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1

Earth-directed ICME magnetic field configurations  

NASA Astrophysics Data System (ADS)

It is known that the geoeffectiveness of interplanetary coronal mass ejections (ICMEs) depends on their magnetic field configuration. However, it remains unclear how the ICME interactions with the solar wind or other solar transient structures affect their magnetic configuration through, say, distortion of their cross-section, or deformation of their front. Obviously, precise space weather forecasting is depended on precise understanding of the evolution of the ICME internal magnetic topology.The goal of this study is to identify the ambient solar wind parameters that affect the flux-rope geometry and magnetic field configuration.

Nieves-Chinchilla, Teresa; Vourlidas, Angelos; Szabo, Adam; Savani, Neel; Mays, M. Leila; Hidalgo, Miguel Angel; Wenyuan, Yu

2015-04-01

2

Progress on Field Reversed Configuration target for Magnetized Target Fusion  

Microsoft Academic Search

We overview the experimental high density Field Reversed Configuration (FRC) approach for a LANL AFRL collaborative physics demonstration of Magnetized Target Fusion (MTF). We show some initial translation data from the Los Alamos FRC experiment FRXL that characterize the MTF translated target plasma. The conical theta coil is expected to generate toroidal magnetic field, helicity, and good curvature field lines,

T. Intrator; G. A. Wurden; P. E. Sieck; W. J. Waganaar; R. Oberto; T. D. Olson; D. Sutherland; J. H. Degnan; E. L. Ruden; M. Domonkos; P. Adamson; C. Grabowski; D. G. Gale; W. Sommars; M. Kostora; M. H. Frese; S. D. Frese; J. F. Camacho; S. K. Coffey; N. F. Roderick; D. J. Amdahl; P. Parks; R. E. Siemon; T. Awe; A. G. Lynn

2009-01-01

3

Formation of active region and quiescent prominence magnetic field configurations  

NASA Technical Reports Server (NTRS)

To investigate the formation of prominences, researchers studied chromospheric mass injection into an overlying coronal dipole magnetic field using a 2-D ideal magnetohydrodynamic (MHD) numerical model. Researchers propose that active region prominences are formed by chromospheric plasmas injected directly into the overlying coronal magnetic field and that quiescent prominences are formed by plasmas evaporated at the interface between spicules and corona. Hence, for the simulation of an active region prominence magnetic field we inject the mass from one side, but use a symmetric mass injection to form a quiescent prominence field configuration. Researchers try to find optimum conditions for the formation of Kippenhahn-Schuluter(K-S)type field configuration for stable support of the injection plasmas. They find that the formation of K-S type field configuration by mass injection requires a delicate balance between injection velocity, density, and overlying magnetic fields. These results may explain why a prominence does not form on every neutral line.

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

1986-01-01

4

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

PubMed

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

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

1999-10-01

5

Parallel heat transport in reversed shear magnetic field configurations  

NASA Astrophysics Data System (ADS)

Transport in magnetized plasmas is a key problem in controlled fusion, space plasmas, and astrophysics. Three issues make this problem particularly challenging: (i) The extreme anisotropy between the parallel (i.e., along the magnetic field), ?, and the perpendicular, ?, conductivities (?/? may exceed 10^10 in fusion plasmas); (ii) Magnetic field lines chaos; and (iii) Nonlocal parallel transport. We have recently developed a Lagrangian Green's function (LG) method to solve the local and non-local parallel (?/?->?) transport equation applicable to integrable and chaotic magnetic fields. footnotetext D. del-Castillo-Negrete, L. Chac'on, PRL, 106, 195004 (2011); D. del-Castillo-Negrete, L. Chac'on, Phys. Plasmas, APS Invited paper, submitted (2011). The proposed method overcomes many of the difficulties faced by standard finite different methods related to the three issues mentioned above. Here we apply the LG method to study transport in reversed shear configurations. We focus on the following problems: (i) separatrix reconnection of magnetic islands and transport; (ii) robustness of shearless, q'=0, transport barriers; (iii) leaky barriers and shearless Cantori.

Blazevski, D.; Del-Castillo-Negrete, D.

2012-03-01

6

Error-field penetration in reversed magnetic shear configurations  

SciTech Connect

Error-field penetration in reversed magnetic shear (RMS) configurations is numerically investigated by using a two-dimensional resistive magnetohydrodynamic model in slab geometry. To explore different dynamic processes in locked modes, three equilibrium states are adopted. Stable, marginal, and unstable current profiles for double tearing modes are designed by varying the current intensity between two resonant surfaces separated by a certain distance. Further, the dynamic characteristics of locked modes in the three RMS states are identified, and the relevant physics mechanisms are elucidated. The scaling behavior of critical perturbation value with initial plasma velocity is numerically obtained, which obeys previously established relevant analytical theory in the viscoresistive regime.

Wang, H. H.; Wang, Z. X.; Wang, X. Q. [MOE Key Laboratory of Materials Modification by Beams of the Ministry of Education, School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116024 (China)] [MOE Key Laboratory of Materials Modification by Beams of the Ministry of Education, School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116024 (China); Wang, X. G. [School of Physics, Peking University, Beijing 100871 (China)] [School of Physics, Peking University, Beijing 100871 (China)

2013-06-15

7

3D MAGNETIC FIELD CONFIGURATION OF THE 2006 DECEMBER 13 FLARE EXTRAPOLATED WITH THE OPTIMIZATION METHOD  

E-print Network

3D MAGNETIC FIELD CONFIGURATION OF THE 2006 DECEMBER 13 FLARE EXTRAPOLATED WITH THE OPTIMIZATION the three-dimensional (3D) vector magnetic field configuration associated with this flare. The general with two-ribbon flares and CMEs. The 3D field configuration before flares can be di- vided into two parts

Wiegelmann, Thomas

8

Toroidal Field Generation and Magnetic Field Relaxation in a Conical Theta Pinch Generated Configuration  

Microsoft Academic Search

Two different cone angles, 10^ circ and 18^circ, were used in this experiment to investigate the effect of the cone angle on the toroidal field generation and magnetic field structure evolution. The configuration was generated in the pinch and then translated into a 15 cm (diameter) x 70 cm (length) stainless steel flux conserver. The hydrogen fill gas was puffed

Kurnia Wira

1988-01-01

9

Resonance and Chaotic Trajectories in Magnetic Field Reversed Configuration  

SciTech Connect

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

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

2005-04-13

10

The magnetic field and magnetospheric configuration of Uranus  

NASA Technical Reports Server (NTRS)

A significant and unique planetary magnetic field discovered by Voyager 2 is presented. A large tilt of 58.6 deg of the magnetic-dipole axis from the rotation axis was found. Combined with a large offset of 0.3 RU of the magnetic dipole from the center of the planet, the moment of 0.23 gauss-RU3 leads to field magnitudes at the surface which vary widely between 0.1 and 1.0 gauss. A simple diagram illustrating the offset tilted dipole of Uranus and some field lines is shown. A more exact and accurate spherical-harmonic model of the planetary field, which includes both dipole and quadrupole moments, is derived. There exists a well-developed bipolar magnetic tail on the night side of the planet which rotates daily about the extended planet-sunline with Uranus because of the large obliquity of the Uranian rotation axis.

Ness, Norman F.; Connerney, John E. P.; Lepping, Ronald P.; Schulz, Michael; Voigt, Gerd-Hannes

1991-01-01

11

Force-Free Magnetic Fields of Closed Configuration Having More Energy Than Open Fields  

NASA Astrophysics Data System (ADS)

Observations of CMEs show an apparent opening of a coronal magnetic field which has assumed a closed configuration before the eruption. In order for this transition of field configuration to occur spontaneously, the pre-eruption closed field must have more energy than the open field. However, as far as force-free fields are concerned, such a transition is energetically forbidden according to the Aly-Sturrock theorem. The theorem states that the maximum energy of the closed force-free fields with the same boundary-normal field distribution and the same field topology is the energy of the corresponding open field. The force-free fields treated in Aly and Sturrock's proofs of the theorem are force-free fields that can be generated from closed potential fields by footpoint motions conserving the boundary normal field distribution and the field topology. The force-free fields investigated in this paper are force-free fields which are not governed by Aly and Sturrock's proofs. We have constructed force-free fields in weak equilibrium, which can be generated in multiple flux systems by a footpoint motion not conserving the boundary normal field distribution. It is found that there exist force-free fields having more magnetic energy than the corresponding open fields. The relevance with observations and the possible mechanisms of CMEs will be discussed.

Choe, G.; Cheng, C.

2002-05-01

12

Toroidal Field Generation and Magnetic Field Relaxation in a Conical Theta Pinch Generated Configuration.  

NASA Astrophysics Data System (ADS)

Two different cone angles, 10^ circ and 18^circ, were used in this experiment to investigate the effect of the cone angle on the toroidal field generation and magnetic field structure evolution. The configuration was generated in the pinch and then translated into a 15 cm (diameter) x 70 cm (length) stainless steel flux conserver. The hydrogen fill gas was puffed from the small end of the cone resulting in a pressure of approximately 15 mT at the middle of the pinch. The peak line-averaged electron density of the plasmoid was 1-3 times 10^{15} cm^ {-3} and its temperature was ~5 eV. The magnetic field structure of the configuration was measured by four 3 dimensional internal magnetic probes. Probes were placed at the same axial location on a given discharge. One of the probes was kept at the machine axis and the other probes formed a concentric circle around the axis. The measured magnetic field components were interpolated using a cubic-spline with a periodic end condition scheme along the circumference of each concentric circle formed by the probes. The magnetic helicity and energy of the configuration were calculated by algorithms which are independent of the chosen axis and the coordinate system. The magnetic fluxes were calculated after the configuration axis was located. Within the range of the examined cone angle, theta <=q 24 ^circ, the averaged toroidal field generation was measured to vary quadratically with the cone angle of the pinch (data for 24^ circ and 1.7^circ were obtained from other experiments). Therefore, a spheromak -like configuration could be generated directly by a Conical Theta Pinch (e.g. 18^circ pinch) if the poloidal and the generated toroidal field had an appropriate distribution. Various experimental evidence, e.g. the time history of the magnetic helicity and energy decay, and the flux conversion indicate that the relaxation of the configuration has occurred in agreement with the Taylor hypothesis. The relaxation parameter, the ratio of the magnetic energy to magnetic helicity, time history indicates that the relaxation behaves like a turbulent relaxation process. For cone angles smaller than 2^circ the relaxation process would not be observed since the relaxation time is longer than the configuration life time. (Abstract shortened with permission of author.).

Wira, Kurnia

13

Unbalanced magnetic field configuration: plasma and film properties.  

PubMed

Coatings of CrN, TiN, ZrN, TaN and NbN were deposited using an unbalanced magnetron sputtering system with two different degrees of unbalancing to investigate the effect of the degree of unbalancing on both plasma characteristics and film properties. The degree of unbalancing was determined by an extensive characterization of the magnetic field fluxes in the X-Z plane perpendicular to the target. Then, the plasma parameters, such as electron temperature, plasma potential, plasma density and ion current density, were obtained for each target and as a function of the unbalance coefficient. The film microstructure, hardness, corrosion and wear resistant were measured to determine the effect of the degree of unbalancing on these properties. The results suggested that the degree of unbalancing, through the variations induced in the ion bombardment and plasma ionization, had a strong influence on the film hardness, microstructure and preferred orientation. PMID:21690858

Rodil, S E; Olaya, J J

2006-08-16

14

Probe measurements of the three-dimensional magnetic field structure in a rotating magnetic field sustained field-reversed configuration  

SciTech Connect

A translatable three-axis probe was constructed and installed on the translation, confinement, and sustainment upgrade (TCSU) experiment. With ninety windings, the probe can simultaneously measure B{sub r}, B{sub ?}, and B{sub z} at 30 radial positions, and can be placed at any desired axial position within the field reversed configuration (FRC) confinement chamber. Positioning the probe at multiple axial positions and taking multiple repeatable shots allows for a full r-z map of the magnetic field. Measurements were made for odd-parity rotating magnetic field (RMF) antennas and even-parity RMF. The steady state data from applying a 10?kHz low pass filter used in conjunction with data at the RMF frequency yields a map of the full 3D rotating field structure. Comparisons will be made to the 3D magnetic structure predicted by NIMROD simulations, with parameters adjusted to match that of the TCSU experiments. The probe provides sufficient data to utilize a Maxwell stress tensor approach to directly measure the torque applied to the FRC's electrons, which combined with a resistive torque model, yields an estimate of the average FRC resistivity.

Velas, K. M. [William E. Boeing Department of Aeronautics and Astronautics, University of Washington, Box 352250, Seattle, Washington 98195-2250 (United States)] [William E. Boeing Department of Aeronautics and Astronautics, University of Washington, Box 352250, Seattle, Washington 98195-2250 (United States); Milroy, R. D. [Plasma Science and Innovation-Center, William E. Boeing Department of Aeronautics and Astronautics, University of Washington, Box 352250, Seattle, Washington 98195-2250 (United States)] [Plasma Science and Innovation-Center, William E. Boeing Department of Aeronautics and Astronautics, University of Washington, Box 352250, Seattle, Washington 98195-2250 (United States)

2014-01-15

15

Study on Axially Distributed Divertor Magnetic Field Configuration in a Mirror Cell  

SciTech Connect

A mirror magnetic field configuration (MFC) is studied in which a divertor is distributed axially using multipole coils. Both configurations of divertor and minimum-B are obtained in a mirror cell. Magnetohydrodynamic (MHD) instability of a mirror cell can be eliminated in this way. Concept of the design and properties of the MFC are discussed.

Islam, M.K.; Nakashima, Y.; Higashizono, Y.; Katanuma, I.; Cho, T

2005-01-15

16

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.

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

2011-01-05

17

Observations of improved confinement in field reversed configurations sustained by antisymmetric rotating magnetic fields  

NASA Astrophysics Data System (ADS)

Rotating magnetic fields (RMF) have been employed to both form and sustain currents in field reversed configurations (FRC). A major concern about this method has been the fear of opening up magnetic field lines with even small ratios of vacuum RMF B? to external confinement field Be. A recently proposed innovation was to use an antisymmetric arrangement of RMF, but vacuum calculations with full RMF penetration showed that very low values of B?/Be would still be required to provide field-line closure. Recent comparisons of symmetric and antisymmetric RMF drive on the translation, confinement, and sustainment (TCS) facility [A. L. Hoffman, H. Y. Guo, J. T. Slough et al., Fusion Sci. Technol. 41, 92 (2002)] have shown strong improvements in the basic confinement properties of the FRCs when using antisymmetric drive, even with ratios of B?/Be as high as 0.3. This is due to normal standard operation with only partial penetration of the RMF beyond the FRC separatrix. The uniform transverse RMF in vacuum is shielded by the conducting plasma, resulting in a mostly azimuthal field near the FRC separatrix with a very small radial component. Simple numerical calculations using analytical solutions for the partially penetrated antisymmetric RMF, superimposed on Grad-Shafranov solutions for the poloidal FRC fields, show good field-line closure for the TCS experimental conditions. The antisymmetric arrangement also leads to more efficient current drive and improved stabilization of rotational modes.

Guo, H. Y.; Hoffman, A. L.; Steinhauer, L. C.

2005-06-01

18

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

SciTech Connect

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

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

2008-10-15

19

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

SciTech Connect

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

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

2010-05-20

20

Rotating magnetic field current drive of high-temperature field reversed configurations with high {zeta} scaling  

SciTech Connect

Greatly reduced recycling and impurity ingestion in the Translation, Confinement, and Sustainment--Upgrade (TCSU) device has allowed much higher plasma temperatures to be achieved in the field reversed configurations (FRC) under rotating magnetic field (RMF) formation and sustainment. The hotter plasmas have higher magnetic fields and much higher diamagnetic electron rotation rates so that the important ratio of average electron rotation frequency to RMF frequency, called {zeta}, approaches unity, for the first time, in TCSU. A large fraction of the RMF power is absorbed by an as yet unexplained (anomalous) mechanism directly proportional to the square of the RMF magnitude. It becomes of relatively lesser significance as the FRC current increases, and simple resistive heating begins to dominate, but the anomalous absorption is useful for initial plasma heating. Measurements of total absorbed power, and comparisons of applied RMF torque to torque on the electrons due to electron-ion friction under high-{zeta} operation, over a range of temperatures and fields, have allowed the separation of the classical Ohmic and anomalous heating to be inferred, and cross-field plasma resistivities to be calculated.

Guo, H. Y.; Hoffman, A. L.; Milroy, R. D. [Redmond Plasma Physics Laboratory, University of Washington, 14700 NE 95th Street, Suite 100, Redmond, Washington 98052 (United States)

2007-11-15

21

Progress on formation of field reversed configurations suitable for subsequent compression to magnetized target fusion conditions  

Microsoft Academic Search

Summary form only given. The design, calculations, and experimental progress on forming Field Reversed Configuration's (FRCs) suitable for subsequent compression by an imploding metal liner to Magnetized Target Fusion (MTF) conditions are presented and discussed. The desired initial FRC parameters are density ~1017 cm-3, temperature ~100 to 300 eV, length ~30 cm, separatrix radius ~2.5 cm, magnetic field between separatrix

J. H. Degnan; T. W. Hussey; G. F. Kiuttu; F. M. Lehr; E. L. Ruden; T. Cavazos; D. Gale; C. Gilman; C. Grabowski; W. Sommars; S. K. Coffey; M. Frese; G. Marklin; R. J. Faehl; T. P. Intrator; R. Kirkpatrick; I. Lindermuth; R. Moses; K. F. Schoenberg; R. E. Siemon; J. M. Taccetti; P. J. Turchi; G. A. Wurden; N. F. Roderick

2001-01-01

22

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

SciTech Connect

Ion heating by application of rotating magnetic fields (RMF) to a prolate field-reversed configuration(FRC) is explored by analytical and numerical techniques. For odd-parity RMF (RMFo), perturbation analysis shows ions in figure-8 orbits gain energy at resonances of the RMFo frequency, ?R, with the figure-8 orbital frequency, ?. Since figure-8 orbits tend to gain the most energy from the RMF and are unlikely to escape in the cusp region (where most losses occur), they are optimal candidates for rapid stochastic heating, as compared to cyclotron and betatron orbits. Comparisons are made between heating caused by even- and odd-parity RMFs and between heating in currently operating and in reactor-scale FRC devices.

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

2007-06-25

23

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

NASA Astrophysics Data System (ADS)

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

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

2006-01-01

24

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

SciTech Connect

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

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

2008-10-15

25

MHD simulations of the flapping instability in tail-like magnetic configurations with guide field  

NASA Astrophysics Data System (ADS)

The flapping (kink) mode developing in the magnetotail-like magnetic configuration with tailward growing normal magnetic component and finite guide field is studied by means of linearized 2-dimensional and non-linear 3-dimensional MHD modeling. We consider a particular case of a weak normal magnetic component (that is, small radius of the magnetic field line curvature), which makes the configuration unstable to a special branch of ballooning instability known as "double-gradient" mode, introduced recently to describe the magnetotail flapping oscillations. The initial tail-like equilibrium is provided by conventional Grad-Shafranov equation. The results of the 2D linearized MHD code are in agreement with the analytical predictions, and the growth rate is found to be close to the peak value provided by an analytical estimate. Both 2D and 3D calculations confirm that the double-gradient mode is excited in a region of large curvature of the magnetic field lines. In agreement with the analytical predictions, non-zero guide field reduces the growth rate significantly for large (compare to the current sheet width L) wave numbers k, hence the modes kL ~ 1 are the fastest growing. Thus, the non-zero guide field introduces a characteristic wavelength corresponding to the dispersion curve peak. For the guide field of ~ 0.5 (in the lobe magnetic field units), the mode decays totally.

Korovinskiy, Daniil; Divin, Andrey; Ivanov, Ivan; Semenov, Vladimir; Erkaev, Nikolay; Artemiev, Anton; Markidis, Stefano; Lapenta, Giovanni; Ivanova, Viktoria; Kubyshkina, Darya

2014-05-01

26

Formation of a field reversed configuration for magnetic and electrostatic confinement of plasma  

DOEpatents

A system and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.

Rostoker, Norman; Binderbauer, Michl; Qerushi, Artan; Tahsiri, Hooshang

2007-02-20

27

Formation of a field reversed configuration for magnetic and electrostatic confinement of plasma  

DOEpatents

A system and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.

Rostoker, Norman; Binderbauer, Michl

2003-12-16

28

Formation of a field reversed configuration for magnetic and electrostatic confinement of plasma  

DOEpatents

A system and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.

Rostoker, Norman; Binderbauer, Michl; Qerushi, Artan; Tahsiri, Hooshang

2006-02-07

29

Applied magnetic field design for the field reversed configuration compression heating experiment.  

PubMed

Detailed calculations of the formation, guide, and mirror applied magnetic fields in the FRC compression-heating experiment (FRCHX) were conducted using a commercially available generalized finite element solver, COMSOL Multiphysics(®). In FRCHX, an applied magnetic field forms, translates, and finally captures the FRC in the liner region sufficiently long to enable compression. Large single turn coils generate the fast magnetic fields necessary for FRC formation. Solenoidal coils produce the magnetic field for translation and capture of the FRC prior to liner implosion. Due to the limited FRC lifetime, liner implosion is initiated before the FRC is injected, and the magnetic flux that diffuses into the liner is compressed. Two-dimensional axisymmetric magnetohydrodynamic simulations using MACH2 were used to specify optimal magnetic field characteristics, and this paper describes the simulations conducted to design magnetic field coils and compression hardware for FRCHX. This paper presents the vacuum solution for the magnetic field. PMID:23635196

Domonkos, M T; Amdahl, D; Camacho, J F; Coffey, S K; Degnan, J H; Delaney, R; Frese, M; Gale, D; Grabowski, T C; Gribble, R; Intrator, T P; McCullough, J; Montano, N; Robinson, P R; Wurden, G

2013-04-01

30

Multichord laser interferometer for the magnetized target fusion program's field reverse configuration  

Microsoft Academic Search

AFRL's Directed Energy Directorate has built a multiple chord 6328 nm interferometer to diagnose a Field Reversed Configuration (FRC) being developed for LANL and AFRL's collaborative Magnetized Target Fusion (MTF) program. The FRC is intended for compression to near thermonuclear fusion conditions by AFRL's Shiva Star capacitor bank. The interferometer is designed to measure the density integral along eight chords

Edward Ruden; Francis Analla; Shouyin Zhang

2002-01-01

31

Thermally induced magnetization switching in Fe/MnAs/GaAs(001): selectable magnetic configurations by temperature and field control.  

PubMed

Spintronic devices currently rely on magnetization control by external magnetic fields or spin-polarized currents. Developing temperature-driven magnetization control has potential for achieving enhanced device functionalities. Recently, there has been much interest in thermally induced magnetisation switching (TIMS), where the temperature control of intrinsic material properties drives a deterministic switching without applying external fields. TIMS, mainly investigated in rare-earth-transition-metal ferrimagnets, has also been observed in epitaxial Fe/MnAs/GaAs(001), where it stems from a completely different physical mechanism. In Fe/MnAs temperature actually modifies the surface dipolar fields associated with the MnAs magnetic microstructure. This in turn determines the effective magnetic field acting on the Fe overlayer. In this way one can reverse the Fe magnetization direction by performing thermal cycles at ambient temperatures. Here we use element selective magnetization measurements to demonstrate that various magnetic configurations of the Fe/MnAs/GaAs(001) system are stabilized predictably by acting on the thermal cycle parameters and on the presence of a bias field. We show in particular that the maximum temperature reached during the cycle affects the final magnetic configuration. Our findings show that applications are possible for fast magnetization switching, where local temperature changes are induced by laser excitations. PMID:25631753

Spezzani, Carlo; Vidal, Franck; Delaunay, Renaud; Eddrief, Mahmoud; Marangolo, Massimiliano; Etgens, Victor H; Popescu, Horia; Sacchi, Maurizio

2015-01-01

32

Thermally induced magnetization switching in Fe/MnAs/GaAs(001): selectable magnetic configurations by temperature and field control  

NASA Astrophysics Data System (ADS)

Spintronic devices currently rely on magnetization control by external magnetic fields or spin-polarized currents. Developing temperature-driven magnetization control has potential for achieving enhanced device functionalities. Recently, there has been much interest in thermally induced magnetisation switching (TIMS), where the temperature control of intrinsic material properties drives a deterministic switching without applying external fields. TIMS, mainly investigated in rare-earth-transition-metal ferrimagnets, has also been observed in epitaxial Fe/MnAs/GaAs(001), where it stems from a completely different physical mechanism. In Fe/MnAs temperature actually modifies the surface dipolar fields associated with the MnAs magnetic microstructure. This in turn determines the effective magnetic field acting on the Fe overlayer. In this way one can reverse the Fe magnetization direction by performing thermal cycles at ambient temperatures. Here we use element selective magnetization measurements to demonstrate that various magnetic configurations of the Fe/MnAs/GaAs(001) system are stabilized predictably by acting on the thermal cycle parameters and on the presence of a bias field. We show in particular that the maximum temperature reached during the cycle affects the final magnetic configuration. Our findings show that applications are possible for fast magnetization switching, where local temperature changes are induced by laser excitations.

Spezzani, Carlo; Vidal, Franck; Delaunay, Renaud; Eddrief, Mahmoud; Marangolo, Massimiliano; Etgens, Victor H.; Popescu, Horia; Sacchi, Maurizio

2015-01-01

33

Thermally induced magnetization switching in Fe/MnAs/GaAs(001): selectable magnetic configurations by temperature and field control  

PubMed Central

Spintronic devices currently rely on magnetization control by external magnetic fields or spin-polarized currents. Developing temperature-driven magnetization control has potential for achieving enhanced device functionalities. Recently, there has been much interest in thermally induced magnetisation switching (TIMS), where the temperature control of intrinsic material properties drives a deterministic switching without applying external fields. TIMS, mainly investigated in rare-earth–transition-metal ferrimagnets, has also been observed in epitaxial Fe/MnAs/GaAs(001), where it stems from a completely different physical mechanism. In Fe/MnAs temperature actually modifies the surface dipolar fields associated with the MnAs magnetic microstructure. This in turn determines the effective magnetic field acting on the Fe overlayer. In this way one can reverse the Fe magnetization direction by performing thermal cycles at ambient temperatures. Here we use element selective magnetization measurements to demonstrate that various magnetic configurations of the Fe/MnAs/GaAs(001) system are stabilized predictably by acting on the thermal cycle parameters and on the presence of a bias field. We show in particular that the maximum temperature reached during the cycle affects the final magnetic configuration. Our findings show that applications are possible for fast magnetization switching, where local temperature changes are induced by laser excitations. PMID:25631753

Spezzani, Carlo; Vidal, Franck; Delaunay, Renaud; Eddrief, Mahmoud; Marangolo, Massimiliano; Etgens, Victor H.; Popescu, Horia; Sacchi, Maurizio

2015-01-01

34

Recovery of the global magnetic field configuration of 78 Virginis from Stokes IQUV line profiles  

NASA Astrophysics Data System (ADS)

The surface magnetic field configuration of the Ap star HD 118022 (78 Vir) has been reconstructed in the framework of the magnetic charge distribution (MCD) method from the analysis of Stokes IQUV spectra obtained using the MuSiCoS spectropolarimeter at Pic du Midi Observatory. Magnetically-sensitive Fe ii lines were primarily employed in the analysis, supposing that iron is evenly distributed over the stellar surface. We show that the Stokes IQUV profile shapes and variations of 78 Vir can be approximately fit assuming a global magnetic field configuration described by a slightly decentered, inclined magnetic dipole of polar surface intensity approximately 3.3 kG. The derived inclinations of the stellar rotational axis to the line of sight i=24 ± 5° as well as to the magnetic dipole axis ?=124 ± 5° are in good agreement with previous estimations by other authors, whereas the sky-projected position angle of the stellar rotation axis ?˜110° is reported here for the first time. In addition, several lines of Cr ii and Ti ii were studied, yielding evidence for non-uniform surface distributions of these elements, and magnetic field results similar to those derived from Fe.

Khalack, V. R.; Wade, G. A.

2006-05-01

35

Electron Acceleration in the Field-reversed Configuration (FRC) by Slowly Rotating Odd-parity Magnetic Fields  

SciTech Connect

The trajectories of individual electrons are studied numerically in a 3D, prolate, FRC [field-reversed configuration] equilibrium magnetic geometry with added small-aplitude, slowly rotating, odd-parity magnetic fields (RFos). RMFos cause electron heating by toroidal acceleration near the 0-point line and by field-parallel acceleration away from it, both followed by scattering from magnetic-field inhomogeneities. Electrons accelerated along the 0-point line move antiparallel to the FRC's current and attain average toroidal angular speeds near that of the RMFo, independent of the sense of RMFo rotation. A conserved transformed Hamiltonian, dependent on electron energy and RMFo sense, controls electron flux-surface coordinate.

Alan H. Glasser; Samuel A. Cohen

2001-04-05

36

RF Wave Characteristics in Large Diameter Plasma with Various Magnetic Field Configurations  

NASA Astrophysics Data System (ADS)

We have been investigating the effect of the magnetic field on the RF (radio frequency) wave phenomenon and the antenna-plasma coupling with an aim to control the plasma parameters in the large diameter (45 cm) plasma produced by a spiral antenna. When the uniform magnetic field was applied, the peaked electron density profile (with the higher density) and the larger antenna-plasma coupling coefficient than those without the field were obtained. The helicon wave with an azimuthal mode number of m=0 was confirmed by the radial and axial profiles of the excited magnetic fields and the dispersion relation. Control of plasma parameters such as the electron density and the uniformity was tried by changing the configurations of the antenna field and the external magnetic field, i.e., uniform, divergent and cusp fields. The effective diameter D_eff (ion saturation current was uniform within ±5 %) in the cusp field improved drastically, e.g., D_eff was up to 27 cm where the electron density was ~10^12 cm-3. The excited wave characteristics depended on the gradient at the line cusp position and the magnitude of the magnetic field, and in the neighborhood of this position showed the different behavior from the observed helicon wave for the case of the uniform field.

Takechi, Seiji; Shinohara, Shunjiro

1998-10-01

37

H{sub 3}{sup +} molecular ion in a magnetic field: Linear parallel configuration  

SciTech Connect

A detailed study of the ground state of the H{sub 3}{sup +} molecular ion in linear configuration, parallel to the magnetic field direction, and its low-lying {sigma}, {pi}, and {delta} states is carried out for magnetic fields B=0-4.414x10{sup 13} G in the Born-Oppenheimer approximation. The variational method is employed with a single trial function which includes electronic correlation in the form exp({gamma}r{sub 12}), where {gamma} is a variational parameter. It is shown that the quantum numbers of the state of the lowest total energy (ground state) depend on the magnetic field strength. The ground state evolves from the spin-singlet {sup 1}{sigma}{sub g} state for weak magnetic fields B(less-or-similar sign)5x10{sup 8} G to a weakly bound spin-triplet {sup 3}{sigma}{sub u} state for intermediate fields and, eventually, to a spin-triplet {sup 3}{pi}{sub u} state for 5x10{sup 10}(less-or-similar sign)B(less-or-similar sign)4.414x10{sup 13} G. Local stability of the linear parallel configuration with respect to possible small deviations is checked.

Turbiner, A. V.; Guevara, N. L.; Lopez Vieyra, J. C. [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-543, 04510 Mexico, D.F. (Mexico)

2007-05-15

38

Superposed epoch analysis of pressure and magnetic field configuration changes in the plasma sheet  

NASA Technical Reports Server (NTRS)

Using data from 41 substorm events in the near-Earth magnetotail, we have combined plasma, energetic ion, and magnetic field data from the AMPTE/IRM spacecraft to perform a superposed epoch analysis of changes in the total pressure and in the magnetic field configuration as a function of time relative to substorm onset. Unloading is evident in the total pressure profile; the pressure decreases by about 20 percent. Pressure changes during the growth phase are not as uniform for the different substorms as the pressure changes during the expansion phase. To study changes in the magnetic field configuration, we have determined the development of the plasma pressure profiles in z for an average of data from 15 to 19 R(E). At substorm onset, the field line dipolarization begins on the innermost field lines and then progresses to the outer field lines. The field lines map the closest to the Earth about 45 min after substorm onset, and then begin to stretch out again during the recovery phase of the substorm.

Kistler, L. M.; Baumjohann, W.; Nagai, T.; Mobius, E.

1993-01-01

39

Overview of Reversed Field Configuration plasma target research at LANL for Magnetized Target Fusion  

Microsoft Academic Search

We overview the Field Reversed Configuration (FRC) experiment at Los Alamos National Laboratory (FRX-L), including the design, plasma physics and diagnostics. The Magnetized Target Fusion project goal is to achieve fusion conditions in a pulsed experiment using relatively small resources during our lifetimes. FRX-L is designed to operate at large density n 10^17 cm-3 and high enough temperature to surmount

T. Intrator; J. Taccetti; G. Wurden; R. Siemon; P. Sanchez; W. Waganaar; S. Y. Zhang; M. Tuszewski; R. Maqueda; D. Begay; C. Bass; J. Campbell; C. Carey; M. Kozar; J. Liang; R. Renneke; C. Grabowski; J. Degnan; W. Sommars; E. Ruden; D. Gale; T. Cavasos

2002-01-01

40

A configurable component-based software system for magnetic field measurements  

SciTech Connect

A new software system to test accelerator magnets has been developed at Fermilab. The magnetic measurement technique involved employs a single stretched wire to measure alignment parameters and magnetic field strength. The software for the system is built on top of a flexible component-based framework, which allows for easy reconfiguration and runtime modification. Various user interface, data acquisition, analysis, and data persistence components can be configured to form different measurement systems that are tailored to specific requirements (e.g., involving magnet type or test stand). The system can also be configured with various measurement sequences or tests, each of them controlled by a dedicated script. It is capable of working interactively as well as executing a preselected sequence of tests. Each test can be parameterized to fit the specific magnet type or test stand requirements. The system has been designed with portability in mind and is capable of working on various platforms, such as Linux, Solaris, and Windows. It can be configured to use a local data acquisition subsystem or a remote data acquisition computer, such as a VME processor running VxWorks. All hardware-oriented components have been developed with a simulation option that allows for running and testing measurements in the absence of data acquisition hardware.

Nogiec, J.M.; DiMarco, J.; Kotelnikov, S.; Trombly-Freytag, K.; Walbridge, D.; Tartaglia, M.; /Fermilab

2005-09-01

41

Inductrack magnet configuration  

DOEpatents

A magnet configuration comprising a pair of Halbach arrays magnetically and structurally connected together are positioned with respect to each other so that a first component of their fields substantially cancels at a first plane between them, and a second component of their fields substantially adds at this first plane. A track of windings is located between the pair of Halbach arrays and a propulsion mechanism is provided for moving the pair of Halbach arrays along the track. When the pair of Halbach arrays move along the track and the track is not located at the first plane, a current is induced in the windings and a restoring force is exerted on the pair of Halbach arrays.

Post, Richard Freeman

2003-12-16

42

Inductrack magnet configuration  

DOEpatents

A magnet configuration comprising a pair of Halbach arrays magnetically and structurally connected together are positioned with respect to each other so that a first component of their fields substantially cancels at a first plane between them, and a second component of their fields substantially adds at this first plane. A track of windings is located between the pair of Halbach arrays and a propulsion mechanism is provided for moving the pair of Halbach arrays along the track. When the pair of Halbach arrays move along the track and the track is not located at the first plane, a current is induced in the windings and a restoring force is exerted on the pair of Halbach arrays.

Post, Richard Freeman

2003-10-14

43

Ion and electron cyclotron wall conditioning in stellarator and tokamak magnetic field configuration on WEGA  

NASA Astrophysics Data System (ADS)

Discharge wall conditioning is an effective tool to improve plasma performance in tokamaks and stellarators. RF Discharge Conditioning (RFDC) techniques are envisaged for use during operational campaigns on superconducting devices like the ITER tokamak and W7-X stellarator, as alternative to DC Glow Discharge Conditioning which is inefficient in presence of magnetic fields. This contribution investigates RFDC in both the ion and electron cyclotron range of frequencies (ICRF and ECRF) on the WEGA device (Max-Planck-Institute for Plasma Physics, Greifswald, Germany) as preparation for W7-X operation. ECRF discharges produced by localised absorption of RF power at EC resonance layers suffer from poor radial discharge homogeneity in the tokamak vacuum magnetic field configuration, severely limiting the plasma wetted wall areas and consequently the conditioning efficiency. The non-localised production of ICRF discharges by collisional RF power absorption features much improved discharge homogeneity making Ion Cyclotron Wall Conditioning (ICWC) the favoured RFDC technique for superconducting tokamaks. RFDC with the stellarator vacuum magnetic field needs to aim at sufficient plasma densities at and outside the last closed flux surface (LCFS), maximising the convective plasma flux along the open field lines to the wall. Whereas for ICRF discharges this condition is easily fulfilled, on WEGA for He-ECRF discharges this could be achieved as well by off axis heating close to the LCFS. In stellarator magnetic field configuration it is found that He-ICWC for wall desaturation is at least one order of magnitude more efficient than He-ECWC. Novel ECWC methods are proposed that can decrease this efficiency gap with ICWC to a factor 2-3. The efficiency difference is less pronounced in case of H2-ICWC and ECWC for isotopic exchange.

Wauters, T.; Laqua, H. P.; Otte, M.; Preynas, M.; Stange, T.; Urlings, P.; Altenburg, Y.; Aßmus, D.; Birus, D.; Louche, F.

2014-02-01

44

Ion and electron cyclotron wall conditioning in stellarator and tokamak magnetic field configuration on WEGA  

SciTech Connect

Discharge wall conditioning is an effective tool to improve plasma performance in tokamaks and stellarators. RF Discharge Conditioning (RFDC) techniques are envisaged for use during operational campaigns on superconducting devices like the ITER tokamak and W7-X stellarator, as alternative to DC Glow Discharge Conditioning which is inefficient in presence of magnetic fields. This contribution investigates RFDC in both the ion and electron cyclotron range of frequencies (ICRF and ECRF) on the WEGA device (Max-Planck-Institute for Plasma Physics, Greifswald, Germany) as preparation for W7-X operation. ECRF discharges produced by localised absorption of RF power at EC resonance layers suffer from poor radial discharge homogeneity in the tokamak vacuum magnetic field configuration, severely limiting the plasma wetted wall areas and consequently the conditioning efficiency. The non-localised production of ICRF discharges by collisional RF power absorption features much improved discharge homogeneity making Ion Cyclotron Wall Conditioning (ICWC) the favoured RFDC technique for superconducting tokamaks. RFDC with the stellarator vacuum magnetic field needs to aim at sufficient plasma densities at and outside the last closed flux surface (LCFS), maximising the convective plasma flux along the open field lines to the wall. Whereas for ICRF discharges this condition is easily fulfilled, on WEGA for He-ECRF discharges this could be achieved as well by off axis heating close to the LCFS. In stellarator magnetic field configuration it is found that He-ICWC for wall desaturation is at least one order of magnitude more efficient than He-ECWC. Novel ECWC methods are proposed that can decrease this efficiency gap with ICWC to a factor 2-3. The efficiency difference is less pronounced in case of H{sub 2}-ICWC and ECWC for isotopic exchange.

Wauters, T.; Louche, F. [Association Euratom-Belgian State, LPP-ERM/KMS, 1000 Brussels (Belgium); Laqua, H. P.; Otte, M.; Preynas, M.; Stange, T.; Altenburg, Y.; Aßmus, D.; Birus, D. [Max Planck Institute for Plasma Physics, EURATOM Association, 17491 Greifswald (Germany); Urlings, P. [Max Planck Institute for Plasma Physics, EURATOM Association, 17491 Greifswald, Germany and University of Technology, Department of Applied Physics, Eindhoven (Netherlands)

2014-02-12

45

A first look into the magnetic field configuration of prominence threads using spectropolarimetric data  

NASA Astrophysics Data System (ADS)

We show preliminary results of an ongoing investigation aimed at determining the configuration of the magnetic field vector in the threads of a quiescent hedgerow solar prominence using high-spatial resolution spectropolarimetric observations taken in the He I 1083.0 nm multiplet. The data consist of a two-dimensional map of a quiescent hedgerow prominence showing vertical threads. The observations were obtained with the Tenerife Infrared Polarimeter attached to the German Vacuum Tower Telescope at the Observatorio del Teide (Spain). The He I 1083.0 nm Stokes signals are interpreted with an inversion code, which takes into account the key physical processes that generate and/or modify circular and linear polarization signals in the He I 1083.0 nm triplet: the Zeeman effect, anisotropic radiation pumping, and the Hanle effect. We present initial results of the inversions, i.e, the strength and orientation of the magnetic field vector along the prominence and in prominence threads.

Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J.

2014-01-01

46

Pre-eruption Magnetic Field Configurations with High Magnetic Energy Storage  

NASA Astrophysics Data System (ADS)

Previously it was believed that the energy of a force-free field cannot exceed the energy of the corresponding open field. This proposition was established as the Aly-Sturrock Theorem. According to this theorem, the energy budget for coronal mass ejections (CMEs) and eruptive flares is very tight. Magnetograms and soft X-ray observations before solar eruptive events often indicate that the pre-eruption magnetic fields consist of multiple flux systems. We construct numerical solutions of force-free magnetic fields in multiple flux systems and investigate their eruption energetics. Our study of multiple flux systems shows that there can be many classes of force-free fields having more energy than the open fields. The energy of an interwinding two-flux system is found to exceed the open field energy for a winding angle near 360 degrees. Comparison of the numerically constructed solutions with observations of active eruption regions also reveals that the eruption indeed takes place for a winding angle slightly larger than 360 degrees. The dynamic evolution from high energy equilibria will be discussed based on 3D MHD simulations.

Choe, G. S.; Cheng, C. Z.

2003-12-01

47

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

SciTech Connect

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

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

2005-11-01

48

Reproducible High Density Field-Reversed Configuration Plasma for Magnetized Target Fusion  

NASA Astrophysics Data System (ADS)

Field-Reversed Configuration (FRC) plasma will be translated into an imploding metal liner in a Magnetized Target Fusion (MTF) scenario. Field-Reversed Theta Pinch technology is employed with programmed cusp fields at the theta coil ends to achieve non-tearing field line reconnection during FRC formation. In the Field Reversed Configuration Experiment with a Liner (FRX-L), an optimum formation procedure is identified. The well-formed FRC plasma has volume-averaged density of 2 - 4x10^22m-3, Te+Ti of 300-500 eV, and plasma lifetime between 15-20 ?s. These parameters are very close to the desired parameters of a target plasma for MTF, and they can be reproduced with standard deviation of less than 10% about the mean in consecutive discharges. Recently, the redesigned crowbar switches have reduced the external main field modulation from 52% previously to 21% now. Better FRC performance is expected in on-going experimental campaigns.

Zhang, Shouyin; Grabowski, Chris; Ruden, Edward

2005-10-01

49

Influence of different types of magnetic fields on the interface shape in a 200 mm Si-EMCZ configuration  

Microsoft Academic Search

Three-dimensional time-dependent simulations were carried out in order to predict the heat transport and interface shape in a 200mm diameter silicon electromagnetic Czochralski (EMCZ) configuration under the influence of two types of magnetic fields: (a) a vertical magnetic (VMF) field and (b) a cusp magnetic field (CMF). It was found that for a CMF, the interface deflection is much higher

D. Vizman; M. Watanabe; J. Friedrich; G. Müller

2007-01-01

50

Effects of magnetic field configuration on the day-night asymmetry of chorus occurrence rate: A numerical study  

NASA Astrophysics Data System (ADS)

Effects of magnetic field configuration on the day-night asymmetry of chorus occurrence rate are investigated using a recently developed hybrid code. Previous observational studies show that dayside chorus occurs in regions where the background magnetic field is nearly homogeneous; these observations suggest that the magnetic field configuration might play a significant role in the dayside chorus excitation. In this work, we use a hybrid code to numerically study the threshold conditions of hot electron distributions required to excite chorus waves for different background magnetic field inhomogeneities. Our numerical experiments demonstrate that in a magnetic field with smaller inhomogeneity, smaller temperature anisotropy and smaller number density of hot electrons are needed to excite chorus waves. This conclusion could help explain the higher occurrence rate of chorus waves on the dayside compared with that on the nightside especially in quiet times.

Tao, X.; Lu, Q.; Wang, S.; Dai, L.

2014-10-01

51

Field-dependent spin chirality and frustration in V and Cu nanomagnets in transverse magnetic field. 2. Spin configurations, chirality and intermediate spin magnetization in distorted trimers  

NASA Astrophysics Data System (ADS)

Correlated spin configurations, magnetizations, frustration, vector ? and scalar ?¯ chiralities are considered for distorted V, /Cu/ anisotropic DM nanomagnets in transverse Bx?X and longitudinal B?Z fields. Different planar configurations in the ground and excited states of distorted nanomagnets in Bx determine different field behavior of the vector chiralities and the degenerate frustration in these states correlated with the M?˜12±(Bx) intermediate spin (IS) magnetization which describes the S12 characteristics, ?=0. Distortion results in the reduced ?<1 chirality in the ground distorted configuration and in the maximum ?z=±1 in the excited states with the planar 120° configurations at avoided level crossing. In B?Z, distorted longitudinal spin-collinear configurations are characterized by the reduced degenerate frustration, out-of-plane staggered and IS M?˜12±(Bz) magnetizations, and in-plane toroidal moments, correlated with the ?, ?¯ chiralities, ?¯=±|?|. The chiralities and IS magnetization in EPR, INS and NMR spectra are considered. The quantitative correlations describe variable spin chirality, frustration and field manipulation of chiralities in nanomagnets.

Belinsky, Moisey I.

2014-05-01

52

About the Influence of the Magnetic Field Configuration on the Levitation Characteristics of the System Superconductor - Array of Magnets  

NASA Astrophysics Data System (ADS)

Interaction of a superconductor with an array of magnets having different orientations of the magnetization vector is theoretically investigated. Based on a critical state model, the interaction force arising in the system superconductor - array of magnets is calculated by the method of finite elements. Optimal configurations of the magnetic system are established in which maximum values of both attractive and repulsive forces are created.

Ermolaev, Yu. S.; Rudnev, I. A.

2014-07-01

53

Global Perturbation Configurations in a Composite Disc System with an Isopedic Magnetic Field  

E-print Network

We construct stationary global configurations of both aligned and unaligned logarithmic spiral perturbations in a composite disc system of stellar and isopedically magnetized gaseous singular isothermal discs (SIDs) coupled by gravity. The thin gaseous SID is threaded across by a vertical magnetic field B_z with a constant ratio of the surface gas mass density to B_z. There exist two classes of stationary magnetohydrodynamic (MHD) solutions with in-phase and out-of-phase density perturbations. For both aligned and unaligned cases with azimuthal periodicities |m|\\geq 2 (m is an integer), there may be two, one, and no solution situations, depending on the chosen parameters. For the transition criteria from an axisymmetric equilibrium to aligned secular bar-like instabilities, the corresponding T/|W| ratio can be much lower than the oft-quoted value of T/|W|\\sim 0.14, where T is the total rotational kinetic energy and W is the total gravitational potential energy plus the magnetic energy. The T/|W| ratios for the two sets of solutions in different ranges are separated by m/(4m+4). For the unaligned cases, we study marginal stabilities for axisymmetric (m=0) and non-axisymmetric (m\

Y. -Q. Lou; Y. Wu

2005-08-28

54

Enhanced absorption Hanle effect in the configuration of crossed laser beam and magnetic field F. Renzoni,1,  

E-print Network

-field-created Zeeman coherences. The Hanle effect investigations of Refs. 11,12 were based on a linearly polarizedEnhanced absorption Hanle effect in the configuration of crossed laser beam and magnetic field F 2001 We have analyzed the Hanle effect on the closed Fg 3Fe 4 D2-line transition of 85 Rb. Exciting

55

Numerical analysis of the trajectories of a single charged particle in a nonadiabatic cusp magnetic field configuration  

NASA Astrophysics Data System (ADS)

The trajectories of a nonrelativistic single charged particle in a nonadiabatic cusped magnetic field configuration are numerically analyzed. Depth of penetration of the particle into the cusped field, multiple reflections and radial excursion of the particle transmitted by the cusped field are discussed. A significant observation was that a meticulous choice of particle and field parameters could lead to several number of reflections. For radial excursion a plateau region over ? was exhibited.

Selvarajan, V.; Vijayalakshmi, K. A.

1995-05-01

56

Three-dimensional MHD simulation of FTEs produced by merging at an isolated point in a sheared magnetic field configuration  

NASA Astrophysics Data System (ADS)

We present predictions for the evolution of FTEs generated by localized bursts of reconnection on a planar magnetopause that separates a magnetosheath region of high densities and weak magnetic field from a magnetospheric region of low densities and strong magnetic field. The magnetic fields present a shear angle of 105 degrees. Reconnection forms a pair of FTEs each crossing the magnetopause in the field reversal region and bulging into the magnetosphere and magnetosheath. At their initial stage they can be characterized as flux tubes since the newly reconnected magnetic field lines are not twisted. Reconnection launches Alfvenic perturbations that propagate along the FTEs generating high-speed jets, which move the pair of FTEs in opposite directions. As the FTE moves, it displaces the ambient magnetic field and plasma producing bipolar magnetic field and plasma velocity signatures normal to the nominal magnetopause in the regions surrounding the FTE. The combination of the ambient plasma with the FTE flows generates a vortical velocity pattern around the reconnected field lines. During its evolution the FTE evolves to a flux rope configuration due to the twist of the magnetic field lines. The alfvenic perturbations propagate faster along the part of the FTE bulging into the magnetosphere than in the magnetosheath, and due to the differences between the plasma and magnetic field properties the perturbations have slightly different signatures in the two regions. As a consequence, the FTEs have different signatures depending on whether the satellite encounters the part bulging into the magnetosphere or into the magnetosheath.

Santos, J. C.; Sibeck, D. G.; Büchner, J.; Gonzalez, W. D.; Ferreira, J. L.

2014-03-01

57

Flux Generation and Sustainment of a Field Reversed Configuration (FRC) with Rotating Magnetic Field (RMF) Current Drive  

NASA Astrophysics Data System (ADS)

The FRC is a unique closed field line configuration where the only confining field is the poloidal field generated by purely diamagnetic currents. With no transformer, the FRC could previously be observed only during decay. The confinement observed however showed encouraging transport and stability.(J.T. Slough et al. Phys. Plasmas 2, 2286 (1995).) Blevin and Thonemann(H.A. Blevin and P.C. Thonemann, Nucl. Fusion Suppl., Part I, 55 (1962).) first demonstrated current drive in a solenoidal magnetic field using a RMF. However in these and experiments at Flinders, the RMF was on the order or larger than the poloidal field generated, and the plasma was wall supported. For RMF current drive to be fusion relevant, the poloidal field generated >> the RMF, and the FRC separatrix must be in vacuum. Both of these requirements have been addressed and met in experiments in the recently constructed STX experiment. To generate the much larger diamagnetic currents, a much larger antenna was constructed (Ra = 0.35 m, and La = 2 m). To produce a 20 G RMF field at 350 kHz (> ion but >> electron gyrofrequency), a circulating power 50 MW was needed. This was accomplished by incorporating the antenna in high Q, LC tank circuit, powered through a step-up transformer, and driven by a solid-state switched power supply, which could deliver >2 MW of ohmic power to the plasma. At 20 G, the RMF generated a magnetic reversal of 400 G. The RMF was not observed to penetrate more than a few cm inside the FRC at any time. The increasing flux generated by the RMF changes the FRC equilibrium and these dynamical effects appear to cause the RMF to be pushed further out radially with reduced current drive efficiency. These edge currents sustained the FRC energy, but the closed flux was still observed to decay, although at a much-reduced rate. Careful control of the external field, as well as the proper match of driven current to the equilibrium FRC will be needed for long-term sustainment. The confinement and behavior of the FRC at these energy densities was determined in a non-destructive way by internal magnetic and Langmuir probes. The results from these and other diagnostics will be presented.

Slough, John

1999-11-01

58

Rotating magnetic field current drive of high-temperature field reversed configurations with high scaling  

E-print Network

, but the anomalous absorption is useful for initial plasma heating. Measurements of total absorbed power and anomalous heating to be inferred, and cross-field plasma resistivities to be calculated. © 2007 American torque falls to zero similar to an induction motor , and the plasma temperature is limited

Washington at Seattle, University of

59

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

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

60

Numerical modelling of the lobes of radio galaxies in cluster environments - II. Magnetic field configuration and observability  

NASA Astrophysics Data System (ADS)

We describe three-dimensional magnetohydrodynamical modelling of powerful radio galaxies in realistic poor cluster environments. This modelling extends our earlier work on the hydrodynamics of radio galaxies as a function of their cluster environment to consider the magnetic field configuration in the lobes and its observational consequences, using a realistic model for the magnetic field in the intracluster medium, very high density contrast in the lobes and high numerical resolution. We confirm, now with a realistic magnetic field model, that lobes have characteristic trajectories in the radio power/linear size diagram which depend strongly on their environment. We investigate the detailed evolution of polarized emission, showing that the lobes evolve from the initially ordered field configuration imposed by our boundary conditions to one in which the longitudinal field comes to dominate. We obtain simulated observations of polarization whose properties are quantitatively consistent with observations. The highly spatially intermittent magnetic field also reproduces the observation that inverse-Compton emission from lobes is much smoother than synchrotron. Our simulations allow us to study the depolarizing effect of the external medium on the lobes, and so to demonstrate that Faraday depolarization from environments of the type we consider can reproduce the integrated fractional polarization properties of large samples and the observed preferential depolarization of the receding lobe.

Hardcastle, M. J.; Krause, M. G. H.

2014-09-01

61

On the Magnetic Field of Pulsars with Realistic Neutron Star Configurations  

NASA Astrophysics Data System (ADS)

We have recently developed a neutron star model fulfilling global and not local charge neutrality, both in the static and in the uniformly rotating cases. The model is described by the coupled Einstein-Maxwell-Thomas-Fermi equations, in which all fundamental interactions are accounted for in the framework of general relativity and relativistic mean field theory. Uniform rotation is introduced following Hartle's formalism. We show that the use of realistic parameters of rotating neutron stars, obtained from numerical integration of the self-consistent axisymmetric general relativistic equations of equilibrium, leads to values of the magnetic field and radiation efficiency of pulsars that are very different from estimates based on fiducial parameters that assume a neutron star mass M = 1.4 M ?, radius R = 10 km, and moment of inertia I = 1045 g cm2. In addition, we compare and contrast the magnetic field inferred from the traditional Newtonian rotating magnetic dipole model with respect to the one obtained from its general relativistic analog, which takes into account the effect of the finite size of the source. We apply these considerations to the specific high-magnetic field pulsar class and show that, indeed, all of these sources can be described as canonical pulsars driven by the rotational energy of the neutron star, and have magnetic fields lower than the quantum critical field for any value of the neutron star mass.

Belvedere, R.; Rueda, Jorge A.; Ruffini, R.

2015-01-01

62

Analytical and numerical study of the flapping instability in tail-like magnetic configurations with guide field  

NASA Astrophysics Data System (ADS)

The flapping (kink) mode developing in the magnetotail-like magnetic configuration with tailward growing normal magnetic component and finite guide field is studied both analytically and by means of linearized 2-dimensional and non-linear 3-dimensional MHD modeling. We consider a particular case of a weak normal magnetic component (that is, small radius of the magnetic field line curvature), which makes the configuration unstable to a so-called “double-gradient” mode, introduced recently to describe the magnetotail flapping oscillations. The initial tail-like equilibrium is provided by approximated solution of the conventional Grad-Shafranov equation. The results of the 2D linearized MHD code are in agreement with the analytical predictions, and the growth rate is found to be close to the peak value provided by an analytical estimate. Both 2D and 3D calculations confirm that the double-gradient mode is excited in a region of large curvature of the magnetic field lines. In agreement with the analytical predictions, non-zero guide field reduces the growth rate significantly for large (compare to the current sheet width L) wave numbers k, hence the modes kL of the order of 1 are the fastest growing. Contrary to the analytical estimates, the dispersion curve of the instability obtained in 3D simulations demonstrates peak in the mentioned wave lengths band even for zero guide field. In turn, the non-zero guide field shifts a characteristic wavelength corresponding to the dispersion curve peak towards the longer wave lengths, decreasing the increment value. For the guide field of the order of 0.5 (in the lobe magnetic field units), the mode decays totally.

Korovinskiy, Daniil; Artemyev, Anton; Divin, Andrey; Ivanov, Ivan; Semenov, Vladimir; Erkaev, Nikolay; Ivanova, Viktoria; Kubyshkina, Daria

63

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

DOEpatents

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

Eberhard, Philippe H. (El Cerrito, CA)

1985-01-01

64

The magnetic field configuration of a solar prominence inferred from spectropolarimetric observations in the He i 10 830 Å triplet  

NASA Astrophysics Data System (ADS)

Context. Determining the magnetic field vector in quiescent solar prominences is possible by interpreting the Hanle and Zeeman effects in spectral lines. However, observational measurements are scarce and lack high spatial resolution. Aims: We determine the magnetic field vector configuration along a quiescent solar prominence by interpreting spectropolarimetric measurements in the He i 1083.0 nm triplet obtained with the Tenerife Infrared Polarimeter installed at the German Vacuum Tower Telescope of the Observatorio del Teide. Methods: The He i 1083.0 nm triplet Stokes profiles were analyzed with an inversion code that takes the physics responsible for the polarization signals in this triplet into account. The results are put into a solar context with the help of extreme ultraviolet observations taken with the Solar Dynamic Observatory and the Solar Terrestrial Relations Observatory satellites. Results: For the most probable magnetic field vector configuration, the analysis depicts a mean field strength of 7 gauss. We do not find local variations in the field strength except that the field is, on average, lower in the prominence body than in the prominence feet, where the field strength reaches ~25 gauss. The averaged magnetic field inclination with respect to the local vertical is ~77°. The acute angle of the magnetic field vector with the prominence main axis is 24° for the sinistral chirality case and 58° for the dextral chirality. These inferences are in rough agreement with previous results obtained from the analysis of data acquired with lower spatial resolutions. A movie is available in electronic form at http://www.aanda.org

Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J.

2014-06-01

65

Impact of rotation on the geometrical configurations of fossil magnetic fields  

NASA Astrophysics Data System (ADS)

The MiMeS project demonstrated that a small fraction of massive stars (around 7%) presents large-scale, stable, generally dipolar magnetic fields at their surface. These fields that do not present any evident correlations with stellar mass or rotation are supposed to be fossil remnants of the initial phases of stellar evolution. They result from the relaxation to MHD equilibrium states, during the formation of stable radiation zones, of initial fields resulting from a previous convective phase. In this work, we present new theoretical results, where we generalize previous studies by taking rotation into account. The properties of relaxed fossil fields are compared to those obtained when rotation is ignored. Consequences for magnetic fields in the radiative envelope of rotating early-type stars and their stability are finally discussed.

Emeriau, C.; Mathis, S.

2015-01-01

66

Anomalous D'yakonov-Perel' spin relaxation in semiconductor quantum wells under a strong magnetic field in the Voigt configuration  

NASA Astrophysics Data System (ADS)

We report an anomalous scaling of the D’yakonov-Perel’ spin relaxation with the momentum relaxation in semiconductor quantum wells under a strong magnetic field in the Voigt configuration. We focus on the case in which the external magnetic field is perpendicular to the spin-orbit-coupling-induced effective magnetic field and its magnitude is much larger than the latter one. It is found that the longitudinal spin relaxation time is proportional to the momentum relaxation time even in the strong-scattering limit, indicating that the D’yakonov-Perel’ spin relaxation demonstrates Elliott-Yafet-like behavior. Moreover, the transverse spin relaxation time is proportional (inversely proportional) to the momentum relaxation time in the strong- (weak-) scattering limit, both in the opposite trends against the well-established conventional D’yakonov-Perel’ spin relaxation behaviors. We further demonstrate that all the above anomalous scaling relations come from the unique form of the effective inhomogeneous broadening.

Zhou, Y.; Yu, T.; Wu, M. W.

2013-06-01

67

Global analysis of effects of magnetic field configuration on melt–crystal interface shape and melt flow in CZ-Si crystal growth  

Microsoft Academic Search

In order to clarify the effects of configuration of magnetic field on the melt–crystal interface shape and the melt convection in a crucible, a set of numerical computations was conducted for a Czochralski furnace for silicon crystals of small diameter by global modeling. Under different combinations of crucible\\/crystal rotation rates, numerical comparisons were carried out for four configurations of magnetic

Lijun Liu; Tomonori Kitashima; Koichi Kakimoto

2005-01-01

68

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

PubMed

The relative locations and characteristics of the distribution lines feeding 434 residences in the Denver metropolitan area were recorded and classified according to the Wertheimer-Leeper code (WL code) as a part of an epidemiological study of the incidence of childhood cancer. The WL code was found to place the mean values of the fields in rank order. However, the standard deviations were approximately the same size as the means. Theoretical calculations indicate that a significant fraction of the low-power magnetic fields can be generated by the distribution lines, especially in the cases where the distribution lines are within 50 feet of the residence. Thus, the wiring code was shown to be a useful method for making a first-order approximation to predict long-term, low-level magnetic fields in residences. PMID:2712837

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

1989-01-01

69

Comparison between hybrid and fully kinetic models of asymmetric magnetic reconnection: Coplanar and guide field configurations  

SciTech Connect

Magnetic reconnection occurring in collisionless environments is a multi-scale process involving both ion and electron kinetic processes. Because of their small mass, the electron scales are difficult to resolve in numerical and satellite data, it is therefore critical to know whether the overall evolution of the reconnection process is influenced by the kinetic nature of the electrons, or is unchanged when assuming a simpler, fluid, electron model. This paper investigates this issue in the general context of an asymmetric current sheet, where both the magnetic field amplitude and the density vary through the discontinuity. A comparison is made between fully kinetic and hybrid kinetic simulations of magnetic reconnection in coplanar and guide field systems. The models share the initial condition but differ in their electron modeling. It is found that the overall evolution of the system, including the reconnection rate, is very similar between both models. The best agreement is found in the guide field system, which confines particle better than the coplanar one, where the locality of the moments is violated by the electron bounce motion. It is also shown that, contrary to the common understanding, reconnection is much faster in the guide field system than in the coplanar one. Both models show this tendency, indicating that the phenomenon is driven by ion kinetic effects and not electron ones.

Aunai, Nicolas; Hesse, Michael; Kuznetsova, Maria; Black, Carrie; Evans, Rebekah [Space Weather Laboratory, Code 674, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States); Zenitani, Seiji [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Smets, Roch [Laboratoire de Physique des Plasmas, Universite Pierre et Marie Curie, Ecole polytechnique, route de Palaiseau, 91128 Palaiseau Cedex (France)

2013-02-15

70

11-13 GHz electron cyclotron resonance plasma source using cylindrically comb-shaped magnetic-field configuration for broad ion-beam processing  

Microsoft Academic Search

An electron cyclotron resonance (ECR) plasma source for broad ion-beam processing has been upgraded by a cylindrically comb-shaped magnetic-field configuration and 11-13 GHz frequency microwaves. A pair of comb-shaped magnets surrounds a large-bore discharge chamber. The magnetic field well confines plasmas with suppressing diffusion toward the axial direction of the cylindrical chamber. The magnetic field is constructed with a multipole

Toyohisa Asaji; Yushi Kato; Fuminobu Sato; Toshiyuki Iida; Junji Saito

2006-01-01

71

Field-dependent spin chirality and frustration in V3 and Cu3 nanomagnets in transverse magnetic field. 1. Correlations between variable planar spin configurations, vector and scalar chiralities and magnetization  

NASA Astrophysics Data System (ADS)

Correlations between field-dependent planar spin configurations, degenerate frustration, energy, vector ?z and scalar ? chiralities, spin canting, total, in-plane staggered and intermediate spin (IS) magnetizations are considered for the V3, Cu nanomagnets in transverse B?Z magnetic field. The planar spin configurations in Bx?X are characterized by the variable axial ?z(Bx) vector chirality correlated with the total in-plane magnetization Mx(Bx) and the IS magnetization M?12±(Bx), which describes the IS S12 behavior, ?(B?)=0. The in-plane staggered magnetization determines the magnitude of the vector chirality ?z. The low-field frustrated planar 120° configurations are transformed by increasing Bx field into the high-field achiral planar spin-collinear configurations. This transition is accompanied by the reduction of the vector chirality ?z and simultaneous increase of the total Mx(Bx) and IS M?12±(Bx) magnetizations. The spin configurations, chiralities and magnetization are highly anisotropic. In longitudinal B?Z field, the frustrated longitudinal spin-collinear configurations are characterized by the correlated maximal vector and scalar chiralities, ?=2?zMz.

Belinsky, Moisey I.

2014-05-01

72

Stable anisotropic plasma confinement in magnetic configurations with convex-concave field lines  

NASA Astrophysics Data System (ADS)

It is shown that a combination of the convex and the concave part of a field line provides a strong stabilizing action against convective (flute-interchange) plasma instability (Tsventoukh 2011 Nucl. Fusion 51 112002). This results in internal peaking of the stable plasma pressure profile that is calculated from the collisionless kinetic stability criterion for any magnetic confinement system with combination of mirrors and cusps. Connection of the convex and concave field line parts results in a reduction of the space charge that drives the unstable E × B motion, as there is an opposite direction of the particle drift in a non-uniform field at convex and concave field lines. The pressure peaking arises at the minimum of the second adiabatic invariant J that takes place at the ‘middle’ of a tandem mirror-cusp transverse cross-section. The position of the minimum in J varies with the particle pitch angle that results in a shift of the peaking position depending on plasma anisotropy. This allows one to improve a stable peaked pressure profile at a convex-concave field by changing the plasma anisotropy over the trap cross-section. Examples of such anisotropic distribution functions are found that give an additional substantial enhancement in the maximal central pressure. Furthermore, the shape of new calculated stable profiles has a wide central plasma layer instead of a narrow peak.

Tsventoukh, M. M.

2014-02-01

73

Passive magnetic bearing configurations  

DOEpatents

A journal bearing provides vertical and radial stability to a rotor of a passive magnetic bearing system when the rotor is not rotating and when it is rotating. In the passive magnetic bearing system, the rotor has a vertical axis of rotation. Without the journal bearing, the rotor is vertically and radially unstable when stationary, and is vertically stable and radially unstable when rotating.

Post, Richard F. (Walnut Creek, CA)

2011-01-25

74

Electron Acceleration in the Field-reversed Configuration (FRC) by Slowly Rotation Odd-parity Magnetic Fields (RMF[subscript o])  

SciTech Connect

The trajectories of individual electrons are studied numerically in a 3D, prolate, FRC [field-reversed configuration] equilibrium magnetic geometry with added small-amplitude, slowly rotating, odd-parity magnetic fields (RMFos). RMFos cause electron heating by toroidal acceleration near the O-point line and by field-parallel acceleration away from it, both followed by scattering from magnetic-field inhomogeneities. Electrons accelerated along the O-point line move antiparallel to the FRC's current and attain average toroidal angular speeds near that of the RMFo, independent of the sense of RMFo rotation. A conserved transformed Hamiltonian, dependent on electron energy and RMFo sense, controls electron flux-surface coordinate.

Glasser, A.H.; Cohen, S.A.

2001-04-05

75

Switching ferroelectric domain configurations using both electric and magnetic fields in Pb(Zr,Ti)O3–Pb(Fe,Ta)O3 single-crystal lamellae  

PubMed Central

Thin single-crystal lamellae cut from Pb(Zr,Ti)O3–Pb(Fe,Ta)O3 ceramic samples have been integrated into simple coplanar capacitor devices. The influence of applied electric and magnetic fields on ferroelectric domain configurations has been mapped, using piezoresponse force microscopy. The extent to which magnetic fields alter the ferroelectric domains was found to be strongly history dependent: after switching had been induced by applying electric fields, the susceptibility of the domains to change under a magnetic field (the effective magnetoelectric coupling parameter) was large. Such large, magnetic field-induced changes resulted in a remanent domain state very similar to the remanent state induced by an electric field. Subsequent magnetic field reversal induced more modest ferroelectric switching. PMID:24421376

Evans, D. M.; Schilling, A.; Kumar, Ashok; Sanchez, D.; Ortega, N.; Katiyar, R. S.; Scott, J. F.; Gregg, J. M.

2014-01-01

76

Switching ferroelectric domain configurations using both electric and magnetic fields in Pb(Zr,Ti)O3-Pb(Fe,Ta)O3 single-crystal lamellae.  

PubMed

Thin single-crystal lamellae cut from Pb(Zr,Ti)O3-Pb(Fe,Ta)O3 ceramic samples have been integrated into simple coplanar capacitor devices. The influence of applied electric and magnetic fields on ferroelectric domain configurations has been mapped, using piezoresponse force microscopy. The extent to which magnetic fields alter the ferroelectric domains was found to be strongly history dependent: after switching had been induced by applying electric fields, the susceptibility of the domains to change under a magnetic field (the effective magnetoelectric coupling parameter) was large. Such large, magnetic field-induced changes resulted in a remanent domain state very similar to the remanent state induced by an electric field. Subsequent magnetic field reversal induced more modest ferroelectric switching. PMID:24421376

Evans, D M; Schilling, A; Kumar, Ashok; Sanchez, D; Ortega, N; Katiyar, R S; Scott, J F; Gregg, J M

2014-02-28

77

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

Microsoft Academic Search

The relative locations and characteristics of the distribution lines feeding 434 residences in the Denver metropolitan area were recorded and classified according to the Wertheimer-Leeper code (WL code) as a part of an epidemiological study of the incidence of childhood cancer. The WL code was found to place the mean values of the fields in rank order. However, the standard

Frank Barnes; Howard Wachtel; David Savitz; Jackson Fuller

1989-01-01

78

Final Report on Development of Optimized Field-Reversed Configuration Plasma Formation Techniques for Magnetized Target Fusion  

SciTech Connect

The University of New Mexico (UNM) proposed a collaboration with Los Alamos National Laboratory (LANL) to develop and test methods for improved formation of field-reversed configuration (FRC) plasmas relevant to magnetized target fusion (MTF) energy research. MTF is an innovative approach for a relatively fast and cheap path to the production of fusion energy that utilizes magnetic confinement to assist in the compression of a hot plasma to thermonuclear conditions by an external driver. LANL is currently pursing demonstration of the MTF concept via compression of an FRC plasma by a metal liner z-pinch in conjunction with the Air Force Research Laboratory in Albuquerque, NM. A key physics issue for the FRC's ultimate success as an MTF target lies in the initial pre-ionization (PI) stage. The PI plasma sets the initial conditions from which the FRC is created. In particular, the PI formation process determines the amount of magnetic flux that can be trapped to form the FRC. A ringing theta pinch ionization (RTPI) technique, such as currently used by the FRX-L device at LANL, has the advantages of high ionization fraction, simplicity (since no additional coils are required), and does not require internal electrodes which can introduce impurities into the plasma. However RTPI has been shown to only trap #24;50% of the initial bias flux at best and imposes additional engineering constraints on the capacitor banks. The amount of trapped flux plays an important role in the FRC's final equilibrium, transport, and stability properties, and provides increased ohmic heating of the FRC through induced currents as the magnetic field decays. Increasing the trapped flux also provides the route to greatest potential gains in FRC lifetime, which is essential to provide enough time to translate and compress the FRC effectively. In conjunction with LANL we initially planned to develop and test a microwave break- down system to improve the initial PI plasma formation. The UNM team would design the microwave optics and oversee the fabrication and assembly of all components and assist with integration into the FRX-L machine control system. LANL would provide a preexisting 65 kW X-band microwave source and some associated waveguide hardware. Once constructed and installed, UNM would take the lead in operating the microwave breakdown system and conducting studies to optimize its use in FRC PI formation in close cooperation with the needs of the LANL MTF team. In conjunction with our LANL collaborators, we decided after starting the project to switch from a microwave plasma breakdown approach to a plasma gun technology to use for enhanced plasma formation in the FRX-L field-reversed configuration experiment at LANL. Plasma guns would be able to provide significantly higher density plasma with greater control over its distribution in time and space within the experiment. This would allow greater control and #12;ne-tuning of the PI plasma formed in the experiment. Multiple plasma guns would be employed to fill a Pyrex glass test chamber (built at UNM) with plasma which would then be characterized and optimized for the MTF effort.

Lynn, Alan

2013-11-01

79

11-13 GHz electron cyclotron resonance plasma source using cylindrically comb-shaped magnetic-field configuration for broad ion-beam processing  

NASA Astrophysics Data System (ADS)

An electron cyclotron resonance (ECR) plasma source for broad ion-beam processing has been upgraded by a cylindrically comb-shaped magnetic-field configuration and 11-13GHz frequency microwaves. A pair of comb-shaped magnets surrounds a large-bore discharge chamber. The magnetic field well confines plasmas with suppressing diffusion toward the axial direction of the cylindrical chamber. The magnetic field is constructed with a multipole and two quasiring permanent magnets. The plasma density clearly increases as compared with that in a simple multipole magnetic-field configuration. The frequency of microwaves output from the traveling-wave tube amplifier can be easily changed with an input signal source. The plasma density for 13GHz is higher than that for 11GHz. The maximum plasma density has reached approximately 1018m-3 at a microwave power of only 350W and a pressure of 1.0Pa. The enhancement of plasma generation by second-harmonic resonance and microwave modes has been investigated. The plasma density and the electron temperature are raised around the second-harmonic resonance zone. And then, the ion saturation current is periodically increased with varying the position of the plate tuner. The distance between the peaks is nearly equal to half of the free-space wavelength of microwave. The efficiency of ECR has been improved by using the comb-shaped magnetic field and raising microwave frequency, and then the high-density plasma source has been accomplished at low microwave power.

Asaji, Toyohisa; Kato, Yushi; Sato, Fuminobu; Iida, Toshiyuki; Saito, Junji

2006-11-01

80

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 thus the compass responds 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.

2014-09-18

81

Equilibrium rotation in field-reversed configurations  

Microsoft Academic Search

The turbulence that drives anomalous transport in field-reversed configurations (FRCs) is believed to break the otherwise closed magnetic surfaces inside the separatrix. This places electrons in the core of the plasma in electrical contact with those in the periphery. This effect was proposed and investigated in the context of spheromaks [D. D. Ryutov, Phys. Plasmas 14, 022506 (2007)]. The opening

Loren Steinhauer; Loren

2008-01-01

82

Magnetic Fields  

E-print Network

In this chapter, we give a brief introduction into the use of the Zeeman effect in astronomy and the general detection of magnetic fields in stars, concentrating on the use of FORS2 for longitudinal magnetic field measurements.

Schöller, Markus

2015-01-01

83

An improved discrete configuration of a cylinder magnet for portable nuclear magnetic resonance instruments  

NASA Astrophysics Data System (ADS)

The continuous magnetization profile approximated by a discrete source is the main reason for the deteriorating magnetic field homogeneity in Halbach magnet. It is identified by comparing the two-dimensional (2D) field solutions of an ideal cylinder magnet with those of a cylinder magnet constructed from several segment magnets. To improve the magnetic field homogeneity, a cylinder magnet from several crescent-shaped magnets is therefore presented. The programed 2D field solutions of the magnet from the crescent-shaped segments verify that the configuration effectively improves the homogeneity inside the cylinder magnet compared to that of a magnet built from simpler segments. For a small magnet with a required field uniformity and magnitude, the configuration has more advantages than a configuration from typical segments. Hence, the magnet is more appropriate for a portable nuclear magnetic resonance instruments.

Chen, Jizhong; Xu, Chunyan

2007-06-01

84

Magnetosphere-ionosphere connection in 3D-force balanced magnetic field configurations driven by empirical plasma sheet pressure under different geomagnetic conditions  

NASA Astrophysics Data System (ADS)

The magnetic field configuration is crucial to plasma sheet dynamics and M-I coupling. More accurate evaluation of its role requires a configuration in force balance with plasma pressure, which cannot be provided by current empirical models. In this study we established 3D force-balanced magnetic field and investigated the characteristics of field configuration and the magnetosphere-ionosphere connection for different Kp levels and solar wind dynamic pressure (PSW). We first constructed an empirical equatorial plasma pressure model using THEMIS and Geotail data, which was then used as the pressure constraint in the Zaharia [2008] magnetic field solver to obtain 3D magnetic field. The model results show that larger convection electric field during higher Kp drives plasma sheet further earthward, resulting in a substantial pressure increase near the Earth, while magnetosphere compression during higher PSW mainly enhances pressure in the tail plasma sheet. Comparing the magnetic field response to the pressure change due to increasing PSW, the Kp associated pressure increase causes the perpendicular current density (J?) peak and associated Region-2 field-aligned currents (FACs) to move deeper earthward, the magnetic field to decrease further in the near-Earth region, and field lines to stretch more significantly. The model magnetic field and its changes with Kp and PSW are found to agree fairly well with THEMIS and Geotail observations. Furthermore, we estimated the ion isotropic boundary (IB) caused by current sheet scattering for different particle energies. The IB equatorial locations match well with the earthward boundary of isotropic ions observed by THEMIS. We found that the IB is located around the transition region of dipolar to tail-like magnetic field and is close to the inner edge of Region-2 FAC. In the ionosphere, the latitudes of the IB are lower at midnight than at dawn/dusk. The IB latitudes decrease with increasing ion energy as well as with increasing Kp and PSW. These features are consistent with the IB latitudes observed by FAST satellite.

Yue, C.; Wang, C.; Zaharia, S. G.; Donovan, E.; Lyons, L. R.

2013-12-01

85

Spin configurations in circular and rectangular vertical quantum dots in a magnetic field: Three-dimensional self-consistent simulations  

NASA Astrophysics Data System (ADS)

The magnetic field dependence of the electronic properties of real single vertical quantum dots in circular and rectangular mesas is investigated within a full three-dimensional multiscale self-consistent approach without any á priori assumptions about the shape and strength of the confinement potential. The calculated zero field electron addition energies are in good agreement with available experimental data for both mesa geometries. Charging diagrams in a magnetic field for number of electrons up to five are also computed. Consistent with the experimental data, we found that the charging curves for the rectangular mesa dot in a magnetic field are flatter and exhibit less features than for a circular mesa dot. Evolution of the singlet-triplet energy separation in the two electron system for both dot geometries in magnetic field was also investigated. In the limit of large field, beyond the singlet-triplet transition, the singlet-triplet energy difference continues to become more negative in a circular mesa dot without any saturation within the range of considered magnetic fields while it is predicted to asymptotically approach zero for the rectangular mesa dot. This different behavior is attributed to the symmetry “breaking” that occurs in the singlet wave-functions in the rectangular mesa dot but not in the circular one.

Melnikov, Dmitriy V.; Matagne, Philippe; Leburton, Jean-Pierre; Austing, D. G.; Yu, G.; Tarucha, S.; Fettig, John; Sobh, Nahil

2005-08-01

86

Controlling precise magnetic field configuration around electron cyclotron resonance zone for enhancing plasma parameters and beam current.  

PubMed

Multi-charged ion source which has wide operating conditions is required in various application fields. We have constructed tandem type ECR ion source (ECRIS); one of the features of its main stage is an additional coil for controlling magnetic field distribution around the mirror bottom precisely. Here the effect of magnetic field variation caused by the additional coil is experimentally considered in terms of plasma parameters and beam current as the first investigation of the main stage plasma. Furthermore, behavior of magnetic lines of force flowing from the ECR zone is calculated, and is compared with measurement results aiming for better understanding of interrelationship between plasma production and ion beam generation on the ECRIS. PMID:24593516

Yano, Keisuke; Kurisu, Yosuke; Nozaki, Dai; Kimura, Daiju; Imai, Youta; Kumakura, Sho; Sato, Fuminobu; Kato, Yushi; Iida, Toshiyuki

2014-02-01

87

Controlling precise magnetic field configuration around electron cyclotron resonance zone for enhancing plasma parameters and beam current  

SciTech Connect

Multi-charged ion source which has wide operating conditions is required in various application fields. We have constructed tandem type ECR ion source (ECRIS); one of the features of its main stage is an additional coil for controlling magnetic field distribution around the mirror bottom precisely. Here the effect of magnetic field variation caused by the additional coil is experimentally considered in terms of plasma parameters and beam current as the first investigation of the main stage plasma. Furthermore, behavior of magnetic lines of force flowing from the ECR zone is calculated, and is compared with measurement results aiming for better understanding of interrelationship between plasma production and ion beam generation on the ECRIS.

Yano, Keisuke, E-mail: yano@i-beam.jp; Kurisu, Yosuke; Nozaki, Dai; Kimura, Daiju; Imai, Youta; Kumakura, Sho; Sato, Fuminobu; Kato, Yushi; Iida, Toshiyuki [Division of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita-shi, Osaka 565-0871 (Japan)] [Division of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita-shi, Osaka 565-0871 (Japan)

2014-02-15

88

Controlling precise magnetic field configuration around electron cyclotron resonance zone for enhancing plasma parameters and beam current  

NASA Astrophysics Data System (ADS)

Multi-charged ion source which has wide operating conditions is required in various application fields. We have constructed tandem type ECR ion source (ECRIS); one of the features of its main stage is an additional coil for controlling magnetic field distribution around the mirror bottom precisely. Here the effect of magnetic field variation caused by the additional coil is experimentally considered in terms of plasma parameters and beam current as the first investigation of the main stage plasma. Furthermore, behavior of magnetic lines of force flowing from the ECR zone is calculated, and is compared with measurement results aiming for better understanding of interrelationship between plasma production and ion beam generation on the ECRIS.

Yano, Keisuke; Kurisu, Yosuke; Nozaki, Dai; Kimura, Daiju; Imai, Youta; Kumakura, Sho; Sato, Fuminobu; Kato, Yushi; Iida, Toshiyuki

2014-02-01

89

11-13 GHz electron cyclotron resonance plasma source using cylindrically comb-shaped magnetic-field configuration for broad ion-beam processing  

SciTech Connect

An electron cyclotron resonance (ECR) plasma source for broad ion-beam processing has been upgraded by a cylindrically comb-shaped magnetic-field configuration and 11-13 GHz frequency microwaves. A pair of comb-shaped magnets surrounds a large-bore discharge chamber. The magnetic field well confines plasmas with suppressing diffusion toward the axial direction of the cylindrical chamber. The magnetic field is constructed with a multipole and two quasiring permanent magnets. The plasma density clearly increases as compared with that in a simple multipole magnetic-field configuration. The frequency of microwaves output from the traveling-wave tube amplifier can be easily changed with an input signal source. The plasma density for 13 GHz is higher than that for 11 GHz. The maximum plasma density has reached approximately 10{sup 18} m{sup -3} at a microwave power of only 350 W and a pressure of 1.0 Pa. The enhancement of plasma generation by second-harmonic resonance and microwave modes has been investigated. The plasma density and the electron temperature are raised around the second-harmonic resonance zone. And then, the ion saturation current is periodically increased with varying the position of the plate tuner. The distance between the peaks is nearly equal to half of the free-space wavelength of microwave. The efficiency of ECR has been improved by using the comb-shaped magnetic field and raising microwave frequency, and then the high-density plasma source has been accomplished at low microwave power.

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

2006-11-15

90

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

E-print Network

of external field shaping, magnetic diffusion, and finite-Larmor radius effects. © 2008 American Institute diffusion, shaping, and finite-Larmor radius stabilization S. P. Gerhardt,1 E. V. Belova,1 M. Yamada,1 H. Ji to the time required for an Alfven wave to traverse the system. However, most FRCs have been ex- perimentally

Ji, Hantao

91

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

92

The Magnetic Field  

NSDL National Science Digital Library

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

Windows to the Universe

1997-12-03

93

Radiation belt data assimilation of a moderate storm event using a magnetic field configuration from the physics-based RAM-SCB model  

NASA Astrophysics Data System (ADS)

Data assimilation using Kalman filters provides an effective way of understanding both spatial and temporal variations in the outer electron radiation belt. Data assimilation is the combination of in situ observations and physical models, using appropriate error statistics to approximate the uncertainties in both the data and the model. The global magnetic field configuration is one essential element in determining the adiabatic invariants for the phase space density (PSD) data used for the radiation belt data assimilation. The lack of a suitable global magnetic field model with high accuracy is still a long-lasting problem. This paper employs a physics-based magnetic field configuration for the first time in a radiation belt data assimilation study for a moderate storm event on 19 December 2002. The magnetic field used in our study is the magnetically self-consistent inner magnetosphere model RAM-SCB, developed at Los Alamos National Laboratory (LANL). Furthermore, we apply a cubic spline interpolation method in converting the differential flux measurements within the energy spectrum, to obtain a more accurate PSD input for the data assimilation than the commonly used linear interpolation approach. Finally, the assimilation is done using an ensemble Kalman filter (EnKF), with a localized adaptive inflation (LAI) technique to appropriately account for model errors in the assimilation and improve the performance of the Kalman filter. The assimilative results are compared with results from another assimilation experiment using the Tsyganenko 2001S (T01S) magnetic field model, to examine the dependence on a magnetic field model. Results indicate that the data assimilations using different magnetic field models capture similar features in the radiation belt dynamics, including the temporal evolution of the electron PSD during a storm and the location of the PSD peak. The assimilated solution predicts the energy differential flux to a relatively good degree when compared with independent LANL-GEO in situ observations. A closer examination suggests that for the chosen storm event, the assimilation using the RAM-SCB predicts a better flux at most energy levels during storm recovery phase but is slightly worse in the storm main phase than the assimilation using the T01S model.

Yu, Y.; Koller, J.; Jordanova, V. K.; Zaharia, S. G.; Godinez, H. C.

2014-05-01

94

Fast electron bremsstrahlung in axisymmetric magnetic configuration  

NASA Astrophysics Data System (ADS)

The nonthermal bremsstrahlung is calculated in a plasma with arbitrary axisymmetric magnetic configuration, taking into account the relativistic angular anisotropy of the radiation cross section at high photon energies, the helical winding of the field lines on the magnetic flux surfaces, and the poloidal variation of the electron distribution function including particle trapping effects. The fast electron dynamics during current drive in tokamaks and reverse field pinches can be investigated in detail by coupling this calculation to a bounce-averaged relativistic Fokker-Planck solver, which calculates the electron distribution function. The asymmetry between high- and low-field side hard x-ray emission intensity that has been measured on the Tore-Supra tokamak [Equipe TORE SUPRA, in Proceedings of the 15th Conference on Plasma Physics and Controlled Nuclear Fusion Research, Seville (International Atomic Energy Agency, Vienna, 1995) Vol. 1, IAEA-CN-60/A1-5 (Institute of Physics, Bristol, U.K., 1995), p. 105] is explained for the first time by the role of trapped electrons. A much stronger poloidal asymmetry is predicted for the line-integrated fast electron bremsstrahlung in the poloidal plane of the Madison Symmetric Torus [R. N. Dexter et al., Fusion Tech. 19, 131 (1991)], since the helical winding of the magnetic field lines is much larger for a reverse field pinch configuration. In this case, the hard x-ray emission is no longer a flux surface quantity, which prevents local reconstructions using a standard Abel inversion, whatever the geometrical arrangement of the lines of sight.

Peysson, Y.; Decker, J.

2008-09-01

95

Fast electron bremsstrahlung in axisymmetric magnetic configuration  

SciTech Connect

The nonthermal bremsstrahlung is calculated in a plasma with arbitrary axisymmetric magnetic configuration, taking into account the relativistic angular anisotropy of the radiation cross section at high photon energies, the helical winding of the field lines on the magnetic flux surfaces, and the poloidal variation of the electron distribution function including particle trapping effects. The fast electron dynamics during current drive in tokamaks and reverse field pinches can be investigated in detail by coupling this calculation to a bounce-averaged relativistic Fokker-Planck solver, which calculates the electron distribution function. The asymmetry between high- and low-field side hard x-ray emission intensity that has been measured on the Tore-Supra tokamak [Equipe TORE SUPRA, in Proceedings of the 15th Conference on Plasma Physics and Controlled Nuclear Fusion Research, Seville (International Atomic Energy Agency, Vienna, 1995) Vol. 1, IAEA-CN-60/A1-5 (Institute of Physics, Bristol, U.K., 1995), p. 105] is explained for the first time by the role of trapped electrons. A much stronger poloidal asymmetry is predicted for the line-integrated fast electron bremsstrahlung in the poloidal plane of the Madison Symmetric Torus [R. N. Dexter et al., Fusion Tech. 19, 131 (1991)], since the helical winding of the magnetic field lines is much larger for a reverse field pinch configuration. In this case, the hard x-ray emission is no longer a flux surface quantity, which prevents local reconstructions using a standard Abel inversion, whatever the geometrical arrangement of the lines of sight.

Peysson, Y.; Decker, J. [Association Euratom-CEA, CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France)

2008-09-15

96

An automated approach to magnetic divertor configuration design  

NASA Astrophysics Data System (ADS)

Automated methods based on optimization can greatly assist computational engineering design in many areas. In this paper an optimization approach to the magnetic design of a nuclear fusion reactor divertor is proposed and applied to a tokamak edge magnetic configuration in a first feasibility study. The approach is based on reduced models for magnetic field and plasma edge, which are integrated with a grid generator into one sensitivity code. The design objective chosen here for demonstrative purposes is to spread the divertor target heat load as much as possible over the entire target area. Constraints on the separatrix position are introduced to eliminate physically irrelevant magnetic field configurations during the optimization cycle. A gradient projection method is used to ensure stable cost function evaluations during optimization. The concept is applied to a configuration with typical Joint European Torus (JET) parameters and it automatically provides plausible configurations with reduced heat load.

Blommaert, M.; Dekeyser, W.; Baelmans, M.; Gauger, N. R.; Reiter, D.

2015-01-01

97

High Energy Electron Confinement in a Magnetic Cusp Configuration  

E-print Network

We report experimental results validating the concept that plasma confinement is enhanced in a magnetic cusp configuration when beta (plasma pressure/magnetic field pressure) is order of unity. This enhancement is required for a fusion power reactor based on cusp confinement to be feasible. The magnetic cusp configuration possesses a critical advantage: the plasma is stable to large scale perturbations. However, early work indicated that plasma loss rates in a reactor based on a cusp configuration were too large for net power production. Grad and others theorized that at high beta a sharp boundary would form between the plasma and the magnetic field, leading to substantially smaller loss rates. The current experiment validates this theoretical conjecture for the first time and represents critical progress toward the Polywell fusion concept which combines a high beta cusp configuration with an electrostatic fusion for a compact, economical, power-producing nuclear fusion reactor.

Park, Jaeyoung; Sieck, Paul E; Offermann, Dustin T; Skillicorn, Michael; Sanchez, Andrew; Davis, Kevin; Alderson, Eric; Lapenta, Giovanni

2014-01-01

98

Magnetic Field Safety Magnetic Field Safety  

E-print Network

Magnetic Field Safety Training #12;Magnetic Field Safety Strong Magnetic Fields exist around energized magnets. High magnetic fields alone are a recognized hazard only for personnel with certain medical conditions such as pacemakers, magnetic implants, or embedded shrapnel. In addition, high magnetic

McQuade, D. Tyler

99

Inductive Sustainment of a Field-Reversed Configuration Stabilized by Shaping, Magnetic Diffusion, and Finite-Larmor-Radius Effects  

E-print Network

injection. The thermoelectric effect may provide a path to configuration sustainment, if the electron drifts, introducing a stabilizing reactive effect. In this Letter, we report long-time inductive, and Finite-Larmor-Radius Effects S. P. Gerhardt, E. V. Belova, M. Yamada, H. Ji, M. Inomoto,* Y. Ren, and B

Ji, Hantao

100

Numerical Study of Global Stability of Field-Reversed Configuration  

Microsoft Academic Search

The Field-Reversed Configuration (FRC) is a compact toroid with negligible toroidal field, in which plasma is confined by a poloidal magnetic field associated with toroidal diamagnetic current carried by the plasma. The FRC offers an unusual fusion reactor potential because of it's compact geometry and high plasma beta. Although many MHD modes are predicted to be unstable, FRCs have been

Elena Belova

1999-01-01

101

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

102

Large-gap magnetic positioning system having advantageous configuration  

NASA Technical Reports Server (NTRS)

A magnetic configuration was devised in which the positioned object is maintained in a stable orientation and position on one side of an opaque plane surface entirely by means of magnetic components on the other side of the plane. The system is effective with or without gravity, and can operate in any orientation. In this system, the positioned object need only contain a simple dipole magnet. The positioning components consist of a group of permanent magnets creating a magnetic field configuration which stabilizes the levitated dipole in all but one degree of freedom, and a magnetic position sensing and force feedback system to actively stabilize the object in the one unstable direction. The system utilizes very low power at equilibrium and can maintain gaps of 50 mm.

Chong, Paul; Commandeur, Colin; Davis, Harold; Whitehead, Lorne

1992-01-01

103

CHAPTER 3. STRUCTURE OF MAGNETIC FIELDS 1 Structure of Magnetic  

E-print Network

CHAPTER 3. STRUCTURE OF MAGNETIC FIELDS 1 Chapter 3 Structure of Magnetic Fields Many of the most in Fig. 3.1, the generic structure of the magnetic field can be open (a­c and f) or closed (d,e). In open). The magnetic field structure in closed configurations (d,e) is toroidal in character or topology. That is, its

Callen, James D.

104

Equilibrium rotation in field-reversed configurations  

NASA Astrophysics Data System (ADS)

The turbulence that drives anomalous transport in field-reversed configurations (FRCs) is believed to break the otherwise closed magnetic surfaces inside the separatrix. This places electrons in the core of the plasma in electrical contact with those in the periphery. This effect was proposed and investigated in the context of spheromaks [D. D. Ryutov, Phys. Plasmas 14, 022506 (2007)]. The opening up of internal magnetic field lines serves to regulate the electrostatic potential in the interior of the plasma, and in turn drives ion rotation. In effect, "end-shorting," a well-known phenomenon in the FRC scrape-off layer, also extends into the plasma interior. For conditions relevant to experiments, the ion rotation can be expressed in terms of equilibrium properties (density and temperature gradients) and as such is the "equilibrium" rotation. This theory is incomplete in that it neglects evolving, transport-related effects that modify the equilibrium and, indirectly, the rotation rate. Consequently, the equilibrium rotation theory is only partially successful in predicting experimental results: although it predicts the average rotation well, the estimated degree of rotational shear seems unlikely, especially at late times in the plasma lifetime.

Steinhauer, Loren

2008-01-01

105

Flare morphologies and coronal field configurations  

NASA Technical Reports Server (NTRS)

Chromospheric flares are the footpoints of closed coronal field lines. In this paper different flare morphologies from observations are presented, and the implied coronal field configurations above the flaring region are examined. Flares are grouped according to the number of ribbons, from an unresolved compact point-like flare to four-ribbon flares. Quiet region flares having characteristics of their own are also presented here. It is found that compact, unresolved point-like flares have two distinct footpoints when viewed in offband H-alpha. The footpoints of some of the compact flares also show increased separation as a function of time. Unlike large two-ribbon flares, the ribbons of many small and/or short-lived two-ribbon flares usually have no measurable separation of ribbons. Multiple-ribbon (three or more ribbon) flares consists of two or more pairs of two-ribbons, or two or more sets of field lines. Parity of the ribbons in multiple-ribbon flares, or the lack of it, depends on the magnetic makeup of the locale of the ribbons. Flares in old quiet regions resulting from sudden filament eruptions show discrete small patches of emissions reflecting the 'spottiness' of the decayed and dispersed field of the quiet region.

Tang, F.

1985-01-01

106

The influence of elevated 50 Hz electric and magnetic fields on implanted cardiac pacemakers: the role of the lead configuration and programming of the sensitivity.  

PubMed

The influence of the electromagnetic interference (EMI) on performance of 15 implanted cardiac pacemakers (12 generator models) was tested during exposure at a high voltage substation. All patients had an adequate spontaneous heart rate during the study. Tests were performed in the ventricular inhibited mode with unipolar sensing in all pacemakers and repeated with bipolar sensing in four pacemakers. The sensitivity was set to a regular, functionally proper level and then to the highest available level. Exposure was done to moderate (1.2-1.7 kV/m) and strong (7.0-8.0 kV/m) electric fields, which correspond to the immediate vicinity of 110 and 400 kV power lines, respectively. In moderate electric fields the output was inhibited in one pacemaker at regular sensitivity (1.7-3.0 mV) and in five pacemakers at the highest sensitivity (0.5-1.25 mV). In strong electric fields the output was inhibited in five pacemakers at regular sensitivity and several pacemakers converted to noise reversion mode at the highest sensitivity. In bipolar mode only one of four pacemakers at high sensitivity (0.5-1.0 mV) was inhibited in the strongest electric field, whereas all four did so in the unipolar mode. One pacemaker with unipolar sensitivity at 0.5 mV was interfered by 63 microT magnetic field. The results confirm that the programmed sensitivity level and the lead configuration markedly influence pacemakers' vulnerability to EMI. Bipolar sensing mode is rather safe in the presence of EMI, which is encountered in public environments. The programmable features of today's pacemakers permit individualized, less stringent safety measures to avoid electromagnetic hazards. PMID:1723194

Toivonen, L; Valjus, J; Hongisto, M; Metso, R

1991-12-01

107

Magnetic fields at Neptune  

NASA Technical Reports Server (NTRS)

The Voyager 2 magnetic field experiment discovered a complex and powerful magnetic field in Neptune, as well as an associated magnetosphere and magnetic tail. As the spacecraft exited the magnetosphere, the magnetic tail appeared to be monopolar. The auroral zones are probably located far from the rotation poles, and may possess complex geometry. The Neptune rings and all its known moons are imbedded deep within the magnetosphere (except for Nereid, which is outside when it lies sunward of the planet); the radiation belts have a complex structure due to the absorption of energetic particles by the moons and rings of Neptune, as well as losses associated with the significant changes in the diurnally varying magnetosphere configuration.

Ness, Norman F.; Acuna, Mario H.; Burlaga, Leonard F.; Connerney, John E. P.; Lepping, Ronald P.

1989-01-01

108

Magnetic Cusp Configuration of the SPL Plasma Generator  

SciTech Connect

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

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

2011-09-26

109

Chaotic motion of charged particles in toroidal magnetic configurations  

E-print Network

We study the motion of a charged particle in a tokamak magnetic field and discuss its chaotic nature. Contrary to most of recent studies, we do not make any assumption on any constant of the motion and solve numerically the cyclotron gyration using Hamiltonian formalism. We take advantage of a symplectic integrator allowing us to make long-time simulations. First considering an idealized magnetic configuration, we add a non generic perturbation corresponding to a magnetic ripple, breaking one of the invariant of the motion. Chaotic motion is then observed and opens questions about the link between chaos of magnetic field lines and chaos of particle trajectories. Second, we return to a axi-symmetric configuration and tune the safety factor (magnetic configuration) in order to recover chaotic motion. In this last setting with two constants of the motion, the presence of chaos implies that no third global constant exists, we highlight this fact by looking at variations of the first order of the magnetic moment in this chaotic setting. We are facing a mixed phase space with both regular and chaotic regions and point out the difficulties in performing a global reduction such as gyrokinetics.

Benjamin Cambon; Xavier Leoncini; Michel Vittot; Rémi Dumont; Xavier Garbet

2014-12-04

110

Compact toroid experiments: spheromaks and field-reversed configurations  

SciTech Connect

Compact toroids (CT) containing both poloidal and toroidal magnetic field spheromaks, are generated in the CTX experiment using a magnetized coaxial plasma gun, and are trapped and stably confined in an oblate flux conserver. Total configuration lifetimes are observed up to approx. 0.8 ms, consistent with classical resistive decay. The field reversed configuration (FRC) is a high beta, axisymmetric, highly prolate compact toroid, containing only poloidal magnetic field, formed in a field-reversed theta pinch. A quiescent confinement period of 30 to 90 ..mu..s with T/sub i/ approx. 200 to 500 eV and n approx. 5 x 10/sup 15/ cm/sup -3/ is terminated by an n = 2 rotational instability. The FRC is stable to MHD modes including the tilting instability.

Quinn, W.E.

1982-01-01

111

Ferrofilm in a magnetic field  

NASA Astrophysics Data System (ADS)

A vertically draining thin ferrofilm under the influence of gravity and a nonuniform magnetic field is considered. It is observed experimentally that the presence of the magnetic field greatly alters the drainage of the film. A mathematical model is developed to describe the behavior. Experiments are conducted for multiple magnetic field configurations. The model is solved for two different sets of boundary conditions and results are compared to experiments. It is shown that the magnetic field structure, the concentration of magnetite in the solution, and the boundary conditions all have noticeable affects on the evolution of the thinning film. Good qualitative agreement between the model and the experiments is observed.

Back, Randy; Beckham, J. Regan

2012-10-01

112

Stability and confinement of spheromaks and field-reversed configurations  

SciTech Connect

The formation, confinement and stability of two types of compact toroids, spheromaks and field reversed configurations (FRC), are reviewed. Spheromaks, which contain both toroidal and poloidal magnetic fields, have been formed with magnetized coaxial plasma guns, by a combination of Z- and theta-pinch techniques and by an electrodeless slow induction technique, and trapped in both prolate and oblate flux conservers. As predicted by theory, the prolate configuration is unstable to the tilt mode, but the oblate configuration with a conducting wall is stable. Configuration lifetimes of up to 0.8 ms are observed. The FRC is a high-beta, highly prolate compact toroid formed with field-reversed theta-pinch techniques and having purely poloidal magnetic field. Theory predicts unstable fluting and internal tilting modes, but they are not observed experimentally. Configurations with high densities approx. 10/sup 15/ cm/sup -3/ and with lifetimes of 50 to 120 ..mu..s are terminated by an n=2 rotational mode of instability.

Quinn, W.E.

1982-01-01

113

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

114

Magnetic reconnection configurations and particle acceleration in solar flares  

E-print Network

Magnetic reconnection configurations and particle acceleration in solar flares P. F. Chen, W. J space under different magnetic configurations. Key words: solar flares, magnetic reconnection, particle, for a review). Magnetic reconnection, as the mechanism of solar flares, provides favorite environments for all

Chen, P. F.

115

Reconnection of stressed magnetic fields  

NASA Technical Reports Server (NTRS)

It is shown that magnetized plasma configurations under magnetic stress relax irreversibly to the state of minimum stress at a rate that is essentially Alfvenic provided a magnetic null is present. The relaxation is effected by the reconnection at the field null and proceeds at a rate proportional to the absolute value of ln(eta) exp-1, where eta is the resistivity. An analytic calculation in the linear regime is presented.

Hassam, A. B.

1992-01-01

116

Magnetic fields in anisotropic relativistic stars  

E-print Network

Relativistic, spherically symmetric configurations consisting of a gravitating magnetized anisotropic fluid are studied. For such configurations, we obtain static equilibrium solutions with an axisymmetric, poloidal magnetic field produced by toroidal electric currents. The presence of such a field results in small deviations of the shape of the configuration from spherical symmetry. This in turn leads to the modification of an equation for the current and correspondingly to changes in the structure of the internal magnetic field for the systems supported by the anisotropic fluid, in contrast to the case of an isotropic fluid, where such deviations do not affect the magnetic field.

Vladimir Folomeev; Vladimir Dzhunushaliev

2015-02-28

117

Magnetic fields in anisotropic relativistic stars  

E-print Network

Relativistic, spherically symmetric configurations consisting of a gravitating magnetized anisotropic fluid are studied. For such configurations, we obtain static equilibrium solutions with an axisymmetric, poloidal magnetic field produced by toroidal electric currents. The presence of such a field results in small deviations of the shape of the configuration from spherical symmetry. This in turn leads to the modification of an equation for the current and correspondingly to changes in the structure of the internal magnetic field for the systems supported by the anisotropic fluid, in contrast to the case of an isotropic fluid, where such deviations do not affect the magnetic field.

Folomeev, Vladimir

2015-01-01

118

Magnetic field sensor  

NASA Astrophysics Data System (ADS)

Earlier papers1-3 in this journal have described experiments on measuring the magnetic fields of current-carrying wires and permanent magnets using magnetic field probes of various kinds. This paper explains how to use an iPad and the free app MagnetMeter-3D Vector Magnetometer and Accelerometer4 (compass HD) to measure the magnetic fields.

Silva, Nicolas

2012-09-01

119

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."

2012-06-26

120

Structure and deformations of strongly magnetized neutron stars with twisted torus configurations  

E-print Network

We construct general relativistic models of stationary, strongly magnetized neutron stars. The magnetic field configuration, obtained by solving the relativistic Grad-Shafranov equation, is a generalization of the twisted torus model recently proposed in the literature; the stellar deformations induced by the magnetic field are computed by solving the perturbed Einstein's equations; stellar matter is modeled using realistic equations of state. We find that in these configurations the poloidal field dominates over the toroidal field and that, if the magnetic field is sufficiently strong during the first phases of the stellar life, it can produce large deformations.

R. Ciolfi; V. Ferrari; L. Gualtieri

2010-10-26

121

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.

2012-08-03

122

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.

123

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.

2014-09-18

124

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,

125

What are 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 Magnetic Math booklet; this booklet can be found on the Space Math@NASA website.

2012-08-03

126

Magnetic fields of galaxies  

Microsoft Academic Search

The current state of the understanding of the magnetic fields of galaxies is reviewed. A simple model of the turbulent dynamo is developed which explains the main observational features of the global magnetic fields of spiral galaxies. The generation of small-scale chaotic magnetic fields in the interstellar medium is also examined. Attention is also given to the role of magnetic

Aleksandr A. Ruzmaikin; Dmitrii D. Sokolov; Anvar M. Shukurov

1988-01-01

127

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.

2012-08-03

128

Plasma-wall interaction in Hall thrusters with magnetic lens configuration  

SciTech Connect

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

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

2012-06-15

129

Neutrino spin-flavor oscillations in electromagnetic fields of various configurations  

E-print Network

We study spin-flavor oscillations of Dirac neutrinos with mixing and having non-zero matrix of magnetic moments in magnetic fields of various configurations. We discuss constant transversal and twisting magnetic fields. To describe the dynamics of Dirac neutrinos we use relativistic quantum mechanics approach based on the exact solutions to the Dirac-Pauli equation in an external electromagnetic field. We derive transition probabilities for different neutrino magnetic moments matrices.

Maxim Dvornikov

2007-08-27

130

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.

131

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

SciTech Connect

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

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

1983-03-01

132

Kinetic Stability of the Field Reversed Configuration  

SciTech Connect

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

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

2002-07-09

133

Graphene Nanoribbon in Sharply Localized Magnetic Fields  

E-print Network

We study the effect of a sharply localized magnetic field on the electron transport in a strip (ribbon) of graphene sheet, which allows to give results for the transmission and reflection probability through magnetic barriers. The magnetic field is taken as a single and double delta type localized functions, which are treated later as the zero width limit of gaussian fields. For both field configurations, we evaluate analytically and numerically their transmission and reflection coefficients. The possibility of spacial confinement due to the inhomogeneous field configuration is also investigated.

Abdulaziz D. Alhaidari; Hocine Bahlouli; Abderrahim El Mouhafid; Ahmed Jellal

2013-03-20

134

Reducing Field Distortion in Magnetic Resonance Imaging  

NASA Technical Reports Server (NTRS)

A concept for a magnetic resonance imaging (MRI) system that would utilize a relatively weak magnetic field provides for several design features that differ significantly from the corresponding features of conventional MRI systems. Notable among these features are a magnetic-field configuration that reduces (relative to the conventional configuration) distortion and blurring of the image, the use of a superconducting quantum interference device (SQUID) magnetometer as the detector, and an imaging procedure suited for the unconventional field configuration and sensor. In a typical application of MRI, a radio-frequency pulse is used to excite precession of the magnetic moments of protons in an applied magnetic field, and the decaying precession is detected for a short time following the pulse. The precession occurs at a resonance frequency proportional to the strengths of the magnetic field and the proton magnetic moment. The magnetic field is configured to vary with position in a known way; hence, by virtue of the aforesaid proportionality, the resonance frequency varies with position in a known way. In other words, position is encoded as resonance frequency. MRI using magnetic fields weaker than those of conventional MRI offers several advantages, including cheaper and smaller equipment, greater compatibility with metallic objects, and higher image quality because of low susceptibility distortion and enhanced spin-lattice-relaxation- time contrast. SQUID MRI is being developed into a practical MRI method for applied magnetic flux densities of the order of only 100 T

Eom, Byeong Ho; Penanen, Konstantin; Hahn, Inseob

2010-01-01

135

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.

Jeffrey Barker

136

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.

2014-09-18

137

Electricity and Magnetic Fields  

NSDL National Science Digital Library

The grand challenge for this legacy cycle unit is for students to design a way to help a recycler separate aluminum from steel scrap metal. In previous lessons, they have looked at how magnetism might be utilized. In this lesson, students think about how they might use magnets and how they might confront the problem of turning the magnetic field off. Through the accompanying activity students explore the nature of an electrically induced magnetic field and its applicability to the needed magnet.

VU Bioengineering RET Program,

138

The configuration of the Brazilian scientific field.  

PubMed

This article describes the configuration of the scientific field in Brazil, characterizing the scientific communities in every major area of knowledge in terms of installed capacity, ability to train new researchers, and capacity for academic production. Empirical data from several sources of information are used to characterize the different communities. Articulating the theoretical contributions of Pierre Bourdieu, Ludwik Fleck, and Thomas Kuhn, the following types of capital are analyzed for each community: social capital (scientific prestige), symbolic capital (dominant paradigm), political capital (leadership in S & T policy), and economic capital (resources). Scientific prestige is analyzed by taking into account the volume of production, activity index, citations, and other indicators. To characterize symbolic capital, the dominant paradigms that distinguish the natural sciences, the humanities, applied sciences, and technology development are analyzed theoretically. Political capital is measured by presidency in one of the main agencies in the S & T national system, and research resources and fellowships define the economic capital. The article discusses the composition of these different types of capital and their correspondence to structural capacities in various communities with the aim of describing the configuration of the Brazilian scientific field. PMID:24676181

Barata, Rita B; Aragão, Erika; de Sousa, Luis E P Fernandes; Santana, Taris M; Barreto, Mauricio L

2014-03-01

139

Formation of Field-reversed-Configuration Plasma with Punctuated-betatron-orbit Electrons  

SciTech Connect

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

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

2010-06-28

140

Magnetic Fields on the Surface of the Sun  

NSDL National Science Digital Library

This is a lesson about magnetism in solar flares. Learners will map magnetic fields around bar magnets and investigate how this configuration relates to magnetic fields of sunspots. This activity requires compasses, bar magnets, and a equipment for the instructor to project a PowerPoint or pdf lecture presentation. This is Activity 1 in the Exploring Magnetism in Solar Flares teachers guide.

141

Magnetic fields at Neptune  

Microsoft Academic Search

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 = 10⁻⁵ gauss) was observed near closest approach, at a

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

1989-01-01

142

Test ion transport in a collisional, field-reversed configuration  

NASA Astrophysics Data System (ADS)

Diffusion of test-ions in a flux-coil generated, collisional, field-reversed configuration is measured via time-resolved tomographic reconstruction of Ar+ optical emission in the predominantly nitrogen plasma. Azimuthal test ion diffusion across magnetic field lines is found to be classical during the stable period of the discharge. Test ion radial confinement is enhanced by a radial electric field, reducing the observed outward radial transport rate below predictions based solely on classical cross-field diffusion rates. Test ion diffusion is ˜500 m2 s-1 during the stable period of the discharge. The electric field inferred from plasma potential measurements and from equilibrium calculations is consistent with the observed reduction in argon transport.

Roche, T.; McWilliams, R.; Heidbrink, W. W.; Bolte, N.; Garate, E. P.; Morehouse, M.; Slepchenkov, M.; Wessel, F.

2014-08-01

143

Magnetic Fields Analogous to electric field, a magnet  

E-print Network

Magnetic Fields Analogous to electric field, a magnet produces a magnetic field, B Set up a B field two ways: Moving electrically charged particles Current in a wire Intrinsic magnetic field Basic) Opposite magnetic poles attract like magnetic poles repel #12;Like the electric field lines

Bertulani, Carlos A. - Department of Physics and Astronomy, Texas A&M University

144

Magnetic Field Problem  

NSDL National Science Digital Library

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

Wolfgang Christian

145

Hybrid equilibria of field-reversed configurations  

SciTech Connect

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

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

2011-11-15

146

Magnetic configurations of planetary obstacles. [solar wind obstacles  

NASA Technical Reports Server (NTRS)

The interaction between planetary magnetospheres and solar wind flow is discussed. A proper planetary magnetosphere results from the interaction of a flowing plasma with a planet having an intrinsic, global, magnetic field of sufficient strength to stand off the impinging plasma. Upstream of such an obstacle a bow shock usually exists. The known magnetospheres have severely asymmetric shapes, being elongated approximately along the solar wind flow direction. Conditions which fundamentally determine the structure of a proper planetary magnetosphere are the state of the externally flowing plasma, the planet's magnetic moment, its vector spin, and the presence and nature of internal plasma sources and any plasma sinks. Planets known to have proper magnetospheres are Earth, Mercury, Jupiter, and Saturn. Uranus and Neptune may also have magnetospheres, with that of Uranus promising to have an exotic field configuration, because the planet's magnetic moment is expected to be nearly aligned with the solar wind flow direction. Venus and Mars are also discussed. Magnetopause surface waves are mentioned.

Lepping, R. P.

1986-01-01

147

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.

2012-08-03

148

Mapping Magnetic Fields  

NSDL National Science Digital Library

This is an activity about magnetism. Using bar magnets, classroom materials, and a compass, learners will explore how bar magnets interact with one another and with other materials, use a compass to find the direction north, and use various materials to make magnetic field lines visible around a bar magnet. This is an activity in a larger poster resource, entitled The Sun Like It's Never Been Seen Before: In 3D.

149

Magnetic bottle configuration to coat 1.3 GHz copper cavities with a Nb sputtered film  

Microsoft Academic Search

An experimental setup to study the deposition of Nb film on a TESLA type copper cavity is under commissioning. The discharge stabilizing magnetic field, in a magnetic bottle configuration, is obtained using coils external to the cavity rather than internal as used for larger cavities. A brief review of the sputtering techniques for SC RF cavities, the dynamics of charged

M. Ferrario; S. Kulinski; M. Minestrini; S. Tazzari

1994-01-01

150

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

E-print Network

of magnetic energy release (as emission of heated plasma and radiation from accelerated particles, with small Introduction The solar corona is formed by a low- plasma where the magnetic field has a key role. One configuration (typically an active region). The resistive term in the induction equation can become large enough

Demoulin, Pascal

151

Magnetic Field Distribution of Permanent Magnet Magnetized by Static Magnetic Field Generated by HTS Bulk Magnet  

Microsoft Academic Search

Demagnetized rare earth magnets (Nd-Fe-B) can be fully magnetized by scanning them in the intense static fields over 3 T of a HTS bulk magnet which was cooled to the temperature range lower than 77K with use of cryo-coolers and activated by the field of 5 T. We precisely examined the magnetic field distributions of magnetized permanent magnets. The magnetic

Tetsuo Oka; Nobutaka Kawasaki; Satoshi Fukui; Jun Ogawa; Takao Sato; Toshihisa Terasawa; Yoshitaka Itoh; Ryohei Yabuno

2012-01-01

152

Improved Spindle Cusp Magnetic Field for ECRIS  

SciTech Connect

Magnetic field of minimum-B configuration is very important for achieving more plasma confinement and closed electron cyclotron resonance (ECR) surface for electron heating and plasma discharge. The spindle cusp magnetic field configuration forms the modified minimum-B configuration. The absolute magnetic field at the chamber surface on mid-plane has been optimized and improved sufficiently and symmetrized to the field at the point cusp positions on the central axis. With enhancement of electrostatic and magnetic mirror action at the cusp positions the density of the plasma as well as confinement is boosted. The system becomes simpler, more compact and cost-effective compared to the conventional one to generate and extract highly charged heavy ions (HCHI). A co-operative and collaborative effort is essential to develop and test such conceived new ECRIS.

Rashid, M.H.; Mallik, C.; Bhandari, R.K. [Variable Energy Cyclotron Centre, Sector-1, Block-AF, Bidhan Nagar, Kolkata- 700 064 (India)

2005-03-15

153

Improved Spindle Cusp Magnetic Field for ECRIS  

NASA Astrophysics Data System (ADS)

Magnetic field of minimum-B configuration is very important for achieving more plasma confinement and closed electron cyclotron resonance (ECR) surface for electron heating and plasma discharge. The spindle cusp magnetic field configuration forms the modified minimum-B configuration. The absolute magnetic field at the chamber surface on mid-plane has been optimized and improved sufficiently and symmetrized to the field at the point cusp positions on the central axis. With enhancement of electrostatic and magnetic mirror action at the cusp positions the density of the plasma as well as confinement is boosted. The system becomes simpler, more compact and cost-effective compared to the conventional one to generate and extract highly charged heavy ions (HCHI). A co-operative and collaborative effort is essential to develop and test such conceived new ECRIS.

Rashid, M. H.; Mallik, C.; Bhandari, R. K.

2005-03-01

154

Interplanetary stream magnetism: Kinematic effects. [solar magnetic fields and wind  

NASA Technical Reports Server (NTRS)

The particle density, and the magnetic field intensity and direction are calculated in corotating streams of the solar wind, assuming that the solar wind velocity is constant and radial and that its azimuthal variations are not two rapid. The effects of the radial velocity profile in corotating streams on the magnetic fields were examined using kinematic approximation and a variety of field configurations on the inner boundary. Kinematic and dynamic effects are discussed.

Burlaga, L. F.; Barouch, E.

1974-01-01

155

Photodetachment in magnetic fields  

Microsoft Academic Search

The behavior of the photodetachment cross section, near threshold, for atomic negative ioris in a magnetic field is described and illustrated with data on photodetachment of electrons from negative sulfur ions. The effect of the final state interaction is discussed and the photodetachment of atomic negative ions in a magnetic field is compared to photoionization of neutral atoms in a

D. J. Larson; R. Stoneman

1982-01-01

156

THE INTERPLANETARY MAGNETIC FIELD  

Microsoft Academic Search

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

V. A. BAILEY

1963-01-01

157

Magnetic field line Hamiltonian  

SciTech Connect

The magnetic field line Hamiltonian and the associated canonical form for the magnetic field are important concepts both for understanding toroidal plasma physics and for practical calculations. A number of important properties of the canonical or Hamiltonian representation are derived and their importance is explained.

Boozer, A.H.

1984-03-01

158

Cosmic Magnetic Fields  

Microsoft Academic Search

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

Elisabete M. de Gouveia Dal Pino; Dal Pino

2006-01-01

159

Magnetic Fields in the Milky Way  

NASA Astrophysics Data System (ADS)

This chapter presents a review of observational studies to determine the magnetic field in the Milky Way, both in the disk and in the halo, focused on recent developments and on magnetic fields in the diffuse interstellar medium. I discuss some terminology which is confusingly or inconsistently used and try to summarize current status of our knowledge on magnetic field configurations and strengths in the Milky Way. Although many open questions still exist, more and more conclusions can be drawn on the large-scale and small-scale components of the Galactic magnetic field. The chapter is concluded with a brief outlook to observational projects in the near future.

Haverkorn, Marijke

160

Electron Trapping in a Magnetic Mirror Configuration  

Microsoft Academic Search

As part of an investigation to form an electron - positron plasma in the laboratory, a single species electron plasma was formed by trapping an externally injected electron beam in a magnetic mirror by electron cyclotron resonance heating. The maximum number of trapped electrons was found to be limited by the reflection of the incident beam due to the space

H. Boehmer; M. Adams; N. Rynn

1996-01-01

161

Novel magnets configuration toward a high performance electrodynamic micro-electro-mechanical-systems microspeaker  

NASA Astrophysics Data System (ADS)

This paper presents a study of different configurations of permanent magnets' to maximize microspeakers' electroacoustic performances. The proposed theoretical approach is based on an analytical model allowing the calculation of the magnetic field created by cylindrical and ring-shaped permanent magnet, making thus possible to analyze different magnetic structures. Several combinations of cylindrical and rings were analyzed in view of maximizing the magnetic field in the vicinity of the voice coil. Taking into account the whole electro-mechano-acoustic behavior of the microspeaker, we present two optimized magnets configurations which increase the efficiency by factors between 2.7 and 5 comparing to previously optimized microspeakers. Moreover, we show that it is possible to get devices twice smaller with efficiencies increased by factors between 1.2 and 3.4.

Sassine, G.; Shahosseini, I.; Woytasik, M.; Martincic, E.; Moulin, J.; Lefeuvre, E.

2014-05-01

162

Cosmological magnetic fields  

E-print Network

Magnetic fields are observed not only in stars, but in galaxies, clusters, and even high redshift Lyman-alpha systems. In principle, these fields could play an important role in structure formation and also affect the anisotropies in the cosmic microwave background radiation (CMB). The study of cosmological magnetic fields aims not only to quantify these effects on large-scale structure and the CMB, but also to answer one of the outstanding puzzles of modern cosmology: when and how do magnetic fields originate? They are either primordial, i.e. created before the onset of structure formation, or they are generated during the process of structure formation itself.

Roy Maartens

2000-07-24

163

Interplanetary Magnetic Field Lines  

NSDL National Science Digital Library

This web page, authored and curated by David P. Stern, 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.

Mendez, J.

164

The Earth's Magnetic Field  

NSDL National Science Digital Library

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

165

Damping of cosmic magnetic fields  

SciTech Connect

We examine the evolution of magnetic fields in an expanding fluid composed of matter and radiation with particular interest in the evolution of cosmic magnetic fields. We derive the propagation velocities and damping rates for relativistic and non-relativistic fast and slow magnetosonic and Alfv{acute e}n waves in the presence of viscous and heat conducting processes. The analysis covers all magnetohydrodynamics modes in the radiation diffusion and the free-streaming regimes. When our results are applied to the evolution of magnetic fields in the early universe, we find that cosmic magnetic fields are damped from prior to the epoch of neutrino decoupling up to recombination. Similar to the case of sound waves propagating in a demagnetized plasma, fast magnetosonic waves are damped by radiation diffusion on all scales smaller than the radiation diffusion length. The characteristic damping scales are the horizon scale at neutrino decoupling (M{sub {nu}}{approx}10{sup {minus}4}M{sub {circle_dot}} in baryons) and the Silk mass at recombination (M{sub {gamma}}{approx}10{sup 13}M{sub {circle_dot}} in baryons). In contrast, the oscillations of slow magnetosonic and Alfv{acute e}n waves get overdamped in the radiation diffusion regime, resulting in frozen-in magnetic field perturbations. Further damping of these perturbations is possible only if before recombination the wave enters a regime in which radiation free-streams on the scale of the perturbation. The maximum damping scale of slow magnetosonic and Alfv{acute e}n modes is always smaller than or equal to the damping scale of fast magnetosonic waves, and depends on the magnetic field strength and its direction relative to the wave vector. Our findings have multifold implications for cosmology. The dissipation of magnetic field energy into heat during the epoch of neutrino decoupling ensures that most magnetic field configurations generated in the very early universe satisfy big bang nucleosynthesis constraints. Further dissipation before recombination constrains models in which primordial magnetic fields give rise to galactic magnetic fields or density perturbations. Finally, the survival of Alfv{acute e}n and slow magnetosonic modes on scales well below the Silk mass may be of significance for the formation of structure on small scales. {copyright} {ital 1998} {ital The American Physical Society}

Jedamzik, K. [Max-Planck-Institut fuer Astrophysik, 85748 Garching bei Muenchen (Germany)] [Max-Planck-Institut fuer Astrophysik, 85748 Garching bei Muenchen (Germany); Katalinic, V.; Olinto, A.V. [Department of Astronomy and Astrophysics and Enrico Fermi Institute, University of Chicago, 5640 S. Ellis Ave., Chicago, Illinois 60637 (United States)] [Department of Astronomy and Astrophysics and Enrico Fermi Institute, University of Chicago, 5640 S. Ellis Ave., Chicago, Illinois 60637 (United States)

1998-03-01

166

High-field superconducting nested coil magnet  

NASA Technical Reports Server (NTRS)

Superconducting magnet, employed in conjunction with five types of superconducting cables in a nested solenoid configuration, produces total, central magnetic field strengths approaching 70 kG. The multiple coils permit maximum information on cable characteristics to be gathered from one test.

Laverick, C.; Lobell, G. M.

1970-01-01

167

Nonlinear electron magnetohydrodynamics physics. I. Whistler spheromaks, mirrors, and field reversed configurations  

SciTech Connect

The nonlinear interactions of time-varying magnetic fields with plasmas is investigated in the regime of electron magnetohydrodynamics. Simple magnetic field geometries are excited in a large laboratory plasma with a loop antenna driven with large oscillatory currents. When the axial loop field opposes the ambient field, the net field can be reversed to create a field-reversed configuration (FRC). In the opposite polarity, a strong field enhancement is produced. The time-varying antenna field excites whistler modes with wave magnetic fields exceeding the ambient magnetic field. The resulting magnetic field topologies have been measured. As the magnetic topology is changed from FRC to strong enhancement, two propagating field configurations resembling spheromaks are excited, one with positive and the other with negative helicity. Such 'whistler spheromaks' propagate with their null points along the weaker ambient magnetic field, with the current density localized around its O-line. In contrast, 'whistler mirrors' which have topologies similar to linear whistlers, except with B{sub wave}>B{sub 0}, have no null regions and, therefore, broad current layers. This paper describes the basic field topologies of whistler spheromaks and mirrors, while companion papers discuss the associated nonlinear phenomena as well as the interaction between them.

Stenzel, R. L.; Urrutia, J. M.; Strohmaier, K. D. [Department of Physics and Astronomy, University of California, Los Angeles, California 90095-1547 (United States)

2008-04-15

168

Nonlinear electron magnetohydrodynamics physics. I. Whistler spheromaks, mirrors, and field reversed configurations  

NASA Astrophysics Data System (ADS)

The nonlinear interactions of time-varying magnetic fields with plasmas is investigated in the regime of electron magnetohydrodynamics. Simple magnetic field geometries are excited in a large laboratory plasma with a loop antenna driven with large oscillatory currents. When the axial loop field opposes the ambient field, the net field can be reversed to create a field-reversed configuration (FRC). In the opposite polarity, a strong field enhancement is produced. The time-varying antenna field excites whistler modes with wave magnetic fields exceeding the ambient magnetic field. The resulting magnetic field topologies have been measured. As the magnetic topology is changed from FRC to strong enhancement, two propagating field configurations resembling spheromaks are excited, one with positive and the other with negative helicity. Such "whistler spheromaks" propagate with their null points along the weaker ambient magnetic field, with the current density localized around its O-line. In contrast, "whistler mirrors" which have topologies similar to linear whistlers, except with Bwave>B0, have no null regions and, therefore, broad current layers. This paper describes the basic field topologies of whistler spheromaks and mirrors, while companion papers discuss the associated nonlinear phenomena as well as the interaction between them.

Stenzel, R. L.; Urrutia, J. M.; Strohmaier, K. D.

2008-04-01

169

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

170

NCSX MAGNETIC CONFIGURATION FLEXIBILITY AND ROBUSTNESS  

E-print Network

- nal transform iext~s! by varying coil currents while con- straining the toroidal field and plasma. There are six coils in each of the three periods of the machine. Stellarator symmetry implies that within any

Hudson, Stuart

171

Sources of Magnetic Field Magnetic Phenomena  

E-print Network

push on currents Moving charges can make and feel magnetic forces. We don't understand how permanent will consider the last piece of the puzzle in electromagnetic - changing magnetic fields can make induction. 15Lecture 9 Sources of Magnetic Field 1 Magnetic Phenomena 1. Magnets can push on each other (and

Tobar, Michael

172

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

173

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.

2012-08-03

174

The First Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

175

Magnetic field screening effect in electroweak model  

E-print Network

It is shown that in the Weinberg-Salam model a magnetic field screening effect for static magnetic solutions takes place. The origin of this phenomenon can be traced to the mutual cancellation of Abelian magnetic fields created by the SU(2) gauge fields and Higgs boson. The effect implies monopole charge screening in the finite energy system of monopoles and antimonopoles. We consider another manifestation of the screening effect which leads to an essential energy decrease of magnetic solutions. Applying a variational method we have found a magnetic field configuration with a topological azimuthal magnetic flux which minimizes the energy functional and possesses a total energy of order 1 TeV. We suppose that a corresponding magnetic bound state exists in the electroweak theory and can be detected by experiment.

A. S. Bakry; D. G. Pak; P. M. Zhang; L. P. Zou

2014-10-03

176

Rotational stability of a long field-reversed configuration  

SciTech Connect

Rotationally driven modes of long systems with dominantly axial magnetic field are considered. We apply the incompressible model and order axial wavenumber small. A recently developed gyro-viscous model is incorporated. A one-dimensional equilibrium is assumed, but radial profiles are arbitrary. The dominant toroidal (azimuthal) mode numbers ?=1 and ?=2 modes are examined for a variety of non-reversed (B) and reversed profiles. Previous results for both systems with rigid rotor equilibria are reproduced. New results are obtained by incorporation of finite axial wavenumber and by relaxing the assumption of rigid electron and ion rotation. It is shown that the frequently troublesome ?=2 field reversed configuration (FRC) mode is not strongly affected by ion kinetic effects (in contrast to non-reversed cases) and is likely stabilized experimentally only by finite length effects. It is also shown that the ?=1 wobble mode has a complicated behavior and is affected by a variety of configuration and profile effects. The rotationally driven ?=1 wobble is completely stabilized by strong rotational shear, which is anticipated to be active in high performance FRC experiments. Thus, observed wobble modes in these systems are likely not driven by rotation alone.

Barnes, D. C., E-mail: coronadocon@msn.com; Steinhauer, L. C. [Tri Alpha Energy, Rancho Santa Margarita, California 92688 (United States)] [Tri Alpha Energy, Rancho Santa Margarita, California 92688 (United States)

2014-02-15

177

Rotational stability of a long field-reversed configuration  

NASA Astrophysics Data System (ADS)

Rotationally driven modes of long systems with dominantly axial magnetic field are considered. We apply the incompressible model and order axial wavenumber small. A recently developed gyro-viscous model is incorporated. A one-dimensional equilibrium is assumed, but radial profiles are arbitrary. The dominant toroidal (azimuthal) mode numbers ? =1 and ? =2 modes are examined for a variety of non-reversed (B) and reversed profiles. Previous results for both systems with rigid rotor equilibria are reproduced. New results are obtained by incorporation of finite axial wavenumber and by relaxing the assumption of rigid electron and ion rotation. It is shown that the frequently troublesome ? =2 field reversed configuration (FRC) mode is not strongly affected by ion kinetic effects (in contrast to non-reversed cases) and is likely stabilized experimentally only by finite length effects. It is also shown that the ? =1 wobble mode has a complicated behavior and is affected by a variety of configuration and profile effects. The rotationally driven ? =1 wobble is completely stabilized by strong rotational shear, which is anticipated to be active in high performance FRC experiments. Thus, observed wobble modes in these systems are likely not driven by rotation alone.

Barnes, D. C.; Steinhauer, L. C.

2014-02-01

178

Magnetic field dosimeter development  

SciTech Connect

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

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

1980-09-01

179

Field errors in superconducting magnets  

SciTech Connect

The mission of this workshop is a discussion of the techniques for tracking particles through arbitrary accelerator field configurations to look for dynamical effects that are suggested by various theoretical models but are not amenable to detailed analysis. A major motivation for this type of study is that many of our accelerator projects are based on the use of superconducting magnets which have field imperfections that are larger and of a more complex nature than those of conventional magnets. Questions such as resonances, uncorrectable closed orbit effects, coupling between planes, and diffusion mechanisms all assume new importance. Since, simultaneously, we are trying to do sophisticated beam manipulations such as stacking, high current accelerator, long life storage, and low loss extraction, we clearly need efficient and accurate tracking programs to proceed with confidence.

Barton, M.Q.

1982-01-01

180

Configurational spin reorientation phase transition in magnetic nanowire arrays  

NASA Astrophysics Data System (ADS)

Classical microscopic spin reorientation phase transitions (RPT) are the result of competing magnetocrystalline anisotropies. RPTs can also be observed in discrete macroscopic systems induced by competing shape anisotropies and magnetostatic coupling. Such a configurational RPT was recently observed in series of self-organized hexagonal arrays of 2.5 ?m long, 25-60 nm diameter circular permalloy nanowires grown in anodic alumina matrix. This RPT is a crossover transition from a one-dimensional easy axis "wire" behavior of weakly interacting uniaxial nanowires to a two-dimensional behavior of strongly coupled "wire film" having an easy plane anisotropy. It is shown that RPT takes place due to the competition between the intrinsic dipolar forces in individual wires and the external dipolar field of interacting nanowires in the array. The crossover occurs at a volume ratio of 0.38 for 65 nm periodicity. The experimental results are in agreement with the semi-analytical calculations of the dipolar interaction fields for these arrays of circular ferromagnetic nanowires, and are interpreted in terms of the Landau phase transition theory. The conditions for the crossover and the order of the phase transition are established. Based on the contribution to the magnetic energy from the flower state at the ends of the wires, it is concluded that the observed transition is of the first order.

Tartakovskaya, Elena V.; Pardavi-Horvath, Martha; Vázquez, Manuel

2010-03-01

181

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

182

Adiabatic model and design of a translating field reversed configuration  

SciTech Connect

We apply an adiabatic evolution model to predict the behavior of a field reversed configuration (FRC) during decompression and translation, as well as during boundary compression. Semi-empirical scaling laws, which were developed and benchmarked primarily for collisionless FRCs, are expected to remain valid even for the collisional regime of FRX-L experiment. We use this approach to outline the design implications for FRX-L, the high density translated FRC experiment at Los Alamos National Laboratory. A conical theta coil is used to accelerate the FRC to the largest practical velocity so it can enter a mirror bounded compression region, where it must be a suitable target for a magnetized target fusion (MTF) implosion. FRX-L provides the physics basis for the integrated MTF plasma compression experiment at the Shiva-Star pulsed power facility at Kirtland Air Force Research Laboratory, where the FRC will be compressed inside a flux conserving cylindrical shell.

Intrator, T. P. [Los Alamos National Laboratory, M.S. E526, Los Alamos, New Mexico 87545 (United States); Siemon, R. E. [Department of Physics, University of Nevada, Reno, Reno, Nevada 89557 (United States); Sieck, P. E. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2008-04-15

183

Magnetic fields of spherical compact stars in a braneworld  

SciTech Connect

We study the stellar magnetic field configuration in dependence on brane tension and present solutions of Maxwell equations in the external background space-time of a magnetized spherical star in a Randall-Sundrum II type braneworld. The star is modeled as a sphere consisting of perfect highly magnetized fluid with infinite conductivity and a frozen-in magnetic field. With respect to solutions for magnetic fields found in the Schwarzschild space-time, brane tension introduces enhancing corrections to the exterior magnetic field which could be relevant for the magnetic fields of magnetized compact objects as pulsars and magnetars and may provide observational evidence for the brane tension.

Ahmedov, B. J.; Fattoyev, F. J. [Institute of Nuclear Physics and Ulugh Beg Astronomical Institute, Tashkent 100052 (Uzbekistan); Abdus Salam International Centre for Theoretical Physics, 34014 Trieste (Italy)

2008-08-15

184

STUDIES OF VARIOUS CONFIGURATION OF PERMANENT MAGNETS TO DEVELOP REPULSIVE TYPE MAGNETIC BEARING  

Microsoft Academic Search

In magnetic bearing system the rotor is levitated in the magnetic field. The magnetic field may be generated in two ways: either by employing electromagnets or by using permanent magnets. Utilizing the repulsive force between permanent magnets for levitating the rotor it is possible to reduce the number of electromagnets used in magnetic bearing system and the corresponding control circuit

S. C. Mukhopadhyay; C. Goonaratne

185

Precise measurement of magnetization characteristics in high pulsed field  

NASA Astrophysics Data System (ADS)

Permanent magnets, especially Nd-Fe-B magnets, are very important engineering elements that are widely used in many applications. The detailed design of electrical and electronic equipment using permanent magnets requires the precise measurement of magnetization characteristics. High pulsed magnetic fields can be used to measure the magnetization characteristics of permanent magnets in the easy and hard magnetization directions. Errors influencing the measurements stem from the relationship between the tested material, pick-up sensor configuration, and excitation coil. We present an analysis of the effect of the sensor construction on the accuracy of the measurements of the material's magnetic properties. We investigated the coaxial and series types sensor configurations.

Nakahata, Y.; Borkowski, B.; Shimoji, H.; Yamada, K.; Todaka, T.; Enokizono, M.

2012-04-01

186

Slow formation of field reversed configurations by colliding high beta counter flows  

Microsoft Academic Search

To produce a field reversed configuration (FRC) without using the very high voltage techniques required in a conventional theta pinch, the author has studied the steady head-on collision of counter plasma streams, flowing along the magnetic field, as ejected from two identical co-axial plasma sources mounted at each end of the apparatus. The study was motivated by the fact that

K. Hirano

1988-01-01

187

Magnetic Field Problem: Current  

NSDL National Science Digital Library

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

Wolfgang Christian

188

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

189

Hidden magnetic configuration in epitaxial La1-rSrzMnO3 films  

SciTech Connect

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

Kao, Chi-Chang

2011-05-23

190

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.

191

Graphene Magnetic Field Sensors  

Microsoft Academic Search

Graphene extraordinary magnetoresistance (EMR) devices have been fabricated and characterized in varying magnetic fields at room temperature. The atomic thickness, high carrier mobility and high current carrying capabilities of graphene are ideally suited for the detection of nanoscale sized magnetic domains. The device sensitivity can reach 10 mV\\/Oe, larger than state of the art InAs 2DEG devices of comparable size

Simone Pisana; Patrick M. Braganca; Ernesto E. Marinero; Bruce A. Gurney

2010-01-01

192

Time Window for Magnetic Reconnection in Plasma Configurations with Velocity Shear  

SciTech Connect

It is shown that the rate of magnetic field line reconnection can be clocked by the evolution of the large-scale processes that are responsible for the formation of the current layers where reconnection can take place. In unsteady plasma configurations, such as those produced by the onset of the Kelvin-Helmholtz instability in a plasma with a velocity shear, qualitatively different magnetic structures are produced depending on how fast the reconnection process develops on the external clock set by the evolving large-scale configuration.

Faganello, M.; Califano, F.; Pegoraro, F. [Physics Department, University of Pisa, Largo Pontecorvo 3, 56127 Pisa (Italy)

2008-10-24

193

MHD waves and instabilities for gravitating, magnetized configurations in motion  

NASA Astrophysics Data System (ADS)

Seismic probing of equilibrium configurations is of course well-known from geophysics, but has also been succesfully used to determine the internal structure of the Sun to an amazing accuracy. The results of helioseismology are quite impressive, although they only exploit an equilibrium structure where inward gravity is balanced by a pressure gradient in a 1D radial fashion. In principle, one can do the same for stationary, gravitating, magnetized plasma equilibria, as needed to perform MHD seismology in astrophysical jets or accretion disks. The introduction of (sheared) differential rotation does require the important switch from diagnosing static to stationary equilibrium configurations. The theory to describe all linear waves and instabilities in ideal MHD, given an exact stationary, gravitating, magnetized plasma equilibrium, in any dimensionality (1D, 2D, 3D) has been known since 1960, and is governed by the Frieman-Rotenberg equation. The full (mathematical) power of spectral theory governing physical eigenmode determination comes into play when using the Frieman-Rotenberg equation for moving equilibria, as applicable to astrophysical jets, accretion disks, but also solar flux ropes with stationary flow patterns. I will review exemplary seismic studies of flowing equilibrium configurations, covering solar to astrophysical configurations in motion. In that case, even essentially 1D configurations require quantification of the spectral web of eigenmodes, organizing the complex eigenfrequency plane.

Keppens, Rony; Goedbloed, Hans J. P.

194

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

Microsoft Academic Search

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

V. N. Rodionov

1998-01-01

195

Preliminary investigation of force-reduced superconducting magnet configurations for advanced technology applications  

SciTech Connect

The feasibility of new high-field low specific weight superconducting magnet designs using force-free fields is being explored analytically and numerically. This report attempts to assess the technical viability of force-free field concepts to produce high-field, low specific weight and large bore volume magnets, which could promote the use of high temperature superconductors. Several force-free/force-reduced magnet configurations are first reviewed, then discussed and assessed. Force-free magnetic fields, fields for which the current flows parallel to the field, have well-known mathematical solutions extending upon infinite domains. These solutions, however, are no longer force-free everywhere for finite geometries. In this preliminary study, force-free solutions such as the Lundquist solutions truncated to a size where the internal field of the coil matches an externally cylindrical magnetic field (also called a Lundquist coil) are numerically modeled and explored. Significant force-reduction for such coils was calculated, which may have some importance for the design of lighter toroidal magnets used in thermonuclear fusion power generation, superconducting magnetic energy storage (SMES), and mobile MHD power generation and propulsion.

Bouillard, J.X.

1992-12-01

196

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.

197

Multiwavelength Magnetic Field Modeling  

NASA Astrophysics Data System (ADS)

We model the large-scale Galactic magnetic fields, including a spiral arm compression to generate anisotropic turbulence, by comparing polarized synchrotron and thermal dust emission. Preliminary results show that in the outer Galaxy, the dust emission comes from regions where the fields are more ordered than average while the situation is reversed in the inner Galaxy. We will attempt in subsequent work to present a more complete picture of what the comparison of these observables tells us about the distribution of the components of the magnetized ISM and about the physics of spiral arm shocks and turbulence.

Jaffe, T. R.

2015-03-01

198

Magnetic Fields in Galaxies  

NASA Astrophysics Data System (ADS)

The origin and evolution of cosmic magnetic fields, their strength and structure in intergalactic space, their first occurrence in young galaxies, and their dynamical importance for galaxy evolution remain widely unknown. Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized radio synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30 ?G) and in central starburst regions (50-100 ?G). Such fields are dynamically important; they can affect gas flows and drive gas inflows in central regions. Polarized radio emission traces ordered fields which can be regular or anisotropic turbulent, generated from isotropic turbulent fields by compression or shear. The strongest ordered fields of 10-15 ?G strength are generally found in interarm regions and follow the orientation of adjacent gas spiral arms. In galaxies with strong density waves, ordered (anisotropic turbulent) fields are also observed at the inner edges of the spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions of starburst galaxies. Ordered fields in interacting galaxies have asymmetric distributions and are an excellent tracer of past interactions between galaxies or with the intergalactic medium. Irregular galaxies host isotropic turbulent fields often of similar strength as in spiral galaxies, but only weak ordered fields. Faraday rotation measures (RM) of the diffuse polarized radio emission from the disks of several galaxies reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by a mean-field ? -? dynamo. So far no indications were found in external galaxies of large-scale field reversals, like the one in the Milky Way. Ordered magnetic fields are also observed in radio halos around edge-on galaxies out to large distances from the plane, with X-shaped patterns. In the outflow cone above a starburst region of NGC 253, RM data indicate a helical magnetic field.

Beck, Rainer

199

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

SciTech Connect

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

Ruden, E. L.; Zhang, Shouyin; Wurden, G. A.; Intrator, T. P.; Renneke, R.; Waganaar, W. J.; Analla, F. T.; Grabowski, T. C. [Air Force Research Laboratory, Directed Energy Directorate, Kirtland AFB, New Mexico 87117 (United States); Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Science Applications International Corporation, Albuquerque, New Mexico 87106 (United States)

2006-10-15

200

Refocusing properties of periodic magnetic fields  

NASA Technical Reports Server (NTRS)

The use of depressed collectors for the efficient collection of spent beams from linear-beam microwave tubes depends on a refocusing procedure in which the space charge forces and transverse velocity components are reduced. The refocusing properties are evaluated of permanent magnet configurations whose axial fields are approximated by constant plateaus or linearly varying fields. The results provide design criteria and show that the refocusing properties can be determined from the plateau fields alone.

Stankiewicz, N.

1976-01-01

201

Fusion space propulsion with a field reversed configuration  

Microsoft Academic Search

The objective of this study is to examine a fusion space propulsion system using D-³He in a reversed field configuration (FRC). Such a configuration provides good confinement and high-..beta.. operation with high power densities in a compact design. The reversed field is maintained by a combination of fuel pellet injection and energetic fusion products which create an azimuthal plasma current.

R. Chapman; G. H. Miley; W. Kernbichler; M. Heindler

1989-01-01

202

Properties of confining gauge field configurations in the pseudoparticle approach  

SciTech Connect

The pseudoparticle approach is a numerical method to approximate path integrals in SU(2) Yang-Mills theory. Path integrals are computed by summing over all gauge field configurations, which can be represented by a linear superposition of a small number of pseudoparticles with amplitudes and color orientations as degrees of freedom. By comparing different pseudoparticle ensembles we determine properties of confining gauge field configurations. Our results indicate the importance of long range interactions between pseudoparticles and of non trivial topological properties.

Wagner, Marc [Institute for Theoretical Physics III, University of Erlangen-Nuernberg, Staudtstrasse 7, 91058 Erlangen (Germany)

2007-02-27

203

CSEM-Steel Hybrid Wiggler\\/Undulator Magnetic Field Studies  

Microsoft Academic Search

Current design of permanent magnet wiggler\\/undulators use either pure charge sheet equivalent material (CSEM) or the CSEM-Steel hybrid configuration. Hybrid configurations offer higher field strength at small gaps, field distributions dominated by the pole surfaces and pole tuning. Nominal performance of the hybrid is generally predicted using a 2-D magnetic design code neglecting transverse geometry. Magnetic measurements are presented showing

K. Halbach; E. Hoyer; S. Marks; D. Plate; D. Shuman

1985-01-01

204

CSEM-Steel hybrid wiggler\\/undulator magnetic field studies  

Microsoft Academic Search

Current design of permanent magnet wiggler\\/undulators use either pure charge sheet equivalent material (CSEM) or the CSEM-Steel hybrid configuration. Hybrid configurations offer higher field strength at small gaps, field distributions dominated by the pole surfaces and pole tuning. Nominal performance of the hybrid is generally predicted using a 2-D magnetic design code neglecting transverse geometry. Magnetic measurements are presented showing

K. Halbach; E. Hoyer; S. Marks; D. Plate; D. Shuman

1985-01-01

205

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

206

Normal glow discharge in axial magnetic field  

NASA Astrophysics Data System (ADS)

Theory and results of mathematical modeling of a glow discharge in a parallel-plate configuration with axial magnetic field is presented. The model consists of continuity equations for electron and ion fluids, the Poisson equation for the self-consistent electric field. Numerical simulation results are presented for two-dimensional glow discharge at various initial conditions. The results are obtained for molecular nitrogen at pressure 1–5 Torr, emf of power supply 1–2 kV, and magnetic field induction B = 0–0.5 T. It is shown that in the presence of the axial magnetic field the glow discharge is rotated around its axis of symmetry. Nevertheless it is shown that in the investigated range of discharge parameters in an axial magnetic field the law of the normal current density is retained.

Surzhikov, S.; Shang, J.

2014-10-01

207

Magnetic fields at Uranus  

NASA Technical Reports Server (NTRS)

The conclusions drawn regarding the structure, behavior and composition of the Uranian magnetic field and magnetosphere as revealed by Voyager 2 data are summarized. The planet had a bipolar magnetotail and a bow shock wave which was observed 23.7 Uranus radii (UR) upstream and a magnetopause at 18.0 UR. The magnetic field observed can be represented by a dipole offset from the planet by 0.3 UR. The field vector and the planetary angular momentum vector formed a 60 deg angle, permitting Uranus to be categorized as an oblique rotator, with auroral zones occurring far from the rotation axis polar zones. The surface magnetic field was estimated to lie between 0.1-1.1 gauss. Both the field and the magnetotail rotated around the planet-sun line in a period of about 17.29 hr. Since the ring system is embedded within the magnetosphere, it is expected that the rings are significant absorbers of radiation belt particles.

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

1986-01-01

208

Ion Heating in Field-Reversed Configuration by Radio-Frequency Waves  

NASA Astrophysics Data System (ADS)

A simple modeling of the recent experiment on plasma heating by radio-frequency (rf) waves in the field-reversed configuration (FRC) is made. In the FRC Injection Experiment device the ion heating by rf pulse was observed. Present analysis indicates that the heating can be explained by the Doppler broadening of the ion cyclotron resonance in the low magnetic field device. These results support the suggestion that the direct heating of the ion majority near the fundamental ion cyclotron frequency should be efficient in low field configurations.

Svidzinski, V. A.; Prager, S. C.

2003-12-01

209

Chaotic magnetic fields: Particle motion and energization  

SciTech Connect

Magnetic field line equations correspond to a Hamiltonian dynamical system, so the features of a Hamiltonian systems can easily be adopted for discussing some essential features of magnetic field lines. The integrability of the magnetic field line equations are discussed by various authors and it can be shown that these equations are, in general, not integrable. We demonstrate several examples of realistic chaotic magnetic fields, produced by asymmetric current configurations. Particular examples of chaotic force-free field and non force-free fields are shown. We have studied, for the first time, the motion of a charged particle in chaotic magnetic fields. It is found that the motion of a charged particle in a chaotic magnetic field is not necessarily chaotic. We also showed that charged particles moving in a time-dependent chaotic magnetic field are energized. Such energization processes could play a dominant role in particle energization in several astrophysical environments including solar corona, solar flares and cosmic ray propagation in space.

Dasgupta, Brahmananda [CSPAR, University of Alabama in Huntsville, Huntsville, AL 35805 (United States); Ram, Abhay K. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Li, Gang [Department of Physics, University of Alabama in Huntsville, Huntsville, AL 35899 and CSPAR, University of Alabama in Huntsville, Huntsville, AL 35805 (United States); Li, Xiaocan [Department of Physics, University of Alabama in Huntsville, Huntsville, AL 35899 (United States)

2014-02-11

210

Evolution of Stellar Magnetic Fields  

NASA Astrophysics Data System (ADS)

Stellar magnetic fields can reliably be characterized by several magnetic activity indicators, such as X-ray or radio luminosity. Physical processes leading to such emission provide important information on dynamic processes in stellar atmospheres and magnetic structuring.

Güdel, Manuel

2015-03-01

211

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

212

Magnetic Fields and Forces in Permanent Magnet Levitated Bearings  

Microsoft Academic Search

Magnetic fields and magnetic forces from magnetic bearings made of circular Halbach permanent-magnet arrays are computed and analyzed. The magnetic fields are calculated using superposition of fields due to patches of magnetization charge at surfaces where the magnetization is discontinuous. The magnetic force from the magnetic bearing is computed using superposition of forces on each patch of magnetization charge. The

Kevin D. Bachovchin; James F. Hoburg; Richard F. Post

2012-01-01

213

A flexible and configurable system to test accelerator magnets  

SciTech Connect

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

Jerzy M. Nogiec et al.

2001-07-20

214

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 ...

Mrs. Merritt

2005-10-18

215

Crustal Magnetic Fields  

NASA Technical Reports Server (NTRS)

Cosmos 49, Polar Orbit Geophysical Observatory (POGO) (Orbiting Geophysical Observatory (OGO-2, 4 and 6)) and Magsat have been the only low-earth orbiting satellites to measure the crustal magnetic field on a global scale. These missions revealed the presence of long- wavelength (> 500 km) crustal anomalies predominantly located over continents. Ground based methods were, for the most part, unable to record these very large-scale features; no doubt due to the problems of assembling continental scale maps from numerous smaller surveys acquired over many years. Questions arose as to the source and nature of these long-wave length anomalies. As a result there was a great stimulant given to the study of the magnetic properties of the lower crust and upper mantle. Some indication as to the nature of these deep sources has been provided by the recent results from the deep crustal drilling programs. In addition, the mechanism of magnetization, induced or remanent, was largely unknown. For computational ease these anomalies were considered to result solely from induced magnetization. However, recent results from Mars Orbiter Laser Altimeter (MOLA), a magnetometer-bearing mission to Mars, have revealed crustal anomalies with dimensions similar to the largest anomalies on Earth. These Martian features could only have been produced by remanent magnetization, since Mars lacks an inducing field. The origin of long-wavelength crustal anomalies, however, has not been completely determined. Several large crustal magnetic anomalies (e.g., Bangui, Kursk, Kiruna and Central Europe) will be discussed and the role of future satellite magnetometer missions (Orsted, SUNSAT and Champ) in their interpretation evaluated.

Taylor, Patrick T.; Ravat, D.; Frawley, James J.

1999-01-01

216

Internal Magnetic Field Measurements on the FIX Experiment  

Microsoft Academic Search

FIX (FRC Injection Experiment) is a Field Reversed Configuration (FRC) used for translation, confinement, and NBI experiments. A Faraday effect probe is being developed for internal magnetic field measurements on FIX. The Faraday effect: in the presence of a magnetic field, a Faraday rotator material will rotate the polarization of light by an angle theta = VBL, where V is

A. Martin; T. Kawada; S. Okada; S. Goto

1999-01-01

217

Internal Magnetic Field Measurements on the FIX-FRC Experiment  

Microsoft Academic Search

FIX (FRC Injection Experiment) is a Field Reversed Configuration (FRC) used for translation, confinement and NBI experiments. A Faraday effect probe has been developed for internal magnetic field measurements on FIX. The Faraday effect: in the presence of a magnetic field, a Faraday rotator will rotate the polarization of light by an angle theta = VBl, where B is the

Adam Martin; Shigefumi Okada; Seiichi Goto

1998-01-01

218

Ohm's law for plasmas in reversed field pinch configuration  

Microsoft Academic Search

An analytical relationship between current density and applied electric field in reversed field pinch (RFP) plasmas has been derived in the framework of the kinetic dynamo theory, that is assuming a radial field-aligned momentum transport caused by the magnetic field stochasticity. This Ohm's law yields current density profiles with a poloidal current density at the edge which can sustain the

E. Martines; F. Vallone

1997-01-01

219

CSEM-steel hybrid wiggler/undulator magnetic field studies  

SciTech Connect

Current design of permanent magnet wiggler/undulators use either pure charge sheet equivalent material (CSEM) or the CSEM-Steel hybrid configuration. Hybrid configurations offer higher field strength at small gaps, field distributions dominated by the pole surfaces and pole tuning. Nominal performance of the hybrid is generally predicted using a 2-D magnetic design code neglecting transverse geometry. Magnetic measurements are presented showing transverse configuration influence on performance, from a combination of models using CSEMs, REC (H/sub c/ = 9.2 kOe) and NdFe (H/sub c/ = 10.7 kOe), different pole widths and end configurations. Results show peak field improvement using NdFe in place of REC in identical models, gap peak field decrease with pole width decrease (all results less than computed 2-D fields), transverse gap field distributions, and importance of CSEM material overhanging the poles in the transverse direction for highest gap fields.

Halbach, K.; Hoyer, E.; Marks, S.; Plate, D.; Shuman, D.

1985-05-01

220

CSEM-Steel hybrid wiggler/undulator magnetic field studies  

SciTech Connect

Current design of permanent magnet wiggler/undulators use either pure charge sheet equivalent material (CSEM) or the CSEM-Steel hybrid configuration. Hybrid configurations offer higher field strength at small gaps, field distributions dominated by the pole surfaces and pole tuning. Nominal performance of the hybrid is generally predicted using a 2-D magnetic design code neglecting transverse geometry. Magnetic measurements are presented showing transverse configuration influence on performance, from a combination of models using CSEMs, REC (H/sub c/ = 9.2 KOe) and NdFe (H/sub c/ = 10.7 kOe), different pole widths and end configurations. Results show peak field improvement using NdFe in place of REC in identical models, gap peak field decrease with pole width decrease (all results less than computed 2-D fields), transverse gap field distributions, and importance of CSEM material overhanging the poles in the transverse direction for highest gap fields. 3 refs., 6 figs.

Halbach, K.; Hoyer, E.; Marks, S.; Plate, D.; Shuman, D.

1985-06-01

221

Magnetic fields in mixed neutron-star-plus-wormhole systems  

NASA Astrophysics Data System (ADS)

We consider mixed configurations consisting of a wormhole filled by a strongly magnetized isotropic or anisotropic neutron fluid. The nontrivial topology of the spacetime is allowed by the presence of exotic matter. By comparing these configurations with ordinary magnetized neutron stars, we clarify the question of how the presence of the nontrivial topology influences the magnetic field distribution inside the fluid. In the case of an anisotropic fluid, we find new solutions describing configurations, where the maximum of the fluid density is shifted from the center. A linear stability analysis shows that these mixed configurations are unstable.

Aringazin, Ascar; Dzhunushaliev, Vladimir; Folomeev, Vladimir; Kleihaus, Burkhard; Kunz, Jutta

2015-04-01

222

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

SciTech Connect

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

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

2012-02-10

223

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

224

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

225

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

226

Magnetic Field Problem: Current and Magnets  

NSDL National Science Digital Library

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

Wolfgang Christian

227

Probing Magnetic Fields With SNRs  

NASA Astrophysics Data System (ADS)

As supernova remnants (SNRs) expand, their shock waves freeze in and compress magnetic field lines they encounter; consequently we can use SNRs as magnifying glasses for interstellar magnetic fields. A simple model is used to derive polarization and rotation measure (RM) signatures of SNRs. This model is exploited to gain knowledge about the large-scale magnetic field in the Milky Way. Three examples are given which indicate a magnetic anomaly, an azimuthal large-scale magnetic field towards the anti-centre, and a chimney that releases magnetic energy from the plane into the halo.

Kothes, Roland

2015-03-01

228

The Galactic Magnetic Field  

NASA Astrophysics Data System (ADS)

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 ?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.

2012-12-01

229

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

230

Plasma transport in a simulated magnetic-divertor configuration  

SciTech Connect

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

Strawitch, C. M.

1981-03-01

231

The Martian magnetic field  

NASA Technical Reports Server (NTRS)

The paper presents an overview of the Martian magnetic field measurements and the criticisms made of them. The measurements of the Mars 2, 3, and 5 spacecraft were interpreted by Dolginov et al. (1976, 1978) to be consistent with an intrinsic planetary magnetic moment of 2.5 times 10 to the 22nd power gauss cu cm, basing this result on the apparent size of the obstacle responsible for deflecting the solar wind and an apparent encounter of the spacecraft with the planetary field. It is shown that if the dependence of the Martian magnetic moment on the rotation rate was linear, the estimate of the moment would be far larger than reported by Dolginov et al. An upper limit of 250 km is calculated for the dynamo radius using the similarity law, compared with 500 km obtained by Dolginov et al. It is concluded that the possible strength of a Martian dynamo is below expectations, and it is likely that the Mars dynamo is not presently operative.

Russell, C. T.

1979-01-01

232

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

233

Recent Results on Field Reversed Configurations from the Translation, Confinement and Sustainment Experiment  

Microsoft Academic Search

The field-reversed configuration (FRC) offers an attractive alternative approach to magnetically confined fusion because of its extremely high beta, simple linear geometry, and natural divertor for helium ash removal. Multi-hundred eV and high density FRCs have been produced using the standard Field Reversed Theta Pinch (RFTP) method, with a confinement scaling that leads to fusion conditions. These FRCs are, however,

Houyang Guo

2005-01-01

234

Directed Plasma Flow across Magnetic Field  

NASA Astrophysics Data System (ADS)

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

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

2008-04-01

235

The ASTROMAG superconducting magnet facility configured for a free flying satellite  

SciTech Connect

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

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

1991-06-01

236

The Astromag Superconducting Magnet Facility Configured for a FreeFlying Satellite  

SciTech Connect

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

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

1991-06-01

237

Magnetic field programming in quadrupole magnetic field-flow fractionation  

NASA Astrophysics Data System (ADS)

Magnetic field-flow fractionation (MgFFF) is a technique for the separation and characterization of magnetic nanoparticles. It is explained that the analysis of polydisperse samples requires a programmed decay of field and field gradient during sample elution. A procedure for achieving reproducible field decay with asymptotic approach to zero field using a quadrupole electromagnet is described. An example of an analysis of a polydisperse sample under programmed field decay is given.

Stephen Williams, P.; Carpino, Francesca; Moore, Lee R.; Zborowski, Maciej

238

Compact low field magnetic resonance imaging magnet: Design and optimization  

NASA Astrophysics Data System (ADS)

Magnetic resonance imaging (MRI) is performed with a very large instrument that allows the patient to be inserted into a region of uniform magnetic field. The field is generated either by an electromagnet (resistive or superconductive) or by a permanent magnet. Electromagnets are designed as air cored solenoids of cylindrical symmetry, with an inner bore of 80-100 cm in diameter. In clinical analysis of peripheral regions of the body (legs, arms, foot, knee, etc.) it would be better to adopt much less expensive magnets leaving the most expensive instruments to applications that require the insertion of the patient in the magnet (head, thorax, abdomen, etc.). These "dedicated" apparati could be smaller and based on resistive magnets that are manufactured and operated at very low cost, particularly if they utilize an iron yoke to reduce power requirements. In order to obtain good field uniformity without the use of a set of shimming coils, we propose both particular construction of a dedicated magnet, using four independently controlled pairs of coils, and an optimization-based strategy for computing, a posteriori, the optimal current values. The optimization phase could be viewed as a low-cost shimming procedure for obtaining the desired magnetic field configuration. Some experimental measurements, confirming the effectiveness of the proposed approach (construction and optimization), have also been reported. In particular, it has been shown that the adoption of the proposed optimization based strategy has allowed the achievement of good uniformity of the magnetic field in about one fourth of the magnet length and about one half of its bore. On the basis of the good experimental results, the dedicated magnet can be used for MRI of peripheral regions of the body and for animal experimentation at very low cost.

Sciandrone, M.; Placidi, G.; Testa, L.; Sotgiu, A.

2000-03-01

239

Scattering by magnetic fields  

Microsoft Academic Search

Consider the scattering amplitude $s(\\\\omega,\\\\omega^\\\\prime;\\\\lambda)$,\\u000a$\\\\omega,\\\\omega^\\\\prime\\\\in{\\\\Bbb S}^{d-1}$, $\\\\lambda > 0$, corresponding to an\\u000aarbitrary short-range magnetic field $B(x)$, $x\\\\in{\\\\Bbb R}^d$. This is a smooth\\u000afunction of $\\\\omega$ and $\\\\omega^\\\\prime$ away from the diagonal\\u000a$\\\\omega=\\\\omega^\\\\prime$ but it may be singular on the diagonal. If $d=2$, then\\u000athe singular part of the scattering amplitude (for example, in the transversal\\u000agauge) is a

D. R. Yafaev

2005-01-01

240

Plasma separation from magnetic field lines in a magnetic nozzle  

NASA Technical Reports Server (NTRS)

This paper discusses conditions for separation of a plasma from the magnetic field of a magnetic nozzle. The analysis assumes a collisionless, quasineutral plasma, and therefore the results represent a lower bound on the amount of detachment possible for a given set of plasma conditions. We show that collisionless separation can occur because finite electron mass inhibits the flow of azimuthal currents in the nozzle. Separation conditions are governed by a parameter G which depends on plasma and nozzle conditions. Several methods of improving plasma detachment are presented, including moving the plasma generation zone downstream from the region of strongest magnetic field and using dual magnets to focus the plasma beam. Plasma detachment can be enhanced by manipulation of the nozzle configuration.

Kaufman, D. A.; Goodwin, D. G.; Sercel, J. C.

1993-01-01

241

Evolution of the interplanetary magnetic field  

SciTech Connect

Remote observations of magnetic field topologies in the solar corona and in situ observations of the solar wind and interplanetary magnetic field (IMF) in interplanetary space are used to examine the temporal evolution of the spatial distribution of open and closed field regions emanating from the Sun. The simple ``open`` configuration of inward and outward pointing sectors in the IMF is periodically disrupted by magnetically distinct coronal mass ejections (CMEs) which erupt from previously closed magnetic field regions in the corona into interplanetary space. At 1 AU, CMEs contain counterstreaming halo electrons which indicate their distinct magnetic topologies. This topology is generally thought to be: plasmoids that are completely disconnected from the Sun; magnetic ``bottles,`` still tied to the corona at both ends; or flux ropes which are only partially disconnected. Fully disconnected plasmoids would have no long term effect on the amount of open flux; however, both in situ observations of details of the halo electron distributions and remote coronagraph observations of radial fields following CMEs indicate that CMEs generally do retain at least partial attached to the Sun. Both the magnetic-bottle and flux rope geometries require some mitigating process to close off previously open fields in order to avoid a flux catastrophe. In addition, the average amount of magnetic flux observed in interplanetary space varies over the solar cycle, also indicating that there must be ways in which new flux is opened and previously open flux is closed off. The most likely scenario for closing off open magnetic fields is for reconnection to occurs above helmet streamers, where oppositely directed field regions are juxtaposed in the corona. These events would serve to return closed field arches to the Sun and release open, U-shaped structures into the solar wind.

McComas, D.J.

1993-05-01

242

Evolution of the interplanetary magnetic field  

SciTech Connect

Remote observations of magnetic field topologies in the solar corona and in situ observations of the solar wind and interplanetary magnetic field (IMF) in interplanetary space are used to examine the temporal evolution of the spatial distribution of open and closed field regions emanating from the Sun. The simple open'' configuration of inward and outward pointing sectors in the IMF is periodically disrupted by magnetically distinct coronal mass ejections (CMEs) which erupt from previously closed magnetic field regions in the corona into interplanetary space. At 1 AU, CMEs contain counterstreaming halo electrons which indicate their distinct magnetic topologies. This topology is generally thought to be: plasmoids that are completely disconnected from the Sun; magnetic bottles,'' still tied to the corona at both ends; or flux ropes which are only partially disconnected. Fully disconnected plasmoids would have no long term effect on the amount of open flux; however, both in situ observations of details of the halo electron distributions and remote coronagraph observations of radial fields following CMEs indicate that CMEs generally do retain at least partial attached to the Sun. Both the magnetic-bottle and flux rope geometries require some mitigating process to close off previously open fields in order to avoid a flux catastrophe. In addition, the average amount of magnetic flux observed in interplanetary space varies over the solar cycle, also indicating that there must be ways in which new flux is opened and previously open flux is closed off. The most likely scenario for closing off open magnetic fields is for reconnection to occurs above helmet streamers, where oppositely directed field regions are juxtaposed in the corona. These events would serve to return closed field arches to the Sun and release open, U-shaped structures into the solar wind.

McComas, D.J.

1993-01-01

243

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

244

Simulation of viscoelastic flows using Brownian configuration fields  

Microsoft Academic Search

In this paper we present a new approach for calculating viscoelastic flows. The polymer stress is not determined from a closed-form constitutive equation, but from a microscopic model. In this description, we replace the collection of individual polymer molecules by an ensemble of configuration fields, representing the internal degrees of freedom of the polymers. Similar to the motion of real

M. A Hulsen; A. P. G van Heel; B. H. A. A van den Brule

1997-01-01

245

Magnetic field studies at Jupiter by Voyager 1: preliminary results  

Microsoft Academic Search

Results obtained by the Goddard Space Flight Center magnetometers on Voyager 1 concerning the large scale configuration of the Jovian bow shock and magnetopause, and the magnetic field in both the inner and outer magnetosphere are highlighted. There is evidence that a magnetic tail extending away from the planet on the nightside is formed by the solar wind-Jovian field interaction.

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

1979-01-01

246

Note on a noncritical holographic model with a magnetic field  

SciTech Connect

We consider a noncritical holographic model constructed from an intersecting brane configuration D4/D4-D4 with an external magnetic field. We investigate the influences of this magnetic field on strongly coupled dynamics by the gauge/gravity correspondence.

Cui Shengliang; Gao Yihong [Key Laboratory of Frontiers in Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, P.O. Box 2735, Beijing 100190 (China); Seo, Yunseok [Center for Quantum Spacetime, Sogang University, Seoul 121-742 (Korea, Republic of); Sin Sangjin [Physics Department, Hanyang University, Seoul 133-791 (Korea, Republic of); Xu Weishui [Center for Quantum Spacetime, Sogang University, Seoul 121-742 (Korea, Republic of); Physics Department, Hanyang University, Seoul 133-791 (Korea, Republic of)

2010-03-15

247

Research facility for the study of power system magnetic fields  

Microsoft Academic Search

A magnetic field research facility was constructed at EPRI's High Voltage Transmission Research Center (HVTRC) for the purpose of reproducing power system magnetic fields under controlled conditions. The facility includes a 1200' overhead distribution line that can be configured in different ways and a water distribution system that can be connected in different ways to the neutral wires. The distribution

L. E. Zaffanella; G. B. Rauch; G. B. Johnson

1991-01-01

248

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

249

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

250

High-frequency electron drift instability in the cross-field configuration of Hall thrusters  

SciTech Connect

A systematic study of a high-frequency electron drift instability is presented. It has very large wave numbers corresponding to wavelengths close to the electron gyroradius. The three-dimensional dispersion relation is derived for a model of a crossed electric and magnetic field configuration existing in the Hall thruster. It is shown that the instability develops in packets of oblique unstable modes perpendicular to the magnetic field. The evolution of the instability is also studied for distorted electron distribution functions obtained in particle-in-cell simulations.

Ducrocq, A.; Adam, J. C.; Heron, A.; Laval, G. [Centre de Physique Theorique, Ecole Polytechnique, CNRS UMR 7644, F-91128, Palaiseau Cedex (France)

2006-10-15

251

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

252

Magnetic field modification of optical magnetic dipoles.  

PubMed

Acting on optical magnetic dipoles opens novel routes to govern light-matter interaction. We demonstrate magnetic field modification of the magnetic dipolar moment characteristic of resonant nanoholes in thin magnetoplasmonic films. This is experimentally shown through the demonstration of the magneto-optical analogue of Babinet's principle, where mirror imaged MO spectral dependencies are obtained for two complementary magnetoplasmonic systems: holes in a perforated metallic layer and a layer of disks on a substrate. PMID:25646869

Armelles, Gaspar; Caballero, Blanca; Cebollada, Alfonso; Garcia-Martin, Antonio; Meneses-Rodríguez, David

2015-03-11

253

Exposure guidelines for magnetic fields  

SciTech Connect

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

Miller, G.

1987-12-01

254

Magnetic fields in massive stars  

Microsoft Academic Search

Although indirect evidence for the presence of magnetic fields in high-mass stars is regularly reported in the literature, the detection of these fields remains an extremely challenging observational problem. We review the recent discoveries of magnetic fields in different types of massive stars and briefly discuss strategies for spectropolarimetric observations to be carried out in the future.

S. Hubrig; M. Scholler; M. Briquet; M. A. Pogodin; R. V. Yudin; J. F. Gonzalez; T. Morel; P. De; R. Ignace; G. Mathys; G. J. Peters

2007-01-01

255

Magnetic fields in massive stars  

E-print Network

Although indirect evidence for the presence of magnetic fields in high-mass stars is regularly reported in the literature, the detection of these fields remains an extremely challenging observational problem. We review the recent discoveries of magnetic fields in different types of massive stars and briefly discuss strategies for spectropolarimetric observations to be carried out in the future.

S. Hubrig

2007-03-09

256

Magnetic-field-dosimetry system  

SciTech Connect

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

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

1981-01-21

257

The Galileo magnetic field investigation  

Microsoft Academic Search

The Galileo Orbiter carries a complement of fields and particles instruments designed to provide data needed to shed light on the structure and dynamical variations of the Jovian magnetosphere. Many questions remain regarding the temporal and spatial properties of the magnetospheric magnetic field, how the magnetic field maintains corotation of the embedded plasma and the circumstances under which corotation breaks

M. G. Kivelson; K. K. Khurana; J. D. Means; C. T. Russell; R. C. Snare

1992-01-01

258

The Effects of Magnetic Nozzle Configurations on Plasma Thrusters  

NASA Technical Reports Server (NTRS)

Over the course of eight years, the Ohio State University has performed research in support of electric propulsion development efforts at the NASA Lewis Research Center, Cleveland, OH. This research has been largely devoted to plasma propulsion systems including MagnetoPlasmaDynamic (MPD) thrusters with externally-applied, solenoidal magnetic fields, hollow cathodes, and Pulsed Plasma Microthrusters (PPT's). Both experimental and theoretical work has been performed, as documented in four master's theses, two doctoral dissertations, and numerous technical papers. The present document is the final report for the grant period 5 December 1987 to 31 December 1995, and summarizes all activities. Detailed discussions of each area of activity are provided in appendices: Appendix 1 - Experimental studies of magnetic nozzle effects on plasma thrusters; Appendix 2 - Numerical modeling of applied-field MPD thrusters; Appendix 3 - Theoretical and experimental studies of hollow cathodes; and Appendix 4 -Theoretical, numerical and experimental studies of pulsed plasma thrusters. Especially notable results include the efficacy of using a solenoidal magnetic field downstream of a plasma thruster to collimate the exhaust flow, the development of a new understanding of applied-field MPD thrusters (based on experimentally-validated results from state-of-the art, numerical simulation) leading to predictions of improved performance, an experimentally-validated, first-principles model for orificed, hollow-cathode behavior, and the first time-dependent, two-dimensional calculations of ablation-fed, pulsed plasma thrusters.

Turchi, P. J.

1997-01-01

259

Two-sublattice magnetic system with fourth-order uniaxial anisotropy and strong antisymmetric exchange in a transverse magnetic field  

Microsoft Academic Search

Discusses the equilibrium configurations and the phase transitions of a semi-classical model system consisting of two equal magnetic moments coupled by isotropic, anisotropic and antisymmetric exchange, with uniaxial anisotropy terms up to fourth order, in the presence of a transverse magnetic field. No restriction is imposed on the values of the interaction parameters. Magnetic configurations of the 'conical' type appear

M. Acquarone

1979-01-01

260

Mercury's magnetic field and interior  

NASA Technical Reports Server (NTRS)

The magnetic-field data collected on Mercury by the Mariner-10 spacecraft present substantial evidence for an intrinsic global magnetic field. However, studies of Mercury's thermal evolution show that it is most likely that the inner core region of Mercury solidified or froze early in the planet's history. Thus, the explanation of Mercury's magnetic field in the framework of the traditional planetary dynamo is less than certain.

Connerney, J. E. P.; Ness, N. F.

1988-01-01

261

Dynamic evolution of coronal magnetic fields  

NASA Technical Reports Server (NTRS)

The response of coronal magnetic fields to photospheric motion is investigated using a time-dependent, two-dimensional MHD simulation. Starting with an initially uniform field, a circular section of the loop base is slowly rotated to represent the photospheric motion. The field lines at the base move with this flow in a manner consistent with the generated electric fields. The subsequent evolution of the field and flow can be characterized as passing through several distinct configurations. In the earliest phase the kinetic energy is negligible, and the current and field are parallel throughout most of the cylinder. This is followed by a period in which the field rotation increases, the axial field at and near the axis increases, and the acial field decreases in two cylindrical regions away from the axis. When the field in an appreciable portion of the cylinder has undergone one complete rotation, a rapid change in field configuration occurs with a large portion of the field making several rotations at large radii and a corresponding large reduction in the axial field.

Steinolfson, Richard S.

1986-01-01

262

The Impact of Well-Field Configuration on Plume Persistence  

NASA Astrophysics Data System (ADS)

It is now recognized that most sites with large groundwater contaminant plumes will require many decades before cleanup will be achieved under current methods and standards. Conceptually, the factors that contribute to plume persistence have long been established, including uncontrolled source zones, dispersed reservoirs of dissolved (present in lower-permeability zones) and sorbed contaminant, and hydraulic-related factors such as non-optimal remedial well-field performance. Of these potential factors, hydraulic phenomena associated with configuration and operation of the well field employed for remedial operations have received minimal attention. The objective of this research is to investigate the influence of well-field configuration on contaminant mass removal and reduction in contaminant mass discharge (CMD). Mathematical modeling, implemented using MODFLOW and MT3D, was conducted to simulate scenarios with different well-field configurations in both homogenous and heterogeneous aquifers. The system was designed such that contaminant was present as only aqueous and sorbed mass (no separate organic-liquid sources). The impacts of several variables on the results are investigated, including pumping rate, layer thickness, and vertical dispersivity. The results are assessed in terms of the relationship between reductions in CMD and reductions in contaminant mass.

Guo, Z.; Brusseau, M.

2013-12-01

263

Vacuum Magnetic Field Mapping of the Compact Toroidal Hybrid (CTH)  

NASA Astrophysics Data System (ADS)

Vacuum magnetic field mapping experiments are performed on the CTH torsatron with a movable electron gun and phosphor-coated screen or movable wand at two different toroidal locations. These experiments compare the experimentally measured magnetic configuration produced by the as-built coil set, to the magnetic configuration simulated with the IFT Biot-Savart code using the measured coil set parameters. Efforts to minimize differences between the experimentally measured location of the magnetic axis and its predicted value utilizing a Singular Value Decomposition (SVD) process result in small modifications of the helical coil winding law used to model the vacuum magnetic field geometry of CTH. Because these studies are performed at relatively low fields B = 0.01 - 0.05 T, a uniform ambient magnetic field is included in the minimization procedure.

Peterson, J. T.; Hanson, J.; Hartwell, G. J.; Knowlton, S. F.; Montgomery, C.; Munoz, J.

2007-11-01

264

Evolution of pulsar magnetic fields  

Microsoft Academic Search

Theoretical considerations of neutron star matter and magnetic fields suggest a picture of the evolution of pulsar dipole moments. At birth the spin axis and magnetic dipole are argued to be roughly aligned. Subsequently the magnetic dipole greatly diminishes in strength and changes its direction until it ultimately makes a large angle with the spin axis. This view is supported

E. Flowers; M. A. Ruderman

1977-01-01

265

Theory of fossil magnetic field  

NASA Astrophysics Data System (ADS)

Theory of fossil magnetic field is based on the observations, analytical estimations and numerical simulations of magnetic flux evolution during star formation in the magnetized cores of molecular clouds. Basic goals, main features of the theory and manifestations of MHD effects in young stellar objects are discussed.

Dudorov, Alexander E.; Khaibrakhmanov, Sergey A.

2015-02-01

266

Zero-dimensional model for field-reversed configurations  

SciTech Connect

A 0-D model has been developed to study energy, particle, and internal flux confinement during the equilibrium phase in field-reversed configurations (FRC's). Earlier work has been extended to include: (1) a 1-D radial equilibrium pressure profile consistent with particle transport calculations; (2) a time-dependent treatment of impurity radiation losses; (3) a more consistent treatment of ohmic power. The 0-D model is described. Example numerical solutions are presented.

Rej, D.J.; Tuszewski, M.

1982-01-01

267

Cosmic Magnetic Fields - An Overview  

NASA Astrophysics Data System (ADS)

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

Wielebinski, Richard; Beck, Rainer

268

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

269

Measurements of magnetic field alignment  

SciTech Connect

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

Kuchnir, M.; Schmidt, E.E.

1987-11-06

270

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

SciTech Connect

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

Bessho, N., E-mail: naoki.bessho@nasa.gov [Department of Astronomy, University of Maryland, College Park, Maryland 20742, USA and Heliophysics Science Division, NASA Goddard Space Flight Center, Maryland 20771 (United States); Bhattacharjee, A. [Center for Heliophysics, Department of Astrophysical Sciences and Princeton Plasma Physics Laboratory, Princeton University, New Jersey 08543 (United States)

2014-10-15

271

Heat pulse propagation in chaotic three-dimensional magnetic fields  

SciTech Connect

Heat pulse propagation in three-dimensional chaotic magnetic fields is studied by numerically solving the parallel heat transport equation using a Lagrangian Green's function (LG) method. The main two problems addressed are: the dependence of the radial transport of heat pulses on the level of magnetic field stochasticity (controlled by the amplitude of the magnetic field perturbation, ?), and the role of reversed shear magnetic field configurations on heat pulse propagation. The role of separatrix reconnection of resonant modes in the shear reversal region, and the role of shearless Cantori in the observed phenomena are also discussed.

Del-Castillo-Negrete, Diego [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Blazevski, Daniel [Institute for Mechanical Systems, ETH, Zurich (Switzerland)

2014-06-01

272

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

DOEpatents

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

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

1991-04-09

273

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

DOEpatents

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

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

1991-01-01

274

The magnetic field of Mercury  

Microsoft Academic Search

The magnetic field of Mercury was measured on two fly-bys of the planet by the Mariner 10 space-craft. The presence of a field at Mercury is interesting for what it implies for both the internal and external sources of field. The internal field of the planet is almost certainly generated by an internal dynamo although there remain many puzzles as

D. J. Southwood

1997-01-01

275

The magnetic field of Mercury  

Microsoft Academic Search

The magnetic field of Mercury was measured on two fly-bys of the planet by the Mariner 10 spacecraft. The presence of a field at Mercury is interesting for what it implies for both the internal and external sources of field. The internal field of the planet is almost certainly generated by an internal dynamo although there remain many puzzles as

D. J. Southwood

1997-01-01

276

Equilibrium rotation in field-reversed configurations Loren Steinhauer  

E-print Network

Received 25 October 2007; accepted 12 December 2007; published online 29 January 2008 The turbulence of spheromaks D. D. Ryutov, Phys. Plasmas 14, 022506 2007 . The opening up of internal magnetic field lines into the plasma interior. For conditions relevant to experiments, the ion rotation can be expressed in terms

Washington at Seattle, University of

277

Topology, magnetic field, and strongly interacting matter  

E-print Network

Gauge theories with compact symmetry groups possess topologically non-trivial configurations of gauge field. This has dramatic implications for the vacuum structure of Quantum Chromo-Dynamics (QCD) and for the behavior of QCD plasma, as well as for condensed matter systems with chiral quasiparticles. I review the current status of the problem with an emphasis on the interplay of chirality with a background magnetic field, and on the observable manifestations of topology in heavy ion collisions, Dirac semimetals, neutron stars, and in the Early Universe.

Dmitri E. Kharzeev

2015-01-06

278

Effect of strong magnetic fields on the pasta phase structure  

E-print Network

The effect of strong magnetic fields on the properties of the pasta structures is calculated within a Thomas Fermi approach using relativistic mean field models to modulate stellar matter. It is shown how quantities such as the size of the clusters and Wigner-Seitz cells, the surface tension and the transition between configurations are affected. It is expected that these effects may give rise to large stresses in the pasta phase if the local magnetic field suffers fluctuations.

Rafael Camargo Rodrigues de Lima; Sidney dos Santos Avancini; Constança Providência

2013-09-09

279

Magnetic Field Analysis of External Rotor Permanent-Magnet Synchronous Motors Using Conformal Mapping  

Microsoft Academic Search

This paper presents analytical and numerical conformal mapping (CM) to analyze magnetic fields originating from permanent magnets and armature winding currents in a slotted air-gap of a surface mounted radial permanent-magnet synchronous motor (SPM), taking into account the effect of arbitrarily curved motor surfaces. We also studied the slotless configuration of the external rotor permanent-magnet motor for the purpose of

Kamel Boughrara; Rachid Ibtiouen; Damir Zarko; Omar Touhami; Abderezzak Rezzoug

2010-01-01

280

Preprocessing Magnetic Fields with Chromospheric Longitudinal Fields  

NASA Astrophysics Data System (ADS)

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.; Kusano, K.

2012-06-01

281

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

282

Effect of AEM energy applicator configuration on magnetic nanoparticle mediated hyperthermia for breast cancer.  

PubMed

Magnetic nanoparticle mediated low heat hyperthermia (42~45( o )C) via alternating electromagnetic (AEM) energy is a promising, cancer specific and minimally-invasive cancer therapy. Iron oxide particles frequently used for this therapy are non-toxic and already used as a contrast agent for magnetic resonance imaging. One important issue in the hyperthermia is applying an appropriate amount of energy to the tumor at various sizes and depths, with a minimal damage to normal tissue. For the therapy to be desirable, the AEM energy applicator needs to be non-invasive and user-friendly. To better understand the effect of the probe on the magnetic field distribution, computer simulation was performed for the field distribution by probes with various configurations. In a solenoid-type probe, the field is mainly inside the probe and, therefore, is difficult to use on body. A pancake-shaped probe is easy to use but the field penetration is shallow and, thus, may better serve surface tumor treatment. A sandwich probe, composed of two pancake probes, has a penetration depth deeper than a pancake probe. The results also showed that the spacing between two adjacent coils and the number of coil turns are very important for controlling the field penetration depth and strength. Experiments were also performed to study the effects of the size and concentration of iron oxide nanoparticles on heating. Among the tested particle sizes of 10~50 nm, 30 nm particles showed the best heating for the same mass. PMID:21445781

Sanapala, Krishna K; Hewaparakrama, Kapila; Kang, Kyung A

2011-01-01

283

Magnetic Field Effects on Plasma Plumes  

NASA Technical Reports Server (NTRS)

Here, we will discuss our numerical studies of plasma jets and loops, of basic interest for plasma propulsion and plasma astrophysics. Space plasma propulsion systems require strong guiding magnetic fields known as magnetic nozzles to control plasma flow and produce thrust. Propulsion methods currently being developed that require magnetic nozzles include the VAriable Specific Impulse Magnetoplasma Rocket (VASIMR) [1] and magnetoplasmadynamic thrusters. Magnetic nozzles are functionally similar to de Laval nozzles, but are inherently more complex due to electromagnetic field interactions. The two crucial physical phenomenon are thrust production and plasma detachment. Thrust production encompasses the energy conversion within the nozzle and momentum transfer to a spacecraft. Plasma detachment through magnetic reconnection addresses the problem of the fluid separating efficiently from the magnetic field lines to produce maximum thrust. Plasma jets similar to those of VASIMR will be studied with particular interest in dual jet configurations, which begin as a plasma loops between two nozzles. This research strives to fulfill a need for computational study of these systems and should culminate with a greater understanding of the crucial physics of magnetic nozzles with dual jet plasma thrusters, as well as astrophysics problems such as magnetic reconnection and dynamics of coronal loops.[2] To study this problem a novel, hybrid kinetic theory and single fluid magnetohydrodynamic (MHD) solver known as the Magneto-Gas Kinetic Method is used.[3] The solver is comprised of a "hydrodynamic" portion based on the Gas Kinetic Method and a "magnetic" portion that accounts for the electromagnetic behaviour of the fluid through source terms based on the resistive MHD equations. This method is being further developed to include additional physics such as the Hall effect. Here, we will discuss the current level of code development, as well as numerical simulation results

Ebersohn, F.; Shebalin, J.; Girimaji, S.; Staack, D.

2012-01-01

284

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

285

The magnetic field of Neptune  

NASA Technical Reports Server (NTRS)

A model is given of the planetary magnetic field of Neptune based on a spherical harmonic analysis of the observations obtained by the Voyager 2. Generalized inverse techniques are used to partially solve a severely underdetermined inverse problem, and the resulting model is nonunique since the observations are limited in spatial distribution. Dipole, quadrupole, and octupole coefficients are estimated independently of other terms, and the parameters are shown to be well constrained by the measurement data. The large-scale features of the magnetic field including dipole tilt, offset, and harmonic content are found to characterize a magnetic field that is similar to that of Uranus. The traits of Neptune's magnetic field are theorized to relate to the 'ice' interior of the planet, and the dynamo-field generation reflects this poorly conducting planet.

Connerney, J. E. P.; Acuna, Mario H.; Ness, Norman F.

1992-01-01

286

Resonant magnetic fields from inflation  

SciTech Connect

We propose a novel scenario to generate primordial magnetic fields during inflation induced by an oscillating coupling of the electromagnetic field to the inflaton. This resonant mechanism has two key advantages over previous proposals. First of all, it generates a narrow band of magnetic fields at any required wavelength, thereby allaying the usual problem of a strongly blue spectrum and its associated backreaction. Secondly, it avoids the need for a strong coupling as the coupling is oscillating rather than growing or decaying exponentially. Despite these major advantages, we find that the backreaction is still far too large during inflation if the generated magnetic fields are required to have a strength of O(10{sup ?15} Gauss) today on observationally interesting scales. We provide a more general no-go argument, proving that this problem will apply to any model in which the magnetic fields are generated on subhorizon scales and freeze after horizon crossing.

Byrnes, Christian T. [CERN, PH-TH Division, CH-1211, Genève 23 (Switzerland); Hollenstein, Lukas; Jain, Rajeev Kumar [Département de Physique Théorique and Center for Astroparticle Physics, Université de Genève, 24, Quai Ernest Ansermet, CH-1211 Genève 4 (Switzerland); Urban, Federico R., E-mail: cbyrnes@cern.ch, E-mail: lukas.hollenstein@unige.ch, E-mail: rajeev.jain@unige.ch, E-mail: urban@phas.ubc.ca [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, B.C. V6T 1Z1 (Canada)

2012-03-01

287

Resonant magnetic fields from inflation  

E-print Network

We propose a novel scenario to generate primordial magnetic fields during inflation induced by an oscillating coupling of the electromagnetic field to the inflaton. This resonant mechanism has two key advantages over previous proposals. First of all, it generates a narrow band of magnetic fields at any required wavelength, thereby allaying the usual problem of a strongly blue spectrum and its associated backreaction. Secondly, it avoids the need for a strong coupling as the coupling is oscillating rather than growing or decaying exponentially. Despite these major advantages, we find that the backreaction is still far too large during inflation if the generated magnetic fields are required to have a strength of order 10^{-15} Gauss today on observationally interesting scales. We provide a more general no-go argument, proving that this problem will apply to any model in which the magnetic fields are generated on subhorizon scales and freeze after horizon crossing.

Christian T. Byrnes; Lukas Hollenstein; Rajeev Kumar Jain; Federico R. Urban

2012-03-06

288

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

SciTech Connect

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

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

2012-06-01

289

Impurity entanglement through electron scattering in a magnetic field  

E-print Network

We study the entanglement of magnetic impurities in an environment of electrons through successive scattering while an external magnetic field is applied. We show that the dynamics of the problem can be approximately described by a reduced model of three interacting spins, which reveals an intuitive view on how spins can be entangled by controlled electron scattering. The role of the magnetic field is rather crucial. Depending on the initial state configuration, the magnetic field can either increase or decrease the resulting entanglement but more importantly it can allow the impurities to be maximally entangled.

Alexandros Metavitsiadis; Raoul Dillenschneider; Sebastian Eggert

2013-12-30

290

Schrödinger operators with magnetic fields  

Microsoft Academic Search

We prove a large number of results about atoms in constant magnetic field including (i) Asymptotic formula for the ground state energy of Hydrogen in large field, (ii) Proof that the ground state of Hydrogen in an arbitrary constant field hasLz = 0 and of the monotonicity of the binding energy as a function ofB, (iii) Borel summability of Zeeman

J. E. Avron; I. W. Herbst; B. Simon

1981-01-01

291

Studying the magnetic fields of cool stars  

NASA Astrophysics Data System (ADS)

Magnetic fields are prevalent in a wide variety of low mass stellar systems and play an important role in their evolution. Yet the process through which these fields are generated is not well understood. To understand how such systems can generate strong field structures characterization of these fields is required. Radio emission traces the fields directly and the properties of this emission can be modeled leading to constraints on the field geometry and magnetic parameters. The new Karl Jansky Very Large Array (VLA) provides highly sensitive radio observations. My thesis involves combining VLA observations with the development of magnetospheric emission models in order to characterize the magnetic fields in two fully convective cool star systems: (1) Young Stellar Objects (YSOs); (2) Ultracool dwarf stars. I conducted multi epoch observations of DG Tau, a YSO with a highly active, collimated outflow. The radio emission observed from this source was found to be optically thick thermal emission with no indication of the magnetic activity observed in X-rays. I determined that the outflow is highly collimated very close to the central source, in agreement with jet launching models. Additionally, I constrained the mass loss of the ionized component of the jet and found that close to the central source the majority of mass is lost through this component. Using lower angular resolution observations, I detected shock formations in the extended jet of DG Tau and modeled their evolution with time. Taking full advantage of the upgraded bandwidth on the VLA, I made wideband observations of two UCDs, TVLM513-46 and 2M 0746+20. Combining these observations with previously published and archival VLA observations I was able to fully characterize the spectral and temporal properties of the radio emission. I found that the emission is dominated by a mildly polarized, non-thermal quiescent component with periodic strongly polarized flare emission. The spectral energy distribution and polarization of the quiescent emission is well modeled using gyrosynchrotron emission with a mean field B ˜100 G, mildly relativistic power-law electrons with a density ne ˜ 105-6 cm-3, and source size of R ˜ 2R*. We were able to model the pulsed emission by coherent electron cyclotron radiation from a small number of isolated loops of high magnetic field (2-3 kG) with scale heights˜1.2-2.7 stellar radii. The loops are well-separated in magnetic longitude, and are not part of a single dipolar magnetosphere. The overall magnetic configuration of both stars appears to confirm recent suggestions that radio over-luminous UCD's have `weak field' non-axisymmetric topologies, but with isolated regions of high magnetic field.

Lynch, Christene Rene

292

Investigating Magnetic Force Fields  

NSDL National Science Digital Library

In this classroom activity, the students will investigate the magnetic pull of a bar magnet at varying distances with the use of paper clips. Students will hypothesize, conduct the experiment, collect the data, and draw conclusions that support their data. Each student will record the experiment and their findings in their science journals. As a class, students will compare each groups' data and their interpretation of the results.

Daryl ("Tish") Monjeau, Bancroft Elementary School, Minneapolis, MN

2012-03-18

293

Preface: Cosmic magnetic fields  

NASA Astrophysics Data System (ADS)

Recent advances in observations and modeling have opened new perspectives for the understanding of fundamental dynamical processes of cosmic magnetism, and associated magnetic activity on the Sun, stars and galaxies. The goal of the Special Issue is to discuss the progress in solar physics and astrophysics, similarities and differences in phenomenology and physics of magnetic phenomena on the Sun and other stars. Space observatories, ground-based telescopes, and new observational methods have provided tremendous amount of data that need to be analyzed and understood. The solar observations discovered multi-scale organization of solar activity, dramatically changing current paradigms of solar variability. On the other side, stellar observations discovered new regimes of dynamics and magnetism that are different from the corresponding solar phenomena, but described by the same physics. Stars represent an astrophysical laboratory for studying the dynamical, magnetic and radiation processes across a broad range of stellar masses and ages. These studies allow us to look at the origin and evolution of our Sun, whereas detailed investigations of the solar magnetism give us a fundamental basis for interpretation and understanding of unresolved stellar data.

Kosovichev, Alexander

2015-02-01

294

The magnetic configuration of the high-latitude cusp and dayside magnetopause under strong magnetic shears  

NASA Astrophysics Data System (ADS)

This paper investigates the structure of the magnetic field near the magnetopause (MP) by analyzing the multiple-point magnetic measurements from the Cluster mission. In this paper, the spatial distribution of the curvature radius of the MP surface at the noon-midnight meridian and for situations with moderate dynamical pressure of solar wind is implied from direct measurements of magnetic field curvature for the first time. The investigation focused on conditions of strong magnetic shear and in which a clear boundary layer is present at the MP. It has been confirmed that the magnetic field lines surrounding the cusp bend sunward at the precusp region and tailward at the postcusp region, implying the existence of a cusp field indentation. The minimum curvature radius of the near-MP field at both precusp and postcusp regions is about 2 RE. As the latitude decreases, the curvature radius at the MP increases gradually, so that, as the subsolar point is approached, the curvature radius of the MP is nearly equal to the geocentric distance. These results compare well with existing MP models but reveal the limitations inherent in such statistical estimates of local MP curvature, particularly surrounding the cusp regions. The analysis of the magnetic measurements has also verified the existence of the magnetic bottles at both precusp and postcusp regions, which may play a role for the trapping of the charged particles of magnetosphere.

Shen, C.; Dunlop, M.; Ma, Y. H.; Chen, Z. Q.; Yan, G. Q.; Liu, Z. X.; Bogdanova, Y. V.; Sibeck, D. G.; Carr, C. M.; Zhang, Q. H.; Lucek, E.

2011-09-01

295

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

296

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

297

The ACE Magnetic Fields Experiment  

Microsoft Academic Search

The magnetic field experiment on ACE provides continuous measurements of the local magnetic field in the interplanetary medium.\\u000a These measurements are essential in the interpretation of simultaneous ACE observations of energetic and thermal particles\\u000a distributions. The experiment consists of a pair of twin, boom- mounted, triaxial fluxgate sensors which are located 165 inches\\u000a (=4.19 m) from the center of the

C. W. Smith; J. L'Heureux; N. F. Ness; M. H. Acuña; L. F. Burlaga; J. Scheifele

1998-01-01

298

Magnetic resonance in an elliptic magnetic field  

E-print Network

The behaviour of a particle with a spin 1/2 and a dipole magnetic moment in a time-varying magnetic field in the form $(h_0 cn(\\omega t,k), h_0 sn(\\omega t,k), H_0 dn(\\omega t,k))$, where $\\omega$ is the driving field frequency, $t$ is the time, $h_0$ and $H_0$ are the field amplitudes, $cn$, $sn$, $dn$ are Jacobi elliptic functions, $ k$ is the modulus of the elliptic functions has been considered. The variation parameter $k$ from zero to 1 gives rise to a wide set of functions from trigonometric shapes to exponential pulse shapes modulating the field. The problem was reduced to the solution of general Heun' equation. The exact solution of the wave function was found at resonance for any $ k$. It has been shown that the transition probability in this case does not depend on $k$. The present study may be useful for analysis interference experiments, improving magnetic spectrometers and the field of quantum computing.

E. A. Ivanchenko

2004-04-20

299

Magnetic Resonance Imaging System Based on Earth's Magnetic Field  

E-print Network

magnetic field can be partly compensated by the receiving coil design and shielding of electromagnetic pick magnetic fields. Common sources of static magnetic fields are super conducting coils, electromagnets, and permanent magnets. The induced magnetization, and thus the signal, is proportional to the magnitude

StepiÂ?nik, Janez

300

The magnetic field of Neptune  

NASA Technical Reports Server (NTRS)

The Voyager 2 observations obtained during the Neptune encounter are used to develop a spherical harmonic model of the planetary magnetic field of Neptune. The model yields a dipole of magnitude 0.14 G R(N) exp 3, tilted by 47 deg toward 72 deg west longitude. Neptune's quadrupole is equal to or exceeding in magnitude the surface dipole field; the octupole is also very large, although less well constrained. The characteristics of the Neptune's magnetic field are illustrated using contour maps of the field on the planet's surface.

Connerney, J. E. P.; Acuna, Mario H.; Ness, Norman F.

1991-01-01

301

The contrasting magnetic fields of superconducting pulsars and magnetars  

NASA Astrophysics Data System (ADS)

We study equilibrium magnetic field configurations in a neutron star (NS) whose core has type-II superconducting protons. Unlike the equations for normal matter, which feature no special field strength, those for superconductors contain the lower critical field, of the order of 1015 G. We find that the ratio of this critical field to the smooth-averaged stellar field at the crust-core boundary is the key feature dictating the field geometry. Our results suggest that pulsar- and magnetar-strength fields have notably different configurations. Field decay for NSs with Bpole ˜ 1014 G could thus result in substantial internal rearrangements, pushing the toroidal field component out of the core; this may be related to observed magnetar activity. In addition, we calculate the magnetically induced ellipticities of our models.

Lander, S. K.

2014-01-01

302

The generation and stability of magnetic fields in CP stars  

E-print Network

A variety of magnetohydrodynamic mechanisms that may play a role in magnetic, chemically peculiar (mCP) stars is reviewed. These involve dynamo mechanisms in laminar flows as well as turbulent environments, and magnetic instabilities of poloidal and toroidal fields as well as combinations of the two. While the proto-stellar phase makes the survival of primordial fields difficult, the variety of magnetic field configurations on mCP stars may be an indication for that they are instability remnants, but there is no process which is clearly superior in explaining the strong fields.

R. Arlt

2008-01-29

303

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

304

The magnetic field of Mercury  

NASA Technical Reports Server (NTRS)

The Mariner 10 spacecraft encountered Mercury three times in 1974-1975. The first and third encounters provided detailed observations of a well-developed detached bow shock wave which results from the interaction of the solar wind. The planet possesses a global magnetic field and a modest magnetosphere, which deflects the solar wind. The field is approximately dipolar, with orientation in the same sense as earth, tilted 12 deg from the rotation axis. The magnetic moment corresponds to an undistorted equatorial field intensity of 350 gammas, approximately 1% of earth's. The field, while unequivocally intrinsic to the planet, may be due to remanent magnetization acquired from an extinct dynamo or a primordial magnetic field or due to a presently active dynamo. The latter possibility appears more plausible at present. In any case, the existence of the magnetic field provides very strong evidence of a mature differentiated planetary interior with a large core (core radius about 0.7 Mercury radius) and a record of the history of planetary formation in the magnetization of the crustal rocks.

Ness, N. F.

1977-01-01

305

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

306

A model of the open magnetosphere. [with field configuration based on Chapman-Ferraro theory  

NASA Technical Reports Server (NTRS)

The Chapman-Ferraro image method is extended to construct an idealized model of the open magnetosphere that responds to a change of the interplanetary field direction as well as to a change of the field magnitude or of the solar wind momentum flux. The magnetopause of the present model is an infinite plane surface having a normal field component distribution that is consistent with the merging theory. An upper limit on the inward displacement of the magnetopause following a southward turning of the interplanetary field is obtained. The results are in fair agreement with a single event reported by Aubry et al. (1971). The model determines the field configuration and the total magnetic flux connecting the magnetosphere to interplanetary space.

Kan, J. R.; Akasofu, S.-I.

1974-01-01

307

Magnetic configurations of the tilted current sheets in magnetotail  

NASA Astrophysics Data System (ADS)

In this research, the geometrical structures of tilted current sheet and tail flapping waves have been analysed based on multiple spacecraft measurements and some features of the tilted current sheets have been made clear for the first time. The geometrical features of the tilted current sheet revealed in this investigation are as follows: (1) The magnetic field lines (MFLs) in the tilted current sheet are generally plane curves and the osculating planes in which the MFLs lie are about vertical to the equatorial plane, while the normal of the tilted current sheet leans severely to the dawn or dusk side. (2) The tilted current sheet may become very thin, the half thickness of its neutral sheet is generally much less than the minimum radius of the curvature of the MFLs. (3) In the neutral sheet, the field-aligned current density becomes very large and has a maximum value at the center of the current sheet. (4) In some cases, the current density is a bifurcated one, and the two humps of the current density often superpose two peaks in the gradient of magnetic strength, indicating that the magnetic gradient drift current is possibly responsible for the formation of the two humps of the current density in some tilted current sheets. Tilted current sheets often appear along with tail current sheet flapping waves. It is found that, in the tail flapping current sheets, the minimum curvature radius of the MFLs in the current sheet is rather large with values around 1 RE, while the neutral sheet may be very thin, with its half thickness being several tenths of RE. During the flapping waves, the current sheet is tilted substantially, and the maximum tilt angle is generally larger than 45°. The phase velocities of these flapping waves are several tens km/s, while their periods and wavelengths are several tens of minutes, and several earth radii, respectively. These tail flapping events generally last several hours and occur during quiet periods or periods of weak magnetospheric activity.

Shen, C.; Rong, Z. J.; Li, X.; Dunlop, M.; Liu, Z. X.; Malova, H. V.; Lucek, E.; Carr, C.

2008-11-01

308

Relationship between magnetic domain configuration and crystallographic orientation in a colossal magnetoresistive material.  

PubMed

We investigated the relationship between the magnetic domain (MD) configuration and crystallographic orientation in a colossal magnetoresistive (CMR) material La(0.69)Ca(0.31)MnO(3) in which anisotropic magnetoresistance (AMR) was observed as well. It was observed that the MD structure with a micrometre scale in the (001) plane collapses when a modulated structure with a nanometre scale emerges near the Curie temperature (T(c)). On the other hand, twin boundaries were observed to develop in the (110) plate, and they pin the MD walls. Like the pinning effect on MD walls, the emergence of vortex-like tadpole closure MDs upon the application of external magnetic field may be an origin of the AMR in La(0.69)Ca(0.31)MnO(3). PMID:20548105

Yu, Xiuzhen; Li, Run-Wei; Asaka, Toru; Ishizuka, Kazuo; Kimoto, Koji; Matsui, Yoshio

2010-08-01

309

Flux Transport and the Sun's Global Magnetic Field  

NASA Technical Reports Server (NTRS)

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

Hathaway, David H.

2010-01-01

310

Effect of magnetic field profile on the anode fall in a Hall-effect thruster dischargea...  

E-print Network

Effect of magnetic field profile on the anode fall in a Hall-effect thruster dischargea... L. Dorf of the magnetic field configuration on the anode fall in an E B discharge of a Hall thruster is studied both that the anode fall in a Hall thruster can be changed from negative to positive by creating a magnetic field

311

Magnetic Field Generation in Stars  

NASA Astrophysics Data System (ADS)

Enormous progress has been made on observing stellar magnetism in stars from the main sequence (particularly thanks to the MiMeS, MAGORI and BOB surveys) through to compact objects. Recent data have thrown into sharper relief the vexed question of the origin of stellar magnetic fields, which remains one of the main unanswered questions in astrophysics. In this chapter we review recent work in this area of research. In particular, we look at the fossil field hypothesis which links magnetism in compact stars to magnetism in main sequence and pre-main sequence stars and we consider why its feasibility has now been questioned particularly in the context of highly magnetic white dwarfs. We also review the fossil versus dynamo debate in the context of neutron stars and the roles played by key physical processes such as buoyancy, helicity, and superfluid turbulence, in the generation and stability of neutron star fields. Independent information on the internal magnetic field of neutron stars will come from future gravitational wave detections. Coherent searches for the Crab pulsar with the Laser Interferometer Gravitational Wave Observatory (LIGO) have already constrained its gravitational wave luminosity to be ?2 % of the observed spin-down luminosity, thus placing a limit of ?1016 G on the internal field. Indirect spin-down limits inferred from recycled pulsars also yield interesting gravitational-wave-related constraints. Thus we may be at the dawn of a new era of exciting discoveries in compact star magnetism driven by the opening of a new, non-electromagnetic observational window. We also review recent advances in the theory and computation of magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo theory. These advances offer insight into the action of stellar dynamos as well as processes which control the diffusive magnetic flux transport in stars.

Ferrario, Lilia; Melatos, Andrew; Zrake, Jonathan

2015-03-01

312

Cosmic Structure of Magnetic Fields  

E-print Network

The simulations of the formation of cosmological structure allows to determine the spatial inhomogeneity of cosmic magnetic fields. Such simulations, however, do not give an absolute number for the strength of the magnetic field due to insufficient spatial resolution. Combining these simulations with observations of the Rotation Measure to distant radio sources allows then to deduce upper limits for the strength of the magnetic field. These upper limits are of order 0.2 - 2 muG along the filaments and sheets of the galaxy distribution. In one case, the sheet outside the Coma cluster, there is a definitive estimate of the strength of the magnetic field consistent with this range. Such estimates are almost three orders of magnitude higher than hitherto assumed usually. High energy cosmic ray particles can be either focussed or strongly scattered in such magnetic filaments and sheets, depending on the initial transverse momentum. The cosmological background in radio and X-ray wavelengths will have contributions from these intergalactic filaments and sheets, should the magnetic fields really be as high as 0.2 - 2 muG.

Peter L. Biermann; Hyesung Kang; Joerg P. Rachen; Dongsu Ryu

1997-09-25

313

Comparison of the field configurations of the magnetotails of Uranus and Neptune  

NASA Technical Reports Server (NTRS)

The magnetic field configuration-states of the magnetotails of the planets Uranus and Neptune are compared. Earth's case is also briefly treated, as well as some related aspects of the other three magnetic planets. In Uranus' case, due to the large tilt (59 deg) of the planet's magnetic dipole with respect to its spin axis and the unusual obliquity of that axis, the angle of attack (alpha) of the solar wind with respect to dipole alignment goes through all possible angles, 0 deg to 180 deg, yielding a very broad spectrum of configuration-states of its tail. Cases are discussed where the planetary magnetic dipole is either aligned with the Sun-planet-line ('pole-on' state) or perpendicular to it and some intermediate states, for both Uranus and Neptune. Only Uranus experiences the pole-on state, which next occurs in November 1999 (+/- 2 months); last year (1993.2) it had the first 'perpendicular' state since Voyager encounter which resembles Earth's case. Neptune never has a pole-on configuration, but it gets as close as alpha = 14 deg from it; the next occurrence is early in 2003. At Voyager encounter Neptune's magnetotail apparently rapidly migrated through a broad spectrum of field structures with near extreme states resembling an Earth-like case on the one hand and a cylindrically symmetric one on the other. Magnetopause 'openness' should dramatically change in terms of the rapidly changing angle of attack throughout a planetary day for these two planets, and this has important implications for their magnetotails. Any future manetospheric mission plans for Uranus or Neptune should take in to consideration the allowed range of values for alpha for the epoch of interest; this is especially of concern for Uranus which has a pole-on state, and all possible alphas, around the middle of 2014, 20 years from now.

Lepping, R. P.

1994-01-01

314

Effect of magnetic configuration on frequency of NBI-driven Alfvén modes in TJ-II  

NASA Astrophysics Data System (ADS)

Excitation of modes in the Alfvénic frequency range, 30 kHz < fAE < 300 kHz, was observed in hydrogen plasma heated by hydrogen neutral beam injection (NBI) in the TJ-II heliac. Co-field and counter-field NBI were injected, and the components of the poloidal magnetic field were varied one by one and in combinations, in order to investigate the beam-driven modes over an extended range of the rotational transform values, 1.51<\\unicode{7548} (0)<1.67 . Taking advantage of the unique TJ-II capabilities, a dynamic magnetic configuration experiment with \\unicode{7548} (? , t) variation during discharges has shown strong effects on the mode frequency via both vacuum \\unicode{7548} changes and induced net plasma current. A drastic frequency increase from ˜50 to ˜250 kHz was observed for some modes when plasma current as low as ±2 kA was induced by small (10%) changes in the vertical field. A comprehensive set of diagnostics including a heavy ion beam probe, magnetic probes and a multi-chord bolometer made it possible to identify the spatial spread of the modes and deduce the internal amplitudes of their plasma density and magnetic field perturbations. A simple analytical model for fAE, based on the local Alfvén eigenmode (AE) dispersion relation, was proposed to characterize the observation. It was shown that all the observations, including vacuum iota and plasma current variations, may be fitted by the model, so the linear mode frequency dependence on \\unicode{7548} (plasma current) and one over square root density dependence present the major features of the NBI-induced AEs in TJ-II, and provide the framework for further experiment-to-theory comparison.

Melnikov, A. V.; Ochando, M.; Ascasibar, E.; Castejon, F.; Cappa, A.; Eliseev, L. G.; Hidalgo, C.; Krupnik, L. I.; Lopez-Fraguas, A.; Liniers, M.; Lysenko, S. E.; de Pablos, J. L.; Perfilov, S. V.; Sharapov, S. E.; Spong, D. A.; Jimenez, J. A.; Ufimtsev, M. V.; Breizman, B. N.; HIBP group; the TJ-II team

2014-12-01

315

Manipulation of magnetic state in nanostructures by perpendicular anisotropy and magnetic field  

SciTech Connect

We investigate the transitions of spin configurations in ultrathin nanostructures by tuning the perpendicular anisotropy (K{sub z}) and out-of-plane magnetic field (H), using the Monte Carlo simulation. It is revealed that enhancing the anisotropy K{sub z} can drive the evolution of in-plane vortex state into intriguing saturated magnetization states under various H, such as the bubble domain state and quadruple-block-domain state etc. The spin configurations of these states exhibit remarkable H-dependence. In addition, the strong effects of geometry and size on the spin configurations of nanostructures are observed. In particular, a series of edged states occur in the circular disk-shaped lattices, and rich intricate saturated magnetization patterns appear in big lattices. It is suggested that the magnetic states can be manipulated by varying the perpendicular anisotropy, magnetic field, and geometry/size of the nanostructures. Furthermore, the stability (retention capacity) of the saturated magnetization states upon varying magnetic field is predicted, suggesting the potential applications of these saturated magnetization states in magnetic field-controlled data storages.

Chen, J. P.; Xie, Y. L.; Chu, P.; Wang, Y. L. [Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Wang, Z. Q.; Gao, X. S. [Institute for Advanced Materials and Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006 (China); Liu, J.-M. [Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Institute for Advanced Materials and Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006 (China)

2014-06-28

316

The magnetic field of Uranus  

NASA Technical Reports Server (NTRS)

Aspherical harmonic model of the planetary magnetic field of Uranus is obtained from the Voyager 2 encounter observations using generalized inverse techniques which allow partial solutions to complex (underdetermined) problems. The Goddard Space Flight Center 'Q3' model is characterized by a large dipole tilt (58.6 deg) relative to the rotation axis, a dipole moment of 0.228 G R(Uranus radii cubed) and an unusually large quadrupole moment. Characteristics of this complex model magnetic field are illustrated using contour maps of the field on the planet's surface and discussed in the context of possible dynamo generation in the relatively poorly conducting 'ice' mantle.

Connerney, J. E. P.; Acuna, Mario H.; Ness, Norman F.

1987-01-01

317

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

318

Magnetic Fields in Molecular Clouds  

E-print Network

Magnetic fields are believed to play an important role in the evolution of molecular clouds, from their large scale structure to dense cores, protostellar envelopes, and protoplanetary disks. How important is unclear, and whether magnetic fields are the dominant force driving star formation at any scale is also unclear. In this review we examine the observational data which address these questions, with particular emphasis on high angular resolution observations. Unfortunately the data do not clarify the situation. It is clear that the fields are important, but to what degree we don't yet know. Observations to date have been limited by the sensitivity of available telescopes and instrumentation. In the future ALMA and the SKA in particular should provide great advances in observational studies of magnetic fields, and we discuss which observations are most desirable when they become available.

Tyler L. Bourke; Alyssa A. Goodman

2004-01-14

319

Modeling Earth's magnetic field variation  

NASA Astrophysics Data System (ADS)

Observations of the Earth's magnetic field taken at the Earth's surface and at satellite altitude have been combined to construct models of the geomagnetic field and its variation. Lesur et al. (2010) developed a kinematic reconstruction of core field changes that satisfied the frozen-flux constraint. By constraining the field evolution to be entirely due to advection of the magnetic field at the core surface it maintained the spatial complexity of the field morphology imposed by a satellite field model backward in time [Wardinski & Lesur,2012]. In this study we attempt a kinematic construction of future variation in Earth's magnetic field variation. Our approach, first seeks to identify typical time scales of the magnetic field and core surface flows present in decadal and millennial field and flow models. Therefore, the individual spherical harmonic coefficients are treated by methods of time series analysis. The second step employs stochastic modelling of the temporal variability of such spherical harmonic coefficients that represent the field and core surface flow. Difficulties arise due to the non-stationary behavior of the field and core surface flow. However, the broad behavior may consist of some homogeneity, which could be captured by a generalized stochastic model that calls for the d'th difference of the time series to be stationary (ARIMA-Model), or by detrending the coefficient time series. By computing stochastic models, we obtain two sets of field-forecasts, the first set is obtained from stochastic models of the Gauss coefficients. Here, first results suggest that secular variation on time scales shorter than 5 years behaves rather randomly and cannot be described sufficiently well by stochastic models. The second set is derived from forward modeling the secular variation using the diffusion-less induction equation (kinematic construction). This approach has not provide consistent results.

Wardinski, I.

2012-12-01

320

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

SciTech Connect

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

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

2012-05-15

321

LABORATORY V MAGNETIC FIELDS AND FORCES  

E-print Network

's technology. Magnets are used today to image parts of the body, to explore the mysteries of the human brain to combine magnets to change the magnetic field at any point. You must determine the map of the magnetic

Minnesota, University of

322

Field Reversed Configuration (FRC) injection and compression experiments  

NASA Astrophysics Data System (ADS)

Experiments on FRC injection into an imploding liner are described, both with and without the operation of the imploding liner. The use of an actual liner limits the FRC diagnostics to observing it entering the liner. For proper choice of operating parameters, guided by 2D-MHD simulations, interferometry, magnetic probe, and collimated light probe data indicate that the FRC enters the liner without leaving it. Other operating parameters result in the FRC entering the liner and bouncing out. Field exclusion lifetime, sufficient for injection and implosion-compression system testing, may need to be increased for better quality implosion-compression. Supported by DOE-OFES.

Degnan, J. H.; Delaney, R.; Domonkos, M.; Grabowski, C.; Lehr, F. M.; Robinson, P.; Ruden, E. L.; White, W.; Wood, H.; Gale, D.; Kostora, M.; Sommars, W.; Frese, M. H.; Frese, S. D.; Camacho, J. F.; Coffey, S. K.; Makhin, V.; Intrator, T. P.; Wurden, G. A.; Sears, J.; Turchi, P. J.; Siemon, R. E.; Fuelling, S.; Bauer, B. S.; Lynn, A. G.

2010-11-01

323

Field Reversed Configuration (FRC) formation and compression using liners  

NASA Astrophysics Data System (ADS)

AFRL and LANL are developing Magnetized Target Fusion (MTF) using the Shiva Star capacitor bank at AFRL to implode an Al liner containing an FRC to raise density and temperature. Experiments at LANL and AFRL explore FRC formation and translation. 2D-MHD calculations with MACH2 look at translation, capturing and compressing the FRC. Extended MHD examines FRC rotation. These guide the design of the compression experiments at AFRL. Field exclusion, interferometer, radiographic, radiation data, and 2D-MHD simulations will be presented. Supported by DOE-OFES.

Degnan, J. H.; Adamson, P.; Domonkos, M.; Ruden, E. L.; Grabowski, C.; Brown, D.; Gale, D.; Kostora, M.; Ralph, D.; Sommars, W.; Frese, M. H.; Frese, S. D.; Amdahl, D. J.; Camacho, J. F.; Coffey, S. K.; Intrator, T. P.; Wurden, G. A.; Hsu, S. C.; Sieck, P.; Turchi, P. J.; Waganaar, W. J.; Siemon, R. E.; Awe, T. J.; Lynn, A. G.; Roderick, N. F.

2008-11-01

324

Magnetic levitation configuration incorporating levitation, guidance and linear synchronous motor  

SciTech Connect

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

Coffey, H.T.

1992-12-31

325

Magnetic levitation configuration incorporating levitation, guidance and linear synchronous motor  

DOEpatents

A propulsion and suspension system for an inductive repulsion type magnetically levitated vehicle which is propelled and suspended by a system which includes propulsion windings which form a linear synchronous motor and conductive guideways, adjacent to the propulsion windings, where both combine to partially encircling the vehicle-borne superconducting magnets. A three phase power source is used with the linear synchronous motor to produce a traveling magnetic wave which in conjunction with the magnets propel the vehicle. The conductive guideway combines with the superconducting magnets to provide for vehicle levitation. 3 figures.

Coffey, H.T.

1993-10-19

326

Magnetic levitation configuration incorporating levitation, guidance and linear synchronous motor  

DOEpatents

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

Coffey, Howard T. (Darien, IL)

1993-01-01

327

Shear-induced inflation of coronal magnetic fields  

NASA Technical Reports Server (NTRS)

Using numerical models of force-free magnetic fields, the shearing of footprints in arcade geometries leading to an inflation of the coronal magnetic field was examined. For each of the shear profiles considered, all of the field lines become elevated compared with the potential field. This includes cases where the shear is concentrated well away from the arcade axis, such that B(sub z), the component of field parallel to the axis, increases outward to produce an inward B(sub z)squared/8 pi magnetic pressure gradient force. These results contrast with an earlier claim, shown to be incorrect, that field lines can sometimes become depressed as a result of shear. It is conjectured that an inflation of the entire field will always result from the shearing of simple arcade configurations. These results have implications for prominence formation, the interplanetary magnetic flux, and possibly also coronal holes.

Klimchuk, James A.

1989-01-01

328

Shear-induced inflation of coronal magnetic fields  

NASA Technical Reports Server (NTRS)

Using numerical models of force-free magnetic fields, the shearing of footprints in arcade geometries leading to an inflation of the coronal magnetic field was examined. For each of the shear profiles considered, all of the field lines become elevated compared with the potential field. This includes cases where the shear is concentrated well away from the arcade axis, such that B(sub z), the component of field parallel to the axis, increases outward to produce an inward B(sub z) squared/8 pi magnetic pressure gradient force. These results contrast with an earlier claim, shown to be incorrect, that field lines can sometimes become depressed as a result of shear. It is conjectured that an inflation of the entire field will always result from the shearing of simple arcade configurations. These results have implications for prominence formation, the interplanetary magnetic flux, and possibly also coronal holes.

Klimchuk, James A.

1990-01-01

329

First Simultaneous Detection of Moving Magnetic Features in Photospheric Intensity and Magnetic Field Data  

E-print Network

The formation and the temporal evolution of a bipolar moving magnetic feature (MMF) was studied with high spatial and temporal resolution. The photometric properties were observed with the New Solar Telescope at Big Bear Solar Observatory using a broadband TiO filter (705.7 nm), while the magnetic field was analyzed using the spectropolarimetric data obtained by Hinode. For the first time, we observed a bipolar MMF simultaneously in intensity images and magnetic field data, and studied the details of its structure. The vector magnetic field and the Doppler velocity of the MMF were also studied. A bipolar MMF having its positive polarity closer to the negative penumbra formed being accompanied by a bright, filamentary structure in the TiO data connecting the MMF and a dark penumbral filament. A fast downflow (polarity. The vector magnetic field obtained from the full Stokes inversion revealed that a bipolar MMF has a U-shaped magnetic field configuration. Our observation...

Lim, Eun-Kyung; Goode, Philip

2012-01-01

330

Magnetic field studies at jupiter by voyager 1: preliminary results.  

PubMed

Results obtained by the Goddard Space Flight Center magnetometers on Voyager 1 are described. These results concern the large-scale configuration of the Jovian bow shock and magnetopause, and the magnetic field in both the inner and outer magnetosphere. There is evidence that a magnetic tail extending away from the planet on the nightside is formed by the solar wind-Jovian field interaction. This is much like Earth's magnetosphere but is a new configuration for Jupiter's magnetosphere not previously considered from earlier Pioneer data. We report on the analysis and interpretation of magnetic field perturbations associated with intense electrical currents (approximately 5 x 10(6) amperes) flowing near or in the magnetic flux tube linking Jupiter with the satellite Jo and induced by the relative motion between Io and the corotating Jovian magnetosphere. These currents may be an important source of heating the ionosphere and interior of Io through Joule dissipation. PMID:17800435

Ness, N F; Acuna, M H; Lepping, R P; Burlaga, L F; Behannon, K W; Neubauer, F M

1979-06-01

331

Progress and Plans for plasma studies on the FRX-L Field Reversed Configuration experiment  

NASA Astrophysics Data System (ADS)

To demonstrate the physics basis for Magnetized Target Fusion, we have designed a Field Reversed Configuration (FRC) target plasma to ultimately be compressed within an imploding metal flux conserver. This high density FRC device, named FRX-L, is operating at Los Alamos as a compact theta-pinch formation FRC. It includes a 0.5 T bias field, 70 kV 250 kHz ringing pre-ionization, a slow cusp bank, and a 1.5 MA, 200 kJ main-theta-coil bank. We show new FRC data with plasma parameters (temperature and lifetime) at the desired MTF design points, while density and magnetic field strengths are a factor of 2-3 low, (although still very high compared to previous FRC plasmas). Diagnostics include multi-chord density, bolometry, and spectroscopy, along with end-on framing camera, and a host of external magnetic measurements. Improvements are planned which will increase the trapped flux in the FRC, (modifications of magnet coils, circuit elements, flux excluder plates, and timing), before translation experiments begin in the coming year. This work is supported by OFES, DoE contract W-7405-ENG-36.

Wurden, G. A.; Intrator, T. P.; Furno, I. G.; Hsu, S. C.; Park, J. Y.; Waganaar, W. J.; Zhang, S. Y.; Degnan, J. H.; Gale, D. G.; Grabowski, C.; Ruden, E. L.; Sommars, W.

2004-11-01

332

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

SciTech Connect

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

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

2010-01-15

333

Indoor localization using magnetic fields  

NASA Astrophysics Data System (ADS)

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

Pathapati Subbu, Kalyan Sasidhar

334

Black holes and magnetic fields  

E-print Network

Stationary axisymmetric magnetic fields are expelled from outer horizons of black holes as they become extremal. Extreme black holes exhibit Meissner effect also within exact Einstein--Maxwell theory and in string theories in higher dimensions. Since maximally rotating black holes are expected to be astrophysically most important, the expulsion of the magnetic flux from their horizons represents a potential threat to an electromagnetic mechanism launching the jets at the account of black-hole rotation.

J. Bicak; V. Karas; T. Ledvinka

2007-04-09

335

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

336

Generation of whistler waves by a rotating magnetic field source A. V. Karavaev,1,a  

E-print Network

discusses the generation of polarized whistler waves radiated from a rotating magnetic field source created- plications to a wide range of areas, such as fusion related field-reversed configuration,1,2 space propulsion

California at Los Angles, University of

337

Magnetic Resonance Imaging at Ultrahigh Fields  

PubMed Central

Since the introduction of 4 T human systems in three academic laboratories circa 1990, rapid progress in imaging and spectroscopy studies in humans at 4 T and animal model systems at 9.4 T have led to the introduction of 7 T and higher magnetic fields for human investigation at about the turn of the century. Work conducted on these platforms has demonstrated the existence of significant advantages in SNR and biological information content at these ultrahigh fields, as well as the presence of numerous challenges. Primary difference from lower fields is the deviation from the near field regime; at the frequencies corresponding to hydrogen resonance conditions at ultrahigh fields, the RF is characterized by attenuated traveling waves in the human body, which leads to image nonuniformities for a given sample-coil configuration because of interferences. These nonuniformities were considered detrimental to the progress of imaging at high field strengths. However, they are advantageous for parallel imaging for signal reception and parallel transmission, two critical technologies that account, to a large extend, for the success of ultrahigh fields. With these technologies, and improvements in instrumentation and imaging methods, ultra-high fields have provided unprecedented gains in imaging of brain function and anatomy, and started to make inroads into investigation of the human torso and extremities. As extensive as they are, these gains still constitute a prelude to what is to come given the increasingly larger effort committed to ultrahigh field research and development of ever better instrumentation and techniques. PMID:24686229

U?urbil, Kamil

2014-01-01

338

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.

339

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.

340

Magnetic Fields above the Surface of aSuperconductor with Internal Magnetism  

SciTech Connect

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

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

2007-06-26

341

Experimental and numerical understanding of localized spin wave mode behavior in broadly tunable spatially complex magnetic configurations  

NASA Astrophysics Data System (ADS)

Spin wave modes confined in a ferromagnetic film by the spatially inhomogeneous magnetic field generated by a scanned micromagnetic tip of a ferromagnetic resonance force microscope (FMRFM) enable microscopic imaging of the internal fields and spin dynamics in nanoscale magnetic devices. Here we report a detailed study of spin wave modes in a thin ferromagnetic film localized by magnetic field configurations frequently encountered in FMRFM experiments, including geometries in which the probe magnetic moment is both parallel and antiparallel to the applied uniform magnetic field. We demonstrate that characteristics of the localized modes, such as resonance field and confinement radius, can be broadly tuned by controlling the orientation of the applied field relative to the film plane. Micromagnetic simulations accurately reproduce our FMRFM spectra allowing quantitative understanding of the localized modes. Our results reveal a general method of generating tightly confined spin wave modes in various geometries with excellent spatial resolution that significantly facilitates the broad application of FMRFM. This paves the way to imaging of magnetic properties and spin wave dynamics in a variety of contexts for uncovering new physics of nanoscale spin excitations.

Du, Chunhui; Adur, Rohan; Wang, Hailong; Manuilov, Sergei A.; Yang, Fengyuan; Pelekhov, Denis V.; Hammel, P. Chris

2014-12-01

342

Origin of astrophysical magnetic fields.  

NASA Astrophysics Data System (ADS)

The standard model for the origin of magnetic fields observed in stars and galaxies is the ?-? dynamo, in which a feedback loop involving differential rotation and helical turbulence leads to exponential amplification of a large-scale field. Recently this model has been criticized on the grounds that the Lorentz forces associated with the buildup of small-scale fields by the turbulence prevents the turbulent diffusion of magnetic field that is an essential part of the model. The author discusses the consequences for cosmology if dynamo theory is wrong, and reviews recent criticisms from a new perspective. They suggest new calculations that can help to decide whether the theory is right or wrong.

Field, George B.

343

Interaction between a rotating electromagnetic field and a plasma contained in a strong constant magnetic field  

Microsoft Academic Search

The paper presents theoretical calculations and the results of experimental studies of the behaviour of a plasma contained in a strong constant magnetic field when a rotating high-frequency field of dipole configuration with frequency ? is superimposed upon it. It is shown that for ?ei > ? (where ?ei is the frequency of collisions between electrons and ions) the high-frequency

R. A. Demirkhanov; T. I. Gutkin; Yu. V. Kursanov; I. R. Yampolsky; Yu. N. Gubin; L. Ya. Malykh; S. N. Lozovsky

1972-01-01

344

Far infrared laser polarimetry and far forward scattering diagnostics for the C-2 field reversed configuration plasmas.  

PubMed

A two-chord far infrared (FIR) laser polarimeter for high speed sub-degree Faraday rotation measurements in the C-2 field reversed configuration experiment is described. It is based on high power proprietary FIR lasers with line width of about 330 Hz. The exceptionally low intrinsic instrument phase error is characterized with figures of merit. Significant toroidal magnetic field with rich dynamics is observed. Simultaneously obtained density fluctuation spectra by far forward scattering are presented. PMID:25430164

Deng, B H; Kinley, J S; Knapp, K; Feng, P; Martinez, R; Weixel, C; Armstrong, S; Hayashi, R; Longman, A; Mendoza, R; Gota, H; Tuszewski, M

2014-11-01

345

Far infrared laser polarimetry and far forward scattering diagnostics for the C-2 field reversed configuration plasmas  

NASA Astrophysics Data System (ADS)

A two-chord far infrared (FIR) laser polarimeter for high speed sub-degree Faraday rotation measurements in the C-2 field reversed configuration experiment is described. It is based on high power proprietary FIR lasers with line width of about 330 Hz. The exceptionally low intrinsic instrument phase error is characterized with figures of merit. Significant toroidal magnetic field with rich dynamics is observed. Simultaneously obtained density fluctuation spectra by far forward scattering are presented.

Deng, B. H.; Kinley, J. S.; Knapp, K.; Feng, P.; Martinez, R.; Weixel, C.; Armstrong, S.; Hayashi, R.; Longman, A.; Mendoza, R.; Gota, H.; Tuszewski, M.

2014-11-01

346

EXPLORER 10 MAGNETIC FIELD MEASUREMENTS  

Microsoft Academic Search

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

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

1963-01-01

347

Effects of magnetic fields on iron electrodeposition  

Microsoft Academic Search

The effects of magnetic fields (of 0–5 T magnetic flux density) on iron electrodeposition were investigated in terms of current efficiency, morphology and crystal orientation. The AFM images showed that the shape of iron grains was angular in no magnetic field and roundish in magnetic fields. The occurrence of preferred orientation parallel to the substrate plane was influenced by an

H. Matsushima; T. Nohira; I. Mogi; Y. Ito

2004-01-01

348

How to Draw Magnetic Fields - I  

NSDL National Science Digital Library

This is an activity about depicting magnetic fields. Learners will observe two provided drawings of magnetic field line patterns for bar magnets in simple orientations of like and unlike polarities and carefully draw the field lines for both orientations. This is the third activity in the Magnetic Math booklet; this booklet can be found on the Space Math@NASA website.

349

DIVERT: a divertor magnetic field line following code  

SciTech Connect

The computer code DIVERT has been written to trace magnetic field lines in the presence of a divertor. Its purpose is to allow a user to estimate the thickness of the plasma scrapeoff region and to provide a visual mapping of the magnetic field lines near the divertor. Included in the code is the capability to provide auxiliary graphics and compute the field ripple. The code can handle a divertor made up of any arrangement of straight line coil segments and will provide a graph of the field line configuration on output.

Morris, R N; Bateman, G

1980-05-01

350

Interplanetary Magnetic Field Guiding Relativistic Particles  

NASA Technical Reports Server (NTRS)

The origin and the propagation of relativistic solar particles (0.5 to few Ge V) in the interplanetary medium remains a debated topic. These relativistic particles, detected at the Earth by neutron monitors have been previously accelerated close to the Sun and are guided by the interplanetary magnetic field (IMF) lines, connecting the acceleration site and the Earth. Usually, the nominal Parker spiral is considered for ensuring the magnetic connection to the Earth. However, in most GLEs the IMF is highly disturbed, and the active regions associated to the GLEs are not always located close to the solar footprint of the nominal Parker spiral. A possible explanation is that relativistic particles are propagating in transient magnetic structures, such as Interplanetary Coronal Mass Ejections (ICMEs). In order to check this interpretation, we studied in detail the interplanetary medium where the particles propagate for 10 GLEs of the last solar cycle. Using the magnetic field and the plasma parameter measurements (ACE/MAG and ACE/SWEPAM), we found widely different IMF configurations. In an independent approach we develop and apply an improved method of the velocity dispersion analysis to energetic protons measured by SoHO/ERNE. We determined the effective path length and the solar release time of protons from these data and also combined them with the neutron monitor data. We found that in most of the GLEs, protons propagate in transient magnetic structures. Moreover, the comparison between the interplanetary magnetic structure and the interplanetary length suggest that the timing of particle arrival at Earth is dominantly determined by the type of IMF in which high energetic particles are propagating. Finally we find that these energetic protons are not significantly scattered during their transport to Earth.

Masson, S.; Demoulin, P.; Dasso, S.; Klein, K. L.

2011-01-01

351

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

352

Jupiter's magnetic field and magnetosphere  

NASA Technical Reports Server (NTRS)

Among the planets of the solar system, Jupiter is unique in connection with its size and its large magnetic moment, second only to the sun's. The Jovian magnetic field was first detected indirectly by radio astronomers who postulated its existence to explain observations of nonthermal radio emissions from Jupiter at decimetric and decametric wavelengths. Since the early radio astronomical studies of the Jovian magnetosphere, four spacecraft have flown by the planet at close distances and have provided in situ information about the geometry of the magnetic field and its strength. The Jovian magnetosphere is described in terms of three principal regions. The inner magnetosphere is the region where the magnetic field created by sources internal to the planet dominates. The region in which the equatorial currents flow is denoted as the middle magnetosphere. In the outer magnetosphere, the field has a large southward component and exhibits large temporal and/or spatial variations in magnitude and direction in response to changes in solar wind pressure.

Acuna, M. H.; Behannon, K. W.; Connerney, J. E. P.

1983-01-01

353

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

354

Dependence of effective internal field of congruent lithium niobate on its domain configuration and stability  

SciTech Connect

Congruent lithium niobate is characterized by its internal field, which arises due to defect clusters within the crystal. Here, it is shown experimentally that this internal field is a function of the molecular configuration in a particular domain and also on the stability of that particular configuration. The measurements of internal field are done using interferometric technique, while the variation of domain configuration is brought about by room temperature high voltage electric field poling.

Das, Ranjit, E-mail: ranjitdas.in@gmail.com, E-mail: souvik2cat@gmail.com, E-mail: srirajib@yahoo.com; Ghosh, Souvik, E-mail: ranjitdas.in@gmail.com, E-mail: souvik2cat@gmail.com, E-mail: srirajib@yahoo.com; Chakraborty, Rajib, E-mail: ranjitdas.in@gmail.com, E-mail: souvik2cat@gmail.com, E-mail: srirajib@yahoo.com [Department of Applied Optics and Photonics, University of Calcutta, JD-2, Sector III, Salt Lake, Kolkata 700098 (India)

2014-06-28

355

Fusion proton diagnostic for the C-2 field reversed configuration  

SciTech Connect

Measurements of the flux of fusion products from high temperature plasmas provide valuable insights into the ion energy distribution, as the fusion reaction rate is a very sensitive function of ion energy. In C-2, where field reversed configuration plasmas are formed by the collision of two compact toroids and partially sustained by high power neutral beam injection [M. Binderbauer et al., Phys. Rev. Lett. 105, 045003 (2010); M. Tuszewski et al., Phys. Rev. Lett. 108, 255008 (2012)], measurements of DD fusion neutron flux are used to diagnose ion temperature and study fast ion confinement and dynamics. In this paper, we will describe the development of a new 3 MeV proton detector that will complement existing neutron detectors. The detector is a large area (50?cm{sup 2}), partially depleted, ion implanted silicon diode operated in a pulse counting regime. While the scintillator-based neutron detectors allow for high time resolution measurements (?100 kHz), they have no spatial or energy resolution. The proton detector will provide 10 cm spatial resolution, allowing us to determine if the axial distribution of fast ions is consistent with classical fast ion theory or whether anomalous scattering mechanisms are active. We will describe in detail the diagnostic design and present initial data from a neutral beam test chamber.

Magee, R. M., E-mail: rmagee@trialphaenergy.com; Clary, R.; Korepanov, S.; Smirnov, A.; Garate, E.; Knapp, K. [Tri Alpha Energy, Inc., Rancho Santa Margarita, California 92688 (United States); Tkachev, A. [Budker Institute of Nuclear Physics, Novosibirsk (Russian Federation)

2014-11-15

356

Fusion proton diagnostic for the C-2 field reversed configuration.  

PubMed

Measurements of the flux of fusion products from high temperature plasmas provide valuable insights into the ion energy distribution, as the fusion reaction rate is a very sensitive function of ion energy. In C-2, where field reversed configuration plasmas are formed by the collision of two compact toroids and partially sustained by high power neutral beam injection [M. Binderbauer et al., Phys. Rev. Lett. 105, 045003 (2010); M. Tuszewski et al., Phys. Rev. Lett. 108, 255008 (2012)], measurements of DD fusion neutron flux are used to diagnose ion temperature and study fast ion confinement and dynamics. In this paper, we will describe the development of a new 3 MeV proton detector that will complement existing neutron detectors. The detector is a large area (50?cm(2)), partially depleted, ion implanted silicon diode operated in a pulse counting regime. While the scintillator-based neutron detectors allow for high time resolution measurements (?100 kHz), they have no spatial or energy resolution. The proton detector will provide 10 cm spatial resolution, allowing us to determine if the axial distribution of fast ions is consistent with classical fast ion theory or whether anomalous scattering mechanisms are active. We will describe in detail the diagnostic design and present initial data from a neutral beam test chamber. PMID:25430264

Magee, R M; Clary, R; Korepanov, S; Smirnov, A; Garate, E; Knapp, K; Tkachev, A

2014-11-01

357

The protostar merger scenario of Ap star magnetic field generation  

NASA Astrophysics Data System (ADS)

We propose that the small fraction of stars that are magnetic can be explained if, towards the end of the formation process, a correspondingly small fraction of stars merge after they have developed substantial radiative envelopes. Magnetic A stars may result from merging stars, and owe their strong magnetism to fields generated by a dynamo mechanism as they merge. We postulate a simple dynamo that generates magnetic field from differential rotation. We limit the growth of magnetic fields by the requirement that the poloidal field stabilizes the toroidal field and vice versa. While magnetic torques dissipate the differential rotation, toroidal field is generated from poloidal field by an ? dynamo. Both poloidal and toroidal fields reach a stable configuration that is independent of the size of small initial seed fields but proportional to the initial differential rotation. We posit the hypothesis that strongly magnetic stars form from the merging of two stellar objects. Highest fields are generated when the merger introduces differential rotation that amounts to its critical break up velocity within the condensed object. Such mergers can also account for the lack of close binaries among these stars.

Lau, H. H. B.; Tout, C. A.; Wickramasinghe, D.; Ferrario, L.

2014-11-01

358

A high-field superferric NMR magnet.  

PubMed

Strong, extensive magnetic fringe fields are a significant problem with magnetic resonance imaging magnets. This is particularly acute with 4-T, whole-body research magnets. To date this problem has been addressed by restricting an extensive zone around the unshielded magnet or by placing external unsaturated iron shielding around the magnet. This paper describes a solution to this problem which uses superconducting coils closely integrated with fully saturated iron elements. A 4-T, 30-cm-bore prototype, based on this design principle, was built and tested. The 5 G fringe field is contained within 1 meter of the magnet bore along the z axis. Homogeneity of the raw magnetic field is 10 ppm over 30% of the magnet's diameter after passive shimming. Compared with an unshielded magnet, 20% less superconductor is required to generate the magnetic field. Images and spectra are presented to demonstrate the magnet's viability for magnetic resonance imaging and spectroscopy. PMID:8419740

Huson, F R; Bryan, R N; MacKay, W W; Herrick, R C; Colvin, J; Ford, J J; Pissanetzky, S; Plishker, G A; Rocha, R; Schmidt, W

1993-01-01

359

Solar models with differential rotation and toroidal magnetic fields  

SciTech Connect

Solar models which could possibly solve the solar neutrino problem without incorporating neutrino oscillations are discussed. In particular it is found that is it possible to h ave solar models with rapid differential rotation and low surface oblateness, if one allows for the presence of strong toroidal magnetic fields with the proper configuration.

Talmadge, C.; Richter, S.; Fischbach, E.

1985-03-01

360

Recent magneto-inertial fusion experiments on the field reversed configuration heating experiment  

NASA Astrophysics Data System (ADS)

Magneto-inertial fusion (MIF) approaches take advantage of an embedded magnetic field to improve plasma energy confinement by reducing thermal conduction relative to conventional inertial confinement fusion (ICF). MIF reduces required precision in the implosion and the convergence ratio. Since 2008 (Wurden et al 2008 IAEA 2008 Fusion Energy Conf. (Geneva, Switzerland, 13-18 October) IC/P4-13 LA-UR-08-0796) and since our prior refereed publication on this topic (Degnan et al 2008 IEEE Trans. Plasma Sci. 36 80), AFRL and LANL have developed further one version of MIF. We have (1) reliably formed, translated, and captured field reversed configurations (FRCs) in magnetic mirrors inside metal shells or liners in preparation for subsequent compression by liner implosion; (2) imploded a liner with interior magnetic mirror field, obtaining evidence for compression of a 1.36 T field to 540 T (3) performed a full system experiment of FRC formation, translation, capture, and imploding liner compression operation; (4) identified by comparison of 2D-MHD simulation and experiments factors limiting the closed-field lifetime of FRCs to about half that required for good liner compression of FRCs to multi-keV, 1019 ion cm-3, high energy density plasma (HEDP) conditions; and (5) designed and prepared hardware to increase that closed-field FRC lifetime to the required amount. Those lifetime experiments are now underway, with the goal of at least doubling closed-field FRC lifetimes and performing FRC implosions to HEDP conditions this year. These experiments have obtained imaging evidence of FRC rotation, and of initial rotation control measures slowing and stopping such rotation. Important improvements in fidelity of simulation to experiment have been achieved, enabling improved guidance and understanding of experiment design and performance.

Degnan, J. H.; Amdahl, D. J.; Domonkos, M.; Lehr, F. M.; Grabowski, C.; Robinson, P. R.; Ruden, E. L.; White, W. M.; Wurden, G. A.; Intrator, T. P.; Sears, J.; Weber, T.; Waganaar, W. J.; Frese, M. H.; Frese, S. D.; Camacho, J. F.; Coffey, S. K.; Makhin, V.; Roderick, N. F.; Gale, D. G.; Kostora, M.; Lerma, A.; McCullough, J. L.; Sommars, W.; Kiuttu, G. F.; Bauer, B.; Fuelling, S. R.; Siemon, R. E.; Lynn, A. G.; Turchi, P. J.

2013-09-01

361

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

362

Magnetic fields in spiral galaxies  

NASA Astrophysics Data System (ADS)

The magnetic field structure in edge-on galaxies observed so far shows a plane-parallel magnetic field component in the disk of the galaxy and an X-shaped field in its halo. The plane-parallel field is thought to be the projected axisymmetric (ASS) disk field as observed in face-on galaxies. Some galaxies addionionally exhibit strong vertical magnetic fields in the halo right above and below the central region of the disk. The mean-field dynamo theory in the disk cannot explain these observed fields without the action of a wind, which also probably plays an important role to keep the vertical scale heights constant in galaxies of different Hubble types and star formation activities, as has been observed in the radio continuum: At ?6 cm the vertical scale heights of the thin disk and the thick disk/halo in a sample of five edge-on galaxies are similar with a mean value of 300 +/- 50 pc for the thin disk and 1.8 +/- 0.2 kpc for the thick disk (a table and references are given in Krause 2011) with our sample including the brightest halo observed so far, NGC 253, with strong star formation, as well as one of the weakest halos, NGC 4565, with weak star formation. If synchrotron emission is the dominant loss process of the relativistic electrons the outer shape of the radio emission should be dumbbell-like as has been observed in several edge-on galaxies like e.g. NGC 253 (Heesen et al. 2009) and NGC 4565. As the synchrotron lifetime t syn at a single frequency is proportional to the total magnetic field strength B t -1.5, a cosmic ray bulk speed (velocity of a galactic wind) can be defined as v CR = h CR /t syn = 2 h z /t syn , where h CR and h z are the scale heights of the cosmic rays and the observed radio emission at this freqnency. Similar observed radio scale heights imply a self regulation mechanism between the galactic wind velocity, the total magnetic field strength and the star formation rate SFR in the disk: v CR ~ B t 1.5 ~ SFR ~ 0.5 (Niklas & Beck 1997).

Krause, Marita

2015-03-01

363

Note: Manipulation of supersonic atomic beams with static magnetic fields  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

364

Slotless Permanent-Magnet Machines: General Analytical Magnetic Field Calculation  

Microsoft Academic Search

This paper presents a general analytical model for predicting the magnetic field of slotless permanent-magnet machines. The model takes into account the effect of eddy currents in conductive regions and notably in conductive permanent magnets without neglecting their remanent field. The modeling of this effect is important for the design of very high speed slotless permanent-magnet machines, as the power

Pierre-Daniel Pfister; Yves Perriard

2011-01-01

365

Cancellation of the ion deflection due to electron-suppression magnetic field in a negative-ion accelerator  

SciTech Connect

A new magnetic configuration is proposed for the suppression of co-extracted electrons in a negative-ion accelerator. This configuration is produced by an arrangement of permanent magnets embedded in one accelerator grid and creates an asymmetric local magnetic field on the upstream and downstream sides of this grid. Thanks to the “concentration” of the magnetic field on the upstream side of the grid, the resulting deflection of the ions due to magnetic field can be “intrinsically” cancelled by calibrating the configuration of permanent magnets. At the same time, the suppression of co-extracted electrons can be improved.

Chitarin, G., E-mail: chitarin@igi.cnr.it [Consorzio RFX, Association EURATOM-ENEA, Corso Stati Uniti 4, 35127 Padova (Italy); Dept. of Management and Engineering, University of Padova, Strad. S. Nicola 3, 36100 Vicenza (Italy); Agostinetti, P.; Aprile, D.; Marconato, N.; Veltri, P. [Consorzio RFX, Association EURATOM-ENEA, Corso Stati Uniti 4, 35127 Padova (Italy)] [Consorzio RFX, Association EURATOM-ENEA, Corso Stati Uniti 4, 35127 Padova (Italy)

2014-02-15

366

Cancellation of the ion deflection due to electron-suppression magnetic field in a negative-ion accelerator.  

PubMed

A new magnetic configuration is proposed for the suppression of co-extracted electrons in a negative-ion accelerator. This configuration is produced by an arrangement of permanent magnets embedded in one accelerator grid and creates an asymmetric local magnetic field on the upstream and downstream sides of this grid. Thanks to the "concentration" of the magnetic field on the upstream side of the grid, the resulting deflection of the ions due to magnetic field can be "intrinsically" cancelled by calibrating the configuration of permanent magnets. At the same time, the suppression of co-extracted electrons can be improved. PMID:24593594

Chitarin, G; Agostinetti, P; Aprile, D; Marconato, N; Veltri, P

2014-02-01

367

Uniform rotating field network structure to efficiently package a magnetic bubble domain memory  

NASA Technical Reports Server (NTRS)

A unique and compact open coil rotating magnetic field network structure to efficiently package an array of bubble domain devices is disclosed. The field network has a configuration which effectively enables selected bubble domain devices from the array to be driven in a vertical magnetic field and in an independent and uniform horizontal rotating magnetic field. The field network is suitably adapted to minimize undesirable inductance effects, improve capabilities of heat dissipation, and facilitate repair or replacement of a bubble device.

Wolfshagen, Ronald G. (Inventor); Ypma, John E. (Inventor); Murray, Glen W. (Inventor); Chen, Thomas T. (Inventor)

1978-01-01

368

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

369

Advances in high field magnetism at Osaka  

NASA Astrophysics Data System (ADS)

Recent advances in high field magnetism mainly done in the High Magnetic Field Laboratory, Osaka University, are reviewed. Various magnetic and electronic properties are induced in high fields; it is emphasized that the newly developed incommensurate mean field model is effective in understanding complex phase diagrams such as in CeSb, CeBi and PrCo 2Si 2.

Date, M.

1989-03-01

370

Current-induced switching of magnetic domains to a perpendicular configuration  

SciTech Connect

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

Waintal, X.; Brouwer, P. W.

2001-06-01

371

Transitions of magnetic configuration at the interface of exchange-coupled bilayers: TbFe/GdFe as a model system  

NASA Astrophysics Data System (ADS)

The magnetization profile that forms in the soft part of an exchange-coupled hard/soft bilayer submitted to a rotating in-plane magnetic field has been studied both theoretically and experimentally. The evolution of the stable magnetic configurations as a function of the field orientation has been determined from micromagnetic calculations, for varying strength of the rotating field. The anisotropic magnetoresistance associated with these configurations has been deduced and compared with experimental results obtained on a TbFe/GdFe ferrimagnetic bilayer. A good agreement is obtained between calculated and measured data, without any parameter adjustment. As the applied field is rotated, a twisted magnetization distribution of Bloch type develops in the soft GdFe layer. The simulations show the existence of several possible stable magnetic profiles. These differ either by the amount of magnetization twist only or by the amount of twist and the chirality of the profile. Transport measurements allow one to determine which configuration is actually adopted by the system and in what circumstances the system switches from one configuration to another. Two types of transition are identified. The first one is related to the existence of a hard axis of magnetization in the GdFe layer. The second one corresponds to a change of chirality of the wall.

Montaigne, F.; Mangin, S.; Henry, Y.

2003-04-01

372

LABORATORY V MAGNETIC FIELDS AND FORCES  

E-print Network

's technology. Magnets are used today to image parts of the body, to explore the mysteries of the human brain to combine magnets to change the magnetic field at any point. You decide to determine the form

Minnesota, University of

373

Comparison of different configurations of NbTi magnetic lenses  

NASA Astrophysics Data System (ADS)

Magnetic lenses are new devices that concentrate magnetic flux by using the diamagnetism of superconductors. Magnetic lenses of two types made from NbTi sheets were constructed; measurements were made on them and they were systematically studied. Type A was constructed by stacking NbTi rings that had identical outer diameters and increasing inner diameters to form a hollow cone. Each ring had a slit to suppress the circumference current. Three construction methods for type A were tested: the rings were stacked with their slits aligned but with no insulation between the rings (A-1), with their slits aligned and with insulation between the rings (A-2), and with their slits in different positions and with insulation between the rings (A-3). For type B, sheets were rolled into hollow cones. Three identical cones were stacked to form a lens (B-1) and a single cone was used as a reference lens (B-2). The lenses were assembled in a cryocooler-cooled cryostat with a NbTi magnet. The quenching behavior, concentration ratio, hysteresis, and decay behavior were measured. Because of its larger dimensions, type B had a larger concentration ratio (2.49 for B-1) than type A (1.87 for A-1). Both lenses (types A and B-1) were quenched when the concentrated flux density reached about 0.64 T. The results suggest that quenching was caused by the NbTi sheet itself.

Zhang, Z. Y.; Matsumoto, S.; Choi, S.; Teranishi, R.; Kiyoshi, T.

2011-10-01

374

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

SciTech Connect

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

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

2006-12-15

375

Quantitative estimates of magnetic field reconnection properties from electric and magnetic field measurements  

E-print Network

Quantitative estimates of magnetic field reconnection properties from electric and magnetic field there are positive electric field components tangential to the magnetopause and a magnetic field component normal to it. Because these three components are the smallest of the six electric and magnetic fields

California at Berkeley, University of

376

Non-Abelian fields in AdS4 spacetime: Axially symmetric, composite configurations  

NASA Astrophysics Data System (ADS)

We construct new finite-energy regular solutions in Einstein-Yang-Mills-SU(2) theory. They are static, axially symmetric and approach at infinity the anti-de Sitter spacetime background. These configurations are characterized by a pair of integers (m ,n ), where m is related to the polar angle and n to the azimuthal angle, being related to the known flat-space monopole-antimonopole chains and vortex rings. Generically, they describe composite configurations with several individual components, possessing a nonzero magnetic charge, even in the absence of a Higgs field. Such Yang-Mills configurations exist already in the probe limit, with the AdS geometry supplying the attractive force needed to balance the repulsive force of Yang-Mills gauge interactions. The gravitating solutions are constructed by numerically solving the elliptic Einstein-DeTurck-Yang-Mills equations. The variation of the gravitational coupling constant ? reveals the existence of two branches of gravitating solutions which bifurcate at some critical value of ? . The lower-energy branch connects to the solutions in the global AdS spacetime, while the upper branch is linked to the generalized Bartnik-McKinnon solutions in asymptotically flat spacetime. Also, a spherically symmetric, closed-form solution is found as a perturbation around the globally anti-de Sitter vacuum state.

Kichakova, Olga; Kunz, Jutta; Radu, Eugen; Shnir, Yasha

2014-12-01

377

Non-Abelian fields in AdS$_4$ spacetime: axially symmetric, composite configurations  

E-print Network

We construct new finite energy regular solutions in Einstein-Yang-Mills-SU(2) theory. They are static, axially symmetric and approach at infinity the anti-de Sitter spacetime background. These configurations are characterized by a pair of integers $(m, n)$, where $m$ is related to the polar angle and $n$ to the azimuthal angle, being related to the known flat space monopole-antimonopole chains and vortex rings. Generically, they describe composite configurations with several individual components, possesing a nonzero magnetic charge, even in the absence of a Higgs field. Such Yang-Mills configurations exist already in the probe limit, the AdS geometry supplying the attractive force needed to balance the repulsive force of Yang-Mills gauge interactions. The gravitating solutions are constructed by numerically solving the elliptic Einstein-DeTurck--Yang-Mills equations. The variation of the gravitational coupling constant $\\alpha$ reveals the existence of two branches of gravitating solutions which bifurcate at some critical value of $\\alpha$. The lower energy branch connects to the solutions in the global AdS spacetime, while the upper branch is linked to the generalized Bartnik-McKinnon solutions in asymptotically flat spacetime. Also, a spherically symmetric, closed form solution is found as a perturbation around the globally anti-de Sitter vacuum state.

Olga Kichakova; Jutta Kunz; Eugen Radu; Yasha Shnir

2014-09-05

378

CORRELATION OF MAGNETIC FIELDS AND ENERGETIC ELECTRONS ON THE IMP 1 SATELLITE  

Microsoft Academic Search

A study of simultaneous magnetic field and energetic particle records from the IMP 1 satellite on the dark side of the earth has shown several distinct correlations that can be understood as diamagnetic effects of charged particle populations. Depression of the mag- netic field in the closed magnetic field line configuration of the particle cusp region is ob- served on

K. A. ANDERSON; N. F. NESS

1966-01-01

379

Wormholes supported by the kink-like configuration of a scalar field  

E-print Network

We study the problem of existence of static spherically symmetric wormholes supported by the kink-like configuration of a scalar field. With this aim we consider a self-consistent, real, nonlinear, nonminimally coupled scalar field $\\phi$ in general relativity with the symmetry-breaking potential $V(\\phi)$ possessing two minima. We classify all possible field configurations ruling out those of them for which wormhole solutions are impossible. Field configurations admitting wormholes are investigated numerically. Such the configurations represent a spherical domain wall localized near the wormhole throat.

S. V. Sushkov; S. -W. Kim

2002-08-23

380

PLANT GROWTH UNDER STATIC MAGNETIC FIELD INFLUENCEê  

Microsoft Academic Search

Already germinated seeds of Zea mays were cultivated in the presence of static magnetic field in order to observe several biochemical changes and stimulation effect on plantlets growth. Magnetic treatment involved the application of five different values of magnetic induction of static magnetic field, ranging between 50 mT and 250 mT, during 14 days. In order to investigate the biochemical

M. RÃCUCIU; D. CREANGÃ; I. HORGA

2008-01-01

381

Configuration-dependent electronic and magnetic properties of graphene monolayers and nanoribbons functionalized with aryl groups  

SciTech Connect

Graphene monolayers functionalized with aryl groups exhibit configuration-dependent electronic and magnetic properties. The aryl groups were adsorbed in pairs of neighboring atoms in the same sublattice A (different sublattices) of graphene monolayers, denoted as the M{sub 2}{sup AA} (M{sub 2}{sup AB}) configuration. The M{sub 2}{sup AA} configuration behaved as a ferromagnetic semiconductor. The band gaps for the majority and minority bands were 1.1 eV and 1.2 eV, respectively. The M{sub 2}{sup AB} configuration behaved as a nonmagnetic semiconductor with a band gap of 0.8 eV. Each aryl group could induce 1 Bohr magneton (?{sub B}) into the molecule-graphene system. Armchair graphene nanoribbons (GNRs) exhibited the same configuration-dependent magnetic properties as the graphene monolayers. The net spin of the functionalized zigzag GNRs was mainly localized on the edges demonstrating an adsorption site-dependent magnetism. For the zigzag GNRs, both the M{sub 2}{sup AA} and M{sub 2}{sup AB} configurations possibly had a magnetic moment. Each aryl group could induce 1.5–3.5 ?{sub B} into the molecule-graphene system. There was a metal-to-insulator transition after adsorption of the aryl groups for the zigzag GNRs.

Tian, Xiaoqing, E-mail: xqtian2008@gmail.com; Gu, Juan [College of Physics and Technology, Shenzhen University, Shenzhen 518060, Guangdong (China)] [College of Physics and Technology, Shenzhen University, Shenzhen 518060, Guangdong (China); Xu, Jian-bin, E-mail: jbxu@ee.cuhk.edu.hk [Department of Electronic Engineering and Materials Science and Technology Research Center, The Chinese University of Hong Kong, Shatin, New Territories (Hong Kong)] [Department of Electronic Engineering and Materials Science and Technology Research Center, The Chinese University of Hong Kong, Shatin, New Territories (Hong Kong)

2014-01-28

382

Field-flow fractionation of nucleic acids and proteins under large-scale gradient magnetic fields  

NASA Astrophysics Data System (ADS)

For the purpose of developing techniques for separating biological macromolecules, the present study reports a magnetic chromatography system employing high performance liquid chromatography and superconducting magnets of 14 and 5T. We observed chromatograms of catalase and albumin, which were eluded from columns that were exposed to magnetic fields of up to 14T with a maximum gradient of 90T/m. Without the magnetic fields, the chromatograms of the macromolecules showed a clear peak, while the chromatograms changed to have separated peaks for the same molecules after exposure to gradient magnetic fields. When the chromatocolumn was placed so the magnetic forces were opposite to the direction of flow, the albumin molecules separated into two groups. In addition, the chromatograms of catalase exposed to the magnetic fields indicated that the retention times of the two kinds of magnetically separated catalase were relatively changed if the column-field configuration was changed. Probably, the balance of paramagnetism in the heme and diamagnetism in the protein controlled the transport velocity under the influence of the gradient magnetic fields. In addition, the transport velocity of DNA molecules in the flow with a high gradient magnetic field was observed using a time-resolved spectrophotometric system.

Iwasaka, M.

2007-05-01

383

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

384

Plasma stability in a dipole magnetic field  

E-print Network

The MHD and kinetic stability of an axially symmetric plasma, confined by a poloidal magnetic field with closed lines, is considered. In such a system the stabilizing effects of plasma compression and magnetic field ...

Simakov, Andrei N., 1974-

2001-01-01

385

Levitation performance of the magnetized bulk high- Tc superconducting magnet with different trapped fields  

NASA Astrophysics Data System (ADS)

To a high- Tc superconducting (HTS) maglev system which needs large levitation force density, the magnetized bulk high- Tc superconductor (HTSC) magnet is a good candidate because it can supply additional repulsive or attractive force above a permanent magnet guideway (PMG). Because the induced supercurrent within a magnetized bulk HTSC is the key parameter for the levitation performance, and it is sensitive to the magnetizing process and field, so the magnetized bulk HTSC magnets with different magnetizing processes had various levitation performances, not only the force magnitude, but also its force relaxation characteristics. Furthermore, the distribution and configuration of the induced supercurrent are also important factor to decide the levitation performance, especially the force relaxation characteristics. This article experimentally investigates the influences of different magnetizing processes and trapped fields on the levitation performance of a magnetized bulk HTSC magnet with smaller size than the magnetic inter-pole distance of PMG, and the obtained results are qualitatively analyzed by the Critical State Model. The test results and analyses of this article are useful for the suitable choice and optimal design of magnetized bulk HTSC magnets.

Liu, W.; Wang, J. S.; Liao, X. L.; Zheng, S. J.; Ma, G. T.; Zheng, J.; Wang, S. Y.

2011-03-01

386

Rotating copper plasmoid in external magnetic field  

SciTech Connect

Effect of nonuniform magnetic field on the expanding copper plasmoid in helium and argon gases using optical emission spectroscopy and fast imaging is presented. We report a peculiar oscillatory rotation of plasmoid in magnetic field and argon ambient. The temporal variation and appearance of the dip in the electron temperature show a direct evidence of the threading and expulsion of the magnetic field lines from the plasmoid. Rayleigh Taylor instability produced at the interface separating magnetic field and plasma is discussed.

Pandey, Pramod K.; Thareja, Raj K. [Department of Physics, Indian Institute of Technology Kanpur, Uttar Pradesh 208 016 (India)

2013-02-15

387

Minireview: Biological effects of magnetic fields  

SciTech Connect

The literature about the biological effects of magnetic fields is reviewed. The authors begin by discussing the weak and/or time variable fields, responsible for subtle changes in the circadian rhythms of superior animals, which are believed to be induced by same sort of resonant mechanism. The safety issues related with the strong magnetic fields and gradients generated by clinical NMR magnets are then considered. The last portion summarizes the debate about the biological effects of strong and uniform magnetic fields.

Villa, M.; Mustarelli, P. (Lab. NMR, Pavia (Italy)); Caprotti, M. (Fondazione Clinica del Lavoro, Pavia (Italy))

1991-01-01

388

Turbulent Fluctuations in TFTR Configurations with Reversed Magnetic Shear  

SciTech Connect

Turbulent fluctuations in plasmas with reversed magnetic shear have been investigated on the Tokamak Fusion Test Reactor. Under intense auxiliary heating, these plasmas are observed to bifurcate into two states with different transport properties. In the state with better confinement, it has been found that the level of fluctuations is very small throughout most of the region with negative shear. By contrast, the state with lower confinement is characterized by large bursts of fluctuations which suggest a competition between the driving and the suppression of turbulence. These results are consistent with the suppression of turbulence by the {ital E}{times}{ital B} velocity shear. {copyright} {ital 1996 The American Physical Society.}

Mazzucato, E.; Batha, S.H.; Beer, M.; Bell, M.; Bell, R.E.; Budny, R.V.; Bush, C.; Hahm, T.S.; Hammett, G.W.; Levinton, F.M.; Nazikian, R.; Park, H.; Rewoldt, G.; Schmidt, G.L.; Synakowski, E.J.; Tang, W.M.; Taylor, G.; Zarnstorff, M.C. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)] [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); [Fusion Physics and Technology, Torrance, California 90503 (United States); [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

1996-10-01

389

Magnetic field response sensor for conductive media  

NASA Technical Reports Server (NTRS)

A magnetic field response sensor comprises an inductor placed at a fixed separation distance from a conductive surface to address the low RF transmissivity of conductive surfaces. The minimum distance for separation is determined by the sensor response. The inductor should be separated from the conductive surface so that the response amplitude exceeds noise level by a recommended 10 dB. An embodiment for closed cavity measurements comprises a capacitor internal to said cavity and an inductor mounted external to the cavity and at a fixed distance from the cavity's wall. An additional embodiment includes a closed cavity configuration wherein multiple sensors and corresponding antenna are positioned inside the cavity, with the antenna and inductors maintained at a fixed distance from the cavity's wall.

Woodard, Stanley E. (Inventor); Taylor, Bryant Douglas (Inventor)

2010-01-01

390

Magnetic field response sensor for conductive media  

NASA Technical Reports Server (NTRS)

A magnetic field response sensor comprises an inductor placed at a fixed separation distance from a conductive surface to address the low RF transmissivity of conductive surfaces. The minimum distance for separation is determined by the sensor response. The inductor should be separated from the conductive surface so that the response amplitude exceeds noise level by a recommended 10 dB. An embodiment for closed cavity measurements comprises a capacitor internal to said cavity and an inductor mounted external to the cavity and at a fixed distance from the cavity's wall. An additional embodiment includes a closed cavity configuration wherein multiple sensors and corresponding antenna are positioned inside the cavity, with the antenna and inductors maintained at a fixed distance from the cavity's wall.

Woodard, Stanley E. (Inventor); Taylor, Bryant D. (Inventor)

2009-01-01

391

Magnetic Field Response Sensor For Conductive Media  

NASA Technical Reports Server (NTRS)

A magnetic field response sensor comprises an inductor placed at a fixed separation distance from a conductive surface to address the low RF transmissivity of conductive surfaces. The minimum distance for separation is determined by the sensor response. The inductor should be separated from the conductive surface so that the response amplitude exceeds noise level by a recommended 10 dB. An embodiment for closed cavity measurements comprises a capacitor internal to said cavity and an inductor mounted external to the cavity and at a fixed distance from the cavity s wall. An additional embodiment includes a closed cavity configuration wherein multiple sensors and corresponding antenna are positioned inside the cavity, with the antenna and inductors maintained at a fixed distance from the cavity s wall.

Woodard, Stanley E. (Inventor); Taylor, Bryant D. (Inventor)

2006-01-01

392

Magnetic monopole and the nature of the static magnetic field  

E-print Network

We investigate the factuality of the hypothetical magnetic monopole and the nature of the static magnetic field. It is shown from many aspects that the concept of the massive magnetic monopoles clearly is physically untrue. We argue that the static magnetic field of a bar magnet, in fact, is the static electric field of the periodically quasi-one-dimensional electric-dipole superlattice, which can be well established in some transition metals with the localized d-electron. This research may shed light on the perfect unification of magnetic and electrical phenomena.

Xiuqing Huang

2008-12-10

393

Anisotropy of magnetic emulsions induced by magnetic and electric fields  

E-print Network

The anisotropy of magnetic emulsions induced by simultaneously acting electric and magnetic fields is theoretically and experimentally investigated. Due to the anisotropy, the electric conductivity and magnetic permeability of a magnetic emulsion are no longer scalar coefficients, but are tensors. The electric conductivity and magnetic permeability tensors of sufficiently diluted emulsions in sufficiently weak electric and magnetic fields are found as functions of the electric and magnetic intensity vectors. The theoretically predicted induced anisotropy was verified experimentally. The experimental data are analyzed and compared with theoretical predictions. The results of the analysis and comparison are discussed.

Yury I. Dikansky; Alexander N. Tyatyushkin; Arthur R. Zakinyan

2011-09-10

394

Magnetic field re-arrangement after prominence eruption  

NASA Technical Reports Server (NTRS)

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

Kopp, R. A.; Poletto, G.

1986-01-01

395

Thermal relaxation of very small solar magnetic structures in intergranules: a process that produces kG magnetic field strengths  

E-print Network

The equilibrium configuration of very small magnetic fluxtubes in an intergranular environment automatically produces kG magnetic field strengths. We argue that such process takes place in the Sun and complements the convective collapse (CC), which is traditionally invoked to explain the formation of kG magnetic concentrations in the solar photosphere. In particular, it can concentrate the very weak magnetic fluxes revealed by the new IR spectro-polarimeters, for which the operation of the CC may have difficulty. As part of the argument, we show the existence of solar magnetic features of very weak fluxes yet concentrated magnetic fields (some 3 x 10^{16} Mx and 1500 G).

J. Sanchez Almeida

2001-03-26

396

Microwave Measurements of Coronal Magnetic Field  

NASA Astrophysics Data System (ADS)

Magnetic field measurements of the solar corona using microwave observation are reviewed. The solar corona is filled with highly ionised plasma and magnetic field. Moving charged particles interact with magnetic field due to Lorentz force. This results in gyration motion perpendicular to the magnetic field and free motion along the magnetic field. Circularly polarized electro-magnetic waves interact with gyrating electrons efficiently and the interaction depends on the sense of circular polarization (right-handed or left-handed). This is the reason why we can measure magnetic field strength through microwave observations. This process does not require complicated quantum physics but the classical treatment is enough. Hence the inversion of measured values to magnetic field strength is simpler than in the case of optical and infrared measurements. There are several methods to measure magnetic field strength through microwave observations. We can divide them into two categories: one is based on emission mechanisms and the other is based on wave propagation. In the case of emission mechanisms, thermal f-f emission, thermal gyro-resonance emission and non-thermal gyro-synchrotron emission can be used to measure magnetic field strength. In the case of wave propagation, polarization reversal due to propagation through quasi-transverse magnetic field region can be used. Examples of distribution of magnetic field strength in the solar corona measured by Nobeyama Radioheliograph will be presented.

Shibasaki, K.

2006-08-01

397

Characteristics of geometric distortion correction with increasing field-of-view in open-configuration MRI.  

PubMed

Open-configuration magnetic resonance imaging (MRI) systems are becoming increasingly desirable for musculoskeletal imaging and image-guided radiotherapy because of their non-claustrophobic configuration. However, geometric image distortion in large fields-of-view (FOV) due to field inhomogeneity and gradient nonlinearity hinders the practical applications of open-type MRI. We demonstrated the use of geometric distortion correction for increasing FOV in open MRI. Geometric distortion was modeled and corrected as a global polynomial function. The appropriate polynomial order was identified as the minimum difference between the coordinates of control points in the distorted MR image space and those predicted by polynomial modeling. The sixth order polynomial function was found to give the optimal value for geometric distortion correction. The area of maximum distortion was<1 pixel with an FOV of 285mm. The correction performance error was increased at most 1.2% and 2.9% for FOVs of 340mm and~400mm compared with the FOV of 285mm. In particular, unresolved distortion was generated by local deformation near the gradient coil center. PMID:24698340

Hong, Cheolpyo; Lee, Dong-Hoon; Han, Bong Soo

2014-07-01

398

Harmonic undulator radiations with constant magnetic field  

NASA Astrophysics Data System (ADS)

Harmonic undulators has been analysed in the presence of constant magnetic field along the direction of main undulator field. The spectrum modifications in harmonic undulator radiations and intensity degradation as a function of constant magnetic field magnitude at fundamental and third harmonics have been evaluated with a numerical integration method and generalised Bessel function. The role of harmonic field to overcome the intensity reduction due to constant magnetic field and energy spread in electron beam has also been demonstrated.

Jeevakhan, Hussain; Mishra, G.

2015-01-01

399

How to Draw Magnetic Fields - II  

NSDL National Science Digital Library

This is an activity about depicting magnetic polarity. Learners will observe several provided drawings of magnetic field line patterns for bar magnets in simple orientations of like and unlike polarities and carefully draw the field lines and depict the polarities for several orientations, including an arrangement of six magnetic poles. This is the fourth activity in the Magnetic Math booklet; this booklet can be found on the Space Math@NASA website.

2012-08-03

400

Observational Test of Coronal Magnetic Field Models I. Comparison with Potential Field Model  

E-print Network

Recent advances have made it possible to obtain two-dimensional line-of-sight magnetic field maps of the solar corona from spectropolarimetric observations of the Fe XIII 1075 nm forbidden coronal emission line. Together with the linear polarization measurements that map the azimuthal direction of the coronal magnetic field, these coronal vector magnetograms now allow for direct observational testing of theoretical coronal magnetic field models. This paper presents a study testing the validity of potential-field coronal magnetic field models. We constructed a theoretical coronal magnetic field model of active region AR 10582 observed by the SOLARC coronagraph in 2004 by a global potential field extrapolation of the synoptic map of Carrington Rotation 2014. Synthesized linear and circular polarization maps from thin layers of the coronal magnetic field model above the active region along the line of sight are compared with the observed maps. We found that reasonable agreement occurs from layers located just above the sunspot of AR 10582, near the plane of the sky. This result provides the first observational evidence that potential field extrapolation can yield a reasonable approximation of the magnetic field configuration of the solar corona for simple and stable active regions.

Yu Liu; Haosheng Lin

2008-05-16

401

Pull-in control due to Casimir forces using external magnetic fields  

E-print Network

We present a theoretical calculation of the pull-in control in capacitive micro switches actuated by Casimir forces, using external magnetic fields. The external magnetic fields induces an optical anisotropy due to the excitation of magneto plasmons, that reduces the Casimir force. The calculations are performed in the Voigt configuration, and the results show that as the magnetic field increases the system becomes more stable. The detachment length for a cantilever is also calculated for a cantilever, showing that it increases with increasing magnetic field. At the pull-in separation, the stiffness of the system decreases with increasing magnetic field.

R. Esquivel-Sirvent; M. A. Palomino-Ovando; G. H. Cocoletzi

2009-07-13

402

Generation and evolution of stable stellar magnetic fields in young A-type stars  

NASA Astrophysics Data System (ADS)

While the presence of magnetic fields on low-mass stars is attributed to a dynamo process that is primarily driven by convective motion, the existence of magnetic fields on intermediate-mass stars very probably has other explanations. This paper focuses on the generation of stable magnetic configurations at the early stages of stellar evolution, and presumes that the fields we detect are nearly constant in time. The convective processing of an initial magnetic field during the pre-main-sequence phase is studied in a very simple model star. Azimuthal magnetic fields are found to be typical remnants in the upcoming radiative envelope after convection has receded.

Arlt, R.

2014-11-01

403

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

404

Interaction Forces Between Multiple Bodies in a Magnetic Field  

NASA Technical Reports Server (NTRS)

Some of the results from experiments to determine the interaction forces between multiple bodies in a magnetic field are presented in this paper. It is shown how the force values and the force directions depend on the configuration of the bodies, their relative positions to each other, and the vector of the primary magnetic field. A number of efficient new automatic loading and assembly machines, as well as manipulators and robots, have been created based on the relationship between bodies and magnetic fields. A few of these patented magnetic devices are presented. The concepts involved open a new way to design universal grippers for robot and other kinds of mechanisms for the manipulation of objects. Some of these concepts can be used for space applications.

Joffe, Benjamin

1996-01-01

405

Ion flow measurements and plasma current analysis in the Irvine Field Reversed Configuration  

E-print Network

Ion flow measurements and plasma current analysis in the Irvine Field Reversed Configuration W. S indicate that there is an ion flow of 7 km/s in the Irvine Field Reversed Configuration. A charge the impurities and hydrogen, the dominant plasma ion species, it is concluded that the ions rotate

Heidbrink, William W.

406

Heat pulse propagation in chaotic three-dimensional magnetic fields  

NASA Astrophysics Data System (ADS)

Heat pulse propagation in three-dimensional chaotic magnetic fields is studied by solving numerically the parallel heat transport equation using a Lagrangian Green's function (LG) method. The LG method provides an efficient and accurate technique that circumvents known limitations of finite elements and finite difference methods. The main two problems addressed are (i) the dependence of the radial transport of heat pulses on the level of magnetic field stochasticity (controlled by the amplitude of the magnetic field perturbation, ?), and (ii) the role of reversed shear magnetic field configurations on heat pulse propagation. In all the cases considered there are no magnetic flux surfaces. However, the radial transport of heat pulses is observed to depend strongly on ? due to the presence of high-order magnetic islands and Cantori. These structures act as quasi-transport barriers which can actually preclude the radial penetration of heat pulses within physically relevant time scales. The dependence of the magnetic field connection length, ?B, on ? is studied in detail. Regions where ?B is large, correlate with regions where the radial propagation of the heat pulse slows down or stops. The decay rate of the temperature maximum, max(t), the time delay of the temperature response as function of the radius, ?, and the radial heat flux \\langle {{\\bit q}\\cdot {\\hat e}_\\psi} \\rangle , are also studied as functions of the magnetic field stochasticity and ?B. In all cases it is observed that the scaling of max with t transitions from sub-diffusive, max ˜ t-1/4, at short times (??t < 105) to a significantly slower, almost flat scaling at longer times (??t > 105). A strong dependence on ? is also observed on ? and \\langle {{\\bit q}\\cdot {\\hat e}_\\psi} \\rangle . Even in the case when there are no flux surfaces nor magnetic field islands, reversed shear magnetic field configurations exhibit unique transport properties. The radial propagation of heat pulses in fully chaotic fields considerably slows down in the shear reversal region and, as a result, the delay time of the temperature response in reversed shear configurations is about an order of magnitude longer than the one observed in monotonic q-profiles. The role of separatrix reconnection of resonant modes in the shear reversal region, and the role of shearless Cantori in the observed phenomena are also discussed.

del-Castillo-Negrete, Diego; Blazevski, Daniel

2014-06-01

407

Overview of C-2 field-reversed configuration experiment plasma diagnostics  

SciTech Connect

A comprehensive diagnostic suite for field-reversed configuration (FRC) plasmas has been developed and installed on the C-2 device at Tri Alpha Energy to investigate the dynamics of FRC formation as well as to understand key FRC physics properties, e.g., confinement and stability, throughout a discharge. C-2 is a unique, large compact-toroid merging device that produces FRC plasmas partially sustained for up to ?5 ms by neutral-beam (NB) injection and end-on plasma-guns for stability control. Fundamental C-2 FRC properties are diagnosed by magnetics, interferometry, Thomson scattering, spectroscopy, bolometry, reflectometry, and NB-related fast-ion/neutral diagnostics. These diagnostics (totaling >50 systems) are essential to support the primary goal of developing a deep understanding of NB-driven FRCs.

Gota, H., E-mail: hgota@trialphaenergy.com; Thompson, M. C.; Tuszewski, M.; Binderbauer, M. W. [Tri Alpha Energy, Inc., Rancho Santa Margarita, California 92688 (United States)

2014-11-15

408

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

SciTech Connect

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

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

2008-06-12

409

Overview of C-2 field-reversed configuration experiment plasma diagnosticsa)  

NASA Astrophysics Data System (ADS)

A comprehensive diagnostic suite for field-reversed configuration (FRC) plasmas has been developed and installed on the C-2 device at Tri Alpha Energy to investigate the dynamics of FRC formation as well as to understand key FRC physics properties, e.g., confinement and stability, throughout a discharge. C-2 is a unique, large compact-toroid merging device that produces FRC plasmas partially sustained for up to ˜5 ms by neutral-beam (NB) injection and end-on plasma-guns for stability control. Fundamental C-2 FRC properties are diagnosed by magnetics, interferometry, Thomson scattering, spectroscopy, bolometry, reflectometry, and NB-related fast-ion/neutral diagnostics. These diagnostics (totaling >50 systems) are essential to support the primary goal of developing a deep understanding of NB-driven FRCs.

Gota, H.; Thompson, M. C.; Tuszewski, M.; Binderbauer, M. W.

2014-11-01

410

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

SciTech Connect

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

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

2012-01-01

411

DC corona discharge ozone production enhanced by magnetic field  

NASA Astrophysics Data System (ADS)

We have studied the effect of a stationary magnetic field on the production of ozone from air at atmospheric pressure by a negative corona discharge in a cylindrical electrode configuration. We used a stainless steel hollow needle placed at the axis of the cylindrical discharge chamber as a cathode. The outer wall of the cylinder was used as an anode. The vector of magnetic induction was perpendicular to the vector of current density. We found that: (a) the magnetic field extends the current voltage range of the discharge; (b) for the discharge in the Trichel pulses regime and in the pulseless glow regime, the magnetic field has no substantial effect on the discharge voltage or on the concentration of ozone that is produced; (c) for the discharge in the filamentary streamer regime for a particular current, the magnetic field increases the discharge voltage and consequently an approximately 30% higher ozone concentration can be obtained; (d) the magnetic field does not substantially increase the maximum ozone production yield. A major advantage of using a magnetic field is that the increase in ozone concentration produced by the discharge can be obtained without additional energy requirements.

Pekárek, S.

2010-01-01

412

The Influence of the Interplanetary Magnetic Field (IMF) on Atmospheric Escape at Mars  

NASA Astrophysics Data System (ADS)

We present a study on the response of Mars’ atmosphere to changes in the interplanetary magnetic field (IMF) configuration, specifically with respect to the atmospheric escape rate via pick up ions and upcoming MAVEN observations.

Curry, S. M.; Luhmann, J. G.; Ma, Y.; Dong, C. F.; Brain, D. A.

2014-07-01

413

Magnetic field driven domain-wall propagation in magnetic nanowires  

SciTech Connect

The mechanism of magnetic field induced magnetic domain-wall (DW) propagation in a nanowire is revealed: A static DW cannot exist in a homogeneous magnetic nanowire when an external magnetic field is applied. Thus, a DW must vary with time under a static magnetic field. A moving DW must dissipate energy due to the Gilbert damping. As a result, the wire has to release its Zeeman energy through the DW propagation along the field direction. The DW propagation speed is proportional to the energy dissipation rate that is determined by the DW structure. The negative differential mobility in the intermediate field is due to the transition from high energy dissipation at low field to low energy dissipation at high field. For the field larger than the so-called Walker breakdown field, DW plane precesses around the wire, leading to the propagation speed oscillation.

Wang, X.R. [Physics Department, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong (China); Yan, P. [Physics Department, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong (China)], E-mail: yanpeng@ust.hk; Lu, J.; He, C. [Physics Department, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong (China)

2009-08-15

414

Magnetism  

NSDL National Science Digital Library

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

University Corporation for Atmospheric Research Windows to the Universe team

2007-12-12

415

Permanent Magnet Ecr Plasma Source With Magnetic Field Optimization  

DOEpatents

In a plasma-producing device, an optimized magnet field for electron cyclotron resonance plasma generation is provided by a shaped pole piece. The shaped pole piece adjusts spacing between the magnet and the resonance zone, creates a convex or concave resonance zone, and decreases stray fields between the resonance zone and the workpiece. For a cylindrical permanent magnet, the pole piece includes a disk adjacent the magnet together with an annular cylindrical sidewall structure axially aligned with the magnet and extending from the base around the permanent magnet. The pole piece directs magnetic field lines into the resonance zone, moving the resonance zone further from the face of the magnet. Additional permanent magnets or magnet arrays may be utilized to control field contours on a local scale. Rather than a permeable material, the sidewall structure may be composed of an annular cylindrical magnetic material having a polarity opposite that of the permanent magnet, creating convex regions in the resonance zone. An annular disk-shaped recurve section at the end of the sidewall structure forms magnetic mirrors keeping the plasma off the pole piece. A recurve section composed of magnetic material having a radial polarity forms convex regions and/or magnetic mirrors within the resonance zone.

Doughty, Frank C. (Plano, TX); Spencer, John E. (Plano, TX)

2000-12-19

416

Magnetic field and plasma wave observations in a plasma cloud at Venus  

Microsoft Academic Search

Pioneer Venus magnetic field and plasma wave data are examined in a particularly clear example of a plasma cloud above the Venus ionosphere. The magnetic configuration is suggestive of acceleration of the plasma cloud by magnetic tension. If the plasma is at rest at the subsolar point, it could be accelerated to approx.90 km\\/sec by the observed stress at the

C.T. Russell; J. G. Luhmann; R. C. Elphic; F. L. Scarf; L. H. Brace

1982-01-01

417

Switchable magnetic bottles and field gradients for particle traps Manuel Vogel Gerhard Birkl Wolfgang Quint  

E-print Network

Switchable magnetic bottles and field gradients for particle traps Manuel Vogel · Gerhard Birkl configurations which find applica- tion in these areas. In particular, we pursue the idea of a magnetic bottle of (switchable) magnetic bottles, in Penning traps (left), in M. Vogel (&) Á G. Birkl Á M. Wiesel Institut fu

Birkl, Gerhard

418

Effect of magnetic field profile on the anode fall in a Hall-effect thruster discharge  

SciTech Connect

The effect of the magnetic field configuration on the anode fall in an E-vectorxB-vector discharge of a Hall thruster is studied both experimentally and theoretically. Plasma potential, electron temperature, and plasma density in the near-anode region are measured with a biased probe in three configurations of the magnetic field. It is observed that the anode fall in a Hall thruster can be changed from negative to positive by creating a magnetic field configuration with a zero magnetic field region. Similar configurations are utilized in some advanced Hall thrusters, like an ATON thruster. Results of the measurements are employed to model a Hall thruster with different magnetic field configurations, including the one with a zero-field region. Different anode sheath regimes observed experimentally are used to set the boundary conditions for the quasineutral plasma. Numerical solutions obtained with a hydrodynamic quasi-one-dimensional model suggest that varying the magnetic field configuration affects the electron mobility both inside and outside the channel, as well as the plasma density distribution along the axis.

Dorf, L.; Raitses, Y.; Fisch, N.J. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

2006-05-15

419

Magnetic fluid flow phenomena in DC and rotating magnetic fields  

E-print Network

An investigation of magnetic fluid experiments and analysis is presented in three parts: a study of magnetic field induced torques in magnetorheological fluids, a characterization and quantitative measurement of properties ...

Rhodes, Scott E. (Scott Edward), 1981-

2004-01-01

420

Field Reversed Configuration (FRC) formation and compression using liners  

NASA Astrophysics Data System (ADS)

FRC capture, field and compression experiments all use 2 T guide and mirror fields established inside the liner. A 12 MA, 4.5 MJ discharge drive the liner implosion. The capture experiments use 3 capacitor discharges into a segmented theta coil surrounding the formation region to form a bias field, pre-ionize the deuterium gas, and provide the reverse field theta discharge which forms the FRC. Two cusp field discharges aid this. The guide and mirror fields enable translation and capture of the FRC. Diagnostics include field exclusion, interferometry, radiography, and radiation detection. Design and parameters are guided by MHD simulations. Supported by DOE-OFES.

Degnan, J. H.; Adamson, P.; Amdahl, D. J.; Delaney, R.; Domonkos, M.; Lehr, F. M.; Ruden, E. L.; Tucker, W.; White, W.; Grabowski, C.; Gale, D.; Kostora, M.; Parker, J.; Sommars, W.; Frese, M. H.; Frese, S. D.; Camacho, J. F.; Coffey, S. K.; Makhin, V.; Intrator, T. F.; Wurden, G. A.; Turchi, P. J.; Siemon, R. E.; Lynn, A. G.; Roderick, N. F.

2009-11-01

421

Behavior of the magnetic structures of the magnetic fluid film under tilted magnetic fields  

Microsoft Academic Search

The patterns of the magnetic structure of the magnetic fluid thin film under tilted magnetic fields were taken to investigate the behavior of magnetic structures. The tilted angle ? is the angle between the direction of applied magnetic field and the normal line of the film. In our previous work, a nearly perfect ordered hexagonal structure in magnetic fluid thin

H. C Yang; I. J Jang; H. E Horng; J. M Wu; Y. C Chiou; Chin-Yih Hong

1999-01-01

422

Behavior of the magnetic structures of the magnetic fluid film under tilted magnetic fields  

Microsoft Academic Search

The patterns of the magnetic structure of the magnetic fluid thin film under tilted magnetic fields were taken to investigate the behavior of magnetic structures. The tilted angle theta is the angle between the direction of applied magnetic field and the normal line of the film. In our previous work, a nearly perfect ordered hexagonal structure in magnetic fluid thin

H. C. Yang; I. J. Jang; H. E. Horng; J. M. Wu; Y. C. Chiou; Chin-Yih Hong

1999-01-01

423

Configuration-induced vortex motion in type-II superconducting films with periodic magnetic dot arrays  

NASA Astrophysics Data System (ADS)

Using the molecular dynamic method we investigate numerically the current driven vortex motion in a superconducting film with periodic arrays of both ferromagnetic (FM) and anti-parallel ferromagnetic (AFM) dots. The simulation results show that in the absence of thermal fluctuation the vortex motion is dominated by the configurations of the magnetic dot array. This guided vortex motion is only observed at the onset of the depinning of the interstitial vortices. Two guided vortex motion mechanisms are discussed in this work. For the AFM configuration the vortex motion is mainly originated by the existence of magnetic dots with opposite magnetized moments, while for the FM case it is mainly dependent on the degree of the condensed packing of the magnetic dot lattice constant.

Chen, Q. H.; Shi, D. Q.; Li, W. X.; Zhu, B. Y.; Moshchalkov, V. V.; Dou, S. X.

2014-06-01

424

Effects of static magnetic fields on nicotinic cholinergic receptor function.  

PubMed

Ligand-gated ion channel kinetics were studied in mammalian transfected cells encoding adult mouse muscle acetylcholine (ACh) receptors. We measured macroscopic and single-channel currents using the outside-out and cell-attached patch-clamp configurations. Cultured cells were exposed to moderate intensity inhomogeneous static magnetic fields up to 180 mT and measurements were performed for temperatures ranging from 5 to 50 °C. We found no significant changes in ACh-elicited macroscopic or single-channel currents. We observed the expected dependence in current decay constants with temperature, but negligible magnetic field influence on the channel's kinetics. PMID:21344459

Tolosa, María Fernanda; Bouzat, Cecilia; Cravero, Walter Rubén

2011-09-01

425

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

426

Transonic Flow Field Analysis for Wing-Fuselage Configurations  

NASA Technical Reports Server (NTRS)

A computational method for simulating the aerodynamics of wing-fuselage configurations at transonic speeds is developed. The finite difference scheme is characterized by a multiple embedded mesh system coupled with a modified or extended small disturbance flow equation. This approach permits a high degree of computational resolution in addition to coordinate system flexibility for treating complex realistic aircraft shapes. To augment the analysis method and permit applications to a wide range of practical engineering design problems, an arbitrary fuselage geometry modeling system is incorporated as well as methodology for computing wing viscous effects. Configuration drag is broken down into its friction, wave, and lift induced components. Typical computed results for isolated bodies, isolated wings, and wing-body combinations are presented. The results are correlated with experimental data. A computer code which employs this methodology is described.

Boppe, C. W.

1980-01-01

427

Particle acceleration and transport in a chaotic magnetic field  

NASA Astrophysics Data System (ADS)

Time-dependent chaotic magnetic field can arise from a simple asymmetric current wire-loop system (CWLS). Such simple CWLSs exist, for example, in solar flares. Indeed one can use an ensemble of such systems to model solar active region magnetic field [1,2]. Here we use test particle simulation to investigate particle transport and energization in such a time-dependent chaotic magnetic field, and through induction, a chaotic electric field. We first construct an ensemble of simple systems based on the estimated size and field strength of solar active region. By following the trajectories of single charged particles, we will examine how particle energy is changed. Diffusion coefficients in both real space and momentum space can be calculated as well as the average trapped time of the particles within chaotic field region. Particle energy spectrum as a function of time will be examined. [1] Dasgupta, B. and Abhay K. Ram, (2007) Chaotic magnetic fields due to asymmetric current configurations -application to cross field diffusion of particles in cosmic rays, (Presented at the 49th Annual Meeting of the DPP, APS, Abstract # BP8.00102) [2] G. Li, B. Dasgupta, G. Webb, and A. K. Ram, (2009) Particle Motion and Energization in a Chaotic Magnetic Field, AIP Conf. Proc. 1183, pp. 201-211; doi: http://dx.doi.org/10.1063/1.3266777

Li, X.; Li, G.; Dasgupta, B.

2012-12-01

428