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1

Sns ring dipole magnetic field quality.  

National Technical Information Service (NTIS)

The large acceptance and compact size of the Spallation Neutron Source (SNS) ring implies the use of short, large aperture dipole magnets, with significant end field errors. The SNS will contain 32 such dipoles. We report magnetic field measurements of th...

Wanderer Jackson Jain Y. Lee Meng Papaphilippou Spataro Tepikian Tsoupas Wei

2002-01-01

2

Magnetic field effects on quantum ring excitons  

SciTech Connect

We study the effect of magnetic field and geometric confinement on excitons confined to a quantum ring. We use analytical matrix elements of the Coulomb interaction and diagonalize numerically the effective-mass Hamiltonian of the problem. To explore the role of different boundary conditions, we investigate the quantum ring structure with a parabolic confinement potential, which allows the wave functions to be expressed in terms of center of mass and relative degrees of freedom of the exciton. On the other hand, wave functions expressed in terms of Bessel functions for electron and hole are used for a hard-wall confinement potential. The binding energy and electron--hole separation of the exciton are calculated as function of the width of the ring and the strength of an external magnetic field. The linear optical susceptibility as a function of magnetic fields is also discussed. We explore the Coulomb electron--hole correlation and magnetic confinement for several ring width and size combinations. The Aharanov--Bohm oscillations of exciton characteristics predicted for one-dimensional rings are found to not be present in these finite-width systems.

Song, Jakyoung; Ulloa, Sergio E.

2001-03-15

3

The ``Shim-a-ring'' magnet: Configurable static magnetic fields using a ring magnet with a concentric ferromagnetic shim  

NASA Astrophysics Data System (ADS)

We introduce a permanent magnet assembly that can be configured to obtain uniform, gradient, or tunable field distribution. The design is composed of a single ring shaped permanent magnet and a concentric ferromagnetic shim. Magnetic field is configured by changing the shape of the air gap inside the ring magnet. Circular cross-section produces up to 0.54 T uniform field, whereas rectangular or triangular cross-sections result in gradient magnetic field distributions. Tunable field from a given ring magnet is obtained by changing the thickness of the ferromagnetic shim or the spacing between the shim and the permanent magnet.

Nath, P.; Chandrana, C. K.; Dunkerley, D.; Neal, J. A.; Platts, D.

2013-05-01

4

IMPACT OF MAGNETIC FIELD INTERFERENCE IN THE SNS RING.  

SciTech Connect

The modest size of the SNS accumulator ring and the use of short, large aperture magnets makes unavoidable the overlapping between the magnetic end fields of the quadrupoles with the adjacent multipole correctors. This interference effect can be quantified through magnetic field simulations and measurements. The impact to the beam dynamics is finally discussed.

PAPAPHILIPPOU,Y.; LEE,Y.Y.; MENG,W.

2001-06-18

5

Ring Current Modeling in a Realistic Magnetic Field Configuration  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

6

Quantum rings in magnetic fields and spin current generation  

NASA Astrophysics Data System (ADS)

We propose three different mechanisms for pumping spin-polarized currents in a ballistic circuit using a time-dependent magnetic field acting on an asymmetrically connected quantum ring at half filling. The first mechanism works thanks to a rotating magnetic field and produces an alternating current with a partial spin polarization. The second mechanism works by rotating the ring in a constant field; like the former case, it produces an alternating charge current, but the spin current is dc. Both methods do not require a spin–orbit interaction to achieve the polarized current, but the rotating ring could be used to measure the spin–orbit interaction in the ring using characteristic oscillations. On the other hand, the last mechanism that we propose depends on the spin–orbit interaction in an essential way, and requires a time-dependent magnetic field in the plane of the ring. This arrangement can be designed to pump a purely spin current. The absence of a charge current is demonstrated analytically. Moreover, a simple formula for the current is derived and compared with the numerical results.

Cini, Michele; Bellucci, Stefano

2014-04-01

7

Excitons and magnetic fields in bidimensional quantum rings  

NASA Astrophysics Data System (ADS)

We present calculations of structural features and magnetic field effects on the properties of an exciton localized in nanometer-size bidimensional quantum rings and disks. The recently developed fractal dimension method [1] is used, where the exciton trial wave function is taken as a product of the unbound electron and hole wave functions in the quantum system, with an arbitrary correlation function that depends only on electron-hole separation. In particular, we consider a realistic confinement potential shape that models quantum rings used in recent experiments. The binding energy, electron-hole separation, and the oscillator strength of the exciton are calculated as function of the width of the ring and magnetic field strength. In addition, we evaluate the magnitude of the in-plane polarization of the exciton for different structure parameters. This in-plane dipole, which arises from the built-in asymmetry of the potential confinement for the electron and hole in the system, produces a strong quantum phase accumulation effect that is reflected in the optical properties of the ring. This Aharonov-Bohm effect for the exciton dipole is similar to the results obtained for type-II quantum dot systems (where the electron and hole lie in different materials and are also polarized in-plane), and from other models of type-I structures [2]. Supported by US-DOE and OU-CMSS [1] I. D. Mikhailov, F. J. Betancur, R. Escorcia and J. Sierra-Ortega, Phys. Stat. Sol., 234(b), 590 (2002) [2] A. O. Govorov, S. E. Ulloa, K. Karrai and R. Warburton, Phys. Rev. B 66, 081309 (2002)

Sierra-Ortega, J.; Mikhailov, I. D.; Ulloa, S. E.; Govorov, A. O.

2003-03-01

8

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

Microsoft Academic Search

A magnetic field line topology with nulls, generated by superimposing a uniform magnetic field onto the field from a distributed ring current, is analyzed. This simple model, which is reminiscent of the structures found in laboratory field reversed configurations and detached plasmoids, is amenable to substantial analytical progress and also facilitates the visualization of the three dimensional field geometry. Four

M. S. Chance; J. M. Greene; T. H. Jensen

1992-01-01

9

Design of a uniform bias magnetic field for giant magnetostrictive actuators applying triple-ring magnets  

NASA Astrophysics Data System (ADS)

Uniform bias magnetic field is very important for giant magnetostrictive actuators (GMA) to fully utilize the performance of giant magnetostrictive materials (GMM). However, it is difficult to keep it uniform when the length to diameter ratio (?) of the GMM is larger than 3.5, though the shapes of the applied GMM are different with ? usually larger than 3.5. In this paper, a design method with triple-ring permanent magnets is established to provide an even bias magnetic field for GMM with varying ?. Firstly, the magnetic circuit model is set up. According to the analysis of the field distribution along the GMM rod, the main factor causing unevenness of the bias magnetic field is confirmed to be the inner leakage flux. A design of triple-ring topology for the magnets is developed to control the inner leakage flux to reduce the unevenness. Then, finite element analysis is adopted to optimize a design which can ensure an unevenness of the bias magnetic field of less than 3% while the ? of a GMM rod is up to 20. Finally, an actual GMA is fabricated with the GMM dimension of ?10 mm × 50 mm (? = 5), and the testing results show that the unevenness of the bias field along the GMM is 1.38%. The bias magnetic system design is practicable, simple and efficient for offering an even bias magnetic field when ? lies in a wide range.

Zhang, Heng; Zhang, Tianli; Jiang, Chengbao

2013-11-01

10

Transient response of single-domain Y-Ba-Cu-O rings to pulsed magnetic fields  

Microsoft Academic Search

Shielding current limits and magnetic diffusion characteristics have been measured at 77 K for a set of YBCO single-domain rings. These were fabricated from melt-textured cylindrical YBCO monoliths that were densified to nearly 100%, and then oriented from a single seed. The rings were surrounded by a drive coil that can, under pulse conditions, achieve applied magnetic fields in excess

T. R. Askew; J. M. Weber; Y. S. Cha; H. Claus; B. W. Veal

2003-01-01

11

Effects of fluctuating magnetic fields on a superconducting bulk rotor shielded with superconducting rings  

NASA Astrophysics Data System (ADS)

We study the effect of a fluctuating magnetic field, which is one of the technical problems for trapped magnetic fields in a bulk superconductor, to realize a practical bulk superconductor rotating machine. Previous research and other's research has shown that fluctuating magnetic fields reduce the strength of trapped magnetic fields in superconducting bulk modules [1, 2]. This deters development of applications of AC rotating machines because superconducting bulk modules are always exposed to a fluctuating magnetic field. Therefore, it is necessary to develop a method to control decrease of the trapped magnetic field. We propose a method to use the shielding ring of a superconducting wire to achieve this goal and the effects are confirmed experimentally [3]. We are now building test equipment for examining the performance of a shielding ring in a bulk rotating machine. This paper reports the test result for the shielding ring applied to the bulk superconducting rotor that is a part of the test equipment.

Yamagishi, K.; Ogawa, J.; Tsukamoto, O.

2014-05-01

12

Planetary rings as relics of plasma proto-rings rotating in the magnetic field of a central body  

NASA Astrophysics Data System (ADS)

A possibility is discussed in accordance to hypothesis by H. Alfven, that the rings of large planets are relics of some plasma proto-rings rotating in the magnetic fields of central bodies. A finite-dimensional mathematical model of the system is synthesized using the solution of the boundary-value problem by the Boubnov - Galerkin method. The dipole magnetic field of the central body is assumed to have a small eccentricity, and the dipole axis - to be inclined at a small angle to the central body's axis of rotation which coincides with the ring's rotation axis. The proto-ring is supposed to be thin and narrow and having the same rotating axis as the central body. A medium forming the ring is cold rarefied plasma with high electron density, so that electric conductivity of the medium tends to infinity, as well as the magnetic Reynolds number. The original mathematical model is reduced to a system of finite-difference equations whose asymptotic analytical solution is obtained. Emphasis is placed on the problems of stability of the ring's steady state rotation and quantization of the eigenvalues of nondimensional sector velocity of the ring with respect to the central body. The solutions corresponding to magneto-gravitational and to magneto-gyroscopic waves are considered It is demonstrated that some rings characterized by integral quantum numbers are stable and long-living, while the rings which are associated with half-integer quantum numbers (rings>) are unstable and short-living. As a result, an evolutionally rife rotating plasma ring turns out to be stratified into a large number of narrow elite rings separated by gaps whose position correspond to anti-rings. The regions of possible existence of elite rings in near-central body space are determined. The main result of eigenvalue spectrum's analysis is as follows. Quantum numbers determining elite eigenvalues of the sector velocity of a ring (normalized in a certain manner) coincide with the quantum numbers appearing in the solution of the Schr¨odingerequation for a hydrogen atom. Perturbations of the elite orbits corresponding to this numbers satisfy the de Brogli quantum-mechanical condition. The solution of the model boundary-value problem has been applied to planetary rings origin and evolution. The main result is a mechanism of stratification of the evolutionally mature plasma proto-ring into a large number of narrow elite rings separated by anti-rings (gaps), which were playing a role of for present-day planetary rings. Another result is the theoretical substantiation of the presence in the nearplanetary space of a region of existence and stability of plasma rings. The data, which had been obtained in the course of the Voyager, Galileo, and Cassini missions were used for verification of theoretical results concerning the planetary rings and Io plasma thorus. The theoretical dates turned out to be in accordance with experimental dates. References Alfven H. Cosmic Plasma. Dordrecht: Reidel, 1961. Rabinovich B.I. Dynamics of Plasma Ring Rotating in the Magnetic Field of Central Body: Magneto-GravitationalWaves // Cosmic Research, 2006. V. 44. No. 1. P. 43-51. Rabinovich B.I. Dynamics of Plasma Ring Rotating in the Magnetic Field of Central Body: Magneto-Gyroscopic Waves. Problems of Stability and Quantization // Cosmic Research, 2006. V. 44. No. 2. P. 146 - 161. Gore, Rick. Voyager 1 at Saturn. Riddles of the Rings // National Geographic, 1981. V. 160. No. 1. P. 3 - 31. Porco, Carolyn. Captain 's Log.: 2004, 184 // The Planetary Report, 2004. V. 24, No. 5. P. 2 - 18.

Rabinovich, B.

2007-08-01

13

Application of ring method to measure surface tensions of liquids in high magnetic field.  

PubMed

The high-magnetic-field tensiometer (HMFT) has been developed to measure surface tensions of liquids in high magnetic field based on the ring method. The HMFT was composed of three parts: weighing system, liquid circulatory system, and supporting system. Some improvements for the conventional tensiometer were made in order to overcome the magnetic effects. The surface tension of acetone was measured using the HMFT. The results showed that the surface tension of acetone linearly varied with the magnetic field intensity and increased by 0.69 mN m(-1) or 2.9% in the magnetic field of 10 T. The HMFT could better determine the surface tension of liquids with and without the magnetic field and it provided a simple and practical way to measure the surface tension of liquids at room temperature in a high magnetic field. PMID:22559548

Li, Chuanjun; Chen, Long; Ren, Zhongming

2012-04-01

14

Control of a two-electron quantum ring with an external magnetic field  

Microsoft Academic Search

We investigate the use of external time-dependent magnetic field for the control of the quantum states in a two-electron quantum ring. The hyperfine interaction of the confined electrons with surrounding nuclei couples the singlet state with the three triplet states. When the external magnetic field is changed, the singlet ground state becomes degenerate with the triplet states allowing singlet–triplet transitions.

Jani Särkkä; Ari Harju

2010-01-01

15

Magnetic field distribution of injection chicane dipoles in Spallation Neutron Source accumulator ring  

NASA Astrophysics Data System (ADS)

We have performed 3D computing simulations to study the magnetic field distribution of the injection chicane dipoles in the SNS accumulator ring. The simulations yield the performance characteristics of the magnets and generate the magnetic field data in three dimensional grids for further beam tracking study. Based on the simulation data, a 3D multipole expansion of the chicane dipole field, consisting of the generalized gradients and their derivatives, has been made. The harmonic and pseudoharmonic components in the expansion give much insight into the magnet physics and can fit directly into theoretical frame work of beam optics. The expansion is quasianalytical by fitting numeric data into interpolation functions. A 5th-order representation of the magnetic field is generated, and the effects of even higher-order terms on the field representation are discussed.

Wang, J. G.

2006-01-01

16

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

SciTech Connect

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

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

1991-07-01

17

Saturn-ring defects around microspheres suspended in nematic liquid crystals: an analogy between confined geometries and magnetic fields.  

PubMed

Particles suspended in a nematic liquid crystal exhibit characteristic dipolar and Saturn-ring configurations. Using results on the magnetic-field behavior of these configurations, we explain the recent observation of the Saturn-ring defect in confined geometries based on the idea that a confining geometry and a magnetic field generate a similar "confinement" for the nematic phase. PMID:12366166

Stark, Holger

2002-09-01

18

Split-ring resonators interacting with a magnetic field at visible frequencies  

NASA Astrophysics Data System (ADS)

Split-ring resonators (SRRs) are attractive owing to the interaction with a magnetic field of incident light. Here, we report the fabrication of uniform arrays of about 360 million Au SRRs with a line width of approximately 50 nm by reactive-monolayer-assisted thermal nanoimprint lithography over a 5-mm square area. Furthermore, we present an experimental demonstration of the oscillation of free electrons excited by a magnetic field at 690 nm in the visible frequency region. The fabrication and optical investigation of SRR arrays over such large areas will facilitate opportunities to realize advanced optical devices.

Tomioka, T.; Kubo, S.; Nakagawa, M.; Hoga, M.; Tanaka, T.

2013-08-01

19

Contactless Magnetic Slip Ring  

NASA Technical Reports Server (NTRS)

A contactless magnetic slip ring is disclosed having a primary coil and a secondary coil. The primary and secondary coils are preferably magnetically coupled together, in a highly reliable efficient manner, by a magnetic layered core. One of the secondary and primary coils is rotatable and the contactless magnetic slip ring provides a substantially constant output.

Kumagai, Hiroyuki (Inventor); Deardon, Joe D. (Inventor)

1997-01-01

20

Magnetic-field-modulated terahertz absorption spectra of a quantum ring  

NASA Astrophysics Data System (ADS)

The magnetic-field-modulated terahertz absorption spectra of a real GaAs quantum ring (QR) are studied by calculating the photon-participated tunneling current through the QR. We find that the absorption of photons can lead to a reduction in the tunneling current and this manifests as dips in the current versus magnetic field curves. There exists a saturation value for the depth of the current dip, which is described by a simple formula. A full width at half maximum less than 10 GHz can be reached for current dips induced by terahertz fields for Rabi frequencies smaller than 2.5 GHz. Our study provides a possible way to realize tunable detection of terahertz fields.

Xie, Yan; Chu, Weidong; Duan, Suqing

2008-07-01

21

Effects of electronic correlations and magnetic field on a molecular ring out of equilibrium  

NASA Astrophysics Data System (ADS)

We study the effects of electron-electron interactions on the steady-state characteristics of a hexagonal molecular ring in a magnetic field as a model for a benzene molecular junction. The system is driven out of equilibrium by applying a bias voltage across two metallic leads. We employ a model Hamiltonian approach to evaluate the effects of on-site as well as nearest-neighbor density-density-type interactions in a physically relevant parameter regime. Results for the steady-state current, charge density, and magnetization in three different junction setups (para, meta, and ortho) are presented. Our findings indicate that interactions beyond the mean-field level renormalize voltage thresholds as well as current plateaus. Electron-electron interactions lead to substantial charge redistribution as compared to the mean-field results. We identify a strong response of the circular current on the electronic structure of the metallic leads. Our results are obtained by steady-state cluster perturbation theory, a systematically improvable approximation to study interacting molecular junctions out of equilibrium, even in magnetic fields. Within this framework, general expressions for the current, charge density, and magnetization in the steady state are derived. The method is flexible and fast and can straightforwardly be applied to effective models as obtained from ab initio calculations.

Nuss, Martin; von der Linden, Wolfgang; Arrigoni, Enrico

2014-04-01

22

Electron exchange between quantum dot and ring by jumping in magnetic field  

NASA Astrophysics Data System (ADS)

Semiconductor heterostructures as quantum dots (QD) or quantum rings (QR) demonstrate discreet atom-like energy level configuration. In the presented work we show that in the weak coupled Double Concentric Quantum Ring (DCQR) electron position jumping can exist due to the energy level crossing. We study DCQR composed of GaAs in an Al0.70Ga0.30As substrate under influence of magnetic field. In our model the DCQR is considered in three dimensional space within single sub-band effective mass approach [1]. Magnetic field is applied in z direction, perpendicular to the DCQR plane. The electron position in DCQR is defined by effective radius which is radius of most probable localization of a single electron. We study electron structure of QD located at the center of QR. The electron position jumping between QD and QR is considered. Discussed will be possibility of experimental implementations of the jumping effect for composite object of QD and QR. [4pt] [1] I. Filikhin, V. M. Suslov and B. Vlahovic, Phys. Rev. B 73, 205332 (2006).

Filikhin, Igor; Matinyan, Sergei; Nimmo, James; Vlahovic, Branislav

2011-03-01

23

Chiral phase transition in relativistic heavy-ion collisions with weak magnetic fields: Ring diagrams in the linear sigma model  

SciTech Connect

Working in the linear sigma model with quarks, we compute the finite-temperature effective potential in the presence of a weak magnetic field, including the contribution of the pion ring diagrams and considering the sigma as a classical field. In the approximation where the pion self-energy is computed perturbatively, we show that there is a region of the parameter space where the effect of the ring diagrams is to preclude the phase transition from happening. Inclusion of the magnetic field has small effects that however become more important as the system evolves to the lowest temperatures allowed in the analysis.

Ayala, Alejandro [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-543, Mexico Distrito Federal 04510 (Mexico); Instituto de Fisica y Matematicas, Universidad Michoacana de San Nicolas de Hidalgo, Apartado Postal 2-82, Morelia, Michoacan 58040 (Mexico); Centro Brasileiro de Pesquisas Fisicas, CBPF-DCP, Rua Dr. Xavier Sigaud 150, 22290-180, Rio de Janeiro (Brazil); Bashir, Adnan; Raya, Alfredo; Sanchez, Angel [Instituto de Fisica y Matematicas, Universidad Michoacana de San Nicolas de Hidalgo, Apartado Postal 2-82, Morelia, Michoacan 58040 (Mexico)

2009-08-01

24

A global analytical representation of the magnetic field produced by the region 2 Birkeland currents and the partial ring current  

NASA Technical Reports Server (NTRS)

A quantitative model is developed of the magnetic field produced by the electric current system of region 2 Birkeland currents, closed via the partial ring current. The distribution of j-perpendicular is computed from a given axially asymmetric spatial distribution of hot isotropic magnetospheric plasma over an infinitely thin L shell in an axisymmetric purely dipolar geomagnetic field, while the field-aligned current density is found from the continuity of the net electric current. The magnetic field distribution is derived by a Biot-Savart integral over the electric current system. An assumed cosine dependence of the plasma pressure on local time makes it possible to reduce the problem of analytical representation of the B field to two dimensions. The obtained numerical fits for the partial ring current/region 2 Birkeland current magnetic field are relatively simple, continuous, and valid throughout the whole extraterrestrial space from ionospheric heights up to tens of earth radii.

Tsyganenko, N. A.

1993-01-01

25

Low-noise flux-gate magnetic-field sensors using ring- and rod-core geometries  

Microsoft Academic Search

We have fabricated ring-core and single-domain rod-core flux-gate magnetic field sensors with 1\\/f noise levels at 1 Hz of 1.4 pT\\/Hz and 3.5 pT\\/Hz, respectively. These noise sensitivities were achieved by applying an electrical current through the core of the flux gate to magnetically bias the magnetic rotation of the core perpendicular to the easy-axis direction. We also found that

R. H. Koch; J. R. Rozen

2001-01-01

26

Influence of the interplanetary magnetic field on the ring current injection rate  

NASA Astrophysics Data System (ADS)

In order to check the validity of Akasofu's ? parameter and of the Vasyliunas et al. (1982) general formula, we examine the dependence of the ring current injection rate, calculated from the Dst index for the period of 1965-1990, on the interplanetary magnetic field (IMF). We compare the influence of the Bz component with the influence of the combination of sin ?/2, where ? is the IMF clock angle, and the IMF magnitude, B, (or the transverse component of the IMF, BT = (By2 + Bz2)1/2) by using the regression analysis in a power law form. The main results are as follows: (1) the exponent for Bz shows higher consistency than that for sin(?/2); (2) we never obtain B2 sin4(?/2) or B2T sin4(?/2), which is the IMF dependence expected from the ? parameter; and (3) the ring current injection rate has a very low correlation with the Alfven Mach number, from which the IMF dependence of the Vasyliunas et al. general formula is assumed to arise. On the basis of the above results we conclude that the ? parameter and the Vasyliunas et al. general formula are less appropriate than a function of Bz, and that the energy coupling function between the solar wind and the Earth's magnetosphere is described better by Bz than by the combination of B (or BT) and sin (?/2). The above results and conclusions are the same as those obtained by Aoki (2005) through the analysis of the AL index.

Aoki, T.

2006-05-01

27

Modeling of Ring Current Energy Content and Magnetic Field During Storms: How Much Do the Results Depend on Model Choice?  

NASA Astrophysics Data System (ADS)

We use the Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM) to trace particles from the plasma sheet to the inner magnetosphere regions and to study the ring current formation during storm times. The IMPTAM model follows drift of ions and electrons with arbitrary pitch angles in time-dependent magnetic and electric fields, assuming that 1st and 2nd adiabatic invariants are conserved. For two storms, one moderate on November 6-7, 1997 and one intense on October 21-23, 1999, we analyze the evolution of model ring current energy content and magnetic field depression produced by the modeled ring current at the Earth. We trace particles in several combinations of electric and magnetic field models such as dipole, Tsyganenko T89, Tsyganenko T96, Tsyganenko and Sitnov TS04 models for magnetic field and Volland-Stern, Boyle et al., and Weimer models for electric field. We also apply 4 different types of boundary distribution in the plasma sheet at different locations. We make model-to-model and model-to-Dst-observed comparisons. The questions to be answered are How much do the results of the storm-time ring current modeling depend on the choice of models and How accurate are the conclusions made from the modeling output?

Ganushkina, N. Y.; Liemohn, M. W.

2009-12-01

28

Ion Rings for Magnetic Fusion  

SciTech Connect

This Final Technical Report presents the results of the program, Ion Rings for Magnetic Fusion, which was carried out under Department of Energy funding during the period August, 1993 to January, 2005. The central objective of the program was to study the properties of field-reversed configurations formed by ion rings. In order to reach this objective, our experimental program, called the Field-reversed Ion Ring Experiment, FIREX, undertook to develop an efficient, economical technology for the production of field-reversed ion rings. A field-reversed configuration (FRC) in which the azimuthal (field-reversing) current is carried by ions with gyro-radius comparable to the magnetic separatrix radius is called a field-reversed ion ring. A background plasma is required for charge neutralization of the ring, and this plasma will be confined within the ring's closed magnetic flux. Ion rings have long been of interest as the basis of compact magnetic fusion reactors, as the basis for a high-power accelerator for an inertial fusion driver, and for other applications of high power ion beams or plasmas of high energy density. Specifically, the FIREX program was intended to address the longstanding question of the contribution of large-orbit ions to the observed stability of experimental FRCs to the MHD tilt mode. Typical experimental FRCs with s {approx} 2-4, where s is the ratio of separatrix radius to ion gyro-radius, have been stable to tilting, but desired values for a fusion reactor, s > 20, should be unstable. The FIREX ring would consist of a plasma with large s for the background ions, but with s {approx} 1 for the ring ions. By varying the proportions of these two populations, the minimum proportion of large-orbit ions necessary for stability could be determined. The incorporation of large-orbit ions, perhaps by neutral-beam injection, into an FRC has been advanced for the purpose of stabilizing, heating, controlling angular momentum, and aiding the formation of a reactor-scale FRC, and the FIREX program was intended to test the ideas behind this approach. We will describe in this report the technological development path and advances in physics understanding that allowed FIREX to reach a regime in which ion rings were reproducibly created with up to about half the current necessary to produce field reversal. Unfortunately, the experiments were limited to this level by a fundamental, unanticipated aspect of the physics of strong ion rings in plasma. The FIREX ring is a strongly anisotropic, current-carrying population of ions moving faster than the Alfven speed in the background plasma. The rapidly changing ring current excites very large-amplitude Alfven waves in the plasma, and these waves strongly affect the ring, causing rapid energy loss in a way that is not compatible with the success of the ring trapping scenario around which FIREX was designed. The result was that FIREX rings were always very short-lived. We will discuss the implication of these results for possible future use of large-orbit ions in FRCs. In short, it appears that a certain range of the parameters characterizing the ring Alfven mach number and distribution function must be avoided to allow the existence of a long-lived energetic ion component in an FRC. This report will explain why FIREX experimental results cannot be directly scaled to quantitatively predict this range for a particular FRC configuration. This will require accurate, three-dimensional simulations. FIREX results do constitute a very good dataset for validating such a code, and simulations already carried out during this program provide a guide to the important physics involved.

Greenly, John, B.

2005-07-31

29

Quantum mechanics on a Möbius ring: Energy levels, symmetry, optical transitions, and level splitting in a magnetic field  

NASA Astrophysics Data System (ADS)

We investigate the quantum mechanical energy levels of an electron constrained to motion on a nanoscale Möbius ring by solving the Schrödinger equation on the curved surface. The dimensions of the ring in terms of the lateral and transverse parameters {u,v} for the Möbius ring allow us to identify the quantum numbers for the levels by (nu,nv). We show that the energy levels can still be labeled using the quantum numbers of the cylindrical ring of the same dimensions. While the Hamiltonian has invariance under parity in parameter space, the rotational symmetry about any axis in configuration space is lost, so that the double degeneracy of energy levels for azimuthal quantum number nu?1, that exists in cylindrical rings, is lifted by a small amount in the Möbius ring. The pattern of level splitting has been identified in terms of the number of twists ? to be 2nu=s? where s is an integer. The scaling properties of the energy levels with respect to the dimensions of the ring are derived; using these properties, our numerical results which are given for a specific geometry can be extended to rings of other commensurate dimensions. The absence of rotational invariance for the Möbius ring manifests itself through the orbital angular momentum Lz not commuting with the Hamiltonian. Its expectation values are found to have nearly integral as well as half-integral values of ?, and its variances are small. The energy levels with half-integral azimuthal quantum numbers (nu) are also close to the approximate formula for the equivalent cylindrical ring, provided such half-integral quantum numbers are allowed for the cylindrical geometry. The Zeeman splitting of the energy levels in an external magnetic field is displayed, together with wave functions at a level anticrossing. The optical transitions between electronic states on the Möbius ring are obtained, and a table of oscillator strengths is provided. The results for energy levels for rings with multiple twists are presented. In view of recent technological advances in the production of graphene sheets, we may anticipate the making of such twisted rings with graphene strips of finite width. Graphene strips of finite width have an open band gap at the K points in the Brillouin zone, so that a nonrelativistic treatment with a small effective mass is appropriate. For Möbius rings of graphene, our results would be directly relevant, and we may anticipate their experimental verification in the near future.

Li, Zehao; Ram-Mohan, L. R.

2012-05-01

30

Quantum ring conductance sensitivity to potential perturbation in an external magnetic field  

NASA Astrophysics Data System (ADS)

We study the sensitivity of quantum ring (QR) conductance to potential perturbation introduced by an external charged probe in the context of scanning gate microscopy experiments and analyze its correspondence to the local density of states at the Fermi level for up to four subbands participating in the transport. We find that the conductance of the QR can be weakly sensitive or almost insensitive to the perturbation potential due to magnetic deflection of the wave function. The conductance becomes very sensitive to external perturbations at localized resonances for which the local density of states can be extracted by conductance mapping.

Chwiej, T.; Szafran, B.

2014-05-01

31

Magnetization switching in Permalloy square ring magnets  

NASA Astrophysics Data System (ADS)

We present the results of a study of magnetization switching in Permalloy square rings using the diffraction magneto-optic Kerr effect combined with numerical micromagnetic simulations. Diffracted loops show a two-step switching process as the external field is swept along both the ring edge and the diagonal. The hysteresis loops calculated from micromagnetic simulations show that switching should occur via a single step transition from a one onion to the reversed onion state for both directions of field applied. We have found that in order to reproduce the observed two-step reversal slight asymmetry has to be introduced into the ring shape. In this case a stable intermediate states appear during switching, accounting for the shape of diffracted loops.

Vavassori, P.; Grimsditch, M.; Novosad, V.; Metlushko, V.; Ilic, B.

2003-05-01

32

Low-noise flux-gate magnetic-field sensors using ring- and rod-core geometries  

NASA Astrophysics Data System (ADS)

We have fabricated ring-core and single-domain rod-core flux-gate magnetic field sensors with 1/f noise levels at 1 Hz of 1.4 pT/Hz and 3.5 pT/Hz, respectively. These noise sensitivities were achieved by applying an electrical current through the core of the flux gate to magnetically bias the magnetic rotation of the core perpendicular to the easy-axis direction. We also found that in the rod-core sensor, the spatial correlation lengths of the magnetic fluctuations were 25 and 40 mm with and without the biasing current. The cross-power spectrum magnitude at 1 Hz was less than 200 fT/Hz.

Koch, R. H.; Rozen, J. R.

2001-03-01

33

Electromagnetic field analysis of septum magnet for APS positron accumulator ring  

SciTech Connect

This report consists of three parts. The first part describes a numerical analysis method for the electromagnetic field analysis of a septum magnet. A novel improvement to the treatment of exciting currents in the time-domain is proposed. The second part discusses numerical predictions of the electromagnetic characteristics of the APS PAR septum. The time variations of stray field and eddy currents are shown for three magnet designs. The last part explores how decreasing the septum material conductivity affects the stray field. The decrease of conductivity may be caused by an inadequate manufacturing of the septum material. The significance of a high quality septum, or flat interface between copper and iron, is emphasized from a point of view of stray field. An ideal method for joining two different metals without distortion, called HIP (Hot Isostatic Pressing), is introduced and recommended based on the authors` experience.

Yokoi, Toshiaki; Turner, L.R.

1995-07-01

34

The effect of an axial magnetic field on the characteristics of concurrent resonances in He-Ne\\/CH4 ring lasers  

Microsoft Academic Search

Experimental data are presented on the effect of an axial magnetic field on the concurrence of counterpropagating waves and characteristics of concurrent resonances in He-Ne\\/CH4 ring lasers. It is shown that the application of a magnetic field to the active medium prevents the shift of a resonance maximum relative to the absorption line center, which improves the frequency repeatability of

V. S. Voitsekhovich; V. M. Grinenko; M. V. Danileiko; A. M. Fal; L. P. Iatsenko

1987-01-01

35

Saturn's periodic magnetic field perturbations caused by a rotating partial ring current  

NASA Astrophysics Data System (ADS)

We demonstrate that the periodic magnetic field perturbations as observed from Cassini are caused by the plasma pressure of the energetic (>2 keV) particle distributions that are periodically injected and subsequently drift around Saturn. Plasma pressures inferred from the Cassini Plasma Spectrometer (CAPS) (<2 keV) and the Magnetospheric Imaging Instrument (MIMI) (>2 keV) are used to compute the three-dimensional pressure-driven currents and their associated magnetic field perturbations. The distribution of the “hot” (>2 keV) plasma pressure is derived from Energetic Neutral Atom (ENA) images obtained by the Ion Neutral Camera (INCA) and in-situ spectral measurements. The radial profile of “cold” (<2 keV) plasma pressure is obtained from statistical studies and is assumed to be azimuthally symmetric.

Brandt, P. C.; Khurana, K. K.; Mitchell, D. G.; Sergis, N.; Dialynas, K.; Carbary, J. F.; Roelof, E. C.; Paranicas, C. P.; Krimigis, S. M.; Mauk, B. H.

2010-11-01

36

CONTROL OF LASER RADIATION PARAMETERS: Influence of a constant magnetic field on non-stationary operation regimes of solid-state ring lasers  

NASA Astrophysics Data System (ADS)

The effect of a constant magnetic field on the nonlinear radiation dynamics of a monolithic chip ring Nd:YAG laser pumped by modulated radiation is studied experimentally. It is found that the application of a constant magnetic field to the active element of the solid-state ring laser operating in the non-stationary regime results in the displacement of the regions of existence of quasi-periodic and chaotic lasing regimes to the low-frequency region of pump power modulation. In addition, the application of a magnetic field to the active element of the laser gives rise to the spectral nonreciprocity.

Kravtsov, Nikolai V.; Chekina, S. N.

2007-02-01

37

Initial and Boundary Conditions for Ion Flux and Magnetic Fields in Ring Current Simulations: Comparison With Satellite Observations  

NASA Astrophysics Data System (ADS)

The initial and boundary conditions used in a ring current simulation can profoundly affect the results. We compare the conditions in simulations of the quiet time and several geomagnetic storm events to measurements by several satellite missions. This will be used to improve future models. The initial conditions typically include the particle flux, the electric field, and the magnetic field at all locations within the simulation volume. The calculation then updates the values of these parameters as a function of time to model a geomagnetic storm or other event. As the event simulation progresses, the boundary conditions also generally vary due to external stimuli. Common boundary conditions include the particle flux, composition, and fields at the external edges of the simulation volume. Depending on the particular ring current simulation, some or all of these conditions may be computed by empirical models, or derived from observations of the event of interest. In some models, rather arbitrary starting conditions are applied, and then the simulation is run for an extended time in order to approach a steady state that is used as the real initial condition. The focus of the comparisons is on the outward radial edge of the models, typically beyond geosynchronous orbit. Some of the particles in this region drift inward under convection and radial diffusion to form the peak of the ring current population. The compared quantities include the ion and electron number flux spectra, pitch angle distributions, and the vector magnetic field. All these vary substantially with position in the magnetosphere, so the comparison is performed in bins in L and magnetic local time. Of particular interest is the mass and charge state composition of the ion boundary condition. Many models of storms use the Young et al. [1982] empirical model of ion composition if detailed measurements during the event are unavailable. This provides the ratio of oxygen to hydrogen density as a function of the Kp and F10.7 indices. We examine the validity of the Young model with the measurements from recent space missions. For example, the particle fluxes and magnetic fields from the self-consistent RCM-E model are compared with empirical models and individual orbits from the CRRES, Polar and SCATHA missions. These satellites made comprehensive measurements of the plasma populations, including ion composition and fields in both solar maximum and solar minimum conditions.

Roeder, J. L.; Lemon, C.; Chen, M. W.; Fennell, J. F.; Guild, T. B.; Zaharia, S. G.

2012-12-01

38

Initial polar magnetic field experiment observations of the low-altitude polar magnetosphere: Monitoring the ring current with polar orbiting spacecraft  

NASA Astrophysics Data System (ADS)

The equatorial ring current and the magnetopause current both contribute to the magnetic field at low altitudes over the polar cap. In this region the magnetic field is dominated by the Earth's internal field and is well described by empirical models. The average change in the magnetic field strength due to external sources (the residual of the observed magnetic field strength upon subtracting the International Geomagnetic Reference Field (IGRF) 95 internal field model) is typically a few tens of nanoTesla, or a few tenths of 1% of the total magnetic field over the polar cap at the altitude of the Polar spacecraft. It is easier to measure such small differences in the total field than in the vector components because the accuracy of the residuals in the vector magnetic field depends on the accuracy of the knowledge of spacecraft pointing which is generally less well known than the position of the spacecraft. In order to isolate the ring current effects on the total field we adjust the Dst index for the contributions of the magnetopause current using the solar wind dynamic pressure, and we adjust the observed field values for the same effect using the Tsyganenko [1996] model. After these adjustments the ring current strength as measured by the adjusted Dst index is well correlated with the residual of the field strength observed in the low-altitude polar region over a wide range of local times except when the spacecraft track is near the noon-midnight meridian. These comparisons, using more than a full year of Polar data, demonstrate that the Tsyganenko [1996] model together with the IGRF 1995 internal field model provides a good baseline for the magnetic field at the altitude of the Polar perigee passes (~5000 km above the Earth's surface). Further they demonstrate that total field measurements from low-altitude polar orbiting spacecraft are potentially useful as monitors of the ring current when they cross the polar cap.

Le, G.; Russell, C. T.

1998-08-01

39

Magnet system for the KEKB main ring  

NASA Astrophysics Data System (ADS)

KEKB is a two-ring electron-positron collider with asymmetric energies of 8 and 3.5 GeV to study CP violation in B meson decay. In KEKB, there are 21 types of magnets; about 1600 in total. About 430 dipole and quadrupole magnets were recycled from TRISTAN, the preceding program. All quadrupole magnets are equipped with vertical and horizontal steering dipole magnets. The number of steering magnets is about 1700. There are 212 sextupole magnets, and all of them are fixed on remotely controlled movers to adjust their positions to the beam passage. All main dipole magnets have back-leg coils to steer beams precisely. All quadrupole and sextupole magnets are equipped with correction coils to have a capability for beam-based alignment. Also one-turn coils are installed as well to each magnetic pole of the main magnets to monitor the magnetic flux in the case of trouble. The magnetic field in all magnets was measured and its quality strictly checked. After field measurement, the magnets were installed and precisely aligned. A cooling water system and a power supply system for these magnets were constructed. Magnet design was started in 1994, and construction of the two rings was completed in November 1998. The parameters of the magnets and the construction of the KEKB magnet system are described. Some of the problems experienced during this construction work are also presented.

Egawa, Kazumi; Endo, Kuninori; Fukuma, Hitoshi; Kubo, Tadashi; Masuzawa, Mika; Ohsawa, Yasunobu; Ohuchi, Norihito; Ozaki, Toshiyuki; Tsuchiya, Kiyosumi; Yoshida, Masato; Sugahara, Ryuhei

2003-02-01

40

Magnetic Fields  

NSDL National Science Digital Library

Students visualize the magnetic field of a strong permanent magnet using a compass. The lesson begins with an analogy to the effect of the earth's magnetic field on a compass. Students see the connection that the compass simply responds to the earth's magnetic field since it is the closest, strongest field, and therefore the compass will respond to the field of the permanent magnets, allowing them the ability to map the field of that magnet in the activity. This information will be important in designing a solution to the grand challenge in activity 4 of the unit.

Vu Bioengineering Ret Program

41

Magnetic Fields  

NSDL National Science Digital Library

This page and its annex describes, in trivial terms, the physics of magnetic fields and the history of its discovery. Included is the work of Halley, Oersted, Ampere and Maxwell. It also describes a way of demonstrating it in the classroom, using a vu-graph projector. Later sections #5, #5a and #6 extend this to magnetic field lines and electromagnetism.

Stern, David

2005-01-04

42

Dynamics of Partial and Symmetrical Ring Current during Magnetic Storm  

Microsoft Academic Search

Storm-time ring current development is the result of plasma injection from magnetospheric tail. Magnetospheric magnetic field variations produced by ring current its symmetrical and asymmetrical parts were analyzed during magnetic storm on 6-14 November 2004 with peak Dst= -373nT. Partial ring current was represented by a set of current circuits consisting from equatorial westward current, field-aligned currents and eastward closure

Vladimir Kalegaev; Ksenia Bakhmina; Fatima Keshtova; Igor Alexeev

2008-01-01

43

CONTROL OF LASER RADIATION PARAMETERS: Spectral nonreciprocity induced by a magnetic field in nonstationary lasing regimes of a solid-state ring laser  

NASA Astrophysics Data System (ADS)

It is found experimentally that the application of a magnetic field to the active element of a monolithic ring Nd:YAG chip laser in nonstationary lasing regimes can result in nonidentical spectral parameters of counterpropagating radiation waves (spectral nonreciprocity) in quasi-periodic and chaotic lasing regimes. The value of the spectral nonreciprocity depends on the coupling coefficient of counterpropagating waves, the excess over the pump threshold, and the optical nonreciprocity of the ring cavity. The obtained results are in good agreement with the results of numerical simulation.

Kravtsov, Nikolai V.; Lariontsev, E. G.; Pashinin, Pavel P.; Sidorov, S. S.; Chekina, S. N.

2004-04-01

44

The remote sensing of Saturn's rings. 1: The magnetic alinement of the ring particles  

NASA Technical Reports Server (NTRS)

Because of the potential implications for the optical properties of Saturn's rings, the orientation of nonspherical ring particles at equilibrium is investigated with respect to four stochastic influences: interactions with the interplanetary medium, interactions with the expected magnetic field of Saturn, thermal fluctuations due to the internal temperature of the ring particles; collisions between ring particles. The solution of the homogeneous Fokker-Planck equation for nearly spherical spheroids is presented and investigated in general. Values of the pertinent physical parameters in the vicinity of Saturn are estimated, and the implications for the alignment of the ring particles are investigated. It is concluded that for some alignment mechanisms, small ring particles can be expected to be almost completely aligned. This alignment results in each particle spinning around its shortest body axis with this axis parallel to the magnetic field direction (perpendicular to the ring plane).

Evans, L. C.

1973-01-01

45

Magnetic fields at Neptune  

SciTech Connect

The National Aeronautics and Space Administration Goddard Space Flight Center-University of Delaware Bartol Research Institute magnetic field experiment on the Voyager 2 spacecraft discovered a strong and complex intrinsic magnetic field of Neptune and an associated magnetosphere and magnetic tail. A maximum magnetic field of nearly 10,000 nanoteslas (1 nanotesla = 10{sup {minus}5} gauss) was observed near closest approach, at a distance of 1.18 R{sub N}. The planetary magnetic field between 4 and 15 R{sub N} can be well represented by an offset tilted magnetic dipole (OTD), displaced from the center of Neptune by the surprisingly large amount of 0.55 R{sub N} and inclined by 47{degrees} with respect to the rotation axis. Within 4 R{sub N}, the magnetic field representation must include localized sources or higher order magnetic multipoles, or both, which are not yet well determined. As the spacecraft exited the magnetosphere, the magnetic tail appeared to be monopolar, and no crossings of an imbedded magnetic field reversal or plasma neutral sheet were observed. The auroral zones are most likely located far from the rotation poles and may have a complicated geometry. The rings and all the known moons of Neptune are imbedded deep inside the magnetosphere, except for Nereid, which is outside when sunward of the planet. The radiation belts will have a complex structure owing to the absorption of energetic particles by the moons and rings of Neptune and losses associated with the significant changes in the diurnally varying magnetosphere configuration. In an astrophysical context, the magnetic field of Neptune, like that of Uranus, may be described as that of an oblique rotator.

Ness, N.F. (Univ. of Delaware, Newark (USA)); Acuna, M.H.; Burlaga, L.F.; Connerney, J.E.P.; Lepping, R.P. (NASA, Greenbelt, MD (USA)); Neubauer, F.M. (Universitaet zu Koln (West Germany))

1989-12-15

46

Correction magnets for the Fermilab Recycler Ring  

SciTech Connect

In the commissioning of the Fermilab Recycler ring the need for higher order corrector magnets in the regions near beam transfers was discovered. Three types of permanent magnet skew quadrupoles, and two types of permanent magnet sextupoles were designed and built. This paper describes the need for these magnets, the design, assembly, and magnetic measurements.

James T Volk et al.

2003-05-27

47

Persistent current in a magnetized Rashba ring  

Microsoft Academic Search

We theoretically study the persistent currents flowing in a Rashba quantum ring subjected to the Rashba spin—orbit interaction. By introducing uniform or nonuniform magnetization into the ring, we find that a nonzero persistent charge current circulates in the ring, which stems from the original equilibrium spin current due to the Rashba spin—orbit interaction. Because of broken time reversal symmetry, the

Zhang Lin; Wang Jun

2011-01-01

48

Interaction of microwaves with ring domains in magnetic garnet films  

Microsoft Academic Search

Magnetic bubble and ring domains are generated in LPE garnet films by locally exciting spin precession near the ferrimagentic resonance frequency at high microwave power densities. Due to the spin precession, radial and azimuthal forces act on the bubbles. The radii of the ring domains vary with the microwave power and the bias field. The stability range of these domains

H. J. Schmitt

1974-01-01

49

Molecular magnets: Lord of the rings  

NASA Astrophysics Data System (ADS)

Magnets built of molecular rings of magnetic ions are fundamental model systems for studying the complex correlations and dynamics of quantum spins at the atomic scale. A new generation of neutron spectrometers can reveal complete four-dimensional maps of the spin correlations in spin rings.

Rüegg, Christian

2012-12-01

50

Evolution of the Storm Magnetic Field Disturbance on Earth's Surface and the Associated Ring Current as Deduced from Multiple Ground Observatories  

NASA Astrophysics Data System (ADS)

Based on the continuous magnetic field measurements of the multiple ground observatories, the structure of the geomagnetic field disturbance and its temporal variations have been investigated, so as to deduce the evolution of the storm ring current. Assuming the geomagnetic field disturbance around Earth is linear in space, the gradient of the corrected H component is obtained from the multiple ground observations. It is found that, the maximum difference of the corrected H component around the Earth surface, as calculated by the gradient of the corrected H component multiplied by the Earth diameter, well represents the asymmetric index Asy-H, but is actually more sensitive to the substorm activities than the Asy-H index. The anti-direction of the gradient of the corrected H component may be regarded as pointing to the position of the maximum partial ring current. It is shown that, for the ordinary storms (Dst>-200nT) (which may be caused by CIRs, long lasting fast solar wind flows, or prolonged south IMF, etc), the maximum partial ring current is located around the duskside during the main phase and the earlier stage of the recovery phase. At the later stage of the recovery phase, the position of the maximum partial ring current keeps rotating eastward, indicating the energetic electrons may play a significant role and the main ring current carriers may be the electrons at this stage. For the severe storms (Dst<-200nT), the position of the maximum partial ring current is not so regular, and there is the evidence that the injected electrons may contribute significantly to the ring current during the main phase of supper storms. Based on physical considerations, this investigation also provides new definitions to the symmetric index Sym-H and asymmetric index Asy-H. It is made possible that, the symmetric index Sym-H and asymmetric index Asy-H may be deduced from the measurements of the geomagnetic observatories located at local but not global area on Earth.

Shen, Chao; Zeng, Gang; Li, Xinlin; Rong, Zhaojin

2014-05-01

51

Fast superconducting magnetic field switch  

SciTech Connect

The superconducting magnetic switch or fast kicker magnet is employed with an 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 than 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. Magnetic switches and particularly fast kicker magnets are used in the accelerator industry to quickly deflect particle beams into and out of various transport lines, storage rings, dumps, and specifically to differentially route individual bunches of particles from a train of bunches which are injected or ejected from a given ring.

Goren, Y.; Mahale, N.K.

1995-12-31

52

Single-ring magnetic cusp low gas pressure ion source  

DOEpatents

A single-ring magnetic cusp low gas pressure ion source designed for use in a sealed, nonpumped neutron generator utilizes a cathode and an anode, three electrically floating electrodes (a reflector behind the cathode, a heat shield around the anode, and an aperture plate), together with a single ring-cusp magnetic field, to establish and energy-filtering mechanism for producing atomic-hydrogen ions.

Bacon, Frank M. (Albuquerque, NM); Brainard, John P. (Albuquerque, NM); O'Hagan, James B. (Albuquerque, NM); Walko, Robert J. (Albuquerque, NM)

1985-01-01

53

Janus Magnetic Rods, Ribbons, and Rings  

NASA Astrophysics Data System (ADS)

Dipolar particles are fundamental building blocks in nature and technology but the roles of anisotropy are seldom explored in their assembly. Here, we fabricate colloidal silica rods coated on one hemicylinder with a thin magnetic layer to satisfy multiple criteria: nearly monodisperse, easily imaged, and magnetic interaction dominant over gravity. We confirm long-predicted features of dipolar assembly and stress the microstructural variety brought about by shape and chemical anisotropy, especially by borrowing knowledge learned from molecules. We describe analogies to liquid crystalline deformations with bend, splay and twist; an analogy to cis/trans isomerism in organic molecules, which in this system can be controllably and reversibly switched; and a field-switching methodology to direct single ribbons into not only single but also multiple rings that can subsequently undergo hierarchical self-assembly. Going beyond earlier investigations of phase behavior, we show that dynamic reconfigurability presents subtle materials issues and possibilities.

Yan, Jing; Chaudhary, Kundan; Bae, Sung Chul; Lewis, Jennifer; Granick, Steve

2013-03-01

54

Magnetization reversal in arrays of Co-rings.  

SciTech Connect

The magnetization behavior of arrays of individual and coupled Co rings has been studied using superconducting quantum interference device magnetometry, magneto-optical imaging, and Lorentz transmission and scanning transmission electron microscopy. The transition from the polarized into the vortex state of isolated rings is shown to occur through the motion and annihilation of head-to-head domain boundaries. The chirality of the vortex state is fixed on subsequent magnetization cycles, indicating that it is predetermined by structural imperfections of the rings. The effect of interactions between the rings has been investigated in arrays of chains of touching rings. For fields applied parallel to the chains rings in extended sections of the chains are found to switch simultaneously. Neighboring rings in these sections can display alternating chirality as well as the same chirality accompanied by a 180{sup o} boundary on the nodes. For fields perpendicular to the chain direction the switching occurs pairwise. This coupling introduces a broad distribution of switching fields and correspondingly a magnetization curve that is significantly broader than that for the parallel orientation.

Welp, U.; Vlasko-Vlasov, V. K.; Hiller, J. M.; Zaluzec, N. J.; Metlushko, V.; Ilic, B.; Materials Science Division; Univ. of Illinois at Chicago; Cornell Univ.

2003-08-01

55

Magnetic record associated with tree ring density: Possible climate proxy  

PubMed Central

A magnetic signature of tree rings was tested as a potential paleo-climatic indicator. We examined wood from sequoia tree, located in Mountain Home State Forest, California, whose tree ring record spans over the period 600 – 1700 A.D. We measured low and high-field magnetic susceptibility, the natural remanent magnetization (NRM), saturation isothermal remanent magnetization (SIRM), and stability against thermal and alternating field (AF) demagnetization. Magnetic investigation of the 200 mm long sequoia material suggests that magnetic efficiency of natural remanence may be a sensitive paleoclimate indicator because it is substantially higher (in average >1%) during the Medieval Warm Epoch (700–1300 A.D.) than during the Little Ice Age (1300–1850 A.D.) where it is <1%. Diamagnetic behavior has been noted to be prevalent in regions with higher tree ring density. The mineralogical nature of the remanence carrier was not directly detected but maghemite is suggested due to low coercivity and absence of Verwey transition. Tree ring density, along with the wood's magnetic remanence efficiency, records the Little Ice Age (LIA) well documented in Europe. Such a record suggests that the European LIA was a global phenomenon. Magnetic analysis of the thermal stability reveals the blocking temperatures near 200 degree C. This phenomenon suggests that the remanent component in this tree may be thermal in origin and was controlled by local thermal condition.

Kletetschka, Gunther; Pruner, Petr; Venhodova, Daniela; Kadlec, Jaroslav

2007-01-01

56

Effects of two-temperature ions, magnetic field, and higher-order nonlinearity on the existence and stability of dust-acoustic solitary waves in Saturn's F ring  

SciTech Connect

Nonlinear propagation of dust-acoustic solitary waves (DASWs) in a strong magnetized dusty plasma comprising warm adiabatic variable-charged dust particles, isothermal electrons, and two-temperature ions is investigated. Applying a reductive perturbation theory, a nonlinear Zakharov-Kuznetsov (ZK) equation for the first-order perturbed potential and a linear inhomogeneous ZK-type equation for the second-order perturbed potential are derived. However, at a certain value of high-temperature ion density, the coefficient of the nonlinear terms of both ZK and ZK-type equations vanishes. Therefore, a new set of expansion physical parameters and stretched coordinates are then used to derive a modified Zakharov-Kuznetsov (mZK) equation for the first-order perturbed potential and a mZK-type equation for the second-order perturbed potential. Stationary solutions of these equations are obtained using a renormalization method. A condition for two-temperature ions assumption is examined for various cosmic dust-laden plasma systems. It is found that this condition is satisfied for Saturn's F ring. The effects of two-temperature ions, magnetic field, and higher-order nonlinearity on the behavior of the DASWs are discussed. To obtain the stability condition of the waves, a method based on energy consideration is used and the condition for stable solitons is derived.

El-Labany, S. K.; Moslem, Waleed M.; Safy, F. M. [Department of Physics, Faculty of Science-Damietta, Mansoura University, 34517 (Egypt); Department of Physics, Faculty of Education-Port Said, Suez Canal University (Egypt); Department of Physics, Faculty of Science-Damietta, Mansoura University, 34517 (Egypt)

2006-08-15

57

Magnetization reversal in arrays of Co rings  

Microsoft Academic Search

The magnetization behavior of arrays of individual and coupled Co rings has been studied using superconducting quantum interference device magnetometry, magneto-optical imaging, and Lorentz transmission and scanning transmission electron microscopy. The transition from the polarized into the vortex state of isolated rings is shown to occur through the motion and annihilation of head-to-head domain boundaries. The chirality of the vortex

U. Welp; V. K. Vlasko-Vlasov; J. M. Hiller; N. J. Zaluzec; V. Metlushko; B. Ilic

2003-01-01

58

Nonlinear split-ring metamaterial slabs for magnetic resonance imaging  

NASA Astrophysics Data System (ADS)

This work analyzes the ability of split-ring metamaterial slabs with zero/high permeability to reject/confine the radiofrequency magnetic field in magnetic resonance imaging systems. Split-ring slabs are designed and fabricated to work in a 1.5 T system. Nonlinear elements consisting of pairs of crossed diodes are inserted in the split-rings, so that the slab permeability can be switched between a value close to unity when interacting with the strong field of the transmitting coil, and zero or high values when interacting with the weak field produced by protons in tissue. Experiments are shown where these slabs locally increase the signal-to-noise-ratio.

Lopez, Marcos A.; Freire, Manuel J.; Algarin, Jose M.; Behr, Volker C.; Jakob, Peter M.; Marqués, Ricardo

2011-03-01

59

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

60

Magnetic measurements on the ring dipoles and quadrupoles for the Los Alamos proton storage ring  

SciTech Connect

This paper discusses magnetic measurements and shimming performed on the ring dipoles and quadrupoles for the Los Alamos Proton Storage Ring (PSR). For the dipoles, point-by-point field maps were obtained using a search coil that could be scanned over a three-dimensional grid. By appropriate machining of removable end blocks, all magnet lengths were adjusted to within 0.01% of a nominal value and all integrated multipoles were set within tolerance. Integrated fields of 20 PSR quadrupoles were measured using a rotating ''Morgan Coil'' and a digital spectrum analyzer. The magnets were shimmed to specifications by adjusting steel bolts threaded through the field clamps. 3 refs., 5 figs., 4 tabs.

Schermer, R.I.; Blind, B.; Jason, A.J.; Sawyer, G.A.

1985-01-01

61

Quantitative model of the magnetospheric magnetic field  

Microsoft Academic Search

Quantitative representations of the magnetic fields associated with the magnetopause currents and the distributed currents (tail and quiet time ring currents) have been developed. These fields are used together with a dipole representation of the main field of the earth to model the total vector magnetospheric magnetic field. The model is based on quiet time data averaged over all 'tilt

W. P. Olson; K. A. Pfitzer

1974-01-01

62

Exploring Magnetic Field Lines  

NSDL National Science Digital Library

In this activity, learners explore the magnetic field of a bar magnet as an introduction to understanding Earth's magnetic field. First, learners explore and play with magnets and compasses. Then, learners trace the field lines of the magnet using the compass on a large piece of paper. This activity will also demonstrate why prominences are always "loops."

Nasa

2012-06-26

63

Earth's Inconstant Magnetic Field  

NSDL National Science Digital Library

This NASA site describes long-term changes in Earth's magnetic field, and how magnetic stripes in the Atlantic seafloor provide evidence for reversals of this field. The site presents a model of Earth's interior that helps explain how Earth's magnetic field is generated and how the reversals occur. A computer-generated image shows the complicated magnetic field in-between reversals.

2007-04-27

64

Exploring Magnetic Fields  

NSDL National Science Digital Library

This is an activity about magnetic fields. Using iron filings, learners will observe magnets in various arrangements to investigate the magnetic field lines of force. This information is then related to magnetic loops on the Sun's surface and the magnetic field of the Earth. This is the second activity in the Exploring the Earth's Magnetic Field: An IMAGE Satellite Guide to the Magnetosphere educators guide.

65

Exploring Magnetic Fields  

NSDL National Science Digital Library

In this activity, students investigate the presence of magnetic fields around magnets, the sun and the earth. They will explore magnetic field lines, understand that magnetic lines of force show the strength and direction of magnetic fields, determine how field lines interact between attracting and repelling magnetic poles, and discover that the earth and sun have magnetic properties. They will also discover that magnetic force is invisible and that a "field of force" is a region or space in which one object can attract or repel another.

66

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,

67

Chiral transition with magnetic fields  

NASA Astrophysics Data System (ADS)

We study the nature of the chiral transition for an effective theory with spontaneous breaking of symmetry, where charged bosons and fermions are subject to the effects of a constant external magnetic field. The problem is studied in terms of the relative intensity of the magnetic field with respect to the mass and the temperature. When the former is the smallest of the scales, we present a suitable method to obtain magnetic and thermal corrections up to ring order at high temperature. By these means, we solve the problem of the instability in the boson sector for these theories, where the squared masses—taken as functions of the order parameter—can vanish and even become negative. The solution is found by considering the screening properties of the plasma, encoded in the resummation of the ring diagrams at high temperature. We also study the case where the magnetic field is the intermediate of the three scales and explore the nature of the chiral transition as we vary the field strength, the coupling constants, and the number of fermions. We show that the critical temperature for the restoration of chiral symmetry monotonically increases from small to intermediate values of the magnetic field and that this temperature is always above the critical temperature for the case when the magnetic field is absent.

Ayala, Alejandro; Hernández, Luis Alberto; Mizher, Ana Júlia; Rojas, Juan Cristóbal; Villavicencio, Cristián

2014-06-01

68

The Storage Ring Magnets of the Australian Synchrotron  

SciTech Connect

A 3 GeV Synchrotron Radiation Source is being built in Melbourne, Australia. Commissioning is foreseen in 2006. The Storage ring has a circumference of 216 m and has a 14 fold DBA structure. For the storage ring the following magnets will be installed: 28 dipoles with a field of 1.3 T, and a gradient of 3.35 T/m; 56 quadrupoles with a gradient of 18 T/m and 28 with a gradient of 10 T/m; 56 sextupoles with a strength of B'' = 350 T/m and 42 with 150 T/m. The sextupoles are equipped with additional coils for horizontal and vertical steering and for a skew quadrupole. The pole profile was determined by scaling the pole profile of the SPEAR magnets [1] to the aperture of the ASP magnets. The magnets are to be supplied by Buckley Systems Ltd in Auckland, New Zealand.

Barg, B.; Jackson, A.; LeBlanc, G.; /Melbourne U.; Huttel, E.; /Karlsruhe, Forschungszentrum; Tanabe, J.; /SLAC

2005-05-11

69

Evaluation of steel ring standards for magnetic particle inspection  

Microsoft Academic Search

The Ketos tool steel ring has become part of most magnetic particle standards in the United States. The rings are used to verify system performance and evaluate the sensitivity of magnetic particle materials. In 1985, two supposedly identical rings yielded a difference in the number of holes detected under identical test conditions. An industry survey of over 100 rings indicated

Hagemaier

1993-01-01

70

Visualizing Magnetic Field Lines  

NSDL National Science Digital Library

In this activity, students take the age old concept of etch-a-sketch a step further. Using iron filings, students begin visualizing magnetic field lines. To do so, students use a compass to read the direction of the magnet's magnetic field. Then, students observe the behavior of iron filings near that magnet as they rotate the filings about the magnet. Finally, students study the behavior of iron filings suspended in mineral oil which displays the magnetic field in three dimensions.

VU Bioengineering RET Program, School of Engineering,

71

Magnetic edge states in Aharonov-Bohm graphene quantum rings  

NASA Astrophysics Data System (ADS)

The effect of electron-electron interaction on the electronic structure of Aharonov-Bohm (AB) graphene quantum rings (GQRs) is explored theoretically using the single-band tight-binding Hamiltonian and the mean-field Hubbard model. The electronic states and magnetic properties of hexagonal, triangular, and circular GQRs with different sizes and zigzag edge terminations are studied. The results show that, although the AB oscillations in the all types of nanoring are affected by the interaction, the spin splitting in the AB oscillations strongly depends on the geometry and the size of graphene nanorings. We found that the total spin of hexagonal and circular rings is zero and therefore, no spin splitting can be observed in the AB oscillations. However, the non-zero magnetization of the triangular rings breaks the degeneracy between spin-up and spin-down electrons, which produces spin-polarized AB oscillations.

Farghadan, R.; Saffarzadeh, A.; Heidari Semiromi, E.

2013-12-01

72

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

SciTech Connect

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

Trbojevic, D.

1986-07-01

73

Mapping Magnetic Fields  

NSDL National Science Digital Library

This is an activity about bar magnets and their invisible magnetic fields. Learners will experiment with magnets and a compass to detect and draw magnetic fields. This is Activity 1 of a larger resource, entitled Exploring the Sun. The NASA spacecraft missions represented by this material include SOHO, TRACE, STEREO, Hinode, and SDO.

74

Magnetic field mapper  

NASA Technical Reports Server (NTRS)

Magnetic field mapper locates imperfections in cadmium sulphide solar cells by detecting and displaying the variations of the normal component of the magnetic field resulting from current density variations. It can also inspect for nonuniformities in other electrically conductive materials.

Masters, R. M.; Stenger, F. J.

1969-01-01

75

The Declining Magnetic Field  

NSDL National Science Digital Library

This is an activity about the declining strength of Earth's magnetic field. Learners will review a graph of magnetic field intensity and calculate the amount by which the field has changed its intensity in the last century, the rate of change of its intensity, and when the field should decrease to zero strength at the current rate of change. Learners will also use evidence from relevant sources to create a conjecture on the effects on Earth of a vanished magnetic field. Access to information sources about Earth's magnetic field strength is needed for this activity. This is Activity 7 in the Exploring Magnetism on Earth teachers guide.

76

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

77

Drawing Magnetic Fields  

NSDL National Science Digital Library

Students use a compass and a permanent magnet to trace the magnetic field lines produced by the magnet. By positioning the compass in enough spots around the magnet, the overall magnet field will be evident from the collection of arrows representing the direction of the compass needle. In activities 3 and 4 of this unit, students will use this information to design a way to solve the grand challenge of separating metal for a recycling company.

Vu Bioengineering Ret Program

78

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

79

1993 Evaluation of steel ring standards for magnetic particle inspection  

Microsoft Academic Search

The Ketos ring standard manufactured from AISI Type 01 (.90 carbon) tool steel has become part of certain US magnetic particle standards such as MIL-STD-1949. The rings are used to verify system performance and for sensitivity evaluation for magnetic particle materials. Some controversy exists concerning the use of the steel ring as a reference standard for the following reasons: inconsistencies

B. Bates; D. Hagemaier; J. Petty; C. Armstrong

1996-01-01

80

Circuits and Magnetic Fields  

NSDL National Science Digital Library

In this activity, students use the same method as in the activity from lesson 2 to explore the magnetism due to electric current instead of a permanent magnet. Students use a compass and circuit to trace the magnetic field lines induced by the electric current moving through the wire. Students develop an understanding of the effect of the electrical current on the compass needle through the induced magnetic field and understand the complexity of a three dimensional field system.

Vu Bioengineering Ret Program

81

Fabrication and tests of prototype quadrupole magnets for the storage ring of the advanced photon source  

SciTech Connect

Prototype quadrupole magnets for the APS storage ring have been fabricated and tested. Mechanical stability of the magnet poles and acceptable field quality have been achieved. Geometries of the pole-end bevels have been studied in order to simplify the design of the magnet end-plate. The field saturation at different segments of the magnet has been measured to evaluate the magnet efficiency. 3 refs., 4 figs., 2 tabs.

Kim, S.H.; Thompson, K.M.; Black, E.L.; Jagger, J.M.

1991-01-01

82

Structural and magnetic transitions in ensembles of mesoscopic Peierls rings in a magnetic flux  

NASA Astrophysics Data System (ADS)

We investigate effects of a magnetic flux ? threading mesoscopic Peierls rings. Both isolated rings and ensembles of rings are considered and quantum phonon fluctuations are accounted for. Significant qualitative and quantitative modifications to the mean field results are obtained. Quantum fluctuations yield a continuous structural Peierls change occurring without symmetry breaking and a ?-dependent tunneling splitting. The latter yields a ?-modulated ultrasound or hypersound absorption that could be detected experimentally. Important differences exist between an isolated ring and an ensemble of rings. To perform ensemble averaging, we propose a new and simple method. Unlike isolated rings, ensembles possess structural and magnetic properties that do not distinguish between average sizes N=4n and N=4n+2 but rather between smaller and larger N. In ensembles, the flux period is hc/2e, half the period for an isolated ring. An appealing magnetic behavior with an interplay between dia- and paramagnetism is found in ensembles that could be experimentally investigated by means of a SQUID technique.

Bâldea, Ioan; Köppel, Horst; Cederbaum, Lorenz S.

1999-09-01

83

Photospheric magnetic fields  

NASA Technical Reports Server (NTRS)

Knowledge on the nature of magnetic fields on the solar surface is reviewed. At least a large part of the magnetic flux in the solar surface is confined to small bundles of lines of force within which the field strength is of the order of 500 gauss. Magnetic fields are closely associated with all types of solar activity. Magnetic flux appears at the surface at the clearly defined birth or regeneration of activity of an active region. As the region ages, the magnetic flux migrates to form large-scale patterns and the polar fields. Some manifestations of the large-scale distribution are discussed.

Howard, R.

1972-01-01

84

Mapping Magnetic Field Lines  

NSDL National Science Digital Library

This is a lesson about the magnetic field of a bar magnet. The lesson begins with an introductory discussion with learners about magnetism to draw out any misconceptions that may be in their minds. Then, learners freely experiment with bar magnets and various materials, such as paper clips, rulers, copper or aluminum wire, and pencils, to discover that magnets attract metals containing iron, nickel, and/or cobalt but not most other materials. Next, learners experiment with using a magnetic compass to discover how it is affected by the magnet and then draw the magnetic field lines of the magnet by putting dots at the location of the compass arrow. This is the first lesson in the first session of the Exploring Magnetism teacher guide.

85

Variations in the ring current and inner-magnetospheric electric field deduced from data assimilation of IMAGE\\/HENA data  

Microsoft Academic Search

We examine the relationship between the temporal variation of the ring current and that of the inner- magnetospheric electric field during a magnetic storm by using data assimilation of ENA observations into a kinetic ring current simulation. Since the dynamics of ring current ions are strongly controlled by the electric field, it is important to know the electric field in

S. Nakano; G. Ueno; Y. Ebihara; M. Fok; S. Ohtani; P. C. Brandt; D. G. Mitchell; K. Keika; T. Higuchi

2007-01-01

86

Direct Observation of the Controlled Magnetization Reversal Processes in Py/Al/Py Assymmetric Ring Stacks  

SciTech Connect

Electron holographic experiments were performed to study the magnetization reversal process of patterned Py/Al/Py (20nm/20nm/10nm) asymmetric ring stacks. By changing the in-plane field applied perpendicular to the ring's symmetric axis, we directly observed the vortex-based magnetization reversal process through controlled domain wall motion and annihilation. The two magnetic layers were found to switch at different critical fields, leading to the existence of various distinct domain state combinations. Quantitative agreement was obtained between measured phase shifts and those derived from micromagnetic calculations, which allows us to resolve the layer-by-layer magnetic behavior as a function of applied external field.

Huang, L.; Schofield, M.A.; Zhu, Y.

2009-07-27

87

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

88

1.2 MV, 800 kA, 150 ns pulsed power generator for powering Field Reversed Ion Ring Experiments  

Microsoft Academic Search

The Field-Reversed Ion Ring Experiment (FIREX) program at Cornell University is designed to reach the goal of producing a field-reversed configuration (FRC) with current carried by an ion ring trapped in a magnetic mirror. Production of an ion-ring FRC is expected to have favorable stability and confinement characteristics for magnetically-confined fusion. Past experimental results, theoretical analysis and ion ring injection

D. E. Anderson; J. B. Greenly; S. C. Glidden; M. Richter

1995-01-01

89

Magnetic Field Viewing Cards  

NASA Astrophysics Data System (ADS)

For some years now laminated cards containing a green, magnetically sensitive film have been available from science education suppliers. When held near a magnet, these cards appear dark green in regions where the field is perpendicular to the card and light green where the field is parallel to the card. The cards can be used to explore the magnetic field near a variety of magnets as well as near wire loops. In this paper we describe how to make these cards and how we have used them in our physics classrooms and labs.

Kanim, Stephen; Thompson, John R.

2005-09-01

90

The galactic magnetic field  

Microsoft Academic Search

Estimates for the scale, geometry and strength of the magnetic field in the galactic system can be derived from observations of polarization properties of radio emission from the Galaxy, extragalactic radio sources and pulsars, and polarization of starlight. Within distances of about 500 parsecs (1 parsec = 3.26 lightyears) from the solar system the magnetic field is directed towards galactic

T A Spoelstra; T. A. T

1977-01-01

91

EDDY CURRENT SEPTUM MAGNETS FOR BOOSTER INJECTION AND EXTRACTION, AND STORAGE RING INJECTION AT SYNCHROTRON SOLEIL  

Microsoft Academic Search

Eddy current thin septum magnets are used to inject or extract the electron beam to\\/from the Booster and to the Storage Ring (SR) of SOLEIL. Good transverse homogeneity in the gap for injected beam, and low leakage field on circulating beam is needed, as well as pulse stability. The Top Up injection mode of the Storage Ring needs a very

P. Lebasque; P. Gros; J. P. Lavieville; J. Da Silva Castro; A. Mary; D. Muller

92

Interplanetary Magnetic Field Lines  

NSDL National Science Digital Library

This web page provides information and a graphical exercise for students regarding the interaction between magnetic field lines and a plasma. The activity involves tracing a typical interplanetary magnetic field line, dragged out of a location on the Sun by the radial flow of the solar wind. This illustrates the way magnetic field lines are "frozen to the plasma" and the wrapping of field lines due to the rotation of the sun. This is part of the work "The Exploration of the Earth's Magnetosphere". A Spanish translation is available.

Stern, David

2005-04-27

93

Exact physical model for magnets in storage rings  

SciTech Connect

In this report we try to make estimates of both kinematic and field effects on the stability of a particle motion, by employing a truly Maxwellian representation of the magnetic field in exact equations of motion. For this purpose we adopt a simple FODO cell model, which repeats periodically to infinity. This model includes only quadrupoles and drifts, leaving out the bending magnets to avoid the problem of the trajectory curvature. We think this model is a physically consistent approximation of a storage ring. We derive several models with different levels of approximation and compare them by evaluating the importance of these effects. The relevance to long-term stability is being investigated in the meantime by comparing the different models with extensive computer simulations. The results will be shown in a subsequent report.

Maletic, D.; Ruggiero, A.G.

1992-12-31

94

Metastable states during magnetization reversal in square permalloy rings  

Microsoft Academic Search

The magnetic reversal process in a two-dimensional array of permalloy square rings is presented. Rings of thickness of 25 nm, of lateral size of 2.1 mum, and with ring width of 240 nm were microfabricated using electron-beam lithography and lift-off techniques. Analysis of the diffracted magneto-optical Kerr effect hysteresis loops, magnetic force microscopy images, and micromagnetic simulations show that the

P. Vavassori; M. Grimsditch; V. Novosad; V. Metlushko; B. Ilic

2003-01-01

95

Asymmetric dipolar ring  

DOEpatents

A device having a dipolar ring surrounding an interior region that is disposed asymmetrically on the ring. The dipolar ring generates a toroidal moment switchable between at least two stable states by a homogeneous field applied to the dipolar ring in the plane of the ring. The ring may be made of ferroelectric or magnetic material. In the former case, the homogeneous field is an electric field and in the latter case, the homogeneous field is a magnetic field.

Prosandeev, Sergey A. (Fayetteville, AR); Ponomareva, Inna V. (Tampa, FL); Kornev, Igor A. (Ill-de-France, FR); Bellaiche, Laurent M. (Fayetteville, AR)

2010-11-16

96

Sonoluminescence in High Magnetic Fields  

Microsoft Academic Search

We have made a detailed study of sonoluminescence (SL) in high magnetic fields. In magnetic field sweeps at constant levels of acoustic drive, SL disappears above a pressure-dependent threshold magnetic field. Sweeps of acoustic drive at fixed magnetic fields show that the upper and lower bounds of forcing pressure that determine the region of SL increase dramatically with magnetic field.

J. B. Young; T. Schmiedel; Woowon Kang

1996-01-01

97

Stability of field-reversed ion rings  

SciTech Connect

Studies of the low-frequency stability of field-reversed ion rings in a dense uniform plasma background have been carried out using a linearized 3-D hybrid simulation model. For a moderately thick ring with aspect ratio on the order of 4:1, the azimuthal mode number l -- 1 radial mode (magnetohydrodynamic precession) is observed to be stable, because of the favorable field gradient arising from image currents in the outer wall. The l -- 1 axial (tilt) mode is unstable for the parameters chosen, as are the l -- 2 radial and axial (kink) modes, and the l -- 3 radial mode. All other modes are observed to be either stable or very weakly unstable; numerical difficulties arising from the local instability of individual orbits in the equilibrium field make it difficult to examine modes with small growth rates. The structures of the various unstable modes range from near rigid to quite complicated in displacement pattern. Some preliminary evidence for the existence of betatron resonance-driven instabilities is noted.

Friedman, A.; Sudan, R.N.; Denavit, J.

1986-10-01

98

Magnetic Bar Field Model  

NSDL National Science Digital Library

The EJS Magnetic Bar Field Model shows the field of a bar magnet and has a movable compass that reports the magnetic field values. The bar magnet model is built by placing a group of magnetic dipoles along the bar magnet. 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 Bar 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_MagneticBarField.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; Franciscouembre; Cox, Anne

2009-09-18

99

Effects of two-temperature electrons, external oblique magnetic field, concentration of charged dust grains and higher-order nonlinearity on dust ion-acoustic solitary waves in Saturn's E-ring  

NASA Astrophysics Data System (ADS)

The purpose of the present work is to investigate some nonlinear properties of the dust ion-acoustic (DIA) solitary waves in a four-component hot-magnetized dusty plasma consisting of charged dust grains, positively charged ions and two-temperature isothermal electrons. Applying a reductive perturbation theory, a nonlinear Korteweg-de Vries (KdV) equation for the first-order perturbed potential and a linear inhomogeneous KdV-type equation for the second-order perturbed potentials are derived. Stationary solutions of these coupled equations are obtained using a renormalization method. A method based on energy consideration is used to obtain a condition for stable solitons. The effects of two different types of isothermal electrons, external oblique magnetic field, concentration of negatively (positively) charged dust grains and higher-order nonlinearity on the nature of the DIA solitary waves are discussed. The numerical results are applied to Saturn's E-ring.

El-Labany, S. K.; Shalaby, M.; El-Shamy, E. F.; El-Sherif, L. S.

2009-09-01

100

Mapping Magnetic Field Lines  

NSDL National Science Digital Library

This is an activity about electromagnetism. Learners will use a compass to map the magnetic field lines surrounding a coil of wire that is connected to a battery. This activity requires a large coil or spool of wire, a source of electricity such as 3 D-cell batteries or an AC to DC power adapter, alligator-clipped wire, and magnetic compasses. This is the third lesson in the second session of the Exploring Magnetism teachers guide.

101

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

102

Solar Magnetic Fields.  

National Technical Information Service (NTIS)

The research work was directed towards the following: (1) Perform necessary laboratory experiments, including a study on the Zeeman effect in absorption. Make observations of the sunspot and general magnetic fields of the sun. (2) Conduct a program of int...

M. Cimino

1966-01-01

103

Coronal magnetic fields  

Microsoft Academic Search

The use of coronal X-ray emission in determining the configuration of the magnetic field lines in the corona is discussed. Spatially-resolved X-ray observations provided by Skylab and subsequently by missions such as OSO-8 and SMM show the solar corona to be inhomogeneous, with open and closed structures determined by the topology of the magnetic field. The scenario provided by observations

R. Pallavicini

1986-01-01

104

Correction of Magnetic Field Distribution within the Optical Radiation Coverage Zone of Magnetic Laser Therapy Apparatuses  

Microsoft Academic Search

Methods for correction of magnetic field distribution within the optical radiation coverage zone of magnetic laser therapy\\u000a apparatuses were developed. These methods in medical apparatuses provide a 3.5–4.0-fold decrease in the magnetic induction\\u000a in the therapeutic zone of ring magnets. Magnetic field strength was optimized using magnetic tips made of soft magnetic materials.\\u000a Engineering solution of magnetotherapeutic apparatuses provides optimal

V. Yu. Plavskii

2011-01-01

105

Direct calculation of the ring current distribution and magnetic structure seen by Cluster during geomagnetic storms  

NASA Astrophysics Data System (ADS)

disturbances caused by the Earth's ring current, particularly during storm time activity, have a dominant effect on the geomagnetic field. Strong currents and large kinetic and magnetic energies can change considerably local field geometry and depress the ground geomagnetic field. The multispacecraft magnetic measurements of Cluster allow extensive in situ coverage of the ring current. We select 48 storm time Cluster crossing events to investigate the variation of the local current density distribution and magnetic configuration of the ring current. We find direct evidence for the existence of an inner, eastward flowing current in addition to the dominant westward current, in the ring plane. The radius of curvature of the magnetic field lines (MFLs) is found to be increasingly reduced at all local times during increasing storm activity, changing the resulting ring current magnetic geometry considerably, where the MFL configuration and the azimuthal current density distribution are asymmetric with the local time. During similar storm activity the radius of curvature of the local MFLs, Rc, is smallest on the nightside to duskside, medium on the dawnside, and largest on the dayside. This change in geometry may have significant influence on the spatial distribution of the particles with various energies in the plasmasphere, ring current, and radiation belts.

Shen, C.; Yang, Y. Y.; Rong, Z. J.; Li, X.; Dunlop, M.; Carr, C. M.; Liu, Z. X.; Baker, D. N.; Chen, Z. Q.; Ji, Y.; Zeng, G.

2014-04-01

106

Near-rings and near-fields  

Microsoft Academic Search

Near-rings are generalized rings: commutativity of addition is not assumed, and 3=more important — only one distributive law is required. The most famous example is the collection of all maps from an additive group into itself w.r.t. function addition and composition. Compared with a standard class of rings, endomorphism rings of abelian groups, one sees that rings describe “linear” maps

Günter F. Pilz

1996-01-01

107

Solar Wind Magnetic Fields  

NASA Technical Reports Server (NTRS)

The magnetic fields originate as coronal fields that are converted into space by the supersonic, infinitely conducting, solar wind. On average, the sun's rotation causes the field to wind up and form an Archimedes Spiral. However, the field direction changes almost continuously on a variety of scales and the irregular nature of these changes is often interpreted as evidence that the solar wind flow is turbulent.

Smith, E. J.

1995-01-01

108

The nonequilibrium of magnetic fields  

Microsoft Academic Search

The more subtle properties of magnetic fields which create nonequilibrium and lead to vigorous activity in otherwise sluggish gas-field systems are evaluated for gross hydromagnetic effects. The gentle manipulation of magnetic fields on a large scale leads to the production of small scale variations and discontinuities, providing intense dissipation of magnetic field in a large scale system. A magnetic field

E. N. Parker

1981-01-01

109

SC correction coils and magnets for the HERA proton ring  

NASA Astrophysics Data System (ADS)

The design, manufacture and performance of correction elements of the HERA proton ring is described. The quadrupole and sextupole correction coils are mounted on the cold beam pipe inside the main dipole magnets. Superferric dipole magnets for orbit correction are located adjacent to the main quadrupole magnets in a common cryostat which also contains the beam monitor.

Daum, C.; Geerinck, J.; Moeller, H.; Heller, R.; Schmueser, P.; Bracke, P.

1986-05-01

110

Microinhomogeneities in Magnetic Fields  

Microsoft Academic Search

Small variations in the fields of magnets, caused by structures or domains in the pole faces, were investigated by moving a small coil in a circular path. It was found that for a given pole face the variations in the field were all about the same size, and decreased exponentially from the pole face. None of the materials tested as

H. H. Brown Jr.; F. Bitter

1956-01-01

111

Magnetic Field Solver  

NASA Technical Reports Server (NTRS)

The Magnetic Field Solver computer program calculates the magnetic field generated by a group of collinear, cylindrical axisymmetric electromagnet coils. Given the current flowing in, and the number of turns, axial position, and axial and radial dimensions of each coil, the program calculates matrix coefficients for a finite-difference system of equations that approximates a two-dimensional partial differential equation for the magnetic potential contributed by the coil. The program iteratively solves these finite-difference equations by use of the modified incomplete Cholesky preconditioned-conjugate-gradient method. The total magnetic potential as a function of axial (z) and radial (r) position is then calculated as a sum of the magnetic potentials of the individual coils, using a high-accuracy interpolation scheme. Then the r and z components of the magnetic field as functions of r and z are calculated from the total magnetic potential by use of a high-accuracy finite-difference scheme. Notably, for the finite-difference calculations, the program generates nonuniform two-dimensional computational meshes from nonuniform one-dimensional meshes. Each mesh is generated in such a way as to minimize the numerical error for a benchmark one-dimensional magnetostatic problem.

Ilin, Andrew V.

2006-01-01

112

Magnetic ionization fronts. I. Parallel magnetic fields  

NASA Astrophysics Data System (ADS)

We solve the continuity equations across an ionization front. By including a plane parallel magnetic field we find significant differences in the allowed velocities of the R- and D-type solutions between the magnetized and non-magnetized cases. These results may have implications for the study of ionization bounded diffuse sources where a moderate or strong magnetic field is expected.

Redman, M. P.; Williams, R. J. R.; Dyson, J. E.; Hartquist, T. W.; Fernandez, B. R.

1998-03-01

113

Transverse Field Profile of the NLC Damping Rings Eletromagnet Wiggler (LCC-0038)  

SciTech Connect

The primary effort for damping ring wiggler studies has been to develop a credible radiation hard electromagnet wiggler conceptual design that meets NLC main electron and positron damping ring physics requirements [1]. Based upon an early assessment of requirements, a hybrid magnet similar to existing designs satisfies basic requirements. However, radiation damage is potentially a serious problem for the Nd-Fe-B permanent magnet material, and cost remains an issue for samarium cobalt magnets. Superconducting magnet designs have not been pursued due to their increased complexity and our unfamiliarity with the technology. Having produced and developed an electromagnet design, we now find that the transverse field roll-off is severe, and recognizing similar experience with beamline 11 at SSRL we believe that the resulting beam quality will not meet the damping ring requirements. We therefore propose, in parallel with more detailed optics studies of the wiggler field requirements, to revisit the hybrid permanent magnet design.

Ross, M

2004-03-19

114

Eruptive solar magnetic fields  

NASA Technical Reports Server (NTRS)

The quasi-steady evolution of solar magnetic fields in response to gradual photospheric changes is considered, with particular attention given to the threshold of a sudden eruption in the solar atmosphere. The formal model of an evolving, force-free field dependent on two Cartesian coordinates is extended to a field which is not force free but in static equilibrium with plasma pressure and gravity. The basic physics is illustrated through the evolution of a loop-shaped electric current sheet enclosing a potential bipolar field with footpoints rooted in the photosphere. A free-boundary problem is posed and then solved for the equilibrium configuration of the current sheet in a hydrostatically supported isothermal atmosphere. As the footpoints move apart to spread a constant photospheric magnetic flux over a larger region, the equilibria available extend the field to increasing heights.

Low, B. C.

1981-01-01

115

The Sun and Magnetic Fields  

NSDL National Science Digital Library

In this activity about magnetic fields and their relation to the Sun, learners will simulate sunspots by using iron filings to show magnetic fields around a bar or cow magnet, and draw the magnetic field surrounding two dipole magnets, both in parallel and perpendicular alignments. Finally, learners examine images of sunspots to relate their magnetic field drawings and observations to what is seen on the Sun.

116

Hybrid permanent magnet quadrupoles for the Recycler Ring at Fermilab  

SciTech Connect

Hybrid Permanent Magnet Quadrupoles are used in several applications for the Fermilab Recycler Ring and associated beam transfer lines. Most of these magnets use a 0.6096 m long iron shell and provide integrated gradients up to 1.4 T-m/m with an iron pole tip radius of 41.6 mm. A 58.4 mm pole radius design is also required. Bricks of 25. 4 mm thick strontium ferrite supply the flux to the back of the pole to produce the desired gradients (0.6 to 2.75 T/m). For temperature compensation, Ni-Fe alloy strips are interspersed between ferrite bricks to subtract flux in a temperature dependent fashion. Adjustments of the permeance of each pole using iron between the pole and the flux return shell permits the matching of pole potentials. Magnetic potentials of the poles are adjusted to the desired value to achieve the prescribed strength and field uniformity based on rotating coil harmonic measurements. Procurement, fabrication, pole potential adjustment, and measured fields will be reported.

Brown, B.C.; Pruss, S.M.; Foster, G.W.; Glass, H.D.; Harding, D.J.; Jackson, G.R.; May, M.R.; Nicol, T.H.; Ostiguy, J.-F.; Schlabach, R.; Volk, J.T.

1997-10-01

117

HMI Magnetic Field Products  

NASA Astrophysics Data System (ADS)

The Helioseismic and Magnetic Imager (HMI) on SDO has measured magnetic field, velocity, and intensity in the photosphere over the full disk continuously since May 2010 with arc-second resolution. Scalar images are measured every 45 seconds. From these basic observables the pipeline automatically identifies and tracks active regions on the solar disk. The vector magnetic field and a variety of summary quantities are determined every 720s in these tracked Space-weather HMI Active Region Patches (SHARPS). Synoptic and synchronic maps are constructed daily and after each Carrington Rotation Most data products are available with definitive scientific calibration after a few day deal at and in a quick-look near-real-time version a few minutes after the observations are made. Uncertainties are determined for the derived products. All of the magnetic field products along with movies and images suitable for browsing are available at http:://Hmi.stanford.edu/magnetic. Other products, e.g. coronal field over active regions, can be computed on demand.

Hoeksema, Jon T.; HMI Magnetic Field Team

2013-07-01

118

Structure of the Brauer ring of a field extension  

Microsoft Academic Search

In 1986, Jacobson has defined the Brauer ring B(E, D) for a finite Galois field extension E\\/D, whose unit group canonically contains the Brauer group of D. In 1993, Cheng Xiang Chen determined the structure of the Brauer ring in the case where the extension is trivial. He revealed that if the Galois group G is trivial, the Brauer ring

Hiroyuki Nakaoka

2008-01-01

119

Magnetic Field and Life  

NSDL National Science Digital Library

This is a lesson where learners explore magnetic forces, fields, and the relationship between electricity. Learners will use this information to infer how the Earth generates a protective magnetic field. The lesson models scientific inquiry using the 5E instructional model and includes teacher notes, prerequisite concepts, common misconceptions, student journal and reading. This is lesson seven in the Astro-Venture Geology Training Unit that were developed to increase students' awareness of and interest in astrobiology and the many career opportunities that utilize science, math and technology skills. The lessons are designed for educators to use with with the Astro-Venture multimedia modules.

120

TOSCA calculations and measurements for the SLAC SLC damping ring dipole magnet  

SciTech Connect

The SLAC damping ring dipole magnet was originally designed with removable nose pieces at the ends. Recently, a set of magnetic measurements was taken of the vertical component of induction along the center of the magnet for four different pole-end configurations and several current settings. The three dimensional computer code TOSCA, which is currently installed on the National Magnetic Fusion Energy Computer Center's Cray X-MP, was used to compute field values for the four configurations at current settings near saturation. Comparisons were made for magnetic induction as well as effective magnetic lengths for the different configurations. 1 ref., 12 figs., 2 tabs.

Early, R.A.; Cobb, J.K.

1985-04-01

121

Nonlinearities induced by magnetic fields in nematic liquid crystals  

NASA Astrophysics Data System (ADS)

We investigated a nonlinear phenomenon arising when a planar oriented NLC cell introduced into a magnetic field was subjected to a laser beam with normal incidence. The limit number of diffraction rings was measured for different magnetic fields, higher than the critical one for the magnetic Freedericksz transition. A dynamical measurement of the fringes number was made for a magnetic field equal to the one for which the maximum number of rings was obtained. Another dynamical measurement was made for a higher field and, in all the cases, the theoretical approach was in good agreement with experimental data.

Stoian, Victor; Cîrtoaje, Cristina; Petrescu, Emil; Motoc, Cornelia

2013-11-01

122

High field superconducting magnets  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

123

The interplanetary magnetic field  

NASA Technical Reports Server (NTRS)

Large-scale properties of the interplanetary magnetic field as determined by the solar wind velocity structure are examined. The various ways in which magnetic fields affect phenomena in the solar wind are summarized. The dominant role of high and low velocity solar wind streams that persist, with fluctuations and evolution, for weeks or months is emphasized. It is suggested that for most purposes the sector structure is better identified with the stream structure than with the magnetic polarity and that the polarity does not necessarily change from one velocity sector to the next. Several mechanisms that might produce the stream structure are considered. The interaction of the high and low velocity streams is analyzed in a model that is steady state when viewed in a frame that corotates with the sun.

Davis, L., Jr.

1972-01-01

124

Ultrafast precessional magnetization reversal by picosecond magnetic field pulse shaping  

NASA Astrophysics Data System (ADS)

Since the invention of the first magnetic memory disk in 1954, much effort has been put into enhancing the speed, bit density and reliability of magnetic memory devices. In the case of magnetic random access memory (MRAM) devices, fast coherent magnetization rotation by precession of the entire memory cell is desired, because reversal by domain-wall motion is much too slow. In principle, the fundamental limit of the switching speed via precession is given by half of the precession period. However, under-critically damped systems exhibit severe ringing and simulations show that, as a consequence, undesired back-switching of magnetic elements of an MRAM can easily be initiated by subsequent write pulses, threatening data integrity. We present a method to reverse the magnetization in under-critically damped systems by coherent rotation of the magnetization while avoiding any ringing. This is achieved by applying specifically shaped magnetic field pulses that match the intrinsic properties of the magnetic elements. We demonstrate, by probing all three magnetization components, that reliable precessional reversal in lithographically structured micrometre-sized elliptical permalloy elements is possible at switching times of about 200ps, which is ten times faster than the natural damping time constant.

Gerrits, Th.; van den Berg, H. A. M.; Hohlfeld, J.; Bär, L.; Rasing, Th.

2002-08-01

125

Conventional magnet storage rings for x-ray lithography  

Microsoft Academic Search

A first pass at the design of a conventional magnet storage ring for x-ray lithogrphy is presented. Electron beam size and power specifications are given, followed by a first pass at a lattice - a 4-fold symmetric, gradient FODO cell lattice using B = 1.6 Tesla C-magnets. (LEW)

M. Bassetti; K. Batchelor; J. Galayda; H. Halama; R. Heese; H. Hsieh; S. Krinsky; J. Murphy; A. van Steenbergen; G. Vignola

1986-01-01

126

Effect of an electric field on the nonlinear optical rectification of a quantum ring  

NASA Astrophysics Data System (ADS)

We have studied the effects of an external electric field on the nonlinear optical rectification of a semiconductor quantum ring. An electric field applied in the ring plane destroys the rotational invariance. Calculations are performed by using the matrix diagonalization method and the compact density-matrix approach within the effective-mass approximation. The results indicate that an increase of electric field gives the red shift of the peak positions of nonlinear optical rectification. The roles of ring size and magnetic field strength as control parameters on this nonlinear property have been investigated. Our results show rich nonlinear optical rectification for quantum rings in the presence of electric fields, which effectively displays the signature of the Aharonov-Bohm oscillation.

Xie, Wenfang

2014-06-01

127

The Earth's Magnetic Field  

NSDL National Science Digital Library

This section of the Windows to the Universe website provides information and images about Earth's magnetic field (the magnetosphere), including detailed information about the aurora borealis, magnets, and solar wind. Windows to the Universe is a user-friendly learning system pertaining to the Earth and Space sciences. The objective of this project is to develop an innovative and engaging website that includes a rich array of documents, including images, movies, animations, and data sets that explore the Earth and Space sciences and the historical and cultural ties between science, exploration and the human experience. Links at the top of each page allow users to navigate between beginner, intermediate and advanced levels.

Johnson, Roberta

2000-07-01

128

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

129

Role of The Impulsive Electric Fields In The Ring Current Formation: Particle Energization and Transport  

NASA Astrophysics Data System (ADS)

It is now accepted that the ring current enhancement is at least partly associated with the injection of energetic particles associated with substorm expansion phase activity. During substorms the electric field is complex and strongly fluctuating, and the level of fluctuations can be an order of magnitude higher (tens of mV/m) than the mean cross-tail field (0.1-1 mV/m). We demonstrate that such fluctuating fields can effec- tively energize the plasma sheet particles and transport them inward to closed drift shells. We trace protons with arbitrary pitch angles numerically in the drift approxi- mation. Tracing is performed in stationary (T96, Volland-Stern) and time-dependent magnetic and electric field models. Time-dependent electric field is given by Gaussian electric field pulse with azimuthal field component propagating inward with constant velocity of 100 km/s. We model particle inward motion and energization by a series of electric field pulses representing substorm activations during May 2-4, 1998 storm event. We show that the formation of the ring current is a combination of large-scale convection and pulsed inward shift and consequent energization of the ring current particles. We estimate the magnetic field depression in the center of the Earth pro- duced by model ring current particles and the ring current total energy and compare them to the observed values of Dst and particle measurements made on Polar.

Ganushkina, N. Y.; Pulkkinen, T. I.

130

Magnetization reversal in asymmetric Co rings studied by micromagnetic simulation  

NASA Astrophysics Data System (ADS)

Previous simulation reports have shown that the magnetization reversal mechanism in the asymmetric rings with the global vortex state is dominated by domain wall movement. This work investigates the asymmetric Co rings with relatively large sizes and thick arms with simulation. Results show that the magnetization reversal processes are dominated by the formation, movement, and annihilation of localized vortex states. 90° decenter of the inner core is favorable for a stable global vortex state with controllable chirality. Either a larger 90° decenter distance or a thicker thickness brings about a higher stability of global vortex state. However, the global vortex state cannot be obtained at remanence in these rings. In the smaller rings, with the global vortex state obtained at remanence, the stability of global vortex state is enhanced when the inner core size grows larger, and it is due to the reduced possibility of the formation of localized vortex state.

Xu, Feng; Wei, Jun; Tan, Weishi; Li, Shandong

2014-05-01

131

Magnetic field of the Earth  

NASA Astrophysics Data System (ADS)

The magnetic field of the Earth has global meaning for a life on the Earth. The world geophysical science explains: - occurrence of a magnetic field of the Earth it is transformation of kinetic energy of movements of the fused iron in the liquid core of Earth - into the magnetic energy; - the warming up of a kernel of the Earth occurs due to radioactive disintegration of elements, with excretion of thermal energy. The world science does not define the reasons: - drift of a magnetic dipole on 0,2 a year to the West; - drift of lithospheric slabs and continents. The author offers: an alternative variant existing in a world science the theories "Geodynamo" - it is the theory « the Magnetic field of the Earth », created on the basis of physical laws. Education of a magnetic field of the Earth occurs at moving the electric charge located in a liquid kernel, at rotation of the Earth. At calculation of a magnetic field is used law the Bio Savara for a ring electric current: dB = . Magnetic induction in a kernel of the Earth: B = 2,58 Gs. According to the law of electromagnetic induction the Faradey, rotation of a iron kernel of the Earth in magnetic field causes occurrence of an electric field Emf which moves electrons from the center of a kernel towards the mantle. So of arise the radial electric currents. The magnetic field amplifies the iron of mantle and a kernel of the Earth. As a result of action of a radial electric field the electrons will flow from the center of a kernel in a layer of an electric charge. The central part of a kernel represents the field with a positive electric charge, which creates inverse magnetic field Binv and Emfinv When ?mfinv = ?mf ; ?inv = B, there will be an inversion a magnetic field of the Earth. It is a fact: drift of a magnetic dipole of the Earth in the western direction approximately 0,2 longitude, into a year. Radial electric currents a actions with the basic magnetic field of a Earth - it turn a kernel. It coincides with laws of electromagnetism. According to a rule of the left hand: if the magnetic field in a kernel is directed to drawing, electric current are directed to an axis of rotation of the Earth, - a action of force clockwise (to West). Definition of the force causing drift a kernel according to the law of Ampere F = IBlsin. Powerful force 3,5 × 1012 Nyton, what makes drift of the central part of a kernel of the Earth on 0,2 the longitude in year to West, and also it is engine of the mechanism of movement of slabs together with continents. Movement of a core of the Earth carry out around of a terrestrial axis one circulation in the western direction in 2000 of years. Linear speed of rotation of a kernel concerning a mantle on border the mantle a kernel: V = × 3,471 × 10 = 3,818 × 10 m/s = 33 m/day = 12 km/years. Considering greater viscosity of a mantle, the powerful energy at rotation of a kernel seize a mantle and lithospheric slabs and makes their collisions as a result of which there are earthquakes and volcano. Continents Northern and Southern America every year separate from the Europe and Africa on several centimeters. Atlantic ocean as a result of movement of these slabs with such speed was formed for 200 million years, that in comparison with the age of the Earth - several billions years, not so long time. Drift of a kernel in the western direction is a principal cause of delay of speed of rotation of the Earth. Flow of radial electric currents allot according to the law of Joule - Lenz, the quantity of warmth : Q = I2Rt = IUt, of thermal energy 6,92 × 1017 calories/year. This defines heating of a kernel and the Earth as a whole. In the valley of the median-Atlantic ridge having numerous volcanos, the lava flow constantly thus warm up waters of Atlantic ocean. It is a fact the warm current Gulf Stream. Thawing of a permafrost and ices of Arctic ocean, of glaciers of Greenland and Antarctica is acknowledgement: the warmth of earth defines character of thawing of glaciers and a permafrost. This is a global warming. The version of the author: the period

Popov, Aleksey

2013-04-01

132

Magnetic Field of the Earth  

NSDL National Science Digital Library

Students can learn about how the magnetic field of the earth is similar to magnets. Go to the following link: Magnetic Field of the Earth 1. What makes the earth like a magnet? 2. How do we measure magnetism? Be sure to check out the fun games and activities on this web site too!! Now click on the following link and listen to a 2 minute presentation about magnetism: Pulse Planet Next go to ...

Merritt, Mrs.

2005-10-18

133

Magnetization reversal and dynamics in non-interacting NiFe mesoscopic ring arrays  

NASA Astrophysics Data System (ADS)

The dynamics of magnetization (M) reversal and relaxation as a function of temperature (T) are reported in three non-interacting NiFe ring arrays having fixed ring outer diameter and varying widths. Additionally, the dependence of M(H) loop on the angle (?) between magnetic field (H) and the plane of the rings is addressed. The M(H) loops show a double step transition from onion state (OS) to vortex state (VS) at all temperatures (T = 3 to 300 K) and angles (? = 0 to 90°). The critical reversal fields HC1 (OS to VS) and HC2 (VS to OS) show a pronounced dependence on T, ring width, and ?. Estimation of the transverse and vortex domain wall energies reveals that the latter is favored in the OS. The OS is also the remanent state in the smallest rings and decays with the effective energy scale (U0/T) of 50 and 32 meV/K at 10 and 300 K, respectively. The robust in-plane anisotropy of magnetization of ring assemblies is established by scaling the M(H) with ?.

Kaur, M.; Husale, S.; Varandani, D.; Gupta, A.; Senguttuvan, T. D.; Mehta, B. R.; Budhani, R. C.

2014-04-01

134

THE GALACTIC MAGNETIC FIELD  

SciTech Connect

With this Letter, we complete our model of the Galactic magnetic field (GMF), by using the WMAP7 22 GHz total synchrotron intensity map and our earlier results to obtain a 13-parameter model of the Galactic random field, and to determine the strength of the striated random field. In combination with our 22-parameter description of the regular GMF, we obtain a very good fit to more than 40,000 extragalactic Faraday rotation measures and the WMAP7 22 GHz polarized and total intensity synchrotron emission maps. The data call for a striated component to the random field whose orientation is aligned with the regular field, having zero mean and rms strength Almost-Equal-To 20% larger than the regular field. A noteworthy feature of the new model is that the regular field has a significant out-of-plane component, which had not been considered earlier. The new GMF model gives a much better description of the totality of data than previous models in the literature.

Jansson, Ronnie; Farrar, Glennys R. [Center for Cosmology and Particle Physics, Department of Physics, New York University, New York, NY 10003 (United States)

2012-12-10

135

Magnetic Field Topology in Jets  

NASA Technical Reports Server (NTRS)

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

Gardiner, T. A.; Frank, A.

2000-01-01

136

The WIND magnetic field investigation  

Microsoft Academic Search

The magnetic field experiment on WIND will provide data for studies of a broad range of scales of structures and fluctuation characteristics of the interplanetary magnetic field throughout the mission, and, where appropriate, relate them to the statics and dynamics of the magnetosphere. The basic instrument of the Magnetic Field Investigation (MFI) is a boom-mounted dual triaxial fluxgate magnetometer and

R. P. Lepping; M. H. Ac?na; L. F. Burlaga; W. M. Farrell; J. A. Slavin; K. H. Schatten; F. Mariani; N. F. Ness; F. M. Neubauer; Y. C. Whang; J. B. Byrnes; R. S. Kennon; P. V. Panetta; J. Scheifele; E. M. Worley

1995-01-01

137

Low field magnetic resonance imaging  

DOEpatents

A method and system of magnetic resonance imaging does not need a large homogenous field to truncate a gradient field. Spatial information is encoded into the spin magnetization by allowing the magnetization to evolve in a non-truncated gradient field and inducing a set of 180 degree rotations prior to signal acquisition.

Pines, Alexander (Berkeley, CA); Sakellariou, Dimitrios (Billancourt, FR); Meriles, Carlos A. (Fort Lee, NJ); Trabesinger, Andreas H. (London, GB)

2010-07-13

138

Electric and magnetic fields  

NASA Technical Reports Server (NTRS)

A number of energy momentum anomalies are described that result from the use of Abraham-Lorentz electromagnetic theory. These anomalies have in common the motion of charged bodies or current carrying conductors relative to the observer. The anomalies can be avoided by using the nonflow approach, based on internal energy of the electromagnetic field. The anomalies can also be avoided by using the flow approach, if all contributions to flow work are included. The general objective of this research is a fundamental physical understanding of electric and magnetic fields which, in turn, might promote the development of new concepts in electric space propulsion. The approach taken is to investigate quantum representations of these fields.

Kaufman, H. R.; Robinson, R. S.; Etters, R. D.

1982-01-01

139

The effect of the mirror's phase shift on the magnetic bias in square ring resonators  

NASA Astrophysics Data System (ADS)

Theoretical and experimental analysis have shown that magnetic field has unavoidable effect on the performances of ring laser gyroscopes. This kind of effect has been called the magnetic bias of ring laser gyroscopes in this article. The affection of the mirror's phase shift on the magnetic bias in square ring resonators has been analyzed in this article. The following parameters which have influence on the magnetic bias such as Ar, B, g and Rsp are taken into account, where Ar is the distortion angle, B is the magnetic field, g is the phase shift of the mirror and Rsp is the difference of the reflectivity for 's' and 'p' type polarizations of light. The affection of parameters gi (i=1, 2, 3, 4) on magnetic bias is analyzed in detail, where gi are the phase shifts of four mirrors respectively. When g1=g2=g3=g4 and gi is near zero, the magnetic bias will become very samll. When g1=g2=g3=g4 and gi is near ?, the magnetic bias will become great. In practice, g1?g2?g3?g4, but, when g1+g2+g3+g4=0, the magnetic bias will become small. Especially, when g1+g2+g3+g4=0 and g1+g2=0, the magnetic bias is very small and can be ignored. In addition, when gi is near ? and g1+g2+g3+g4=4?, the magnetic bias is small. Especially, when gi is near ?, g1+g2+g3+g4=4? and g1+g2 =2?, the magnetic bias is very small and can be ignored. Based on these novel results, the magnetic bias can be eliminated by controlling the phase shifts of four mirrors accurately in film coating process. The research on the magnetic bias of ring resonators is very important for improving the performance of ring laser gyroscopes. These findings are important to the research on high precision and super high precision ring laser gyroscopes.

Kang, Zhenglong; Yuan, Jie; Chen, Meixiong; Long, Xingwu; Wang, Fei; Zhou, Jian; Yu, Xudong

2012-05-01

140

The fluxgate ring-core internal field  

Microsoft Academic Search

A large number of measured demagnetizing factors for fluxgate ring cores of a wide range of cross section shapes have been compiled from the literature and plotted against the core cross-sectional area over the squared mean core diameter. The points group close to a straight line through the origin. The local demagnetizing factor is used, and the conversion to the

F. Primdahl; Peter Brauer; José M. G. Merayo; Otto V. Nielsen

2002-01-01

141

Working principle of voltage controlled differential magnetic field sensor  

NASA Astrophysics Data System (ADS)

In this letter the authors present the experimental data illustrating the working mechanism of the high sensitivity differential magnetic field sensor. Further, the authors report for the data showing the possibility for realizing a voltage controlled magnetic field. The sensor works on the following principle. A constant voltage is applied to the ring section of the sensor at the resonance frequency which induces magnetic field in the dot section. If an external magnetic object is brought in the vicinity of the dot section, then the resulting differential magnetic field induces change in the voltage gain due to magnetoelectric effect.

Kim, Hyeoungwoo; Islam, Rashed A.; Priya, Shashank

2007-01-01

142

FAST TRACK COMMUNICATION: Electrical observation of asymmetric magnetization configurations in the vortex state of NiFe and Co rings  

Microsoft Academic Search

Anisotropic magnetoresistance (AMR) measurements have been used to probe the detailed reversal mechanism of 3 µm diameter, 15 nm thick NiFe and Co rings. In the vortex state, small changes in the resistance are associated with distortion or buckling in the section of the ring magnetized antiparallel to the applied field, and the resistance changes can be similar in magnitude

Chunghee Nam; M. D. Mascaro; B. G. Ng; C. A. Ross

2009-01-01

143

Electrical observation of asymmetric magnetization configurations in the vortex state of NiFe and Co rings  

Microsoft Academic Search

Anisotropic magnetoresistance (AMR) measurements have been used to probe the detailed reversal mechanism of 3 µm diameter, 15 nm thick NiFe and Co rings. In the vortex state, small changes in the resistance are associated with distortion or buckling in the section of the ring magnetized antiparallel to the applied field, and the resistance changes can be similar in magnitude

Chunghee Nam; M D Mascaro; B G Ng; C A Ross

2009-01-01

144

Magnets for the proton storage ring at Los Alamos  

SciTech Connect

The Proton Storage Ring at Los Alamos will store 800-MeV protons from the LAMPF accelerator. The magnets are mostly dc excited, of high quality. Special features include construction of a curved 36/sup 0/ laminated dipole core on a straight reference bar, septum magnets with sol-gel glassy insulation, and a high-gradient dipole to strip H/sup -/ to H/sup 0/ for injection.

Harvey, A.

1983-01-01

145

Hybrid permanent magnet quadrupoles for the Recycler Ring at Fermilab  

Microsoft Academic Search

Hybrid Permanent Magnet Quadrupoles are used in several applications for the Fermilab Recycler Ring and associated beam transfer lines. Most of these magnets use a 0.6096 m long iron shell and provide integrated gradients up to 1.4 T-m\\/m with an iron pole tip radius of 41.6 mm. A 58.4 mm pole radius design is also required. Bricks of 25. 4

B. C. Brown; S. M. Pruss; G. W. Foster; H. D. Glass; D. J. Harding; G. R. Jackson; M. R. May; T. H. Nicol; J.-F. Ostiguy; R. Schlabach; J. T. Volk

1997-01-01

146

Photonic Magnetic Field Sensor  

NASA Astrophysics Data System (ADS)

Small, in-line polarization rotators or isolators to reduce feedback in fiber optic links can be the basis for excellent magnetic field sensors. Based on the giant magneto-optical (GMO) or Faraday effect in iron garnets, they with a magnetic field of a few hundred Gauss, (20 mT) for an interaction length for an optical beam of a few millimeters achieve a polarization rotation or phase shift of 45 deg (1/8 cycle). When powered by a small laser diode, with the induced linear phase shift recovered at the shot noise limit, we have demonstrated sensitivities at the 3.3 nT/Hz1/2 level for frequencies from less than 1 Hz to frequencies into the high kHz range. Through further improvements; an increase in interaction length, better materials and by far the greatest factor, the addition of a flux concentrator, sensitivities at the pT/Hz1/2 level appear to be within reach. We will detail such a design and discuss the issues that may limit achieving these goals.

Wyntjes, Geert

2002-02-01

147

The Heliospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

The heliospheric magnetic field (HMF) is the extension of the coronal magnetic field carried out into the solar system by the solar wind. It is the means by which the Sun interacts with planetary magnetospheres and channels charged particles propagating through the heliosphere. As the HMF remains rooted at the solar photosphere as the Sun rotates, the large-scale HMF traces out an Archimedean spiral. This pattern is distorted by the interaction of fast and slow solar wind streams, as well as the interplanetary manifestations of transient solar eruptions called coronal mass ejections. On the smaller scale, the HMF exhibits an array of waves, discontinuities, and turbulence, which give hints to the solar wind formation process. This review aims to summarise observations and theory of the small- and large-scale structure of the HMF. Solar-cycle and cycle-to-cycle evolution of the HMF is discussed in terms of recent spacecraft observations and pre-spaceage proxies for the HMF in geomagnetic and galactic cosmic ray records.

Owens, Mathew J.; Forsyth, Robert J.

2013-11-01

148

Design of illumination system in ring field capsule endoscope  

NASA Astrophysics Data System (ADS)

This paper is researching about the illumination system in ring field capsule endoscope. It is difficult to obtain the uniform illumination on the observed object because the light intensity of LED will be changed along its angular displacement and same as luminous intensity distribution curve. So we use the optical design software which is Advanced Systems Analysis Program (ASAP) to build a photometric model for the optimal design of LED illumination system in ring field capsule endoscope. In this paper, the optimal design of illumination uniformity in the ring field capsule endoscope is from origin 0.128 up to optimum 0.603 and it would advance the image quality of ring field capsule endoscope greatly.

Jeng, Wei-De; Mang, Ou-Yang; Chen, Yu-Ta; Wu, Ying-Yi

2011-02-01

149

Magnetic Fields: Visible and Permanent.  

ERIC Educational Resources Information Center

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

Winkeljohn, Dorothy R.; Earl, Robert D.

1983-01-01

150

Inelastic magnetic scattering of polarized neutrons by a superconducting ring  

SciTech Connect

The inelastic scattering of cold neutrons by a ring leads to quantum jumps of a superconducting current which correspond to a decrease in the fluxoid quantum number by one or several units while the change in the ring energy is transferred to the kinetic energy of the scattered neutron. The scattering cross sections of transversely polarized neutrons have been calculated for a thin type-II superconductor ring, the thickness of which is smaller than the field penetration depth but larger than the electron mean free path.

Agafonov, A. I., E-mail: aai@isssph.kiae.ru [Russian Research Center Kurchatov Institute (Russian Federation)

2011-12-15

151

Electron Tunneling in Quantum Rings in an Electric Field  

NASA Astrophysics Data System (ADS)

Double concentric quantum rings (DCQRs) composed of InGaAs in a GaAs substrate utilizing a kp-perturbation single sub-band approach with the effective potential approach were theoretically studied. Two dimensional (2D) objects were considered. Statistical analysis of these DCQRs in the absents of an applied electric field were compared with these DCQRs when a static electric field was applied to them. The statistical analysis consist of taking the difference of the probability of finding an electron in the inner ring and outer ring, dividing by the sum of these probabilities.

Adelegan, Oluwafemi; Vlahovic, Branislav; Filikin, Igor; Matinyan, Sergei; Nimmo, James

2013-04-01

152

Magnetic fields of Jupiter and Saturn  

SciTech Connect

The magnetic fields of Jupiter and Saturn and the characteristics of their magnetospheres, formed by interaction with the solar wind, are discussed. The origins of both magnetic fields are associated with a dynamo process deep in the planetary interior. The Jovian magnetosphere is analogous to that of a pulsar magnetosphere: a massive central body with a rapid rotation and an associated intense magnetic field. Its most distinctive feature is its magnetodisk of concentrated plasma and particle flux, and reduced magnetic field intensity. The magnetopause near the subsolar point has been observed at radial distances ranging over 50 to 100 Jovian radii, implying a relatively compressible obstacle to solar wind flow. The composition of an embedded current sheet within the magnetic tail is believed to be influenced by volcanic eruptions and emissions from Io. Spectral troughs of the Jovian radiation belts have been interpreted as possible ring particles. The Saturnian magnetosphere appears to be more like the earth in its topology. It is mainly characterized by a dipole axis parallel to the rotational axis of the planet and a magnetic field intensity much less than expected.

Ness, N.F.

1981-01-01

153

Design of impulse magnetizing fixtures for the radial homopolar magnetization of isotropic NdFeB ring magnets  

Microsoft Academic Search

This paper is concerned with the design of homopolar impulse-magnetization fixtures for isotropic NdFeB ring magnets. It discusses the merits of various fixture topologies and describes a design methodology that employs both analytical and finite-element techniques. It illustrates the utility of the design methodology by presenting a case study of the homopolar magnetization of annular isotropic NdFeB ring magnets for

C. D. Riley; G. W. Jewell; D. Howe

2000-01-01

154

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.

Goren, Yehuda (Mountain View, CA); Mahale, Narayan K. (The Woodlands, TX)

1996-01-01

155

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

156

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

157

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

158

Reconnection of Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

Birn, J.; Priest, E. R.

2007-01-01

159

The Magnetic Field of a Model Radiation Belt, Numerically Computed  

Microsoft Academic Search

The magnetic field of a model ring-current belt encircling the earth symmetri- cally is numerically calculated, to a first approximation, for a particular model belt already discussed by Akasou and Chapman (1961a). They calculated the first approximation to the field only for points in the equatorial plane. The whole distribution of the field is here dis- cussed, and for a

Syuh-Ichi Akasofu; Joseph C. Cain; Sydney Chapman

1961-01-01

160

PERMANENT MAGNET DESIGNS WITH LARGE VARIATIONS IN FIELD STRENGTH.  

SciTech Connect

The use of permanent magnets has been investigated as an option for electron cooling ring for the proposed luminosity upgrade of RHIC. Several methods have been developed that allow a large variation in field strength. These design concepts were verified with computer simulations using finite element codes. It will be shown that the field uniformity is maintained while the field strength is mechanically adjusted.

GUPTA,R.

2004-01-21

161

Impact failure of metallic rings by a magnetic pulse technique  

NASA Astrophysics Data System (ADS)

Metallic rings made of D16 aluminum alloy are studied upon the application of a distributed radial load by a magnetic pulse technique. Two approaches making it possible to decrease the period of the sin-wave load by seven and fifty times are developed. In addition, they allow one to determine the instant of rupture of the ring from a flash arising at rupture with the help of a photodetector. Simultaneously, the load pulse and a signal from the photodetector are displayed with a digital oscilloscope. It is shown that, when the load pulse shortens, the ductile component of fracture declines and the samples fail in a more brittle manner.

Morozov, V. A.; Petrov, Yu. V.; Lukin, A. A.; Kats, V. M.; Udovik, A. G.; Atroshenko, S. A.; Gribanov, D. A.; Fedorovsky, G. D.

2011-06-01

162

Matter in strong magnetic fields  

Microsoft Academic Search

The properties of matter are drastically modified by strong magnetic fields, B>>m2ee3c\\/h3=2.35×109 G (1 G=10-4 T), as are typically found on the surfaces of neutron stars. In such strong magnetic fields, the Coulomb force on an electron acts as a small perturbation compared to the magnetic force. The strong-field condition can also be mimicked in laboratory semiconductors. Because of the

Dong Lai

2001-01-01

163

Two-dimensional equilibrium of field-reversed ion rings  

NASA Astrophysics Data System (ADS)

The axially symmetric equilibrium of intense ion rings is examined for field-reversed configurations. A rigid rotor model is assumed for the ion distribution, with background or accompanying electrons providing space charge neutralization. This equilibrium configuration is described by three macroscopic quantities, the ring particle density, the ring pressure, and the azimuthal component of the vector potential. Within the Vlasov-Maxwell framework, these quantities must satisfy Ampere's law and the pressure balance equation. The system of equations is completed assuming that the pressure and the density satisfy a general power law (equation of state). The equilibrium solution for intense ion layers (one dimensional problem) is examined in the general case, but for intense ion rings (two dimensional problem) the analysis is restricted to the uniform particle density case. The sharp boundary that separates the constant density and zero density regions is approximated by a stepwise function and determined for several values of the ring parameters.

Ludwig, G. O.

1980-05-01

164

Convectively stable pressure profile in magnetic confinement systems with internal rings  

SciTech Connect

A convectively stable pressure profile in a long multiple-mirror (corrugated) magnetic confinement system with internal current-carrying rings is calculated. The plasma energy content in the axial region can be increased by using an internal ring that reverses the on-axis magnetic field direction and gives rise to an average magnetic well near the axis. The pressure profile in the outer region-outside the magnetic well-is considered in detail. It is shown that, in the radial pressure profile, a pedestal can be formed that leads to a higher pressure drop between the center and the plasma edge. The pressure profile is calculated from the Kruskal-Oberman criterion-a necessary and sufficient condition for the convective stability of a collisionless plasma. The revealed pedestal arises near the boundary of the average magnetic well in the region of the smallest but alternating-sign curvature of the magnetic field lines due to a break in the convectively stable pressure profile. Such a shape of the stable pressure profile can be attributed to the stabilizing effect of the alternating-sign curvature of the field lines in the multiple-mirror magnetic confinement systems under consideration.

Tsventoukh, M. M. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

2010-06-15

165

Current density waves in open mesoscopic rings driven by time-periodic magnetic fluxes.  

PubMed

Quantum coherent transport through open mesoscopic Aharonov-Bohm rings (driven by static fluxes) have been studied extensively. Here, by using quantum waveguide theory and the Floquet theorem we investigate the quantum transport of electrons along an open mesoscopic ring threaded by a time-periodic magnetic flux. We predicate that current density waves could be excited along such an open ring. As a consequence, a net current could be generated along the lead with only one reservoir, if the lead additionally connects to such a normal-metal loop driven by the time-dependent flux. These phenomena could be explained by photon-assisted processes, due to the interaction between the transported electrons and the applied oscillating external fields. We also discuss how the time-average currents (along the ring and the lead) depend on the amplitude and frequency of the applied oscillating fluxes. PMID:21393680

Yan, Cong-Hua; Wei, Lian-Fu

2010-05-12

166

Current density waves in open mesoscopic rings driven by time-periodic magnetic fluxes  

NASA Astrophysics Data System (ADS)

Quantum coherent transport through open mesoscopic Aharonov-Bohm rings (driven by static fluxes) have been studied extensively. Here, by using quantum waveguide theory and the Floquet theorem we investigate the quantum transport of electrons along an open mesoscopic ring threaded by a time-periodic magnetic flux. We predicate that current density waves could be excited along such an open ring. As a consequence, a net current could be generated along the lead with only one reservoir, if the lead additionally connects to such a normal-metal loop driven by the time-dependent flux. These phenomena could be explained by photon-assisted processes, due to the interaction between the transported electrons and the applied oscillating external fields. We also discuss how the time-average currents (along the ring and the lead) depend on the amplitude and frequency of the applied oscillating fluxes.

Yan, Cong-Hua; Wei, Lian-Fu

2010-05-01

167

Magnetic fields around evolved stars  

NASA Astrophysics Data System (ADS)

A number of mechanisms, such as magnetic fields, (binary) companions and circumstellar disks have been suggested to be the cause of non-spherical PNe and in particular collimated outflows. This work investigates one of these mechanisms: the magnetic fields. While MHD simulations show that the fields can indeed be important, few observations of magnetic fields have been done so far. We used the VLBA to observe five evolved stars, with the goal of detecting the magnetic field by means of water maser polarization. The sample consists in four AGB stars (IK Tau, RT Vir, IRC+60370 and AP Lyn) and one pPN (OH231.8+4.2). In four of the five sources, several strong maser features were detected allowing us to measure the linear and/or circular polarization. Based on the circular polarization detections, we infer the strength of the component of the field along the line of sight to be between ~30 mG and ~330 mG in the water maser regions of these four sources. When extrapolated to the surface of the stars, the magnetic field strength would be between a few hundred mG and a few Gauss when assuming a toroidal field geometry and higher when assuming more complex magnetic fields. We conclude that the magnetic energy we derived in the water maser regions is higher than the thermal and kinetic energy, leading to the conclusion that, indeed, magnetic fields probably play an important role in shaping Planetary Nebulae.

Leal-Ferreira, M.; Vlemmings, W.; Kemball, A.; Amiri, N.; Maercker, M.; Ramstedt, S.; Olofsson, G.

2014-04-01

168

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

169

How Does the Ring Current and the Inner Magnetospheric Electric Fields Control Each Other?  

NASA Astrophysics Data System (ADS)

The ring current plays a unique role in the production of the electric field of the inner magnetosphere. Pressure and magnetic field gradients are associated with electrical currents that close through the ionosphere, responsible for maintaining the electric field of the inner magnetosphere in a self-consistent way. This type of global magnetosphere-ionosphere coupling is currently modeled by many groups. Global energetic neutral atom (ENA) observations of the ring current provide the reality against which the models are validated. Data-model comparison is the method by which knowledge of the inner magnetospheric electric field is obtained. The results depend on how wide of an energy range and angular resolution the data can provide. The High- and Medium Energy Neutral Atom (MENA and HENA) imagers on board the IMAGE spacecraft has provided us with almost six years of data from ~1 keV to about 200 keV for hydrogen and ~50 to about 300 keV for oxygen. We aim at retrieving the morphology (local-time and radial position of the ring current ion intensity peak) of the ring current for the full energy range for most of the mission and statiscally bin the location as a function of solar wind conditions and season. We also investigate how the ring current morphology depends on cross-polar cap potential, auroral oval size, and ring current strength.

Brandt, P. C.; Zheng, Y.; Demajistre, R.; Mitchell, D. G.; Roelof, E. C.; Jahn, J.-; Henderson, M. G.; Pollock, C.

2006-05-01

170

Magnetic response to applied electrostatic field in external magnetic field  

NASA Astrophysics Data System (ADS)

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

Adorno, T. C.; Gitman, D. M.; Shabad, A. E.

2014-04-01

171

The Extended Coronal Magnetic Field.  

National Technical Information Service (NTIS)

The coronal magnetic field should contain many field lines connecting the photosphere to interplanetary space. A sharp boundary separates two adjacent sectors of opposite polarity. The large-scale structure of the corona is related to the photospheric sec...

J. M. Wilcox

1970-01-01

172

Flares and Changing Magnetic Fields.  

National Technical Information Service (NTIS)

One of the principal objectives of the magnetic field observing program at the Sacramento Peak Observatory has been to discover whether there are any observable changes in the photospheric fields at the time of flares.

D. M. Rust

1972-01-01

173

Ring current-energy balance during intense magnetic storms  

NASA Astrophysics Data System (ADS)

The energy-rate balance that governs the storm-time ring current is analyzed in terms of the Burton-McPherron-Russell equation (Burton et al., 1975). This is a first order differential equation relating the time variation of the pressure corrected Dst index, with the energy input to the magnetosphere. Based on the Burton et al. equation, we have analyzed in detail the geomagnetic storm of February 11, 2004. The energy input is taken proportional to the interplanetary electric field, Q(t) = ?BsV, where Bs is the southward component of the interplanetary magnetic field in GSM coordinates, V is the flow speed of the solar wind and ? a constant. The equation is integrated using the OMNI-combined interplanetary data and, the value of the decay time is estimated from a best fit of the response to the observed curve. For this storm we also use a rectangular approximation for the energy input function, thus allowing an analytical solution of the Burton et al. equation. The results from this approximation are then compared to the numerical solution. The study is also extended to the geomagnetic storm of April 22, 2001. This analysis seems to indicate that the Burton et al. equation should contain also a corrective term proportional to the second time derivative of the Dst index. This corrective term might become important for intense storms, with an effect of counteracting the growth of |Dst| before the energy input from the interplanetary medium declines, such that the value of |Dst| starts to decrease instead of continuing to grow.

Clua de Gonzalez, A. L.; Gonzalez, W. D.

2013-12-01

174

Dresden pulsed magnetic field facility  

NASA Astrophysics Data System (ADS)

We report on the status quo of the Dresden High Magnetic Field Laboratory (HLD) that is being set up at the Forschungszentrum Dresden-Rossendorf in Dresden, Germany. First pulsed-field coils reaching up to 71 T with a pulse duration of about 100 ms have been designed, constructed, and tested. A two-coil 100 T magnet and a long-pulse (1000 ms) 60 T magnet are under construction. Electrical-transport and magnetization experiments are running routinely in the pilot laboratory at the IFW Dresden. The feasibility of NMR experiments in pulsed-field environments has been proven.

Wosnitza, J.; Bianchi, A. D.; Freudenberger, J.; Haase, J.; Herrmannsdörfer, T.; Kozlova, N.; Schultz, L.; Skourski, Y.; Zherlitsyn, S.; Zvyagin, S. A.

2007-03-01

175

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

2013-08-01

176

Persistent current and low-field magnetic susceptibility in one channel mesoscopic loops and Möbius strips  

Microsoft Academic Search

I study persistent current and low-field magnetic susceptibility of one-dimensional normal metal mesoscopic rings and Möbius strips threaded by slowly varying magnetic flux phi. In strictly one-channel perfect rings, current shows saw-tooth-like variation with phi for the cases where the rings contain odd and even number of electrons Ne respectively. But in disordered rings, current shows a continuous variation with

Santanu K. Maiti

2006-01-01

177

Persistent current and low-field magnetic susceptibility in one channel mesoscopic loops and Möbius strips  

Microsoft Academic Search

I study persistent current and low-field magnetic susceptibility of one-dimensional normal metal mesoscopic rings and Möbius strips threaded by slowly varying magnetic flux ?. In strictly one-channel perfect rings, current shows saw-tooth-like variation with ? for the cases where the rings contain odd and even number of electrons Ne respectively. But in disordered rings, current shows a continuous variation with

Santanu K Maiti

2006-01-01

178

Plasma rotation by electric and magnetic fields in a discharge cylinder  

Microsoft Academic Search

A theoretical model for an electric discharge consisting of a spatially diverging plasma sustained electrically between a small ring cathode and a larger ring anode in a cylindrical chamber with an axial magnetic field is developed to study the rotation of the discharge plasma in the crossed electric and magnetic fields. The associated boundary-value problem for the coupled partial differential

H. E. Wilhelm; S. H. Hong

1977-01-01

179

Plasma rotation by electric and magnetic fields in a discharge cylinder  

Microsoft Academic Search

A theoretical model for an electric discharge is developed consisting of a spatially diverging plasma sustained electrically between a small ring cathode and a larger ring anode in a cylindrical chamber with an axial magnetic field, to study the rotation of the discharge plasma in the crossed electric and magnetic fields. The associated boundary-value problem for the coupled partial differential

H. E. Wilhelm; S. H. Hong

1977-01-01

180

Magnetic field sensor by orthoferrites  

Microsoft Academic Search

Among all ferromagnets orthoferrites possess the highest velocities of domain wall motion. Dynamic properties of a magnetic field meter based on domain wall dynamics in yttrium orthoferrite are reported. It is shown that at low driving magnetic fields and at frequencies up to the MHz band domain wall dynamics can be adequately described by linear equations. In a wide range

Y. S. Didosyan; V. Y. Barash; N. A. Bovarin; H. Hauser; P. Fulmek

1997-01-01

181

THE CLUSTER MAGNETIC FIELD INVESTIGATION  

Microsoft Academic Search

The Cluster mission provides a new opportunity to study plasma processes and structures in the near-Earth plasma environment. Four-point measurements of the magnetic field will enable the analysis of the three dimensional structure and dynamics of a range of phenomena which shape the macroscopic properties of the magnetosphere. Difference measurements of the magnetic field data will be combined to derive

A. Balogh; M. W. Dunlop; S. W. H. Cowley; D. J. Southwood; J. G. Thomlinson; K. H. Glassmeier; G. Musmann; H. Luhr; S. Buchert; M. H. AcuÑA; D. H. Fairfield; J. A. Slavin; W. Riedler; K. Schwingenschuh; M. G. Kivelson

1997-01-01

182

Non-disjunction mutations in Drosophila exposed to magnetic fields  

NASA Astrophysics Data System (ADS)

The frequency of XO mutations in Drosophila melanogaster was significantly higher than normal in magnetic field exposed, immature males, than in exposed, mature males. Mutation levels increased with magnetic field strength. Intercellular rings of black magnetic particles were formed in the high magnetic flux region of dorsally exposed, early stage pupae and to a lesser degree in the abdomen of young adult females. Orientation of minute, chromosome associated, magnetic domains within the microenvironment of the developing organism was believed to alter oxidative processes within maturing X+ sperm which during fertilization were incompatible with and destructive to an Xw chromosome in the zygote.

Levengood, W. C.

1987-09-01

183

Dresden pulsed magnetic field facility  

Microsoft Academic Search

We report on the status quo of the Dresden High Magnetic Field Laboratory (HLD) that is being set up at the Forschungszentrum Dresden-Rossendorf in Dresden, Germany. First pulsed-field coils reaching up to 71T with a pulse duration of about 100ms have been designed, constructed, and tested. A two-coil 100T magnet and a long-pulse (1000ms) 60T magnet are under construction. Electrical-transport

J. Wosnitza; A. D. Bianchi; J. Freudenberger; J. Haase; T. Herrmannsdörfer; N. Kozlova; L. Schultz; Y. Skourski; S. Zherlitsyn; S. A. Zvyagin

2007-01-01

184

Sub-nanosecond resolution x-ray magnetic circular dichroism photoemission electron microscopy of magnetization processes in a permalloy ring  

NASA Astrophysics Data System (ADS)

Fast magnetization processes in a microstructured permalloy ring with 80 µm o.d. and 30 nm thickness have been observed by photoemission electron microscopy exploiting x-ray magnetic circular dichroism as the magnetic contrast mechanism. As a high speed probe we employed synchrotron radiation pulses at the ESRF (Grenoble) operated in 16-bunch mode, yielding photon pulses of 105 ps FWHM with a period of 176 ns. Fast magnetic field pulses have been generated by means of current pulses through coplanar waveguides with the magnetic structure being lithographically prepared on their surface. A stroboscopic pump-probe set-up with a variable time delay between the field pulse and photon pulse allowed us to take snapshots of the dynamic response of the magnetic domain structure. We observed coherent magnetization rotation during the leading edge part of the field pulse, the formation of a characteristic domain pattern ('onion state') in the plateau region of the pulse and the fast formation of a striped domain pattern (incoherent magnetization rotation) during the trailing edge part of the field pulse. A numerical simulation confirmed essential features of the stroboscopic image series.

Neeb, D.; Krasyuk, A.; Oelsner, A.; Nepijko, S. A.; Elmers, H. J.; Kuksov, A.; Schneider, C. M.; Schönhense, G.

2005-04-01

185

Superconductivity at High Magnetic Fields  

Microsoft Academic Search

Using pulsed-magnetic-field techniques, we have studied the magnetic-field-induced superconducting transitions of alloys in the systems Ti-V, Ti-Nb, Ti-Ta, Ti-Mo, Zr-Nb, Hf-Nb, Hf-Ta, U-Nb, and U-Mo. For concentrated alloys the low-current-density resistive critical field Hr(J<~10 A\\/cm2) is nearly independent of the amount of cold working and the relative orientations of magnetic field, current, and anisotropic defect structure. The observed values of

T. G. Berlincourt; R. R. Hake

1963-01-01

186

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

187

High latitude solar magnetic fields  

NASA Technical Reports Server (NTRS)

Kitt Peak magnetograms are used to measure polar magnetic fields. The polar mean absolute field increases at the same time as the polar mean field decreases. That is, the polar mean absolute field varies in phase with solar activity, in contrast to the out of phase variation of the mean polar field. It is found that the polar fields have a large bipolar component even at solar minimum, with a magnitude equal to that found at low latitudes outside the active latitude bands.

Murray, Norman

1992-01-01

188

Rings  

SciTech Connect

The essence of vortex physics is that at certain low-energy scales elementary excitations of a point particle theory can behave like strings rather than particles. Vortices are the resulting string-like solutions; their thickness sets the distance scale beyond which physics is string-like rather than particle-like. String degrees of freedom are massless in the sense that excitations on a string can have an arbitrarily low frequency. Non-string degrees of freedom correspond to massive particles and are absent from the low energy spectrum. This article considers only field theories with vortices at low energies. The possible existence of a class of solitons in these vortex theories will be discussed. They are vortex rings: they are localized and finite in energy, and able to carry the quantum numbers of point particles. Rings are thus particle-like solutions of a vortex theory, which is itself a limit of a point particle field theory.

Davis, R.L.

1989-01-01

189

Deformation of a magnetic dipole field by trapped particles  

Microsoft Academic Search

A model for the stormtime ring current, based on a self-consistent steady state solution of Vlasov's and Maxwell's equations for a finite pressure plasma immersed in the earth's dipole field, is described. The particular choice of the particle distribution function is justified by the good fit to OGO 3 particle energy density and the Explorer 26 magnetic field measurements made

K. Lackner

1970-01-01

190

PREPROCESSING MAGNETIC FIELDS WITH CHROMOSPHERIC LONGITUDINAL FIELDS  

SciTech Connect

Nonlinear force-free field (NLFFF) extrapolation is a powerful tool for the modeling of the magnetic field in the solar corona. However, since the photospheric magnetic field does not in general satisfy the force-free condition, some kind of processing is required to assimilate data into the model. In this paper, we report the results of new preprocessing for the NLFFF extrapolation. Through this preprocessing, we expect to obtain magnetic field data similar to those in the chromosphere. In our preprocessing, we add a new term concerning chromospheric longitudinal fields into the optimization function proposed by Wiegelmann et al. We perform a parameter survey of six free parameters to find minimum force- and torque-freeness with the simulated-annealing method. Analyzed data are a photospheric vector magnetogram of AR 10953 observed with the Hinode spectropolarimeter and a chromospheric longitudinal magnetogram observed with SOLIS spectropolarimeter. It is found that some preprocessed fields show the smallest force- and torque-freeness and are very similar to the chromospheric longitudinal fields. On the other hand, other preprocessed fields show noisy maps, although the force- and torque-freeness are of the same order. By analyzing preprocessed noisy maps in the wave number space, we found that small and large wave number components balance out on the force-free index. We also discuss our iteration limit of the simulated-annealing method and magnetic structure broadening in the chromosphere.

Yamamoto, Tetsuya T. [Solar-Terrestrial Environment Laboratory, Nagoya University, Chikusa-ku, Nagoya 464-8601 (Japan); Kusano, K., E-mail: tyamamot@stelab.nagoya-u.ac.jp [Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Kanagawa 236-0001 (Japan)

2012-06-20

191

Magnetic field structure evolution in rotating magnetic field plasmas  

SciTech Connect

A study of magnetic field structure evolution during 40-ms plasma discharge has been performed in a new device with 80 cm long/40 cm diameter cylindrical chamber, in which a plasma current I{sub p}{approx_equal}2 kA was driven and sustained by a rotating magnetic field. The main focus of the experiments is on how the changes in externally applied magnetic field affect the current profile and magnetic field in plasma. During plasma discharge, a pulse current was briefly fed to a magnetic coil located at the midplane (middle coil). The magnetic field in cross section of plasma was scanned with pickup probes. Two regimes were studied: without and with an external toroidal field (TF) produced by axial I{sub z} current. With a relatively small current (I{sub m} {<=} 600 A) in the middle coil, the plasma current is boosted up to 5 kA. The magnetic flux surfaces become extended along the axial Z direction, sometimes with the formation of doublet shape plasma. The regime without TF appears to be less stable, presumably due to the reversal of plasma current in central area of plasma column.

Petrov, Yuri; Yang Xiaokang; Huang, T.-S. [Prairie View A and M University, Prairie View, Texas 77446 (United States)

2008-07-15

192

Spinning magnetic fields  

Microsoft Academic Search

A possible electrical charge model based on the spinning time invariant point magnetic dipole within the framework of classical physics is outlined, as suggested by the admissible circular trajectory of a test charge around the magnetic dipole in its equatorial plane. The model depends on the moving force line hypothesis which has been claimed to have been disproved. The controversy

Jovan Djuric

1975-01-01

193

Magnetic fields in galaxy clusters  

NASA Astrophysics Data System (ADS)

While it is established that galaxy clusters host magnetic fields of the order of a few ?G, both, their origin as well as their role in the intracluster medium (ICM) remain unclear. I will review the observational evidence for magnetic fields in galaxy clusters and present various lines of research that study the effects of magnetic fields in the ICM. Magnetic fields affect the way in which galaxies interact with the ICM, they may render the ICM buoyantly unstable in the presence of anisotropic thermal conduction, and they affect the thermal structure of the gas in cluster cores. Finally, opportunities for future research in this field, in particular in light of new radio telescopes is highlighted.

Brüggen, M.

2013-06-01

194

Preflare magnetic and velocity fields  

NASA Technical Reports Server (NTRS)

A characterization is given of the preflare magnetic field, using theoretical models of force free fields together with observed field structure to determine the general morphology. Direct observational evidence for sheared magnetic fields is presented. The role of this magnetic shear in the flare process is considered within the context of a MHD model that describes the buildup of magnetic energy, and the concept of a critical value of shear is explored. The related subject of electric currents in the preflare state is discussed next, with emphasis on new insights provided by direct calculations of the vertical electric current density from vector magnetograph data and on the role of these currents in producing preflare brightenings. Results from investigations concerning velocity fields in flaring active regions, describing observations and analyses of preflare ejecta, sheared velocities, and vortical motions near flaring sites are given. This is followed by a critical review of prevalent concepts concerning the association of flux emergence with flares

Hagyard, M. J.; Gaizauskas, V.; Chapman, G. A.; Deloach, A. C.; Gary, G. A.; Jones, H. P.; Karpen, J. T.; Martres, M.-J.; Porter, J. G.; Schmeider, B.

1986-01-01

195

SCALING LAW FOR THE IMPACT OF MAGNET FRINGE FIELDS.  

SciTech Connect

A general scaling law can be derived for the relative momentum deflection produced on a particle beam by fringe fields, to leading order. The formalism is applied to two concrete examples, for magnets having dipole and quadrupole symmetry. During recent years, the impact of magnet fringe fields is becoming increasingly important for rings of relatively small circumference but large acceptance. A few years ago, following some heuristic arguments, a scaling law was proposed [1], for the relative deflection of particles passing through a magnet fringe-field. In fact, after appropriate expansion of the magnetic fields in Cartesian coordinates, which generalizes the expansions of Steffen [2], one can show that this scaling law is true for any multipole magnet, at leading order in the transverse coefficients [3]. This paper intends to provide the scaling law to estimate the impact of fringe fields in the special cases of magnets with dipole and quadrupole symmetry.

WEI,J.; PAPAPHILIPPOU,Y.; TALMAN,R.

2000-06-30

196

Magnetic Field Effect Transistors.  

National Technical Information Service (NTIS)

It has been demonstrated that magnetic Cr02 can be selectively deposited on semiconductor substrates and polymide resin plastics with feature resolution smaller than micron. In addition, hard coatings have been fabricated to protect active devices as well...

J. T. Spencer P. A. Dowben

1990-01-01

197

The Design and Construction of Permanent Magnet Lambertsons for the Recycler Ring at Fermilab  

Microsoft Academic Search

This paper will show and discuss the simple design of a permanent magnet Lambertson used to extract and inject 8 Gev. beam from the Main Injector Ring to the Recycler Ring, and from the Recycler Ring to the Main Injector. Pictures will show how four different magnets used to form the injection and extraction double dog legs are made from

M. P. May; G. W. Foster; G. J. Jackson; T. L. Schmitz

1997-01-01

198

Large Dayside Geosynchronous Magnetic Field Compressions: Model Expectations vs. Observations  

Microsoft Academic Search

The geosynchronous magnetic field has been measured routinely for nearly 40 years. It responds to the magnetosphere's major current systems including the magnetopause current, the ring current, field-aligned currents, and the tail current. As a consequence, these measurements are valuable for probing many aspects of solar wind-magnetosphere coupling. In this presentation we will show puzzling observations of large-amplitude dayside magnetic

H. J. Singer; M. J. Wiltberger; T. G. Onsager; P. T. Loto'Ainu

2008-01-01

199

Magnetic Fields in the Sun.  

National Technical Information Service (NTIS)

The observed properties of solar magnetic fields are reviewed, with particular reference to the complexities imposed on the field by motions of the highly conducting gas. Turbulent interactions between gas and field lead to heating or cooling of the gas a...

D. J. Mullan

1974-01-01

200

Evolution of ring-field systems in microlithography  

NASA Astrophysics Data System (ADS)

Offner's ring-field all-reflecting triplet was the first successful projection system used in microlithography. It evolved over several generations, increasing NA and field size, reducing the feature sizes printed from three down to one micron. Because of its relative simplicity, large field size and broad spectral bandwidth it became the dominant optical design used in microlithography until the early 1980's, when the demise of optical lithography was predicted. Rumours of the death of optics turned out to be exaggerated; what happened instead was a metamorphosis to more complex optical designs. A reduction ring-field system was developed, but the inevitable loss of concentricity led to a dramatic increase in complexity. Higher NA reduction projection optics have therefore been full-field, either all-refracting or catadioptric using a beamsplitter and a single mirror. At the present time, the terminal illness of optical lithography is once again being prognosed, but now at 0.1 micro feature sizes early in the next millenium. If optics has a future beyond that, it lies at wavelengths below the practical transmission cut-off of all refracting materials. Scanning all-reflecting ring-field systems are therefore poised for a resurgence, based on their well-established advantage of rotational symmetry and consequent small aberration variations over a small, annular field. This paper explores some such designs that potentially could take optical lithography down to the region of 0.025 micron features.

Williamson, David M.

1998-09-01

201

The polar heliospheric magnetic field  

NASA Technical Reports Server (NTRS)

It is suggested that the polar heliospheric magnetic field, at large heliocentric distances, may deviate considerably from the generally accepted Archimedean spiral. Instead, it is suggested that the large-scale field near the poles may be dominated by randomly-oriented transverse magnetic fields with magnitude much larger than the average spiral. The average vector field is still the spiral, but the average magnitude may be much larger. In addition, the field direction is transverse to the radial direction most of the time instead of being nearly radial. This magnetic-field structure has important consequences for the transport of cosmic rays. Preliminary model calculations suggest changes in the radial gradient of galactic cosmic rays which may improve agreement with observations.

Jokipii, J. R.; Kota, J.

1989-01-01

202

Theorem on magnet fringe field.  

National Technical Information Service (NTIS)

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)...

J. Wei R. Talman

1995-01-01

203

Majorana Neutrinos and Magnetic Fields.  

National Technical Information Service (NTIS)

It is stressed that if neutrinos are massive they are probably of Majorana type. This implies that their magnetic moment form factor vanishes identically so that the previously discussed phenomenon of spin rotation in a magnetic field would not appear to ...

J. Schechter J. W. F. Valle

1981-01-01

204

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

205

Neutron in Strong Magnetic Fields  

NASA Astrophysics Data System (ADS)

A relativistic world-line Hamiltonian for strongly interacting 3q systems in a magnetic field is derived from the path integral for the corresponding Green's function. The neutral baryon Hamiltonian in the magnetic field obeys the pseudomomentum conservation and allows a factorization of the c.m. and internal motion. The resulting expression for the baryon mass in the magnetic field is written explicitly with the account of hyperfine, one pion exchange, and one gluon exchange (color Coulomb) interaction. The neutron mass is fast decreasing with the magnetic field, losing 1/2 of its value at eB ˜0.25 GeV2 and is nearly zero at eB ˜0.5 GeV2. Possible physical consequences of the calculated mass trajectory of the neutron, Mn(B), are presented and discussed.

Andreichikov, M. A.; Kerbikov, B. O.; Orlovsky, V. D.; Simonov, Yu. A.

2014-04-01

206

Fast and reliable kicker magnets for the SLC damping rings  

SciTech Connect

The design, construction, and operation of a kicker magnet with superior electromagnetic performance and greatly improved radiation tolerance is described. A short flux return of high mu ferrite improves the field strength and linearity with current, and novel metallic field-confining structures minimize the inductance. An 8-cell structure with capacitance integrated into each cell makes the magnet a nearly perfect transmission line. The capacitor dielectric is 1 cm thick alumina-loaded epoxy, processed to eliminate air voids, and cast in a multiple step procedure developed to circumvent epoxy shrinkage. The magnet operates with pulses of up to 40 kV and 3.2 kA at 120 Hz, with magnet transit times of less than 35 nsec and field rise and fall times of less than 60 nsec.

Mattison, T.S.; Cassel, R.L.; Donaldson, A.R.; Gross, G.

1995-06-01

207

Poloidal field superconducting ring coil case and support structure design  

SciTech Connect

Conceptual design studies have been carried out at the Fusion Engineering Design Center (FEDC) on a succession of tokamak devices. In order to quickly assess the technical feasibility and to estimate the costs of competing poloidal field (PF) systems, it is desirable to develop simple, but accurate, rules for the structural design of these coils. In this paper we describe the rules developed for superconducting ring coils and illustrate their application to a specific example. This methodology may be easily adapted to resistive ring coil design.

Hooper, R.J.; Hunter, B.L.

1983-01-01

208

Solar magnetic fields and convection  

Microsoft Academic Search

The flux-rope model of solar magnetic fields is developed further by the use of a variety of observational results.(i)It is confirmed that magnetic fields emerging to form active regions are already in the form of helically twisted flux ropes.(ii)A flux rope is not a homogeneous structure but is made up of hundreds or thousands of flux fibres. These are individually

J. H. Piddington

1976-01-01

209

Solar magnetic fields: an introduction  

Microsoft Academic Search

The magnetic field of the Sun is thought to be produced by a dynamo in the solar interior and exhibits its greatest influence\\u000a on the solar plasma in the tenuous outer layers of the solar atmosphere, where it lies at the heart of almost every major\\u000a phenomenon. Most direct observations of the magnetic field are restricted to the solar surface,

S. K. Solanki

210

Spontaneous thermal magnetic field fluctuation  

SciTech Connect

In recent days, the relativistic version of the classic Weibel instability received renewed attention for its potential role as a mechanism to generate cosmic magnetic fields. However, one of the key conceptual foundations in association with the Weibel instability has not been addressed in the literature. Namely, the spontaneous emission of magnetic field fluctuation, which is supposed to provide the seed perturbation for the Weibel instability, has not been adequately discussed. The present Brief Communication addresses this issue.

Yoon, Peter H. [Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States)

2007-06-15

211

Operational experience with SLC damping ring kicker magnets  

SciTech Connect

The damping ring kickers for the SLAC Linear Collider must provide 7 mrad kicks to 1.2 GeV beams with 60 nsec rise and fall times and fit in a 50 cm length around a 21 mm diameter ceramic beam pipe. This requires that they operate at up to 40 KV. The construction and operation of two types of quasi-coaxial ferrite magnet potted with RTV silicone rubber is discussed. Production yield has been improved by changes in RTV degassing, transfer, and cure. Operation lifetime is dominated by voltage, radiation, and thermal cycling. 4 refs., 2 figs.

Mattison, T.; Cassel, R.; Donaldson, A.; Gross, G.; Harvey, A.

1991-05-01

212

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

213

Optical sensor of magnetic fields  

DOEpatents

An optical magnetic field strength sensor for measuring the field strength of a magnetic field comprising a dilute magnetic semi-conductor probe having first and second ends, longitudinally positioned in the magnetic field for providing Faraday polarization rotation of light passing therethrough relative to the strength of the magnetic field. Light provided by a remote light source is propagated through an optical fiber coupler and a single optical fiber strand between the probe and the light source for providing a light path therebetween. A polarizer and an apparatus for rotating the polarization of the light is provided in the light path and a reflector is carried by the second end of the probe for reflecting the light back through the probe and thence through the polarizer to the optical coupler. A photo detector apparatus is operably connected to the optical coupler for detecting and measuring the intensity of the reflected light and comparing same to the light source intensity whereby the magnetic field strength may be calculated.

Butler, M.A.; Martin, S.J.

1986-03-25

214

Magnetic confinement in a ring-cusp ion thruster discharge plasma  

SciTech Connect

An experimental investigation, in conjunction with a volume averaged analytical model, has been developed to improve the confinement and production of the discharge plasma for plasma thrusters and ion sources. The research conducted explores the discharge performance of a ring-cusp ion source based on the magnetic field configuration, geometry, and power level. Analytical formulations for electron and ion confinement are developed to predict the ionization efficiency for a given discharge chamber design. Explicit determination of discharge loss and volume averaged plasma parameters are obtained via a series of experimental measurements on a ring-cusp NASA Solar Technology Application Readiness (NSTAR) ion thruster to assess the validity of the analytical model. Measurements of the discharge loss with multiple magnetic field configurations compare well with plasma parameter predictions for propellant utilizations between 80% and 95%. The results indicate that increasing the magnetic strength of the first closed magnetic contour line reduces Maxwellian electron diffusion and electrostatically confines the ion population and subsequent loss to the anode wall. The results also indicate that increasing the strength and minimizing the area of the magnetic cusps improves primary electron confinement, increasing the probability of an ionization collision prior to loss at the cusp.

Sengupta, Anita [NASA Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, California 91109 (United States)

2009-05-01

215

Fabrication and test of prototype ring magnets for the ALS (Advanced Light Source)  

SciTech Connect

Prototype Models for the Advanced Light Source (ALS) Booster Dipole, Quadrupole and Sextupole and the Storage Ring Gradient Magnet, Quadrupole and Sextupole have been constructed. The Booster Magnet Prototypes have been tested. The Storage Ring Magnets are presently undergoing tests and magnetic measurements. This paper reviews the designs and parameters for these magnets, briefly describes features of the magnet designs which respond to the special constraints imposed by the requirements for both accelerator rings, and reviews some of the results of magnet measurements for the prototype. 13 refs., 7 figs., 1 tab.

Tanabe, J.; Avery, R.; Caylor, R.; Green, M.I.; Hoyer, E.; Halbach, K.; Hernandez, S.; Humphries, D.; Kajiyama, Y.; Keller, R.; Low, W.; Marks, S.; Milburn, J.; Yee, D.

1989-03-01

216

A RING OF POLARIZED LIGHT: EVIDENCE FOR TWISTED CORONAL MAGNETISM IN CAVITIES  

SciTech Connect

Coronal prominence cavities may be manifestations of twisted or sheared magnetic fields capable of storing the energy required to drive solar eruptions. The Coronal Multi-Channel Polarimeter (CoMP), recently installed at Mauna Loa Solar Observatory, can measure polarimetric signatures of current-carrying magnetohydrodynamic (MHD) systems. For the first time, this instrument offers the capability of daily full-Sun observations of the forbidden lines of Fe XIII with high enough spatial resolution and throughput to measure polarimetric signatures of current-carrying MHD systems. By forward-calculating CoMP observables from analytic MHD models of spheromak-type magnetic flux ropes, we show that a predicted observable for such flux ropes oriented along the line of sight is a bright ring of linear polarization surrounding a region where the linear polarization strength is relatively depleted. We present CoMP observations of a coronal cavity possessing such a polarization ring.

Dove, J. B. [Metropolitan State College of Denver, P.O. Box 173362, Denver, CO 80217-3362 (United States); Gibson, S. E.; Rachmeler, L. A.; Tomczyk, S.; Judge, P. [HAO, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 (United States)

2011-04-10

217

Magnetic field analysis and optimal design of magnetic bearing  

Microsoft Academic Search

Magnetic field distribution of a radial magnetic bearing with sixteen-pole was analyzed by using finite element method. It was verified by magnetic field measurement. Magnetic bearing structure was optimized based on finite element analysis (FEA) and magnetic circuit method. Optimization was done in object of maximum magnetic force. Two optimizations had similar results. Analysis showed that FEA-based optimization is more

Han Wu; Chunguang Xu; Dingguo Xiao; Juan Hao

2009-01-01

218

Magnetic fields in quiescent prominences  

SciTech Connect

The origin of the axial fields in high-latitude quiescent prominences is considered. The fact that almost all quiescent prominences obey the same hemisphere-dependent rule strongly suggests that the solar differential rotation plays an important role in producing the axial fields. However, the observations are inconsistent with the hypothesis that the axial fields are produced by differential rotation acting on an existing coronal magnetic field. Several possible explanations for this discrepancy are considered. The possibility that the sign of the axial field depends on the topology of the magnetic field in which the prominence is embedded is examined, as is the possibility that the neutral line is tilted with respect to the east-west direction, so that differential rotation causes the neutral line also to rotate with time. The possibility that the axial fields of quiescent prominences have their origin below the solar surface is also considered. 29 refs.

Van Ballegooijen, A.A.; Martens, P.C.H. (Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (USA))

1990-09-01

219

Magnetic-flux-induced persistent currents in nonlinear mesoscopic rings  

NASA Astrophysics Data System (ADS)

We investigate magnetic-flux-induced persistent currents (PCs) in a one-dimensional nonlinear mesoscopic ring based on the Frenkel-Kontorova (FK) model. By applying a transfer-matrix technique, the energy spectra, the PCs, and the Thouless exponent are theoretically obtained. It is shown that the energy spectrum splits into sub-bands when the on-site energy is gradually increased, and in the flux-dependent energy spectra, the energy levels show different behaviors over the transition by breaking of analyticity. Meanwhile, the PC is determined by the magnetic flux, the on-site energy, and the Fermi level. The increment of the on-site energy leads to a dramatic suppression of the PC. When the Fermi level is in the vicinity of ``band'' gaps, the PC is limited considerably; otherwise, the PC increases by several orders of magnitude. The suppressed PC is related to the electronic localization of the FK ring, which is described by the Thouless exponents. Our investigations provide detailed information about the influence of nonlinear structure on the PC and contribute to its potential application in quantum devices.

Zhang, R. L.; Qi, D. X.; Peng, R. W.; Li, J.; Fan, R. H.; Huang, R. S.; Wang, Mu

2011-04-01

220

Algebraic and geometric properties of Bethe Ansatz eigenfunctions on a pentagonal magnetic ring  

NASA Astrophysics Data System (ADS)

The exact solution of the eigenproblem of the Heisenberg Hamiltonian for the XXX model in the case of a magnetic ring with N=5 nodes is presented in a closed algebraic form. It is demonstrated that the eigenproblem itself is expressible within the extension of the prime field Q of rationals by the primitive fifth root of unity, whereas the associated Bethe parameters, i.e. pseudomomenta, phases of scattering, and spectral parameters, require some finite field extensions, such that the nonlinearity remains algebraic rather than transcendental. Classification of exact Bethe Ansatz eigenstates in terms of rigged string configurations is presented.

Milewski, J.; Banaszak, G.; Lulek, T.; Labuz, M.

2011-02-01

221

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

222

C/NOFS Magnetic Field Measurements in the Low-latitude Ionosphere during Magnetic Storms  

NASA Astrophysics Data System (ADS)

The Vector Electric Field Investigation suite on the C/NOFS satellite includes a fluxgate magnetometer to monitor the Earth's magnetic fields in the low-latitude ionosphere. Measurements yield full magnetic vectors every second over the range of ± 45,000 nT with a one-bit resolution of 1.37 nT (16 bit A/D) in each component. The sensor's primary responsibility is to support calculations of both V×B and E×B with greater accuracy than can be obtained using standard magnetic field models. The data also contain information about large-scale current systems, that, when analyzed in conjunction with electric field measurements, promise to significantly expand understanding of equatorial electrodynamics. We first compare in situ measurements with the POMME (POtsdam Magnetic Model of the Earth) model to establish in-flight sensor "calibrations" and to compute magnetic residuals. At low latitudes the residuals are predominately products of the ring current during magnetic storms. Since C/NOFS provides a complete coverage of all local times every 97 minutes, magnetic field data allow studies of the temporal evolution and local-time variations of stormtime ring current. The analysis demonstrates the feasibility of using instrumented spacecraft in low-inclination orbits to extract a timely proxy for the provisional Dst index and to specify the ring current's evolution.

Le, G.; Burke, W. J.; Pfaff, R. F.; Freudenreich, H. T.; Maus, S.; Luhr, H.

2011-12-01

223

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

224

Alternating magnetic field assisted magnetization reversal in ferromagnetic antidot  

NASA Astrophysics Data System (ADS)

Although the effects of high-frequency electromagnetic waves on magnetization reversal have been extensively studied, the influence of a low-frequency ac field on magnetization reversal has seldom been examined. In this study, we measured the magnetoresistance and examined the magnetic switching process of Permalloy antidot thin films under an alternating magnetic field with a frequency of 25 kHz. When no alternating magnetic field was present, the transitional field of the antidot thin films decreased as the angle of the direct magnetic field increased. When an alternating magnetic field was present, the transitional field exhibited the same trend. We compared the magnetization process of the antidot thin films with and without the alternating magnetic field and determined that the alternating field can facilitate the transition of magnetization, specifically, by lowering the transitional field with the highest variation rate (33.73%).

Huang, Hao-Ting; Ger, Tzong-Rong; Huang, Chen-Yu; Liao, Kuei-Tien; Wang, Pei-Jen; Lai, Jun-Yang; Chen, Jiann-Yeu; Lai, Mei-Feng

2014-05-01

225

Theory of a ring laser. [electromagnetic field and wave equations  

NASA Technical Reports Server (NTRS)

Development of a systematic formulation of the theory of a ring laser which is based on first principles and uses a well-known model for laser operation. A simple physical derivation of the electromagnetic field equations for a noninertial reference frame in uniform rotation is presented, and an attempt is made to clarify the nature of the Fox-Li modes for an open polygonal resonator. The polarization of the active medium is obtained by using a Fourier-series method which permits the formulation of a strong-signal theory, and solutions are given in terms of continued fractions. It is shown that when such a continued fraction is expanded to third order in the fields, the familiar small-signal ring-laser theory is obtained.

Menegozzi, L. N.; Lamb, W. E., Jr.

1973-01-01

226

Homometallic and Heterometallic Antiferromagnetic Rings: Magnetic Properties Studied by Nuclear Magnetic Resonance  

SciTech Connect

The aim of the present thesis is to investigate the local magnetic properties of homometallic Cr{sub 8} antiferromagnetic (AFM) ring and the changes occurring by replacing one Cr{sup 3+} ion with diamagnetic Cd{sup 2+} (Cr{sub 7}Cd) and with Ni{sup 2+} (Cr{sub 7}Ni). In the heterometallic ring a redistribution of the local magnetic moment is expected in the low temperature ground state. We have investigated those changes by both {sup 53}Cr-NMR and {sup 19}F-NMR. We have determined the order of magnitude of the transferred hyperfine coupling constant {sup 19}F - M{sup +} where M{sup +} = Cr{sup 3+}, Ni{sup 2+} in the different rings. This latter result gives useful information about the overlapping of the electronic wavefunctions involved in the coordinative bond.

Casadei, Cecilia

2012-05-09

227

High-field magnets and high-field superconductors  

Microsoft Academic Search

This paper gives a brief historical review of the development of high magnetic fields and high field superconductors including brief summaries of the early developments of high magnetic fields and the Francis Bitter National Magnet Laboratory (FBNML). The start of the first revolution (when large critical currents in Nb3Sn were observed in high magnetic fields) and the development of practical

Simon Foner; Francis Bitter

1995-01-01

228

Magnetic Fields in Irregular Galaxies: NGC 4214  

Microsoft Academic Search

Magnetic fields are an important component of the interstellar medium of galaxies. They provide support, transfer energy from supernovae, provide a possible heating mechanism, and channel gas flows (Beck 2004). Despite the importance of magnetic fields in the ISM, it is not well known what generates and sustains galactic magnetic fields or how magnetic fields, gas, and stars interact in

Amanda A. Kepley; E. M. Wilcots; T. Robishaw; C. Heiles; E. Zweibel

2006-01-01

229

Solar magnetic fields - The Italian contribution  

Microsoft Academic Search

A short account is given of the methods of observation, the characteristics of solar magnetic fields, the relationships between velocity and magnetic fields, the theoretical approaches, and the possibilities opened by studies of stellar activity of the solar type. In discussing the classification and characteristics of solar magnetic fields, attention is given to normal bipolar regions, large-scale unipolar magnetic fields,

D. Fabbri; G. Godoli; F. Mazzucconi

1982-01-01

230

Progress in Solar Magnetic Field Extrapolation  

Microsoft Academic Search

Solar magnetic field is the predominant factor of the solar activities. Precise measurements of solar magnetic fields so far are still confined to the thin layer of the solar photosphere. In order to understand the nature of the coronal magnetic fields, it becomes necessary to extrapolate the coronal magnetic fields based on theoretical models using observed photospheric magnetograms as boundary

Juan Hao; Mei Zhang

2007-01-01

231

Satellite to study earth's magnetic field  

NASA Technical Reports Server (NTRS)

The Magnetic Field Satellite (Magsat) designed to measure the near earth magnetic field and crustal anomalies is briefly described. A scalar magnetometer to measure the magnitude of the earth's crustal magnetic field and a vector magnetometer to measure magnetic field direction as well as magnitude are included. The mission and its objectives are summarized along with the data collection and processing system.

1979-01-01

232

Variable-field permanent magnet quadrupole for the SSC  

SciTech Connect

A set of compact variable-field permanent-magnet quadrupoles have been designed, fabricated, and tested for use In the SSC linac matching section. The quadrupoles have 24 mm-diameter apertures and 40 mm-long poles. The hybrid (permanent-magnet and iron) design, uses a fixed core of magnet material (NdFeB) and iron (C-1006) surrounded by a rotating ring of the same magnet material and iron. The quadrupole gradient-length product can be smoothly varied from a minimum of 0.7 T up to a maximum, of 4.3 T by a 90{degrees} rotation of the outer ring of iron and magnet material.

Barlow, D.B.; Kraus, R.H. Jr.; Martinez, R.P.; Meyer, R.E.

1993-10-01

233

On the motion of the field of a permanent magnet  

NASA Astrophysics Data System (ADS)

A description is given of a series of recent experiments using a rotating magnetic circuit comprising a permanent magnet ring and yoke, and a stationary conductor in the air gap between the ring and yoke. The EMF induced in this case cannot be described by a simple application of Faraday's flux law. This is because the magnetic flux in the air gap and the area of the gap both remain constant. The experimental results are best explained by the fact that the magnetic field itself rotates with the rotating magnet. This is controversial in the scientific and educational literature, as shown by citations from various authors (e.g. Feynman, Tamm and Landau all disagree, and with each other). However, these experiments, which may be readily reproduced, do in fact settle the question.

Leus, Vladimir; Taylor, Stephen

2011-09-01

234

Observations of Mercury's magnetic field  

NASA Technical Reports Server (NTRS)

Magnetic field data obtained by Mariner 10 during the third and final encounter with the planet Mercury on 16 March 1975 were studied. A well developed bow shock and modest magnetosphere, previously observed at first encounter on 29 March 1974, were again observed. In addition, a much stronger magnetic field near closest approach, 400 gamma versus 98 gamma, was observed at an altitude of 327 km and approximately 70 deg north Mercurian latitude. Spherical harmonic analysis of the data provide an estimate of the centered planetary magnetic dipole of 4.7 x 10 to the 22nd power Gauss/cu cm with the axis tilted 12 deg to the rotation axis and in the same sense as Earth's. The interplanetary field was sufficiently different between first and third encounters that in addition to the very large field magnitude observed, it argues strongly against a complex induction process generating the observed planetary field. While a possibility exists that Mercury possesses a remanent field due to magnetization early in its formation, a present day active dynamo seems to be a more likely candidate for its origin.

Ness, N. F.; Behannon, K. W.; Lepping, R. P.; Whang, Y. C.

1975-01-01

235

Exact transfer functions for the PEP storage ring magnets and some general characteristics and techniques  

SciTech Connect

The exact, ion-optical transfer functions for the dipoles, quadrupoles and sextupoles of the PEP standard PODC cell are calculated for any single particle with initial coordinates (r, p, s). Modifications resulting from radiative energy loss are also calculated and discussed. These functions allow one to characterize individual magnets or classes of magnets by their aberrations and thereby simplify their study and correction. In contrast to high-energy spectrometers where aberrations are often analyzed away, those in storage rings drive series of high order resonances, even for perfect magnets (2), that can produce stop bands and other effects which can seriously limit performance. Thus, one would like to eliminate them altogether or failing this to develop local and global correction schemes. Even then, one should expect higher order effects to influence injection, extraction or single-pass systems either because of orbit distortions or overly large phase spece distortions such as may occur in low-beta insertions or any final-focus optics. The term exact means that the results here are based on solving the relativistic Lorentz force equation with accurate representations of measured magnetostatic fields. Such fields satisfy Maxwell's equations and are the actual fields seen by a particle as it propagates around a real storage ring. This is discussed in detail and illustrated with examples that show that this is possible, practical and may even be useful.

Spencer, J.E.

1982-05-01

236

Deflections in magnet fringe fields.  

PubMed

A transverse multipole expansion is derived, including the longitudinal components necessarily present in regions of varying magnetic field profile. It can be used for exact numerical orbit following through the fringe-field regions of magnets whose end designs introduce no extraneous components, i.e., fields not required to be present by Maxwell's equations. Analytic evaluations of the deflections are obtained in various approximations. Mainly emphasized is a "straight-line approximation," in which particle orbits are treated as straight lines through the fringe-field regions. This approximation leads to a readily-evaluated figure of merit, the ratio of rms end deflection to nominal body deflection, that can be used to determine whether or not a fringe field can be neglected. Deflections in "critical" cases (e.g., near intersection regions) are analyzed in the same approximation. PMID:12786502

Papaphilippou, Y; Wei, J; Talman, R

2003-04-01

237

Magnetic field tomography, helical magnetic fields and Faraday depolarization  

NASA Astrophysics Data System (ADS)

Wide-band radio polarization observations offer the possibility to recover information about the magnetic fields in synchrotron sources, such as details of their three-dimensional configuration, that has previously been inaccessible. The key physical process involved is the Faraday rotation of the polarized emission in the source (and elsewhere along the wave's propagation path to the observer). In order to proceed, reliable methods are required for inverting the signals observed in wavelength space into useful data in Faraday space, with robust estimates of their uncertainty. In this paper, we examine how variations of the intrinsic angle of polarized emission ?0 with the Faraday depth ? within a source affect the observable quantities. Using simple models for the Faraday dispersion F(?) and ?0(?), along with the current and planned properties of the main radio interferometers, we demonstrate how degeneracies among the parameters describing the magneto-ionic medium can be minimized by combining observations in different wavebands. We also discuss how depolarization by Faraday dispersion due to a random component of the magnetic field attenuates the variations in the spectral energy distribution of the polarization and shifts its peak towards shorter wavelengths. This additional effect reduces the prospect of recovering the characteristics of the magnetic field helicity in magneto-ionic media dominated by the turbulent component of the magnetic field.

Horellou, C.; Fletcher, A.

2014-07-01

238

In-plane anisotropy of coercive field in permalloy square ring arrays.  

SciTech Connect

Magnetic ring arrays are promising candidates for application in magnetic random access memory devices. The magnetic reversal processes and anisotropy of the coercivity in arrays of square-shaped nanorings with different spacings were investigated by vector magneto-optical Kerr effect magnetometry, magnetic force microscopy, and micromagnetic simulations. Two-step magnetization reversal demonstrates fourfold symmetry in the film plane resulting from the shape anisotropy in rings. Our numerical simulations show good agreement with the experiment.

Goncharov, A. V.; Zhukov, A. A.; Metlushko, V. V.; Bordignon, G.; Fangohr, H.; Karapetrov, G.; de Groot, P. A. J.; Ilic, B.; Materials Science Division; Univ. Southampton; Univ. Illinois at Chicago; Cornell Univ.

2006-04-15

239

Formation of Magnetic Particle Chains in Ultra High Magnetic Field  

Microsoft Academic Search

Magnetic particles form chain-like clusters in the magnetic field. This phenomenon is of interest in two separate fields, one is a development system of the laser printer and another is an electromagnetic manipulation of biological cells. Experiments on the chain formation in air and oil have been performed in the ultra high magnetic field created by a superconducting magnet. It

Hiroyuki Kawamoto; Masatomo Teshima; Hiroyuki Takahashi; Nobuyuki Nakayama; Noriyuki Hirota

2007-01-01

240

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

241

Magnetic Forces and Field Line Density  

NSDL National Science Digital Library

This is an activity about depicting the relative strength of magnetic fields using field line density. Learners will use the magnetic field line drawing of six magnetic poles created in a previous activity and identify the areas of strong, weak, and medium magnetic intensity using the density of magnetic field lines. This is the fifth activity in the Magnetic Math booklet; this booklet can be found on the Space Math@NASA website. How to Draw Magnetic Fields - II in the Magnetic Math booklet must be completed prior to this activity.

242

Magnetic Fields of the Earth and Sun  

NSDL National Science Digital Library

This is an activity that compares the magnetic field of the Earth to the complex magnetic field of the Sun. Using images of the Earth and Sun that have magnets attached in appropriate orientations, learners will use a handheld magnetic field detector to observe the magnetic field of the Earth and compare it to that of the Sun, especially in sunspot areas. For each group of students, this activity requires use of a handheld magnetic field detector, such as a Magnaprobe or a similar device, a bar magnet, and ten small disc magnets.

243

The magnetic and electric fields induced by superparamagnetic magnetite in honeybees  

Microsoft Academic Search

Hairs on the abdomen of honeybees contain dendrites and a rod and ring structure composed of black particles, presumed to be superparamagnetic (SPM) magnetite. The rod and ring were divided into compartments and each compartment approximated by a dipole. The magnetic fields were calculated at a point P at various locations for a change of the external geomagnetic field from

H. Schilf; G. Canal

1993-01-01

244

Symmetry classes connected with the magnetic Heisenberg ring  

NASA Astrophysics Data System (ADS)

It is well-known (see [1]) that for a Heisenberg magnet symmetry operators and symmetry classes can be defined in a very similar way as for tensors (see e.g. [2, 3, 4]). Newer papers which consider the action of permutations on the Hilbert space Ti of the Heisenberg magnet are [5, 6, 7, 8]. We define symmetry classes and commutation symmetries in the Hilbert space H of the 1D spin-1/2 Heisenberg magnetic ring with N sites and investigate them by means of tools from the representation theory of symmetric groups C[SN] such as decompositions of ideals of the group ring C[SN], idempotents of C[SN], discrete Fourier transforms of SN, Littlewood-Richardson products. In particular, we determine smallest symmetry classes and stability subgroups of both single eigenvectors v and subspaces U of eigenvectors of the Hamiltonian H of the magnet. Expectedly, the symmetry classes defined by stability subgroups of v or U are bigger than the corresponding smallest symmetry classes of v or U, respectively. The determination of the smallest symmetry class for U bases on an algorithm which calculates explicitely a generating idempotent for a non-direct sum of right ideals of C[SN]. Let U(r1,r2)? be a subspace of eigenvectors of a fixed eigenvalue ? of H with weight (r1,r2). If one determines the smallest symmetry class for every v epsilon U(r1,r2)? then one can observe jumps of the symmetry behaviour. For "generic" v epsilon U(r1,r2)? all smallest symmetry classes have the same maximal dimension d and 'structure'. But U(r1,r2)? can contain linear subspaces on which the dimension of the smallest symmetry class of v jumps to a value smaller than d. Then the stability subgroup of v can increase. We can calculate such jumps explicitely. In our investigations we use computer calculations by means of the Mathematica packages PERMS and HRing.

Fiedler, B.

2008-03-01

245

BEC manipulation with fictitious magnetic fields  

Microsoft Academic Search

The interaction of Bose-Einstein condensate (BEC) atoms with counterpropagating laser beams can often be represented by fictitious magnetic fields [1]. These fictitious fields can be combined with ordinary magnetic fields to produce total fields whose amplitudes vary in space on the scale of the laser wavelength. When the strengths of such magnetic fields are positioned in the neighborhood of a

Jeffrey Heward; Mark Edwards; Charles W. Clark

2010-01-01

246

Flares and changing magnetic fields  

Microsoft Academic Search

An observational study of maps of the longitudinal component of the photospheric fields in flaring active regions leads to the following conclusions:(1)The broad-wing Ha kernels characteristic of the impulsive phase of flares occur within 10? of neutral lines encircling features of isolated magnetic polarity (‘satellite sunspots’).(2)Photospheric field changes intimately associated with several importance 1 flares and one importance 2B flare

David M. Rust

1972-01-01

247

Ohm's Law for Mean Magnetic Fields.  

National Technical Information Service (NTIS)

The magnetic fields associated with plasmas frequently exhibit small amplitude MHD fluctuations. It is useful to have equations for the magnetic field averaged over these fluctuations, the so-called mean field equations. Under very general assumptions it ...

A. H. Boozer

1986-01-01

248

Crystal field and magnetic properties  

NASA Technical Reports Server (NTRS)

Magnetization and magnetic susceptibility measurements have been made in the temperature range 1.3 to 4.2 K on powdered samples of ErH3. The susceptibility exhibits Curie-Weiss behavior from 4.2 to 2 K, and intercepts the negative temperature axis at theta = 1.05 + or - 0.05 K, indicating that the material is antiferromagnetic. The low field effective moment is 6.77 + or - 0.27 Bohr magnetons per ion. The magnetization exhibits a temperature independent contribution, the slope of which is (5 + or - 1.2) x 10 to the -6th Weber m/kg Tesla. The saturation moment is 3.84 + or - 1 - 0.15 Bohr magnetons per ion. The results can be qualitatively explained by the effects of crystal fields on the magnetic ions. No definitive assignment of a crystal field ground state can be given, nor can a clear choice between cubically or hexagonally symmetric crystal fields be made. For hexagonal symmetry, the first excited state is estimated to be 86 to 100 K above the ground state. For cubic symmetry, the splitting is on the order of 160 to 180 K.

Flood, D. J.

1977-01-01

249

Swarm: ESA's Magnetic Field Mission  

Microsoft Academic Search

Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme. The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal evolution. The Mission shall deliver data that allow access to new insights into the Earth system by improving our understanding of the Earth's interior and near-Earth electro-magnetic environment.

R. Haagmans; Y. Menard; R. Floberghagen; G. Plank; M. R. Drinkwater

2010-01-01

250

Transverse Magnetic Field Propellant Isolator  

NASA Technical Reports Server (NTRS)

An alternative high voltage isolator for electric propulsion and ground-based ion source applications has been designed and tested. This design employs a transverse magnetic field that increases the breakdown voltage. The design can greatly enhance the operating range of laboratory isolators used for high voltage applications.

Foster, John E.

2000-01-01

251

Observation of magnetic fluctuations and rapid density decay of magnetospheric plasma in Ring Trap 1  

NASA Astrophysics Data System (ADS)

The Ring Trap 1 device, a magnetospheric configuration generated by a levitated dipole field magnet, has created high-? (local ? ~ 70%) plasma by using electron cyclotron resonance heating (ECH). When a large population of energetic electrons is generated at low neutral gas pressure operation, high frequency magnetic fluctuations are observed. When the fluctuations are strongly excited, rapid loss of plasma was simultaneously observed especially in a quiet decay phase after the ECH microwave power is turned off. Although the plasma is confined in a strongly inhomogeneous dipole field configuration, the frequency spectra of the fluctuations have sharp frequency peaks, implying spatially localized sources of the fluctuations. The fluctuations are stabilized by decreasing the hot electron component below approximately 40%, realizing stable high-? confinement.

Saitoh, H.; Yoshida, Z.; Morikawa, J.; Yano, Y.; Mikami, H.; Kasaoka, N.; Sakamoto, W.

2012-06-01

252

Observation of magnetic fluctuations and rapid density decay of magnetospheric plasma in Ring Trap 1  

SciTech Connect

The Ring Trap 1 device, a magnetospheric configuration generated by a levitated dipole field magnet, has created high-{beta} (local {beta} {approx} 70%) plasma by using electron cyclotron resonance heating (ECH). When a large population of energetic electrons is generated at low neutral gas pressure operation, high frequency magnetic fluctuations are observed. When the fluctuations are strongly excited, rapid loss of plasma was simultaneously observed especially in a quiet decay phase after the ECH microwave power is turned off. Although the plasma is confined in a strongly inhomogeneous dipole field configuration, the frequency spectra of the fluctuations have sharp frequency peaks, implying spatially localized sources of the fluctuations. The fluctuations are stabilized by decreasing the hot electron component below approximately 40%, realizing stable high-{beta} confinement.

Saitoh, H.; Yoshida, Z.; Morikawa, J.; Yano, Y.; Mikami, H.; Kasaoka, N.; Sakamoto, W. [Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan)

2012-06-15

253

Large-scale solar magnetic fields  

Microsoft Academic Search

Topics discussed in this review of large-scale solar magnetic fields include large-scale magnetic surface features, the solar activity cycle and the large-scale patterns, and magnetic fields in the corona. Features considered include the decay of active regions, the background field pattern, the polar fields, giant regular structures, expansion of the field in surface harmonics, and the average inclination of magnetic-field

R. Howard

1977-01-01

254

Pioneer 10 and 11 (Jupiter and Saturn) magnetic field experiments  

NASA Technical Reports Server (NTRS)

Magnet field data obtained by the vector helium magnetometer (VHM) during the encounters of Jupiter (Pioneer 10 and 11) and Saturn (Pioneer 11) was analyzed and interpreted. The puzzling characteristics of the Jovian and Saturnian magnetospheric magnetic fields were studied. An apparent substorm (including thinning of the dayside tail current sheet) was observed at Jupiter, as well as evidence suggesting that at the magnetopause the cusp is at an abnormally low latitude. The characteristics of Saturn's ring current as observed by Pioneer 11 were dramatically different from those suggested by the Voyager observations. Most importantly, very strong perturbations in the azimuthal ring current magnetic field suggest that the plane of the ring was not in the dipole equatorial plane, being tilted 5 to 10 deg. relative to the dipole and undergoing significant changes during the encounter. When these changing currents were corrected for, an improved planetary field determination was obtained. In addition, the ring and azimuthal currents at Saturn displayed significantly different time dependences.

Jones, D. E.

1986-01-01

255

PULSED MAGNETS AND PULSER UNITS FOR THE BOOSTER AND STORAGE RING OF THE DIAMOND LIGHT SOURCE  

Microsoft Academic Search

The Diamond booster and storage ring facility has ten pulsed magnet systems, five for the booster (injection and extraction) and five for the storage ring (injection septum and four bump kickers). Each has its own specific requirements although commonality of design has been adopted where possible. Design and construction principles and results of magnet and pulser testing are discussed as

V. C. Kempson; J. A. Dobbing; G. M. A. Duller; N. Hauge; G. Hilleke; C. Hansen

256

Magnetic fields in the sun  

NASA Technical Reports Server (NTRS)

The observed properties of solar magnetic fields are reviewed, with particular reference to the complexities imposed on the field by motions of the highly conducting gas. Turbulent interactions between gas and field lead to heating or cooling of the gas according to whether the field energy density is less or greater than the maximum kinetic energy density in the convection zone. The field strength above which cooling sets in is 700 gauss. A weak solar dipole field may be primeval, but dynamo action is also important in generating new flux. The dynamo is probably not confined to the convection zone, but extends throughout most of the volume of the sun. Planetary tides appear to play a role in driving the dynamo.

Mullan, D. J.

1974-01-01

257

The magnetic field experiment for Bepi-Colombo MMO, 2  

Microsoft Academic Search

The MERMAG-M consortium is now preparing to propose a magnetic field experiment for Bepi-Colombo MMO. We have examined the design and performance of magnetometers to measure fields around Mercury with good accuracy. It consists of two sets of ring-core geometry sensor and electronic system with an extensible arm. One of the sensors (outboard) is mounted at the top of the

A. Matsuoka; W. Baumjohann

2003-01-01

258

Relationship of the ring current plasma pressure from ENA images and field-aligned currents  

NASA Astrophysics Data System (ADS)

The steady state MHD force balance equation and current continuity show that pressure gradients in the equatorial ring current are associated with field-aligned currents (FAC) for large spatial and slow temporal scale changes of the magnetic field. To obtain the ring current pressure, ion distributions are inverted from ENA images obtained by IMAGE/HENA and MENA and used to calculate the plasma density, temperature, and pressure for a series of geomagnetic storms/substorms on 22 January, 12 February, 9 and 10 March, 29 May, 23 September and 13 October in 2004. FAC patterns in the high-latitude ionosphere are derived from the Weimer 2005 FAC model with time shifted solar wind and IMF driven input parameters. Comparing the ring current pressure with the field-aligned current pattern mapped to the equator shows the dynamics of the relationship between the plasma pressure/pressure gradients and field-aligned currents for the series of storms/substorms addressed in this presentation.

Zhang, X.; Perez, J. D.; C:Son Brandt, P.; Mitchell, D. G.; Jahn, J.; Pollock, C. J.; Weimer, D. R.

2005-12-01

259

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

2010-06-30

260

Oxide superconductors under magnetic field  

NASA Technical Reports Server (NTRS)

One of the current most serious problems for the oxide superconductors from the standpoint of practical application is the various novel features derived mainly from their extremely short coherence. In particular, the coherence length so far observed in the cuprate superconductors is in the range of 0.1 nm perpendicular to the CuO2 plane. This seems to be creating most of the difficulties in the device fabrication and in the performance under the magnetic field. Some of the superconducting properties under the magnetic field will be discussed in terms of the short coherence length. A model will be presented based on the gradual strengthening of the pinning force with decrease in temperature and the weak coupling at the grain boundaries. Secondly, the broadening of the superconducting transition under the magnetic field is discussed. This is observed significantly only when the field is applied perpendicular to the basal plane and the relative orientation of the current to the field is insignificant in determining the extent of the broadening. Besides, the change in the strength of the pinning force does not affect the width of the broadening. From these observations discussions will be made on a model based on the giant fluctuation. Based on this model, it is predicted that the coherence length along the c-axis will be the single most important material parameter to determine the performance of the superconductor under a strong magnetic field. It seems that BYCO is superior in this regard to Bi- or Tl-systems as far as the performance at 77 K is considered, although another material with the coherence length slightly longer along the c-axis is still highly desired.

Kitazawa, K.

1990-01-01

261

Oxide superconductors under magnetic field  

NASA Technical Reports Server (NTRS)

One of the current most serious problems for the oxide superconductors from the standpoint of practical application is the various novel features derived mainly from their extremely short coherence. In particular, the coherence length so far observed in the cuprate superconductors is in the range of 0.1 nm perpendicular to the CuO2 plane. This seems to be creating most of the difficulties in the device fabrication and in the performance under the magnetic field. Some of the superconducting properties under the magnetic field will be discussed in terms of the short coherence length. A model will be presented based on the gradual strengthening of the pinning force with decrease in temperature and the weak coupling at the grain boundaries. Secondly, the broadening of the superconducting transition under the magnetic field is discussed. This is observed significantly only when the field is applied perpendicular to the basal plane and the relative orientation of the current to the field is insignificant in determining the extent of broadening. Besides, the change in the strength of the pinning force does not affect the width of the broadening. From these observations discussions will be made on a model based on the giant fluctuation. Based on this model, it is predicted that the coherence length along the c-axis will be the single most important material parameter to determine the performance of the superconductor under a strong magnetic field. It seems that BYCO is superior in this regard to Bi- or Tl-systems as far as the performance at 77 K is considered, although another material with the coherence length slightly longer along the c-axis is still highly desired.

Kitazawa, K.

1991-01-01

262

Magnetic field structure generation in collisional dusty plasmas  

NASA Astrophysics Data System (ADS)

A perpendicular ion drift is proposed as a possible mechanism for the generation of magnetic field structures in a highly collisional dusty plasma. The basic dissipation mechanism is assumed to be the dust-neutral momentum exchange, so that plasmas with a small ionization fraction are natural candidates for experiments. The model reduces to a nonlinear partial differential equation for the vector potential. The conditions for linear instability are presented. Possible stationary states are periodic arrangements for the magnetic field, described by a Lienard equation. The fully depleted (ion-dust) case is also considered in detail. Applications of the present work to magnetic field structures in planetary rings, comets and low-temperature dusty plasma experiments are discussed. A necessary condition for the validity of the model is a sufficiently slow time-scale of the generated magnetic fields in dusty plasmas.

Kant Shukla, Padma; Haas, Fernando

2008-11-01

263

Dynamics of Magnetic Bubbles in Acoustic and Magnetic Fields  

Microsoft Academic Search

We report on shelled bubbles that can be manipulated with magnetic fields. The magnetic shell consists of self-assembled magnetic nanoparticles. The magnetic susceptibility of the bubbles is proportional to the surface area, chib=(9±3×10-6m)r2 where r is the radius. Magnetic bubbles are compressible in moderate acoustic fields. A bubble with a radius of 121mum oscillates in resonance in a sound field

Xue Zhao; Pedro A. Quinto-Su; Claus-Dieter Ohl

2009-01-01

264

Equatorial electric fields during magnetically disturbed conditions 2. Implications of simultaneous auroral and equatorial measurements  

Microsoft Academic Search

Simultaneous auroral and equatorial electric field data are used along with magnetic field data to study anomalous electric field patterns during disturbed times. During some substorms, accompanied by ring current activity, the worldwide equatorial zonal electric field component reverses from the normal pattern. This is interpreted as a partial closure of high latitude field aligned currents in the dayside, low

C.A. Gonzales; M.C. Kelley; B.G. Fejer; J.F. Vickrey; R.F. Woodman

1979-01-01

265

Diagnostics of vector magnetic fields  

NASA Technical Reports Server (NTRS)

It is shown that the vector magnetic fields derived from observations with a filter magnetograph will be severely distorted if the spatially unresolved magnetic structure is not properly accounted for. Thus the apparent vector field will appear much more horizontal than it really is, but this distortion is strongly dependent on the area factor and the temperature line weakenings. As the available fluxtube models are not sufficiently well determined, it is not possible to correct the filter magnetograph observations for these effects in a reliable way, although a crude correction is of course much better than no correction at all. The solution to this diagnostic problem is to observe simultaneously in suitable combinations of spectral lines, and/or use Stokes line profiles recorded with very high spectral resolution. The diagnostic power of using a Fourier transform spectrometer for polarimetry is shown and some results from I and V spectra are illustrated. The line asymmetries caused by mass motions inside the fluxtubes adds an extra complication to the diagnostic problem, in particular as there are indications that the motions are nonstationary in nature. The temperature structure appears to be a function of fluxtube diameter, as a clear difference between plage and network fluxtubes was revealed. The divergence of the magnetic field with height plays an essential role in the explanation of the Stokes V asymmetries (in combination with the mass motions). A self consistent treatment of the subarcsec field geometry may be required to allow an accurate derivation of the spatially averaged vector magnetic field from spectrally resolved data.

Stenflo, J. O.

1985-01-01

266

Explaining Mercury's peculiar magnetic field  

NASA Astrophysics Data System (ADS)

MESSENGER magnetometer data revealed that Mercury's magnetic field is not only particularly weak but also has a peculiar geometry. The MESSENGER team finds that the location of the magnetic equator always lies significantly north of the geographic equator, is largely independent of the distance to the planet, and also varies only weakly with longitude. The field is best described by an axial dipole that is offset to the north by about 20% of the planetary radius. In terms of classical Gauss coefficients, this translates into a low axial dipole component of g10= -190 nT but a relatively large axial quadrupole contribution that amounts to roughly 40% of this value. The axial octupole is also sizable while higher harmonic contributions are much weaker. Very remarkable is also the fact that the equatorial dipole contribution is very small, consistent with a dipole tilt below 0.8 degree, and this is also true for the other non-axisymmetic field contributions. We analyze several numerical dynamos concerning their capability of explaining Mercury's magnetic field. Classical schemes geared to model the geomagnetic field typically show a much weaker quadrupole component and thus a smaller offset. The onset only becomes larger when the dynamo operates in the multipolar regime at higher Rayleigh numbers. However, since the more complex dynamics generally promotes all higher multipole contributions the location of the magnetic equator varies strongly with longitude and distance to the planet. The situation improves when introducing a stably stratified outer layer in the dynamo region, representing either a rigid FeS layer or a sub-adiabatic core-mantle boundary heat flux. This layer filters out the higher harmonic contributions and the field not only becomes sufficiently weak but also assumes a Mercury like offset geometry during a few percent of the simulation time. To increase the likelihood for the offset configuration, the north-south symmetry must be permanently broken and we explore two scenarios. Increasing the heat flux through the northern hemisphere of the core-mantle boundary is an obvious choice but is not supported by current models for Mercury's mantle. We find that a combination of internal rather than bottom driving and an increased heat flux through the equatorial region of the core-mantle boundary also promotes the required symmetry breaking and results in very Mercury like fields. The reason is that the imposed heat flux pattern, though being equatorially symmetric, lowers the critical Rayleigh number for the onset of equatorially anti-symmetric convection modes. In both scenarios, a stably stratified layer or a feedback coupling to the magnetospheric field is required for lowering the field strength to Mercury-like values.

Wicht, Johannes; Cao, Hao; Heyner, Daniel; Dietrich, Wieland; Christensen, Ulrich R.

2014-05-01

267

Magnetic domain structure in thin film under alternate magnetic field  

Microsoft Academic Search

Magnetic domain structures in a garnet thin film under alternate magnetic fields have been investigated. In alternate magnetic fields, a labyrinth structure approaches a parallel-stripe structure. The competition among the segment clusters, in which stripes have different directions, causes stable dynamical domain structures. With the increase of the amplitude of alternate fields, the segment clusters become small.

M. Mino; H. Yamazaki

2004-01-01

268

Magnetic domain structure in thin film under alternate magnetic field  

NASA Astrophysics Data System (ADS)

Magnetic domain structures in a garnet thin film under alternate magnetic fields have been investigated. In alternate magnetic fields, a labyrinth structure approaches a parallel-stripe structure. The competition among the segment clusters, in which stripes have different directions, causes stable dynamical domain structures. With the increase of the amplitude of alternate fields, the segment clusters become small.

Mino, M.; Yamazaki, H.

269

Magnetic domain structure in thin film under alternate magnetic field  

NASA Astrophysics Data System (ADS)

Magnetic domain structures in a garnet thin film under alternate magnetic fields have been investigated. In alternate magnetic fields, a labyrinth structure approaches a parallel-stripe structure. The competition among the segment clusters, in which stripes have different directions, causes stable dynamical domain structures. With the increase of the amplitude of alternate fields, the segment clusters become small.

Mino, M.; Yamazaki, H.

2004-05-01

270

Comparing Magnetic Fields on Earth and Mars  

NASA Video Gallery

This animation compares the magnetic fields on Earth and Mars. The Earth has a large-scale planetary magnetic field that can protect it from space weather and other hazards. Mars, on the other hand...

271

Measurements of Solar Vector Magnetic Fields  

NASA Technical Reports Server (NTRS)

Various aspects of the measurement of solar magnetic fields are presented. The four major subdivisions of the study are: (1) theoretical understanding of solar vector magnetic fields; (3) techniques for interpretation of observational data; and (4) techniques for data display.

Hagyard, M. J. (editor)

1985-01-01

272

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

273

Magnetic order of UPt3 in high magnetic fields  

NASA Astrophysics Data System (ADS)

The weak magnetic order of the heavy-fermion superconductor UPt3 has been investigated by elastic neutron-scattering measurements in magnetic fields up to 12 T along the a and c axes of the hexagonal crystal structure. The small antiferromagnetically ordered moment of 0.02?B/(U atom) shows only a weak dependence on the applied magnetic field and no sign of a domain repopulation for B?a. In high magnetic fields an increase in the magnetic correlation length is observed for magnetic fields along the c axis.

van Dijk, N. H.; Fåk, B.; Regnault, L. P.; Huxley, A.; Fernández-Díaz, M.-T.

1998-08-01

274

Magnetically tunable negative permeability metamaterial composed by split ring resonators and ferrite rods.  

PubMed

We experimentally demonstrate a tunable negative permeability metamaterial (NPM) at microwave frequencies by introducing yttrium iron garnet (YIG) rods into a periodic array of split ring resonators (SRRs). Different from those tuned by controlling the capacitance of equivalent LC circuit of SRR, this metamaterial is based on a mechanism of magnetically tuning the inductance via the active ambient effective permeability. For magnetic fields from 0 to 2000 Oe and from 3200 to 6000 Oe, the resonance frequencies of the metamaterial can blueshift about 350 MHz and redshift about 315 MHz, respectively. Both shifts are completely continuous and reversible. Correspondingly, the tunable negative permeabilities are widened by about 360 MHz and 200 MHz compared to that without YIG rods. PMID:18545595

Kang, Lei; Zhao, Qian; Zhao, Hongjie; Zhou, Ji

2008-06-01

275

Crustal Magnetic Fields of Terrestrial Planets  

Microsoft Academic Search

Magnetic field measurements are very valuable, as they provide constraints on the interior of the telluric planets and Moon.\\u000a The Earth possesses a planetary scale magnetic field, generated in the conductive and convective outer core. This global magnetic\\u000a field is superimposed on the magnetic field generated by the rocks of the crust, of induced (i.e. aligned on the current main

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

2010-01-01

276

Magnetic holes in the solar wind. [(interplanetary magnetic fields)  

NASA Technical Reports Server (NTRS)

An analysis is presented of high resolution interplanetary magnetic field measurements from the magnetometer on Explorer 43 which showed that low magnetic field intensities in the solar wind at 1 AU occur as distinct depressions or 'holes'. These magnetic holes are new kinetic-scale phenomena, having a characteristic dimension on the order of 20,000 km. They occurred at a rate of 1.5/day in the 18-day time span (March 18 to April 6, 1971) that was analyzed. Most of the magnetic holes are characterized by both a depression in the absolute value of the magnetic field, and a change in the magnetic field direction; some of these are possibly the result of magnetic merging. However, in other cases the magnetic field direction does not change; such holes are not due to magnetic merging, but might be a diamagnetic effect due to localized plasma inhomogeneities.

Turner, J. M.; Burlaga, L. F.; Ness, N. F.; Lemaire, J. F.

1976-01-01

277

Design of a superferric dipole magnet with high field quality in the aperture  

Microsoft Academic Search

A project to design and construct a new international accelerator was proposed by GSI (Darmstadt, Germany). This project includes the design of several new facilities. One of them is a collector ring (CR). The magnets of the CR operate at constant field (DC), but the level of this field varies for different operational tasks. The magnet system of the CR

Alexander Kalimov; Gebhard Moritz; Al Zeller

2004-01-01

278

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

Swarm is the fifth Earth Explorer mission in ESA’s Living Planet Programme. The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal evolution. The Mission shall deliver data that allow access to new insights into the Earth system by improving our understanding of the Earth’s interior and near-Earth electro-magnetic environment. After release from a single launcher, a side-by-side flying slowly decaying lower pair of satellites will be released at an initial altitude of about 490 km together with a third satellite that 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 that are required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission aims to provide a unique view into Earth 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 development phase, will be addressed. The mission is scheduled for launch in 2012.

Haagmans, R.; Menard, Y.; Floberghagen, R.; Plank, G.; Drinkwater, M. R.

2010-12-01

279

Magnetic field sensors using GMR multilayer  

Microsoft Academic Search

Wheatstone bridge magnetic field sensors using giant magnetoresistive ratio (GMR) multilayers were designed, fabricated, and evaluated. The GMR ranged from 10% to 20% with saturation fields of 60 Oe to 300 Oe. The multilater resistances decreased linearly with magnetic field and showed little hysteresis. In one sensor configuration, a permanent magnet bias was placed between two pairs of magnetoresistors, each

J. Daughton; J. Brown; E. Chen; R. Beech; A. Pohm; W. Kude

1994-01-01

280

The measurement of solar magnetic fields  

Microsoft Academic Search

Methods for studying solar magnetic fields are examined, taking into account Zeeman and Hanle effects, radio observations, the influence of magnetic fields in solar structures, theoretical extrapolations of photospheric measurements, in situ measurements in the solar-wind region, and meteorite records of the primordial solar magnetic field. Instrumental techniques for optical polarization measurements are considered and an interpretation of optical polarization

J. O. Stenflo

1978-01-01

281

MR imaging at high magnetic fields  

Microsoft Academic Search

Recently, more investigators have been applying higher magnetic field strengths (3–4 Tesla) in research and clinical settings. Higher magnetic field strength is expected to afford higher spatial resolution and\\/or a decrease in the length of total scan time due to its higher signal intensity. Besides MR signal intensity, however, there are several factors which are magnetic field dependent, thus the

Masaya Takahashi; Hidemasa Uematsu; Hiroto Hatabu

2003-01-01

282

Magnetic field navigation in an indoor environment  

Microsoft Academic Search

This paper describes a method that has been developed to aid an inertial navigation system when GNSS signals are not available, by taking advantage of the uniqueness of magnetic field variations. Most indoor environments have many different features (ferrous structural materials or contents, electrical currents, etc.) which perturb the Earths natural magnetic field. The variations in the magnetic field in

William Storms; Jeremiah Shockley; John Raquet

2010-01-01

283

PLASMA CONFINEMENT USING ROTATING MAGNETIC FIELDS  

Microsoft Academic Search

An investigation was made of the current distribution set up by a ; magnetic field rotating about the axis of a cylindrical plasma. If the plasma ; resistivity was sufficiently small electrons rotated with the magnetic field ; producing a steady azimuthal current. In conjunction with an externally applied ; axial magnetic field such a system can be used to

H. Blevin; P. C. Thonemann

1961-01-01

284

Magnetic field quality analysis using ANSYS.  

National Technical Information Service (NTIS)

The design of superconducting magnets for particles accelerators requires a high quality of the magnetic field. This paper presents an ANSYS 4.4A Post 1 macro that computes the field quality performing a Fourier analysis of the magnetic field. The results...

D. Dell'Orco Y. Chen

1991-01-01

285

Magnetic field effect for cellulose nanofiber alignment  

Microsoft Academic Search

Regenerated cellulose formed into cellulose nanofibers under strong magnetic field and aligned perpendicularly to the magnetic field. Well-aligned microfibrils were found as the exposure time of the magnetic field increased. Better alignment and more crystalline structure of the cellulose resulted in the increased decomposition temperature of the material. X-ray crystallograms showed that crystallinity index of the cellulose increased as the

Jaehwan Kim; Yi Chen; Kwang-Sun Kang; Young-Bin Park; Mark Schwartz

2008-01-01

286

An ancient lunar magnetic dipole field  

Microsoft Academic Search

Theories giving the source of the previously hypothesized ancient strong lunar magnetic field and reasons for its disappearance are presented. It is suggested that since it was demonstrated that the moon possessed a small iron core, a dynamo process within this core may have accounted for the field. The disappearance of this magnetizing field can be explained; either the magnetic

S. K. Runcorn

1975-01-01

287

Passive Superconducting Flux Conservers for Rotating-Magnetic-Field-Driven Field-Reversed Configurations  

SciTech Connect

The Princeton Field-Reversed Configuration (PFRC) experiment employs an odd-parity rotating magnetic field (RMFo) current drive and plasma heating system to form and sustain high-? plasmas. For radial confinement, an array of coaxial, internal, passive, flux-conserving (FC) rings applies magnetic pressure to the plasma while still allowing radio-frequency RMFo from external coils to reach the plasma. The 3 ms pulse duration of the present experiment is limited by the skin time (?fc) of its room-temperature copper FC rings. To explore plasma phenomena with longer characteristic times, the pulse duration of the next-generation PFRC-2 device will exceed 100 ms, necessitating FC rings with (?fc > 300 ms. In this paper we review the physics of internal, discrete, passive FCs and describe the evolution of the PFRC's FC array. We then detail new experiments that have produced higher performance FC rings that contain embedded high-temperature superconducting (HTS) tapes. Several HTS tape winding configurations have been studied and a wide range of extended skin times, from 0.4 s to over 103 s, has been achieved. The new FC rings must carry up to 3 kA of current to balance the expected PFRC-2 plasma pressure, so the dependence of the HTS-FC critical current on the winding configuration and temperature was also studied. From these experiments, the key HTS-FC design considerations have been identified and HTS-FC rings with the desired performance characteristics have been produced.

E. Oz, C.E. Myers, M.R. Edwards, B. Berlinger, A. Brooks, and S.A. Cohen

2011-01-05

288

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

289

Magnetic field gradient measurement on magnetic cards using magnetic force microscopy  

Microsoft Academic Search

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

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

2002-01-01

290

Magnetic Fields in Molecular Clouds  

NASA Astrophysics Data System (ADS)

Maps of far-infrared and submillimeter polarization vectors have typically been examined one-at-a-time for magnetic field structure related to processes such as gravitational collapse, differential rotation, expanding H II regions, or tidal stripping. The same maps can be used to determine angular dispersion due to turbulence in molecular clouds, where the turbulent dispersion is distinguished from dispersion due to curvature of the large-scale structure or the apparent dispersion due to measurement error. Taking into account the differences between the dispersion due to magneto-hydrodynamic waves in the arms of the Galaxy and dispersion due to turbulence in molecular clouds, one can infer field strengths in dense clouds using a method analogous to that used by Chandresekhar & Fermi to determine field strengths in the Galactic plane. With an accurate archive of flux and polarization maps one can also determine three-dimensional cloud shapes and field orientations, or look for correlations between fields in molecular clouds and fields in the surrounding medium.

Hildebrand, R. H.

2009-12-01

291

Interplanetary magnetic field data book  

NASA Technical Reports Server (NTRS)

An interplanetary magnetic field (IMF) data set is presented that is uniform with respect to inclusion of cislunar IMF data only, and which has as complete time coverage as presently possible over a full solar cycle. Macroscale phenomena in the interplanetary medium (sector structure, heliolatitude variations, solar cycle variations, etc.) and other phenomena (e.g., ground level cosmic-ray events) for which knowledge of the IMF with hourly resolution is necessary, are discussed. Listings and plots of cislunar hourly averaged IMP parameters over the period November 27, 1963, to May 17, 1974, are presented along with discussion of the mutual consistency of the IMF data used herein. The magnetic tape from which the plots and listings were generated, which is available from the National Space Science Data Center (NSSDC), is also discussed.

King, J. H.

1975-01-01

292

The Giotto magnetic field investigation  

NASA Technical Reports Server (NTRS)

The Giotto spacecraft will carry sensors for investigating the interplanetary magnetic field while en route and the interaction between the solar wind magnetoplasma and Halley's Comet neutral gas outflow during close approach. Giotto will carry an outboard biaxial fluxgate system and inboard electronics. The instrumentation draws 1.2 kW and weighs 1.31 kg. Sampling rates will be 28/sec during close encounter, covering selectable ranges from 16 nT to 65,535 nT. In-flight calibration techniques are under development to ensure magnetic cleanliness will be obtained. Measurements are also planned of the inbound bow shock, the magnetosheath and the cometary ionopause. The data will be collected as close as 1000 km from the comet surface.

Neubauer, F. M.; Musmann, G.; Acuna, M. H.; Burlaga, L. F.; Ness, N. F.; Mariani, F.; Wallis, M.; Ungstrup, E.; Schmidt, H.

1983-01-01

293

Rings  

NASA Astrophysics Data System (ADS)

Rings recounts one of the most fascinating stories to emerge from our recent exploration of the solar system. In the past decade scientists have learned more about this beautiful astronomical phenomenon than was ever known before. James Elliot played a leading role in the scientific group that discovered the rings of Uranus, and Richard Kerr has covered Voyager's encounters with Jupiter, Saturn, and Uranus for Science magazine. Together they capture the excitement of the new discoveries - the first since Galileo observed Saturn's rings in 1610 - while showing the central role serendipity can play in scientific progress. James Elliot is Professor of Astronomy and Physics at MIT and Director of the George R. Wallace, Jr., Astrophysical Observatory. Richard Kerr is a senior writer on the research news staff of Science magazine. Copies of the tape that recorded the discovery of the Uranian rings are available from The MIT Press.

Elliot, James; Kerr, Richard

1987-04-01

294

Magnetic anisotropy of the antiferromagnetic ring [Cr8F8Piv16].  

PubMed

A new tetragonal (P42(1)2) crystalline form of [Cr8F8Piv16] (HPiv = pivalic acid, trimethyl acetic acid) is reported. The ring-shaped molecules, which are aligned in a parallel fashion in the unit cell, form almost perfectly planar, regular octagons. The interaction between the CrIII ions is antiferromagnetic (J = 12 cm(-1)) which results in a S = 0 spin ground state. The low-lying spin excited states were investigated by cantilever torque magnetometry (CTM) and high-frequency EPR (HFEPR). The compound shows hard-axis anisotropy. The axial zero-field splitting (ZFS) parameters of the first two spin excited states (S = 1 and S = 2, respectively) are D1 = 1.59(3) cm(-1) or 1.63 cm(-1) (from CTM and HFEPR, respectively) and D2 = 0.37 cm(-1) (from HFEPR). The dipolar contributions to the ZFS of the S = 1 and S = 2 spin states were calculated with the point dipolar approximation. These contributions proved to be less than the combined single-ion contributions. Angular overlap model calculations that used parameters obtained from the electronic absorption spectrum, showed that the unique axis of the single-ion ZFS is at an angle of 19.3(1) degrees with respect to the ring axis. The excellent agreement between the experimental and the theoretical results show the validity of the used methods for the analysis of the magnetic anisotropy in antiferromagnetic CrIII rings. PMID:11826863

van Slageren, Joris; Sessoli, Roberta; Gatteschi, Dante; Smith, Andrew A; Helliwell, Madeleine; Winpenny, Richard E P; Cornia, Andrea; Barra, Anne-Laure; Jansen, Aloysius G M; Rentschler, Eva; Timco, Grigore A

2002-01-01

295

Graphene in high magnetic fields  

NASA Astrophysics Data System (ADS)

Carbon-based nano-materials, such as graphene and carbon nanotubes, represent a fascinating research area aiming at exploring their remarkable physical and electronic properties. These materials not only constitute a playground for physicists, they are also very promising for practical applications and are envisioned as elementary bricks of the future of the nano-electronics. As for graphene, its potential already lies in the domain of opto-electronics where its unique electronic and optical properties can be fully exploited. Indeed, recent technological advances have demonstrated its effectiveness in the fabrication of solar cells and ultra-fast lasers, as well as touch-screens and sensitive photo-detectors. Although the photo-voltaic technology is now dominated by silicon-based devices, the use of graphene could very well provide higher efficiency. However, before the applied research to take place, one must first demonstrates the operativeness of carbon-based nano-materials, and this is where the fundamental research comes into play. In this context, the use of magnetic field has been proven extremely useful for addressing their fundamental properties as it provides an external and adjustable parameter which drastically modifies their electronic band structure. In order to induce some significant changes, very high magnetic fields are required and can be provided using both DC and pulsed technology, depending of the experimental constraints. In this article, we review some of the challenging experiments on single nano-objects performed in high magnetic and low temperature. We shall mainly focus on the high-field magneto-optical and magneto-transport experiments which provided comprehensive understanding of the peculiar Landau level quantization of the Dirac-type charge carriers in graphene and thin graphite.

Orlita, Milan; Escoffier, Walter; Plochocka, Paulina; Raquet, Bertrand; Zeitler, Uli

2013-01-01

296

Suppression of magnetic relaxation by a transverse alternating magnetic field  

SciTech Connect

The evolution of the spatial distribution of the magnetic induction in a superconductor after the action of the alternating magnetic field perpendicular to the trapped magnetic flux has been analyzed. The observed stabilization of the magnetic induction profile is attributed to the increase in the pinning force, so that the screening current density becomes subcritical. The last statement is corroborated by direct measurements.

Voloshin, I. F.; Kalinov, A. V.; Fisher, L. M. [All-Russia Electrical Engineering Institute (Russian Federation)], E-mail: fisher@vei.ru; Yampol'skii, V. A. [National Academy of Sciences of Ukraine, Institute of Radiophysics and Electronics (Ukraine)], E-mail: yam@vk.kharkov.ua

2007-07-15

297

Magnetic field sources and their threat to magnetic media  

NASA Technical Reports Server (NTRS)

Magnetic storage media (tapes, disks, cards, etc.) may be damaged by external magnetic fields. The potential for such damage has been researched, but no objective standard exists for the protection of such media. This paper summarizes a magnetic storage facility standard, Publication 933, that ensures magnetic protection of data storage media.

Jewell, Steve

1993-01-01

298

Magnetic nanostructures as amplifiers of transverse fields in magnetic resonance.  

PubMed

We introduce the concept of amplifying the transverse magnetic fields produced and/or detected with inductive coils in magnetic resonance settings by using the reversible transverse susceptibility properties of magnetic nanostructures. First, we describe the theoretical formalism of magnetic flux amplification through the coil in the presence of a large perpendicular DC magnetic field (typical of magnetic resonance systems) achieved through the singularity in the reversible transverse susceptibility in anisotropic single domain magnetic nanoparticles. We experimentally demonstrate the concept of transverse magnetic flux amplification in an inductive coil system using oriented nanoparticles with uni-axial magnetic anisotropy. We also propose a composite ferromagnetic/anti-ferromagnetic core/shell nanostructure system with uni-directional magnetic anisotropy that, in principle, provides maximal transverse magnetic flux amplification. PMID:16039099

Barbic, Mladen; Scherer, Axel

2005-09-01

299

Thinned fiber Bragg grating magnetic field sensor with magnetic fluid  

Microsoft Academic Search

The refractive index of magnetic fluid may be changed by external magnetic field. Therefore, through measuring its refractive index, the intensity of the magnetic field can be obtained. Fiber Bragg grating (FBG) is sensitive to the refractive index surrounding its cladding when the diameter of cladding is reduced to a certain degree. In order to prove the sensitivity of the

Ciming Zhou; Li Ding; Dongli Wang; Yaqi Kuang; Desheng Jiang

2011-01-01

300

The Galactic Magnetic Field as Viewed from the VLA  

NASA Astrophysics Data System (ADS)

Interstellar magnetic fields play critical roles in many astrophysical processes. Yet despite their importance, our knowledge about magnetic fields in our Galaxy remains limited. For the field within the Milky Way much of what we do know comes from radio astronomy, through observations of polarization and Faraday rotation measures (RMs) of extragalactic sources and pulsars. A high angular density of RM measurements in several critical areas of the Galaxy is needed to clarify the Galactic magnetic field structure. Understanding the overall structure of the magnetic field will subsequently help us determine the origin and evolution of the field. In an effort to determine the overall structure of the field, Sun et al. (2008) produced 3 models of the Galactic magnetic field based on RM measurements available at the time. These models made distinct predictions for RMs in a region of the inner Galaxy at low Galactic latitude. Using observations made with the Very Large Array (VLA), we have determined RMs for sources in this critical region. In this talk we will present the results of our study and show how the RMs strongly support the ASS+RING model.

van Eck, Cameron; Brown, Jo-Anne

2009-05-01

301

Magnetic field in a turbulent galactic disk  

Microsoft Academic Search

A simple kinematic model has been applied to simulate the evolution of the interstellar magnetic field permanently twisted by turbulent gas motions accompanied by effects of the field diffusion. The magnetic field was found to develop well-ordered twisted structures over the whole gas parcel analyzed. This field configuration has a preferred sense of twisting dependent on the helicity of the

Katarzyna Otmianowska-Mazur; Marek Urbanik; Artur Terech

1992-01-01

302

A spatio-temporal dipole simulation of gastrointestinal magnetic fields.  

PubMed

We have developed a simulation of magnetic fields from gastrointestinal (GI) smooth muscle. Current sources are modeled as depolarization dipoles at the leading edge of the isopotential ring of electrical control activity (ECA) that is driven by coupled cells in the GI musculature. The dipole moment resulting from the known transmembrane potential distribution varies in frequency and phase depending on location in the GI tract. Magnetic fields in a homogeneous volume conductor are computed using the law of Biot-Savart and characterized by their spatial and temporal variation. The model predicts that the natural ECA frequency gradient may be detected by magnetic field detectors outside the abdomen. It also shows that propagation of the ECA in the gastric musculature results in propagating magnetic field patterns. Uncoupling of gastric smooth muscle cells disrupts the normal magnetic field propagation pattern. Intestinal ischemia, which has been experimentally characterized by lower-than-normal ECA frequencies, also produces external magnetic fields with lower ECA frequencies. PMID:12848351

Bradshaw, L Alan; Myers, Andrew; Wikswo, John P; Richards, William O

2003-07-01

303

Magnetic design of trim excitations for the advanced light source storage ring sextupole.  

National Technical Information Service (NTIS)

The Advanced Light Source (ALS) storage ring sextupole is a unique multi-purpose magnet. It is designed to operate as a sextupole with three auxiliary trim modes: horizontal steering, vertical steering, and skew quadrupole. A perturbation theory for iron-...

S. Marks

1995-01-01

304

Absolute extinction cross section of individual magnetic split-ring resonators  

Microsoft Academic Search

We measure the absolute extinction cross section spectra of individual split-ring resonators (fundamental magnetic resonance at 1.4-mum wavelength). The experiments are compared with a simple electric-circuit model and with microscopic calculations.

Martin Husnik; Matthias W. Klein; Martin Wegener; Michael König; Jens Niegemann; Kurt Busch; Nils Feth; STEFAN LINDEN

2008-01-01

305

Low-field magnetic properties of wide Fe-Ni metallic glass strips  

Microsoft Academic Search

Wide samples of continuous-cast metallic glass ribbons fabricated to tape-wound or punched-ring core configurations are shown to possess the same attractive low-field magnetic properties as are observed in narrow ribbons of similar composition. Annealing ring-laminated cores in crossed fields leads to lower core loss than for metallic glass (wide or narrow) annealed only in a circumferential field.

R. O'Handley; M. Narasimhan

1979-01-01

306

Spin dephasing in a magnetic dipole field.  

PubMed

Transverse relaxation by dephasing in an inhomogeneous field is a general mechanism in physics, for example, in semiconductor physics, muon spectroscopy, or nuclear magnetic resonance. In magnetic resonance imaging the transverse relaxation provides information on the properties of several biological tissues. Since the dipole field is the most important part of the multipole expansion of the local inhomogeneous field, dephasing in a dipole field is highly important in relaxation theory. However, there have been no analytical solutions which describe the dephasing in a magnetic dipole field. In this work we give a complete analytical solution for the dephasing in a magnetic dipole field which is valid over the whole dynamic range. PMID:23004789

Ziener, C H; Kampf, T; Reents, G; Schlemmer, H-P; Bauer, W R

2012-05-01

307

Magnetic field effects on microwave absorbing materials  

NASA Technical Reports Server (NTRS)

The objective of this program was to gather information to formulate a microwave absorber that can work in the presence of strong constant direct current (DC) magnetic fields. The program was conducted in four steps. The first step was to investigate the electrical and magnetic properties of magnetic and ferrite microwave absorbers in the presence of strong magnetic fields. This included both experimental measurements and a literature survey of properties that may be applicable to finding an appropriate absorbing material. The second step was to identify those material properties that will produce desirable absorptive properties in the presence of intense magnetic fields and determine the range of magnetic field in which the absorbers remain effective. The third step was to establish ferrite absorber designs that will produce low reflection and adequate absorption in the presence of intense inhomogeneous static magnetic fields. The fourth and final step was to prepare and test samples of such magnetic microwave absorbers if such designs seem practical.

Goldberg, Ira; Hollingsworth, Charles S.; Mckinney, Ted M.

1991-01-01

308

The Wind Magnetic Field Investigation  

NASA Astrophysics Data System (ADS)

The magnetic field experiment on WIND will provide data for studies of a broad range of scales of structures and fluctuation characteristics of the interplanetary magnetic field throughout the mission, and, where appropriate, relate them to the statics and dynamics of the magnetosphere. The basic instrument of the Magnetic Field Investigation (MFI) is a boom-mounted dual triaxial fluxgate magnetometer and associated electronics. The dual configuration provides redundancy and also permits accurate removal of the dipolar portion of the spacecraft magnetic field. The instrument provides (1) near real-time data at nominally one vector per 92 s as key parameter data for broad dissemination, (2) rapid data at 10.9 vectors s-1 for standard analysis, and (3) occasionally, snapshot (SS) memory data and Fast Fourier Transform data (FFT), both based on 44 vectors s-1. These measurements will be precise (0.025%), accurate, ultra-sensitive (0.008 nT/step quantization), and where the sensor noise level is <0.006 nT r.m.s. for 0 10 Hz. The digital processing unit utilizes a 12-bit microprocessor controlled analogue-to-digital converter. The instrument features a very wide dynamic range of measurement capability, from ±4 nT up to ±65 536 nT per axis in eight discrete ranges. (The upper range permits complete testing in the Earth's field.) In the FTT mode power spectral density elements are transmitted to the ground as fast as once every 23 s (high rate), and 2.7 min of SS memory time series data, triggered automatically by pre-set command, requires typically about 5.1 hours for transmission. Standard data products are expected to be the following vector field averages: 0.0227-s (detail data from SS), 0.092 s (‘detail’ in standard mode), 3 s, 1 min, and 1 hour, in both GSE and GSM coordinates, as well as the FFT spectral elements. As has been our team's tradition, high instrument reliability is obtained by the use of fully redundant systems and extremely conservative designs. We plan studies of the solar wind: (1) as a collisionless plasma laboratory, at all time scales, macro, meso and micro, but concentrating on the kinetic scale, the highest time resolution of the instrument (=0.022 s), (2) as a consequence of solar energy and mass output, (3) as an external source of plasma that can couple mass, momentum, and energy to the Earth's magnetosphere, and (4) as it is modified as a consequence of its imbedded field interacting with the moon. Since the GEOTAIL Inboard Magnetometer (GIM), which is similar to the MFI instrument, was developed by members of our team, we provide a brief discussion of GIM related science objectives, along with MFI related science goals.

Lepping, R. P.; Ac?na, M. H.; Burlaga, L. F.; Farrell, W. M.; Slavin, J. A.; Schatten, K. H.; Mariani, F.; Ness, N. F.; Neubauer, F. M.; Whang, Y. C.; Byrnes, J. B.; Kennon, R. S.; Panetta, P. V.; Scheifele, J.; Worley, E. M.

1995-02-01

309

Topological Description of Coronal Magnetic Fields.  

National Technical Information Service (NTIS)

Determining the structure and behavior of solar coronal magnetic fields is a central problem in solar physics. At the photosphere, the field is believed to be strongly localized into discrete flux tubes. After providing a rigorous definition of field topo...

M. A. Berger

1986-01-01

310

Structured electrodeposition in magnetic gradient fields  

NASA Astrophysics Data System (ADS)

Electrodeposition in superimposed magnetic gradient fields is a new and promising method of structuring metal deposits while avoiding masking techniques. The magnetic properties of the ions involved, their concentrations, the electrochemical deposition parameters, and the amplitude of the applied magnetic gradient field determine the structure generated. This structure can be thicker in regions of high magnetic field gradients. It can also be free-standing or inversely structured. The complex mechanism of structured electrodeposition of metallic layers in superimposed magnetic gradient fields was studied by different experimental methods, by analytical methods and by numerical simulation and will be discussed comprehensively.

Uhlemann, Margitta; Tschulik, Kristina; Gebert, Annett; Mutschke, Gerd; Fröhlich, Jochen; Bund, Andreas; Yang, Xuegeng; Eckert, Kerstin

2013-03-01

311

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

312

Anhysteretic Remanent Magnetization in Small Steady Fields  

Microsoft Academic Search

The phenomenon called anhysteretic remanent magnetization, ARM, has been known for a long time, but it has received relatively little attention. A knowledge of this type of magnetization is required in proper application of alternating field demagnetization tech- niques to rock magnetism problems. Over a wide range of low values of the steady field Ho, the ARM intensity is a

Bob J. Patton; John L. Fitch

1962-01-01

313

On Magnetic Field Generation Mechanisms in Astrophysics  

Microsoft Academic Search

Magnetic chemically peculiar stars (CP stars) are characterized by a strong magnetic field, peculiar chemical composition and slow rotation. Since the origin and evolution of CP stars may be responsible for such unusual features, understanding the mechanisms of generation of the magnetic field is one of the ways to learn more about the CP star characteristics. At present there are

O. G. Cherny

2011-01-01

314

Orienting Paramecium with intense static magnetic fields  

Microsoft Academic Search

Recent experiments on cell division suggest the application of intense static magnetic fields as a novel tool for the manipulation of biological systems [1]. The magnetic field appears to couple to the intrinsic anisotropies in the diamagnetic components of the cells. Here, we present measurements of the intrinsic average diamagnetic anisotropy of the whole single celled ciliate, Paramecium Caudatum. Magnetic

James M. Valles Jr.; Karine Guevorkian; Carl Quindel

2004-01-01

315

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

316

The structure of helical interplanetary magnetic fields  

NASA Technical Reports Server (NTRS)

The interplanetary magnetic field is known to be highly helical. Although the detailed spatial structure of the fields has yet to be elucidated, the helicity spectrum has been conjectured to result from a random walk in the direction of a constant magnitude magnetic field vector. A model using three-dimensional fluctuations with variations in B is demonstrated giving a good fit to the helicity spectrum as well as to other properties of the interplanetary magnetic field.

Goldstein, M. L.; Roberts, D. A.; Fitch, C. A.

1991-01-01

317

Analysis of magnetic field levels at KSC  

NASA Technical Reports Server (NTRS)

The scope of this work is to evaluate the magnetic field levels of distribution systems and other equipment at Kennedy Space Center (KSC). Magnetic fields levels in several operational areas and various facilities are investigated. Three dimensional mappings and contour are provided along with the measured data. Furthermore, the portion of magnetic fields generated by the 60 Hz fundamental frequency and the portion generated by harmonics are examined. Finally, possible mitigation techniques for attenuating fields from electric panels are discussed.

Christodoulou, Christos G.

1994-01-01

318

The moving-ring field-reversed mirror prototype reactor  

NASA Astrophysics Data System (ADS)

A prototype fusion reactor was designed based on magnetic field reversed plasma confinement. A set of physics, technology, and mechanical design criteria were developed in order to make this concept attractive. Six major criteria guide the commercial prototype design. The prototype must: (1) produce net electricity decisively P sub net 70% of P sub gross; (2) scale to an economical commercial plant and have small physical size; (3) have all features required of a correcial upgrade plant (H-3 breeding, etc.); (4) minimize exotic technology and maintenance complexity; (5) promise significantly lower safety hazards than fission plants (environmentally and socially acceptable); and (6) be modular in design to permit repetitive production of components.

Smith, A. C., Jr.; Carlson, G. A.; Fleischmann, H. H.; Grossman, W., Jr.; Kammash, T.; Schultz, K. R.; Woodall, D. M.

1981-03-01

319

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

320

Magnetizing technique for permanent magnets by intense static fields generated by HTS bulk magnets: Numerical Analysis  

NASA Astrophysics Data System (ADS)

A demagnetized Nd-Fe-B permanent magnet was scanned in the strong magnetic field space just above the magnetic pole containing a HTS bulk magnet which generates the magnetic field 3.4 T. The magnet sample was subsequently found to be fully magnetized in the open space of the static magnetic fields. The finite element method was carried out for the static field magnetization of a permanent magnet using a HTS bulk magnet. Previously, our research group experimentally demonstrated the possibility of full magnetization of rare earth permanent magnets with high-performance magnetic properties with use of the static field of HTS bulk magnets. In the present study, however, we succeeded for the first time in visualizing the behavior of the magnetizing field of the bulk magnet during the magnetization process and the shape of the magnetic field inside the body being magnetized. By applying this kind of numerical analysis to the magnetization for planned motor rotors which incorporate rare-earth permanent magnets, we hope to study the fully magnetized regions for the new magnetizing method using bulk magnets and to give motor designing a high degree of freedom.

N. Kawasaki; Oka, T.; Fukui, S.; Ogawa, J.; Sato, T.; Terasawa, T.; Itoh, Y.

321

Magnetic field topology of the RS CVn star II Pegasi  

NASA Astrophysics Data System (ADS)

Context. The dynamo processes in cool active stars generate complex magnetic fields responsible for prominent surface stellar activity and variability at different time scales. For a small number of cool stars magnetic field topologies were reconstructed from the time series of spectropolarimetric observations using the Zeeman Doppler imaging (ZDI) method, often yielding surprising and controversial results. Aims: In this study we follow a long-term evolution of the magnetic field topology of the RS CVn binary star II Peg using a more self-consistent and physically more meaningful modelling approach compared to previous ZDI studies. Methods: We collected high-resolution circular polarisation observations of II Peg using the SOFIN spectropolarimeter at the Nordic Optical Telescope. These data cover 12 epochs spread over 7 years, comprising one of the most comprehensive spectropolarimetric data sets acquired for a cool active star. A multi-line diagnostic technique in combination with a new ZDI code is applied to interpret these observations. Results: We have succeeded in detecting clear magnetic field signatures in average Stokes V profiles for all 12 data sets. These profiles typically have complex shapes and amplitudes of ~10-3 of the unpolarised continuum, corresponding to mean longitudinal fields of 50-100 G. Magnetic inversions using these data reveals evolving magnetic fields with typical local strengths of 0.5-1.0 kG and complex topologies. Despite using a self-consistent magnetic and temperature mapping technique, we do not find a clear correlation between magnetic and temperature features in the ZDI maps. Neither do we confirm the presence of persistent azimuthal field rings found in other RS CVn stars. Reconstruction of the magnetic field topology of II Peg reveals significant evolution of both the surface magnetic field structure and the extended magnetospheric field geometry on the time scale covered by our observations. From 2004 to 2010 the total field energy drastically declined and the field became less axisymmetric. This also coincided with the transition from predominantly poloidal to mainly toroidal field topology. Conclusions: A qualitative comparison of the ZDI maps of II Peg with the prediction of dynamo theory suggests that the magnetic field in this star is produced mainly by the turbulent ?2 dynamo rather than the solar ?? dynamo. Our results do not show a clear active longitude system, nor is there evidence of the presence of an azimuthal dynamo wave. Based on observations obtained with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, at the Spanish Observatorio del Roque de los Muchachos of the Instituto Astrofisica de Canarias.

Kochukhov, O.; Mantere, M. J.; Hackman, T.; Ilyin, I.

2013-02-01

322

Effects of magnetic fields on mosquitoes.  

PubMed

Phylogenetically diverse organisms, including some insects, are able to detect and respond to magnetic fields comparable to the Earth's magnetic field. Because of their tremendous importance to public health, mosquitoes were tested for the presence of remanent ferromagnetic material indicative of a biological compass and also tested for behavioral responses to magnetic fields. Using a superconducting quantum interferometry device, we found that significant remnant was probably due to attraction of ferromagnetic dust onto the surface of live or dead mosquitoes. Most mosquitoes placed in a 1.0-gauss, uniform magnetic field moved until they were oriented parallel to the field. Two of 3 species of mosquitoes tested took fewer blood meals in a rotating magnetic field than in the Earth's normal magnetic field. PMID:10901636

Strickman, D; Timberlake, B; Estrada-Franco, J; Weissman, M; Fenimore, P W; Novak, R J

2000-06-01

323

Rapid decay of storm time ring current due to pitch angle scattering in curved field line  

NASA Astrophysics Data System (ADS)

The storm time ring current sometimes exhibits rapid decay, as suggested from the Dst index, but the underlying mechanism is unknown. By means of a simulation with pitch angle scattering due to the field line curvature (FLC), together with the charge exchange and adiabatic loss cone loss, we investigated rapid decay of the storm time ring current for the large magnetic storm that occurred on 12 August 2000. When all three loss processes were included, the Dst (SYM-H) index showed rapid recovery with an e-folding time of ˜6 h. However, without FLC scattering, the simulated Dst (SYM-H) index showed a slower recovery with an e-folding time of ˜12 h. Overall flux of energetic neutral hydrogen with energy ? 39 keV was significantly reduced by the FLC scattering and is consistent with data from the high energy neutral analyzer (HENA) on board the IMAGE satellite. Power of precipitating protons showed a fairly good agreement with data from the far ultraviolet (FUV) imager on board IMAGE. These fairly good agreements with observations lead to the possible conclusion that the FLC scattering is a significant loss mechanism for the ring current ions, and the main oval of the proton aurora is likely a manifestation of the precipitating loss of the protons for this particular storm.

Ebihara, Y.; Fok, M.-C.; Immel, T. J.; Brandt, P. C.

2011-03-01

324

Magnetized black holes and black rings in the higher dimensional dilaton gravity  

NASA Astrophysics Data System (ADS)

In this paper we consider magnetized black holes and black rings in the higher dimensional dilaton gravity. Our study is based on exact solutions generated by applying a Harrison transformation to known asymptotically flat black hole and black ring solutions in higher dimensional spacetimes. The explicit solutions include the magnetized version of the higher dimensional Schwarzschild-Tangherlini black holes, Myers-Perry black holes, and five-dimensional (dipole) black rings. The basic physical quantities of the magnetized objects are calculated. We also discuss some properties of the solutions and their thermodynamics. The ultrarelativistic limits of the magnetized solutions are briefly discussed and an explicit example is given for the D-dimensional magnetized Schwarzschild-Tangherlini black holes.

Yazadjiev, Stoytcho S.

2006-03-01

325

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

326

Magnetic fields in the early Universe  

NASA Astrophysics Data System (ADS)

We give a pedagogical introduction to two aspects of magnetic fields in the early Universe. We first focus on how to formulate electrodynamics in curved space time, defining appropriate magnetic and electric fields and writing Maxwell equations in terms of these fields. We then specialize to the case of magnetohydrodynamics in the expanding Universe. We emphasize the usefulness of tetrads in this context. We then review the generation of magnetic fields during the inflationary era, deriving in detail the predicted magnetic and electric spectra for some models. We discuss potential problems arising from back reaction effects and from the large variation of the coupling constants required for such field generation.

Subramanian, K.

2010-01-01

327

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

328

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

329

MAGNETIC BRAIDING AND PARALLEL ELECTRIC FIELDS  

SciTech Connect

The braiding of the solar coronal magnetic field via photospheric motions-with subsequent relaxation and magnetic reconnection-is one of the most widely debated ideas of solar physics. We readdress the theory in light of developments in three-dimensional magnetic reconnection theory. It is known that the integrated parallel electric field along field lines is the key quantity determining the rate of reconnection, in contrast with the two-dimensional case where the electric field itself is the important quantity. We demonstrate that this difference becomes crucial for sufficiently complex magnetic field structures. A numerical method is used to relax a braided magnetic field toward an ideal force-free equilibrium; the field is found to remain smooth throughout the relaxation, with only large-scale current structures. However, a highly filamentary integrated parallel current structure with extremely short length-scales is found in the field, with the associated gradients intensifying during the relaxation process. An analytical model is developed to show that, in a coronal situation, the length scales associated with the integrated parallel current structures will rapidly decrease with increasing complexity, or degree of braiding, of the magnetic field. Analysis shows the decrease in these length scales will, for any finite resistivity, eventually become inconsistent with the stability of the coronal field. Thus the inevitable consequence of the magnetic braiding process is a loss of equilibrium of the magnetic field, probably via magnetic reconnection events.

Wilmot-Smith, A. L.; Hornig, G.; Pontin, D. I. [Division of Mathematics, University of Dundee, Dundee DD1 4HN (United Kingdom)], E-mail: antonia@maths.dundee.ac.uk

2009-05-10

330

Exploring Magnetic Fields in Your Environment  

NSDL National Science Digital Library

This is a lesson about measuring magnetic field directions of Earth and in the environment. First, learners go outside, far away from buildings, power lines, or anything electrical or metal, and use compasses to identify magnetic North. Next, they use the compasses to probe whether there are any sources of magnetic fields in the local environment, including around electronic equipment such as a CD player and speakers. This is the first lesson in the second session of the Exploring Magnetism teacher guide.

331

Horizontal magnetic fields in the solar photosphere  

Microsoft Academic Search

Two-dimensional simulations of time-dependent solar magnetogranulation are used to analyze the horizontal magnetic fields and the response of the synthesized Stokes profiles of the IR FeI lambda1564.85 nm line to the magnetic fields. The 1.5-h series of MHD models used for the analyses reproduces a region of the magnetic network in the photosphere with an unsigned magnetic flux density of

V. A. Sheminova

2009-01-01

332

Horizontal magnetic fields in the solar photosphere  

Microsoft Academic Search

Two-dimensional simulations of time-dependent solar magnetogranulation are used to analyze the horizontal magnetic fields\\u000a and the response of the synthesized Stokes profiles of the IR FeI ?1564.85 nm line to the magnetic fields. The 1.5-h series of MHD models used for the analyses reproduces a region of the magnetic\\u000a network in the photosphere with an unsigned magnetic flux density of

V. A. Sheminova

2009-01-01

333

A magnetospheric magnetic field model with flexible internal current systems  

SciTech Connect

A three dimensional B-field model of the Earth's magnetosphere satisfying the condition {del} {center dot} B = 0 is described. Highly flexible ring and cross-tail current systems are combined with the vacuum B-field model of Voigt (1981), a fully shielded dipole within a fixed magnetopause geometry. The ring current consists of nested eastward and westward flowing current distributions which tilt with and remain axially symmetric about the magnetic dipole axis. To include realistic flexing of the current sheet with dipole tilt, the intensity and position of the westward flowing cross-tail current in the midnight meridian can be represented by arbitrary functions of the distance along the magnetotail. Model configurations are completely specified by four initial physical input parameters: the dipole tilt angle, the magnetopause stand-off distance, the geomagnetic index D{sup st}, and the midnight equatorward boundary of the diffuse aurora. These parameters determine the relative position and strength of both the ring and cross-tail currents and provide for a diverse array of configurations including many degrees of magnetotail field stretching. The resulting equatorial flux levels, {Delta}B profiles, and the dipole tilt-dependent shape and position of the neutral sheet compare well with observations. With additional input parameters, the reconfiguration of the geomagnetic tail during magnetospheric substorms is modeled and incorporated into a magnetic field simulation of an observed substorm event. The ring and cross-tail currents, as prescribed by the set of initial input parameters, follow a physically reasonable sequence of development and magnetic flux densities are in general agreement with geosynchronous observations of the event.

Hilmer, R.V.

1989-01-01

334

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

335

The National High Magnetic Field Laboratory  

Microsoft Academic Search

The National High Magnetic Field Laboratory (NHMFL) was established in 1990, on the basis of a collaboration between Florida State University (FSU), the University of Florida (UF) and Los Alamos National Laboratory (LANL). The main campus for the NHMFL is located in Tallahassee, Florida, and its general purpose DC magnetic field facility is described in this paper. The pulsed field

B. L. Brandt; S. Hannahs; H. J. Schneider-Muntau; G. Boebinger; N. S. Sullivan

2001-01-01

336

Representation of magnetic fields in space  

NASA Technical Reports Server (NTRS)

Several methods by which a magnetic field in space can be represented are reviewed with particular attention to problems of the observed geomagnetic field. Time dependence is assumed to be negligible, and five main classes of representation are described by vector potential, scalar potential, orthogonal vectors, Euler potentials, and expanded magnetic field.

Stern, D. P.

1975-01-01

337

Primordial magnetic fields from superconducting cosmic strings  

Microsoft Academic Search

This paper explores the possibility of generation of a primordial magnetic field by a network of charged-current carrying cosmic strings. The field is created by vorticity, generated in the primordial plasma due to the strings' motion and gravitational pull. In the case of superconducting strings formed at the breaking of grand unification, it is found that strong magnetic fields of

Konstantinos Dimopoulos

1998-01-01

338

DC-based magnetic field controller  

DOEpatents

A magnetic field controller for laboratory devices and in particular to dc operated magnetic field controllers for mass spectrometers, comprising a dc power supply in combination with improvements to a hall probe subsystem, display subsystem, preamplifier, field control subsystem, and an output stage.

Kotter, Dale K. (Shelley, ID); Rankin, Richard A. (Ammon, ID); Morgan, John P,. (Idaho Falls, ID)

1994-01-01

339

Manipulating Cells with Static Magnetic Fields  

Microsoft Academic Search

We review our investigations of the use of static magnetic fields, B, for manipulating cells and cellular processes. We describe how B fields modify the cell division pattern of frog embryos and consequently can be used to probe the pattern determinants. We also observe that magnetic fields modify the swimming behavior of Paramecium Caudatum. We describe these modifications and their

J. M. Valles; K. Guevorkian

2005-01-01

340

Imaging of magnetic colloids under the influence of magnetic field by cryogenic transmission electron microscopy  

NASA Astrophysics Data System (ADS)

The application of superparamagnetic nanoparticles for in vivo magnetic resonance imaging (MRI) under external ac magnetic field has attracted considerable research efforts in recent years. However, it is unclear how superparamagnetic nanostructures arrange themselves in fluidic environment under external magnetic field. Here, we report direct visualization of the effect of applied magnetic field to the ferrofluids (about 6 nm superparamagnetic magnetite (Fe3O4) nanoparticle ``colloidal'' suspension) using the cryogenic transmission electron microscopy (cryo-TEM). While long dipole chains (up to millimeter range) of the magnetite along the magnetic lines are found in samples dried inside the magnetic field, only short dipole chains (within tens of nanometer scale) with random orientations are observed in the wet sample observed by cryo-TEM. In the wet sample, aggregations of medium-length dipole chains (up to hundreds of nanometer) can be observed at the areas where the nanoparticles are ``solidified'' when phase separation occurs. In situ formation of flux-closure rings is observed at the edge where vitreous ice sublimes due to high-energy electron radiation that leaves magnetite nanoparticles isolated in the vacuum. Such observations may help elucidate the nature of magnetic field-induced assembly in fluidic environment as in the physiological aqueous conditions in MRI and related applications.

Wu, Jinsong; Aslam, M.; Dravid, Vinayak P.

2008-08-01

341

Possible Generation of Self-Magnetic Fields  

SciTech Connect

The earth generates its own magnetic field via a dynamo effect in a conducting fluid. The sun and some other stars also generate self-magnetic fields on large spatial scales and long timescales. Laser-produced plasmas generate intense self-magnetic fields on very short spatial and time scales. Could similar phenomena occur on intermediate spatial scales and timescales, such as in a laboratory plasma? Two questions are posed for consideration: (a) At high electromagnetic wave power input into a low-pressure gas could a significant self-magnetic field be generated? (b) If a self-magnetic field were generated, would it evolve toward a minimum-energy state? If the answers turned out to be affirmative, then the use of self-magnetic fields could have interesting applications.

Dolan, Thomas J. [International Atomic Energy Agency, Vienna (Austria)

2001-09-15

342

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)] [Tennessee Technological Univ., Cookeville, TN (United States)

1997-03-01

343

Probing interstellar magnetic fields with Supernova remnants  

NASA Astrophysics Data System (ADS)

As Supernova remnants expand, their shock waves are freezing in and compressing the magnetic field lines they encounter; consequently we can use Supernova remnants as magnifying glasses for their ambient magnetic fields. We will describe a simple model to determine emission, polarization, and rotation measure characteristics of adiabatically expanding Supernova remnants and how we can exploit this model to gain information about the large scale magnetic field in our Galaxy. We will give two examples: The SNR DA530, which is located high above the Galactic plane, reveals information about the magnetic field in the halo of our Galaxy. The SNR G182.4+4.3 is located close to the anti-centre of our Galaxy and reveals the most probable direction where the large-scale magnetic field is perpendicular to the line of sight. This may help to decide on the large-scale magnetic field configuration of our Galaxy. But more observations of SNRs are needed.

Kothes, Roland; Brown, Jo-Anne

2009-04-01

344

Magnetic field sensor for isotropically sensing an incident magnetic field in a sensor plane  

NASA Technical Reports Server (NTRS)

A magnetic field sensor that isotropically senses an incident magnetic field. This is preferably accomplished by providing a magnetic field sensor device that has one or more circular shaped magnetoresistive sensor elements for sensing the incident magnetic field. The magnetoresistive material used is preferably isotropic, and may be a CMR material or some form of a GMR material. Because the sensor elements are circular in shape, shape anisotropy is eliminated. Thus, the resulting magnetic field sensor device provides an output that is relatively independent of the direction of the incident magnetic field in the sensor plane.

Pant, Bharat B. (Inventor); Wan, Hong (Inventor)

2001-01-01

345

Trapped magnetic field measurements on HTS bulk by peak controlled pulsed field magnetization  

NASA Astrophysics Data System (ADS)

For the past several years, we have studied the high-temperature superconducting (HTS) synchronous motor assembled with melt-textured Gd-Ba-Cu-O bulk magnets. If the single pulse field magnetizes a bulk effectively, size of electrical motor will become small for the strong magnetic field of the HTS magnets without reducing output power of motor. In the previous study, we showed that the HTS bulk was magnetized to excellent cone-shape magnetic field distribution by using the waveform control pulse magnetization (WCPM) method. The WCPM technique made possible the active control of the waveform on which magnetic flux motion depended. We generated the pulse waveform with controlled risetime for HTS bulk magnetization to suppress the magnetic flux motion which decreases magnetization efficiency. The pulsed maximum magnetic flux density with slow risetime is not beyond the maximum magnetic flux density which is trapped by the static field magnetization. But, as for applying the pulse which has fast risetime, the magnetic flux which exceed greatly the threshold penetrates the bulk and causes the disorder of the trapped magnetic distribution. This fact suggests the possibility that the threshold at pulsed magnetization influences the dynamic magnetic flux motion. In this study, Gd-Ba-Cu-O bulk is magnetized by the controlled arbitrary trapezoidal shape pulse, of which the maximum magnetic flux density is controlled not to exceed the threshold. We will present the trapped magnetic characteristics and the technique to generate the controlled pulsed field.

Ida, Tetsuya; Watasaki, Masahiro; Kimura, Yosuke; Miki, Motohiro; Izumi, Mitsuru

2010-06-01

346

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 2012. 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 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 approaching 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 to the Swarm user community. The setup of Swarm ground segment and the contents of the data products will be addressed. More information on the Swarm mission can be found at the mission web site (see URL below).

Drinkwater, M. R.; Haagmans, R.; Floberghagen, R.; Plank, G.; Menard, Y.

2011-12-01

347

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 fall 2012. 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 three 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. In case the Swarm satellites are already in orbit, a summary of the on-going mission operations activities will be given.

Plank, G.; Floberghagen, R.; Menard, Y.; Haagmans, R.

2012-12-01

348

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 fall 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 three 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. In case the Swarm satellites are already in orbit, a summary of the on-going mission operations activities will be given. More information on Swarm can be found at www.esa.int/esaLP/LPswarm.html.

Plank, G.; Floberghagen, R.; Menard, Y.; Haagmans, R.

2013-12-01

349

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

350

Microstructure and magnetic properties of backward extruded NdFeB ring magnets by the CAPA process  

NASA Astrophysics Data System (ADS)

The inhomogeneity in microstructure and magnetic properties of a ring magnet prepared by backward extrusion with a current-applied pressure-assisted process has been investigated. The initial part (top part) of a ring magnet prepared by back extrusion shows a high coercivity which is comparable to the raw powder. It exhibits isotropic characteristics along the three orthogonal directions probably due to small deformation. The last part (bottom part) of the ring magnet has a a low coercivity with large grains because high current flows through the pressurized punches during the whole deformation process as to increase the temperature and grain growth. The middle part is under an appropriate deformation with short time exposure at high temperature, therefore it maintains a relatively high remanent polarization with high coercivity.

Kim, Hyoung-Tae; Kim, Yoon-Bae

2004-06-01

351

Plasma behaviour in a rotating magnetic field  

Microsoft Academic Search

A system was constructed and used to study the behavior of a plasma in a rotating magnetic field in a toroidal system. The plasma density is first formed by RF pre-ionization at low pressure in the presence of a quasi-steady toroidal magnetic field of 0.4 T. The 1.85 MHz rotating magnetic field is generated by two perpendicular four-turn coils driven

M. R. Shubaly

1974-01-01

352

Influence of Segmentation of Ring-Shaped NdFeB Magnets with Parallel Magnetization on Cylindrical Actuators.  

PubMed

This work analyses the effects of segmentation followed by parallel magnetization of ring-shaped NdFeB permanent magnets used in slotless cylindrical linear actuators. The main purpose of the work is to evaluate the effects of that segmentation on the performance of the actuator and to present a general overview of the influence of parallel magnetization by varying the number of segments and comparing the results with ideal radially magnetized rings. The analysis is first performed by modelling mathematically the radial and circumferential components of magnetization for both radial and parallel magnetizations, followed by an analysis carried out by means of the 3D finite element method. Results obtained from the models are validated by measuring radial and tangential components of magnetic flux distribution in the air gap on a prototype which employs magnet rings with eight segments each with parallel magnetization. The axial force produced by the actuator was also measured and compared with the results obtained from numerical models. Although this analysis focused on a specific topology of cylindrical actuator, the observed effects on the topology could be extended to others in which surface-mounted permanent magnets are employed, including rotating electrical machines. PMID:25051032

Eckert, Paulo Roberto; Goltz, Evandro Claiton; Filho, Aly Ferreira Flores

2014-01-01

353

Field and current-induced magnetization reversal studied through spatially resolved point-contacts  

NASA Astrophysics Data System (ADS)

We present results from scanning tunneling microscopy based point-contact measurements of the local resistance in octagon shaped, Co(20 nm)/Cu(5 nm)/Fe19Ni81(2.5 nm) spin-valve rings. Through this technique one can detect the magnetoresistance with spatial resolution, and link it to magnetic domain wall motion within the ring. Measurements with varying currents indicate current-induced effects leading to offsets in the magnetic fields required for magnetic switching. The offsets can be attributed to current-induced spin-transfer torque effects for the thin Fe19Ni81 layer and to Oersted field effects for the thick Co layer.

Saxegaard, Magne; Yang, Dezheng; Wahlström, Erik; Bru?as, Rimantas; Hanson, Maj

2010-05-01

354

Magnet calculations at the Grenoble High Magnetic Field Laboratory  

Microsoft Academic Search

An axisymmetrical constrained semi-analytic optimization process is our basic tool for designing magnets. Developments of 3-D numerical models are undertaken to complement this approach. Such models are needed to investigate the overall behavior of our magnets. They are likely to provide suitable insights to solve the design problems arising from the demand for high magnetic field with both great spatial

Christophe Trophime; Konstantin Egorov; François Debray; W. Joss; G. Aubert

2002-01-01

355

Magnetization curve of spin ice in a [111] magnetic field  

Microsoft Academic Search

Spin ice in a magnetic field in the [111] direction displays two magnetization plateaus: one at saturation and an intermediate one with finite entropy. We study the crossovers between the different regimes from a point of view of (entropically) interacting defects. We develop an analytical theory for the nearest-neighbor spin ice model, which covers most of the magnetization curve. We

S. V. Isakov; K. S. Raman; R. Moessner; S. L. Sondhi

2004-01-01

356

Lunar surface magnetic field concentrations antipodal to young large impact basins  

NASA Technical Reports Server (NTRS)

Planetary electron reflection magnetometry data of the Apollo 15 and 16 subsatellites indicate the presence of major regions of strong surface magnetic fields near the antipodes of four large, young, ringed impact basins. While mechanisms yielding surface magnetic field concentrations antipodal to impact basins are not yet clear, the present results' indicated period of strong lunar magnetic fields, at between about 3.85 and 3.6 aeons, is consistent with lunar paleomagnetic sample data. The origin of the strong surface magnetic fields is discussed.

Lin, R. P.; Anderson, K. A.; Hood, L. L.

1988-01-01

357

The effect of the solar magnetic field on dust-particle orbits in the F corona  

NASA Astrophysics Data System (ADS)

In order to determine whether the solar magnetic field can align circumsolar dust into rings such as those described by Mizutani et al. (1984), the solar magnetic field is divided into its various multipole components and theoretical expressions are derived to determine the effect of each of these components on the orbital elements of circumsolar dust. Simulations are then carried out to determine the effect of a dynamic solar magnetic field on such particles using actual values of the solar magnetic field supplied by Hoeksema (1984). These results are compared to observations of the F corona.

Rusk, Edwin T.

1988-10-01

358

Development of Experimental Superconducting Magnet for the Collector Ring of FAIR Project  

Microsoft Academic Search

A pool cooled experimental magnet based on the copper stabilized NbTi superconducting wire was designed, fabricated and tested, in order to evaluate the engineering design of the dipole superconducting magnet for the collector ring (CR) of the facility for antiproton and ion research (FAIR) project. In this paper, the experimental setup including quench protection system was presented. Performance of the

Yinfeng Zhu; Weiyue Wu; Songtao Wu; Houchang Xu; Changle Liu

2010-01-01

359

Magnetic design of trim excitations for the Advanced Light Source storage ring sextupole  

Microsoft Academic Search

The Advanced Light Source (ALS) storage ring sextupole is a unique multi-purpose magnet. It is designed to operate as a sextupole with three auxiliary trim modes: horizontal steering, vertical steering, and skew quadrupole. A perturbation theory for iron-dominated magnets developed by Klaus Halbach (1969) provides the basis for this design. The three trim excitations are produced by violating sextupole symmetry

S. Marks

1996-01-01

360

Magnetic design of trim excitations for the Advanced Light Source storage ring sextupole  

Microsoft Academic Search

The Advanced Light Source (ALS) storage ring sextupole is a unique multi-purpose magnet. It is designed to operate as a sextupole with three auxiliary trim modes: horizontal steering, vertical steering, and skew quadrupole. A perturbation theory for iron-dominated magnets developed by Klaus Halbach provides the basis for this design. The three trim excitations are produced by violating sextupole symmetry and

S Marks

1995-01-01

361

Flow Transitions in a Rotating Magnetic Field  

NASA Technical Reports Server (NTRS)

Critical Rayleigh numbers have been measured in a liquid metal cylinder of finite height in the presence of a rotating magnetic field. Several different stability regimes were observed, which were determined by the values of the Rayleigh and Hartmann numbers. For weak rotating magnetic fields and small Rayleigh numbers, the experimental observations can be explained by the existence of a single non-axisymmetric meridional roll rotating around the cylinder, driven by the azimuthal component of the magnetic field. The measured dependence of rotational velocity on magnetic field strength is consistent with the existence of laminar flow in this regime.

Volz, M. P.; Mazuruk, K.

1996-01-01

362

Horizontal magnetic fields in the solar photosphere  

NASA Astrophysics Data System (ADS)

Two-dimensional simulations of time-dependent solar magnetogranulation are used to analyze the horizontal magnetic fields and the response of the synthesized Stokes profiles of the IR FeI ?1564.85 nm line to the magnetic fields. The 1.5-h series of MHD models used for the analyses reproduces a region of the magnetic network in the photosphere with an unsigned magnetic flux density of 192 G at the solar surface. According to the magnetic-field distribution obtained, the most probable absolute strength of the horizontal magnetic field at an optical depth of ? 5 = 1( ? 5 denotes ? at ? = 500 nm) is 50 G, while the mean value is 244 G. On average, the horizontal magnetic fields are stronger than the vertical fields to heights of about 400 km in the photosphere due to their higher density and the larger area they occupy. The maximum factor by which the horizontal fields are greater is 1.5. Strong horizontal magnetic flux tubes emerge at the surface as spots with field strengths of more than 500 G. These are smaller than granules in size, and have lifetimes of 3-6 min. They form in the photosphere due to the expulsion of magnetic fields by convective flows coming from deep subphotospheric layers. The data obtained qualitatively agree with observations with the Hinode space observatory.

Sheminova, V. A.

2009-05-01

363

Ferroelectric Cathodes in Transverse Magnetic Fields  

SciTech Connect

Experimental investigations of a planar ferroelectric cathode in a transverse magnetic field up to 3 kGs are presented. It is shown that the transverse magnetic field affects differently the operation of ferroelectric plasma cathodes in ''bright'' and ''dark'' modes in vacuum. In the ''bright'' mode, when the surface plasma is formed, the application of the transverse magnetic field leads to an increase of the surface plasma density. In the ''dark'' mode, the magnetic field inhibits the development of electron avalanches along the surface, as it does similarly in other kinds of surface discharges in the pre-breakdown mode.

Alexander Dunaevsky; Yevgeny Raitses; Nathaniel J. Fisch

2002-07-29

364

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

365

Magnetic monopole field exposed by electrons  

NASA Astrophysics Data System (ADS)

The experimental search for magnetic monopole particles has, so far, been in vain. Nevertheless, these elusive particles of magnetic charge have fuelled a rich field of theoretical study. Here, we created an approximation of a magnetic monopole in free space at the end of a long, nanoscopically thin magnetic needle. We experimentally demonstrate that the interaction of this approximate magnetic monopole field with a beam of electrons produces an electron vortex state, as theoretically predicted for a true magnetic monopole. This fundamental quantum mechanical scattering experiment is independent of the speed of the electrons and has consequences for all situations where electrons meet such monopole magnetic fields, as, for example, in solids. The set-up not only shows an attractive way to produce electron vortex states but also provides a unique insight into monopole fields and shows that electron vortices might well occur in unexplored solid-state physics situations.

Béché, Armand; van Boxem, Ruben; van Tendeloo, Gustaaf; Verbeeck, Jo

2014-01-01

366

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

367

Concentrator of magnetic field of light  

NASA Astrophysics Data System (ADS)

In the recent decade metamaterials with magnetic permeability different than unity and unusual response to the magnetic field of incident light have been intensively explored. Existence of magnetic artificial materials created an interest in a scanning near-field magnetic microscope for studies of magnetic responses of subwavelength elementary cells of those metamaterials. We present a method of measuring magnetic responses of such elementary cells within a wide range of optical frequencies with single probes of two types. The first type probe is made of a tapered silica fiber with radial metal stripes separated by equidistant slits of constant angular width. The second type probe is similar to metal coated, corrugated, tapered fiber apertured SNOM probe, but in this case corrugations are radially oriented. Both types of probes have internal illumination with azimuthally polarized light. In the near-field they concentrate into a subwavelength spot the longitudinal magnetic field component which is much stronger than the perpendicular electric one.

Wróbel, Piotr; Stefaniuk, Tomasz; Antosiewicz, Tomasz J.; Szoplik, Tomasz

2012-05-01

368

Ohm's Law for Mean Magnetic Fields.  

National Technical Information Service (NTIS)

Spatially complicated magnetic fields are frequently treated as the sum of a large, slowly varying, mean field and a small, rapidly varying, field. The primary effect of the small field is to modify the Ohm's law of the mean field. A set of plausible assu...

A. H. Boozer

1984-01-01

369

Magnetic field evolution in interacting galaxies  

NASA Astrophysics Data System (ADS)

Aims: Violent gravitational interactions can change the morphologies of galaxies and, by means of merging, transform them into elliptical galaxies. We aim to investigate how they affect the evolution of galactic magnetic fields. Methods: We selected 16 systems of interacting galaxies with available VLA archive radio data at 4.86 and 1.4 GHz and compared their radio emission and estimated magnetic field strengths with their star-forming activity, far-infrared emission, and the stage of tidal interaction. Results: The estimated mean of total magnetic field strength for our sample of interacting galaxies is 14 ± 5 ?G, which is larger than for the non-interacting objects. The field regularity (of 0.27 ± 0.09) is lower than in typical spirals and indicates enhanced production of random magnetic fields in the interacting objects. We find a general evolution of magnetic fields: for weak interactions the strength of magnetic field is almost constant (10-15 ?G) as interaction advances, then it increases up to 2× , peaks at the nuclear coalescence (25 ?G), and decreases again, down to 5-6 ?G, for the post-merger remnants. The main production of magnetic fields in colliding galaxies thus terminates somewhere close to the nuclear coalescence, after which magnetic field diffuses. The magnetic field strength for whole galaxies is weakly affected by the star formation rate (SFR), while the dependence is higher for galactic centres. We show that the morphological distortions visible in the radio total and polarized emission do not depend statistically on the global or local SFRs, while they do increase (especially in the polarization) with the advance of interaction. The constructed radio-far-infrared relations for interacting and non-interacting galaxies display a similar balance between the generation of cosmic rays, magnetic fields, and the production of the thermal energy and dust radiation. Conclusions: The regular magnetic fields are much more sensitive to morphological distortions induced by tidal interactions than are the random fields. As a result the polarized emission could be yet another indicator of an ongoing merging process. The found evolution of magnetic field with advancing interaction would definitely imply a stronger effect of magnetic fields on the galaxy surroundings in the earlier cosmological epochs. The process of strong gravitational interactions can efficiently magnetize the merger's surroundings, having a similar magnetizing effect on intergalactic medium as supernova explosions or galactic winds. If interacting galaxies generate some ultra-high energy cosmic rays (UHECRs), the disk or magnetized outflows can deflect them (up to 23°), and make an association of the observed UHECRs with the sites of their origin very uncertain.

Drzazga, R. T.; Chy?y, K. T.; Jurusik, W.; Wiórkiewicz, K.

2011-09-01

370

Calculation of the Magnetic Interaction of Neighboring Magnets for the Future High-Energy Storage Ring at the FAIR Facility  

Microsoft Academic Search

The Forschungszentrum Ju??lich is responsible for the complete design and the construction of the High-Energy Storage Ring HESR , at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany. This includes the layout and provision of all magnets where the dipole, quadrupole and sextupole magnets are the most important. All magnets will be iron-dominated and normally conductive.

Ulf Bechstedt; Helmut Soltner

2010-01-01

371

Effects of magnetic non-linearities on a stored proton beam and their implications for superconducting storage rings  

SciTech Connect

A nonlinear lens may be used to study the effect of high-order multipolar field imperfections on a stored proton beam. Such a nonlinear lens is particulary suitable to simulate field imperfections of the types encountered in coil dominated superconducting magnets. We have studied experimentally at the SPS the effect of high order (5th and 8th) single isolated resonances driven by the nonlinear lens. The width of these resonances is of the order one expects to be caused by field errors in superconducting magnets of the SSC type. The experiment shows that, in absence of tune modulation, these resonances are harmless. Slow crossings of the resonance, on the other hand, have destructive effects on the beam, much more so than fast crossings caused by synchrotron oscillations. In the design of future storage rings, sources of low-frequency tune modulation should be avoided as a way to reduce the harmful effects of high order multipolar field imperfection.

Cornacchia, M.; Evans, L.

1985-06-01

372

Magnetic field properties of SSC model dipole magnets  

SciTech Connect

SSC 1.5m model dipole magnets were built and tested at Fermilab. Magnetic field properties were studied in term of transfer function variation and multipole components. The results were satisfactory. Observation of periodicity of remanent field along the axis is also reported.

Wake, M.; Bossert, R.; Carson, J.; Delchamps, S.; Jaffery, T.S.; Kinney, W.; Koska, W.; Lamm, M.J.; Strait, J. (Fermi National Accelerator Lab., Batavia, IL (United States)); Butteris, J.; Sims, R.; Winters, M. (Superconducting Super Collider Lab., Dallas, TX (United States))

1992-09-01

373

Enhancement of thermal conductivity of magnetic nanofluids in magnetic field  

Microsoft Academic Search

Ahstract- This paper investigated the enhancement of thermal conductivity of engine oil based magnetite (Fe304) nanofluids, which were prepared via a co-precipitation method with and without ultrasound assistance, in the presence of external magnetic field. The thermal conductivity was determined using a thermal constants analyzer. Effects of particle size, particle volume fraction and magnetic field on the thermal conductivity ratio

Innocent Nkurikiyimfura; Yanmin Wangl; Zhidong Panl; Dawei Hul

2011-01-01

374

The AGN origin of cluster magnetic fields  

NASA Astrophysics Data System (ADS)

The origin of magnetic fields in galaxy clusters is one of the most fascinating but challenging problems in astrophysics. In this dissertation, the possibility of an Active Galactic Nucleus (AGN) origin of cluster magnetic fields is studied through state of the art simulations of magnetic field evolution in large scale structure formation using a newly developed cosmological Adaptive Mesh Refinement (AMR) Magnetohydrodynamics (MHD) code -- EnzoMHD. After presenting a complete but concise description and verification of the code, we discuss the creation of magnetic fields through the Biermann Battery effect during first star formation and galaxy cluster formation. We find that magnetic fields are produced as predicted by theory in both cases. For the first star formation, we obtain a lower limit of (~ 10 -9 G) for magnetic fields when the first generation stars form. On the other hand, we find that the magnetic energy is amplified 4 orders of magnitude within ~ 10 Gyr during cluster formation. We then study magnetic field injection from AGN into the Intra- Cluster Medium (ICM) and their impact on the ICM. We reproduce the X-ray cavities as well as weak shocks seen in observations in the simulation, and further confirm the idea that AGN outburst must contain lots of magnetic energy (up to 10 61 ergs) and the magnetic fields play an important part in the formation of jet/lobe system. We present high resolution simulations of cluster formation with magnetic fields injected from high redshift AGN. We find that these local magnetic fields are spread quickly throughout the whole cluster by cluster mergers. The ICM is in a turbulent state with a Kolmogorov-like power spectrum. Magnetic fields are amplified to and maintained at the observational level of a few mG by bulk flows at large scale and the ICM turbulence at small scale. The total magnetic energy increases about 25 times to ~ 1.2 × 10^61 ergs at the present time. We conclude that magnetic fields from AGN at high redshift may provide sufficient initial magnetic fields to magnetize the whole cluster.

Xu, Hao

375

Atoms in Crossed Electric and Magnetic Fields  

NASA Astrophysics Data System (ADS)

In this dissertation, extensive experimental and theoretical work pertaining to three interesting aspects of the interaction of atoms with crossed electric and magnetic fields is presented. The first experiment discussed deals with the effects of weak crossed fields on sodium atoms. A fluorescence spectrum of laser excited sodium n = 11 states in an electric field of 2560 V/cm perpendicular to a magnetic field of 4.4 kG is presented, along with a comparison to theory. The data show the important effects of m-mixing and residual degeneracies which remain in the crossed fields. The next topic presented is the theoretical prediction of novel resonances, termed "quasi-Penning resonances," corresponding to electron states localized away from the nucleus at the Stark saddlepoint in strong crossed electric and magnetic fields. The stability and possibility for observation of these resonances is explored. Finally, extensive experimental maps of data are presented which compare laser induced ionization spectra of sodium atoms in crossed electric and magnetic fields to spectra in an electric field atone. The experiment explores the energy region of the electric field saddlepoint, where quasi-Penning resonances are predicted to occur. The magnetic field is too weak for the observation of these resonances, but the experiment provides important groundwork for the understanding of future experiments in strong crossed fields. The magnetic field is seen to cause splitting of some transitions due to the interaction of the electron spin with the magnetic field. Also, magnetic field induced state mixing causes a redistribution of oscillator strengths leading to changes in peak heights and auto-ionizing line widths. On the whole, however, the effect of the weak crossed magnetic field on the sodium Stark spectra remains small.

Korevaar, Eric John

1987-09-01

376

Magnetism and local molecular field.  

PubMed

Despite its somewhat naive simplicity, the method of the local molecular field has had undeniable success in satisfactorily explaining a large number of previously known facts and in opening the way for the discovery of new facts. Let us note, however, that all the structures that have been discussed above are collinear structures: on the average (in time) all the atomic magnets pointing in one or the opposite direction are parallel to a single direction. However, the local molecular field method can also be extended to noncollinear structures such as that of helimagnetism, which Yoshimori and Villain discovered independently in an absolutely unexpected manner; one can thus interpret phenomena in a remarkably simple and concrete manner. Nevertheless, the method can hardly be recommended for more complex structures such as the umbrella structure, which requires the decomposition of the principal crystal lattice into a large number of sublattices. Indeed, under these conditions an atom belonging to a given sublattice has only a very small number of neighbors (one or two) in each of the other sublattices, and the molecular field method, which consists in replacing the instantaneous action of an atom by that of an average atom, will be more likely to yield a correct result, the larger the number of atoms to which it is applied. Its correctness probably also increases as the atomic spin becomes larger. Independently of this problem, the method applied to a large number of sublattices completely loses its chief advantage, simplicity. The method also involves more insidious traps. If a judicious choice of parameters is made, the method can lead one to calculate curves and thermal variations of the spontaneous magnetization or paramagnetic susceptibility that coincide remarkably well with the experimental results, for example, to within a few thousandths. Under these conditions, one could expect that the elementary interaction energies deduced from these parameters would correspond to the actual values with the same accuracy. This is not so; errors of 10 to 20 percent and even greater are frequently made in this manner. A certain amount of caution thus becomes imperative. On the other hand, recourse to the local molecular field seems indispensable since more rigorous methods lead to insurmountable complications. Consider for example that the rigorous solution is not yet known for the simplest case, that of a simple cubic lattice with identical atoms of spin 1/2, and interactions reduced to those present between nearest-neighbor atoms. How then should one treat the case of garnets with 160 atoms in the unit cell, spins up to 5/2, and at least six different coupling constants? One must therefore be lenient toward the imperfections of the molecular field methods, considering the simplicity with which the successes recalled in the first few lines of these conclusions were obtained. PMID:17757022

Néel, L

1971-12-01

377

Photospheric magnetic field rotation: Rigid and differential  

Microsoft Academic Search

An autocorrelation of the direction of the large-scale photospheric magnetic field observed during 1959–1967 has yielded evidence that the field structure at some heliographic latitudes can display both differential rotation and rigid rotation properties.

John M. Wilcox; Kenneth H. Schatten; Andrew S. Tanenbaum; Robert Howard

1970-01-01

378

Photospheric Magnetic Field Rotation: Rigid And Differential.  

National Technical Information Service (NTIS)

An autocorrelation of the direction of the large-scale photospheric magnetic field observed during 1959-1967 has yielded evidence that the field structure at a given heliographic latitude can display both differential rotation and rigid rotation propertie...

J. M. Wilcox K. H. Schatten A. S. Tanenbaum R. Howard

1970-01-01

379

Cosmic Rays in the Earth'S Magnetic Field.  

National Technical Information Service (NTIS)

Studies are presented of the behavior of cosmic rays in the earth's magnetic field. It discusses the theory of motion of charged particles in an idealized field model and presents results of trajectory calculations of asymptotic directions and cutoff rigi...

L. I. Dorman V. S. Smirnov M. I. Tyasto

1973-01-01

380

Magnetohydrodynamics of the Earth'S Magnetic Field.  

National Technical Information Service (NTIS)

A survey of observational and theoretical work pertaining to the origin of planetary magnetic fields is given with special emphasis on the dynamo theory which attempts to explain these fields as arising from magnetohydrodynamic regenerative action. Some p...

G. Venezian

1967-01-01

381

The Evolution of the Earth's Magnetic Field.  

ERIC Educational Resources Information Center

Describes the change of earth's magnetic field at the boundary between the outer core and the mantle. Measurement techniques used during the last 300 years are considered. Discusses the theories and research for explaining the field change. (YP)

Bloxham, Jeremy; Gubbins, David

1989-01-01

382

Thinned fiber Bragg grating magnetic field sensor with magnetic fluid  

NASA Astrophysics Data System (ADS)

The refractive index of magnetic fluid may be changed by external magnetic field. Therefore, through measuring its refractive index, the intensity of the magnetic field can be obtained. Fiber Bragg grating (FBG) is sensitive to the refractive index surrounding its cladding when the diameter of cladding is reduced to a certain degree. In order to prove the sensitivity of the thinned fiber Bragg grating to refractive index, series of experiments, such as the fabrication of thinned FBG, tuning magnetic field and obtaining spectral characterizations, are carried out. After the FBG is etched for 193 minutes by HF solution at 22%, the FBG starts to be sensitive to the surrounding refractive index and the Bragg wavelength decreases sharply with the etching process. The thinned FBG has been packaged to a container filled with MF. Using a tunable magnetic field the refractive index of magnetic fluid could be changed and the Bragg wavelength of FBG shifts correspondingly. Both the wavelength and the light power are sensitive to magnetic field and the sensitivity of wavelength is 2.3 pm/mT at least in the condition of proposed experiment. The obtained results show that the thinned FBG sensor with magnetic fluid could be applicable for magnetic field and current sensing.

Zhou, Ciming; Ding, Li; Wang, Dongli; Kuang, Yaqi; Jiang, Desheng

2011-05-01

383

Protecting SQUID metamaterials against stray magnetic fields  

NASA Astrophysics Data System (ADS)

Using superconducting quantum interference devices (SQUIDs) as the basic, low-loss elements of thin-film metamaterials has one main advantage: their resonance frequency is easily tunable by applying a weak magnetic field. The downside, however, is a strong sensitivity to stray and inhomogeneous magnetic fields. In this work, we demonstrate that even small magnetic fields from electronic components destroy the collective, resonant behaviour of the SQUID metamaterial. We also show how the effect of these fields can be minimized. As a first step, magnetic shielding decreases any initially present fields, including the earth’s magnetic field. However, further measures such as improvements in the sample geometry have to be taken to avoid the trapping of Abrikosov vortices.

Butz, S.; Jung, P.; Filippenko, L. V.; Koshelets, V. P.; Ustinov, A. V.

2013-09-01

384

Coronal magnetic fields and the solar wind  

NASA Technical Reports Server (NTRS)

Current information is presented on coronal magnetic fields as they bear on problems of the solar wind. Both steady state fields and coronal transient events are considered. A brief critique is given of the methods of calculating coronal magnetic fields including the potential (current free) models, exact solutions for the solar wind and field interaction, and source surface models. These solutions are compared with the meager quantitative observations which are available at this time. Qualitative comparisons between the shapes of calculated magnetic field lines and the forms visible in the solar corona at several recent eclipses are displayed. These suggest that: (1) coronal streamers develop above extended magnetic arcades which connect unipolar regions of opposite polarity; and (2) loops, arches, and rays in the corona correspond to preferentially filled magnetic tubes in the approximately potential field.

Newkirk, G., Jr.

1972-01-01

385

Capillary hydrodynamic effects in high magnetic fields  

Microsoft Academic Search

A set of hydrodynamic equations has been applied to processes occurring in nonconductive fluids placed into magnetic fields. The equations are valid for equilibrium magnetization within the framework of a continuous medium. The ranges of physical parameters have been evaluated for which magnetization of a fluid should be taken into account in problems concerning the determination of equilibrium forms, and

B. M. Berkovskii; N. N. Smirnov

1988-01-01

386

Magnetic Dipole Fields in Unsaturated Cubic Crystals  

Microsoft Academic Search

The mean value of the randomly directed local magnetic field at a lattice point in each of two cubic arrays, (I) and (F), of equal magnetic dipoles is computed under the following restrictions: (a) The orientation of neighboring dipoles is independent. (b) The direction of each dipole axis is one of the easy directions of magnetization for a ferromagnetic metal

L. W. McKeehan

1933-01-01

387

Coronal magnetic fields produced by photospheric shear  

SciTech Connect

The magneto-frictional method is used for computing force free fields to examine the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. It found that the energy of the sheared field can be arbitrarily large compared with the potential field. It is also found that it is possible to fit the magnetic energy, as a function of shear, by a simple functional form.

Sturrock, P.A.; Yang, W.H.

1987-10-01

388

Coronal magnetic fields produced by photospheric shear  

NASA Technical Reports Server (NTRS)

The magneto-frictional method is used for computing force free fields to examine the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. It found that the energy of the sheared field can be arbitrarily large compared with the potential field. It is also found that it is possible to fit the magnetic energy, as a function of shear, by a simple functional form.

Sturrock, P. A.; Yang, W.-H.

1987-01-01

389

Modeling Magnetic Field Topology at Jupiter with the Khurana Magnetic Field Model  

NASA Astrophysics Data System (ADS)

To explore the degree of coupling between the interplanetary magnetic field (IMF) and Jupiter's magnetosphere, we traced magnetic field lines from the polar region of the planet using the Khurana [1997, 2005] magnetic field model. We used a parameterized definition of the Jovian magnetopause created by Joy et al. [2002] that varies with the value of the solar wind dynamic pressure. We searched for field lines that cross the magnetopause and that potentially connect to the interplanetary magnetic field. We further explored the variation on magnetic field structure with local time orientation of Jupiter's dipole (i.e. Central Meridian Longitude) as well as upstream solar wind and IMF conditions.

Cohen, I.; Bagenal, F.

2008-12-01

390

Observation of field-induced domain wall propagation in magnetic nanowires by magnetic transmission X-ray microscopy  

SciTech Connect

Magnetic transmission X-ray microscopy (M-TXM) is used to image domain walls in magnetic ring structures formed by a 300 nm wide, 24 nm thick Ni{sub 81}Fe{sub 19} nanowire. Both transverse and vortex type domain walls are observed after application of different field sequences. Domain walls can be observed by comparing images obtained from opposite field sequences, or else domain wall propagation observed by comparing successive images in a particular field sequence. This demonstrates the potential use of M-TXM in developing and understanding planar magnetic nanowire behavior.

Bryan, M. T.; Fry, P. W.; Fischer, P.; Allwood, D. A.

2007-12-01

391

Disruption of coronal magnetic field arcades  

NASA Technical Reports Server (NTRS)

The ideal and resistive properties of isolated large-scale coronal magnetic arcades are studied using axisymmetric solutions of the time-dependent magnetohydrodynamic (MHD) equations in spherical geometry. We examine how flares and coronal mass ejections may be initiated by sudden disruptions of the magnetic field. The evolution of coronal arcades in response to applied shearing photospheric flows indicates that disruptive behavior can occur beyond a critical shear. The disruption can be traced to ideal MHD magnetic nonequilibrium. The magnetic field expands outward in a process that opens the field lines and produces a tangential discontinuity in the magnetic field. In the presence of plasma resistivity, the resulting current sheet is the site of rapid reconnection, leading to an impulsive release of magnetic energy, fast flows, and the ejection of a plasmoid. We relate these results to previous studies of force-free fields and to the properties of the open-field configuration. We show that the field lines in an arcade are forced open when the magnetic energy approaches (but is still below) the open-field energy, creating a partially open field in which most of the field lines extend away from the solar surface. Preliminary application of this model to helmet streamers indicates that it is relevant to the initiation of coronal mass ejections.

Mikic, Zoran; Linker, Jon A.

1994-01-01

392

Comparison of the mean photospheric magnetic field and the interplanetary magnetic field  

Microsoft Academic Search

The mean photospheric magnetic field of the sun seen as a star has been compared with the interplanetary magnetic field observed with spacecraft near the earth. Each change in polarity of the mean solar field is followed about 4 1\\/2 days later by a change in polarity of the interplanetary field (sector boundary). The scaling of the field magnitude from

A. Severny; J. M. Wilcox; P. H. Scherrer; D. S. Colburn

1970-01-01

393

Diffusion of magnetic field via turbulent reconnection  

NASA Astrophysics Data System (ADS)

The diffusion of astrophysical magnetic fields in conducting fluids in the presence of turbulence depends on whether magnetic fields can change their topology via reconnection in highly conducting media. Recent progress in understanding fast magnetic reconnection in the presence of turbulence is reassuring that the magnetic field behavior in computer simulations and turbulent astrophysical environments is similar, as far as magnetic reconnection is concerned. This makes it meaningful to perform MHD simulations of turbulent flows in order to understand the diffusion of magnetic field in astrophysical environments. Our studies of magnetic field diffusion in turbulent medium reveal interesting new phenomena. First of all, our 3D MHD simulations initiated with anti-correlating magnetic field and gaseous density exhibit at later times a de-correlation of the magnetic field and density, which corresponds well to the observations of the interstellar media. While earlier studies stressed the role of either ambipolar diffusion or time-dependent turbulent fluctuations for de-correlating magnetic field and density, we get the effect of permanent de-correlation with one fluid code, i.e. without invoking ambipolar diffusion. In addition, in the presence of gravity and turbulence, our 3D simulations show the decrease of the magnetic flux-to-mass ratio as the gaseous density at the center of the gravitational potential increases. We observe this effect both in the situations when we start with equilibrium distributions of gas and magnetic field and when we follow the evolution of collapsing dynamically unstable configurations. Thus the process of turbulent magnetic field removal should be applicable both to quasi-static subcritical molecular clouds and cores and violently collapsing supercritical entities. The increase of the gravitational potential as well as the magnetization of the gas increases the segregation of the mass and magnetic flux in the saturated final state of the simulations, supporting the notion that the reconnection-enabled diffusivity relaxes the magnetic field + gas system in the gravitational field to its minimal energy state. This effect is expected to play an important role in star formation, from its initial stages of concentrating interstellar gas to the final stages of the accretion to the forming protostar.

Santos de Lima, Reinaldo; Lazarian, Alexander; de Gouveia Dal Pino, Elisabete M.; Cho, Jungyeon

2010-05-01

394

Bipolar Flow in a Special Magnetic Field.  

National Technical Information Service (NTIS)

It is shown that, in a magnetic field, the effective compensation of the space charge of an ion flow by electrons can occur. By selecting the appropriate magnetic fields, one can achieve as high a reciprocal compensation of the electron and ion space char...

V. N. Danilov

1964-01-01

395

Variability and topology of solar magnetic field  

Microsoft Academic Search

Observations of the large scale magnetic field in the photosphere taken at the Wilcox Solar Observatory since 1976 up to 2005 have been analyzed to deduce its latitudinal and longitudinal structures, its differential rotation, and their variability in time. The main results are the following: - The latitudinal structure of the solar magnetic field with a period of polarity change

E. A. Gavryuseva

2006-01-01

396

Does the solar magnetic field increase?  

Microsoft Academic Search

We consider measurements of the general magnetic field (GMF) of the Sun as a star at four world observatories from 1968 until\\u000a 1999. We show that, within the error limits, the mean strength of the photospheric magnetic field H (of its longitudinal component, in magnitude) has not changed over the last 32 years. This is in conflict with the recent

V. A. Kotov; I. V. Kotova

2001-01-01

397

Magnetic fields, branes, and noncommutative geometry  

Microsoft Academic Search

We construct a simple physical model of a particle moving on the infinite noncommutative 2-plane. The model consists of a pair of opposite charges moving in a strong magnetic field. In addition, the charges are connected by a spring. In the limit of large magnetic field, the charges are frozen into the lowest Landau levels. Interactions of such particles include

Daniela Bigatti; Leonard Susskind

2000-01-01

398

Astrophysical magnetic fields and nonlinear dynamo theory  

Microsoft Academic Search

The current understanding of astrophysical magnetic fields is reviewed, focusing on their generation and maintenance by turbulence. In the astrophysical context this generation is usually explained by a self-excited dynamo, which involves flows that can amplify a weak ‘seed’ magnetic field exponentially fast. Particular emphasis is placed on the nonlinear saturation of the dynamo. Analytic and numerical results are discussed

Axel Brandenburg; Kandaswamy Subramanian

2005-01-01

399

High magnetic field facility at Osaka University  

Microsoft Academic Search

The high magnetic field facility of Osaka University, equipped with several kinds of non-destructive magnets, is described. The field strength produced for practical use is up to 80 T and time durations are from 0.4 ms to 40 ms. Various kinds of experiments, from physics to biology, are carried on there.

A. Yamagishi; M. Date

1989-01-01

400

Lightning Magnetic Field Measurements around Langmuir Laboratory  

Microsoft Academic Search

In the absence of artificial conductors, underground lightning transients are produced by diffusion of the horizontal surface magnetic field of a return stroke vertically downward into the conducting earth. The changing magnetic flux produces an orthogonal horizontal electric field, generating a dispersive, lossy transverse electromagnetic wave that penetrates a hundred meters or more into the ground according to the skin

M. Stock; P. R. Krehbiel; W. Rison; G. D. Aulich; H. E. Edens; R. G. Sonnenfeld

2010-01-01

401

Magnetic fields and the solar corona  

Microsoft Academic Search

Coronal magnetic fields calculated by the methods developed in Paper I (Altschuler and Newkirk, 1969) and the empirical description of the solar corona of November 1966 derived in Paper II (Newkirket al., 1970) are combined in order to investigate what connection exists between the magnetic fields and the density structure of the corona.

Gordon Newkirk; Martin D. Altschuler

1970-01-01

402

Heliospheric Magnetic Field Structure At Solar Maximum  

Microsoft Academic Search

The evolution of the heliospheric magnetic field (HMF) from the relative simplicity at solar minimum has been charted by the Ulysses spacecraft through the ascending phase of the solar cycle through the recent maximum activity epoch. The changes that occurred in solar and coronal magnetic fields from 1997 to 2001 are reflected in a com- plex way in the evolution

A. Balogh; E. J. Smith; R. J. Forsyth; G. H. Jones; D. J. McComas

2002-01-01

403

Plasma in a Rotating Magnetic Field  

Microsoft Academic Search

This paper addresses the interaction between plasma and a magnetic field rotating with uniform an angular velocity and amplitude. For our analysis, we assume a plasma with infinite conductivity and constant viscosity coefficients. Starting from the basic equations, we search for exact solutions with respect to velocity and magnetic field. Then, we study the stability of the exact solution and

Mauro Bologna; Bernardo Tellini; Filippo Giraldi

2008-01-01

404

Manipulation of molecular structures with magnetic fields  

Microsoft Academic Search

The present thesis deals with the use of magnetic fields as a handle to manipulate matter at a molecular level and as a tool to probe molecular properties or inter molecular interactions. The work consists of in situ optical studies of (polymer) liquid crystals and molecular aggregates in high magnetic fields up to 20T, together with a description of the

Marius Iosif Boamfa

2003-01-01

405

Coulomb crystals in the magnetic field.  

PubMed

The body-centered-cubic Coulomb crystal of ions in the presence of a uniform magnetic field is studied using the rigid electron background approximation. The phonon mode spectra are calculated for a wide range of magnetic-field strengths and for several orientations of the field in the crystal. The phonon spectra are used to calculate the phonon contribution to the crystal energy, entropy, specific heat, Debye-Waller factor of ions, and the rms ion displacements from the lattice nodes for a broad range of densities, temperatures, chemical compositions, and magnetic fields. Strong magnetic field dramatically alters the properties of quantum crystals. The phonon specific heat increases by many orders of magnitude. The ion displacements from their equilibrium positions become strongly anisotropic. The results can be relevant for dusty plasmas, ion plasmas in Penning traps, and especially for the crust of magnetars (neutron stars with superstrong magnetic fields B > or approximately equal 10(14) G ). The effect of the magnetic field on ion displacements in a strongly magnetized neutron star crust can suppress the nuclear reaction rates and make them extremely sensitive to the magnetic-field direction. PMID:19905459

Baiko, D A

2009-10-01

406

Space Quantization in a Gyrating Magnetic Field  

Microsoft Academic Search

The nonadiabatic transitions which a system with angular momentum J makes in a magnetic field which is rotating about an axis inclined with respect to the field are calculated. It is shown that the effects depend on the sign of the magnetic moment of the system. We therefore have an absolute method for measuring the sign and magnitude of the

I. I. Rabi

1937-01-01

407

Solar Magnetic Field: Zeeman and Hanle Effects  

NASA Astrophysics Data System (ADS)

An external magnetic field causes the atomic energy levels to split into different sublevels, and the emitted radiation becomes polarized. This phenomenon is called the ZEEMAN EFFECT. When atoms in a magnetic field scatter radiation via bound-bound transitions, the phase relations or quantum interferences between the Zeeman-split sublevels give rise to POLARIZATION phenomena that go under the nam...

Stenflo, J.; Murdin, P.

2001-10-01

408

First VIKING results: magnetic field measurements  

Microsoft Academic Search

The VIKING spacecraft carries a high-resolution Magnetic Field Experiment for the operational purpose of determining spacecraft attitude and to fulfill the scientific objectives of providing magnetic-field measurements necessary for the determination of particle pitch angles, identification of geospace boundaries, and the study of magnetospheric current systems and plasma processes. This experiment includes a fluxgate magnetometer system with the sensors mounted

T A Potemra; L J Zanetti; R E Erlandson; G Gustafsson; M H Acuna

1988-01-01

409

Two-axis magnetic field sensor  

NASA Technical Reports Server (NTRS)

A ferromagnetic thin-film based magnetic field sensor with first and second sensitive direction sensing structures each having a nonmagnetic intermediate layer with two major surfaces on opposite sides thereof having a magnetization reference layer on one and an anisotropic ferromagnetic material sensing layer on the other having a length in a selected length direction and a smaller width perpendicular thereto and parallel to the relatively fixed magnetization direction. The relatively fixed magnetization direction of said magnetization reference layer in each is oriented in substantially parallel to the substrate but substantially perpendicular to that of the other. An annealing process is used to form the desired magnetization directions.

Jander, Albrecht (Inventor); Nordman, Catherine A. (Inventor); Qian, Zhenghong (Inventor); Smith, Carl H. (Inventor)

2006-01-01

410

The Physics of Attraction and Repulsion: Magnetism and Magnetic Fields  

NASA Astrophysics Data System (ADS)

The development of new materials with improved magnetic properties completely changed the modern world in the past decades. Recent progress is predominantly due to a better understanding of magnetism that has gone far beyond compass needles rotating in a magnetic field and bar magnets attracting or repelling each other. New magnetic materials are used to build smaller and smaller read/write heads and hard disks with increased storage capacity, developments that are responsible the revolution in the computer industry. Another example is the field of magnetic levitation that became feasible for commercial applications with the discovery of new superconducting materials, and a prototype train is under development in Japan. In medicine, the development of magnetic resonance imaging (MRI) provides an alternative to other (destructive) radiation techniques.

Nakotte, Heinz

2001-11-01

411

The levitation characteristics of the magnetic substances using trapped HTS bulk annuli with various magnetic field distributions  

NASA Astrophysics Data System (ADS)

We have been investigating the levitation system without any mechanical contact which is composed of a field-cooled ring-shaped high temperature superconducting (HTS) bulks [1]. In this proposed levitation system, the trapped magnetic field distributions of stacked HTS bulk are very important. In this paper, the spherical solenoid magnet composed of seven solenoid coils with different inner and outer diameters was designed and fabricated as a new magnetic source. The fabricated spherical solenoid magnet can easily make a homogeneous and various magnetic field distributions in inner space of stacked HTS bulk annuli by controlling the emerging currents of each coil. By using this spherical solenoid magnet, we tried to make a large magnetic field gradient in inner space of HTS bulk annuli, and it is very important on the levitation of magnetic substances. In order to improve the levitation properties of magnetic substances with various sizes, the external fields were reapplied to the initially trapped HTS bulk magnets. We could generate a large magnetic field gradient along the axial direction in inner space of HTS bulk annuli, and obtain the improved levitation height of samples by the proposed reapplied field method.

Kim, S. B.; Ikegami, T.; Matsunaga, J.; Fujii, Y.; Onodera, H.

2013-11-01

412

Vehicle detection using a magnetic field sensor  

Microsoft Academic Search

The measurement of vehicle magnetic moments and the results from use of a fluxgate magnetic sensor to actuate a lighting system from the magnetic fields of passing vehicles is reported. A typical U.S. automobile has a magnetic moment of about 200 A-m2(Ampere-meters2), while for a school bus it is about 2000 A-m2. When the vehicle is modeled as an ideal

S. V. Marshall

1978-01-01

413

Photospheric sources of magnetic field aligned currents  

NASA Astrophysics Data System (ADS)

Distortions of the photospheric magnetic field topology in the photosphere cause twists (field-aligned currents) to propagate along field lines up into the coronal magnetic field. It is noted that for small-scale magnetic loops, these currents have a duration that is long in comparison with the propagation time of Alfven waves along the loop. This gives rise to quasi-static twists of the coronal field lines rather than propagating Alfven waves. The magnetic field-aligned currents associated with such twisted fields may lead to resistive MHD instabilities that are similar to Tokamak instabilities (Waddell et al., 1979; Carreras et al., 1980). For this reason, they may figure prominently in small-scale chromospheric and coronal activity.

Nordlund, A.

414

Permanent magnet edge-field quadrupole  

DOEpatents

Planar permanent magnet edge-field quadrupoles for use in particle accelerating machines and in insertion devices designed to generate spontaneous or coherent radiation from moving charged particles are disclosed. The invention comprises four magnetized rectangular pieces of permanent magnet material with substantially similar dimensions arranged into two planar arrays situated to generate a field with a substantially dominant quadrupole component in regions close to the device axis. 10 figs.

Tatchyn, R.O.

1997-01-21

415

Permanent magnet edge-field quadrupole  

DOEpatents

Planar permanent magnet edge-field quadrupoles for use in particle accelerating machines and in insertion devices designed to generate spontaneous or coherent radiation from moving charged particles are disclosed. The invention comprises four magnetized rectangular pieces of permanent magnet material with substantially similar dimensions arranged into two planar arrays situated to generate a field with a substantially dominant quadrupole component in regions close to the device axis.

Tatchyn, Roman O. (Mountain View, CA)

1997-01-01

416

Magnetic resonance imaging: effects of magnetic field strength  

SciTech Connect

Magnetic resonance images of the head, abdomen, and pelvis of normal adult men were obtained using varying magnetic field strength, and measurements of T1 and T2 relaxations and of signal-to-noise (SN) ratios were determined. For any one spin echo sequence, gray/white matter contrast decreases and muscle/fat contrast increases with field. SN levels rise rapidly up to 3.0 kgauss and then change more slowly, actually dropping for muscle. The optimum field for magnetic resonance imaging depends on tissue type, body part, and imaging sequence, so that it does not have a unique value. Magnetic resonance systems that operate in the 3.0-5.0 kgauss range achieve most or all of the gains that can be achieved by higher magnetic fields.

Crooks, L.E.; Arakawa, M.; Hoenninger, J.; McCarten, B.; Watts, J.; Kaufman, L.

1984-04-01

417

Organic Superconductors at Extremely High Magnetic Fields  

ScienceCinema

Intense magnetic fields are an essential tool for understanding layered superconductors. Fundamental electronic properties of organic superconductors are revealed in intense (60 tesla) magnetic fields. Properties such as the topology of the Fermi surface and the nature of the superconducting order parameter are revealed. With modest maximum critical temperatures {approx}13K the charge transfer salt organic superconductors prove to be incredibly valuable materials as their electronically clean nature and layered (highly anisotropic) structures yield insights to the high temperature superconductors. Observation of de Haas-van Alphen and Shubnikov-de Haas quantum oscillatory phenomena, magnetic field induced superconductivity and re-entrant superconductivity are some of the physical phenomena observed in the charge transfer organic superconductors. In this talk, I will discuss the nature of organic superconductors and give an overview of the generation of intense magnetic fields; from the 60 tesla millisecond duration to the extreme 1000 tesla microsecond pulsed magnetic fields.

418

Processing of polymers in high magnetic fields  

SciTech Connect

Many organic molecules and polymers have an anisotropic diamagnetic susceptibility, and thus can be aligned in high magnetic fields. The presence of liquid crystallinity allows cooperative motions of the individual molecules, and thus the magnetic energy becomes greater than the thermal energy at experimentally obtainable field strengths. This work has determined the effect of magnetic field alignment on the thermal expansion and mechanical properties of liquid crystalline thermosets in the laboratory. Further advances in magnet design are needed to make magnetic field alignment a commercially viable approach to polymer processing. The liquid crystal thermoset chosen for this study is the diglycidyl ether of dihydroxy-{alpha}-methylstilbene cured with the diamine sulfamilamide. This thermoset has been cured at field strengths up to 18 Tesla.

Douglas, E.P.; Smith, M.E.; Benicewicz, B.C. [Los Alamos National Lab., NM (United States); Earls, J.D.; Priester, R.D. Jr. [Dow Chemical Co., Freeport, TX (United States)

1996-05-01

419

Levitation of a magnet by an alternating magnetic field  

NASA Astrophysics Data System (ADS)

An experiment is described in which a small strong cylindrical magnet is levitated by a vertical non-uniform alternating magnetic field. Surprisingly, no superimposed constant field is necessary, but the levitation can be explained when the vertical motion of the magnet is taken into account. The theoretical mean levitation force is (0.26 ± 0.06) N, which is in good agreement with the levitated weight of (0.239 ± 0.001) N. This experiment is suitable for an undergraduate laboratory, particularly as a final year project. Students have found it interesting, and it sharpens up knowledge of basic magnetism.

Gough, W.; Hunt, M. O.; Summerskill, W. S. H.

2013-01-01

420

Magnetic Helicity and Large Scale Magnetic Fields: A Primer  

NASA Astrophysics Data System (ADS)

Magnetic fields of laboratory, planetary, stellar, and galactic plasmas commonly exhibit significant order on large temporal or spatial scales compared to the otherwise random motions within the hosting system. Such ordered fields can be measured in the case of planets, stars, and galaxies, or inferred indirectly by the action of their dynamical influence, such as jets. Whether large scale fields are amplified in situ or a remnant from previous stages of an object's history is often debated for objects without a definitive magnetic activity cycle. Magnetic helicity, a measure of twist and linkage of magnetic field lines, is a unifying tool for understanding large scale field evolution for both mechanisms of origin. Its importance stems from its two basic properties: (1) magnetic helicity is typically better conserved than magnetic energy; and (2) the magnetic energy associated with a fixed amount of magnetic helicity is minimized when the system relaxes this helical structure to the largest scale available. Here I discuss how magnetic helicity has come to help us understand the saturation of and sustenance of large scale dynamos, the need for either local or global helicity fluxes to avoid dynamo quenching, and the associated observational consequences. I also discuss how magnetic helicity acts as a hindrance to turbulent diffusion of large scale fields, and thus a helper for fossil remnant large scale field origin models in some contexts. I briefly discuss the connection between large scale fields and accretion disk theory as well. The goal here is to provide a conceptual primer to help the reader efficiently penetrate the literature.

Blackman, Eric G.

2014-04-01

421

Ohm's law for mean magnetic fields  

SciTech Connect

Spatially complicated magnetic fields are frequently treated as the sum of a large, slowly varying, mean field and a small, rapidly varying, field. The primary effect of the small field is to modify the Ohm's law of the mean field. A set of plausible assumptions leads to a form of the mean field Ohm's law which is fundamentally different from the conventional alpha effect of dynamo theory.

Boozer, A.H.

1984-11-01

422

Dependence of the magnitude and direction of the persistent current on the magnetic flux in superconducting rings  

SciTech Connect

The obtained periodic magnetic-field dependences I{sub c+}({phi}/{phi}{sub 0}) and I{sub c-}({phi}/{phi}{sub 0}) of the critical current measured in opposite directions on asymmetric superconducting aluminum rings has made it possible to explain previously observed quantum oscillations of dc voltage as a result of alternating current rectification. It was found that a higher rectification efficiency of both single rings and ring systems is caused by hysteresis of the current-voltage characteristics. The asymmetry of current-voltage characteristics providing the rectification effect is due to the relative shifts of the magnetic dependences I{sub c-}({phi}/{phi}{sub 0}) = I{sub c+}({phi}/{phi}{sub 0} + {delta}{phi}) of the critical current measured in opposite directions. This shift means that the position of I{sub c+}({phi}/{phi}{sub 0}) and I{sub c-}({phi}/{phi}{sub 0}) minima does not correspond to n + 0.5 magnetic flux {phi} quanta, which is in direct contradiction to measured Little-Parks resistance oscillations. Despite this contradiction, the amplitude I{sub c,an}({phi}/{phi}{sub 0}) = I{sub c+}({phi}/{phi}{sub 0}) - I{sub c-}({phi}/{phi}{sub 0}) of critical current anisotropy oscillations and its variations with temperature correspond to the expected amplitude of persistent current oscillations and its variations with temperature.

Gurtovoi, V. L.; Dubonos, S. V.; Nikulov, A. V., E-mail: nikulov@ipmt-hpm.ac.ru; Osipov, N. N.; Tulin, V. A. [Russian Academy of Sciences, Institute of Microelectronic Technology and High-Purity Materials (Russian Federation)

2007-12-15

423

CONSTRUCTION AND POWER TEST OF THE EXTRACTION KICKER MAGNET FOR SNS ACCUMULATOR RING.  

SciTech Connect

Two extraction kicker magnet assemblies that contain seven individual pulsed magnet modules each will kick the proton beam vertically out of the SNS accumulator ring into the aperture of the extraction Lambertson septum magnet. The proton beam then travels to the 1.4 MW SNS target assembly. The 14 kicker magnets and major components of the kicker assembly have been fabricated in BNL. The inner surfaces of the kicker magnets were coated with TiN to reduce the secondary electron yield. All 14 PFN power supplies have been built, tested and delivered to OWL. Before final installation, a partial assembly of the kicker system with three kicker magnets was assembled to test the functions of each critical component in the system. In this paper we report the progress of the construction of the kicker components, the TIN coating of the magnets, the installation procedure of the magnets and the full power test of the kicker with the PFN power supply.

PAI, C.; HAHN, H.; HSEUH, H.; LEE, Y.; MENG, W.; MI,J.; SANDBERG, J.; TODD, R.; ET AL.

2005-05-16

424

Dynamic Magnetic Field Applications for Materials Processing  

NASA Technical Reports Server (NTRS)

Magnetic fields, variable in time and space, can be used to control convection in electrically conducting melts. Flow induced by these fields has been found to be beneficial for crystal growth applications. It allows increased crystal growth rates, and improves homogeneity and quality. Particularly beneficial is the natural convection damping capability of alternating magnetic fields. One well-known example is the rotating magnetic field (RMF) configuration. RMF induces liquid motion consisting of a swirling basic flow and a meridional secondary flow. In addition to crystal growth applications, RMF can also be used for mixing non-homogeneous melts in continuous metal castings. These applied aspects have stimulated increasing research on RMF-induced fluid dynamics. A novel type of magnetic field configuration consisting of an axisymmetric magnetostatic wave, designated the traveling magnetic field (TMF), has been recently proposed. It induces a basic flow in the form of a single vortex. TMF may find use in crystal growth techniques such as the vertical Bridgman (VB), float zone (FZ), and the traveling heater method. In this review, both methods, RMF and TMF are presented. Our recent theoretical and experimental results include such topics as localized TMF, natural convection dumping using TMF in a vertical Bridgman configuration, the traveling heater method, and the Lorentz force induced by TMF as a function of frequency. Experimentally, alloy mixing results, with and without applied TMF, will be presented. Finally, advantages of the traveling magnetic field, in comparison to the more mature rotating magnetic field method, will be discussed.

Mazuruk, K.; Grugel, Richard N.; Motakef, S.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

425

Interstellar Magnetic Field Surrounding the Heliopause  

NASA Astrophysics Data System (ADS)

This paper presents a three-dimensional analytical solution, in the limit of very low plasma ?-ratio, for the distortion of the interstellar magnetic field surrounding the heliopause. The solution is obtained using a line dipole method that is the integration of point dipole along a semi-infinite line; it represents the magnetic field caused by the presence of the heliopause. The solution allows the variation of the undisturbed magnetic field at any inclination angle. The heliosphere is considered as having blunt-nosed geometry on the upwind side and it asymptotically approaches a cylindrical geometry having an open exit for the continuous outflow of the solar wind on the downwind side. The heliopause is treated as a magnetohydrodynamic tangential discontinuity; the interstellar magnetic field lines at the boundary are tangential to the heliopause. The interstellar magnetic field is substantially distorted due to the presence of the heliopause. The solution shows the draping of the field lines around the heliopause. The magnetic field strength varies substantially near the surface of the heliopause. The effect on the magnetic field due to the presence of the heliopause penetrates very deep into the interstellar space; the depth of penetration is of the same order of magnitude as the scale length of the heliosphere.

Whang, Y. C.

2010-02-01

426

INTERSTELLAR MAGNETIC FIELD SURROUNDING THE HELIOPAUSE  

SciTech Connect

This paper presents a three-dimensional analytical solution, in the limit of very low plasma beta-ratio, for the distortion of the interstellar magnetic field surrounding the heliopause. The solution is obtained using a line dipole method that is the integration of point dipole along a semi-infinite line; it represents the magnetic field caused by the presence of the heliopause. The solution allows the variation of the undisturbed magnetic field at any inclination angle. The heliosphere is considered as having blunt-nosed geometry on the upwind side and it asymptotically approaches a cylindrical geometry having an open exit for the continuous outflow of the solar wind on the downwind side. The heliopause is treated as a magnetohydrodynamic tangential discontinuity; the interstellar magnetic field lines at the boundary are tangential to the heliopause. The interstellar magnetic field is substantially distorted due to the presence of the heliopause. The solution shows the draping of the field lines around the heliopause. The magnetic field strength varies substantially near the surface of the heliopause. The effect on the magnetic field due to the presence of the heliopause penetrates very deep into the interstellar space; the depth of penetration is of the same order of magnitude as the scale length of the heliosphere.

Whang, Y. C., E-mail: whang@cua.ed [Catholic University of America, Washington, DC 20064 (United States)

2010-02-20

427

Magnetic-field-controlled reconfigurable semiconductor logic.  

PubMed

Logic devices based on magnetism show promise for increasing computational efficiency while decreasing consumed power. They offer zero quiescent power and yet combine novel functions such as programmable logic operation and non-volatile built-in memory. However, practical efforts to adapt a magnetic device to logic suffer from a low signal-to-noise ratio and other performance attributes that are not adequate for logic gates. Rather than exploiting magnetoresistive effects that result from spin-dependent transport of carriers, we have approached the development of a magnetic logic device in a different way: we use the phenomenon of large magnetoresistance found in non-magnetic semiconductors in high electric fields. Here we report a device showing a strong diode characteristic that is highly sensitive to both the sign and the magnitude of an external magnetic field, offering a reversible change between two different characteristic states by the application of a magnetic field. This feature results from magnetic control of carrier generation and recombination in an InSb p-n bilayer channel. Simple circuits combining such elementary devices are fabricated and tested, and Boolean logic functions including AND, OR, NAND and NOR are performed. They are programmed dynamically by external electric or magnetic signals, demonstrating magnetic-field-controlled semiconductor reconfigurable logic at room temperature. This magnetic technology permits a new kind of spintronic device, characterized as a current switch rather than a voltage switch, and provides a simple and compact platform for non-volatile reconfigurable logic devices. PMID:23364687

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

2013-02-01

428

Bending of magnetic filaments under a magnetic field  

NASA Astrophysics Data System (ADS)

Magnetic beads and superparamagnetic (SP) colloid particles have successfully been employed for micromechanical manipulation of soft material, in situ probing of elastic properties, and design of smart materials (ferrogels). Here we derive analytical expressions for the equilibrium shape of magnetic fibers, considering two end-member cases, (a) SP or single-domain particles concentrated at the free end of cantilevered rods or tubes, and (b) filaments consisting of SP particles, with this case being mathematically equivalent to tubes containing SP particles. Our analysis yields also metastable equilibrium states (MES’s), which only exist above a critical filament length, but become more stable with increasing magnetic field. The MES’s for case (a) are, like the ground state, circular arcs, but more strongly bent. The multiform MES’s in case (b), which comprise hairpin, sinuous, or even closed shapes, have recently been observed in experiments, too. We also study the effect of gravity on the balance between bending and magnetic energy, which leads to curves with inflection point if the influence of gravity is stronger than that of the magnetic field. Because of their simple experimental realization, case (a) magnetic filaments are deemed highly suitable for micromechanical experiments on long chains of polymer molecules. Another potential application of cantilevered magnetic filaments with magnetic material attached to the free end is in scanning probe microscopes. Because the magnetic field due to the magnetic tip is comparatively weak, the magnetization structure of the sample to be investigated would not be affected by the probe. Thus, for the examination of magnetically soft materials, probes in the form of magnetic filaments may hold advantages over tips usually employed in magnetic force microscopy.

Shcherbakov, Valera P.; Winklhofer, Michael

2004-12-01

429

Polarized radiation diagnostics of stellar magnetic fields  

NASA Astrophysics Data System (ADS)

The main techniques used to diagnose magnetic fields in stars from polarimetric observations are presented. First, a summary of the physics of spectral line formation in the presence of a magnetic field is given. Departures from the simple case of linear Zeeman effect are briefly considered: partial Paschen-Back effect, contribution of hyperfine structure, and combined Stark and Zeeman effects. Important approximate solutions of the equation of transfer of polarized light in spectral lines are introduced. The procedure for disk-integration of emergent Stokes profiles, which is central to stellar magnetic field studies, is described, with special attention to the treatment of stellar rotation. This formalism is used to discuss the determination of the mean longitudinal magnetic field (through the photographic technique and through Balmer line photopolarimetry). This is done within the specific framework of Ap stars, which, with their unique large-scale organized magnetic fields, are an ideal laboratory for studies of stellar magnetism. Special attention is paid to those Ap stars whose magnetically split line components are resolved in high-dispersion Stokes I spectra, and to the determination of their mean magnetic field modulus. Various techniques of exploitation of the information contained in polarized spectral line profiles are reviewed: the moment technique (in particular, the determination of the crossover and of the mean quadratic field), Zeeman-Doppler imaging, and least-squares deconvolution. The prospects that these methods open for linear polarization studies are sketched. The way in which linear polarization diagnostics complement their Stokes I and V counterparts is emphasized by consideration of the results of broad band linear polarization measurements. Illustrations of the use of various diagnostics to derive properties of the magnetic fields of Ap stars are given. This is used to show the interest of deriving more physically realistic models of the geometric structure of these fields. How this can possibly be achieved is briefly discussed. An overview of the current status of polarimetric studies of magnetic fields in non-degenerate stars of other types is presented. The final section is devoted to magnetic fields of white dwarfs. Current knowledge of magnetic fields of isolated white dwarfs is briefly reviewed. Diagnostic techniques are discussed, with particular emphasis on the variety of physical processes to be considered for understanding of spectral line formation over the broad range of magnetic field strengths encountered in these stars.

Mathys, Gautier

430

Mercury's internal magnetic field: Constraints on fields of crustal origin  

Microsoft Academic Search

Observations of Mercury's internal magnetic field during MESSENGER's first flyby (M1) and the first and third flybys of Mariner 10 (M10-I, M10-III) suggest that small-scale crustal magnetic fields, if they exist, are at the limit of resolution. Small-scale crustal fields are most easily identified near closest approach (CA) as features with wavelengths comparable to, or larger than, the spacecraft altitude.

M. E. Purucker; T. J. Sabaka; S. C. Solomon; B. J. Anderson; H. Korth; M. T. Zuber; G. A. Neumann; J. W. Head; C. L. Johnson; H. Uno

2008-01-01

431

Dirac equation in magnetic-solenoid field  

Microsoft Academic Search

We consider the Dirac equation in the magnetic-solenoid field (the field of a solenoid and a collinear uniform magnetic field). For the case of Aharonov-Bohm solenoid, we construct self-adjoint extensions of the Dirac Hamiltonian using von Neumann’s theory of deficiency indices. We find self-adjoint extensions of the Dirac Hamiltonian and boundary conditions at the AB solenoid. Besides, for the first

S. P. Gavrilov; D. M. Gitman; A. A. Smirnov

2004-01-01

432

Write field asymmetry in perpendicular magnetic recording  

NASA Astrophysics Data System (ADS)

We present a systematic study of write field asymmetry by using micromagnetic modeling for a perpendicular magnetic recording (PMR) writer structure. Parameters investigated include initial magnetization condition, write current amplitude, write current frequency, and initial write current polarity. It is found that the write current amplitude and frequency (data rate) are the dominant factors that impact the field asymmetry. Lower write current amplitude and higher write current frequency will deteriorate the write field asymmetry, causing recording performance (such as bit error rate) degradation.

Li, Zhanjie; Bai, Daniel Z.; Lin, Ed; Mao, Sining

2012-04-01

433

Aligning Paramecium caudatum with Static Magnetic Fields  

Microsoft Academic Search

As they negotiate their environs, unicellular organisms adjust their swimming in response to various physical fields such as temperature, chemical gradients, and electric fields. Because of the weak magnetic properties of most biological materials, however, they do not respond to the earth’s magnetic field (5×10?5 Tesla) except in rare cases. Here, we show that the trajectories of Paramecium caudatum align

Karine Guevorkian; James M. Valles

2006-01-01

434

Ohm's law for mean magnetic fields  

SciTech Connect

The magnetic fields associated with plasmas frequently exhibit small amplitude MHD fluctuations. It is useful to have equations for the magnetic field averaged over these fluctuations, the so-called mean field equations. Under very general assumptions it is shown that the effect of MHD fluctuations on a force-free plasma can be represented by one parameter in Ohm's law, which is effectively the coefficient of electric current viscosity.

Boozer, A.H.

1986-05-01

435

Turbulence and Magnetic Fields in Astrophysical Plasmas  

Microsoft Academic Search

Magnetic fields permeate the Universe. They are found in planets, stars, accretion discs, galaxies, clusters of galaxies,\\u000a and the intergalactic medium. While there is often a component of the field that is spatially coherent at the scale of the\\u000a astrophysical object, the field lines are tangled chaotically and there are magnetic fluctuations at scales that range over\\u000a orders of magnitude.

Alexander A. Schekochihin; Steven C Cowley

2007-01-01

436

METALLIZATION OF CERAMIC VACUUM CHAMBERS FOR SNS RING INJECTION KICKER MAGNETS.  

SciTech Connect

Ceramic chambers will be used in the pulsed kicker magnets for the injection of H{sup -} into the US Spallation Neutron Source (SNS) accumulator ring. There are two reasons for using ceramic chambers in kickers: (1) to avoid shielding of a fast-changing external magnetic field by metallic chamber walls; and (2) to reduce heating due to eddy currents. The inner surfaces of the ceramic chambers will be coated with a conductive layer, possibly titanium (Ti) or copper with a titanium nitride (TiN) overlayer, to reduce the beam coupling impedance and provide passage for beam image current. This paper describes the development of sputtering method for the 0.83m long 16cm inner diameter ceramic chambers. Coatings of Ti, Cu and TiN with thicknesses up to 10 {micro}m were produced by means of DC magnetron sputtering. The difficulty of coating insulators was overcome with the introduction of an anode screen. Films with good adhesion, uniform longitudinal thickness, and conductivity were produced.

HE,P.; HSEUH,H.C.; TODD,R.J.

2002-04-22

437

Faraday's Magnetic Field Induction Experiment  

NSDL National Science Digital Library

This java simulation illustrates magnetic induction in a wire coil. The user can move a magnet in and out along the axis of a coil while a galvanometer shows the current induced in the coil. The deflection depends on the speed at which the coil moves.

Davidson, Michael

2010-12-29

438

The Measurement of Magnetic Fields  

ERIC Educational Resources Information Center

Discusses five experimental methods used by senior high school students to provide an accurate calibration curve of magnet current against the magnetic flux density produced by an electromagnet. Compares the relative merits of the five methods, both as measurements and from an educational viewpoint. (JR)

Berridge, H. J. J.

1973-01-01

439

Biological effects of high DC magnetic fields  

SciTech Connect

The principal focus of the program is the analysis of magnetic field effects on physiological functions in experimental animals and selected organ and tissue systems. A major research effort has involved the use of electrical recording techniques to detect functional alterations in the cardiovascular, neural, and visual systems during the application of DC magnetic fields. These systems involve ionic conduction processes, and are therefore potentially sensitive to electrodynamic interactions with an applied magnetic field. In the specific case of the visual system, magnetic interactions could also arise through orientational effects on the magnetically anisotropic photopigment molecules within retinal photoreceptor cells. In addition to studies with potentially sensitive target tissues, an evaluation is being made of magnetic field effects on a broad range of other physiological functions in laboratory mammals, including the measurement of circadian rhythms using noninvasive recording techniques. Results of investigations of magnetic field effects on the conformation of DNA, and on the growth and development of plants and insects are also reported. Figures and tables provide a brief summary of some representative observations in each of the research areas described. No significant alterations were observed in any of the physiological parameters examined to date, with the exception of major changes that occur in the electrocardiogram during magnetic field exposure. Studies with several species of animals have provided evidence that this phenomenon is attributable to electrical potentials that are induced during pulsatile blood flow in the aorta and in other major vessels of the circulatory system.

Tenforde, T.S.

1981-06-01

440

Magnetic field effects on dielectrophoresis in manganites  

NASA Astrophysics Data System (ADS)

Perovskite-type manganese oxides (manganites) are of interest for many of the different properties they possess, including colossal magnetoresistance (CMR) and ferroelectric behavior. With the application of an electric field, large resistance decreases have been noted near the insulator-to-metal transition temperature in samples of (La1-yPry)1-xCaxMnO3 (LPCMO). Two proposed models have emerged to explain the behavior, dielectric breakdown and dielectrophoresis, with experimental evidence showing some aspects of the dielectrophoresis model to be correct. However, neither model accounts for magnetic interactions among the ferromagnetic metallic regions and the effects of a magnetic field applied in conjunction with an electric field. We have performed measurements on LPCMO samples by varying the strength and orientation of the magnetic field and the applied voltage. Cross-shaped microstructures have been made on LPCMO samples to allow us to investigate the effects of sample size on dielectrophoresis. We will present resistance and magnetization data obtained on LPCMO samples at various magnetic field strengths, magnetic field orientations, and sample sizes to elucidate the effect of magnetic interactions on dielectrophoresis induced transport and magnetic properties.

Grant, Daniel; Dragiev, Galin; Biswas, Amlan

2013-03-01