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1

Understanding magnetic field reversal mechanisms in mesoscopic magnetic multilayer ring structures  

E-print Network

Patterned pseudo spin-valve rings show great promise for device applications due to their non-volatility and variety of stable magnetic states. However, the magnetic reversal of these elements under an applied field is ...

Ng, Bryan

2008-01-01

2

Externally controlled local magnetic field in a conducting mesoscopic ring coupled to a quantum wire  

NASA Astrophysics Data System (ADS)

In the present work, the possibility of regulating local magnetic field in a quantum ring is investigated theoretically. The ring is coupled to a quantum wire and subjected to an in-plane electric field. Under a finite bias voltage across the wire a net circulating current is established in the ring which produces a strong magnetic field at its centre. This magnetic field can be tuned externally in a wide range by regulating the in-plane electric field, and thus, our present system can be utilized to control magnetic field at a specific region. The feasibility of this quantum system in designing spin-based quantum devices is also analyzed.

Maiti, Santanu K.

2015-01-01

3

Detection of ground states in frustrated molecular rings by in-field local magnetization profiles  

NASA Astrophysics Data System (ADS)

It is demonstrated by means of exact numerical methods that the ground state of nine-membered frustrated homometallic chromium-based molecular rings with a single bond defect can be unambiguously determined by the in-field local magnetization profiles, which exhibit characteristic patterns. The strength of the coupling corresponding to the defect can be determined by both total and local magnetization measurements on single crystals with the field perpendicular to the ring. This approach is illustrated with a recently synthesized chromium ring Cr9Cl2, which is experimentally characterized by low-temperature magnetic measurements and analyzed by means of the microscopic quantum model. The strength of the coupling corresponding to the defect is estimated by fitting the magnetic susceptibility of a powder sample and independently confirmed from the experimental intersection point of total magnetization profiles preserving the typical values of the remaining parameters, which are well established for known chromium rings.

Antkowiak, M.; Koz?owski, P.; Kamieniarz, G.; Timco, G. A.; Tuna, F.; Winpenny, R. E. P.

2013-05-01

4

Magnetic-field decay of three interlocked flux rings with zero linking number  

SciTech Connect

The resistive decay of chains of three interlocked magnetic flux rings is considered. Depending on the relative orientation of the magnetic field in the three rings, the late-time decay can be either fast or slow. Thus, the qualitative degree of tangledness is less important than the actual value of the linking number or, equivalently, the net magnetic helicity. Our results do not suggest that invariants of higher order than that of the magnetic helicity need to be considered to characterize the decay of the field.

Del Sordo, Fabio; Candelaresi, Simon; Brandenburg, Axel [NORDITA, AlbaNova University Center, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden and Department of Astronomy, Stockholm University, SE 10691 Stockholm (Sweden)

2010-03-15

5

Radial magnetic field measurements with a Hall probe device in the muon (g-2) storage ring magnet at BNL  

Microsoft Academic Search

A Hall probe device has been built to measure the radial component of the magnetic field in the muon (g-2) storage ring at Brookhaven National Laboratory. The ultraprecise (g-2) magnet provides a dominantly vertical magnetic field of about 1.45T. In order to limit the vertical shift of the muon orbit, the average radial field component should be no more than

S. I. Redin; N. M. Ryskulov; G. V. Fedotovich; B. I. Khazin; G. M. Bunce; G. T. Danby; J. W. Jackson; W. M. Morse; R. Prigl; Y. K. Semertzidis; E. Efstathiadis; B. L. Roberts; A. Grossmann; K. Jungmann; G. zu Putlitz; P. von Walter; S. K. Dhawan; F. J. M. Farley; M. Grosse-Perdekamp; V. W. Hughes; D. Kawall

2001-01-01

6

Formation of field-reversed ion rings in a magnetized background plasma  

SciTech Connect

In typical field-reversed ion ring experiments, an intense annular ion beam is injected across a magnetic cusp into neutral gas immersed in a solenoidal magnetic field. In anticipation of a new experimental thrust to create strong field-reversed ion rings the beam evolution is investigated in a preformed background plasma on a time scale greater than an ion cyclotron period, using a new two and a half-dimensional (21/2-D) hybrid, particle-in-cell (PIC) code FIRE, in which the beam and background ions are treated as macro-particles and the electrons as a massless fluid. It is shown that under appropriate conditions axial beam bunching occurs in the downstream applied field and a compact field-reversed ring is formed. It is observed that the ring is reflected in a ramped magnetic field. Upon reflection its axial velocity is very much less than that expected from a single particle model due to the transfer of the mean axial momentum to the background ions. This increases the time available to apply a pulsed mirror for trapping the ring experimentally. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Omelchenko, Y.A.; Sudan, R.N. [Laboratory of Plasma Studies, Cornell University, Ithaca, New York 14853 (United States)] [Laboratory of Plasma Studies, Cornell University, Ithaca, New York 14853 (United States)

1995-07-01

7

Control of generation regimes of ring chip laser under the action of the stationary magnetic field  

SciTech Connect

We consider realisation of different generation regimes in an autonomous ring chip laser, which is a rather complicated problem. We offer and demonstrate a simple and effective method for controlling the radiation dynamics of a ring Nd:YAG chip laser when it is subjected to a stationary magnetic field producing both frequency and substantial amplitude nonreciprocities. The amplitude and frequency nonreciprocities of a ring cavity, arising under the action of this magnetic field, change when the magnet is moved with respect to the active element of the chip laser. Some self-modulation and stationary generation regimes as well as the regime of beatings and dynamic chaos regime are experimentally realised. Temporal and spectral characteristics of radiation are studied and conditions for the appearance of the generation regime are found. (control of laser radiation parameters)

Aulova, T V; Kravtsov, Nikolai V; Lariontsev, E G; Chekina, S N; Firsov, V V [D.V. Skobel'tsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)] [D.V. Skobel'tsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

2013-05-31

8

On the delayed gas breakdown in a ringing theta-pinch with bias magnetic field  

SciTech Connect

A single particle model and particle-in-cell simulations are used to elucidate the breakdown physics in a ringing theta-pinch with a bias magnetic field. Previous experimental results show that gas breakdown occurs when the bias magnetic field is nullified by the theta-pinch magnetic field. The analyses presented here agree with the experimental results and show that electron kinetic energy does not exceed the ionization threshold of deuterium until the net magnetic field is approximately zero. Despite the presence of a strong electric field, the gyromotion of electrons within the bias magnetic field prevents them from gaining energy necessary to ionize the gas. Parametric analysis of the peak electron energy as a function of the bias and pre-ionization magnetic fields reveals that: (1) when the bias magnetic field is Almost-Equal-To 97% of the pre-ionization magnetic field, peak electron energies are highly erratic resulting in poor overall ionization, and (2) full ionization with repeatable behavior requires a pre-ionization to bias magnetic field ratio of approximately 2 to 1 or higher.

Meeks, Warner C.; Rovey, Joshua L. [Mechanical and Aerospace Engineering, Missouri University of Science and Technology, Rolla, Missouri 65409-0050 (United States)

2012-05-15

9

GaAs (Ga, Al)As double quantum rings: confinement and magnetic field effects  

NASA Astrophysics Data System (ADS)

Here we address a theoretical study of concentric GaAs-(Ga, Al)As double quantum rings, under a magnetic field applied perpendicularly to the ring plane. Electron-hole transition energies are calculated as a function of the system geometry confinement, following a single-particle picture, neglecting interaction effects. We adopted an effective-mass approximation, within a hard potential model calculation, exactly solved by using confluent hypergeometric functions. A huge dependence on the barrier width value and on the external ring width of the Ga1-xAlxAs coupled rings is found for the transition energy values. The results show a high competition between geometric and magnetic-field confinement, leading to an increase of the electron-hole energies with the magnetic field, and a reducing behavior as the outer ring width is assumed to be larger. Our results are in quite good agreement with the experimental data by Mano et al (2005 Nano Lett. 5 425).

Culchac, F. J.; Porras-Montenegro, N.; Latgé, A.

2008-07-01

10

Magnetospheric environments of outer planet rings - influence of Saturn's axially symmetric magnetic field  

SciTech Connect

Saturn's main rings exist within a zone of negligible magnetospheric losses and surface alteration effects, substantially due to the solid-body absorption of inwardly diffusing magnetospheric particles. This process is presently shown to be especially efficient in the inner magnetosphere of Saturn, due to the near-axial symmetry of the planetary magnetic field relative to the equatorial rotation plane; under the assumption of comparable diffusion rates, the inward magnetospheric particle transport is far more inhibited in the inner Saturnian magnetosphere than in the same regions of Jupiter and Uranus, even when only rings of comparable widths and depths are considered. In light of this, ring particle surface exposure to the ion fluxes of the radiation belt remains a prepossessing rationale for low Uranian ring albedos. 86 references.

Hood, L.L.

1987-07-01

11

Magnetospheric environments of outer planet rings - Influence of Saturn's axially symmetric magnetic field  

NASA Technical Reports Server (NTRS)

Saturn's main rings exist within a zone of negligible magnetospheric losses and surface alteration effects, substantially due to the solid-body absorption of inwardly diffusing magnetospheric particles. This process is presently shown to be especially efficient in the inner magnetosphere of Saturn, due to the near-axial symmetry of the planetary magnetic field relative to the equatorial rotation plane; under the assumption of comparable diffusion rates, the inward magnetospheric particle transport is far more inhibited in the inner Saturnian magnetosphere than in the same regions of Jupiter and Uranus, even when only rings of comparable widths and depths are considered. In light of this, ring particle surface exposure to the ion fluxes of the radiation belt remains a prepossessing rationale for low Uranian ring albedos.

Hood, L. L.

1987-01-01

12

Spin-Peierls instabilities of antiferromagnetic rings in a magnetic field  

NASA Astrophysics Data System (ADS)

Motivated by the intriguing properties of magnetic molecular wheels at field-induced level crossings, we investigate the spin-Peierls instability of antiferromagnetic rings in a field by exact diagonalizations of a microscopic spin model coupled to the lattice via a distortion-dependent Dzyaloshinskii-Moriya interaction. We show that, beyond the unconditional instability at level crossings for infinitesimal magnetoelastic coupling, the model is characterized by a stronger tendency to distort at higher level crossings and by a dramatic angular dependence with very sharp torque anomalies when the field is almost in the plane of the ring. These predictions are shown to compare remarkably well with available torque and nuclear magnetic resonance data on CsFe8 .

Lante, Valeria; Rousochatzakis, Ioannis; Penc, Karlo; Waldmann, Oliver; Mila, Frédéric

2009-05-01

13

Magnet Falling Through Ring Model  

NSDL National Science Digital Library

The Magnet Falling Through Ring model shows the dynamics and the induced current when a magnet falls through a conducting ring. The current in the ring is computed by electromagnetic induction using to Faradayâs law and the induced emf is proportional to the negative of the rate of change of magnetic flux ?. The direction of the induced current is determined by Lenzâs law, the induced current produces magnetic field which tends to oppose the change in magnetic flux that induces such currents. The Magnet Falling Through Ring model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_mosem2_em_MagnetFallingThroughRing.jar file will run the program if Java is installed.

Franciscouembre

2010-09-03

14

Contactless Magnetic Slip Ring  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

15

Field reversed ion rings  

SciTech Connect

In typical field-reversed ion ring experiments, an intense annular ion beam is injected across a plasma-filled magnetic cusp region into a neutral gas immersed in a ramped solenoidal magnetic field. Assuming the characteristic ionization time is much shorter than the long ({ital t}{approx_gt}2{pi}/{Omega}{sub {ital i}}) beam evolution time scale, we investigate the formation of an ion ring in the background plasma followed by field reversal, using a 21/2-D hybrid, PIC code FIRE, in which the beam and background ions are treated as particles and the electrons as a massless fluid. We show that beam bunching and trapping occurs downstream in a ramped magnetic field for an appropriate set of experimental parameters. We find that a compact ion ring is formed and a large field reversal {zeta}={delta}{ital B}/{ital B}{approx_gt}1 on axis develops. We also observe significant deceleration of the ring on reflection due to the transfer of its axial momentum to the background ions, which creates favorable trapping conditions. {copyright} {ital 1995 American Institute of Physics.}

Sudan, R.N.; Omelchenko, Y.A. [Laboratory of Plasma Studies, Cornell University, Ithaca, New York 14853 (United States)

1995-09-01

16

Magnetic field control of the intraband optical absorption in two-dimensional quantum rings  

SciTech Connect

Linear and nonlinear optical absorption coefficients of the two-dimensional semiconductor ring in the perpendicular magnetic field B are calculated within independent electron approximation. Characteristic feature of the energy spectrum are crossings of the levels with adjacent nonpositive magnetic quantum numbers as the intensity B changes. It is shown that the absorption coefficient of the associated optical transition is drastically decreased at the fields corresponding to the crossing. Proposed model of the Volcano disc allows to get simple mathematical analytical results, which provide clear physical interpretation. An interplay between positive linear and intensity-dependent negative cubic absorption coefficients is discussed; in particular, critical light intensity at which additional resonances appear in the total absorption dependence on the light frequency is calculated as a function of the magnetic field and levels' broadening.

Olendski, O., E-mail: oolendski@ksu.edu.sa [King Abdullah Institute for Nanotechnology, King Saud University, P.O. Box 2454, Riyadh 11451 (Saudi Arabia); Barakat, T., E-mail: tbarakat@ksu.edu.sa [Department of Physics, King Saud University, P.O. Box 2454, Riyadh 11451 (Saudi Arabia)

2014-02-28

17

Prosthetic heart valves and annuloplasty rings: assessment of magnetic field interactions, heating, and artifacts at 1.5 Tesla.  

PubMed

The purpose of this study was to determine the magnetic resonance (MR) safety aspects and artifacts for three different heart valve prostheses and two different annuloplasty rings that have not been evaluated previously in association with the 1.5-T MR environment. Ex vivo testing was performed using previously described techniques for the evaluation of magnetic field interactions (deflection angle and torque), heating (gel-filled phantom and fluoroptic thermometry; 15 min of MR imaging at a whole body-averaged specific absorption rate of 1.2 W/kg), and artifacts (using T1-weighted, spin echo, and gradient echo pulse sequences). One heart valve prosthesis and one annuloplasty ring showed no magnetic field interactions. Two heart valve prostheses and one annuloplasty ring displayed relatively minor magnetic field interactions (i.e., deflection angle < or = 6 degrees, torque, +1). Heating was < or = 0.7 degrees C for the five different implants. Artifacts varied depending on the amount and type of metal used to make the implants. For the three heart valve prostheses and two annuloplasty rings, the lack of substantial magnetic field interactions and relatively minor hearing indicated that MR procedures may be conducted safetly in patients with these implants using MR systems operating with static magneticfields of 1.5 T or less. Notably, these findings essentially apply to 54 different heart valve prostheses and 37 different annuloplasty rings (i.e., based on the various models and sizes available for these implants). PMID:11777223

Shellock, F G

2001-01-01

18

Ion Rings for Magnetic Fusion  

SciTech Connect

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

Greenly, John, B.

2005-07-31

19

Magnetic remanent states and quasistatic switching behavior of Fe split-rings for spin field-effect-transistor applications  

E-print Network

The magnetic remanent states and switching behavior of Fe thin-film split-rings are investigated using magnetic force microscopy, magnetoresistance measurements, and micromagnetic simulations in order to assess their ...

Lee, J. H.

20

Electromagnetic field analysis of septum magnet for APS positron accumulator ring  

SciTech Connect

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

Yokoi, Toshiaki; Turner, L.R.

1995-07-01

21

Magnetic ring for stripping enhancement  

SciTech Connect

A ring designed to recycle ions through a stripping medium offers the possibility for increasing output of the desired charge state by up to 4x. This could be a very important component of a Radioactive Nuclear Beam Facility. In order for such a ring to work effectively it must satisfy certain design conditions. These include achromaticity at the stripper, a dispersed region for an extraction magnet, and a number of first and higher order optics constraints which are necessary to insure that the beam emittance is not degraded unduly by the ring. An example is given of a candidate design of a stripping ring.

Selph, F.

1992-10-01

22

Binding energy of hydrogen-like donor impurity and photoionization cross-section in InAs Pöschl–Teller quantum ring under applied magnetic field  

Microsoft Academic Search

Using the variational method and the effective mass approximation, we have studied the binding energy and the photoionization cross-section of a donor impurity in InAs Pöschl–Teller quantum rings under applied magnetic fields. This work reports the binding energy and the photoionization cross-section dependencies on the geometry of the structure, impurity positions, asymmetry of the confining potential, magnetic field, and incident

M. G. Barseghyan; Alireza Hakimyfard; Marwan Zuhair; C. A. Duque; A. A. Kirakosyan

2011-01-01

23

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

24

PHYSICAL REVIEW B 85, 155440 (2012) Magnetic fields effects on the electronic conduction properties of molecular ring structures  

E-print Network

PHYSICAL REVIEW B 85, 155440 (2012) Magnetic fields effects on the electronic conduction properties; published 20 April 2012) While mesoscopic conducting loops are sensitive to external magnetic fields. In this paper, we study the effect of magnetic field on electronic transport in molecular conduction junctions

Hod, Oded

25

Effects of geometry and impurities on quantum rings in magnetic fields RID D-3014-2009  

E-print Network

of the spectrum.2 We examine in this paper the energetics of circular, square-shaped, and impurity-doped two-dimensional #1;2D#2; quantum rings containing up to N#3;20 strongly interacting electrons. We shall focus on the measurable quantities...;1/2#2;#6;Te?#1;1/6#2;#6;V + O#1;#6;5#2; , #1;A3#2; where T = 1 2m#1; #1;2 1 2m#1; #5;#21;x2 + #21;y2#6;, #1; = p + eA#1;r#2; #1;A4#2; is the kinetic-energy operator. We have defined the local modified potential31,32 as V? = V + 148#6; 2#5;V,#5;T...

Aichinger, M.; Chin, Siu A.; Krotscheck, E.; Rasanen, E.

2006-01-01

26

Electromagnetic Field Analysis of Septum Magnet for APS Positron Accumulator Ring  

E-print Network

" Nonlinear characteristics of magnetic subst;mce " Single/plural electric circuits of septum current which enables us to: " Consider arbitrary electric circuits over different materials (Appendix A for Electric Circuit Evaluation For the investigation of the effect of electric circuit connectivity to stray

Kemner, Ken

27

Magnetic Fields  

NSDL National Science Digital Library

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

Stern, David

2005-01-04

28

Phonon confinement effect on the polaron states in a double quantum ring structure in the presence of electric and magnetic fields  

NASA Astrophysics Data System (ADS)

In the framework of effective mass approximation the polaron problem in double quantum ring structures in the presence of perpendicular electric and magnetic fields with taken into account the effect of phonon confinement is considered. We derived general expressions for the normalized eigenfunctions of the confined optical and interface optical phonon modes and the dispersion relation for interface optical phonons as well as electron-confined optical phonon and electron-interface optical phonon Fröhlich interaction Hamiltonians in the double quantum ring system. Results reveal that the electron-optical phonon coupling leads to the decrease of the electron ground state energy. We have shown that the polaron energy exhibits a pronounced local maximum (minimuum) in dependence on an electric (magnetic) field which corresponds to the sharp decrease (increase) of the polaronic contributions due to confined optical and interface optical phonon modes.

Yeranosyan, Mkrtich A.; Vartanian, Arshak L.; Shahbandari, Abbas; Kirakosyan, Albert A.

2015-01-01

29

Comparison of Simulated and Observed Ring Current Magnetic Field and Ion Fluxes and ENA Intensity during the 5 April 2010 Storm  

NASA Astrophysics Data System (ADS)

In this study we compare simulated and observed stormtime magnetic intensities, proton flux spectra and ENA intensity for the 5 April 2010 storm (minimum Dst ? -73 nT) to test how well self-consistent simulations can simultaneously reproduce these quantities. We simulate the ring current and plasma sheet using the magnetically and electrostatically self-consistent Rice Convection Model-Equilibrium (RCM-E) [Lemon et al., JGR, 2004] with a time-varying magnetopause driven by upstream solar wind and interplanetary magnetic field (IMF) conditions. We use ion temperatures inferred from TWINS energetic neutral atom (ENA) images and THEMIS/ESA and SST ion data, and proton densities from the empirical IMF-dependent model of Tsyganenko and Mukai [JGR, 2003] to guide our specification of the plasma sheet at 10 RE, our plasma boundary location in the RCM-E. The oxygen to proton density ratio at the plasma boundary is specified from the empirical Young et al. [JGR, 1982] study. We compare the simulated magnetic intensity with the magnetic intensity measured by magnetometers on the GOES satellites at geosynchronous (GEO) altitude (6.6 Earth radii) and on THEMIS satellites. The simulated and observed proton spectra (GOES-14/MAGPD) at GEO and global ENA intensity (TWINS 1 and 2) are compared. We discuss the response of the ring current magnetic field and ion flux distribution to expansions and compressions of the magnetosphere associated with the dynamic solar wind pressure for this storm event.

Chen, M. W.; Lemon, C.; Guild, T. B.; Schulz, M.; Lui, A.; Keesee, A. M.; Goldstein, J.; Rodriguez, J. V.

2011-12-01

30

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

NASA Technical Reports Server (NTRS)

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

Evans, L. C.

1973-01-01

31

Essential properties of a D2+ molecular complex confined in ring-like nanostructures under external probes: Magnetic field and hydrostatic pressure  

NASA Astrophysics Data System (ADS)

A rigorous adiabatic approximation is used to investigate the energy states of the singly ionized double-donors D2+ complex formed by the coupling of a conduction band electron and two donor centers in a quantum ring with rectangular cross-section. The effects of changing the relative position between the Coulombic centers and the quantum ring geometry parameters, as well as the influence of external probes such as applied magnetic fields and hydrostatic pressure, are particularly studied, highlighting the important contribution of the repulsive inter-center interaction. The suppression of the Aharonov-Bohm ground state oscillations associated with the localization of the electron by the fixed donors is discussed. Comparison between the essential properties of an actual hydrogen ion H2+ and those of the D2+ complex trapped within a quantum ring shows that the strong electron confinement substantially increases the D2+ stability effects.

R-Fulla, M.; Marín, J. H.; Gutiérrez, W.; Mora-Ramos, M. E.; Duque, C. A.

2014-03-01

32

Magnetic properties of small multi-layered rings  

E-print Network

Thin film rings can be an alternative geometry of magnetic memory cells, in which data bits are stored by the chirality of the flux-closed or 'vortex' state of the ring. The absence of the stray field in the vortex state ...

Jung, Wonjoon

2007-01-01

33

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

34

Frustrated magnetic vortices in a triad of permalloy rings: Magneto-optical Kerr effect, magnetic force microscopy, and micromagnetic simulations  

E-print Network

Frustrated magnetic vortices in a triad of permalloy rings: Magneto-optical Kerr effect, magnetic of magnetic vortices, leaving at least one ring in a magnetically frustrated state. The properties October 2005; published 28 March 2006 The field dependent magnetization of three mutually touching

Metlushko, Vitali

35

Fast superconducting magnetic field switch  

SciTech Connect

The superconducting magnetic switch or fast kicker magnet is employed with an electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater than the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles. Magnetic switches and particularly fast kicker magnets are used in the accelerator industry to quickly deflect particle beams into and out of various transport lines, storage rings, dumps, and specifically to differentially route individual bunches of particles from a train of bunches which are injected or ejected from a given ring.

Goren, Y.; Mahale, N.K.

1995-12-31

36

Magnetic Bloch oscillations in nanowire superlattice rings.  

PubMed

The recent growth of semiconductor nanowire superlattices encourages hope that Bloch-like oscillations in such structures formed into rings may soon be observed in the presence of a time-dependent magnetic flux threading the ring. These magnetic Bloch oscillations are a consequence of Faraday's law; the time-dependent flux produces an electromotive force around the ring, thus leading to the Bloch-like oscillations. In the spectroscopic domain, generalized Wannier-Stark states are found that are manifestations of the emf-induced localization of the states. PMID:15169431

Citrin, D S

2004-05-14

37

Magnetic record associated with tree ring density: Possible climate proxy  

PubMed Central

A magnetic signature of tree rings was tested as a potential paleo-climatic indicator. We examined wood from sequoia tree, located in Mountain Home State Forest, California, whose tree ring record spans over the period 600 – 1700 A.D. We measured low and high-field magnetic susceptibility, the natural remanent magnetization (NRM), saturation isothermal remanent magnetization (SIRM), and stability against thermal and alternating field (AF) demagnetization. Magnetic investigation of the 200 mm long sequoia material suggests that magnetic efficiency of natural remanence may be a sensitive paleoclimate indicator because it is substantially higher (in average >1%) during the Medieval Warm Epoch (700–1300 A.D.) than during the Little Ice Age (1300–1850 A.D.) where it is <1%. Diamagnetic behavior has been noted to be prevalent in regions with higher tree ring density. The mineralogical nature of the remanence carrier was not directly detected but maghemite is suggested due to low coercivity and absence of Verwey transition. Tree ring density, along with the wood's magnetic remanence efficiency, records the Little Ice Age (LIA) well documented in Europe. Such a record suggests that the European LIA was a global phenomenon. Magnetic analysis of the thermal stability reveals the blocking temperatures near 200 degree C. This phenomenon suggests that the remanent component in this tree may be thermal in origin and was controlled by local thermal condition. PMID:17381844

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

2007-01-01

38

BNL superconducting storage ring magnet update  

Microsoft Academic Search

This report updates the various performance data, design and specifications for the storage ring and experimental series dipole and quadrupole magnets as well as the working line and correction coil systems. The working line system includes the closed orbit dipoles, the quadrupole trim, sextupoles, octapoles, decapoles and duodecapoles. These are the magnets in the standard subunits of the Brookhaven National

A. McInturff; E. Bleser; P. Dahl; J. Kaugerts; K. Robins; W. Sampson

1979-01-01

39

Magnet design for a low-emittance storage ring  

PubMed Central

The MAX?IV 3?GeV storage ring, currently under construction, pursues the goal of low electron beam emittance by using a multi-bend achromat magnet lattice, which is realised by having several consecutive magnet elements precision-machined out of a common solid iron block, 2.3–3.4?m long. With this magnet design solution, instead of having 1320 individual magnets, the MAX?IV 3?GeV storage ring is built up using 140 integrated ‘magnet block’ units, containing all these magnet elements. Major features of this magnet block design are compactness, vibration stability and that the alignment of magnet elements within each unit is given by the mechanical accuracy of the CNC machining rather than individual field measurement and adjustment. This article presents practical engineering details of implementing this magnet design solution, and mechanical + magnetic field measurement results from the magnet production series. At the time of writing (spring 2014), the production series, which is totally outsourced to industry, is roughly half way through, with mechanical/magnetic QA conforming to specifications. It is the conclusion of the authors that the MAX?IV magnet block concept, which has sometimes been described as new or innovative, is from a manufacturing point of view simply a collection of known mature production methods and measurement procedures, which can be executed at fixed cost with a low level of risk. PMID:25177980

Johansson, Martin; Anderberg, Bengt; Lindgren, Lars-Johan

2014-01-01

40

Magnet design for a low-emittance storage ring.  

PubMed

The MAX?IV 3?GeV storage ring, currently under construction, pursues the goal of low electron beam emittance by using a multi-bend achromat magnet lattice, which is realised by having several consecutive magnet elements precision-machined out of a common solid iron block, 2.3-3.4?m long. With this magnet design solution, instead of having 1320 individual magnets, the MAX?IV 3?GeV storage ring is built up using 140 integrated `magnet block' units, containing all these magnet elements. Major features of this magnet block design are compactness, vibration stability and that the alignment of magnet elements within each unit is given by the mechanical accuracy of the CNC machining rather than individual field measurement and adjustment. This article presents practical engineering details of implementing this magnet design solution, and mechanical + magnetic field measurement results from the magnet production series. At the time of writing (spring 2014), the production series, which is totally outsourced to industry, is roughly half way through, with mechanical/magnetic QA conforming to specifications. It is the conclusion of the authors that the MAX?IV magnet block concept, which has sometimes been described as new or innovative, is from a manufacturing point of view simply a collection of known mature production methods and measurement procedures, which can be executed at fixed cost with a low level of risk. PMID:25177980

Johansson, Martin; Anderberg, Bengt; Lindgren, Lars Johan

2014-09-01

41

Magnet designs for muon collider ring and interactions regions  

SciTech Connect

Conceptual designs of superconducting magnets for the storage ring of a Muon Collider with a 1.5 TeV c.o.m. energy and an average luminosity of 10{sup 34} cm{sup -2}s{sup -1} are presented. All magnets are based on Nb{sub 3}Sn superconductor and designed to provide an adequate operating field/field gradient in the aperture with the critical current margin required for reliable magnet operation in the machine. Magnet cross-sections were optimized to achieve the accelerator field quality in the magnet aperture occupied with beams. The magnets and corresponding protective measures are designed to handle about 0.5 kW/m of dynamic heat load from the muon beam decays. Magnet parameters are reported and compared with the requirements.

Zlobin, A.V.; Alexahin, Y.I.; Kashikhin, V.V.; Mokhov, N.V.; /Fermilab

2010-05-01

42

Statistical analyses of the magnet data for the advanced photon source storage ring magnets  

SciTech Connect

The statistics of the measured magnetic data of 80 dipole, 400 quadrupole, and 280 sextupole magnets of conventional resistive designs for the APS storage ring is summarized. In order to accommodate the vacuum chamber, the curved dipole has a C-type cross section and the quadrupole and sextupole cross sections have 180{degrees} and 120{degrees} symmetries, respectively. The data statistics include the integrated main fields, multipole coefficients, magnetic and mechanical axes, and roll angles of the main fields. The average and rms values of the measured magnet data meet the storage ring requirements.

Kim, S.H.; Carnegie, D.W.; Doose, C.; Hogrefe, R.; Kim, K.; Merl, R.

1995-05-01

43

Condenser for illuminating a ring field  

DOEpatents

A series of segments of a parent aspheric mirror having one foci at at a si-point source of radiation and the other foci at the radius of a ring field have all but one or all of their beams translated and rotated by sets of mirrors such that all of the beams pass through the real entrance pupil of a ring field camera about one of the beams and fall onto the ring field radius as a coincident image as an arc of the ring field.

Sweatt, William C. (Albuquerque, NM)

1994-01-01

44

Condenser for illuminating a ring field  

DOEpatents

A series of segments of a parent aspheric mirror having one foci at a point source of radiation and the other foci at the radius of a ring field have all but one or all of their beams translated and rotated by sets of mirrors such that all of the beams pass through the real entrance pupil of a ring field camera about one of the beams and fall onto the ring field radius as a coincident image as an arc of the ring field. 5 figs.

Sweatt, W.C.

1994-11-01

45

Generation of vortex rings by nonstationary laser wake field  

SciTech Connect

A new concept of generating quasistatic magnetic fields, vortex rings, and electron jets in an isotropic homogeneous plasma is presented. The propagation of plasma waves, generated by a relativistically intense short pulse laser, is investigated by using the kinetic model and a novel nonpotential, time-dependent ponderomotive force is derived by obtaining a hydrodynamic equation of motion. This force can in turn generate quasistatic magnetic fields, vortex rings, and electron jets. It is also shown that the vortex rings can become a means for accelerating electrons, which are initially in equilibrium. The conservation of canonical momentum circulation and the frozen-in condition for the vorticity is discussed. The excitation of the vortex waves by the modulation of the amplitude of the plasma waves is considered. These vortex waves, which generate a lower hybrid mode propagating across the generated magnetic field, are also investigated.

Tsintsadze, N.L.; Murtaza, G.; Shah, H.A. [Department of Physics, Tbilisi State University, Chavchavadze 3 (Georgia); National Centre for Mathematics, G.C. University, Lahore 54000 (Pakistan); Department of Physics, G.C. University, Lahore 54000 (Pakistan)

2006-01-15

46

Sensitivity of ring analysis to near-surface magnetism  

E-print Network

While magnetic field has only second order effects on global sound waves, it can affect the mode frequencies and flow fields inferred using local helioseismology. A strong localized field can bias our results when one try to infer global scale flows such as the meridional circulation. On the other hand, one important object of research in this area is to determine whether one can detect changes in frequencies or sub-surface flow fields that could be a precursor of surface magnetic events. In this paper we review recent development in this area focusing on results obtained with the ring-diagram analysis technique.

Corbard, T

2014-01-01

47

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

SciTech Connect

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

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

2006-08-15

48

Frustrated magnetic vortices in a triad of permalloy rings: Magneto-optical Kerr effect, magnetic force microscopy, and micromagnetic simulations  

Microsoft Academic Search

The field dependent magnetization of three mutually touching permalloy rings were investigated by means of the magneto-optical Kerr effect, magnetic force microscopy, and micromagnetic simulations. Each ring has a width of 0.2-1.8mum , an outer diameter of 4mum , and a thickness of 17nm . Decreasing an applied magnetic field from saturation leads to the nucleation and annihilation of magnetic

V. Rose; K. Buchanan; S.-H. Chung; M. Grimsditch; V. Metlushko; A. Hoffmann; V. Novosad; S. D. Bader; H. Ibach

2006-01-01

49

The Magnet Lattice of the MAX IV Storage Rings  

Microsoft Academic Search

A successor of the present MAX facility is currently being studied. This proposed MAX IV facility will then have two new storage rings operated at 1.5 and 3 GeV respectively. The magnet lattices of the two storage rings are almost identical and the rings are placed coaxially, one on top of the other. A third ring, the MAX III ring,

M. Eriksson; L.-J. Lindgren; H. Tarawneh

2004-01-01

50

Magnetic edge states in Aharonov-Bohm graphene quantum rings  

SciTech Connect

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

Farghadan, R., E-mail: rfarghadan@kashanu.ac.ir; Heidari Semiromi, E. [Department of Physics, University of Kashan, Kashan (Iran, Islamic Republic of); Saffarzadeh, A. [Department of Physics, Payame Noor University, P.O. Box 19395-3697 Tehran (Iran, Islamic Republic of); Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A 1S6 (Canada)

2013-12-07

51

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.

52

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

53

Magnetic flux shielding for the precision muon g-2 storage ring superconducting inflector  

Microsoft Academic Search

A muon g-2 experiment (E821) at the AGS requires knowledge of the magnetic field over muon orbits at the level of 0.1 ppm. The superconducting inflector involves a double cosine theta winding; this design approximately cancels its fringe field. Nevertheless its residual field would effect the homogeneity of the storage ring magnetic field. A method of using a superconducting sheet

G. T. Danby; W. Meng; W. B. Sampson; K. Woodle

1994-01-01

54

Magnetic flux shielding for the precision muon g-2 storage ring superconducting inflector  

Microsoft Academic Search

The muon g-2 experiment (E821) at the AGS requires a precision in the magnetic field over muon orbit at the level of 0.1 ppm. Injection is done with a superconducting inflector involving a double cosine theta winding approximately cancels its fringe field. Nevertheless its residual field would effect the homogeneity of the storage ring magnetic field. A method of using

W. Meng; W. B. Sampson; M. Suenaga; K. Woodle

1993-01-01

55

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,

56

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.

57

Magnetic field line Hamiltonian  

SciTech Connect

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

Boozer, A.H.

1985-02-01

58

Tuning of exciton states in a magnetic quantum ring  

NASA Astrophysics Data System (ADS)

The exciton states in a CdTe quantum ring subjected to an external magnetic field containing a single magnetic impurity are investigated. We have used the multiband approximation which includes the heavy hole-light hole coupling effects. The electron-hole spin interactions and the s, p-d interactions between the electron, the hole and the magnetic impurity are also included. The exciton energy levels and optical transitions are evaluated using the exact diagonalization scheme. We show that due to the spin interactions it is possible to change the bright exciton state into the dark state and vice versa with the help of a magnetic field. We propose a new route to experimentally estimate the s, p-d spin interaction constants.

Ghazaryan, Areg; Manaselyan, Aram; Chakraborty, Tapash

2015-02-01

59

Induction technique for superconducting rings between field cooling and zero field cooling  

NASA Astrophysics Data System (ADS)

We report an induction procedure for superconducting rings. In this technique, a sample is cooled until the liquid nitrogen temperature at zero magnetic field. Then, a magnetic field is applied to the sample using a closed magnetic circuit through the hole of the ring. The induced current in the sample is dissipated due to the heating produced by the current flowing through a counter-wound coil of constantan situated around the superconductor. The coil current is switched off when the superconducting current is completely dissipated. Few seconds later, the whole sample recovers its superconductivity and the magnetic field is removed from its hole. The superconductor generates a current and the magnetic field through the hole remains constant.

González-Jorge, H.; Quelle, I.; Romaní, L.; Domarco, G.

2007-08-01

60

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

61

A volume birdcage coil with an adjustable sliding tuner ring for neuroimaging in high field vertical magnets: ex and in vivo applications at 21.1 T  

PubMed Central

A tunable 900 MHz transmit/receive volume coil was constructed for 1H MR imaging of biological samples in a 21.1 T vertical bore magnet. To accommodate a diverse range of specimen and RF loads at such a high frequency, a sliding-ring adaptation of a low-pass birdcage was implemented through simultaneous alteration of distributed capacitance. To make efficient use of the constrained space inside the vertical bore, a modular probe design was implemented with a bottom-adjustable tuning and matching apparatus. The sliding ring coil displays good homogeneity and sufficient tuning range for different samples of various dimensions representing large span of RF loads. High resolution in vivo and ex vivo images of large rats (up to 350 g), mice and human postmortem tissues were obtained to demonstrate coil functionality and to provide examples of potential applications at 21.1 T. PMID:22750638

Qian, Chunqi; Masad, Ihssan S.; Rosenberg, Jens T.; Elumalai, Malathy; Brey, William W.; Grant, Samuel C.; Gor’kov, Peter L.

2012-01-01

62

A volume birdcage coil with an adjustable sliding tuner ring for neuroimaging in high field vertical magnets: Ex and in vivo applications at 21.1 T  

NASA Astrophysics Data System (ADS)

A tunable 900 MHz transmit/receive volume coil was constructed for 1H MR imaging of biological samples in a 21.1 T vertical bore magnet. To accommodate a diverse range of specimen and RF loads at such a high frequency, a sliding-ring adaptation of a low-pass birdcage was implemented through simultaneous alteration of distributed capacitance. To make efficient use of the constrained space inside the vertical bore, a modular probe design was implemented with a bottom-adjustable tuning and matching apparatus. The sliding ring coil displays good homogeneity and sufficient tuning range for different samples of various dimensions representing large span of RF loads. High resolution in vivo and ex vivo images of large rats (up to 350 g), mice and human postmortem tissues were obtained to demonstrate coil functionality and to provide examples of potential applications at 21.1 T.

Qian, Chunqi; Masad, Ihssan S.; Rosenberg, Jens T.; Elumalai, Malathy; Brey, William W.; Grant, Samuel C.; Gor'kov, Peter L.

2012-08-01

63

Large magnetic storage ring for Bose-Einstein condensates  

SciTech Connect

Cold atomic clouds and Bose-Einstein condensates have been stored in a 10 cm diameter vertically oriented magnetic ring. An azimuthal magnetic field enables low-loss propagation of atomic clouds over a total distance of 2 m, with a heating rate of less than 50 nK/s. The vertical geometry was used to split an atomic cloud into two counter-rotating clouds which were recombined after one revolution. The system will be ideal for studying condensate collisions and ultimately Sagnac interferometry.

Arnold, A. S.; Garvie, C. S.; Riis, E. [Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom)

2006-04-15

64

The Magnetic and Shielding Effects of Ring Current on Radiation Belt Dynamics  

NASA Technical Reports Server (NTRS)

The ring current plays many key roles in controlling magnetospheric dynamics. A well-known example is the magnetic depression produced by the ring current, which alters the drift paths of radiation belt electrons and may cause significant electron flux dropout. Little attention is paid to the ring current shielding effect on radiation belt dynamics. A recent simulation study that combines the Comprehensive Ring Current Model (CRCM) with the Radiation Belt Environment (RBE) model has revealed that the ring current-associated shielding field directly and/or indirectly weakens the relativistic electron flux increase during magnetic storms. In this talk, we will discuss how ring current magnetic field and electric shielding moderate the radiation belt enhancement.

Fok, Mei-Ching

2012-01-01

65

Introduction to Magnetic Fields  

NSDL National Science Digital Library

This is an activity about magnetic fields. Learners will use various magnets, magnetic film, and a compass to see and illustrate what magnetic fields look like. This is the fourth activity as part of the iMAGiNETICspace: Where Imagination, Magnetism, and Space Collide educator's guide. Instructions for downloading the iBook educator's guide and the associated Transmedia book student guide are available at the resource link.

2013-05-06

66

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

67

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,

68

Circuits and Magnetic Fields  

NSDL National Science Digital Library

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

VU Bioengineering RET Program,

69

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

70

Quantification of magnetic force microscopy using a micronscale current ring  

E-print Network

Quantification of magnetic force microscopy using a micronscale current ring Linshu Konga magnetic force microscopy MFM . A MFM tip's effective magnetic charge, q, and effective magnetic moment to be 0.1 Oe/nm2 . © 1997 American Institute of Physics. S0003-6951 97 03115-X Magnetic force microscopy

71

The First Magnetic Fields  

E-print Network

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 is 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 genera...

Widrow, Lawrence M; Schleicher, Dominik; Subramanian, Kandaswamy; Tsagas, Christos G; Treumann, Rudolf A

2011-01-01

72

High-Field Combined-Function Magnets for a 1.5 x 1.5 TeV Muon Collider Storage Ring  

SciTech Connect

Designs and parameters of dipoles and combined-function quadrupoles for bending arc lattice of a 1.5x1.5 TeV muon collider with an average luminosity of 4x1034 cm{sup -2}s{sup -1} are presented. The magnets use the Nb{sub 3}Sn superconductor and provide the required gradients and fields with the appropriate operating margins and field quality. The magnet apertures accommodate tungsten liners to minimize the dynamic heat load in the superconducting coils.

Kashikhin, V.V.; Alexahin, Y.; Mokhov, N.V.; Zlobin, A.V.; /Fermilab

2012-05-01

73

Solar magnetic fields - Extended.  

NASA Technical Reports Server (NTRS)

Spacecraft observations of the interplanetary magnetic field have revealed that almost always each solar rotation can be divided into sectors, within each of which the field has a predominant polarity toward the sun or away from the sun. Comparisons of this interplanetary magnetic sector pattern with observations of the photospheric magnetic field have revealed a similar solar magnetic pattern. The boundaries between solar magnetic sectors are approximately in the north-south direction over a wide range of latitudes on both sides of the equator. This solar magnetic sector structure can be described as a rotating dipole whose magnetic axis makes an angle of approximately 90 deg with the axis of rotation. Possible similarities between this solar-sector magnetism and the models derived from observations of stellar magnetism are discussed.

Wilcox, J. M.

1971-01-01

74

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.

75

Cyclic Magnetic Field Reconnection  

NASA Astrophysics Data System (ADS)

Using a 2.5D electromagnetic particle-in-cell model, we study the magnetic field reconnection around the rotating plasma embedded in a magnetic field. Considering plasma rotation driven by an external electric field, it was found that during one rotational cycle, first the magnetic field energy increases and then decreases to its initial value. The magnetic reconnection occurring during this cycle plays two roles: first, it produces the closed magnetic islands and later on it reopens them to the initial form of magnetic field lines. Thus, the magnetic reconnection can be cyclically repeated in following plasma rotations. Simultaneously, the kinetic particle energy in the system increases due to dissipative processes in this externally driven plasma system. We think that this cyclic reconnection can operate around rapidly rotating stars and in the plasma vortices formed in unstable plasma flows.

Karlický, Marian

2009-02-01

76

ACCELERATION-292 Kicker Magnets for an FFAG Ring for  

E-print Network

MUC-NOTE- ACCELERATION-292 Kicker Magnets for an FFAG Ring for Muons Eberhard Keil CERN, Geneva Mathematica Packages", CERN-SL/99-053 (AP) to the design of kicker magnets for extraction from an FFAG ring for acclerating muons. For the pulsed kicker, I use formulae of R.B.Palmer, which he presented during the FFAG

Keil, Eberhard

77

Magnetic field generator  

DOEpatents

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

Krienin, Frank (Shoreham, NY)

1990-01-01

78

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

79

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

80

The solar magnetic field  

Microsoft Academic Search

The magnetic field of the Sun is the underlying cause of the many diverse phenomena combined under the heading of solar activity. Here we describe the magnetic field as it threads its way from the bottom of the convection zone, where it is built up by the solar dynamo, to the solar surface, where it manifests itself in the form

Sami K. Solanki; Bernd Inhester; Manfred Schüssler

2006-01-01

81

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

82

Ring magnets for the synchrotron x-ray source at ANL  

SciTech Connect

The designs of the bending, focusing, and correction magnetic for the storage ring are described. The computer-optimized pole-tip contours of the dipole, quadrupole, and sextupole magnets and the construction and assembly techniques keep the field errors within the specified limits. Horizontal and vertical steering corrections are provided by separate magnets in addition to a steering capability included in the sextupole magnets.

Praeg, W.F.; Thompson, K.M.; Kim, S.H.

1987-03-01

83

Interplanetary Magnetic Field Lines  

NSDL National Science Digital Library

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

Stern, David

2005-04-27

84

Solar polar magnetic field  

NASA Astrophysics Data System (ADS)

The solar polar magnetic field has attracted the attention of researchers since the polar magnetic field reversal was revealed in the middle of the last century (Babcock and Livingston, 1958). The polar magnetic field has regularly reversed because the magnetic flux is transported from the sunspot formation zone owing to differential rotation, meridional circulation, and turbulent diffusion. However, modeling of these processes leads to ambiguous conclusions, as a result of which it is sometimes unclear whether a transport model is actual. Thus, according to the last Hinode data, the problem of a standard transport model (Shiota et al., 2012) consists in that a decrease in the polar magnetic flux in the Southern Hemisphere lags behind such a decrease in the flux in the Northern Hemisphere (from 2008 to June 2012). On the other hand, Svalgaard and Kamide (2012) consider that the asymmetry in the sign reversal simply results from the asymmetry in the emerging flux in the sunspot formation region. A detailed study of the polar magnetic flux evolution according to the Solar Dynamics Observatory (SDO) data for May 2010-December 2012 is illustrated in the present work. Helioseismic & Magnetic Imager (HMI) magnetic data in the form of a magnetic field component along the line of sight (the time resolution is 720 s) are used here. The magnetic fluxes in sunspot formation regions and at high latitudes have been compared.

Benevolenskaya, E. E.

2013-12-01

85

POWER SUPPLIES FOR THE BENDING MAGNETS OF THE BEP AND VEPP-2000 STORAGE RING  

E-print Network

POWER SUPPLIES FOR THE BENDING MAGNETS OF THE BEP AND VEPP-2000 STORAGE RING S.S. Vasichev, V of the collider. The beam energy change lead to the necessity to develop new power supplies for the main field for the supplies and design of the power part has been revised completely. POWER SUPPLY FOR THE BENDING MAGNETS

Kozak, Victor R.

86

The Magnet Lattice of the MAX IV Storage Rings  

SciTech Connect

A successor of the present MAX facility is currently being studied. This proposed MAX IV facility will then have two new storage rings operated at 1.5 and 3 GeV respectively. The magnet lattices of the two storage rings are almost identical and the rings are placed coaxially, one on top of the other. A third ring, the MAX III ring, now under construction, should be transferred to the new facility. These three rings will then offer dipole IR radiation and undulator radiation from 5 eV up to 20 keV. The total number of straight sections is 32, of which 28 could be used for insertion devices. A 3 GeV linear accelerator will be used as injector for the three rings. The linac could also be used as a Free Electron Laser source. The magnet lattice of the two new rings is described below. The electron beam emittance of the 3 GeV storage ring is 0.86 nm rad and 0.3 nm rad for the 1.5 GeV ring. The circumference of the rings is 286 m.

Eriksson, M.; Lindgren, L.-J.; Tarawneh, H. [MAXlab, Lund University, Lund (Sweden)

2004-05-12

87

Detecting Exoplanetary Magnetic Fields  

NASA Astrophysics Data System (ADS)

Asymmetries in exoplanet transits are proving to be a useful tool for furthering our understanding of magnetic activity on both stars and planets outside our Solar System.Near-UV observations of the WASP-12 system have revealed asymmetries in the timing of the transit when compared with the optical light curve. A number of possible explanations have been suggested for this variation, including the presence of a magnetospheric bow shock arising from the interaction of the planet's magnetic field with the stellar wind from it's host star. Such observations provide the first method for directly detecting the presence of a magnetic field on exoplanets.The shape and size of such asymmetries is highly dependent on the structure of the host stars magnetic field at the time of observation. This implies we may observe highly varying near-UV transit light curves for the same system. These variations can then be used to learn about the geometry of the host star's magnetic field.In this presentation I will show modelling a bow shock around an exoplanet can help us to not only detect, but also also place constraints on the magnetic field strength of hot Jupiters. For some systems, such as HD 189733, we have maps of the surface magnetic field of the star at various epochs. I will also show how incorporating these maps into a stellar wind model, I can model the formation of a bow shock around the planet and hence demonstrate the variability of the near-UV transits.

Llama, Joe

2015-01-01

88

Eruptive solar magnetic fields  

Microsoft Academic Search

This paper considers the quasi-steady evolution of solar magnetic fields in response to gradual photospheric changes. Special interest is taken in the threshold of a sudden eruption in the solar atmosphere. The formal model of an evolving, force-free field dependent on two Cartesian coordinates has been treated previously, and we extend it to a field which is not force free

B. C. Low

1981-01-01

89

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.

90

Acoustic ringing effects in pulsed nuclear magnetic resonance probes  

Microsoft Academic Search

The troublesome spurious ringing phenomenon found in pulsed nuclear magnetic resonance probes is explained in terms of the electromagnetic generation and detection of ultrasonic waves. A few techniques for eliminating this problem are discussed.

M. L. Buess; G. L. Petersen

1978-01-01

91

Acoustic ringing effects in pulsed nuclear magnetic resonance probes.  

PubMed

The troublesome spurious ringing phenomenon found in pulsed nuclear magnetic resonance probes is explained in terms of the electromagnetic generation and detection of ultrasonic waves. A few techniques for eliminating this problem are discussed. PMID:18699271

Buess, M L; Petersen, G L

1978-08-01

92

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

93

Solar magnetic fields  

Microsoft Academic Search

Since the structuring and variability of the Sun and other stars are governed by magnetic fields, much of present-day stellar\\u000a physics centers around the measurement and understanding of the magnetic fields and their interactions. The Sun, being a prototypical\\u000a star, plays a unique role in astrophysics, since its proximity allows the fundamental processes to be explored in detail.\\u000a The PRL

J. O. Stenflo

2008-01-01

94

Solar magnetic fields  

Microsoft Academic Search

This paper is a review of our observational knowledge on solar magnetic fields. In Section 1 we make an attempt to summarize all observations of the general magnetic field (m.f.) of the Sun. Section 2 deals with the local m.f. at low latitudes and their connection with some features on the disk. The m.f. of sunspots and their peculiar character

A. Severny

1964-01-01

95

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

SciTech Connect

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

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

1985-04-01

96

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

SciTech Connect

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

Ross, M

2004-03-19

97

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

98

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

99

Two-dimensional equilibrium of field-reversed ion rings  

Microsoft Academic Search

The axially symmetric equilibrium of intense ion rings is examined for field-reversed configurations. A rigid rotor model is assumed for the ion distribution, with background or accompanying electrons providing space charge neutralization. This equilibrium configuration is described by three macroscopic quantities, the ring particle density, the ring pressure, and the azimuthal component of the vector potential. Within the Vlasov-Maxwell framework,

G. O. Ludwig

1980-01-01

100

Study of magnetic properties of magnetic force microscopy probes using micronscale current rings  

E-print Network

Study of magnetic properties of magnetic force microscopy probes using micronscale current rings, fabricated using electron-beam lithography, were used to calibrate magnetic force microscopy MFM . A MFM tip magnetic force microscopy MFM is an essential tool for characterizing magnetic ma- terials in submicron

101

Electrically silent magnetic fields.  

PubMed Central

There has been a significant controversy over the past decade regarding the relative information content of bioelectric and biomagnetic signals. In this paper we present a new, theoretical example of an electrically-silent magnetic field, based on a bidomain model of a cylindrical strand of tissue generalized to include off-diagonal components in the conductivity tensors. The physical interpretation of the off-diagonal components is explained, and analytic expressions for the electrical potential and the magnetic field are found. These expressions show that information not obtainable from electrical potential measurements can be obtained from measurements of the magnetic field in systems with conductivity tensors more complicated than those previously examined. PMID:3779008

Roth, B J; Wikswo, J P

1986-01-01

102

Correlation of lunar far-side magnetized regions with ringed impact basins  

USGS Publications Warehouse

By the method of electron reflection, we have identified seven well-defined magnetized regions in the equatorial belt of the lunar far side sampled by the Apollo 16 Particles and Fields subsatellite. Most of these surface magnetic fields lie within one basin radius from the rim of a ringed impact basin, where thick deposits of basin ejecta are observed or inferred. The strongest of the seven magnetic features is linear, at least 250 km long, and radial to the Freundlich-Sharonov basin. The apparent correlation with basin ejecta suggests some form of impact origin for the observed permanently magnetized regions. ?? 1979.

Anderson, K.A.; Wilhelms, D.E.

1979-01-01

103

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

104

Solar magnetic fields and convection. IX - A primordial magnetic field  

Microsoft Academic Search

Observational evidence is reviewed in an attempt to decide between a reversing (dynamo) and a nonreversing primordial solar poloidal magnetic field. The data examined include Zeeman-effect measurements, measurements of gross magnetic fluxes in individual magnetic elements, determinations of average field strength, observations of polar-cap magnetic fields, eclipse observations of coronal structure, and observations of interplanetary-magnetic-field polarity reversals. It is suggested

J. H. Piddington

1977-01-01

105

Designing magnets with prescribed magnetic fields  

NASA Astrophysics Data System (ADS)

We present a novel design method capable of finding the magnetization densities that generate prescribed magnetic fields. The method is based on the solution to a simple variational inequality and the resulting designs have simple piecewise-constant magnetization densities. By this method, we obtain new designs of magnets that generate commonly used magnetic fields: uniform magnetic fields, self-shielding fields, quadrupole fields and sextupole fields. Further, it is worth noting that this method is not limited to the presented examples, and in particular, three-dimensional designs can be constructed in a similar manner. In conclusion, this novel design method is anticipated to have broad applications where specific magnetic fields are important for the performance of the devices.

Liu, Liping

2011-03-01

106

Muon g-2 Measurement: Determination of the Magnetic Field  

Microsoft Academic Search

Determination of the magnetic field B in the muon storage ring of the muon g-2 experiment (E821) in Brookhaven National Laboratory is obtained from NMR measurements[1] with probes in a hermetically sealed trolley which can be moved around the storage ring in vacuum. Each of 17 probes inside the trolley has a precision of 0.04ppm(rms) in a constant magnetic field

Huaizhang Deng; Ralf Prigl

2001-01-01

107

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

108

Fracture of metallic rings during magnetic-pulse shock loading  

NASA Astrophysics Data System (ADS)

Metallic rings made of aluminum and copper foils are studied after the action of a distributed radial magnetic-pulse load. Two loading approach modifications allowed us to substantially decrease the period of an applied sinusoidal load and to determine the time from load application to sample failure. A method is proposed to estimate the radial force on a metallic ring from coil turns. The profiles of radial pressure on the inner ring surface are measured, and the circumferential tensile stresses in ring fracture are determined. Microstructural studies of failed ring samples show that they underwent dynamic recrystallization. It is found that, as the operating load period shortens, the fraction of the ductile component in a fracture surface decreases and the samples undergo more brittle fracture.

Morozov, V. A.; Petrov, Yu. V.; Lukin, A. A.; Atroshenko, S. A.; Gribanov, D. A.

2014-09-01

109

Nuclear Magnetic Resonance and Magnetic Field Measurements  

NSDL National Science Digital Library

This laboratory is designed for students to become familiar with the principles and detection techniques of Nuclear Magnetic Resonance (NMR), examine the relationship between current and magnetic field in an electromagnet, and gain experience in the use of magnetic field measurement techniques.

2012-01-04

110

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

111

The Earth's Magnetic Field  

NSDL National Science Digital Library

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

Johnson, Roberta

2000-07-01

112

Equilibrium and stability studies of plasmas confined in a dipole magnetic field using magnetic measurements  

E-print Network

The Levitated Dipole Experiment (LDX) is the first experiment of its kind to use a levitated current ring to confine a plasma in a dipole magnetic field. Unlike most other confinement devices, plasma compressibility ...

Karim, Ishtak

2007-01-01

113

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

114

Behavior of multi-component magnetic colloidal systems in tunable magnetic fields and applications in biosensing  

NASA Astrophysics Data System (ADS)

A system consisting of multiple-component beads, such as superparamagnetic beads, nonmagnetic beads and magnetorheological (MR) fluid, can display some very amazing and special properties when subjected to an external magnetic field because the MR fluid can act on both types of beads synchronously as a magnetic medium. Some novel structures and phenomena were discovered and are discussed in our work, including 'ring-structures', 'small-ring' and 'ring-chains' in static or rotational magnetic fields. If both probe and target molecules are attached consisting of functionalized superparamagnetic beads and non-magnetic beads, respectively, the ring-structure could be maintained due to biomolecular bonding, even after removing the external magnetic field. Using these remnant rings, we raised two protocols for biosensing: a two-dimensional biosensor using a magnetic self-assembled colloidal ring-structure, and an improved magneto-optical transmittance (MT) method. In the former protocol, we define the small nonmagnetic particles as "petals" because the whole structure looks like a flower. It was proved that the number of remnant ring petals was a function of the concentration of the target molecules', with a concentration range from 0.0768 ng/mL ~ 3.8419 ng/mL, making it a promising technology for applications involving biosensing. In the latter protocol, the use of larger individual units made the magnetic particle chain longer, which was considered to be a promising way of improving the sensitivity of the MT method.

Yang, Ye; Li, Zhengcao; Ko, Pil Ju; Sandhu, Adarsh

2012-03-01

115

Two-dimensional equilibrium of field reversed ion rings  

Microsoft Academic Search

The axially symmetric equilibrium of intense ion rings is examined for field-reversed configurations. A rigid-rotor model is assumed for the ion distribution, with background or accompanying electrons providing space charge neutralization. This equilibrium configuration is described by three macroscopic quantities, the ring particle density, the ring pressure, and the azimuthal component of the vector potential. Within the Vlasov-Maxwell framework, these

G O Ludwig

1981-01-01

116

Permanent Magnet Storage Rings for Microlithography and FEL Sources  

Microsoft Academic Search

Permanent magnet technology is rapidly improving and it seems possible now to design and build dedicated electron storage rings for peculiar applications such as microlithography and free electron laser. A low capital cost as well as a low operational cost (no power supplies) may lead to industrial solutions. In this paper the authors describe two possible design studies for machines

J. Le Duff; Y. Petroff

1983-01-01

117

Mars Observer magnetic fields investigation  

Microsoft Academic Search

The magnetic fields experiment designed for the Mars Observer mission will provide definitive measurements of the Martian magnetic field from the transition and mapping orbits planned for the Mars Observer. The paper describes the instruments (which include a classical magnetometer and an electron reflection magnetometer) and techniques designed to investigate the nature of the Martian magnetic field and the Mars-solar

J. E. P. Connerney; P. Wasilewski; R. P. Lin; K. A. Anderson; C. W. Carlson; J. McFadden; D. W. Curtis; H. Reme; A. Cros; J. L. Médale; J. A. Sauvaud; C. d'Uston; S. J. Bauer; P. Cloutier; Michael Mayhew; N. F. Ness

1992-01-01

118

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

119

Magnetic field switchable dry adhesives.  

PubMed

A magnetic field controllable dry adhesive device is manufactured. The normal adhesion force can be increased or decreased depending on the presence of an applied magnetic field. If the magnetic field is present during the entire normal adhesion test cycle which includes both applying a preloading force and measuring the pulloff pressure, a decrease in adhesion is observed when compared to when there is no applied magnetic field. Similarly, if the magnetic field is present only during the preload portion of the normal adhesion test cycle, a decrease in adhesion is observed because of an increased stiffness of the magnetically controlled dry adhesive device. When the applied magnetic field is present during only the pulloff portion of the normal adhesion test cycle, either an increase or a decrease in normal adhesion is observed depending on the direction of the applied magnetic field. PMID:25588470

Krahn, Jeffrey; Bovero, Enrico; Menon, Carlo

2015-02-01

120

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

121

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

122

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

123

Magnetic Propeller for Uniform Magnetic Field Levitation  

E-print Network

Three new approaches to generating thrust in uniform magnetic fields are proposed. The first direction is based on employing Lorentz force acting on partial magnetically shielded 8-shaped loop with current in external magnetic field, whereby a net force rather than a torque origins. Another approach, called a Virtual Wire System, is based on creating a magnetic field having an energetic symmetry (a virtual wire), with further superposition of external field. The external field breaks the symmetry causing origination of a net force. Unlike a wire with current, having radial energetic symmetry, the symmetry of the Virtual Wire System is closer to an axial wire. The third approach refers to the first two. It is based on creation of developed surface system, comprising the elements of the first two types. The developed surface approach is a way to drastically increase a thrust-to-weight ratio. The conducted experiments have confirmed feasibility of the proposed approaches.

Mark Krinker; Alexander Bolonkin

2008-07-12

124

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

125

Fast superconducting magnetic field switch  

DOEpatents

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

Goren, Y.; Mahale, N.K.

1996-08-06

126

Radiation effects in a muon collider ring and dipole magnet protection  

SciTech Connect

The requirements and operating conditions for a Muon Collider Storage Ring (MCSR) pose significant challenges to superconducting magnets. The dipole magnets should provide a high magnetic field to reduce the ring circumference and thus maximize the number of muon collisions during their lifetime. One third of the beam energy is continuously deposited along the lattice by the decay electrons at the rate of 0.5 kW/m for a 1.5-TeV c.o.m. and a luminosity of 10{sup 34} cm{sup -2}s{sup -1}. Unlike dipoles in proton machines, the MCSR dipoles should allow this dynamic heat load to escape the magnet helium volume in the horizontal plane, predominantly towards the ring center. This paper presents the analysis and comparison of radiation effects in MCSR based on two dipole magnets designs. Tungsten masks in the interconnect regions are used in both cases to mitigate the unprecedented dynamic heat deposition and radiation in the magnet coils.

Mokhov, N.V.; Kashikhin, V.V.; Novitski, I.; Zlobin, A.V.; /Fermilab

2011-03-01

127

Fast and reliable kicker magnets for the SLC damping rings  

Microsoft Academic Search

The design, construction, and operation of a kicker magnet with superior electromagnetic performance and greatly improved radiation tolerance is described. A short flux return of high mu ferrite improves the field strength and linearity with current, and novel metallic field-confining structures minimize the inductance. An 8-cell structure with capacitance integrated into each cell makes the magnet a nearly perfect transmission

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

1995-01-01

128

Ring current-energy balance during intense magnetic storms  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

129

Master equations for pulsed magnetic fields: Application to magnetic molecules  

NASA Astrophysics Data System (ADS)

We extend spin-lattice relaxation theory to incorporate the use of pulsed magnetic fields for probing the hysteresis effects and magnetization steps and plateaus exhibited, at low temperatures, by the dynamical magnetization of magnetic molecules. The main assumption made is that the lattice degrees of freedom equilibrate in times much shorter than both the experimental time scale (determined by the sweep rate) and the typical spin-lattice relaxation time. We first consider the isotropic case (a magnetic molecule with a ground state of spin S well separated from the excited levels and also the general isotropic Heisenberg-Hamiltonian where all energy levels are relevant) and then we include small off-diagonal terms in the spin Hamiltonian to take into account the Landau-Zener-Stückelberg (LZS) effect. In the first case, and for an S=1/2 magnetic molecule we arrive at the generalized Bloch equation recently used for the magnetic molecule {V6} in [Phys. Rev. Lett. 94, 147204 (2005)]. An analogous equation is derived for the magnetization, at low temperatures, of antiferromagnetic ring systems. The LZS effect is discussed for magnetic molecules with a low spin ground state, for which we arrive at a very convenient set of equations that take into account the combined effects of LZS and thermal transitions. In particular, these equations explain the deviation from exact magnetization reversal at B?0 observed in {V6} . They also account for the small magnetization plateaus (“magnetic Foehn effect”), following the LZS steps that have been observed in several magnetic molecules. Finally, we discuss the role of the phonon bottleneck effect at low temperatures and specifically we indicate how this can give rise to a pronounced Foehn effect.

Rousochatzakis, Ioannis; Luban, Marshall

2005-10-01

130

[Magnetic fields and fish behavior].  

PubMed

In the review, contemporary data on the influence of natural and artificial magnetic fields on fish behavior are considered. In this regard, elasmobranchs and teleosts appear to be studied most exhaustively. Elasmobranchs and some teleosts are able to perceive magnetic fields via electroreceptors. A number of teleosts can sense magnetic fields via sensory cells containing crystals of biogenic magnetite. Laboratory experiments and field observations indicate the influence of magnetic fields on fish locomotor activity and spatial distribution. The geomagnetic field can be used by fish for navigation. Besides, artificial magnetic fields and natural fluctuations of the geomagnetic field can affect fish embryos leading to alterations in their development. It is suggested that, afterwards, these alterations can have an effect on fish behavior. PMID:25508098

2013-01-01

131

[Magnetic fields and fish behavior].  

PubMed

In the review, contemporary data on the influence of natural and artificial magnetic fields on fish behavior are considered. In this regard, elasmobranchs and teleosts appear to be studied most exhaustively. Elasmobranchs and some teleosts are able to perceive magnetic fields via electroreceptors. A number of teleosts can sense magnetic fields via sensory cells containing crystals of biogenic magnetite. Laboratory experiments and field observations indicate the influence of magnetic fields on fish locomotor activity and spatial distribution. The geomagnetic field can be used by fish for navigation. Besides, artificial magnetic fields and natural fluctuations of the geomagnetic field can affect fish embryos leading to alterations in their development. It is suggested that, afterwards, these alterations can have an effect on fish behavior. PMID:25438567

Krylov, V V; Iziumov, Iu G; Izvekov, E I; Nepomniashchikh, V A

2013-01-01

132

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

133

Operational experience with SLC damping ring kicker magnets  

Microsoft Academic Search

The damping ring kickers for the SLAC Linear Collider (SLC) must provide 7-Mrad kicks to 1.2-GeV beams with 60-nsec rise and fall times and fit in a 50-cm length around a 21-mm-diameter ceramic beam pipe. This requires that they operate at up to 40 kV. The construction and operation of two types of quasi-coaxial ferrite magnet potted with RTV silicone

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

1991-01-01

134

Magnetic-field-dosimetry system  

DOEpatents

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

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

1981-01-21

135

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

136

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

137

Statistical analyses of the magnet data for the Advanced Photon Source storage ring magnets  

Microsoft Academic Search

The statistics of the measured magnetic data of 80 dipole, 400 quadrupole, and 280 sextupole magnets of conventional resistive designs for the APS storage ring is summarized. In order to accommodate the vacuum chamber, the curved dipole has a C-type cross section and the quadrupole and sextupole cross sections have 180? and 120? symmetries, respectively. The data statistics include the

S. H. Kim; D. W. Carnegie; C. Doose; R. Hogrefe; K. Kim; R. Merl

1996-01-01

138

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

139

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

140

A magnetic field model for wigglers and undulators  

Microsoft Academic Search

Recent interest in applications of wiggler magnets in storage rings has motivated efforts to incorporate their effects in calculations of beam dynamics. This paper presents an analytic model of wiggler fields that can be used with symplectic integration to evaluate such effects. Coefficients needed by the model are generated by fitting to the results of a finite-element field calculation. The

D. Sagan; J. A. Crittenden; D. Rubin; E. Forest

2003-01-01

141

Rings  

SciTech Connect

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

Davis, R.L.

1989-01-01

142

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

143

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 interesting plasmas are permeated by or imbedded in magnetic fields.1 As shown in Fig. 3.1, the magnetic field properties of magnetic fields in plasmas can be discussed without specifying a model for the plasma

Callen, James D.

144

Magnetic Field Problem: Measuring Current  

NSDL National Science Digital Library

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

Christian, Wolfgang; Belloni, Mario

2007-03-03

145

Studies of solar magnetic fields  

Microsoft Academic Search

An estimate of the average magnetic field strength at the poles of the Sun from Mount Wilson measurements is made by comparing low latitude magnetic measurements in the same regions made near the center of the disk and near the limb. There is still some uncertainty because the orientation angle of the field lines in the meridional plane is unknown,

Robert Howard

1977-01-01

146

Characterisation and magnetic field properties of multianode photomultiplier tubes  

NASA Astrophysics Data System (ADS)

We report on studies of the Hamamatsu model R11265 Multianode Photomultiplier as part of the effort to qualify their use in the upgrade of the LHCb Ring Imaging Cherenkov Detectors. Comparisons with the known model R7600 are also made. Of particular interest is the behaviour of the MaPMT in magnetic fields comparable to the residual fringe field of the LHCb bending magnet ranging up to 25 Gauss.

Eisenhardt, Stephan; Luo, Haofei; Morris, Adam; Needham, Matthew; Neill, Josh

2014-12-01

147

Solar magnetic fields and convection  

Microsoft Academic Search

The solar magnetic fields observed in active regions and their residues are thought to be parts of toroidal field systems renewed every 11-yr cycle from a poloidal field. The latter may be either a reversing (dynamo) field or a non-reversing, primordial field. The latter view was held for some 70 yr, but the apparent reversals of the polar-cap fields in

J. H. Piddington

1977-01-01

148

Magnetic confinement in a ring-cusp ion thruster discharge plasma  

SciTech Connect

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

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

2009-05-01

149

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

SciTech Connect

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

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

2011-04-10

150

MonitoRing - Magnetic induction measurement at your fingertip  

NASA Astrophysics Data System (ADS)

The device presented in this paper is a sensor for monitoring pulse by measuring the bioimpedance of the thumb in an unobtrusive way. The sensor is based on magnetic induction measurement, a non-contact technique for measuring impedance changes of objects [1]. The sensor head of the presented system has the form of a ring and is worn on the finger. The developed technique renders the possibility of easy and unnoticed pulse recording during every day activities without the need for, e.g. electrodes, a pulse belt around the chest, or a pulse photoplethysmographic finger or ear clip.

Teichmann, D.; Foussier, J.; Löschcke, D.; Leonhardt, S.; Walter, M.

2013-04-01

151

STORAGE RING AND INTERACTION REGION MAGNETS FOR A ?+?- HIGGS FACTORY.  

SciTech Connect

A low-energy Muon Collider (MC) offers unique opportunities to study the recently found Higgs boson. However, due to a relatively large beam emittance with moderate cooling in this machine, large-aperture high- field superconducting (SC) magnets are required. The magnets need also an adequate margin to operate at a large radiation load from the muon decay showers. General specifications of the SC dipoles and quadrupoles for the 125 GeV c.o.m. Higgs Factory with an average luminosity of ~2x10**31 cm-2s-1 are formulated. Magnet conceptual designs and parameters are reported. The impact of the magnet fringe fields on the beam dynamics as well as the IR and lattice magnet protection from radiation are also reported and discussed.

Zlobin, A.V.; Alexahin, Y.I.; Kappin, V.V.; Kashikhin, V.V.; Mokhov, N.V.; Striganov, S.I.; Tropin, I.S.

2013-09-25

152

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

153

POWER SUPPLIES FOR THE BENDING MAGNETS OF THE BEP AND VEPP-2000 STORAGE RING  

E-print Network

POWER SUPPLIES FOR THE BENDING MAGNETS OF THE BEP AND VEPP-2000 STORAGE RING K.M. Gorchakov, S new complex VEPP-2000. The two new power supply for bending magnet was built for BEP and VEPP-2000 storage ring. POWER SUPPLY FOR THE BENDING MAGNETS OF THE BEP Below are the parameters of the supply (the

Kozak, Victor R.

154

Thermometers in Low Magnetic Fields  

NASA Astrophysics Data System (ADS)

In this article the effect of low amplitude DC magnetic fields on different types of thermometers is discussed. By means of a precision water-cooled electromagnet, the effect of a magnetic field on platinum resistance thermometers, thermistors, and type T, J, and K thermocouples was investigated, while thermometers were thermally stabilized in thermostatic baths. Four different baths were used for temperatures from 77 K (-196 °C) to 353 K (80 °C): liquid nitrogen bath (nitrogen boiling point at atmospheric pressure), ice-point bath, room-temperature air bath, and hot-water bath. The generated DC magnetic field of high relative precision (2 × 10-4 at 1 T, 4 × 10-5 short-term stability) and high relative uniformity (2 × 10-5 over 1 cm2, 10 mm gap) had a magnetic flux density of 1 T in the center of the gap between the magnet pole caps. The results indicate a magnetic effect of up to 100 mK due to a 1 T magnetic field for the types of thermocouples composed of ferromagnetic materials (Fe, Cr, Ni). For platinum resistance thermometers, thermistors, and non-magnetic type T thermocouples, the detected magnetic effect was weaker, i.e., under 10 mK.

Geršak, G.; Beguš, S.

2010-09-01

155

Low-Magnetic-Field Magnetars  

NASA Astrophysics Data System (ADS)

It is now widely accepted that soft gamma repeaters and anomalous X-ray pulsars are the observational manifestations of magnetars, i.e. sources powered by their own magnetic energy. This view was supported by the fact that these "magnetar candidates" exhibited, without exception, a surface dipole magnetic field (as inferred from the spin-down rate) in excess of the electron critical field (? 4.4×1013 G). The recent discovery of fully qualified magnetars, SGR 0418+5729 and Swift J1822.3-1606, with dipole magnetic field well in the range of ordinary radio pulsars posed a challenge to the standard picture, showing that a very strong field is not necessary for the onset of magnetar activity (chiefly bursts and outbursts). Here we summarize the observational status of the low-magnetic-field magnetars and discuss their properties in the context of the mainstream magnetar model and its main alternatives.

Turolla, Roberto; Esposito, Paolo

2013-11-01

156

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

157

condensate in constant magnetic fields  

Microsoft Academic Search

We solve the Dirac equation in the presence of a constant magnetic field in (3+1) and (2+1) dimensions. Quantizing the fermion field, we calculate the condensate from first principles for parity conserving and violating Lagrangians for arbitrary field strength. We make a comparison with the results already known in the literature for some particular cases and point out the relevance

M. de J Anguiano-Galicia; A. Bashir; A. Raya

2007-01-01

158

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

159

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

160

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

SciTech Connect

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

Casadei, Cecilia

2012-05-09

161

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

162

The magnetic field of Canopus  

Microsoft Academic Search

Zeeman spectrograms taken at the ESO in 1978 for Canopus (F0 Ib-II) confirm the presence of the weak magnetic field detected by Schermann (1977) and Rakosch et al. (1977), and a new period of 6.90 days for the Canopus magnetic field variation is proposed. It is noted that with the MSHIFT-technique (Weiss et al., 1978) the plate-mean Zeeman shifts can

W. W. Weiss

1986-01-01

163

Solar magnetic fields and convection  

Microsoft Academic Search

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

J. H. Piddington

1976-01-01

164

Least Squares Magnetic-Field Optimization for Portable Nuclear Magnetic Resonance Magnet Design  

SciTech Connect

Single-sided and mobile nuclear magnetic resonance (NMR) sensors have the advantages of portability, low cost, and low power consumption compared to conventional high-field NMR and magnetic resonance imaging (MRI) systems. We present fast, flexible, and easy-to-implement target field algorithms for mobile NMR and MRI magnet design. The optimization finds a global optimum ina cost function that minimizes the error in the target magnetic field in the sense of least squares. When the technique is tested on a ring array of permanent-magnet elements, the solution matches the classical dipole Halbach solution. For a single-sided handheld NMR sensor, the algorithm yields a 640 G field homogeneous to 16 100 ppm across a 1.9 cc volume located 1.5 cm above the top of the magnets and homogeneous to 32 200 ppm over a 7.6 cc volume. This regime is adequate for MRI applications. We demonstrate that the homogeneous region can be continuously moved away from the sensor by rotating magnet rod elements, opening the way for NMR sensors with adjustable"sensitive volumes."

Paulsen, Jeffrey L; Franck, John; Demas, Vasiliki; Bouchard, Louis-S.

2008-03-27

165

Interaction of bulk superconductors with flywheel rings made of multiple permanent magnets  

NASA Astrophysics Data System (ADS)

Compared to conventional mechanical bearings, superconducting bearings have the advantage that there is no friction loss. Thus the superconducting bearings are employed for a flywheel energy storage device, and thereby one can construct the system that stores the energy for a long duration. Hence, superconducting flywheel energy storage system has attracted worldwide attention. For practical applications of the superconducting energy storage system, the stored energy must be maximized that can be achieved by either increasing the diameter of the levitated flywheel or the rotational velocity. Since the suspended flywheel in the superconducting flywheel energy storage system is made of permanent magnets, its size is limited by the size of permanent magnets. In addition, when the rotational speed is increased, there is possibility for the magnet ring to fracture due to a large centrifugal force. We therefore proposed the construction of the magnetic flywheel ring by simply arranging small permanent magnets pasted into machined grooves in Al disk 650 mm in diameter. Then we measured the force interaction between superconductor sample and a invented flywheel design. We have found that the field is almost uniform when the distance from the flywheel surface exceeded 15 mm, showing that frictionless rotation is possible at the gap larger than 15 mm. Furthermore, the repulsive force density was 0.48 N/cm 2 at 15 mm, which demonstrates that the mass of 161.32 kg can be levitated.

Ikeda, M.; Wongsatanawarid, A.; Seki, H.; Murakami, M.

2009-10-01

166

Magnetic field induced dynamical chaos  

SciTech Connect

In this article, we have studied the dynamics of a particle having charge in the presence of a magnetic field. The motion of the particle is confined in the x–y plane under a two dimensional nonlinear potential. We have shown that constant magnetic field induced dynamical chaos is possible even for a force which is derived from a simple potential. For a given strength of the magnetic field, initial position, and velocity of the particle, the dynamics may be regular, but it may become chaotic when the field is time dependent. Chaotic dynamics is very often if the field is time dependent. Origin of chaos has been explored using the Hamiltonian function of the dynamics in terms of action and angle variables. Applicability of the present study has been discussed with a few examples.

Ray, Somrita; Baura, Alendu; Bag, Bidhan Chandra, E-mail: bidhanchandra.bag@visva-bharati.ac.in [Department of Chemistry, Visva-Bharati, Santiniketan 731 235 (India)

2013-12-15

167

The Magnetic Fields of the Solar Interior  

NASA Astrophysics Data System (ADS)

Measuring the internal magnetic fields of the Sun would provide important constraints on our understanding of the mechanisms that underly solar activity. In this work, we have used a full solar cycle's worth of high quality helioseismic data from the Michelson Doppler Imager (MDI) instrument onboard the SOHO spacecraft to explore changes in the interior thermal structure, using the techniques of both global and local helioseismology. We have also used these data to attempt to directly measure the magnetic fields in the convection zone. We have found that the interior of the Sun changed slightly but significantly over the course of the last solar cycle. Analyzing the global mode frequencies measured during solar cycle 23, we find a change, which we interpret as a change in the sound speed, at the base of the convection zone. At r = (0.712+0.0097-0.0029)R ? , the change in sound speed is a decrease of deltac²/ c² = (7.23 +/- 2.08) x 10--5. Modeling the effects of magnetic fields on the helioseismic splitting coefficients, we find that a field of strength necessary to cause the thermal change we find is not detectable with our data. We find that the signal that is there can be explained by a shallow toroidal field with a weak poloidal component. This field is tightly correlated with surface activity. We find that the toroidal field peaks at r0 = 0.999 R? and r = 0.996 R? , with peak field strengths of 380 +/- 30 G and 1.4 +/- 0.2 kG for the shallower and deeper fields, respectively. The peak strength of the poloidal field is 124 +/- 17 G. We employ ring diagram analysis to explore these layers of the Sun in more detail. We confirm earlier results that helioseismic frequencies increase in active regions, where strong surface magnetic fields are present, and that acoustic power is suppressed. We find that the changes in frequency depend somewhat on the surface geometry of the magnetic fields. Finally, we find in a large sample of active regions that the thermal structure beneath sunspots is a two layer structure with slower soundspeed in the shallower layers (above approximately r = 0.98 R? ) and a faster sound speed between approximately r = 0.975 R? and r = 0.985 R? .

Baldner, Charles S.

168

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

169

Damping of cosmic magnetic fields  

NASA Astrophysics Data System (ADS)

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 Alfvén 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?~10-4Msolar in baryons) and the Silk mass at recombination (M?~1013Msolar in baryons). In contrast, the oscillations of slow magnetosonic and Alfvén 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 Alfvén 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 Alfvén and slow magnetosonic modes on scales well below the Silk mass may be of significance for the formation of structure on small scales.

Jedamzik, Karsten; Katalini?, Višnja; Olinto, Angela V.

1998-03-01

170

Magnetic fields in protoplanetary disks  

E-print Network

Magnetic fields likely play a key role in the dynamics and evolution of protoplanetary discs. They have the potential to efficiently transport angular momentum by MHD turbulence or via the magnetocentrifugal acceleration of outflows from the disk surface, and magnetically-driven mixing has implications for disk chemistry and evolution of the grain population. However, the weak ionisation of protoplanetary discs means that magnetic fields may not be able to effectively couple to the matter. I present calculations of the ionisation equilibrium and magnetic diffusivity as a function of height from the disk midplane at radii of 1 and 5 AU. Dust grains tend to suppress magnetic coupling by soaking up electrons and ions from the gas phase and reducing the conductivity of the gas by many orders of magnitude. However, once grains have grown to a few microns in size their effect starts to wane and magnetic fields can begin to couple to the gas even at the disk midplane. Because ions are generally decoupled from the magnetic field by neutral collisions while electrons are not, the Hall effect tends to dominate the diffusion of the magnetic field when it is able to partially couple to the gas. For a standard population of 0.1 micron grains the active surface layers have a combined column of about 2 g/cm^2 at 1 AU; by the time grains have aggregated to 3 microns the active surface density is 80 g/cm^2. In the absence of grains, x-rays maintain magnetic coupling to 10% of the disk material at 1 AU (150 g/cm^2). At 5 AU the entire disk thickness becomes active once grains have aggregated to 1 micron in size.

Mark Wardle

2007-04-07

171

Magnetoresistance behavior of elliptical ring nanomagnets in close proximity with magnetic elements  

E-print Network

Magnetoresistance behavior of elliptical ring nanomagnets in close proximity with magnetic elements investigated the giant magnetoresistance GMR responses of the pseudospin valve elliptical rings in close packed ring arrays can be used effec- tively to control the vortex stability.9 In the present work

Adeyeye, Adekunle

172

Chaotic Spin-Wave Solitons in Magnetic Film Feedback Rings Zihui Wang,1  

E-print Network

-generation of a single spin-wave soliton pulse in the ring. When the pulse circulates in the ring, its amplitude varies are the signatures of a soliton. The overall time-domain signal resulting from the circulation of the pulse showsChaotic Spin-Wave Solitons in Magnetic Film Feedback Rings Zihui Wang,1 Aaron Hagerstrom,1 Justin Q

173

Calixarene-stabilised cobalt nanoparticle rings: Self-assembly and collective magnetic properties Alexander Weia  

E-print Network

Calixarene-stabilised cobalt nanoparticle rings: Self-assembly and collective magnetic properties 10 October 2008) Calixarenes can be used to promote the self-assembly of thermoremanent cobalt phenomenon. Keywords: calixarenes; encapsulation; magnetism; nanoparticles; self-assembly; transmission

Dunin-Borkowski, Rafal E.

174

Multipole Shimming of Permanent Magnets Using Harmonic CorrectorRings  

SciTech Connect

Shimming systems are required to provide sufficient fieldhomogeneity for high resolution NMR. In certain specialized applications,such as rotating-field NMR and portable (ex-situ) NMR, permanentmagnet-based shimming systems can provide considerable advantages. Wepresent a simple two-dimensional shimming method based on harmoniccorrector rings which can provide arbitrary multipole order shimmingcorrections. Results demonstrate, for example, that quadrupolar ordershimming improves the linewidth by up to and order of magnitude. Anadditional order of magnitude reduction is in principle achievable byultilizing this shimming method for z-gradient correction and higherorder xy gradients.

Jachmann, Rebecca C.; Trease, David R.; Bouchard, Louis-S.; Sakellariou, Dimitris; Martin, Rachel W.; Schlueter, Ross D.; Budinger,Thomas F.; Pines, Alexander

2006-10-23

175

Smallscale Solar Magnetic Fields - an Overview  

Microsoft Academic Search

An overview is given of the observational and the theoretical methods used to investigate solar magnetic fields. It includes an introduction to the Stokes parameters, their radiative transfer in the presence of a magnetic field, and empirical techniques used to measure various properties of solar magnetic features, such as the strength and direction of the magnetic field, magnetic flux, temperature,

Sami K. Solanki

1993-01-01

176

Observation of Magnetic Level Repulsion in Fe6:Li Molecular Antiferromagnetic Rings  

NASA Astrophysics Data System (ADS)

Heat capacity (C), magnetic torque, and proton NMR relaxation rate (1/T1) measurements were performed on Fe6:Li single crystals in order to study the crossings between S = 0 and S = 1 and between S = 1 and S = 2 magnetic states of the molecular rings, at magnetic fields Bc1 = 11.7 T and Bc2 = 22.4 T, respectively. C vs B data at 0.78 K show that the energy gap between two states remains finite at Bc's ( ?1/kB = 0.86 K and ?2/kB = 2.36 K) thus proving that levels repel each other. The large ?1 value may also explain the anomalously large width of the peak in 1/T1 vs B, around Bc1. This anticrossing, unexpected in a centrosymmetric system, requires a revision of the Hamiltonian.

Affronte, M.; Cornia, A.; Lascialfari, A.; Borsa, F.; Gatteschi, D.; Hinderer, J.; Horvati?, M.; Jansen, A. G.; Julien, M.-H.

2002-04-01

177

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

SciTech Connect

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

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

2012-06-15

178

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

179

Investigation of magnetic resonances for different split-ring resonator parameters and designs  

Microsoft Academic Search

We investigate the magnetic resonance of split-ring resonators (SRR) experimentally and numerically. The dependence of the geometrical parameters on the magnetic resonance frequency of SRR is studied. We further investigate the effect of lumped capacitors integrated to the SRR on the magnetic resonance frequency for tunable SRR designs. Different resonator structures are shown to exhibit magnetic resonances at various frequencies

Koray Aydin; Irfan Bulu; Kaan Guven; Maria Kafesaki; Costas M Soukoulis; Ekmel Ozbay

2005-01-01

180

Control of damping partition numbers in a ring accelerator with rf electromagnetic fields.  

PubMed

A novel scheme to reduce transverse beam emittance in a ring accelerator is proposed by using a pair of coupling cavities as a basic unit to control damping partition numbers. As indicated by Robinson in 1958, a simple rf electromagnetic field (e.g., a TM210 mode by a single coupling cavity) cannot control the damping partition of three eigenoscillation modes in a ring accelerator due to the cancellation between the contributions from the magnetic and electric fields. Based on both analytical and numerical studies, we show that a pair of coupling cavities that satisfy phase and optics matching conditions can overcome this cancellation. The results indicate that the horizontal emittance is reducible to the theoretical limit based on the steady state condition and also, the emittance is reducible below the reduction limit under a nonsteady state by driving the coupling cavities with gated signals. PMID:25167275

Shimosaki, Yoshito; Tanaka, Hitoshi

2013-04-12

181

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

NASA Technical Reports Server (NTRS)

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

Jones, D. E.

1986-01-01

182

The Giotto magnetic-field investigation  

NASA Technical Reports Server (NTRS)

The objectives of the Giotto magnetometer experiment are the investigation of the interaction between Comet Halley and the solar wind 0.9 AU from the Sun, to within 500 km of the cometary nucleus, and the study of the interplanetary magnetic field. The instrumentation consists of a triaxial and a separate biaxial system of fluxgate sensors of the ring-core type, the associated analog electronics and a digital processor. The measuring ranges of + or 1 16 up to + or - 65536 nT are digitized by a 12-bit analog-to-digital converter. Memory modes allow the bridging of gaps in telemetry coverage of up to 10 days. Because of the dust hazard near closest approach, a magnetometer boom could not be included in the spacecraft design. The magnetic contamination problem was attacked by the use of two magnetometers and by a magnetic-cleanliness program. In-flight results show that the instrument is working flawlessly, though magnetic-contamination problems remain.

Neubauer, F. M.; Acuna, M. H.; Burlaga, L. F.; Franke, B.; Gramkow, B.; Mariani, F.; Musmann, G.; Ness, N. F.; Schmidt, H. U.; Terenzi, T.

1986-01-01

183

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.

184

Photospheric and coronal magnetic fields  

SciTech Connect

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

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

1991-01-01

185

Large-scale solar magnetic fields  

Microsoft Academic Search

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

R. Howard

1977-01-01

186

Magnetic Field - Stellar Winds Interaction  

NASA Astrophysics Data System (ADS)

As per the recent study by the MiMeS collaboration, only about 10% of massive stars possess organized global magnetic fields, typically dipolar in nature. The competition between such magnetic fields and highly non-linear radiative forces that drive the stellar winds leads to a highly complex interaction. Such an interplay can lead to a number of observable phenomena, e.g. X-ray, wind confinement, rapid stellar spindown. However, due to its complexity, such an interaction cannot usually be modeled analytically, instead numerical modeling becomes a necessary tool. In this talk, I will discuss how numerical magnetohydrodynamic (MHD) simulations are employed to understand the nature of such magnetized massive star winds.

ud-Doula, Asif

2015-01-01

187

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.

188

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

189

Studies of solar magnetic fields  

Microsoft Academic Search

The telescope, spectrograph, and magnetograph at the 150-ft Tower Telescope are described, and a chronology of changes in the instrumentation is given. The average magnetic field strengths over the last seven years are discussed. The changes in polarity at the poles of the Sun are described. The characteristics of these polarity reversals at both poles are similar. A reversal is

Robert Howard

1974-01-01

190

Ring current decay time model: Forecasting the recovery phase of magnetic storms  

NASA Astrophysics Data System (ADS)

Magnetic storms are caused by changes in the currents flowing near the Earth, particularly by the enhanced ring current. One important thing related to storms development is to know how, how much and how long the energy injected into the inner magnetosphere enhancing the ring current during the main phase will be available there before to be fully dissipated during the recovery phase. The ring current dynamics is described through the energy balance equation, where a key role is played by the decay time parameter ?. Two kind of models depending on diverse geophysical parameters have been introduced for this important function. One of them, based on the generally observed dependence on Dst, and the other depending on the energy input related to the electric field vBS, where v is the solar wind velocity and BS is the southward component of the interplanetary magnetic field. In this work we analyze the recovery phase of storms comparing the two kind of models through diverse study cases from the OMNI database. We assume that the decay time depends on Dst and Dst-peak during the recovery of storms because during that phase the energy injection, usually considered as proportional to vBS, ceases. We show that the observed data during the early recovery is better described by the model based on Dst, but during the late recovery it is necessary to include, as a fastener, an exponential model resulting from a constant or null injection. This indicates that the whole recovery phase of storms should be described by a two-step model which considers both approaches.

Monreal MacMahon, Ricardo; Llop-Romero, Cecilia

2010-05-01

191

Observation of spin-wave soliton fractals in magnetic film active feedback rings.  

PubMed

The manifestation of fractals in soliton dynamics has been observed for the first time. The experiment utilized self-generated spin-wave envelope solitons in a magnetic film based active feedback ring. At high ring gain, the soliton that circulates in the ring breathes in a fractal pattern. The corresponding power frequency spectrum shows a comb structure, with each peak in the comb having its own comb, and so on, to finer and finer scales. PMID:16712392

Wu, Mingzhong; Kalinikos, Boris A; Carr, Lincoln D; Patton, Carl E

2006-05-12

192

Kinetic model of the inner magnetosphere with arbitrary magnetic field  

NASA Astrophysics Data System (ADS)

Theoretical and numerical modifications to an inner magnetosphere model—Hot Electron Ion Drift Integrator (HEIDI)—were implemented, in order to accommodate for a nondipolar arbitrary magnetic field. While the dipolar solution for the geomagnetic field during quiet times represents a reasonable assumption in the near-Earth closed field region, during storm activity this assumption becomes invalid. HEIDI solves the time-dependent, gyration- and bounce-averaged kinetic equation for the phase space density of one or more ring current species. New equations are derived for the bounce-averaged coefficients for the distribution function, and their numerical implementation is discussed. Also, numerically solving all the bounce-averaged coefficients for the dipole case does not change the results significantly from the analytical approximation of Ejiri (1978). However, distorting the magnetic field changes all bounce-averaged coefficients that make up the kinetic equation. Initial simulations show that changing the magnetic field changes the whole topology of the ring current. This is because the drifts are altered due to dayside compression and nightside stretching of the field. Therefore, at certain locations, the nondipolar magnetic drifts can dominate the convective drifts, considerably altering the pressure distribution in the equatorial plane.

Ilie, Raluca; Liemohn, Michael W.; Toth, Gabor; Skoug, Ruth M.

2012-04-01

193

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

194

Development Trends in High Field Magnet Technology  

Microsoft Academic Search

The production of high magnetic fields using low temperature superconductors (LTS) has become common place. However, large magnet sizes and associated high cooling costs have often precluded the full utilization of these research capabilities. Recent advances in internal Sn superconductors and cryogen free technology have opened up a new era in superconducting magnet development. Ultra-compact, laboratory sized magnets producing fields

R. Harrison; R. Bateman; J. Brown; F. Domptail; C. M. Friend; P. Ghoshal; C. King; A. Van der Linden; Z. Melhem; P. Noonan; A. Twin; M. Field; S. Hong; J. Parrell; Y. Zhang

2008-01-01

195

Variability in Martian Magnetic Field Topology  

NASA Astrophysics Data System (ADS)

We have determined the locations of open and closed magnetic field lines at Mars as a function of four different controlling influences: solar wind magnetic field direction, solar wind pressure, martian season, and solar EUV flux.

Brain, D. A.; Halekas, J. S.; Eastwood, J. P.; Ulusen, D.; Lillis, R. J.

2014-07-01

196

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

197

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

198

Topological constraints in magnetic field relaxation  

NASA Astrophysics Data System (ADS)

Stability and reconnection of magnetic fields play a fundamental role in natural and manmade plasma. In these applications the field's topology determines the stability of the magnetic field. Here I will describe the importance of one topology quantifier, the magnetic helicity, which impedes any free decay of the magnetic energy. Further constraints come from the fixed point index which hinders the field to relax into the Taylor state.

Candelaresi, S.

2014-10-01

199

Anomalous global strings and primordial magnetic fields  

SciTech Connect

We propose a new mechanism for the generation of primordial magnetic fields, making use of the magnetic fields which are induced by anomalous global strings, such as pion and axion strings, which couple to electromagnetism via Wess-Zumino type interactions. We calculate the magnitude and coherence length of these fields. They are seen to depend on the string dynamics. With optimistic assumptions, both the magnitude and coherence scale of the induced magnetic fields can be large enough to explain the seed magnetic fields of greater than 10{sup {minus}23} G necessary to produce the observed galactic magnetic fields via the galactic dynamo mechanism. {copyright} {ital 1999} {ital The American Physical Society}

Brandenberger, R.H. [Department of Physics, Brown University, Providence, Rhode Island 02912 (United States)] [Department of Physics, Brown University, Providence, Rhode Island 02912 (United States); Zhang, X. [CCAST (World Laboratory), P.O. Box 8730, Beijing 100080, Peoples Republic of (China)] [CCAST (World Laboratory), P.O. Box 8730, Beijing 100080, Peoples Republic of (China); [Institute of High Energy Physics, Academia Sinica, Beijing 100039, Peoples Republic of (China)

1999-04-01

200

Applied Magnetic Field Enhances Arc Vapor Deposition  

NASA Technical Reports Server (NTRS)

Applied magnetic field enhances performance of vaporization part of arc vapor deposition apparatus. When no magnetic field applied by external means, arc wonders semirandomly over cathode, with net motion toward electrical feedthrough. When magnetic field applied arc moves circumferentially around cathode, and downward motion suppressed.

Miller, T. A.; Loutfy, R. O.; Withers, J. C.

1993-01-01

201

Mars: a magnetic field due to thermoremanence?  

Microsoft Academic Search

Presently available magnetic field data suggest a dipole moment of Mars of less than 10?4 times the Earth's dipole moment. Presumably, Mars does not have an active dynamo at present which could give rise to a significant magnetic field. Nevertheless, the presently available data do not rule out a minor intrinsic field which may originate from a magnetized lithosphere. The

Martin Leweling; Tilman Spohn

1997-01-01

202

MAXWELLIAN FIELD EXPANSION OF HELICAL MAGNET  

Microsoft Academic Search

Three dimensional (3D) magnetic field calculated by the computer code TOSCA was analyzed including the fring- ing field region. The magnetic field in the median plane was well simulated by a simple function. Off median plane, contributions from the coils should be taken into account. Superconducting helical dipole magnets will be used in RHIC as Siberian snakes and rotators(1). Extensive

K. Hatanaka; T. Katayama; T. Tominaka

1998-01-01

203

Prediction of the interplanetary magnetic field strength  

Microsoft Academic Search

A new model of the coronal and interplanetary magnetic field can predict both the interplanetary magnetic field strength and its polarity from measurements of the photospheric magnetic field. The model includes the effects of the large-scale horizontal electric currents flowing in the inner corona, of the warped heliospheric current sheet in the upper corona, and of volume currents flowing in

Xuepu Zhao; J. Todd Hoeksema

1995-01-01

204

CORONAL MAGNETIC FIELD MEASUREMENTS THROUGH GYRORESONANCE EMISSION  

E-print Network

observations have provided a direct measurement of magnetic field strengths in the solar corona. It is a happy probes of the magnetic field strength above active regions, and this unique capability is one to a different magnetic field strength, the coronal structure can be "peeled away" by using different frequencies

White, Stephen

205

Morphology and magnetic flux distribution in superparamagnetic, single-crystalline Fe3O4 nanoparticle rings  

NASA Astrophysics Data System (ADS)

This study reports on the correlation between crystal orientation and magnetic flux distribution of Fe3O4 nanoparticles in the form of self-assembled rings. High-resolution transmission electron microscopy demonstrated that the nanoparticles were single-crystalline, highly monodispersed, (25 nm average diameter), and showed no appreciable lattice imperfections such as twins or stacking faults. Electron holography studies of these superparamagnetic nanoparticle rings indicated significant fluctuations in the magnetic flux lines, consistent with variations in the magnetocrystalline anisotropy of the nanoparticles. The observations provide useful information for a deeper understanding of the micromagnetics of ultrasmall nanoparticles, where the magnetic dipolar interaction competes with the magnetic anisotropy.

Takeno, Yumu; Murakami, Yasukazu; Sato, Takeshi; Tanigaki, Toshiaki; Park, Hyun Soon; Shindo, Daisuke; Ferguson, R. Matthew; Krishnan, Kannan M.

2014-11-01

206

Morphology and magnetic flux distribution in superparamagnetic, single-crystalline Fe3O4 nanoparticle rings.  

PubMed

This study reports on the correlation between crystal orientation and magnetic flux distribution of Fe3O4 nanoparticles in the form of self-assembled rings. High-resolution transmission electron microscopy demonstrated that the nanoparticles were single-crystalline, highly monodispersed, (25?nm average diameter), and showed no appreciable lattice imperfections such as twins or stacking faults. Electron holography studies of these superparamagnetic nanoparticle rings indicated significant fluctuations in the magnetic flux lines, consistent with variations in the magnetocrystalline anisotropy of the nanoparticles. The observations provide useful information for a deeper understanding of the micromagnetics of ultrasmall nanoparticles, where the magnetic dipolar interaction competes with the magnetic anisotropy. PMID:25422526

Takeno, Yumu; Murakami, Yasukazu; Sato, Takeshi; Tanigaki, Toshiaki; Park, Hyun Soon; Shindo, Daisuke; Ferguson, R Matthew; Krishnan, Kannan M

2014-11-01

207

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

208

Domain structures in complex 3D magnetic fields  

NASA Astrophysics Data System (ADS)

The numerous magnetic fragments that populate the mixed-polarity, quiet-Sun photosphere give rise to many interesting topological features in the corona. In light of this, much recent work has gone into classifying the configurations that arise from simple, point-source potential-field models in efforts to determine the nature of the quiet-Sun magnetic field. These studies have ranged from systematic and detailed examinations of magnetic fields arising from only a handful of sources, involving classifying the configurations that arise (and how some states may bifurcate into other states), to statistical studies of the overall properties of fields arising from hundreds of magnetic sources. Such studies have greatly increased our understanding of what we might expect the magnetic field over the quiet Sun to behave like; the purpose of the study presented here is to extend this understanding further by examining the structure of the individual domains (the regions in space through which pairs of opposite-polarity sources are connected). In particular, the features of lesser-known domain structures that are absent from fields arising from only a few sources and overlooked by sweeping statistical studies are documented. In spite of the incredible complexity of the coronal field, previous studies have shown that there are only two types of building block in a potential field arising from coplanar point sources: namely, an isolated dome, bounded by a single unbroken separatrix surface, and a separator-ring domain, engirdled by a ring of separators. However, it is demonstrated here how both isolated domains and separator-ring domains may be categorised further depending upon their particular geometrical and topological traits. As many models predict coronal heating at topologically distinct features in magnetic fields such as null points, separators and separatrices, for any such models to be applied to general fields would require a scheme for identifying which topological features are related to a given domain. The study here explores some of the issues that would need to be taken into account by such a scheme, and in particular the problems associated with trying to deduce the properties of a general magnetic field from knowledge of domain footprints alone. Animated 3D-rotational views of some of the figures in this manuscript may be viewed in AVI, MPEG and animated-GIF formats by visiting http://www-solar.mcs.st-and.ac.uk/robertc/animations/blocks.html and following the desired link.

Close, R. M.; Parnell, C. E.; Priest, E. R.

209

Magnetic field sources and their threat to magnetic media  

NASA Technical Reports Server (NTRS)

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

Jewell, Steve

1993-01-01

210

Quantitative digital detection of magnetic beads using pseudo-spin-valve rings for multiplexed bioassays  

NASA Astrophysics Data System (ADS)

We present a magnetic multiplexed assay technology which encodes the identities of target biomolecules according to the moment of magnetic beads to which they are attached. An active digital technique based on a microfabricated magnetoresistive ring-shaped sensor is demonstrated, which can distinguish the magnetic moments of micron-sized superparamagnetic beads. We propose that this development is key to combining nonvolatile magnetic labeling with biochemical libraries for high-throughput bioassays and rapid multiplexed detection.

Llandro, J.; Hayward, T. J.; Morecroft, D.; Bland, J. A. C.; Castaño, F. J.; Colin, I. A.; Ross, C. A.

2007-11-01

211

Thinned fiber Bragg grating magnetic field sensor with magnetic fluid  

Microsoft Academic Search

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

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

2011-01-01

212

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

213

Features of the Martian Magnetic Field Structure  

Microsoft Academic Search

Based on the single-fluid MHD model of Mars space simulation, this paper has studied the magnetic field structure in the near-Mars space and investigated the influence of Martian crustal magnetic anomalies on the magnetic field structure. In the process of the solar wind interaction with Mars, the bow shock and magnetic pile-up region are produced. The interplanetary magnetic lines are

Yi-Teng Zhang; Lei Li

2009-01-01

214

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.

215

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

216

Graphene in high magnetic fields  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

217

Dipole in a magnetic field, work, and quantum spin.  

PubMed

The behavior of an atom in a nonuniform magnetic field is analyzed, as well as the motion of a classical magnetic dipole (a spinning charged ball) and a rotating charged ring. For the atom it is shown that, while the magnetic field does no work on the electron-orbital contribution to the magnetic moment (the source of translational kinetic energy being the internal energy of the atom), whether or not it does work on the electron-spin contribution to the magnetic moment depends on whether the electron has an intrinsic rotational kinetic energy associated with its spin. A rotational kinetic energy for the electron is shown to be consistent with the Dirac equation. If the electron does have a rotational kinetic energy, the acceleration of a silver atom in a Stern-Gerlach experiment or the emission of a photon from an electron spin flip can be explained without requiring the magnetic field to do work. For a constant magnetic field gradient along the z axis, it is found that the classical objects oscillate in simple harmonic motion along the z axis, the total kinetic energy -- translational plus rotational -- being a constant of the motion. For the charged ball, the change in rotational kinetic energy is associated only with a change in the precession frequency, the rotation rate about the figure axis remaining constant. PMID:18517545

Deissler, Robert J

2008-03-01

218

Vlasov Equation In Magnetic Field  

E-print Network

The linearized Vlasov equation for a plasma system in a uniform magnetic field and the corresponding linear Vlasov operator are studied. The spectrum and the corresponding eigenfunctions of the Vlasov operator are found. The spectrum of this operator consists of two parts: one is continuous and real; the other is discrete and complex. Interestingly, the real eigenvalues are infinitely degenerate, which causes difficulty solving this initial value problem by using the conventional eigenfunction expansion method. Finally, the Vlasov equation is solved by the resolvent method.

Biao Wu

1999-09-07

219

An analytic solar magnetic field model  

Microsoft Academic Search

We describe a simple analytic model for the magnetic field in the solar corona and interplanetary space which is appropriate to solar minimum conditions. The model combines an azimuthal current sheet in the equatorial plane with an axisymmetric multipole field representing the internal magnetic field of the Sun. The radial component of the field filling interplanetary space is approximately monopolar

M. Banaszkiewicz; W. I. Axford; J. F. McKenzie

1998-01-01

220

On the origin of solar magnetic fields  

Microsoft Academic Search

A fresh approach to the theoretical problems raised by observations of solar magnetic fields is outlined. Tentative conclusions are made that the large-scale magnetic field from which Cowling's (1953) hypothetical toroidal field is generated by differential rotation is not itself regenerated by diffusive processes in the sun's outer layers and that this field enters the differentially rotating layer from below

D. Layzer; R. Rosner; H. T. Doyle

1979-01-01

221

Magnetic field effects on microwave absorbing materials  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

222

Full 180° magnetization reversal with electric fields.  

PubMed

Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals. PMID:25512070

Wang, J J; Hu, J M; Ma, J; Zhang, J X; Chen, L Q; Nan, C W

2014-01-01

223

Full 180° Magnetization Reversal with Electric Fields  

NASA Astrophysics Data System (ADS)

Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals.

Wang, J. J.; Hu, J. M.; Ma, J.; Zhang, J. X.; Chen, L. Q.; Nan, C. W.

2014-12-01

224

Full 180° Magnetization Reversal with Electric Fields  

PubMed Central

Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals. PMID:25512070

Wang, J. J.; Hu, J. M.; Ma, J.; Zhang, J. X.; Chen, L. Q.; Nan, C. W.

2014-01-01

225

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

PubMed Central

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

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

2014-01-01

226

Magnetic field effects on the motion of circumplanetary dust  

NASA Astrophysics Data System (ADS)

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

Jontof-Hutter, Daniel Simon

227

Sub arcsec evolution of solar magnetic fields  

Microsoft Academic Search

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

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

2006-01-01

228

Exploring Magnetic Fields with a Compass  

ERIC Educational Resources Information Center

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

Lunk, Brandon; Beichner, Robert

2011-01-01

229

Discovery of Magnetic Fields in CPNs  

NASA Astrophysics Data System (ADS)

For the first time we have directly detected magnetic fields in central stars of planetary nebulae by means of spectro-polarimetry with FORS1 at the VLT. In all four objects of our sample we found kilogauss magnetic fields, in NGC 1360 and LSS 1362 with very high significance, while in Abell 36 and EGB 5 the existence of a magnetic field is probable but with less certainty. This discovery supports the hypothesis that the non-spherical symmetry of most planetary nebulae is caused by magnetic fields in AGB stars. Our high discovery rate demands mechanisms to prevent full conservation of magnetic flux during the transition to white dwarfs.

Jordan, S.; Werner, K.; O'Toole, S. J.

2005-07-01

230

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

Microsoft Academic Search

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

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

2010-01-01

231

Neutrino Conversions in Solar Random Magnetic Fields  

E-print Network

We consider the effect of a random magnetic field in the convective zone of the Sun superimposed to a regular magnetic field on resonant neutrino spin-flavour oscillations. We argue for the existence of a field of strongly chaotic nature at the bottom of the convective zone. In contrast to previous attempts we employ in addition a model motivated regular twisting magnetic field profile. In this scenario electron antineutrinos are produced through cascades like $\

V. B Semikoz; E. Torrente-Lujan

1998-09-16

232

Differential rotation of solar magnetic fields  

Microsoft Academic Search

The connection of the differential rotation of solar magnetic fields with the field sign and strength is studied. The synoptic\\u000a maps of magnetic fields over the last three solar cycles taken at the Kitt Peak Observatory served as input data for the study.\\u000a The algorithm of magnetic field filtering over 14 chosen strengt intervals and successive 5-degree latitude zones was

O. A. Andreyeva; Ya. I. Zyelyk; N. N. Stepanian

2008-01-01

233

Magnetic field waves at Uranus  

NASA Technical Reports Server (NTRS)

The research efforts funded by the Uranus Data Analysis Program (UDAP) grant to the Bartol Research Institute (BRI) involved the study of magnetic field waves associated with the Uranian bow shock. Upstream wave studies are motivated as a study of the physics of collisionless shocks. Collisionless shocks in plasmas are capable of 'reflecting' a fraction of the incoming thermal particle distribution and directing the resulting energetic particle motion back into the upstream region. Once within the upstream region, the backward streaming energetic particles convey information of the approaching shock to the supersonic flow. This particle population is responsible for the generation of upstream magnetic and electrostatic fluctuations known as 'upstream waves', for slowing the incoming wind prior to the formation of the shock ramp, and for heating of the upstream plasma. The waves produced at Uranus not only differed in several regards from the observations at other planetary bow shocks, but also gave new information regarding the nature of the reflected particle populations which were largely unmeasurable by the particle instruments. Four distinct magnetic field wave types were observed upstream of the Uranian bow shock: low-frequency Alfven or fast magnetosonic waves excited by energetic protons originating at or behind the bow shock; whistler wave bursts driven by gyrating ion distributions within the shock ramp; and two whistler wave types simultaneously observed upstream of the flanks of the shock and argued to arise from resonance with energetic electrons. In addition, observations of energetic particle distributions by the LECP experiment, thermal particle populations observed by the PLS experiment, and electron plasma oscillations recorded by the PWS experiment proved instrumental to this study and are included to some degree in the papers and presentations supported by this grant.

Smith, Charles W.; Goldstein, Melvyn L.; Lepping, Ronald P.; Mish, William H.; Wong, Hung K.

1994-01-01

234

Early experiences with magnetic rings in resection of the distal colon.  

PubMed

We have developed an anastomosis technique for resection of the distal colon based on the principle of submucosal layer apposition. The anastomosis apparatus consists of two rings of Ertalyte (polyester-polyethyleneterephtalate) containing two magnetic rings of polymer bonded rare earth cobalt. For low anastomoses we developed a magnetic ring holder, protecting cap and hexagonal connecting rod. The working principle is based on progressive compression leading to necrosis of the intermediate mucosal and submucosal layers by increasing magnetic force while bowel healing takes place. After 7 to 17 days the magnets cut through and are propelled by peristalis out of the anastomotic region. From our initial series of five patients we performed three sigmoid resections and two low anterior resections. There were no postoperative complications. Sigmoidoscopic and radiological investigations two weeks postoperatively, showed no evidence of leakage or anastomotic narrowing. The technique and the special advantages of the apparatus are discussed. PMID:7366876

Jansen, A; Keeman, J N; Davies, G A; Klopper, P J

1980-01-01

235

Triangular Ring Sensor with Long Evanescent Field on the Total Internal Reflection Mirror  

NASA Astrophysics Data System (ADS)

A novel biosensor based on a triangular resonator with a long evanescent field on a total internal reflection (TIR) mirror is proposed, and its sensing properties are analyzed for the first time. The sensing properties of the triangular ring resonator are found to be useful in realizing biological and chemical sensors, when the TIR mirror with a sharp incident angle increases the evanescent field owing to the Goos-Hänchen shift. For transverse electric polarized light, an extinction ratio of 16 dB is achieved by changing the refractive index of 1 ×10-5 in the outer region of the TIR mirror block. Then, an extinction ratio of 28 dB and a resonance shift of 160 pm are observed by changing the refractive index of 1 ×10-5 for transverse magnetic polarization.

Kim, Doo Gun; Choi, Young-Wan

2009-07-01

236

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

SciTech Connect

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

Cornacchia, M.; Evans, L.

1985-06-01

237

Bipolar pulse field for magnetic refrigeration  

DOEpatents

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

Lubell, Martin S. (Oak Ridge, TN)

1994-01-01

238

Ringing rocks barren block field, East-Central Pennsylvania  

NASA Astrophysics Data System (ADS)

Huge residual boulders on and near the surface of the woodlands on the slopes of Coffman Hill probably are corestones of a for derived from the early Jurassic diabase sill. Accordingly, they were produced in two stages - first by chemical weathering along joints before Cenozoic regional uplift, then by exhumation of the blocks during Cenozoic dissection of the old lowland surface. The Ringing Rocks barren block field within the woodlands probably resulted from local mass transport of large boulders from a higher part of Coffman Hill by periglacial creep and solifluction during the Pleistocene epoch. Loss of forest cover and removal of matrix from the patch of boulders exposed the blocks to further mechanical and chemical weathering. Persistent shattering of the boulders along joints and minor movement of smaller derived blocks destroyed any inherited debris-flow pattern. Pitting on the bare joint surfaces has resulted from effective solution by rain in the absence of forest shelter and a mantle of soil. In contrast, exfoliation predominates in the surrounding wooded residual boulder field.

Psilovikos, A.; Van Houten, F. B.

1982-06-01

239

Quantum ring solitons and nonlocal effects in plasma wake field excitations  

SciTech Connect

A theoretical investigation of the quantum transverse beam motion for a cold relativistic charged particle beam travelling in a cold, collisionless, strongly magnetized plasma is carried out. This is done by taking into account both the individual quantum nature of the beam particles (single-particle uncertainty relations and spin) and the self consistent interaction generated by the plasma wake field excitation. By adopting a fluid model of a strongly magnetized plasma, the analysis is carried out in the overdense regime (dilute beams) and in the long beam limit. It is shown that the quantum description of the collective transverse beam dynamics is provided by a pair of coupled nonlinear governing equations. It comprises a Poisson-like equation for the plasma wake potential (driven by the beam density) and a 2D spinorial Schroedinger equation for the wave function, whose squared modulus is proportional to the beam density, that is obtained in the Hartree's mean field approximation, after disregarding the exchange interactions. The analysis of this pair of equations, which in general exhibits a strong nonlocal character, is carried out analytically as well as numerically in both the linear and the nonlinear regimes, showing the existence of the quantum beam vortices in the form of Laguerre-Gauss modes and ring envelope solitons, respectively. In particular, when the relation between the plasma wake field response and the beam probability density is strictly local, the pair of the governing equations is reduced to the 2D Gross-Pitaevskii equation that allows one to establish the conditions for the self focusing and collapse. These conditions include the quantum nature of the beam particles. Finally, when the relation between the plasma wake field response and the beam probability density is moderately nonlocal, the above pair of equations permits to follow the spatio-temporal evolution of a quantum ring envelope soliton. Such a structure exhibits small or violent breathing, but it remains very stable for long time.

Fedele, R.; Tanjia, F. [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II', and INFN, Napoli (Italy); De Nicola, S. [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II', and INFN, Napoli (Italy); Istituto Nazionale di Ottica - C. N. R., Pozzuoli (Italy); Jovanovic, D. [Institute of Physics, University of Belgrade, Belgrade (Serbia); Shukla, P. K. [Center of Advanced Studies in Physical Sciences, Ruhr-Universitaet Bochum, Bochum (Germany)

2012-10-15

240

Polar magnetic field reversals on the Sun  

NASA Astrophysics Data System (ADS)

The polar magnetic fields on the Sun have been an attractive subject for solar researches since Babcock measured them in solar cycle 19. One of the remarkable features of the polar magnetic fields is their reversal during the maxima of 11-year sunspot cycles. I have present results of the investigations of the polar magnetic field using SOHO-mdi data. It is found, that the polar magnetic field reversal is detected with mdi data for polar region within 78° 88°. The North Pole has changed polarity in CR1975 (April 2001). The South reversed later in CR1980 (September 2001). The total unsigned magnetic flux does not show the dramatic decreasing during the polar reversals due to omnipresent bi-polar small-scale magnetic elements. The observational and theoretical aspects of the polar magnetic field reversals are discussed.

Benevolenskaya, Elena E.

2007-08-01

241

Exploring Magnetic Fields in Your Environment  

NSDL National Science Digital Library

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

242

On magnetic-field-induced dissipationless electric current in nanowires  

E-print Network

We propose a general design of a metallic double-nanowire structure which may support an equilibrium dissipationless electric current in the presence of magnetic field. The structure consists of a compact wire element of a specific shape, which is periodically extended in one spatial dimension. Topologically, each wire element is equivalent to a ring, which supports a dissipationless current in the presence of magnetic flux similarly to the persistent electric current in a normal metal nanoring. Geometrically, each wire element breaks spatial inversion symmetry so that the equilibrium electric current through the device becomes nonzero. We also argue that the same effect should exist in long planar chiral nanoribbons subjected to external magnetic field.

M. N. Chernodub

2013-03-28

243

Cosmological Magnetic Fields and CMBR Polarization  

E-print Network

A simple introduction to physics of CMBR polarization and the Faraday rotation of the latter in cosmic magnetic field is presented. The content of the lecture is the following: 1. Description of polarization of photons. 2. Polarization field of CMBR. 3. Faraday effect. 4. Cosmic magnetic fields. 5. Faraday rotation of CMBR polarization.

A. D. Dolgov

2005-03-21

244

Representation of magnetic fields in space  

NASA Technical Reports Server (NTRS)

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

Stern, D. P.

1975-01-01

245

Fiber Bragg Grating Magnetic Field Sensor  

Microsoft Academic Search

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

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

2006-01-01

246

Investigations of planetary ring phenomena  

NASA Technical Reports Server (NTRS)

Faint planetary rings, their dynamical behavior and physical properties, were the main focus of the research efforts. The motion of weakly-charged dust through the gravitational and magnetic fields of Jupiter were examined. Several topics concerning features of Saturn's rings were addressed. The origin and fate of the Uranian ring dust is presently being studied.

Burns, Joseph A.

1987-01-01

247

Static uniform magnetic fields and amoebae  

SciTech Connect

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

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

1997-03-01

248

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

249

Magnetic field waves at Uranus  

NASA Technical Reports Server (NTRS)

The proposed research efforts funded by the UDAP grant to the BRI involve the study of magnetic field waves associated with the Uranian bow shock. This is a collaborative venture bringing together investigators at the BRI, Southwest Research Institute (SwRI), and Goddard Space Flight Center (GSFC). In addition, other collaborations have been formed with investigators granted UDAP funds for similar studies and with investigators affiliated with other Voyager experiments. These investigations and the corresponding collaborations are included in the report. The proposed effort as originally conceived included an examination of waves downstream from the shock within the magnetosheath. However, the observations of unexpected complexity and diversity within the upstream region have necessitated that we confine our efforts to those observations recorded upstream of the bow shock on the inbound and outbound legs of the encounter by the Voyager 2 spacecraft.

Smith, Charles W.; Goldstein, Melvyn L.; Lepping, Ronald P.; Mish, William H.; Wong, Hung K.

1991-01-01

250

Lattice distortions in magnetic fields  

NASA Astrophysics Data System (ADS)

A study is made of the stability of the possible lattice structures which result from the magnetic-field-induced lattice deformation introduced by Araujo and Khmelnitskii. The deformed lattice may either be the result of a single distortion occurring along a particular direction or of a superposition of distortions in different directions. In a noninteracting electron model the energy variation of the electron system will determine which final lattice structure is the most stable. When electron interactions are considered in the Hartree approximation we find that the energy variation of the electron system alone will not determine which final structure is the most stable. The latter is then imposed by the lattice itself. If the distortion turns out to be unidirectional then the corresponding charge-density wave should be weakly pinned even in the absence of impurities.

Araujo, Miguel A. N.

1996-09-01

251

Extraterrestrial Magnetic Fields: Achievements and Opportunities  

Microsoft Academic Search

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

EDWARD J. SMITHAND; Charles Sonett

1976-01-01

252

Femtotesla Magnetic Field Measurement with Magnetoresistive Sensors  

Microsoft Academic Search

The measurement of magnetic fields in the femtotesla (fT, 10-15 tesla) range is important for applications such as magnetometry, quantum computing, solid-state nuclear magnetic resonance, and magnetoencephalography. The only sensors capable of detecting these very small fields have been based on low-temperature superconducting quantum interference devices operating at 4.2 kelvin. We present a magnetic field sensor that combines a superconducting

Myriam Pannetier; Claude Fermon; Gerald Le Goff; Juha Simola; Emma Kerr

2004-01-01

253

Dynamics of solar magnetic fields. VI  

Microsoft Academic Search

A mathematical model is developed to consider the evolution of force-free magnetic fields in relation to the displacements of their foot-points. For a magnetic field depending on only two Cartesian coordinates and time, the problem reduces to solving a nonlinear elliptic partial differential equation. As illustration of the physical process, two specific examples of evolving force-free magnetic fields are examined

B. C. Low; Y. Nakagawa

1975-01-01

254

Modeling solar force-free magnetic fields  

Microsoft Academic Search

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

B. C. Low; Y. Q. Lou

1990-01-01

255

Fractal properties of solar magnetic fields  

Microsoft Academic Search

We study the spatial properties of solar magnetic fields using data from the Solar Vector Magnetograph of the Marshall Space\\u000a Flight Center (MSFC) (FeI 5250.2 Å) and SOHO\\/MDI longitudinal magnetic field measurements (Ni 6767.8 Å) (96-min full-disk\\u000a maps). Our study is focused on two objects: the fractal properties of sunspots and the fractal properties of the spatial magnetic\\u000a field distribution

B. A. Ioshpa; V. N. Obridko; E. A. Rudenchik

2008-01-01

256

Fractal properties of solar magnetic fields  

Microsoft Academic Search

We study the spatial properties of solar magnetic fields using data from the Solar Vector Magnetograph of the Marshall Space Flight Center (MSFC) (FeI 5250.2 Å) and SOHO\\/MDI longitudinal magnetic field measurements (Ni 6767.8 Å) (96-min full-disk maps). Our study is focused on two objects: the fractal properties of sunspots and the fractal properties of the spatial magnetic field distribution

B. A. Ioshpa; V. N. Obridko; E. A. Rudenchik

2008-01-01

257

Ferroelectric Cathodes in Transverse Magnetic Fields  

SciTech Connect

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

Alexander Dunaevsky; Yevgeny Raitses; Nathaniel J. Fisch

2002-07-29

258

Magnetic field measurements in tokamak plasmas  

SciTech Connect

The measurement of the poloidal magnetic field in a tokamak plasma from the Zeeman splitting and polarization of the magnetic dipole radiation from heavy ions is discussed. When viewed from a direction perpendicular to the toroidal field, the effect of the poloidal field on the circularly polarized radiation is detectable using a photoelectric polarimeter. The Zeeman splittings for a number of magnetic dipole transitions with wavelengths in the range 2300--9300 A are presented. An imaging polarimeter is proposed that can measure the poloidal magnetic field with space and time resolution.

Feldman, U.; Seely, J.F.; Sheeley,Jr., N.R.; Suckewer, S.; Title, A.M.

1984-11-01

259

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

2015-01-26

260

Five years of magnetic field management  

SciTech Connect

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

Durkin, C.J.; Fogarty, R.P.; Halleran, T.M.; Mark, Dr. D.A.; Mukhopadhyay, A.

1995-01-01

261

Studies of strong magnetic field produced by permanent magnet array for magnetic refrigeration  

NASA Astrophysics Data System (ADS)

The success of a room temperature magnetic refrigerator (RTMR) depends critically on two essential parts: a high magnetic field and a magnetic refrigerant material with large magnetocaloric effect. A carefully designed hollow cylindrical permanent magnet array (HCPMA) can be used to provide strong magnetic field in the cavity, the magnitude of the resulting static field can be even greater than the remanence magnetization of the magnets comprising a HCPMA. A thorough understanding of the magnetic field distribution will provide an invaluable insight into the design and optimization of HCPMA in the reciprocating and rotary RTMR systems. Here, we show a construction of a 16 piece HCPMA with realistic dimensions and we illustrate the mechanism of generating a high magnetic field in such device. We present an effective way to calculate the field distribution of a permanent magnet array with finite size and an unsymmetrical geometry. Furthermore, detailed numerical results of the magnetic field distribution and its dependence on device dimensions are presented.

Xu, X. N.; Lu, D. W.; Yuan, G. Q.; Han, Y. S.; Jin, X.

2004-06-01

262

Magnetic monopole field exposed by electrons  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

263

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in fall 2012. The objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution using a constellation of three identical satellites. The mission shall deliver data that allow access to new insights into the Earth system by improved scientific understanding of the Earth's interior and near-Earth electromagnetic environment. After launch and triple satellite release at an initial altitude of about 490 km, a pair of the satellites will fly side-by-side with slowly decaying altitude, while the third satellite will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission science goals are to provide a unique view into Earth's core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently in the final stage of the development phase, will be addressed. A consortium of European scientific institutes is developing a distributed processing system to produce geophysical (Level 2) data products for the Swarm user community. The setup of the Swarm ground segment and the contents of the data products will be addressed. In case the Swarm satellites are already in orbit, a summary of the on-going mission operations activities will be given.

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

2012-12-01

264

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

265

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

266

Magnetic field optimization of permanent magnet undulators for arbitrary polarization  

NASA Astrophysics Data System (ADS)

Techniques for improving the magnetic field quality of APPLE II undulators are discussed. Individual block characterization including the inhomogeneities of the magnetization permits a precise prediction of field integrals as required for sorting. Specific shimming procedures adapted to the magnetic design of APPLE II undulators have to be employed in order to meet the stringent requirements of insertion devices in third generation synchrotron radiation sources as demonstrated for BESSY.

Bahrdt, J.; Frentrup, W.; Gaupp, A.; Scheer, M.; Englisch, U.

2004-01-01

267

SIMULATING MAGNETIC FIELDS IN THE ANTENNAE GALAXIES  

SciTech Connect

We present self-consistent high-resolution simulations of NGC 4038/4039 (the 'Antennae galaxies') including star formation, supernova feedback, and magnetic fields performed with the N-body/smoothed particle hydrodynamic (SPH) code GADGET, in which magnetohydrodynamics are followed with the SPH method. We vary the initial magnetic field in the progenitor disks from 10{sup -9} to 10{sup -4} G. At the time of the best match with the central region of the Antennae system, the magnetic field has been amplified by compression and shear flows to an equilibrium field value of {approx}10 {mu}G, independent of the initial seed field. These simulations are a proof of the principle that galaxy mergers are efficient drivers for the cosmic evolution of magnetic fields. We present a detailed analysis of the magnetic field structure in the central overlap region. Simulated radio and polarization maps are in good morphological and quantitative agreement with the observations. In particular, the two cores with the highest synchrotron intensity and ridges of regular magnetic fields between the cores and at the root of the southern tidal arm develop naturally in our simulations. This indicates that the simulations are capable of realistically following the evolution of the magnetic fields in a highly nonlinear environment. We also discuss the relevance of the amplification effect for present-day magnetic fields in the context of hierarchical structure formation.

Kotarba, H.; Karl, S. J.; Naab, T.; Johansson, P. H.; Lesch, H. [University Observatory Munich, Scheinerstr. 1, D-81679 Munich (Germany); Dolag, K.; Stasyszyn, F. A., E-mail: kotarba@usm.lmu.d [Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85741 Garching (Germany)

2010-06-20

268

Fine structure of solar magnetic fields  

Microsoft Academic Search

The deduction of magnetic fields from chromospheric structure is extended to active regions and transverse fields. Fields independently predicted by these rules from a high resolution Ha filtergram are compared with a high resolution magnetogram. The Ha method has the advantage over conventional magnetograms that it shows transverse fields and relates the fields to the real Sun. It has the

Harold Zirin

1972-01-01

269

Magnetic-field effects in non-magnetic glasses  

NASA Astrophysics Data System (ADS)

Recently, it was found that the multi-component glass a-BaO-Al2O3-SiO2 exhibits unusual magnetic properties at very low temperatures. Thus the question arises whether this is a specialty of that particular glass or a more general phenomenon. We report here on our studies of the magnetic-field dependence of the dielectric properties of the borosilicate glass BK7 which contains only a negligible amount of magnetic impurities. Since this glass also responds sensitively to magnetic fields, our investigations demonstrate that the reaction of glasses to magnetic fields is not caused by magnetic impurities but reflects a more general phenomenon. In addition, we have observed that the variation of the dielectric constant and the loss angle with magnetic field depend on the amplitude of the electric field that is used to measure the glass capacitance. We present the data and discuss possible origins of the magnetic-field phenomena in non-magnetic glasses.

Wohlfahrt, M.; Strehlow, P.; Enss, C.; Hunklinger, S.

2001-12-01

270

Thinned fiber Bragg grating magnetic field sensor with magnetic fluid  

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

271

Improved field stability in RFQ structures with vane-coupling rings  

SciTech Connect

The small apertures common in many RFQ linac designs lead to tuning difficulties, primarily because asymmetries in the quadrant fields can arise as a result of small non-uniformities in the vane-to-vane capacitances. Sensitivity to such capacitance or other tuning variation in the quadrants is greatly reduced by the introduction of pairs of vane-coupling rings that provide periodic electrical connections between diametrically opposite vanes. Results of measurements on a cold model RFQ structure with and without vane-coupling rings are presented. The number of rings required for field stabilization and the effect of rings on mode frequencies are discussed.

Schneider, H.R.; Lancaster, H.

1983-03-01

272

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

SciTech Connect

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

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

2005-05-16

273

Videomagnetograph studies of solar magnetic fields  

Microsoft Academic Search

Observations of magnetic field diffusion in weak plage regions have been made using the analog videomagnetograph at the California Institute of Technology. Points of magnetic flux, usually described as ‘vertex points’ of the magnetic network, were found to have a mean lifetime of three to four days, and to disperse primarily by means of two mechanisms: a random walk with

Robert C. Smithson

1973-01-01

274

Ultrahigh Q-factor and figure of merit Fano metamaterial based on dark ring magnetic mode  

NASA Astrophysics Data System (ADS)

A planar terahertz (THz) metamaterial with both ultrahigh quality (Q) factor and high figure of merit (FOM) based on the ring magnetic mode and Fano resonance is proposed. The nonradiative dark modes are induced by the tiny symmetry breaking of the symmetrical split resonance rings (sSRR) under the normal illumination of THz waves with both electric and magnetic components lay in the structure plane. The samples are fabricated and measured with a conventional THz time-domain spectroscopy. Such a sharp and pronounced resonance can benefit the applications such as biosensor, narrowband filter, and laser sparser.

Wang, Bo; Xie, Zhenwei; Feng, Shengfei; Zhang, Bo; Zhang, Yan

2015-01-01

275

The Moessbauer effect in homogeneous magnetic field  

E-print Network

We derive the probability of the Moessbauer effect realized by the charged particle moving in the homogeneous magnetic field, or, in accelerating field. The submitted approach represents new deal of the Moessbauer physics. Key

Miroslav Pardy

2014-03-20

276

Magnetic field decay in model SSC dipoles  

SciTech Connect

We have observed that some of our model SSC dipoles have long time constant decays of the magnetic field harmonics with amplitudes large enough to result in significant beam loss, if they are not corrected. The magnets were run at constant current at the SSC injection field level of 0.3 tesla for one to three hours and changes in the magnetic field were observed. One explanation for the observed field decay is time dependent superconductor magnetization. Another explanation involves flux creep or flux flow. Data are presented on how the decay changes with previous flux history. Similar magnets with different Nb-Ti filament spacings and matrix materials have different long time field decay. A theoretical model using proximity coupling and flux creep for the observed field decay is discussed. 10 refs., 5 figs., 2 tabs.

Gilbert, W.S.; Althaus, R.F.; Barale, P.J.; Benjegerdes, R.W.; Green, M.A.; Green, M.I.; Scanlan, R.M.

1988-08-01

277

Magnetic Field Seeding through Supernova Feedback  

NASA Astrophysics Data System (ADS)

Stellar feedback occurring at small-scales can significantly impact the evolution of galaxies at much larger scales. For example, an appropriate feedback mechanism, including thermal and radiative components, can help regulate star formation, particularly in low-mass galaxies. While feedback models are generally prevalent in numerical simulations, the magnetic component is often neglected. However, measurements of galaxies indicate the presence of fields with a strength on the order of µG. Previous studies have demonstrated the formation of these fields through the amplification of a primordial magnetic field. Here, we describe a self-consistent prescription where magnetic fields are injected in supernova injections, calibrated by observations of magnetic fields in supernova remnants. These fields will then become seeds that evolve by way of mixing and turbulence to result in galactic-scale magnetic fields. As a proof of concept, we apply this method to model the supernova of a single Population III star and trace the evolution of the injected magnetic field. Future studies will apply this prescription to study not only the effects of magnetic fields on galaxy formation and evolution, but also the growth of the magnetized bubbles that form in the IGM.

Koh, Daegene; Wise, John

2015-01-01

278

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

2011-03-21

279

Exact scattering matrix of graphs in magnetic field and quantum noise  

NASA Astrophysics Data System (ADS)

We consider arbitrary quantum wire networks modelled by finite, noncompact, connected quantum graphs in the presence of an external magnetic field. We find a general formula for the total scattering matrix of the network in terms of its local scattering properties and its metric structure. This is applied to a quantum ring with N external edges. Connecting the external edges of the ring to heat reservoirs, we study the quantum transport on the graph in ambient magnetic field. We consider two types of dynamics on the ring: the free Schrödinger and the free massless Dirac equations. For each case, a detailed study of the thermal noise is performed analytically. Interestingly enough, in presence of a magnetic field, the standard linear Johnson-Nyquist law for the low temperature behaviour of the thermal noise becomes nonlinear. The precise regime of validity of this effect is discussed and a typical signature of the underlying dynamics is observed.

Caudrelier, Vincent; Mintchev, Mihail; Ragoucy, Eric

2014-08-01

280

Parker's magnetic field and relativistic jets  

NASA Astrophysics Data System (ADS)

We consider the motion of high-energy charged particles (cosmic rays) in Parker's spiral magnetic field. We show that under radial particle ejection from a sphere outside which there is Parker's magnetic field, all of the particles escaping from the sphere are focused either along the field symmetry axis or in the equatorial plane, depending on the field polarity. Based on the results obtained, we propose a possible model that explains the origin of relativistic jets.

Kichigin, G. N.

2014-10-01

281

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

SciTech Connect

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

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

2002-04-22

282

Magnetic isotope and magnetic field effects on the DNA synthesis  

PubMed Central

Magnetic isotope and magnetic field effects on the rate of DNA synthesis catalysed by polymerases ? with isotopic ions 24Mg2+, 25Mg2+ and 26Mg2+ in the catalytic sites were detected. No difference in enzymatic activity was found between polymerases ? carrying 24Mg2+ and 26Mg2+ ions with spinless, non-magnetic nuclei 24Mg and 26Mg. However, 25Mg2+ ions with magnetic nucleus 25Mg were shown to suppress enzymatic activity by two to three times with respect to the enzymatic activity of polymerases ? with 24Mg2+ and 26Mg2+ ions. Such an isotopic dependence directly indicates that in the DNA synthesis magnetic mass-independent isotope effect functions. Similar effect is exhibited by polymerases ? with Zn2+ ions carrying magnetic 67Zn and non-magnetic 64Zn nuclei, respectively. A new, ion–radical mechanism of the DNA synthesis is suggested to explain these effects. Magnetic field dependence of the magnesium-catalysed DNA synthesis is in a perfect agreement with the proposed ion–radical mechanism. It is pointed out that the magnetic isotope and magnetic field effects may be used for medicinal purposes (trans-cranial magnetic treatment of cognitive deceases, cell proliferation, control of the cancer cells, etc). PMID:23851636

Buchachenko, Anatoly L.; Orlov, Alexei P.; Kuznetsov, Dmitry A.; Breslavskaya, Natalia N.

2013-01-01

283

MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. I. FORCE-FREE MAGNETIC FIELDS B. Fornberg,2  

E-print Network

MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. I. FORCE-FREE MAGNETIC FIELDS N. Flyer,1 B Axisymmetric force-free magnetic fields external to a unit sphere are studied as solutions to boundary value against expansion into the unbounded space. This property as a basic mechanism for solar coronal mass

Fornberg, Bengt

284

The magnetic field of ? Ori A  

NASA Astrophysics Data System (ADS)

Magnetic fields play a significant role in the evolution of massive stars. About 7% of massive stars are found to be magnetic at a level detectable with current instrumentation (Wade et al. 2013) and only a few magnetic O stars are known. Detecting magnetic field in O stars is particularly challenging because they only have few, often broad, lines to measure the field, which leads to a deficit in the knowledge of the basic magnetic properties of O stars. We present new spectropolarimetric Narval observations of ? Ori A. We also provide a new analysis of both the new and older data taking binarity into account. The aim of this study was to confirm the presence of a magnetic field in ? Ori A. We identify that it belongs to ? Ori Aa and characterize it.

Blazère, A.; Neiner, C.; Bouret, J.-C.; Tkachenko, A.

2015-01-01

285

High concentration ferronematics in low magnetic fields  

E-print Network

We investigated experimentally the magneto-optical and dielectric properties of magnetic-nanoparticle-doped nematic liquid crystals (ferronematics). Our studies focus on the effect of the very small orienting bias magnetic field $B_{bias}$, and that of the nematic director pretilt at the boundary surfaces in our systems sensitive to low magnetic fields. Based on the results we assert that $B_{bias}$ is not necessarily required for a detectable response to low magnetic fields, and that the initial pretilt, as well as the aggregation of the nanoparticles play an important (though not yet explored enough) role.

T. Tóth-Katona; P. Salamon; N. Éber; N. Tomašovi?ová; Z. Mitróová; P. Kop?anský

2014-09-05

286

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

287

Fluctuating magnetic field induced resonant activation.  

PubMed

In this paper, we have studied the properties of a Brownian particle at stationary state in the presence of a fluctuating magnetic field. Time dependence of the field makes the system thermodynamically open. As a signature of that the steady state distribution function becomes function of damping strength, intensity of fluctuations and constant parts of the applied magnetic field. It also depends on the correlation time of the fluctuating magnetic field. Our another observation is that the random magnetic field can induce the resonant activation phenomenon. Here correlation time is increased under the fixed variance of the fluctuating field. But if the correlation time (?) increases under the fixed field strength then the mean first passage time rapidly grows at low ? and it almost converges at other limit. This is sharp contrast to the usual colored noise driven open system case where the mean first passage time diverges exponentially. We have also observed that a giant enhancement of barrier crossing rate occurs particularly at large strength of constant parts of the applied magnetic field even for very weak fluctuating magnetic field. Finally, break down of the Arrhenius result and disappearance of the Kramers' turn over phenomenon may occur in the presence of a fluctuating magnetic field. PMID:25494726

Mondal, Shrabani; Das, Sudip; Baura, Alendu; Bag, Bidhan Chandra

2014-12-14

288

Fluctuating magnetic field induced resonant activation  

NASA Astrophysics Data System (ADS)

In this paper, we have studied the properties of a Brownian particle at stationary state in the presence of a fluctuating magnetic field. Time dependence of the field makes the system thermodynamically open. As a signature of that the steady state distribution function becomes function of damping strength, intensity of fluctuations and constant parts of the applied magnetic field. It also depends on the correlation time of the fluctuating magnetic field. Our another observation is that the random magnetic field can induce the resonant activation phenomenon. Here correlation time is increased under the fixed variance of the fluctuating field. But if the correlation time (?) increases under the fixed field strength then the mean first passage time rapidly grows at low ? and it almost converges at other limit. This is sharp contrast to the usual colored noise driven open system case where the mean first passage time diverges exponentially. We have also observed that a giant enhancement of barrier crossing rate occurs particularly at large strength of constant parts of the applied magnetic field even for very weak fluctuating magnetic field. Finally, break down of the Arrhenius result and disappearance of the Kramers' turn over phenomenon may occur in the presence of a fluctuating magnetic field.

Mondal, Shrabani; Das, Sudip; Baura, Alendu; Bag, Bidhan Chandra

2014-12-01

289

Homogenization of nanostructured media in magnetic field  

NASA Astrophysics Data System (ADS)

Problem of homogenization of nanostructured media in magnetic field has been considered. Possibility of introduction of effective material parameters dielectric permittivity and magnetic permeability for three classes of media such as magnetic metal nanostructures, film metal-dielectric composite media and 3D-nanocomposites on the base of opal matrices has been investigated. It has been stated that the introduction of effective parameters far from magnetic resonance conditions is possible at millimeter waveband frequencies. Strict introduction of effective magnetic permeability of nanostructured media near magnetic resonance is not possible.

Rinkevich, A. B.; Perov, D. V.

2014-11-01

290

Two-axis magnetic field sensor  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

291

Orientation effects in pulsed magnetic field treatment  

Microsoft Academic Search

This paper presents the orientation effects on residual stress release by pulsed magnetic field treatment. Specimens are produced by tungsten inert gas (TIG) welding and the initial residual stresses in them are measured by the hole-drilling method. With different orientations these specimens are treated in the same magnetic field and the residual stresses are measured for the second time. By

Cai Zhipeng; Lin Jian; Zhao Haiyan; Lu Anli

2005-01-01

292

A search for weak stellar magnetic fields  

Microsoft Academic Search

The magnetic fields of normal main sequence stars, supergiants, and mercury-manganese stars were measured in metal lines with the magnetometer of the main stellar spectrograph and in hydrogen lines with the spectropolarimeter at the 6-meter telescope. These data were analyzed statistically with data obtained by other authors. It is concluded that the dipole magnetic fields of the stars studied hardly

Yu. V. Glagolevskij; I. I. Romanyuk; I. D. Najdenov; V. G. Shtol

1991-01-01

293

Magnetic Fields at the Center of Coils  

ERIC Educational Resources Information Center

In this note we synthesize and extend expressions for the magnetic field at the center of very short and very long current-carrying coils. Elementary physics textbooks present the following equation for the magnetic field inside a very long current-carrying coil (solenoid): B[subscript sol] = µ[subscript 0] (N/L) I, (1) where I is the current, N…

Binder, Philippe; Hui, Kaleonui; Goldman, Jesse

2014-01-01

294

Space Quantization in a Gyrating Magnetic Field  

Microsoft Academic Search

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

I. I. Rabi

1937-01-01

295

The magnetic field of an infinite solenoid  

NASA Astrophysics Data System (ADS)

We use the Biot-Savart law for filamentary currents to show that the magnetic field produced by an infinitely long straight strip of infinitesimal width carrying a uniform transverse surface current can be written in simple geometrical terms. We use this result to calculate the magnetic field of an infinite solenoid of arbitrary but uniform cross-sectional shape.

Espinosa, Olivier; Slusarenko, Viktor

2003-09-01

296

Coulomb crystals in the magnetic field.  

PubMed

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

Baiko, D A

2009-10-01

297

Does the solar magnetic field increase?  

Microsoft Academic Search

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

V. A. Kotov; I. V. Kotova

2001-01-01

298

Permanent magnet edge-field quadrupole  

DOEpatents

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

Tatchyn, R.O.

1997-01-21

299

Permanent magnet edge-field quadrupole  

DOEpatents

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

Tatchyn, Roman O. (Mountain View, CA)

1997-01-01

300

Solar magnetic fields and the dynamo theory  

Microsoft Academic Search

Unlike Earth’s dipolar magnetic fields, solar magnetic fields consist of wide ranges of length-scales and strengths, and interestingly, they evolve in a cyclic fashion with a 22-year periodicity. A magnetohydrodynamic dynamo operating in the Sun is most likely responsible for producing the solar magnetic activity cycle. While the first solar dynamo models were built half a century ago, recent views

M. Dikpati

2005-01-01

301

Fields from a relativistic magnetic explosion  

NASA Astrophysics Data System (ADS)

Following Prendergast, we study the relativistically expanding electromagnetic fields generated by an axisymmetric explosion of magnetic energy in a small volume. The magnetic field expands uniformly either within a cone or in all directions and it is therefore accompanied by an electric field. In the highly conducting plasma, the charges move to annul the electric field in the frame of the moving plasma. The solutions presented are analytical and semi-analytical. We find that the time-scale for the winding up of the initial magnetic field is crucial, as short time-scales lead to strong radiant fields. Assuming a magnetic field of 1013G emerging from a magnetosphere of 109cm, we end with a jet when confined by a pressure environment that falls more slowly than r-4. The jet carries energy of 1051erg, which is mostly due to differential rotation at the base.

Gourgouliatos, K. N.; Lynden-Bell, D.

2008-11-01

302

Magnetic field amplification in supernova shock precursor  

NASA Astrophysics Data System (ADS)

Galactic cosmic rays are believed to be mostly accelerated at supernova shocks. However, the interstellar magnetic field is too weak to efficiently accelerate galactic cosmic rays up to the highest energies. A stronger magnetic field in the preshock region could provide the efficiency required. Cosmic ray streaming instability has been claimed to be responsible for the amplification of precursor magnetic fields. An alternative mechanism has been proposed in which the cosmic ray pressure gradient forms the shock precursor and drives turbulence, amplifying the magnetic field via the small-scale dynamo. We explore this last scenario through 3-D MHD numerical simulations. We show under which conditions an efficient amplification of the magnetic field is achieved.

Del Valle, Maria Victoria; Lazarian, Alex

303

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

304

Dynamics of ring current and electric fields in the inner magnetosphere during disturbed periods: CRCM–BATS-R-US coupled model  

Microsoft Academic Search

We present simulation results from a one-way coupled global MHD model (Block-Adaptive-Tree Solar-Wind Roe-Type Upwind Scheme, BATS-R-US) and kinetic ring current models (Comprehensive Ring Current Model, CRCM, and Fok Ring Current, FokRC). The BATS-R-US provides the CRCM\\/FokRC with magnetic field information and plasma density\\/temperature at the polar CRCM\\/FokRC boundary. The CRCM uses an electric potential from the BATS-R-US ionospheric solver

N. Buzulukova; M.-C. Fok; A. Pulkkinen; M. Kuznetsova; T. E. Moore; A. Glocer; P. C. Brandt; G. Tóth; L. Rastätter

2010-01-01

305

Subnanosecond magnetization dynamics induced by a pulsed magnetic field in diluted magnetic semiconductor quantum wells  

NASA Astrophysics Data System (ADS)

The magnetization dynamics induced by a pulsed magnetic field is investigated by time- and polarization-resolved photoluminescene measurements in (Cd,Mn)Te/(Cd,Mg)Te quantum wells. The magnetization dynamics of Mn2+ ions is found to be strongly dependent on the external static magnetic field. A dynamical response of the magnetization on a subnanosecond time scale is observed at zero static magnetic field, while it drastically slows down and approaches the spin-lattice relaxation time constant for a nonzero static field. Theoretical calculations emphasize the importance of local spin interactions that interplay with the Zeeman interaction for the observed magnetization dynamics.

Chen, Y. S.; Wiater, M.; Karczewski, G.; Wojtowicz, T.; Bacher, G.

2013-04-01

306

Warm inflation in presence of magnetic fields  

SciTech Connect

We present preliminary results on the possible effects that primordial magnetic fields can have for a warm inflation scenario, based on global supersymmetry, with a new-inflation-type potential. This work is motivated by two considerations: first, magnetic fields seem to be present in the universe on all scales which rises de possibility that they could also permeate the early universe; second, the recent emergence of inflationary models where the inflaton is not assumed to be isolated but instead it is taken as an interacting field, even during the inflationary expansion. The effects of magnetic fields are included resorting to Schwinger's proper time method.

Piccinelli, Gabriella [Centro Tecnológico, FES Aragón, Universidad Nacional Autónoma de México, Avenida Rancho Seco S/N, Bosques de Aragón, Nezahualcóyotl, Estado de México 57130 (Mexico)] [Centro Tecnológico, FES Aragón, Universidad Nacional Autónoma de México, Avenida Rancho Seco S/N, Bosques de Aragón, Nezahualcóyotl, Estado de México 57130 (Mexico); Sánchez, Ángel [Department of Physics, University of Texas at El Paso, El Paso, Texas 79968 (United States)] [Department of Physics, University of Texas at El Paso, El Paso, Texas 79968 (United States); Ayala, Alejandro; Mizher, Ana Julia [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Apartado Postal 70-543, México Distrito Federal 04510 (Mexico)] [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Apartado Postal 70-543, México Distrito Federal 04510 (Mexico)

2013-07-23

307

Electroabsorption in a narrow gap semiconductor nanotube in the field of uniformly charged ring  

NASA Astrophysics Data System (ADS)

The electronic states as well as interband and intraband electrooptical transitions are considered for the narrow gap InSb nanotube in the field of homogeneously charged ring. The problem is solved in the framework of the variational approach. The field of the charged ring is brought to the field of the modified one dimensional Coulomb-like potential. Physically appropriate wave functions are suggested for this potential and the intensities of the threshold frequencies of the electrooptical transitions are calculated.

Harutyunyan, V. A.; Kazaryan, E. M.; Sarkisyan, H. A.

2014-11-01

308

Antiaromatic Character of 16 ? Electron Octaethylporphyrins: Magnetically Induced Ring Currents from DFT-GIMIC Calculations.  

PubMed

The magnetically induced current density susceptibility, also called current density, has been calculated for a recently synthesized octaethylporphyrin (OEP) zinc(II) dication with formally 16 ? electrons. Numerical integration of the current density passing selected chemical bonds yields the current pathway around the porphyrinoid ring and the strength of the ring current. The current strengths show that the OEP-Zn(II) dication is strongly antiaromatic, as also concluded experimentally. The calculation of the ring current pathway shows that all 24 ? electrons participate in the transport of the ring current because the current splits into inner and outer branches of practically equal strengths at the four pyrrolic rings. The corresponding neutral octaethylporphyrinoid without Zn and inner hydrogens is found to be antiaromatic, sustaining a paratropic ring current along the inner pathway with 16 ? electrons. The neutral OEP-Zn(II) molecule with formally 18 ? electrons is found to be almost as aromatic as free-base porphyrin. However, also in this case, all 26 ? electrons contribute to the ring current, as for free-base porphyrin. A comparison of calculated and measured (1)H NMR chemical shifts is presented. The current strength susceptibility under experimental conditions has been estimated by assuming a linear relation between experimental shielding constants and calculated current strengths. PMID:25141236

Fliegl, Heike; Pichierri, Fabio; Sundholm, Dage

2014-08-28

309

Evolution of Magnetic Fields in Supernova Remnants  

E-print Network

Supernova remnants (SNR) are now widely believed to be a source of cosmic rays (CRs) up to an energy of 1 PeV. The magnetic fields required to accelerate CRs to sufficiently high energies need to be much higher than can result from compression of the circumstellar medium (CSM) by a factor 4, as is the case in strong shocks. Non-thermal synchrotron maps of these regions indicate that indeed the magnetic field is much stronger, and for young SNRs has a dominant radial component while for old SNRs it is mainly toroidal. How these magnetic fields get enhanced, or why the field orientation is mainly radial for young remnants, is not yet fully understood. We use an adaptive mesh refinement MHD code, AMRVAC, to simulate the evolution of supernova remnants and to see if we can reproduce a mainly radial magnetic field in early stages of evolution. We follow the evolution of the SNR with three different configurations of the initial magnetic field in the CSM: an initially mainly toroidal field, a turbulent magnetic field, and a field parallel to the symmetry axis. Although for the latter two topologies a significant radial field component arises at the contact discontinuity due to the Rayleigh-Taylor instability, no radial component can be seen out to the forward shock. Ideal MHD appears not sufficient to explain observations. Possibly a higher compression ratio and additional turbulence due to dominant presence of CRs can help us to better reproduce the observations in future studies.

K. M. Schure; J. Vink; A. Achterberg; R. Keppens

2008-10-28

310

Field Mapping System for Solenoid Magnet  

NASA Astrophysics Data System (ADS)

A three-dimensional Hall probe mapping system for measuring the solenoid magnet of PLS photo-cathode RF e-gun has been developed. It can map the solenoid field either in Cartesian or in cylindrical coordinate system with a measurement reproducibility better than 5 × 10-5 T. The system has three axis motors: one for the azimuthal direction and the other two for the x and z direction. This architecture makes the measuring system simple in fabrication. The magnetic center was calculated using the measured axial component of magnetic field Bz in Cartesian coordinate system because the accuracy of magnetic axis measurement could be improved significantly by using Bz, instead of the radial component of magnetic field Br. This paper describes the measurement system and summarizes the measurement results for the solenoid magnetic of PLS photo-cathode RF e-gun.

Park, K. H.; Jung, Y. K.; Kim, D. E.; Lee, H. G.; Park, S. J.; Chung, C. W.; Kang, B. K.

2007-01-01

311

Magnetic fields in noninvasive brain stimulation.  

PubMed

The idea that magnetic fields could be used therapeutically arose 2000 years ago. These therapeutic possibilities were expanded after the discovery of electromagnetic induction by the Englishman Michael Faraday and the American Joseph Henry. In 1896, Arsène d'Arsonval reported his experience with noninvasive brain magnetic stimulation to the scientific French community. In the second half of the 20th century, changing magnetic fields emerged as a noninvasive tool to study the nervous system and to modulate neural function. In 1985, Barker, Jalinous, and Freeston presented transcranial magnetic stimulation, a relatively focal and painless technique. Transcranial magnetic stimulation has been proposed as a clinical neurophysiology tool and as a potential adjuvant treatment for psychiatric and neurologic conditions. This article aims to contextualize the progress of use of magnetic fields in the history of neuroscience and medical sciences, until 1985. PMID:23787954

Vidal-Dourado, Marcos; Conforto, Adriana Bastos; Caboclo, Luis Otávio Sales Ferreira; Scaff, Milberto; Guilhoto, Laura Maria de Figueiredo Ferreira; Yacubian, Elza Márcia Targas

2014-04-01

312

Origin of magnetic fields in galaxies  

SciTech Connect

Microgauss magnetic fields are observed in all galaxies at low and high redshifts. The origin of these intense magnetic fields is a challenging question in astrophysics. We show here that the natural plasma fluctuations in the primordial Universe (assumed to be random), predicted by the fluctuation -dissipation theorem, predicts {approx}0.034 {mu}G fields over {approx}0.3 kpc regions in galaxies. If the dipole magnetic fields predicted by the fluctuation-dissipation theorem are not completely random, microgauss fields over regions > or approx. 0.34 kpc are easily obtained. The model is thus a strong candidate for resolving the problem of the origin of magnetic fields in < or approx. 10{sup 9} years in high redshift galaxies.

Souza, Rafael S. de; Opher, Reuven [IAG, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, CEP 05508-900, Sao Paulo, SP (Brazil)

2010-03-15

313

Probing Primordial Magnetic Fields Using Ly? Clouds  

NASA Astrophysics Data System (ADS)

From previous studies of the effect of primordial magnetic fields on early structure formation, we know that the presence of primordial magnetic fields during early structure formation could induce more perturbations at small scales (at present 1-10 h -1 Mpc) as compared to the usual ?CDM theory. Matter power spectra over these scales are effectively probed by cosmological observables such as shear correlation and Ly? clouds. In this paper we discuss the implications of primordial magnetic fields on the distribution of Ly? clouds. We simulate the line-of-sight density fluctuation including the contribution coming from the primordial magnetic fields. We compute the evolution of Ly? opacity for this case and compare our theoretical estimates of Ly? opacity with the existing data to constrain the parameters of the primordial magnetic fields. We also discuss the case when the two density fields are correlated. Our analysis yields an upper bound of roughly 0.3-0.6 nG on the magnetic field strength for a range of nearly scale-invariant models, corresponding to a magnetic field power spectrum index n ~= -3.

Pandey, Kanhaiya L.; Sethi, Shiv K.

2013-01-01

314

Magnetic-field-controlled reconfigurable semiconductor logic.  

PubMed

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

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

2013-02-01

315

External-field-free magnetic biosensor  

SciTech Connect

In this paper, we report a magnetic nanoparticle (MNP) detection scheme without the presence of any external magnetic field. The proposed magnetic sensor uses a patterned groove structure within the sensor so that no external magnetic field is needed to magnetize the MNPs. An example is given based on a giant magnetoresistance (GMR) sensing device with a spin valve structure. For this structure, the detection of MNPs located inside the groove and near the free layer is demonstrated under no external magnetic field. Micromagnetic simulations are performed to calculate the signal to noise level of this detection scheme. A maximum signal to noise ratio (SNR) of 18.6?dB from one iron oxide magnetic nanoparticle with 8?nm radius is achieved. As proof of concept, this external-field-free GMR sensor with groove structure of 200?nm?×?200?nm is fabricated using a photo and an electron beam integrated lithography process. Using this sensor, the feasibility demonstration of the detection SNR of 9.3?dB is achieved for 30??l magnetic nanoparticles suspension (30?nm iron oxide particles, 1?mg/ml). This proposed external-field-free sensor structure is not limited to GMR devices and could be applicable to other magnetic biosensing devices.

Li, Yuanpeng; Wang, Yi; Klein, Todd; Wang, Jian-Ping, E-mail: jpwang@umn.edu [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

2014-03-24

316

External-field-free magnetic biosensor  

NASA Astrophysics Data System (ADS)

In this paper, we report a magnetic nanoparticle (MNP) detection scheme without the presence of any external magnetic field. The proposed magnetic sensor uses a patterned groove structure within the sensor so that no external magnetic field is needed to magnetize the MNPs. An example is given based on a giant magnetoresistance (GMR) sensing device with a spin valve structure. For this structure, the detection of MNPs located inside the groove and near the free layer is demonstrated under no external magnetic field. Micromagnetic simulations are performed to calculate the signal to noise level of this detection scheme. A maximum signal to noise ratio (SNR) of 18.6 dB from one iron oxide magnetic nanoparticle with 8 nm radius is achieved. As proof of concept, this external-field-free GMR sensor with groove structure of 200 nm × 200 nm is fabricated using a photo and an electron beam integrated lithography process. Using this sensor, the feasibility demonstration of the detection SNR of 9.3 dB is achieved for 30 ?l magnetic nanoparticles suspension (30 nm iron oxide particles, 1 mg/ml). This proposed external-field-free sensor structure is not limited to GMR devices and could be applicable to other magnetic biosensing devices.

Li, Yuanpeng; Wang, Yi; Klein, Todd; Wang, Jian-Ping

2014-03-01

317

Fully quantum-mechanical model of a SQUID ring coupled to an electromagnetic field  

Microsoft Academic Search

A quantum system comprising of a monochromatic electromagnetic field coupled to a superconducting quantum interference device (SQUID) ring with sinusoidal nonlinearity is studied. A magnetostatic flux Phix is also threading the SQUID ring, and is used to control the coupling between the two systems. It is shown that for special values of Phix the system is strongly coupled. The time

M. J. Everitt; P. B. Stiffell; T. D. Clark; A. Vourdas; J. F. Ralph; H. Prance; R. J. Prance

2001-01-01

318

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

319

Magnetic field corrections to solar oscillation frequencies  

NASA Technical Reports Server (NTRS)

It is argued that the frequencies of both the solar p- and g-modes of oscillation are modified by a magnetic field. In particular, the decrease in p-mode frequencies is attributed to a magnetic field within the solar interior evolving over the solar cycle. Field strengths at the base of the convection zone of at least 500,000 G are required.

Roberts, B.; Campbell, W. R.

1986-01-01

320

Magnetic properties and hyperfine interactions in Cr8, Cr7Cd, and Cr7Ni molecular rings from 19F-NMR  

SciTech Connect

A detailed experimental investigation of the 19F nuclear magnetic resonance is made on single crystals of the homometallic Cr8 antiferromagnetic molecular ring and heterometallic Cr7Cd and Cr7 Ni rings in the low temperature ground state. Since the F? ion is located midway between neighboring magnetic metal ions in the ring, the 19F-NMR spectra yield information about the local electronic spin density and 19F hyperfine interactions. In Cr8, where the ground state is a singlet with total spin S T = 0, the 19F-NMR spectra at 1.7 K and low external magnetic field display a single narrow line, while when the magnetic field is increased towards the first level crossing field, satellite lines appear in the 19F-NMR spectrum, indicating a progressive increase in the Boltzmann population of the first excited state S T = 1. In the heterometallic rings, Cr7Cd and Cr7 Ni, whose ground state is magnetic with S T = 3/2 and S T = 1/2, respectively, the 19F-NMR spectrum has a complicated structure which depends on the strength and orientation of the magnetic field, due to both isotropic and anisotropic transferred hyperfine interactions and classical dipolar interactions. From the 19F-NMR spectra in single crystals we estimated the transferred hyperfine constants for both the F?-Ni2+ and the F?-Cd2+ bonds. The values of the hyperfine constants compare well to the ones known for F?-Ni2+ in KNiF3 and NiF2 and for F?-Cr3+ in K2NaCrF6. The results are discussed in terms of hybridization of the 2s, 2p orbitals of the F? ion and the d orbitals of the magnetic ion. Finally, we discuss the implications of our results for the electron-spin decoherence.

Bordonali, L.; Garlatti, E.; Casadei, C. M.; Furukawa, Y.; Lascialfari, A.; Carretta, S.; Troiani, F.; Timco, G.; Winpenny, R. E.; Borsa, F.

2014-04-14

321

Magnetic properties and hyperfine interactions in Cr8, Cr7Cd, and Cr7Ni molecular rings from 19F-NMR  

NASA Astrophysics Data System (ADS)

A detailed experimental investigation of the 19F nuclear magnetic resonance is made on single crystals of the homometallic Cr8 antiferromagnetic molecular ring and heterometallic Cr7Cd and Cr7Ni rings in the low temperature ground state. Since the F- ion is located midway between neighboring magnetic metal ions in the ring, the 19F-NMR spectra yield information about the local electronic spin density and 19F hyperfine interactions. In Cr8, where the ground state is a singlet with total spin ST = 0, the 19F-NMR spectra at 1.7 K and low external magnetic field display a single narrow line, while when the magnetic field is increased towards the first level crossing field, satellite lines appear in the 19F-NMR spectrum, indicating a progressive increase in the Boltzmann population of the first excited state ST = 1. In the heterometallic rings, Cr7Cd and Cr7Ni, whose ground state is magnetic with ST = 3/2 and ST = 1/2, respectively, the 19F-NMR spectrum has a complicated structure which depends on the strength and orientation of the magnetic field, due to both isotropic and anisotropic transferred hyperfine interactions and classical dipolar interactions. From the 19F-NMR spectra in single crystals we estimated the transferred hyperfine constants for both the F--Ni2+ and the F--Cd2+ bonds. The values of the hyperfine constants compare well to the ones known for F--Ni2+ in KNiF3 and NiF2 and for F--Cr3+ in K2NaCrF6. The results are discussed in terms of hybridization of the 2s, 2p orbitals of the F- ion and the d orbitals of the magnetic ion. Finally, we discuss the implications of our results for the electron-spin decoherence.

Bordonali, L.; Garlatti, E.; Casadei, C. M.; Furukawa, Y.; Lascialfari, A.; Carretta, S.; Troiani, F.; Timco, G.; Winpenny, R. E. P.; Borsa, F.

2014-04-01

322

Vector Magnetic Field in Emerging Flux Regions  

NASA Astrophysics Data System (ADS)

A crucial phase in magnetic flux emergence is the rise of magnetic flux tubes through the solar photosphere, which represents a severe transition between the very different environments of the solar interior and corona. Multi-wavelength observations with Flare Genesis, TRACE, SoHO, and more recently with the vector magnetographs at THEMIS and Hida (DST) led to the following conclusions. The fragmented magnetic field in the emergence region - with dipped field lines or bald patches - is directly related with Ellerman bombs, arch filament systems, and overlying coronal loops. Measurements of vector magnetic fields have given evidence that undulating "serpentine" fields are present while magnetic flux tubes cross the photosphere. See the sketch below, and for more detail see Pariat et al. (2004, 2007); Watanabe et al. (2008):

Schmieder, B.; Pariat, E.

323

Advanced magnetic calculations for high magnetic field compact ion source  

NASA Astrophysics Data System (ADS)

The design of the advanced electronic cyclotronic resonance ion source (ECRIS) requires relatively high axial and radial magnetic inductions to allow the ECR frequency increase and to take advantage of the subsequent density increase (scaling laws). The last improvements of the commercial rare-earth magnet characteristics open new opportunities for ECRIS and enable the design of very high hexapolar magnetic fields for next generation compact ECRIS. Moreover, the high temperature superconducting (HTS) wires allow designing reliable and compact axial field coils (30 K cooled) at a very effective cost. It is thus very relevant to study a compact hybrid ECRIS using high remanence magnet and HTS technologies. In such a design, the volume of the plasma chamber is a free parameter that can be adjusted to the user requirement. It can be dedicated to very high ionic current production or high charge state production, pulsed, or cw operations. This paper presents the three-dimensional overall simulation of a 3 T axial magnetic field compact ECRIS with a high radial field sextupole composed with several magnet types and reaching ˜1.9 T in front of the radially magnetized magnets. This design study will lead to the building of the 28-40 GHz A-PHOENIX source at the laboratory which will deliver its first beam by the end of 2004.

Thuillier, T.; Curdy, J.-C.; Lamy, T.; Sole, P.; Sortais, P.; Vieux-Rochaz, J.-L.; Voulot, D.

2004-05-01

324

Magnetic reconnection at the edge of Uranus's magnetic field  

NASA Astrophysics Data System (ADS)

A new modeling study sheds light on how the magnetosphere of Uranus compares to those of other planets. Magnetospheres around the inner planets Mercury and Earth are primarily driven by the solar wind—the charged particles spewed out from the Sun—through magnetic reconnection, in which the planet's magnetic field lines break and reconnect, releasing energy in the process.

Balcerak, Ernie

2014-09-01

325

Anisotropy of magnetic susceptibility measured in variable weak magnetic fields  

NASA Astrophysics Data System (ADS)

Theory of the low-field anisotropy of magnetic susceptibility (AMS) of rocks is based on the assumption of the linear relationship between magnetization and magnetizing field, resulting in field independent susceptibility. This relationship is by definition valid in diamagnetic and paramagnetic minerals, while in ferrimagnetic and antiferromagnetic minerals this relationship is in general non-linear (represented by hysteresis loop), being linear only in very weak fields in which the initial susceptibility is measured. Among these minerals, magnetite shows no field variation of susceptibility and its anisotropy in the low fields used in common AMS meters. In pyrrhotite, hematite and titanomagnetite bearing rocks, in which these minerals are very fine-grained, the field variation of susceptibility is insignificant. Using linear theory in calculating the AMS is fully legitimate in all these cases. In pyrrhotite, hematite, and titanomagnetite bearing rocks, in which these minerals are relatively coarse-grained (typically hundreds of micrometers), clear field variation of magnetic susceptibility may exist even in the low fields used in common AMS meters, often resulting in bad fit of the susceptibility tensor to the measured data. Strictly speaking, linear theory in calculating the AMS is in general incorrect in this case. The KLY-3S Kappabridge has been modified in such a way to enable AMS measurement also in the fields down to 3 A/m. Examples are shown of the effect of this field decrease on the measured data.

Pokorny, J.; Suza, P.; Hrouda, F.

2003-04-01

326

Particle Transport in Therapeutic Magnetic Fields  

NASA Astrophysics Data System (ADS)

Iron oxide magnetic nanoparticles, in ferrofluids or as magnetic microspheres, offer magnetic maneuverability, biochemical surface functionalization, and magnetic relaxation under the influence of an alternating field. The use of these properties for clinical applications requires an understanding of particles, forces, and scalar transport at various length scales. This review explains the behavior of magnetic nano- and microparticles during magnetic drug targeting and magnetic fluid hyperthermia, and the microfluidic transport of these particles in bioMEMS (biomedical microelectromechanical systems) devices for ex vivo therapeutic and diagnostic applications. Magnetic particle transport, the momentum interaction of these particles with a host fluid in a flow, and thermal transport in a particle-infused tissue are characterized through the governing electrodynamic, hydrodynamic, and scalar transport equations.

Puri, Ishwar K.; Ganguly, Ranjan

2014-01-01

327

The Measurement of Magnetic Fields  

ERIC Educational Resources Information Center

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

Berridge, H. J. J.

1973-01-01

328

Faraday's Magnetic Field Induction Experiment  

NSDL National Science Digital Library

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

Davidson, Michael

2010-12-29

329

The CMS Magnetic Field Map Performance  

E-print Network

The Compact Muon Solenoid (CMS) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive featuresinclude a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10000-ton return yoke made of construction steel. Accurate characterization of the magnetic field everywhere in the CMS detector is required. During two major tests of the CMS magnet the magnetic flux density was measured inside the coil in a cylinder of 3.448 m diameter and 7 m length with a specially designed field-mapping pneumatic machine as well as in 140 discrete regions of the CMS yoke with NMR probes, 3-D Hall sensors and flux-loops. A TOSCA 3-D model of the CMS magnet has been developed to describe the magnetic field everywhere outside the tracking volume measured with the field-mapping machine. A volume based representation of the magnetic field is used to provide the CMS simulation and reconstruction software with the magnetic field values. The value of the field at a given point of a volume is obtained by interpolation from a regular grid of values resulting from a TOSCA calculation or, when available, from a parameterization. The results of the measurements and calculations are presented, compared and discussed.

V. I. Klyukhin; N. Amapane; V. Andreev; A. Ball; B. Curé; A. Hervé; A. Gaddi; H. Gerwig; V. Karimaki; R. Loveless; M. Mulders; S. Popescu; L. I. Sarycheva; T. Virdee

2011-10-04

330

Magnetic field in a prototype kicker magnet for the KAON Factory  

Microsoft Academic Search

Kicker magnets are required for all ring-to-ring transfers in the 5 rings of the proposed KAON Factory. The kick must rise from 1% to 99% of full strength during the time interval of gaps (80 ns to 160 ns) created in the beam so that beam extraction losses are minimized. The “kick” strength must have a uniformity of ±1% over

Gary D. Wait; Michael J. Barnes; Hy J. Tran

1994-01-01

331

Generation of high magnetic fields using superconducting magnets  

Microsoft Academic Search

High-field superconducting magnets have opened new frontiers for several kinds of applications, such as fusion reactors, particle accelerators, and nuclear magnetic resonance (NMR) spectrometers. The present record for the highest field in a fully superconducting state is 23.4T. It was achieved with a combination of NbTi, Nb3Sn, and Bi-2212 conductors in 1999. Since high Tc (critical temperature) superconductors (HTS) have

T. Kiyoshi; A. Otsuka; M. Kosuge; M. Yuyama; H. Nagai; F. Matsumoto

2006-01-01

332

Generation of Vortex Beams with Strong Longitudinally Polarized Magnetic Field by Using a Metasurface  

E-print Network

A novel method of generation and synthesis of azimuthally E-polarized vortex beams is presented. Along the axis of propagation such beams have a strong longitudinally polarized magnetic field where ideally there is no electric field. We show how these beams can be constructed through the interference of Laguerre-Gaussian beams carrying orbital angular momentum. As an example, we present a metasurface made of double-split ring slot pairs and report a good agreement between simulated and analytical results. Both a high magnetic-to-electric-field contrast ratio and a magnetic field enhancement are achieved. We also investigate the metasurface physical constraints to convert a linearly polarized beam into an azimuthally E- polarized beam and characterize the performance of magnetic field enhancement and electric field suppression of a realistic metasurface. These findings are potentially useful for novel optical spectroscopy related to magnetic dipolar transitions and for optical manipulation of particles with sp...

Veysi, Mehdi; Capolino, Filippo

2014-01-01

333

Magnetic Field Measurement with Ground State Alignment  

NASA Astrophysics Data System (ADS)

Observational studies of magnetic fields are crucial. We introduce a process "ground state alignment" as a new way to determine the magnetic field direction in diffuse medium. The alignment is due to anisotropic radiation impinging on the atom/ion. The consequence of the process is the polarization of spectral lines resulting from scattering and absorption from aligned atomic/ionic species with fine or hyperfine structure. The magnetic field induces precession and realign the atom/ion and therefore the polarization of the emitted or absorbed radiation reflects the direction of the magnetic field. The atoms get aligned at their low levels and, as the life-time of the atoms/ions we deal with is long, the alignment induced by anisotropic radiation is susceptible to extremely weak magnetic fields (1 G ? B ? 10^{-15} G). In fact, the effects of atomic/ionic alignment were studied in the laboratory decades ago, mostly in relation to the maser research. Recently, the atomic effect has been already detected in observations from circumstellar medium and this is a harbinger of future extensive magnetic field studies. A unique feature of the atomic realignment is that they can reveal the 3D orientation of magnetic field. In this chapter, we shall review the basic physical processes involved in atomic realignment. We shall also discuss its applications to interplanetary, circumstellar and interstellar magnetic fields. In addition, our research reveals that the polarization of the radiation arising from the transitions between fine and hyperfine states of the ground level can provide a unique diagnostics of magnetic fields in the Epoch of Reionization.

Yan, Huirong; Lazarian, A.

334

Magnetic Fields from Heterotic Cosmic Strings  

E-print Network

Large-scale magnetic fields are observed today to be coherent on galactic scales. While there exists an explanation for their amplification and their specific configuration in spiral galaxies -- the dynamo mechanism -- a satisfying explanation for the original seed fields required is still lacking. Cosmic strings are compelling candidates because of their scaling properties, which would guarantee the coherence on cosmological scales of any resultant magnetic fields at the time of galaxy formation. We present a mechanism for the production of primordial seed magnetic fields from heterotic cosmic strings arising from M theory. More specifically, we make use of heterotic cosmic strings stemming from M5--branes wrapped around four of the compact internal dimensions. These objects are stable on cosmological time scales and carry charged zero modes. Therefore a scaling solution of such defects will generate seed magnetic fields which are coherent on galactic scales today.

Gwyn, Rhiannon; Brandenberger, Robert H; Dasgupta, Keshav

2008-01-01

335

Magnetic fields from heterotic cosmic strings  

SciTech Connect

Large-scale magnetic fields are observed today to be coherent on galactic scales. While there exists an explanation for their amplification and their specific configuration in spiral galaxies--the dynamo mechanism--a satisfying explanation for the original seed fields required is still lacking. Cosmic strings are compelling candidates because of their scaling properties, which would guarantee the coherence on cosmological scales of any resultant magnetic fields at the time of galaxy formation. We present a mechanism for the production of primordial seed magnetic fields from heterotic cosmic strings arising from M theory. More specifically, we make use of heterotic cosmic strings stemming from M5-branes wrapped around four of the compact internal dimensions. These objects are stable on cosmological time scales and carry charged zero modes. Therefore a scaling solution of such defects will generate seed magnetic fields which are coherent on galactic scales today.

Gwyn, Rhiannon; Alexander, Stephon H.; Brandenberger, Robert H.; Dasgupta, Keshav [Department of Physics, McGill University, Montreal, Quebec, H3A 2T8 (Canada); Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802-6300 (United States); Department of Physics and Astronomy, Koshland Center for Integrated Sciences, Haverford College, Haverford, Pennsylvania 19041 (United States); Department of Physics, McGill University, Montreal, Quebec, H3A 2T8 (Canada)

2009-04-15

336

The magnetic field of Mercury, part 1  

NASA Technical Reports Server (NTRS)

An updated analysis and interpretation is presented of the magnetic field observations obtained during the Mariner 10 encounter with the planet Mercury. The combination of data relating to position of the detached bow shock wave and magnetopause, and the geometry and magnitude of the magnetic field within the magnetosphere-like region surrounding Mercury, lead to the conclusion that an internal planetary field exists with dipole moment approximately 5.1 x 10 the 22nd power Gauss sq cm. The dipole axis has a polarity sense similar to earth's and is tilted 7 deg from the normal to Mercury's orbital plane. The magnetic field observations reveal a significant distortion of the modest Hermean field (350 Gamma at the equator) by the solar wind flow and the formation of a magnetic tail and neutral sheet which begins close to the planet on the night side. The composite data is not consistent with a complex induction process driven by the solar wind flow.

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

1974-01-01

337

Magnetic field induced optical vortex beam rotation  

E-print Network

Light with orbital angular momentum (OAM) has drawn a great deal of attention for its important applications in the fields of precise optical measurements and high capacity optical communications. Here we adopt a method to study the rotation of a light beam, which is based on magnetic field induced circular birefringence in warm 87Rb atomic vapor. The dependence of the rotation angle to the intensity of the magnetic field makes it appropriate for weak magnetic field measurement. We derive a detail theoretical description that is in well agreement with the experimental observations. The experiment shows here provides a new method for precise measurement of magnetic field intensity and expands the application of OAM-carrying light.

Shi, Shuai; Zhou, Zhi-Yuan; Li, Yan; Zhang, Wei; Shi, Bao-Sen

2015-01-01

338

Novel layout of a bi-metallic nanoring for magnetic field pulse generation from light  

NASA Astrophysics Data System (ADS)

Recently Tsiatmas et al proposed using a nanoring made of two different metallic sectors to generate a magnetic pulse from a laser pulse [1]. Non-uniform heating of the ring creates very large temperature gradients, which drive thermoelectric currents, and this creates a localized magnetic field. However, heat from the laser pulse may result in the melting of the nanoring. We propose a symmetric structure made of four metallic sectors, which results in a higher magnetic field generation together with a lower lattice temperature. We also show that the magnetic field depends strongly on the size of the metallic sectors and interpret the results with the help of the electromotive forces, the overall ring resistance, and Biot–Savart law.

Vienne, Guillaume; Chen, Xiaoye; Shi Teh, Ying; Jye Ng, Ying; Oon Chia, Nyap; Ooi, Ching Pin

2015-01-01

339

QCD string breaking in strong magnetic field  

NASA Astrophysics Data System (ADS)

At sufficiently large separation between a quark and an antiquark the quantum chromodynamics (QCD) string breaks into parts due to creation of light quark-antiquark pairs. We show that a background magnetic field affects the breaking of the QCD string oriented in the transverse directions with respect to the axis of the magnetic field. Using semiclassical approach we argue that above certain, the background magnetic field eB ?0.3 GeV2 breaking of the transverse string should become energetically unfavorable.

Chernodub, M. N.

2014-09-01

340

Magnetic fields from second-order interactions  

E-print Network

It is well known that when two types of perturbations interact in cosmological perturbation theory, the interaction may lead to the generation of a third type. In this article we discuss the generation of magnetic fields from such interactions. We determine conditions under which the interaction of a first-order magnetic field with a first-order scalar-or vector-, or tensor-perturbations would lead to the generation of second order magnetic field. The analysis is done in a covariant-index-free approach, but could be done in the standard covariant indexed-approach.

Bob Osano

2014-03-21

341

Small-scale solar magnetic fields  

E-print Network

As we resolve ever smaller structures in the solar atmosphere, it has become clear that magnetism is an important component of those small structures. Small-scale magnetism holds the key to many poorly understood facets of solar magnetism on all scales, such as the existence of a local dynamo, chromospheric heating, and flux emergence, to name a few. Here, we review our knowledge of small-scale photospheric fields, with particular emphasis on quiet-sun field, and discuss the implications of several results obtained recently using new instruments, as well as future prospects in this field of research.

A. G. de Wijn; J. O. Stenflo; S. K. Solanki; S. Tsuneta

2008-12-24

342

The magnetic field of solar prominences  

E-print Network

In his famous monographs, Einar Tandberg-Hanssen writes that "the single, physically most important parameter to study in prominences may be the magnetic field. Shapes, motions, and in fact the very existence of prominences depend on the nature of the magnetic field threading the prominence plasma". Hereafter we sumarize recent contributions and advances in our knowledge about the magnetic field of solar prominences. It mostly relies on high resolution and high sensitivity spectropolarimetry made both in the visible and in the near infrared.

F. Paletou

2008-10-15

343

Environmental magnetic fields: Influences on early embryogenesis  

SciTech Connect

A 10-mG, 50 to 60-Hz magnetic field is in the intensity and frequency range that people worldwide are often exposed to in homes and in the workplace. Studies about the effects of 50- to 100-Hz electromagnetic fields on various species of animal embryos (fish, chick, fly, sea urchin, rat, and mouse) indicate that early stages of embryonic development are responsive to fluctuating magnetic fields. Chick, sea urchin, and mouse embryos are responsive to magnetic field intensities of 10-100 mG. Results from studies on sea urchin embryos indicate that exposure to conditions of rotating 60-Hz magnetic fields, e.g., similar to those in our environment, interferes with cell proliferation at the morula stage in a manner dependent on field intensity. The cleavage stages, prior to the 64-cell stage, were not delayed by this rotating 60-Hz magnetic field suggesting that the ionic surges, DNA replication, and translational events essential for early cleavage stages were not significantly altered. Studies of histone synthesis in early sea urchin embryos indicated that the rotating 60-Hz magnetic field decreased zygotic expression of early histone genes at the morula stage and suggests that this decrease in early histone production was limiting to cell proliferation. Whether these comparative observations from animal development studies will be paralleled by results from studies of human embryogenesis, as suggested by some epidemiology studies, has yet to be established. 38 refs.

Cameron, I.L.; Hardman, W.E.; Winters, W.D.; Zimmerman, S.; Zimmerman, A.M. (Univ. of Texas Health Science Center, San Antonio (United States))

1993-04-01

344

Magnetic fields of the terrestrial planets  

NASA Technical Reports Server (NTRS)

The four terrestrial planets, together with the Earth's Moon, provide a significant range of conditions under which dynamo action could occur. All five bodies have been visited by spacecraft, and from three of the five bodies (Earth, Moon and Mars) we have samples of planetary material upon which paleomagnetic studies have been undertaken. At the present time, only the Earth and Mercury appear to have a significant dipole magnetic field. However, the Moon, and possibly Mars, appear to have had ancient planetary dynamos. Venus does not now have a significant planetary magnetic field, and the high surface temperatures should have prevented the recording of evidence of any ancient magnetic field. Since the solidification of the solid inner core is thought to be the energy source for the terrestrial magnetic field, and since smaller bodies evolve thermally more rapidly than larger bodies, we conjecture that the terrestrial planets are today in three different phases of magnetic activity. Venus is in a predynamo phase, not having cooled to the point of core solidification. Mercury and the Earth are in the middle of their dynamo phase, with Mercury perhaps near the end of its activity. Mars and the Moon seem to be well past their dynamo phase. Much needs to be done in the study of the magnetism of the terrestrial planets. We need to characterize the multipole harmonic structure of the Mercury magnetic field plus its secular variation, and we need to analyze returned samples to attempt to unfold the long-term history of Mercury's dynamo. We need to more thoroughly map the magnetism of the lunar surface and to analyze samples obtained from a wider area of the lunar surface. We need a more complete survey of the present Martian magnetic field and samples from a range of different ages of Martian surface material. Finally, a better characterization of the secular variation of the terrestrial magnetic field is needed in order to unfold the workings of the terrestrial dynamo.

Russell, C. T.

1993-01-01

345

Field orientation dependent vortex formation in individual multilayer triangular rings  

E-print Network

from forward onion state to reverse onion state via an intermediate vortex state, otherwise there is a direct transition from forward onion state to reverse onion states. This phenomenon in triangular rings a transition from forward onion state to reverse onion state via an intermediate vortex state, otherwise

Adeyeye, Adekunle

346

The CMS Magnetic Field Map Performance  

E-print Network

The Compact Muon Solenoid (CMS) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive featuresinclude a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10000-ton return yoke made of construction steel. Accurate characterization of the magnetic field everywhere in the CMS detector is required. During two major tests of the CMS magnet the magnetic flux density was measured inside the coil in a cylinder of 3.448 m diameter and 7 m length with a specially designed field-mapping pneumatic machine as well as in 140 discrete regions of the CMS yoke with NMR probes, 3-D Hall sensors and flux-loops. A TOSCA 3-D model of the CMS magnet has been developed to describe the magnetic field everywhere outside the tracking volume measured with the field-mapping machine. A volume based representation of the magnetic field is used to provide the CMS simulation and reconstruction software with the magnetic field ...

Klyukhin, VI; Sarycheva, L I; Klyukhin, V I; Ball, A; Gaddi, A; Amapane, N; Gerwig, H; Andreev, V; Cure, B; Mulders, M; Loveless, R; Karimaki, V; Popescu, S; Herve, A

2010-01-01

347

Space applications of superconductivity - High field magnets  

NASA Technical Reports Server (NTRS)

The paper discusses developments in superconducting magnets and their applications in space technology. Superconducting magnets are characterized by high fields (to 15T and higher) and high current densities combined with low mass and small size. The superconducting materials and coil design are being improved and new high-strength composites are being used for magnet structural components. Such problems as maintaining low cooling temperatures (near 4 K) for long periods of time and degradation of existing high-field superconductors at low strain levels can be remedied by research and engineering. Some of the proposed space applications of superconducting magnets include: cosmic ray analysis with magnetic spectrometers, energy storage and conversion, energy generation by magnetohydrodynamic and thermonuclear fusion techniques, and propulsion. Several operational superconducting magnet systems are detailed.

Fickett, F. R.

1979-01-01

348

Field Directed Ordering in Magnetic Nanocrystal Structures  

NASA Astrophysics Data System (ADS)

Iron oxide nanocrystals (NCs) have been the focus of intense research owing to the observation of tunable magnetic properties which could lead to advances in many fields including magnetic storage devices and medicine. We have been targeting the use of iron oxide NCs as magnetoresistance (MR) based sensors using ordered NC arrays. In this work, we will present our efforts toward using external magnetic fields to induce intraparticle ordering in iron oxide NC drop cast films. We use x-ray diffraction to analyze effects of the external fields on the NC array structure, while using SQUID magnetometry to probe the effects of NC interactions on the magnetic properties of iron oxide NCs ranging from 5 - 20 nm in diameter. MR measurements suggest large changes in the MR ratio can be achieved using the directed ordering approach for NC arrays. Our work could provide new avenues towards the fabrication of new magnetic devices.

Lawson, Stuart; Meulenberg, Robert

2013-03-01

349

Juno and Jupiter's Magnetic Field (Invited)  

NASA Astrophysics Data System (ADS)

The Juno spacecraft, launched in August 2011, will reach Jupiter in early July 2016, where it will enter a polar orbit, with an 11 day period and a perijove altitude of approximately 5000 km. The baseline mission will last for one year during which Juno will complete 32 orbits, evenly spaced in longitude. The baseline mission presents an unparalleled opportunity for investigating Jupiter's magnetic field. In many ways Jupiter is a better planet for studying dynamo-generated magnetic fields than the Earth: there are no crustal fields, of course, which otherwise mask the dynamo-generated field at high degree; and an orbiting spacecraft can get proportionately much closer to the dynamo region. Assuming Jupiter's dynamo extends to 0.8 Rj, Juno at closet approach is only 0.3 Rc above the dynamo, while Earth orbiting magnetic field missions sample the field at least 1 Rc above the dynamo (where Rc is the respective outer core or dynamo region radius). Juno's MAG Investigation delivers magnetic measurements with exceptional vector accuracy (100 ppm) via two FGM sensors, each co-located with a dedicated pair of non-magnetic star cameras for attitude determination at the sensor. We expect to image Jupiter's dynamo with unsurpassed resolution. Accordingly, we anticipate that the Juno magnetic field investigation may place important constraints on Jupiter's interior structure, and hence on the formation and evolution of Jupiter.

Bloxham, J.; Connerney, J. E.; Jorgensen, J. L.

2013-12-01

350

Negative Index of Refraction Observed in a Single Layer of ClosedRing Magnetic Dipole Resonators  

SciTech Connect

We report the results of a spectroscopic study of a singlelayer of metallic single closed ring resonators on free-standing thinmembrane at near-normal and grazing angles of incidence. When themagnetic component of the light is perpendicular to the ring plane, weobserve a negative index of refraction down to -1 around 150 terahertz(THz), attributed to a strong magnetic dipolar resonance and a broadelectric resonance in this metamaterial. We experimentally identify thedifferent resonance modes and the spectral region of negative refractiveindex on a series of samples with different feature and lattice sizes,comparing to electromagnetic simulations.

Hao, Zhao; Martin, Michael C.; Harteneck, Bruce; Cabrini,Stefano; Anderson, Erik H.

2007-11-27

351

Current Sheets in Stressed Coronal Magnetic Fields  

NASA Astrophysics Data System (ADS)

The extrapolation of magnetic fields into the solar corona generally assumes that the fields are fully relaxed - all possible reconnection has occurred. This assumption is in conflict with the low magnetic diffusivity in the corona. I will present initial results on extrapolation based on stressed magnetic fields - those for which no reconnection has occurred. As an opposite extreme to traditional methods, stressed fields offer a different view of coronal fields. The locations of current sheets between flux systems are directly determined. Observational evidence of coronal reconnection can test the completeness of the extrapolation, as the field lines spanning flux systems must be in contact prior to reconnection. This work is supported by NASA SEC GI grant NAG5-13020.

Labonte, B. J.

2003-12-01

352

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

353

Interpretation of Solar Magnetic Field Strength Observations  

Microsoft Academic Search

This study based on longitudinal Zeeman effect magnetograms and spectral line scans investigates the dependence of solar surface magnetic fields on the spectral line used and the way the line is sampled to estimate the magnetic flux emerging above the solar atmosphere and penetrating to the corona from magnetograms of the Mt. Wilson 150-foot tower synoptic program (MWO). We have

R. K. Ulrich; L. Bertello; J. E. Boyden; L. Webster

2009-01-01

354

High field magnets at the international laboratory Wroclaw  

Microsoft Academic Search

At Wroclaw high magnetic fields have been produced since the late 1960s. At present there are several magnets for stationary fields and one magnet for pulsed fields. The biggest, Bitter-type magnet generates magnetic fields up to 20 T, total power exceeds 6.0 MW.

K. Trojnar; N. Koppetzki

1989-01-01

355

The Magnetic Field of Helmholtz Coils  

ERIC Educational Resources Information Center

Describes the magnetic field of Helmholtz coils qualitatively and then provides the basis for a quantitative expression. Since the mathematical calculations are very involved, a computer program for solving the mathematical expression is presented and explained. (GS)

Berridge, H. J. J.

1975-01-01

356

Heat Capacity Measurements in Pulsed Magnetic Fields  

SciTech Connect

The new NHMFL 60T quasi-continuous magnet produces a flat-top field for a period of 100 ms at 60 Tesla, and for longer time at lower fields, e.g. 0.5 s at 45 Tesla. We have developed for the first time the capability to measure heat capacity at very high magnetic fields in the NHMFL 60T quasi-continuous magnet at LANL, using a probe built out of various plastic materials. The field plateau allows us to utilize a heat-pulse method to obtain heat capacity data. Proof-of-principle heat capacity experiments were performed on a variety of correlated electron systems. Both magnet performance characteristics and physical properties of various materials studied hold out a promise of wide application of this new tool.

Jaime, M.; Movshovich, R.; Sarrao, J.L.; Kim, J.; Stewart, G.; Beyermann, W.P.; Canfield, P.C.

1998-10-23

357

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

358

A Holographic Bound on Cosmic Magnetic Fields  

E-print Network

Magnetic fields large enough to be observable are ubiquitous in astrophysics, even at extremely large length scales. This has led to the suggestion that such fields are seeded at very early (inflationary) times, and subsequently amplified by various processes involving, for example, dynamo effects. Many such mechanisms give rise to extremely large magnetic fields at the end of inflationary reheating, and therefore also during the quark-gluon plasma epoch of the early universe. Such plasmas have a well-known holographic description. We show that holography imposes an upper bound on the intensity of magnetic fields (scaled by the squared temperature) in these circumstances, and that the values expected in some models of cosmic magnetism come close to attaining that bound.

McInnes, Brett

2015-01-01

359

Lunar magnetic field measurements with a cubesat  

E-print Network

We have developed a mission concept that uses 3-unit cubesats to perform new measurements of lunar magnetic fields, less than 100 meters above the Moon’s surface. The mission calls for sending the cubesats on impact ...

Garrick-Bethell, Ian

360

Cyclic evolution and reversal of the solar magnetic field. I. The large-scale magnetic fields  

E-print Network

On the base of the solar magnetic field measurements obtained in Stanford in 1976--2003 the properties of the cyclic evolution of the large-scale magnetic field are investigated. Some regularities are found in longitudinal and latitudinal evolution of the magnetic field in cycles 21, 22 and 23. The cyclic development of the large-scale magnetic field can be divided into two main phases. The phase I, which includes a period approximately from two years before and until three years after the maximum of the solar cycle, is studied in detail. It is found that before the reversal of the large-scale magnetic field the neutral line of the magnetic field in antipodal longitudinal intervals shifts from the equator to opposite directions in cycles 21 and 22, but not in cycle 23. During the sign reversal of the large-scale magnetic field in cycles 21 and 22 in the antipodal longitudinal intervals the magnetic field of opposite polarity is observed in all latitudes, thereby forming an equatorial dipole. After the magnetic field reversal a longitudinal oscillation of the magnetic neutral line with regard to the equator takes place, which has a period about 2 years and damps to the minimum of the 11-year cycle. The intervening longitudinal intervals of the large-scale magnetic field correspond to positions of the active longitudes of sunspot activity, thus indicating a close connection of the large-scale and the local magnetic fields. In evolution of the large-scale magnetic field a periodicity with period $1.23\\pm0.16$ year is revealed, which is close to the period found by helioseismological methods in variations of the solar rotation near the tachocline.

R. N. Ikhsanov; V. G. Ivanov

2003-10-20

361

Low Temperature Thermometry in High Magnetic Fields  

Microsoft Academic Search

The calibration and reproducibilty of various commercial and homemade thermometers have been investigated over a temperature range from 20 mK to 4.2 K and magnetic field strength from 0 to 16 Tesla. The performance of resistance thermometers made of different materials varies widely as a function of magnetic field. One type (Scientific Instruments RO600) is found to have a relatively

Gary G. Ihas; L. Frederick; J. P. McFarland

1998-01-01

362

Search for weak magnetic fields of stars  

Microsoft Academic Search

The magnetic fields of some normal stars of the main sequence, supergiants and Hg-Mn stars have been measured from metallic and hydrogen lines on the 6-m telescope with the Fabry-Perot magnetometer and spectropolarimeter. These results and the data of other authors are statistically analysed. A conclusion is drawn that the studied types of stars hardly contain a magnetic field exceeding

Yu. V. Glagolevskij; I. I. Romanyuk; I. D. Najdenov; V. G. Shtol

1989-01-01

363

Magnetic field effects on mass transport  

Microsoft Academic Search

It has been shown that the stationary limiting diffusion current on a steady electrode is proportional to {ital B}¹³{ital C}⁴³ where {ital C} is the electroactive species concentration and {ital B} the magnetic field intensity. A new impedance technique is developed which consists of the frequency response analysis of the limiting diffusion current to a sinusoidal magnetic field perturbation. In

O. Aaboubi; J. P. Chopart; J. Douglade; C. Gabrielli; B. Tribollet

1990-01-01

364

The magnetic field investigation on Cluster  

NASA Technical Reports Server (NTRS)

The magnetic field investigation of the Cluster four-spacecraft mission is designed to provide intercalibrated measurements of the B magnetic field vector. The instrumentation and data processing of the mission are discussed. The instrumentation is identical on the four spacecraft. It consists of two triaxial fluxgate sensors and of a failure tolerant data processing unit. The combined analysis of the four spacecraft data will yield such parameters as the current density vector, wave vectors, and the geometry and structure of discontinuities.

Balogh, A.; Cowley, S. W. H.; Southwood, D. J.; Musmann, G.; Luhr, H.; Neubauer, F. M.; Glassmeier, K.-H.; Riedler, W.; Heyn, M. F.; Acuna, M. H.

1988-01-01

365

The large-scale solar magnetic field  

Microsoft Academic Search

The large-scale photospheric magnetic field, measured by the Mt. Wilson magnetograph, has been analyzed in terms of surface harmonics (Pnm)(?)cosmf and Pnm(?)sinmf) for the years 1959 through 1972. Our results are as follows. The single harmonic which most often characterized the general solar magnetic field throughout the period of observation corresponds to a dipole lying in the plane of the

Martin D. Altschuler; Dorothy E. Trotter; Gordon Newkirk; Robert Howard

1974-01-01

366

Strain Sensors for High Field Pulse Magnets  

Microsoft Academic Search

\\u000a In this paper we present an investigation into several strain sensing technologies that are being considered to monitor mechanical\\u000a deformation within the steel reinforcement shells used in high field pulsed magnets. Such systems generally operate at cryogenic\\u000a temperatures to mitigate heating issues that are inherent in the coils of nondestructive, high field pulsed magnets. The objective\\u000a of this preliminary study

Christian Martinez; Yan Zheng; Daniel Easton; Kevin M Farinholt

2009-01-01

367

Planetary Magnetic Fields and Climate Evolution  

NASA Astrophysics Data System (ADS)

We explore the possible connections between magnetic fields and climate at the terrestrial bodies Venus, Earth, Mars, and Titan. Magnetic fields are thought to have negligible effects on the processes that change a planet's climate, except for processes that alter the abundance of atmospheric gases. Particles can be added or removed at the top of an atmosphere, where collisions are infrequent and a more substantial fraction of particles are ionized (and therefore subject to magnetic forces) than at lower altitudes. The absence of a global magnetic field at Mars for much of its history may have contributed to the removal of a substantial fraction of its atmosphere to space. The persistence of a global magnetic field should have decreased both ionization and removal of atmospheric ions by several processes, and may have indirectly decreased the loss rate of neutral particles as well. While it is convenient to think of magnetic fields as shields for planetary atmospheres from impinging plasma (such as the solar wind), observations of ions escaping from Earth's polar cusp regions suggest that magnetic shielding effects may not be as effective as previously thought. One explanation that requires further testing is that magnetic fields transfer momentum and energy from incident plasma to localized regions of the atmosphere, resulting in similar (or possibly greater) escape rates than if the momentum and energy were imparted more globally to the atmosphere in the absence of a magnetic field. Trace gases can be important for climate despite their low relative abundance in planetary atmospheres. At Venus, removal of O+ over the history of the planet has likely contributed to the loss of water from the atmosphere, leading to a runaway greenhouse situation and having implications for the chemistry of atmosphere-surface interactions. Conversely, Titan's robust atmospheric chemistry may result from the addition of trace amounts of oxygen from Saturn's magnetosphere, which then participate in chemical reactions that produce carbon monoxide (CO) and carbon dioxide (CO2). Models of the entire atmosphere system (including planetary plasma interactions) should continue to shed light on the connections between magnetic fields and climate, as well as models that consider a single planetary body in both magnetized and unmagnetized states. Future measurements, such as those that will be made by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft to Mars, will provide better constraints on the importance of magnetic fields in the evolution of atmospheres.

Brain, D. A.; Leblanc, F.; Luhmann, J. G.; Moore, T. E.; Tian, F.

368

Nuclear magnetic resonance in magnets with a helicoidal magnetic structure in an external magnetic field  

NASA Astrophysics Data System (ADS)

In this review, the static and dynamic properties of a magnet with a helicoidal magnetic structure placed in an external magnetic field are discussed. The results of the investigation of its ground state and spectra, as well as the amplitudes of the spin excitations are presented. The temperature and field dependences of the basic thermodynamic characteristics (heat capacity, magnetization, and magnetic susceptibility) have been calculated in the spin-wave approximation. The results of calculating the local and integral dynamic magnetic susceptibility are given. This set of data represents a methodical basis for constructing a consistent (in the framework of unified approximations) picture of the NMR absorption in the magnet under consideration. Both local NMR characteristics (resonance frequency, line broadening, enhancement coefficient) and integral characteristics (resultant shape of the absorption line with its specific features) have been calculated. The effective Hamiltonian of the Suhl-Nakamura interaction of nuclear spins through spin waves has been constructed. The second moment and the local broadening of the line of the NMR absorption caused by this interaction have been calculated. The role of the basic local inhomogeneities in the formation of the integral line of the NMR absorption has been analyzed. The opportunities for the experimental NMR investigations in magnets with a chiral spin structure are discussed.

Tankeyev, A. P.; Borich, M. A.; Smagin, V. V.

2014-11-01

369

Magnetic Field Problem: Mesuring Current in Wire  

NSDL National Science Digital Library

A wire carrying an unknown current is shown above. An external magnetic field that has constant magnitude and direction is applied to the top half of the simulation (The gray rectangle is at the boundary for your reference). In addition, there is the magnetic field produced by the current in the wire. The direction arrows show the vector sum of these two fields. (The color of the direction arrows represents the magnitude of the field as before.) Observe the force vector and the force/length in the yellow message box in the lower left hand corner.

Wolfgang Christian

370

Magnetic field transfer device and method  

DOEpatents

A magnetic field transfer device includes a pair of oppositely wound inner coils which each include at least one winding around an inner coil axis, and an outer coil which includes at least one winding around an outer coil axis. The windings may be formed of superconductors. The axes of the two inner coils are parallel and laterally spaced from each other so that the inner coils are positioned in side-by-side relation. The outer coil is outwardly positioned from the inner coils and rotatable relative to the inner coils about a rotational axis substantially perpendicular to the inner coil axes to generate a hypothetical surface which substantially encloses the inner coils. The outer coil rotates relative to the inner coils between a first position in which the outer coil axis is substantially parallel to the inner coil axes and the outer coil augments the magnetic field formed in one of the inner coils, and a second position 180[degree] from the first position, in which the augmented magnetic field is transferred into the other inner coil and reoriented 180[degree] from the original magnetic field. The magnetic field transfer device allows a magnetic field to be transferred between volumes with negligible work being required to rotate the outer coil with respect to the inner coils. 16 figs.

Wipf, S.L.

1990-02-13

371

Magnetic field transfer device and method  

DOEpatents

A magnetic field transfer device includes a pair of oppositely wound inner coils which each include at least one winding around an inner coil axis, and an outer coil which includes at least one winding around an outer coil axis. The windings may be formed of superconductors. The axes of the two inner coils are parallel and laterally spaced from each other so that the inner coils are positioned in side-by-side relation. The outer coil is outwardly positioned from the inner coils and rotatable relative to the inner coils about a rotational axis substantially perpendicular to the inner coil axes to generate a hypothetical surface which substantially encloses the inner coils. The outer coil rotates relative to the inner coils between a first position in which the outer coil axis is substantially parallel to the inner coil axes and the outer coil augments the magnetic field formed in one of the inner coils, and a second position 180.degree. from the first position, in which the augmented magnetic field is transferred into the other inner coil and reoriented 180.degree. from the original magnetic field. The magnetic field transfer device allows a magnetic field to be transferred between volumes with negligible work being required to rotate the outer coil with respect to the inner coils.

Wipf, Stefan L. (Hamburg, DE)

1990-01-01

372

Electrostatic acceleration of helicon plasma using a cusped magnetic field  

NASA Astrophysics Data System (ADS)

The electrostatic acceleration of helicon plasma is investigated using an electrostatic potential exerted between the ring anode at the helicon source exit and an off-axis hollow cathode in the downstream region. In the downstream region, the magnetic field for the helicon source, which is generated by a solenoid coil, is modified using permanent magnets and a yoke, forming an almost magnetic field-free region surrounded by an annular cusp field. Using a retarding potential analyzer, two primary ion energy peaks, where the lower peak corresponds to the space potential and the higher one to the ion beam, are detected in the field-free region. Using argon as the working gas with a helicon power of 1.5 kW and a mass flow rate of 0.21 mg/s, the ion beam energy is on the order of the applied acceleration voltage. In particular, with an acceleration voltage lower than 150 V, the ion beam energy even exceeds the applied acceleration voltage by an amount on the order of the electron thermal energy at the exit of the helicon plasma source. The ion beam energy profile strongly depends on the helicon power and the applied acceleration voltage. Since by this method the whole working gas from the helicon plasma source can, in principle, be accelerated, this device can be applied as a noble electrostatic thruster for space propulsion.

Harada, S.; Baba, T.; Uchigashima, A.; Yokota, S.; Iwakawa, A.; Sasoh, A.; Yamazaki, T.; Shimizu, H.

2014-11-01

373

A two-step ring current decay time model during the passive recovery phase of magnetic storms  

NASA Astrophysics Data System (ADS)

Magnetic storms are caused by changes in the currents flowing near the Earth, particularly by the enhanced ring current. The ring current dynamics is described through the energy balance equation, where a key role is played by the decay time parameter ?. Two kind of models depending on diverse geophysical parameters have been introduced for this important function. One of them, based on the generally observed dependence on Dst, and the other depending on the energy input related to the electric field vBS, where v is the solar wind velocity and BS is the magnitude of the southward component of the interplanetary magnetic field. A comparison of both models and a 1 h-forecast of Dst was done previously. In this work we further analyze them doing a longtime-forecast of the passive recovery phase of storms (almost null injection, vBS?Ec=0.49mV/m) through diverse study cases from the OMNI database. We assume that the decay time depends on Dst and Dst-peak because during that phase the energy injection, usually considered as proportional to vBS, ceases. We show that the observed data during the early recovery is better described by the model based on Dst, but during the late recovery is better correlated with an exponential function. This indicates that the whole recovery phase of storms should be described by a two-step model which considers both approaches.

Monreal MacMahon, R.; Llop-Romero, C.

2011-08-01

374

Laminated magnet field coil sheath  

DOEpatents

A method for manufacturing a magnetic cable trim coil in a sheath assembly for use in a cryogenic particle accelerator. A precisely positioned pattern of trim coil turns is bonded to a flexible substrate sheath that is capable of withstanding cryogenic operating conditions. In the method of the invention the flexible substrate sheath, with the trim coil pattern precisely location relative to a bore tube assembly of an accelerator and is then bonded to the bore tube with a tape suitable for cryogenic application. The resultant assembly can be readily handled and installed within an iron magnet yoke assembly of a suitable cryogenic particle accelerator. 1 fig.

Skaritka, J.R.

1987-05-15

375

Laminated magnet field coil sheath  

DOEpatents

a method for manufacturing a magnet cable trim coil in a sheath assembly for use in a cryogenic particle accelerator. A precisely positioned pattern of trim coil turns is bonded to a flexible substrate sheath that is capable of withstanding cryogenic operating conditions. In the method of the invention the flexible sheath, with the trim coil pattern precisely positioned thereon, is accurately positioned at a precise location relative to a bore tube assembly of an accelerator and is then bonded to the bore tube with a tape suitable for cryogenic application. The resultant assembly can be readily handled and installed within an iron magnet yoke assembly of a suitable cryogenic particle accelerator.

Skaritka, John R. (Coram, NY)

1987-12-01

376

Generation of strong magnetic field using 60 mm? superconducting bulk magnet and its application to magnetron sputtering device  

NASA Astrophysics Data System (ADS)

To make a practical application of a superconducting bulk magnet (SBM), it is necessary that the SBM generates a strong and stable magnetic field in a working space and the magnet can be handled without any special care that would be needed because of the use of a superconductor. To satisfy these requirements, we have designed a portable and user-friendly magnet system consisting of a small air-cooled type refrigerator and a bulk superconductor. By using the stress-controlling magnetization technique, we could achieve a magnetic flux density of 8.0 T on the bulk surface and 6.5 T over the vacuum chamber surface of the refrigerator, when a 60 mm? Gd-Ba-Cu-O bulk superconductor reinforced with a 5 mm thick stainless steel ring was magnetized by field cooling in 8.5 T to 27 K. We have confirmed that the bulk magnet system coupled with a battery is quite portable and can be delivered to any location by using a car with an electric power outlet in the cabin. We have constructed a magnetron sputtering device that employs a bulk magnet system delivered from the place of magnetization by this method. This sputtering device exhibits several unique features such as deposition at a very low Ar gas pressure because the magnetic field is 20 times stronger than that obtained by a conventional device in the working space.

Yanagi, Y.; Matsuda, T.; Hazama, H.; Yokouchi, K.; Yoshikawa, M.; Itoh, Y.; Oka, T.; Ikuta, H.; Mizutani, U.

2005-10-01

377

Dynamic signatures of quiet sun magnetic fields  

NASA Technical Reports Server (NTRS)

The collision and disappearance of opposite polarity fields is observed most frequently at the borders of network cells. Due to observational limitations, the frequency, magnitude, and spatial distribution of magnetic flux loss have not yet been quantitatively determined at the borders or within the interiors of the cells. However, in agreement with published hypotheses of other authors, the disapperance of magnetic flux is speculated to be a consequence of either gradual or rapid magnetic reconnection which could be the means of converting magnetic energy into the kinetic, thermal, and nonthermal sources of energy for microflares, spicules, the solar wind, and the heating of the solar corona.

Martin, S. F.

1983-01-01

378

H2+ in a weak magnetic field  

NASA Astrophysics Data System (ADS)

The electronic energy of H2+ in magnetic fields of up to B=0.2{{B}0} (or 4.7× {{10}4} T) is investigated. Numerical values of the magnetic susceptibility for both the diamagnetic and paramagnetic contributions are reported for arbitrary orientations of the molecule in the magnetic field. It is shown that both diamagnetic and paramagnetic susceptibilities grow with inclination, while paramagnetic susceptibility is systematically much smaller than the diamagnetic one. Accurate two-dimensional Born–Oppenheimer surfaces are obtained with special trial functions. Using these surfaces, vibrational and rotational states are computed and analyzed for the isotopologues H2+ and D2+.

Medel Cobaxin, Héctor; Alijah, Alexander; López Vieyra, Juan Carlos; Turbiner, Alexander V.

2015-02-01

379

Effects of static magnetic fields on plants.  

NASA Astrophysics Data System (ADS)

In our recent experiment on STS-107 (MFA-Biotube) we took advantage of the magnetic heterogeneity of the gravity receptor cells of flax roots, namely stronger diamagnetism of starch-filled amyloplasts compared to cytoplasm (? ? < 0). High gradient magnetic fields (HGMF, grad(H2/2) up to 109-1010 Oe2/cm) of the experimental chambers (MFCs) repelled amyloplasts from the zones of stronger field thus providing a directional stimulus for plant gravisensing system in microgravity, and causing the roots to react. Such reaction was observed in the video downlink pictures. Unfortunately, the ``Columbia'' tragedy caused loss of the plant material and most of the images, thus preventing us from detailed studies of the results. Currently we are looking for a possibility to repeat this experiment. Therefore, it is very important to understand, what other effects (besides displacing amyloplasts) static magnetic fields with intensities 0 to 2.5104 Oe, and with the size of the area of non-uniformity 10-3 to 1 cm. These effects were estimated theoretically and tested experimentally. No statistically significant differences in growth rates or rates of gravicurvature were observed in experiments with Linum, Arabidopsis, Hordeum, Avena, Ceratodon and Chara between the plants grown in uniform magnetic fields of various intensities (102 to 2.5104 Oe) and those grown in the Earth's magnetic field. Microscopic studies also did not detect any structural differences between test and control plants. The magnitudes of possible effects of static magnetic fields on plant cells and organs (including effects on ion currents, magneto-hydrodynamic effects in moving cytoplasm, ponderomotive forces on other cellular structures, effects on some biochemical reactions and biomolecules) were estimated theoretically. The estimations have shown, that these effects are small compared to the thermodynamic noise and thus are insignificant. Both theoretical estimations and control experiments confirm, that intracellular magnetophoresis of statoliths is the only significant effect of the magnetic field on plant cells and organs in the tested magnetic systems.

Kuznetsov, O.

380

Studies of solar magnetic fields  

Microsoft Academic Search

Magnetic flux data from the Mount Wilson magnetograph are examined over the interval 1967–1973. The total flux in the north is greater than that in the south by about 7% over this interval, reflecting a higher level of activity in the northern hemisphere. Close to 95% of the total flux is confined to latitudes equatorward of 40°, which means that

Robert Howard

1974-01-01

381

Fast Reconnection of Weak Magnetic Fields  

NASA Technical Reports Server (NTRS)

Fast magnetic reconnection refers to annihilation or topological rearrangement of magnetic fields on a timescale that is independent (or nearly independent) of the plasma resistivity. The resistivity of astrophysical plasmas is so low that reconnection is of little practical interest unless it is fast. Yet, the theory of fast magnetic reconnection is on uncertain ground, as models must avoid the tendency of magnetic fields to pile up at the reconnection layer, slowing down the flow. In this paper it is shown that these problems can be avoided to some extent if the flow is three dimensional. On the other hand, it is shown that in the limited but important case of incompressible stagnation point flows, every flow will amplify most magnetic fields. Although examples of fast magnetic reconnection abound, a weak, disordered magnetic field embedded in stagnation point flow will in general be amplified, and should eventually modify the flow. These results support recent arguments against the operation of turbulent resistivity in highly conducting fluids.

Zweibel, Ellen G.

1998-01-01

382

Near equipment magnetic field verification and scaling  

NASA Astrophysics Data System (ADS)

Magnetic field measurements are essential to the success of many scientific space missions. Outside of the Earth's magnetic field the biggest potential source of magnetic field contamination of these measurements is emitted by the spacecraft. Spacecraft magnetic cleanliness is enforced through the application of strict ground verification requirements for spacecraft equipment and instruments. Due to increasingly strict AC magnetic field requirements, many spacecraft units cannot be verified on the ground using existing techniques. These measurements must instead be taken close to the equipment under test (EUT) and then extrapolated. A traditional dipole power law of -3 (with a field fall-off proportional to r-3) cannot be applied at these close distances without risk of underestimating the field emitted by the EUT, but we demonstrate that a power law of -2 is too conservative. We propose a compromise that uses a power law of -2 up to a distance equal to 3 times the unit size, beyond which a dipole power law can be applied. When extrapolating from a distance of 0.20 to 1.00 m from the centre of a 0.20 m wide EUT, we demonstrate that this method avoids an underprediction of the field, and is at least twice as accurate as performing the extrapolation with a fixed power law of -2.

Pudney, M. A.; Carr, C. M.; Schwartz, S. J.; Howarth, S. I.

2013-07-01

383

Magnetic field dependence of plasma relaxation times  

NASA Technical Reports Server (NTRS)

A previously derived Fokker-Planck collision integral for an electron plasma in a dc magnetic field is examined in the limit in which the Debye length is greater than the thermal gyroradius, which is in turn greater than the mean distance of closest approach. It is demonstrated that the collision integral can be satisfactorily approximated by the classical Landau value (which ignores the presence of a dc magnetic field) if the following replacement is made: In the Coulomb logarithm, the Debye length is replaced by the gyroradius. This induces a fundamental logarithmic dependence on magnetic field in the relaxation times. Numerical comparison of the asymptotic approximations with the previously derived exact results is made, and good agreement is found. The simplification this introduces into the description of collision processes in magnetized plasma is considerable.

Montgomery, D.; Joyce, G.; Turner, L.

1974-01-01

384

Magnetic field production after inflation  

E-print Network

We study the electromagnetic field production during preheating after hybrid inflation in a model with the field content of the Standard Model, coupled to a singlet inflaton. We find that very soon after symmetry breaking our system enters a regime of kinetic turbulence, characterized by a self-similar behaviour of the energy spectra and a power-like dependence on time of the inflaton and Higgs field variances.

Andres Diaz-Gil; J. Garcia-Bellido; M. Garcia Perez; A. Gonzalez-Arroyo

2005-09-22

385

Probing strong magnetic fields with cyclotron lines  

NASA Astrophysics Data System (ADS)

The physics of accretion of X-ray pulsars are dominated by very strong magnetic fields of of the order of 1012 Gauss. The only direct measure of these magnetic fields is the spectral analysis of cyclotron resonance scattering features (CRSFs). Electron CRSFs can form as broad harmonic absorption features in the keV regime when X- ray photons resonantly scatter with quantized electrons in the strongly magnetized accretion plasma. Recently, also the detection of proton CRSFs for magnetars has been claimed, rendering the basic understanding of the formation of CRSFs an important factor also for another class of fascinating extreme objects. In both cases, the line positions are directly linked to the magnetic field strength of the neutron star. Using Monte Carlo simulations, we perform a detailed study of the line shapes and positions of electron cyclotron lines of accreting neutron stars. These are indicators not only of the magnetic field strength but also give insight into the geometry of accretion, the structure of the magnetic field and gravitational effects around the compact object. For the first time ever, we have build a simulation based XSPEC model application to quantitatively compare our theoretical results to real observed source data. Recent results and their meaning for the physical picture of accreting X-ray pulsars from a comparison of the Monte Carlo Model to a set of sources are presented.

Schönherr, Gabriele; Wilms, Jörn; Kretschmar, Peter; Kreykenbohm, Ingo; Pottschmidt, Katja; Suchy, Slawo; Rothschild, Rick; Caballero, Isabel

386

Tailoring magnetic field gradient design to magnet cryostat geometry.  

PubMed

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

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

2006-01-01

387

Primordial Magnetic Fields from Dark Energy  

E-print Network

Evidences indicate that the dark energy constitutes about two thirds of the critical density of the universe. If the dark energy is an evolving pseudo scalar field that couples to electromagnetism, a cosmic magnetic seed field can be produced via spinoidal instability during the formation of large-scale structures.

Da-Shin Lee; Wolung Lee; Kin-Wang Ng

2002-08-30

388

Galactic magnetic fields and hierarchical galaxy formation  

E-print Network

A framework is introduced for coupling the evolution of galactic magnetic fields sustained by the mean-field dynamo with the formation and evolution of galaxies in the cold dark matter cosmology. Estimates of the steady-state strength of the large-scale and turbulence magnetic fields from mean-field and fluctuation dynamo models are used together with galaxy properties predicted by semi-analytic models of galaxy formation for a population of spiral galaxies. We find that the field strength is mostly controlled by the evolving gas content of the galaxies. Thus, because of the differences in the implementation of the star formation law, feedback from supernovae and ram-pressure stripping, each of the galaxy formation models considered predicts a distribution of field strengths with unique features. The most prominent of them is the difference in typical magnetic fields strengths obtained for the satellite and central galaxies populations as well as the typical strength of the large-scale magnetic field in galax...

Rodrigues, Luiz Felippe S; Fletcher, Andrew; Baugh, Carlton

2015-01-01

389

Ionospheric magnetic fields at Venus and Mars  

NASA Astrophysics Data System (ADS)

Mars Global Surveyor (MGS) and Venus Express(VEX) spacecraft have provided us a wealth of insitu observations of characteristics of induced magnetospheres of Mars and Venus at low altitudes during the periods of solar minimum. At such conditions the interplanetary magnetic field (IMF) penetrates deeply inside the ionosphere while the solar wind is terminated at higher altitudes. We present the measurements made by MGS and VEX in the ionospheres of both planets which reveal similar features of the magnetization. The arising magnetic field pattern occurs strongly asymmetrical with respect to the direction of the cross-flow component of the IMF revealing either a sudden straightening of the field lines with a release of the magnetic field stresses or a sudden rotation of the magnetic field vector with a reversal of the sign of the cross-flow component. Such an asymmetrical response is observed at altitudes where the motion of ions and electrons is decoupled and collisional effects become important for generation of the electric currents Asymmetry in the field topology significantly modifies a plasma transport to the night side.

Dubinin, E.; Fraenz, M.; Zhang, T. L.; Woch, J.; Wei, Y.

2014-04-01

390

Passive magnetic shielding in static gradient fields  

NASA Astrophysics Data System (ADS)

The effect of passive magnetic shielding on dc magnetic field gradients imposed by both external and internal sources is studied for two idealized shield models: concentric spherical and infinitely-long cylindrical shells of linear material. It is found that higher-order multipoles of an externally applied magnetic field are always shielded progressively better for either geometry by a factor related to the order of the multipole. In regard to the design of internal coil systems, we determine reaction factors for the general multipole field and provide examples of how one can take advantage of the coupling of the coils to the innermost shell to optimize the uniformity of the field. Furthermore, we provide formulae relevant to active magnetic compensation systems which attempt to stabilize the interior fields by sensing and cancelling the exterior fields close to the outermost shell. Overall this work provides a comprehensive framework that is useful for the analysis and optimization of dc magnetic shields, serving as a theoretical and conceptual design guide as well as a starting point and benchmark for finite-element analysis.

Bidinosti, C. P.; Martin, J. W.

2014-04-01

391

Field and thermal modeling of magnetizing fixture by impulse  

Microsoft Academic Search

In a capacitor discharge impulse magnetizer, a magnet is magnetized by the discharging current of capacitors. This paper describes a method for exact parameter estimation of impulse magnetizer and a method for field and thermal analysis of impulse magnetizer using this parameter. As the detailed field and thermal characteristics of impulse magnetizer can be obtained, the efficient design of impulse

Pill-Soo Kim; Yong Kim

2003-01-01

392

Magnet power supply control of the NSLS VUV and x-ray storage rings transfer lines  

SciTech Connect

The transfer lines for NSLS VUV and x-ray storage rings have been split. New power supplies have been incorporated with existing ones. The existing microprocessor system has been upgraded in order to control the additional functions. This system expands the input/output port of the microprocessor to an addressable serial/parallel link to each magnet power supply. The implementation of this system will be discussed.

Klein, J.D.; Ramamoorthy, S.; Singh, O.; Smith, J.D.

1985-01-01

393

Estimate of the primordial magnetic field helicity.  

PubMed

Electroweak baryogenesis proceeds via changes in the non-Abelian Chern-Simons number. It is argued that these changes generate a primordial magnetic field with left-handed helicity. The helicity density of the primordial magnetic field today is then estimated to be given by approximately 10(2)n(b), where n(b) approximately 10(-6)/cm(3) is the present cosmological baryon number density. With certain assumptions about the inverse cascade we find that the field strength at recombination is approximately 10(-13) G on a comoving coherence scale approximately 0.1 pc. PMID:11736556

Vachaspati, T

2001-12-17

394

Active acoustic metamaterials with tunable effective mass density by gradient magnetic fields  

NASA Astrophysics Data System (ADS)

Magnetically controlled acoustic metamaterials are designed and experimentally studied. Magneto-acoustic metamaterials are fabricated by covering an aluminum circular ring with magnetorheological elastomer. The resonant frequency of the structured elastomer is actively tunable by external gradient magnetic field, allowing for values of effective mass density of metamaterials to be adjusted in the low-frequency region. A prestressed plate theory is proposed to explain the shifting of the resonant frequency induced by the magnetic field and coincides very well with the experimental results. It is found that the tunability of magneto-acoustic metamaterials is attributed to the competition between the magnetic-field-induced prestress and the structural flexural rigidity. The proposed magneto-acoustic metamaterials realize the dynamic tuning of effective mass density with non-contact and fast-response gradient magnetic fields, providing a degree of freedom for full control of sound.

Chen, Xing; Xu, Xianchen; Ai, Shigang; Chen, HaoSen; Pei, Yongmao; Zhou, Xiaoming

2014-08-01

395

Small-scale solar magnetic fields: An overview  

Microsoft Academic Search

An overview is given of the observational and the theoretical methods used to investigate solar magnetic fields. It includes an introduction to the Stokes parameters, their radiative transfer in the presence of a magnetic field, and empirical techniques used to measure various properties of solar magnetic features, such as the strength and direction of the magnetic field, magnetic flux, temperature,

Sami K. Solanki

1993-01-01

396

Compute Values of Earth's Magnetic Field  

NSDL National Science Digital Library

The program run from this form computes the values of the Earth's magnetic field parameters for a given location and date or date range. Input required is the date and location (in latitude and longitude) of interest. Links to the U.S. Census Bureau's U.S. Gazeteer and the Getty Thesaurus assists in determing the latitude and longitude for locations of interest. The magnetic parameters (D, I, H, X, Y, Z, and F) are computed based on the latest International Geomagnetic Reference Field (IGRF), a Schmidt quasinormalized spherical harmonic model of the magnetic field. Accuracies for the angular components (Declination, D and Inclination, I) are reported in degrees and minutes of arc and are generally within 30 minutes. Accuracies for the force components (Horizontal - H, North - X, East - Y, Vertical - Z, and Total force - F) are generally within 25 nanotesla. A link to frequently-asked questions about the geomagnetic field of Earth is provided as background material.

397

Anomalous electron trapping by localized magnetic fields  

NASA Astrophysics Data System (ADS)

We consider an electron with an anomalous magnetic moment g > 2 confined to a plane and interacting with a non-zero magnetic field B perpendicular to the plane. We show that if B has compact support and the magnetic flux in natural units is 0305-4470/32/16/011/img6, the corresponding Pauli Hamiltonian has at least 0305-4470/32/16/011/img7 bound states, without making any assumptions about the field profile. Furthermore, in the zero-flux case there is a pair of bound states with opposite spin orientations. Using a Birman-Schwinger technique, we extend the last claim to a weak rotationally symmetric field with 0305-4470/32/16/011/img8, thus correcting a recent result. Finally, we show that under mild regularity assumptions existence of the bound states can also be proved for non-symmetric fields with tails.

Bentosela, F.; Cavalcanti, R. M.; Exner, P.; Zagrebnov, V. A.

1999-04-01

398

A Holographic Bound on Cosmic Magnetic Fields  

E-print Network

Magnetic fields large enough to be observable are ubiquitous in astrophysics, even at extremely large length scales. This has led to the suggestion that such fields are seeded at very early (inflationary) times, and subsequently amplified by various processes involving, for example, dynamo effects. Many such mechanisms give rise to extremely large magnetic fields at the end of inflationary reheating, and therefore also during the quark-gluon plasma epoch of the early universe. Such plasmas have a well-known holographic description in terms of a thermal asymptotically AdS black hole. We show that holography imposes an upper bound on the intensity of magnetic fields ($\\approx \\; 3.6 \\times 10^{18}\\;\\; \\text{gauss}$ at the hadronization temperature) in these circumstances; this is above, but not far above, the values expected in some models of cosmic magnetogenesis.

Brett McInnes

2015-01-01

399

Ion Thruster Discharge Performance Per Magnetic Field Topography  

NASA Technical Reports Server (NTRS)

DC-ION is a detailed computational model for predicting the plasma characteristics of rain-cusp ion thrusters. The advanced magnetic field meshing algorithm used by DC-ION allows precise treatment of the secondary electron flow. This capability allows self-consistent estimates of plasma potential that improves the overall consistency of the results of the discharge model described in Reference [refJPC05mod1]. Plasma potential estimates allow the model to predict the onset of plasma instabilities, and important shortcoming of the previous model for optimizing the design of discharge chambers. A magnetic field mesh simplifies the plasma flow calculations, for both the ions and the secondary electrons, and significantly reduces numerical diffusion that can occur with meshes not aligned with the magnetic field. Comparing the results of this model to experimental data shows that the behavior of the primary electrons, and the precise manner of their confinement, dictates the fundamental efficiency of ring-cusp. This correlation is evident in simulations of the conventionally sized NSTAR thruster (30 cm diameter) and the miniature MiXI thruster (3 cm diameter).

Wirz, Richard E.; Goebel, Dan

2006-01-01

400

DNA-Assembled Nanoparticle Rings Exhibit Electric and Magnetic Resonances at Visible Frequencies.  

PubMed

Metallic nanostructures can be used to manipulate light on the subwavelength scale to create tailored optical material properties. Next to electric responses, artificial optical magnetism is of particular interest but difficult to achieve at visible wavelengths. DNA-self-assembly has proved to serve as a viable method to template plasmonic materials with nanometer precision and to produce large quantities of metallic objects with high yields. We present here the fabrication of self-assembled ring-shaped plasmonic metamolecules that are composed of four to eight single metal nanoparticles with full stoichiometric and geometric control. Scattering spectra of single rings as well as absorption spectra of solutions containing the metamolecules are used to examine the unique plasmonic features, which are compared to computational simulations. We demonstrate that the electric and magnetic plasmon resonance modes strongly correlate with the exact shape of the structures. In particular, our computations reveal the magnetic plasmons only for particle rings of broken symmetries, which is consistent with our experimental data. We stress the feasibility of DNA self-assembly as a method to create bulk plasmonic materials and metamolecules that may be applied as building blocks in plasmonic devices. PMID:25611357

Roller, Eva-Maria; Khorashad, Larousse Khosravi; Fedoruk, Michael; Schreiber, Robert; Govorov, Alexander O; Liedl, Tim

2015-02-11

401

Electronic structure and magnetic properties of a molecular octanuclear chromium-based ring.  

PubMed

A comprehensive study of electronic and magnetic properties of Cr8F8Piv16 (HPiv = pivalic acid, trimethyl acetic acid) molecular ring is presented. The total, local and orbital projected density of states are calculated by the first principle density functional theory calculations using the package SIESTA. The original molecule has been approximated by replacing the pivallic groups by H atoms (hydrogen saturation). Electron density, deformation density, electrostatic potential and spin density maps are analyzed and compared with experiment for the first time. Magnetic properties are investigated in detail. Magnetic moments are calculated using two different approaches: the Mulliken one and integration of muffin-tin sphere with a given radius. Different magnetic configurations (ferromagnetic, antiferromagnetic and many more with randomly distributed spins up and down) are considered to extract exchange interaction parameter J and check the stability of its estimate. PMID:22400306

Slusarski, T; Brzostowski, B; Tomecka, D; Kamieniarz, G

2011-10-01

402

Potential Magnetic Field around a Helical Flux Rope Current Structure in the Solar Corona  

NASA Astrophysics Data System (ADS)

We consider the potential magnetic field associated with a helical electric line current flow, idealizing the near-potential coronal field within which a highly localized twisted current structure is embedded. It is found that this field has a significant axial component off the helical magnetic axis where there is no current flow, such that the flux winds around the axis. The helical line current field, in including the effects of flux rope writhe, is therefore more topologically complex than the straight line and ring current fields sometimes used in solar flux rope models. The axial flux in magnetic fields around confined current structures may be affected by the writhe of these current structures such that the field twists preferentially with the same handedness as the writhe. This property of fields around confined current structures with writhe may be relevant to classes of coronal magnetic flux ropes, including structures observed to have sigmoidal forms in soft X-rays and prominence magnetic fields. For example, ``bald patches'' and the associated heating by Parker current sheet dissipation seem likely. Thus, some measurements of flux rope magnetic helicities may derive from external, near-potential fields. The predicted hemispheric preference for positive and negative magnetic helicities is consistent with observational results for prominences and sigmoids and past theoretical results for flux rope internal fields.

Petrie, G. J. D.

2007-05-01

403

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

404

Feasibility of a storage ring for polar molecules in strong-field-seeking states  

Microsoft Academic Search

We show, through modeling and simulation, that it is feasible to construct a storage ring that will store dense bunches of strong-field-seeking polar molecules at 30 m\\/s (kinetic energy of 2 K) and hold them, for several minutes, against losses due to defocusing, oscillations, and diffusion. The ring, 3 m in diameter, has straight sections that afford access to the

Hiroshi Nishimura; Glen Lambertson; Juris G. Kalnins; Harvey Gould

2004-01-01

405

Magnetic Field Generation in Galactic Plasmas  

NASA Astrophysics Data System (ADS)

The origin of the magnetic field in the universe is one of the great problems in astrophysics. The observed magnetic fields in spiral galaxies, for example, are of the order of microgauss and are coherent over galactic scales. It is usually assumed that turbulent fluid motions will enhance a seed field. In the present work we investigate the growth of the magnetic field in plasmas with high magnetic Prandtl number (the ratio of viscosity to resistivity). This growth occurs initially at scales below the viscous scale [1]. Kinney et al. [2] showed that in 2D the field saturates at an amplitude independent of the mean scale of the field. We discuss the initial growth in the three dimensional case where the dynamics of the field are on scales less than the viscosity scale [3]. At low initial field, the field grows and the scale decreases until the resistive scale is reached. The field then grows at a reduced rate until it reaches an equilibrium with the mean scale at a resistive scale. At higher initial amplitude, the field saturates before the mean scale has decreased to the resistive scale. The subsequent evolution is a slow decrease of the scale to the resistive scale, at which point it reaches equilibrium and stops evolving. To explain the large scale coherence of galactic fields, an inverse cascade is necessary. There is no evidence of an inverse cascade. We will present results for extended physics models including tensor viscosity and ambipular diffusion. [1] R. Kulsrud, and S. Anderson, Astrophys. J., 396, 606 (1992); A. Gruzinov, S. Cowley, and R. Sudan, Phys.Rev.Lett., 77, 4342 (1996). [2] R. M. Kinney, B. Chandran, S. Cowley, J. C. McWilliams, Astrophys. J., accepted to publication (2000). [3] M. Opher, S. Cowley, R. M. Kinney, B. Chandran, J. Maron and J.C. McWilliams, in preparation (2000).

Opher, Merav; Cowley, Steve; Maron, Jason; McWilliams, James

2000-10-01

406

Magnetic Field Generation in Galactic Plasmas  

NASA Astrophysics Data System (ADS)

The origin of the magnetic field in the universe is one of the great problems in astrophysics. The observed magnetic fields in spiral galaxies, for example, are of the order of microgauss and are coherent over galactic scales. Its is usually assumed that turbulent fluid motions will enhance a seed field. In the present work we invetigate the growth of the magnetic field in plasmas with high magnetic Prandtl number (the ratio of viscosity to resistivity). This growth occur initially at scales below the viscous scale [1]. Kinney et al. [2] showed that in 2D the field saturates at an amplitude independent of the mean scale of the field. We discuss the initial growth in the three dimensional case where the dynamics of the field on scales less than the viscosity scale [3]. At low initial field, the field grows and the scale decreases until the resistive scale is reached. The field then grows at a reduced rate until it reaches an equilibrium with the mean scale at a resistive scale. At higher initial amplitude, the field saturates before the mean scale has decreased to the resistive scale. The subsequent evolution is a slow decrease of the scale to the resistive scale, at which point it reaches equilibrium and stops evolving. To explain the large scale coherence of galactic fields, an inverse cascade is necessary. There is no evidence of an inverse cascade. We will present results for extended physics models including tensor viscosity and ambipular diffusion. [1] R. Kulsrud, and S. Anderson, Astrophys. J., 396, 606 (1992); A. Gruzinov, S. Cowley, and R. Sudan, Phys.Rev.Lett., 77, 4342 (1996). [2] R. M. Kinney, B. Chandran, S. Cowley, J. C. McWilliams, Astrophys. J., accepted to publication (2000). [3] M. Opher, S. Cowley, A. Schekochihin, R. M. Kinney, B. Chandran, J. Maron and J.C. McWilliams, in preparation (2001).

Opher, M.; Cowley, S.; Schekochihin, A.; Kinney, R. M.; Chandran, B.; Maron, J.; McWilliams, J. C.

2001-05-01

407

Magnetic Fields and Massive Star Formation  

E-print Network

Massive stars ($M > 8$ \\msun) typically form in parsec-scale molecular clumps that collapse and fragment, leading to the birth of a cluster of stellar objects. We investigate the role of magnetic fields in this process through dust polarization at 870 $\\mu$m obtained with the Submillimeter Array (SMA). The SMA observations reveal polarization at scales of $\\lsim$ 0.1 pc. The polarization pattern in these objects ranges from ordered hour-glass configurations to more chaotic distributions. By comparing the SMA data with the single dish data at parsec scales, we found that magnetic fields at dense core scales are either aligned within $40^\\circ$ of or perpendicular to the parsec-scale magnetic fields. This finding indicates that magnetic fields play an important role during the collapse and fragmentation of massive molecular clumps and the formation of dense cores. We further compare magnetic fields in dense cores with the major axis of molecular outflows. Despite a limited number of outflows, we found that the ...

Zhang, Qizhou; Girart, Josep M; Hauyu,; Liu,; Tang, Ya-Wen; Koch, Patrick M; Li, Zhi-Yun; Keto, Eric; Ho, Paul T P; Rao, Ramprasad; Lai, Shih-Ping; Ching, Tao-Chung; Frau, Pau; Chen, How-Huan; Li, Hua-Bai; Padovani, Marco; Bontemps, Sylvain; Csengeri, Timea; Juarez, Carmen

2014-01-01

408

Magnetic fields of the outer planets  

NASA Technical Reports Server (NTRS)

It is difficult to imagine a group of planetary dynamos more diverse than those visited by the Pioneer and Voyager spacecraft. The magnetic field of Jupiter is large in magnitude and has a dipole axis within 10 deg of its rotation axis, comfortably consistent with the paleomagnetic history of the geodynamo. Saturn's remarkable (zonal harmonic) magnetic field has an axis of symmetry that is indistinguishable from its rotation axis (mush less than 1 deg angular separation); it is also highly antisymmetric with respect to the equator plane. According to one hypothesis, the spin symmetry may arise from the differential rotation of an electrically conducting and stably stratified layer above the dynamo. The magnetic fields of Uranus and Neptune are very much alike, and equally unlike those of the other known magnetized planets. These two planets are characterized by a large dipole tilts (59 deg and 47 deg, respectively) and quadrupole moments (Schmidt-normalized quadrupole/dipole ratio approximately equal 1.0). These properties may be characteristic of dynamo generation in the relatively poorly conducting 'ice' interiors of Uranus and Neptune. Characteristics of these planetary magnetic fields are illustrated using contour maps of the field on the planet's surface and discussed in the context of planetary interiors and dynamo generation.

Connerney, J. E. P.

1993-01-01

409

Reducing blood viscosity with magnetic fields  

NASA Astrophysics Data System (ADS)

Blood viscosity is a major factor in heart disease. When blood viscosity increases, it damages blood vessels and increases the risk of heart attacks. Currently, the only method of treatment is to take drugs such as aspirin, which has, however, several unwanted side effects. Here we report our finding that blood viscosity can be reduced with magnetic fields of 1 T or above in the blood flow direction. One magnetic field pulse of 1.3 T lasting ˜1 min can reduce the blood viscosity by 20%-30%. After the exposure, in the absence of magnetic field, the blood viscosity slowly moves up, but takes a couple of hours to return to the original value. The process is repeatable. Reapplying the magnetic field reduces the blood viscosity again. By selecting the magnetic field strength and duration, we can keep the blood viscosity within the normal range. In addition, such viscosity reduction does not affect the red blood cells’ normal function. This technology has much potential for physical therapy.

Tao, R.; Huang, K.

2011-07-01

410

Magnetic Field Noise Changes Effect of Combined Magnetic Field on Gravitropic Reaction of Cress Roots.  

NASA Astrophysics Data System (ADS)

The gravitropic reaction of cress roots in combined magnetic field was studied in details. It was shown that the negative roots gravitropism observed at the frequency of alternating component of combined magnetic field adjusted to the Ca ion cyclotron frequency could be observed only at Nayquist magnetic field noise level under 5 nT/Hz. While the magnetic noise level was increasing the negative gravitropism was disappearing. The inhibition of gravitropic reaction was observed in all cases. The effect was accompanied by the changes in the noise spectrum generated by cress roots.

Bogatina, Nina; Kordyum, Elizabeth; Sheykina, Nadezhda

411

A model of the magnetosheath magnetic field during magnetic clouds  

NASA Astrophysics Data System (ADS)

Magnetic clouds (MCs) are huge interplanetary structures which originate from the Sun and have a paramount importance in driving magnetospheric storms. Before reaching the magnetosphere, MCs interact with the Earth's bow shock. This may alter their structure and therefore modify their expected geoeffectivity. We develop a simple 3-D model of the magnetosheath adapted to MCs conditions. This model is the first to describe the interaction of MCs with the bow shock and their propagation inside the magnetosheath. We find that when the MC encounters the Earth centrally and with its axis perpendicular to the Sun-Earth line, the MC's magnetic structure remains mostly unchanged from the solar wind to the magnetosheath. In this case, the entire dayside magnetosheath is located downstream of a quasi-perpendicular bow shock. When the MC is encountered far from its centre, or when its axis has a large tilt towards the ecliptic plane, the MC's structure downstream of the bow shock differs significantly from that upstream. Moreover, the MC's structure also differs from one region of the magnetosheath to another and these differences vary with time and space as the MC passes by. In these cases, the bow shock configuration is mainly quasi-parallel. Strong magnetic field asymmetries arise in the magnetosheath; the sign of the magnetic field north-south component may change from the solar wind to some parts of the magnetosheath. We stress the importance of the Bx component. We estimate the regions where the magnetosheath and magnetospheric magnetic fields are anti-parallel at the magnetopause (i.e. favourable to reconnection). We find that the location of anti-parallel fields varies with time as the MCs move past Earth's environment, and that they may be situated near the subsolar region even for an initially northward magnetic field upstream of the bow shock. Our results point out the major role played by the bow shock configuration in modifying or keeping the structure of the MCs unchanged. Note that this model is not restricted to MCs, it can be used to describe the magnetosheath magnetic field under an arbitrary slowly varying interplanetary magnetic field.

Turc, L.; Fontaine, D.; Savoini, P.; Kilpua, E. K. J.

2014-02-01

412

Boundary Conformal Field Theory and Fusion Ring Representations  

E-print Network

To an RCFT corresponds two combinatorial structures: the amplitude of a torus (the 1-loop partition function of a closed string, sometimes called a modular invariant), and a representation of the fusion ring (called a NIM-rep or equivalently a fusion graph, and closely related to the 1-loop partition function of an open string). In this paper we develop some basic theory of NIM-reps, obtain several new NIM-rep classifications, and compare them with the corresponding modular invariant classifications. Among other things, we make the following fairly disturbing observation: there are infinitely many (WZW) modular invariants which do not correspond to any NIM-rep. The resolution could be that those modular invariants are physically sick. Is classifying modular invariants really the right thing to do? For current algebras, the answer seems to be: Usually but not always. For finite groups a la Dijkgraaf-Vafa-Verlinde-Verlinde, the answer seems to be: Rarely.

T. Gannon

2002-02-12

413

Exploring Magnetic Fields with a Compass  

NASA Astrophysics Data System (ADS)

A compass is an excellent classroom tool for the exploration of magnetic fields. Any student can tell you that a compass is used to determine which direction is north, but when paired with some basic trigonometry, the compass can be used to actually measure the strength of the magnetic field due to a nearby magnet or current-carrying wire. In this paper, we present a series of simple activities adapted from the Matter & Interactions textbook for doing just this. Interestingly, these simple measurements are comparable to predictions made by the Bohr model of the atom. Although antiquated, Bohr's atom can lead the way to a deeper analysis of the atomic properties of magnets. Although originally developed for an introductory calculus-based course, these activities can easily be adapted for use in an algebra-based class or even at the high school level.

Lunk, Brandon; Beichner, Robert

2011-01-01

414

Magnetic field configuration of the theta aurora  

NASA Technical Reports Server (NTRS)

A magnetic configuration of the open magnetosphere is described which is conducive to the formation of the theta aurora when the IMF has a significant northward component. A magnetic field topology and polar cap configuration, derived from a quantitative model of the open magnetosphere that incorporates Crooker's antiparallel merging hypothesis, are presented. Under this hypothesis, when the IMF has a northward component, the dayside merging line bifurcates, leaving a large fraction of the subsolar magnetopause untouched by the merging process. The polar cap, defined by tracing magnetic field lines that connect from the solar wind to the earth, is similarly bifurcated, leaving a sun-aligned stagnation region that is not magnetically connected to the solar wind and may plausibly be associated with the sun-aligned 'bar' of the theta aurora. The model provides testable predictions with regard to the position of this 'convection gap' in both Northern and Southern Hemispheres as functions of IMF direction.

Toffoletto, F. R.; Hill, T. W.

1990-01-01

415

Visualizing Planetary Magnetic Fields (and Why You Should Care)  

E-print Network

on Mars (and Venus) · Focus on differences in the magnetic fields using "global compass maps" (see me in the magnetic fields · In the absence of a global magnetic field (Mars and Venus like), the solar wind can magnetic field lines · Mars ­ (felt like) years in the making Photographic World Premier! (We

Fillingim, Matthew

416

High magnetic field ohmically decoupled non-contact technology  

DOEpatents

Methods and apparatus are described for high magnetic field ohmically decoupled non-contact treatment of conductive materials in a high magnetic field. A method includes applying a high magnetic field to at least a portion of a conductive material; and applying an inductive magnetic field to at least a fraction of the conductive material to induce a surface current within the fraction of the conductive material, the surface current generating a substantially bi-directional force that defines a vibration. The high magnetic field and the inductive magnetic field are substantially confocal, the fraction of the conductive material is located within the portion of the conductive material and ohmic heating from the surface current is ohmically decoupled from the vibration. An apparatus includes a high magnetic field coil defining an applied high magnetic field; an inductive magnetic field coil coupled to the high magnetic field coil, the inductive magnetic field coil defining an applied inductive magnetic field; and a processing zone located within both the applied high magnetic field and the applied inductive magnetic field. The high magnetic field and the inductive magnetic field are substantially confocal, and ohmic heating of a conductive material located in the processing zone is ohmically decoupled from a vibration of the conductive material.

Wilgen, John (Oak Ridge, TN) [Oak Ridge, TN; Kisner, Roger (Knoxville, TN) [Knoxville, TN; Ludtka, Gerard (Oak Ridge, TN) [Oak Ridge, TN; Ludtka, Gail (Oak Ridge, TN) [Oak Ridge, TN; Jaramillo, Roger (Knoxville, TN) [Knoxville, TN

2009-05-19

417

Structuration of the Solar Plasma by the Magnetic Field  

E-print Network

Structuration of the Solar Plasma by the Magnetic Field Pascal D'emoulin and Karl­Ludwig Klein of the magnetic field in the solar atmosphere. The magnetic field emanating from the solar inte­ rior governs Solar magnetic fields are created at the bottom of the convection zone from the kinetic energy

Demoulin, Pascal

418

Lesson Summary Students will learn about the magnetic fields of  

E-print Network

Knowledge & Skills Understanding of: · Magnetic field lines · Magnetic field strength decreases. Introducing the Interplanetary Magnetic Field (IMF) and Solar Wind 1. First have the students answerLesson Summary Students will learn about the magnetic fields of the Sun and Earth. This activity

Mojzsis, Stephen J.

419

STRESS GERMINATION RING TEST WITH IIRB AND FIELD VALIDATION IN MICHIGAN  

Technology Transfer Automated Retrieval System (TEKTRAN)

This test was conducted to validate field emergence on lines selected by European breeding companies for a ‘ring test’ to evaluate the water germination stress test developed at East Lansing for predicting relative field emergence. Water and hydrogen peroxide germination tests were conducted prior t...

420

Iron Electrode Potential in a Magnetic Field  

Microsoft Academic Search

REFERENCE is made in text-books on magnetism to experiments by Paillot1 and others in which potential differences such as 0.05 volt for 30,000 gauss were obtained between an iron electrode in the field and another which is not. It seems, however, that one should expect only the much smaller potential difference calculable by equating the magnetic energy change involved per

A. L. Parson

1942-01-01

421

Interpretation of Solar Magnetic Field Strength Observations  

Microsoft Academic Search

This study based on longitudinal Zeeman effect magnetograms and spectral line scans investigates the dependence of solar surface\\u000a magnetic fields on the spectral line used and the way the line is sampled to estimate the magnetic flux emerging above the\\u000a solar atmosphere and penetrating to the corona from magnetograms of the Mt. Wilson 150-foot tower synoptic program (MWO).\\u000a We have

R. K. Ulrich; L. Bertello; J. E. Boyden; L. Webster

2009-01-01

422

Flux buildup in field reversed configurations using rotating magnetic fields  

NASA Astrophysics Data System (ADS)

Rotating magnetic field (RMF) current drive is a very attractive method for both increasing the flux and sustaining the current in field reversed configurations (FRC). It has been demonstrated in low temperature, low field rotamaks, and will now be applied to a new translation, confinement, and sustainment (TCS) experiment attached to the LSX/mod (Large s field-reversed configuration Experiment) facility [Hoffman et al. Fusion Technol. 23, 185 (1993)]. Previous RMF calculations have been concerned primarily with the plasma currents and particle orbits produced in one-dimensional cylinders with the rotating field strength of near equal magnitude to the confining axial field. Both fluid current and particle orbits are calculated here in the more interesting regime appropriate to TCS and reactors where the confinement field far exceeds the rotating field strength. New insight is gained into both the flux buildup requirements for two-dimensional equilibria and into the limits on ion rotation in this high confinement field regime.

Hoffman, Alan L.

1998-04-01

423

Ring dykes as partially captured inclined sheets: insights from field observations and numerical modelling  

NASA Astrophysics Data System (ADS)

The subsurface structure of caldera-bounding ring faults remains a contentious issue. Analogue models provide useful insights into an underlying fault structure; however, results are commonly benchmarked only by near-surface observations and geophysical interpretations. Here we present field observations of a deeply eroded and uniquely well exposed section of caldera ring fault in a Tertiary central volcano in south-western Iceland. The Hafnarfjall ring fault represents the outermost fault complex of an elliptical caldera with an original diameter of approximately 5 km. Vertical displacement is estimated to be > 300 m on the steeply inward-dipping ring fault. Field observations (presented here) of the exposed section of the ring fault, however, show that the fault does not exhibit a constant dip. Hafnarfjall is a predominantly basaltic edifice made of many hundreds of lava flows, although thin layers of tuff and intrusions of more evolved magmas are also observed. These layers have contrasting mechanical properties; therefore local heterogeneities within the original edifice may have altered the stress field enough to influence the propagation of ring faults during collapse. The lava pile on the outer margins of the caldera dips shallowly to the southeast. Within the caldera, dips increase dramatically toward the centre of subsidence and, furthermore, increase with depth. Several thin (< 1 m) dykes occupy an approximately 5 m section within the ring fault; this region is interpreted to have once acted mechanically as the fault core with a lower stiffness or Young's modulus than the surrounding host rock. Many faults which have been active over an extended period develop a damage zone around the fault core; this is a zone of high fracture frequency which is generally stiffer than the core but softer or more compliant than the surrounding host rock. We observe a number of inclined sheets, presumably originating from the shallow magma chamber within the caldera margin, which become either arrested or deflected upon contact with the ring fault. Sheets that deflect into the fault may be wrongly interpreted at the surface as a ring dyke directly connected with extrusion of magma during collapse caldera formation. Using the commercial numerical modelling software COMSOL, we offer a mechanical explanation for the deflection of inclined sheets into sub-vertical dykes at a mechanically stratified fault damage zone and core. A model is proposed whereby ring faults can act as a barrier for the propagation of inclined sheets away from a magma chamber within the caldera. Furthermore, stress field homogenisation within the fault core can promote vertical dyke propagation, which offers a further explanation for the prevalence of renewed volcanism along caldera ring faults.

Browning, John; Gudmundsson, Agust

2014-05-01

424

Magnetic Field Problem: Determining Current  

NSDL National Science Digital Library

A wire carrying an unknown current out of the page is shown above. You may also double-click in the animation to create a field line. Assume that the distance given is in cm and B is given in milli Tesla.

Christian, Wolfgang; Belloni, Mario

2007-03-03

425

Lunar magnetic permeability, magnetic fields, and electrical conductivity temperature  

NASA Technical Reports Server (NTRS)

In the time period 1969-1972 a total of five magnetometers were deployed on the lunar surface during four Apollo missions. Data from these instruments, along with simultaneous measurements from other experiments on the moon and in lunar orbit, were used to study properties of the lunar interior and the lunar environment. The principal scientific results from analyses of the magnetic field data are discussed. The results are presented in the following main categories: (1) lunar electrical conductivity, temperature, and structure; (2) lunar magnetic permeability, iron abundance, and core size limits; (3) the local remnant magnetic fields, their interaction with the solar wind, and a thermoelectric generator model for their origin. Relevant publications and presented papers are listed.

Parkin, C. W.

1978-01-01

426

Semiconductor nanocrystals in a magnetic field  

NASA Astrophysics Data System (ADS)

The influence of a magnetic field on the electron and hole energy spectra of spherical uniform and multilayer semiconductor nanocrystals is investigated. The calculations are performed within the k.p method and envelope function approximation. The valence subband mixing is taken into account by considering a two-band Hamiltonian for the hole states. It is shown that the magnetic-field dependence of the energy spectrum varies strongly with the size and composition of the nanocrystals. Several interesting phenomena, like spatial polar separation of the one-electron charge density in quantum dot-quantum well structures or crossover from confinement in the external shell to the internal core in quantum dot-quantum barrier systems under the influence of a magnetic field are reported.

Planelles, J.; Díaz, J. G.; Climente, J.; Jaskólski, W.

2002-05-01

427

Bound states in a strong magnetic field  

SciTech Connect

We expect a strong magnetic field to be produced in the perpendicular direction to the reaction plane, in a noncentral heavy-ion collision . The strength of the magnetic field is estimated to be eB{approx}m{sup 2}{sub {pi}}{approx} 0.02 GeV{sup 2} at the RHIC and eB{approx} 15m{sup 2}{sub {pi}}{approx} 0.3 GeV{sup 2} at the LHC. We investigate the effects of the magnetic field on B{sup 0} and D{sup 0} mesons, focusing on the changes of the energy levels and of the mass of the bound states.

Machado, C. S.; Navarra, F. S.; Noronha, J.; Oliveira, E. G. [Instituto de Fisica, Universidade de Sao Paulo Rua do Matao, Travessa R, 187, 05508-090 Sao Paulo, SP (Brazil); Ferreira Filho, L. G. [Departamento de Matematica e Computacao, Faculdade de Tecnologia, Universidade do Estado do Rio de Janeiro Rodovia Presidente Dutra, km 298, Polo Industrial, CEP 27537-000, Resende, RJ (Brazil)

2013-03-25

428

Firefly flashing under strong static magnetic field.  

PubMed

Firefly flashing has been the subject of numerous scientific investigations. Here we present in vivo flashes from male specimens of three species of fireflies-two Japanese species Luciola cruciata, Luciola lateralis and one Indian species Luciola praeusta-positioned under a superconducting magnet. When the OFF state of the firefly becomes long after flashing in an immobile state under the strong static magnetic field of strength 10 Tesla for a long time, which varies widely from species to species as well as from specimen to specimen, the effect of the field becomes noticeable. The flashes in general are more rapid, and occasionally overlap to produce broad compound flashes. We present the broadest flashes recorded to date, and propose that the strong static magnetic field affects the neural activities of fireflies, especially those in the spent up or 'exhausted' condition. PMID:22131061

Barua, Anurup Gohain; Iwasaka, Masakazu; Miyashita, Yuito; Kurita, Satoru; Owada, Norio

2012-02-01

429

Constraints on a Primordial Magnetic Field  

SciTech Connect

We derive an upper limit of B{sub 0}{lt}3.4{times}10{sup -9}({Omega}{sub 0}h{sup 2}{sub 50}){sup 1/2} G on the present strength of any primordial homogeneous magnetic field. The microwave background anisotropy created by cosmological magnetic fields is calculated in the most general flat and open anisotropic cosmologies containing expansion-rate and 3-curvature anisotropies. Our limit is derived from a statistical analysis of the 4-year Cosmic Background Explorer (COBE) data for anisotropy patterns characteristic of homogeneous anisotropy averaged over all possible sky orientations with respect to the COBE receiver. The limits we obtain on homogeneous magnetic fields are stronger than those imposed by nucleosynthesis. {copyright} {ital 1997} {ital The American Physical Society}

Barrow, J.D.; Ferreira, P.G.; Silk, J. [Center for Particle Astrophysics, and Departments of Astronomy and Physics, University of California, Berkely, California 94720-7304 (United States)] [Center for Particle Astrophysics, and Departments of Astronomy and Physics, University of California, Berkely, California 94720-7304 (United States); Barrow, J.D. [Astronomy Centre, University of Sussex, Brighton BN1 9QH (United Kingdom)] [Astronomy Centre, University of Sussex, Brighton BN1 9QH (United Kingdom)

1997-05-01

430

Magnetic field coupled velocimeters - year one  

NASA Astrophysics Data System (ADS)

The major elements of the theoretical analysis and numerical simulation phase of a multi-year research program to demonstrate the viability of a totally nonintrusive, magnetically coupled velocimeter has been completed. The velocimeter R/D program was undertaken to yield a device capable of accurately measuring the mean and the turbulent velocity structure of flow-fields typical of rocket combustion chambers and exhaust nozzles. A drive dipole magnetic field array was designed to produce a harmonically varying, spatially localized and controlled field which penetrates flow-fields to produce eddy and motional currents. A probe array has been designed to differentiate those currents from each other and the drive array currents by analytically inverting the measured fields to yield the spatial structure of flow velocity and conductivity. An experimental test of the basic approach (using a electrolytic test chamber) has verified key elements in the analysis. A small, bench scale combustor test of the approach has begun.

Spight, C.

1981-01-01

431

The symmetry properties of planetary magnetic fields  

NASA Technical Reports Server (NTRS)

This paper provides a comparative study of the geometrical structures of the magnetic fields of earth, Jupiter, Saturn, and Uranus, starting from the traditional multipolar representations of these fields. For earth, Jupiter, and Saturn, the centered dipole, quadrupole, and octupole contributions are included, while at Uranus only the dipole and quadrupole contributions are considered. It is found that there are a number of common features of the magnetic fields of earth and Jupiter. Compared to earth and Jupiter, the Saturnian field exhibits not only a high degree of symmetry about the rotation axis but also a high degree of antisymmetry about the equatorial plane. The Uranian field shows strong deviations from both such symmetries. Nevertheless, there remain features common to all four planets.

Raedler, Karl-Heinz; Ness, Norman F.

1990-01-01

432

The interplanetary magnetic field from a time-dependent solar magnetic field  

Microsoft Academic Search

Effects of the time dependence of the sun's magnetic field on the interplanetary field in the solar wind are considered. General expressions for the interplanetary field are developed under the assumptions that the radial component of the sun's field at some reference surface can be described in terms of spherical harmonics with coefficients which are functions of time represented by

P. J. Coleman Jr.

1976-01-01

433

The interplanetary magnetic field from a time-dependent solar magnetic field  

Microsoft Academic Search

Effects of the time dependence of the sun's magnetic field upon the interplanetary field in the solar wind are considered. General expressions for the interplanetary field are developed under the assumptions that the radial component of the sun's field at some reference surface râ can be described in terms of spherical harmonics with coefficients which are functions of time represented

P. J. Jr

1976-01-01

434

The symmetry properties of planetary magnetic fields  

SciTech Connect

This paper provides a comparative study of the geometrical structures of the magnetic fields of Earth, Jupiter, Saturn, and Uranus, starting from the traditional multipolar representations of these fields. For Earth, Jupiter, and Saturn the centered dipole, quadrupole, and octupole contributions are included, while at Uranus, only the dipole and quadrupole contributoins are considered. The magnetic fields are analyzed by decomposing them into those parts which have simple symmetry properties with respect to the rotation axis and the equatorial plane. It is found that there are a number of common features of the magnetic fields of Earth and Jupiter. Compared to Earth and Jupiter, the Saturnian field exhibits not only a high degree of symmetry about the rotation axis, by now rather well known, but also a high degree of antisymmetry about the equatorial plane. The Uranian field shows strong deviations from both such symmetries. Nevertheless, there remain features common to all four planets. The implications of these results for dynamo models are discussed. With a vgiew to Cowling's theorem the symmetry of the fields is investigated with respect to not only the rotation axis but also to other axes intersecting the plaentary center. Surprisingly, the high degree of asymmetry of the Uranian field that is observed with respect to the rotation axis reduces considerably to being compare to that for Earth or Jupiter when the appropriate axis is employed.

Raedler, K.H. (Zentral Inst. fuer Astrophysik, Potsdam-Babelsberg (East Germany)); Ness, N.F. (Univ. of Delaware, Newark (United States))

1990-03-01

435

Magnetic Field Control of Structures and Properties of Diamagnetic Molecular Assemblies  

NASA Astrophysics Data System (ADS)

Wormlike and small threadlike micelles, whose radii of gyration were more than 120 nm, were grown under steady magnetic fields. Their gyration radius increased in magnetic fields. The aromatic rings stabilized the threadlike micelles containing salicylic ions. Hexagonal mesophases, comprised of hexadecyltrimethylammonium and silicate ions, as assemblies of rodlike micelles, developed in magnetic fields. They led to the formation of mesoporous silicas. The deformation of dipalmitoyl-phosphatidylcholine and dioctadecyldimethylammonium chloride in membranes led to fusion and division of their vesicles under magnetic fields of up to 30 T. The magnetofusion and magnetodivision of vesicles depended significantly on magnetic field intensity, particle size, and aromatic compounds doping, consistent with the theory for magnetic deformation. The change in vesicle size gave an estimation of the local curvature of the membrane. N-isopropylacrylamide (NIPA) gels prepared under steady magnetic fields (H?28 T) showed more significant discontinuity in the volume phase transition and were softer than gels prepared at zero field. Moreover, magnetic fields induced structural anisotropy, transparency, and volume phase transition. These results suggest that the NIPA chains were oriented and made less cross-linking (dangling chain formation in gel networks).

Otsuka, I.; Takahashi, T.; Yaguchi, Y.; Abe, H.; Ozeki, S.

2005-07-01

436

Solar atmospheric rotation and the magnetic field  

NASA Astrophysics Data System (ADS)

Solar rotation is known for more than four centuries, yet it is still an unresolved issue of solar physics. The rotation has been measured by three methods e.g. Feature tracing, Spectroscopic and flux modulation. We have used the last quite extensively for the estimation of rotation of the solar outer atmosphere, namely chromosphere and corona. These studies used Radio, X-ray and EUV images of the Sun. These investigations have provided quite detailed and systematic information of the solar rotation and its variability. This has established that solar atmosphere has differential rotation and the differentiality has a significant temporal and spatial variability. The spatial variability show that there is North-South asymmetry in the rotation of solar atmosphere. This asymmetry changes sign every solar cycle. This may be related to "Hale cycle". In this paper we tried to combine the Radio, X-ray and EUV estimates of rotation by comparative interpolation. The combined rotation profiles are drawn in the space-time coordinate in the same format as the longitudinal averaged magnetic field. The average magnetic field shows beautiful butterfly structures and poleward flow of the magnetic fields of opposite polarity. Preliminary comparison show that asymmetric differential rotation of the solar atmosphere peaks when the magnetic filed structure is more complex. In this paper a detail comparison of the magnetic field and solar atmospheric rotation will presented.

Chandra, Satish; Vats, Hari

2012-07-01

437

A magnetically field-controllable phononic crystal  

NASA Astrophysics Data System (ADS)

Phononic crystals are periodic structures consist of different materials in an elastic medium designed to interact with elastic waves. These crystals have practical applications, such as, frequency filters, beam splitters, sound or vibration protectors, acoustic lasers, acoustic mirrors and elastic waveguides. In this study, the wave propagation in a tunable phononic crystal is investigated. The magnetically controllable phononic crystal consists of a soft magnetorheological elastic medium undergoing large deformations upon the application of a magnetic field. Finite deformations and induced magnetic fields influence wave propagation characteristics in the periodic structure. The soft matrix is modeled as a hyperelastic elastomer to take into account the material nonlinearity. The integrated effects of material properties, transformation of the geometry of the unit cell, and the induced magnetic field, are used to tune the band structure of the periodic structure. Both analytical and finite element methods are employed to evaluate the dispersion diagrams considering Bloch boundary conditions. Results show that the applied magnetic field significantly affect the width and the position of band-gaps.

Bayat, Alireza; Gordaninejad, Faramarz

2014-04-01

438

Force on a storage ring vacuum chamber after sudden turn-off of a magnet power supply  

NASA Astrophysics Data System (ADS)

We are commissioning a 2.5 GeV synchrotron radiation source (SRS) where electrons travel in high vacuum inside the vacuum chambers made of aluminum alloys. These chambers are kept between the pole gaps of magnets and are made to facilitate the radiation coming out of the storage ring to the experimental station. These chambers are connected by metallic bellows. During the commissioning phase of the SRS, the metallic bellows became ruptured due to the frequent tripping of the dipole magnet power supply. The machine was down for quite some time. In the case of a power supply trip, the current in the magnets decays exponentially. It was observed experimentally that the fast B field decay generates a large eddy current in the chambers and consequently the chambers are subjected to a huge Lorentz force. This motivated us to develop a theoretical model to study the force acting on a metallic plate when exposed to an exponentially decaying field and then to extend it for a rectangular vacuum chamber. The problem is formulated using Maxwell’s equations and converted to the inhomogeneous Helmholtz equation. After taking the Laplace transform, the equation is solved with appropriate boundary conditions. Final results are obtained after taking the appropriate inverse Laplace transform. The expressions for eddy current contour and magnetic field produced by the eddy current are also derived. Variations of the force on chambers of different wall thickness due to spatially varying and exponentially time decaying field are presented. The result is a general theory which can be applied to different geometries and calculation of power loss as well. Comparisons are made with results obtained by simulation using a finite element based code, for quick verification of the theoretical model.

Sinha, Gautam; Prabhu, S. S.

2011-10-01

439

Statistical ring current of Saturn  

NASA Astrophysics Data System (ADS)

The statistical ring current of Saturn has been determined from the curl of the median magnetic field derived from over 5 years of observations of the Cassini magnetometer. The main issue addressed here is the calculation of the statistical ring current of Saturn by directly computing, for the first time, the symmetrical part of the ring current J from the Maxwell equation ? × B = ?0J from assembling the perturbation magnetic field B from 2004 through 2010. This study validates previous studies, based on fewer data and not using ? × B, and shows that the ring current flows eastward (in the +? or corotation direction) and extends from ˜3 RS to at least ˜20 RS (1 RS = 60,268 km), which is the vicinity of the dayside magnetopause; that the ring current has a peak strength of ˜75 pA/m2 at ˜9.5 RS; and that the ring current has a half-width of ˜1.5 RS. Two outcomes of this study are that the ring current bends northward, as suggested by the “bowl” model of Saturn's plasma sheet, and that the total ring current is 9.2 ± 1.0 MA. In the context of future endeavors, the statistical ring current presented here can be used for calculations of the magnetic field of Saturn for particle drifts, field line mapping, and J × B force.

Carbary, J. F.; Achilleos, N.; Arridge, C. S.

2012-06-01

440

The Hanle effect in a random magnetic field. Dependence of the polarization on statistical properties of the magnetic field  

Microsoft Academic Search

Context: The Hanle effect is used to determine weak turbulent magnetic fields in the solar atmosphere, usually assuming that the angular distribution is isotropic, the magnetic field strength constant, and that micro-turbulence holds, i.e. that the magnetic field correlation length is much less than a photon mean free path. Aims: To examine the sensitivity of turbulent magnetic field measurements to

H. Frisch; L. S. Anusha; M. Sampoorna; K. N. Nagendra

2009-01-01

441

A new ring structure for muon (g-2) measurements  

Microsoft Academic Search

In this storage ring of discrete magnets with uniform field and edge focusing, the field averaged over the orbit is independent of orbit radius (particle momentum). This ring is suitable for measuring the anomalous magnetic moment of the muon. The field, averaged over the orbit, can be calibrated by injecting horizontally polarized protons of the same momentum and measuring the

F. J. M. Farley

2004-01-01

442

Magnetic field behavior beyond the laser spot  

SciTech Connect

A self-consistent, analytic solution for the two-dimensional, rotationally symmetric, time varying problem of the interaction of a laser plasma with its self-generated magnetic field has been determined at lateral locations away from the laser spot. The plasma is described by a two-fluid model, with the magnitude of the electron velocity much greater than the ion velocity. Increased spatial gradients in the density and velocity around the magnetic field maximum have been found. This leads to a double humped ion-velocity spectrum, which could be interpreted in terms of a two-temperature electron distribution, in qualitative agreement with experiment.

Goldman, S.R.; Schmalz, R.F.

1987-11-01

443

Ultracold plasma dynamics in a magnetic field  

NASA Astrophysics Data System (ADS)

Plasmas, often called the fourth state of matter and the most common one in the universe, have parameters varying by many orders of magnitude, from temperature of a few hundred kelvin in the Earth's ionosphere to 10 16 K in the magnetosphere of a pulsar. Ultracold plasmas, produced by photoionizing a sample of laser-cooled and trapped atoms near the ionization limit, have extended traditional neutral plasma parameters by many orders of magnitude, to electron temperatures below 1 K and ion temperatures in the tens of muK to a few Kelvin, and densities of 105 cm -3 to 1010 cm-3. These plasmas thus provide a testing ground to study basic plasma theory in a clean and simple system with or without a magnetic field. Previous studies of ultracold plasmas have primarily concentrated on temperature measurements, collective modes and expansion dynamics in the absence of magnetic fields. This thesis presents the first study of ultracold plasma dynamics in a magnetic field. The presence of a magnetic field during the expansion can initiate various phenomena, such as plasma confinement and plasma instabilities. While the electron temperatures are very low in ultracold plasmas, we need only tens of Gauss of magnetic field to observe significant effects on the expansion dynamics. To probe the ultraocold plasma dynamics in a magnetic field, we developed a new diagnostic - projection imaging, which images the ion distribution by extracting the ions with a high voltage pulse onto a position-sensitive detector. Early in the lifetime of the plasma (< 20 mus), the size of the image is dominated by the time-of-flight Coulomb explosion of the dense ion cloud. For later times, we measure the 2-D Gaussian width of the ion image, obtaining the transverse expansion velocity as a function of magnetic field (up to 70 G), and observe that the transverse expansion velocity scales as B-1/2, explained by a nonlinear ambipolar diffusion model that involes anisotropic diffusion in two different directions. We also present the first observation of a plasma instability in an expanding ultracold plasma. We observe periodic emission of electrons from an ultracold plasma in weak, crossed magnetic and electric fields, and a strong perturbed electron density distribution in electron time-of-flight projection images. We identify this instability as a high-frequency electron drift instability due to the coupling between the electron drift wave and electron cyclotron harmonic, which has large wavenumbers corresponding to wavelengths close to the electron gyroradius.

Zhang, Xianli

444

Superconductive magnetic-field-trapping device  

NASA Technical Reports Server (NTRS)

An apparatus which enables the establishment of a magnetic field in air that has the same intensity as the ones in ferromagnetic materials is described. The apparatus is comprised of a core of ferromagnetic material and is surrounded by a cylinder made of a material that has superconducting properties when cooled below a critical temperature. A method is provided for producing a magnetic field through the ferromagnetic core. The core can also be split and pulled apart when it is required that the center of the cavity be left empty.

Hildebrandt, A. F.; Elleman, D. D.; Whitmore, F. C. (inventors)

1965-01-01

445

Neutrino conversions in solar random magnetic fields  

NASA Astrophysics Data System (ADS)

We consider the effect of a random magnetic field in the convective zone of the Sun superimposed to a regular magnetic field on resonant neutrino spin-flavor oscillations. We argue for the existence of a field of strongly chaotic nature at the bottom of the convective zone. In contrast to previous attempts we employ a model motivated regular magnetic field profile: it is a static field solution to the solar equilibrium hydro-magnetic equations. These solutions have been known for a long time in the literature. We show for the first time that in addition they are twisting solutions. In this scenario electron antineutrinos are produced through cascades like ?eL-->??L-- >?~eR, The detection of ?~eR at Earth would be a long-awaited signature of the Majorana nature of the neutrino. The expected signals in the different experiments (SK, GALLEX-SAGE, Homestake) are obtained as a function of the level of noise, regular magnetic field and neutrino mixing parameters. Previous results obtained for small mixing and ad-hoc regular magnetic profiles are reobtained. We confirm the strong suppression for a large part of the parameter space of the ?~eR-flux for high energy boron neutrinos in agreement with present data of the SK experiment. We find that MSW (Mikheyev-Smirnov-Wolfenstein) regions (?m2~=10-5 eV2, both small and large mixing solutions) are stable up to very large levels of noise (P=0.7-0.8) but they are acceptable from the point of view of antineutrino production only for moderate levels of noise (P~=0.95). For strong noise and a reasonable regular magnetic field, any parameter region (?m2, sin 2 2?) is excluded. As a consequence, we are allowed to reverse the problem and to put limits on the r.m.s. field strength and transition magnetic moments by demanding a particle physics solution to the SNP in this scenario.

Semikoz, V. B.; Torrente-Lujan, E.

1999-09-01

446

Measurements of magnetic fields in solar prominences  

NASA Technical Reports Server (NTRS)

Magnetic fields can be measured, in solar prominences, by means of two different basic mechanisms that are responsible for the introduction (or the reduction) of a given amount of polarization in spectral lines: these are the Zeeman effect and the Hanle effect. Through the splitting of the magnetic components of a spectral line, the Zeeman effect is capable of introducing a certain amount of circular polarization across the line profile. The Hanle effect consist of a modification of the linear polarization that is induced in spectral lines by the anisotropic illumination of the prominence plasma by the photospheric radiation field. These two effects are briefly discussed.

Deglinnocenti, Egidio Landi

1986-01-01

447

Preliminary Results of Performance Measurements on a Cylindrical Hall-Effect Thruster with Magnetic Field Generated by Permanent Magnets  

NASA Technical Reports Server (NTRS)

The performance of a low-power cylindrical Hall thruster, which more readily lends itself to miniaturization and low-power operation than a conventional (annular) Hall thruster, was measured using a planar plasma probe and a thrust stand. The field in the cylindrical thruster was produced using permanent magnets, promising a power reduction over previous cylindrical thruster iterations that employed electromagnets to generate the required magnetic field topology. Two sets of ring-shaped permanent magnets are used, and two different field configurations can be produced by reorienting the poles of one magnet relative to the other. A plasma probe measuring ion flux in the plume is used to estimate the current utilization for the two magnetic configurations. The measurements indicate that electron transport is impeded much more eff