang; Petrov, Yuri; Huang, Tian-Sen

2009-11-01

43

Measurements accounting for the impediment of ion spin-up in rotating magnetic field driven field reversed configurations  

NASA Astrophysics Data System (ADS)

Improved vacuum hygiene, wall conditioning, and reduced recycling in the rotating magnetic field (RMF) driven translation, confinement, and sustainment-upgrade (TCSU) field reversed configuration experiment have made possible a more accurate assessment of the forces affecting ion spin-up. This issue is critical in plasmas sustained by RMFs, such as TCSU since ion spin-up can substantially reduce or cancel the RMF current drive effect. Several diagnostics are brought to bear, including a 3-axis translatable magnetic probe allowing the first experimental measurement of the end shorting effect. These results show that the ion rotation is determined by a balance between electron-ion friction, the end shorting effect, and ion drag against neutrals.

Deards, C. L.; Hoffman, A. L.; Steinhauer, L. C.

2011-11-01

44

Magnetic diagnostic suite of the C-2 field-reversed configuration experiment confinement vessel.  

PubMed

Magnetic measurements are a fundamental part of determining the size and shape of field-reversed configuration (FRC) plasmas in the C-2 device. The magnetic probe suite consists of 44 in-vessel and ex-vessel probes constructed using various technologies: ultra-high vacuum compatible mineral-insulated cable, nested triple axis coils hand-wound on ceramic bobbins, and commercial chip inductors mounted on printed circuit boards. Together, these probes measure the three-dimensional excluded flux profile of the FRC, which approximates the shape of the separatrix between the confined plasma volume and the scrape-off layer. High accuracy is achieved by using the extensive probe measurements to compensate for non-ideal effects such as flux leakage through the vacuum vessel and bulk motion of the FRC towards the wall. A subset of the probes is also used as a set of Mirnov arrays that provide sensitive detection of perturbations and oscillations of the FRC. PMID:23126883

Thompson, M C; Douglass, J D; Feng, P; Knapp, K; Luo, Y; Mendoza, R; Patel, V; Tuszewski, M; Van Drie, A D

2012-10-01

45

Particle Diffusion in Chaotic Magnetic Fields Generated by Asymmetric Current Configurations  

Microsoft Academic Search

The observed cross-field diffusion of charged particles in cosmic rays is assumed to be due to the chaotic nature of the interplanetary\\/intergalactic magnetic fields. Among the classic works on this subject have been those of Parker [1] and Jokipii [2]. Parker considered the passage of cosmic ray particles and energetic solar particles in a large scale magnetic field containing small

A. K. Ram; B. Dasgupta

2008-01-01

46

Resolution of the 180° Ambiguity for Inverse Horizontal Magnetic Field Configurations  

NASA Astrophysics Data System (ADS)

A well-known problem in solar physics is that solutions for the transverse magnetic field direction are ambiguous with respect to a 180° reversal in the field direction. In this paper we focus on three methods for the removal of the 180° ambiguity applied to three MHD models. These methods are (1) the reference field method, (2) the method of magnetic pressure gradient, and (3) the magnetic field divergence-free method. All three methods are noniterative, and methods 2 and 3 are analytical and fast. We apply these methods to three MHD equilibrium model fields: (1) an analytical solution of a nonlinear force-free magnetic field equilibrium from Low, (2) a simulation of an emerging twisted flux tube from Fan & Gibson, and (3) a pre-eruptive twisted magnetic flux rope equilibrium reached by relaxation from Amari et al. We measure the success of methods within ``inverse horizontal field'' regions in the boundary, which are mathematically defined by B????Bz>0. When such regions overlap with the magnetic field neutral lines, they are known as ``bald patches'' (BPs) or inverse topology. Our most important conclusion is that the magnetic divergence-free method is far more successful than the other two methods within BPs. This method requires a second level of measurements of the vertical magnetic field. As high-quality multilevel magnetograms will come online in the near future, our work shows that multilayer magnetic field measurements will be highly desirable to objectively and successfully tackle the 180° ambiguity problem.

Li, Jing; Amari, Tahar; Fan, Yuhong

2007-01-01

47

Chaotic magnetic fields due to asymmetric current configurations - application to cross-field diffusion of particles in cosmic rays  

Microsoft Academic Search

The observed cross-field diffusion of charged particles in cosmic ray transport is assumed to be due to chaotic nature of the interplanetary\\/intergalactic magnetic fields. The particles are accelerated and energized by the temporal fluctuations of the magnetic field. The generation of chaotic magnetic fields is ad hoc and the characteristics of the fields are chosen to satisfy the observations. We

B. Dasgupta; A. K. Ram

2007-01-01

48

Chaotic Magnetic Fields due to Asymmetric Current Configurations - Modeling Cross-Field Diffusion of Charged Particles in Cosmic Rays  

Microsoft Academic Search

The observed cross-field diffusion of charged particles in cosmic ray transport is assumed to be due to chaotic nature of the interplanetary\\/intergalactic magnetic fields. The particles are accelerated and energized by the temporal fluctuations of the magnetic field. The generation of chaotic magnetic fields is ad hoc and the characteristics of the fields are chosen to satisfy the observations. We

A. K. Ram; B. Dasgupta

2007-01-01

49

Control of the radial electric field shear by modification of the magnetic field configuration in LHD  

Microsoft Academic Search

Control of the radial electric field, Er, is considered to be important in helical plasmas, because the radial electric field and its shear are expected to reduce neoclassical and anomalous transport, respectively. In general, the radial electric field can be controlled by changing the collisionality, and positive or negative electric fields have been obtained by decreasing or increasing the electron

K. Ida; M. Yoshinuma; M. Yokoyama; S. Inagaki; N. Tamura; B. J. Peterson; T. Morisaki; S. Masuzaki; A. Komori; Y. Nagayama; K. Tanaka; K. Narihara; K. Y. Watanabe; C. D. Beidler

2005-01-01

50

Multichord Laser Interferometry on the Magnetized Target Fusion Program's FRL-X Field Reversed Configuration  

NASA Astrophysics Data System (ADS)

AFRL's Directed Energy Directorate has built a multiple chord 6328 nm interferometer to diagnose a Field Reversed Configuration (FRC) being developed for LANL and AFRL's collaborative Magnetized Target Fusion (MTF) program. The FRC is intended for compression to near thermonuclear fusion conditions by AFRL's Shiva Star capacitor bank. The interferometer is designed to measure the density integral along eight chords of the uncompressed FRC vs. time. This permits Abel inversion to determine the density profile history. The reference beam is split off with a Bragg cell, raising its frequency by 80 MHz. This permits RF quadrature mixing of the interference signal. The probe traverses a 10 cm diameter quartz tube containing the FRC. A similar tube is placed in the reference path to compensate for refractive distortion. Focusing the beams at tube transit further mitigates distortion. Preliminary design validation experiments at LANL using 2 chords have been successfully completed, and the upgrade to 8 chords is in progress. Results to date will be presented.

Ruden, Edward; Analla, Francis; Zhang, Shouyin

2002-11-01

51

Transition from drift to interchange instabilities in an open magnetic field line configuration  

SciTech Connect

The transition from a regime dominated by drift instabilities to a regime dominated by pure interchange instabilities is investigated and characterized in the simple magnetized toroidal device TORPEX [TORoidal Plasma EXperiment, A. Fasoli et al., Phys. of Plasmas 13, 055906 (2006)]. The magnetic field lines are helical, with a dominant toroidal component and a smaller vertical component. Instabilities with a drift character are observed in the favorable curvature region, on the high field side with respect to the maximum of the background density profile. For a limited range of values of the vertical field they coexist with interchange instabilities in the unfavorable curvature region, on the plasma low field side. With increasing vertical magnetic field magnitude, a gradual transition between the two regimes is observed on the low field side, controlled by the value of the field line connection length. The observed transition follows the predictions of a two-fluid linear model.

Poli, F. M.; Ricci, P.; Fasoli, A.; Podesta, M. [CRPP-EPFL, Association EURATOM-Confederation Suisse, Lausanne (Switzerland)

2008-03-15

52

Derivation of the Magnetic Field Configuration above a Solar Active Region using Spatio-spectral Radio Data from the OVSA  

NASA Astrophysics Data System (ADS)

We present an analysis of multi-frequency radio imaging data derived from observations of AR 10923 taken with the Owens Valley Solar Array on November 10, 2006. This region was chosen because its relative simplicity (alpha configuration) and medium-large size (450 millionths) sunspot may simplify the analysis. The observations span 22 frequencies from 1.4 to 10.6 GHz range. Joint VLA observations were used to increase the spectral resolution of the data, and to provide a means of cross-calibration for the OVSA data. The spectral shapes derived from the brightness temperature maps were used to (1) directly determine the magnetic field at the highest optically thick gyroresonance layer when possible, and (2) an upper bound for it when the spectrum was dominated by free-free emission. Values for the electron temperature and the column emission measure were also derived from the radio spectra. Comparisons of the radio maps with EUV observations from SOHO/EIT were then used to relate the various temperatures and determine a plausible model of the electron density and magnetic field configurations above this active region. The magnetic field model is compared to force-free field extrapolations made from co-temporal Hinode SOT-SP observations of this active region. The differences and similarities are used to asses the validity of the method and magnetic field deduced from OVSA data, which initially has few data points from which to extrapolate the overall magnetic field.

Tun, Samuel D.

2009-05-01

53

Application of a magnetized coaxial plasma gun for formation of a high-beta field-reversed configuration  

Microsoft Academic Search

We have tested a field-reversed configuration (FRC) formation with a spheromak injection for the first time. In this method, initial pre-ionized plasma is injected as a magnetized spheromak-like plasmoid into the discharge chamber prior to main field reversal. The FRC plasma with an electron density of 1.3×1021m?3, a separatrix radius of 0.04m and a plasma length of 0.8m was produced

T. Nishida; T. Kiguchi; T. Asai; T. Takahashi; Y. Matsuzawa; T. Okano; Y. Nogi

2006-01-01

54

Field and plasma configuration of a filament overlying a solar bipolar magnetic region  

Microsoft Academic Search

This paper presents an analytic model for a finite-size straight filament suspended horizontally in a steady state over a bipolar magnetic region. The equations of magnetostatic equilibrium are integrated exactly. The solution obtained illustrates the roles played by the electric current, magnetic field, pressure, and plasma weight in the balance of force everywhere in space. Basic properties are discussed. We

B. C. Low

1981-01-01

55

The Size of the Solid Inner Core and Magnetic Field Configuration at the Dynamo surface  

NASA Astrophysics Data System (ADS)

In a recent study (Cao et al., 2012) based on in-situ magnetic field measurements made by the Cassini spacecraft, several distinct features of Saturn's magnetic field have been revealed. The field at the dynamo surface is found to be strongly concentrated near the spin-poles with little hemispherical asymmetry. This field geometry corresponds to a zig-zag shape magnetic spectrum with pronounced odd degree terms and all odd degree magnetic moments possess the same sign. This is in contrast to the field properties at the core surface of the Earth and in convection-driven geodynamo simulations, where the field near the spin-poles is at a relative minimum compared to field at mid-latitude. In this study, we propose that the absence of a solid inner core inside the planet could be responsible for the poleward flux concentration at the dynamo surface. The simple physical picture underlying this hypothesis is the concentration of convection columns near the spin axis after the solid inner core as an obstacle is removed. We test this hypothesis using numerical dynamo simulations. The heat source in our model is the uniform secular cooling of the planet. Different heat flux patterns at the outer boundary are also applied. In the end, we explore the possible field geometries at the dynamo surface of Jupiter, Uranus and Neptune consistent with the available in-situ observations at each planet. Properties including the Lowes spectrum, field symmetry are analyzed.

Cao, H.; Russell, C. T.; Wicht, J.; Christensen, U. R.; Dougherty, M. K.

2012-04-01

56

The TITAN magnet configuration  

SciTech Connect

The TITAN study uses copper-alloy ohmic-heating coils (OHC) to startup inductively a reversed-field-pinch (RFP) fusion reactor. The plasma equilibrium is maintained with a pair of superconducting equilibrium-field coils (EFCs). A second pair of copper EFCs provides the necessary trimming of the equilibrium field during plasma transients. A compact toroidal-field-coil (TFC) set is provided by an integrated blanket/coil (IBC). The IBC concept also is applied to the toroidal-field divertor coils. Steady-state operation is achieved with oscillating-field current drive, which oscillates at low amplitude and frequency the OHCs, EFCs, the TFCs, and divertor coils about their steady-state currents. An integrated magnet design, which uses low-field, low technology coils, and the related design basis is given. 18 refs.

Bathke, C.G.

1987-01-01

57

Point sensitive NMR imaging system using a magnetic field configuration with a spatial minimum  

DOEpatents

A point-sensitive NMR imaging system (10) in which a main solenoid coil (11) produces a relatively strong and substantially uniform magnetic field and a pair of perturbing coils (PZ1 and PZ2) powered by current in the same direction superimposes a pair of relatively weak perturbing fields on the main field to produce a resultant point of minimum field strength at a desired location in a direction along the Z-axis. Two other pairs of perturbing coils (PX1, PX2; PY1, PY2) superimpose relatively weak field gradients on the main field in directions along the X- and Y-axes to locate the minimum field point at a desired location in a plane normal to the Z-axes. An RF generator (22) irradiates a tissue specimen in the field with radio frequency energy so that desired nuclei in a small volume at the point of minimum field strength will resonate.

Eberhard, Philippe H. (El Cerrito, CA)

1985-01-01

58

Influence of demagnetization coil configuration on residual field in an extremely magnetically shielded room: Model and measurements  

NASA Astrophysics Data System (ADS)

The Berlin magnetically shielded room 2 (BMSR-2) features a magnetic residual field below 500 pT and a field gradient level less than 0.5 pT/mm, which are needed for very sensitive human biomagnetic recordings or low field NMR. Nevertheless, below 15 Hz, signals are compromised by an additional noise contribution due to vibration forced sensor movements in the field gradient. Due to extreme shielding, the residual field and its homogeneity are determined mainly by the demagnetization results of the mumetal shells. Eight different demagnetization coil configurations can be realized, each results in a characteristic field pattern. The spatial dc flux density inside BMSR-2 is measured with a movable superconducting quantum interference device system with an accuracy better than 50 pT. Residual field and field distribution of the current-driven coils fit well to an air-core coil model, if the high permeable core and the return lines outside of the shells are neglected. Finally, we homogenize the residual field by selecting a proper coil configuration.

Knappe-Grueneberg, Silvia; Schnabel, Allard; Wuebbeler, Gerd; Burghoff, Martin

2008-04-01

59

Use of wiring configuration and wiring codes for estimating externally generated electric and magnetic fields  

SciTech Connect

The relative locations and characteristics of the distribution lines feeding 434 residences in the Denver metropolitan area were recorded and classified according to the Wertheimer-Leeper code (WL code) as a part of an epidemiological study of the incidence of childhood cancer. The WL code was found to place the mean values of the fields in rank order. However, the standard deviations were approximately the same size as the means. Theoretical calculations indicate that a significant fraction of the low-power magnetic fields can be generated by the distribution lines, especially in the cases where the distribution lines are within 50 feet of the residence. Thus, the wiring code was shown to be a useful method for making a first-order approximation to predict long-term, low-level magnetic fields in residences.

Barnes, F.; Wachtel, H.; Savitz, D.; Fuller, J.

1989-01-01

60

Neutral two-body systems in inhomogeneous magnetic fields: the quadrupole configuration  

NASA Astrophysics Data System (ADS)

We investigate the theoretical foundations of neutral two-body systems exposed to an inhomogeneous magnetic field. Various representations for the Hamiltonian describing the coupled centre-of-mass and internal motion are derived. For the specific case of a magnetic quadrupole field we establish the continuous and discrete symmetries and show that the energy levels of the interacting system are two-fold degenerate. We exploit the symmetries in two alternative ways and derive corresponding effective equations of motion. The first approach eliminates two of the six spatial degrees of freedom and leads to an (infinite) set of coupled channel equations for the spin and spatial degrees of freedom. The second approach introduces the projection of the total angular momentum onto the symmetry axis of the quadrupole field as a canonical momentum, thereby eliminating the corresponding cyclic angle.

Bock, Hannes; Lesanovsky, Igor; Schmelcher, Peter

2005-04-01

61

MHD simulation of magnetic field configuration above the active region NOAA 10365  

NASA Astrophysics Data System (ADS)

The current sheet (CS) creation before a flare in the vicinity of a singular line above the active region NOAA 10365 is shown in numerical experiments. Such a way the possibility of energy accumulation for a solar flare is demonstrated. These data and results of observation confirm the electrodynamical solar flare model that explains solar flares and CME appearance during CS disruption. The model explains also all phenomena observed in flares. For correct reproduction of the real boundary conditions the magnetic flux between spots should be taken into account. The full system of 3D MHD equations are solved using the PERESVET code. For setting the boundary conditions the method of photospheric magnetic maps is used. Such a method permits to take into account all evolution of photospherical magnetic field during several days before the flare.

Podgorny, A. I.; Podgorny, I. M.

2012-11-01

62

Rising Microwave Frequency of a Broad-Ion-Beam ECR Source with Cylindrically Comb-Shaped Magnetic Field Configuration  

SciTech Connect

An 11-13 GHz electron cyclotron resonance (ECR) plasma source with a cylindrically comb-shaped magnetic field configuration has been examined in order to apply to ion beam processing. The ion saturation current density has been measured using a Langmuir probe. It was found that the ion density linearly increases as gas pressure and microwave power increases. The maximum ion density at 13 GHz microwaves is 37.4 mA/cm2 under low microwave power. The ion beam extractor which has multihole apertures has been constructed at the end of the magnet. The ion beam current has reached 20 mA at the microwave power of only 300 W. The ion beam current has clearly increased by rising microwave frequency as well as the tendency of the plasma density.

Asaji, Toyohisa [Division of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Development Center of Advanced Technology, Tateyama Machine Co., Ltd., 30 Shimonoban, Toyama, 930-1305 (Japan); Kato, Yushi; Sasaki, Hiroshi; Kubo, Takashi; Sato, Fuminobu; Iida, Toshiyuki [Division of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Saito, Junji [Development Center of Advanced Technology, Tateyama Machine Co., Ltd., 30 Shimonoban, Toyama, 930-1305 (Japan)

2006-11-13

63

Plasma equilibrium in axisymmetric poloidal magnetic field configurations in flux coordinates  

SciTech Connect

A simple derivation is given of equilibrium equations in flux coordinates in the general case of an anisotropic-pressure plasma. The issue of how to formulate the boundary conditions for these equations is discussed for two types of configurations-a straight system and a system with an internal conductor. Examples of numerical solutions to the equilibrium problem for these configurations are presented.

Arsenin, V. V.; Terekhin, P. N. [Russian Research Centre Kurchatov Institute (Russian Federation)

2011-08-15

64

Stable transport and side-focusing of sheet electron beams in periodically cusped magnetic field configurations  

Microsoft Academic Search

Sheet electron beams and configurations with multiple electron beams have the potential to make possible higher power sources of microwave radiation due to their ability to transport high currents, at reduced current densities, through a single narrow RF interaction circuit. Possible microwave device applications using sheet electron beams include sheet-beam klystrons, grating TWTs, and planar FELs. Historically, implementation of sheet

J. Anderson; M. A. Basten; L. Rauth; J. H. Booske; J. Joe; J. E. Scharer

1995-01-01

65

Configuration of Particle Drain for the High Energy Charged Particles in the Magnetic Dipole Field.  

National Technical Information Service (NTIS)

The boundary of particle leakage from the magnetic dipole trap depending on the value of adiabatic parameter is investigated. By trajectory computation a generalized analytical expression is determined for the shape of particle drain by x less than or equ...

I. V. Amirkhanov E. P. Zhidkov V. V. Ignatov A. N. Il'ina V. D. Il'in

1987-01-01

66

Trapped magnetic field profiles of arrays of (Gd,Y)Ba2Cu3Ox superconductor tape in different stacking configurations  

NASA Astrophysics Data System (ADS)

Trapped magnetic field profiles were investigated in thin film (Gd,Y)Ba2Cu3Ox superconducting tapes stacked in different configurations consisting of three 12 mm wide, 36 mm long tapes per layer. The trapped magnetic field values were found to increase monotonically with the increasing number of tape layers in the stack. A crisscross arrangement of the tapes was found to yield a more uniform trapped-field profile than a straight arrangement of the tapes. Furthermore, the decay rate of the trapped magnetic field as a function of distance from the tape stack surface was found to be lower in the crisscross arrangement.

Selva, Kavita; Majkic, Goran

2013-11-01

67

Comparison of magnetic-field distribution of noncompact and compact parallel transmission-line configurations  

Microsoft Academic Search

The continuous increasing demand of electricity contradicts with the increasing difficulty to secure corridors to construct new transmission lines. This paper investigates alternatives regarding parallel lines from the point of view of the magnetic flux density level under and around current-carrying conductors of the lines. The first alternative is for existing transmission lines by converting a three-phase double-circuit line to

A. A. Dahab; F. K. Amoura; W. S. Abu-Elhaija

2005-01-01

68

Observation of collisionless thermalization of a plasmoid with a field-reversed configuration in a magnetic mirror  

NASA Astrophysics Data System (ADS)

A systematic translation study of field-reversed configurations (FRCs) has been conducted on the FRC Injection Experiment (FIX) machine [Okada et al., in Fusion Energy 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 2, p. 229]. Plasma density and temperature of a translated FRC moving at supersonic speed are measured in the downstream magnetic mirror of FIX to verify a shock jump there when the FRC is reflected. A significant jump is observed. Moreover, the time evolution of the Carbon V Doppler profile is measured both quasi-parallel and perpendicular to the direction of FRC motion. Distinct transitions from Gaussian to non-Gaussian shapes are clearly seen in both profiles before and after the shock jump. Also, the ion mean-free path in the downstream magnetic mirror is calculated to be much longer than the characteristic width of the shock jump. These results indicate that the thermalization of flow energy in the translated FRC in the mirror is produced by a collisionless process, implying that this heating mechanism can be realized even in a reactor regime.

Himura, H.; Ueoka, S.; Hase, M.; Yoshida, R.; Okada, S.; Goto, S.

1998-12-01

69

Magnetic configuration studies in a compact Torsatron  

SciTech Connect

An overview is presented of an experimental program of magnetic field line mapping on the research-grade Compact Auburn Torsatron (CAT). The vacuum magnetic flux surfaces of the CAT device have been experimentally mapped in a variety of magnetic configurations. The results are compared with an extensive computer model in order to validate the coil design. In initial field mapping experiments, an up-down symmetry was identified in the vacuum magnetic surfaces, and was corrected with the use of a radial trim field. Magnetic islands are observed and their size has been reduced, also through the use of auxiliary trim coils. The Compact Auburn Torsatron is equipped with two pairs of large Helmholtz coils producing mutually orthogonal magnetic fields in the horizontal plane, and two pairs of helical saddle coils wound directly on the toroidal vacuum vessel. These trim coils are used to control the size and phase of the t = 1/2 magnetic island. Through a systematic variation of trim field components, the authors demonstrate a reduction of the inherent t = 1/2 magnetic island size by a factor of three. The technique is applicable to correcting small error fields in larger helical confinement devices. The measurements of island size are compared with measurements of magnetic field line rotation within the island, and are found to be in good agreement with first-order perturbation theory.

Knowlton, S.F.; Gandy, R.F.; Hanson, J.D.; Hartwell, G.J.; Lin, H. (Auburn Univ., AL (United States))

1993-09-01

70

Upgraded coil configuration for ISABELLE magnets  

SciTech Connect

Achievement of the design field of 5 T in the ISABELLE dipole magnets is turning out to be more arduous than expected and several avenues of improvement are being pursued. One possibility for improving training and peak field performance is discussed in this paper. It has been recognized that the inert spacers with their adjacent active turns in the cosine magnet windings can be replaced by a double thickness braid operating at approximately half-current density in 46 of the 190 turns. Since the high-field region occurs in the low current density turns near the poles, a performance improvement can be expected. It has been verified that the proposed coil configuration satisfies the field requirements and details thereof are given. Results from an experimental magnet in which superconducting spacer turns are used to simulate half-current density windings are presented. Construction of thick braid coils is being planned and the status of these magnets is reviewed.

Hahn, H.; Dahl, P.F.; Kaugerts, J.E.; Prodell, A.G.

1981-01-01

71

Inductive sustainment of oblate field-reversed configurations with the assistance of magnetic diffusion, shaping, and finite-Larmor radius stabilization  

SciTech Connect

Oblate field-reversed configurations (FRCs) have been sustained for >300 {mu}s, or >15 magnetic diffusion times, through the use of an inductive solenoid. These argon FRCs can have their poloidal flux sustained or increased, depending on the timing and strength of the induction. An inward pinch is observed during sustainment, leading to a peaking of the pressure profile and maintenance of the FRC equilibrium. The good stability observed in argon (and krypton) does not transfer to lighter gases, which develop terminal co-interchange instabilities. The stability in argon and krypton is attributed to a combination of external field shaping, magnetic diffusion, and finite-Larmor radius effects.

Gerhardt, S. P.; Belova, E. V.; Yamada, M.; Ji, H.; Jacobson, C. M.; McGeehan, B.; Ren, Y. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Inomoto, M. [Osaka University, Osaka 565-0871 (Japan); Maqueda, R. [Nova Photonics, Princeton, New Jersey 08540 (United States)

2008-02-15

72

Initial Design of the 60 Megawatt Rotating Magnetic Field (RMF) Oscillator System for the University of Washington ''TCS'' Field Reversed Configuration Experiment  

SciTech Connect

This paper presents the initial electrical and mechanical design of two phase-locked 30 Megawatt RMS, 150 kHz oscillator systems used for current drive and plasma sustainment of the ''Translation, Confinement, and Sustainment'' (TCS) field reversed configuration (FRC) plasma. By the application of orthogonally-placed saddle coils on the surface of the glass vacuum vessel, the phase-controlled rotating magnetic field perturbation will induce an electric field in the plasma which should counter the intrinsic ohmic decay of the plasma, and maintain the FRC. Each system utilizes a bank of 6 parallel magnetically beamed ML8618 triodes. These devices are rated at 250 Amperes cathode current and a 45 kV plate voltage. An advantage of the magnetically beamed triode is their extreme efficiency, requiring only 2.5 kW of filament and a few amps and a few kV of grid drive. Each 3.5 uH saddle coil is configured with an adjustable tank circuit (for tuning). Assuming no losses and a nominal 18 kV plate voltage, the tubes can circulate about 30 kV and 9 kA (pk to pk) in the saddle coil antenna, a circulating power of over 33 megawatts RMS. On each cycle the tubes can kick in up to 1500 Amperes, providing a robust phase control. DC high-voltage from the tubes is isolated from the saddle coil antennas and tank circuits by a 1:1 coaxial air-core balun transformer. To control the ML8618's phase and amplitude, fast 150 Ampere ''totem-pole'' grid drivers, an ''on'' hot-deck and an ''off'' hot-deck are utilized. The hot-decks use up to 6 each 3CPX1500A7 slotted radial beam triodes. By adjusting the conduction angle, amplitude may be regulated, with inter-pulse timing, phase angle can be controlled. A central feedback timing chassis monitors each systems' saddle coil antenna and appropriately derives each systems timing signals. Fiber-optic cables are used to isolate between the control room timing chassis and the remote power oscillator system. Complete system design detail will be presented in addition to anticipated (computer generated) performance characteristics. Initial design and construction began in FY97, and will continue through FY98, with delivery to the experiment in FY99, for commencement of physics experiments on sustaining the FRC.

Reass, W.A.; Miera, D.A.; Wurden, G.A.

1997-10-06

73

Cross-field motion of plasma blob-filaments and related particle flux in an open magnetic field line configuration on QUEST  

NASA Astrophysics Data System (ADS)

Blob-filaments have been observed by combined measurement with a fast camera and a movable Langmuir probe in an open magnetic field line configuration of electron cyclotron resonance (ECR) heating plasma in QUEST. Blob-filaments extended along field lines do correspond to over-dense plasma structures and propagated across the field lines to the outer wall. The radial velocity of the blob structure, Vb, was obtained by three methods and was dominantly driven by the E × B force. The radial velocity, size of the blob showed good agreements with the results obtained by sheath-connected interchange theoretical model. Vb corresponds to roughly 0.02-0.07 of the local sound speed (Cs) in QUEST. The higher moments (skewness S and kurtosis K) representing the shape of PDF of density fluctuation are studied. Their least squares fitting with quadratic polynomial is K = (1.60 ± 0.27)S2 - (0.46 ± 0.20). The larger blob structures, occurring only 10% of the time, can carry more than 60% loss of the entire radial particle flux.

QUEST Group; Liu, H. Q.; Hanada, K.; Nishino, N.; Ogata, R.; Ishiguro, M.; Gao, X.; Zushi, H.; Nakamura, K.; Fujisawa, A.; Idei, H.; Hasegawa, M.

2013-07-01

74

Effect of axial magnetic field on three-dimensional instability of natural convection in a vertical Bridgman growth configuration  

Microsoft Academic Search

A study of the effect of an externally imposed magnetic field on the axisymmetry-breaking instability of an axisymmetric convective flow, associated with crystal growth from bulk of melt, is presented. Convection in a vertical cylinder with a parabolic temperature profile on the sidewall is considered as a representative model. A parametric study of the dependence of the critical Grashof number

A. Yu. Gelfgat; P. Z. Bar-Yoseph; A. Solan

2001-01-01

75

Adiabatic invariants for field-reversed configurations  

SciTech Connect

Field reversed configurations (FRCs) are characterized by azimuthal symmetry, so two exact constants of the particle motion are the total particle energy E and the canonical angular momentum P/sub theta/. For many purposes it is desirable to construct a third (diabatic) constant of the motion if this is possible. It is shown that for parameters characteristic of current FRCs that the magnetic moment ..mu.. is a poor adiabatic invariant, while the radial action J is conserved rather well.

Schwarzmeier, J.L.; Lewis, H.R.; Seyler, C.E.

1982-01-01

76

Counter effects of meridional flows and magnetic fields in stationary axisymmetric self-gravitating barotropes under the ideal MHD approximation: clear examples - toroidal configurations  

NASA Astrophysics Data System (ADS)

We obtain the general forms for the current density and the vorticity from the integrability conditions of the basic equations which govern the stationary states of axisymmetric magnetized self-gravitating barotropic objects with meridional flows under the ideal magnetohydrodynamics (MHD) approximation. As seen from the stationary condition equations for such bodies, the presence of the meridional flows and that of the poloidal magnetic fields act oppositely on the internal structures. The different actions of these two physical quantities, the meridional flows and the poloidal magnetic fields, could be clearly seen through stationary structures of the toroidal gaseous configurations around central point masses in the framework of Newtonian gravity because the effects of the two physical quantities can be seen in an amplified way for toroidal systems compared to those for spheroidal stars. The meridional flows make the structures more compact, i.e. the widths of toroids thinner, while the poloidal magnetic fields are apt to elongate the density contours in a certain direction depending on the situation. Therefore, the simultaneous presence of the internal flows and the magnetic fields would work as if there were no such different actions within and around the stationary gaseous objects such as axisymmetric magnetized toroids with internal motions around central compact objects under the ideal MHD approximation, although these two quantities might exist in real systems.

Fujisawa, Kotaro; Takahashi, Rohta; Yoshida, Shijun; Eriguchi, Yoshiharu

2013-05-01

77

The Magnetic Field  

NSDL National Science Digital Library

This webpage is part of the University Corporation for Atmospheric Research (UCAR) Windows to the Universe program. It describes the nature and configuration of magnetic fields, which are the result of moving electric charges, including how they cause magnetic objects to orient themselves along the direction of the magnetic force points, which are illustrated as lines. Magnetic field lines by convention point outwards at the north magnetic pole and inward at the south magnetic pole. The site features text, scientific illustrations and an animation. Text and vocabulary are selectable for the beginning, intermediate, or advanced reader.

Universe, Windows T.

1997-12-03

78

Configuration of Nematic Liquid Crystals around Particles under External Fields  

Microsoft Academic Search

We present the results of our numerical attempts to simulate the configuration of a nematic liquid crystal around a spherical particle. We focus on the effect of an external field, such as a magnetic field or a flow field, on the director configuration and the topological defects accompanied by the particles. The use of adaptive mesh refinement together with a

Jun-Ichi Fukuda; Holger Stark; Makoto Yoneya; Hiroshi Yokoyama

2004-01-01

79

Dynamics and interaction of plasma currents with large self-magnetic fields and their relaxation toward a force-free configuration  

NASA Astrophysics Data System (ADS)

The dynamics of current channels with large self-generated magnetic fields in a background plasma and, in particular, their relaxation toward a force-free configuration is investigated. Relaxation, in the sense of the theoretical conception of Woltjer and Taylor, to configurations regarded as minimum energy states, described by the Beltrami equations J = mu sub 0 exp -1(tilde) x B = alpha(B), is reexamined in light of Salingaros' theoretical results. Detailed 3-D measurements in a quiescent laboratory plasma of 10 m length and 50 cm diameter yield the magnetic field B(x,y,z,t) and the plasma parameters, n(x,y,z,t), k(T sub e)(x,y,z,t) and V sub pl(x,y,z,t) at several thousand measurement locations. The plasma current J, plasma pressure p = nkT, pressure gradient force, tilde(p), and J x B force, are determined and relaxation toward a force-free configuration that includes pressure gradient forces, i.e., the validity of J x B = tilde(p), is tested. The temporal relaxation of a single current channel and the spatial relaxation of a dual current system is illustrated. A strong increase of alignment of the current density vector J and the total magnetic field B sub 0 + B sub self as a function of the distance from the plasma source is found. The return currents that prevent the two current channels from twisting about each other, after turn-off of the externally applied electric field, are identified and the conversion of the dual current system into a twin-axial system is shown.

Pfister, Hans

80

Solar Energetic Particle Events in the 23rd Solar Cycle: Interplanetary Magnetic Field Configuration and Statistical Relationship with Flares and CMEs  

NASA Astrophysics Data System (ADS)

We study the influence of the large-scale interplanetary magnetic field configuration on the solar energetic particles (SEPs) as detected at different satellites near Earth and on the correlation of their peak intensities with the parent solar activity. We selected SEP events associated with X- and M-class flares at western longitudes, in order to ensure good magnetic connection to Earth. These events were classified into two categories according to the global interplanetary magnetic field (IMF) configuration present during the SEP propagation to 1 AU: standard solar wind or interplanetary coronal mass ejections (ICMEs). Our analysis shows that around 20 % of all particle events are detected when the spacecraft is immersed in an ICME. The correlation of the peak particle intensity with the projected speed of the SEP-associated coronal mass ejection is similar in the two IMF categories of proton and electron events, ? 0.6. The SEP events within ICMEs show stronger correlation between the peak proton intensity and the soft X-ray flux of the associated solar flare, with correlation coefficient r=0.67±0.13, compared to the SEP events propagating in the standard solar wind, r=0.36±0.13. The difference is more pronounced for near-relativistic electrons. The main reason for the different correlation behavior seems to be the larger spread of the flare longitude in the SEP sample detected in the solar wind as compared to SEP events within ICMEs. We discuss to what extent observational bias, different physical processes (particle injection, transport, etc.), and the IMF configuration can influence the relationship between SEPs and coronal activity.

Miteva, R.; Klein, K.-L.; Malandraki, O.; Dorrian, G.

2013-02-01

81

Magnetic field in a finite toroidal domain  

SciTech Connect

The magnetic field structure in a domain surrounded by a closed toroidal magnetic surface is analyzed. It is shown that ergodization of magnetic field lines is possible even in a regular field configuration (with nonvanishing toroidal component). A unified approach is used to describe magnetic fields with nested toroidal (possibly asymmetric) flux surfaces, magnetic islands, and ergodic field lines.

Ilgisonis, V. I.; Skovoroda, A. A., E-mail: skovorod@nfi.kiae.r [Russian Research Centre Kurchatov Institute (Russian Federation)

2010-05-15

82

Magnetic Field Issues in Magnetic Resonance Imaging  

Microsoft Academic Search

Advances in Magnetic Resonance Imaging depend on the capability of the available hardware. Specifically, for the main magnet configuration, using derivative constraints, we can create a static magnetic field with reduced levels of inhomogeneity over a prescribed imaging volume. In the gradient coil, the entire design for the axial elliptical coil, and the mathematical foundation for the transverse elliptical coil

Labros Spiridon Petropoulos

1993-01-01

83

Structure and magnetic configurations of accretion disk-dynamo models  

NASA Astrophysics Data System (ADS)

The influence of large-scale magnetic fields on the structure of accretion disks is studied. The magnetic field is obtained by a self-consistent nonlinear dynamo model with magnetic pressure strongly influencing the density stratification which itself feeds back to the field generation. The resulting magnetic field geometry is discussed in relation to the accretion disk wind theory. Regarding new results of MHD turbulence simulations, both possible signs of the alpha -effect are allowed (Brandenburg & Donner 1997). In the canonical case of positive alpha the resulting field is of quadrupolar symmetry. The field strength is about 50% of the value for dynamo models nonlinearly limited by alpha -quenching. The temperature profiles as well as the disk geometry remain nearly unchanged. The viscous stress remains the key transporter of angular momentum driving the accretion inflow. For negative alpha , however, a stationary dipolar structure of the magnetic field results. The additional magnetic torque at the disk surface changes the profile of the effective temperature significantly to a profile which is more flat. The magnetic torque becomes of the same order as the radial viscous torque. The inclination angle of the poloidal field exceeds 30o even for a magnetic Prandtl number of order unity, and also the criterion for poloidal collimation after Spruit et al. (1997) is fulfilled. The dynamo-generated magnetic field configuration thus supports the magnetic wind launching concept for accretion disks for realistic turbulent magnetic Prandtl numbers.

Rekowski, M. v.; Rüdiger, G.; Elstner, D.

2000-01-01

84

Stellar atmospheres with magnetic field  

Microsoft Academic Search

It is proposed that the most probable configuration of the magnetic field in the atmosphere of an Ap star is an almost force-free, poloidal field, close to a low-order multipole. Such a magnetic field can not change the structure of the atmosphere to any great extent, but the vertical component of the Lorentz force can decrease the effective gravity by

K. Stepien

1980-01-01

85

Design and characterization of 2.45 GHz electron cyclotron resonance plasma source with magnetron magnetic field configuration for high flux of hyperthermal neutral beam  

SciTech Connect

A 2.45 GHz electron cyclotron resonance (ECR) source with a magnetron magnetic field configuration was developed to meet the demand of a hyperthermal neutral beam (HNB) flux on a substrate of more than 1x10{sup 15} cm{sup -2} s{sup -1} for industrial applications. The parameters of the operating pressure, ion density, electron temperature, and distance between the neutralization plate and the substrate for the HNB source are specified in a theoretical analysis. The electron temperature and the ion density are measured to characterize the ECR HNB source using a Langmuir probe and optical emission spectroscopy. The parameters of the ECR HNB source are in good agreement with the theoretically specified parameters.

Kim, Seong Bong [Department of Physics, Pohang University of Science and Technology, San 31, Hyoja-dong, Nam-gu, Pohang 790-784 (Korea, Republic of); Convergence Plasma Research Center, National Fusion Research Institute, Gwahangno 113, Yuseong-gu, Daejeon 305-333 (Korea, Republic of); Kim, Dae Chul; Yoo, Suk Jae [Convergence Plasma Research Center, National Fusion Research Institute, Gwahangno 113, Yuseong-gu, Daejeon 305-333 (Korea, Republic of); Namkung, Won; Cho, Moohyun [Department of Physics, Pohang University of Science and Technology, San 31, Hyoja-dong, Nam-gu, Pohang 790-784 (Korea, Republic of)

2010-08-15

86

Design and characterization of 2.45 GHz electron cyclotron resonance plasma source with magnetron magnetic field configuration for high flux of hyperthermal neutral beam.  

PubMed

A 2.45 GHz electron cyclotron resonance (ECR) source with a magnetron magnetic field configuration was developed to meet the demand of a hyperthermal neutral beam (HNB) flux on a substrate of more than 1x10(15) cm(-2) s(-1) for industrial applications. The parameters of the operating pressure, ion density, electron temperature, and distance between the neutralization plate and the substrate for the HNB source are specified in a theoretical analysis. The electron temperature and the ion density are measured to characterize the ECR HNB source using a Langmuir probe and optical emission spectroscopy. The parameters of the ECR HNB source are in good agreement with the theoretically specified parameters. PMID:20815600

Kim, Seong Bong; Kim, Dae Chul; Namkung, Won; Cho, Moohyun; Yoo, Suk Jae

2010-08-01

87

Evaluation of heliostat field/receiver configurations  

SciTech Connect

This report evaluates and compares north heliostat field/cavity receiver configurations and surround heliostat field/external receiver configurations. The receiver coolants are molten nitrate salts and liquid sodium. Both field/receiver configurations use molten salt thermal storage; the sodium receiver is thermally connected to thermal storage by a sodium-to-salt heat exchanger. The heliostat filed size is fixed at 1,000,000 square meters of reflective area, and the delivered molten salt temperature is fixed at 566/sup 0/C. The delivered thermal power varies from 500 to 600 MW/sub t/, depending on the overall system efficiency. The generic north heliostat field/cavity receiver configurations were found to be 6 to 10 percent efficient than a generic surround field/external receiver configuration. There was little or no difference found in the transient performance of a molten salt receiver compared to a sodium receiver connected to a sodium-to-salt heat exchanger. Four configurations were of particular interest: (1) a north heliostat field/single cavity molten salt receiver, (2) a surround heliostat field/external cylinder molten salt receiver, (3) a surround heliostat field/external cylinder liquid sodium receiver, and (4) a north heliostat field/single cavity liquid sodium receiver. It was found that the surround field/liquid sodium external receiver configuration may provide energy at a 14 percent lower levelized energy cost than a north field/molten salt cavity receiver configuration. However, the cost advantage of the surround field/liquid sodium external receiver is not conclusive because of uncertainties in system component costs.

Faas, S.E.; Winters, W.S.

1986-03-01

88

Spatiotemporal dynamics and transport reduction in helical magnetic configuration  

SciTech Connect

Effects of multihelicity confinement magnetic fields on turbulent transport and zonal flows are investigated by means of spatiotemporal analysis of gyrokinetic Vlasov simulation results for the ion temperature gradient turbulence, where the standard and the inward-shifted configurations of the Large Helical Device are considered. The analysis of simulation results demonstrates that fluctuations of electrostatic potential for zonal flows exhibit spatiotemporal chaos in both configurations. However, the intensity of chaos found is considerably decreased in the inward-shifted configuration consistent with improved confinement. Enhanced zonal flow generation in the inward shifted case is accompanied by transport reduction which may be a direct consequence of chaos suppression.

Rajkovic, Milan [Institute of Nuclear Sciences Vinca, Belgrade 11001 (Serbia); National Institute for Fusion Science, Toki 509-5292 (Japan); Watanabe, Tomo-Hiko; Skoric, Milos [National Institute for Fusion Science, Toki 509-5292 (Japan)

2009-09-15

89

Alternative poloidal field configurations for ITER  

SciTech Connect

The US Home Team has investigated the physics and engineering issues for two alternate poloidal field coil configurations for ITER. The first is called the Segmented CS configuration, where all of the solenoid modules are pancake-wound. The second option, termed the Hybrid CS configuration, utilizes a layer-wound central module and pancake-wound end modules. Performance comparisons are presented for the baseline design and the two alternate PF configurations, characterizing the 21 MA reference scenario. Alternate operating modes such as reverse-shear operation and a 17 MA driven mode were evaluated, but are not reported here.

Bulmer, R.H.; Neilson, G.H.

1997-09-02

90

An optimal magnetic tip configuration for magnetic-resonance force microscopy of microscale buried features  

NASA Astrophysics Data System (ADS)

To date, magnetic-resonance force microscopes employing a magnetic-field gradient source mounted to a microcantilever have suffered from a deleterious dependence of the effective cantilever spring constant on the external magnetic field. A ``magnet-on-tip'' configuration is introduced in which this dependence has been decreased by at least 200 fold, making it feasible to perform arbitrary-sample micron-scale magnetic resonance force microscopy at very high magnetic field. Alternating-gradient cantilever magnetometry is used to quantify the effect and to prove that the existing model of the tip-field interaction is only qualitatively correct. A model is proposed which quantitatively describes the tip-field interaction in the traditional tip configuration.

Marohn, John A.; Fainchtein, Raúl; Smith, Doran D.

1998-12-01

91

Kinetic Stabilization of Field-Reversed Configurations.  

National Technical Information Service (NTIS)

The tilt instability in field-reversed configurations (FRC's) may be roughly divided into two categories, depending on the nature of the unstable eigenfunction. The internal tilt instability, which could also be called an n = 1 ballooning mode, is defined...

J. L. Schwarzmeier H. R. Lewis D. C. Barnes C. E. Seyler

1985-01-01

92

Magnetic Cusp Configuration of the SPL Plasma Generator  

SciTech Connect

The Superconducting Proton Linac (SPL) is a novel linear accelerator concept currently studied at CERN. As part of this study, a new Cs-free, RF-driven external antenna H{sup -} plasma generator has been developed to withstand an average thermal load of 6 kW. The magnetic configuration of the new plasma generator includes a dodecapole cusp field and a filter field separating the plasma heating and H{sup -} production regions. Ferrites surrounding the RF antenna serve in enhancing the coupling of the RF to the plasma. Due to the space requirements of the plasma chamber cooling circuit, the cusp magnets are pushed outwards compared to Linac4 and the cusp field strength in the plasma region is reduced by 40% when N-S magnetized magnets are used. The cusp field strength and plasma confinement can be improved by replacing the N-S magnets with offset Halbach elements of which each consists of three magnetic sub-elements with different magnetization direction. A design challenge is the dissipation of RF power induced by eddy currents in the cusp and filter magnets which may lead to overheating and demagnetization. In view of this, a copper magnet cage has been developed that shields the cusp magnets from the radiation of the RF antenna.

Kronberger, Matthias; Chaudet, Elodie; Favre, Gilles; Lettry, Jacques; Kuechler, Detlef; Moyret, Pierre; Paoluzzi, Mauro; Prever-Loiri, Laurent; Schmitzer, Claus; Scrivens, Richard; Steyaert, Didier [CERN, 385 Route de Meyrin, 1211 Geneva (Switzerland)

2011-09-26

93

Local modes of field-reversed configurations  

SciTech Connect

The local stability of field-reversed configurations (FRC) is analyzed using hydrodynamic stability theory. The equation of state includes both compressibility and double-adiabatic effects. For the first time, eigenmodes of the linearized equations of motion have been computed. The most unstable modes have fast growth rates, comparable to the Alfven transit time across the FRC radius; i.e., somewhat faster than the frequency (or growth rate) of global modes. In realistic equilibria, the most unstable local modes concentrate, ballooning-mode style, in the high curvature region of magnetic flux lines. The familiar interchange stability criterion is irrelevant for FRCs, since the actual eigenmodes differ markedly from interchange, both in structure and stability. The appearance of [ital fast] local modes raises the possibility that they may regulate FRC equilibria. However, surprisingly, equilibria with realistic internal structure (i.e. resembling experiments) are [ital more] unstable to ideal local modes than less realistic equilibria, as have often been studied theoretically. Thus, a nonideal theory will be needed to explain the equilibria observed in experiments.

Ishida, A. (Department of Environmental Science, Faculty of Science, Niigata University, Ikarashi, Niigata 950-21 (Japan)); Shibata, N. (Department of Physics, Faculty of Science, Niigata University, Ikarashi, Niigata 950-21 (Japan)); Steinhauer, L.C. (Redmond Plasma Physics Laboratory, University of Washington, Redmond, Washington 98052 (United States))

1994-12-01

94

Quasi-separatrix layers in solar flares. II. Observed magnetic configurations  

Microsoft Academic Search

We show that the location of Halpha or OV flare brightenings is related to the properties of the field-line linkage of the underlying magnetic region. The coronal magnetic field is extrapolated from the observed photospheric field assuming a linear force-free field configuration in order to determine the regions of rapid change in field-line linkage, called \\

P. Demoulin; L. G. Bagala; C. H. Mandrini; J. C. Henoux; M. G. Rovira

1997-01-01

95

Magnetic fields in astrophysics  

Microsoft Academic Search

The evidence of cosmic magnetism is examined, taking into account the Zeeman effect, beats in atomic transitions, the Hanle effect, Faraday rotation, gyro-lines, and the strength and scale of magnetic fields in astrophysics. The origin of magnetic fields is considered along with dynamos, the conditions for magnetic field generation, the topology of flows, magnetic fields in stationary flows, kinematic turbulent

Ia. B. Zeldovich; A. A. Ruzmaikin; D. D. Sokolov

1983-01-01

96

A Paul trap configuration to simulate intense non-neutral beam propagation over large distances through a periodic focusing quadrupole magnetic field  

SciTech Connect

This paper considers an intense non-neutral charged particle beam propagating in the z-direction through a periodic focusing quadrupole magnetic field with transverse focusing force, -{kappa}{sub q}(s)[xe{sub x}-ye{sub y}], on the beam particles. Here, s={beta}{sub b}ct is the axial coordinate, ({gamma}{sub b}-1)m{sub b}c{sup 2} is the directed axial kinetic energy of the beam particles, q{sub b} and m{sub b} are the charge and rest mass, respectively, of a beam particle, and the oscillatory lattice coefficient satisfies {kappa}{sub q}(s+S)={kappa}{sub q}(s), where S is the axial periodicity length of the focusing field. The particle motion in the beam frame is assumed to be nonrelativistic, and the Vlasov-Maxwell equations are employed to describe the nonlinear evolution of the distribution function f{sub b}(x,y,x{sup '},y{sup '},s) and the (normalized) self-field potential {psi}(x,y,s)=q{sub b}{phi}(x,y,s)/{gamma}{sub b}{sup 3}m{sub b}{beta}{sub b}{sup 2}c{sup 2} in the transverse laboratory-frame phase space (x,y,x{sup '},y{sup '}), assuming a thin beam with characteristic radius r{sub b}<configuration in which a long non-neutral plasma column (L>>r{sub p}) is confined axially by applied dc voltages V=const on end cylinders at z={+-}L, and transverse confinement in the x-y plane is provided by segmented cylindrical electrodes (at radius r{sub w}) with applied oscillatory voltages {+-}V{sub 0}(t) over 90 degree sign segments. Here, V{sub 0}(t+T)=V{sub 0}(t), where T=const is the oscillation period, and the oscillatory quadrupole focusing force on a particle with charge q and mass m near the cylinder axis is -m{kappa}{sub q}(t)[xe{sub x}-ye{sub y}], where {kappa}{sub q}(t){identical_to}8qV{sub 0}(t)/{pi}mr{sub w}{sup 2}. (c) 2000 American Institute of Physics.

Davidson, Ronald C. [Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Qin, Hong [Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Shvets, Gennady [Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)

2000-03-01

97

Effective heat conduction in a configuration with nonoverlapped magnetic islands  

SciTech Connect

The effective radial heat conduction {kappa}{sub eff} in a plasma configuration with nonoverlapped magnetic island chains is assessed by applying an ''optimal path'' method. This approach implies that heat is transported predominantly along paths rendering the minimum temperature variation and is related to the principle of minimum entropy production. Paths combined of up to three radial sections and two segments aligned along magnetic field lines are considered. It is demonstrated that the enhancement of {kappa}{sub eff} over the level of perpendicular heat conduction {kappa}{sub perpendicular} arising due to flows along magnetic field lines is controlled only by the Chirikov parameter and by the value 4b{sub r}{sup 2}{kappa}{sub parallel}/{kappa}{sub perpendicular}, where b{sub r} is the relative amplitude of the radial field resonant harmonic and {kappa}{sub parallel} is the parallel heat conduction.

Gupta, A.; Tokar, M. Z. [Institut fuer Energieforschung - Plasmaphysik, Forschungszentrum Juelich, Association EURATOM-FZJ, Trilateral Euregio Cluster, Juelich (Germany)

2008-03-15

98

Transport of Impurity Ions in a Field-Reversed Configuration  

NASA Astrophysics Data System (ADS)

In this dissertation, the diffusion rate of impurity species ions in a flux-coil generated, field-reversed configuration is directly measured. A tomographic diagnostic has been developed and implemented to accomplish this task. The diffusion of impurity species ions is shown to behave classically, after ambipolar effects are taken into account. The observed diffusion coefficient is often found to be far less than predicted classically. It is even negative at times. This implies that a strong, confining electric field is impeding the escape of the ions. The rigid rotor solution to the Vlasov/Maxwell equations provides a prediction of the plasma distribution function, through internal magnetic field measurements. It also predicts the structure of the electric and magnetic fields. Measurement of these fields allow verification of the analysis of the diffusion data. In the following we show: Dperp ? 500 m2/s and the electric field contributes to ion confinement.

Roche, Thomas Jonathan

99

Where will efficient energy release occur in 3-D magnetic configurations?  

Microsoft Academic Search

The energy needed to power flares is thought to be stored in the coronal magnetic field. However, the energy release is efficient only at very small scales. Magnetic configurations with a complex topology, i.e. with separatrices, are the most obvious configurations where current sheets can form, and then, reconnection can efficiently occur. This has been confirmed for several flares computing

P. Démoulin

2007-01-01

100

Magnetic Fields Matter  

NSDL National Science Digital Library

This lesson introduces students to the effects of magnetic fields in matter addressing permanent magnets, diamagnetism, paramagnetism, ferromagnetism, and magnetization. First students must compare the magnetic field of a solenoid to the magnetic field of a permanent magnet. Students then learn the response of diamagnetic, paramagnetic, and ferromagnetic material to a magnetic field. Now aware of the mechanism causing a solid to respond to a field, students learn how to measure the response by looking at the net magnetic moment per unit volume of the material.

VU Bioengineering RET Program, School of Engineering,

101

Magnetic field line Hamiltonian  

SciTech Connect

The basic properties of the Hamiltonian representation of magnetic fields in canonical form are reviewed. The theory of canonical magnetic perturbation theory is then developed and applied to the time evolution of a magnetic field embedded in a toroidal plasma. Finally, the extension of the energy principle to tearing modes, utilizing the magnetic field line Hamiltonian, is outlined.

Boozer, A.H.

1985-02-01

102

Numerical Simulation In Magnetic Drug Targeting. Magnetic Field Source Optimization  

Microsoft Academic Search

\\u000a This paper presents numerical simulation model and results on magnetic drug targeting therapy. The study aims at investigating\\u000a the aggregate blood - magnetic carrier flow interaction with an external magnetic field. Another objective was finding the\\u000a optimal magnetic field source configuration that provides for flows that best assist in magnetic drug targeting. In order\\u000a to evaluate the effects we used

A. Dobre; A. M. Morega

103

Lowest 1?g and 1?u states of the hydrogen molecule in strong magnetic fields: An application of the configuration-interaction method with Hylleraas-Gaussian basis set  

NASA Astrophysics Data System (ADS)

With the Hylleraas-Gaussian basis set, in which the term of r121 is expanded approximately in Gaussian-type geminals, a full configuration-interaction (CI) method is applied to calculate the lowest 1?g and 1?u states of the hydrogen molecule in magnetic fields up to 2.35 × 107 T. In the absence of magnetic field, the total energies of the lowest 1?g and 1?u states in our calculation are -1.174 447 7(4) at the equilibrium distance of R = 1.40 a.u and -0.756 613 4(6) at R = 2.43 a.u., respectively. Compared to the CI method with Gaussian basis set, a significant improvement in the precision of the total energies and the dissociation energies at corresponding equilibrium distances has been achieved. The z1-z2 probability density distributions in different field regions are calculated and analyzed.

Song, Xuanyu; Qiao, Haoxue; Wang, Xiaofeng

2012-08-01

104

Nonequilibrium dynamics of emergent field configurations  

NASA Astrophysics Data System (ADS)

The processes by which nonlinear physical systems approach thermal equilibrium is of great importance in many areas of science. Central to this is the mechanism by which energy is transferred between the many degrees of freedom comprising these systems. With this in mind, in this research the nonequilibrium dynamics of nonperturbative fluctuations within Ginzburg-Landau models are investigated. In particular, two questions are addressed. In both cases the system is initially prepared in one of two minima of a double-well potential. First, within the context of a (2 + 1) dimensional field theory, we investigate whether emergent spatio-temporal coherent structures play a dynamcal role in the equilibration of the field. We find that the answer is sensitive to the initial temperature of the system. At low initial temperatures, the dynamics are well approximated with a time-dependent mean-field theory. For higher temperatures, the strong nonlinear coupling between the modes in the field does give rise to the synchronized emergence of coherent spatio-temporal configurations, identified with oscillons. These are long-lived coherent field configurations characterized by their persistent oscillatory behavior at their core. This initial global emergence is seen to be a consequence of resonant behavior in the long wavelength modes in the system. A second question concerns the emergence of disorder in a highly viscous system modeled by a (3 + 1) dimensional field theory. An integro-differential Boltzmann equation is derived to model the thermal nucleation of precursors of one phase within the homogeneous background. The fraction of the volume populated by these precursors is computed as a function of temperature. This model is capable of describing the onset of percolation, characterizing the approach to criticality (i.e. disorder). It also provides a nonperturbative correction to the critical temperature based on the nonequilibrium dynamics of the system.

Howell, Rafael Cassidy

105

Magnetization configurations and reversal of thin magnetic nanotubes with uniaxial anisotropy  

NASA Astrophysics Data System (ADS)

We present calculations of the magnetization configuration and reversal behavior of magnetic nanotubes with uniaxial anisotropy by means of two-dimensional micromagnetic simulations and analytical methods. The tube radii R from 50 to 150 nm and the tube length /radius aspect ratio L/R<=20 were explored. For a finite length of magnetic nanotubes the magnetization configuration is characterized by a uniformly magnetized along the tube axis middle part and two nonuniform curling states of a length Lc in two ends of the tube with the same or opposite magnetization rotating senses, referring as C-state or B-state, respectively. We found that the magnetization configuration of the C-state exists for thin nanotubes with the tube thickness, ?R, in the range of ?R/R<=0.2. For thicker nanotubes the strong magnetostatic stray field forces the change of rotating senses of the end domains in opposite directions (the B-state). The transition from the C-state to a vortex state with in-plane magnetization is described as function of the tube geometrical parameters. The nanotube hysteresis loops and switching fields were calculated. The simple analytical model was developed to describe the nanotube magnetization reversal reducing its description to the Stoner-Wohlfarth model with effective parameters. The equilibrium state of nanotube is described in terms of ?, the angle of the magnetization deviation from the intrinsic tube easy axis. The L/R dependence of the C-state magnetization, the shape of hysteresis loops and the switching field values are described by a dependence of ? on L/R.

Chen, A. P.; Guslienko, K. Y.; Gonzalez, J.

2010-10-01

106

Kinetic Stability of the Field Reversed Configuration  

SciTech Connect

New computational results are presented which advance the understanding of the stability properties of the Field-Reversed Configuration (FRC). The FRC is an innovative confinement approach that offers a unique fusion reactor potential because of its compact and simple geometry, translation properties, and high plasma beta. One of the most important issues is FRC stability with respect to low-n (toroidal mode number) MHD modes. There is a clear discrepancy between the predictions of standard MHD theory that many modes should be unstable on the MHD time scale, and the observed macroscopic resilience of FRCs in experiments.

E.V. Belova; R.C. Davidson; H. Ji; and M. Yamada

2002-07-09

107

Beta value at separatrix of field-reversed configuration  

SciTech Connect

A pressure profile inside and outside a separatrix of a field-reversed configuration is determined by comparing three types of assumed pressure profiles with the radial profile of bremsstrahlung. It is found that the pressure profile is flatter near the field null than the rigid rotor profile. Edge-layer parameters as beta value at the separatrix, separatrix radius, and edge-layer width are determined from the pressure profile. The reliability of those parameters is confirmed by a magnetic method measuring an excluded flux radius.

Ikeyama, Taeko; Hiroi, Masanori; Nogi, Yasuyuki [College of Science and Technology, Nihon University, Tokyo 101-8308 (Japan); Ohkuma, Yasunori [College of Industrial Technology, Nihon University, Chiba 275-8576 (Japan)

2009-04-15

108

Magnetosphere of Uranus: plasma sources, convection, and field configuration  

SciTech Connect

At the time of the Voyager 2 flyby of Uranus, the planetary rotational axis will be roughly antiparallel to the solar wind flow. If Uranus has a magnetic dipole moment that is approximately aligned with its spin axis, and if the heliospheric shock has not been encountered, we will have the rare opportunity to observe a ''pole-on'' magnetosphere as discussed qualitatively by Siscoe. Qualitative arguments based on analogy with Earth, Jupiter, and Saturn suggest that the magnetosphere of Uranus may lack a source of plasma adequate to produce significant internal currents, internal convection, and associated effects. In order to provide a test of this hypothesis with the forthcoming Voyager measurements, we have constructed a class of approximately self-consistent quantitative magnetohydrostatic equilibrium configurations for a pole-on magnetosphere with variable plasma pressure parameters. Given a few simplifying assumptions, the geometries of the magnetic field and of the tail current sheet can be computed for a given distribution of trapped plasma pressure. The configurations have a single funnel-shaped polar cusp that points directly into the solar wind and a cylindrical tail plasma sheet whose currents close within the tail rather than on the tail magnetopause, and whose length depends on the rate of decrease of thermal plasma pressure down the tail. Interconnection between magnetospheric and interplanetary fields results in a highly asymmetric tail-field configuration. These features were predicted qualtitatively by Siscoe; the quantitative models presented here may be useful in the interpretation of Voyager encounter results.

Voigt, G.; Hill, T.W.; Dessler, A.J.

1983-03-01

109

Solar Magnetic Field  

NASA Astrophysics Data System (ADS)

Electrical currents flowing in the solar plasma generate a magnetic field, which is detected in the SOLAR ATMOSPHERE by spectroscopic and polarization measurements (SOLAR MAGNETIC FIELD: INFERENCE BY POLARIMETRY). The SOLAR WIND carries the magnetic field into interplanetary space where it can be measured directly by instruments on space probes....

Schüssler, M.; Murdin, P.

2000-11-01

110

Plasma-wall interaction in Hall thrusters with magnetic lens configuration  

SciTech Connect

Some recently developed Hall thrusters utilize a magnetic field configuration in which the field lines penetrate the thruster walls at a high incidence angle. This so-called magnetic lens leads to an electric field pointing away from the walls, which is expected to reduce ion losses and improve thruster efficiency. This configuration also introduces an interesting behavior in the sheath formation. At sufficiently large angles, ions are repelled from the wall, and sheath collapse is expected. We use a plasma simulation code to investigate this phenomenon in detail. We consider the role of the magnetic field incidence angle, secondary electron emission, and a magnetic mirror. Numerical study confirms the theoretical predictions, and at large angles, ions are seen to turn away from the wall. We also consider the role of the magnetic field geometry on ion wall flux and channel erosion, and observe reduction in both quantities as the magnetic field incidence angle is increased.

Brieda, Lubos; Keidar, Michael [Department of Mechanical and Aerospace Engineering, George Washington University, 801 22nd St., Washington, DC 20052 (United States)

2012-06-15

111

THE RADIO PROPERTIES AND MAGNETIC FIELD CONFIGURATION IN THE CRAB-LIKE PULSAR WIND NEBULA G54.1+0.3  

SciTech Connect

We present a multifrequency radio investigation of the Crab-like pulsar wind nebula (PWN) G54.1+0.3 using the Very Large Array. The high resolution of the observations reveals that G54.1+0.3 has a complex radio structure which includes filamentary and loop-like structures that are magnetized, a diffuse extent similar to the associated diffuse X-ray emission. But the radio and X-ray structures in the central region differ strikingly, indicating that they trace very different forms of particle injection from the pulsar and/or particle acceleration in the nebula. No spectral index gradient is detected in the radio emission across the PWN, whereas the X-ray emission softens outward in the nebula. The extensive radio polarization allows us to image in detail the intrinsic magnetic field, which is well-ordered and reveals that a number of loop-like filaments are strongly magnetized. In addition, we determine that there are both radial and toroidal components to the magnetic field structure of the PWN. Strong mid-infrared (IR) emission detected in Spitzer Space Telescope data is closely correlated with the radio emission arising from the southern edge of G54.1+0.3. In particular, the distributions of radio and X-ray emission compared with the mid-IR emission suggest that the PWN may be interacting with this interstellar cloud. This may be the first PWN where we are directly detecting its interplay with an interstellar cloud that has survived the impact of the supernova explosion associated with the pulsar's progenitor.

Lang, Cornelia C.; Clubb, Kelsey I. [Department of Physics and Astronomy, 703 Van Allen Hall, University of Iowa, Iowa City, IA 52242 (United States); Wang, Q. Daniel; Lu Fangjun, E-mail: cornelia-lang@uiowa.ed [Department of Astronomy, University of Massachusetts, Amherst, MA 01002 (United States)

2010-02-01

112

Magnetically Robust Non-Fermi Liquid Behavior in Heavy Fermion Systems with f2-Configuration: Competition between Crystalline-Electric-Field and Kondo-Yosida Singlets  

NASA Astrophysics Data System (ADS)

In f2-based heavy fermion systems with a crystalline-electric-field (CEF) singlet ground state, the non-Fermi liquid (NFL) arises around the quantum critical point (QCP) due to the competition between the CEF singlet and the Kondo-Yosida singlet states. In such a case, the characteristic temperature TF* at which the entropy starts to decrease toward zero is suppressed by the effect of the competition, compared to both energy scales characterizing each singlet state, the lower Kondo temperature (TK2) and the CEF splitting (?). We show that in the case of tetragonal symmetry TF* is not affected by the magnetic field up to Hz* which is determined by the distance from the QCP or characteristic energy scales of each singlet states, not by TF* itself. As a result, in the vicinity of QCP, there are parameter regions where the NFL is robust against the magnetic field, at an observable temperature range T > TF*, up to Hz* which is far larger than TF* and less than \\min(TK2,?). Our result suggests that such an anomalous NFL behavior can arise also in systems with other CEF symmetry, which might provide us with the basis to understand the anomalous behaviors of UBe13.

Nishiyama, Shinya; Matsuura, Hiroyasu; Miyake, Kazumasa

2010-10-01

113

Formation of field-reversed-configuration plasma with punctuated-betatron-orbit electrons.  

PubMed

We describe ab initio, self-consistent, 3D, fully electromagnetic numerical simulations of current drive and field-reversed-configuration plasma formation by odd-parity rotating magnetic fields (RMF{o}). Magnetic-separatrix formation and field reversal are attained from an initial mirror configuration. A population of punctuated-betatron-orbit electrons, generated by the RMF{o}, carries the majority of the field-normal azimuthal electrical current responsible for field reversal. Appreciable current and plasma pressure exist outside the magnetic separatrix whose shape is modulated by the RMF{o} phase. The predicted plasma density and electron energy distribution compare favorably with RMF{o} experiments. PMID:20867454

Welch, D R; Cohen, S A; Genoni, T C; Glasser, A H

2010-07-01

114

The Magnetic Field  

NSDL National Science Digital Library

This demonstration of the magnetic field lines of Earth uses a bar magnet, iron filings, and a compass. The site explains how to measure the magnetic field of the Earth by measuring the direction a compass points from various points on the surface. There is also an explanation of why the north magnetic pole on Earth is actually, by definition, the south pole of a magnet.

Barker, Jeffrey

115

Tilt stability and compression heating studies of field-reversed configurations.  

National Technical Information Service (NTIS)

The first observations of internal tilt instabilities in field-reversed configurations (FRCs) are reported. Detailed comparisons with theory establish that data from an array of external magnetic probes are signatures of these destructive plasma instabili...

D. J. Rej M. Tuszewski D. C. Barnes G. A. Barnes R. E. Chrien

1990-01-01

116

Magnetic-field effects on vacuum insulator flashover  

Microsoft Academic Search

The effect of magnetic fields on dielectric surface breakdown in vacuum and simulated LEO conditions is investigated using pulsed test voltages. Predictions from the saturated secondary electron emission avalanche breakdown model and experimental results both show magnetic insulation effects at magnetic-field amplitudes as low as 0.1 T. The most favorable configuration for magnetic insulation is with the magnetic field oriented

M. Lehr; R. Korzekwa; H. Krompholz; M. Kristiansen

1992-01-01

117

Hybrid equilibria of field-reversed configurations  

SciTech Connect

This paper presents the first detailed model of hybrid equilibria relevant to field-reversed configuration experiments, leading to a system of equations that are solved for a range of fully two-dimensional equilibria. Several features of these highly kinetic objects are explored. The range of equilibria is primarily dependent on a single free parameter related to the flow shear. The level of flow shear has a profound effect on the structure, especially near the separatrix. This likely has a strong influence on both stability and transport properties. Higher flow shear is favorable in every respect. The key factor behind the influence of flow shear is the relatively rapid end loss of unconfined ions. Differences between hybrid and static-fluid equilibrium models are highlighted, including the integrity of surface functions, the effect of flow shear, and the scrape-off layer thickness.

Steinhauer, Loren C. [Department of Aeronautics and Astronautics, University of Washington, Seattle, Washington 98195 (United States)

2011-11-15

118

Magnetic Field Problem  

NSDL National Science Digital Library

The above animations represent two typical bar magnets each with a North and South pole. The arrows represent the direction of the magnetic field. The color of the arrows represents the magnitude of the field with magnitude increasing as the color changes from blue to green to red to black. You may drag either magnet and double-click anywhere inside the animation to add a magnetic field line, and mouse-down to read the magnitude of the magnetic field at that point.

Christian, Wolfgang; Belloni, Mario

2007-03-03

119

Optimized configurations of autostable superconducting magnetic bearings for practical applications  

SciTech Connect

In order to establish an optimized bearing design for a flywheel for energy storage, the authors have studied model bearing configurations involving bulk YBCO pellets and double-dipole magnet configurations. They were interested to see what is the correlation between the maximum attainable levitation force, measured for a typical bearing gap of 3 mm, and the separation between the magnetic poles. Equal polarity (north-north) and alternate polarity (north-south) configurations were investigated. The maximum levitation force was obtained with the alternate polarity arrangement for a separation between the magnetic poles of 6 mm. It represents an increase of 19% compared to a non-optimized configuration. The experiments demonstrate that configurations of superconducting magnetic bearings can be optimized to obtain better levitation properties.

Schoechlin, A.; Ritter, T.; Bornemann, H.J. [Forschungszentrum Karlsruhe GmbH (Germany)

1995-11-01

120

Electromagnetic drift instabilities in high-beta plasma under conditions of a field reversed configuration  

SciTech Connect

Electromagnetic drift instabilities are studied in the conditions of a field reversed configuration (FRC). Dispersion equation is based on the set of Vlasov-Maxwell equations taking into account nonadiabatic responses both of ions and electrons. Considered drift instabilities are caused by density and temperature gradients. It is assumed that magnetic field of the FRC is purely poloidal. Two kinds of magnetic field nonuniformity are considered: (i) perpendicular gradient due to high beta values (beta is the plasma pressure/magnetic pressure) and (ii) curvature of magnetic lines. There is low frequency drift instability existing for high-beta regimes. Modes of such instability can propagate transversally to the unperturbed magnetic field lines.

Chirkov, A. Yu.; Khvesyuk, V. I. [Bauman Moscow State Technical University, 2-nd Baumanskaya, 5, Moscow 105005 (Russian Federation)

2010-01-15

121

Magnetic Fields in Galaxies  

NASA Astrophysics Data System (ADS)

Most of the visible matter in the Universe is ionized so that cosmic magnetic fields are quite easy to generate and, due to the lack of magnetic monopoles, hard to destroy. Magnetic fields have been measured in or around practically all celestial objects, either by in situ measurements of spacecrafts or by the electromagnetic radiation of embedded cosmic rays, gas, or dust. The Earth, the Sun, solar planets, stars, pulsars, the Milky Way, nearby galaxies, more distant (radio) galaxies, quasars, and even intergalactic space in clusters of galaxies have significant magnetic fields, and even larger volumes of the Universe may be permeated by "dark" magnetic fields. Information on cosmic magnetic fields has increased enormously as the result of the rapid development of observational methods, especially in radio astronomy. In the Milky Way, a wealth of magnetic phenomena was discovered, which are only partly related to objects visible in other spectral ranges. The large-scale structure of the Milky Way's magnetic field is still under debate. The available data for external galaxies can well be explained by field amplification and ordering via the dynamo mechanism. The measured field strengths and the similarity of field patterns and flow patterns of the diffuse ionized gas give strong indication that galactic magnetic fields are dynamically important. They may affect the formation of spiral arms, outflows, and the general evolution of galaxies. In spite of our increasing knowledge on magnetic fields, many important questions on the origin and evolution of magnetic fields, their first occurrence in young galaxies, or the existence of large-scale intergalactic fields remained unanswered. The present upgrades of existing instruments and several planned radio astronomy projects have defined cosmic magnetism as one of their key science projects.

Beck, Rainer; Wielebinski, Richard

122

Intergalactic magnetic fields  

Microsoft Academic Search

There is no observational support to the hypothesis of the most large-scale homogeneous magnetic field in the Universe. The best upper limit is given by interpretation of the Faraday rotation from the extragalactic radio sources. However the magnetic fields can be generated in the clusters of galaxies by a turbulence in the wakes of moving galaxies. These fields have an

A. A. Ruzmajkin

1991-01-01

123

Magnetic Field Example 1  

NSDL National Science Digital Library

Clicking on the different links below will produce different magnetic fields in the box above. The wires (perpendicular to the screen) or coils (in and out of the screen) are not visible, but you can determine what they are from the field. You can also click on a point to read off the magnetic field at that place.

Christian, Wolfgang; Belloni, Mario

2008-02-19

124

Melatonin and magnetic fields.  

PubMed

There is public health concern raised by epidemiological studies indicating that extremely low frequency electric and magnetic fields generated by electric power distribution systems in the environment may be hazardous. Possible carcinogenic effects of magnetic field in combination with suggested oncostatic action of melatonin lead to the hypothesis that the primary effects of electric and magnetic fields exposure is a reduction of melatonin synthesis which, in turn, may promote cancer growth. In this review the data on the influence of magnetic fields on melatonin synthesis, both in the animals and humans, are briefly presented and discussed. PMID:12019358

Karasek, Michal; Lerchl, Alexander

2002-04-01

125

Magnetic Bearing Configurations: Theoretical and Experimental Studies  

Microsoft Academic Search

A radial magnetic bearing, consisting of two permanent magnets, is an attractive choice because of its zero wear, negligible friction, and low cost, but it suffers from low load capacity, low radial stiffness, lack of damping, and high axial instability. To enhance the radial load and radial stiffness, and reduce the axial thrust, we have made a theoretical and experimental

Pranab Samanta; Harish Hirani

2008-01-01

126

High field magnetic resonance  

US Patent & Trademark Office Database

A magnetic resonance system is disclosed. The system includes a transceiver having a multichannel receiver and a multichannel transmitter, where each channel of the transmitter is configured for independent selection of frequency, phase, time, space, and magnitude, and each channel of the receiver is configured for independent selection of space, time, frequency, phase and gain. The system also includes a magnetic resonance coil having a plurality of current elements, with each element coupled in one to one relation with a channel of the receiver and a channel of the transmitter. The system further includes a processor coupled to the transceiver, such that the processor is configured to execute instructions to control a current in each element and to perform a non-linear algorithm to shim the coil.

2010-09-21

127

Magnetic fields in neutron stars  

NASA Astrophysics Data System (ADS)

This work aims at studying how magnetic fields affect the observational properties and the long-term evolution of isolated neutron stars, which are the strongest magnets in the universe. The extreme physical conditions met inside these astronomical sources complicate their theoretical study, but, thanks to the increasing wealth of radio and X-ray data, great advances have been made over the last years. A neutron star is surrounded by magnetized plasma, the so-called magnetosphere. Modeling its global configuration is important to understand the observational properties of the most magnetized neutron stars, magnetars. On the other hand, magnetic fields in the interior are thought to evolve on long time-scales, from thousands to millions of years. The magnetic evolution is coupled to the thermal one, which has been the subject of study in the last decades. An important part of this thesis presents the state-of-the-art of the magneto-thermal evolution models of neutron stars during the first million of years, studied by means of detailed simulations. The numerical code here described is the first one to consistently consider the coupling of magnetic field and temperature, with the inclusion of both the Ohmic dissipation and the Hall drift in the crust.

Viganò, Daniele

2013-09-01

128

Magnetic field generator  

DOEpatents

A magnetic field generating device provides a useful magnetic field within a specific retgion, while keeping nearby surrounding regions virtually field free. By placing an appropriate current density along a flux line of the source, the stray field effects of the generator may be contained. One current carrying structure may support a truncated cosine distribution, and it may be surrounded by a current structure which follows a flux line that would occur in a full coaxial double cosine distribution. Strong magnetic fields may be generated and contained using superconducting cables to approximate required current surfaces.

Krienin, Frank (Shoreham, NY)

1990-01-01

129

On Cosmic Magnetic Fields  

NASA Astrophysics Data System (ADS)

Magnetic fields are present in all astrophysical media. However, many models and interpretations of observations often ignore them, because magnetic fields are difficult to handle and because they produce complicated morphological features. Here we will comment on the basic intuitive properties, which even if not completely true, provide a first guiding insight on the physics of a particular astrophysical problem. These magnetic properties are not mathematically demonstrated here. How magnetic fields evolve and how they introduce dynamical effects are considered, also including a short comment on General Relativity Magnetohydrodynamics. In a second part we consider some audacious and speculative matters. They are answers to three questions: a) How draw a cube without lifting the pencil from the paper so that when the pen passes through the same side do in the same direction? B) Are MILAGRO anisotropies miraculous? C) Do cosmic magnetic lenses exist?. The last two questions deal with issues related with the interplay between magnetic fields and cosmic ray propagation.

Florido, E.; Battaner, E.

2010-12-01

130

Magnetic fields at Uranus  

Microsoft Academic Search

The conclusions drawn regarding the structure, behavior and composition of the Uranian magnetic field and magnetosphere as revealed by Voyager 2 data are summarized. The planet had a bipolar magnetotail and a bow shock wave which was observed 23.7 Uranus radii (UR) upstream and a magnetopause at 18.0 UR. The magnetic field observed can be represented by a dipole offset

N. F. Ness; M. H. Acuna; K. W. Behannon; L. F. Burlaga; J. E. P. Connerney; R. P. Lepping

1986-01-01

131

THE INTERPLANETARY MAGNETIC FIELD  

Microsoft Academic Search

A new analysis of magnetic and concurrent plasma data collected from the ; space probes Pionecr 5, Explorer 10, and Mariner 2 yields a new model of the ; interplanetary magnetic field. It is hypothesized that the observed ; interplanetary field F\\/sub i\\/ is due to motion of the magnetometer relative to a ; negatively charged rotating sun from which

V. A. BAILEY

1963-01-01

132

Cosmic Magnetic Fields  

Microsoft Academic Search

Most of the visible matter in the Universe is in a plasma state, or more specifically is composed of ionized or partially ionized gas permeated by magnetic fields. Thanks to recent advances on the theory and detection of cosmic magnetic fields there has been a worldwide growing interest in the study of their role on the formation of astrophysical sources

Elisabete M. de Gouveia Dal Pino; Dal Pino

2006-01-01

133

Dynamic stabilization of nonequilibrium domain configurations in magnetic squares with high amplitude excitations  

NASA Astrophysics Data System (ADS)

We explore the linear and nonlinear dynamic regimes of micrometer-scale soft magnetic squares with an in-plane uniaxial anisotropy, recording the response of the magnetization in the spatial domain under a continuous sinusoidal excitation with time-resolved scanning transmission x-ray microscopy. Increasing the excitation field amplitude leads to the dynamic stabilization of nonequilibrium domain configurations, which appear at threshold amplitudes and return to the equilibrium configuration when the amplitude is reduced. On imaging the magnetization in the transition region between two stable magnetic configurations, we observe small domains originating from the vortex core. Dynamic micromagnetic simulations of the domain configuration provide qualitative agreement with the experimental data and insight into the energy dissipation and spin wave contributions.

Stevenson, S. E.; Moutafis, C.; Heldt, G.; Chopdekar, R. V.; Quitmann, C.; Heyderman, L. J.; Raabe, J.

2013-02-01

134

Dynamic processes in field-reversed-configuration compact toroids  

SciTech Connect

In this lecture, the dynamic processes involved in field-reversed configuration (FRC) formation, translation, and compression will be reviewed. Though the FRC is related to the field-reversed mirror concept, the formation method used in most experiments is a variant of the field-reversed THETA-pinch. Formation of the FRC eqilibrium occurs rapidly, usually in less than 20 ..mu..s. The formation sequence consists of several coupled processes: preionization; radial implosion and compression; magnetic field line closure; axial contraction; equilibrium formation. Recent experiments and theory have led to a significantly improved understanding of these processes; however, the experimental method still relies on a somewhat empirical approach which involves the optimization of initial preionization plasma parameters and symmetry. New improvements in FRC formation methods include the use of lower voltages which extrapolate better to larger devices. The axial translation of compact toroid plasmas offers an attractive engineering convenience in a fusion reactor. FRC translation has been demonstrated in several experiments worldwide, and these plasmas are found to be robust, moving at speeds up to the Alfven velocity over distances of up to 16 m, with no degradation in the confinement. Compact toroids are ideal for magnetic compression. Translated FRCs have been compressed and heated by imploding liners. Upcoming experiments will rely on external flux compression to heat a translater FRC at 1-GW power levels. 39 refs.

Rej, D.J.

1987-01-01

135

The Earth's Magnetic Field  

NSDL National Science Digital Library

The magnetic field of the Earth is contained in a region called the magnetosphere. The magnetosphere prevents most of the particles from the sun, carried in solar wind, from hitting the Earth. This site, produced by the University Corporation for Atmospheric Research (UCAR), uses text, scientific illustrations,and remote imagery to explain the occurrence and nature of planetary magnetic fields and magnetospheres, how these fields interact with the solar wind to produce phenomena like auroras, and how magnetic fields of the earth and other planets can be detected and measured by satellite-borne magnetometers.

136

CONFIGURATION MANAGEMENT SYSTEM FOR THE LHC SUPERCONDUCTING MAGNET TEST BENCHES  

Microsoft Academic Search

The configuration management system for the Large Hadron Collider (LHC) superconducting magnet test facility has been integrated with the already existing software enforcing quality assurance procedures of the LHC - the Manufacturing and Test Folder (MTF). Such a solution provides one common access point to all the data relevant to each of the tested magnets. The MTF software was developed

T. Ladzinski; M. Gateau; P. Martel; A. Siemko; D. Widegren

2003-01-01

137

Liquid first walls for magnetic fusion energy configurations  

NASA Astrophysics Data System (ADS)

Liquids (~7 neutron mean free paths thick), with certain restrictions, can probably be used in magnetic fusion designs between the burning plasma and the structural materials of the fusion power core. If this works there would be a number of profound advantages: a cost of electricity lower by as much as a factor of 2; removal of the need to develop new first wall materials, saving over 4 billion US dollars in development costs; a reduction of the amount and kinds of wastes generated in the plant; and the wider choice of materials permitted. The amount of material that evaporates from the liquid which can be allowed to enter the burning plasma is estimated to be less than 0.7% for lithium, 1.9% for Flibe (Li2BeF4 or LiBeF3) and 0.01% for Li17Pb83. The ability of the edge plasma to attenuate the vapour by ionization appears to exceed this requirement. This ionized vapour would be swept along open field lines into a remote burial chamber. The most practical systems would be those with topological open field lines on the outer surface, as is the case with a field reversed configuration (FRC), a spheromak, a Z pinch or a mirror machine. In a tokamak, including a spherical tokamak, the field lines outside the separatrix are restricted to a small volume inside the toroidal coil making for difficulties in introducing the liquid and removing the ionized vapour, i.e. the configuration is not open ended

Moir, R. W.

1997-04-01

138

Production of negative hydrogen ions in a large multicusp ion source with double-magnetic filter configuration.  

National Technical Information Service (NTIS)

The production of the negative hydrogen ions in a large multicusp ion source has been investigated in a double-magnetic filter (DMF) configuration. In the DMF configuration, the energetic electrons are trapped by the mirror of a magnetic multicusp field, ...

A. Ando Y. Takeiri O. Kaneko Y. Oka M. Wada

1992-01-01

139

Production of negative hydrogen ions in a large multicusp ion source with double-magnetic filter configuration  

Microsoft Academic Search

The production of the negative hydrogen ions in a large multicusp ion source has been investigated in a double-magnetic filter (DMF) configuration. In the DMF configuration, the energetic electrons are trapped by the mirror of a magnetic multicusp field, and only the thermal electrons are present in the center of the arc chamber. A large amount of H(-) ions of

A. Ando; Y. Takeiri; O. Kaneko; Y. Oka; M. Wada; T. Kuroda

1992-01-01

140

Stationary non-axisymmetric configurations of magnetized singular isothermal discs  

NASA Astrophysics Data System (ADS)

We construct both aligned and unaligned (logarithmic spiral) stationary configurations of non-axisymmetric magnetohydrodynamic (MHD) discs from either a full or a partial razor-thin power-law axisymmetric magnetized singular isothermal disc (MSID) that is embedded with a coplanar azimuthal magnetic field B? of a non-force-free radial scaling r-1/2 and that rotates differentially with a flat rotation curve of speed aD, where a is the isothermal speed of sound and D is the dimensionless rotation parameter. Analytical solutions and stability criteria for determining D2 are derived. For aligned non-axisymmetric MSIDs, eccentric m= 1 displacements may occur at arbitrary D2 in a full MSID but are allowed only with a2D2=C2A/2 in a partial MSID (where CA is the Alfvén speed), while each case of |m|>= 1 gives two possible values of D2 for purely azimuthal propagations of fast and slow MHD density waves (FMDWs and SMDWs) that appear stationary in an inertial frame of reference. For disc galaxies modelled by a partial MSID resulting from a massive dark matter halo with a flat rotation curve and a2D2>>C2A, stationary aligned perturbations of m= 1 are not allowed. For unaligned logarithmic spiral MSIDs with |m|>= 1, there exist again two values of D2, corresponding to FMDWs and SMDWs that propagate in both radial and azimuthal directions relative to the MSID and that appear stationary in an inertial frame of reference. The larger D2 is always physically valid, while the smaller D2 is valid only for a > CA/2 with a positive surface mass density ?0. For observational diagnostics, we examine the spatial phase relationships among enhancements of gas density and magnetic field, and velocity perturbations. These results are useful for probing magnetized bars, or lopsided, normal and barred spiral galaxies and for testing numerical MHD codes. In the case of NGC 6946, interlaced optical and magnetic field spiral patterns of SMDWs can persist in a disc with a flat rotation curve. Theoretical issues regarding the modal formalism and the MSID perspective are also discussed.

Lou, Yu-Qing

2002-11-01

141

The First Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

Widrow, Lawrence M.; Ryu, Dongsu; Schleicher, Dominik R. G.; Subramanian, Kandaswamy; Tsagas, Christos G.; Treumann, Rudolf A.

2012-05-01

142

Magnetic Field Lines  

NSDL National Science Digital Library

This activity will introduce students to the idea of magnetic field lines--a concept they have probably encountered but may not fully grasp. Completing this activity and reading the corresponding background information should enable students to understand

Horton, Michael

2009-05-30

143

Magnetic field dosimeter development  

SciTech Connect

In recent years there has been increased concern over potential health hazards related to exposure of personnel to magnetic fields. If exposure standards are to be established, then a means for measuring magnetic field dose must be available. To meet this need, the Department of Energy has funded development of prototype dosimeters at the Battelle Pacific Northwest Laboratory. This manual reviews the principle of operation of the dosimeter and also contains step-by-step instructions for its operation.

Lemon, D.K.; Skorpik, J.R.; Eick, J.L.

1980-09-01

144

Magnetization configurations and reversal of magnetic nanotubes with opposite chiralities of the end domains  

NASA Astrophysics Data System (ADS)

For thick soft magnetic nanotubes with an anisotropy axis directed along the nanotube length the equilibrium energy ground states present magnetization configurations with opposite rotating senses in two tube ends (B-state), referring as antiparallel chiralities of the end vortex domains. For nanotubes with outer radius R of 50 nm, 100 nm and 150 nm, and length L = (2.5-20)R the B-state remanent magnetization and the reversal field dependence on tube thickness and anisotropy strength are studied by using both two-dimensional simulation and analytic methods. The equilibrium states, the hysteresis loops and the switching field values calculated numerically are presented as the functions of tube size and material parameters. For the short nanotubes the domain walls patterns, such as transverse walls and vortex walls, nucleating in the tube center, as well as the hysteresis loops of the nanotubes with transverse walls are presented. The numerical results are interpreted by a simple analytical model in which the equilibrium state of nanotube is described by ?, the angle of the magnetization M deviation from the intrinsic tube easy axis. ? as a function of the tube aspect ratio L/R, tube thickness ?R, and uniaxial anisotropy constant Ku, obtained by minimizing the total magnetic energy, well describes dependences of the shape of hysteresis loops and switching field values on the tube geometric and material parameters in the B-state.

Chen, Ai-Ping; Gonzalez, Julian M.; Guslienko, Konstantin Y.

2011-04-01

145

Magnetic field confinement for magnetically levitated vehicles  

SciTech Connect

A magnetically levitated vehicle adapted for movement along a guide way, comprising: a passenger compartment; first and second primary magnet means secured on the vehicle to produce a magnetic field having a magnetic flux density extending outward from the primary magnet means, to support the vehicle above and spaced from the guide way; and a plurality of confining magnets disposed on the vehicle to confine the magnetic flux extending outward from the primary magnet means and to reduce the strength of the primary magnetic field in the passenger compartment; wherein the primary magnet means has a capacity to produce a primary magnetic field having a maximum strength of at least 200 gauss in the passenger compartment, and the confining magnets maintain the strength of the primary magnetic field in the passenger compartment below 5 gauss.

Proise, M.

1993-05-25

146

Development of Hybrid Thermistor Free of Magnetic Field Effect  

Microsoft Academic Search

A hybrid thermistor was developed to realize a thermometer which is practically free of the magnetic field effect. Its design involves placing two kinds of thermistors in a bridge configuration so that the magnetic field effects cancel each other. The effect of the magnetic fields on the proposed sensor was precisely studied using the triple point of water. The correction

Koichi Nara

2005-01-01

147

Configuration and temperature dependence of magnetic damping in spin valves  

SciTech Connect

Using vector-analyzer ferromagnetic resonance, we have studied the microwave susceptibility of a Py/Co/Cu/Co/MnIr spin valve over a large temperature range (5-450 K) and as a function of the magnetic configuration. An effective magnetization and Gilbert damping constant of 1.1 T and 0.021, respectively, are found for the permalloy free layer, with no discernible variation in temperature observed for either quantities. In contrast, the pinned layer magnetization is reduced by heating, and the exchange bias collapses near a temperature of 450 K. The ferromagnetic resonance linewidth of the free layer increases by 500 MHz when the layer magnetizations are aligned in antiparallel, which is attributed to a configuration-dependent contribution to the damping from spin pumping effects.

Joyeux, X.; Devolder, T.; Kim, Joo-Von; Gomez de la Torre, Y.; Eimer, S.; Chappert, C. [Institut d'Electronique Fondamentale, University Paris-Sud, 91405 Orsay (France); UMR8622, CNRS, University Paris-Sud, 91405 Orsay (France)

2011-09-15

148

Planetary magnetic fields  

Microsoft Academic Search

The past several years have seen dramatic developments in the study of planetary magnetic fields, including a wealth of new data, mainly from the Galilean satellites and Mars, together with major improvements in our theoretical modeling effort of the dynamo process believed responsible for large planetary fields. These dynamos arise from thermal or compositional convection in fluid regions of large

David J. Stevenson

2003-01-01

149

Magnetic Multipole Field Model  

NSDL National Science Digital Library

The EJS Magnetic Multipole Field Model shows the field of a magnetic dipole or quadrupole with little compasses that indicate direction and relative field strength. A slider changes the angular orientation of the dipole and a movable compass shows the magnetic field direction and magnitude. Compass values can be recorded into a data table and analyzed using a built-in data analysis tool. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. The Magnetic Multipole Field model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_em_MagneticMultipoleField.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Christian, Wolfgang; Cox, Anne; Franciscouembre

2010-02-14

150

Magnetic Field Measurement System  

SciTech Connect

A magnetic field measurement system was designed, built and installed at MAX Lab, Sweden for the purpose of characterizing the magnetic field produced by Insertion Devices (see Figure 1). The measurement system consists of a large granite beam roughly 2 feet square and 14 feet long that has been polished beyond laboratory grade for flatness and straightness. The granite precision coupled with the design of the carriage yielded minimum position deviations as measured at the probe tip. The Hall probe data collection and compensation technique allows exceptional resolution and range while taking data on the fly to programmable sample spacing. Additional flip coil provides field integral data.

Kulesza, Joe; Johnson, Eric; Lyndaker, Aaron; Deyhim, Alex; Waterman, Dave; Blomqvist, K. Ingvar [Advanced Design Consulting USA, 126 Ridge Road, P.O. Box 187, Lansing, NY 14882 (United States); Dunn, Jonathan Hunter [MAX-lab, SE-221 00 Lund (Sweden)

2007-01-19

151

Magnetic Field Problem: Current  

NSDL National Science Digital Library

A cross section of a circular wire loop carrying an unknown current is shown above. The arrows represent the direction of the magnetic field. The color of the arrows represents the magnitude of the field with magnitude increasing as the color changes from blue to green to red to black. You can double-click in the animation to add magnetic field lines, click-drag the center of the loop to reposition it, and click-drag the top or bottom of the loop to change its size.

Christian, Wolfgang; Belloni, Mario

2007-03-03

152

Crustal magnetic field of Mars  

Microsoft Academic Search

The equivalent source dipole technique is used to model the three components of the Martian lithospheric magnetic field. We use magnetic field measurements made on board the Mars Global Surveyor spacecraft. Different input dipole meshes are presented and evaluated. Because there is no global, Earth-like, inducing magnetic field, the magnetization directions are solved for together with the magnetization intensity. A

B. Langlais; M. E. Purucker; M. Mandea

2004-01-01

153

Nuclear ? -decay and photoproduction of e + e ? pairs in intense electromagnetic fields with a complex configuration  

Microsoft Academic Search

The effect of an intense electromagnetic field formed by the superposition of a constant magnetic field and a laser-type field\\u000a on nuclear ?-decay and on pair production by two g-rays with different polarizations is studied. Time integral representations are obtained\\u000a for the total probabilities of these processes without restrictions on the strengths of the fields making up the configuration.\\u000a Despite

V. N. Rodionov

1998-01-01

154

Formation of Field-Reversed-Configuration Plasma with Punctuated-Betatron-Orbit Electrons  

SciTech Connect

We describe ab initio, self-consistent, 3D, fully electromagnetic numerical simulations of current drive and field-reversed-configuration plasma formation by odd-parity rotating magnetic fields (RMF{sub o}). Magnetic-separatrix formation and field reversal are attained from an initial mirror configuration. A population of punctuated-betatron-orbit electrons, generated by the RMF{sub o}, carries the majority of the field-normal azimuthal electrical current responsible for field reversal. Appreciable current and plasma pressure exist outside the magnetic separatrix whose shape is modulated by the RMF{sub o} phase. The predicted plasma density and electron energy distribution compare favorably with RMF{sub o} experiments.

Welch, D. R.; Genoni, T. C. [Voss Scientific, Albuquerque, New Mexico 87108 (United States); Cohen, S. A. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08544 (United States); Glasser, A. H. [Department of Aeronautics and Astronautics, University of Washington, Seattle, Washington 98195 (United States)

2010-07-02

155

Magnetic field structures in chemically peculiar stars  

NASA Astrophysics Data System (ADS)

We report the results of magnetic field modelling of around 50 CP stars, performed using the "magnetic charges" technique. The modelling shows that the sample reveals four main types of magnetic configurations: 1) a central dipole, 2) a dipole, shifted along the axis, 3) a dipole, shifted across the axis, and 4) complex structures. The vast majority of stars has the field structure of a dipole, shifted from the center of the star. This shift can have any direction, both along and across the axis. A small percentage of stars possess field structures, formed by two or more dipoles.

Glagolevskij, Yu. V.

2011-04-01

156

Magnetic Fields in Galaxies  

NASA Astrophysics Data System (ADS)

Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized emission traces turbulent fields which are strongest in spiral arms and bars (20-30 ?G) and in central starburst regions (50-100 ?G). Such fields are dynamically important, e.g. they can drive gas inflows in central regions. Polarized emission traces ordered fields which can be regular or anisotropic random, generated from isotropic random fields by compression or shear. The strongest ordered fields of 10-15 ?G strength are generally found in interarm regions and follow the orientation of adjacent gas spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions of starburst galaxies. Faraday rotation measures (RM) of the diffuse polarized radio emission from the disks of several spiral galaxies reveal large-scale patterns, which are signatures of regular fields generated by a mean-field dynamo. However, in most spiral galaxies observed so far the field structure is more complicated. Ordered fields in interacting galaxies have asymmetric distributions and are an excellent tracer of past interactions between galaxies or with the intergalactic medium. Ordered magnetic fields are also observed in radio halos around edge-on galaxies, out to large distances from the plane, with X-shaped patterns. Future observations of polarized emission at high frequencies, with the EVLA, the SKA and its precursors, will trace galactic magnetic fields in unprecedented detail. Low-frequency telescopes (e.g. LOFAR and MWA) are ideal to search for diffuse emission and small RMs from weak interstellar and intergalactic fields.

Beck, Rainer

2012-05-01

157

The induced magnetic field.  

PubMed

Aromaticity is indispensable for explaining a variety of chemical behaviors, including reactivity, structural features, relative energetic stabilities, and spectroscopic properties. When interpreted as the spatial delocalization of ?-electrons, it represents the driving force for the stabilization of many planar molecular structures. A delocalized electron system is sensitive to an external magnetic field; it responds with an induced magnetic field having a particularly long range. The shape of the induced magnetic field reflects the size and strength of the system of delocalized electrons and can have a large influence on neighboring molecules. In 2004, we proposed using the induced magnetic field as a means of estimating the degree of electron delocalization and aromaticity in planar as well as in nonplanar molecules. We have since tested the method on aromatic, antiaromatic, and nonaromatic compounds, and a refinement now allows the individual treatment of core-, ?-, and ?-electrons. In this Account, we describe the use of the induced magnetic field as an analytical probe for electron delocalization and its application to a large series of uncommon molecules. The compounds include borazine; all-metal aromatic systems Al(4)(n-); molecular stars Si(5)Li(n)(6-n); electronically stabilized planar tetracoordinate carbon; planar hypercoordinate atoms inside boron wheels; and planar boron wheels with fluxional internal boron cluster moieties. In all cases, we have observed that planar structures show a high degree of electron delocalization in the ?-electrons and, in some examples, also in the ?-framework. Quantitatively, the induced magnetic field has contributions from the entire electronic system of a molecule, but at long range the contributions arising from the delocalized electronic ?-system dominate. The induced magnetic field can only indirectly be confirmed by experiment, for example, through intermolecular contributions to NMR chemical shifts. We show that calculating the induced field is a useful method for understanding any planar organic or inorganic system, as it corresponds to the intuitive Pople model for explaining the anomalous proton chemical shifts in aromatic molecules. Indeed, aromatic, antiaromatic, and nonaromatic molecules show differing responses to an external field; that is, they reduce, augment, or do not affect the external field at long range. The induced field can be dissected into different orbital contributions, in the same way that the nucleus-independent chemical shift or the shielding function can be separated into component contributions. The result is a versatile tool that is particularly useful in the analysis of planar, densely packed systems with strong orbital contributions directly atop individual atoms. PMID:21848282

Islas, Rafael; Heine, Thomas; Merino, Gabriel

2011-08-17

158

Multichord optical interferometry of FRX-L's field reversed configuration  

NASA Astrophysics Data System (ADS)

A 0.633 ?m laser interferometer provides detailed time resolved information about the spatial distribution of the plasma density of field reversed configurations (FRC's) produced by the FRX-L experiment at Los Alamos National Laboratory. This experiment is an effort to produce a magnetized plasma with closed field lines suitable for compression by a solid metal liner imploded by the Shiva Star capacitor bank at the Air Force Research Laboratory. The interferometer probes a fanned array of eight chords through the FRC midplane, measuring the line integrated free electron density via its effect on optical phase shift relative to eight reference beams as a function of time. The reference beams are given nominally identical optical paths, except that they are folded for compactness and given an 80 MHz higher optical frequency by use of a Bragg cell beam splitter. After the beams are recombined, interference results in 80 MHz electromagnetic beat waves with dynamic phase shifts equal to those of the corresponding optical probes. Quadrature mixing of the electronically monitored light is then performed with rf components. Noteworthy features of the interferometer's design are the unique compact folding scheme of the reference paths, inclusion of a fused quartz tube in the reference path similar to that of the FRC's vacuum vessel to compensate for cylindrical lensing, and transmission of the interfering light via optical fibers to a rf shielded room for processing. Extraneous contributions to the phase shift due to vibration resulting from the system's pulsed magnetic field, and dynamic refractive changes in or near the fused quartz tube wall (possibly due to radiation heating) are corrected for.

Ruden, E. L.; Zhang, Shouyin; Wurden, G. A.; Intrator, T. P.; Renneke, R.; Waganaar, W. J.; Analla, F. T.; Grabowski, T. C.

2006-10-01

159

Thick Liquid-Walled, Field-Reversed Configuration  

SciTech Connect

A thick flowing layer of liquid (e.g., flibe--a molten salt, or Sn{sub 80}Li{sub 20}--a liquid metal) protects the structural walls of the field-reversed configuration (FRC) so that they can last the life of the plant even with intense 14 MeV neutron bombardment from the D-T fusion reaction. The surface temperature of the liquid rises as it passes from the inlet nozzles to the exit or receiver nozzles due to absorption of line and bremsstrahlung radiation, and neutrons. The surface temperature can be reduced by enhancement of convection near the surface to transport hot surface liquid into the cooler interior. This surface temperature must be compatible with a practical heat transport and energy recovery system. The evaporative flux from the wall driven by the surface temperature must also result in an acceptable impurity level in the core plasma. The shielding of the core by the edge plasma is modeled with a 2D transport code for the resulting impurity ions; these ions are either swept out to the distant end tanks, or diffuse to the hot plasma core. An auxiliary plasma between the edge plasma and the liquid wall can further attenuate evaporating flux of atoms and molecules by ionization. The current in this auxiliary plasma might serve as the antenna for the current drive method, which produces a rotating magnetic field. Another method of current drive uses small spheromaks injected along the magnetic fields, which additionally provide fueling along with pellet fueling if necessary.

Moir, R W; Bulmer, R H; Gulec, K; Fogarty, P; Nelson, B; Ohnishi, M; Rensink, M; Rognlien, T D; Santarious, J F; Sze, D K

2000-09-22

160

Hidden magnetic configuration in epitaxial La1-rSrzMnO3 films  

SciTech Connect

We present an unreported magnetic configuration in epitaxial La{sub 1-x}Sr{sub x}MnO{sub 3} (x {approx} 0.3) (LSMO) films grown on strontium titanate (STO). X-ray magnetic circular dichroism indicates that the remanent magnetic state of thick LSMO films is opposite to the direction of applied magnetic field. Spectroscopic and scattering measurements reveal that the average Mn valence varies from mixed Mn{sup 3+}/Mn{sup 4+} to an enriched Mn{sup 3+} region near the STO interface, resulting in a compressive lattice along a, b-axis and a possible electronic reconstruction in the Mn e{sub g} orbital (d{sub 3z{sup 2}-r{sup 2}}). This reconstruction may provide a mechanism for coupling the Mn{sup 3+} moments antiferromagnetically along the surface normal direction, and in turn may lead to the observed reversed magnetic configuration.

Kao, Chi-Chang

2011-05-23

161

Hidden magnetic configuration in epitaxial La(1-x) Sr(x) MnO3 films.  

PubMed

We present an unreported magnetic configuration in epitaxial La(1-x) Sr(x) MnO3 (x ? 0.3) (LSMO) films grown on strontium titanate (STO). X-ray magnetic circular dichroism indicates that the remanent magnetic state of thick LSMO films is opposite to the direction of the applied magnetic field. Spectroscopic and scattering measurements reveal that the average Mn valence varies from mixed Mn(3+)/Mn(4+) to an enriched Mn3+ region near the STO interface, resulting in a compressive lattice along the a, b axis and a possible electronic reconstruction in the Mn e(g) orbital (d(3)z(2)-r(2). This reconstruction may provide a mechanism for coupling the Mn3+ moments antiferromagnetically along the surface normal direction, and in turn may lead to the observed reversed magnetic configuration. PMID:21231622

Lee, J-S; Arena, D A; Yu, P; Nelson, C S; Fan, R; Kinane, C J; Langridge, S; Rossell, M D; Ramesh, R; Kao, C-C

2010-12-14

162

Hidden Magnetic Configuration in Epitaxial La1-x SrxMnO3 Films  

SciTech Connect

We present an unreported magnetic configuration in epitaxial La{sub 1-x}Sr{sub x}MnO{sub 3} (x {approx} 0.3) (LSMO) films grown on strontium titanate (STO). X-ray magnetic circular dichroism indicates that the remanent magnetic state of thick LSMO films is opposite to the direction of the applied magnetic field. Spectroscopic and scattering measurements reveal that the average Mn valence varies from mixed Mn{sup 3+}/Mn{sup 4+} to an enriched Mn{sup 3+} region near the STO interface, resulting in a compressive lattice along the a, b axis and a possible electronic reconstruction in the Mn e{sub g} orbital (d{sub 3z{sup 2}-r{sup 2}}). This reconstruction may provide a mechanism for coupling the Mn{sup 3+} moments antiferromagnetically along the surface normal direction, and in turn may lead to the observed reversed magnetic configuration.

Lee, J.S.; Arena, D.A.; Yu, P.; Nelson, C.S.; Fan, R.; Kinane, C.J.; Langridge, S.; Rossell, M.D.; Ramesh, R.; Kao, C.C.

2010-12-17

163

Magnetic field annihilators: invisible magnetization at the magnetic equator  

Microsoft Academic Search

Some distributions of magnetization give rise to magnetic fields that vanish everywhere above the surface, rendering these distributions of magnetization completely invisible. They are the annihilators of the magnetic inverse problem. Known examples are the infinite sheet with constant magnetization and the spherical shell of constant susceptibility magnetized by an arbitrary internal field. Here, we show that remarkably more interesting

S. Maus; V. Haak

2003-01-01

164

Stable magnetic fields in stellar interiors  

NASA Astrophysics Data System (ADS)

We investigate the 50-year old hypothesis that the magnetic fields of the Ap stars are stable equilibria that have survived in these stars since their formation. With numerical simulations we find that stable magnetic field configurations indeed appear to exist under the conditions in the radiative interior of a star. Confirming a hypothesis by Prendergast (1956, ApJ, 123, 498), the configurations have roughly equal poloidal and toroidal field strengths. We find that tori of such twisted fields can form as remnants of the decay of an unstable random initial field. In agreement with observations, the appearance at the surface is an approximate dipole with smaller contributions from higher multipoles, and the surface field strength can increase with the age of the star. The results of this paper were summarised by Braithwaite & Spruit (2004, Nature, 431, 891).

Braithwaite, J.; Nordlund, Å.

2006-05-01

165

Plasma acceleration in current sheets formed in helium in two- and three-dimensional magnetic configurations  

NASA Astrophysics Data System (ADS)

The processes of heating and acceleration of plasma in current sheets formed in 2D and 3D magnetic configurations with an X-line in helium plasma have been investigated using spectroscopic methods. It is found that, in 2D magnetic configurations, plasma flows with energies of 400-1000 eV, which are substantially higher than the ion thermal energy, are generated and propagate along the width (the larger transverse dimension) of the sheet. In 3D configurations, the influence of the longitudinal (directed along the X-line) component of the magnetic field on the plasma parameters in the current sheet has been studied. It is shown that plasma acceleration caused by the Ampère force can be spatially inhomogeneous in the direction perpendicular to the sheet surface, which should lead to sheared plasma flows in the sheet.

Kyrie, N. P.; Frank, A. G.

2012-12-01

166

Magnetic dipole configurations on honeycomb lattices: effect of finite size and boundaries.  

PubMed

Artificial dipolar spin-ice patterns have attracted much attention recently because of their rich configurations and excitations in the form of Dirac strings connecting magnetic monopoles. We have analysed the distribution of excitations in the form of strings and vertices carrying magnetic charges Q=±3q in honeycomb artificial spin-ice patterns. Two types of patterns are compared, those that terminate with open hexagons and those with closed hexagons. The dipole configurations and the frequency of spin-ice rule-violating Q=±3q vertices depend slightly on the boundary conditions of the pattern. Upon rotation of the patterns by 2? in a coercive magnetic field of 500 Oe, complete reversibility of the charge and string configuration is observed. PMID:23166380

Schumann, Alexandra; Zabel, Hartmut

2012-12-28

167

The role of geomagnetic field configuration in EMIC wave generation  

NASA Astrophysics Data System (ADS)

Global configuration of the geomagnetic field plays an important role in magnetospheric dynamics. We study the effect of field configuration on electromagnetic ion-cyclotron (EMIC) wave growth with test particle simulations. As an initial study, we quantitatively examine the accuracy of several empirical geomagnetic field models widely in use. We study two years characterized by very different space weather conditions: 1996 and 2003. The year 1996, at solar minimum, exhibited many high-speed streams and a few co-rotating interaction regions, but was generally quiet. In contrast, 2003 included the "Halloween storm," one of the most intense geomagnetic storms on record caused by a coronal mass ejection. The performance of each model, as measured by prediction efficiency and skill score, is evaluated as a function of magnetospheric conditions (reflected by the geomagnetic index, Kp) and magnetic local time. We subsequently developed a new MHD/particle method to study electromagnetic ion-cyclotron (EMIC) wave growth in a realistic and dynamic magnetosphere. We simulate the phase space density dynamics of warm plasma particles in magnetospheric electromagnetic fields from the global Lyon-Fedder-Mobarry (LFM) MHD code and 3D test-particle trajectories. We use these results to compute temperature anisotropies and plasma densities. We then compute the convective EMIC wave growth rate using these macroscopic plasma quantities, and thus generate a spatiotemporal picture of the growth of these waves. We use our new MHD/particle method for studying EMIC wave growth to simulate a compression event observed on 29 June 2007 and compare the results with observations from ground observatories and spacecraft measurements. We then study the time evolution of various quantities to discern physical mechanisms leading to simulated wave growth. A fairly at simulated temperature profile in time suggested an absence of energizing processes during this event. This can be explained by two possible mechanisms: temperature anisotropy induced by drift shell splitting (DSS), and the bulk execution of unusual particle trajectories called Shabansky orbits. Finally, we used test particle simulations in a static analytic model field to study the two non-energizing processes. We show that Shabansky orbits executed in bulk provide a temperature anisotropy distinct from DSS-induced temperature anisotropy, and we discuss the two origins of this new physical mechanism for anisotropy generation.

McCollough, J. P.

168

Magnetic configurations of Co(111) nanostripes with competing shape and crystalline anisotropies  

NASA Astrophysics Data System (ADS)

Nanostripes with varying widths are lithographed on Co thin films with strong magnetic anisotropy resulting from the epitaxial growth onto vicinal Si(111) substrate. The competition between magnetocrystalline and shape anisotropies is used to tune the magnetic behavior of Co nanostripes. Single domain configuration is observed for nanostructures where magnetocrystalline and shape anisotropies go along the same direction. However, more complicated configurations such as open stripe domains can be developed when both anisotropies compete. The nanostructures have been experimentally characterized by longitudinal magneto-optical Kerr effect and magnetic force microscopy (MFM). Micromagnetic simulations performed by finite-element and finite difference codes are in good agreement with the experimental results. The use of MFM based techniques such as the variable field magnetic force microscopy and the so-called three-dimensional modes has allowed us to follow the evolution of the domains and domain walls under externally applied magnetic fields, i.e., to deeply understand the magnetization reversal process in the multidomain nanostripes. In particular, the nanostripes with competing anisotropies and a high aspect ratio present vortex configuration along the domain walls which have a key role in the magnetization reversal process.

Ivanov, Yu. P.; Iglesias-Freire, O.; Pustovalov, E. V.; Chubykalo-Fesenko, O.; Asenjo, A.

2013-05-01

169

The Primordial Origin Model of Magnetic Fields in Spiral Galaxies  

NASA Astrophysics Data System (ADS)

We propose a primordial-origin model for composite configurations of global magnetic fields in spiral galaxies. We show that a uniform tilted magnetic field wound up into a rotating disk galaxy can evolve into composite magnetic configurations comprising bisymmetric spiral (S = BSS), axisymmetric spiral (A = ASS), plane-reversed spiral (PR), and/or ring (R) fields in the disk, and vertical (V) fields in the center. By MHD simulations we show that these composite galactic fields are indeed created from a weak primordial uniform field, and that different configurations can co-exist in the same galaxy. We show that spiral fields trigger the growth of two-armed gaseous arms. The centrally accumulated vertical fields are twisted and produce a jet toward the halo. We found that the more vertical was the initial uniform field, the stronger was the formed magnetic field in the galactic disk.

Sofue, Yoshiaki; Machida, Mami; Kudoh, Takahiro

2010-10-01

170

Field-reversed configuration profiles and resistivities inferred from the radial line-integral density profile  

Microsoft Academic Search

The beta and magnetic field profiles of field-reversed configurations (FRC’s) can be inferred from the radial profile of the line-integral density together with a temperature model. When these profiles are combined with the particle and flux decay times, the plasma resistivities at the field null and separatrix can also be deduced. This method is applied to a class of FRC’s

R. E. Chrien; S. Okada

1987-01-01

171

Magnetic fields generated by power lines  

Microsoft Academic Search

In this paper the authors compute the magnetic fields generated by a lot of typical power line configurations and compare these values with the results given both by analytical models and by measurements. The computations have been made by means of a flexible calculation code developed by the authors. This code overcomes some simplifying assumptions introduced in previous analytical studies.

A. Geri; A. Locatelli; G. M. Veca

1995-01-01

172

Field-reversed configuration (FRC) experiments  

SciTech Connect

FRCs with equilibrium separatrix radii up to 0.18 m have been formed and studied in FRX-C/LSM. For best formation conditions at low fill pressure, the particle confinement exceeds the predictions of LHD transport calculations by up to a factor of two; however, the inferred flux confinement is more anomalous than in smaller FRCs. Higher bias field produces axial shocks and degradation in confinement, while higher fill pressure results in gross fluting during formation. FRCs have been formed in TRX with s from 2 to 6. These relatively collisional FRCs exhibit flux lifetimes of 10 {yields} 20 kinetic growth times for the internal tilt mode. The coaxial slow source has produced annular FRCs in a coaxial coil geometry on slow time scales using low voltages. 16 refs., 4 figs., 1 tab.

Siemon, R.E.; Chrien, R.E.; Hugrass, W.N.; Okada, S.; Rej, D.J.; Taggart, D.P.; Tuszewski, M.; Webster, R.B.; Wright, B.L.; Slough, J.T.; Crawford, E.A.; Hoffman, A.L.; Milroy, R.D.; Vlases, G.C.; Brooks, R.D.; Kronast, B.; Pietrzyk, Z.A.; Raman, R.; Smith, R.

1988-01-01

173

Classical field configurations and infrared slavery  

NASA Astrophysics Data System (ADS)

The problem of determining the energy of two spinor particles interacting through massless-particle exchange is analyzed using the path-integral method. A form for the long-range interaction energy is obtained by analyzing an abridged vertex derived from the parent theory. This abridged vertex describes the radiation of zero-momentum particles by pointlike sources. A path-integral formalism for calculating the energy of the radiation field associated with this abridged vertex is developed and applications are made to determine the energy necessary for adiabatic separation of two sources in quantum electrodynamics and for an SU(2) Yang-Mills theory. The latter theory is shown to be consistent with confinement via infrared slavery.

Swanson, Mark S.

1987-09-01

174

Magnetic Field Measurements in Beam Guiding Magnets  

Microsoft Academic Search

Electromagnets used as beam guiding elements in particle accelerators and colliders require very tight tole-rances on their magnetic fields and on their alignment along the particle path. This article describes the methods and equipment used for magnetic measurements in beam transport magnets. Descriptions are given of magnetic resonance techniques, various induction coil methods, Hall generator measurements, the fluxgate magnetometer as

K. N. Henrichsen

1998-01-01

175

Magnetic Field Issues in Magnetic Resonance Imaging.  

NASA Astrophysics Data System (ADS)

Advances in Magnetic Resonance Imaging depend on the capability of the available hardware. Specifically, for the main magnet configuration, using derivative constraints, we can create a static magnetic field with reduced levels of inhomogeneity over a prescribed imaging volume. In the gradient coil, the entire design for the axial elliptical coil, and the mathematical foundation for the transverse elliptical coil have been presented. Also, the design of a self-shielded cylindrical gradient coil with a restricted length has been presented. In order to generate gradient coils adequate for head imaging without including the human shoulders in the design, asymmetric cylindrical coils in which the gradient center is shifted axially towards the end of a finite cylinder have been introduced and theoretical as well as experimental results have been presented. In order to eliminate eddy current effects in the design of the non-shielded asymmetric gradient coils, the self-shielded asymmetric cylindrical gradient coil geometry has been introduced. Continuing the development of novel geometries for the gradient coils, the complete set of self-shielded cylindrical gradient coils, which are designed such that the x component of the magnetic field varies linearly along the three traditional gradient axes, has been presented. In order to understand the behavior of the rf field inside a dielectric object, a mathematical model is briefly presented. Although specific methods can provide an indication of the rf behavior inside a loosely dielectric object, finite element methodology is the ultimate approach for modeling the human torso and generating an accurate picture for the shape of the rf field inside this dielectric object. For this purpose we have developed a 3D finite element model, using the Coulomb gauge condition as a constraint. Agreement with the heterogeneous multilayer planar model has been established, while agreement with theoretical results from the spherical model and experimental results from the cylindrical model at 170 M H z is very good and provides an encouraging sign for using this finite element approach for modeling the rf inside the human body. (Abstract shortened by UMI.).

Petropoulos, Labros Spiridon

176

The Heliospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

The Heliospheric Magnetic Field (HMF) is the physical framework in which energetic particles and cosmic rays propagate. Changes in the large scale structure of the magnetic field lead to short- and long term changes in cosmic ray intensities, in particular in anti-phase with solar activity. The origin of the HMF in the corona is well understood and inner heliospheric observations can generally be linked to their coronal sources. The structure of heliospheric magnetic polarities and the heliospheric current sheet separating the dominant solar polarities are reviewed here over longer than a solar cycle, using the three dimensional heliospheric observations by Ulysses. The dynamics of the HMF around solar minimum activity is reviewed and the development of stream interaction regions following the stable flow patterns of fast and slow solar wind in the inner heliosphere is described. The complex dynamics that affects the evolution of the stream interaction regions leads to a more chaotic structure of the HMF in the outer heliosphere is described and discussed on the basis of the Voyager observations. Around solar maximum, solar activity is dominated by frequent transients, resulting in the interplanetary counterparts of Coronal Mass Ejections (ICMEs). These produce a complex aperiodic pattern of structures in the inner heliosphere, at all heliolatitudes. These structures continue to interact and evolve as they travel to the outer heliosphere. However, linking the observations in the inner and outer heliospheres is possible in the case of the largest solar transients that, despite their evolutions, remain recognizably large structures and lead to the formation of Merged Interaction Regions (MIRs) that may well form a quasi-spherical, "global" shell of enhanced magnetic fields around the Sun at large distances. For the transport of energetic particles and cosmic rays, the fluctuations in the magnetic field and their description in alternative turbulent models remains a very important research topic. These are also briefly reviewed in this paper.

Balogh, André; Erdõs, Géza

2013-06-01

177

Vacuum magnetic field mapping experiments for validated determination of the helical field coil location in stellarators  

SciTech Connect

Understanding the behavior of plasmas in magnetic confinement fusion devices typically requires accurate knowledge of the magnetic field structure. In stellarator-type confinement devices, the helical magnetic field is produced by currents in external coils and may be traced experimentally in the absence of plasma through the experimental technique of vacuum magnetic field mapping. Field mapping experiments, such as these, were performed on the recently constructed compact toroidal hybrid to verify the range of accessible magnetic configurations, compare the actual magnetic configuration with the design configuration, and identify any vacuum field errors that lead to perturbations of the vacuum magnetic flux surfaces. Furthermore, through the use of a new coil optimization routine, modifications are made to the simulation coil model such that better agreement exists between the experimental and simulation results. An outline of the optimization procedure is discussed in conjunction with the results of one such optimization process performed on the helical field coil.

Peterson, J.; Hanson, J.; Hartwell, G.; Knowlton, S. [Department of Physics, Auburn University, Auburn, Alabama 36849 (United States)

2010-03-15

178

Effect of Crossed Magnetic Field on Ozone Production in Air  

Microsoft Academic Search

An application of magnetic field, B to a discharge chamber under transverse electric field, E is studied, with the objective to view the effect of magnetic field to the electrons in a plasma. Theory of gas discharge stated that this configuration will create a helical motion to electrons due to gradient drift or gyration. Experimental result from previous research showed,

Z. Buntat; I. R. Smith; N. A. M. Razali

2009-01-01

179

Magnetic fields and cancer  

SciTech Connect

This letter is a response to an article by Savitz and Kaune, EHP 101:76-80. W-L wire code was applied to data from a 1988 Denver study, and an association was reported between high W-L wire code and childhood cancer. This author discusses several studies and provides explanations which weakens the argument that classification error resulted in an appreciable reduction in the association between W-L high wire code and childhood cancer. In conclusion, the fact that new wire code is only weakly correlated with magnetic field measurements (in the same manner as the original W-L wire code) suggests that the newly reported stronger association with childhood cancer is likely due to factors other than magnetic fields. Differential residential mobility and differential residential age are two possible explanations and are suggestive that the reported association may be false.

Jones, T.L.

1993-10-01

180

A flexible and configurable system to test accelerator magnets  

SciTech Connect

Fermilab's accelerator magnet R and D programs, including production of superconducting high gradient quadrupoles for the LHC insertion regions, require rigorous yet flexible magnetic measurement systems. Measurement systems must be capable of handling various types of hardware and extensible to all measurement technologies and analysis algorithms. A tailorable software system that satisfies these requirements is discussed. This single system, capable of distributed parallel signal processing, is built on top of a flexible component-based framework that allows for easy reconfiguration and run-time modification. Both core and domain-specific components can be assembled into various magnet test or analysis systems. The system configured to comprise a rotating coil harmonics measurement is presented. Technologies as Java, OODB, XML, JavaBeans, software bus and component-based architectures are used.

Jerzy M. Nogiec et al.

2001-07-20

181

Magnetic Field Extrapolations And Current Sheets  

NASA Astrophysics Data System (ADS)

Solar flares and coronal mass ejections (CMEs) --- phenomena which impact our society, but are scientifically interesting in themselves --- are driven by free magnetic energy in the coronal magnetic field. Since the coronal magnetic field cannot be directly measured, modelers often extrapolate the coronal field from the photospheric magnetograms --- the only field measurements routinely available. The best extrapolation techniques assume that the field is force free (coronal currents parallel the magnetic field), but that currents are not simply a linear function of the magnetic field. Recent tests, however, suggest that such non-linear force-free field (NLFFF) extrapolation techniques often underestimate free magnetic energy. We hypothesize that, since relaxation-based NLFFF techniques tend to smooth field discontinuities, such approaches will fail when current sheets are present. Here, we test this hypothesis by applying the Optimization NLFFF method to two configurations from an MHD simulation --- one with strong current concentrations, and one with weak concentrations. This work is supported by a NASA Sun-Earth Connections Theory grant to UC-Berkeley.

Welsch, Brian; De Moortel, I.; McTiernan, J. M.

2007-05-01

182

Magnetization reversal in ultrashort magnetic field pulses  

NASA Astrophysics Data System (ADS)

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

Bauer, M.; Lopusnik, R.; Fassbender, J.; Hillebrands, B.

2000-08-01

183

Magnetic Field Problem: Current and Magnets  

NSDL National Science Digital Library

The above animations represent two typical bar magnets each with a North and South pole. The arrows represent the direction of the magnetic field. A wire is placed between the magnets and a current that comes out of the page can be turned on.

Christian, Wolfgang; Belloni, Mario

2007-03-03

184

Two Types of Magnetic Reconnection in Coronal Bright Points and the Corresponding Magnetic Configuration  

NASA Astrophysics Data System (ADS)

Coronal bright points (CBPs) are long-lived small-scale brightenings in the solar corona. They are generally explained by magnetic reconnection. However, the corresponding magnetic configurations are not well understood. We carry out a detailed multi-wavelength analysis of two neighboring CBPs on 2007 March 16, observed in soft X-ray (SXR) and EUV channels. It is seen that the SXR light curves present quasi-periodic flashes with an interval of ~1 hr superposed over the long-lived mild brightenings, suggesting that the SXR brightenings of this type of CBPs might consist of two components: one is the gentle brightenings and the other is the CBP flashes. It is found that the strong flashes of the bigger CBP are always accompanied by SXR jets. The potential field extrapolation indicates that both CBPs are covered by a dome-like separatrix surface, with a magnetic null point above. We propose that the repetitive CBP flashes, as well as the recurrent SXR jets, result from the impulsive null-point reconnection, while the long-lived brightenings are due to the interchange reconnection along the separatrix surface. Although the EUV images at high-temperature lines resemble the SXR appearance, the 171 Å and 195 Å channels reveal that the blurry CBP in SXR consists of a cusp-shaped loop and several separate bright patches, which are explained to be due to the null-point reconnection and the separatrix reconnection, respectively.

Zhang, Q. M.; Chen, P. F.; Guo, Y.; Fang, C.; Ding, M. D.

2012-02-01

185

TWO TYPES OF MAGNETIC RECONNECTION IN CORONAL BRIGHT POINTS AND THE CORRESPONDING MAGNETIC CONFIGURATION  

SciTech Connect

Coronal bright points (CBPs) are long-lived small-scale brightenings in the solar corona. They are generally explained by magnetic reconnection. However, the corresponding magnetic configurations are not well understood. We carry out a detailed multi-wavelength analysis of two neighboring CBPs on 2007 March 16, observed in soft X-ray (SXR) and EUV channels. It is seen that the SXR light curves present quasi-periodic flashes with an interval of {approx}1 hr superposed over the long-lived mild brightenings, suggesting that the SXR brightenings of this type of CBPs might consist of two components: one is the gentle brightenings and the other is the CBP flashes. It is found that the strong flashes of the bigger CBP are always accompanied by SXR jets. The potential field extrapolation indicates that both CBPs are covered by a dome-like separatrix surface, with a magnetic null point above. We propose that the repetitive CBP flashes, as well as the recurrent SXR jets, result from the impulsive null-point reconnection, while the long-lived brightenings are due to the interchange reconnection along the separatrix surface. Although the EUV images at high-temperature lines resemble the SXR appearance, the 171 Angstrom-Sign and 195 Angstrom-Sign channels reveal that the blurry CBP in SXR consists of a cusp-shaped loop and several separate bright patches, which are explained to be due to the null-point reconnection and the separatrix reconnection, respectively.

Zhang, Q. M.; Chen, P. F.; Guo, Y.; Fang, C.; Ding, M. D., E-mail: chenpf@nju.edu.cn [Department of Astronomy, Nanjing University, Nanjing 210093 (China)

2012-02-10

186

D-3He fuels in a field-reversed configuration  

NASA Astrophysics Data System (ADS)

Favorable features of the D-He(3) fuel cycle in a field-reversed configuration are described. Based on a theoretical analysis, it was found that the estimated plant efficiency is more than 70 percent and the 14 MeV neutron power fraction is as small as 1 percent. To reach the D-He(3) initiation temperature of 100 keV with a reasonable external power source, a D-T configuration can first be ignited and then the fuel altered to D-3He. Heating of the plasma is attributed to energetic fusion charged particles and no additional heating is necessary. The equilibria of D-3He ignited plasmas may be self-sustained due to the preferential trapping of fusion protons in a field-reversed configuration.

Momota, Hiromu; Okamoto, Masao; Nomura, Yasuyuki; Ohnishi, Masami; Berk, Herbert L.; Tajima, Toshiki

1987-11-01

187

Integrated semiconductor magnetic field sensors  

Microsoft Academic Search

Recent developments in integrated silicon magnetic devices are reviewed, with particular attention given to integrated Hall plates, magnetic field-effect transistors, vertical and lateral bipolar magnetotransistors, magnetodiodes, and current-domain magnetometers. Also described are current developments in integrated magnetic field sensors based on III-V semiconductors and bulk Hall-effect devices. The discussion also covers magnetic device modeling and the incorporation of magnetic devices

H. P. Baltes; R. S. Popovic

1986-01-01

188

Where will efficient energy release occur in 3D magnetic configurations?  

NASA Astrophysics Data System (ADS)

The energy needed to power flares is thought to be stored in the coronal magnetic field However the energy release which results in thermal energy brightenings is efficient only at very small scales Magnetic configurations with a complex topology i e with separatrices are the most obvious configurations where current layers then reconnection can efficiently occur This has been confirmed for several flares by computing the coronal field and by comparing the locations of the flare loops and ribbons to the deduced 3D magnetic topology However this view is too restrictive taking into account the variety of observed solar flaring configurations Indeed Quasi-Separatrix Layers QSLs which are regions where there is a drastic change in field-line linkage generalize the definition of separatrices They permit us to understand where reconnection occurs in a broader variety of flares than separatrices do The location where the QSL are the thinnest called Hyperbolic Flux Tube HFT is the location for the strongest electric field and current being generated This is a good candidate for the region where particle acceleration can occur efficiently

Demoulin, P.

189

Directed Plasma Flow across Magnetic Field  

NASA Astrophysics Data System (ADS)

The Hall effect plays a significant role in the penetration of plasma flows across magnetic field. For example, its effect may become dominant in the solar wind penetration into the magnetosphere, in the magnetic field advection in wire array z-pinch precursors, or in the arcing of magnetically insulated transmission lines. An experiment performed at the Nevada Terawatt Facility explored the penetration of plasma with large Hall parameter (˜10) across ambient magnetic field. The plasma was produced by ablation with the short pulse high intensity laser Leopard (0.35 ps, 10^17W/cm^2) and the magnetic field with the pulsed power generator Zebra (50 T). The expanding plasma assumed a jet configuration and propagated beyond a distance consistent with a diamagnetic bubble model. Without magnetic field, the plasma expansion was close to hemispherical. The ability to produce the plasma and the magnetic field with distinct generators allows a controlled, quasi-continuous variation of the Hall parameter and other plasma parameters making the experiments useful for benchmarking numerical simulations.

Presura, R.; Stepanenko, Y.; Neff, S.; Sotnikov, V. I.

2008-04-01

190

Planetary magnetic fields  

NASA Astrophysics Data System (ADS)

The past several years have seen dramatic developments in the study of planetary magnetic fields, including a wealth of new data, mainly from the Galilean satellites and Mars, together with major improvements in our theoretical modeling effort of the dynamo process believed responsible for large planetary fields. These dynamos arise from thermal or compositional convection in fluid regions of large radial extent. The relevant electrical conductivities range from metallic values to values that may be only about 1% or less that of a typical metal, appropriate to ionic fluids and semiconductors. In all planets, the Coriolis force is dynamically important, but slow rotation may be more favorable for a dynamo than fast rotation. The maintenance and persistence of convection appears to be easy in gas giants and ice-rich giants, but is not assured in terrestrial planets because the quite high electrical conductivity of iron-rich cores guarantees a high thermal conductivity (through the Wiedemann-Franz law), which allows for a large core heat flow by conduction alone. In this sense, high electrical conductivity is unfavorable for a dynamo in a metallic core. Planetary dynamos mostly appear to operate with an internal field ~(2??/?)1/2 where ? is the fluid density, ? is the planetary rotation rate and ? is the conductivity (SI units). Earth, Ganymede, Jupiter, Saturn, Uranus, Neptune, and maybe Mercury have dynamos, Mars has large remanent magnetism from an ancient dynamo, and the Moon might also require an ancient dynamo. Venus is devoid of a detectable global field but may have had a dynamo in the past. The presence or absence of a dynamo in a terrestrial body (including Ganymede) appears to depend mainly on the thermal histories and energy sources of these bodies, especially the convective state of the silicate mantle and the existence and history of a growing inner solid core. Induced fields observed in Europa and Callisto indicate the strong likelihood of water oceans in these bodies.

Stevenson, David J.

2003-03-01

191

Particle confinement scaling in field-reversed configurations  

SciTech Connect

The particle confinement time in field-reversed configurations has been experimentally investigated in the FRX-C device. The measured confinement times of 70 to 190 ..mu..s are consistent with R/sup 2//rho/sub i0/ scaling and are in good agreement with theoretical predictions of lower-hybrid-drift--induced particle transport.

McKenna, K.F.; Armstrong, W.T.; Bartsch, R.R.

1983-05-30

192

Thick Liquid-Walled, Field-Reversed Configuration.  

National Technical Information Service (NTIS)

A thick flowing layer of liquid protects the structural walls of the field-reversed configuration (FRC) so that they can last the life of the plant even with intense 14 MeV neutron bombardment from the D-T fusion reaction. The surface temperature of the l...

R. W. Moir R. H. Bulmer K. Gulec P. Fogarty B. Nelson M. Ohnishi

2000-01-01

193

New magnetic configuration in paramagnetic phase of HoCo2  

NASA Astrophysics Data System (ADS)

X-ray magnetic circular dichroism (XMCD) measurements on HoCo2 reveal the inversion of Co moment at temperatures higher than the critical temperature, Tc, showing that the net magnetization under a field of the Ho and Co sublattices remain antiparallel even above Tc. The Ho moment also changes its orientation to align antiparallel to the applied field at high temperature giving rise to a new magnetic configuration in the paramagnetic regime. Transverse susceptibility (TS) and small angle neutron scattering (SANS) measurements performed above Tc indicate the existence of sizable magnetic short-range correlated regions in HoCo2. First principles calculations based on spin polarized local-density approximation, LSDA+U havebeen performed to obtain insights on the origin of the short-range correlated volume.

Bonilla, C. M.; Calvo, I.; Herrero-Albillos, J.; Figueroa, A. I.; Castan-Guerrero, C.; Bartolomé, J.; Rodriguez-Velamazan, J. A.; Schmitz, D.; Weschke, E.; Paudyal, D.; Pecharsky, V. K.; Gschneidner, K. A.; Bartolomé, F.; García, L. M.

2012-04-01

194

Tunable surface plasmon polaritons in metal-strip waveguides with magnetized semiconductor substrates in Voigt configuration  

NASA Astrophysics Data System (ADS)

The properties of surface plasmon polaritons (SPPs) in a magnetically tunable strip waveguide geometry comprising of a metal film of finite width deposited on a magnetized semiconductor and covered by an isotropic dielectric material were studied in Voigt configuration. The method of lines was used to compute the dispersion relation of fundamental modes, and the dependence of the propagation constant on metal film dimensions, material parameters and biasing magnetic field was considered. The bounded SPPs are nonreciprocal with respect to the direction of the biasing magnetic field, producing a nonreciprocal phase shift of the order of 2-18 rad mm-1 at a wavelength of excitation 1.55 ?m. Moreover, controlled propagation of SPP modes and their effective tuning are possible in this strip geometry, which enables the design and development of tunable optoelectronic devices.

Mathew, Gishamol; Mathew, Vincent

2012-05-01

195

Local deformations of ferrogels induced by uniform magnetic fields  

Microsoft Academic Search

In this work we present anisotropic light scattering measurements of local deformation in systems composed by a dispersion of nanometric magnetic particles in a polymer gel, or ferrogel, in the presence of uniform magnetic fields. Two experimental configurations were used in which the scattering vector q was parallel and perpendicular to the magnetic induction B. We have seen that the

Alvaro V. Teixeira; Pedro Licinio

2005-01-01

196

Plasma Dynamics in Pulsed Strong Magnetic Fields  

NASA Astrophysics Data System (ADS)

We describe recent studies of the interaction of fast-rising magnetic fields with multi-species plasmas of densities 10^13-10^15 cm-3. The configurations studied are planar or coaxial gaps, prefilled with plasmas that are driven by 80-400 ns current pulses. The diagnostics is based on time-dependent spectroscopic observations that are spatially resolved in 3D using plasma-doping techniques. The measurements include the magnetic-field structure (from Zeeman splitting), ion velocity distributions (from Doppler profiles), electric fields (from line shapes of allowed and forbidden transitions), and non-Maxwellian electron energy distribution (from line ratios). It is found that the magnetic field propagates in the plasma faster than expected from diffusion. Also, the field spatial distribution is inconsistent with diffusion. The observed broad current channel, as well as non-dependence of the magnetic field evolution on the current polarity, cannot be explained by the available Hall-field theories. Moreover, detailed observations reveal that magnetic field penetration and plasma reflection occur simultaneously, leading to ion-species separation [1, 2], which are also not predicted by Hall-field theories. Measurements of the reflected-proton velocities (twice the magnetic field velocity) show that the protons dissipate a significant fraction of the magnetic field energy. A possible mechanism previously formulated for astrophysical plasmas, based on the formation of small-scale density fluctuations (perhaps as a result of the Rayleigh-Taylor instability) that lead to field penetration via the Hall mechanism, has recently been suggested. The new phenomena observed require novel theoretical treatments. Applications include plasmas under high currents and space physics. 1. A. Weingarten et al., Phys. Rev. Lett. 87, 115004 (2001). 2. R. Arad, et al., Phys. Plasmas 10, 112 (2003).

Maron, Yitzhak

2003-10-01

197

The ASTROMAG superconducting magnet facility configured for a free flying satellite  

SciTech Connect

ASTROMAG is a particle astrophysics facility that was originally configured for the Space Station. The heart of the ASTROMAG facility is a large superconducting magnet which is cooled using superfluid helium. The task of resizing the facility so that it will fly in a satellite in a high angle of inclination orbit is driven by the launch weight capability of the launch rocket and the desire to be able to do nearly the same physics as the Space Station version of ASTROMAG. In order to reduce the launch weight, the magnet and its cryogenic system had to be downsized, yet the integrated field generated by the magnet in the particle detectors has to match the Space Station version of the magnet. The use of aluminum matrix superconductor and oriented composite materials in the magnet insulation permits one to achieve this goal. The net magnetic dipole moment from the ASTROMAG magnet must be small to minimize the torque due to interaction with the earth's magnetic field. The ASTROMAG magnet consists of identical two coils 1.67 meters apart. The two coils are connected in series in persistent mode. Each coil is designed to carry 2.34 million ampere turns. Both coils are mounted on the same magnetic axis and they operate at opposite polarity. This reduces the dipole moment by a factor of more than 1000. This is tolerable for the Space Station version of the magnet. A magnet operating on a free flying satellite requires additional compensation. This report presents the magnet parameters of a free flying version of ASTROMAG and the parameters of the space cryogenic system for the magnet. 12 refs., 6 figs.

Green, M.A.; Smoot, G.F.

1991-06-01

198

Magnetic connectivity of coronal fields: geometrical versus topological description  

Microsoft Academic Search

We analyse the mapping produced by the field lines which connect photospheric areas of positive and negative magnetic polarity on the Sun. The geometrical quantities independent of the direction of such a mapping (from positive to negative polarity, and vice versa) are introduced. They yield a complete description of the field line connectivity in coronal magnetic configurations and, in particular,

V. S. Titov; G. Hornig

2002-01-01

199

Tailoring magnetic field gradient design to magnet cryostat geometry.  

PubMed

Eddy currents induced within a magnetic resonance imaging (MRI) cryostat bore during pulsing of gradient coils can be applied constructively together with the gradient currents that generate them, to obtain good quality gradient uniformities within a specified imaging volume over time. This can be achieved by simultaneously optimizing the spatial distribution and temporal pre-emphasis of the gradient coil current, to account for the spatial and temporal variation of the secondary magnetic fields due to the induced eddy currents. This method allows the tailored design of gradient coil/magnet configurations and consequent engineering trade-offs. To compute the transient eddy currents within a realistic cryostat vessel, a low-frequency finite-difference time-domain (FDTD) method using total-field scattered-field (TFSF) scheme has been performed and validated. PMID:17945575

Trakic, A; Liu, F; Lopez, H S; Wang, H; Crozier, S

2006-01-01

200

Fast superconducting magnetic field switch  

DOEpatents

The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater that the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles. 6 figs.

Goren, Y.; Mahale, N.K.

1996-08-06

201

Detection of electric field around field-reversed configuration plasma  

SciTech Connect

Electric-field probes consisting of copper plates are developed to measure electric fields in a vacuum region around a plasma. The probes detect oscillating electric fields with a maximum strength of approximately 100 V/m through a discharge. Reproducible signals from the probes are obtained with an unstable phase dominated by a rotational instability. It is found that the azimuthal structure of the electric field can be explained by the sum of an n=2 mode charge distribution and a convex-surface electron distribution on the deformed separatrix at the unstable phase. The former distribution agrees with that anticipated from the diamagnetic drift motions of plasma when the rotational instability occurs. The latter distribution suggests that an electron-rich plasma covers the separatrix.

Ikeyama, Taeko; Hiroi, Masanori; Nogi, Yasuyuki [College of Science and Technology, Nihon University, Tokyo 101-8308 (Japan); Ohkuma, Yasunori [College of Industrial Technology, Nihon University, Chiba 275-8576 (Japan)

2010-01-15

202

Evolution of twisted magnetic fields  

SciTech Connect

The magnetic field of the solar corona evolves quasistatically in response to slowly changing photospheric boundary conditions. The magnetic topology is preserved by the low resistivity of the solar atmosphere. We show that a magnetic flux coordinate system simplifies the problem of calculating field evolution with invariant topology. As an example, we calculate the equilibrium of a thin magnetic flux tube with small twist per unit length.

Zweibel, E.G.; Boozer, A.H.

1985-02-01

203

Exposure guidelines for magnetic fields  

SciTech Connect

The powerful magnetic fields produced by a controlled fusion experiment at Lawrence Livermore National Laboratory (LLNL) necessitated the development of personnel-exposure guidelines for steady magnetic fields. A literature search and conversations with active researchers showed that it is currently possible to develop preliminary exposure guidelines for steady magnetic fields. An overview of the results of past research into the bioeffects of magnetic fields was compiled, along with a discussion of hazards that may be encountered by people with sickle-cell anemia or medical electronic and prosthetic implants. The LLNL steady magnetic-field exposure guidelines along with a review of developments concerning the safety of time-varying fields were also presented in this compilation. Guidelines developed elsewhere for time varying fields were also given. Further research is needed to develop exposure standards for both steady or time-varying fields.

Miller, G.

1987-12-01

204

Microprobe for Measuring Magnetic Fields  

Microsoft Academic Search

The Hall effect has been widely utilized to measure magnetic fields. The relatively simple geometry of a Hall element suggested the use of such a device on a microscale as a probe to examine magnetic fields of small structures. Hall probes are described which were constructed with a sensitive area about 10×10 ?. Fields of less than 0.01 gauss were

D. D. Roshon Jr.

1962-01-01

205

Magnetic fields in galactic jets  

Microsoft Academic Search

The jet region of M87 is discussed to illustrate the astrophysical observations of radio sources, with note made of magnetic field phenomena contributing to radio frequency emissions. The jet appearing in M87 has been modelled as a continuous supersonic flow of plasma embedded in a self-consistent, ordered magnetic field. The field has both parallel and helical components, and may work

A. Ferrari

1982-01-01

206

Protogalactic evolution and magnetic fields  

Microsoft Academic Search

We show that the relatively strong magnetic fields ($\\\\ge 1 \\\\mu$G) in high\\u000aredshift objects can be explained by the combined action of an evolving\\u000aprotogalactic fluctuation and electrodynamic processes providing the magnetic\\u000aseed fields. Three different seed field mechanisms are reviewed and\\u000aincorporated into a spherical \\

Harald Lesch; Masashi Chiba

1994-01-01

207

Protogalactic evolution and magnetic fields  

Microsoft Academic Search

We show that the relatively strong magnetic fields (>=1muG) in high redshift objects can be explained by the combined action of an evolving protogalactic fluctuation and electrodynamic processes providing the magnetic seed fields. Three different seed field mechanisms are reviewed and incorporated into a spherical \\

H. Lesch; M. Chiba

1995-01-01

208

Magnetic-field-dosimetry system  

DOEpatents

A device is provided for measuring the magnetic field dose and peak field exposure. The device includes three Hall-effect sensors all perpendicular to each other, sensing the three dimensional magnetic field and associated electronics for data storage, calculating, retrieving and display.

Lemon, D.K.; Skorpik, J.R.; Eick, J.L.

1981-01-21

209

Transport in a stochastic magnetic field  

SciTech Connect

Collisional heat transport in a stochastic magnetic field configuration is investigated. Well above stochastic threshold, a numerical solution of a Chirikov-Taylor model shows a short-time nonlocal regime, but at large time the Rechester-Rosenbluth effective diffusion is confirmed. Near stochastic threshold, subdiffusive behavior is observed for short mean free paths. The nature of this subdiffusive behavior is understood in terms of the spectrum of islands in the stochastic sea.

White, R.B.; Wu, Yanlin [Princeton Univ., NJ (United States). Plasma Physics Lab.; Rax, J.M. [Association Euratom-CEA, Centre d`Etudes Nucleaires de Cadarache, 13 -Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee

1992-09-01

210

Transport in a stochastic magnetic field  

SciTech Connect

Collisional heat transport in a stochastic magnetic field configuration is investigated. Well above stochastic threshold, a numerical solution of a Chirikov-Taylor model shows a short-time nonlocal regime, but at large time the Rechester-Rosenbluth effective diffusion is confirmed. Near stochastic threshold, subdiffusive behavior is observed for short mean free paths. The nature of this subdiffusive behavior is understood in terms of the spectrum of islands in the stochastic sea.

White, R.B.; Wu, Yanlin (Princeton Univ., NJ (United States). Plasma Physics Lab.); Rax, J.M. (Association Euratom-CEA, Centre d'Etudes Nucleaires de Cadarache, 13 -Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee)

1992-01-01

211

Magnetic field draping about coronal mass ejecta  

SciTech Connect

Fast coronal mass ejecta (CMEs) accelerate and deflect the slower moving solar wind plasma which piles up ahead of them as they propagate out through the heliosphere. This acceleration and deflection, in turn, causes the interplanetary magnetic field (IMF) imbedded in the upstream solar wind to drape about the ejecta. Draping should cause substantial out-of-the-ecliptic magnetic fields at some locations ahead of CMEs, and radial fields behind and along the flanks. At the Earth, draping can be an important factor in the generation of some magnetic storms and substorms, while in the outer heliosphere draping may produce very large magnetotail-like configurations, somewhat analogous to those observed behind Venus and comets. 17 refs.

McComas, D.J.; Gosling, J.T.

1987-01-01

212

Magnetic Field Topology and Observed Energy Release Locations  

NASA Astrophysics Data System (ADS)

The magnetic field is thought to be the source of the energy release in many and varied observed coronal phenomena, from the less energetic coronal heating to the most violent flares and prominence eruptions. These phenomena involve not only very different scales from the energetic, but also from the temporal, point of view. Magnetic field reconnection, which is efficient only at very small spatial scales, has been the energy release mechanism that has been so far proposed. From a theoretical point of view, magnetic configurations with a complex topology, i.e. having separatrices, are the ones where current sheets can form in 2D. When going to 3D, and if the photospheric magnetic field is described by a series of isolated polarities (surrounded by field free regions), a complete topological description is given by the skeleton formed by null points, spines, fans and separators, and associated separatrices. However, if the photosphere is fully magnetized, most of the above topological structures disappear: only separatrices associated to coronal magnetic nulls remain. An extra set of separatrices is associated to the field lines curved up above the photosphere (defining the bald-patch locations). For some observed magnetic configurations, those topological structures are enough to understand where flare brightenings appear as a result of magnetic field reconnection. However, solar active phenomena are seen to occur also in a larger variety of configurations. Quasi-separatrix layers, which are regions where there is a drastic change in field-line linkage, generalize the concept of separatrices to magnetic configurations without magnetic null points and bald patches. We will review examples of observed flaring regions and their topologies that show us that magnetic reconnection can occur in wider variety of magnetic configurations than traditionally thought.

Mandrini, C. H.

2006-08-01

213

Magnetic fields with photon beams: Monte Carlo calculations for a model magnetic field.  

PubMed

Strong transverse magnetic fields can produce very large dose enhancements and reductions in localized regions of a patient under irradiation by a photon beam. We have suggested a model magnetic field which can be expected to produce such large dose enhancements and reductions, and we have carried out EGS4 Monte Carlo calculations to examine this effect for a 6x6 cm2 photon beam of energy 15, 30, or 45 MV penetrating a water phantom. Our model magnetic field has a nominal (center) strength B0 ranging between 1 and 5 T, and a maximum strength within the geometric beam which is 2.2xB0. For all three beam energies, there is significant dose enhancement for B0 = 2 T which increases greatly for B0 = 3 T, but stronger magnetic fields increase the enhancement further only for the 45-MV beam. Correspondingly, there is major reduction in the dose just distal to this region of large dose enhancement, resulting from secondary electrons and positrons originating upstream which are depositing energy in the dose-enhancement region rather than continuing further into the patient. The dose peak region is fairly narrow (in depth), but the magnetic field can be shifted along the longitudinal axis to produce a flat peak region of medium width (approximately 2 cm) or of large width (approximately 4 cm), with rapid dose dropoffs on either side. For the 30-MV beam with B0 = 3 T, we found a dose enhancement of 55% for the narrow-width configuration, 32% for the medium-width configuration, and 23% for the large-width configuration; for the 45-MV beam with B0 = 3 T, the enhancements were quite similar, but for the 15-MV beam they were considerably less. For all of these 30-MV configurations, the dose reductions were approximately 30%, and they were approximately 40% for the 45-MV configurations. PMID:11190956

Jette, D

2000-12-01

214

On the nonintegrability of magnetic field lines  

NASA Astrophysics Data System (ADS)

We prove the existence of a magnetic field created by a planar configuration of piecewise rectilinear wires which is not holomorphically integrable when considered as a vector field in C3. This is a counterexample to the S. Stefanescu conjecture (1986) in the holomorphic setting. In particular the method of the proof gives an easy way of showing that the corresponding real vector field does not admit a real polynomial first integral which provides also an alternative way of contradicting the Stefanescu conjecture in the polynomial setting.

Mahdi, Adam; Valls, Claudia

2013-05-01

215

Heat pipes for use in a magnetic field  

DOEpatents

A heat pipe configuration is described for use in a magnetic field environment of a fusion reactor. Heat pipes for operation in a magnetic field when liquid metal working fluids are used are optimized by flattening of the heat pipes having an unobstructed annulus which significantly reduces the adverse side region effect of the prior known cylindrically configured heat pipes. The flattened heat pipes operating in a magnetic field can remove 2 to 3 times the heat as a cylindrical heat pipe of the same cross sectional area.

Werner, R.W.; Hoffman, M.A.

1981-04-29

216

Heat pipes for use in a magnetic field  

DOEpatents

A heat pipe configuration for use in a magnetic field environment of a fusion reactor. Heat pipes for operation in a magnetic field when liquid metal working fluids are used are optimized by flattening of the heat pipes having an unobstructed annulus which significantly reduces the adverse side region effect of the prior known cylindrically configured heat pipes. The flattened heat pipes operating in a magnetic field can remove 2--3 times the heat as a cylindrical heat pipe of the same cross sectional area.

Werner, Richard W. (San Ramon, CA); Hoffman, Myron A. (Davis, CA)

1983-01-01

217

Inhomogeneous field configurations and the electroweak phase transition  

Microsoft Academic Search

We investigate the effects of inhomogeneous scalar field configurations on the electroweak phase transition. For this purpose we calculate the leading perturbative correction to the wave function correction term Z(cphi,T), i.e., the kinetic term in the effective action, for the electroweak standard model at finite temperature and the top quark self-mass. Our finding for the fermionic contribution to Z(cphi,T) is

Dirk-Uwe Jungnickel; Dirk Walliser

1994-01-01

218

In situ tailoring of magnetization configuration in NiFe film deposited onto flexible substrate  

NASA Astrophysics Data System (ADS)

In this paper, we study the effect of mechanical stress on the domain configuration of a NiFe film obliquely deposited on a compliant polyimide substrate. To this end, we have developed a new method combining in situ mechanical tests with magnetic force microscopy (MFM) imaging. This approach allows changing the static magnetization structure of the film by controlling the stress-induced anisotropy. In the absence of applied stress and magnetic field, the sample shows stripe domains with an in-plane tilted direction with respect to the stress axis. After saturating the film, application of an increasing stress regenerates progressively a stripe domains structure with a modified in-plane magnetization direction.

Karboul-Trojet, W.; Faurie, D.; Aït-Yahiatène, E.; Roussigné, Y.; Mazaleyrat, F.; Chérif, S. M.

2012-04-01

219

Magnetic tunnel junctions for low magnetic field sensing  

NASA Astrophysics Data System (ADS)

In this thesis, we did a comprehensive investigation on the relationship between spin-dependent tunneling and structural variation in junction devices. Magnetic, microstructural, and transport studies have shown a significant improvement in exchange-bias, a reduced barrier roughness, and an enhanced magnetoresistance for samples after magnetic annealing. We have examined different magnetic configurations required for sensing applications and presented some results of using MTJ sensors to detect AC magnetic fields created by electrical current flow and DC stray field distributions of patterned magnetic materials. We have studied the low frequency noise in MTJ sensors. We have found that the 1/f noise in MTJs has magnetic as well as electrical origins, and is strongly affected by the junction's internal structure. The magnetic noise comes from magnetization fluctuations in the free FM layer and can be understood using the fluctuation-dissipation theorem. While the field-independent electrical noise due to charge trapping in the barrier, is observed in the less optimized MTJs sensors, and has an amplitude at least one order of magnitude higher than the noise component due to magnetization fluctuations. In addition, we have studied the magnetization switching of Cobalt rings with varying anisotropy utilizing scanning magnetoresistive microscopy. We have for the first time observed a complicated multi-domain intermediate phase during the transition between onion states for samples with strong anisotropy. This is in contrast to as deposited samples, which reverse by simple domain wall motion and feature an intermediate vortex state. The result is further analyzed by micro magnetic simulations.

Liu, Xiaoyong

220

The Sun's global magnetic field.  

PubMed

Our present-day understanding of solar and stellar magnetic fields is discussed from both an observational and theoretical viewpoint. To begin with, observations of the Sun's large-scale magnetic field are described, along with recent advances in measuring the spatial distribution of magnetic fields on other stars. Following this, magnetic flux transport models used to simulate photospheric magnetic fields and the wide variety of techniques used to deduce global coronal magnetic fields are considered. The application and comparison of these models to the Sun's open flux, hemispheric pattern of solar filaments and coronal mass ejections are then discussed. Finally, recent developments in the construction of steady-state global magnetohydrodynamic models are considered, along with key areas of future research. PMID:22665897

Mackay, Duncan H

2012-07-13

221

Plasma Expansion in Presence of Electric and Magnetic Fields  

SciTech Connect

The presence of electric and magnetic fields in high enthalpy nozzle flows can produce strong effects. In particular, non equilibrium conditions can be observed when this field are present. In this work we have investigated two different field configurations in supersonic nozzle: first of all we have studied the cooperative effect of electric and magnetic field applied inside the nozzle and secondly we have investigated the role of non equilibrium distribution produced in the reservoir by electric discharge (plasma jet)

Colonna, Gianpiero; Capitelli, Mario [Dipartimento di Chimica, Universita di Bari (Italy); CNR-IMIP, Bari Section (Italy)

2005-05-16

222

Field reversed configuration confinement enhancement through edge biasing and neutral beam injection.  

PubMed

Field reversed configurations (FRCs) with high confinement are obtained in the C-2 device by combining plasma gun edge biasing and neutral beam injection. The plasma gun creates an inward radial electric field that counters the usual FRC spin-up. The n = 2 rotational instability is stabilized without applying quadrupole magnetic fields. The FRCs are nearly axisymmetric, which enables fast ion confinement. The plasma gun also produces E × B shear in the FRC edge layer, which may explain the observed improved particle transport. The FRC confinement times are improved by factors 2 to 4, and the plasma lifetimes are extended from 1 to up to 4 ms. PMID:23004613

Tuszewski, M; Smirnov, A; Thompson, M C; Korepanov, S; Akhmetov, T; Ivanov, A; Voskoboynikov, R; Schmitz, L; Barnes, D; Binderbauer, M W; Brown, R; Bui, D Q; Clary, R; Conroy, K D; Deng, B H; Dettrick, S A; Douglass, J D; Garate, E; Glass, F J; Gota, H; Guo, H Y; Gupta, D; Gupta, S; Kinley, J S; Knapp, K; Longman, A; Hollins, M; Li, X L; Luo, Y; Mendoza, R; Mok, Y; Necas, A; Primavera, S; Ruskov, E; Schroeder, J H; Sevier, L; Sibley, A; Song, Y; Sun, X; Trask, E; Van Drie, A D; Walters, J K; Wyman, M D

2012-06-21

223

Adorable reversed field configuration with self-fields effect in a fel  

NASA Astrophysics Data System (ADS)

The dynamical behavior of relativistic electron governed by the combination of a realistic helical-wiggler free-electron laser (FEL) with a uniform axial guide magnetic field is investigated by the consideration of the effect of the relativistic electrons self-fields. The electron beam is assumed to have uniform density. In Raman regime, a three-dimensional Hamiltonian approach is derived in detail. The consideration of the additional scalar potential ? s represents the basic feature of the analysis. The approach recognized the two usual constants of motion: one concerns the total energy while the other is the canonical axial angular momentum hat P_{z'}. After some tedious algebra, the dynamical variables problems are solved analytically to study stable and unstable fixed point. The additional scalar potential ? s changes the nature of groups, in group II orbits reversed field configuration near hat ? _0 = 0 converted to a simple group II. At the time of the variation of ? the energetic interaction zones are discussed. The stability zones of fixed points that allow an excellent interaction between the electron and the existing fields are limited. To validate our model, we apply it to the well-known experience of Conde and Bekefi [Phys. Lett. 67, 3082 (1991)] and get some encouraging results.

El-Bahi, R.

2012-09-01

224

Microwave Measurements of Coronal Magnetic Field  

Microsoft Academic Search

Magnetic field measurements of the solar corona using microwave observation are reviewed. The solar corona is filled with highly ionised plasma and magnetic field. Moving charged particles interact with magnetic field due to Lorentz force. This results in gyration motion perpendicular to the magnetic field and free motion along the magnetic field. Circularly polarized electro-magnetic waves interact with gyrating electrons

K. Shibasaki

2006-01-01

225

Magnetic Field of Mars  

NASA Astrophysics Data System (ADS)

An internal potential function was created using the averaged MGS vector data released by Mario Acuna for altitudes from 95 to 209 km above the Martian geoid, all longitudes, and latitudes from 87 degrees south to 78 degrees north. Even with some gaps in coverage it is found that a consistent internal potential function can be derived up to spherical harmonic terms of n = 65 using all three components of the data. Weighting the data according to the standard errors given, the model fits to 7-8 nT rms. The energy density spectrum of the harmonics is seen to peak near n = 39 with a value of 7 J/cu km and fall off to less than 0.5 J/cu km below n = 15 and above n = 55. Contour maps of the X (north) component drawn for 100 km altitude show the strongly anomalous region centered at 60 degrees S latitude and 180 degrees longitude, as well as the alternating east-west trends already observed by other groups. Maps of the other components show the anomalous region, but not the east-west trends. The dichotomy is also maintained with much weaker anomalies bounding the northern plains. The results herein as as well as those of others is limited by the sparse low-altitude data coverage as well as the accuracy of the observations in the face of significant spacecraft fields. Work by Connerney and Acuna have mitigated these sources somewhat, but the design of the spacecraft did not lend itself to accurate observations. Recent results reported by David Mitchell of the ER group have shown that the field observations are significantly influenced by the solar wind with the possibility that the present results may only reflect that portion of the internal field visible above 95 km altitude. Depending on the solar wind, the anomaly field may be shielded or distorted to produce spurious results. The spectrum we have obtained so far may only see the stronger portion of the signal with a significant weaker component hidden. Measurements of crustal anomalies versus relative ages of source bodies combined with later absolute dating of Martian geologic units could lead to a quantitative constraint on the thermal history of the planet, i.e. the time when convective dynamo generation ceased in the core. Determination of directions of magnetization of anomaly sources as a function of age combined with the expectation that the Martian dynamo field was roughly aligned with the rotation axis would lead to a means of investigating polar wandering for Mars. Preliminary analysis of two magnetic anomalies in the northern polar region has yielded paleomagnetic pole positions near 50 N, 135 W, about 30 degrees north of Olympus Mons. This location is roughly consistent with the orientation of the planet expected theoretically prior to the formation of the Tharsis region. In the future, more accurate observations of the vector field at the lowest possible altitudes would significantly improve our understanding of Martian thermal history, polar wandering, and upper crustal evolution. Mapping potential resources (e.g., iron-rich source bodies) for future practical use would also be a side benefit. Additional information is contained in the original abstract.

Cain, J. C.; Ferguson, B.; Mozzoni, D.; Hood, L.

2000-07-01

226

A self-consistent calculation of rotating magnetic fields  

SciTech Connect

A self-consistent method is described for determining the static magnetic-field reduction in a magnetized plasma with a specified density profile by radio-frequency (rf)-driven rotating magnetic fields (RMFs). Electron-ion collisions and transport losses are included in the analysis. Application of RMF current drive to tandem mirrors and rotomak reactors is considered. The results of the calculations show that magnetic wells can be produced in mirror configurations, and reversal of applied static magnetic fields can be generated in rotomark geometrics by RMF for modest investments of rf power at frequencies for which the rf technology is economically attractive.

Sperling, J.L.; Glassman, A.J.; Moses, K.G.; Quon, B.H.

1986-07-01

227

Evolution of primordial magnetic fields  

NASA Astrophysics Data System (ADS)

Here we briefly summarise the main phases which determine the dynamical evolution of primordial magnetic fields in the early universe. On the one hand, strong fields undergo damping due to excitations of plasma fluctuations, and, on the other hand, weak magnetic fields will be strongly amplified by the small-scale dynamo in a turbulent environment. We find that, under reasonable assumptions concerning the efficiency of a putative magnetogenesis era during cosmic phase transitions, surprisingly strong magnetic fields 10-13-10-11 G on comparatively small scales 100 pc -10 kpc may survive to prior to structure formation. Additionally, any weak magnetic field will be exponentially amplified during the collapse of the first minihalos until they reach equipartition with the turbulent kinetic energy. Hence, we argue that it seems possible for cluster magnetic fields to be entirely of primordial origin.

Banerjee, R.

2013-06-01

228

Measuring interfacial magnetic configurations with Polarized Neutron Reflectometry  

NASA Astrophysics Data System (ADS)

Polarized neutron reflectivity (PNR) is ideally suited for imaging both vertical structural and magnetic variations in the complex magnetic multilayers [1]. During the talk will be described particularly how this technique allows obtaining the magnetic depth-profile of exchange-coupled bilayer. For instance, Gd40Fe60/ Tb12Fe88 is a model system to study exchange-bias phenomena origin in anti-ferromagnetically coupled AF/FM system, like FeF2/Fe. In these systems, unusual properties are observed such as a transition from positive to negative exchange bias field HE as the cooling field Hcf is swept from small to large positive value [2]. Combining complementary techniques that are macroscopic magnetization measurements and PNR, we have demonstrated that the above properties, e.g. the cooling field dependence of HE, come from an interfacial domain wall (iDW) frozen in the TbFe as the sample is cooled down under a field [3, 4]. Moreover, PNR measurements have recently revealed that the frozen iDW is metastable and that the exchange bias training effect in TbFe/GdFe results from the thermally assisted relaxation of the iDW, with field cycling [4, 5]. Overall, PNR studies concerning the TbFe/GdFe have brought strong insights into the exchange bias mechanisms in exchange coupled hard/soft systems with in-plane anisotropy. However we have demonstrated as well that this powerful technique can be applied to systems with perpendicular magnetic anisotropy (PMA). Although, in that case, the perpendicular moments are parallel to the scattering vector and do not give rise to scattering via the neutron selection rules, we have used a unconventional geometry to obtain a depth-dependent magnetic profile of a PMA exchange-coupled system. Specifically, we have characterized antiferromagnetically-coupled, TbFeCo/[Co/Pd] multilayers [6]. [4pt] [1] K.V. O'Donovan et al., Phys. Rev. Lett. 88, 067201 (2002). [0pt] [2] J. Nogues and al. Phys. Rev. Lett. 76, 4624 (1996) [0pt] [3] Y. Henry et al., Phys. Rev. B 73, 134420 (2006) [0pt] [4] T. Hauet et al., Phys. Rev. Lett. 96, 067207 (2006) [0pt] [5] T. Hauet et al., Appl. Phys. Lett. 91, 022505 (2007) [0pt] [6] S. Watson et al., Appl. Phys. Lett. 92, 202507 (2008)

Hauet, Thomas

2009-03-01

229

Cosmic Magnetic Fields - An Overview  

NASA Astrophysics Data System (ADS)

Magnetic fields have been known in antiquity. Aristotle attributes the first of what could be called a scientific discussion on magnetism to Thales, who lived from about 625 BC. In China “magnetic carts” were in use to help the Emperor in his journeys of inspection. Plinius comments that in the Asia Minor province of Magnesia shepherds' staffs get at times “glued” to a stone, a alodestone. In Europe the magnetic compass came through the Arab sailors who met the Portuguese explorers. The first scientific treatise on magnetism, “De Magnete”, was published by William Gilbert who in 1600 described his experiments and suggested that the Earth was a huge magnet. Johannes Kepler was a correspondent of Gilbert and at times suggested that planetary motion was due to magnetic forces. Alas, this concept was demolished by Isaac Newton,who seeing the falling apple decided that gravity was enough. This concept of dealing with gravitational forces only remains en vogue even today. The explanations why magnetic effects must be neglected go from “magnetic energy is only 1% of gravitation” to “magnetic fields only complicate the beautiful computer solutions”. What is disregarded is the fact that magnetic effects are very directional(not omni-directional as gravity) and also the fact that magnetic fields are seen every where in our cosmic universe.

Wielebinski, Richard; Beck, Rainer

230

Integrability of magnetic fields created by current distributions  

NASA Astrophysics Data System (ADS)

The existence of first integrals and periodic orbits of magnetic fields created by thin wires is investigated. When the current lines are planar we prove that magnetic orbits are closed near the wires and we provide two examples of magnetic fields without polynomial first integrals, thus contradicting Stefanescu's conjecture. When the current lines are non-planar we provide some examples of rectilinear configurations giving rise to helicoidal orbits near the wires and to chaotic portraits.

Aguirre, J.; Giné, J.; Peralta-Salas, D.

2008-01-01

231

Measurements of magnetic field alignment  

SciTech Connect

The procedure for installing Superconducting Super Collider (SSC) dipoles in their respective cryostats involves aligning the average direction of their field with the vertical to an accuracy of 0.5 mrad. The equipment developed for carrying on these measurements is described and the measurements performed on the first few prototypes SSC magnets are presented. The field angle as a function of position in these 16.6 m long magnets is a characteristic of the individual magnet with possible feedback information to its manufacturing procedure. A comparison of this vertical alignment characteristic with a magnetic field intensity (by NMR) characteristic for one of the prototypes is also presented. 5 refs., 7 figs.

Kuchnir, M.; Schmidt, E.E.

1987-11-06

232

Origin of cosmic magnetic fields.  

PubMed

We calculate, in the free Maxwell theory, the renormalized quantum vacuum expectation value of the two-point magnetic correlation function in de Sitter inflation. We find that quantum magnetic fluctuations remain constant during inflation instead of being washed out adiabatically, as usually assumed in the literature. The quantum-to-classical transition of super-Hubble magnetic modes during inflation allow us to treat the magnetic field classically after reheating, when it is coupled to the primeval plasma. The actual magnetic field is scale independent and has an intensity of few×10(-12)??G if the energy scale of inflation is few×10(16)??GeV. Such a field accounts for galactic and galaxy cluster magnetic fields. PMID:23971556

Campanelli, Leonardo

2013-08-06

233

Vector optical fields with polarization distributions similar to electric and magnetic field lines.  

PubMed

We present, design and generate a new kind of vector optical fields with linear polarization distributions modeling to electric and magnetic field lines. The geometric configurations of "electric charges" and "magnetic charges" can engineer the spatial structure and symmetry of polarizations of vector optical field, providing additional degrees of freedom assisting in controlling the field symmetry at the focus and allowing engineering of the field distribution at the focus to the specific applications. PMID:23842405

Pan, Yue; Li, Si-Min; Mao, Lei; Kong, Ling-Jun; Li, Yongnan; Tu, Chenghou; Wang, Pei; Wang, Hui-Tian

2013-07-01

234

Magnetic Field Problem: Measuring Current  

NSDL National Science Digital Library

A cross section of two circular wire loops carrying the exact same current is shown above (position given in centimeters and magnetic field given in milli-Tesla). You can click-drag to read the magnitude of the magnetic field.

Christian, Wolfgang; Belloni, Mario

2007-03-03

235

Laboratory Measurements of Astrophysical Magnetic Fields  

NASA Astrophysics Data System (ADS)

It has been proposed that high Mach number collisionless shocks propagating in an initially unmagnetized plasma play a major role in the magnetization of large scale structures in the Universe. A detailed study of the experimental configuration necessary to scale such environments down to laboratory dimensions will be presented. We will show initial results from preliminary experiments conducted at the Phoenix laser (UCLA) and the LULI laser (Ecole Polytechnique) where collisionless shocks are generated by the expansion of exploding foils driven by energetic laser beams. The time evolution of the magnetic field is probed with induction coils placed at 10 cm from the laser focus. We will discuss various mechanisms of magnetic field generation and compare them with the experimental results.

Murphy, C. D.; Miniati, F.; Edwards, M.; Mithen, J.; Bell, A. R.; Constantin, C.; Everson, E.; Schaeffer, D.; Niemann, C.; Ravasio, A.; Brambrink, E.; Benuzzi-Mounaix, A.; Koenig, M.; Gregory, C.; Woolsey, N.; Park, H.-S.; Remington, B.; Ryutov, D.; Bingham, R.; Gargate, L.; Spitkovsky, A.; Gregori, G.

2010-11-01

236

Apparatus for storing high magnetic fields having reduced mechanical forces and reduced magnetic pollution  

DOEpatents

The present invention identifies several configurations of conducting elements capable of storing extremely high magnetic fields for the purpose of energy storage or for other uses, wherein forces experienced by the conducting elements and the magnetic field pollution produced at locations away from the configuration are both significantly reduced over those which are present as a result of the generation of such high fields by currently proposed techniques. It is anticipated that the use of superconducting materials will both permit the attainment of such high fields and further permit such fields to be generated with vastly improved efficiency.

Prueitt, Melvin L. (Los Alamos, NM); Mueller, Fred M. (Los Alamos, NM); Smith, James L. (Los Alamos, NM)

1991-01-01

237

Apparatus for storing high magnetic fields having reduced mechanical forces and reduced magnetic pollution  

DOEpatents

The present invention identifies several configurations of conducting elements capable of storing extremely high magnetic fields for the purpose of energy storage or for other uses, wherein forces experienced by the conducting elements and the magnetic field pollution produced at locations away from the configuration are both significantly reduced over those which are present as a result of the generation of such high fields by currently proposed techniques. It is anticipated that the use of superconducting materials will both permit the attainment of such high fields and further permit such fields to be generated with vastly improved efficiency. 15 figures.

Prueitt, M.L.; Mueller, F.M.; Smith, J.L.

1991-04-09

238

Los Alamos field-reversed configuration (FRC) research  

SciTech Connect

Recent experimental results are discussed for a compact toroid produced by a field-reversed theta-pinch and containing purely poloidal magnetic fields. The confinement time is found to vary inversely with the ion gyro-radius and to be approximately independent of ion temperature for fixed gyro-radius. Within a coil of fixed radius, the plasmoid major radius R was varied by approx. 30% and the confinement appears to scale as R/sup 2/. A semi-empirical formation model has been formulated that predicts reasonably well the plasma parameters as magnetic field and fill pressure are varied in present experiments. The model is used to predict parameters in larger devices under construction.

Armstrong, W.T.; Bartsch, R.R.; Cochrane, J.C.; Linford, R.K.; Lipson, J.; McKenna, K.F.; Platts, D.A.; Sherwood, E.G.; Siemon, R.E.; Tuszewski, M.

1981-01-01

239

Diffusive processes in a stochastic magnetic field  

SciTech Connect

The statistical representation of a fluctuating (stochastic) magnetic field configuration is studied in detail. The Eulerian correlation functions of the magnetic field are determined, taking into account all geometrical constraints: these objects form a nondiagonal matrix. The Lagrangian correlations, within the reasonable Corrsin approximation, are reduced to a single scalar function, determined by an integral equation. The mean square perpendicular deviation of a geometrical point moving along a perturbed field line is determined by a nonlinear second-order differential equation. The separation of neighboring field lines in a stochastic magnetic field is studied. We find exponentiation lengths of both signs describing, in particular, a decay (on the average) of any initial anisotropy. The vanishing sum of these exponentiation lengths ensures the existence of an invariant which was overlooked in previous works. Next, the separation of a particle`s trajectory from the magnetic field line to which it was initially attached is studied by a similar method. Here too an initial phase of exponential separation appears. Assuming the existence of a final diffusive phase, anomalous diffusion coefficients are found for both weakly and strongly collisional limits. The latter is identical to the well known Rechester-Rosenbluth coefficient, which is obtained here by a more quantitative (though not entirely deductive) treatment than in earlier works.

Wang, H.; Vlad, M.; Vanden Eijnden, E.; Spineanu, F.; Misguich, J.H.; Balescu, R. [Association Euratom-Etat Belge sur la Fusion, Physique Statistique et Plasmas, Code Postal 231, Universite Libre de Bruxelles, Campus Plaine, Boulevard du Triomphe, 1050 Bruxelles (Belgium)]|[Association Euratom-Commissariat a l`Energie Atomique sur la Fusion, Departement de Recherches sur la Fusion Controle, Centre d`Etudes de Cadarache, 13108 Saint-Paul-lez-Durance Cedex (France)

1995-05-01

240

Large-Scale Magnetic Fields in Magnetohydrodynamic Turbulence  

NASA Astrophysics Data System (ADS)

High Reynolds number magnetohydrodynamic turbulence in the presence of zero-flux large-scale magnetic fields is investigated as a function of the magnetic field strength. For a variety of flow configurations, the energy dissipation rate ? follows the scaling ??Urms3/? even when the large-scale magnetic field energy is twenty times larger than the kinetic energy. A further increase of the magnetic energy showed a transition to the ??Urms2Brms/? scaling implying that magnetic shear becomes more efficient at this point at cascading the energy than the velocity fluctuations. Strongly helical configurations form nonturbulent helicity condensates that deviate from these scalings. Weak turbulence scaling was absent from the investigation. Finally, the magnetic energy spectra support the Kolmogorov spectrum k-5/3 while kinetic energy spectra are closer to the Iroshnikov-Kraichnan spectrum k-3/2 as observed in the solar wind.

Alexakis, Alexandros

2013-02-01

241

Ferroelectric Polarization Flop in a Frustrated Magnet MnWO4 Induced by a Magnetic Field  

NASA Astrophysics Data System (ADS)

The relationship between magnetic order and ferroelectric properties has been investigated for MnWO4 with a long-wavelength magnetic structure. Spontaneous electric polarization is observed in an elliptical spiral spin phase. The magnetic-field dependence of electric polarization indicates that the noncollinear spin configuration plays a key role for the appearance of the ferroelectric phase. An electric polarization flop from the b direction to the a direction has been observed when a magnetic field above 10 T is applied along the b axis. This result demonstrates that an electric polarization flop can be induced by a magnetic field in a simple system without rare-earth 4f moments.

Taniguchi, K.; Abe, N.; Takenobu, T.; Iwasa, Y.; Arima, T.

2006-09-01

242

Magnetic fields and scintillator performance  

SciTech Connect

Experimental data have shown that the light output of a scintillator depends on the magnitude of the externally applied magnetic fields, and that this variation can affect the calorimeter calibration and possibly resolution. The goal of the measurements presented here is to study the light yield of scintillators in high magnetic fields in conditions that are similar to those anticipated for the LHC CMS detector. Two independent measurements were performed, the first at Fermilab and the second at the National High Magnetic Field Laboratory at Florida State University.

Green, D.; Ronzhin, A. [Fermi National Accelerator Lab., Batavia, IL (United States); Hagopian, V. [Florida State Univ., Tallahasse, FL (United States)

1995-06-01

243

Broad Ion Beam Extraction from Large Bore ECR Ion Source with Cylindrically Comb-Shaped Magnetic Fields Configuration by Feeding Simultaneously 11 to 13 GHz and 2.45 GHz Microwaves  

SciTech Connect

We tried to enlarge the operation window of an electron cyclotron resonance (ECR) ion source for producing the ECR plasma confined by cylindrically comb-shaped magnetic field, and for extracting the broad ion beam under the low pressures and low microwave powers. The magnetic field by permanent magnets constructs ECR zones at different positions for 2.45 GHz and 11 to 13 GHz microwaves, respectively. According to probe measurements, profiles of plasma density and temperature are different for using each single microwave. We conduct production of ECR plasma by launching simultaneously these two frequency microwaves, and obtain flat profiles of the electron density and the electron temperature. These profiles are not achieved by feeding single frequency microwave. It is found that plasma can be controllable on spatial profiles beyond wide operation window of plasma parameters. We conducted preliminary extracting and forming large bore ion beam from this source. We will make this source a part of tandem type ion source for the first stage. We investigated feasibility and hope to realize the device which has wide range operation window in a single device to produce many kinds of ion beams as like to universal source based on ECR ion source.

Kato, Y.; Satani, T.; Matsui, Y.; Watanabe, T.; Sato, F.; Iida, T. [Osaka Univ., 2-1 Yamada-oka, Suita, Osaka 565-0871 (Japan); Muramatsu, M.; Kitagawa, A. [NIRS, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555 (Japan); Tanaka, K.; Asaji, T. [Tateyama Machine Co. Ltd., 30 Shimonoban, Toyama, Toyama 930-1305 (Japan)

2008-11-03

244

Magnetic field structure of Mercury  

NASA Astrophysics Data System (ADS)

Recently planet Mercury—an unexplored territory in our solar system—has been of much interest to the scientific community due to recent flybys of the spacecraft MESSENGER that discovered its intrinsic stationary and large-scale dipole like magnetic field structure with an intensity of ˜300nT confirming Mariner 10 observations. In the present study, with the observed constraint of Mercury's atmospheric magnetic field structure, internal magnetic field structure is modeled as a solution of magnetic diffusion equation. In this study, Mercury's internal structure mainly consists of a stable stratified fluid core and the convective mantle. For simplicity, magnetic diffusivity in both parts of the structure is considered to be uniform and constant with a value represented by a suitable averages. It is further assumed that vigorous convection in the mantle disposes of the electric currents leading to a very high diffusivity in that region. Thus, in order to satisfy observed atmospheric magnetic field structure, Mercury's most likely magnetic field structure consists of a solution of MHD diffusion equation in the core and a combined multipolar (dipole and quadrupole like magnetic field structures embedded in the uniform field) solution of a current free like magnetic field structure in the mantle and in the atmosphere. With imposition of appropriate boundary conditions at the core-mantle boundary for the first two diffusion eigen modes, in order to satisfy the observed field structure, present study puts the constraint on Mercury's core radius to be ˜2000km.From the estimated magnetic diffusivity and the core radius, it is also possible to estimate the two diffusion eigen modes with their diffusion time scales of ˜8.6 and 3.7 billion years respectively suggesting that the planet inherits its present-day magnetic field structure from the solar Nebula. It is proposed that permanency of such a large-scale magnetic field structure of the planet is attained during Mercury's early evolutionary history of heavy bombardments by the asteroids and comets supporting the giant impact hypothesis for the formation of Mercury.

Hiremath, K. M.

2012-04-01

245

Equivalent source mapping of lunar magnetic field  

NASA Astrophysics Data System (ADS)

JAXA (Japan Aerospace Exploration Agency) shall launch the SELENE (SELenological and ENgineering Explorer) spacecraft this autumn. Amongst many instruments, it has a magnetometer (LMAG: Lunar MAGnetomter) which will measure the magnetic field on the orbit around the Moon. The nominal orbit of the SELENE is about 100km in altitudes for 1 year observation. Although the extended mission is still not determined, LMAG team is requesting a low altitude (less than 50km) observation, if the remaining fuel allows. We are preparing data processing software for the mission. Here, we report an objective scheme for mapping the lunar crustal magnetic field from the orbital measurement data of unequal altitudes. In this study, the magnetic field is restored by solving a linear inverse-problem determining the sources distributed on the lunar surface to satisfy the observational data, which is known as the equivalent source method. Our scheme has three features improving the method: First, the source calculation is performed simultaneously with detrending. Second, magnetic charges (magnetic monopoles) are used as the equivalent sources. It reduces the density of the sources for the same smoothness in produced field, comparing to the dipole sauces. Third, the number of sources is taken large enough to avoid the problem of configuration of the sources, instead the damped least square assuming the strength of each charge is similar to the next one, and the smoothness factor is determined by minimizing Akaike's Bayesian Information Criterion (ABIC). It guarantees the objectivity of the calculation, in other words, there is no adjustable parameter which may depend of the researcher dealing the data analyses. For testing the scheme, we apply this method to the Lunar Prospector magnetometer data, and provide magnetic field map in the region centered at several regions of strong crustal field including the Reiner Gamma anomaly. The stability of the method and the resolution of the anomaly map are found to be satisfactory.

Toyoshima, M.; Shibuya, H.

2007-12-01

246

Cosmic Magnetic Fields – An Overview  

Microsoft Academic Search

\\u000a Magnetic fields have been known in antiquity. Aristotle attributes the first of what could be called a scientific discussion\\u000a on magnetism to Thales, who lived from about 625 BC. In China “magnetic carts” were in use to help the Emperor in his journeys\\u000a of inspection. Plinius comments that in the Asia Minor province of Magnesia shepherds’ staffs get at times

Richard Wielebinski; Rainer Beck

2010-01-01

247

Magnetic Pumping in Spatially Inhomogeneous Magnetic Fields.  

National Technical Information Service (NTIS)

Magnetic pumping by major-radius oscillation of a toroidal plasma can be made more practical by introducing a major-radius range within which the vertical-field gradient is sufficiently great so that major-radius perturbations are marginally stable or, be...

H. P. Furth R. A. Ellis

1972-01-01

248

Simulations of Photospheric Magnetic Fields  

Microsoft Academic Search

We have run plots of artificial data, which mimic solar magnetograms, through standard algorithms to critique several results reported in the literature. In studying correlation algorithms, we show that the differences in the profiles for the differential rotation of the photospheric magnetic field stem from different methods of averaging. We verify that the lifetimes of small magnetic features, or of

A. A. Smith; H. B. Snodgrass

1999-01-01

249

Measuring Earth's Magnetic Field Simply.  

ERIC Educational Resources Information Center

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

Stewart, Gay B.

2000-01-01

250

Magnetic Field Waves at Uranus.  

National Technical Information Service (NTIS)

The proposed research efforts funded by the UDAP grant to the BRI involve the study of magnetic field waves associated with the Uranian bow shock. This is a collaborative venture bringing together investigators at the BRI, Southwest Research Institute (Sw...

C. W. Smith M. L. Goldstein R. P. Lepping W. H. Mish H. K. Wong

1991-01-01

251

NUMERICAL SIMULATION OF SOLAR MICROFLARES IN A CANOPY-TYPE MAGNETIC CONFIGURATION  

SciTech Connect

Microflares are small activities in the solar low atmosphere; some are in the low corona while others are in the chromosphere. Observations show that some of the microflares are triggered by magnetic reconnection between the emerging flux and a pre-existing background magnetic field. We perform 2.5-dimensional, compressible, resistive magnetohydrodynamic simulations of the magnetic reconnection with gravity considered. The background magnetic field is a canopy-type configuration that is rooted at the boundary of the solar supergranule. By changing the bottom boundary conditions in the simulation, a new magnetic flux emerges at the center of the supergranule and reconnects with the canopy-type magnetic field. We successfully simulate the coronal and chromospheric microflares whose current sheets are located at the corona and the chromosphere, respectively. The microflare with a coronal origin has a larger size and a higher temperature enhancement than the microflare with a chromospheric origin. In the microflares with coronal origins, we also found a hot jet ({approx}1.8 Multiplication-Sign 10{sup 6} K), which is probably related to the observational extreme ultraviolet or soft X-ray jets, and a cold jet ({approx}10{sup 4} K), which is similar to the observational H{alpha}/Ca surges. However, there is only a H{alpha}/Ca bright point in the microflares that have chromospheric origins. The study of parameter dependence shows that the size and strength of the emerging magnetic flux are the key parameters that determine the height of the reconnection location, and they further determine the different observational features of the microflares.

Jiang, R.-L.; Fang, C.; Chen, P.-F., E-mail: rljiang@nju.edu.cn [School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China)

2012-06-01

252

Numerical Simulation of Solar Microflares in a Canopy-type Magnetic Configuration  

NASA Astrophysics Data System (ADS)

Microflares are small activities in the solar low atmosphere; some are in the low corona while others are in the chromosphere. Observations show that some of the microflares are triggered by magnetic reconnection between the emerging flux and a pre-existing background magnetic field. We perform 2.5-dimensional, compressible, resistive magnetohydrodynamic simulations of the magnetic reconnection with gravity considered. The background magnetic field is a canopy-type configuration that is rooted at the boundary of the solar supergranule. By changing the bottom boundary conditions in the simulation, a new magnetic flux emerges at the center of the supergranule and reconnects with the canopy-type magnetic field. We successfully simulate the coronal and chromospheric microflares whose current sheets are located at the corona and the chromosphere, respectively. The microflare with a coronal origin has a larger size and a higher temperature enhancement than the microflare with a chromospheric origin. In the microflares with coronal origins, we also found a hot jet (~1.8 × 106 K), which is probably related to the observational extreme ultraviolet or soft X-ray jets, and a cold jet (~104 K), which is similar to the observational H?/Ca surges. However, there is only a H?/Ca bright point in the microflares that have chromospheric origins. The study of parameter dependence shows that the size and strength of the emerging magnetic flux are the key parameters that determine the height of the reconnection location, and they further determine the different observational features of the microflares.

Jiang, R.-L.; Fang, C.; Chen, P.-F.

2012-06-01

253

Magnetic fields in merging spirals - the Antennae  

NASA Astrophysics Data System (ADS)

We present an extensive study of magnetic fields in a system of merging galaxies. We obtained for NGC 4038/39 (the Antennae) radio total intensity and polarization maps at 8.44 GHz, 4.86 GHz and 1.49 GHz using the VLA in the C and D configurations. The galaxy pair possesses bright, extended radio emission filling the body of the whole system, with no dominant nuclear sources. The radio thermal fraction of NGC 4038/39 was found to be about 50% at 10.45 GHz, higher than in normal spirals. Most of the thermal emission is associated with star-forming regions, but only a part of these are weakly visible in the optical domain because of strong obscuration. The mean total magnetic fields in both galaxies are about two times stronger (?20 ?G) than in normal spirals. However, the degree of field regularity is rather low, implying tangling of the regular component in regions with interaction-enhanced star formation. Our data combined with those in H I, H?, X-rays and in far infrared allow us to study local interrelations between different gas phases and magnetic fields. We distinguish several radio-emitting regions with different physical properties and at various evolutionary stages: the rudimentary magnetic spiral, the northern cool part of the dark cloud complex extending between the galaxies, its warm southern region, its southernmost star-forming region deficient in radio emission, and the highly polarized northeastern ridge associated with the base of an unfolding tidal tail. The whole region of the dark cloud complex shows a coherent magnetic field structure, probably tracing the line of collision between the arms of merging spirals while the total radio emission reveals hidden star formation nests. The southern region is a particularly intense merger-triggered starburst. Highly tangled magnetic fields reach there strengths of ?30 ?G, even larger than in both individual galaxies, possibly due to compression of the original fields pulled out from the parent disks. In the northeastern ridge, away from star-forming regions, the magnetic field is highly coherent with a strong regular component of 10 ?G tracing gas shearing motions along the tidal tail. We find no signs of field compression by infalling gas there. The radio spectrum is much steeper in this region indicating aging of the CR electron population as they move away from their sources in star-forming regions. Modelling Faraday rotation data shows that we deal with a three-dimensionally curved structure of magnetic fields, becoming almost parallel to the sky plane in the southeastern part of the ridge.

Chy?y, K. T.; Beck, R.

2004-04-01

254

Thermometers in Low Magnetic Fields  

Microsoft Academic Search

In this article the effect of low amplitude DC magnetic fields on different types of thermometers is discussed. By means of\\u000a a precision water-cooled electromagnet, the effect of a magnetic field on platinum resistance thermometers, thermistors, and\\u000a type T, J, and K thermocouples was investigated, while thermometers were thermally stabilized in thermostatic baths. Four\\u000a different baths were used for temperatures

G. Gersak; S. Begus

2010-01-01

255

Superconductive magnetic energy storage (SMES) external fields and safety considerations  

SciTech Connect

This paper addresses preferred SMES configurations and the external magnetic fields which they generate. Possible biological effects of fields are reviewed briefly. It is proposed that SMES units be fenced at the 10 gauss (1 mT) level to keep unrestricted areas safe, even for persons with cardiac pacemakers. For a full size 5000 MWh (1.8 {times} 10 {sup 13} J) SMES the magnetic field decreases to 10 gauss at a radial distance of 2 km from the center of the coil. Other considerations related to the environmental impact of large SMES magnetic fields are discussed briefly.

Polk, C. (Rhode Island Univ., Kingston, RI (United States). Dept. of Electrical Engineering); Boom, R.W.; Eyssa, Y.M. (Wisconsin Univ., Madison, WI (United States). Applied Superconductivity Center)

1992-01-01

256

Theorem on magnet fringe field  

SciTech Connect

Transverse particle motion in particle accelerators is governed almost totally by non-solenoidal magnets for which the body magnetic field can be expressed as a series expansion of the normal (b{sub n}) and skew (a{sub n}) multipoles, B{sub y} + iB{sub x} = {summation}(b{sub n} + ia{sub n})(x + iy){sup n}, where x, y, and z denote horizontal, vertical, and longitudinal (along the magnet) coordinates. Since the magnet length L is necessarily finite, deflections are actually proportional to ``field integrals`` such as {bar B}L {equivalent_to} {integral} B(x,y,z)dz where the integration range starts well before the magnet and ends well after it. For {bar a}{sub n}, {bar b}{sub n}, {bar B}{sub x}, and {bar B}{sub y} defined this way, the same expansion Eq. 1 is valid and the ``standard`` approximation is to neglect any deflections not described by this expansion, in spite of the fact that Maxwell`s equations demand the presence of longitudinal field components at the magnet ends. The purpose of this note is to provide a semi-quantitative estimate of the importance of {vert_bar}{Delta}p{sub {proportional_to}}{vert_bar}, the transverse deflection produced by the ion-gitudinal component of the fringe field at one magnet end relative to {vert_bar}{Delta}p{sub 0}{vert_bar}, the total deflection produced by passage through the whole magnet. To emphasize the generality and simplicity of the result it is given in the form of a theorem. The essence of the proof is an evaluation of the contribution of the longitudinal field B{sub x} from the vicinity of one magnet end since, along a path parallel to the magnet axis such as path BC.

Wei, Jie [Brookhaven National Lab., Upton, NY (United States); Talman, R. [Cornell Univ., Ithaca, NY (United States). Lab. of Nuclear Studies

1995-12-31

257

Flux Transport and the Sun's Global Magnetic Field (Invited)  

NASA Astrophysics Data System (ADS)

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

Hathaway, D. H.

2010-12-01

258

Synthetic magnetic fields for ultracold neutral atoms.  

PubMed

Neutral atomic Bose condensates and degenerate Fermi gases have been used to realize important many-body phenomena in their most simple and essential forms, without many of the complexities usually associated with material systems. However, the charge neutrality of these systems presents an apparent limitation-a wide range of intriguing phenomena arise from the Lorentz force for charged particles in a magnetic field, such as the fractional quantum Hall effect in two-dimensional electron systems. The limitation can be circumvented by exploiting the equivalence of the Lorentz force and the Coriolis force to create synthetic magnetic fields in rotating neutral systems. This was demonstrated by the appearance of quantized vortices in pioneering experiments on rotating quantum gases, a hallmark of superfluids or superconductors in a magnetic field. However, because of technical issues limiting the maximum rotation velocity, the metastable nature of the rotating state and the difficulty of applying stable rotating optical lattices, rotational approaches are not able to reach the large fields required for quantum Hall physics. Here we experimentally realize an optically synthesized magnetic field for ultracold neutral atoms, which is evident from the appearance of vortices in our Bose-Einstein condensate. Our approach uses a spatially dependent optical coupling between internal states of the atoms, yielding a Berry's phase sufficient to create large synthetic magnetic fields, and is not subject to the limitations of rotating systems. With a suitable lattice configuration, it should be possible to reach the quantum Hall regime, potentially enabling studies of topological quantum computation. PMID:19956256

Lin, Y-J; Compton, R L; Jiménez-García, K; Porto, J V; Spielman, I B

2009-12-01

259

TUBE88 - A code which computes magnetic field lines  

NASA Astrophysics Data System (ADS)

TUBE88 computes magnetic field lines in cylindrical or toroidal geometry (using cylindrical coordinates (r, ?, z)) and calculates the intersections of those field lines with specified planes. It is an outgrowth of a code first written in 1967. A fourth-order predictor-corrector method is used to integrate the field line coordinates. The magnetic field may be computed in several ways: (a) through specification of currents flowing in very specific helical and circular elements together with a ``1/r'' field and a vertical field, (b) as a Fourier series in the angular variale or (c) in a specific coordinate system suited to a toroidally helical domain. Extensive graphics are provided for users of the Cray Time-Sharing System (CTSS). Applications of the code have included analysis of vacuum magnetic field configurations and post processing magnetic field data produced by MHD codes, for example. Current address: Sandia National Laboratory, Livermore, CA 94550, USA.

Mirin, A. A.; Martin, D. R.; O'Neill, N. J.

1989-04-01

260

The large-s field-reversed configuration experiment  

SciTech Connect

The Large-s Experiment (LSX) was built to study the formation and equilibrium properties of field-reversed configurations (FRCs) as the scale size increases. The dynamic, field-reversed theta-pinch method of FRC creation produces axial and azimuthal deformations and makes formation difficult, especially in large devices with large s (number of internal gyroradii) where it is difficult to achieve initial plasma uniformity. However, with the proper technique, these formation distortions can be minimized and are then observed to decay with time. This suggests that the basic stability and robustness of FRCs formed, and in some cases translated, in smaller devices may also characterize larger FRCs. Elaborate formation controls were included on LSX to provide the initial uniformity and symmetry necessary to minimize formation disturbances, and stable FRCs could be formed up to the design goal of s = 8. For x [le] 4, the formation distortions decayed away completely, resulting in symmetric equilibrium FRCs with record confinement times up to 0.5 ms, agreeing with previous empirical scaling laws ([tau][proportional to]sR). Above s = 4, reasonably long-lived (up to 0.3 ms) configurations could still be formed, but the initial formation distortions were so large that they never completely decayed away, and the equilibrium confinement was degraded from the empirical expectations. The LSX was only operational for 1 yr, and it is not known whether s = 4 represents a fundamental limit for good confinement in simple (no ion beam stabilization) FRCs or whether it simply reflects a limit of present formation technology. Ideally, s could be increased through flux buildup from neutral beams. Since the addition of kinetic or beam ions will probably be desirable for heating, sustainment, and further stabilization of magnetohydrodynamic modes at reactor-level s values, neutral beam injection is the next logical step in FRC development. 24 refs., 21 figs., 2 tabs.

Hoffman, A.L.; Carey, L.N.; Crawford, E.A.; Harding, D.G.; DeHart, T.E.; McDonald, K.F.; McNeil, J.L.; Milroy, R.D.; Slough, J.T. (STI Optronics, Bellevue, WA (United States)); Maqueda, R.; Wurden, G.A. (Univ. of Washington, Seattle (United States))

1993-03-01

261

Magnetospheres of accreting compact stars possessing multipole magnetic fields  

SciTech Connect

The magnetospheres of accreting compact stars (neutron stars and white dwarfs) are examined. It is assumed that the compact star possesses a multipole magnetic field. The shape of the magnetosphere for the two-dimensional analog of spherically symmetric accretion and the magnetic-field configuration for the case of disk accretion are found with the help of conformal mappings. The results of a generalization of the two-dimensional solution to the real three-dimensional case are discussed.

Lipunov, V.M.

1978-11-01

262

A new high performance field reversed configuration operating regime in the C-2 device  

SciTech Connect

Large field reversed configurations (FRCs) are produced in the C-2 device by combining dynamic formation and merging processes. The good confinement of these FRCs must be further improved to achieve sustainment with neutral beam (NB) injection and pellet fuelling. A plasma gun is installed at one end of the C-2 device to attempt electric field control of the FRC edge layer. The gun inward radial electric field counters the usual FRC spin-up and mitigates the n = 2 rotational instability without applying quadrupole magnetic fields. Better plasma centering is also obtained, presumably from line-tying to the gun electrodes. The combined effects of the plasma gun and of neutral beam injection lead to the high performance FRC operating regime, with FRC lifetimes up to 3 ms and with FRC confinement times improved by factors 2 to 4.

Tuszewski, M.; Smirnov, A.; Thompson, M. C.; Barnes, D.; Binderbauer, M. W.; Brown, R.; Bui, D. Q.; Clary, R.; Conroy, K. D.; Deng, B. H.; Dettrick, S. A.; Douglass, J. D.; Garate, E.; Glass, F. J.; Gota, H.; Guo, H.Y.; Gupta, D.; Gupta, S.; Kinley, J. S.; Knapp, K. [Tri Alpha Energy, Inc., P.O. Box 7010, Rancho Santa Margarita, California 92688 (United States); and others

2012-05-15

263

The use of high magnetic fields at the study of magnetism and superconductivity in intermetallic compounds  

SciTech Connect

Magnetic fields have a large impact on the magnetic and superconducting properties of solids. High magnetic fields are required to reach magnetic saturation along a hard magnetic direction in a variety of rare-earth intermetallics, to break the ferrimagnetic moment configuration in specific 3d-4f intermetallics, to quench the strongly correlated electron states in heavy fermion compounds, to reach the upper critical fields in several classes of superconductors, to study flux-pinning phenomena in the high-{Tc} superconductors, etc. In the present review, the attention is focused to the field interval 20--50 tesla. Experiments in this field range are the privilege of specialized high magnetic field laboratories. There is a lively activity in this area of research with the number of participating institutes continuously growing.

Franse, J.J.M.; Boer, F.R. de; Frings, P.H.; Visser, A. de [Univ. of Amsterdam (Netherlands). Van der Waals-Zeeman Lab.

1994-03-01

264

MAGNETIC FIELD MEASUREMENTS FOR FAST-CHANGING MAGNETIC FIELDS.  

SciTech Connect

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

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

2004-10-03

265

Polar plumes' orientation and the Sun's global magnetic field  

NASA Astrophysics Data System (ADS)

Aims: We characterize the orientation of polar plumes as a tracer of the large-scale coronal magnetic field configuration. We monitor in particular the north and south magnetic pole locations and the magnetic opening during 2007-2008 and provide some understanding of the variations in these quantities. Methods: The polar plume orientation is determined by applying the Hough-wavelet transform to a series of EUV images and extracting the key Hough space parameters of the resulting maps. The same procedure is applied to the polar cap field inclination derived from extrapolating magnetograms generated by a surface flux transport model. Results: We observe that the position where the magnetic field is radial (the Sun's magnetic poles) reflects the global organization of magnetic field on the solar surface, and we suggest that this opens the possibility of both detecting flux emergence anywhere on the solar surface (including the far side) and better constraining the reorganization of the corona after flux emergence.

de Patoul, Judith; Inhester, Bernd; Cameron, Robert

2013-10-01

266

Black holes and magnetic fields  

NASA Astrophysics Data System (ADS)

The exact mechanism of formation of highly relativistic jets from galactic nuclei and microquasars remains unknown but most accepted models involve a central black hole and a strong external magnetic field. This idea is based on assumption that the black hole rotates and the magnetic field threads its horizon. Magnetic torques provide a link between the hole and the surrounding plasma which then becomes accelerated. We first review our work on black holes immersed in external stationary vacuum (electro)magnetic fields in both test-field approximation and within exact general-relativistic solutions. A special attention will be paid to the Meissner-type effect of the expulsion of the flux of external axisymmetric stationary fields across rotating (or charged) black holes when they approach extremal states. This is a potential threat to any electromagnetic mechanism launching the jets at the account of black-hole rotation because it inhibits the extraction of black-hole rotational energy. We show that the otherwise very useful "membrane viewpoint of black holes" advocated by Thorne, Price and Macdonald does not represent an adequate formalism in the context of the field expulsion from extreme black holes. After briefly summarizing the results for black holes in magnetic fields in higher dimensions - the expulsion of stationary axisymmetric fields was demonstrated to occur also for extremal black-hole solutions in string theory and Kaluza-Klein theory - we shall review astrophysically relevant axisymmetric numerical simulations reported recently by Gammie, Komissarov, Krolik and others. Although the field expulsion has not yet been observed in these time-dependent simulations, they may still be too far away from the extreme limit at which the black-hole Meissner effect should show up. We mention some open problems which, according to our view, deserve further investigation.

Bi?ák, Ji?í; Karas, Vladimír; Ledvinka, Tomáš

2007-04-01

267

Simulations of magnetic fields in the cosmos  

Microsoft Academic Search

The origin of large-scale magnetic fields in clusters of galaxies remains controversial. The intergalactic magnetic field within filaments should be less polluted by magnetised outflows from active galaxies than magnetic fields in clusters. Therefore, filaments may be a better laboratory to study magnetic field amplification by structure formation than galaxy clusters, which typically host many more active galaxies. We present

M. Brüggen; M. Hoeft

2006-01-01

268

Indoor localization using magnetic fields  

NASA Astrophysics Data System (ADS)

Indoor localization consists of locating oneself inside new buildings. GPS does not work indoors due to multipath reflection and signal blockage. WiFi based systems assume ubiquitous availability and infrastructure based systems require expensive installations, hence making indoor localization an open problem. This dissertation consists of solving the problem of indoor localization by thoroughly exploiting the indoor ambient magnetic fields comprising mainly of disturbances termed as anomalies in the Earth's magnetic field caused by pillars, doors and elevators in hallways which are ferromagnetic in nature. By observing uniqueness in magnetic signatures collected from different campus buildings, the work presents the identification of landmarks and guideposts from these signatures and further develops magnetic maps of buildings - all of which can be used to locate and navigate people indoors. To understand the reason behind these anomalies, first a comparison between the measured and model generated Earth's magnetic field is made, verifying the presence of a constant field without any disturbances. Then by modeling the magnetic field behavior of different pillars such as steel reinforced concrete, solid steel, and other structures like doors and elevators, the interaction of the Earth's field with the ferromagnetic fields is described thereby explaining the causes of the uniqueness in the signatures that comprise these disturbances. Next, by employing the dynamic time warping algorithm to account for time differences in signatures obtained from users walking at different speeds, an indoor localization application capable of classifying locations using the magnetic signatures is developed solely on the smart phone. The application required users to walk short distances of 3-6 m anywhere in hallway to be located with accuracies of 80-99%. The classification framework was further validated with over 90% accuracies using model generated magnetic signatures representing hallways with different kinds of pillars, doors and elevators. All in all, this dissertation contributes the following: 1) provides a framework for understanding the presence of ambient magnetic fields indoors and utilizing them to solve the indoor localization problem; 2) develops an application that is independent of the user and the smart phones and 3) requires no other infrastructure since it is deployed on a device that encapsulates the sensing, computing and inferring functionalities, thereby making it a novel contribution to the mobile and pervasive computing domain.

Pathapati Subbu, Kalyan Sasidhar

269

Numerical analyses of trapped field magnet and stable levitation region of HTSC  

SciTech Connect

Stable levitation with a permanent magnet and a bulk high {Tc} superconductor (HTSC) is examined numerically by using the critical state model and the frozen field model. Differences between a permanent magnet and a trapped field magnet are first discussed from property of levitation force. Stable levitation region of the HTSC on a ring magnet and on a solenoid coil are calculated with the numerical methods. Obtained results are discussed from difference of the magnetic field configuration.

Tsuchimoto, M.; Kojima, T.; Waki, H.; Honma, T. [Hokkaido Univ., Sapporo (Japan)

1995-05-01

270

A method to measure specific absorption rate of nanoparticles in colloidal suspension using different configurations of radio-frequency fields  

PubMed Central

We report a method for characterization of the efficiency of radio-frequency (rf) heating of nanoparticles (NPs) suspended in an aqueous medium. Measurements were carried out for water suspended 5?nm superparamagnetic iron-oxide NPs with 30?nm dextran matrix for three different configurations of rf electric and magnetic fields. A 30?MHz high-Q resonator was designed to measure samples placed inside a parallel plate capacitor and solenoid coil with or without an rf electric field shield. All components of rf losses were analyzed and rf electric and magnetic field induced heating of NPs and the dispersion medium was determined and discussed.

Ketharnath, Dhivya; Pande, Rohit; Xie, Leiming; Srinivasan, Srimeenakshi; Godin, Biana; Wosik, Jarek

2012-01-01

271

A method to measure specific absorption rate of nanoparticles in colloidal suspension using different configurations of radio-frequency fields.  

PubMed

We report a method for characterization of the efficiency of radio-frequency (rf) heating of nanoparticles (NPs) suspended in an aqueous medium. Measurements were carried out for water suspended 5?nm superparamagnetic iron-oxide NPs with 30?nm dextran matrix for three different configurations of rf electric and magnetic fields. A 30?MHz high-Q resonator was designed to measure samples placed inside a parallel plate capacitor and solenoid coil with or without an rf electric field shield. All components of rf losses were analyzed and rf electric and magnetic field induced heating of NPs and the dispersion medium was determined and discussed. PMID:22991480

Ketharnath, Dhivya; Pande, Rohit; Xie, Leiming; Srinivasan, Srimeenakshi; Godin, Biana; Wosik, Jarek

2012-08-24

272

A method to measure specific absorption rate of nanoparticles in colloidal suspension using different configurations of radio-frequency fields  

NASA Astrophysics Data System (ADS)

We report a method for characterization of the efficiency of radio-frequency (rf) heating of nanoparticles (NPs) suspended in an aqueous medium. Measurements were carried out for water suspended 5 nm superparamagnetic iron-oxide NPs with 30 nm dextran matrix for three different configurations of rf electric and magnetic fields. A 30 MHz high-Q resonator was designed to measure samples placed inside a parallel plate capacitor and solenoid coil with or without an rf electric field shield. All components of rf losses were analyzed and rf electric and magnetic field induced heating of NPs and the dispersion medium was determined and discussed.

Ketharnath, Dhivya; Pande, Rohit; Xie, Leiming; Srinivasan, Srimeenakshi; Godin, Biana; Wosik, Jarek

2012-08-01

273

Magnetic properties of TbFe2 particles prepared by magnetic field assisted ball milling  

NASA Astrophysics Data System (ADS)

The alloy of TbFe2 was studied by ball milling with and without the presence of external magnetic field. While the structure and powder morphology of the alloy were investigated using scanning electron microscope and X-ray diffraction, the magnetization was investigated using vibrating sample and superconducting quantum interference device magnetometers. The rate of particle reduction with ball milling is comparatively higher in the presence of external magnetic field than without it. Consequently, owing to a large fraction of particles acquiring near single domain configuration under the field assisted milling condition, the coercivity derived from these particles are as high as 6500 Oe than that of particles obtained without the aid of external magnetic field which is around 3850 Oe. The field cooled low temperature magnetization exhibits a large coercivity and skew in the shape of the magnetization curve due to the large anisotropy.

Arout Chelvane, J.; Palit, Mithun; Basumatary, Himalay; Pandian, S.

2013-10-01

274

Advances in the physics of plasma confinement in stellerator magnetic configurations  

Microsoft Academic Search

Stellarators use three-dimensional magnetic field shaping to provide stable plasma confinement without the need for driven plasma currents or stabilizing feedback systems. The maximum plasma beta (plasma pressure normalized to magnetic pressure) that can be confined in the W7-AS stellarator was explored by varying the shape of the magnetic field, the heating power, and the magnetic field strength. The maximum

Michael C. Zarnstorff

2003-01-01

275

HMI Magnetic Field Data Products  

NASA Astrophysics Data System (ADS)

The Helioseismic and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory (SDO) spacecraft will begin observing the solar photospheric magnetic field continuously after commissioning in early 2009. This paper describes the HMI magnetic processing pipeline and the expected data products that will be available. The full disk line-of-sight magnetic field will be available every minute with 1" resolution. Comparable vector measurements collected over a three-minute time interval will ordinarily be averaged for at least 10 minutes before inversion. Useful Quick Look products for forecasting purposes will be available a few minutes after observation. Final products will be computed within 36 hours and made available through the SDO Joint Science Operations Center (JSOC). Three kinds of magnetic data products have been defined - standard, on-demand, and on-request. Standard products, such as frequently updated synoptic charts, are made all the time on a fixed cadence. On-demand products, such as high cadence full-disk disambiguated vector magnetograms, will be generated whenever a user asks for them. On-request products, such as high-resolution time series of MHD model solutions, will be generated as resources allow. This paper describes the observations, magnetograms, synoptic and synchronic products, and field model calculations that will be produced by the HMI magnetic pipeline.

Hoeksema, J.; Hmi, M. T.

2008-05-01

276

Tunneling in a magnetic field  

SciTech Connect

Quantum tunneling across a static potential barrier in a static magnetic field is very sensitive to an analytical form of the potential barrier. Depending on that, the oscillatory structure of the modulus of the wave function can be formed in the direction of tunneling. Due to an underbarrier interference, the probability of tunneling through a higher barrier can be larger than through a lower one. For some barriers the quantum interference of underbarrier cyclotron paths results in a strong enhancement of tunneling. This occurs in the vicinity of the certain magnetic field and is referred to as Euclidean resonance. This strongly contrasts to the Wentzel, Kramers, and Brillouin type tunneling which occurs with no magnetic field.

Ivlev, B. [Department of Physics and Astronomy and NanoCenter, University of South Carolina, Columbia, South Carolina 29208 (United States) and Instituto de Fisica, Universidad Autonoma de San Luis Potosi, San Luis Potosi, San Luis Potosi 78000 Mexico

2006-05-15

277

Thermalization in external magnetic field  

NASA Astrophysics Data System (ADS)

In the AdS/CFT framework meson thermalization in the presence of a constant external magnetic field in a strongly coupled gauge theory has been studied. In the gravitational description the thermalization of mesons corresponds to the horizon formation on the flavour D7-brane which is embedded in the AdS 5 × S 5 background in the probe limit. The apparent horizon forms due to the time-dependent change in the baryon number chemical potential, the injection of baryons in the gauge theory. We will numerically show that the thermalization happens even faster in the presence of the magnetic field on the probe brane. We observe that this reduction in the thermalization time sustains up to a specific value of the magnetic field.

Ali-Akbari, Mohammad; Ebrahim, Hajar

2013-03-01

278

Design of Power Electronics Driven PMSM with Constant Torque by Special Magnetic Circuit and Permanent Magnet Configuration  

Microsoft Academic Search

Special and high efficiency variable speed drives use permanent magnet synchronous motors (PMSM) and power electronics. New dispositions for PMSM with regard to a special magnetic circuit design and new shapes of permanent magnet configurations are investigated. In order to obtain a better rotation performance and to reduce the torque ripple we propose the power electronics current control in support

W. Czernin; F. Asehenbrenner; H. Weiss

2006-01-01

279

Magnetic dipole transitions in 4d{sup N} configurations of tungsten ions  

SciTech Connect

Magnetic dipole transitions between the levels of ground 4d{sup N} configurations of tungsten ions were analyzed by employing a large basis of interacting configurations. Previously introduced configuration interaction strength between two configurations was used to determine the configurations with the largest contribution to wave functions of atomic states for the considered configurations. Collisional-radiative modeling was performed for the levels of the ground configuration coupled through electric dipole transitions with 4p{sup 5}4d{sup N+1} and 4d{sup N-1}4f configurations. New identification of some lines observed in the electron-beam ion trap plasma was proposed based on calculations in which wavelength convergence was reached.

Jonauskas, V.; Kisielius, R.; Kyniene, A.; Kucas, S.; Norrington, P. H. [Institute of Theoretical Physics and Astronomy, Vilnius University, A. Gostauto 12, LT-01108 Vilnius (Lithuania); Department of Applied Mathematics and Theoretical Physics, Queen's University of Belfast, Belfast BT7 1NN, Northern Ireland, United Kingdon (United Kingdom)

2010-01-15

280

Magnetic levitation configuration incorporating levitation, guidance and linear synchronous motor  

DOEpatents

A propulsion and suspension system for an inductive repulsion type magnetically levitated vehicle which is propelled and suspended by a system which includes propulsion windings which form a linear synchronous motor and conductive guideways, adjacent to the propulsion windings, where both combine to partially encircling the vehicle-borne superconducting magnets. A three phase power source is used with the linear synchronous motor to produce a traveling magnetic wave which in conjunction with the magnets propel the vehicle. The conductive guideway combines with the superconducting magnets to provide for vehicle leviation.

Coffey, H.T.

1992-12-31

281

Photospheric Magnetic Field: Quiet Sun  

NASA Astrophysics Data System (ADS)

The solar photosphere is the layer in which the magnetic field has been most reliably and most often measured. Zeeman- and Hanle-effect based probes have revealed many details of a rich variety of structures and dynamic processes, but the number of open and debated questions has remained large. The magnetic field in the quiet Sun has maintained a particularly large number of secrets and has been a topic of a particularly lively debate as new observations and analysis techniques have revealed new and often unexpected aspects of its organization, physical structure and origin.

Solanki, S. K.

2009-06-01

282

Langmuir chains of ions in linearly and circularly polarized electromagnetic field crossed with the magnetic field  

NASA Astrophysics Data System (ADS)

We have recently discovered that so called Langmuir [1] states of Helium can stabilize in both the circularly polarized electromagnetic and the magnetic fields when the fields are crossed and two electrons are rotating in the configuration when the two parallel single-electron circular trajectories have the both particles moving in the spatial phase. The stability islands in the fields strength planes have exotic shapes and the configurations are bistable geometrically. Here we discover the whole chains of ions when the single Langmuir configuration is additionally experiencing the infinite chain of neighbouring ions and alike space-periodic configurations. This leads to self-stabilization and Born-Opennheimer binding of Hydrogen, helium or higher charged ions in chains parallel to the magnetic field and when the CP field vector is perpendicular. The excitations along the chain are plasmon-like and have the physical meaning of the deviation from the CP field rotation helicity. Ones the linearly polarized field is superposed from two circularly polarized counterrotating fields similar configurations exist by the geometric argument. Numerical simulations using the recently discovered Cartesian-hypespherical coordinates method previously applied to Langmuir configurations themself are also presented. [1] M. Kalinski, L. Hansen, and D. Farrelly, ``Nondispersive Two-Electron Wave Packets in a Helium Atom,'' Phys. Rev. Lett. 95, 103001 (2005).

Kalinski, Matt

2010-03-01

283

Large-scale structure of the solar corona magnetic field  

NASA Astrophysics Data System (ADS)

The configuration of the solar corona magnetic field has been studied. Data on the position of the K-corona emission polarization plane during the solar eclipses of September 21, 1941; February 25, 1952; and August 1, 2008, were used as an indicator of the magnetic field line orientation. Based on an analysis of these data, a conclusion has been made that the studied configuration has a large-scale organization in the form of a cellular structure with an alternating field reversal. The estimated cell size was 61° ± 6° (or 36° ± 2°) in longitude with a latitudinal extension of 40°-50° in the range of visible distances 1.3-2.0 R Sun . A comparison of the detected cellular structure of the coronal magnetic field with synoptic {ie908-1} maps indicated that the structure latitudinal boundaries vary insignificantly within 1.1-2.0 R Sun . The possible causes of the formation of the magnetic field large-scale cellular configuration in the corona and the conditions for the transformation of this configuration into a two-sector structure are discussed.

Merzlyakov, V. L.; Starkova, L. I.

2012-12-01

284

Photospheric and coronal magnetic fields  

SciTech Connect

Research on small-scale and large-scale photospheric and coronal magnetic fields during 1987-1990 is reviewed, focusing on observational studies. Particular attention is given to the new techniques, which include the correlation tracking of granules, the use of highly Zeeman-sensitive infrared spectral lines and multiple lines to deduce small-scale field strength, the application of long integration times coupled with good seeing conditions to study weak fields, and the use of high-resolution CCD detectors together with computer image-processing techniques to obtain images with unsurpassed spatial resolution. Synoptic observations of large-scale fields during the sunspot cycle are also discussed. 101 refs.

Sheeley, N.R., Jr. (USAF, Geophysics Laboratory, Hanscom AFB, MA (United States))

1991-01-01

285

Vibrating H3+ in a Uniform Magnetic Field  

NASA Astrophysics Data System (ADS)

Potential energy surfaces are obtained for singlet H3+ in magnetic fields of up to 2350 T. The magnetic interaction was treated by first-order perturbation theory and the interaction terms computed ab initio. They were then fitted to a functional form and added to a recent, highly accurate adiabatic potential energy surface. In its most stable orientation, the molecule is arranged such that the magnetic field vector is in the molecular plane. The most stable configuration is no longer D3h as in the field-free case, but C2v, though the stabilization energy is extremely small, of the order of 0.01 cm-1 for a 2350 T field. Finally, we have calculated, for a range of magnetic field strengths and orientations, all the vibrational eigenvalues that are below the barrier to linearity in the field-free case.

Medel Cobaxin, Héctor; Alijah, Alexander

2013-10-01

286

Field-aligned accelerations by plasma shocks propagating through interstellar magnetic fields  

SciTech Connect

A kinetic model of particle acceleration by plasma shocks is analyzed theoretically and with numerical calculations. The shocks are propagating through weakly magnetized background plasmas, namely interstellar magnetic fields (IMFs). Particles located at the shock front are accelerated parallel to the magnetic field of the shock; this is defined as the field-aligned acceleration (FAA). The cross angle between IMF and the magnetic field of the shock plays an important role in creating the magnetic neutral sheet at the shock front. A test particle trapped by the neutral sheet obtains enormous energy due to the FAA. A reasonable formula for the highest energy gain is derived from theoretical analysis of the relativistic equations of motion. A possible configuration of the electric and magnetic fields in supernova remnants is also proposed by way of example.

Takeuchi, Satoshi [Department of Environmental Sciences, University of Yamanashi, 4-3-11 Takeda, Kofu, Yamanashi 400-8511 (Japan)

2012-07-15

287

Magnetic Field from Loops Model  

NSDL National Science Digital Library

The EJSMagnetic Field from Loops model computes the B-field created by an electric current through a straight wire, a closed loop, and a solenoid. Users can adjust the vertical position of the slice through the 3D field. The Magnetic Field from Loops model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_ntnu_MagneticFielfFromLoops.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models for classical mechanics are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Christian, Wolfgang; Hwang, Fu-Kwun

2008-11-17

288

Magnetic field generation in Galactic molecular clouds  

NASA Astrophysics Data System (ADS)

We investigate the magnetic field which is generated by turbulent motions of a weakly ionized gas. Galactic molecular clouds give us an example of such a medium. As in the Kazantsev-Kraichnan model we assume a medium to be homogeneous and a neutral gas velocity field to be isotropic and ? correlated in time. We take into consideration the presence of a mean magnetic field, which defines a preferred direction in space and eliminates isotropy of magnetic field correlators. Evolution equations for the anisotropic correlation function are derived. Isotropic cases with zero mean magnetic field as well as with small mean magnetic field are investigated. It is shown that stationary bounded solutions exist only in the presence of the mean magnetic field for the Kolmogorov neutral gas turbulence. The dependence of the magnetic field fluctuations amplitude on the mean field is calculated. The stationary anisotropic solution for the magnetic turbulence is also obtained for large values of the mean magnetic field.

Istomin, Ya. N.; Kiselev, A.

2013-10-01

289

FIELD CHARACTERIZATION OF XFEL QUADRUPOLE MAGNETS  

Microsoft Academic Search

A rotating coil setup for magnetic field characterization and fiducialization of XFEL quadrupole magnets is pre- sented. The instrument allows measurement of the rel- ative position of the magnetic axis with accuracy better than 1 ?m and measurement of weak magnetic error field components. Tests and evaluation based on a FLASH quadrupole magnet are presented together with a discus- sion

A. Hedqvist; H. Danared; F. Hellberg; J. Pfluger

290

EXPLORER 10 MAGNETIC FIELD MEASUREMENTS  

Microsoft Academic Search

Magnetic field measurements made by means of Explorer 10 over geocentric ; distances of 1.8 to 42.6R\\/sub e\\/ on March 25experiment on the same satellite are ; referenced in interpretations. The close-in data are consistent with the ; existence of a very weak ring current below 3R\\/sub e\\/ along the trajectory, but ; alternative explanations for the field deviations are

J. P. Heppner; N. F. Ness; C. S. Scearce; T. L. Skillman

1963-01-01

291

Magnetic fields in extragalactic jets  

Microsoft Academic Search

Observations indicate that jets (i.e., charged particle beams) are emitted from the central black hole sources of active galactic nuclei and quasars. Magnetic fields are produced in e(-)-p or e(-)-e(+)-p jets when electrons (and positrons) are slowed with respect to protons in the jets. Interaction with an ambient interstellar gas or external radiation field can cause such drift velocities. Calculations

William K. Rose

1987-01-01

292

Magnetic fields in extragalactic jets  

Microsoft Academic Search

Observations indicate that jets are emitted from the central black hole sources of active galactic nuclei and quasars. Magnetic fields are produced in e--p or e--e+-p jets when electrons and positrons are slowed with respect to protons in the jets. Interaction with an ambient interstellar gas or external radiation field can cause such drift velocities. In this paper calculations for

William K. Rose

1987-01-01

293

The somatosensory evoked magnetic fields  

Microsoft Academic Search

Averaged magnetoencephalography (MEG) following somatosensory stimulation, somatosensory evoked magnetic field(s) (SEF), in humans are reviewed. The equivalent current dipole(s) (ECD) of the primary and the following middle-latency components of SEF following electrical stimulation within 80–100 ms are estimated in area 3b of the primary somatosensory cortex (SI), the posterior bank of the central sulcus, in the hemisphere contralateral to the

Ryusuke Kakigi; Minoru Hoshiyama; Motoko Shimojo; Daisuke Naka; Hiroshi Yamasaki; Shoko Watanabe; Jing Xiang; Kazuaki Maeda; Khanh Lam; Kazuya Itomi; Akinori Nakamura

2000-01-01

294

High-latitude convection patterns for various large-scale field-aligned current configurations  

SciTech Connect

The large-scale field-aligned current system for persistent northward interplanetary magnetic field (IMF) is typically different from that for persistent southward IMF. One characteristic difference is that for northward IMF there is often a large-scale field-aligned current system poleward of the main auroral oval. This current system (the NBZ current) typically occupies a large function of the region poleward of the region 1 and 2 currents. The present paper models the high-latitude convection as a function of the large-scale field-aligned currents. In particular, a possible evolution of the convection pattern as the current system changes from a typical configuration for southward IMF to a configuration representing northward IMF (or vice versa) is presented. Depending on additional assumptions, for example about the y-component of the IMF, the convection pattern could either turn directly from a two-cell type to a four-cell type, or a three-cell type pattern could show up as an intermediate state. An interesting although rather surprising result of this study is that different ways of balancing the NBZ currents has a minor influence on the large-scale convection pattern.

Blomberg, L.G.; Marklund, G.T. (Royal Inst. of Tech., Stockholm (Sweden))

1991-04-01

295

Magnetic Fields above the Surface of aSuperconductor with Internal Magnetism  

SciTech Connect

The author presents a method for calculating the magnetic fields near a planar surface of a superconductor with a given intrinsic magnetization in the London limit. He computes solutions for various magnetic domain boundary configurations and derives relations between the spectral densities of the magnetization and the resulting field in the vacuum half space, which are useful if the magnetization can be considered as a statistical quantity and its features are too small to be resolved individually. The results are useful for analyzing and designing magnetic scanning experiments. Application to existing data from such experiments on Sr{sub 2}RuO{sub 4} show that a domain wall would have been detectable, but the magnetic field of randomly oriented small domains and small defects may have been smaller than the experimental noise level.

Bluhm, Hendrik; /Stanford U., Phys. Dept. /SLAC, SSRl

2007-06-26

296

Ring shaped magnetic field transducer based on the GMI effect  

Microsoft Academic Search

In this paper the design of a magnetic-field-to-voltage transducer based on the giant magnetoimpedance phenomenon (GMI) is proposed, characterized by an innovative geometric configuration. In order to attain the best near-field sensibility and far-field immunity, the transducer's sensitive element and electronic circuit were planned and implemented. By thoroughly characterizing them it was possible to obtain an estimate of the transducer's

F Pompéia; L A P Gusmão; C R Hall Barbosa; E Costa Monteiro; L A P Gonçalves; F L A Machado

2008-01-01

297

Advances in Magnetic Field Sensors  

Microsoft Academic Search

The most important milestone in the field of magnetic sensors was when AMR sensors started to replace Hall sensors in many applications where the greater sensitivity of AMRs was an advantage. GMR and SDT sensors finally found applications. We also review the development of miniaturization of fluxgate sensors and refer briefly to SQUIDs, resonant sensors, GMIs, and magnetomechanical sensors.

Pavel Ripka; Michal Janosek

2010-01-01

298

Random Field Effect in Magnets.  

National Technical Information Service (NTIS)

In order to explore the consequences of random field effects we have carried out a series of neutron scattering experiments on three prototypical diluted Ising magnets. The systems studied are Rb sub 2 Co sub 7 Mg sub 3 F sub 4 which is a model two dimens...

R. J. Birgeneau

1982-01-01

299

Magnetic Field Waves at Uranus.  

National Technical Information Service (NTIS)

The research efforts funded by the Uranus Data Analysis Program (UDAP) grant to the Bartol Research Institute (BRI) involved the study of magnetic field waves associated with the Uranian bow shock. Upstream wave studies are motivated as a study of the phy...

C. W. Smith M. L. Goldstein R. P. Lepping W. H. Mish H. K. Wong

1994-01-01

300

NMR imaging in the earth's magnetic field.  

PubMed

The most important and very expensive part of a magnetic resonance imaging set-up is the magnet, which is capable of generating a constant and highly homogeneous magnetic field. Here a new MR imaging technique without the magnet is introduced. This technique uses the earth's magnetic field instead of a magnetic field created by a magnet. This new method has not yet reached the stage of medical application, but the first images obtained by MRIE (magnetic resonance imaging in the earth's field) show that the resolution is close to that expected based on sensitivity estimations. PMID:2233218

Stepisnik, J; Erzen, V; Kos, M

1990-09-01

301

Separation of magnetic field lines  

SciTech Connect

The field lines of magnetic fields that depend on three spatial coordinates are shown to have a fundamentally different behavior from those that depend on two coordinates. Unlike two-coordinate cases, a flux tube in a magnetic field that depends on all three spatial coordinates that has a circular cross section at one location along the tube characteristically has a highly distorted cross section at other locations. In an ideal evolution of a magnetic field, the current densities typically increase. Crudely stated, if the current densities increase by a factor {sigma}, the ratio of the long to the short distance across a cross section of a flux tube characteristically increases by e{sup 2{sigma}}, and the ratio of the longer distance to the initial radius increases as e{sup {sigma}}. Electron inertia prevents a plasma from isolating two magnetic field structures on a distance scale shorter than c/{omega}{sub pe}, which is about 10 cm in the solar corona, and reconnection must be triggered if {sigma} becomes sufficiently large. The radius of the sun, R{sub Circled-Dot-Operator }=7 Multiplication-Sign 10{sup 10}cm is about e{sup 23} times larger, so when {sigma} Greater-Than-Or-Equivalent-To 23, two lines separated by c/{omega}{sub pe} at one location can be separated by the full scale of any magnetic structures in the corona at another. The conditions for achieving a large exponentiation, {sigma}, are derived, and the importance of exponentiation is discussed.

Boozer, Allen H. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)

2012-11-15

302

Near-field imaging of ultrathin magnetic films with in-plane magnetization.  

PubMed

A new approach to near-field magneto-optical imaging was developed capable of visualization of in-plane magnetization of ultrathin magnetic structures. The approach relies on the magneto-optical effect specific for thin magnetic layers and employs near-field transmission measurements of longitudinal and/or transverse magneto-optical effect arising from the presence of thin film interfaces. The near-field magneto-optical contrast of in-plane domain structure of ultrathin Co film has been demonstrated in different polarization configurations. PMID:12641761

Dickson, W; Takahashi, S; Pollard, R; Atkinson, R; Zayats, A V

2003-03-01

303

High-performance magnetic field and quasi-current sensors  

Microsoft Academic Search

Summary form only given. Magnetic field sensors have been constructed from two pieces of polarizing optical fiber fusion spliced to a single piece of low birefringence optical fiber. This configuration was mounted on a quartz bar for good geometric stability. A 780-nm laser diode pigtailed with polarizing fiber is used as the optical source for the sensor and light at

J. W. Dawson; T. W. MacDougall; E. Hernandez

1996-01-01

304

Active Region Magnetic Fields. I. Plage Fields  

NASA Astrophysics Data System (ADS)

We present observations taken with the Advanced Stokes Polarimeter (ASP) in active-region plages and study the frequency distribution of the magnetic field strength (B), inclination with respect to vertical ( gamma ), azimuthal orientation ( chi ), and filling factor (f). The most common values at disk center are B = 1400 G, gamma < 10 deg, no preferred east-west orientation, and f = 15%. At disk center, there is a component of weak (<1000 G), more horizontal fields that corresponds to arching field lines connecting footpoints of different polarities. The center-to-limb variation (CLV) of the field strength shows that, close to the limb ( mu = 0.3), the field strength is reduced to 800 G from its disk-center value. This can be interpreted as a gradient of B with height in solar plages of around -3 G km-1. From this CLV study, we also deduce that magnetic field lines remain vertical for the entire range of heights involved. A similar analysis is performed for structures found in active regions that show a continuous distribution of azimuths (resembling sunspots) but that do not have a darkening in continuum. These "azimuth centers" show slightly larger values of B than normal plages, in particular at their magnetic center. Filling factors are also larger on average for these structures. The velocities in the magnetic component of active regions have been studied for both averaged Stokes profiles over the entire active region and for the spatially resolved data. The averaged profiles (more representative of high filling factor regions) do not show any significant mean velocities. However, the spatial average of Doppler velocities derived from the spatially resolved profiles (i.e., unweighted by filling factor) show a net redshift at disk center of 200 m s-1. The spatially resolved velocities show a strong dependence on filling factor. Both mean velocities and standard deviations are reduced when the filling factor increases. This is interpreted as a reduction of the p-mode amplitude within the magnetic component. Strong evidence for velocities transverse to the magnetic field lines has been found. Typical rms values are between 200 and 300 m s-1, depending on the filling factor. The possible importance of these transverse motions for the dynamics of the upper atmospheric layers is discussed. The asymmetries of the Stokes profiles and their CLV have been studied. The averaged Stokes V profiles show amplitude and area asymmetries that are positive at disk center and become negative at the limb. Both asymmetries, and for the two Fe I lines, are maximized away from disk center. The spatially resolved amplitude asymmetries show a clear dependence on filling factor: the larger the filling factor, the smaller the amplitude asymmetry. On the other hand, the area asymmetry is almost independent of the filling factor. The only observed dependence is the existence of negative area-asymmetry profiles at disk center for filling factors smaller than 0.2. Around 20% of the observed points in a given plage have negative area asymmetry. The amplitude asymmetry of Stokes V is, on the other hand, always positive. The amplitude asymmetries of the linear polarization profiles are observed to have the same sign as the Stokes V profiles. Similarly, the same CLV variation of the linear polarization amplitude asymmetries as for Stokes V has been found. The scenarios in which this similarity can exist are studied in some detail.

Martinez Pillet, V.; Lites, B. W.; Skumanich, A.

1997-01-01

305

Electron dynamics in inhomogeneous magnetic fields.  

PubMed

This review explores the dynamics of two-dimensional electrons in magnetic potentials that vary on scales smaller than the mean free path. The physics of microscopically inhomogeneous magnetic fields relates to important fundamental problems in the fractional quantum Hall effect, superconductivity, spintronics and graphene physics and spins out promising applications which will be described here. After introducing the initial work done on electron localization in random magnetic fields, the experimental methods for fabricating magnetic potentials are presented. Drift-diffusion phenomena are then described, which include commensurability oscillations, magnetic channelling, resistance resonance effects and magnetic dots. We then review quantum phenomena in magnetic potentials including magnetic quantum wires, magnetic minibands in superlattices, rectification by snake states, quantum tunnelling and Klein tunnelling. The third part is devoted to spintronics in inhomogeneous magnetic fields. This covers spin filtering by magnetic field gradients and circular magnetic fields, electrically induced spin resonance, spin resonance fluorescence and coherent spin manipulation. PMID:21393794

Nogaret, Alain

2010-06-04

306

Magnetic fields in the cosmos  

SciTech Connect

Although only a small part of available energy in the universe is invested in magnetic fields, they are responsible for most of the continual violent activity in the cosmos. There is a single, generic explanation for the ability of bodies as different as a dense, cold planet and a tenuous hot galactic disk to generate a magnetic field. The explanation, first worked out for the earth, comes from the discipline of magnetohydrodynamics. The cosmos is filled with fluids capable of carrying electric currents. The magnetic fields entrained in these fluids are stretched and folded by the fluid motion, gaining energy in the process. In other words, the turbulent fluids function as dynamos. However, the dynamo mechanism by itself cannot account for the exceptionally strong field of some stars. Because of such gaps in information, the rival hypothesis that there are primordial fields cannot be disproved. The balance of evidence, however, indicates that the planets, sun, most stars and the galaxy function as colossal dynamos. (SC)

Parker, E.N.

1983-08-01

307

Note: Manipulation of supersonic atomic beams with static magnetic fields.  

PubMed

The inhomogeneous magnetic field of a permanent-magnet planar Halbach array is used to either deflect or to specularly reflect a supersonic beam of neutral atoms. Metastable neon and helium beams are tested to experimentally evaluate the performance of this array in a range of configurations. Results are compared with numerical simulations and the device is presented as a high precision tool for the manipulation of neutral atom beams. PMID:24028135

Gardner, Jamie; Castillo-Garza, Rodrigo; Raizen, Mark G

2013-09-01

308

Behavior of magnetic liquids in an inhomogeneous magnetic field  

SciTech Connect

The authors present experimental results from the investigation of the behavior of certain magnetic liquids differeing in the degree of stability in inhomogenous magnetic fields. The growth of holding presure of sealing step at rest is reviewed and the increase of effective viscosity in inhomogeneous magnetic fields is studied. The behaviors of magnetic liquids in an inhomogeneous magnetic field are sensitive to structural changes caused by the field. Significant differences are demonstrated between magnetic liquids with the same saturation magnetization but different particle size distribution.

Anton, I.; Bika, D.; Potents, I.; Vekash, L.

1986-01-01

309

Dynamic formation of a hot field reversed configuration with improved confinement by supersonic merging of two colliding high-? compact toroids.  

PubMed

A hot stable field-reversed configuration (FRC) has been produced in the C-2 experiment by colliding and merging two high-? plasmoids preformed by the dynamic version of field-reversed ?-pinch technology. The merging process exhibits the highest poloidal flux amplification obtained in a magnetic confinement system (over tenfold increase). Most of the kinetic energy is converted into thermal energy with total temperature (T{i}+T{e}) exceeding 0.5 keV. The final FRC state exhibits a record FRC lifetime with flux confinement approaching classical values. These findings should have significant implications for fusion research and the physics of magnetic reconnection. PMID:20867853

Binderbauer, M W; Guo, H Y; Tuszewski, M; Putvinski, S; Sevier, L; Barnes, D; Rostoker, N; Anderson, M G; Andow, R; Bonelli, L; Brandi, F; Brown, R; Bui, D Q; Bystritskii, V; Ceccherini, F; Clary, R; Cheung, A H; Conroy, K D; Deng, B H; Dettrick, S A; Douglass, J D; Feng, P; Galeotti, L; Garate, E; Giammanco, F; Glass, F J; Gornostaeva, O; Gota, H; Gupta, D; Gupta, S; Kinley, J S; Knapp, K; Korepanov, S; Hollins, M; Isakov, I; Jose, V A; Li, X L; Luo, Y; Marsili, P; Mendoza, R; Meekins, M; Mok, Y; Necas, A; Paganini, E; Pegoraro, F; Pousa-Hijos, R; Primavera, S; Ruskov, E; Qerushi, A; Schmitz, L; Schroeder, J H; Sibley, A; Smirnov, A; Song, Y; Sun, X; Thompson, M C; Van Drie, A D; Walters, J K; Wyman, M D

2010-07-22

310

Stationary perturbation configurations in a composite system of stellar and coplanarly magnetized gaseous singular isothermal discs  

NASA Astrophysics Data System (ADS)

We construct aligned and unaligned stationary perturbation configurations in a composite system of stellar and coplanarly magnetized gaseous singular isothermal discs (SIDs) coupled by gravity. This study extends recent analyses on (magnetized) SIDs by Shu et al., Lou and Lou & Shen. By this model, we intend to provide a conceptual framework to gain insights for multiwavelength large-scale structural observations of disc galaxies. Both SIDs are approximated to be razor thin and are in a self-consistent axisymmetric background equilibrium with power-law surface mass densities and flat rotation curves. The gaseous SID is embedded with a coplanar azimuthal magnetic field B?(r) of a radial scaling r-1/2 that is not force-free. In comparison with the SID problems studied earlier, there are three possible classes of stationary solutions allowed by more dynamic freedoms. To identify physical solutions, we explore parameter space involving three dimensionless parameters: ratio ? of Alfvén speed to sound speed in the magnetized gaseous SID; ratio ? of the square of the stellar velocity dispersion to the gas sound speed; and ratio ? of the surface mass densities of the two SIDs. For both aligned and unaligned spiral cases with azimuthal periodicities |m| >= 2, one of the three solution branches is always physical, while the other two branches might become invalid when ? exceeds certain critical values. For the onset criteria from an axisymmetric equilibrium to aligned secular bar-like instabilities, the corresponding ratio, which varies with ?, ? and ?, may be considerably lower than the oft-quoted value of , where is the total kinetic energy, is the total gravitational potential energy and is the total magnetic energy. For unaligned spiral cases, we examine marginal instabilities for axisymmetric (|m| = 0) and non-axisymmetric (|m| > 0) disturbances. The resulting marginal stability curves differ from the previous ones. The case of a composite partial magnetized SID system is also investigated to include the gravitational effect of an axisymmetric dark matter halo on the SID equilibrium. We further examine the phase relationship among the mass densities of the two SIDs and azimuthal magnetic field perturbation. Our exact global perturbation solutions and critical points are valuable for testing numerical magnetohydrodynamic codes. For galactic applications, our model analysis contains more realistic elements and offers useful insights into the structures and dynamics of disc galaxies consisting of stars and magnetized gas.

Lou, Yu-Qing; Zou, Yue

2004-06-01

311

Linear Stability Analysis Of A Magnetic/Non-Magnetic Fluid Coflow In The Presence Of A Magnetic Field  

NASA Astrophysics Data System (ADS)

Ferrofluids are colloidal suspensions of magnetic nanoparticles in carrier liquids. Being both magnetic and a liquid, they are readily maneuvered from a distance using magnetic fields. When functionalized with different antibodies or medicinal compounds, the ferrofluid can be used for various purposes, e.g., to detect bacteria or for targeted drug delivery. We have considered a coflow where two fluids are separated by a vertical surface parallel to the direction of gravity. For simplicity the flow is assumed to be inviscid and incompressible. We have investigated two configurations depending on the position of the magnet relative to the channel. When the magnet is placed adjacent to the vertical wall along which the magnetic fluid is flowing, the magnetic fluid stays close to the wall unless perturbed by the shear due to a velocity difference. It results in a very stable system. In the second case, the magnet is placed close to the wall along which the non-magnetic fluid flows. The magnetic fluid gets attracted towards the magnet and tries to flow toward it when it gets resisted by the non-magnetic fluid. This configuration is inherently unstable and responds to small perturbations. The surface tension force resists the perturbation of smaller wavelengths. The relative effects of different forces are characterized by magnetic pressure number, Weber number and magnetic Weber number.

de, Anindya; Puri, Ishwar

2007-11-01

312

Experimental profile evolution of a high-density field-reversed configuration  

SciTech Connect

A field-reversed configuration (FRC) gains angular momentum over time, eventually resulting in an n=2 rotational instability (invariant under rotation by {pi}) terminating confinement. To study this, a laser interferometer probes the time history of line integrated plasma density along eight chords of the high-density ({approx}10{sup 17} cm{sup -3}) field-reversed configuration experiment with a liner. Abel and tomographic inversions provide density profiles during the FRC's azimuthally symmetric phase, and over a period when the rotational mode has saturated and rotates with a roughly fixed profile, respectively. During the latter part of the symmetric phase, the FRC approximates a magnetohydrodynamic (MHD) equilibrium, allowing the axial magnetic-field profile to be calculated from pressure balance. Basic FRC properties such as temperature and poloidal flux are then inferred. The subsequent two-dimensional n=2 density profiles provide angular momentum information needed to set bounds on prior values of the stability relevant parameter {alpha} (rotational to ion diamagnetic drift frequency ratio), in addition to a view of plasma kinematics useful for benchmarking plasma models of higher order than MHD.

Ruden, E. L.; Zhang, Shouyin; Intrator, T. P.; Wurden, G. A. [Air Force Research Laboratory, Directed Energy Directorate, 3550 Aberdeen Avenue SE, Kirtland AFB, New Mexico, 87117-5776 (United States); Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2006-12-15

313

Local deformations of ferrogels induced by uniform magnetic fields  

NASA Astrophysics Data System (ADS)

In this work we present anisotropic light scattering measurements of local deformation in systems composed by a dispersion of nanometric magnetic particles in a polymer gel, or ferrogel, in the presence of uniform magnetic fields. Two experimental configurations were used in which the scattering vector q was parallel and perpendicular to the magnetic induction B. We have seen that the scattered intensity increases in the parallel configuration as B increases and decreases in the perpendicular configuration. These intensity variations are opposite to those observed using X-rays (Phys. Rev. E 67 (2003) 021504), where the length scales q-1 are comparable to the particle size. In all experiments the variation of the scattered intensity closely follows a Langevin type function. The anisotropic scattered light intensity variation was related to long-range deformations in the polymer matrix.

Teixeira, Alvaro V.; Licinio, Pedro

2005-03-01

314

SQUID-Detected Magnetic Resonance Imaging in Microtesla Magnetic Fields  

Microsoft Academic Search

We describe studies of nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) of liquid samples at room temperature in microtesla magnetic fields. The nuclear spins are prepolarized in a strong transient field. The magnetic signals generated by the precessing spins, which range in frequency from tens of Hz to several kHz, are detected by a low-transition temperature dc

R. McDermott; N. Kelso; S. K. Lee; M. MöBetale; M. Mück; W. Myers; B. ten Haken; H. C. Seton; A. H. Trabesinger; A. Pines; J. Clarke

2004-01-01

315

Two dimensional frustrated magnets in high magnetic field  

Microsoft Academic Search

Frustrated magnets in high magnetic field have a long history of offering beautiful surprises to the patient investigator. Here we present the results of extensive classical Monte Carlo simulations of a variety of models of two dimensional magnets in magnetic field, together with complementary spin wave analysis. Striking results include (i) a massively enhanced magnetocaloric effect in antiferromagnets bordering on

L. Seabra; N. Shannon; P. Sindzingre; T. Momoi; B. Schmidt; P. Thalmeier

2009-01-01

316

Effect of configurational order on the magnetic characteristics of Co-Ni-Ga ferromagnetic shape memory alloys  

NASA Astrophysics Data System (ADS)

In most of the ternary (and higher-order) ferromagnetic shape memory alloys (FSMAs) with compositions close to the A2BC stoichiometry, the austenite phase exhibits L21-type ordering. Recent investigations of the Co-Ni-Ga FSMA system, however, suggest that the austenite phase has B2-type ordering, although definite confirmation remains elusive. In this work, we present a theoretical investigation of the effect of configurational order on the magnetic properties of the ordered (L21) and disordered (B2) FSMA Co2NiGa. Through the use of calculations based on density functional theory, we predict the structural and magnetic properties (including magnetic exchange constants) of ordered and disordered Co2NiGa alloys. We validate our calculation of the magnetic exchange constants by extracting the Curie temperatures of the austenite and martensite structures and comparing them to experimental results. By constructing a q-state Potts magnetic Hamiltonian and through the use of lattice Monte Carlo simulation, we predict the finite-temperature behavior of the magnetization and magnetic susceptibility as well as the magnetic specific heat and entropy. The role of configurational order in the magnetic properties of the phases involved in the martensitic phase transformation is discussed, and predictions of the magnitude of the magnetic contributions to the transformation entropy are presented. The calculations are compared to experimental information available in the literature as well as experiments performed by the authors. It is concluded that in FSMAs magnetism plays a fundamental role in determining the relative stability of the austenite and martensite phases, which in turn determines the martensitic transformation temperature Ms, irrespective of whether magnetic fields are used to drive the transformation.

Singh, Navdeep; Dogan, Ebubekir; Karaman, Ibrahim; Arróyave, Raymundo

2011-11-01

317

Generation of Whistler Wave by a Rotating Magnetic Field Source  

NASA Astrophysics Data System (ADS)

The interaction of Rotating Magnetic Fields (RMF) with plasmas is a fundamental plasma physics problem with implications to fusion related Field-Reversed Configurations (FRC), space propulsion, astronaut protection from cosmic rays in long interstellar travel, control of the energetic population in the radiation belts and near zone processes in pulsar magnetospheres. In this paper we report recent experiments on the generation of whistler waves with a new type RMF-based antenna. The experiments were conducted on UCLA's Large Plasma Device (LAPD). The Rotating Magnetic Field (RMF) is created using poly-phased loop antennas. A number of parameter combinations, e.g. plasma density, background magnetic field, and driving current, were used. It was found that RMF created by a two phase-delayed loop antenna drives significant currents along the ambient magnetic field. The measured amplitude of induced wave field was proportional to the square-root of the plasma density. The spatial decay rate for the wave perturbation across the background magnetic field was found to scale with the plasma skin depth. A small amplitude second harmonic was also measured. The paper will also present analytic and simulation results that account for the experimental results; in particular, the scaling of the induced magnetic field as a function of the RMF and plasma parameters and the spatial decay rate of magnetic field. Applications of RMF as an efficient radiation source of plasma waves in space plasmas will be discussed. This work was sponsored by ONR MURI Grant 5-28828

Karavaev, A.; Papadopoulos, K.; Shao, X.; Sharma, A. S.; Gigliotti, A.; Gekelman, W.; Pribyl, P.; Vincena, S.

2008-12-01

318

The HMI Magnetic Field Pipeline  

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

319

Effects of Strong Magnetic Fields on Neutron Star Structure  

NASA Astrophysics Data System (ADS)

We study static neutron stars with poloidal magnetic fields and a simple class of electric current distributions consistent with the requirement of stationarity. For this class of electric current distributions, we find that magnetic fields are too large for static configurations to exist when the magnetic force pushes a sufficient amount of mass off-center that the gravitational force points outward near the origin in the equatorial plane. (In our coordinates an outward gravitational force corresponds to ?lngtt/?r>0, where t and r are respectively time and radial coordinates and gtt is coefficient of dt2 in the line element.) For the equations of state (EOSs) employed in previous work, we obtain configurations of higher mass than had been reported; we also present results with more recent EOSs. For all EOSs studied, we find that the maximum mass among these static configurations with magnetic fields is noticeably larger than the maximum mass attainable by uniform rotation, and that for fixed values of baryon number the maximum mass configurations are all characterized by an off-center density maximum.

Cardall, Christian Y.; Prakash, Madappa; Lattimer, James M.

2001-06-01

320

Magnetic Resonance Imaging System Based on Earth's Magnetic Field  

Microsoft Academic Search

This article describes both the setup and the use of a system for magnetic resonance imaging (MRI) in the Earth's magnetic field. Phase instability caused by temporal fluctuations of Earth's field can be successfully improved by using a reference signal from a separate Earth's field nuclear magnetic resonance (NMR) spectrometer\\/magnetometer. In imaging, it is important to correctly determine the phase

Ales Mohoric; Gorazd Planinsic; Miha Kos; Andrej Duh; Janez Stepisnik

2004-01-01

321

Magnetic field of atrial depolarization.  

PubMed

The isomagnetic maps of normal subjects and patients with right and left atrial overloading were recorded to determine the characteristic features of the magnetic field of atrial depolarization. The isomagnetic maps examined in this study indicated the instantaneous current source, which specifically localizes the current sources due to the right and left atria, respectively. The magnetic field recorded with a second derivative gradiometer clearly detected the cardiac current source from the right atrium, which is located close to the anterior chest wall, thus this method improved the diagnostic sensitivity for right atrial overloading. In patients with left atrial overloading, the isomagnetic map showed multiple dipoles due to the right and left atria, respectively, which are difficult to be detected by the electrocardiogram or isopotential map. These results suggest that the magnetocardiogram provides useful information on the current source to supplement information obtained by the conventional electrocardiogram. PMID:2978585

Takeuchi, A; Watanabe, K; Katayama, M; Nomura, M; Nakaya, Y; Mori, H

322

Current-induced switching of magnetic domains to a perpendicular configuration  

SciTech Connect

In a ferromagnet{endash}normal-metal{endash}ferromagnet trilayer, a current flowing perpendicularly to the layers creates a torque on the magnetic moments of the ferromagnets. When one of the contacts is superconducting, the torque not only favors parallel or antiparallel alignment of the magnetic moments, as is the case for two normal contacts, but can also favor a configuration where the two moments are perpendicular. In addition, whereas the conductance for parallel and antiparallel magnetic moments is the same, signalling the absence of giant magnetoresistance in the usual sense, the conductance is greater in the perpendicular configuration. Thus, a negative magnetoconductance is predicted, in contrast with the usual giant magnetoresistance.

Waintal, X.; Brouwer, P. W.

2001-06-01

323

POLOIDAL MAGNETIC FIELD TOPOLOGY FOR TOKAMAKS WITH CURRENT HOLES  

SciTech Connect

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

Puerta, Julio; Martin, Pablo; Castro, Enrique [Universidad Simon Bolivar, Departamento de Fisica, Plasma Physics Laboratory, Caracas (Venezuela, Bolivarian Republic of)

2009-07-26

324

Analysis of the vector magnetic fields of complex sunspots  

NASA Astrophysics Data System (ADS)

An analysis of the vector magnetic field in the delta-configurations of two complex sunspot groups is presented, noting several characteristics identified in the delta-configurations. The observations of regions 2469 (S12E80) and 2470 (S21E83) took place in May, 1980 with a vector magnetograph, verified by optical viewing. Longitudinal magnetic field plots located the delta-configurations in relation to the transverse field neutral line. It is shown that data on the polarization yields qualitative information on the magnetic field strengths, while the azimuth of the transverse field can be obtained from the relative intensities of linear polarization measurements aligned with respect to the magnetograph analyses axis at 0 and 90 deg, and at the plus and minus 45 deg positions. Details of the longitudinal fields are discussed. A strong, sheared transverse field component is found to be a signature of strong delta. A weak delta is accompanied by a weak longitudinal gradient with an unsheared transverse component of variable strength.

Patty, S. R.

325

Anisotropic Magnetism in Field-Structured Composites  

SciTech Connect

Magnetic field-structured-composites (FSCs) are made by structuring magnetic particle suspensions in uniaxial or biaxial (e.g. rotating) magnetic fields, while polymerizing the suspending resin. A uniaxial field produces chain-like particle structures, and a biaxial field produces sheet-like particle structures. In either case, these anisotropic structures affect the measured magnetic hysteresis loops, with the magnetic remanence and susceptibility increased significantly along the axis of the structuring field, and decreased slightly orthogonal to the structuring field, relative to the unstructured particle composite. The coercivity is essentially unaffected by structuring. We present data for FSCs of magnetically soft particles, and demonstrate that the altered magnetism can be accounted for by considering the large local fields that occur in FSCs. FSCS of magnetically hard particles show unexpectedly large anisotropies in the remanence, and this is due to the local field effects in combination with the large crystalline anisotropy of this material.

Anderson, Robert A.; Martin, James E.; Odinek, Judy; Venturini, Eugene

1999-06-24

326

Studies on Somatosensory Evoked Magnetic Fields.  

National Technical Information Service (NTIS)

Spatiotemporal patterns of somatosensory evoked magnetic fields to stimulation of upper and lower limb nerves were examined in healthy humans. The studies summarized here provide the first magnetic field maps over the primary foot projection area after li...

J. Huttunen

1987-01-01

327

Luminescence in applied magnetic fields  

NASA Astrophysics Data System (ADS)

Metal complexes and solids were synthesized and subjected to photoexcitation measurements under the influence of externally applied magnetic fields. The photoluminescence of complexes of rhodium (I) and iridium (I) displayed both field induced emission bands and a many fold shortening of the excited state lifetime. Both the decay rates and the induced emission band intensities showed a quadratic dependence on the applied field. A several fold shortening of the phosphorescence from the octaphosphitoplatinum (II) anion under an applied field (50 T) was also observed. Spectroscopic studies of several bis (N-heterocyclic) complexes of copper (I) were also concluded and complete group theoretic assignments of the charge transfer excited states were made. The technique of Thermal Modulation was perfected and applied to the study of the exited states of transition metal complexes with near degenerate emitting states.

Crosby, G. A.

1989-08-01

328

Simulations of Photospheric Magnetic Fields  

NASA Astrophysics Data System (ADS)

We have run plots of artificial data, which mimic solar magnetograms, through standard algorithms to critique several results reported in the literature. In studying correlation algorithms, we show that the differences in the profiles for the differential rotation of the photospheric magnetic field stem from different methods of averaging. We verify that the lifetimes of small magnetic features, or of small patterns of these features in the large-scale background field, are on the order of months, rather than a few days. We also show that a meridional flow which is cycle dependent creates an artifact in the correlation-determined magnetic rotation which looks like a torsional oscillation; and we compare this artifact to the torsional patterns that have been reported. Finally, we simulate the time development of a large-scale background field created solely from an input of artifical, finite-lifetime 'sunspot' bipoles. In this simulation, we separately examine the effects of differential rotation, meridional flow and Brownian motion (random walk, which we use rather than diffusion), and the inclination angles of the sunspot bipoles (Joy's law). We find, concurring with surface transport equation models, that a critical factor for producing the patterns seen on the Sun is the inclination angle of the bipolar active regions. This work was supported by NSF grant 9416999.

Smith, A. A.; Snodgrass, H. B.

1999-05-01

329

Liquid first walls for magnetic fusion energy configurations  

Microsoft Academic Search

Liquids (~7 neutron mean free paths thick), with certain restrictions, can probably be used in magnetic fusion designs between the burning plasma and the structural materials of the fusion power core. If this works there would be a number of profound advantages: a cost of electricity lower by as much as a factor of 2; removal of the need to

R. W. Moir

1997-01-01

330

Field Concentrator Based Resonant Magnetic Sensor  

Microsoft Academic Search

A novel resonant magnetic sensor based on the combination of a mechanical resonator and a magnetic field concentrator with two gaps is reported. In contrast to previous Lorentz force based resonant magnetic sensors, a high sensitivity is achieved without modulated driving current and complex feedback electronics. Furthermore, compared to magnetic moment based resonant magnetic sensors, the new concept requires no

S. Brugger; P. Simon; O. Paul

2006-01-01

331

Color Superconducting Matter in a Magnetic Field  

SciTech Connect

We investigate the effect of a magnetic field on cold dense quark matter using an effective model with four-Fermi interactions. We find that the gap parameters representing the predominant pairing between the different quark flavors show oscillatory behavior as a function of the magnetic field. We point out that due to electric and color neutrality constraints the magnetic fields as strong as presumably existing inside magnetars might induce significant deviations from the gap structure at a zero magnetic field.

Fukushima, Kenji [RIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973 (United States); Warringa, Harmen J. [Department of Physics, Bldg. 510A, Brookhaven National Laboratory, Upton, New York 11973 (United States)

2008-01-25

332

Intensity distribution of strong magnetic fields created by opposing linear Halbach assemblies of permanent magnets  

NASA Astrophysics Data System (ADS)

The work is devoted to the geometrical configuration of permanent magnets on the basis of opposing geometrically linear assemblies (e.g. Halbach arrays) for the generation of strong magnetic fields, which have been theoretically modeled and experimentally verified. The implementation of these opposing assemblies using NdFeB magnets of a total weight of 3.75 kg provided a value of magnetic induction in the middle of an air gap of a width of 20 mm that was higher by 56% in comparison with the simplest possible design. When the air gap width was 3 mm, the induction reached a value of 2.16 T, which represents an increase of more than 100%. Simultaneously, however, unlike in the simplest possible parallel configuration, opposing Halbach assemblies have shown, in the middle of an air gap, a significant decrease of the magnetic induction values when passing from the middle of the assemblies in the direction parallel to the x-axis.

Žežulka, Václav; Pištora, Jaromír; Les?ák, Michal; Straka, Pavel; Ciprian, Dalibor; Foukal, Jaroslav

2013-11-01

333

Magnetic field gradient measurement on magnetic cards using magnetic force microscopy  

NASA Astrophysics Data System (ADS)

The magnetic field gradients of magnetic stripe cards, which are developed for classifying magnetic particles used in magnetic particle inspections, have been measured using a magnetic force microscope (MFM). The magnetic force exerted on a MFM probe by the stray field emanating from the card was measured to determine the field gradients. The results are in good agreement with the field gradients estimated from the magnetizing field strengths used in the encoding process. .

Lo, C. C. H.; Leib, J.; Jiles, D. C.; Chedister, W. C.

2002-05-01

334

Neutron Laue Diffraction Study on the Magnetic Phase Diagram of Multiferroic MnWO4 under Pulsed High Magnetic Fields  

NASA Astrophysics Data System (ADS)

We have combined time-of-flight neutron Laue diffraction and pulsed high magnetic fields at the Spallation Neutron Source to study the phase diagram of the multiferroic material MnWO4. The control of the field-pulse timing enabled an exploration of magnetic Bragg scattering through the time dependence of both the neutron wavelength and the pulsed magnetic field. This allowed us to observe several magnetic Bragg peaks in different field-induced phases of MnWO4 with a single instrument configuration. These phases were not previously amenable to neutron diffraction studies due to the large fields involved.

Nojiri, H.; Yoshii, S.; Yasui, M.; Okada, K.; Matsuda, M.; Jung, J.-S.; Kimura, T.; Santodonato, L.; Granroth, G. E.; Ross, K. A.; Carlo, J. P.; Gaulin, B. D.

2011-06-01

335

Neutron Laue diffraction study on the magnetic phase diagram of multiferroic MnWO4 under pulsed high magnetic fields.  

PubMed

We have combined time-of-flight neutron Laue diffraction and pulsed high magnetic fields at the Spallation Neutron Source to study the phase diagram of the multiferroic material MnWO(4). The control of the field-pulse timing enabled an exploration of magnetic Bragg scattering through the time dependence of both the neutron wavelength and the pulsed magnetic field. This allowed us to observe several magnetic Bragg peaks in different field-induced phases of MnWO(4) with a single instrument configuration. These phases were not previously amenable to neutron diffraction studies due to the large fields involved. PMID:21770542

Nojiri, H; Yoshii, S; Yasui, M; Okada, K; Matsuda, M; Jung, J-S; Kimura, T; Santodonato, L; Granroth, G E; Ross, K A; Carlo, J P; Gaulin, B D

2011-06-08

336

Magnetic fields in the early Universe  

Microsoft Academic Search

This review concerns the origin and the possible effects of magnetic fields in the early Universe. We start by providing the reader with a short overview of the current state of the art of observations of cosmic magnetic fields. We then illustrate the arguments in favor of a primordial origin of magnetic fields in the galaxies and in the clusters

Dario Grasso; Hector R. Rubinstein

2001-01-01

337

Primordial magnetic field limits from cosmological data  

SciTech Connect

We study limits on a primordial magnetic field arising from cosmological data, including that from big bang nucleosynthesis, cosmic microwave background polarization plane Faraday rotation limits, and large-scale structure formation. We show that the physically relevant quantity is the value of the effective magnetic field, and limits on it are independent of how the magnetic field was generated.

Kahniashvili, Tina [McWilliams Center for Cosmology and Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213 (United States); Department of Physics, Laurentian University, Ramsey Lake Road, Sudbury, Ontario P3E 2C (Canada); Abastumani Astrophysical Observatory, Ilia State University, 2A Kazbegi Ave, Tbilisi, GE-0160 (Georgia); Tevzadze, Alexander G. [Abastumani Astrophysical Observatory, Ilia State University, 2A Kazbegi Ave, Tbilisi, GE-0160 (Georgia); Faculty of Exact and Natural Sciences, Tbilisi State University, 1 Chavchavadze Avenue, Tbilisi, GE-0128 (Georgia); Sethi, Shiv K. [McWilliams Center for Cosmology and Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213 (United States); Raman Research Institute, Sadashivanagar, Bangalore 560080 (India); Pandey, Kanhaiya [Raman Research Institute, Sadashivanagar, Bangalore 560080 (India); Ratra, Bharat [Department of Physics, Kansas State University, 116 Cardwell Hall, Manhattan, Kansas 66506 (United States)

2010-10-15

338

Penetration of plasma across a magnetic field  

NASA Astrophysics Data System (ADS)

Experiments were performed at the Nevada Terawatt Facility to investigate the plasma penetration across an externally applied magnetic field. In experiment, a short-pulse laser ablates a polyethylene laser target, producing a plasma which interacts with an external magnetic field. The mechanism which allows the plasma to penetrate the applied magnetic field in experiment will be discussed.

Plechaty, C.; Presura, R.; Wright, S.; Neff, S.; Haboub, A.

2009-08-01

339

Magnetic field reversals in the Milky Way  

Microsoft Academic Search

Radio observations of nearby spiral galaxies have tremendously enhanced our knowledge of their global magnetic field distributions. Recent theoretical developments in the area of dynamos have also helped in the interpretation of magnetic field data in spiral galaxies. When it comes to the magnetic field in the Milky Way galaxy, our position in the Milky Way's galactic disk hinders our

J. P. Vallee

1996-01-01

340

Transmission line magnetic fields; Measurements and calculations  

Microsoft Academic Search

Recent controversy over 60 Hz magnetic fields has heightened public awareness of overhead transmission lines. As a result, there is increasing motivation to study the magnetic fields form transmission lines. The most cost effective means to conduct research into transmission line magnetic fields is with computer or reduced-scale line models. However, from the standpoint of public perception and acceptance, it

B. A. Clairmont; G. B. Johnson; J. H. Dunlap

1992-01-01

341

Primordial magnetic field limits from cosmological data  

NASA Astrophysics Data System (ADS)

We study limits on a primordial magnetic field arising from cosmological data, including that from big bang nucleosynthesis, cosmic microwave background polarization plane Faraday rotation limits, and large-scale structure formation. We show that the physically relevant quantity is the value of the effective magnetic field, and limits on it are independent of how the magnetic field was generated.

Kahniashvili, Tina; Tevzadze, Alexander G.; Sethi, Shiv K.; Pandey, Kanhaiya; Ratra, Bharat

2010-10-01

342

Evolution of normal pulsar magnetic fields  

NASA Astrophysics Data System (ADS)

Results and new progress of the origin and evolution of pulsar magnetic fields are reviewed. Lots of models about how such strong magnetic fields were generated, mainly two kinds of structures were proposed for initial magnetic fields: fields confined in the cores and fields confined in the crusts of neutron stars. No consensus has been reached on whether the magnetic fields decay or not, despite some observational evidence for the evolution of magnetic fields. The discrepancy between characteristic ages and kinematic ages indicates that the magnetic fields decay exponentially. On the other hand, the braking indices of several young pulsars and the comparison between pulsar characteristic ages and the ages of associated supernova remnants suggest that the magnetic fields of young pulsars grow like a power-law. Pulsar population synthesis is one of the most important methods to investigate the evolution of magnetic fields. Many simulations show that if magnetic fields do decay exponentially, the e-folding decay time should be 100 Myr or longer. The numerical calculations of the Ohmic decay in the crust indicate that the scenario of exponential decay is oversimple, and the evolution could be divided into four possible phases approximately: exponential decay, no decay, power-law decay and exponential decay again. The model of magnetic fields expulsion induced by spin-down suggests that the magnetic fields decay only in a period between 107yr and 108yr.

Sun, Xiaohui; Han, Jinlin

2002-06-01

343

Magnetic field re-arrangement after prominence eruption  

SciTech Connect

It has long been known that magnetic reconnection plays a fundamental role in a variety of solar events. Although mainly invoked in flare problems, large-scale loops interconnecting active regions, evolving coronal hole boundaries, the solar magnetic cycle itself, provide different evidence of phenomena which involve magnetic reconnection. A further example might be given by the magnetic field rearrangement which occurs after the eruption of a prominence. Since most often a prominence reforms after its disappearance and may be observed at about the same position it occupied before erupting, the magnetic field has to undergo a temporary disruption to relax back, via reconnection, to a configuration similar to the previous one. The above sequence of events is best observable in the case of two-ribbon (2-R) flares but most probably is associated with all filament eruptions. Even if the explanation of the magnetic field rearrangement after 2-R flares in terms of reconnection is generally accepted, the lack of a three-dimensional model capable of describing the field reconfiguration, has prevented, up to now, a thorough analysis of its topology as traced by H..cap alpha../x-ray loops. The purpose of the present work is to present a numerical technique which enables one to predict and visualize the reconnected configuration, at any time t, and therefore allows one to make a significant comparison of observations and model predictions throughout the whole process. 5 refs., 3 figs.

Kopp, R.A.; Poletto, G.

1986-01-01

344

Field-reversed configuration formation scheme utilizing a spheromak and solenoid induction  

SciTech Connect

A new field-reversed configuration (FRC) formation technique is described, where a spheromak transitions to a FRC with inductive current drive. The transition is accomplished only in argon and krypton plasmas, where low-n kink modes are suppressed; spheromaks with a lighter majority species, such as neon and helium, either display a terminal tilt-mode, or an n=2 kink instability, both resulting in discharge termination. The stability of argon and krypton plasmas through the transition is attributed to the rapid magnetic diffusion of the currents that drive the kink-instability. The decay of helicity during the transition is consistent with that expected from resistivity. This observation indicates a new scheme to form a FRC plasma, provided stability to low-n modes is maintained, as well as a unique situation where the FRC is a preferred state.

Gerhardt, S. P.; Belova, E. V.; Yamada, M.; Ji, H.; Ren, Y.; McGeehan, B. [Princeton Plasma Physics Laboratory, Plainsboro, New Jersey 08543 (United States); Inomoto, M. [Osaka University, Osaka 565-0871 (Japan)

2008-03-15

345

Field-Reversed Configuration Formation Scheme Utilizing a Spheromak and Solenoid Induction  

SciTech Connect

A new field-reversed configuration (FRC) formation technique is described, where a spheromak transitions to a FRC with inductive current drive. The transition is accomplished only in argon and krypton plasmas, where low-n kink modes are suppressed; spheromaks with a lighter majority species, such as neon and helium, either display a terminal tilt-mode, or an n=2 kink instability, both resulting in discharge termination. The stability of argon and krypton plasmas through the transition is attributed to the rapid magnetic diffusion of the currents that drive the kink-instability. The decay of helicity during the transition is consistent with that expected from resistivity. This observation indicates a new scheme to form a FRC plasma, provided stability to low-n modes is maintained, as well as a unique situation where the FRC is a preferred state.

S.P. Gerhardt, E.V. Belova, M. Yamada, H. Ji, Y. Ren, B. McGeehan, and M. Inomoto

2008-06-12

346

Deformable homeotropic nematic droplets in a magnetic field  

NASA Astrophysics Data System (ADS)

We present a Frank-Oseen elasticity theory for the shape and structure of deformable nematic droplets with homeotropic surface anchoring in the presence of a magnetic field. Inspired by recent experimental observations, we focus on the case where the magnetic susceptibility is negative, and find that small drops have a lens shape with a homogeneous director field for any magnetic-field strength, whereas larger drops are spherical and have a radial director field, at least if the magnetic field is weak. For strong magnetic fields the hedgehog configuration transforms into a split-core line defect that, depending on the anchoring strength, can be accompanied by an elongation of the tactoid itself. We present a three-dimensional phase diagram that shows the tactoid shape and director field for a given anchoring strength, tactoid size, and magnetic-field strength. Our findings rationalize the different shapes and structures that recently have been observed experimentally for nematic droplets found in dispersions of gibbsite platelets in two types of solvent.

Otten, Ronald H. J.; van der Schoot, Paul

2012-10-01

347

Thermal Relaxation of Very Small Solar Magnetic Structures in Intergranules: A Process That Produces Kilogauss Magnetic Field Strengths  

NASA Astrophysics Data System (ADS)

The equilibrium configuration of very small magnetic flux tubes in an intergranular environment automatically produces kilogauss magnetic field strengths. We argue that such a process takes place in the Sun and complements the convective collapse (CC), which is traditionally invoked to explain the formation of kilogauss magnetic concentrations in the solar photosphere. In particular, it can concentrate the very weak magnetic fluxes revealed by the new IR spectropolarimeters, for which the operation of the CC may have difficulty. As part of the argument, we show the existence of solar magnetic features of very weak fluxes yet concentrated magnetic fields (some 3×1016 Mx and 1500 G).

Sánchez Almeida, J.

2001-08-01

348

Ferroelectric polarization flop in a frustrated magnet MnWO4 induced by a magnetic field.  

PubMed

The relationship between magnetic order and ferroelectric properties has been investigated for MnWO4 with a long-wavelength magnetic structure. Spontaneous electric polarization is observed in an elliptical spiral spin phase. The magnetic-field dependence of electric polarization indicates that the noncollinear spin configuration plays a key role for the appearance of the ferroelectric phase. An electric polarization flop from the b direction to the a direction has been observed when a magnetic field above 10 T is applied along the b axis. This result demonstrates that an electric polarization flop can be induced by a magnetic field in a simple system without rare-earth 4f moments. PMID:17026396

Taniguchi, K; Abe, N; Takenobu, T; Iwasa, Y; Arima, T

2006-08-30

349

Crustal Magnetic Fields of Terrestrial Planets  

NASA Astrophysics Data System (ADS)

Magnetic field measurements are very valuable, as they provide constraints on the interior of the telluric planets and Moon. The Earth possesses a planetary scale magnetic field, generated in the conductive and convective outer core. This global magnetic field is superimposed on the magnetic field generated by the rocks of the crust, of induced (i.e. aligned on the current main field) or remanent (i.e. aligned on the past magnetic field). The crustal magnetic field on the Earth is very small scale, reflecting the processes (internal or external) that shaped the Earth. At spacecraft altitude, it reaches an amplitude of about 20 nT. Mars, on the contrary, lacks today a magnetic field of core origin. Instead, there is only a remanent magnetic field, which is one to two orders of magnitude larger than the terrestrial one at spacecraft altitude. The heterogeneous distribution of the Martian magnetic anomalies reflects the processes that built the Martian crust, dominated by igneous and cratering processes. These latter processes seem to be the driving ones in building the lunar magnetic field. As Mars, the Moon has no core-generated magnetic field. Crustal magnetic features are very weak, reaching only 30 nT at 30-km altitude. Their distribution is heterogeneous too, but the most intense anomalies are located at the antipodes of the largest impact basins. The picture is completed with Mercury, which seems to possess an Earth-like, global magnetic field, which however is weaker than expected. Magnetic exploration of Mercury is underway, and will possibly allow the Hermean crustal field to be characterized. This paper presents recent advances in our understanding and interpretation of the crustal magnetic field of the telluric planets and Moon.

Langlais, Benoit; Lesur, Vincent; Purucker, Michael E.; Connerney, Jack E. P.; Mandea, Mioara

2010-05-01

350

Nuclear magnetic resonance apparatus for pulsed high magnetic fields  

NASA Astrophysics Data System (ADS)

A nuclear magnetic resonance apparatus for experiments in pulsed high magnetic fields is described. The magnetic field pulses created together with various magnet coils determine the requirements such an apparatus has to fulfill to be operated successfully in pulsed fields. Independent of the chosen coil it is desirable to operate the entire experiment at the highest possible bandwidth such that a correspondingly large temporal fraction of the magnetic field pulse can be used to probe a given sample. Our apparatus offers a bandwidth of up to 20 MHz and has been tested successfully at the Hochfeld-Magnetlabor Dresden, even in a very fast dual coil magnet that has produced a peak field of 94.2 T. Using a medium-sized single coil with a significantly slower dependence, it is possible to perform advanced multi-pulse nuclear magnetic resonance experiments. As an example we discuss a Carr-Purcell spin echo sequence at a field of 62 T.

Meier, Benno; Kohlrautz, Jonas; Haase, Jürgen; Braun, Marco; Wolff-Fabris, Frederik; Kampert, Erik; Herrmannsdörfer, Thomas; Wosnitza, Joachim

2012-08-01

351

Analyzing and Modeling the Magnetic Field of Mars  

NASA Astrophysics Data System (ADS)

Presently Mars possesses no intrinsic magnetic field; rather its crust exhibits strong remanent magnetization primarily in the Southern Highlands. The deficiency of magnetization surrounding volcanic provinces and impact basins on Mars is attributed to evidence suggesting that the crust gained its magnetic remanence early on via an internal dynamo. This dynamo is believed to have become extinct by the time of the last major impacts. Measurements taken by Mars Global Surveyor (MGS) have been used to create a new map of Mars' crustal magnetic field. We present an analysis of these data in conjunction with topographical data taken from the Mars Orbiter Laser Altimeter (MOLA) to determine if magnetization in Mars' southern regions correlates with surface features displayed on topographic maps. MGS and MOLA data were used to identify and study a region of intense magnetic field beneath a 1500 km section of an impact basin in the western hemisphere of the Southern Highlands. In conjunction with the development of models and intensity plots for the radial component of this field, analysis of the possible shape, configuration and composition of the magnetic material beneath the crater was performed. Our models showed that the magnetic signature beneath the impact basin was produced by two adjacent blocks of magnetic material within the Martian crust. We found that the blocks were most likely rectangular in shape and were relatively closely spaced. They also possessed properties similar to those of stainless steel permanent magnets with magnetization directions of -90 degrees, and -45 degrees, respectively. The results of this research will contribute to future studies of Mars, specifically of its present magnetic state, magnetic history, and impact record. This research was made possible via funding from the North Carolina Space Grant Consortium.

Quick, L. C.; Acuna, M. H.; Connerney, J. E. P.

2005-12-01

352

Innovating approaches to the generation of intense magnetic fields : design and optimization of a 4 Tesla permanent magnet flux source  

Microsoft Academic Search

An original permanent magnet flux source is designed in order to generate a magnetic field of several Tesla. The magnet configuration and discretization of the structure are optimized with the help of numerical simulation software developed at LEG (DIPOLE-3D, FLUX2D & FLUX3D). The model of spheroidal flux source presented in the paper creates a field in excess of 4.3 T

F. Bloch; O. Cugat; G. Meunier; J. C. Toussaint

1998-01-01

353

Near Field Spectroscopy of Quantum Dots Under Magnetic Field  

Microsoft Academic Search

We present the basic steps for the study of the linear near field absorption spectra of semiconductor quantum dots under magnetic field of variable orientation. We show that the application of the magnetic field alone is sufficient to induce -increasing the spot illuminated by the near field probe- interesting features to the absorption spectra.

Anna Zora; Constantinos Simserides; Georgios Triberis

2005-01-01

354

Near Field Spectroscopy of Quantum Dots Under Magnetic Field  

Microsoft Academic Search

We present the basic steps for the study of the linear near field absorption spectra of semiconductor quantum dots under magnetic field of variable orientation. We show that the application of the magnetic field alone is sufficient to induce -increasing the spot illuminated by the near field probe- interesting features to the absorption spectra.

Anna Zora; Constantinos Simserides; Georgios Triberis

2004-01-01

355

Magnetic field effects on the motion of circumplanetary dust  

NASA Astrophysics Data System (ADS)

Hypervelocity impacts on satellites or ring particles replenish circumplanetary dusty rings with grains of all sizes. Due to interactions with the plasma environment and sunlight, these grains become electrically charged. We study the motion of charged dust grains launched at the Kepler orbital speed, under the combined effects of gravity and the electromagnetic force. We conduct numerical simulations of dust grain trajectories, covering a broad range of launch distances from the planetary surface to beyond synchronous orbit, and the full range of charge-to-mass ratios from ions to rocks, with both positive and negative electric potentials. Initially, we assume that dust grains have a constant electric potential, and, treating the spinning planetary magnetic field as an aligned and centered dipole, we map regions of radial instability (positive grains only), where dust grains are driven to escape or collide with the planet at high speed, and vertical instability (both positive and negative charges) whereby grains launched near the equatorial plane and are forced up magnetic field lines to high latitudes, where they may collide with the planet. We derive analytical criteria for local stability in the equatorial plane, and solve for the boundaries between all unstable and stable outcomes. Comparing our analytical solutions to our numerical simulations, we develop an extensive model for the radial, vertical and azimuthal motions of dust grains of arbitrary size and launch location. We test these solutions at Jupiter and Saturn, both of whose magnetic fields are reasonably well represented by aligned dipoles, as well as at the Earth, whose magnetic field is close to an anti-aligned dipole. We then evaluate the robustness of our stability boundaries to more general conditions. Firstly, we examine the effects of non-zero launch speeds, of up to 0.5 km s?1, in the frame of the parent body. Although these only weakly affect stability boundaries, we find that the influence of a launch impulse on stability boundaries strongly depends on its direction. Secondly, we focus on the effects of higher-order magnetic field components on orbital stability. We find that vertical stability boundaries are particularly sensitive to a moderate vertical offset in an aligned dipolar magnetic field. This configuration suffices as a model for Saturn's full magnetic field. The vertical instability also expands to cover a wider range of launch distances in slightly tilted magnetic dipoles, like the magnetic field configurations for Earth and Jupiter. By contrast, our radial stability criteria remain largely unaffected by both dipolar tilts and vertical offsets. Nevertheless, a tilted dipole magnetic field model introduces non-axisymmetric forces on orbiting dust grains, which are exacerbated by the inclusion of other higher-order magnetic field components, including the quadrupolar and octupolar terms. Dust grains whose orbital periods are commensurate with the spatial periodicities of a rotating non-axisymmetric magnetic field experience destabilizing Lorentz resonances. These have been studied by other authors for the largest dust grains moving on perturbed Keplerian ellipses. With Jupiter's full magnetic field as our model, we extend the concept of Lorentz resonances to smaller dust grains and find that these can destabilize trajectories on surprisingly short timescales, and even cause negatively-charged dust grains to escape within weeks. We provide detailed numerically-derived stability maps highlighting the destabilizing effects of specific higher-order terms in Jupiter's magnetic field, and we develop analytical solutions for the radial locations of these resonances for all charge-to-mass ratios. We include stability maps for the full magnetic field configurations of Jupiter, Saturn, and Earth, to compare with our analytics. We further provide numerically-derived stability maps for the tortured magnetic fields of Uranus and Neptune. Relaxing the assumption of constant electric charges on dust, we test the effects of time-variable grain charg

Jontof-Hutter, Daniel Simon

356

The origins of lunar crustal magnetic fields  

NASA Astrophysics Data System (ADS)

This thesis is devoted to understanding the origins of lunar crustal magnetism. We wish to understand the processes which have created and modified the crustal magnetic field distribution that we observe today, and to determine whether the Moon ever had an active magnetohydrodynamic dynamo. Previously, our only measurements of lunar magnetic fields came from the Explorer 35 and Apollo missions. Data coverage was incomplete, but sufficient to establish some systematics of the crustal field distribution. With new data from the Magnetometer and Electron Reflectometer instrument on Lunar Prospector, we have generated the first completely global maps of the lunar crustal fields. We use measurements of electrons magnetically reflected above the lunar surface, which we then correct for the effects of electrostatic fields (which also reflect electrons), and convert to estimates of surface magnetic fields. The resulting global map shows that impact basins and craters (especially the youngest) generally have low magnetic fields, suggesting impact demagnetization, primarily by shock effects. A secondary signature of some large lunar basins (especially older ones) is the presence of a more localized central magnetic anomaly. Meanwhile, the largest regions of strong crustal fields lie antipodal to young large impact basins, suggesting shock remanent magnetization due to a combination of antipodal focussing of seismic energy and/or ejecta and plasma compression of ambient magnetic fields. Smaller regions of strong magnetic fields are sometimes associated with basin ejecta, and basin and crater ejecta terranes have the strongest average fields outside of the antipodal regions. This implies that impact-generated magnetization may extend beyond the antipodal regions. The antipodal, non-antipodal, and central basin magnetic fields, as well as returned samples, can all be used to estimate the lunar magnetic field history and place constraints on a possible lunar dynamo. All of these quantities provide evidence for stronger magnetic fields early in the Moon's history, and thereby suggest the existence of an ancient core dynamo.

Halekas, Jasper S.

357

Magnetic field observations in Comet Halley's coma  

NASA Astrophysics Data System (ADS)

During the encounter with Comet Halley, the magnetometer (MISCHA) aboard the Vega 1 spacecraft observed an increased level of magnetic field turbulence, resulting from an upstream bow wave. Both Vega spacecraft measured a peak field strength of 70-80 nT and observed draping of magnetic field lines around the cometary obstacle. An unexpected rotation of the magnetic field vector was observed, which may reflect either penetration of magnetic field lines into a diffuse layer related to the contact surface separating the solar-wind and cometary plasma, or the persistence of pre-existing interplanetary field structures.

Riedler, W.; Schwingenschuh, K.; Yeroshenko, Ye. G.; Styashkin, V. A.; Russell, C. T.

1986-05-01

358

Magnetic Configuration Effects on Fast Ion Losses Induced by Fast Ion Driven Toroidal Alfvén Eigenmodes in the Large Helical Device  

NASA Astrophysics Data System (ADS)

Beam-ion losses induced by fast-ion-driven toroidal Alfvén eigenmodes (TAE) were measured with a scintillator-based lost fast-ion probe (SLIP) in the large helical device (LHD). The SLIP gave simultaneously the energy E and the pitch angle ? = arccos(?///?) distribution of the lost fast ions. The loss fluxes were investigated for three typical magnetic configurations of Rax_vac = 3.60 m, 3.75 m, and 3.90 m, where Rax_vac is the magnetic axis position of the vacuum field. Dominant losses induced by TAEs in these three configurations were observed in the E/? regions of 50~190 keV/40°, 40~170 keV/25°, and 30~190 keV/30°, respectively. Lost-ion fluxes induced by TAEs depend clearly on the amplitude of TAE magnetic fluctuations, Rax_vac and the toroidal field strength Bt. The increment of the loss fluxes has the dependence of (bTAE/Bt)s. The power s increases from s = 1 to 3 with the increase of the magnetic axis position in finite beta plasmas.

Ogawa, K.; Isobe, M.; Toi, K.; Watanabe, F.; A. Spong, D.; Shimizu, A.; Osakabe, M.; S. Darrow, D.; Ohdachi, S.; Sakakibara, S.; LHD Experiment Group

2012-04-01

359

Magnetic Configuration Effects on Fast Ion Losses Induced by Fast Ion Driven Toroidal Alfven Eigenmodes in the Large Helical Device  

SciTech Connect

Beam-ion losses induced by fast-ion-driven toroidal Alfven eigenmodes (TAE) were measured with a scintillator-based lost fast-ion probe (SLIP) in the large helical device (LHD). The SLIP gave simultaneously the energy E and the pitch angle chi = arccos(v(parallel to)/v) distribution of the lost fast ions. The loss fluxes were investigated for three typical magnetic configurations of R{sub ax{_}vac} = 3.60 m, 3.75 m, and 3.90 m, where R{sub ax{_}vac} is the magnetic axis position of the vacuum field. Dominant losses induced by TAEs in these three configurations were observed in the E/chi regions of 50 similar to 190 keV/40 degrees, 40 similar to 170 keV/25 degrees, and 30 similar to 190 keV/30 degrees, respectively. Lost-ion fluxes induced by TAEs depend clearly on the amplitude of TAE magnetic fluctuations, R{sub ax{_}vac} and the toroidal field strength B{sub t}. The increment of the loss fluxes has the dependence of (b{sub TAE}/B{sub t}){sup s}. The power s increases from s = 1 to 3 with the increase of the magnetic axis position in finite beta plasmas.

Ogawa, K. [Nagoya University, Japan; Isobe, M. [National Institute for Fusion Science, Toki, Japan; Watanabe, F. [Kyoto University, Japan; Spong, Donald A [ORNL; Shimizu, A. [National Institute for Fusion Science, Toki, Japan; Osakabe, M. [National Institute for Fusion Science, Toki, Japan; Ohdachi, S. [National Institute for Fusion Science, Toki, Japan; Sakakibara, S. [National Institute for Fusion Science, Toki, Japan

2012-01-01

360

System including a hard disk drive and stray magnetic field sensor and associated method  

US Patent & Trademark Office Database

A system includes a host device and a disk drive interfaced with the host device are described as well as an associated method. The disk drive includes a magnetic media for storing information using an actuator arrangement to perform a data access by moving at least one head proximate to the magnetic media. The information may be subject to corruption when the disk drive is exposed, during the data access, to a given stray magnetic field having a given minimum magnetic field intensity. The given stray magnetic field will not corrupt the information on the magnetic media with the actuator arrangement positioned away from the magnetic media. A stray magnetic field protection arrangement is configured for detecting an ambient magnetic environment for use in causing the actuator arrangement to park responsive to the detection of at least the given minimum magnetic field intensity.

Partee; Charles (Lyons, CO)

2010-12-28

361

Stability of the toroidal magnetic field in rotating stars  

NASA Astrophysics Data System (ADS)

The magnetic field in stellar radiation zones can play an important role in phenomena such as mixing, angular momentum transport, etc. We study the effect of rotation on the stability of a predominantly toroidal magnetic field in the radiation zone. In particular we considered the stability in spherical geometry by means of a linear analysis in the Boussinesq approximation. It is found that the effect of rotation on the stability depends on a magnetic configuration. If the toroidal field increases with the spherical radius, the instability cannot be suppressed entirely even by a very fast rotation. Rotation can only decrease the growth rate of instability. If the field decreases with the radius, the instability has a threshold and can be completey suppressed.

Bonanno, A.; Urpin, V.

2013-04-01

362

Magnetic field seeding by galactic winds  

Microsoft Academic Search

The origin of intergalactic magnetic fields is still a mystery and several scenarios have been proposed so far: among them, primordial phase transitions, structure-formation shocks and galactic outflows. In this work, we investigate how efficiently galactic winds can provide an intense and widespread `seed' magnetization. This may be used to explain the magnetic fields observed today in clusters of galaxies

Serena Bertone; Corina Vogt; Torsten Enßlin

2006-01-01

363

Invited Safety of Strong, Static Magnetic Fields  

Microsoft Academic Search

Issues associated with the exposure of patients to strong, static magnetic fields during magnetic resonance imaging (MRI) are reviewed and discussed. The history of human exposure to magnetic fields is reviewed, and the contra- dictory nature of the literature regarding effects on human health is described. In the absence of ferromagnetic for- eign bodies, there is no replicated scientific study

John F. Schenck

2000-01-01

364

Intergalactic Magnetic Fields from Quasar Outflows  

Microsoft Academic Search

Outflows from quasars inevitably pollute the intergalactic medium (IGM) with magnetic fields. The short-lived activity of a quasar leaves behind an expanding magnetized bubble in the IGM. We model the expansion of the remnant quasar bubbles and calculate their distribution as a function of size and magnetic field strength at different redshifts. We generically find that by a redshift z~3,

Steven R. Furlanetto; Abraham Loeb

2001-01-01

365

Magnetic fields in Local Group dwarf irregulars  

Microsoft Academic Search

Aims: We wish to clarify whether strong magnetic fields can be effectively generated in typically low-mass dwarf galaxies and to assess the role of dwarf galaxies in the magnetization of the Universe. Methods: We performed a search for radio emission and magnetic fields in an unbiased sample of 12 Local Group (LG) irregular and dwarf irregular galaxies with the 100-m

K. T. Chyzy; M. Wezgowiec; R. Beck; D. J. Bomans

2011-01-01

366

Deformation of Water by a Magnetic Field  

ERIC Educational Resources Information Center

|After the discovery that superconducting magnets could levitate diamagnetic objects, researchers became interested in measuring the repulsion of diamagnetic fluids in strong magnetic fields, which was given the name "The Moses Effect." Both for the levitation experiments and the quantitative studies on liquids, the large magnetic fields necessary…

Chen, Zijun; Dahlberg, E. Dan

2011-01-01

367

Baking a magnetic-field display  

NASA Astrophysics Data System (ADS)

Copy machine developer powder is an alternative for creating permanent displays of magnetic fields. A thin layer of developer powder on a sheet of paper placed over a magnet can be baked in the oven, producing a lasting image of a magnetic field.

Cavanaugh, Terence; Cavanaugh, Catherine

1998-02-01

368

Exploring Magnetic Fields with a Compass  

ERIC Educational Resources Information Center

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

Lunk, Brandon; Beichner, Robert

2011-01-01

369

Cluster magnetic fields from galactic outflows  

Microsoft Academic Search

We performed cosmological, magnetohydrodynamical simulations to follow the evolution of magnetic fields in galaxy clusters, exploring the possibility that the origin of the magnetic seed fields is galactic outflows during the starburst phase of galactic evolution. To do this, we coupled a semi-analytical model for magnetized galactic winds as suggested by Bertone, Vogt & Enßlin to our cosmological simulation. We

J. Donnert; K. Dolag; H. Lesch; E. Müller

2009-01-01

370

Sub arcsec evolution of solar magnetic fields  

Microsoft Academic Search

Context: .The evolution of the concentrated magnetic field in flux tubes is one challenge of the nowadays Solar physics which requires time sequence with high spatial resolution. Aims: .Our objective is to follow the properties of the magnetic concentrations during their life, in intensity (continuum and line core), magnetic field and Doppler velocity. Methods: .We have observed solar region NOAA

Th. Roudier; J. M. Malherbe; J. Moity; S. Rondi; P. Mein; Ch. Coutard

2006-01-01

371

An Extraordinary Magnetic Field Map of Mars  

NASA Astrophysics Data System (ADS)

A new global map of the magnetic field of Mars, with an order of magnitude improved sensitivity to crustal magnetization, is derived from Mars Global Surveyor mapping orbit magnetic field data. With this comes greatly improved spatial resolution and geologic intrpretation.

Connerney, J. E. P.; Acuna, M. H.; Ness, N. F.; Mitchell, D. L.; Lin, R. P.

2004-03-01

372

Parallel heat transport in integrable and chaotic magnetic fields  

SciTech Connect

The study of transport in magnetized plasmas is a problem of fundamental interest in controlled fusion, space plasmas, and astrophysics research. Three issues make this problem particularly challenging: (i) The extreme anisotropy between the parallel (i.e., along the magnetic field), {chi}{sub ||} , and the perpendicular, {chi}{sub Up-Tack }, conductivities ({chi}{sub ||} /{chi}{sub Up-Tack} may exceed 10{sup 10} in fusion plasmas); (ii) Nonlocal parallel transport in the limit of small collisionality; and (iii) Magnetic field lines chaos which in general complicates (and may preclude) the construction of magnetic field line coordinates. Motivated by these issues, we present a Lagrangian Green's function method to solve the local and non-local parallel transport equation applicable to integrable and chaotic magnetic fields in arbitrary geometry. The method avoids by construction the numerical pollution issues of grid-based algorithms. The potential of the approach is demonstrated with nontrivial applications to integrable (magnetic island), weakly chaotic (Devil's staircase), and fully chaotic magnetic field configurations. For the latter, numerical solutions of the parallel heat transport equation show that the effective radial transport, with local and non-local parallel closures, is non-diffusive, thus casting doubts on the applicability of quasilinear diffusion descriptions. General conditions for the existence of non-diffusive, multivalued flux-gradient relations in the temperature evolution are derived.

Castillo-Negrete, D. del; Chacon, L. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-8071 (United States)

2012-05-15

373

Parallel heat transport in integrable and chaotic magnetic fields  

SciTech Connect

The study of transport in magnetized plasmas is a problem of fundamental interest in controlled fusion, space plasmas, and astrophysics research. Three issues make this problem particularly chal- lenging: (i) The extreme anisotropy between the parallel (i.e., along the magnetic field), , and the perpendicular, , conductivities ( / may exceed 1010 in fusion plasmas); (ii) Magnetic field lines chaos which in general complicates (and may preclude) the construction of magnetic field line coordinates; and (iii) Nonlocal parallel transport in the limit of small collisionality. Motivated by these issues, we present a Lagrangian Green s function method to solve the local and non-local parallel transport equation applicable to integrable and chaotic magnetic fields in arbitrary geom- etry. The method avoids by construction the numerical pollution issues of grid-based algorithms. The potential of the approach is demonstrated with nontrivial applications to integrable (magnetic island chain), weakly chaotic (devil s staircase), and fully chaotic magnetic field configurations. For the latter, numerical solutions of the parallel heat transport equation show that the effective radial transport, with local and non-local closures, is non-diffusive, thus casting doubts on the appropriateness of the applicability of quasilinear diffusion descriptions. General conditions for the existence of non-diffusive, multivalued flux-gradient relations in the temperature evolution are derived.

Del-Castillo-Negrete, Diego B [ORNL; Chacon, Luis [ORNL

2012-01-01

374

A coupling between electric circuits and 2D magnetic field modeling  

Microsoft Academic Search

A method which enables coupling between equations of electric circuits consisting of a lumped element RLC configuration and a magnetic field model is presented. The coupling between the finite-element and the boundary-element methods is used to compute the magnetic field produced by conductors excited by an electric circuit. The conductors involved in this computation may be connected according to any

A. Nicolet; F. Delince; N. Bamps; A. Genon; W. Legros

1993-01-01

375

Annular Josephson tunnel junctions in an external magnetic field: The statics  

Microsoft Academic Search

We have investigated the static configurations of the phase inside an annular Josephson tunnel junction in the presence of an externally applied magnetic field. We report here a detailed study of the dependence on the magnetic field of the critical current for different annular geometries. The periodic conditions for the phase difference across the barrier are derived from fluxoid quantization.

N. Martucciello; R. Monaco

1996-01-01

376

Modification of interdendritic convection in directional solidification by a uniform magnetic field  

Microsoft Academic Search

Because of thermoelectric effects, a local current density appears in the dendritic network during the solidification of a metallic alloy. Thus, when a magnetic field is applied, a Lorentz force is created. Two alloys are solidified directionally in the horizontal configuration under a transverse magnetic field with the result that this force opposes the natural solutal buoyancy force. The experimental

P. Lehmann; R. Moreau; D. Camel; R. Bolcato

1998-01-01

377

Pure Gauge Configurations and Tachyon Solutions to String Field Theories Equations of Motion  

Microsoft Academic Search

In constructions of analytical solutions to open string field theories pure\\u000agauge configurations parameterized by wedge states play an essential role.\\u000aThese pure gauge configurations are constructed as perturbation expansions and\\u000ato guaranty that these configurations are asymptotical solutions to equations\\u000aof motions one needs to study convergence of the perturbation expansions. We\\u000ademonstrate that for the large parameter of

I. Ya. Aref'eva; Roman V. Gorbachev; Dmitry A. Grigoryev; Pavel N. Khromov; Maxim V. Maltsev; P. B. Medvedev

2009-01-01

378

Rotating magnetic beacons magnetic field strength size in SAGD  

Microsoft Academic Search

Rotation magnetic beacons magnetic field strength is very important to drill parallel horizontal twin wells in steam assisted\\u000a gravity drainage (SAGD). This paper analyzes a small magnet with a diameter of 25.4 mm. At each end, there is a length of\\u000a 12.6 mm with permanent magnet, and in the middle, there is a length of 78mm with magnetic materials. The

Bing Tu; Desheng Li; Enhuai Lin; Bin Luo; Jian He; Lezhi Ye; Jiliang Liu; Yuezhong Wang

2010-01-01

379

Electric field detectors in a coupled ring configuration: preliminary results  

Microsoft Academic Search

A novel architecture for sensing weak dc magneticfields exploits the co- operation between nonlinear coupled systems and ferroelectric devices. Sensors for static electric fields (E-fields) based on unidirection- ally coupled nonlinear dynamical systems1 are currently un- der development. They will exploit the synergic use of bistable ferroelectric materials, micromachining technologies, and novel sensing strategies. Considerable practical interest in such de-

Bruno Ando; Salvatore Baglio; Alberto Ascia; Adi R. Bulsara

2007-01-01

380

Beam Fields in an Integrated Cavity, Coupler and Window Configuration  

SciTech Connect

In a multi-bunch high current storage ring, beam generated fields couple strongly into the RF cavity coupler structure when beam arrival times are in resonance with cavity fields. In this study the integrated effect of beam fields over several thousand RF periods is simulated for the complete cavity, coupler, window and waveguide system of the PEP-II B-factory storage ring collider. We show that the beam generated fields at frequencies corresponding to several bunch spacings for this case gives rise to high field strength near the ceramic window which could limit the performance of future high current storage rings such as PEP-X or Super B-factories.

Weathersby, Stephen; Novokhatski, Alexander; /SLAC

2010-02-10

381

Optimal design and comparison of stator winding configurations in permanent magnet assisted synchronous reluctance generator  

Microsoft Academic Search

This paper presents design of high performance permanent magnet-assisted synchronous reluctance generators (PMa-SynRG) for 3 kW tactical quiet generator set. Adding the proper quantity of permanent magnets into the synchronous reluctance generator rotor core can offer large constant power-speed range, high efficiency and high power factor. Different stator winding configurations such as distributed windings and concentrated windings are compared using

Jeihoon Baek; Mina M. Rahimian; Hamid A. Toliyat

2009-01-01

382

Unique topological characterization of braided magnetic fields  

NASA Astrophysics Data System (ADS)

We introduce a topological flux function to quantify the topology of magnetic braids: non-zero, line-tied magnetic fields whose field lines all connect between two boundaries. This scalar function is an ideal invariant defined on a cross-section of the magnetic field, and measures the average poloidal magnetic flux around any given field line, or the average pairwise crossing number between a given field line and all others. Moreover, its integral over the cross-section yields the relative magnetic helicity. Using the fact that the flux function is also an action in the Hamiltonian formulation of the field line equations, we prove that it uniquely characterizes the field line mapping and hence the magnetic topology.

Yeates, A. R.; Hornig, G.

2013-01-01

383

Plasma Magnet: Using a Rotating Magnetic Field to Couple Thrust From the Solar Wind  

NASA Astrophysics Data System (ADS)

The Plasma Magnet concept aims to provide a large magnetic barrier to couple thrust from the solar wind. A spacecraft using Plasma Magnet propulsion would be able to move throughout the solar system faster and more efficiently than possible using conventional chemical or electric propulsion. This dramatic improvement in performance is made possible by coupling thrust from the solar wind. The Plasma Magnet drives electrical currents in plasma surrounding the spacecraft using a rotating magnetic field (RMF). RMF has been successfully used to drive currents of several thousand amps in Field Reversed Configurations (FRC) and Rotamak plasma configurations during the course of international fusion research efforts. However, these experiments have used RMF current drive in the region inside the RMF coils. For the Plasma Magnet concept to be successful, RMF current drive must be successfully used to drive currents external to and at large distances from the RMF coils. Preliminary computer simulations indicate that RMF can drive currents outside the RMF coils. Preliminary experimental investigations of the Plasma Magnet concept are also underway. The poster presented will feature these results and a description of the Plasma Magnet concept in the context of advanced spacecraft propulsion.

Giersch, Louis; Slough, John; Winglee, Robert; Andreason, Samuel

2004-11-01

384

Magnetism  

NSDL National Science Digital Library

This webpage is part of the University Corporation for Atmospheric Research (UCAR) Windows to the Universe program. It describes the nature and configuration of magnetic fields, which are the result of moving electric charges, including how they cause magnetic objects to orient themselves along the direction of the magnetic force points, which are illustrated as lines. Magnetic field lines by convention point outwards at the north magnetic pole and inward at the south magnetic pole. The site features text, scientific illustrations and an animation. Text and vocabulary are selectable for the beginning, intermediate, or advanced reader.

Team, University C.

2007-12-12

385

Ion pump using cylindrically symmetric spindle magnetic field  

NASA Astrophysics Data System (ADS)

For all accelerators and many research and industries, excellent vacuum conditions are required and the highest possible pumping rates are necessary. For most applications the standard ion sputtering pump (ISP) meets these requirements and is optimal for financial point of view also. The physical principle of the ISP is well known and many companies manufacture variety of ISP. Most of them use dipole magnetic field produced by permanent magnet and electric dipole field between the electrodes in which tenuous plasma is created because of interaction of between the relatively fast electrons slow residual gas atoms. Performance of an ISP depends basically on the electron cloud density in between the titanium electrodes but in the available present configurations no consideration has been given to electron confinement which needs a mirror magnetic field. If this is incorporated it will make a robust ISP surely; furthermore, the requirement of constant feeding of high voltage to electrodes for supplying sufficient number of electrons will be reduced too. A study has been performed to create sufficient rotationally symmetric spindle magnetic field (SMF) with inherent presence of magnetic mirror effect to electron motion to confine them for longer time for enhancing the density of electron cloud between the electrodes. It will lessen the electric power feeding the electrodes and lengthen their life-time. Construction of further compact and robust ISP is envisaged herein. The field simulation using the commercially available permanent magnet together with simulation of electron motion in such field will be presented and discussed in the paper.

Rashid, M. H.

2012-11-01

386

Modified magnetic confinement configurations based on understanding helicity dissipation and pressure driven modes in the spheromak  

SciTech Connect

Recent results from the spheromak work at Los Alamos include: In decaying spheromaks in the mesh flux conserver, the rate of current decay dI/dt depends only on the density n/sub e/ (not on I or T/sub e/ as might be expected classically). The particular dependence of dI/dt on n/sub e/ suggests that most of the helicity is dissipated in the field error regions at the edge where electron-neutral hydrogen collisions dominate the electrical resistance. A new solid-wall, titanium-gettered flux conserver has been commissioned, resulting in less field errors than with previous mesh flux conserver. A factor of four decrease in dI/dt has been observed. In this new flux conserver, clear evidence of a pressure-driven instability has been obtained. To our knowledge, this is the first time a pressure driven interchange mode has been directly observed in a toroidal geometry. Peak ..beta.. values observed before the onset of the mode are of the same order as those predicted at the corresponding Mercier limits (..beta../sub c/ approx. 1%). As a result, flux conserver shapes with higher ..beta../sub c/ are now being considered by us. The ..beta../sub c/ calculations have been made using Taylor-like (minimum energy) magnetic profiles. By changing the flux conserver shape, the q profile of the minimum-energy state can be varied continuously from RFP-like to tokamak-like. The highest ..beta../sub c/ (approx.10%) are found at these two extremes of the range of magnetic configurations. 3 refs.

Jarboe, T.R.; Barnes, C.W.; Fernandez, J.C.; Henins, I.; Marklin, G.J.; Wysocki, F.J.

1988-01-01

387

High Performance Field-Reversed Configuration Plasmas in the C-2 Device  

NASA Astrophysics Data System (ADS)

A high temperature, stable, long-lived field-reversed configuration (FRC) plasma state has been produced in the C-2 device by dynamically colliding and merging two oppositely directed compact toroids, by biasing edge plasma near the FRC separatrix from a plasma-gun (PG) located at one end of the C-2 device, and by neutral-beam (NB) injection. The PG creates an inward radial electric field (Er<0) which counters the usual FRC spin-up in the ion diamagnetic direction and mitigates the n = 2 rotational instability without applying quadrupole magnetic fields. Better plasma centering is also obtained, presumably from line-tying to the gun electrodes. The PG produces ExB velocity shear in the FRC edge layer which may explain observations of improved transport properties The FRCs are nearly axisymmetric, which enables fast ion confinement. The combined effects of the PG and of NB injection yield a new High Performance FRC (HPF) regime with confinement times improved by factors 2 to 4 and FRC lifetimes extended from 1 to 3 ms. A second PG was newly installed at the other end of the C-2 device, and new experimental campaigns with 2 PGs have been explored. Characteristics of the HPF regime will be presented at the meeting as well as newly obtained results with 2 PGs and NBs.

Gota, H.; Tuszewski, M.; Smirnov, A.; Guo, H.; Binderbauer, M.; Barnes, D.; Akhmetov, T.; Ivanov, A.

2012-10-01

388

Boston University Physics Applets: Magnetic Field Demonstration  

NSDL National Science Digital Library

This web page is an interactive physics simulation that explores magnetic fields. The user can add currents coming into or out of a simulated grid, and see the fields created. There is also a selection of pre-created fields, including bar magnets, loops, opposing magnets, and coils in uniform fields. Double-clicking on any point displays the full loop created by the magnetic field. This item is part of a larger collection of introductory physics simulations developed by the author. This is part of a collection of similar simulation-based student activities.

Duffy, Andrew

2008-08-23

389

Electric charge catalysis by magnetic fields and a nontrivial holonomy  

NASA Astrophysics Data System (ADS)

We describe a generic mechanism by which a system of Dirac fermions in thermal equilibrium acquires electric charge in an external magnetic field. To this end the fermions should have an additional quantum number, isospin, or color and should be subject to a second magnetic field, which distinguishes the isospin or color, as well as to a corresponding isospin chemical potential. The role of the latter can be also played by a nontrivial holonomy (Polyakov loop) along the Euclidean time direction. The charge is accumulated since the degeneracies of occupied lowest Landau levels for particles of positive isospin and antiparticles of negative isospin are different. We discuss two physical systems where this phenomenon can be realized. One is monolayer graphene, where the isospin is associated with two valleys in the Brillouin zone, and the strain-induced pseudomagnetic field acts differently on charge carriers in different valleys. Another is hot QCD, for which the relevant non-Abelian field configurations with both nonzero chromomagnetic field and a nontrivial Polyakov loop can be realized as calorons—topological solutions of Yang-Mills equations at finite temperature. The induced electric charge on the caloron field configuration is studied numerically. We argue that due to the fluctuations of holonomy, the external magnetic field should tend to suppress charge fluctuations in the quark-gluon plasma and estimate the importance of this effect for off-central heavy-ion collisions.

Bruckmann, F.; Buividovich, P. V.; Sulejmanpasic, T.

2013-08-01

390

Bipolar pulse field for magnetic refrigeration  

DOEpatents

A magnetic refrigeration apparatus includes first and second steady state magnets, each having a field of substantially equal strength and opposite polarity, first and second bodies made of magnetocaloric material disposed respectively in the influence of the fields of the first and second steady state magnets, and a pulsed magnet, concentric with the first and second steady state magnets, and having a field which cycles between the fields of the first and second steady state magnets, thereby cyclically magnetizing and demagnetizing and thus heating and cooling the first and second bodies. Heat exchange apparatus of suitable design can be used to expose a working fluid to the first and second bodies of magnetocaloric material. A controller is provided to synchronize the flow of working fluid with the changing states of magnetization of the first and second bodies.

Lubell, Martin S. (Oak Ridge, TN)

1994-01-01

391

Bipolar pulse field for magnetic refrigeration  

DOEpatents

A magnetic refrigeration apparatus includes first and second steady state magnets, each having a field of substantially equal strength and opposite polarity, first and second bodies made of magnetocaloric material disposed respectively in the influence of the fields of the first and second steady state magnets, and a pulsed magnet, concentric with the first and second steady state magnets, and having a field which cycles between the fields of the first and second steady state magnets, thereby cyclically magnetizing and demagnetizing and thus heating and cooling the first and second bodies. Heat exchange apparatus of suitable design can be used to expose a working fluid to the first and second bodies of magnetocaloric material. A controller is provided to synchronize the flow of working fluid with the changing states of magnetization of the first and second bodies. 2 figs.

Lubell, M.S.

1994-10-25

392

Near-Field Magnetic Dipole Moment Analysis.  

National Technical Information Service (NTIS)

This paper describes the data analysis technique used for magnetic testing at the NASA Goddard Space Flight Center (GSFC). Excellent results have been obtained using this technique to convert a spacecraft s measured magnetic field data into its respective...

P. K. Harris

2003-01-01

393

Constant Current Source for Stable Magnetic Fields.  

National Technical Information Service (NTIS)

An electronic control system for stabilization of currents in magnetic fields is described. Three superimposed control stages with different characteristics provide optimum elimination of all interfering factors. The use of electrostatic and magnetic shie...

K. Weyand

1976-01-01

394

Effect of magnetic field on the characteristics of a hollow cathode ion source  

Microsoft Academic Search

The effect of magnetic field on the performance of a hollow cathode ion source was experimentally studied. The field strength and the field distribution around the hollow cathode were changed step by step and the source parameters were recorded for each step. The result showed that with the optimum field configuration the discharge was stabilized even at low-operating gas pressures

Shigeru Tanaka; Masato Akiba; Hiroshi Horiike; Yoshikazu Okumura; Yoshihiro Ohara

1983-01-01

395

THE EARTH'S YOUNG MAGNETIC FIELD  

Microsoft Academic Search

Invisible lines of magnetic force enclose our planet in what scientists call adipolarmagneticfield. Today these lines go from magnetic south to magnetic north, which are offset a few degrees from the geographic poles. Some minerals, like magnetite, can \\

Trevor Major

396

Propagation and damping characteristics of low-frequency waves in field-reversed configuration plasmas  

SciTech Connect

Propagation and damping properties of low-frequency waves in extremely high beta plasmas have been investigated in the field-reversed configuration plasma injection experiment apparatus. Two distinct wave modes were excited by different antenna geometry and the radial structures of their magnetic components were measured in detail. Due to the high beta nature of the plasma, the Alfven resonance predicted for the cold plasma vanished and the wave with small parallel wave number k{sub z}{approx}2.5 m{sup -1} propagated in a broad area across the separatrix. The wave exhibited moderate dissipation, which was suggestive of the resistive damping. The wave with large parallel wave number k{sub z}{approx}7.0 m{sup -1}, however, underwent quite strong damping inside the separatrix. Transit-time magnetic pumping, which converts the wave energy to the ion parallel kinetic energy, is most likely to be responsible for this strong damping since the wave's parallel phase velocity is close to the ion thermal velocity.

Inomoto, Michiaki; Yamamoto, Satoshi; Iwasawa, Naotaka; Kitano, Katsuhisa; Okada, Shigefumi [Center for Atomic and Molecular Technologies, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan)

2007-10-15

397

Model of the influence of magnetic fields on a plasma electrode Pockels cell  

SciTech Connect

We describe a model which gives the effects of magnetic fields on a plasma electrode Pockels cell. The fields arise from the return currents to the cathode as well as from neighboring devices such as amplifier flashlamps. In effect, electrons are treated as a static, planar fluid moving under the influence of magnetic fields, the electric field of the discharge, electron pressure gradients, and electron-atom elastic collisions. This leads to a closed two- dimensional equation for the electron density, which is solved subject to appropriate boundary collisions. The model is applied to four cases-. the baseline NIF configuration with magnetic fields due to balanced return currents; a case with unbalanced return currents; the reverser configuration containing an external field parallel to the main plasma current; and a configuration with a field perpendicular to both the current and the optical direction.

Boley, C.D.; Rhodes, M.A.

1996-10-01

398

Arc Discharges in a Curved Magnetic Field.  

National Technical Information Service (NTIS)

An experiment on arc discharges in hydrogen in a curved magnetic field is described. For a few milliseconds the discharge current flowed between two electrodes along the field lines of a toroidal magnetic field over an angle of 258 deg. The plasma was not...

F. C. Schueller

1974-01-01

399

Is the intergalactic magnetic field primordial?  

Microsoft Academic Search

We consider the various methods used to constrain the possible field strength of the present day intergalactic field and findB0(G)-10 as a probable upper bound. It is suggested that the observed intergalactic magnetic field might not be primordial in origin but rather the result of magnetic flux leakage from galaxies and clusters of galaxies.

Martin Beech

1985-01-01

400

Intergalactic magnetic field and galactic WARPS  

Microsoft Academic Search

An alternative explanation of galactic warps is proposed, in which the intergalactic magnetic field (IGMF) is responsible for these structures. The model predicts that, to be efficient, the magnetic field must have a direction not much different from 45 deg with the galactic plane. The required values of the field strength are uncertain, of about 10 nG, higher values being

E. Battaner; E. Florido; M. L. Sanchez-Saavedra

1990-01-01

401

Fiber Bragg Grating Magnetic Field Sensor  

Microsoft Academic Search

In this paper we demonstrate experimentally a magnetic field sensor using a fiber Bragg grating. The shift in the Bragg condition as a result of strain applied on the fiber mounted on a nickel base by the magnetic field gives an indirect measure of the field. The proposed method overcomes the need for long fiber lengths required in methods such

K. V. Madhav; K. Ravi Kumar; T. Srinivas; S. Asokan

2006-01-01

402

Is the intergalactic magnetic field primordial?  

NASA Astrophysics Data System (ADS)

The various methods used to constrain the possible field strength of the present day intergalactic field are considered, and Bzero (G) less than 10 to the -10th is found as a probable upper bound. It is suggested that the observed intergalactic magnetic field might not be primordial in origin but rather the result of magnetic flux leakage from galaxies and clusters of galaxies.

Beech, M.

1985-11-01

403

Fiber Optic Magnetic Field Sensors Using Metallic Glass Coatings.  

NASA Astrophysics Data System (ADS)

In this thesis we have investigated the use of a magnetostrictive material with a single-mode optical fiber for detecting weak magnetic fields. The amorphous alloy Metglas^circler 2605SC (Fe_{81}B_ {13.5}Si_{3.5} C_2) was chosen as the magnetostrictive material because of the combination of its large magnetostriction and small magnetic anisotropy field among all available metals. For efficient coupling between the magnetostrictive material and the optical fiber, the magnetostrictive material was directly deposited onto the single-mode optical fiber. The coated fibers were used as the sensing element in the fiber optic magnetic field sensor (FOMS). Very high quality thick metallic glass films of the Metglas 2605 SC have been deposited using triode-magneton sputtering. This is the first time such material has been successfully deposited onto an optical fiber or onto any other substrate. The films were also deposited onto glass slides to allow the study of the magnetic properties of the film. The thicknesses of these films were 5-15 mum. The magnetic property of primary interest for our sensor application is the induced longitudinal magnetostrictive strain. However, the other magnetic properties such as magnetic anisotropy, surface and bulk coercivities, magnetic homogeneity and magnetization all affect the magnetostrictive response of the material. We have used ferromagnetic resonance (FMR) at microwave frequencies to study the magnetic anisotropy and homogeneity; vibrating sample magnetometry (VSM) to study the bulk magnetic hysteresis responses and coercivity; and the longitudinal magneto-optic kerr effect (LMOKE) to study the surface magnetic hysteresis responses and coercivity. The isothermalmagnetic annealing effect on these properties has also been studied in detail. The fiber optic magnetic field sensor constructed using the metallic-glass-coated fiber was tested. An electronic feedback control loop using a PZT cylinder was constructed for stabilizing the sensor operation. Magnetic field detection at different dither frequencies was studied in detail. The estimated minimum detectable magnetic field was about 3 times 10^{-7 } Oe. A simplified elastic model was used for the theoretical calculation of the phase shift induced in a metallic-glass -coated optical fiber with a longitudinal applied magnetic field. The phase shift as a function of coating thickness was calculated, and the experimental results at certain thicknesses were compared with the calculation. The frequency response of the FOMS was also studied in some detail. Three different configurations were used for the study of the frequency response. The results indicate that the resonances observed in the FOMS are most likely related to the mechanical resonance of the optical fiber.

Wang, Yu.

1990-01-01

404

Static uniform magnetic fields and amoebae  

SciTech Connect

Three species of potentially pathogenic amoebae were exposed to 71 and 106.5 mT from constant homogeneous magnetic fields and examined for inhibition of population growth. The number of amoebae for three species was significantly less than controls after a 72 h exposure to the magnetic fields when the temperature was 20 C or above. Axenic cultures, i.e., cultures grown without bacteria, were significantly affected after only 24 h. In 20 of 21 tests using the three species, the magnetic field significantly inhibited the growth of amoebae. In one test in which the temperature was 20 C for 48 h, exposure to the magnetic field was not inhibitory. Final numbers of magnetic field-exposed amoebae ranged from 9 to 72% lower than the final numbers of unexposed controls, depending on the species. This research may lead to disinfection strategies utilizing magnetic fields for surfaces on which pathogenic amoebae may proliferate.

Berk, S.G.; Srikanth, S.; Mahajan, S.M.; Ventrice, C.A. [Tennessee Technological Univ., Cookeville, TN (United States)

1997-03-01

405

Configuration Optimization of Underground Cables inside a Large Magnetic Steel Casing for Best Ampacity  

NASA Astrophysics Data System (ADS)

This thesis presents a method for optimizing cable configuration inside a large magnetic cylindrical steel casing, from the total ampacity point of view. The method is comprised of two main parts, namely: 1) analytically calculating the electromagnetic losses in the steel casing and sheathed cables, for an arbitrary cables configuration, and 2) implementing an algorithm for determining the optimal cables configuration to obtain the best total ampacity. The first part involves approximating the eddy current and hysteresis losses in the casing and cables. The calculation is based on the theory of images, which this thesis expands to apply to casings having both high magnetic permeability and high electric conductivity at the same time. The method of images, in combination with approximating the cable conductors and sheaths as multiple physical filaments, is used to compute the final current distributions in the cables and pipe and thus the associated losses. The accuracy of this computation is assessed against numerical solutions obtained using the Maxwell finite element program by Ansoft. Next, the optimal cable configuration is determined by applying a proposed two-level optimization algorithm. At the outer level, a combinatorial optimization based on a genetic algorithm explores the different possible configurations. The performance of every configuration is evaluated according to its total ampacity, which is calculated using a convex optimization algorithm. The convex optimization algorithm, which forms the inner level of the overall optimization procedure, is based on the barrier method. This proposed optimization procedure is tested for a duct bank installation containing twelve cables and fifteen ducts, comprising two circuits and two cables per phase, and compared with a brute force method of considering all possible configurations. The optimization process is also applied to an installation consisting of a single circuit inside a large magnetic steel casing.

Moutassem, Wael

406

Circuitry, systems and methods for detecting magnetic fields  

SciTech Connect

Circuitry for detecting magnetic fields includes a first magnetoresistive sensor and a second magnetoresistive sensor configured to form a gradiometer. The circuitry includes a digital signal processor and a first feedback loop coupled between the first magnetoresistive sensor and the digital signal processor. A second feedback loop which is discrete from the first feedback loop is coupled between the second magnetoresistive sensor and the digital signal processor.

Kotter, Dale K. (Shelley, ID); Spencer, David F. (Idaho Falls, ID); Roybal, Lyle G. (Idaho Falls, ID); Rohrbaugh, David T. (Idaho Falls, ID)

2010-09-14

407

Magnetic-field asymmetry of nonlinear thermoelectric and heat transport  

NASA Astrophysics Data System (ADS)

Nonlinear transport coefficients do not obey, in general, reciprocity relations. We here discuss the magnetic-field asymmetries that arise in thermoelectric and heat transport of mesoscopic systems. Based on a scattering theory of weakly nonlinear transport, we analyze the leading-order symmetry parameters in terms of the screening potential response to either voltage or temperature shifts. We apply our general results to a quantum Hall antidot system. Interestingly, we find that certain symmetry parameters show a dependence on the measurement configuration.

Hwang, Sun-Yong; Sánchez, David; Lee, Minchul; López, Rosa

2013-10-01

408

Flux loss during the equilibrium phase of field-reversed configurations  

SciTech Connect

Field-reversed configurations are consistently formed at low filling pressures in the FRX-C device, with decay time of the trapped flux after formation much larger than the stable period. This contrasts with previous experimental observations.

Tuszewski, M.; Armstrong, W.T.; Bartsch, R.R.; Chrien, R.E.; Cochrane, J.C. Jr.; Kewish, R.W. Jr.; Klingner, P.; Linford, R.K.; McKenna, K.F.; Rej, D.J.; Sherwood, E.G.; Siemon, R.E.

1982-10-01

409

Extraterrestrial Magnetic Fields: Achievements and Opportunities  

Microsoft Academic Search

The major scientific achievements associated with the measurement of magnetic fields in space over the past decade and a half are reviewed. Aspects of space technology relevant to magnetic-field observations are discussed, including the different types of magnetometers used and how they operate, problems arising from spacecraft-generated magnetic fields and the appropriate countermeasures that have been developed and on-board processing

EDWARD J. SMITHAND; Charles Sonett

1976-01-01

410

Modeling solar force-free magnetic fields  

Microsoft Academic Search

A class of nonlinear force-free magnetic fields is presented, described in terms of the solutions to a second-order, nonlinear ordinary differential equation. These magnetic fields are three-dimensional, filling the infinite half-space above a plane where the lines of force are anchored. They model the magnetic fields of the sun over active regions with a striking geometric realism. The total energy

B. C. Low; Y. Q. Lou

1990-01-01

411

Induced Magnetic Anisotropy of Ferrofluid Frozen in Magnetic Fields  

Microsoft Academic Search

The magnetization process of a ferrofluid whose carrier fluid is paraffin was investigated in the temperature range from 77 K to 300 K, as a function of the cooling field intensity and freezing rate. Phase transitions between the liquid and solid states can be simulated by using the ferrofluids as a magnetic probe. A uniaxial magnetic anisotropy was induced by

N. Inaba; H. Miyajima; S. Taketomi; S. Chikazumi

1989-01-01

412

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in 2013. The objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution using a constellation of 3 identical satellites. The Mission shall deliver data that allow access to new insights into the Earth system by improved scientific understanding of the Earth's interior and near-Earth electromagnetic environment. After launch and triple satellite release at an initial altitude of about 490 km, a pair of the satellites will fly side-by-side with slowly decaying altitude, while the third satellite will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission science goals are to provide a unique view into Earth's core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently in the final stage of the development phase, will be addressed. A consortium of European scientific institutes is developing a distributed processing system to produce geophysical (Level 2) data products for the Swarm user community. The setup of the Swarm ground segment and the contents of the data products will be addressed. More information on Swarm can be found at www.esa.int/esaLP/LPswarm.html.

Plank, Gernot; Haagmans, Roger; Floberghagen, Rune; Menard, Yvon

2013-04-01

413

Effects of TSTO Orbiter Configuration on Supersonic Flow Field with Aerodynamic Interactions  

Microsoft Academic Search

Supersonic flow fields around Two-Stage-To-Orbit (TSTO) models with different configurations have been experimentally examined in this paper. Four configurations for the orbiter have been considered: A) a hemisphere-cylinder, B) a hemisphere-cylinder with a flat bottom, C) an obliquely truncated circular cylinder, and D) a cone-cylinder. All the flow fields around these models showed complicated shock\\/shock and shock\\/boundary-layer interactions, which can

Keiichi Kitamura; Koichi Mori; Katsuhisa Hanai; Tsutomu Yabashi; Hiroshi Ozawa; Yoshiaki Nakamura

2007-01-01

414

Pre-Eruption Magnetic Configurations in the Low Atmosphere of Solar Active Regions  

NASA Astrophysics Data System (ADS)

Major solar eruptions, namely flares and coronal mass ejections, rely on significant local accumulations of non-potential (free; stored in electric currents) magnetic energy and, quite likely, magnetic helicity in the solar atmosphere. Without [both of] them, eruptions cannot be powered. Simple tests can show that most free energy and helicity reside close to the lower atmospheric boundary in solar active regions, i.e. their photospheric or low chromospheric interface. Therefore, the pre-eruption configuration in this boundary should reflect these high free-energy and helicity conditions that jointly determine the degree of non-potentiality in active regions. We review the two main active-region photospheric/low-chromospheric configurations leading to major eruptions: instances of intense magnetic flux emergence in the absence of intense magnetic polarity inversion lines (PILs), and instances of strong PILs. In these configurations we discuss multiple measures that can be thought of as proxies of free magnetic energy and helicity and we outline a method to actually calculate these budgets. Combining information from different, but concerted, analyses and approaches, a new picture of eruption initiation emerges. We highlight this new insight and project on its physical plausibility and the advances that it may bring.

Georgoulis, Manolis K.

2012-07-01

415

Five years of magnetic field management  

SciTech Connect

The extensive publicity of epidemiological studies inferring correlation between 60 Hz magnetic fields and childhood leukemia prompted world wide research programs that have as a goal to determine if low frequency magnetic fields represent any risk for the general population, children or utility workers. While supporting this research effort through EPRI, Con Edison embarked on a technical research program aimed to: characterize magnetic fields as to intensity and variation in time; and investigate practical means to manage these magnetic fields through currently known methods. The final goal of these research projects is to establish viable methods to reduce magnetic field intensity to desired values at reasonable distances from the sources. This goal was pursued step by step, starting with an inventory of the main sources of magnetic fields in substations, distribution and transmission facilities and generating plants. The characterization of the sources helped to identify typical cases and select specific cases, far practical applications. The next step was to analyze the specific cases and develop design criteria for managing the magnetic fields in new installations. These criteria included physical arrangement of equipment based oil calculation of magnetic fields, cancellation effect, desired maximum field intensity at specific points and shielding with high magnetic permeability metals (mu-metal and steel). This paper summarizes the authors` experiences and shows the results of the specific projects completed in recent years.

Durkin, C.J.; Fogarty, R.P.; Halleran, T.M.; Mark, Dr. D.A.; Mukhopadhyay, A.

1995-01-01

416

Quark matter in a strong magnetic field  

SciTech Connect

The effect of a strong magnetic field on the stability and gross properties of bulk as well as quasibulk quark matter is investigated using the conventional MIT bag model. Both the Landau diamagnetism and the paramagnetism of quark matter are studied. How the quark hadron phase transition is affected by the presence of a strong magnetic field is also investigated. The equation of state of strange quark matter changes significantly in a strong magnetic field. It is also shown that the thermal nucleation of quark bubbles in a compact metastable state of neutron matter is completely forbidden in the presence of a strong magnetic field. {copyright} {ital 1996 The American Physical Society.}

Chakrabarty, S. [Department of Physics, University of Kalyani, District: Nadia, West Bengal 741 235 (India)]|[Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411 007 (India)

1996-07-01

417

Two dimensional frustrated magnets in high magnetic field  

NASA Astrophysics Data System (ADS)

Frustrated magnets in high magnetic field have a long history of offering beautiful surprises to the patient investigator. Here we present the results of extensive classical Monte Carlo simulations of a variety of models of two dimensional magnets in magnetic field, together with complementary spin wave analysis. Striking results include (i) a massively enhanced magnetocaloric effect in antiferromagnets bordering on ferromagnetic order, (ii) a route to an m = 1/3 magnetization plateau on a square lattice, and (iii) a cascade of phase transitions in a simple model of AgNiO2.

Seabra, L.; Shannon, N.; Sindzingre, P.; Momoi, T.; Schmidt, B.; Thalmeier, P.

2009-01-01

418

The Magnetic Fields of the Quiet Sun  

NASA Astrophysics Data System (ADS)

This work reviews our understanding of the magnetic fields observed in the quiet Sun. The subject has undergone a major change during the last decade (quiet revolution), and it will remain changing since the techniques of diagnostic employed so far are known to be severely biased. Keeping these caveats in mind, our work covers the main observational properties of the quiet Sun magnetic fields: magnetic field strengths, unsigned magnetic flux densities, magnetic field inclinations, as well as the temporal evolution on short time-scales (loop emergence), and long time-scales (solar cycle). We also summarize the main theoretical ideas put forward to explain the origin of the quiet Sun magnetism. A final prospective section points out various areas of solar physics where the quiet Sun magnetism may have an important physical role to play (chromospheric and coronal structure, solar wind acceleration, and solar elemental abundances).

Sánchez Almeida, J.; Martínez González, M.

2011-04-01

419

Equilibrium electrons in free-electron lasers with a 3D helical wiggler and a guide magnetic field: Nonlinear simulations  

NASA Astrophysics Data System (ADS)

Nonlinear simulations are devoted to the comparative study of the equilibrium electrons’ motion and stability in the combination of a three-dimensional helical wiggler and a positive or reversed guide magnetic field, where effects of the self-field, off-axis guiding center and adiabatic magnetic field are included. It is shown that a reversed guide magnetic field configuration brings the electron motion much smaller Larmor radius and transverse displacement span than a positive guide magnetic field does, and consequently, provides better transportation quality of the electron beam. Although the electron motion far